WO2024152637A1 - 正极活性材料、及其制备方法、二次电池、电池模块、电池包和用电装置 - Google Patents

正极活性材料、及其制备方法、二次电池、电池模块、电池包和用电装置 Download PDF

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WO2024152637A1
WO2024152637A1 PCT/CN2023/126243 CN2023126243W WO2024152637A1 WO 2024152637 A1 WO2024152637 A1 WO 2024152637A1 CN 2023126243 W CN2023126243 W CN 2023126243W WO 2024152637 A1 WO2024152637 A1 WO 2024152637A1
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positive electrode
electrode active
active material
battery
carbon
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English (en)
French (fr)
Inventor
赵玉珍
官英杰
杨惠玲
秦猛
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 EP23917105.1A priority Critical patent/EP4618194A4/en
Priority to JP2025528787A priority patent/JP2025539124A/ja
Publication of WO2024152637A1 publication Critical patent/WO2024152637A1/zh
Priority to US19/218,652 priority patent/US20250286047A1/en
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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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/10—Primary casings; Jackets or wrappings
    • H01M50/102—Primary casings; Jackets or wrappings characterised by their shape or physical structure
    • H01M50/103—Primary casings; Jackets or wrappings characterised by their shape or physical structure prismatic or rectangular
    • 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
    • H01M4/364—Composites as mixtures
    • 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
    • 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
    • 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
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    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/521—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of iron for aqueous cells
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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
    • H01M4/36—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
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • 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
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • 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
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • 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 technical field of secondary batteries, and in particular to a positive electrode active material, a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device.
  • Sodium batteries have great application potential in large-scale energy storage due to their abundant reserves, low price and wide operating temperature.
  • iron-based polyanion compounds As a popular cathode material for new sodium batteries, iron-based polyanion compounds have significant advantages such as abundant resources, high operating voltage, good cycle stability and environmental friendliness.
  • the current sodium batteries using iron-based polyanion compounds as cathode materials still have problems such as low electronic conductivity, low discharge capacity and poor cycle performance. They cannot meet the application needs of the new generation of electrochemical systems.
  • the present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode active material, into which magnesium element is introduced to achieve the dual effects of lattice doping and composite modification, which can effectively reduce the residual alkali content of the positive electrode active material and improve the cycle performance and rate performance of the battery.
  • a positive electrode active material for a secondary battery comprising an iron-based polyanion compound composited with a carbon material and a magnesium-containing oxide, wherein the iron-based polyanion compound has the following general formula: Na 4 Fe 3-x M x Mg y (PO 4 ) 2 P 2 O 7 /C
  • M comprises a transition metal element, 0 ⁇ x ⁇ 0.5, 0 ⁇ y ⁇ 0.18.
  • part of the magnesium element can be doped into the lattice of the iron-based polyanion compound, replacing the iron element or transition metal element in the lattice of the iron-based polyanion compound, thereby improving the ionic conductivity and electronic conductivity of the positive electrode active material, and improving the ion and electron conductivity of the positive electrode active material.
  • part of the magnesium element is distributed on the surface of the iron-based polyanion compound in the form of magnesium oxide, reducing the direct contact between the surface of the positive electrode active material and the moisture in the environment, reducing the residual alkali content of the positive electrode active material, and improving the stability and processability of the positive electrode active material.
  • the positive electrode active material also has a higher gram capacity, which is conducive to improving the energy density of its battery.
  • the magnesium-containing oxide is distributed on at least a portion of the surface of the primary particles of the iron-based polyanionic compound.
  • the magnesium oxide is distributed on part or all of the surface of the primary particles of the iron-based polyanionic compound, which can effectively reduce the direct contact between the surface of the positive electrode active material and the moisture in the environment, reduce the residual alkali content of the positive electrode active material, and improve the stability and processability of the positive electrode active material.
  • the mass content of magnesium in the positive electrode active material is 0.02% to 0.7%.
  • controlling the mass content of the magnesium element in the positive electrode active material to 0.02% to 0.7% is beneficial to reducing the residual alkali content of the positive electrode active material, improving the stability and processability of the positive electrode active material, and enhancing the cycle performance and rate performance of the battery.
  • M comprises one or more of Ni, Co, Mn, Cu, V, Ti, Mo, Nb, W, Cr, Zn, Zr, and Ca, and may be one or more of Ni, Co, Mn, Cu, V, and Ca.
  • transition metal elements into iron-based polyanion compounds is beneficial to increasing the voltage platform of positive electrode active materials, improving the ionic conductivity and electronic conductivity of the materials, reducing the polarization of the battery, and improving the battery cycle performance and rate performance.
  • the M comprises Ni, Co, Mn, Cu, V, Ca At least two.
  • Controlling M to include at least two of Ni, Co, Mn, Cu, V, and Ca is beneficial to further improving the rate performance of the battery.
  • the carbon material is coated on the surface of the iron-based polyanion compound in the form of a carbon film, or the carbon material is distributed between the primary ions of the iron-based polyanion compound in the form of particles.
  • Carbon material is coated on the surface of the iron-based polyanion compound in the form of a carbon film, or carbon material is distributed between the primary ions of the iron-based polyanion compound in the form of particles, which can effectively improve the conductivity of the positive electrode active material and the battery performance.
  • the carbon material includes one or more of amorphous carbon, conductive carbon black, carbon nanotubes and graphene.
  • the above carbon materials are easy to disperse and process, and form carbon composites with iron-based polyanion compounds to improve the conductivity of positive electrode active materials and battery performance.
  • the crystallinity of conductive carbon black, carbon nanotubes or graphene is higher than that of amorphous carbon, the conductivity of carbon materials including conductive carbon black, carbon nanotubes or graphene is better than that of carbon materials including amorphous carbon.
  • the mass content of the carbon material is 0.5% to 6%, and optionally 1% to 3.6%.
  • controlling the mass content of the carbon material to 0.5% to 6% is conducive to achieving a balance between the gram capacity and conductivity of the positive electrode active material, while obtaining a higher gram capacity and better cycle performance and rate performance. Avoiding too low a mass content of the carbon material, which leads to poor conductivity of the positive electrode active material, is not conducive to the volatilization of the capacity of the positive electrode active material, and also avoiding too high a mass content of the carbon material, which leads to a decrease in the gram capacity of the positive electrode active material and poor compaction performance. Based on the total mass of the positive electrode active material, controlling the mass content of the carbon material to 1% to 3.6% is conducive to further improving the gram capacity of the positive electrode active material and further improving the capacity of the battery.
  • the gram capacity of the positive electrode active material is ⁇ 98 mAh/g.
  • a positive electrode active material having a capacity of ⁇ 98 mAh/g is beneficial for improving the capacity of the battery and broadening the application of the battery.
  • the residual alkali content of NaHCO 3 in the positive electrode active material is less than 1.2%.
