WO2024164143A1 - 正极活性材料及其制备方法、正极极片、电池和用电装置 - Google Patents

正极活性材料及其制备方法、正极极片、电池和用电装置 Download PDF

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WO2024164143A1
WO2024164143A1 PCT/CN2023/074786 CN2023074786W WO2024164143A1 WO 2024164143 A1 WO2024164143 A1 WO 2024164143A1 CN 2023074786 W CN2023074786 W CN 2023074786W WO 2024164143 A1 WO2024164143 A1 WO 2024164143A1
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Prior art keywords
positive electrode
active material
electrode active
coating layer
carbon
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English (en)
French (fr)
Inventor
蒋耀
张欣欣
欧阳楚英
袁天赐
王志强
陈尚栋
徐波
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to CN202380009128.1A priority Critical patent/CN116897444A/zh
Priority to KR1020257016621A priority patent/KR20250088624A/ko
Priority to JP2025531794A priority patent/JP2025539469A/ja
Priority to EP23920356.5A priority patent/EP4604201A4/en
Priority to PCT/CN2023/074786 priority patent/WO2024164143A1/zh
Publication of WO2024164143A1 publication Critical patent/WO2024164143A1/zh
Priority to US19/210,813 priority patent/US20250279415A1/en
Anticipated expiration legal-status Critical
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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
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • 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
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • 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
    • 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
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • 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
    • C01P2006/12—Surface area
    • 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
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • 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 relates to the field of batteries, and in particular, to positive electrode active materials and preparation methods thereof, positive electrode sheets, batteries and electrical devices.
  • lithium-ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, and are widely used in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. At present, there are still many problems to be solved in the industrial production and application of lithium-ion batteries.
  • the present application proposes a positive electrode active material, comprising: a core; a carbon coating layer, the carbon coating layer at least covering a portion of the surface of the core, wherein the molar ratio of sp2 hybridized carbon atoms to sp3 hybridized carbon atoms in the carbon coating layer is not less than 0.5.
  • the water absorption of the positive electrode active material can be reduced.
  • the core includes phosphate; preferably, the phosphate includes at least one of lithium manganese phosphate, lithium iron phosphate and lithium manganese iron phosphate.
  • the core material can be carbon coated on the surface to improve its conductivity and optimize the performance of the battery using the core material.
  • the core includes LiMPO 4
  • the M element includes Mn and non-Mn elements. Therefore, the core material can be carbon coated on its surface to improve its conductivity and optimize the performance of a battery using the core material.
  • the second doping element includes one or more elements selected from B (boron), S, Si and N.
  • the core includes 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, A includes one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements of B (boron), S, Si and N.
  • B boron
  • the core includes Li1 +xCmMn1 - yAyP1- zRzO4 - nDn , 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, n is any value in the range of 0.001 to 0.1, m is any value in the range of 0.9 to 1.1, the C includes one or more elements of Zn, Al, Na, K, Mg, Nb, Mo and W, the A includes one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, the R includes one or more elements of B (boron), S, Si and N, and the D includes one or more elements of S, F, Cl and Br.
  • the molar ratio of sp2 hybridized carbon atoms to sp3 hybridized carbon atoms in the carbon coating layer is not less than 0.8.
  • the structural order of the carbon coating layer can be improved, the structure of the carbon coating layer can be made denser, and the pores on the carbon coating layer can be reduced, thereby further reducing the water absorption of the positive electrode active material.
  • the thickness of the carbon coating layer is not greater than 10 nm; preferably, the thickness of the carbon coating layer is 4 nm-8 nm.
  • the conductivity of the positive electrode active material is improved while reducing the water absorption.
  • the carbon content in the positive electrode active material is not more than 3wt%, preferably, the carbon content in the positive electrode active material is 1wt%-2.5wt%.
  • the positive electrode active material can have both good conductivity and low water absorption.
  • the specific surface area of the positive electrode active material is not greater than 25 m 2 /g, preferably, the specific surface area of the positive electrode active material is not greater than 18 m 2 /g.
  • the positive electrode active material can have high conductivity, high gram capacity and low water absorption.
  • the median particle size of the positive electrode active material is not greater than 2 ⁇ m; preferably, the median particle size of the positive electrode active material is 0.5 ⁇ m-1.5 ⁇ m.
  • the lithium ion migration rate of the positive electrode active material can be increased, and the gram capacity of the positive electrode active material can be increased.
  • the powder resistivity of the positive electrode active material is not greater than 200 ⁇ cm; preferably, the powder resistivity of the positive electrode active material is not greater than 100 ⁇ cm.
  • the conductivity of the positive electrode active material can be further improved by setting the carbon coating layer while maintaining low water absorption.
  • the present application proposes a method for preparing a positive electrode active material, providing a core; A carbon coating layer is formed on at least part of the surface of the core.
  • the forming of the carbon coating layer on at least part of the surface of the core includes: forming a pre-carbon coating layer on the surface of the core by a carbon source to obtain a pre-coated positive electrode active material; sintering the pre-coated positive electrode active material under an inert gas atmosphere to form the carbon coating layer to obtain the positive electrode active material, and the carbon source includes a first carbon source and a second carbon source.
  • a carbon coating layer with a high degree of graphitization can be formed on the surface of the core.
  • the forming of the carbon coating layer on at least part of the surface of the core includes: mixing the core with the first carbon source, and obtaining a first coated positive electrode active material through a first sintering process, and mixing the first coated positive electrode active material with the second carbon source, and obtaining the positive electrode active material through a second sintering process.
  • a carbon coating layer with a high degree of graphitization can be formed on the surface of the core.
  • the first carbon source includes at least one of polyvinyl alcohol, polyethylene glycol and citric acid; and the second carbon source includes at least one of starch, sucrose and glucose.
  • a carbon coating layer with a high degree of graphitization can be formed on the surface of the inner core.
  • the molecular weight of the first carbon source is not less than 1000, and preferably, the molecular weight of the first carbon source is 2000-5000.
  • a carbon coating layer with a high degree of graphitization can be obtained.
  • the sintering temperature is 650° C.-800° C.
  • the sintering time is 6 h-12 h.
  • the temperature of the first sintering treatment is 350° C.-800° C.
  • the time of the first sintering treatment is 6 h-12 h.
  • the temperature of the second sintering treatment is 650° C.-850° C.
  • the time of the second sintering treatment is 6 hours-24 hours.
  • the present application proposes a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is located on one side of the positive electrode current collector, and the positive electrode active material layer comprises the aforementioned positive electrode active material, and/or the positive electrode active material layer comprises the positive electrode active material prepared by the aforementioned method. Therefore, the positive electrode sheet has all the characteristics and advantages of the aforementioned positive electrode active material, which will not be described in detail here.
  • the present application proposes a battery, comprising: a positive electrode sheet, wherein the positive electrode sheet is the aforementioned positive electrode sheet. Therefore, the battery has all the features and advantages of the aforementioned positive electrode sheet, which will not be described in detail here.
  • the present application proposes an electrical device, comprising: a battery, wherein the battery is the aforementioned battery. Therefore, the electrical device has all the features and advantages of the aforementioned battery, which will not be described in detail here.
  • FIG1 shows a schematic structural diagram of a positive electrode sheet according to an embodiment of the present application
  • FIG2 is a schematic diagram of a battery according to an embodiment of the present application.
  • FIG3 is an exploded view of the battery of one embodiment of the present application shown in FIG2 ;
  • FIG4 is a schematic diagram of a battery module according to an embodiment of the present application.
  • FIG5 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG6 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG5 ;
  • FIG. 7 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application.
  • 1 battery pack; 2: upper case; 3: lower case; 4: battery module; 5: battery; 10: positive electrode plate; 11: positive electrode current collector; 12: positive electrode active material layer; 51: shell; 52: electrode assembly; 53: top cover assembly.
  • the present application proposes a positive electrode active material, comprising: a core; a carbon coating layer, the carbon coating layer at least covering a portion of the surface of the core, wherein the molar ratio of sp2 hybridized carbon atoms to sp3 hybridized carbon atoms in the carbon coating layer is not less than 0.5.
  • the pore structure of the carbon coating layer is relatively dense, which can significantly reduce the water absorption capacity of the carbon coating layer, thereby reducing the water absorption of the positive electrode active material, thereby improving the safety performance and cycle performance of the battery.
  • the potential of lithium-ion batteries is significantly higher than the stable voltage range of water, lithium-ion batteries are very sensitive to moisture. Even trace amounts of moisture will seriously affect the performance of lithium-ion batteries. Therefore, the moisture content in the materials must be strictly controlled throughout the production process. For example, in the production process of the battery, the pole pieces need to be dried after the current collector is coated, the pole pieces need to be dried after cold pressing, and the battery cells need to be dried after winding, etc., and the environmental moisture needs to be strictly controlled throughout the battery production process. The drying process and environmental moisture control during the battery production process consume a lot of energy, complicating the battery production process.
  • the inventors found that in order to improve the conductivity of the inner core, the conductivity of the positive electrode active material can be improved by forming a carbon coating on the inner core surface. Furthermore, when the carbon coating of the positive electrode active material is in a loose and porous state, the loose and porous carbon coating structure will accelerate the absorption and storage of water by the positive electrode active material, thereby making the water absorption and water storage capacity of the positive electrode active material stronger, so that the positive electrode active material will absorb water during storage and processing, and ultimately lead to a higher water content in the positive electrode active material. The presence of high water content in the battery will cause the lithium salt in the electrolyte to decompose, which significantly reduces the cycle performance of the battery.
  • the inventors found that if the moisture in the positive electrode active material is removed as much as possible by simply increasing the drying temperature and extending the drying time, it will cause problems such as excessive energy consumption and a significant extension of the process time. In addition, long-term high-temperature drying treatment will also cause aging and failure of other components in the battery cell, such as the diaphragm component, which will significantly increase the manufacturing cost. Based on the above theoretical analysis and experimental research, the inventors found that by improving the pore state of the carbon coating layer of the positive electrode active material, the water absorption of the positive electrode active material can be effectively reduced without adding additional process flow and improving the process environment.
  • the inventors found that when the molar ratio of sp2 hybridized carbon atoms to sp3 hybridized carbon atoms in the carbon coating layer on the surface of the inner core is not less than 0.5, the orderliness of the structure of the carbon coating layer of the positive electrode active material is relatively high, and the pore structure of the carbon coating layer has a high density and a small pore size distribution range.
