WO2023184368A1 - 正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置 - Google Patents

正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置 Download PDF

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WO2023184368A1
WO2023184368A1 PCT/CN2022/084465 CN2022084465W WO2023184368A1 WO 2023184368 A1 WO2023184368 A1 WO 2023184368A1 CN 2022084465 W CN2022084465 W CN 2022084465W WO 2023184368 A1 WO2023184368 A1 WO 2023184368A1
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coating layer
active material
coating
optionally
core
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English (en)
French (fr)
Inventor
马晴岩
官英杰
赵玉珍
温严
黄起森
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to PCT/CN2022/084465 priority Critical patent/WO2023184368A1/zh
Priority to CN202280019404.8A priority patent/CN117043985A/zh
Priority to EP22902480.7A priority patent/EP4276946A4/en
Priority to US18/337,127 priority patent/US20230327091A1/en
Publication of WO2023184368A1 publication Critical patent/WO2023184368A1/zh
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C01P2004/84—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases one phase coated with the other
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application belongs to the field of battery technology, and specifically relates to a positive active material, its preparation method, a positive electrode sheet, a secondary battery and an electrical device containing the same.
  • lithium manganese phosphate has become one of the most popular cathode active materials due to its advantages of high capacity, good safety performance and rich sources of raw materials.
  • lithium manganese phosphate is prone to manganese ions dissolving during charging, resulting in rapid capacity attenuation. Therefore, it is necessary to provide a cathode active material with good comprehensive properties.
  • the purpose of this application is to provide a cathode active material, a preparation method thereof, a cathode plate, a secondary battery and an electrical device containing the same, which can enable the secondary battery using the cathode active material to have a higher energy density. As well as good cycle performance, rate performance and safety performance.
  • the shell includes a first coating layer coating the core, a second coating layer coating the first coating layer, a third coating layer coating the second coating layer, and a coating layer.
  • the fourth coating layer of the third coating layer wherein,
  • the first coating layer includes crystalline pyrophosphate Li a MP 2 O 7 and/or M b (P 2 O 7 ) c , 0 ⁇ a ⁇ 2, 1 ⁇ b ⁇ 4, 1 ⁇ c ⁇ 6,
  • the values of a, b and c satisfy the following conditions: the crystalline pyrophosphate Li a MP 2 O 7 or M b (P 2 O 7 ) c remains electrically neutral,
  • M in the crystalline pyrophosphate Li a MP 2 O 7 and M b (P 2 O 7 ) c is each independently selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, One or more elements from Nb and Al;
  • the second coating layer includes crystalline phosphate XPO 4 , and X is one or more selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al. an element;
  • the fourth coating layer includes a polymer, and the polymer includes one or more selected from polysiloxane with a linear structure and polysiloxane with a cyclic structure.
  • the cathode active material can Achieving significantly reduced manganese ion dissolution and reduced lattice change rate, its use in secondary batteries can improve the cycle performance, rate performance, safety performance of the battery and increase the capacity of the battery.
  • the polymer includes at least one structural unit represented by Formula 1,
  • R 1 and R 2 each independently represent H or at least one of the group consisting of the following functional groups: -COOH, -OH, -SH, -CN, -SCN, amino, phosphate group, carboxylate group, amide group, aldehyde group, sulfonyl group, polyether segment, C1 ⁇ C20 aliphatic hydrocarbon group, C1 ⁇ C20 halogenated aliphatic hydrocarbon group, C1 ⁇ C20 heteroaliphatic hydrocarbon group, C1 ⁇ C20 halogenated heteroaliphatic hydrocarbon group, C6 ⁇ C20 aromatic hydrocarbon group, C6 ⁇ C20 halogenated aromatic hydrocarbon group, C2 ⁇ C20 heteroaromatic hydrocarbon group, C2 ⁇ C20 halogenated heteroaromatic hydrocarbon group; optionally, R 1 and R 2 each independently represent H or at least one of the group consisting of the following functional groups: -OH, -SH, amino, phosphate group, polyether segment, C1 ⁇ C8 alkyl, C1
  • These functional groups can complex manganese ions, reduce the dissolution of manganese ions, and can also remove F-containing ions in the electrolyte, further alleviate the erosion of the acidic substances in the electrolyte on the surface of the positive active material, reduce interface side reactions, and reduce gas production, further Improve the cycle performance and high-temperature storage performance of secondary batteries.
  • the linear-structured polysiloxane further includes an end-capping group.
  • the end-capping group includes at least one of the following functional groups: polyether, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl.
  • the linear structure polysiloxane includes polydimethylsiloxane, polydiethylsiloxane, polymethylethylsiloxane, polymethylvinylsiloxane Silicone, polyphenylmethylsiloxane, polymethylhydrogensiloxane, carboxyl functionalized polysiloxane, epoxy-terminated polysiloxane, methoxy-terminated polydimethylsiloxane , Polymethylchloropropylsiloxane, Mercaptopropylpolysiloxane, Aminoethylaminopropylpolydimethylsiloxane, Terminated hydroxypropylpolysiloxane, Terminated hydroxylpolydimethylsiloxane alkane, terminal polyether polydimethylsiloxane, side chain aminopropyl polysiloxane, aminopropyl terminal polydimethylsiloxane, side chain hydroxy
  • the cyclic structure polysiloxane includes 1,3,5,7-octamethylcyclotetrasiloxane, 1,3,5,7-tetrahydro-1, 3,5,7-tetramethylcyclotetrasiloxane, cyclopentasiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, 2,4,6,8- Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, cyclic polymethylvinylsiloxane, hexamethylcyclooctasiloxane, tetradecamethylcycloheptasiloxane One or more of alkane and cyclic polydimethylsiloxane.
  • the polymer is selected from linear structured polysiloxanes.
  • the electrons in the ring of polysiloxane with a cyclic structure have a certain degree of delocalization. Therefore, compared with polysiloxane with a linear structure, its Si-O skeleton has less affinity for electron-rich F-containing ions. is smaller, the removal rate of F ions in the electrolyte is slightly lower, and the improvement effect on the cycle performance of the secondary battery is slightly less.
  • the polymer has a number average molecular weight of less than 300,000, optionally from 400 to 200,000.
  • the cathode active material can also achieve both good kinetic properties and high-temperature storage properties.
  • the mass percentage of polar functional groups in the polysiloxane is ⁇ , 0 ⁇ 50%, optionally, 5% ⁇ 30%.
  • the content of polar functional groups in polysiloxane is within an appropriate range, its coating and modification effect on the core will be better.
  • the coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, and more preferably 2- 4% by weight, based on the weight of the core.
  • the coating amount of the third coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, and more preferably greater than 0 and less than or equal to 2% by weight, based on the weight of the core.
  • the coating amount of the four coating layers is preferably within the above range, so that the core can be fully coated without sacrificing the cathode activity.
  • the kinetic performance, cycle performance and safety performance of the secondary battery can be further improved.
  • the thickness of the first cladding layer is 1-10 nm. This can avoid possible adverse effects on the dynamic properties of the material when the first coating layer is too thick, and avoid the problem that the first coating layer cannot effectively hinder the migration of transition metal ions when it is too thin.
  • the thickness of the second cladding layer is 2-15 nm.
  • the surface structure of the second coating layer is stable and has little side reaction with the electrolyte, so it can effectively reduce interface side reactions, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.
  • the thickness of the fourth coating layer is 2-10 nm. This can improve the electrolyte stability of the cathode active material, reduce the erosion of the electrolyte on the surface of the cathode active material, and avoid the possible adverse effects on the dynamic properties of the cathode active material when it is too thick.
  • the interplanar distance of the crystalline pyrophosphate in the first coating layer ranges from 0.293 to 0.470 nm, and the angle range of the crystal direction (111) ranges from 18.00° to 32.00°;
  • the interplanar distance of the crystalline phosphate in the second coating layer ranges from 0.244 to 0.425 nm, and the included angle of the crystal direction (111) ranges from 20.00° to 37.00°.
  • Crystalline pyrophosphate and crystalline phosphate within the above-mentioned crystal plane spacing and included angle range can more effectively suppress the lattice change rate of lithium manganese phosphate and the dissolution of manganese ions during the lithium deintercalation process, thereby improving the secondary battery High temperature cycle performance and high temperature storage performance.
  • the ratio of y to 1-y is 1:10 to 1:1, optionally 1:4 to 1:1. As a result, the cycle performance and rate performance of the secondary battery are further improved.
  • the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249. As a result, the cycle performance and rate performance of the secondary battery are further improved.
  • the carbon in the third coating layer is a mixture of SP2 form carbon and SP3 form carbon.
  • the molar ratio of the SP2 form carbon to SP3 form carbon is in the range of 0.1-10 Any value within the range, optionally any value within the range of 2.0-3.0. This application improves the overall performance of the secondary battery by limiting the molar ratio of SP2 form carbon to SP3 form carbon within the above range.
  • the manganese element content is in the range of 10%-35% by weight, optionally in the range of 15%-30% by weight, and more optionally in the range of 17% by weight. %-20% by weight.
  • it can effectively avoid problems such as deterioration of structural stability and density decrease of the positive active material that may be caused by excessive manganese content, thereby improving the performance of the secondary battery such as cycle, storage and compaction density; and it can avoid the problem of excessive manganese content. Too small an element content may cause problems such as a low voltage platform, thereby increasing the energy density of the secondary battery.
  • the content of phosphorus element is in the range of 12% to 25% by weight, optionally in the range of 15% to 20% by weight.
  • the following situations can be effectively avoided: If the content of phosphorus is too large, the covalency of P-O may be too strong and affect the conductivity of small polarons, thereby affecting the conductivity of the cathode active material; if the content of phosphorus is too small, , which may reduce the stability of the core, the pyrophosphate in the first coating layer, and/or the phosphate lattice structure in the second coating layer, thereby affecting the overall stability of the cathode active material. sex.
  • the weight ratio of manganese element to phosphorus element ranges from 0.90 to 1.25, optionally from 0.95 to 1.20. At this time, the following situations can be effectively avoided: If the weight ratio is too large, it may increase the dissolution of manganese ions, affecting the stability of the positive active material and the cycle performance and storage performance of the secondary battery; if the weight ratio is too small, it may cause The discharge voltage platform of the positive active material is reduced, thereby reducing the energy density of the secondary battery.
  • the lattice change rate of the cathode active material before and after complete deintercalation of lithium is 4% or less, optionally 3.8% or less, and more optionally 2.0-3.8%.
  • the positive active material can improve the capacity performance and rate performance of the secondary battery.
  • the surface oxygen valence state of the cathode active material is -1.90 or less, optionally -1.90 to -1.98. Therefore, by limiting the surface oxygen valence state of the positive electrode active material to the above range as described above, the interface side reaction between the positive electrode active material and the electrolyte can be reduced, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.
  • a second aspect of this application provides a method for preparing a cathode active material, which includes the following steps:
  • the step of providing core material the core chemical formula is Li 1+x Mn 1-y A y P 1-z R z O 4 , where x is any value in the range of -0.100 to 0.100, and y is in the range of 0.001 to 0.100.
  • z is any value within the range of 0.001 to 0.100
  • the A is selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co , one or more elements among Ga, Sn, Sb, Nb and Ge, optionally one or more elements among Fe, Ti, V, Ni, Co and Mg
  • the R is selected from B, One or more elements among Si, N and S, optionally, the R is an element selected from B, Si, N and S;
  • Coating step Provide Li a MP 2 O 7 and/or M b (P 2 O 7 ) c and XPO 4 suspension respectively, add the core material to the above suspension and mix, and sintering to obtain The core of the first coating layer, the second coating layer and the third coating layer is obtained by dry-coating the core with the first coating layer, the second coating layer and the third coating layer with the polymer.
  • the salt Li a MP 2 O 7 or M b (P 2 O 7 ) c maintains electrical neutrality;
  • the M is each independently selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and one or more elements from Al;
  • the X is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al;
  • the polymer includes one or more selected from polysiloxane with linear structure and polysiloxane with cyclic structure;
  • the positive active material has a core-shell structure, which includes the inner core and a shell covering the inner core.
  • the shell includes a first coating layer covering the inner core, and a first coating layer covering the first outer core.
  • the second coating layer includes crystalline phosphate XPO 4
  • the third coating layer is carbon
  • the fourth coating layer includes a polymer, and the polymer includes one or more selected from the group consisting of polysiloxane with a linear structure and polysiloxane with a cyclic structure.
  • the step of providing core material includes the following steps:
  • Step (1) Mix and stir the manganese source, the dopant of element A and the acid in a container to obtain manganese salt particles doped with element A;
  • Step (2) Mix the manganese salt particles doped with element A with a lithium source, a phosphorus source and a dopant of element R in a solvent to obtain a slurry, and then sinter under the protection of an inert gas atmosphere to obtain doping.
  • element A and element R there is a core of element A and element R, wherein the core doped with element A and element R is Li 1+x Mn 1-y A y P 1-z R z O 4 , x is between -0.100 and 0.100 Any value within the range, y is any value within the range of 0.001 to 0.500, z is any value within the range of 0.001 to 0.100, and the A is selected from Zn, Al, Na, K, Mg, Mo, W, One or more elements from Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements from Fe, Ti, V, Ni, Co and Mg element, and the R is one or more elements selected from the group consisting of B, Si, N, and S. Alternatively, the R is one element selected from the group consisting of B, Si, N, and S.
  • the step (1) is mixed at a temperature of 20-120°C, optionally 40-120°C.
  • the stirring in step (1) is performed at 400-700 rpm for 1-9 hours, optionally 3-7 hours.
  • the prepared core and the cathode active material produced therefrom have fewer lattice defects, which is beneficial to inhibiting the dissolution of manganese ions and reducing the interaction between the cathode active material and the cathode active material. Interfacial side reactions of the electrolyte, thereby improving the cycle performance and safety performance of secondary batteries.
  • the step (2) is mixed at a temperature of 20-120°C, optionally 40-120°C, for 1-10 hours.
  • the dopant of element A is selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, One or more of the elements, carbonates, sulfates, chlorides, nitrates, organic acid salts, oxides, and hydroxides of one or more elements among Sb, Nb, and Ge.
  • the dopant of the element R is an inorganic acid, an organic acid, a sulfate, a chloride salt, or one or more elements selected from B, Si, N, and S.
  • the coating step includes:
  • the first coating step dissolve the source of the element M, the phosphorus source and the acid, and optionally the lithium source in a solvent to obtain a first coating layer suspension; combine the core obtained in the step of providing the core material with the third The first coating layer suspension obtained in the first coating step is thoroughly mixed, dried, and then sintered to obtain the material covered by the first coating layer;
  • the second coating step dissolve the source of element
  • the second coating layer suspension obtained in the second coating step is thoroughly mixed, dried, and then sintered to obtain a material covered with two coating layers;
  • the third coating step Dissolve the carbon source in the solvent and fully dissolve it to obtain a third coating layer solution; then add the two-layer coating layer-coated material obtained in the second coating step to the third coating layer layer solution, mix evenly, dry, and then sinter to obtain a material covered with three coating layers;
  • the fourth coating step Dissolve the polymer in the solvent and fully dissolve it to obtain a fourth coating layer solution; then add the three-layer coating layer-coated material obtained in the third coating step to the fourth coating layer layer solution, mix evenly, and dry to obtain a material covered with four coating layers, that is, the positive electrode active material, or mix the material covered with three coating layers obtained in the third coating step with the polymer evenly, Then, the material covered with four coating layers is sintered, which is the cathode active material.
  • the pH of the solution in which the source of element M, the phosphorus source and the acid, and optionally the lithium source are dissolved is controlled to be 3.5-6.5, and then the solution is stirred and reacted 1- 5 hours, then the solution is warmed to 50-120°C and maintained at this temperature for 2-10 hours.
  • the sintering is performed at 650-800°C for 2-6 hours.
  • the capacity development, cycle performance, high temperature storage performance, rate performance, etc. of the secondary battery prepared using the cathode active material can be ensured or even improved.
  • sintering is performed at 500-700°C for 6-10 hours.
  • the sintering in the third coating step is performed at 700-800°C for 6-10 hours.
  • the capacity development and compaction density of the positive electrode active material can be improved.
  • the solid-liquid contact angle between the positive electrode film layer and the non-aqueous organic solvent is between 3° and 90°, optionally between 3° and 60°, and further in Between 10° and 30°.
  • the contact angle is within a suitable range, the secondary battery can achieve both high energy density and good rate performance, cycle performance and high-temperature storage performance.
  • the porosity of the positive electrode film layer is 15% to 50%, optionally 15% to 30%.
  • the secondary battery can achieve both high energy density and good rate performance, cycle performance and high-temperature storage performance.
  • the positive electrode sheet of the present application is used in secondary batteries and can improve the energy density, cycle performance, rate performance and safety performance of secondary batteries.
  • a fourth aspect of this application provides a secondary battery, including the positive active material of the first aspect of this application, or the positive active material prepared by the method of the second aspect of this application, or the positive electrode sheet of the third aspect of this application.
  • a fifth aspect of the present application provides an electrical device, including the secondary battery of the fourth aspect of the present application.
  • the positive electrode sheet, secondary battery, and electrical device of the present application include the positive active material of the present application, and thus have at least the same advantages as the positive active material.
  • FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. 1 .
  • FIG. 3 is a schematic diagram of an embodiment of the battery module of the present application.
  • FIG. 4 is a schematic diagram of an embodiment of the battery pack of the present application.
  • FIG. 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of an embodiment of a power consumption device including the secondary battery of the present application as a power source.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5.
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • step (c) means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.
  • coating layer refers to the material layer coated on the lithium manganese phosphate core.
  • the material layer can completely or partially cover the lithium manganese phosphate core.
  • coating layer is used " is only for convenience of description and is not intended to limit the present invention.
  • each coating layer can be completely covered or partially covered.
  • thickness of the coating layer refers to the thickness of the material layer coating the lithium manganese phosphate core in the radial direction of the lithium manganese phosphate core.
  • the median particle size Dv50 refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%.
  • the median particle diameter Dv50 of the material can be determined using laser diffraction particle size analysis. For example, refer to the standard GB/T 19077-2016 and use a laser particle size analyzer (such as Malvern Master Size 3000) for measurement.
  • aliphatic hydrocarbon group includes alkyl, alkenyl and alkynyl groups
  • heteroaliphatic hydrocarbon group means that the aliphatic hydrocarbon group contains heteroatoms (such as N, O, S, etc.).
  • heteroalkyl refers to an alkyl group containing heteroatoms (such as N, O, S, etc.), such as alkoxy, alkylthio, etc.
  • the metallic manganese produced in this way is equivalent to a "catalyst", which can catalyze the decomposition of the SEI film (solid electrolyte interphase, solid electrolyte interface film) on the surface of the negative electrode to produce by-products; part of the by-products is gas, thus causing secondary battery failure. expansion, affecting the safety performance of the secondary battery; in addition, another part of the by-product is deposited on the surface of the negative electrode, which will hinder the passage of lithium ions in and out of the negative electrode, causing the impedance of the secondary battery to increase, thus affecting the dynamic performance of the secondary battery. In addition, in order to replenish the lost SEI film, the electrolyte and active lithium inside the battery are continuously consumed, which will have an irreversible impact on the capacity retention rate of the secondary battery.
  • the first aspect of the application provides a new type of cathode active material with a core-shell structure, which includes a core and a shell covering the core, wherein,
  • the chemical formula of the core is Li 1+x Mn 1-y A y P 1-z R z O 4 , x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, and the A is selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, One or more elements from Nb and Ge, optionally one or more elements from Fe, Ti, V, Ni, Co and Mg, and the R is selected from B, Si, N and S One or more elements, optionally, the R is an element selected from B, Si, N and S;
  • the shell includes a first coating layer coating the core, a second coating layer coating the first coating layer, a third coating layer coating the second coating layer, and a coating layer.
  • the fourth coating layer of the third coating layer wherein,
  • the first coating layer includes crystalline pyrophosphate Li a MP 2 O 7 and/or M b (P 2 O 7 ) c , 0 ⁇ a ⁇ 2, 1 ⁇ b ⁇ 4, 1 ⁇ c ⁇ 6,
  • the values of a, b and c satisfy the following conditions: the crystalline pyrophosphate Li a MP 2 O 7 or M b (P 2 O 7 ) c remains electrically neutral, and the crystalline pyrophosphate Li a MP M in 2 O 7 and M b (P 2 O 7 ) c is each independently one or more selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al element;
  • the second coating layer includes crystalline phosphate XPO 4 , and X is one or more selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al. an element;
  • the third coating layer is carbon
  • the fourth coating layer includes a polymer, and the polymer includes one or more selected from polysiloxane with a linear structure and polysiloxane with a cyclic structure.
  • the above-mentioned limitation on the numerical range of y is not only a limitation on the stoichiometric number of each element as A, but also on each element as A. Limitation of the sum of the stoichiometric numbers of elements. For example, when A is two or more elements A1, A2...An, the stoichiometric numbers y1, y2...yn of A1, A2...An each need to fall within the numerical range of y defined in this application, and y1 , y2...yn and the sum must also fall within this numerical range. Similarly, for the case where R is two or more elements, the limitation on the numerical range of the R stoichiometric number in this application also has the above meaning.
  • one of n1, n2, n3, and n4 is zero, and the rest are not zero; more optionally, two of n1, n2, n3, and n4 are zero, and the rest are not zero; also optionally, Three of n1, n2, n3, and n4 are zero, and the rest are not zero.
  • the cathode active material of the present application can improve the capacity, cycle performance, rate performance and safety performance of the secondary battery.
  • the lithium manganese phosphate cathode active material of the present application has a core-shell structure.
  • the dissolution of manganese ions reduces the migration of manganese ions to the negative electrode, reduces the consumption of electrolyte due to the decomposition of the SEI film, improves the cycle performance and safety performance of secondary batteries, and can also promote the adjustment of Mn-O bonds and reduce the lithium ion migration barrier.
  • the core by coating the core with a first coating layer including crystalline pyrophosphate, the migration resistance of manganese ions can be further increased, its dissolution is reduced, and surface impurities are reduced.
  • Lithium content reducing the contact between the core and the electrolyte, thereby reducing interface side reactions, reducing gas production, and improving the high-temperature storage performance, cycle performance and safety performance of secondary batteries; by further coating the crystalline state with excellent ability to conduct lithium ions
  • the phosphate coating layer can effectively reduce the interface side reactions between the positive electrode active material and the electrolyte, thereby improving the high-temperature cycle and storage performance of the secondary battery; by further coating the carbon layer as the third coating layer, it can further improve Safety performance and dynamic performance of secondary batteries; by further coating the polymer as the fourth coating layer, it can further hinder the migration of manganese ions into the electrolyte, reduce the erosion of the electrolyte on the surface of the positive active material, and reduce the interface side reactions, reduce gas production, and further improve the cycle performance and high-temperature storage performance of secondary batteries.
  • the element A doped at the manganese position of lithium manganese phosphate also helps to reduce the lattice change rate of lithium manganese phosphate during the deintercalation process of lithium and improve the active material of lithium manganese phosphate cathode. Structural stability, greatly reducing the dissolution of manganese ions and reducing oxygen activity on the particle surface; the element R doped at the phosphorus position also helps to change the ease of Mn-O bond length change, thereby improving electronic conductivity and reducing lithium Ion migration barrier promotes lithium ion migration and improves the rate performance of secondary batteries.