  • the residual alkali content of NaHCO 3 in the positive electrode active material is less than 1.2%, which can effectively improve its stability and processability.
  • the second aspect of the present application provides a method for preparing a positive electrode active material for a secondary battery, comprising the following steps:
  • the mixed slurry is dried and then calcined to prepare the positive electrode active material, wherein the positive electrode active material comprises an iron-based polyanion compound and a magnesium-containing oxide, and the iron-based polyanion compound has the following general formula: Na 4 Fe 3-x M x Mg y (PO 4 ) 2 P 2 O 7 /C
  • M comprises a transition metal element, 0 ⁇ x ⁇ 0.5, 0 ⁇ y ⁇ 0.18.
  • the preparation method of the positive electrode active material is simple and the production cost is low.
  • the prepared positive electrode active material has a lower residual alkali content and a higher gram capacity, and the battery thereof has excellent cycle performance and rate performance.
  • the step of drying the mixed slurry and then calcining the mixed slurry comprises the following steps:
  • the precursor powder is calcined in steps, with the first step calcination temperature being 300° C. to 400° C. and the calcination time being 3 h to 6 h, and the second step calcination temperature being 500° C. to 600° C. and the calcination time being 8 h to 15 h, to prepare the positive electrode active material.
  • Step-by-step calcination is beneficial to the full reaction of the precursor powder, improves the crystallinity and phase purity of the prepared positive electrode active material, reduces the amount of residual alkali on the surface of the positive electrode active material, improves the stability and processability of the positive electrode active material, increases the gram capacity of the positive electrode active material, and improves the battery cycle performance and rate performance.
  • the second step calcination temperature is 525°C to 575°C, and can be optionally 550°C to 575°C.
  • Controlling the second step calcination temperature to 525°C ⁇ 575°C is conducive to further reducing the residual alkali on the surface of the active material, improving the conductivity of the material, and enhancing the cycle performance and rate performance of the battery. Further controlling the second step calcination temperature to 550°C ⁇ 575°C is conducive to greater It can improve the capacity retention rate of the battery after 200 cycles and the capacity retention rate at 3C rate to a certain extent, and improve the battery's cycle performance and rate performance to a greater extent.
  • the second step calcination time is 10 h to 14 h.
  • Controlling the second step calcination time to 10h to 14h is beneficial to obtaining highly crystalline and high-purity positive electrode active materials.
  • the insulation time by controlling the insulation time, the particle size of the primary grains and the amount of residual alkali on the surface of the material can be controlled, thereby improving the gram capacity of the material and the cycle rate performance of the battery.
  • the M source includes one or more of nickel nitrate, nickel acetate, cobalt nitrate, manganese nitrate, cobalt acetate, manganese acetate, nickel oxalate, cobalt oxalate, manganese oxalate, nickel oxide, cobalt oxide, and manganese oxide.
  • the magnesium source includes one or more of magnesium nitrate, magnesium carbonate, magnesium acetate, magnesium hydroxide, magnesium oxalate, and magnesium oxide.
  • the carbon source includes one or more of sucrose, tannic acid, polyethylene glycol, polyacrylonitrile, cellulose, polyvinyl pyrrolidone, sucrose, oxalic acid, glucose, ascorbic acid, polyethylene, citric acid, conductive carbon black, carbon nanotubes, and graphene.
  • the carbon source is easy to produce carbon materials coated on the surface of the iron-based polyanion compound or distributed between the primary particles of the iron-based polyanion compound under high temperature calcination, thereby improving the conductivity of the positive electrode active material.
  • the amorphous carbon formed by one or more carbon sources including sucrose, tannic acid, polyethylene glycol, polyacrylonitrile, cellulose, polyvinyl pyrrolidone, sucrose, oxalic acid, glucose, ascorbic acid, polyethylene, citric acid, conductive carbon black, carbon nanotubes, and graphene has a low crystallinity, while the carbon material generated by one or more carbon sources including conductive carbon black, carbon nanotubes, and graphene has a high crystallinity, so the carbon material generated by one or more carbon sources including conductive carbon black, carbon nanotubes, and graphene has a more excellent conductive property.
  • a third aspect of the present application provides a secondary battery, comprising a positive electrode plate, wherein the positive electrode plate comprises the positive electrode active material described in any embodiment or the positive electrode active material prepared by the preparation method described in any embodiment.
  • the secondary battery is a negative electrode-free sodium battery.
  • the secondary battery further comprises a negative electrode sheet, wherein the negative electrode
  • the pole piece includes a negative electrode current collector and a primer layer arranged on at least one surface of the negative electrode current collector, wherein the primer layer includes one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.
  • the above-mentioned base coating layer not only has excellent conductivity, but also facilitates the uniform deposition of metal ions on the surface of the current collector, thereby improving the cycle performance and safety of the battery.
  • the surface density of the primer layer is 5 g/m 2 to 50 g/m 2 .
  • the undercoat layer with an area density of 5 g/m 2 to 50 g/m 2 is conducive to the uniform distribution of nucleation sites and promotes the uniform deposition of metals, while not affecting the transmission behavior of electrons.
  • the primer layer has a thickness of 2 ⁇ m to 100 ⁇ m.
  • Controlling the thickness of the base coating to be 2 ⁇ m to 100 ⁇ m can provide enough nucleation sites to facilitate uniform deposition of metal ions and inhibit dendrites.
  • a fourth aspect of the present application provides a battery module, comprising the secondary battery of the third aspect of the present application.
  • a fifth aspect of the present application provides a battery pack, comprising the secondary battery of the third aspect of the present application or the battery module of the fourth aspect of the present application.
  • the sixth aspect of the present application provides an electrical device, comprising at least one of the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, and the battery pack of the fifth aspect of the present application.
  • FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG2 is an exploded view of the secondary battery of one embodiment of the present application shown in FIG1 ;
  • FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.
  • FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;
  • FIG. 6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.
  • “Scope” disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range.
  • the scope limited in this way can be including end values or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.
  • the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers.
  • the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations.
  • a parameter is expressed as an integer ⁇ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
  • 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.
  • the method may also include step (c), which means that step Step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.
  • the “include” and “comprising” mentioned in this application represent open-ended or closed-ended expressions.
  • the “include” and “comprising” may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B”. More specifically, any of the following conditions satisfies the condition "A or B”: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).
  • polyanion compounds have become one of the popular positive electrode materials for sodium batteries because of their abundant resources, environmental friendliness, ease of large-scale production, open sodium ion diffusion channels, and good thermal stability and cycle stability.
  • the surface of polyanion compound materials has a high amount of residual alkali, and exposure to air can easily lead to an increase in residual alkali on the surface of the material, causing the gram capacity to deteriorate, thereby affecting the performance of the battery. Therefore, it is necessary to develop a positive electrode active material with low residual alkali, excellent electrochemical properties, and can be used for high-rate batteries to meet the application needs of the new generation of electrochemical systems.