  • it is difficult for external moisture to enter the pores of the carbon coating layer thereby effectively reducing the water absorption and water storage properties of the positive electrode active material, achieving improved battery safety and cycle performance, effectively saving energy consumption during the drying process, and significantly reducing production costs.
  • the type of the core is not particularly limited, for example, the core may include phosphate; preferably, the phosphate may include at least one of lithium manganese phosphate, lithium iron phosphate and lithium manganese iron phosphate.
  • Lithium manganese phosphate, lithium iron phosphate and lithium manganese iron phosphate have high gram capacity and low raw material cost. Since the positive electrode active material undergoes electrochemical reaction when used in the battery, the participation of electrons is required. Therefore, in order to increase the electron transfer between particles and the electron transfer between different positions inside the particles, a material with better conductivity can be used. By using a carbon layer to coat the surface of the phosphate core, a positive electrode active material with low cost, high gram capacity and high conductivity can be obtained, and the battery performance using the positive electrode active material is optimized.
  • the type of the core is not particularly limited, for example, the core may include LiMPO 4 , and the M element includes Mn and non-Mn elements.
  • the non-Mn element may include one or both of a first doping element and a second doping element, the first doping element being manganese-doped, and the second doping element being phosphorus-doped.
  • the first doping element and the second doping element can not only effectively reduce manganese dissolution, thereby reducing manganese ions migrating to the negative electrode, reducing electrolyte consumption due to SEI film decomposition, and improving the cycle performance and safety performance of the secondary battery, but can also promote Mn-O bond adjustment, reduce lithium ion migration barriers, promote lithium ion migration, and improve the rate performance of the battery.
  • the type of the first doping element is not particularly limited.
  • the first doping element may include Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and One or more elements in Ge; preferably, the first doping element may include at least two of Fe, Ti, V, Ni, Co and Mg.
  • the first doping element can further reduce the lattice change rate of the positive electrode active material and reduce the surface activity of the material, thereby inhibiting the dissolution of Mn and the interface side reaction between the positive electrode material and the electrolyte.
  • the doping of two or more metals can increase the synergistic effect between elements, reduce the lattice change rate of the material while increasing the battery capacity, and enhance the kinetic performance of the battery.
  • the type of the second doping element is not particularly limited.
  • the second doping element may include one or more elements of B (boron), S, Si and N.
  • the second doping element can increase the rate of change of the Mn-O bond, improve the small polaron migration barrier of the positive electrode active material, and improve the electronic conductivity.
  • the doping of the second element can also reduce the concentration of antisite defects in the material, improve the kinetic properties and gram capacity of the material, and change the morphology of the material, thereby improving the compaction density of the material.
  • the type of the core is not particularly limited.
  • the core may include 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, 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,
  • A includes one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements of B (boron), S, Si and N.
  • the manganese-doping element A selected from the above elements helps to reduce the lattice change rate of lithium manganese phosphate in the process of lithium insertion and extraction, improves the structural stability of the positive electrode active material, greatly reduces the dissolution of manganese and reduces the oxygen activity on the surface of the particles; the phosphorus-doping element R selected from the above elements also helps to change the difficulty of the Mn-O bond length change, thereby improving the electronic conductivity and reducing the lithium ion migration barrier, promoting lithium ion migration, and improving the rate performance of the secondary battery. If the value of x is too small, the lithium content of the entire core will be reduced, affecting the gram capacity of the positive electrode active material.
  • the y value will limit the total amount of all doping elements. If y is too small, that is, the doping amount is too small, the doping element will not work. If y exceeds 0.5, it will lead to a small amount of Mn in the system, affecting the voltage platform of the positive electrode active material.
  • the R element is doped at the position of P. Since the PO tetrahedron is relatively stable, a large z value will affect the stability of the positive electrode active material. Therefore, when x, y and z are selected from the above range, the positive electrode active material can have better performance.
  • the above-mentioned limitation on the numerical range of x, y, z or m is not only a limitation on the stoichiometric number of each element as the site, but also a limitation on the sum of the stoichiometric numbers of each element as the site.
  • the type of the core is not particularly limited.
  • the core may include Li 1+x C m Mn 1-y A y P 1-z R z O 4-n D n .
  • the size of x is affected by the valence of A and R and the size of y and z to ensure that the entire system is electrically neutral. If the value of x is too small, the lithium content of the entire core system will be reduced, affecting the gram capacity of the material.
  • the y value will limit the total amount of all doping elements. If y is too small, that is, the doping amount is too little, the doping element will not work. If y exceeds 0.5, the Mn content in the system will be less, affecting the voltage platform of the material.
  • the R element is doped at the position of P. Since the PO tetrahedron is relatively stable, and a large z value will affect the stability of the material, the z value is limited to 0.001-0.100. More specifically, 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, n is any value in the range of 0.001 to 0.1, and m is any value in the range of 0.9 to 1.1.
  • 1+x is selected from the range of 0.9 to 1.1, such as 0.97, 0.977, 0.984, 0.988, 0.99, 0.991, 0.992, 0.993, 0.994, 0.995, 0.996, 0.997, 0.998, 1.01
  • x is selected from the range of 0.001 to 0.1, such as 0.001, 0.005
  • y is selected from the range of 0.001 to 0.5, such as 0.001 , 0.005, 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.34, 0.345, 0.349, 0.35, 0.4
  • z is selected from the range of 0.001 to 0.1, for example, 0.001, 0.005, 0.08, 0.1
  • n is selected from the range of 0.001 to 0.1, for example, 0.001, 0.005, 0.08, 0.1
  • the positive electrode active material is electrically neutral.
  • C includes one or more elements of Zn, Al, Na, K, Mg, Nb, Mo and W
  • A includes one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge
  • R includes one or more elements of B (boron), S, Si and N
  • D includes one or more elements of S, F, Cl and Br.
  • the carbon structure and characteristics of the carbon coating layer can be measured by Raman spectroscopy, specifically: first measure the Raman spectrum of the positive electrode active material, and obtain Ig / Id (where Id is the peak intensity of sp3 hybridized carbon atoms, Ig is the peak intensity of sp2 hybridized carbon atoms, and the peak intensity ratio is the ratio of the peak height of sp2 hybridized carbon atoms to the peak height of sp3 hybridized carbon atoms) by peak separation of the energy spectrum of the Raman test, thereby obtaining the molar ratio of sp2 hybridized carbon to sp3 hybridized carbon.
  • Id is the peak intensity of sp3 hybridized carbon atoms
  • Ig is the peak intensity of sp2 hybridized carbon atoms
  • the peak intensity ratio is the ratio of the peak height of sp2 hybridized carbon atoms to the peak height of sp3 hybridized carbon atoms
  • the molar ratio of sp2 hybridized carbon atoms to sp3 hybridized carbon atoms in the carbon coating layer of the positive electrode active material is not particularly limited.
  • the molar ratio of sp2 hybridized carbon atoms to sp3 hybridized carbon atoms in the carbon coating layer may be not less than 0.5, and preferably, the molar ratio of sp2 hybridized carbon atoms to sp3 hybridized carbon atoms in the carbon coating layer may be not less than 0.8.
  • the carbon coating layer on the surface of the core has a higher degree of graphitization and a denser structure, which can reduce the water absorption of the carbon coating layer and enable the carbon coating layer to achieve good conductivity, ensuring the passage of lithium ions, which is beneficial to improving the cycle performance and safety performance of the positive electrode active material.
  • the thickness of the carbon coating layer is not particularly limited.
  • the thickness of the carbon coating layer may be 10 nm; preferably, the thickness of the carbon coating layer is 4 nm-8 nm. It is only necessary to form a thin carbon coating layer on the surface of the core to effectively improve the conductivity of the positive electrode active material, and to improve the compaction performance when the positive electrode active material is used to prepare the battery pole piece.
  • the thickness of the carbon coating layer is greater than 10 nm, it is easier to form a carbon coating layer containing larger pores, which will increase the possibility of the carbon coating layer absorbing water and storing moisture.
  • An overly thick carbon coating layer will affect the release and embedding of lithium ions in the core, and significantly reduce the gram capacity of the positive electrode active material.
  • the thickness of the carbon coating layer can be tested by referring to the following method: a thin slice of about 100 nm thickness is cut from the middle of a single particle of the positive electrode active material by FIB, and then the slice is subjected to TEM test to obtain the original TEM test image, and the original image format (xx.dm3) is saved. The original image obtained from the TEM test was opened in the Digital Micrograph software. The carbon coating layer was identified through the lattice spacing and angle information, and the thickness of the carbon coating layer was measured. The thickness of the selected particles was measured at three locations and the average value was taken.
  • the mass fraction of carbon in the positive electrode active material is not particularly limited.
  • the content of carbon in the positive electrode active material may be no more than 3wt% based on the sum of the mass of the core and the mass of the carbon coating.
  • the content of carbon in the positive electrode active material may be 1wt%-2.5wt%.
  • the mass fraction of carbon in the positive electrode active material is no more than 3wt%, the content of carbon in the positive electrode active material is appropriate, which can improve the conductivity of the positive electrode active material, enhance the electron transfer between particles, and promote the migration of lithium ions, and will not cause the gram capacity of the positive electrode active material to deteriorate due to excessive carbon content.
  • the mass fraction of carbon in the positive electrode active material is greater than 3wt%, it is difficult to form a carbon coating with a high degree of graphitization on the surface of the core, and it is easier to form a carbon coating with larger pores, which will increase the possibility of the carbon coating absorbing and storing water.
  • the mass fraction of carbon in the positive electrode active material can be tested as follows: turn on all power switches of the carbon-sulfur analyzer, press and hold the "zero" button, open the oxygen valve of the carbon-sulfur analyzer, and adjust the oxygen pressure to 0.02-0.04MPa. Turn on "front oxygen” and “rear control” and adjust the flowmeter to about 100L/h.
  • the specific surface area of the positive electrode active material is not particularly limited.
  • the specific surface area of the positive electrode active material is not greater than 25 m 2 /g.
  • the specific surface area of the positive electrode active material is not greater than 18 m 2 /g.
  • the pore structure of the carbon coating layer is relatively dense, and the ability to absorb water is relatively weak, so that the positive electrode active material can have higher conductivity, higher gram capacity and lower water absorption.
  • the specific surface area of the positive electrode active material can be tested according to the following method: Use the American Micrometer multi-station fully automatic specific surface area and pore analyzer GeminiVII2390, take about 7g The samples were placed in a 9cc long tube with a bulb, degassed at 150°C for 15 minutes, and then placed in the host for testing to obtain BET data.