  • the entire core system remains electrically neutral, ensuring that there are as few defects and impurities in the cathode active material as possible. If there is an excess of transition metal (such as manganese) in the cathode active material, since the structure of the material system itself is relatively stable, the excess transition metal is likely to precipitate in the form of elemental substances, or form a heterogeneous phase inside the crystal lattice, maintaining the electrical neutrality. Sex can minimize such impurities. In addition, ensuring the electrical neutrality of the system can also generate lithium vacancies in the cathode active material in some cases, thereby making the kinetic properties of the cathode active material better.
  • transition metal such as manganese
  • the average particle size range of the core prepared in this application is 50-500nm, and the Dv50 is 200-300nm.
  • the primary particle sizes of the core are all in the range of 50-500nm, and Dv50 is 200-300nm. If the average particle size of the core is too large (more than 500nm), the capacity of the secondary battery using this material will be affected; if the average particle size of the core is too small, the specific surface area will be large, and it will be easy to agglomerate and difficult to Achieve uniform coverage.
  • the inventor of the present application cut out the middle region (core region) of the prepared cathode active material particles through a focused ion beam (FIB for short), and used a transmission electron microscope (TEM for short) and X-ray energy spectrum analysis (EDS for short) was tested and found that each element was evenly distributed without aggregation.
  • FIB focused ion beam
  • TEM transmission electron microscope
  • EDS X-ray energy spectrum analysis
  • crystalline means that the degree of crystallinity is above 50%, that is, from 50% to 100%. Crystallinity less than 50% is called glassy state (or amorphous state).
  • the crystalline pyrophosphates and crystalline phosphates described herein have a crystallinity of 50% to 100%.
  • Pyrophosphate and phosphate with a certain degree of crystallinity are not only conducive to giving full play to the pyrophosphate coating layer's ability to hinder the elution of manganese ions and the phosphate coating layer's excellent ability to conduct lithium ions and reduce interface side reactions, but also enable The pyrophosphate coating layer and the phosphate coating layer can achieve better lattice matching, thereby achieving a tighter combination of the coating layers.
  • the crystallinity of the first coating layer material crystalline pyrophosphate and the second coating layer material crystalline phosphate of the positive electrode active material can be tested by conventional technical means in the art, for example, by density methods, infrared spectroscopy, differential scanning calorimetry and nuclear magnetic resonance absorption methods, and can also be tested by, for example, X-ray diffraction.
  • a specific X-ray diffraction method for testing the crystallinity of the first coating layer crystalline pyrophosphate and the second coating layer crystalline phosphate of the positive electrode active material may include the following steps: take a certain amount of positive electrode active material powder, The total scattering intensity is measured by The state is independent; then the crystalline scattering and amorphous scattering are separated from the diffraction pattern. The crystallinity is the ratio of the crystalline part scattering to the total scattering intensity.
  • the crystallinity of pyrophosphate and phosphate in the coating layer can be adjusted, for example, by adjusting the process conditions of the sintering process, such as sintering temperature, sintering time, and the like.
  • pyrophosphate serves as the first coating layer to effectively isolate the doped metal ions from the electrolyte.
  • the structure of crystalline pyrophosphate is stable. Therefore, crystalline pyrophosphate coating can effectively inhibit the dissolution of transition metals and improve cycle performance.
  • the bond between the first cladding layer and the core is similar to a heterojunction, and the strength of the bond is limited by the degree of lattice matching.
  • the degree of bonding between the first cladding layer and the core is measured mainly by calculating the mismatch between the lattice constants of the core and the cladding. In this application, after the A and R elements are doped in the core, the matching degree between the core and the first cladding layer is improved compared with the non-doped elements. can be brought closer together.
  • Crystalline phosphate was chosen as the second coating layer, firstly, because it has a high lattice match with the first layer of coating crystalline pyrophosphate (the mismatch is only 3%); secondly, phosphate Its own stability is better than that of pyrophosphate, and coating pyrophosphate with it will help improve the stability of the cathode active material.
  • the structure of crystalline phosphate is very stable and has excellent ability to conduct lithium ions. Therefore, coating with crystalline phosphate can effectively reduce the interface side reactions between the positive electrode active material and the electrolyte, thereby improving the performance of secondary batteries. High temperature cycle performance and high temperature storage performance.
  • the lattice matching between the second cladding layer and the first cladding layer is similar to the above-mentioned combination between the first cladding layer and the core.
  • the lattice mismatch is less than 5%, the lattice matching is relatively small. Well, the two are easily combined closely.
  • carbon is used as the third coating layer. Since electrochemical reactions occur when used in secondary batteries, electrons are required to participate. Therefore, in order to increase electron transmission between particles and at different locations on the particles, materials with excellent conductive properties can be used. Carbon is used to coat the positive active material. Carbon coating can effectively improve the conductive properties and desolvation ability of cathode active materials.
  • the fourth coating layer includes one or more of polysiloxane with a linear structure and polysiloxane with a cyclic structure.
  • the Si-O skeleton of the polysiloxane can remove F-containing ions in the electrolyte. Alleviating the erosion of acidic substances on the surface of the positive active material; polysiloxane has a certain degree of hydrophobicity, which can increase the contact angle between the electrolyte and the positive electrode piece, further alleviating the erosion of the electrolyte on the surface of the positive active material; in addition, the fourth package
  • the coating also serves to reduce contact between the electrolyte and the core.
  • the average particle size of the primary particles of the cathode active material ranges from 50 to 500 nm, and the volume median particle size Dv50 ranges from 200 to 300 nm. Since particles will agglomerate, the actual measured secondary particle size after agglomeration may be 500-40000nm.
  • the size of the positive active material particles will affect the processing of the material and the compacted density performance of the pole piece. By selecting the average particle size of the primary particles to be within the above range, the following situation can be effectively avoided: the average particle size of the primary particles of the positive electrode active material is too small, which may cause particle agglomeration, difficulty in dispersion, and requires more adhesive.
  • the binder causes the electrode piece to be less brittle; the average particle size of the primary particles of the positive electrode active material is too large, which may cause larger gaps between particles and reduce the compacted density.
  • the lattice change rate of lithium manganese phosphate and the dissolution of manganese ions during the lithium deintercalation process can be effectively suppressed, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.
  • the interplanar distance of the crystalline pyrophosphate in the first coating layer ranges from 0.293 to 0.470 nm, and the angle range of the crystal direction (111) ranges from 18.00° to 32.00°; the third The interplanar spacing of the crystalline phosphate in the second coating layer ranges from 0.244 to 0.425 nm, and the included angle of the crystal orientation (111) ranges from 20.00° to 37.00°.
  • Both the first coating layer and the second coating layer in the cathode active material described in this application use crystalline materials.
  • the crystalline pyrophosphate and crystalline phosphate in the coating layer can be characterized by conventional technical means in the art, or by means of a transmission electron microscope (TEM), for example. Under TEM, the core and cladding layers can be distinguished by testing the interplanar spacing.
  • TEM transmission electron microscope
  • the specific testing method for the interplanar spacing and angle of crystalline pyrophosphate and crystalline phosphate in the coating layer may include the following steps: take a certain amount of coated positive electrode active material sample powder in a test tube, and place it in a test tube. Inject a solvent such as alcohol into the test tube, and then stir thoroughly to disperse. Then use a clean disposable plastic straw to take an appropriate amount of the above solution and drop it on the 300 mesh copper grid. At this time, some powder will remain on the copper grid. Transfer the copper grid together with the sample. Go to the TEM sample cavity for testing and obtain the original TEM test picture. Open the original picture obtained by the above TEM test in the diffractometer software, and perform Fourier transform to obtain the diffraction pattern. Measure the distance from the diffraction spot in the diffraction pattern to the center position to obtain the interplanar spacing. The angle can be calculated according to the Bragg equation. Calculated.
  • the difference between the interplanar spacing range of crystalline pyrophosphate and the existence of crystalline phosphate can be directly judged by the value of the interplanar spacing.
  • Crystalline pyrophosphate and crystalline phosphate within the above-mentioned crystal plane spacing and included angle range can more effectively suppress the lattice change rate of lithium manganese phosphate and the dissolution of manganese ions during the lithium deintercalation process, thereby improving the secondary battery High temperature cycle performance and high temperature storage performance.
  • the ratio of y to 1-y is 1:10 to 1:1, optionally 1:4 to 1:1.
  • y represents the sum of the stoichiometric numbers of the Mn-site doping element A.
  • the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249.
  • z represents the sum of stoichiometric numbers of the P-site doping elements R.
  • the carbon in the third coating layer is a mixture of SP2 form carbon and SP3 form carbon.
  • the molar ratio of the SP2 form carbon to SP3 form carbon is in the range of 0.1-10. Any value, selectable as any value in the range of 2.0-3.0.
  • the molar ratio of the SP2 form carbon to the SP3 form carbon may be about 0.1, about 0.2, about 03, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1, About 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10, or within any range of any of the above values.
  • the comprehensive electrochemical performance of the secondary battery is improved.
  • the following situation can be effectively avoided: If the carbon in the cladding layer is all amorphous In the SP3 form, the conductivity is poor; if they are all in the graphitized SP2 form, although the conductivity is good, there are few lithium ion paths, which is not conducive to the deintercalation of lithium ions.
  • limiting the molar ratio of SP2 form carbon to SP3 form carbon within the above range can not only achieve good conductivity, but also ensure the passage of lithium ions, which is beneficial to improving the kinetic performance and cycle performance of secondary batteries.
  • the structure and characteristics of the third coating layer carbon can be measured by Raman (Raman) spectroscopy.
  • the specific test method is as follows: by peak splitting the energy spectrum of the Raman test, Id/Ig is obtained (where Id is SP3 form carbon The peak intensity of Ig is the peak intensity of SP2 form carbon), so as to confirm the molar ratio of the two.
  • the polymer in the fourth coating layer includes at least one structural unit represented by Formula 1,
  • R 1 and R 2 each independently represent H or at least one of the group consisting of the following functional groups: -COOH, -OH, -SH, -CN, -SCN, amino, phosphate group, carboxylate group, amide group, aldehyde group, sulfonyl group, polyether segment, C1 ⁇ C20 aliphatic hydrocarbon group, C1 ⁇ C20 halogenated aliphatic hydrocarbon group, C1 ⁇ C20 heteroaliphatic hydrocarbon group, C1 ⁇ C20 halogenated heteroaliphatic hydrocarbon group, C6 ⁇ C20 aromatic hydrocarbon group, C6 ⁇ C20 halogenated aromatic hydrocarbon group, C2 ⁇ C20 heteroaromatic hydrocarbon group, C2 ⁇ C20 halogenated heteroaromatic hydrocarbon group.
  • R 1 and R 2 each independently represent H or at least one of the group consisting of the following functional groups: -OH, -SH, amino, phosphate group, polyether segment, C1 to C8 alkyl, C1 ⁇ C8 haloalkyl, C1 ⁇ C8 heteroalkyl, C1 ⁇ C8 haloheteroalkyl, C2 ⁇ C8 alkenyl, C2 ⁇ C8 haloalkenyl.
  • These functional groups can complex manganese ions, reduce the dissolution of manganese ions, and can also remove F-containing ions in the electrolyte, further alleviate the erosion of the acidic substances in the electrolyte on the surface of the positive active material, reduce interface side reactions, and reduce gas production, further Improve the cycle performance and high-temperature storage performance of secondary batteries.
  • the linear-structured polysiloxane may further include an end-capping group.
  • the end-capping group includes at least one of the following functional groups: polyether, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl.
  • the linear structure polysiloxane includes hydroxyl-terminated polydimethylsiloxane, mercaptopropyl polysiloxane, aminoethylaminopropyl polydimethylsiloxane, side chain polysiloxane One or more of ether grafted polydimethylsiloxane and side chain phosphate grafted polydimethylsiloxane.
  • the cathode active material can also have both good kinetic properties and high-temperature storage properties. And it can effectively avoid the following situations: the number average molecular weight of the polymer is too small, and it has no obvious coating modification effect on the core, and the improvement of the cycle performance of the secondary battery is not obvious; the number average molecular weight of the polymer is too large, and its The hydrophobicity may be strong, which may affect the kinetic performance of the secondary battery, and may also lead to poor coating modification effects.
  • the mass percentage of polar functional groups in the polysiloxane is ⁇ , 0 ⁇ 50%, optionally, 5% ⁇ 30%.
  • “mass percentage of polar functional groups in polysiloxane” refers to the mass proportion of polar functional groups in R 1 , R 2 and end-capping groups in polysiloxane.
  • ⁇ represents the mass fraction of these polar functional groups in polysiloxane; when the above polar functional groups are not directly connected to silicon atoms, ⁇ represents the sum of the polar functional groups and their The sum of the mass fractions of directly connected divalent to tetravalent methyl groups (such as -CH 2 , -CH-, -C-, etc.) in polysiloxane, where "divalent to tetravalent methyl" means the same as the polar
  • divalent to tetravalent methyl groups such as -CH 2 , -CH-, -C-, etc.
  • ⁇ refers to the mass percentage of -CF 3 , excluding the ethylene group; taking polymethylchloropropylsiloxane as an example, ⁇ is Refers to the mass percentage of -CH 2 Cl, excluding the ethylene group; taking hydroxypropyl-terminated polydimethylsiloxane as an example, ⁇ refers to the mass percentage of -CH 2 OH.
  • the mass percentage of polar functional groups in polysiloxane can be determined by methods known in the art, such as titration (such as acid-base titration, redox titration, precipitation titration), infrared spectroscopy, and nuclear magnetic resonance. Determined by spectroscopy.
  • the coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, and more optionally greater than 0 and less than or equal to 5.5% by weight. Equal to 2% by weight, based on the weight of the core.
  • the coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, and more optionally 2-4% by weight. , based on the weight of the core.
  • the coating amount of the third coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, and more optionally greater than 0 and less than or equal to 5.5% by weight. Equal to 2% by weight, based on the weight of the core.
  • the coating amount of the fourth coating layer is greater than 0 and less than or equal to 10% by weight, optionally greater than 0 and less than or equal to 5% by weight, and more optionally greater than 0 and less than or equal to 5% by weight. Equal to 2% by weight, based on the weight of the core with the first cladding layer, the second cladding layer and the third cladding layer.
  • the coating amount of the four coating layers is preferably within the above range, so that the core can be fully coated without sacrificing the cathode activity.
  • the kinetic performance, cycle performance and safety performance of the secondary battery can be further improved.
  • the coating amount is within the above range, the following situations can be effectively avoided: Too little coating means that the thickness of the coating layer is thin, which may not effectively hinder the migration of transition metals; Excessive coating amount means that the coating layer is too thick, which will affect the migration of Li + and thus affect the rate performance of the cathode active material.
  • the coating amount is within the above range, the following situations can be effectively avoided: too much coating amount may affect the overall platform voltage of the cathode active material; too little coating amount may not Achieve adequate coverage.
  • the carbon coating mainly plays the role of enhancing electron transmission between particles.
  • the structure also contains a large amount of amorphous carbon, the density of carbon is low. Therefore, if the coating amount is too high, If it is large, it will affect the compaction density of the pole piece.
  • the coating amount of the coating layer is within the above range, the following situations can be effectively avoided: when the coating amount of the coating layer is too low, its coating modification effect on the core may not be obvious; When the coating amount of the coating is too high, the battery impedance may increase, which may affect the rate performance and cycle performance of the battery.
  • the thickness of the first cladding layer is 1-10 nm.
  • the thickness of the second cladding layer is 2-15 nm.
  • the thickness of the third cladding layer is 2-25 nm.
  • the thickness of the third cladding layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm , about 13nm, about 14nm, about 15nm, about 16nm, about 17nm, about 18nm, about 19nm, about 20nm, about 21nm, about 22nm, about 23nm, about 24nm or about 25nm, or within any range of any of the above values.
  • the thickness of the fourth cladding layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, or about 10 nm, or at any value above. within any range.
  • the thickness of the first coating layer ranges from 1 to 10 nm, it is possible to avoid the possible adverse effects on the dynamic properties of the cathode active material when it is too thick, and it is possible to avoid the possibility that it may not be able to effectively block transition metal ions when it is too thin. migration issues.
  • the conductivity of the cathode active material can be increased and the compaction density of the cathode electrode sheet prepared using the cathode active material can be increased.
  • the thickness of the fourth coating layer ranges from 2 to 10 nm, it can improve the electrolyte stability of the cathode active material, reduce the erosion of the surface of the cathode active material by the electrolyte, and avoid possible damage to the cathode activity when it is too thick. Adverse effects on material dynamic properties.
  • the thickness test of the coating layer is mainly carried out through FIB.
  • the specific method may include the following steps: randomly select a single particle from the positive electrode active material powder to be tested, cut a slice with a thickness of about 100nm from the middle position or near the middle position of the selected particle, and then Conduct TEM test on the sheet, measure the thickness of the coating layer, measure 3-5 positions, and take the average value.
  • the manganese element content is in the range of 10%-35% by weight, optionally in the range of 15%-30% by weight, more optionally in the range of 17%-20% by weight, based on the weight of the cathode active material. Within the weight % range.
  • the content of the phosphorus element is in the range of 12% to 25% by weight, optionally in the range of 15% to 20% by weight, based on the weight of the cathode active material.
  • the weight ratio of manganese element to phosphorus element ranges from 0.90 to 1.25, optionally from 0.95 to 1.20.
  • the content of manganese may correspond to the content of the core.
  • limiting the content of the manganese element to the above range can effectively avoid problems such as deterioration in structural stability and density reduction of the positive electrode active material that may be caused by excessive manganese element content, thereby improving the secondary battery. It can improve the cycle, storage and compaction density performance; and can avoid problems such as low voltage platform that may be caused if the manganese content is too small, thus improving the energy density of secondary batteries.
  • limiting the content of the phosphorus element to the above range can effectively avoid the following situation: if the content of the phosphorus element is too large, the covalent nature of P-O may be too strong and affect the conductivity of small polarons, thus Affects the conductivity of the cathode active material; if the content of phosphorus is too small, the pyrophosphate in the core, the first coating layer and/or the phosphate in the second coating layer may crystallize The stability of the lattice structure decreases, thereby affecting the overall stability of the cathode active material.
  • the weight ratio of manganese to phosphorus content has the following impact on the performance of secondary batteries: If the weight ratio is too large, it means that there is too much manganese element, and the dissolution of manganese ions increases, which affects the stability and capacity of the cathode active material, thereby affecting the secondary battery.
  • the measurement of manganese and phosphorus elements can be carried out using conventional technical means in this field.
  • the following method is used to determine the content of manganese and phosphorus: dissolve the material in dilute hydrochloric acid (concentration 10-30%), use ICP to test the content of each element in the solution, and then measure and convert the content of manganese. Get its weight ratio.
  • the lattice change rate of the cathode active material with a core-shell structure before and after complete deintercalation of lithium is 4% or less, optionally 3.8% or less, and more preferably 2.0-3.8%.
  • the lithium deintercalation process of lithium manganese phosphate is a two-phase reaction.
  • the interfacial stress of the two phases is determined by the lattice change rate before and after lithium deintercalation.
  • the cathode active material with a core-shell structure described in the present application can achieve a lattice change rate of less than 4% before and after deintercalation of lithium. Therefore, the use of the cathode active material can improve the rate performance of the secondary battery.
  • the lattice change rate can be measured by methods known in the art, such as X-ray diffraction (XRD) patterns.
  • the Li/Mn anti-site defect concentration of the cathode active material having a core-shell structure is 4% or less, optionally 2.2% or less, and more preferably 1.5-2.2%.
  • the Li/Mn anti-site defect described in this application refers to the interchange of positions of Li + and Mn 2+ in the LiMnPO 4 crystal lattice.
  • the Li/Mn antisite defect concentration refers to the percentage of Li + exchanged with Mn 2+ to the total amount of Li + .
  • the Li/Mn antisite defect concentration can be tested in accordance with JIS K 0131-1996, for example.
  • the cathode active material with a core-shell structure described in this application can achieve the above-mentioned lower Li/Mn anti-site defect concentration.
  • the mechanism is not very clear, the inventor of the present application speculates that because Li + and Mn 2+ will exchange positions in the LiMnPO 4 lattice, and the Li + transmission channel is a one-dimensional channel, Mn 2+ is in Li + It will be difficult to migrate in the channel, thus hindering the transport of Li + . Therefore, the cathode active material with a core-shell structure described in this application has a low Li/Mn anti-site defect concentration within the above range. Therefore, it can avoid Mn 2+ from hindering the transport of Li + and at the same time improve the cathode activity. Capacity play and rate performance of materials.
  • the positive active material has a compacted density at 3T of 2.2g/cm or more, optionally 2.2g/ cm3 or more and 2.8g/ cm3 or less.
  • the compacted density can be measured according to GB/T 24533-2009.
  • the stable valence state of oxygen is originally -2.
  • its surface valence state is below -1.7.
  • EELS electron energy loss spectroscopy
  • a second aspect of the application provides a method for preparing a cathode active material, including the following steps:
  • the step of providing core material the core chemical formula is Li 1+x Mn 1-y A y P 1-z R z O 4 , where x is any value in the range of -0.100 to 0.100, and y is in the range of 0.001 to 0.100.
  • z is any value within the range of 0.001 to 0.100
  • the A is selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co , one or more elements among Ga, Sn, Sb, Nb and Ge, optionally one or more elements among Fe, Ti, V, Ni, Co and Mg
  • the R is selected from B, One or more elements among Si, N and S, optionally, the R is an element selected from B, Si, N and S;
  • Coating step Provide Li a MP 2 O 7 and/or M b (P 2 O 7 ) c and XPO 4 suspension respectively, add the core material to the above suspension and mix, and sintering to obtain The core of the first coating layer, the second coating layer and the third coating layer is obtained by dry-coating the core with the first coating layer, the second coating layer and the third coating layer with the polymer.
  • the salt Li a MP 2 O 7 or M b (P 2 O 7 ) c maintains electrical neutrality;
  • the M is each independently selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and one or more elements from Al;
  • the X is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al;
  • the polymer includes one or more selected from polysiloxane with linear structure and polysiloxane with cyclic structure;
  • the positive active material has a core-shell structure, which includes the inner core and a shell covering the inner core.
  • the shell includes a first coating layer covering the inner core, and a first coating layer covering the first outer core.
  • the second coating layer includes crystalline phosphate XPO 4
  • the third coating layer is carbon
  • the fourth coating layer includes a polymer, and the polymer includes one or more selected from the group consisting of polysiloxane with a linear structure and polysiloxane with a cyclic structure.
  • the step of providing core material includes the following steps:
  • Step (1) Mix and stir the manganese source, the dopant of element A and the acid in a container to obtain manganese salt particles doped with element A;
  • Step (2) Mix the manganese salt particles doped with element A with a lithium source, a phosphorus source and a dopant of element R in a solvent to obtain a slurry, and then sinter under the protection of an inert gas atmosphere to obtain doping.
  • element A and element R there is a core of element A and element R, wherein the core doped with element A and element R is Li 1+x Mn 1-y A y P 1-z R z O 4 , x is between -0.100 and 0.100 Any value within the range, y is any value within the range of 0.001 to 0.500, z is any value within the range of 0.001 to 0.100, and the A is selected from Zn, Al, Na, K, Mg, Mo, W, One or more elements from Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements from Fe, Ti, V, Ni, Co and Mg element, and the R is one or more elements selected from the group consisting of B, Si, N, and S. Alternatively, the R is one element selected from the group consisting of B, Si, N, and S.