  • the present application proposes a positive electrode active material for a secondary battery, which positive electrode active material includes an iron-based polyanion compound composited with a carbon material and a magnesium-containing oxide, and the iron-based polyanion compound has the following general formula: Na 4 Fe 3-x M x Mg y (PO 4 ) 2 P 2 O 7 /C, wherein M contains a transition metal element, 0 ⁇ x ⁇ 0.5, 0 ⁇ y ⁇ 0.18.
  • transition metal element refers to elements of Groups IIIB to VIIB, VIII, and Groups IB to IIB in the periodic table.
  • x can be selected as 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5.
  • y can be selected from 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16 or 0.17.
  • part of the magnesium element can be doped into the lattice of the iron-based polyanion compound, replacing the iron element or transition metal element in the lattice of the iron-based polyanion compound, thereby improving the ionic conductivity and electronic conductivity of the positive electrode active material, and improving the ion and electron conductivity of the positive electrode active material.
  • part of the magnesium element is distributed on the surface of the iron-based polyanion compound in the form of magnesium oxide, reducing the direct contact between the surface of the positive electrode active material and the moisture in the environment, reducing the residual alkali content of the positive electrode active material, and improving the stability and processability of the positive electrode active material.
  • the positive electrode active material also has a higher gram capacity, which is conducive to improving the energy density of its battery.
  • gram capacity refers to the amount of electricity released per gram of positive electrode active material, which can reflect the capacity of the battery and can be tested by any known method.
  • the magnesium-containing oxide is distributed on at least a portion of the surface of the primary particles of the iron-based polyanionic compound.
  • primary particles refers to particles of the iron-based polyanionic compound before agglomeration, and the particle size of the primary particles of the iron-based polyanionic compound ranges from 30 nm to 120 nm.
  • the magnesium-containing oxide includes magnesium oxide.
  • the magnesium-containing oxide is distributed on a portion of the surface of the primary particles of the iron-based polyanionic compound.
  • the magnesium-containing oxide is distributed over the entire surface of the primary particles of the iron-based polyanionic compound.
  • the magnesium oxide is distributed on part or all of the surface of the primary particles of the iron-based polyanion compound, which can effectively reduce the direct contact between the positive electrode active material and the moisture in the environment, reduce the residual alkali content of the positive electrode active material, and improve the stability and processability of the positive electrode active material.
  • the mass content of magnesium in the positive electrode active material is 0.02% to 0.7% based on the total mass of the positive electrode active material. In some embodiments, the mass content of magnesium in the positive electrode active material is 0.02% to 0.7% based on the total mass of the positive electrode active material. It is 0.02%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65% or 0.7%.
  • the magnesium element in the positive electrode active material includes Mg in an iron-based polyanion compound and magnesium in a magnesium-containing oxide.
  • the mass content of magnesium in the positive electrode active material can be tested by any means known in the art.
  • reference can be made to standards YS/T 1006.2-2014, GB/T 23367.2-2009 or YS/T 1028.5-2015.
  • an inductively coupled plasma emission spectrometer (Thermo, ICAP7400; PerkinElmer, Avio200) can be used to measure the luminescence intensity of magnesium in the sample to be tested, and standard samples of magnesium with different contents are configured to measure their luminescence intensity as a standard curve, and the mass content of magnesium in the sample to be tested is determined in the standard curve according to the luminescence intensity of magnesium in the sample to be tested.
  • controlling the mass content of the magnesium element in the positive electrode active material to 0.02% to 0.7% is beneficial to reducing the residual alkali content of the positive electrode active material, improving the stability and processability of the positive electrode active material, increasing the gram capacity of the positive electrode active material and its capacity retention rate at the 3C rate of the battery, and improving the cycle performance and rate performance of the battery.
  • M comprises one or more of Ni, Co, Mn, Cu, V, Ti, Mo, Nb, W, Cr, Zn, Zr, and Ca, and may be one or more of Ni, Co, Mn, Cu, V, and Ca.
  • M comprises Ni. In some embodiments, M comprises Co. In some embodiments, M comprises Mn. In some embodiments, M comprises Ca. In some embodiments, M comprises Cu.
  • transition metal elements into iron-based polyanionic compounds is beneficial to increase the voltage platform of positive electrode active materials, improve the ionic conductivity and electronic conductivity of materials, reduce the polarization of batteries, and improve the battery cycle performance and rate performance.
  • M includes at least two of Ni, Co, Mn, Cu, V, and Ca.
  • M comprises Ni and Mn. In some embodiments, M comprises Mn and Co. In some embodiments, M comprises Ni and Co. In some embodiments, M comprises Ni and Ca. In some embodiments, M comprises Mn, Ni, and Co.
  • Controlling M to include at least two of Ni, Co, Mn, Cu, V, and Ca is beneficial to further improving the rate performance of the battery.
  • the carbon material is coated on the surface of the iron-based polyanion compound in the form of a carbon film, or the carbon material is distributed between the primary ions of the iron-based polyanion compound in the form of particles.
  • the carbon material is coated on the surface of the iron-based polyanion compound in the form of a carbon film.
  • the carbon material is in the form of particles distributed between the primary ions of the iron-based polyanionic compound.
  • Carbon material is coated on the surface of the iron-based polyanion compound in the form of a carbon film, or carbon material is distributed between the primary ions of the iron-based polyanion compound in the form of particles, which can effectively improve the conductivity of the positive electrode active material and the battery performance.
  • the carbon material includes one or more of amorphous carbon, conductive carbon black, carbon nanotubes, and graphene.
  • the carbon material comprises amorphous carbon. In some embodiments, the carbon material comprises conductive carbon black. In some embodiments, the carbon material comprises graphene. In some embodiments, the carbon material comprises carbon nanotubes.
  • the carbon material is easy to be combined with the iron-based polyanion compound to improve the conductivity of the positive electrode active material.
  • the crystallinity of conductive carbon black, carbon nanotubes or graphene is higher than that of amorphous carbon, the conductivity of the carbon material including conductive carbon black, carbon nanotubes or graphene is better than that of the carbon material including amorphous carbon.
  • the mass content of the carbon material is 0.5% to 6%, and can be 1% to 3.6%. In some embodiments, based on the total mass of the positive electrode active material, the mass content of the carbon material can be 0.5%, 1%, 1.1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 3.6%, 4%, 4.5%, 5%, 5.5% or 6%.
  • controlling the mass content of the carbon material to 0.5% to 6% is conducive to achieving a balance between the gram capacity and conductivity of the positive electrode active material, while obtaining a higher gram capacity and better cycle performance and rate performance. Avoiding too low a mass content of the carbon material will lead to poor conductivity of the positive electrode active material, which is not conducive to the performance of the positive electrode active material. Capacity volatilization also avoids excessive carbon material content, which leads to a decrease in the gram capacity of the positive electrode active material and the impact of compaction density. Based on the total mass of the positive electrode active material, controlling the mass content of the carbon material to 1% to 3.6% is conducive to further increasing the gram capacity of the positive electrode active material and further improving the capacity of the battery.