  • the particle size of the positive electrode active material is not particularly limited.
  • the median particle size of the positive electrode active material may be no greater than 2 ⁇ m; preferably, the median particle size of the positive electrode active material may be 0.5 ⁇ m-1.5 ⁇ m.
  • the particle size of the positive electrode active material is within the above range, the particle size of the positive electrode active material is smaller, the lithium ion migration rate is faster, and the gram capacity of the positive electrode active material can be effectively increased.
  • the median particle size of the positive electrode active material can be tested and obtained by referring to the following method: Equipment model: Malvern 3000 (MasterSizer3000) laser particle size analyzer, reference standard process: GB/T19077-2016/ISO13320:2009, specific test process: Take an appropriate amount of the sample to be tested (the sample concentration is guaranteed to be 8-12% shading), add 20ml of deionized water, and simultaneously ultra-high temperature for 5min (53KHz/120W) to ensure that the sample is completely dispersed, and then test according to GB/T19077-2016/ISO13320:2009 standard.
  • the conductivity of the positive electrode active material can be significantly improved.
  • the powder resistivity of the phosphate core positive electrode active material with a carbon coating layer on the surface may be no more than 200 ⁇ cm; preferably, the powder resistivity of the positive electrode active material may be no more than 100 ⁇ cm.
  • the lower powder resistivity can effectively reduce the interfacial impedance between the positive electrode active materials, thereby reducing the energy dissipation caused by the internal resistance of the positive electrode active material.
  • the powder resistivity of the positive electrode active material can be tested by referring to the following method: Use the Yuanneng Technology PRCD1000 device to test the powder resistivity, turn on the power of the device and the test software, use a balance to weigh the powder required for the test, use a fixture to press the powder into a thin sheet, put the thin sheet into the device, configure the test parameters, test pressure 5t, hold pressure time 5s, click test, display the test results after the test is completed, and record this result.
  • the present application proposes a method for preparing a positive electrode active material, whereby the aforementioned positive electrode active material can be obtained by a relatively simple method. Therefore, the method has all the characteristics and advantages of the aforementioned positive electrode active material, which will not be described in detail here.
  • the method for preparing a positive electrode active material comprises the following steps:
  • a core of a positive electrode active material is provided in this step, and the type of the core of the positive electrode active material is not particularly limited.
  • the core can select a positive electrode active material with a higher gram capacity, for example, the core can select a phosphate positive electrode active material such as lithium manganese phosphate, lithium iron phosphate and lithium manganese iron phosphate; the core can also select at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and a lithium-rich manganese-based solid solution.
  • the conductivity of the positive electrode active material can be further improved, thereby obtaining a positive electrode active material with both higher gram capacity and better cycle performance.
  • a carbon coating layer is formed on at least a portion of the surface of the inner core. Specifically, the following steps may be included:
  • a pre-carbon coating layer is formed on the surface of the inner core to obtain a pre-coated positive electrode active material.
  • the method for forming the pre-carbon coating layer on the surface of the inner core is not particularly limited.
  • the carbon source and the inner core can be placed in the same reaction container, and the carbon source can react on the surface of the inner core by hydrothermal treatment, thereby forming a carbon coating layer on the surface of the inner core; the carbon source and the inner core can also be placed in a ball milling device, such as a sand mill, and the carbon source can be mechanically mixed to form a carbon coating layer on the surface of the inner core.
  • the carbon source includes a first carbon source and a second carbon source
  • the first carbon source includes at least one of polyvinyl alcohol, polyethylene glycol and citric acid
  • the second carbon source includes at least one of starch, sucrose and glucose.
  • the molecular weight of the first carbon source is not less than 1000, and more preferably, the molecular weight of the first carbon source can be 2000-5000.
  • a pre-carbon coating layer with uniform distribution and relatively uniform thickness can be formed on the surface of the inner core by ball milling, which is conducive to forming a dense and uniform carbon coating layer pore structure after sintering.
  • a and/or B may include the case of A alone, the case of B alone, or any of the cases of A and B, where A and B are only used for examples and may be any technical feature connected by “and/or" in the present application.
  • the pre-coated positive active material is sintered to obtain the positive active material.
  • the sintering treatment should be carried out under an inert atmosphere to avoid oxidation reaction of the carbon source and thus fail to obtain a carbon coating layer with a high degree of graphitization.
  • the type of inert gas is not particularly limited.
  • the inert gas may include at least one of nitrogen and helium.
  • the conditions of the sintering treatment are not particularly limited.
  • the temperature of the sintering treatment may be 650°C-800°C, and the time of the sintering treatment may be 6h-12h.
  • a carbon coating layer with a high degree of graphitization can be formed on the surface of the inner core.
  • the degree of graphitization of the carbon coating layer can be effectively controlled, and the carbon coating layer has a dense pore structure and better conductivity.
  • a carbon coating layer is formed on at least a portion of the surface of the inner core. Specifically, the following steps may be further included:
  • a first carbon coating layer is formed on the surface of the inner core by a first carbon source to obtain a first coated positive electrode active material.
  • the type of the first carbon source is not particularly limited.
  • the first carbon source may include at least one of polyvinyl alcohol, polyethylene glycol (PEG) and citric acid.
  • the molecular weight of the first carbon source may be not less than 1000.
  • the molecular weight of the first carbon source is 2000-5000. More specifically, the first The carbon source may be polyethylene glycol with a molecular weight of 2000-4000.
  • the conditions of the first sintering treatment are not particularly limited.
  • the temperature of the first sintering treatment can be 350°C-800°C
  • the time of the first sintering treatment can be 6h-12h, so that a carbon coating layer with a high degree of graphitization can be finally formed on the surface of the inner core.
  • the positive electrode active material is obtained by the second sintering process in this step.
  • the type of the second carbon source is not particularly limited, for example, the second carbon source may include at least one of starch, sucrose and glucose.
  • the second carbon source may be glucose.
  • mixing the first coated positive electrode active material with the second carbon source may include: adding the second carbon source to an optional solvent and dissolving it at 20-60°C, then adding the first coated positive electrode active material to the aforementioned solvent containing the second carbon source, and then grinding and mixing for 6h-24h to obtain a mixed liquid, which is then dried and used for a second sintering treatment.
  • the conditions of the second sintering treatment are not particularly limited.
  • the temperature of the second sintering treatment can be 650°C-850°C, and the time of the second sintering treatment can be 6h-24h, so that a carbon coating layer with a molar ratio of sp2 hybridized carbon atoms to sp3 hybridized carbon atoms of not less than 0.5 can be formed on the surface of the inner core.
  • the present application proposes a positive electrode sheet 10, comprising a positive electrode collector 11 and a positive electrode active material layer 12, wherein the positive electrode active material layer 12 is located on one side of the positive electrode collector 11, and the positive electrode active material layer 12 comprises the aforementioned positive electrode active material.
  • the positive electrode sheet has all the features and advantages of the aforementioned positive electrode active material, which will not be described in detail here.
  • the positive electrode collector 11 has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material layer 12 can be disposed on any one or both of the two opposite surfaces of the positive electrode collector 11.
  • the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the adhesive and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.
  • a solvent such as N-methylpyrrolidone
  • the adhesive is a high molecular polymer, which mainly functions to bond and maintain the positive electrode active material, enhance the contact between the positive electrode active material and the conductive agent and the positive electrode active material and the current collector, and also stabilize the structure of the pole piece.
  • the type of adhesive is not particularly limited, for example, the adhesive may include at least one of polyvinylidene fluoride and polyacrylonitrile.
  • the present application proposes a battery, comprising: a positive electrode sheet, the positive electrode sheet being the aforementioned positive electrode sheet.
  • the battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.
  • active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet.
  • the electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.
  • the separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.
  • the present application has no particular restrictions on the shape of the battery, which may be cylindrical, square or any other shape.
  • FIG. 2 is a battery 5 of a square structure as an example.
  • the outer packaging may include a shell 51 and a cover plate 53.
  • the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity.
  • the positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 contained in the battery 5 may be one or more, and those skilled in the art can select according to specific actual needs.
  • batteries can be assembled into battery modules, and the number of batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.
  • Figure 4 is a battery module 4 as an example. Referring to Figure 4, in the battery module 4, a plurality of batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. The plurality of batteries 5 can further be fixed by fasteners.
  • the battery module 4 can also include a housing having a housing space, and a plurality of batteries 5 are accommodated in the housing space.
  • 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 one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.
  • Figures 5 and 6 are battery packs 1 as an example.
  • 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 body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery module 4.
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application proposes an electrical device, including: a battery, which is the aforementioned battery. Therefore, the electrical device has all the characteristics and advantages of the aforementioned battery, which will not be repeated here.
  • the battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device.
  • the electrical device may include 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, etc. Vehicles, ships, satellites, energy storage systems, etc., but not limited thereto.
  • the power-consuming device can select batteries, battery modules or battery packs according to its usage requirements.
  • FIG7 is an example of an electric device.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • a battery pack or a battery module may be used.
  • the power-consuming device may also be a mobile phone, a tablet computer, a laptop computer, etc.
  • the device is usually required to be light and thin, and a battery may be used as a power source.
  • Embodiment 1 is a diagrammatic representation of Embodiment 1:
  • Step S1 689.6g manganese carbonate, 455.27g ferrous carbonate, 4.65g cobalt sulfate, and 4.87g vanadium dichloride are added to a mixer and mixed thoroughly for 6h. The obtained mixture is then transferred to a reactor, and 5L deionized water and 1260.6g oxalic acid dihydrate are added, heated to 80°C, stirred at a speed of 500rpm for 6h, and mixed evenly until the reaction is terminated and no bubbles are generated, to obtain a Fe, Co, and V co-doped manganese oxalate suspension. The suspension is then filtered, dried at 120°C, and sand-milled to obtain Fe, Co, V, and S co-doped manganese oxalate particles with a particle size of 100nm.
  • Step S2 Take 1793.1g of manganese oxalate prepared in step S1, 368.3g of lithium carbonate, 1146.6g of ammonium dihydrogen phosphate and 4.9g of dilute sulfuric acid, add them to 20L of deionized water, stir them thoroughly, and evenly mix and react at 80°C for 10h to obtain a slurry. The slurry is transferred to a spray drying device for spray drying and granulation to obtain a powder.