  • the preparation method of the present application has no particular limitation on the source of materials.
  • the source of a certain element may include one of the elements, sulfates, halides, nitrates, organic acid salts, oxides or hydroxides of the element. or more, the precursor is the source that can achieve the purpose of the preparation method of the present application.
  • the dopant of element A is selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and one or more of the respective elements, carbonates, sulfates, chlorides, nitrates, organic acid salts, oxides, and hydroxides of one or more elements in Ge.
  • the dopant of the element R is an inorganic acid, a acid, an organic acid, a sulfate, a chloride salt, or one or more elements selected from B, Si, N, and S.
  • the manganese source may be a manganese-containing material known in the art that can be used to prepare lithium manganese phosphate.
  • the manganese source may be one or more selected from the group consisting of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.
  • the acid may be one or more selected from organic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, silicic acid, silicic acid, etc., and organic acids such as oxalic acid.
  • the acid is a dilute organic acid with a concentration of 60% by weight or less.
  • the lithium source may be a lithium-containing substance known in the art that can be used to prepare lithium manganese phosphate.
  • the lithium source is one or more selected from the group consisting of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.
  • the dopant of element A and the acid react in a solvent to obtain a manganese salt suspension doped with element A
  • the suspension is filtered and dried. , and sanded to obtain element A-doped manganese salt particles with a particle size of 50-200 nm.
  • the step (2) is mixed at a temperature of 20-120°C, optionally 40-120°C, for 1-12 hours.
  • the reaction temperature in step (2) can be about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C or about 120°C. °C; the mixing described in step (2) is carried out for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, About 11 hours or about 12 hours; optionally, the reaction temperature and mixing time in step (2) can be within any range of any of the above values.
  • the sintering conditions in the process of preparing A element and R element doped lithium manganese phosphate are: sintering at 600-950°C for 4-10 seconds under an inert gas or a mixed atmosphere of inert gas and hydrogen. hours; optionally, the sintering can be performed at about 650°C, about 700°C, about 750°C, about 800°C, about 850°C or about 900°C for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours; optionally, the sintering temperature and sintering time can be within any range of any of the above values.
  • the protective atmosphere is a mixed gas of 70-90% nitrogen by volume and 10-30% hydrogen by volume.
  • the first coating step dissolve the source of the element M, the phosphorus source and the acid, and optionally the lithium source in a solvent to obtain a first coating layer suspension; combine the core obtained in the step of providing the core material with the third The first coating layer suspension obtained in the first coating step is thoroughly mixed, dried, and then sintered to obtain the material covered by the first coating layer;
  • the third coating step Dissolve the carbon source in the solvent and fully dissolve it to obtain a third coating layer solution; then add the two-layer coating layer-coated material obtained in the second coating step to the third coating layer layer solution, mix evenly, dry, and then sinter to obtain a material covered with three coating layers;
  • the source of the element M is one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al.
  • the source of the element One or more of carbonates, sulfates, chlorides, nitrates, organic acid salts, oxides, and hydroxides.
  • the carbon source is one or more selected from starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.
  • the pH of the solution in which the source of element M, the phosphorus source and the acid, and optionally the lithium source are dissolved is controlled to be 3.5-6.5, and then stirred and reacted for 1-5 hours, The solution is then warmed to 50-120°C and maintained at this temperature for 2-10 hours.
  • sintering is performed at 650-800°C for 2-6 hours.
  • the reaction proceeds fully.
  • the reaction is carried out for about 1.5 hours, about 2 hours, about 3 hours, about 4 hours, about 4.5 hours or about 5 hours.
  • the reaction time of the reaction can be within any range of any of the above values.
  • the pH of the solution is controlled to be 4-6.
  • the solution is heated to about 55°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C or about 120°C, And keep at this temperature for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; optionally, the first coating In this step, the heating temperature and holding time may be within any range of any of the above values.
  • the sintering may be performed at about 650°C, about 700°C, about 750°C, or about 800°C for about 2 hours, about 3 hours, about 4 hours, about 5 hours or about 6 hours; optionally, the sintering temperature and sintering time can be within any range of any of the above values.
  • the first coating step by controlling the sintering temperature and time within the above range, the following situation can be effectively avoided: when the sintering temperature in the first coating step is too low and the sintering time is too short, As a result, the crystallinity of the first coating layer is low and there are more amorphous substances, which will lead to a decrease in the effect of inhibiting metal dissolution, thereby affecting the cycle performance and high-temperature storage performance of the secondary battery; and when the sintering temperature is too high, it will cause The presence of impurities in the first coating layer will also affect its effect of inhibiting metal dissolution, thereby affecting the cycle performance and high-temperature storage performance of the secondary battery. If the sintering time is too long, the thickness of the first coating layer will increase. , affecting the migration of Li + , thereby affecting the capacity performance and rate performance of the cathode active material.
  • the second coating step after the source of element And maintain this temperature for 2-10 hours. In some embodiments, in the second coating step, sintering is performed at 500-700°C for 6-10 hours.
  • the reaction proceeds fully.
  • the reaction is carried out for about 1.5 hours, about 2 hours, about 3 hours, about 4 hours, about 4.5 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours hours, about 9 hours or about 10 hours.
  • the reaction time of the reaction can be within any range of any of the above values.
  • the solution is heated to about 65°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C, about 120°C, about 130°C, About 140°C or about 150°C, and maintained at that temperature for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours;
  • the temperature and holding time of the heating can be within any range of any of the above values.
  • the sintering may be performed at about 550°C, about 600°C, or about 700°C for about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours;
  • the sintering temperature and sintering time may be within any range of any of the above values.
  • the second coating step by controlling the sintering temperature and time within the above range, the following situation can be effectively avoided: when the sintering temperature in the second coating step is too low and the sintering time is too short, As a result, the crystallinity of the second coating layer is low and the amorphous state is more, which reduces the surface reactivity of the cathode active material, thus affecting the cycle performance and high-temperature storage performance of the secondary battery.
  • the sintering temperature is too high, it will The appearance of impurities in the second coating layer will also affect its effect of reducing the surface reactivity of the positive active material, thus affecting the cycle performance and high-temperature storage performance of the secondary battery.
  • the second coating layer When the sintering time is too long, the second coating layer will The increased thickness of the coating affects the voltage platform of the positive active material, thereby reducing the energy density of the secondary battery.
  • the sintering in the third coating step is performed at 700-800°C for 6-10 hours.
  • the sintering may be performed at about 700°C, about 750°C, or about 800°C for about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours;
  • the sintering temperature and sintering time may be within any range of any of the above values.
  • the third coating step by controlling the sintering temperature and time within the above range, the following situation can be effectively avoided: when the sintering temperature in the third coating step is too low, the third coating The degree of graphitization of the third coating layer decreases, which affects its conductivity, thereby affecting the capacity of the cathode active material; when the sintering temperature is too high, the degree of graphitization of the third coating layer is too high, affecting the transmission of Li + , thereby affecting the cathode The capacity development of active materials, etc.; when the sintering time is too short, the coating layer will be too thin, affecting its conductivity, thereby affecting the capacity development of the positive active material; when the sintering time is too long, the coating layer will be too thick, affecting The compacted density of the positive active material, etc.
  • the drying can be performed at 100°C to 200°C, optionally 110°C to 190°C, and more optionally 120°C to 180°C. °C, or even more optionally, 120°C to 170°C, the most optional drying temperature is 120°C to 160°C, the drying time can be 3-9 hours, optionally 4-8 hours, more optionally 5 -7 hours, the best option is about 6 hours.
  • the drying (wet coating process) in the fourth coating step can be performed at 100°C to 200°C, optionally 110°C to 190°C, more optionally 120°C to 180°C, It can even be carried out at a drying temperature of 120°C to 170°C, and the best option is 120°C to 160°C.
  • the drying time is 3-9 hours, optionally 4-8 hours, and even more optionally 5-7 hours. , the most optional is about 6 hours.
  • the sintering (dry coating process) in the fourth coating step may be performed at 200-300°C for 4-10 hours.
  • the sintering may be performed at about 200°C, about 250°C, or about 300°C for about 4 hours, about 6 hours, about 8 hours, or about 10 hours; optionally,
  • the sintering temperature and sintering time may be within any range of any of the above values.
  • the fourth coating step by controlling the sintering temperature and time within the above range, the following situation can be effectively avoided: when the sintering temperature in the fourth coating step is too low or the sintering time is too short, it may cause the second The bond between the fourth coating layer and the third coating layer is not strong enough; when the sintering temperature is too high or the sintering time is too long, the polymer in the fourth coating layer may be carbonized and cannot remove F ions contained in the electrolyte. effect.
  • the secondary battery prepared by the cathode active material prepared by the cathode active material preparation method described in the present application has reduced dissolution of Mn and Mn-site doping elements after cycling, and has high-temperature storage performance, cycle performance and rate performance. Improved. In addition, the sources of raw materials are wide, the cost is low, and the process is simple, which is conducive to industrialization.
  • a third aspect of the present application provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode film layer includes the positive electrode active material of the first aspect of the present application or is formed by the positive electrode active material of the present application.
  • the cathode active material prepared by the method of the second aspect is applied, and the content of the cathode active material in the cathode film layer is 90-99.5% by weight, based on the total weight of the cathode film layer.
  • the positive electrode current collector has two surfaces opposite in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode film layer optionally further includes a positive electrode conductive agent.
  • a positive electrode conductive agent includes superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, and graphene. , at least one of carbon nanofibers.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • a metal foil aluminum foil can be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may be selected from at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.
  • the polymer material base layer can be selected from the group consisting of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), poly Ethylene (PE), etc.
  • the positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying, and cold pressing.
  • the positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring evenly.
  • the solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.
  • each positive electrode film layer (such as contact angle, porosity, etc.) given in this application refer to the parameters of the positive electrode film layer on one side of the positive electrode current collector.
  • the positive electrode film layer is disposed on both sides of the positive electrode current collector, if the parameters of the positive electrode film layer on either side meet the requirements of this application, it is deemed to fall within the protection scope of this application.
  • the above-mentioned parameter tests for the positive electrode film layer can be performed by sampling and testing during the preparation process of the electrode sheet or battery, or by sampling and testing from the prepared battery.
  • Secondary batteries also known as rechargeable batteries or storage batteries, refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged.
  • a secondary battery includes an electrode assembly and an electrolyte.
  • the electrode assembly includes a positive electrode plate, a negative electrode plate and a separator.
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows active ions to pass through.
  • the electrolyte plays a role in conducting active ions between the positive electrode piece and the negative electrode piece.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material.
  • the negative electrode current collector has two surfaces opposite in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode film layer optionally further includes a negative electrode conductive agent.
  • a negative electrode conductive agent may include superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite At least one of alkenes and carbon nanofibers.
  • the negative electrode film layer optionally further includes a negative electrode binder.
  • a negative electrode binder may include styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, At least one of polyacrylic acid PAA, polymethacrylic acid PMAA, polyacrylic acid sodium PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), carboxymethyl chitosan (CMCS) kind.
  • SBR styrene-butadiene rubber
  • SR-1B water-soluble unsaturated resin
  • acrylic resin for example, At least one of polyacrylic acid PAA, polymethacrylic acid PMAA, polyacrylic acid sodium PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), carboxymethyl chitosan (CMCS) kind.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the metal foil copper foil can be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may be selected from at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.
  • the polymer material base layer can be selected from the group consisting of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), poly Ethylene (PE), etc.
  • the electrolyte is an electrolyte solution that includes an electrolyte salt and a solvent.
  • the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate ( DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF) , methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate At least one of (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl
  • additives are optionally included in the electrolyte.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery performance. Additives for low temperature power performance, etc.
  • the material of the isolation membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation film may be a single-layer film or a multi-layer composite film. When the isolation film is a multi-layer composite film, the materials of each layer may be the same or different.
  • the positive electrode piece, the isolation film and the negative electrode piece can be made into an electrode assembly through a winding process or a lamination process.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the soft bag may be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.
  • This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. As shown in FIG. 1 , a square-structured secondary battery 5 is shown as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 is used to cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or several, and can be adjusted according to needs.
  • the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte may be assembled to form a secondary battery.
  • the positive electrode sheet, isolation film, and negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process.
  • the electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum packaging, standing, and Through processes such as formation and shaping, secondary batteries are obtained.
  • the secondary batteries according to the present application can be assembled into a battery module.
  • the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 3 is a schematic diagram of the battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 arranged in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 is used to cover the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • a fifth aspect of the present application provides an electrical device, which includes at least one of a secondary battery, a battery module, or a battery pack of the present application.
  • the secondary battery, battery module or battery pack may be used as a power source for the electrical device or as an energy storage unit for the electrical device.
  • the electrical device may be, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric Golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • FIG. 6 is a schematic diagram of an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • battery packs or battery modules can be used.
  • Step 1 Preparation of cathode active material
  • Step S2 Preparation of core Li 0.997 Mn 0.60 Fe 0.393 V 0.004 Co 0.003 P 0.997 S 0.003 O 4
  • Step S3 Preparation of the first coating layer suspension
  • Li 2 FeP 2 O 7 solution dissolve 7.4g lithium carbonate, 11.6g ferrous carbonate, 23.0g ammonium dihydrogen phosphate and 12.6g oxalic acid dihydrate in 500mL deionized water, control the pH to 5, then stir and keep at room temperature The reaction was carried out for 2 hours to obtain a solution, and then the temperature of the solution was raised to 80°C and maintained at this temperature for 4 hours to obtain a first coating layer suspension.
  • Step S4 Coating of the first coating layer
  • step S2 Add 1571.9g of the doped lithium manganese phosphate core material obtained in step S2 to the first coating layer suspension (coating material content is 15.7g) obtained in step S3, stir and mix thoroughly for 6 hours, and mix After uniformity, it was transferred to an oven at 120°C to dry for 6 hours, and then sintered at 650°C for 6 hours to obtain the pyrophosphate-coated material.
  • Step S5 Preparation of the second coating layer suspension
  • Step S6 Coating with the second coating layer
  • step S4 Add 1586.8g of the pyrophosphate-coated material obtained in step S4 to the second coating layer suspension (coating material content is 47.1g) obtained in step S5, stir and mix thoroughly for 6 hours, and mix After uniformity, it is transferred to an oven at 120°C for drying for 6 hours, and then sintered at 700°C for 8 hours to obtain a two-layer coated material.
  • Step S7 Preparation of the third coating layer aqueous solution
  • sucrose aqueous solution Dissolve 37.3g of sucrose in 500g of deionized water, then stir and fully dissolve to obtain a sucrose aqueous solution.
  • Step S8 Coating of the third coating layer
  • Step S9 Coating of the fourth coating layer
  • the four-layer coated cathode active material prepared above, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) in a weight ratio of 97.0:1.2:1.8 , stir and mix evenly to obtain the positive electrode slurry. Then, the positive electrode slurry is evenly coated on the aluminum foil at a density of 0.280g/ 1540.25mm2 , dried, cold pressed, and cut to obtain the positive electrode piece.
  • NMP N-methylpyrrolidone
  • Example 2 The method is similar to that in Example 1. The differences are shown in Table 7 and Table 8 below, and the coating amount of the fourth coating layer is 1%, based on the three-layer coated material obtained in step S8. weight scale.
  • Examples 43 to 53 replace the hydroxyl-terminated polydimethylsiloxane in Example 1 with mercaptopropylpolysiloxane (the polar functional group is -CH 2 SH, the mass percentage is 15%, the number average Molecular weight is 2000), aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH 2 NH 2 and -CH 2 NH-, mass percentage is 12%, number average molecular weight is 3700), Side chain polyether grafted polydimethylsiloxane (polar functional group is polyether segment, mass percentage is 7.1%, number average molecular weight is 15412), side chain phosphate grafted polydimethylsiloxane Alkane (polar functional group is phosphate group, mass percentage is 1.42%, number average molecular weight is 15600), polydimethylsiloxane (polar functional group mass percentage is approximately 0%, number average mole
  • Example 54 to 59 replace the coating amount of the hydroxyl-terminated polydimethylsiloxane in Example 1 with 0.01% by weight, 0.1% by weight, 2% by weight, 5% by weight, 10% by weight, and 12% by weight respectively. , based on the weight of the three-layer coated material obtained in step S8.
  • Example 6 The procedure was similar to that in Example 1, and the differences are shown in Table 9 below.
  • Examples 60 to 66 replaced the hydroxyl-terminated polydimethylsiloxane in Example 1 with polydimethylsiloxane with number average molecular weights of 400, 10000, 50000, 80000, 100000, 300000, and 400000 respectively.
  • the first coating layer material and/or the second coating layer material used are in the crystalline state by default.
  • the positive active material sample is prepared into a buckle, and the buckle is charged at a small rate of 0.05C until the current is reduced to 0.01C. Then take out the positive electrode piece from the battery and soak it in dimethyl carbonate (DMC) for 8 hours. Then it is dried, scraped into powder, and particles with a particle size less than 500nm are screened out. Take a sample and calculate its unit cell volume v1 in the same way as the above-mentioned test of fresh samples, and use (v0-v1)/v0 ⁇ 100% as the lattice change rate (unit cell volume change rate) before and after complete deintercalation of lithium. in the table.
  • DMC dimethyl carbonate
  • the cathode active material sample prepared above Take 5 g of the cathode active material sample prepared above and prepare a buckle according to the buckle preparation method described in the above embodiment. Charge with a small rate of 0.05C until the current is reduced to 0.01C. Then take out the positive electrode piece from the battery and soak it in DMC for 8 hours. Then it is dried, scraped into powder, and particles with a particle size less than 500nm are screened out. The obtained particles were measured with electron energy loss spectroscopy (EELS, the instrument model used was Talos F200S) to obtain the energy loss near-edge structure (ELNES), which reflects the density of states and energy level distribution of the element. According to the density of states and energy level distribution, the number of occupied electrons is calculated by integrating the valence band density of states data, thereby deducing the valence state of the charged surface oxygen.
  • EELS electron energy loss spectroscopy
  • the full cells prepared in the above embodiments and comparative examples were discharged to a cut-off voltage of 2.0V using a 0.1C rate after being cycled at 45°C until the capacity decayed to 80%. Then disassemble the battery, take out the negative electrode piece, randomly pick 30 discs of unit area (1540.25mm 2 ) on the negative electrode piece, and use Agilent ICP-OES730 to test the inductively coupled plasma emission spectrum (ICP). Calculate the amounts of Fe (if the Mn site of the cathode active material is doped with Fe) and Mn based on the ICP results, and then calculate the dissolution amount of Mn (and Fe doped at the Mn site) after cycles. The test standard is based on EPA-6010D-2014.
  • Porosity P [(V2-V1)/V2] ⁇ 100%.
  • V1 (cm 3 ) represents the true volume, which can be measured by using an inert gas with a small molecular diameter (such as helium) through the substitution method, combining Archimedes' principle and Bohr's law.
  • V2 (cm 3 ) represents the apparent volume
  • V2 S ⁇ H ⁇ A
  • S (cm 2 ) represents the area
  • H (cm) represents the thickness
  • A represents the number of samples.
  • the button batteries prepared in the above embodiments and comparative examples were charged to 4.3V at 0.1C, then charged at a constant voltage of 4.3V until the current was less than or equal to 0.05mA, left to stand for 5 minutes, and then discharged to 2.0V at 0.1C.
  • the discharge capacity at this time is the initial gram capacity, recorded as D0.
  • the fresh full batteries prepared in the above examples and comparative examples were allowed to stand for 5 minutes, and then discharged to 2.5V at 1/3C. Let it stand for 5 minutes, charge at 1/3C to 4.3V, and then charge at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. Let it stand for 5 minutes, and record the charging capacity at this time as C0. Discharge to 2.5V according to 1/3C, let it sit for 5 minutes, then charge to 4.3V according to 3C, let it stand for 5 minutes, and record the charging capacity at this time as C1.
  • the 3C charging constant current ratio is C1/C0 ⁇ 100%.
  • the full cells prepared in each of the above-described Examples and Comparative Examples were stored at 60° C. at 100% state of charge (SOC). Measure the open circuit voltage (OCV) and AC internal resistance (IMP) of the battery before, after and during storage to monitor SOC, and measure the volume of the battery. The full battery was taken out after every 48 hours of storage, and the open circuit voltage (OCV) and internal resistance (IMP) were tested after leaving it for 1 hour. After cooling to room temperature, the battery volume was measured using the drainage method.
  • SOC state of charge
  • the drainage method is to first separately measure the gravity F 1 of the battery using a balance that automatically converts units based on the dial data, and then completely place the battery in deionized water (density is known to be 1g/cm 3 ), and measure the gravity F of the battery at this time.
  • the buoyancy force F on the battery is F 1 -F 2
  • the battery volume V (F 1 -F 2 )/( ⁇ g).
  • the batteries in all embodiments always maintained an SOC of more than 99% during this test until the end of storage.
  • the thickness test of the coating layer mainly uses FIB to cut slices with a thickness of about 100nm from the middle of a single particle of the cathode active material prepared above, and then conducts TEM testing on the slices to obtain the original TEM test picture.
  • the thickness of the selected particles was measured at three locations and averaged.
  • This test is performed by Raman spectroscopy. By peak splitting the energy spectrum of the Raman test, Id/Ig is obtained, where Id is the peak intensity of SP3 form carbon, and Ig is the peak intensity of SP2 form carbon, thereby confirming the molar ratio of the two.
  • ACSTEM Spherical aberration electron microscopy
  • Table 10 shows the powder properties of the positive active materials in Examples 1-29 and Comparative Examples 1-18 and the properties of the prepared positive electrode sheets and batteries.
  • Table 11 shows the thickness of each coating layer of the cathode active material prepared in Examples 1-14 and Comparative Examples 3-4 and 12 and the weight ratio of manganese element and phosphorus element.
  • Table 12 shows the powder properties of the positive active materials and the properties of the prepared positive electrode sheets and batteries in Examples 30-42.
  • Table 13 shows the interplanar spacing and included angle of the first cladding layer material and the second cladding layer material in Examples 1 and 30-42.
  • Table 14 shows the powder properties of the positive active materials and the properties of the prepared positive electrode sheets and batteries in Examples 43-66.
  • the embodiment achieved a smaller lattice change rate, a smaller Li/Mn anti-site defect concentration, a larger compaction density, and a surface oxygen closer to -2 valence. valence state, less Mn and Fe dissolution after cycling, and better battery performance, such as better high-temperature storage performance and high-temperature cycle performance.