  • the gram capacity of the positive electrode active material is ⁇ 98 mAh/g.
  • the gram capacity of the positive electrode active material may be 98 mAh/g, 100 mAh/g, 105 mAh/g, 110 mAh/g, 115 mAh/g, 120 mAh/g, or 125 mAh/g.
  • the gram capacity of the positive electrode active material can be tested by any means known in the art. As an example, at 25°C and normal pressure, charge the button cell at a constant current of 0.1C to a voltage of 4V, then charge at a constant voltage of 4V until the current drops to 0.05C, and record the charge specific capacity at this time, which is the first sodium removal capacity; then discharge at a constant current of 0.1C to a voltage of 1.5V, and record the discharge specific capacity at this time, which is the first sodium insertion capacity.
  • the gram capacity of the positive electrode active material is the first sodium insertion capacity.
  • a positive electrode active material having a capacity of ⁇ 98 mAh/g is beneficial for improving the capacity of the battery and broadening the application of the battery.
  • the NaHCO 3 residual alkali content of the positive electrode active material is less than 1.2% based on the total mass of the positive electrode active material.
  • the residual alkali amount of NaHCO 3 in the positive electrode active material may be selected to be 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1% or 1.15% based on the total mass of the positive electrode active material.
  • the residual alkali content of NaHCO3 in the positive electrode active material can be tested by any means known in the art. As an example, it is determined by the chemical reagent potentiometric titration method, for example, the standard GB/T 9725-2007 can be referred to. Specifically, the Swiss Metrohm 905Titrando potentiometric titrator can be used to dissolve the positive electrode active material in deionized water, and the aqueous solution of the positive electrode active material is titrated with a standard titration solution. Each time 0.1 ml of the standard titration solution is added, the potential or pH value is recorded, and the titration is stopped when the potential or pH value does not change much.
  • the mass of NaHCO3 obtained by calculating is divided by the mass of the positive electrode active material to obtain the mass content.
  • the residual alkali content of NaHCO 3 in the positive electrode active material is less than 1.2%, which can effectively improve its stability and processability.
  • the present application also proposes a method for preparing a positive electrode active material for a secondary battery, comprising the following steps:
  • the mixed slurry is dried and then calcined to prepare a positive electrode active material, wherein the positive electrode active material comprises an iron-based polyanion compound and a magnesium-containing oxide, wherein the iron-based polyanion compound has the following general formula: Na 4 Fe 3-x M x Mg y (PO 4 ) 2 P 2 O 7 /C
  • M comprises a transition metal element, 0 ⁇ x ⁇ 0.5, 0 ⁇ y ⁇ 0.18.
  • the preparation method of the positive electrode active material is simple and the production cost is low.
  • the prepared positive electrode active material has a lower residual alkali content and a higher gram capacity, and the battery thereof has excellent cycle performance and rate performance.
  • transition metals into positive electrode active materials is beneficial to improving the ionic conductivity and electronic conductivity of the materials, and enhancing the cycle performance and rate performance of the battery.
  • the feedstock also includes a carbon source.
  • carbon source is beneficial to introduce conductive carbon elements into the positive electrode active material, thereby improving the conductivity of the positive electrode active material.
  • drying the mixed slurry and then calcining it comprises the following steps:
  • the precursor powder is calcined in steps, with the first step calcination temperature being 300°C to 400°C and the calcination time being 3h to 6h, and the second step calcination temperature being 500°C to 600°C and the calcination time being 8h to 15h to prepare the positive electrode active material.
  • Step-by-step calcination is beneficial to the full reaction of the precursor powder, improves the crystallinity and phase purity of the prepared positive electrode active material, reduces the amount of residual alkali on the surface of the positive electrode active material, improves the stability and processability of the positive electrode active material, increases the gram capacity of the positive electrode active material, and improves the battery cycle performance and rate performance.
  • the second step calcination temperature is 525°C to 575°C, which can be selected from 550°C ⁇ 575°C.
  • Controlling the second step calcination temperature to 525°C ⁇ 575°C is conducive to further reducing the residual alkali on the surface of the active material, improving the conductivity of the material, and enhancing the cycle performance and rate performance of the battery. Further controlling the second step calcination temperature to 550°C ⁇ 575°C is conducive to further improving the cycle performance and rate performance of the battery.
  • the second calcination time is 10 h to 14 h.
  • Controlling the second step calcination time to 10h to 14h is beneficial to obtaining highly crystalline and high-purity positive electrode active materials.
  • the insulation time by controlling the insulation time, the particle size of the primary grains and the amount of residual alkali on the surface of the material can be controlled, thereby improving the gram capacity of the material and the cycle rate performance of the battery.
  • the M source includes one or more of nickel nitrate, nickel acetate, cobalt nitrate, manganese nitrate, cobalt acetate, manganese acetate, nickel oxalate, cobalt oxalate, manganese oxalate, nickel oxide, cobalt oxide, and manganese oxide.
  • the magnesium source includes one or more of magnesium nitrate, magnesium carbonate, magnesium acetate, magnesium hydroxide, magnesium oxalate, and magnesium oxide.
  • the carbon source includes one or more of sucrose, tannic acid, polyethylene glycol, polyacrylonitrile, cellulose, polyvinyl pyrrolidone, sucrose, oxalic acid, glucose, ascorbic acid, polyethylene, citric acid, conductive carbon black, carbon nanotubes, and graphene.
  • the carbon source includes one or more of sucrose, tannic acid, polyethylene glycol, polyacrylonitrile, cellulose, polyvinyl pyrrolidone, sucrose, oxalic acid, glucose, ascorbic acid, polyethylene, and citric acid.
  • the carbon source includes one or more of conductive carbon black, carbon nanotubes, and graphene.
  • the carbon source is easy to produce carbon materials coated on the surface of the iron-based polyanion compound or distributed between the primary particles of the iron-based polyanion compound under high temperature calcination, thereby improving the conductivity of the positive electrode active material.
  • the amorphous carbon formed by one or more carbon sources including sucrose, tannic acid, polyethylene glycol, polyacrylonitrile, cellulose, polyvinyl pyrrolidone, sucrose, oxalic acid, glucose, ascorbic acid, polyethylene, citric acid, conductive carbon black, carbon nanotubes, and graphene has a low crystallinity, while the carbon material generated by one or more carbon sources including conductive carbon black, carbon nanotubes, and graphene has a low crystallinity.
  • the crystallinity is relatively high, so the carbon material generated from one or more carbon sources including conductive carbon black, carbon nanotubes, and graphene has better conductive properties.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer formed on at least a portion of the surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material in some embodiments.
  • the positive electrode active material layer may further include a conductive agent to improve the conductivity of the positive electrode.