  • the powder is sintered in a roller kiln at 700°C for 4h to obtain the core of the positive electrode active material 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 PEG-1000 is selected as the first carbon source, 58.2g of PEG-1000 is dissolved in 500g of deionized water, and then stirred and fully dissolved to obtain an aqueous solution. 1571.9g of the above core material is added to the solution, and stirred and mixed together for 6h until the mixture is uniformly mixed, and then spray-dried and subjected to a first sintering treatment, the first sintering treatment temperature is 600°C, and the first sintering treatment time is 9h, thereby obtaining a first coated positive electrode active material after the first sintering treatment;
  • Step S4 Glucose was selected as the second carbon source, 37.3 g of glucose was dissolved in 500 g of deionized water, and then stirred and fully dissolved to obtain a glucose aqueous solution. 1603.3 g of the first coated positive electrode active material obtained in step S3 was added to the glucose solution, and stirred and mixed for 6 hours until the mixture was uniformly mixed. After spray drying, a second sintering treatment was performed. The second sintering treatment was performed. The temperature of the sintering treatment is 750° C., and the time of the second sintering treatment is 20 hours, so that the positive electrode active material is obtained through the second sintering treatment.
  • Examples 2-20 and Comparative Examples 1-3 are the same as Example 1, except for the selection of carbon source and the temperature of sintering treatment, see Table 1 for details.
  • PEG-1000 refers to polyethylene glycol with a molecular weight of 900-1100
  • PEG-1500 refers to polyethylene glycol with a molecular weight of 1350-1650
  • PEG-2000 refers to polyethylene glycol with a molecular weight of 1800-2200
  • PEG-3000 refers to polyethylene glycol with a molecular weight of 2700-3300
  • PEG-4000 refers to polyethylene glycol with a molecular weight of 3500-4400
  • PEG-6000 refers to polyethylene glycol with a molecular weight of 5500-7000
  • PEG-8000 refers to polyethylene glycol with a molecular weight of 7200-8800
  • PEG-10000 refers to polyethylene glycol with a molecular weight of 8500-11500
  • PEG-20000 refers to polyethylene glycol with a molecular weight of 19000-21000.
  • Carbon coating thickness test The thickness of the carbon coating is tested by cutting a thin slice of about 100nm from the middle of a single particle of the positive active material prepared above by FIB, and then performing TEM test on the thin slice to obtain the original TEM test image and save the original image format (xx.dm3).
  • the original image obtained by the above TEM test is opened in the Digital Micrograph software, and the carbon coating is identified through the lattice spacing and angle information, and the thickness of the carbon coating is measured. The thickness of the selected particle is measured at three positions and the average value is taken.
  • Test of carbon content in positive electrode active materials Turn on all power switches of the carbon-sulfur analyzer, press and hold the "zero" button, open the oxygen valve of the carbon-sulfur analyzer, and adjust the oxygen pressure to 0.02-0.04MPa. Turn on "front oxygen” and “rear control”, and adjust the flowmeter to about 100L/h. Add silicon-molybdenum powder (0.3g), weighed sample (250mg), tin particles (0.3g), and pure iron (1g) to the crucible in sequence, and close the crucible. Click the "test” button to start the test. The test results will be automatically displayed after the test is completed. This result is recorded as the C content.
  • Specific surface area test of positive electrode active materials Use the American Microelectronics multi-station fully automatic specific surface area and pore analyzer GeminiVII2390, take about 7g of positive electrode active material sample and put it into a 9cc long tube with a bulb, degas at 150°C for 15min, and then put it into the host test to obtain BET data.
  • Test of median particle size of positive electrode active materials Equipment model: Malvern 3000 (MasterSizer3000) laser particle size analyzer, reference standard process: GB/T19077-2016/ISO13320:2009, specific test process: Take an appropriate amount of the sample to be tested (the sample concentration is guaranteed to be 8-12% shading), add 20ml of deionized water, and ultraviolet for 5min (53KHz/120W) to ensure that the sample is completely dispersed, and then test according to GB/T19077-2016/ISO13320:2009 standard.
  • Test of the resistivity of the positive electrode active material powder Use the Yuanneng Technology PRCD1000 device to test the resistivity of the powder. Turn on the power of the device and the test software. Use a balance to weigh the powder required for the test. Use a fixture to press the powder into a thin sheet. Put the thin sheet into the device. Configure the test parameters, test pressure 5t, pressure holding time 5s, click test, and the test will be displayed after the test is completed. As a result, record this result.
  • Test of water absorption of positive electrode active materials Take 5g positive electrode active material sample, heat and dry it at 110°C for 12h, then put the sample into a vial, and put the vial containing the sample into the automatic sampling system of Karl Fischer equipment. During the test, heat the vial containing the sample at 250°C and pass dry gas into it, blow the gas in the vial into the titration cup for absorption titration, and convert the result into the water content of the solid sample.
  • test of gram capacity of positive electrode active materials (1) Preparation of button cells: The positive electrode active materials, polyvinylidene fluoride (PVDF) and acetylene black prepared above are added to N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5, and stirred in a drying room to form a slurry. The slurry is coated on aluminum foil, dried and cold pressed to form a positive electrode sheet. The coating amount is 0.2g/ cm2 , and the compaction density is 2.0g/ cm3 .
  • PVDF polyvinylidene fluoride
  • NMP N-methylpyrrolidone
  • a lithium sheet is used as the negative electrode, and a solution of 1 mol/L LiPF6 in a volume ratio of 1:1:1 of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) is used as the electrolyte. Together with the positive electrode sheet prepared above, it is assembled into a button cell in a button box.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • Full batteries were prepared using the positive electrode active materials in Examples 1-11 and Comparative Examples 1-3, respectively.
  • the preparation of the full batteries was as follows:
  • the positive electrode active material was mixed evenly with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in a weight ratio of 92:2.5:5.5 in an N-methylpyrrolidone solvent system, and then coated on an aluminum foil, dried, and cold pressed to obtain a positive electrode sheet.
  • the coating amount was 0.4 g/cm 2 and the compaction density was 2.4 g/cm 3 .
  • the negative electrode active material artificial graphite, hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were mixed evenly in deionized water at a weight ratio of 90:5:2:2:1, and then coated on copper foil, dried, and cold pressed to obtain a negative electrode sheet.
  • the coating amount was 0.2g/ cm2
  • the compaction density was 1.7g/ cm3 .
  • the positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrodes to play a role of isolation, and then wound to obtain a bare cell.
  • the bare cell is placed in an outer package, injected with electrolyte and packaged to obtain a full battery.
  • the full battery in Examples 1-11 and Comparative Examples 1-3 was subjected to a cycle performance test.
  • the full battery cycle performance test is as follows: Under a constant temperature environment of 45°C, at 2.5V-4.3V, the full battery is charged to 4.3V at 1C, and then charged at a constant voltage at 4.3V until the current is less than or equal to 0.05mA. Let it stand for 5 minutes, then discharge it to 2.5V at 1C, and record the discharge capacity at this time as D 0. Repeat the above charge and discharge cycle until the discharge capacity is reduced to 80% of D 0. Record the number of cycles the battery has gone through at this time. The test results are shown in Table 2.
  • test results show that when the molar ratio of sp2 hybridized carbon to sp3 hybridized carbon in the carbon coating layer of the positive electrode active material is less than 0.5, the water absorption of the positive electrode active material is significantly improved, reaching more than 890 ppm. Correspondingly, excessive water content will cause the lithium salt in the battery electrolyte to decompose, which will significantly reduce the battery's cycle performance.
  • the same kind of core is selected for subsequent preparation of positive electrode active materials, that is, the selection of the aforementioned core material is exemplary.
  • the relevant features of the carbon coating layer of the positive electrode active material in the present application can be combined with other core materials in a suitable manner.
  • the types of core materials may include at least one of lithium manganese phosphate, lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium-rich manganese-based solid solution.