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Abstract

本申请提供一种正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置，所述正极活性材料具有核-壳结构，包括内核及包覆所述内核的壳，所述内核的化学式为Li 1+xMn 1-yA yP 1-zR zO 4，所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层、包覆所述第二包覆层的第三包覆层以及包覆所述第三包覆层的第四包覆层。本申请的正极活性材料能使二次电池具有较高的能量密度以及良好的循环性能、倍率性能和安全性能。

Description

正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置 技术领域
本申请属于电池技术领域，具体涉及一种正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置。
背景技术
近年来，二次电池被广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。随着二次电池的应用及推广，其安全性能受到越来越多的关注。磷酸锰锂由于具有容量高、安全性能好及原材料来源丰富等优势成为了目前最受关注的正极活性材料之一，然而磷酸锰锂在充电时容易发生锰离子溶出，导致容量迅速衰减。因此，有必要提供一种综合性能良好的正极活性材料。
发明内容
本申请的目的在于提供一种正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置，其能使应用所述正极活性材料的二次电池具有较高的能量密度以及良好的循环性能、倍率性能和安全性能。
本申请第一方面提供一种具有核-壳结构的正极活性材料，其包括内核及包覆所述内核的壳，其中，
所述内核的化学式为Li 1+xMn 1-yA yP 1-zR zO 4，x为在-0.100至0.100范围内的任意数值，y为在0.001至0.500范围内的任意数值，z为在0.001至0.100范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，所述R为选自B、Si、N和S中的一种或多种元素，可选地，所述R为选自B、Si、N和S中的一种元素；
所述x、y和z的值满足以下条件：使整个内核保持电中性；
所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层、包覆所述第二包覆层的第三包覆层以及包覆所述第三包覆层的第四包覆层，其中，
所述第一包覆层包括晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，0≤a≤2，1≤b≤4，1≤c≤6，所述a、b和c的值满足以下条件：使晶态焦磷酸盐Li aMP 2O 7或M b(P 2O 7) c保持电中性，
所述晶态焦磷酸盐Li aMP 2O 7和M b(P 2O 7) c中的M各自独立地为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；
所述第二包覆层包括晶态磷酸盐XPO 4，所述X为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；
所述第三包覆层为碳；
所述第四包覆层包括聚合物，所述聚合物包括选自线状结构的聚硅氧烷、环状结构的聚硅氧烷中的一种或多种。
发明人在进行大量研究后发现，通过对磷酸锰锂进行改性以及对磷酸锰锂的多层包覆，能够得到一种新型的具有核-壳结构的正极活性材料，所述正极活性材料能够实现显著降低的锰离子溶出以及降低的晶格变化率，其用于二次电池中，能够改善电池的循环性能、倍率性能、安全性能并且提高电池的容量发挥。
在本申请的任意实施方式中，所述聚合物包含至少一种式1所示的结构单元，
Figure PCTCN2022084465-appb-000001
R 1、R 2分别独立地表示H或由以下官能团组成的组中的至少一种：-COOH、-OH、-SH、-CN、-SCN、氨基、磷酸酯基、羧酸酯基、酰胺基、醛基、磺酰基、聚醚链段、C1～C20脂肪烃基、C1～C20卤代脂肪烃基、C1～C20杂脂肪烃基、C1～C20卤代杂脂肪烃基、C6～C20芳香烃基、C6～C20卤代芳香烃基、C2～C20杂芳香烃基、C2～C20卤代杂芳香烃基；可选地，R 1、R 2分别独立地表示H或由以下官能团组成的组中的至少一种：-OH、-SH、氨基、磷酸酯基、聚醚链段、C1～C8烷基、C1～C8卤代烷基、C1～C8杂烷基、C1～C8卤代杂烷基、C2～C8烯基、C2～C8卤代烯基。
这些官能团能够络合锰离子，减少锰离子溶出，同时还可以去除电解液中的含F离子，进一步缓解电解液中酸性物质对于正极活性材料表面的侵蚀、减少界面副反应、减少产气，进一步提高二次电池的循环性能和高温存储性能。
在本申请的任意实施方式中，所述线状结构的聚硅氧烷还包含封端基。可选地，所述封端基包括以下官能团组成的组中的至少一种：聚醚、C1～C8烷基、C1～C8卤代烷基、C1～C8杂烷基、C1～C8卤代杂烷基、C2～C8烯基、C2～C8卤代烯基、C6～C20芳香烃基、C1～C8烷氧基、C2～C8环氧基、羟基、C1～C8羟基烷基、氨基、C1～C8氨基烷基、羧基、C1～C8羧基烷基。
在本申请的任意实施方式中，所述线状结构的聚硅氧烷包括聚二甲基硅氧烷、聚二乙基硅氧烷、聚甲基乙基硅氧烷、聚甲基乙烯基硅氧烷、聚苯基甲基硅氧烷、聚甲基氢硅氧烷、羧基功能化聚硅氧烷、端环氧基聚硅氧烷、甲氧基封端聚二甲基硅氧烷、聚甲基氯丙基硅氧烷、巯丙基聚硅氧烷、氨乙基氨丙基聚二甲基硅氧烷、端羟丙基聚硅氧烷、端羟基聚二甲基硅氧烷、端基聚醚聚二甲基硅氧烷、侧链氨丙基聚硅氧烷、氨丙基封端聚二甲基硅氧烷、侧链羟甲基聚硅氧烷、侧链羟丙基聚硅氧烷、侧链聚醚接枝聚二甲基硅氧烷、侧链磷酸酯接枝聚二甲基硅氧烷中的一种或多种。
可选地包括端羟基聚二甲基硅氧烷、巯丙基聚硅氧烷、氨乙基氨丙基聚二甲基硅氧烷、侧链聚醚接枝聚二甲基硅氧烷、侧链磷酸酯接枝聚二甲基硅氧烷中的一种或多种。
在本申请的任意实施方式中，所述环状结构的聚硅氧烷包括1,3,5,7-八甲基环四硅氧烷、1,3,5,7-四氢-1,3,5,7-四甲基环四硅氧烷、环五聚二甲基硅氧烷、2,4,6,8-四甲基环四硅氧烷、2,4,6,8-四甲基-2,4,6,8-四乙烯基环四硅氧烷、环状聚甲基乙烯基硅氧烷、十六甲基环八硅氧烷、十四甲基环七硅氧烷、环状聚二甲基硅氧烷中的一种或多种。
在本申请的任意实施方式中，所述聚合物选自线状结构的聚硅氧烷。环状结构的聚硅氧烷的环中电子具有一定的离域性，因此，与线状结构的聚硅氧烷相比，其Si-O骨架对于富含电子的含F离子的亲和性较小，进而对电解液中含F离子的去除率略低，对二次电池循环性能的改善效果略差。
在本申请的任意实施方式中，所述聚合物的数均分子量在300000以下，可选地为400至200000。聚合物的数均分子量在合适的范围内时，还能够使正极活性材料同时兼顾良好的动力学性能和高温存储性能。
在本申请的任意实施方式中，所述聚硅氧烷中极性官能团的质量百分含量为α，0≤α＜50％，可选地，5％≤α≤30％。聚硅氧烷中极性官能团含量在合适的范围内时，其对内核的包覆改性效果更好。
在本申请的任意实施方式中，所述第一包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为大于0且小于或等于2重量％，基于所述内核的重量计。
在本申请的任意实施方式中，所述第二包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为2-4重量％，基于所述内核的重量计。
在本申请的任意实施方式中，所述第三包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为大于0且小于或等于2重量％，基于所述内核的重量计。
在本申请的任意实施方式中，所述第四包覆层的包覆量为大于0且小于或等于10重量％，可选为大于0且小于或等于5重量％，更可选为大于0且小于或等于2重量％，基于具有第一包覆层、第二包覆层和第三包覆层的内核的重量计。
本申请所述的具有核-壳结构的正极活性材料中，四层包覆层的包覆量优选在上述范围内，由此能够对所述内核进行充分包覆，并同时在不牺牲正极活性材料克容量的前提下，进一步改善二次电池的动力学性能、循环性能和安全性能。
在本申请的任意实施方式中，所述第一包覆层的厚度为1-10nm。此时能够避免第一包覆层过厚时可能产生的对材料的动力学性能的不利影响，且能够避免第一包覆层过薄时不能有效阻碍过渡金属离子的迁移的问题。
在本申请的任意实施方式中，所述第二包覆层的厚度为2-15nm。此时，所述第二包覆层的表面结构稳定，与电解液的副反应小，因此能够有效减轻界面副反应，从而提升二次电池的高温循环性能和高温存储性能。
在本申请的任意实施方式中，所述第三包覆层的厚度为2-25nm。此时能够提升正极活性材料的电导率并且提升使用所述正极活性材料制备的正极极片的压实密度。
在本申请的任意实施方式中，所述第四包覆层的厚度为2-10nm。此时能够提升正极活性材料的电解液稳定性、减少电解液对正极活性材料表面的侵蚀，并避免过厚时可能 产生的对正极活性材料动力学性能的不利影响。
在本申请的任意实施方式中，所述第一包覆层中的晶态焦磷酸盐的晶面间距范围为0.293-0.470nm，晶向(111)的夹角范围为18.00°-32.00°；所述第二包覆层中的晶态磷酸盐的晶面间距范围为0.244-0.425nm，晶向(111)的夹角范围为20.00°-37.00°。
在上述晶面间距和夹角范围内的晶态焦磷酸盐和晶态磷酸盐，能够更有效地抑制脱嵌锂过程中磷酸锰锂的晶格变化率和锰离子溶出，从而提升二次电池的高温循环性能和高温存储性能。
在本申请的任意实施方式中，y与1-y的比值为1:10至1:1，可选为1:4至1:1。由此，进一步提升二次电池的循环性能和倍率性能。
在本申请的任意实施方式中，z与1-z的比值为1:9至1:999，可选为1:499至1:249。由此，进一步提升二次电池的循环性能和倍率性能。
在本申请的任意实施方式中，所述第三包覆层的碳为SP2形态碳与SP3形态碳的混合物，可选地，所述SP2形态碳与SP3形态碳的摩尔比为在0.1-10范围内的任意数值，可选为在2.0-3.0范围内的任意数值。本申请通过将SP2形态碳与SP3形态碳的摩尔比限制在上述范围内，提升了二次电池的综合性能。
在本申请的任意实施方式中，基于正极活性材料的重量计，锰元素含量在10重量％-35重量％范围内，可选在15重量％-30重量％范围内，更可选在17重量％-20重量％范围内。此时能够有效避免若锰元素含量过大可能会引起的正极活性材料结构稳定性变差、密度下降等问题，从而提升二次电池的循环、存储和压实密度等性能；且能够避免若锰元含量过小可能会导致的电压平台低等问题，从而提升二次电池的能量密度。
在本申请的任意实施方式中，磷元素的含量在12重量％-25重量％范围内，可选在15重量％-20重量％范围内。此时能够有效避免以下情况：若磷元素的含量过大，可能会导致P-O的共价性过强而影响小极化子导电，从而影响正极活性材料的电导率；若磷元素的含量过小，可能会使所述内核、所述第一包覆层中的焦磷酸盐和/或所述第二包覆层中的磷酸盐晶格结构的稳定性下降，从而影响正极活性材料整体的稳定性。
在本申请的任意实施方式中，锰元素和磷元素的重量比范围为0.90-1.25，可选为0.95-1.20。此时能够有效避免以下情况：若该重量比过大，可能会导致锰离子溶出增加，影响正极活性材料的稳定性和二次电池的循环性能及存储性能；若该重量比过小，可能会使正极活性材料的放电电压平台下降，从而使二次电池的能量密度降低。
在本申请的任意实施方式中，所述正极活性材料在完全脱嵌锂前后的晶格变化率为4％以下，可选为3.8％以下，更可选为2.0-3.8％。此时所述正极活性材料能够改善二次电池的容量发挥和倍率性能。
在本申请的任意实施方式中，所述正极活性材料的Li/Mn反位缺陷浓度为4％以下，可选为2.2％以下，更可选为1.5-2.2％。通过Li/Mn反位缺陷浓度在上述范围内，能够避免Mn 2+阻碍Li +的传输，同时提升正极活性材料的容量发挥和倍率性能。
在本申请的任意实施方式中，所述正极活性材料在3T下的压实密度为2.2g/cm 3以上，可选地为2.2g/cm 3以上且2.8g/cm 3以下。由此，有利于提高二次电池的体积能量密度。
在本申请的任意实施方式中，所述正极活性材料的表面氧价态为-1.90以下，可选地为-1.90至-1.98。由此，通过如上所述将正极活性材料的表面氧价态限定在上述范围内， 能够减轻正极活性材料与电解液的界面副反应，从而改善二次电池的循环性能和高温存储性能等。
本申请第二方面提供一种正极活性材料的制备方法，包括以下步骤：
提供内核材料的步骤：所述内核化学式为Li 1+xMn 1-yA yP 1-zR zO 4，其中，x为在-0.100至0.100范围内的任意数值，y为在0.001至0.500范围内的任意数值，z为在0.001至0.100范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，所述R为选自B、Si、N和S中的一种或多种元素，可选地，所述R为选自B、Si、N和S中的一种元素；
包覆步骤：分别提供Li aMP 2O 7和/或M b(P 2O 7) c以及XPO 4悬浊液，将所述内核材料加入到上述悬浊液中并混合，经烧结获得具有第一包覆层、第二包覆层和第三包覆层的内核，将获得的具有第一包覆层、第二包覆层和第三包覆层的内核与聚合物通过干法包覆或湿法包覆，得到正极活性材料，其中，0≤a≤2，1≤b≤4，1≤c≤6，所述a、b和c的值满足以下条件：使晶态焦磷酸盐Li aMP 2O 7或M b(P 2O 7) c保持电中性；所述M各自独立地为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；所述X为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；所述聚合物包括选自线状结构的聚硅氧烷、环状结构的聚硅氧烷中的一种或多种；
其中，所述正极活性材料具有核-壳结构，其包括所述内核及包覆所述内核的壳，所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层、包覆所述第二包覆层的第三包覆层以及包覆所述第三包覆层的第四包覆层，所述第一包覆层包括晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，所述第二包覆层包括晶态磷酸盐XPO 4，所述第三包覆层为碳，所述第四包覆层包括聚合物，所述聚合物包括选自线状结构的聚硅氧烷、环状结构的聚硅氧烷中的一种或多种。
在本申请的任意实施方式中，所述提供内核材料的步骤包括以下步骤：
步骤(1)：将锰源、元素A的掺杂剂和酸在容器中混合并搅拌，得到掺杂有元素A的锰盐颗粒；
步骤(2)：将所述掺杂有元素A的锰盐颗粒与锂源、磷源和元素R的掺杂剂在溶剂中混合并得到浆料，在惰性气体气氛保护下烧结后得到掺杂有元素A和元素R的内核，其中，所述掺杂有元素A和元素R的内核为Li 1+xMn 1-yA yP 1-zR zO 4，x为在-0.100至0.100范围内的任意数值，y为在0.001至0.500范围内的任意数值，z为在0.001至0.100范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，所述R为选自B、Si、N和S中的一种或多种元素，可选地，所述R为选自B、Si、N和S中的一种元素。
在本申请的任意实施方式中，所述步骤(1)在20-120℃、可选为40-120℃的温度下进行混合。
在本申请的任意实施方式中，所述步骤(1)中所述搅拌在400-700rpm下进行1-9小时，可选地为3-7小时。
当内核颗粒制备过程中的加热温度和搅拌时间处于上述范围内时，制备获得的内核以及由其制得的正极活性材料的晶格缺陷较少，有利于抑制锰离子溶出，减少正极活性材料与电解液的界面副反应，从而改善二次电池的循环性能和安全性能。
在本申请的任意实施方式中，所述步骤(2)在20-120℃、可选为40-120℃的温度下进行混合1-10小时。
在本申请的任意实施方式中，所述元素A的掺杂剂为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素各自的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
在本申请的任意实施方式中，所述元素R的掺杂剂为选自B、Si、N和S中的一种或多种元素各自的无机酸、有机酸、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
在本申请的任意实施方式中，所述包覆步骤包括：
第一包覆步骤：将元素M的源、磷源和酸以及任选地锂源，溶于溶剂中，得到第一包覆层悬浊液；将提供内核材料的步骤中获得的内核与第一包覆步骤获得的第一包覆层悬浊液充分混合，干燥，然后烧结，得到第一包覆层包覆的材料；
第二包覆步骤：将元素X的源、磷源和酸溶于溶剂中，得到第二包覆层悬浊液；将第一包覆步骤中获得的第一包覆层包覆的材料与第二包覆步骤获得的第二包覆层悬浊液充分混合，干燥，然后烧结，得到两层包覆层包覆的材料；
第三包覆步骤：将碳源溶于溶剂中，充分溶解得到第三包覆层溶液；然后将第二包覆步骤中获得的两层包覆层包覆的材料加入所述第三包覆层溶液中，混合均匀，干燥，然后烧结得到三层包覆层包覆的材料；
第四包覆步骤：将聚合物溶于溶剂中，充分溶解得到第四包覆层溶液；然后将第三包覆步骤中获得的三层包覆层包覆的材料加入所述第四包覆层溶液中，混合均匀，干燥，得到四层包覆层包覆的材料，即正极活性材料，或者将第三包覆步骤中获得的三层包覆层包覆的材料与聚合物混合均匀，然后烧结得到四层包覆层包覆的材料，即正极活性材料。
在本申请的任意实施方式中，所述第一包覆步骤中，控制溶解有元素M的源、磷源和酸以及任选地锂源的溶液pH为3.5-6.5，然后搅拌并反应1-5小时，然后将所述溶液升温至50-120℃，并保持该温度2-10小时。
在本申请的任意实施方式中，所述第一包覆步骤中，所述烧结在650-800℃下进行2-6小时。
通过将所述第一包覆步骤的条件控制在上述范围内，能够保证甚至改善使用所述正极活性材料制备的二次电池的容量发挥、循环性能、高温存储性能以及倍率性能等。
在本申请的任意实施方式中，所述第二包覆步骤中，将元素X的源、磷源和酸溶于溶剂后，搅拌并反应1-10小时，然后将所述溶液升温至60-150℃，并保持该温度2-10小时。
在本申请的任意实施方式中，所述第二包覆步骤中，烧结在500-700℃下进行6-10小时。
在所述提供内核材料的步骤和所述第一包覆步骤和所述第二包覆步骤中，在烧结之前，即，在发生化学反应的内核材料的制备中(步骤(1)-(2))以及在第一包覆层悬浮液和第二包覆层悬浮液的制备中，通过如上所述选择的反应温度和反应时间，能够避免以下情况：反应温度过低时，则反应无法发生或反应速率较慢；温度过高时，产物分解或形成杂相；反应时间过长时，产物粒径较大，可能会增加后续工艺的时间和难度；反应时间过短时，则反应不完全，获得的产物较少。
在本申请的任意实施方式中，所述第三包覆步骤中的烧结在700-800℃下进行6-10小时。
通过将所述第三包覆步骤的条件控制在上述范围内，能够改善正极活性材料的容量发挥和压实密度。
本申请所述的正极活性材料的制备方法，原料来源广泛、成本低廉，工艺简单，有利于实现工业化。
本申请第三方面提供一种正极极片，包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，所述正极膜层包括本申请第一方面的正极活性材料、或通过本申请第二方面的方法制备的正极活性材料，并且所述正极活性材料在所述正极膜层中的含量为90-99.5重量％，基于所述正极膜层的总重量计。
在本申请的任意实施方式中，所述正极活性材料在所述正极膜层中的含量为95-99.5重量％，基于所述正极膜层的总重量计。
在本申请的任意实施方式中，所述正极膜层与非水有机溶剂之间的固液接触角在3°至90°之间，可选地在3°至60°之间，进一步地在10°至30°之间。接触角在合适的范围内时，二次电池能够同时兼顾较高的能量密度以及良好的倍率性能、循环性能以及高温存储性能。
在本申请的任意实施方式中，所述正极膜层的孔隙率为15％至50％，可选地为15％至30％。孔隙率在合适的范围内时，二次电池能够同时兼顾较高的能量密度以及良好的倍率性能、循环性能以及高温存储性能。
本申请的正极极片用于二次电池中，能够改善二次电池能量密度、循环性能、倍率性能和安全性能。
本申请第四方面提供一种二次电池，包括本申请第一方面的正极活性材料、或通过本申请第二方面的方法制备的正极活性材料、或本申请第三方面的正极极片。
本申请第五方面提供一种用电装置，包括本申请第四方面的二次电池。
本申请的正极极片、二次电池、用电装置包括本申请的正极活性材料，因而至少具有与所述正极活性材料相同的优势。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请的二次电池的一实施方式的示意图。
图2是图1的二次电池的实施方式的分解示意图。
图3是本申请的电池模块的一实施方式的示意图。
图4是本申请的电池包的一实施方式的示意图。
图5是图4所示的电池包的实施方式的分解示意图。
图6是包含本申请的二次电池作为电源的用电装置的一实施方式的示意图。
在附图中，附图未必按照实际的比例绘制。其中，附图标记说明如下：1电池包，2上箱体，3下箱体，4电池模块，5二次电池，51壳体，52电极组件，53盖板。
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组 分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
本申请中，“约”某个数值表示一个范围，表示该数值±10％的范围。
需要说明的是，在本文中，术语“包覆层”是指包覆在磷酸锰锂内核上的物质层，所述物质层可以完全或部分地包覆磷酸锰锂内核，使用“包覆层”只是为了便于描述，并不意图限制本发明。另外，每一层包覆层可以是完全包覆，也可以是部分包覆。同样地，术语“包覆层的厚度”是指包覆在磷酸锰锂内核上的所述物质层在磷酸锰锂内核径向上的厚度。
在本文中，中值粒径Dv50是指材料累计体积分布百分数达到50％时所对应的粒径。在本申请中，材料的中值粒径Dv50可采用激光衍射粒度分析法测定。例如参照标准GB/T 19077-2016，使用激光粒度分析仪(例如Malvern Master Size 3000)进行测定。
在本文中，术语“脂肪烃基”包括烷基、烯基和炔基，术语“杂脂肪烃基”是指脂肪烃基中含有杂原子(例如N、O、S等)。术语“杂烷基”是指烷基中含有杂原子(例如N、O、S等)，例如可以为烷氧基、烷硫基等。
本申请发明人在实际作业中发现，目前现有的磷酸锰锂正极活性材料在深度充放电过程中，锰离子溶出比较严重。虽然现有技术中有尝试对磷酸锰锂进行磷酸铁锂包覆，从而减少界面副反应，但这种包覆无法阻止溶出的锰离子继续向电解液中迁移。溶出的锰离子在迁移到负极后，被还原成金属锰。这样产生的金属锰相当于“催化剂”，能够催化负极表面的SEI膜(solid electrolyte interphase，固态电解质界面膜)分解，产生副产物；所述副产物的一部分为气体，因此导致会二次电池发生膨胀，影响二次电池的安全性能；另外，所述副产物的另一部分沉积在负极表面，会阻碍锂离子进出负极的通道，造成二次电池阻抗增加，从而影响二次电池的动力学性能。此外，为补充损失的SEI膜，电解液和电池内部的活性锂被不断消耗，会给二次电池容量保持率带来不可逆的影响。