  • the conductive agent may be selected from one or more of Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene and carbon nanofibers.
  • the positive electrode active material layer may further include a binder to firmly bind the positive electrode active material and the optional conductive agent to the positive electrode current collector.
  • the binder may be selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMA) and carboxymethyl chitosan (CMCS).
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PAA polyacrylic acid
  • PVA polyvinyl alcohol
  • EVA ethylene-vinyl acetate copolymer
  • SBR styrene-butadiene rubber
  • CMC carboxymethyl cellulose
  • SA sodium al
  • the positive electrode current collector may be a conductive carbon sheet, a metal foil, a carbon-coated metal foil, a porous metal plate or a composite current collector.
  • the conductive carbon material of the conductive carbon sheet may be selected from one or more of Super P, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene and carbon nanofibers
  • the metal material of the metal foil, the carbon-coated metal foil and the porous metal plate may be independently selected from at least one of copper, aluminum, nickel and stainless steel
  • the composite current collector may be a composite current collector formed by a metal foil and a polymer base film.
  • 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 binder 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 secondary battery further includes a separator.
  • the present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fiber.
  • the isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.
  • the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.
  • the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.
  • 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 package, such as a bag-type soft package.
  • the material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.
  • a secondary battery includes a positive electrode plate, wherein the positive electrode plate includes a positive electrode active material in some embodiments or a positive electrode active material prepared by a preparation method in some embodiments.
  • the secondary battery further includes a negative electrode sheet, a separator, and an electrolyte.
  • the secondary battery is a negative electrode-free sodium battery.
  • the negative electrode-free sodium battery does not pre-deposit negative electrode active materials, and only contains a negative electrode current collector.
  • the sodium ions obtain electrons on the anode side and deposit metallic sodium on the surface of the current collector to form a sodium metal phase.
  • the metallic sodium can be converted into sodium ions and return to the positive electrode to achieve cyclic charge and discharge.
  • the negative electrode-free sodium battery can obtain a higher energy density because it is not limited by the negative electrode material.
  • the CB value of the negative electrode-free sodium battery is less than or equal to 0.1.
  • the CB value is the unit area capacity of the negative electrode in the secondary battery divided by the unit area capacity of the positive electrode.
  • the capacity per unit area of the electrode is small, and the CB value of the secondary battery is less than or equal to 0.1.
  • the secondary battery includes a negative electrode sheet, which may include only a negative electrode current collector without containing a negative electrode active material.
  • the negative electrode sheet may also be pre-deposited with a metal phase on the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate.
  • the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode plate includes a negative electrode current collector and a primer layer disposed on at least one surface of the negative electrode current collector, and the primer layer includes one or more of carbon nanotubes, graphite, graphene, silver composite carbon nanoparticles, and tin composite carbon nanoparticles.
  • the above-mentioned base coating layer not only has excellent conductivity, but also facilitates the uniform deposition of metal ions on the surface of the negative electrode-free battery collector, thereby improving the cycle performance and safety of the battery.
  • the surface density of the primer layer is 5 g/m 2 to 50 g/m 2 .
  • the area density of the base coating layer may be selected to be 5 g/ m2 , 10 g/ m2 , 15 g/ m2 , 20 g/ m2 , 25 g/ m2 , 30 g/ m2 , 35 g/ m2 , 40 g/ m2 , 45 g/ m2 , or 50 g/ m2 .
  • the undercoat layer with a surface density of 5 g/m 2 to 50 g/m 2 is beneficial to the uniform distribution of negative electrode nucleation sites in the negative electrode-free battery, promotes the uniform deposition of metal, and does not affect the transmission behavior of electrons.
  • the primer layer has a thickness of 2 ⁇ m to 100 ⁇ m.
  • the thickness of the primer layer may be 2 ⁇ m, 5 ⁇ m, 10 ⁇ m, 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, 55 ⁇ m, 60 ⁇ m, 65 ⁇ m, 70 ⁇ m, 75 ⁇ m, 80 ⁇ m, 85 ⁇ m, 90 ⁇ m, 95 ⁇ m, or 100 ⁇ m.
  • the above-mentioned undercoat layer is too thin to be used as a negative electrode active material.
  • it is used as an undercoat layer to reduce the nucleation overpotential of sodium, which is beneficial to the uniform distribution of metal ions. Deposition, inhibiting dendrites.
  • FIG. 1 is a secondary battery 5 of a square structure as an example
  • FIG. 2 is an exploded view of the secondary battery 5 .
  • the outer package 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 membrane 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 non-Newtonian fluid electrolyte composition is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • secondary batteries may be assembled into a battery module.
  • the number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.
  • FIG3 is a battery module 3 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 3. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.
  • the battery module 3 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.
  • the battery modules described above may also be assembled into a battery pack.
  • the battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.
  • FIG4 and FIG5 are battery packs 1 as an example.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed 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 modules 4.
  • the plurality of battery modules 4 can be arranged in the battery box in any manner.
  • an electric device comprising at least one of a secondary battery of any embodiment, a battery module of any embodiment, or a battery pack of any embodiment.
  • the electrical device includes at least one of the secondary battery, battery module, or battery pack provided in the present application.
  • the secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or 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, ships and satellites, energy storage systems, etc., but are not limited thereto.
  • a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.
  • Fig. 6 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, etc.
  • a battery pack or a battery module may be used.
  • the device may be a mobile phone, a tablet computer, a notebook computer, etc.
  • a device is usually required to be light and thin, and a secondary battery may be used as a power source.
  • 0.1 mol sodium pyrophosphate, 0.3 mol ferrous oxalate, 0.2 mol diammonium phosphate, 0.01 mol glucose and 0.006 mol magnesium acetate were added into 200 ml deionized water and ground by a sand mill for 10 h to obtain a mixed slurry; the mixed slurry was spray dried. Drying treatment is performed to obtain dry precursor powder; the precursor is placed in a tubular furnace, nitrogen is passed as a protective gas, and the first step of calcination is performed, the temperature is raised to 300°C and kept warm for 4 hours, and then the second step of calcination is performed, the temperature is raised to 550°C and kept warm for 12 hours to obtain the positive electrode active material.
  • 10wt% polyvinylidene fluoride binder is fully dissolved in N-methylpyrrolidone (NMP), and then 10wt% carbon black conductive agent and 80wt% of the above positive electrode active material are added and stirred to obtain positive electrode slurry.
  • NMP N-methylpyrrolidone
  • the slurry is evenly coated on the surface of the current collector aluminum foil, and then transferred to a vacuum drying oven for complete drying.
  • the dried electrode sheet is rolled and punched to obtain a positive electrode sheet.
  • Carbon nanotubes and carboxymethyl cellulose (CMC) were added to deionized water at a mass ratio of 1:0.4 and stirred into a uniform slurry, and the slurry was coated on the surface of the negative electrode current collector copper foil to form a primer layer, which was then transferred to a vacuum drying oven for complete drying and then punched.