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Abstract

本公开提供了正极活性材料及其制备方法、正极极片、电池和用电装置，正极活性材料包括：内核；碳包覆层，所述碳包覆层至少覆盖所述内核的部分表面，其中，所述碳包覆层中的sp3杂化碳原子与sp2杂化碳原子的摩尔比不小于0.5。

Description

正极活性材料及其制备方法、正极极片、电池和用电装置 技术领域
本申请涉及电池领域，具体地，涉及正极活性材料及其制备方法、正极极片、电池和用电装置。
背景技术
近年来，随着锂离子电池技术的发展，锂离子电池广泛应用于水力、火力、风力和太阳能电站等储能电源系统，并在电动工具、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有着广泛应用。目前锂离子电池在工业化生产及应用层面仍然有较多问题有待解决。
申请内容
在本申请的一个方面，本申请提出了一种正极活性材料，包括：内核；碳包覆层，所述碳包覆层至少覆盖所述内核的部分表面，其中，所述碳包覆层中sp2杂化碳原子与sp3杂化碳原子的摩尔比不小于0.5。由此，可以降低正极活性材料的吸水性。
根据本申请的实施例，所述内核包括磷酸盐；优选地，所述磷酸盐包括锂锰磷酸盐、锂铁磷酸盐和锂锰铁磷酸盐中的至少一种。由此，可以通过对该内核材料进行表面碳包覆，以提高其电导率，优化使用该内核材料的电池性能。
根据本申请的实施例，所述内核包括LiMPO4，所述M元素包括Mn和非Mn元素。由此，可以通过对该内核材料进行表面碳包覆，以提高其电导率，优化使用该内核材料的电池性能。
根据本申请的实施例，所述非Mn元素包括第一掺杂元素和第二掺杂元素中的一种或两种，所述第一掺杂元素为锰位掺杂，所述第二掺杂元素为磷位掺杂。由此，可以提高正极活性材料的循环稳定性。
根据本申请的实施例，所述第一掺杂元素包括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；优选地，所述第一掺杂元素包括Fe、Ti、V、Ni、Co和Mg中的至少两种。由此，可以进一步正极活性材料的克容量。
根据本申请的实施例，所述第二掺杂元素包括B(硼)、S、Si和N中的一种或多种元素。由此，可以进一步正极活性材料的克容量。
根据本申请的实施例，所述内核包括Li1+xMn1-yAyP1-zRzO4，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包括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，所述R包括B(硼)、S、Si和N中的一种或多种元素。由此，可以提高正极活性材料的结构稳定性和容量发挥。
根据本申请的实施例，所述内核包括Li1+xCmMn1-yAyP1-zRzO4-nDn，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，n为在0.001至0.1范围内的任意数值，m为在0.9至1.1范围内的任意数值，所述C包括Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素，所述A包括Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，所述R包括B(硼)、S、Si和N中的一种或多种元素，所述D包括S、F、Cl和Br中的一种或多种元素。由此，可以进一步提高正极活性材料的克容量和压实密度。
根据本申请的实施例，所述碳包覆层中sp2杂化碳原子与sp3杂化碳原子的摩尔比不小于0.8。由此，可以使得提高碳包覆层的结构有序性，使得碳包覆层结构更为致密，减少碳包覆层上的孔隙，从而进一步降低正极活性材料的吸水性。
根据本申请的实施例，所述碳包覆层的厚度不大于10nm；优选地，所述碳包覆层的厚度为4nm-8nm。由此，在降低吸水性的同时，提高正极活性材料的电导率。
根据本申请的实施例，所述正极活性材料中碳元素的含量不大于3wt％，优选地，所述正极活性材料中碳元素的含量为1wt％-2.5wt％。由此，可以使得正极活性材料兼具较好的导电性和较低的吸水性。
根据本申请的实施例，所述正极活性材料的比表面积不大于25m2/g，优选地，所述正极活性材料的比表面积不大于18m2/g。由此，可以使得正极活性材料兼具较高的导电性、较高的克容量以及较低的吸水性。
根据本申请的实施例，所述正极活性材料的中值粒径不大于2μm；优选地，所述正极活性材料的中值粒径为0.5μm-1.5μm。由此，可以提高正极活性材料的锂离子迁移速率，提高正极活性材料的克容量。
根据本申请的实施例，所述正极活性材料的粉末电阻率为不大于200Ω·cm；优选地，所述正极活性材料的粉末电阻率不大于100Ω·cm。由此，可以通过碳包覆层的设置进一步提高正极活性材料的导电性，同时保持较低的吸水性。
在本申请的又一个方面，本申请提出了一种制备正极活性材料的方法，提供内核；在 所述内核的至少部分表面形成碳包覆层。由此，可以通过较为简便的方法获得前述的正极活性材料，该方法具有前述正极活性材料的全部特征及优点，在此不再赘述。
根据本申请的实施例，所述在所述内核的至少部分表面形成碳包覆层包括：通过碳源在所述内核表面形成预碳包覆层以获得预包覆正极活性材料；在惰性气体气氛下对所述预包覆正极活性材料进行烧结处理以形成所述碳包覆层，以获得所述正极活性材料，所述碳源包括第一碳源和第二碳源。由此，可以在内核表面形成具有较高石墨化度的碳包覆层。
根据本申请的实施例，所述在所述内核的至少部分表面形成碳包覆层包括：将所述内核与所述第一碳源混合，并通过第一烧结处理得到第一包覆正极活性材料，将所述第一包覆正极活性材料与所述第二碳源混合，并通过第二烧结处理得到所述正极活性材料。由此，可以在内核表面形成具有较高石墨化度的碳包覆层。
根据本申请的实施例，所述第一碳源包括聚乙烯醇、聚乙二醇和柠檬酸中的至少一种；所述第二碳源包括淀粉、蔗糖和葡萄糖中的至少一种。由此，可以在内核表面形成具有较高石墨化度的碳包覆层。
根据本申请的实施例，所述第一碳源为聚合物时，所述第一碳源的分子量不少于1000，优选地，所述第一碳源的分子量为2000-5000。由此，可以获得具有较高石墨化度的碳包覆层。
根据本申请的实施例，所述烧结处理的温度为650℃-800℃，所述烧结处理的时间为6h-12h。由此，可以在内核表面形成具有较高石墨化度的碳包覆层。
根据本申请的实施例，所述第一烧结处理的温度为350℃-800℃，所述第一烧结处理的时间为6h-12h。由此，可以在内核表面形成具有较高石墨化度的碳包覆层。
根据本申请的实施例，所述第二烧结处理的温度为650℃-850℃，所述第二烧结处理的时间为6h-24h。由此，可以在内核表面形成具有较高石墨化度的碳包覆层。
在本申请的又一个方面，本申请提出了一种正极极片，包括正极集流体和正极活性材料层，所述正极活性材料层位于所述正极集流体的一侧，所述正极活性材料层包括前述的正极活性材料，和/或所述正极活性材料层包括采用前述的方法制备得到的正极活性材料。由此，该正极极片具有前述正极活性材料的全部特征及优点，在此不再赘述。
在本申请的又一个方面，本申请提出了一种电池，包括：正极极片，所述正极极片为前述的正极极片。由此，该电池具有前述正极极片全部特征及优点，在此不再赘述。
在本申请的又一个方面，本申请提出了一种用电装置，包括：电池，所述电池为前述的电池。由此，该用电装置具有前述电池的全部特征及优点，在此不再赘述。
附图说明
本申请的上述和/或附加的方面和优点从结合下面附图对实施例的描述中将变得明显和容易理解，其中：
图1显示了根据本申请一个实施例的正极极片的结构示意图；
图2是本申请一实施方式的电池的示意图；
图3是图2所示的本申请一实施方式的电池的分解图；
图4是本申请一实施方式的电池模块的示意图；
图5是本申请一实施方式的电池包的示意图；
图6是图5所示的本申请一实施方式的电池包的分解图；
图7是本申请一实施方式的电池用作电源的用电装置的示意图。
附图标记说明：
1：电池包；2：上箱体；3：下箱体；4：电池模块；5：电池；10：正极极片；11：正极集流体；12：正极活性材料层；51：壳体；52：电极组件；53：顶盖组件。
具体实施方式
下面详细描述本公开的实施例。下面描述的实施例是示例性的，仅用于解释本公开，而不能理解为对本公开的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。
在本申请的一个方面，本申请提出了一种正极活性材料，包括：内核；碳包覆层，碳包覆层至少覆盖内核的部分表面，其中，碳包覆层中sp2杂化碳原子与sp3杂化碳原子的摩尔比不小于0.5。当正极活性材料中碳包覆层中的sp2杂化碳原子与sp3杂化碳原子位于前述范围内时，碳包覆层的孔结构较为致密，可以显著降低碳包覆层的吸水能力，进而降低正极活性材料的吸水性，从而提高电池的安全性能和循环性能。
为了便于理解，下面对于本申请中的正极活性材料具有上述有益效果的原理进行说明：
由于锂离子电池的电势明显高于水的稳定电压范围，故锂离子电池对水分十分敏感，微量的水分都会严重地影响锂离子电池的性能，因此在整个生产过程中都必须要严格控制材料中的水分含量，例如，在电池的生产过程中，需要在集流体涂布后对极片进行烘干处理，在冷压后对极片进行烘干处理，在电芯卷绕后对电芯进行烘干处理等，以及在电池的整个生产过程中都需要对环境水分进行严格控制。电池的生产过程中的烘干处理和环境水分控制会消耗极大的能量，使得电池的生产工艺流程复杂化。
在本申请中，发明人发现，为了提高内核的导电性，可以通过在内核表面形成碳包覆层以改善正极活性材料的电导率。进一步地，当正极活性材料的碳包覆层呈现为疏松多孔的状态时，疏松多孔的碳包覆层结构会加速正极活性材料对于水分的吸收以及存储，进而使得正极活性材料的吸水能力和储水能力均较强，从而使得正极活性材料在存储、加工过程中均会发生吸水现象，最终导致正极活性材料的含水量较高。电池中高含量水分的存在会导致电解液中的锂盐发生分解，使得电池的循环性能明显降低。
进一步地，发明人发现，若仅通过增加烘干处理的温度、延长烘干时间等操作以尽可能地除尽正极活性材料中的水分会造成能量的过度消耗、工艺时间的明显延长等问题，且长时间的高温烘干处理也会对电芯中的其它组件，如隔膜组件等造成老化失效等不利影响，使得制造成本明显提升。在前述理论分析和实验探究的基础上，发明人发现，通过改善正极活性材料碳包覆层的孔状态可以在不额外增加工艺流程和改善工艺环境的基础上，有效地降低正极活性材料的吸水性。具体地，发明人发现，当内核表面碳包覆层中sp2杂化碳原子与sp3杂化碳原子的摩尔比不小于0.5时，正极活性材料碳包覆层结构的有序性较高，碳包覆层的孔结构具有较高的致密性和较小的孔径分布范围，在电池的生产过程中，外界的水分很难进入碳包覆层的孔内，从而有效降低了正极活性材料的吸水性和储水性能，实现电池安全性能和循环性能的提高，有效节省烘干过程中的能耗，显著降低生产成本。
根据本申请的一些实施例，内核的种类不受特别限制，例如，内核可以包括磷酸盐；优选地，磷酸盐可以包括锂锰磷酸盐、锂铁磷酸盐和锂锰铁磷酸盐中的至少一种。锂锰磷酸盐、锂铁磷酸盐和锂锰铁磷酸盐具有较高的克容量和较低的原材料成本，由于正极活性材料在电池中应用时会发生电化学反应，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，以及颗粒内部不同位置间的电子传输，可以使用具有较优导电性能的材料，通过采用碳层包覆磷酸盐内核表面，可以获得兼具低成本、高克容量和高电导率的正极活性材料，优化使用正极活性材料的电池性能。
根据本申请的一些实施例，内核的种类不受特别限制，例如，内核可以包括LiMPO4，M元素包括Mn和非Mn元素。优选地，非Mn元素可以包括第一掺杂元素和第二掺杂元素中的一种或两种，第一掺杂元素为锰位掺杂，第二掺杂元素为磷位掺杂。第一掺杂元素和第二掺杂元素不仅可有效减少锰溶出，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，提高电池的倍率性能。