发明人在进行大量研究后发现，通过对磷酸锰锂进行改性以及对磷酸锰锂的多层包覆，能够得到一种新型的具有核-壳结构的正极活性材料，所述正极活性材料能够实现显著降低的锰离子溶出以及降低的晶格变化率，其用于二次电池中，能够改善电池的循环性能、倍率性能、安全性能并且提高电池的容量发挥。
正极活性材料
本申请的第一方面提供了一种新型的具有核-壳结构的正极活性材料，其包括内核及包覆所述内核的壳，其中，
所述内核的化学式为Li 1+xMn 1-yA yP 1-zR zO 4，x为在-0.100至0.100范围内的任意数值，y为在0.001至0.500范围内的任意数值，z为在0.001至0.100范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，所述R为选自B、Si、N和S中的一种或多种元素，可选地，所述R为选自B、Si、N和S中的一种元素；
所述x、y和z的值满足以下条件：使整个内核保持电中性；
所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层、包覆所述第二包覆层的第三包覆层以及包覆所述第三包覆层的第四包覆层，其中，
所述第一包覆层包括晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，0≤a≤2，1≤b≤4，1≤c≤6，所述a、b和c的值满足以下条件：使晶态焦磷酸盐Li aMP 2O 7或M b(P 2O 7) c保持电中性，所述晶态焦磷酸盐Li aMP 2O 7和M b(P 2O 7) c中的M各自独立地为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；
所述第二包覆层包括晶态磷酸盐XPO 4，所述X为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；
所述第三包覆层为碳；
所述第四包覆层包括聚合物，所述聚合物包括选自线状结构的聚硅氧烷、环状结构的聚硅氧烷中的一种或多种。
除非另有说明，否则上述内核的化学式中，当A为两种以上元素时，上述对于y数值范围的限定不仅是对每种作为A的元素的化学计量数的限定，也是对各个作为A的元素的化学计量数之和的限定。例如当A为两种以上元素A1、A2……An时，A1、A2……An各自的化学计量数y1、y2……yn各自均需落入本申请对y限定的数值范围内，且y1、y2……yn之和也需落入该数值范围内。类似地，对于R为两种以上元素的情况，本申请中对R化学计量数的数值范围的限定也具有上述含义。
在一个可选的实施方式中，当A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种、两种、三种或四种元素时，A y为Q n1D n2E n3K n4，其中n1+n2+n3+n4＝y，且n1、n2、n3、n4均为正数且不同时为零，Q、D、E、K各自独立地为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge的一种，可选地，Q、D、E、K中至少一个为Fe。可选地，n1、n2、n3、n4之一为零，其余不为零；更可选地，n1、n2、n3、n4中的两个为零，其余不为零；还可选地，n1、n2、n3、n4中的三个为零，其余不为零。所述内核Li 1+xMn 1-yA yP 1-zR zO 4中，在锰位掺杂一种、两种、三种或四种上述A元素是有利的，可选地，掺杂一种、两种或三种上述A元素；此外，在磷位掺杂一种或两种R元素是有利的，这样有利于使掺杂元素均匀分布。
所述内核Li 1+xMn 1-yA yP 1-zR zO 4中，x的大小受A和R的价态大小以及y和z的大小的影响，以保证整个体系呈现电中性。如果x的值过小，会导致整个内核体系的含锂量降低，影响正极活性材料的容量发挥。y值会限制所有掺杂元素的总量，如果y过小，即掺杂量过少，掺杂元素起不到作用，如果y超过0.5，会导致体系中的Mn含量较少，影响材料的电压平台。所述R元素掺杂在P的位置，由于P-O四面体较稳定，而z值过大会影响材料的稳定性，因此将z值限定为0.001至0.100。
本申请的正极活性材料能够提高二次电池的容量发挥、循环性能、倍率性能和安全性能。虽然机理尚不清楚，但推测是本申请的磷酸锰锂正极活性材料为核-壳结构，其中通过对磷酸锰锂内核的锰位和磷位分别掺杂元素A和元素R，不仅可有效减少锰离子溶出，进而减少迁移到负极的锰离子，减少因SEI膜分解而消耗的电解液，提高二次电池的循环性能和安全性能，还能够促进Mn-O键调整，降低锂离子迁移势垒，促进锂离子迁移， 提高二次电池的倍率性能；通过对内核包覆包括晶态焦磷酸盐的第一包覆层，能够进一步增大锰离子的迁移阻力，减少其溶出，并减少表面杂锂含量、减少内核与电解液的接触，从而减少界面副反应、减少产气，提高二次电池的高温存储性能、循环性能和安全性能；通过进一步包覆具有优异导锂离子的能力的晶态磷酸盐包覆层，可以使正极活性材料与电解液的界面副反应有效降低，进而改善二次电池的高温循环及存储性能；通过再进一步包覆碳层作为第三包覆层，能够进一步提升二次电池的安全性能和动力学性能；通过再进一步包覆聚合物作为第四包覆层，能够进一步阻碍锰离子迁移到电解液中，并减少电解液对正极活性材料表面的侵蚀、减少界面副反应、减少产气，进一步提高二次电池的循环性能和高温存储性能。
此外，在所述内核中，在磷酸锰锂的锰位掺杂的元素A还有助于减小该材料在脱嵌锂过程中磷酸锰锂的晶格变化率，提高磷酸锰锂正极活性材料的结构稳定性，大大减少锰离子的溶出并降低颗粒表面的氧活性；在磷位掺杂的元素R还有助于改变Mn-O键长变化的难易程度，从而改善电子电导并降低锂离子迁移势垒，促进锂离子迁移，提高二次电池的倍率性能。
另外，整个内核体系保持电中性，能够保证正极活性材料中的缺陷和杂相尽量少。如果正极活性材料中存在过量的过渡金属(例如锰)，由于该材料体系本身结构较稳定，那么多余的过渡金属很可能会以单质的形式析出，或在晶格内部形成杂相，保持电中性可使这样的杂相尽量少。另外，保证体系电中性还可以在部分情况下使正极活性材料中产生锂空位，从而使正极活性材料的动力学性能更优异。
本申请制备的内核的平均粒径范围为50-500nm，Dv50为200-300nm。内核的一次颗粒大小均在50-500nm的范围内，Dv50为200-300nm。如果所述内核平均粒径过大(超过500nm)，则使用该材料的二次电池的容量发挥会受到影响；如果所述内核平均粒径过小，则其比表面积较大，容易团聚，难以实现均匀包覆。
通过工艺控制(例如，对各种源的材料进行充分混合、研磨)，能够保证各元素在晶格中均匀分布，不出现聚集的情况。A元素和R元素掺杂后的磷酸锰锂的X射线衍射(XRD)图谱中的主要特征峰位置与未掺杂的LiMnPO 4的一致，说明掺杂过程没有引入杂质相，因此，所述内核性能的改善主要是来自元素掺杂，而不是杂相导致的。本申请发明人在制备本申请所述的正极活性材料后，通过聚焦离子束(简称FIB)切取已制备好的正极活性材料颗粒的中间区域(内核区域)，通过透射电子显微镜(简称TEM)以及X射线能谱分析(简称EDS)进行测试发现，各元素分布均匀，未出现聚集。
本申请中，晶态意指结晶度在50％以上，即50％至100％。结晶度小于50％的称为玻璃态(或非晶态)。本申请所述的晶态焦磷酸盐和晶态磷酸盐的结晶度为50％至100％。具备一定结晶度的焦磷酸盐和磷酸盐不但有利于充分发挥焦磷酸盐包覆层阻碍锰离子溶出和磷酸盐包覆层优异的导锂离子的能力、减少界面副反应的功能，而且能够使得焦磷酸盐包覆层和磷酸盐包覆层能够更好的进行晶格匹配，从而能够实现包覆层更紧密的结合。
本申请中，所述正极活性材料的第一包覆层物质晶态焦磷酸盐和第二包覆层物质晶态磷酸盐的结晶度可以通过本领域中常规的技术手段来测试，例如通过密度法、红外光谱法、差示扫描量热法和核磁共振吸收方法测量，也可以通过例如，X射线衍射法来测试。
具体的X射线衍射法测试正极活性材料的第一包覆层晶态焦磷酸盐和第二包覆层晶态磷酸盐的结晶度的方法可以包括以下步骤：取一定量的正极活性材料粉末，通过X射线测得总散射强度，它是整个空间物质的散射强度之和，只与初级射线的强度、正极活性材料粉末化学结构、参加衍射的总电子数即质量多少有关，而与样品的序态无关；然后从衍射图上将结晶散射和非结晶散射分开，结晶度即是结晶部分散射对散射总强度之比。
需要说明的是，在本申请中，包覆层中的焦磷酸盐和磷酸盐的结晶度例如可通过调整烧结过程的工艺条件例如烧结温度、烧结时间等进行调节。
本申请中，由于金属离子在焦磷酸盐中难以迁移，因此焦磷酸盐作为第一包覆层可以将掺杂金属离子与电解液进行有效隔离。晶态焦磷酸盐的结构稳定，因此，晶态焦磷酸盐包覆能够有效抑制过渡金属的溶出，改善循环性能。
第一包覆层与核之间的结合类似于异质结，其结合的牢固程度受晶格匹配程度的限制。晶格失配在5％以下时，晶格匹配较好，两者容易结合紧密。紧密的结合能够保证在后续的循环过程中，包覆层不会脱落，有利于保证正极活性材料的长期稳定性。第一包覆层与核之间的结合程度的衡量主要通过计算核与包覆各晶格常数的失配度来进行。本申请中，在所述内核中掺杂了A和R元素后，与不掺杂元素相比，所述内核与第一包覆层的匹配度得到改善，内核与焦磷酸盐包覆层之间能够更紧密地结合在一起。
选择晶态磷酸盐作为第二包覆层，首先，是因为它与第一层包覆物晶态焦磷酸盐的晶格匹配度较高(失配度仅为3％)；其次，磷酸盐本身的稳定性好于焦磷酸盐，用其包覆焦磷酸盐有利于提高正极活性材料的稳定性。晶态磷酸盐的结构很稳定，其具有优异导锂离子的能力，因此，使用晶态磷酸盐进行包覆能够使正极活性材料与电解液的界面副反应得到有效降低，从而改善二次电池的高温循环性能及高温存储性能。第二包覆层和第一包覆层之间的晶格匹配方式等，与上述第一包覆层和核之间的结合情况相似，晶格失配在5％以下时，晶格匹配较好，两者容易结合紧密。
碳作为第三包覆层的主要原因是碳层的电子导电性较好。由于在二次电池中应用时发生的是电化学反应，需要有电子的参与，因此，为了增加颗粒与颗粒之间的电子传输，以及颗粒上不同位置的电子传输，可以使用具有优异导电性能的碳来对正极活性材料进行包覆。碳包覆可有效改善正极活性材料的导电性能和去溶剂化能力。
第四包覆层包括线状结构的聚硅氧烷、环状结构的聚硅氧烷中的一种或多种，聚硅氧烷的Si-O骨架可以去除电解液中的含F离子，缓解酸性物质对于正极活性材料表面的侵蚀；聚硅氧烷具有一定的憎水性，能增加电解液与正极极片的接触角，进一步缓解电解液对于正极活性材料表面的侵蚀；此外，第四包覆层也可以起到减少电解液和内核接触的作用。
在一些实施方式中，所述正极活性材料的一次颗粒的平均粒径范围为50-500nm，体积中值粒径Dv50在200-300nm范围内。由于颗粒会发生团聚，因此实际测得团聚后的二次颗粒大小可能为500-40000nm。正极活性材料颗粒的大小会影响材料的加工和极片的压实密度性能。通过选择一次颗粒的平均粒径在上述范围内，从而能够有效避免以下情况：所述正极活性材料的一次颗粒的平均粒径太小，可能会引起颗粒团聚，分散困难，并且 需要较多的粘结剂，导致极片脆性较差；所述正极活性材料的一次颗粒的平均粒径太大，可能会使颗粒间的空隙较大，压实密度降低。
通过上述方案，能够有效抑制脱嵌锂过程中磷酸锰锂的晶格变化率和锰离子溶出，从而提升二次电池的高温循环性能和高温存储性能。
在一些实施方式中，所述第一包覆层中的晶态焦磷酸盐的晶面间距范围为0.293-0.470nm，晶向(111)的夹角范围为18.00°-32.00°；所述第二包覆层中的晶态磷酸盐的晶面间距范围为0.244-0.425nm，晶向(111)的夹角范围为20.00°-37.00°。
本申请所述的正极活性材料中的第一包覆层和第二包覆层均使用晶态物质。对于包覆层中的晶态焦磷酸盐和晶态磷酸盐，可通过本领域中常规的技术手段进行表征，也可以例如借助透射电镜(TEM)进行表征。在TEM下，通过测试晶面间距可以区分内核和包覆层。
包覆层中的晶态焦磷酸盐和晶态磷酸盐的晶面间距和夹角的具体测试方法可以包括以下步骤：取一定量的经包覆的正极活性材料样品粉末于试管中，并在试管中注入溶剂如酒精，然后进行充分搅拌分散，然后用干净的一次性塑料吸管取适量上述溶液滴加在300目铜网上，此时，部分粉末将在铜网上残留，将铜网连带样品转移至TEM样品腔中进行测试，得到TEM测试原始图片。将上述TEM测试所得原始图片在衍射仪软件中打开，并进行傅里叶变换得到衍射花样，量取衍射花样中衍射光斑到中心位置的距离，即可得到晶面间距，夹角可根据布拉格方程进行计算得到。
晶态焦磷酸盐的晶面间距范围和晶态磷酸盐的存在差异，可通过晶面间距的数值直接进行判断。
在上述晶面间距和夹角范围内的晶态焦磷酸盐和晶态磷酸盐，能够更有效地抑制脱嵌锂过程中磷酸锰锂的晶格变化率和锰离子溶出，从而提升二次电池的高温循环性能和高温存储性能。
在一些实施方式中，在所述内核中，y与1-y的比值为1:10至1:1，可选为1:4至1:1。此处y表示Mn位掺杂元素A的化学计量数之和。在满足上述条件时，使用所述正极活性材料的二次电池的能量密度和循环性能可进一步提升。
在一些实施方式中，在所述内核中，z与1-z的比值为1:9至1:999，可选为1:499至1:249。此处z表示P位掺杂元素R的化学计量数之和。在满足上述条件时，使用所述正极活性材料的二次电池的能量密度和循环性能可进一步提升。
在一些实施方式中，所述第三包覆层的碳为SP2形态碳与SP3形态碳的混合物，可选地，所述SP2形态碳与SP3形态碳的摩尔比为在0.1-10范围内的任意数值，可选为在2.0-3.0范围内的任意数值。
在一些实施方式中，所述SP2形态碳与SP3形态碳的摩尔比可为约0.1、约0.2、约03、约0.4、约0.5、约0.6、约0.7、约0.8、约0.9、约1、约2、约3、约4、约5、约6、约7、约8、约9或约10，或在上述任意值的任意范围内。
通过选择碳包覆层中碳的形态，从而提升二次电池的综合电化学性能。具体来说，通过使用SP2形态碳和SP3形态碳的混合形态并将SP2形态碳和SP3形态碳的比例限制在一定范围内，能够有效避免以下情况：如果包覆层中的碳都是无定形SP3形态，则导电性差；如果都是石墨化的SP2形态，则虽然导电性良好，但是锂离子通路少，不利于锂离子 的脱嵌。另外，将SP2形态碳与SP3形态碳的摩尔比限制在上述范围内，既能实现良好的导电性，又能保证锂离子的通路，因此有利于提升二次电池的动力学性能和循环性能。
所述第三包覆层碳的SP2形态和SP3形态的混合比可以通过烧结条件例如烧结温度和烧结时间来控制。例如，在使用蔗糖作为碳源制备第三包覆层的情况下，使蔗糖在高温下进行裂解后，在第二包覆层上沉积同时在高温作用下，会产生既有SP3形态也有SP2形态的碳包覆层。SP2形态碳和SP3形态碳的比例可以通过选择高温裂解条件和烧结条件来调控。
所述第三包覆层碳的结构和特征可通过拉曼(Raman)光谱进行测定，具体测试方法如下：通过对Raman测试的能谱进行分峰，得到Id/Ig(其中Id为SP3形态碳的峰强度，Ig为SP2形态碳的峰强度)，从而确认两者的摩尔比。
在一些实施方式中，所述第四包覆层中的聚合物包含至少一种式1所示的结构单元，
Figure PCTCN2022084465-appb-000002
R 1、R 2分别独立地表示H或由以下官能团组成的组中的至少一种：-COOH、-OH、-SH、-CN、-SCN、氨基、磷酸酯基、羧酸酯基、酰胺基、醛基、磺酰基、聚醚链段、C1～C20脂肪烃基、C1～C20卤代脂肪烃基、C1～C20杂脂肪烃基、C1～C20卤代杂脂肪烃基、C6～C20芳香烃基、C6～C20卤代芳香烃基、C2～C20杂芳香烃基、C2～C20卤代杂芳香烃基。可选地，R 1、R 2分别独立地表示H或由以下官能团组成的组中的至少一种：-OH、-SH、氨基、磷酸酯基、聚醚链段、C1～C8烷基、C1～C8卤代烷基、C1～C8杂烷基、C1～C8卤代杂烷基、C2～C8烯基、C2～C8卤代烯基。
这些官能团能够络合锰离子，减少锰离子溶出，同时还可以去除电解液中的含F离子，进一步缓解电解液中酸性物质对于正极活性材料表面的侵蚀、减少界面副反应、减少产气，进一步提高二次电池的循环性能和高温存储性能。
在一些实施方式中，所述线状结构的聚硅氧烷还可以包含封端基。可选地，所述封端基包括以下官能团组成的组中的至少一种：聚醚、C1～C8烷基、C1～C8卤代烷基、C1～C8杂烷基、C1～C8卤代杂烷基、C2～C8烯基、C2～C8卤代烯基、C6～C20芳香烃基、C1～C8烷氧基、C2～C8环氧基、羟基、C1～C8羟基烷基、氨基、C1～C8氨基烷基、羧基、C1～C8羧基烷基。
作为示例，所述线状结构的聚硅氧烷包括聚二甲基硅氧烷、聚二乙基硅氧烷、聚甲基乙基硅氧烷、聚甲基乙烯基硅氧烷、聚苯基甲基硅氧烷、聚甲基氢硅氧烷、羧基功能化聚硅氧烷、端环氧基聚硅氧烷、甲氧基封端聚二甲基硅氧烷、聚甲基氯丙基硅氧烷、巯丙基聚硅氧烷、氨乙基氨丙基聚二甲基硅氧烷、端羟丙基聚硅氧烷、端羟基聚二甲基硅氧烷、端基聚醚聚二甲基硅氧烷、侧链氨丙基聚硅氧烷、氨丙基封端聚二甲基硅氧烷、侧链羟甲基聚硅氧烷、侧链羟丙基聚硅氧烷、侧链聚醚接枝聚二甲基硅氧烷、侧链磷酸酯接枝聚二甲基硅氧烷中的一种或多种。
可选地，所述线状结构的聚硅氧烷包括端羟基聚二甲基硅氧烷、巯丙基聚硅氧烷、氨乙基氨丙基聚二甲基硅氧烷、侧链聚醚接枝聚二甲基硅氧烷、侧链磷酸酯接枝聚二甲基硅氧烷中的一种或多种。
作为示例，所述环状结构的聚硅氧烷包括1,3,5,7-八甲基环四硅氧烷、1,3,5,7-四氢-1,3,5,7-四甲基环四硅氧烷、环五聚二甲基硅氧烷、2,4,6,8-四甲基环四硅氧烷、2,4,6,8-四甲基-2,4,6,8-四乙烯基环四硅氧烷、环状聚甲基乙烯基硅氧烷、十六甲基环八硅氧烷、十四甲基环七硅氧烷、环状聚二甲基硅氧烷中的一种或多种。
在一些实施方式中，所述聚合物选自线状结构的聚硅氧烷。环状结构的聚硅氧烷的环中电子具有一定的离域性，因此，与线状结构的聚硅氧烷相比，其Si-O骨架对于富含电子的含F离子的亲和性较小，进而对电解液中含F离子的去除率略低，对二次电池循环性能的改善效果略差。
在一些实施方式中，所述聚合物的数均分子量在300000以下，例如，可以为400至300000、400至200000、400至100000、400至80000、400至50000、400至20000、400至10000、1000至100000、1000至50000、1000至20000、1000至10000。聚合物的数均分子量可通过本领域中已知的方法，例如采用凝胶渗透色谱法(GPC)进行测定。测试仪器可以采用PL-GPC220高温凝胶渗透色谱仪。在本申请，“聚合物”既可以是低聚物也可以是高聚物，本申请对此并不限制。
聚合物的数均分子量在合适的范围内时，还可以使正极活性材料同时兼顾良好的动力学性能和高温存储性能。并能够有效避免以下情况：聚合物的数均分子量太小，对内核起不到明显的包覆改性效果，对二次电池循环性能的提升不明显；聚合物的数均分子量太大，其疏水性可能较强，由此可能影响二次电池的动力学性能，同时也可能导致包覆改性效果不佳。
在一些实施方式中，所述聚硅氧烷中极性官能团的质量百分含量为α，0≤α＜50％，可选地，5％≤α≤30％。
在本申请中，“聚硅氧烷中极性官能团的质量百分含量”是指R 1、R 2以及封端基中的极性官能团在聚硅氧烷中的质量占比。在本申请中，极性官能团包括-COOH、-OH、-SH、-CN、-SCN、氨基(包括-NH 2、-NH-)、磷酸酯基、羧酸酯基(-COO-)、酰胺基(-CONH-)、醛基(-CHO)、磺酰基(-S(＝O) 2-)、聚醚链段、卤素、烷氧基、环氧基中的一种或多种。当上述极性官能团与硅原子直接连接时，α即表示这些极性官能团在聚硅氧烷中的质量分数；当上述极性官能团与硅原子不是直接连接时，则α表示极性官能团和与其直接连接的二价至四价甲基(例如-CH 2、-CH-、-C-等)在聚硅氧烷中的质量分数之和，这里“二价至四价甲基”表示与极性官能团直接连接且位于极性官能团和硅原子之间的碳原子以及碳原子上连接的其他非极性官能团。以聚甲基三氟丙基硅氧烷为例，α是指其中-CF 3的质量百分含量，不包括其中的亚乙基；以聚甲基氯丙基硅氧烷为例，α是指-CH 2Cl的质量百分含量，不包括其中的亚乙基；以羟丙基封端的聚二甲基硅氧烷为例，α是指-CH 2OH的质量百分含量。聚硅氧烷中极性官能团的质量百分含量可通过本领域中已知的方法，例如采用滴定法(例如酸碱滴定法、氧化还原滴定法、沉淀滴定法)、红外光谱法、核磁共振谱法进行测定。
聚硅氧烷中极性官能团含量在合适的范围内时，其对内核的包覆改性效果更好。并能够有效避免以下情况：聚硅氧烷中极性官能团含量太高时，其去除电解液中含F离子的作用不会进一步提升，但是可能导致电解液与正极极片的接触角变小，由此导致对二次电池循环性能的改善效果不明显。
在一些实施方式中，所述第一包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为大于0且小于或等于2重量％，基于所述内核的重量计。
在一些实施方式中，所述第二包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为2-4重量％，基于所述内核的重量计。
在一些实施方式中，所述第三包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为大于0且小于或等于2重量％，基于所述内核的重量计。
在一些实施方式中，所述第四包覆层的包覆量为大于0且小于或等于10重量％，可选为大于0且小于或等于5重量％，更可选为大于0且小于或等于2重量％，基于具有第一包覆层、第二包覆层和第三包覆层的内核的重量计。
本申请中，每一层的包覆量均不为零。
本申请所述的具有核-壳结构的正极活性材料中，四层包覆层的包覆量优选在上述范围内，由此能够对所述内核进行充分包覆，并同时在不牺牲正极活性材料克容量的前提下，进一步改善二次电池的动力学性能、循环性能和安全性能。
对于第一包覆层而言，通过包覆量在上述范围内，则能够有效避免以下情况：包覆量过少则意味着包覆层厚度较薄，可能无法有效阻碍过渡金属的迁移；包覆量过大则意味着包覆层过厚，会影响Li +的迁移，进而影响正极活性材料的倍率性能。
对于第二包覆层而言，通过包覆量在上述范围内，则能够有效避免以下情况：包覆量过多，可能会影响正极活性材料整体的平台电压；包覆量过少，可能无法实现足够的包覆效果。
对于第三包覆层而言，碳包覆主要起到增强颗粒间的电子传输的作用，然而由于结构中还含有大量的无定形碳，因此碳的密度较低，因此，如果包覆量过大，会影响极片的压实密度。
对于第四包覆层而言，通过包覆量在上述范围内，则能够有效避免以下情况：包覆层的包覆量太低时，其对内核的包覆改性效果可能不明显；包覆层的包覆量太高时，电池阻抗可能增加，由此可能影响电池的倍率性能和循环性能等。
在一些实施方式中，所述第一包覆层的厚度为1-10nm。
在一些实施方式中，所述第二包覆层的厚度为2-15nm。
在一些实施方式中，所述第三包覆层的厚度为2-25nm。
在一些实施方式中，所述第四包覆层的厚度为2-10nm。
在一些实施方式中，所述第一包覆层的厚度可为约2nm、约3nm、约4nm、约5nm、约6nm、约7nm、约8nm、约9nm或约10nm，或在上述任意数值的任意范围内。
在一些实施方式中，所述第二包覆层的厚度可为约2nm、约3nm、约4nm、约5nm、约6nm、约7nm、约8nm、约9nm、约10nm、约11nm、约12nm、约13nm、约14nm、约15nm，或在上述任意数值的任意范围内。
在一些实施方式中，所述第三层包覆层的厚度可为约2nm、约3nm、约4nm、约5nm、约6nm、约7nm、约8nm、约9nm、约10nm、约11nm、约12nm、约13nm、约14nm、约15nm、约16nm、约17nm、约18nm、约19nm、约20nm、约21nm、约22nm、约23nm、约24nm或约25nm，或在上述任意数值的任意范围内。