  • the thickness of the primer layer was 20 ⁇ m and the surface density was 25 g/m 2 .
  • a negative electrode sheet without a negative electrode structure was obtained.
  • sodium hexafluorophosphate NaPF 6 was dissolved in an organic solvent, ethylene glycol dimethyl ether (DME), and stirred evenly to obtain an electrolyte with a sodium salt concentration of 1 mol/L.
  • DME ethylene glycol dimethyl ether
  • Polypropylene film is used as the isolation film.
  • a button cell was assembled using a sodium metal sheet as the counter electrode, a Celgard 2400 isolation membrane, and injected with electrolyte.
  • the positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, the separator is placed between the positive and negative electrode sheets to play an isolating role, and the above electrolyte is added to assemble a stacked battery.
  • the negative electrode-free sodium battery product of Example 1 is obtained.
  • the preparation method of the batteries of Examples 2 to 6 is similar to that of the battery of Example 1, but the The mass content of carbon element in the positive electrode active material is shown in Table 1.
  • the preparation method of the battery of Example 7 is similar to that of the battery of Example 1, but the preparation method of the positive electrode active material is adjusted, and the preparation method is as follows:
  • 0.1 mol of sodium pyrophosphate, 0.28 mol of ferrous oxalate, 0.2 mol of ammonium dihydrogen phosphate, 0.04 mol of glucose, 0.02 mol of manganese oxalate (M source) and 0.006 mol of magnesium acetate were added into 200 ml of deionized water, and ground by a sand mill for 10 hours to obtain a mixed slurry; the mixed slurry was dried by a spray drying device to obtain a dry precursor powder; the precursor powder was placed in a tubular furnace, nitrogen was passed as a protective gas, the temperature was raised to 300° C. and kept for 4 hours, and then the temperature was raised to 550° C. and kept for 12 hours to obtain a positive electrode active material.
  • the preparation method of the battery of Comparative Example 1 is similar to that of the battery of Example 1, but the preparation method of the positive electrode active material is adjusted, and the preparation method is as follows:
  • 0.1 mol of sodium pyrophosphate, 0.3 mol of ferrous oxalate and 0.2 mol of ammonium dihydrogen phosphate were added to 200 ml of water and ground with a sand mill for 10 hours to obtain a mixed slurry; the mixed slurry was dried by a spray drying device to obtain a dry precursor powder; the precursor was placed in a tubular furnace, nitrogen was passed as a protective gas, and the first step of calcination was carried out, and the temperature was raised to The temperature was kept at 300°C for 4 hours, and then the second calcination was carried out, the temperature was raised to 550°C and kept for 12 hours to obtain the positive electrode active material.
  • the preparation method of the battery of Comparative Example 2 is similar to that of the battery of Comparative Example 1, but carbon material is introduced into the positive electrode active material.
  • the specific parameters are shown in Table 1.
  • the preparation method of the battery of Comparative Example 3 is similar to that of the battery of Comparative Example 2, but magnesium is introduced into the positive electrode active material.
  • the specific parameters are shown in Table 1.
  • the composition of the positive electrode active material is determined by inductively coupled plasma (ICP) spectroscopy analysis, for example, the standard YS/T 1006.2-2014, GB/T 23367.2-2009 or YS/T 1028.5-2015 can be referred to.
  • ICP inductively coupled plasma
  • an inductively coupled plasma emission spectrometer (Thermo, ICAP7400; PerkinElmer, Avio200) can be used to measure the luminescence intensity of the magnesium element in the sample to be tested, and standard samples of different contents of magnesium element are configured to measure their luminescence intensity as a standard curve, and the mass content of the magnesium element in the sample to be tested is determined in the standard curve according to the luminescence intensity of the magnesium element.
  • the prepared positive electrode active material is tested for residual alkali content.
  • the residual alkali content of NaHCO 3 refers to the mass of NaHCO 3 measured as a percentage of the mass content of the positive electrode active material. It is determined by the chemical reagent potentiometric titration method, for example, the standard GB/T 9725-2007 can be referred to. Specifically, a Swiss Metrohm 905Titrando potentiometric titrator can be used to dissolve the positive electrode active material in deionized water, and the aqueous solution of the positive electrode active material is titrated with a standard titration solution.
  • the gram capacity test process of button cell is as follows: at 25°C and normal pressure, charge the button cell at a constant current of 0.1C to a voltage of 4V, then charge at a constant voltage of 4V until the current drops to 0.05C, record the charge specific capacity at this time, which is the first sodium removal capacity; then discharge at a constant current of 0.1C to a voltage of 1.5V, record the discharge specific capacity at this time, which is the first sodium insertion capacity.
  • the gram capacity of the positive electrode active material is the first sodium insertion capacity.
  • the test process of the full battery capacity retention rate is as follows: at 25°C, the prepared full battery is charged to 3.7V at a constant current of 1C, then charged at a constant voltage of 3.7V until the current drops to 0.05C, and then discharged to 1.5V at 1C, and the obtained capacity is recorded as the initial capacity (C0). Repeat the above steps for the same full battery, and record the discharge capacity (Cn) of the full battery after the nth cycle at the same time.
  • the full battery capacity retention rate data corresponding to the embodiment or comparative example in Table 1 is the data measured after 200 cycles under the above test conditions, that is, the value of P200.
  • the test process of the comparative example and other embodiments is the same as above.
  • the rate performance test process is as follows: at 25°C, the prepared battery is placed in a 25°C thermostat, and allowed to stand for 30 minutes to allow the battery to reach a constant temperature.
  • the battery that has reached a constant temperature is charged to 3.7V at 0.33C constant current at 25°C, charged to 0.05C at 3.7V, allowed to stand for 5 minutes, and then discharged to 1.5V at 0.33C constant current, allowed to stand for 5 minutes, and the capacity C1 of 0.33C discharge is obtained; then charged to 3.7V at 0.33C constant current, charged to 0.05C at 3.7V, allowed to stand for 5 minutes, and then discharged to 1.5V at 3C constant current, allowed to stand for 5 minutes, and then discharged to 1.5V at 3C constant current, allowed to stand for 5 minutes, and the capacity C2 of 3C discharge is obtained.
  • the batteries of the embodiments and comparative examples were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 1 below.
  • Examples 1 to 31 are all positive electrode active materials for secondary batteries, including iron-based polyanion compounds and magnesium-containing oxides, and the iron-based polyanion compounds have the following general formula: Na4Fe3-xMxMgy ( PO4 ) 2P2O7 / C, wherein M contains a transition metal element, 0 ⁇ x ⁇ 0.5 , and 0 ⁇ y ⁇ 0.18.
  • magnesium is The doping in the sub-compound and the residue of the oxide derived from the magnesium source on the surface of the iron-based polyanion compound effectively reduce the residual alkali amount of the positive electrode active material, increase the gram capacity of the positive electrode active material, and improve the capacity retention rate of the battery at high rate.