根据本申请的一些实施例，第一掺杂元素的种类不受特别限制，例如，第一掺杂元素可以包括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；优选地，第一掺杂元素可以包括Fe、Ti、V、Ni、Co和Mg中的至少两种。第一掺杂元素能够进一步降低该正极活性材料的晶格变化率，降低材料的表面活性，从而抑制Mn溶出和正极材料与电解液的界面副反应。通过掺杂上述范围内的两种或更多种金属，有利于增强掺杂效果，进一步降低表面氧活性，从而抑制锰的溶出。另外，多个元素的掺杂能够增加元素间的协同作用，在提高电池容量的同时，减少材料的晶格变化率，增强电池的动力学性能。
根据本申请的一些实施例，第二掺杂元素的种类不受特别限制，例如，第二掺杂元素可以包括B(硼)、S、Si和N中的一种或多种元素。第二掺杂元素可以提高Mn-O键的变化速率，改善该正极活性材料的小极化子迁移势垒，提升电子电导率。另外，第二元素的掺杂还能够减小材料中的反位缺陷浓度，提高材料的动力学性能和克容量，还可以改变材料形貌，从而提升材料的压实密度。
根据本申请的一些实施例，内核的种类不受特别限制，例如，内核可以包括Li1+xMn1-yAyP1-zRzO4，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，A包括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，R包括B(硼)、S、Si和N中的一种或多种元素。选自上述元素的锰位掺杂元素A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，提高正极活性材料的结构稳定性，大大减少锰的溶出并降低颗粒表面的氧活性；选自上述元素的磷位掺杂元素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。如果x的值过小，会导致整个内核的含锂量降低，影响正极活性材料的克容量发挥。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，影响正极活性材料的电压平台。R元素掺杂在P的位置，由于P-O四面体较稳定，z值过大会影响正极活性材料的稳定性。因此，当x、y和z选自上述范围时，正极活性材料可以具有较优的性能。
除非另有说明，否则上述内核的化学式中，当某掺杂位点具有两种以上元素时，上述对于x、y、z或m数值范围的限定不仅是对每种作为该位点的元素的化学计量数的限定，也是对各个作为该位点的元素的化学计量数之和的限定。例如，当具有化学式为Li1+xMn1-yAyP1-zRzO4的化合物时，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。
根据本申请的一些实施例，内核的种类不受特别限制，例如，内核可以包括Li1+xCmMn1-yAyP1-zRzO4-nDn，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，影响材料的克容量发挥。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。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0.001-0.100。更具体地，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，n为在0.001至0.1范围内的任意数值，m为在0.9至1.1范围内的任意数值。例如，1+x选自0.9至1.1的范围，例如为0.97、0.977、0.984、0.988、0.99、0.991、0.992、0.993、0.994、0.995、0.996、0.997、0.998、1.01，x选自0.001至0.1的范围，例如为0.001、0.005，y选自0.001至0.5的范围，例如为0.001、0.005、0.02、0.05、0.1、0.15、0.2、0.25、0.3、0.34、0.345、0.349、0.35、0.4，z选自0.001至0.1的范围，例如为0.001、0.005、0.08、0.1，n选自0.001至0.1的范围，例如为0.001、0.005、0.08、0.1，并且正极活性材料为电中性的。C包括Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素，A包括Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，R包括B(硼)、S、Si和N中的一种或多种元素，D包括S、F、Cl和Br中的一种或多种元素。通过在化合物的Li位、Mn位、P位和O位同时以特定量掺杂特定的元素，能够获得明显改善的倍率性能，同时显著减少了Mn与Mn位掺杂元素的溶出，获得了显著改善的循环性能和/或高温稳定性，并且正极活性材料的克容量和压实密度也可以得到提高。
根据本申请的一些实施例，碳包覆层的碳结构和特征可通过拉曼(Raman)光谱进行测定，具体地：首先测量正极活材料的拉曼图谱，通过对拉曼测试的能谱进行分峰，得到Ig/Id(其中Id为sp3杂化碳原子的峰强度，Ig为sp2杂化碳原子的峰强度，该峰强度比即sp2杂化碳原子的峰高度与sp3杂化碳原子的峰高度之比)，从而得到sp2杂化碳与sp3杂化碳的摩尔比。正极活性材料碳包覆层中的sp2杂化碳原子与sp3杂化碳原子的摩尔比不受特别限制，例如，碳包覆层中的sp2杂化碳原子与sp3杂化碳原子的摩尔比可以不小于0.5，优选地，碳包覆层中的sp2杂化碳原子与sp3杂化碳原子的摩尔比可以不小于0.8。当碳包覆层中的sp2杂化碳原子与sp3杂化碳原子的摩尔比位于上述范围内时，内核表面的碳包覆层具有较高的石墨化度，碳包覆层的结构更为致密，既能降低碳包覆层的吸水性，又能使得碳包覆层实现良好的导电性，保证锂离子的通路，有利于提高正极活性材料的循环性能和安全性能。当sp2杂化碳原子与sp3杂化碳原子的摩尔比小于0.5时，碳包覆层中无定形sp3 形态的碳原子较多，碳包覆层的结构较为疏松多孔，不利降低碳包覆层的吸水性，且碳包覆层导电性较差。
根据本申请的一些实施例，碳包覆层的厚度不受特别限制，例如，碳包覆层的厚度可为10nm；优选地，碳包覆层的厚度为4nm-8nm。仅需要在内核的表面形成较薄碳包覆层即可有效改善正极活性材料的导电性，并且可以改善使用正极活性材料制备电池极片时的压密性能，当碳包覆层的厚度大于10nm时，更易于形成含有较大孔隙的碳包覆层，会使得碳包覆层吸水并存储水分的可能性变大，过厚的碳包覆层会影响内核锂离子的脱出和嵌入，使得正极活性材料的克容量明显降低。碳包覆层的厚度可以参照如下方法测试得到：通过FIB从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，保存原始图片格式(xx.dm3)。将上述TEM测试所得原始图片在Digital Micrograph软件中打开，通过晶格间距和夹角信息，识别出碳包覆层，量取碳包覆层的厚度。对所选颗粒测量三个位置处的厚度，取平均值。
根据本申请的一些实施例，正极活性材料中碳元素的质量分数不受特别限制，例如，以内核的质量与碳包覆层的质量之和计，正极活性材料中碳元素的含量可以不大于3wt％，优选地，正极活性材料中碳元素的含量可以为1wt％-2.5wt％。当正极活性材料中碳元素的质量分数不大于3wt％时，正极活性材料中碳元素的含量适当，既可以提高正极活性材料的导电性，增强颗粒间的电子传输，促进锂离子的迁移，又不会因为碳含量过多导致正极活性材料的克容量发生恶化。当正极活性材料中碳元素的质量分数大于3wt％时，难以在内核表面形成具有较高石墨化度的碳包覆层，且更易于形成含有较大孔隙的碳包覆层，会使得碳包覆层吸水并存储水分的可能性变大。正极活性材料中碳元素的质量分数可以参照如下方法测试得到：打开碳硫分析仪所有电源开关，按住“对零”按钮，打开碳硫分析仪的氧气阀，调节氧气，压力在0.02-0.04MPa。打开“前氧”“后控”，调节流量计控制在100L/h左右。在坩锅内依次加入硅钼粉(0.3g)，称好的样品(250mg)，锡粒(0.3g)，纯铁(1g)，合上坩锅。点击“测试”按钮，即可开始测试，测试完成自动显示测试结果，记录此结果即为C含量。
根据本申请的一些实施例，正极活性材料的比表面积不受特别限制，例如，正极活性材料的比表面积不大于25m2/g，优选地，正极活性材料的比表面积不大于18m2/g。当正极活性材料的比表面积位于上述范围内时，碳包覆层的孔结构较为致密，对于水分的吸收能力较弱，可以使得正极活性材料兼具较高的导电性、较高的克容量以及较低的吸水性。当正极活性材料的比表面积大于25m2/g时，正极活性材料的比表面积过大，正极活性材料的吸水性越强，从而会导致电池的循环性能降低。正极活性材料的比表面积可以参照如下方法测试得到：使用美国麦克多站式全自动比表面积与孔隙分析仪GeminiVII2390，取约7g 左右的样品放入9cc带球泡的长管中，150℃脱气15min，随后放入主机测试得到BET数据。
根据本申请的一些实施例，正极活性材料的粒径不受特别限制，例如，正极活性材料的中值粒径可以不大于2μm；优选地，正极活性材料的中值粒径可以为0.5μm-1.5μm。当正极活性材料的粒径位于上述范围时，正极活性材料的粒径较小，锂离子迁移速率较快，可有效提高正极活性材料的克容量。正极活性材料的中值粒径可以参照如下方法测试得到：设备型号：马尔文3000(MasterSizer3000)激光粒度仪，参考标准流程：GB/T19077-2016/ISO13320:2009，具体测试流程：取待测样品适量(样品浓度保证8～12％遮光度即可)，加入20ml去离子水，同时外超5min(53KHz/120W)，确保样品完全分散，之后按照GB/T19077-2016/ISO13320:2009标准进行测试。
根据本申请的一些实施例，通过在内核的至少部分表面进行多孔碳包覆层，例如多孔碳层的包覆，可以显著提高正极活性材料的导电性，例如，表面具有碳包覆层的磷酸盐内核正极活性材料的粉末电阻率可不大于200Ω·cm；优选地，正极活性材料的粉末电阻率可不大于100Ω·cm，较低的粉末电阻率可以有效降低正极活性材料之间的界面阻抗，从而可以减少因正极活性材料内阻所带来的能量耗散。正极活性材料的粉末电阻率可以参照如下方法测试得到：使用元能科技PRCD1000设备测试粉末电阻率，打开设备电源和测试软件，使用天平称取测试所需粉末，使用治具将粉末压成薄片，将薄片放入设备内，配置测试参数，测试压力5t，保压时间5s，点击测试，测试完成后显示测试结果，记录此结果。
在本申请中，无论是否使用“大约”或“约”等字眼，所有在此公开了的数字均为近似值。每一个数字的数值有可能会出现10％以下的差异或者本领域人员认为的合理的差异，如1％、2％、3％、4％或5％的差异。
在本申请的又一个方面，本申请提出了一种制备正极活性材料的方法，由此，可以通过较为简便的方法获得前述的正极活性材料，因此，该方法具有前述正极活性材料的全部特征及优点，在此不再赘述。具体地，制备正极活性材料的方法包括以下步骤：
S100：提供内核
根据本申请的一些实施例，在该步骤提供正极活性材料的内核，正极活性材料内核的种类不受特别限制，例如，内核可以选择具有较高克容量的正极活性材料，例如，内核可以选择锂锰磷酸盐、锂铁磷酸盐和锂锰铁磷酸盐等磷酸盐正极活性材料；内核还可以选择钴酸锂、锰酸锂、镍钴锰酸锂、镍钴铝酸锂和富锂锰基固溶体中的至少一种，通过在内核表面形成碳包覆层可以进一步提高正极活性材料的导电性，从而获得兼具较高克容量、较优循环性能的正极活性材料。
S200：在内核的至少部分表面形成碳包覆层
根据本申请的一些实施例，在该步骤中在内核的至少部分表面形成碳包覆层，具体地，可以包括以下步骤：