在一些实施方式中，所述第四包覆层的厚度可为约2nm、约3nm、约4nm、约5nm、约6nm、约7nm、约8nm、约9nm或约10nm，或在上述任意数值的任意范围内。
当所述第一包覆层的厚度范围为1-10nm时，能够避免过厚时可能产生的对正极活性材料的动力学性能的不利影响，且能够避免过薄时可能无法有效阻碍过渡金属离子的迁移的问题。
当所述第二包覆层的厚度在2-15nm范围内时，所述第二包覆层的表面结构稳定，与电解液的副反应小，因此能够有效减轻界面副反应，从而提升二次电池的高温循环性能和高温存储性能。
当所述第三包覆层的厚度范围为2-25nm时，能够提升正极活性材料的电导率并且提升使用所述正极活性材料制备的正极极片的压实密度。
当所述第四包覆层的厚度范围为2-10nm时，能够提升正极活性材料的电解液稳定性、减少电解液对正极活性材料表面的侵蚀，并避免过厚时可能产生的对正极活性材料动力学性能的不利影响。
包覆层的厚度大小测试主要通过FIB进行，具体方法可以包括以下步骤：从待测正极活性材料粉末中随机选取单个颗粒，从所选颗粒中间位置或中间位置附近切取100nm左右厚度的薄片，然后对薄片进行TEM测试，量取包覆层的厚度，测量3-5个位置，取平均值。
在一些实施方式中，基于正极活性材料的重量计，锰元素含量在10重量％-35重量％范围内，可选在15重量％-30重量％范围内，更可选在17重量％-20重量％范围内。
在一些实施方式中，基于正极活性材料的重量计，磷元素的含量在12重量％-25重量％范围内，可选在15重量％-20重量％范围内。
在一些实施方式中，锰元素和磷元素的重量比范围为0.90-1.25，可选为0.95-1.20。
在本申请中，在仅正极活性材料的内核中含有锰的情况下，锰的含量可与内核的含量相对应。
在本申请中，将所述锰元素的含量限制在上述范围内，能够有效避免若锰元素含量过大可能会引起的正极活性材料结构稳定性变差、密度下降等问题，从而提升二次电池的循环、存储和压实密度等性能；且能够避免若锰元含量过小可能会导致的电压平台低等问题，从而提升二次电池的能量密度。
本申请中，将所述磷元素的含量限制在上述范围内，能够有效避免以下情况：若磷元素的含量过大，可能会导致P-O的共价性过强而影响小极化子导电，从而影响正极活性材料的电导率；若磷元素的含量过小，可能会使所述内核、所述第一包覆层中的焦磷酸 盐和/或所述第二包覆层中的磷酸盐晶格结构的稳定性下降，从而影响正极活性材料整体的稳定性。
锰与磷含量重量比大小对二次电池的性能具有以下影响：该重量比过大，意味着锰元素过多，锰离子溶出增加，影响正极活性材料的稳定性和容量发挥，进而影响二次电池的循环性能及存储性能；该重量比过小，意味着磷元素过多，则容易形成杂相，会使正极活性材料的放电电压平台下降，从而使二次电池的能量密度降低。
锰元素和磷元素的测量可采用本领域中常规的技术手段进行。特别地，采用以下方法测定锰元素和磷元素的含量：将材料在稀盐酸中(浓度10-30％)溶解，利用ICP测试溶液各元素的含量，然后对锰元素的含量进行测量和换算，得到其重量占比。
在一些实施方式中，所述具有核-壳结构的正极活性材料在完全脱嵌锂前后的晶格变化率为4％以下，可选为3.8％以下，更可选为2.0-3.8％。
磷酸锰锂(LiMnPO 4)的脱嵌锂过程是两相反应。两相的界面应力由脱嵌锂前后的晶格变化率大小决定，晶格变化率越小，界面应力越小，Li +传输越容易。因此，减小内核的晶格变化率将有利于增强Li +的传输能力，从而改善二次电池的倍率性能。本申请所述的具有核-壳结构的正极活性材料能够实现4％以下的脱嵌锂前后的晶格变化率，因此使用所述正极活性材料能够改善二次电池的倍率性能。晶格变化率可通过本领域中已知的方法，例如X射线衍射(XRD)图谱测得。
在一些实施方式中，所述具有核-壳结构的正极活性材料的Li/Mn反位缺陷浓度为4％以下，可选为2.2％以下，更可选为1.5-2.2％。
本申请所述的Li/Mn反位缺陷，指的是LiMnPO 4晶格中，Li +与Mn 2+的位置发生互换。相应地，Li/Mn反位缺陷浓度指的是与Mn 2+发生互换的Li +占Li +总量的百分比。本申请中，Li/Mn反位缺陷浓度例如，可以依据JIS K 0131-1996进行测试。
本申请所述的具有核-壳结构的正极活性材料能够实现上述较低的Li/Mn反位缺陷浓度。虽然机理尚不十分清楚，但本申请发明人推测，由于LiMnPO 4晶格中，Li +与Mn 2+会发生位置互换，而Li +传输通道为一维通道，因此Mn 2+在Li +通道中将难以迁移，进而阻碍Li +的传输。由此，本申请所述的具有核-壳结构的正极活性材料由于Li/Mn反位缺陷浓度较低，在上述范围内，因此，能够避免Mn 2+阻碍Li +的传输，同时提升正极活性材料的容量发挥和倍率性能。
在一些实施方式中，所述正极活性材料在3T下的压实密度为2.2g/cm 3以上，可选地为2.2g/cm 3以上且2.8g/cm 3以下。压实密度越高，单位体积正极活性材料的重量越大，因此提高压实密度有利于提高二次电池的体积能量密度。压实密度可依据GB/T 24533-2009测量。
在一些实施方式中，所述正极活性材料的表面氧价态为-1.90以下，可选地为-1.90至-1.98。
氧的稳定价态本为-2价，价态越接近-2价，其得电子能力越强，即氧化性越强，通常情况下，其表面价态在-1.7以下。本申请通过如上所述将正极活性材料的表面氧价态限定在上述范围内，能够减轻正极活性材料与电解液的界面副反应，从而改善二次电池的循环性能和高温存储性能等。
表面氧价态可通过本领域中已知的方法测量，例如通过电子能量损失谱(EELS)测量。
制备方法
本申请的第二方面提供一种正极活性材料的制备方法，包括以下步骤：
提供内核材料的步骤：所述内核化学式为Li 1+xMn 1-yA yP 1-zR zO 4，其中，x为在-0.100至0.100范围内的任意数值，y为在0.001至0.500范围内的任意数值，z为在0.001至0.100范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，所述R为选自B、Si、N和S中的一种或多种元素，可选地，所述R为选自B、Si、N和S中的一种元素；
包覆步骤：分别提供Li aMP 2O 7和/或M b(P 2O 7) c以及XPO 4悬浊液，将所述内核材料加入到上述悬浊液中并混合，经烧结获得具有第一包覆层、第二包覆层和第三包覆层的内核，将获得的具有第一包覆层、第二包覆层和第三包覆层的内核与聚合物通过干法包覆或湿法包覆，得到正极活性材料，其中，0≤a≤2，1≤b≤4，1≤c≤6，所述a、b和c的值满足以下条件：使晶态焦磷酸盐Li aMP 2O 7或M b(P 2O 7) c保持电中性；所述M各自独立地为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；所述X为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；所述聚合物包括选自线状结构的聚硅氧烷、环状结构的聚硅氧烷中的一种或多种；
其中，所述正极活性材料具有核-壳结构，其包括所述内核及包覆所述内核的壳，所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层、包覆所述第二包覆层的第三包覆层以及包覆所述第三包覆层的第四包覆层，所述第一包覆层包括晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，所述第二包覆层包括晶态磷酸盐XPO 4，所述第三包覆层为碳，所述第四包覆层包括聚合物，所述聚合物包括选自线状结构的聚硅氧烷、环状结构的聚硅氧烷中的一种或多种。
在一些实施方式中，所述提供内核材料的步骤包括以下步骤：
步骤(1)：将锰源、元素A的掺杂剂和酸在容器中混合并搅拌，得到掺杂有元素A的锰盐颗粒；
步骤(2)：将所述掺杂有元素A的锰盐颗粒与锂源、磷源和元素R的掺杂剂在溶剂中混合并得到浆料，在惰性气体气氛保护下烧结后得到掺杂有元素A和元素R的内核，其中，所述掺杂有元素A和元素R的内核为Li 1+xMn 1-yA yP 1-zR zO 4，x为在-0.100至0.100范围内的任意数值，y为在0.001至0.500范围内的任意数值，z为在0.001至0.100范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，所述R为选自B、Si、N和S中的一种或多种元素，可选地，所述R为选自B、Si、N和S中的一种元素。
本申请的制备方法对材料的来源并没有特别的限制，某种元素的来源可包括该元素的单质、硫酸盐、卤化物、硝酸盐、有机酸盐、氧化物或氢氧化物中的一种或多种，前体是该来源可实现本申请制备方法的目的。
在一些实施方式中，所述元素A的掺杂剂为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素各自的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
在一些实施方式中，所述元素R的掺杂剂为选自B、Si、N和S中的一种或多种元素各自的无机酸、亚酸、有机酸、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种；
本申请中，锰源可为本领域已知的可用于制备磷酸锰锂的含锰物质。作为示例，所述锰源可为选自单质锰、二氧化锰、磷酸锰、草酸锰、碳酸锰中的一种或多种。
本申请中，酸可为选自盐酸、硫酸、硝酸、磷酸、硅酸、亚硅酸等有机酸和有机酸如草酸中的一种或多种。在一些实施方式中，所述酸为浓度为60重量％以下的稀的有机酸。
本申请中，锂源可为本领域已知的可用于制备磷酸锰锂的含锂物质。作为示例，所述锂源为选自碳酸锂、氢氧化锂、磷酸锂、磷酸二氢锂中的一种或多种。
本申请中，磷源可为本领域已知的可用于制备磷酸锰锂的含磷物质。作为示例，所述磷源为选自磷酸氢二铵、磷酸二氢铵、磷酸铵和磷酸中的一种或多种。
在一些实施方式中，在所述锰源、所述元素A的掺杂剂与所述酸在溶剂中反应得到掺杂有元素A的锰盐悬浮液后，将所述悬浮液过滤，烘干，并进行砂磨以得到粒径为50-200nm的经元素A掺杂的锰盐颗粒。
在一些实施方式中，将步骤(2)中的浆料进行干燥得到粉料，然后将粉料烧结得到掺杂有元素A和元素R的内核。
在一些实施方式中，所述步骤(1)在20-120℃、可选为40-120℃的温度下进行混合。
在一些实施方式中，所述步骤(1)中所述搅拌在400-700rpm下进行1-9小时，可选地为3-7小时。
可选地，所述步骤(1)中的反应温度可在约30℃、约50℃、约60℃、约70℃、约80℃、约90℃、约100℃、约110℃或约120℃进行；所述步骤(1)中所述搅拌进行约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时或约9小时；可选地，所述步骤(1)中的反应温度、搅拌时间可在上述任意数值的任意范围内。
在一些实施方式中，所述步骤(2)在20-120℃、可选为40-120℃的温度下进行混合1-12小时。可选地，所述步骤(2)中的反应温度可在约30℃、约50℃、约60℃、约70℃、约80℃、约90℃、约100℃、约110℃或约120℃进行；所述步骤(2)中所述混合进行约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时、约10小时、约11小时或约12小时；可选地，所述步骤(2)中的反应温度、混合时间可在上述任意数值的任意范围内。
当内核颗粒制备过程中的温度和时间处于上述范围内时，制备获得的内核以及由其制得的正极活性材料的晶格缺陷较少，有利于抑制锰离子溶出，减少正极活性材料与电解液的界面副反应，从而改善二次电池的循环性能和安全性能。
在一些实施方式中，可选地，在制备A元素和R元素掺杂的磷酸锰锂颗粒的过程中，控制溶液pH为3.5-6，可选地，控制溶液pH为4-6，更可选地，控制溶液pH为4-5。需 要说明的是，在本申请中可通过本领域通常使用的方法调节所得混合物的pH，例如可通过添加酸或碱。
在一些实施方式中，可选地，在步骤(2)中，所述掺杂有元素A的锰盐颗粒与锂源、磷源的摩尔比为1:(0.5-2.1):(0.5-2.1)，更可选地，所述掺杂有元素A的锰盐颗粒与锂源、磷源的摩尔比为约1:1:1。
在一些实施方式中，可选地，制备A元素和R元素掺杂的磷酸锰锂过程中的烧结条件为：在惰性气体或惰性气体与氢气混合气氛下在600-950℃下烧结4-10小时；可选地，所述烧结可在约650℃、约700℃、约750℃、约800℃、约850℃或约900℃下烧结约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时；可选地，所述烧结的温度、烧结时间可在上述任意数值的任意范围内。在制备A元素和R元素掺杂的磷酸锰锂过程中，烧结温度过低以及烧结时间过短时，会导致正极活性材料内核的结晶度较低，会影响整体的性能发挥，而烧结温度过高时，正极活性材料内核中容易出现杂相，从而影响整体的性能发挥；烧结时间过长时，正极活性材料内核颗粒长的较大，从而影响容量发挥、压实密度和倍率性能等。
在一些实施方式中，可选地，保护气氛为70-90体积％氮气和10-30体积％氢气的混合气体。
在一些实施方式中，所述包覆步骤包括：
第一包覆步骤：将元素M的源、磷源和酸以及任选地锂源，溶于溶剂中，得到第一包覆层悬浊液；将提供内核材料的步骤中获得的内核与第一包覆步骤获得的第一包覆层悬浊液充分混合，干燥，然后烧结，得到第一包覆层包覆的材料；
第二包覆步骤：将元素X的源、磷源和酸溶于溶剂中，得到第二包覆层悬浊液；将第一包覆步骤中获得的第一包覆层包覆的材料与第二包覆步骤获得的第二包覆层悬浊液充分混合，干燥，然后烧结，得到两层包覆层包覆的材料；
第三包覆步骤：将碳源溶于溶剂中，充分溶解得到第三包覆层溶液；然后将第二包覆步骤中获得的两层包覆层包覆的材料加入所述第三包覆层溶液中，混合均匀，干燥，然后烧结得到三层包覆层包覆的材料；
第四包覆步骤：将聚合物溶于溶剂中，充分溶解得到第四包覆层溶液；然后将第三包覆步骤中获得的三层包覆层包覆的材料加入所述第四包覆层溶液中，混合均匀，干燥，得到四层包覆层包覆的材料，即正极活性材料，或者将第三包覆步骤中获得的三层包覆层包覆的材料与聚合物混合均匀，然后烧结得到四层包覆层包覆的材料，即正极活性材料。
在一些实施方式中，所述元素M的源为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素各自的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
在一些实施方式中，所述元素X的源为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素各自的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
所述元素A、R、M、X各自的源的加入量取决于目标掺杂量，锂源、锰源和磷源的用量之比符合化学计量比。
作为示例，所述碳源为选自淀粉、蔗糖、葡萄糖、聚乙烯醇、聚乙二醇、柠檬酸中的一种或多种。
在一些实施方式中，所述第一包覆步骤中，控制溶解有元素M的源、磷源和酸以及任选地锂源的溶液pH为3.5-6.5，然后搅拌并反应1-5小时，然后将所述溶液升温至50-120℃，并保持该温度2-10小时。在一些实施方式中，所述第一包覆步骤中，烧结在650-800℃下进行2-6小时。
可选地，在第一包覆步骤中，所述反应充分进行。可选地，在第一包覆步骤中，所述反应进行约1.5小时、约2小时、约3小时、约4小时、约4.5小时或约5小时。可选地，第一包覆步骤中，所述反应的反应时间可在上述任意数值的任意范围内。
可选地，在第一包覆步骤中，控制溶液pH为4-6。可选地，在第一包覆步骤中，将所述溶液升温至约55℃、约60℃、约70℃、约80℃、约90℃、约100℃、约110℃或约120℃，并在该温度下保持约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时；可选地，第一包覆步骤中，所述升温的温度和保持时间可在上述任意数值的任意范围内。
可选地，在所述第一包覆步骤中，所述烧结可在约650℃、约700℃、约750℃、或约800℃下烧结约2小时、约3小时、约4小时、约5小时或约6小时；可选地，所述烧结的温度、烧结时间可在上述任意数值的任意范围内。
在所述第一包覆步骤中，通过将烧结温度和时间控制在以上范围内，能够有效避免以下情况：当所述第一包覆步骤中的烧结温度过低以及烧结时间过短时，会导致第一包覆层的结晶度低，非晶态物质较多，这样会导致抑制金属溶出的效果下降，从而影响二次电池的循环性能和高温存储性能；而烧结温度过高时，会导致第一包覆层出现杂相，也会影响到其抑制金属溶出的效果，从而影响二次电池的循环性能和高温存储性能等；烧结时间过长时，会使第一包覆层的厚度增加，影响Li +的迁移，从而影响正极活性材料的容量发挥和倍率性能等。
在一些实施方式中，所述第二包覆步骤中，将元素X的源、磷源和酸溶于溶剂后，搅拌并反应1-10小时，然后将所述溶液升温至60-150℃，并保持该温度2-10小时。在一些实施方式中，所述第二包覆步骤中，烧结在500-700℃下进行6-10小时。
可选地，在第二包覆步骤中，所述反应充分进行。可选地，在第二包覆步骤中，所述反应进行约1.5小时、约2小时、约3小时、约4小时、约4.5小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时。可选地，第二包覆步骤中，所述反应的反应时间可在上述任意数值的任意范围内。
可选地，在第二包覆步骤中，将所述溶液升温至约65℃、约70℃、约80℃、约90℃、约100℃、约110℃、约120℃、约130℃、约140℃或约150℃，并在该温度下保持约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时；可选地，第二包覆步骤中，所述升温的温度和保持时间可在上述任意数值的任意范围内。
在所述提供内核材料的步骤和所述第一包覆步骤和所述第二包覆步骤中，在烧结之前，即，在发生化学反应的内核材料的制备中(步骤(1)-(2))以及在第一包覆层悬浮液和第二包覆层悬浮液的制备中，通过如上所述选择适当的反应温度和反应时间，从 而能够有效避免以下情况：反应温度过低时，则反应无法发生或反应速率较慢；温度过高时，产物分解或形成杂相；反应时间过长时，产物粒径较大，可能会增加后续工艺的时间和难度；反应时间过短时，则反应不完全，获得的产物较少。
可选地，在第二包覆步骤中，所述烧结可在约550℃、约600℃或约700℃下烧结约6小时、约7小时、约8小时、约9小时或约10小时；可选地，所述烧结的温度、烧结时间可在上述任意数值的任意范围内。
在所述第二包覆步骤中，通过将烧结温度和时间控制在以上范围内，能够有效避免以下情况：当所述第二包覆步骤中的烧结温度过低以及烧结时间过短时，会导致第二包覆层的结晶度低，非晶态较多，降低正极活性材料表面反应活性的性能下降，从而影响二次电池的循环性能和高温存储性能等；而烧结温度过高时，会导致第二包覆层出现杂相，也会影响到其降低正极活性材料表面反应活性的效果，从而影响二次电池的循环性能和高温存储性能等；烧结时间过长时，会使第二包覆层的厚度增加，影响正极活性材料的电压平台，从而使二次电池的能量密度下降等。
在一些实施方式中，所述第三包覆步骤中的烧结在700-800℃下进行6-10小时。可选地，在第三包覆步骤中，所述烧结可在约700℃、约750℃或约800℃下烧结约6小时、约7小时、约8小时、约9小时或约10小时；可选地，所述烧结的温度、烧结时间可在上述任意数值的任意范围内。
在所述第三包覆步骤中，通过将烧结温度和时间控制在以上范围内，能够有效避免以下情况：当所述第三包覆步骤中的烧结温度过低时，会导致第三包覆层的石墨化程度下降，影响其导电性，从而影响正极活性材料的容量发挥；烧结温度过高时，会造成第三包覆层的石墨化程度过高，影响Li +的传输，从而影响正极活性材料的容量发挥等；烧结时间过短时，会导致包覆层过薄，影响其导电性，从而影响正极活性材料的容量发挥；烧结时间过长时，会导致包覆层过厚，影响正极活性材料的压实密度等。
在上述第一包覆步骤、第二包覆步骤、第三包覆步骤中，所述干燥均可以在100℃至200℃、可选为110℃至190℃、更可选为120℃至180℃、甚至更可选为120℃至170℃、最可选为120℃至160℃的干燥温度下进行，干燥时间可以为3-9小时、可选为4-8小时，更可选为5-7小时，最可选为约6小时。
在一些实施方式中，所述第四包覆步骤中的干燥(湿法包覆工艺)可在100℃至200℃、可选为110℃至190℃、更可选为120℃至180℃、甚至更可选为120℃至170℃、最可选为120℃至160℃的干燥温度下进行，干燥时间为3-9小时、可选为4-8小时，更可选为5-7小时，最可选为约6小时。
在一些实施方式中，所述第四包覆步骤中的烧结(干法包覆工艺)可在200-300℃下进行4-10小时。可选地，在第四包覆步骤中，所述烧结可在约200℃、约250℃或约300℃下烧结约4小时、约6小时、约8小时或约10小时；可选地，所述烧结的温度、烧结时间可在上述任意数值的任意范围内。
在第四包覆步骤中，通过将烧结温度和时间控制在以上范围内，能够有效避免以下情况：当所述第四包覆步骤中的烧结温度过低或烧结时间过短时，可能导致第四包覆层与第三包覆层的结合不够牢固；烧结温度过高或烧结时间过长时，可能造成第四包覆层中的聚合物碳化，不能起到去除电解液中含F离子的作用。
通过本申请所述的正极活性材料的制备方法所制备的正极活性材料，其制备的二次电池在循环后Mn与Mn位掺杂元素的溶出量降低，且高温存储性能、循环性能和倍率性能得到改善。另外，原料来源广泛、成本低廉，工艺简单，有利于实现工业化。
正极极片
本申请的第三方面提供一种正极极片，其包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，所述正极膜层包括本申请第一方面的正极活性材料或通过本申请第二方面的方法制备的正极活性材料，并且所述正极活性材料在所述正极膜层中的含量为90-99.5重量％，基于所述正极膜层的总重量计。所述正极集流体具有在自身厚度方向相对的两个表面，所述正极膜层设置于所述正极集流体的两个相对表面中的任意一者或两者上。
在一些实施方式中，所述正极活性材料在所述正极膜层中的含量为95-99.5重量％，基于所述正极膜层的总重量计。
正极膜层并不排除除了本申请第一方面的正极活性材料或通过本申请第二方面的方法制备的正极活性材料之外的其他正极活性材料，例如正极膜层还可以包括锂过渡金属氧化物及其改性化合物中的至少一种。作为示例，所述其他正极活性材料可包括锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其改性化合物中的至少一种。
在一些实施方式中，所述正极膜层还可选地包括正极导电剂。本申请对所述正极导电剂的种类没有特别的限制，作为示例，所述正极导电剂包括超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯、碳纳米纤维中的至少一种。
在一些实施方式中，所述正极膜层还可选地包括正极粘结剂。本申请对所述正极粘结剂的种类没有特别的限制，作为示例，所述正极粘结剂可包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物、含氟丙烯酸酯类树脂中的至少一种。