  • the y value in the positive electrode active material is controlled to be greater than 0 and less than 0.18, so as to increase the gram capacity of the positive electrode active material, improve the capacity retention rate of the battery after 200 cycles and the capacity retention rate at 3C rate.
  • positive electrode active materials including magnesium oxide and Mg-doped iron-based polyanion compounds are beneficial to reducing the residual alkali amount of the positive electrode active material, increasing the gram capacity of the positive electrode active material, and improving the capacity retention rate of the battery after 200 cycles and the capacity retention rate at 3C rate.
  • the mass content of the carbon material is controlled to be 0.5% to 6%, which is beneficial to improving the conductivity of the positive electrode active material, improving the gram capacity of the positive electrode active material, and improving the capacity retention rate of the battery after 200 cycles and the capacity retention rate at 3C rate.
  • the mass content of the carbon material is controlled to be 1% to 3.6%, which is beneficial to further improve the gram capacity of the positive electrode active material.
  • the positive electrode active material introduces magnesium element and magnesium oxide, and the total mass content of magnesium element in the positive electrode active material is controlled to be 0.02% to 0.7% based on the total mass of the positive electrode active material, which is beneficial to reduce the residual alkali amount of the positive electrode active material, increase the gram capacity of the positive electrode active material, and improve the capacity retention rate of the battery at 3C rate.
  • controlling the calcination temperature to 500°C to 600°C is beneficial to reducing the residual alkali content of the positive electrode active material, increasing the gram capacity of the positive electrode active material, and improving the capacity retention rate of the battery after 200 cycles and the capacity retention rate at 3C rate.
  • controlling the calcination temperature to 500°C to 600°C is beneficial to reducing the residual alkali content of the positive electrode active material, increasing the gram capacity of the positive electrode active material, and increasing the capacity retention rate of the battery after 200 cycles and the capacity retention rate at 3C rate.
  • the calcination temperature is 525°C to 575°C, which is beneficial to further improve the gram capacity of the positive electrode active material, improve the capacity retention rate of the battery after 200 cycles and the capacity retention rate at 3C rate. From the comparison between Examples 7 and 20 and Examples 18 to 19 and 21, it can be seen that controlling the calcination temperature to 550°C to 575°C is beneficial to further improve the capacity retention rate of the battery after 200 cycles and the capacity retention rate at 3C rate.
  • controlling the transition metal elements in the positive electrode active material to include one or more of Ni, Co, Mn, and Ca is beneficial to reducing the residual alkali content of the positive electrode active material, increasing the gram capacity of the positive electrode active material, and improving the capacity retention rate of the battery after 200 cycles and the capacity retention rate at a 3C rate.
  • Example 26 and Examples 7 and 29, and Example 27 and Examples 7 and 30, it can be seen that compared with the transition metal element in the positive electrode active material containing only one of Ni, Co, and Mn, controlling the transition metal element in the positive electrode active material to contain two of Ni, Co, and Mn is beneficial to further improve the capacity retention rate of the battery at a 3C rate.