S211：通过碳源在内核表面形成预碳包覆层
根据本申请的一些实施例，在该步骤中在内核表面形成预碳包覆层以获得预包覆正极活性材料，在内核表面形成预碳包覆层的方法不受特别限制，例如，可将碳源与内核置于同一反应容器中，通过水热处理令碳源在内核表面发生反应，从而在内核表面形成碳包覆层；还可以将碳源与内核置于球磨设备，如砂磨机中，通过机械混合使得碳源在内核表面形成碳包覆层。根据本申请的另一些实施例，碳源包括第一碳源和第二碳源，第一碳源包括聚乙烯醇、聚乙二醇和柠檬酸中的至少一种；第二碳源包括淀粉、蔗糖和葡萄糖中的至少一种。优选地，第一碳源的分子量不少于1000，更优选地，第一碳源的分子量可以为2000-5000。由此，通过球磨处理即可以在内核表面形成均匀分布的、厚度较为一致的预碳包覆层，进而有利于烧结处理后形成致密、均匀的碳包覆层孔结构。
在本申请的描述中，“A和/或B”可以包括单独A的情况，单独B的情况，A和B的情况的任一种，其中A、B仅用于举例，其可以是本申请中使用“和/或”连接的任意技术特征。
S212：在惰性气体气氛下对预包覆正极活性材料进行烧结处理
根据本申请的一些实施例，在该步骤中对预包覆正极活性材料进行烧结处理以获得正极活性材料，烧结处理应在惰性气氛下进行，从而避免碳源发生氧化反应从而无法获得具有较高石墨化度的碳包覆层，惰性气体的种类不受特别限制，例如，惰性气体可以包括氮气和氦气中的至少一种。烧结处理的条件不受特别限制，例如，所述烧结处理的温度可以为650℃-800℃，烧结处理的时间可以为6h-12h。由此，可以在内核表面形成具有较高石墨化度的碳包覆层。发明人发现，随着烧结处理的温度升高，碳包覆层中碳的石墨化程度也会升高。通过控制烧结处理的最高烧结处理可以有效控制碳包覆层的石墨化度，碳包覆层具有致密的孔结构和较优的导电性。
根据本申请的另一些实施例，在该步骤中在内核的至少部分表面形成碳包覆层，具体地，还可以包括以下步骤：
S221：将内核与第一碳源混合，并进行第一烧结处理
根据本申请的一些实施例，在该步骤中通过第一碳源在内核表面形成第一碳包覆层，以得到第一包覆正极活性材料，第一碳源的种类不受特别限制，例如，第一碳源可以包括聚乙烯醇、聚乙二醇(PEG)和柠檬酸中的至少一种。具体地，第一碳源为聚合物时，第一碳源的分子量可以不少于1000，优选地，第一碳源的分子量为2000-5000。更具体地，第一 碳源的可以为分子量2000-4000的聚乙二醇。
根据本申请的一些实施例，第一烧结处理的条件也不受特别限制，例如，第一烧结处理的温度可以为350℃-800℃，第一烧结处理的时间可以为6h-12h，从而可以最终在内核表面形成具有较高石墨化度的碳包覆层。
S222：将第一包覆正极活性材料与第二碳源混合，并进行第二烧结处理
根据本申请的一些实施例，在该步骤中通过第二烧结处理得到正极活性材料。第二碳源的种类不受特别限制，例如，第二碳源可以包括淀粉、蔗糖和葡萄糖中的至少一种。优选地，第二碳源可以为葡萄糖。
根据本申请的一些实施例，将第一包覆正极活性材料与第二碳源混合可以包括：将第二碳源加入可选的溶剂中，并在20-60℃下溶解后，再将第一包覆正极活性材料加入前述含有第二碳源的溶剂中，再经过研磨混合6h-24h得到混合液体后，干燥后再用于第二烧结处理。
根据本申请的一些实施例，第二烧结处理的条件也不受特别限制，例如，第二烧结处理的温度可以为650℃-850℃，第二烧结处理的时间可以为6h-24h，从而可以在内核表面形成sp2杂化碳原子与sp3杂化碳原子的摩尔比不小于0.5的碳包覆层。
在本申请的又一个方面，参考图1，本申请提出了一种正极极片10，包括正极集流体11和正极活性材料层12，正极活性材料层12位于正极集流体11的一侧，正极活性材料层12包括前述的正极活性材料。由此，该正极极片具有前述正极活性材料的全部特征及优点，在此不再赘述。作为示例，正极集流体11具有在其自身厚度方向相对的两个表面，正极活性材料层12可以设置在正极集流体11相对的两个表面的其中任意一者或两者上。
根据本申请的一些实施例，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如正极活性材料、导电剂、粘接剂和任意其他的组分分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。
根据本申请的一些实施例，粘接剂为高分子聚合物，其主要作用有粘接和保持正极活性材料、增强正极活性材料与导电剂以及正极活性材料与集流体之间的接触，同时还可以稳定极片的结构。根据本申请的另一些实施例，粘接剂的种类也不受特别限制，例如，粘接剂可以包括聚偏二氟乙烯和聚丙烯腈中的至少一种。
在本申请的又一方面，本申请提出了一种电池，包括：正极极片，正极极片为前述的正极极片。由此，该电池具有前述正极极片全部特征及优点，在此不再赘述。通常情况下， 电池包括正极极片、负极极片、电解质和隔离膜。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。电解质在正极极片和负极极片之间起到传导离子的作用。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，同时可以使离子通过。
根据本申请的一些实施例，本申请对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。例如，图2是作为一个示例的方形结构的电池5。具体地，参照图3，外包装可包括壳体51和盖板53。其中，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能够盖设于开口，以封闭容纳腔。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封装于容纳腔内。电解液浸润于电极组件52中。电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
根据本申请的一些实施例，电池可以组装成电池模块，电池模块所含电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。图4是作为一个示例的电池模块4。参照图4，在电池模块4中，多个电池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电池5进行固定。电池模块4还可以包括具有容纳空间的外壳，多个电池5容纳于该容纳空间。
在本申请的描述中，“多个”的含义是两个或两个以上。
根据本申请的一些实施例，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为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。图5和图6是作为一个示例的电池包1。参照图5和图6，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能够盖设于下箱体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。
在本申请的又一方面，本申请提出了一种用电装置，包括：电池，电池为前述的电池。由此，该用电装置具有前述电池的全部特征及优点，在此不再赘述。电池、电池模块、或电池包可以用作用电装置的电源，也可以用作用电装置的能量存储单元。用电装置可以包括移动设备(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，但不限于此。用电装置可以根据其使用需求来选择电池、电池模块或电池包。
根据本申请的一些实施例，图7是作为一个示例的用电装置。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电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
根据本申请的一些实施例，用电装置还可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用电池作为电源。
下面通过具体的实施例对本申请的方案进行说明，需要说明的是，下面的实施例仅用于说明本申请，而不应视为限定本申请的范围。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
实施例1：
步骤S1：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6h。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6h，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Fe、Co、V和S共掺杂草酸锰颗粒。
步骤S2：取步骤S1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10h，得到浆料。将浆料转入喷雾干燥设备中进行喷雾干燥造粒，得到粉料。在保护气氛(90％氮气和10％氢气)中，700℃下将所述粉料在辊道窑中进行烧结4h，得到正极活性材料的内核Li0.997Mn0.60Fe0.393V0.004Co0.003P0.997S0.003O4。
步骤S3：选用PEG-1000作为第一碳源，将58.2gPEG-1000溶于500g去离子水中，然后搅拌并充分溶解，得到水溶液。将上述内核材料1571.9g加入到该溶液中，一同搅拌混合6h至混合均匀，经喷雾干燥后进行第一烧结处理，第一烧结处理温度的温度为600℃，第一烧结处理的时间为9h，从而经过第一烧结处理得到第一包覆正极活性材料；
步骤S4：选用葡萄糖作为第二碳源，将37.3g葡萄糖溶于500g去离子水中，然后搅拌并充分溶解，得到葡萄糖水溶液。将步骤S3所得1603.3g第一包覆正极活性材料加入到前述葡萄糖溶液中，一同搅拌混合6h至混合均匀，经喷雾干燥后进行第二烧结处理，第二烧 结处理的温度为750℃，第二烧结处理的时间为20h，从而经过第二烧结处理得到正极活性材料。
实施例2-20，对比例1-3与实施例1相同，所不同的是碳源的选择以及烧结处理的温度，具体参见表1。
表1

需要说明的是，PEG-1000指分子量为900-1100的聚乙二醇，PEG-1500指分子量为1350-1650的聚乙二醇，PEG-2000指分子量为1800-2200的聚乙二醇，PEG-3000指分子量为2700-3300的聚乙二醇，PEG-4000指分子量为3500-4400的聚乙二醇，PEG-6000指分子量为5500-7000的聚乙二醇，PEG-8000指分子量为7200-8800的聚乙二醇，PEG-10000指分子量为8500-11500的聚乙二醇，PEG-20000指分子量为19000-21000的聚乙二醇。
对实施例1-11，对比例1-3中的正极活性材料进行下列测试，测试结果见表2：
1、碳包覆层中碳原子杂化形态的测定：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Ig/Id，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。
2、碳包覆层厚度测试：碳包覆层的厚度大小测试通过FIB从前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，保存原始图片格式(xx.dm3)。将上述TEM测试所得原始图片在Digital Micrograph软件中打开，通过晶格间距和夹角信息，识别出碳包覆层，量取碳包覆层的厚度。对所选颗粒测量三个位置处的厚度，取平均值。
3、正极活性材料中碳元素含量测试：打开碳硫分析仪所有电源开关，按住“对零”按钮，打开碳硫分析仪的氧气阀，调节氧气，压力在0.02-0.04MPa。打开“前氧”“后控”，调节流量计控制在100L/h左右。在坩锅内依次加入硅钼粉(0.3g)，称好的样品(250mg)，锡粒(0.3g)，纯铁(1g)，合上坩锅。点击“测试”按钮，即可开始测试，测试完成自动显示测试结果，记录此结果即为C含量。