在一些实施方式中，所述正极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铝箔。复合集流体可包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层。作为示例，金属材料可选自铝、铝合金、镍、镍合金、钛、钛合金、银、银合金中的至少一种。作为示例，高分子材料基层可选自聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等。
在一些实施方式中，所述正极膜层与非水有机溶剂之间的固液接触角在3°至90°之间，可选地在3°至60°之间，进一步地在10°至30°之间。接触角在合适的范围内时，二次电池能够同时兼顾较高的能量密度以及良好的倍率性能、循环性能以及高温存储性能。并能够有效避免以下情况：接触角太小时，聚合物可能不能起到很好的包覆改善效果；接触角太大时，可能会造成正极膜层的电解液浸润性变差，影响二次电池的倍率性能和循环性能等。正极膜层与非水有机溶剂之间的固液接触角为本领域公知的含义，可采用本领域已知的方法进行测试，例如可以参照GBT 30693-2014进行测定。一个示例性的测试方法包括如下步骤：室温下，将非水有机溶剂液滴滴在正极极片表面，通过接触角测量仪测试其在60秒内的接触角。测试仪器可以采用德国LAUDA Scientific公司的LSA 200型 光学接触角测量仪。非水有机溶剂可采用本领域公知的用于二次电池非水电解液的非水有机溶剂，可选地，所述非水有机溶剂采用碳酸乙烯酯(EC)。
在一些实施方式中，所述正极膜层的孔隙率为15％至50％，可选地为15％至30％。孔隙率在合适的范围内时，二次电池能够同时兼顾较高的能量密度以及良好的倍率性能、循环性能以及高温存储性能。并能够有效避免以下情况：孔隙率太小时，可能会造成正极膜层的电解液浸润性变差，影响二次电池的倍率性能和循环性能等；孔隙率太大时，可能会影响二次电池整体的能量密度。正极膜层的孔隙率为本领域公知的含义，可采用本领域已知的方法进行测试，例如可以参照GB/T 24586-2009进行测定。
所述正极膜层通常是将正极浆料涂布在正极集流体上，经干燥、冷压而成的。所述正极浆料通常是将正极活性材料、可选的导电剂、可选的粘结剂以及任意的其他组分分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)，但不限于此。
需要说明的是，本申请所给的各正极膜层参数(例如接触角、孔隙率等)均指正极集流体单侧的正极膜层的参数。当正极膜层设置在正极集流体的两侧时，其中任意一侧的正极膜层参数满足本申请，即认为落入本申请的保护范围内。
此外，上述针对正极膜层的各参数测试，可以在极片或电池制备过程中取样测试，也可以从制备好的电池中取样测试。
当上述测试样品是从制备好的电池中取样时，作为示例，可以按如下步骤进行取样：将电池做放电处理(为了安全起见，一般使电池处于满放状态)；将电池拆卸后取出正极极片，使用碳酸二甲酯(DMC)将正极极片浸泡一定时间(例如2-10小时)；然后将正极极片取出并在一定温度和时间下干燥处理(例如60℃、4小时)，干燥后取出正极极片，此时即可以在干燥后的正极极片中取样测试本申请上述的正极膜层相关的各参数。
二次电池
本申请第四方面提供了一种二次电池，其包括本申请第三方面的正极极片。
二次电池又称为充电电池或蓄电池，是指在电池放电后可通过充电的方式使活性材料激活而继续使用的电池。通常情况下，二次电池包括电极组件和电解质，电极组件包括正极极片、负极极片和隔离膜。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使活性离子通过。电解质在正极极片和负极极片之间起到传导活性离子的作用。
[正极极片]
本申请的二次电池中使用的正极极片为本申请第三方面任一实施例所述的正极极片。
[负极极片]
在一些实施方式中，所述负极极片包括负极集流体以及设置在所述负极集流体至少一个表面且包括负极活性材料的负极膜层。例如，所述负极集流体具有在自身厚度方向相对的两个表面，所述负极膜层设置在所述负极集流体的两个相对表面中的任意一者或两者上。
所述负极活性材料可采用本领域公知的用于二次电池的负极活性材料。作为示例，所述负极活性材料包括但不限于天然石墨、人造石墨、软炭、硬炭、硅基材料、锡基材料、钛酸锂中的至少一种。所述硅基材料可包括单质硅、硅氧化物、硅碳复合物、硅氮复合物、硅合金材料中的至少一种。所述锡基材料可包括单质锡、锡氧化物、锡合金材 料中的至少一种。本申请并不限定于这些材料，还可以使用其他可被用作二次电池负极活性材料的传统公知的材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，所述负极膜层还可选地包括负极导电剂。本申请对所述负极导电剂的种类没有特别的限制，作为示例，所述负极导电剂可包括超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯、碳纳米纤维中的至少一种。
在一些实施方式中，所述负极膜层还可选地包括负极粘结剂。本申请对所述负极粘结剂的种类没有特别的限制，作为示例，所述负极粘结剂可包括丁苯橡胶(SBR)、水溶性不饱和树脂SR-1B、水性丙烯酸类树脂(例如，聚丙烯酸PAA、聚甲基丙烯酸PMAA、聚丙烯酸钠PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，所述负极膜层还可选地包括其他助剂。作为示例，其他助剂可包括增稠剂，例如，羧甲基纤维素钠(CMC)、PTC热敏电阻材料等。
在一些实施方式中，所述负极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铜箔。复合集流体可包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层。作为示例，金属材料可选自铜、铜合金、镍、镍合金、钛、钛合金、银、银合金中的至少一种。作为示例，高分子材料基层可选自聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等。
所述负极膜层通常是将负极浆料涂布在负极集流体上，经干燥、冷压而成的。所述负极浆料通常是将负极活性材料、可选的导电剂、可选地粘结剂、其他可选的助剂分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水，但不限于此。
所述负极极片并不排除除了所述负极膜层之外的其他附加功能层。例如在某些实施例中，本申请所述的负极极片还包括夹在所述负极集流体和所述负极膜层之间、设置于所述负极集流体表面的导电底涂层(例如由导电剂和粘结剂组成)。在另外一些实施例中，本申请所述的负极极片还包括覆盖在所述负极膜层表面的保护层。
[电解质]
本申请对所述电解质的种类没有具体的限制，可根据需求进行选择。例如，所述电解质可以选自固态电解质及液态电解质(即电解液)中的至少一种。
在一些实施方式中，所述电解质采用电解液，所述电解液包括电解质盐和溶剂。
所述电解质盐的种类不受具体的限制，可根据实际需求进行选择。在一些实施方式中，作为示例，所述电解质盐可包括六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)、四氟草酸磷酸锂(LiTFOP)中的至少一种。
所述溶剂的种类不受具体的限制，可根据实际需求进行选择。在一些实施方式中，作为示例，所述溶剂可包括碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯 (EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的至少一种。
在一些实施方式中，所述电解液中还可选地包括添加剂。例如，所述添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温功率性能的添加剂等。
[隔离膜]
采用电解液的二次电池、以及一些采用固态电解质的二次电池中，还包括隔离膜。所述隔离膜设置在所述正极极片和所述负极极片之间，主要起到防止正负极短路的作用，同时可以使活性离子通过。本申请对所述隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，所述隔离膜的材质可以包括玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。所述隔离膜可以是单层薄膜，也可以是多层复合薄膜。当所述隔离膜为多层复合薄膜时，各层的材料相同或不同。
在一些实施方式中，所述正极极片、所述隔离膜和所述负极极片可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，所述二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，所述二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。所述二次电池的外包装也可以是软包，例如袋式软包。所述软包的材质可以是塑料，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的至少一种。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图1是作为一个示例的方形结构的二次电池5。
在一些实施方式中，如图2所示，外包装可包括壳体51和盖板53。壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53用于盖设所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或几个，可根据需求来调节。
本申请的二次电池的制备方法是公知的。在一些实施方式中，可将正极极片、隔离膜、负极极片和电解液组装形成二次电池。作为示例，可将正极极片、隔离膜、负极极片经卷绕工艺或叠片工艺形成电极组件，将电极组件置于外包装中，烘干后注入电解液，经过真空封装、静置、化成、整形等工序，得到二次电池。
在本申请的一些实施例中，根据本申请的二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图3是作为一个示例的电池模块4的示意图。如图3所示，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图4和图5是作为一个示例的电池包1的示意图。如图4和图5所示，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2用于盖设下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
用电装置
本申请的第五方面提供一种用电装置，所述用电装置包括本申请的二次电池、电池模块、或电池包中的至少一种。所述二次电池、电池模块或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
所述用电装置可以根据其使用需求来选择二次电池、电池模块或电池包。
图6是作为一个示例的用电装置的示意图。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比、和比值都是基于质量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
本申请实施例涉及的原材料来源如下：
名称 化学式 厂家 规格
碳酸锰 MnCO 3 山东西亚化学工业有限公司 1Kg
碳酸锂 Li 2CO 3 山东西亚化学工业有限公司 1Kg
碳酸镁 MgCO 3 山东西亚化学工业有限公司 1Kg
碳酸锌 ZnCO 3 武汉鑫儒化工有限公司 25Kg
碳酸亚铁 FeCO 3 西安兰之光精细材料有限公司 1Kg
硫酸镍 NiCO 3 山东西亚化学工业有限公司 1Kg
硫酸钛 Ti(SO 4) 2 山东西亚化学工业有限公司 1Kg
硫酸钴 CoSO 4 厦门志信化学有限公司 500g
二氯化钒 VCl 2 上海金锦乐实业有限公司 1Kg
二水合草酸 C 2H 2O 4.2(H 2O) 上海金锦乐实业有限公司 1Kg
磷酸二氢铵 NH 4H 2PO 4 上海澄绍生物科技有限公司 500g
蔗糖 C 12H 22O 11 上海源叶生物科技有限公司 100g
稀硫酸 H 2SO 4 深圳海思安生物技术有限公司 质量分数60％
稀硝酸 HNO 3 安徽凌天精细化工有限公司 质量分数60％
亚硅酸 H 2SiO 3 上海源叶生物科技有限公司 100g，质量分数99.8％
I.电池制备
实施例1
步骤1：正极活性材料的制备
步骤S1：制备Fe、Co、V和S共掺杂的草酸锰
将689.6g碳酸锰、455.27g碳酸亚铁、4.65g硫酸钴、4.87g二氯化钒加入混料机中充分混合6小时。然后将得到的混合物转入反应釜中，并加入5L去离子水和1260.6g二水合草酸，加热至80℃，以500rpm的转速充分搅拌6小时，混合均匀，直至反应终止无气泡产生，得到Fe、Co、和V共掺杂的草酸锰悬浮液。然后将悬浮液过滤，在120℃下烘干，再进行砂磨，得到粒径为100nm的草酸锰颗粒。
步骤S2：制备内核Li 0.997Mn 0.60Fe 0.393V 0.004Co 0.003P 0.997S 0.003O 4
取(1)中制备的草酸锰1793.1g以及368.3g碳酸锂、1146.6g磷酸二氢铵和4.9g稀硫酸，将它们加入到20L去离子水中，充分搅拌，在80℃下均匀混合反应10小时，得到浆料。将所述浆料转入喷雾干燥设备中进行喷雾干燥造粒，在250℃的温度下进行干燥，得到粉料。在保护气氛(90％氮气和10％氢气)中，在700℃下将所述粉料在辊道窑中进行烧结4小时，得到上述内核材料。
步骤S3：第一包覆层悬浊液的制备
制备Li 2FeP 2O 7溶液，将7.4g碳酸锂，11.6g碳酸亚铁，23.0g磷酸二氢铵和12.6g二水合草酸溶于500mL去离子水中，控制pH为5，然后搅拌并在室温下反应2小时得到溶液，之后将该溶液升温到80℃并保持此温度4小时，得到第一包覆层悬浊液。
步骤S4：第一包覆层的包覆
将步骤S2中获得的掺杂后的1571.9g磷酸锰锂内核材料加入到步骤S3中获得的第一包覆层悬浊液(包覆物质含量为15.7g)中，充分搅拌混合6小时，混合均匀后，转入120℃烘箱中干燥6小时，然后在650℃下烧结6小时得到焦磷酸盐包覆后的材料。
步骤S5：第二包覆层悬浊液的制备
将3.7g碳酸锂、11.6g碳酸亚铁、11.5g磷酸二氢铵和12.6g二水合草酸溶于1500mL去离子水中，然后搅拌并反应6小时得到溶液，之后将该溶液升温到120℃并保持此温度6小时，得到第二包覆层悬浊液。
步骤S6：第二包覆层的包覆
将步骤S4中获得的1586.8g的焦磷酸盐包覆后的材料加入到步骤S5中得到的第二包覆层悬浊液(包覆物质含量为47.1g)中，充分搅拌混合6小时，混合均匀后，转入120℃烘箱中干燥6小时，然后700℃烧结8小时得到两层包覆后的材料。
步骤S7：第三包覆层水溶液的制备
将37.3g蔗糖溶于500g去离子水中，然后搅拌并充分溶解，得到蔗糖水溶液。
步骤S8：第三包覆层的包覆
将步骤S6中获得的两层包覆的材料1633.9g加入到步骤S7中得到的蔗糖溶液中，一同搅拌混合6小时，混合均匀后，转入150℃烘箱中干燥6小时，然后在700℃下烧结10小时得到三层包覆后的材料。
步骤S9：第四包覆层的包覆
将端羟基聚二甲基硅氧烷溶于二甲苯中形成第四包覆液，然后向其中加入步骤S8中获得的三层包覆后的材料搅拌均匀形成混合浆料，再将混合浆料置于湿包机中，在氮气气氛中、120℃干燥4小时，得到四层包覆的正极活性材料。其中，端羟基聚二甲基硅氧烷的极性官能团(即-OH)的质量百分含量为3.4％、数均分子量为1000，包覆量为1重量％，基于步骤S8中获得的三层包覆后的材料的重量计。
步骤2：正极极片的制备
将上述制备的四层包覆后的正极活性材料、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按重量比为97.0:1.2:1.8加入到N-甲基吡咯烷酮(NMP)中，搅拌混合均匀，得到正极浆料。然后将正极浆料按0.280g/1540.25mm 2均匀涂覆于铝箔上，经烘干、冷压、分切，得到正极极片。
步骤3：负极极片的制备
将负极活性材料人造石墨、硬碳、导电剂乙炔黑、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC)按照重量比为90:5:2:2:1溶于溶剂去离子水中，搅拌混合均匀后制备成负极浆料。将负极浆料按0.117g/1540.25mm 2均匀涂覆在负极集流体铜箔上，经过烘干、冷压、分切，得到负极极片。
步骤4：电解液的制备
在氩气气氛手套箱中(H 2O<0.1ppm，O 2<0.1ppm)，将有机溶剂碳酸乙烯酯(EC)/碳酸甲乙酯(EMC)按照体积比3/7混合均匀，加入12.5重量％(基于碳酸乙烯酯/碳酸甲乙酯溶剂的重量计)LiPF 6溶解于上述有机溶剂中，搅拌均匀，得到电解液。
步骤5：隔离膜的制备
使用市售的厚度为20μm、平均孔径为80nm的PP-PE共聚物微孔薄膜(来自卓高电子科技公司，型号20)。
步骤6：全电池的制备
将上述获得的正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正负极中间起到隔离的作用，并卷绕得到电极组件。将电极组件置于外包装中，注入上述电解液并封装，得到全电池(下文也称“全电”)。
【扣式电池的制备】
将上述制备的正极活性材料、聚偏二氟乙烯(PVDF)、乙炔黑以90:5:5的重量比加入至N-甲基吡咯烷酮(NMP)中，在干燥房中搅拌制成浆料。在铝箔上涂覆上述浆料，干燥、冷压制成正极极片。涂覆量为0.2g/cm 2，压实密度为2.0g/cm 3。
采用锂片作为负极，采用1mol/L的LiPF 6在体积比1:1:1的碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和碳酸二甲酯(DMC)中的溶液为电解液，与上述制备的正极极片一起在扣电箱中组装成扣式电池(下文也称“扣电”)。
实施例2至29和对比例1至18
以类似于实施例1的方式制备实施例2至29和对比例1至18中的正极活性材料和电池，正极活性材料的制备中的不同之处参见表1至表6，其中，对比例1-2、4-10和12未包覆第一层，因此没有步骤S3、S4；对比例1-11未包覆第二层，因此没有步骤S5-S6；对比例1-18均未包覆第四层，因此没有步骤S9；实施例2至4中第四包覆层的包覆量分别为2％、5％、8％，基于步骤S8中获得的三层包覆后的材料的重量计；实施例8至10中第四包覆层的包覆量均为2％，基于步骤S8中获得的三层包覆后的材料的重量计；实施例5至7、11至29中第四包覆层的包覆量均为1％，基于步骤S8中获得的三层包覆后的材料的重量计。
实施例30至42
以类似于实施例1中的方法进行，不同之处参见下表7和表8，并且第四包覆层的包覆量均为1％，基于步骤S8中获得的三层包覆后的材料的重量计。
实施例43至53
以类似于实施例1中的方法进行，不同之处参见下表9。实施例43至53将实施例1中的端羟基聚二甲基硅氧烷分别替换为巯丙基聚硅氧烷(极性官能团为-CH 2SH，质量百分含量为15％，数均分子量为2000)、氨乙基氨丙基聚二甲基硅氧烷(极性官能团为-CH 2NH 2和-CH 2NH-，质量百分含量为12％，数均分子量为3700)、侧链聚醚接枝聚二甲基硅氧烷(极性官能团为聚醚链段，质量百分含量为7.1％，数均分子量为15412)、侧链磷酸酯接枝聚二甲基硅氧烷(极性官能团为磷酸酯基，质量百分含量为1.42％，数均分子量为15600)、聚二甲基硅氧烷(极性官能团质量百分含量约为0％，数均分子量为1200)、聚甲基氯丙基硅氧烷(极性官能团为-CH 2Cl，质量百分含量为30.2％，数均分子量为2500)、端环氧基聚硅氧烷(极性官能团为环氧基，质量百分含量为0.42％，数均分子量为10000)、端基聚醚聚二甲基硅氧烷(极性官能团为聚醚链段，质量百分含量为10％，数均分子量为2000)、1,3,5,7-八甲基环四硅氧烷(极性官能团质量百分含量约为0％，分子量为280)、环五聚二甲基硅氧烷(极性官能团质量百分含量约为0％，分子量为370)、端基聚醚聚二甲基硅氧烷(极性官能团为聚醚链段，质量百分含量为55％，数均分子量为25000)。
实施例54至59
以类似于实施例1中的方法进行，不同之处参见下表9。实施例54至59将实施例1中的端羟基聚二甲基硅氧烷的包覆量分别替换为0.01重量％、0.1重量％、2重量％、5重量％、10重量％、12重量％，基于步骤S8中获得的三层包覆后的材料的重量计。
实施例60至66
以类似于实施例1中的方法进行，不同之处参见下表9。实施例60至66将实施例1中的端羟基聚二甲基硅氧烷分别替换为数均分子量为400、10000、50000、80000、100000、300000、400000的聚二甲基硅氧烷。
另外，本申请所有实施例和对比例中，如未标明，则使用的第一包覆层物质和/或第二包覆层物质均默认为晶态。
Figure PCTCN2022084465-appb-000003
Figure PCTCN2022084465-appb-000004
Figure PCTCN2022084465-appb-000005
表2：第一包覆层悬浊液的制备(步骤S3)
Figure PCTCN2022084465-appb-000006
表3：第一包覆层的包覆(步骤S4)
Figure PCTCN2022084465-appb-000007
表4：第二包覆层悬浊液的制备(步骤S5)
Figure PCTCN2022084465-appb-000008
表5：第二包覆层的包覆(步骤S6)
Figure PCTCN2022084465-appb-000009
表6：第三层包覆层的包覆(步骤S8)
Figure PCTCN2022084465-appb-000010
Figure PCTCN2022084465-appb-000011
表7：第一包覆层物质的考察
Figure PCTCN2022084465-appb-000012
表8：第二包覆层物质的考察
Figure PCTCN2022084465-appb-000013
表9：第四包覆层的考察
Figure PCTCN2022084465-appb-000014
II.性能评价
1.晶格变化率测量方法
在25℃恒温环境下，将正极活性材料样品置于X射线粉末衍射仪(型号为Bruker D8 Discover)中，采用1°/分钟对样品进行测试，并对测试数据进行整理分析，参照标准PDF卡片，计算出此时的晶格常数a0、b0、c0和v0(a0、b0和c0表示晶胞各个方向上的长度大小，v0表示晶胞体积，可通过XRD精修结果直接获取)。
采用上述实施例中扣电制备方法，将所述正极活性材料样品制备成扣电，并对上述扣电以0.05C小倍率进行充电，直至电流减小至0.01C。然后将扣电中的正极极片取出，并置于碳酸二甲酯(DMC)中浸泡8小时。然后烘干，刮粉，并筛选出其中粒径小于500nm的颗粒。取样并按照与上述测试新鲜样品同样的方式计算出其晶胞体积v1，将(v0-v1)/v0×100％作为其完全脱嵌锂前后的晶格变化率(晶胞体积变化率)示于表中。
2.Li/Mn反位缺陷浓度
将“晶格变化率测量方法”中测试的XRD结果与标准晶体的PDF(Powder Diffraction File)卡片对比，得出Li/Mn反位缺陷浓度。具体而言，将“晶格变化率测量方法”中测试的XRD结果导入通用结构分析系统(GSAS)软件中，自动获得精修结果，其中包含了不同原子的占位情况，通过读取精修结果获得Li/Mn反位缺陷浓度。
3.压实密度
取5g的上述制得的正极活性材料粉末放于压实专用模具(美国CARVER模具，型号13mm)中，然后将模具放在压实密度仪器上。施加3T(吨)的压力，在设备上读出压力下粉末的厚度(卸压后的厚度，用于测试的容器的面积为1540.25mm 2)，通过ρ＝m/v，计算出压实密度。