4、正极活性材料比表面积测试：使用美国麦克多站式全自动比表面积与孔隙分析仪GeminiVII2390，取约7g左右的正极活性材料样品放入9cc带球泡的长管中，150℃脱气15min，随后放入主机测试得到BET数据。
5、正极活性材料中值粒径测试：设备型号：马尔文3000(MasterSizer3000)激光粒度仪，参考标准流程：GB/T19077-2016/ISO13320:2009，具体测试流程：取待测样品适量(样品浓度保证8～12％遮光度即可)，加入20ml去离子水，同时外超5min(53KHz/120W)，确保样品完全分散，之后按照GB/T19077-2016/ISO13320:2009标准进行测试。
6、正极活性材料粉末电阻率测试：使用元能科技PRCD1000设备测试粉末电阻率，打开设备电源和测试软件，使用天平称取测试所需粉末，使用治具将粉末压成薄片，将薄片放入设备内，配置测试参数，测试压力5t，保压时间5s，点击测试，测试完成后显示测试 结果，记录此结果。
7、正极活性材料吸水性的测试：取5g正极活性材料样品，将其在110℃下加热干燥12h，然后将样品装入西林瓶中，并将装有样品的西林瓶放入卡尔费休设备自动进样系统，测试时对装有样品的西林瓶进行250℃加热并通入干燥的气体，将西林瓶内气体吹扫到滴定杯中进行吸收滴定，并将结果折算成固体样品水含量。
8、正极活性材料克容量的测试：(1)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/cm2，压实密度为2.0g/cm3。采用锂片作为负极，采用1mol/L的LiPF6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)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。
(2)扣式电池初始克容量的测量：在2.5～4.3V下，将扣式电池按照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5min，然后按照0.1C放电至2.0V，此时的放电容量为初始克容量，记为正极活性材料的克容量。
采用实施例1-11，对比例1-3中的正极活性材料分别制备全电池，全电池的制备如下：
将上述正极活性材料与导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按重量比92：2.5：5.5在N-甲基吡咯烷酮溶剂体系中混合均匀后，涂覆于铝箔上并烘干、冷压，得到正极极片。涂覆量为0.4g/cm2，压实密度为2.4g/cm3。
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90：5：2：2：1在去离子水中混合均匀后，涂覆于铜箔上烘干、冷压，得到负极极片。涂覆量为0.2g/cm2，压实密度为1.7g/cm3。
以聚乙烯(PE)多孔聚合薄膜作为隔离膜，将正极极片、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，并卷绕得到裸电芯。将裸电芯置于外包装中，注入电解液并封装，得到全电池。
对实施例1-11，对比例1-3中的全电池进行循环性能测试。全电池循环性能测试如下：在45℃的恒温环境下，在2.5V-4.3V下，将全电池按照1C充电至4.3V，然后在4.3V下恒压充电至电流小于等于0.05mA。静置5min，然后按照1C放电至2.5V，记录此时的放电容量为D0。重复前述充放电循环，直至放电容量降低到D0的80％。记录此时电池经过的循环圈数。测试结果见表2。
表2

测试结果表明：当正极活性材料的碳包覆层中sp2杂化碳与sp3杂化碳的摩尔比小于0.5时，正极活性材料的吸水性明显提高，均达到了890ppm以上，相应地，过高的含水量会导致电池电解液中的锂盐发生分解，使得电池的循环性能明显降低。
可以理解的是，在前述的实施例以及对比例的设置中为了控制变量，均选用同种内核进行后续正极活性材料的制备，即前述内核材料的选择是示例性的，本申请中正极活性材料碳包覆层的相关特征可以与其它的内核材料以合适的方式结合，例如，内核材料的种类可以包括锂锰磷酸盐、锂铁磷酸盐、锂锰铁磷酸盐、钴酸锂、锰酸锂、镍钴锰酸锂、镍钴铝酸锂和富锂锰基固溶体中的至少一种，通过在内核表面形成前述的碳包覆层即可以进一步提高正极活性材料的导电性，获得兼具较高克容量、较优循环性能的正极活性材料。
除非另外说明，本申请所使用的所有科技术语具有与本申请所属领域技术人员的通常理解相同的含义。本申请涉及的所有专利和公开出版物通过引用方式整体并入本申请。术语“包含”或“包括”为开放式表达，即包括本申请所指明的内容，但并不排除其他方面的内容。
在本说明书的描述中，参考术语“一个实施例”、“另一个实施例”等的描述意指结合该实施例描述的具体特征、结构、材料或者特点包含于本申请的至少一个实施例中。在本说明书中，对上述术语的示意性表述不必须针对的是相同的实施例或示例。而且，描述的具体特征、结构、材料或者特点可以在任一个或多个实施例或示例中以合适的方式结合。此外，在不相互矛盾的情况下，本领域的技术人员可以将本说明书中描述的不同实施例或示例以及不同实施例或示例的特征进行结合和组合。另外，需要说明的是，本说明书中，术语“第一”、“第二”仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。
尽管上面已经示出和描述了本申请的实施例，可以理解的是，上述实施例是示例性的，不能理解为对本申请的限制，本领域的普通技术人员在本申请的范围内可以对上述实施例进行变化、修改、替换和变型。

Claims (25)

  1. 一种正极活性材料，其中，包括：
    内核；
    碳包覆层，所述碳包覆层至少覆盖所述内核的部分表面，
    其中，所述碳包覆层中sp2杂化碳原子与sp3杂化碳原子的摩尔比不小于0.5。
  2. 根据权利要求1所述的正极活性材料，其中，所述内核包括磷酸盐；优选地，所述磷酸盐包括锂锰磷酸盐、锂铁磷酸盐和锂锰铁磷酸盐中的至少一种。
  3. 根据权利要求1所述的正极活性材料，其中，所述内核包括LiMPO4，所述M元素包括Mn和非Mn元素。
  4. 根据权利要求3所述的正极活性材料，其中，所述非Mn元素包括第一掺杂元素和第二掺杂元素中的一种或两种，所述第一掺杂元素为锰位掺杂，所述第二掺杂元素为磷位掺杂。
  5. 根据权利要求4所述的正极活性材料，其中，所述第一掺杂元素包括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；优选地，所述第一掺杂元素包括Fe、Ti、V、Ni、Co和Mg中的至少两种。
  6. 根据权利要求4所述的正极活性材料，其中，所述第二掺杂元素包括B(硼)、S、Si和N中的一种或多种元素。
  7. 根据权利要求3-6任一项所述的正极活性材料，其中，所述内核包括Li1+xMn1-yAyP1-zRzO4，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包括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，所述R包括B(硼)、S、Si和N中的一种或多种元素。
  8. 根据权利要求3-6任一项所述的正极活性材料，其中，所述内核包括Li1+xCmMn1-yAyP1-zRzO4-nDn，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，n为在0.001至0.1范围内的任意数值，m为在0.9至1.1范围内的任意数值，所述C包括Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素，所述A包括Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，所述R包括B(硼)、S、Si和N中的一种或多种元素，所述D包括S、F、Cl和Br中的一种或多种元素。
  9. 根据权利要求1-8任一项所述的正极活性材料，其中，所述碳包覆层中sp2杂化碳原子与sp3杂化碳原子的摩尔比不小于0.8。
  10. 根据权利要求1-9任一项所述的正极活性材料，其中，所述碳包覆层的厚度不大于 10nm；优选地，所述碳包覆层的厚度为4nm-8nm。
  11. 根据权利要求1-10任一项所述的正极活性材料，其中，所述正极活性材料中碳元素的含量不大于3wt％；优选地，所述正极活性材料中碳元素的含量为1wt％-2.5wt％。
  12. 根据权利要求1-11任一项所述的正极活性材料，其中，所述正极活性材料的比表面积不大于25m2/g，优选地，所述正极活性材料的比表面积不大于18m2/g。
  13. 根据权利要求1-12任一项所述的正极活性材料，其中，所述正极活性材料的中值粒径不大于2μm；优选地，所述正极活性材料的中值粒径为0.5μm-1.5μm。
  14. 根据权利要求1-13任一项所述的正极活性材料，其中，所述正极活性材料的粉末电阻率不大于200Ω·cm；优选地，所述正极活性材料的粉末电阻率不大于100Ω·cm。
  15. 一种制备正极活性材料的方法，其中，
    提供内核；
    在所述内核的至少部分表面形成碳包覆层，其中，所述碳包覆层中sp2杂化碳原子与sp3杂化碳原子的摩尔比不小于0.5。
  16. 根据权利要求15所述的方法，其中，所述在所述内核的至少部分表面形成碳包覆层包括：通过碳源在所述内核表面形成预碳包覆层以获得预包覆正极活性材料；对所述预包覆正极活性材料进行烧结处理以形成所述碳包覆层，以获得所述正极活性材料，所述碳源包括第一碳源和第二碳源。
  17. 根据权利要求15所述的方法，其中，所述在所述内核的至少部分表面形成碳包覆层包括：将所述内核与所述第一碳源混合，并通过第一烧结处理得到第一包覆正极活性材料，将所述第一包覆正极活性材料与所述第二碳源混合，并通过第二烧结处理得到所述正极活性材料。
  18. 根据权利要求16或17所述的方法，其中，所述第一碳源包括聚乙烯醇、聚乙二醇和柠檬酸中的至少一种；所述第二碳源包括淀粉、蔗糖和葡萄糖中的至少一种。
  19. 根据权利要求16-18任一项所述的方法，其中，所述第一碳源为聚合物时，所述第一碳源的分子量不少于1000，优选地，所述第一碳源的分子量为2000-5000。
  20. 根据权利要求16、18或19所述的方法，其中，所述烧结处理的温度为650℃-800℃，所述烧结处理的时间为6h-12h。
  21. 根据权利要求17-19任一项所述的方法，其中，所述第一烧结处理的温度为350℃-800℃，所述第一烧结处理的时间为6h-12h。
  22. 根据权利要求17-19任一项所述的方法，其中，所述第二烧结处理的温度为650℃-850℃，所述第二烧结处理的时间为6h-24h。
  23. 一种正极极片，其中，包括正极集流体和正极活性材料层，所述正极活性材料层位 于所述正极集流体的一侧，所述正极活性材料层包括权利要求1-14任一项所述的正极活性材料，和/或所述正极活性材料层包括采用权利要求15-22任一项所述的方法制备得到的正极活性材料。
  24. 一种电池，其中，包括：正极极片，所述正极极片为权利要求23所述的正极极片。
  25. 一种用电装置，其中，包括：电池，所述电池为权利要求24所述的电池。
PCT/CN2023/074786 2023-02-07 2023-02-07 正极活性材料及其制备方法、正极极片、电池和用电装置 Ceased WO2024164143A1 (zh)

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