4.表面氧价态
取5g上述制得的正极活性材料样品按照上述实施例中所述扣电制备方法制备成扣电。对扣电采用0.05C小倍率进行充电，直至电流减小至0.01C。然后将扣电中的正极极片取出，并置于DMC中浸泡8小时。然后烘干，刮粉，并筛选出其中粒径小于500nm的颗粒。将所得颗粒用电子能量损失谱(EELS，所用仪器型号为Talos F200S)进行测量，获取能量损失近边结构(ELNES)，其反映元素的态密度和能级分布情况。根据态密度和能级分布，通过对价带态密度数据进行积分，算出占据的电子数，从而推算出充电后的表面氧的价态。
5.过渡金属Mn(以及Mn位掺杂的Fe)溶出测试
将45℃下循环至容量衰减至80％后的上述各个实施例和对比例制备的全电池采用0.1C倍率进行放电至截止电压2.0V。然后将电池拆开，取出负极极片，在负极极片上随机取30个单位面积(1540.25mm 2)的圆片，用Agilent ICP-OES730测试电感耦合等离子体发射光谱(ICP)。根据ICP结果计算其中Fe(如果正极活性材料的Mn位掺杂有Fe的话)和Mn的量，从而计算循环后Mn(以及Mn位掺杂的Fe)的溶出量。测试标准依据EPA-6010D-2014。
6.正极活性材料中锰元素和磷元素的测量
将5g上述制得的正极活性材料在100mL逆王水(浓盐酸：浓硝酸＝1:3)中溶解，利用ICP测试溶液各元素的含量，然后对锰元素或磷元素的含量进行测量和换算(锰元素或磷元素的量/正极活性材料的量×100％)，得到其重量占比。
7.接触角测试
室温下，将碳酸乙烯酯(EC)液滴滴在正极膜层表面，采用德国LAUDA Scientific公司的LSA 200型光学接触角测量仪测试其在60秒内的固液接触角。
8.孔隙率测试
通过胶带剥离正极膜层，参照GB/T 24586-2009测试正极膜层的孔隙率。孔隙率P＝[(V2-V1)/V2]×100％。
V1(cm 3)表示真体积，可以利用具有小分子直径的惰性气体(例如氦气)通过置换法，结合阿基米德原理和玻尔定律进行测定。
V2(cm 3)表示表观体积，V2＝S×H×A，S(cm 2)表示面积，H(cm)表示厚度，A表示样品数。
9.扣式电池初始克容量测量方法
将上述各实施例和对比例制备的扣式电池按照0.1C充电至4.3V，然后在4.3V下恒压充电至电流小于等于0.05mA，静置5分钟，然后按照0.1C放电至2.0V，此时的放电容量为初始克容量，记为D0。
10. 3C充电恒流比
在25℃恒温环境下，将上述各个实施例和对比例制备的新鲜全电池静置5分钟，按照1/3C放电至2.5V。静置5分钟，按照1/3C充电至4.3V，然后在4.3V下恒压充电至电流小于等于0.05mA。静置5分钟，记录此时的充电容量为C0。按照1/3C放电至2.5V，静置5分钟，再按照3C充电至4.3V，静置5分钟，记录此时的充电容量为C1。3C充电恒流比即为C1/C0×100％。
3C充电恒流比越高，说明二次电池的倍率性能越好。
11.全电池60℃存储30天电池膨胀测试
在60℃下，存储100％充电状态(SOC)的上述各个实施例和对比例制备的全电池。在存储前后及过程中测量电池的开路电压(OCV)和交流内阻(IMP)以监控SOC，并测量电池的体积。其中在每存储48小时后取出全电池，静置1小时后测试开路电压(OCV)、内阻(IMP)，并在冷却至室温后用排水法测量电池体积。排水法即先用表盘数据自动进行单位转换的天平单独测量电池的重力F 1，然后将电池完全置于去离子水(密度已知为1g/cm 3)中，测量此时的电池的重力F 2，电池受到的浮力F 浮即为F 1-F 2，然后根据阿基米德原理F 浮＝ρ×g×V 排，计算得到电池体积V＝(F 1-F 2)/(ρ×g)。
由OCV、IMP测试结果来看，本测试过程中直至存储结束，全部实施例的电池始终保持99％以上的SOC。
存储30天后，测量电池体积，并计算相对于存储前的电池体积，存储后的电池体积增加的百分比。
12.全电池45℃下循环性能测试
在45℃的恒温环境下，将全电池按照1C充电至4.3V，然后在4.3V下恒压充电至电流≤0.05mA，静置5分钟，然后按照1C放电至2.5V，容量记为D0。重复前述过程，直至容量衰减到D0的80％，记录此时的重复次数，即为45℃下80％容量保持率对应的循环圈数。
13.晶面间距和夹角测试
取1g上述制得的各正极活性材料粉末于50mL的试管中，并在试管中注入10mL质量分数为75％的酒精，搅拌分散30分钟，然后用干净的一次性塑料吸管取适量上述溶液滴加在300目铜网上，此时，部分粉末将在铜网上残留，将铜网连带样品转移至TEM(Talos F200s G2)样品腔中进行测试，得到TEM测试原始图片。
将上述TEM测试所得原始图片在DigitalMicrograph软件中打开，并进行傅里叶变换(点击操作后由软件自动完成)得到衍射花样，量取衍射花样中衍射光斑到中心位置的距离，即可得到晶面间距，夹角根据布拉格方程进行计算得到。
通过得到的晶面间距和相应夹角数据，与其标准值比对，即可对包覆层的不同物质进行识别。
14.包覆层厚度测试
包覆层的厚度大小测试主要通过FIB从上述制得的正极活性材料单个颗粒中间切取100nm左右厚度的薄片，然后对薄片进行TEM测试，得到TEM测试原始图片。
将上述TEM测试所得原始图片在DigitalMicrograph软件中打开，通过晶格间距和夹角信息，识别出包覆层，量取包覆层的厚度。
对所选颗粒测量三个位置处的厚度，取平均值。
15.第三层包覆层碳中SP2形态和SP3形态摩尔比的测定
本测试通过拉曼(Raman)光谱进行。通过对Raman测试的能谱进行分峰，得到Id/Ig，其中Id为SP3形态碳的峰强度，Ig为SP2形态碳的峰强度，从而确认两者的摩尔比。
16.内核化学式及不同包覆层组成的测定
采用球差电镜仪(ACSTEM)对正极活性材料内部微观结构和表面结构进行高空间分辨率表征，结合三维重构技术得到正极活性材料的内核化学式及不同包覆层的组成。
表10示出实施例1-29和对比例1-18中正极活性材料的粉料性能及所制备的正极极片和电池的性能。
表11示出实施例1-14和对比例3-4、12中制备的正极活性材料每一层包覆层的厚度以及锰元素和磷元素的重量比。
表12示出实施例30-42中正极活性材料的粉料性能及所制备的正极极片和电池的性能。
表13示出实施例1、30-42中第一包覆层物质和第二包覆层物质的晶面间距和夹角。
表14示出实施例43-66中正极活性材料的粉料性能及所制备的正极极片和电池的性能。
Figure PCTCN2022084465-appb-000015
Figure PCTCN2022084465-appb-000016
Figure PCTCN2022084465-appb-000017
Figure PCTCN2022084465-appb-000018
Figure PCTCN2022084465-appb-000019
由表10可见，与对比例相比，实施例实现了更小的晶格变化率、更小的Li/Mn反位缺陷浓度、更大的压实密度、更接近于-2价的表面氧价态、更少的循环后Mn和Fe溶出量以及更好的电池性能，例如更好的高温存储性能和高温循环性能。
由表11可以看出，通过对磷酸锰铁锂(含锰量35％，含磷量约20％)的锰位和磷位进行掺杂以及四层包覆，正极活性材料中的锰元素含量以及锰元素与磷元素的重量含量比明显降低；此外，将实施例1-14与对比例3、对比例4、对比例12相比，结合表10可知，正极活性材料中锰元素和磷元素的降低会使得锰离子和铁离子溶出量降低以及其制备的二次电池的性能提升。
由表12可知，采用包含本申请范围内的其他元素的第一包覆层和第二包覆层同样获得了具有良好性能的正极活性材料并实现了良好的电池性能结果。
由表13可知，本申请第一包覆层和第二包覆层的晶面间距和夹角均在本申请所述范围内。
由表14可知，在其他元素相同的情况下，选择满足具有合适的极性官能团含量、数均分子量、包覆量中的一者或者多者的聚硅氧烷作为第四包覆层，能够在不影响能量密度和动力学性能的前提下，进一步改善二次电池的循环性能和/或高温存储性能。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (24)

  1. 一种具有核-壳结构的正极活性材料，包括内核及包覆所述内核的壳，其中，
    所述内核的化学式为Li 1+xMn 1-yA yP 1-zR zO 4，x为在-0.100至0.100范围内的任意数值，y为在0.001至0.500范围内的任意数值，z为在0.001至0.100范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，所述R为选自B、Si、N和S中的一种或多种元素，可选地，所述R为选自B、Si、N和S中的一种元素；
    所述x、y和z的值满足以下条件：使整个内核保持电中性；
    所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层、包覆所述第二包覆层的第三包覆层以及包覆所述第三包覆层的第四包覆层，其中，
    所述第一包覆层包括晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，0≤a≤2，1≤b≤4，1≤c≤6，所述a、b和c的值满足以下条件：使晶态焦磷酸盐Li aMP 2O 7或M b(P 2O 7) c保持电中性，
    所述晶态焦磷酸盐Li aMP 2O 7和M b(P 2O 7) c中的M各自独立地为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；
    所述第二包覆层包括晶态磷酸盐XPO 4，所述X为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；
    所述第三包覆层为碳；
    所述第四包覆层包括聚合物，所述聚合物包括选自线状结构的聚硅氧烷、环状结构的聚硅氧烷中的一种或多种。
  2. 根据权利要求1所述的正极活性材料，其中，所述聚合物包含至少一种式1所示的结构单元，
    Figure PCTCN2022084465-appb-100001
    R 1、R 2分别独立地表示H或由以下官能团组成的组中的至少一种：-COOH、-OH、-SH、-CN、-SCN、氨基、磷酸酯基、羧酸酯基、酰胺基、醛基、磺酰基、聚醚链段、C1～C20脂肪烃基、C1～C20卤代脂肪烃基、C1～C20杂脂肪烃基、C1～C20卤代杂脂肪烃基、C6～C20芳香烃基、C6～C20卤代芳香烃基、C2～C20杂芳香烃基、C2～C20卤代杂芳香烃基；
    可选地，R 1、R 2分别独立地表示H或由以下官能团组成的组中的至少一种：-OH、-SH、氨基、磷酸酯基、聚醚链段、C1～C8烷基、C1～C8卤代烷基、C1～C8杂烷基、C1～C8卤代杂烷基、C2～C8烯基、C2～C8卤代烯基。
  3. 根据权利要求1或2所述的正极活性材料，所述线状结构的聚硅氧烷还包含封端基，
    可选地，所述封端基包括以下官能团组成的组中的至少一种：聚醚、C1～C8烷基、C1～C8卤代烷基、C1～C8杂烷基、C1～C8卤代杂烷基、C2～C8烯基、C2～C8卤代烯基、 C6～C20芳香烃基、C1～C8烷氧基、C2～C8环氧基、羟基、C1～C8羟基烷基、氨基、C1～C8氨基烷基、羧基、C1～C8羧基烷基。
  4. 根据权利要求1-3中任一项所述的正极活性材料，其中，所述线状结构的聚硅氧烷包括聚二甲基硅氧烷、聚二乙基硅氧烷、聚甲基乙基硅氧烷、聚甲基乙烯基硅氧烷、聚苯基甲基硅氧烷、聚甲基氢硅氧烷、羧基功能化聚硅氧烷、端环氧基聚硅氧烷、甲氧基封端聚二甲基硅氧烷、聚甲基氯丙基硅氧烷、巯丙基聚硅氧烷、氨乙基氨丙基聚二甲基硅氧烷、端羟丙基聚硅氧烷、端羟基聚二甲基硅氧烷、端基聚醚聚二甲基硅氧烷、侧链氨丙基聚硅氧烷、氨丙基封端聚二甲基硅氧烷、侧链羟甲基聚硅氧烷、侧链羟丙基聚硅氧烷、侧链聚醚接枝聚二甲基硅氧烷、侧链磷酸酯接枝聚二甲基硅氧烷中的一种或多种，可选地包括端羟基聚二甲基硅氧烷、巯丙基聚硅氧烷、氨乙基氨丙基聚二甲基硅氧烷、侧链聚醚接枝聚二甲基硅氧烷、侧链磷酸酯接枝聚二甲基硅氧烷中的一种或多种；和/或，
    所述环状结构的聚硅氧烷包括1,3,5,7-八甲基环四硅氧烷、1,3,5,7-四氢-1,3,5,7-四甲基环四硅氧烷、环五聚二甲基硅氧烷、2,4,6,8-四甲基环四硅氧烷、2,4,6,8-四甲基-2,4,6,8-四乙烯基环四硅氧烷、环状聚甲基乙烯基硅氧烷、十六甲基环八硅氧烷、十四甲基环七硅氧烷、环状聚二甲基硅氧烷中的一种或多种。
  5. 根据权利要求1-4中任一项所述的正极活性材料，其中，所述聚合物选自线状结构的聚硅氧烷。
  6. 根据权利要求1-5中任一项所述的正极活性材料，其中，所述聚合物的数均分子量在300000以下，可选地为400至200000。
  7. 根据权利要求1-6中任一项所述的正极活性材料，其中，所述聚硅氧烷中极性官能团的质量百分含量为α，0≤α＜50％，可选地，5％≤α≤30％。
  8. 根据权利要求1-7中任一项所述的正极活性材料，其中，
    所述第一包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为大于0且小于或等于2重量％，基于所述内核的重量计；和/或
    所述第二包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为2-4重量％，基于所述内核的重量计；和/或
    所述第三包覆层的包覆量为大于0且小于或等于6重量％，可选为大于0且小于或等于5.5重量％，更可选为大于0且小于或等于2重量％，基于所述内核的重量计；和/或
    所述第四包覆层的包覆量为大于0且小于或等于10重量％，可选为大于0且小于或等于5重量％，更可选为大于0且小于或等于2重量％，基于具有第一包覆层、第二包覆层和第三包覆层的内核的重量计。
  9. 根据权利要求1-8中任一项所述的正极活性材料，其中，
    所述第一包覆层的厚度为1-10nm；和/或
    所述第二包覆层的厚度为2-15nm；和/或
    所述第三包覆层的厚度为2-25nm；和/或
    所述第四包覆层的厚度为2-10nm。
  10. 根据权利要求1-9中任一项所述的正极活性材料，其中，
    所述第一包覆层中的晶态焦磷酸盐的晶面间距范围为0.293-0.470nm，晶向(111)的夹角范围为18.00°-32.00°；所述第二包覆层中的晶态磷酸盐的晶面间距范围为0.244-0.425nm，晶向(111)的夹角范围为20.00°-37.00°。
  11. 根据权利要求1-10中任一项所述的正极活性材料，其中，在所述内核中，
    y与1-y的比值为1:10至1:1，可选为1:4至1:1；和/或，
    z与1-z的比值为1:9至1:999，可选为1:499至1:249。
  12. 根据权利要求1-11中任一项所述的正极活性材料，其中，所述第三包覆层的碳为SP2形态碳与SP3形态碳的混合物，可选地，所述SP2形态碳与SP3形态碳的摩尔比为在0.1-10范围内的任意数值，可选为在2.0-3.0范围内的任意数值。
  13. 根据权利要求1-12中任一项所述的正极活性材料，其中，
    基于正极活性材料的重量计，锰元素含量在10重量％-35重量％范围内，可选在15重量％-30重量％范围内，更可选在17重量％-20重量％范围内，磷元素的含量在12重量％-25重量％范围内，可选在15重量％-20重量％范围内，锰元素和磷元素的重量比范围为0.90-1.25，可选为0.95-1.20。
  14. 根据权利要求1-13中任一项所述的正极活性材料，其中，所述正极活性材料满足如下条件(1)至(4)中的至少一者：
    (1)所述正极活性材料在完全脱嵌锂前后的晶格变化率为4％以下，可选为3.8％以下，更可选为2.0-3.8％；
    (2)所述正极活性材料的Li/Mn反位缺陷浓度为4％以下，可选为2.2％以下，更可选为1.5-2.2％；
    (3)所述正极活性材料在3T下的压实密度为2.2g/cm 3以上，可选地为2.2g/cm 3以上且2.8g/cm 3以下；
    (4)所述正极活性材料的表面氧价态为-1.90以下，可选地为-1.90至-1.98。
  15. 一种正极活性材料的制备方法，包括以下步骤：
    提供内核材料的步骤：所述内核化学式为Li 1+xMn 1-yA yP 1-zR zO 4，其中，x为在-0.100至0.100范围内的任意数值，y为在0.001至0.500范围内的任意数值，z为在0.001至0.100范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，所述R为选自B、Si、N和S中的一种或多种元素，可选地，所述R为选自B、Si、N和S中的一种元素；
    包覆步骤：分别提供Li aMP 2O 7和/或M b(P 2O 7) c以及XPO 4悬浊液，将所述内核材料加入到上述悬浊液中并混合，经烧结获得具有第一包覆层、第二包覆层和第三包覆层的内核，将获得的具有第一包覆层、第二包覆层和第三包覆层的内核与聚合物通过干法包覆或湿法包覆，得到正极活性材料，其中，0≤a≤2，1≤b≤4，1≤c≤6，所述a、b和c的值满足以下条件：使晶态焦磷酸盐Li aMP 2O 7或M b(P 2O 7) c保持电中性；所述M各自独立地为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；所述X为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素；所述聚合物包括选自线状结构的聚硅氧烷、环状结构的聚硅氧烷中的一种或多种；
    其中，所述正极活性材料具有核-壳结构，其包括所述内核及包覆所述内核的壳，所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层、包覆所述第二包覆层的第三包覆层以及包覆所述第三包覆层的第四包覆层，所述第一包覆层包括晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，所述第二包覆层包括晶态磷酸盐XPO 4，所述第三包覆层为碳，所述第四包覆层包括聚合物，所述聚合物包括选自线状结构的聚硅氧烷、环状结构的聚硅氧烷中的一种或多种。
  16. 根据权利要求15所述的正极活性材料的制备方法，其中，所述提供内核材料的步骤包括以下步骤：
    步骤(1)：将锰源、元素A的掺杂剂和酸在容器中混合并搅拌，得到掺杂有元素A的锰盐颗粒；
    步骤(2)：将所述掺杂有元素A的锰盐颗粒与锂源、磷源和元素R的掺杂剂在溶剂中混合并得到浆料，在惰性气体气氛保护下烧结后得到掺杂有元素A和元素R的内核，其中，所述掺杂有元素A和元素R的内核为Li 1+xMn 1-yA yP 1-zR zO 4，x为在-0.100至0.100范围内的任意数值，y为在0.001至0.500范围内的任意数值，z为在0.001至0.100范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，所述R为选自B、Si、N和S中的一种或多种元素，可选地，所述R为选自B、Si、N和S中的一种元素。
  17. 根据权利要求16所述的正极活性材料的制备方法，其中，
    所述步骤(1)在20-120℃、可选为40-120℃的温度下进行混合；和/或
    所述步骤(1)中所述搅拌在400-700rpm下进行1-9小时，可选地为3-7小时；和/或
    所述步骤(2)在20-120℃、可选为40-120℃的温度下进行混合1-10小时。
  18. 根据权利要求16-17中任一项所述的正极活性材料的制备方法，其中，
    所述元素A的掺杂剂为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素各自的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种；和/或，
    所述元素R的掺杂剂为选自B、Si、N和S中的一种或多种元素各自的无机酸、有机酸、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
  19. 根据权利要求15-18中任一项所述的正极活性材料的制备方法，其中，所述包覆步骤包括：
    第一包覆步骤：将元素M的源、磷源和酸以及任选地锂源，溶于溶剂中，得到第一包覆层悬浊液；将提供内核材料的步骤中获得的内核与第一包覆步骤获得的第一包覆层悬浊液充分混合，干燥，然后烧结，得到第一包覆层包覆的材料；
    第二包覆步骤：将元素X的源、磷源和酸溶于溶剂中，得到第二包覆层悬浊液；将第一包覆步骤中获得的第一包覆层包覆的材料与第二包覆步骤获得的第二包覆层悬浊液充分混合，干燥，然后烧结，得到两层包覆层包覆的材料；
    第三包覆步骤：将碳源溶于溶剂中，充分溶解得到第三包覆层溶液；然后将第二包覆步骤中获得的两层包覆层包覆的材料加入所述第三包覆层溶液中，混合均匀，干燥，然后烧结得到三层包覆层包覆的材料；
    第四包覆步骤：将聚合物溶于溶剂中，充分溶解得到第四包覆层溶液；然后将第三包覆步骤中获得的三层包覆层包覆的材料加入所述第四包覆层溶液中，混合均匀，干燥，得到四层包覆层包覆的材料，即正极活性材料，或者将第三包覆步骤中获得的三层包覆层包覆的材料与聚合物混合均匀，然后烧结得到四层包覆层包覆的材料，即正极活性材料。
  20. 根据权利要求19所述的正极活性材料的制备方法，其中，
    所述第一包覆步骤中，控制溶解有元素M的源、磷源和酸以及任选地锂源的溶液pH为3.5-6.5，然后搅拌并反应1-5小时，然后将所述溶液升温至50-120℃，并保持该温度2-10小时；和/或，
    所述第一包覆步骤中的烧结在650-800℃下进行2-6小时；和/或，
    所述第二包覆步骤中，将元素X的源、磷源和酸溶于溶剂后，搅拌并反应1-10小时，然后将所述溶液升温至60-150℃，并保持该温度2-10小时；和/或，
    所述第二包覆步骤中的烧结在500-700℃下进行6-10小时；和/或，
    所述第三包覆步骤中的烧结在700-800℃下进行6-10小时。
  21. 一种正极极片，其包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，所述正极膜层包括权利要求1-14中任一项所述的正极活性材料、或通过权利要求15-20中任一项所述的正极活性材料制备方法制备的正极活性材料，并且所述正极活性材料在所述正极膜层中的含量为90-99.5重量％，可选为95-99.5重量％，基于所述正极膜层的总重量计。
  22. 根据权利要求21所述的正极极片，其中，
    所述正极膜层与非水有机溶剂之间的固液接触角在3°至90°之间，可选地在3°至60°之间，进一步地在10°至30°之间；和/或，
    所述正极膜层的孔隙率为15％至50％，可选地为15％至30％。
  23. 一种二次电池，包括权利要求1-14中任一项所述的正极活性材料、或通过权利要求15-20中任一项所述的正极活性材料制备方法制备的正极活性材料、或权利要求21-22中任一项所述的正极极片。
  24. 一种用电装置，包括权利要求23所述的二次电池。
PCT/CN2022/084465 2022-03-31 2022-03-31 正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置 Ceased WO2023184368A1 (zh)

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