  • Example 28 and Examples 26 to 27 it can be seen that compared with the transition metal element in the positive electrode active material containing only two of Ni, Co, and Mn, controlling the transition metal element in the positive electrode active material to contain three of Ni, Co, and Mn is beneficial to further improve the capacity retention rate of the battery at a 3C rate.

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Abstract

本申请提供了一种正极活性材料、及其制备方法、二次电池、电池模块、电池包和用电装置。该正极活性材料作为二次电池用正极活性材料，包括碳材料复合的铁基聚阴离子化合物和含镁氧化物，铁基聚阴离子化合物具有如下通式：Na4Fe3-xMxMgy(PO4)2P2O7，其中，M包含过渡金属元素，0≤x≤0.5，0<y<0.18。该正极活性材料具有较低的残碱量、以及其电池具有优异的循环性能和倍率性能。

Description

正极活性材料、及其制备方法、二次电池、电池模块、电池包和用电装置
交叉引用
本申请引用于2023年1月16日递交的名称为“正极活性材料、及其制备方法、二次电池、电池模块、电池包和用电装置”的第202310070398.5号中国专利申请，其通过引用被全部并入本申请。
技术领域
本申请涉及二次电池技术领域，尤其涉及一种正极活性材料、及其制备方法、二次电池、电池模块、电池包和用电装置。
背景技术
钠电池由于具有丰富的储量，较低的价格以及宽的工作温度，在大型储能方面具有巨大的应用潜力。
铁基聚阴离子化合物作为新型钠电池的热门正极材料，具有资源多、工作电压高、循环稳定性好和环境友好等显著优点。但目前以铁基聚阴离子化合物作为正极材料的钠电池仍然存在着电子电导率低、放电容量低、循环性能差等问题。无法满足新一代电化学体系的应用需要。
发明内容
本申请是鉴于上述课题而进行的，其目的在于提供一种正极活性材料，该正极活性材料中引入了镁元素，实现晶格掺杂和复合改性的双重效果，能够有效降低正极活性材料的残碱量、提高电池的循环性能和倍率性能。
本申请的第一方面，提供了一种二次电池用正极活性材料，包括碳材料复合的铁基聚阴离子化合物和含镁氧化物，所述铁基聚阴离子化合物具有如下通式：Na4Fe3-xMxMgy(PO4)2P2O7/C
其中，M包含过渡金属元素，0≤x≤0.5，0<y<0.18。
在正极活性材料中引入镁元素，一方面，部分镁元素可掺杂进入铁基聚阴离子化合物晶格内部，取代铁基聚阴离子化合物晶格中的铁元素或过渡金属元素，从而提高正极活性材料的离子电导率和电子电导率，改善正极活性材料的导离子和导电子性能。另一方面，部分镁元素以含镁氧化物的形式分布于铁基聚阴离子化合物的表面，减少正极活性材料材料表面与环境中水分直接接触，降低正极活性材料的残碱量，改善正极活性材料稳定性及可加工性能。并且，该正极活性材料还具有较高的克容量，有利于提高其电池的能量密度。
在正极活性材料中引入碳材料，可以有效提高正极活性材料的导电性和电池性能。
在任意实施方式中，所述含镁氧化物分布于所述铁基聚阴离子化合物的一次粒子的至少部分表面上。
含镁氧化物分布于铁基聚阴离子离子化合物一次粒子的部分表面上或者全部表面上，可有效地减少正极活性材料表面与环境中水分直接接触，降低正极活性材料的残碱量，改善正极活性材料稳定性及可加工性能。
在任意实施方式中，基于所述正极活性材料的总质量计，所述正极活性材料中镁元素的质量含量为0.02％～0.7％。
基于正极活性材料的总质量计，控制正极活性材料中镁元素的质量含量为0.02％～0.7％，有利于降低正极活性材料的残碱量，改善正极活性材料稳定性及可加工性能，提升电池的循环性能和倍率性能。
在任意实施方式中，所述M包含Ni、Co、Mn、Cu、V、Ti、Mo、Nb、W、Cr、Zn、Zr、Ca中的一种或多种，可选Ni、Co、Mn、Cu、V、Ca中的一种或多种。
铁基聚阴离子化合物中引入过渡金属元素的掺杂，有利于提高正极活性材料的电压平台，改善材料的离子电导率和电子电导率，降低电池的极化，提升电池循环性能和倍率性能。
在任意实施方式中，所述M包含Ni、Co、Mn、Cu、V、Ca中 的至少两种。
控制M包含Ni、Co、Mn、Cu、V、Ca中的至少两种，有利于进一步提高电池的倍率性能。
在任意实施方式中，所述碳材料以碳膜的形式包覆于所述铁基聚阴离子化合物的表面或者所述碳材料以颗粒的形式分布于所述铁基聚阴离子化合物的一次离子之间。
碳材料以碳膜的形式包覆于铁基聚阴离子化合物的表面或者碳材料以颗粒的形式分布于铁基聚阴离子化合物的一次离子之间，均可以有效提高正极活性材料的导电性和电池性能。
在任意实施方式中，所述碳材料包括无定形碳、导电炭黑、碳纳米管和石墨烯中的一种或多种。
上述碳材料易于分散加工，与铁基聚阴离子化合物形成碳复合，提高正极活性材料的导电性和电池性能。其中，由于导电炭黑、碳纳米管或石墨烯的结晶度均高于无定形碳，故包括导电炭黑、碳纳米管或石墨烯的碳材料的导电性优于包括无定形碳的碳材料的导电性。
在任意实施方式中，基于所述正极活性材料的总质量计，所述碳材料的质量含量为0.5％～6％，可选为1％～3.6％。
基于正极活性材料的总质量计，控制碳材料的质量含量为0.5％～6％，有利于达到正极活性材料的克容量与导电性之间的平衡，同时获得更高的克容量和更优的循环性能与倍率性能。避免碳材料质量含量过低导致正极活性材料导电性差，不利于正极活性材料的容量挥发，也避免碳材料质量含量过高，导致正极活性材料的克容量降低，压实性能变差。基于正极活性材料的总质量计，控制碳材料的质量含量为1％～3.6％，有利于进一步提高正极活性材料的克容量，进一步提升电池的容量。
在任意实施方式中，所述正极活性材料的克容量为≥98mAh/g。
具有≥98mAh/g克容量的正极活性材料有利于提升其电池的容量，拓宽了电池的应用。
在任意实施方式中，基于所述正极活性材料的总质量计，所述 正极活性材料的NaHCO3残碱量小于1.2％。
基于正极活性材料的总质量计，正极活性材料的NaHCO3残碱量小于1.2％，可有效的提升其稳定性及可加工性能。
本申请的第二方面提供一种二次电池用正极活性材料的制备方法，包括以下步骤：
将包含铁源、钠源、磷源、镁源的原料溶于水中，得到混合浆料，所述原料中可选地包括M源，所述M源包括含有过渡金属的盐；
将混合浆料干燥后进行煅烧，制备所述正极活性材料，所述正极活性材料包括铁基聚阴离子化合物和含镁氧化物，所述铁基聚阴离子化合物具有如下通式：
Na4Fe3-xMxMgy(PO4)2P2O7/C
其中，M包含过渡金属元素，0≤x≤0.5，0<y<0.18。
上述正极活性材料的制备方法简单，制作成本低。制备的正极活性材料具有较低的残碱量和较高的克容量，其电池具有优异的循环性能和倍率性能。
在任意实施方式中，所述将混合浆料干燥后进行煅烧包括以下步骤：
将混合浆料进行干燥处理，得到前驱体粉末；
将前驱体粉末进行分步煅烧，第一步煅烧温度为300℃～400℃，煅烧时间为3h～6h，第二步煅烧温度为500℃～600℃，煅烧时间为8h～15h，制备所述正极活性材料。
分步煅烧有利于前驱体粉末的充分反应，提升所制备正极活性材料的结晶性及物相纯度，降低正极活性材料表面的残碱量，改善正极活性材料稳定性及可加工性能，提高正极活性材料的克容量、改善电池循环性能和倍率性能。
在任意实施方式中，所述第二步煅烧温度为525℃～575℃，可选为550℃～575℃。
控制第二步煅烧温度为525℃～575℃，有利于进一步降低活性材料表面的残碱量，改善材料的导电性，提升电池的循环性能和倍率性能。进一步控制第二步煅烧温度为550℃～575℃，有利于更大 程度上提高电池循环200圈的容量保持率和3C倍率下的容量保持率，更大程度上提升电池的循环性能和倍率性能。
在任意实施方式中，所述第二步煅烧时间为10h～14h。
控制第二步煅烧时间为10h～14h，有利于获得高结晶性高纯度的正极活性材料，同时通过控制保温时间，可控制一次晶粒的粒径大小和材料表面的残碱量，进而改善材料的克容量和电池的循环倍率性能。
在任意实施方式中，所述M源包括硝酸镍、乙酸镍、硝酸钴、硝酸锰、乙酸钴、乙酸锰、草酸镍、草酸钴、草酸锰、氧化镍、氧化钴、氧化锰中的一种或多种。
在任意实施方式中，所述镁源包括硝酸镁、碳酸镁、乙酸镁、氢氧化镁、草酸镁、氧化镁中的一种或多种。
在任意实施方式中，所述碳源包括蔗糖、单宁酸、聚乙二醇、聚丙烯腈、纤维素、聚乙烯吡咯烷酮、蔗糖、草酸、葡萄糖、抗坏血酸、聚乙烯、柠檬酸、导电炭黑、碳纳米管、石墨烯中的一种或多种。
上述碳源在高温的煅烧下易生产碳材料包覆于铁基聚阴离子化合物的表面或者分布于铁基聚阴离子化合物的一次粒子之间，提高正极活性材料的导电性。其中，由于煅烧温度的影响，包括蔗糖、单宁酸、聚乙二醇、聚丙烯腈、纤维素、聚乙烯吡咯烷酮、蔗糖、草酸、葡萄糖、抗坏血酸、聚乙烯、柠檬酸、导电炭黑、碳纳米管、石墨烯中一种或多种的碳源形成的无定形碳的结晶度较低，而包括导电炭黑、碳纳米管、石墨烯中一种或多种的碳源生成的碳材料的结晶度较高，故包括导电炭黑、碳纳米管、石墨烯中一种或多种的碳源生成的碳材料具有更优异的导电性能。
本申请的第三方面提供一种二次电池，包括正极极片，所述正极极片包括任意实施方式中所述的正极活性材料或任意实施方式中所述的制备方法制备所得的正极活性材料。
在任意实施方式中，所述二次电池是无负极钠电池。
在任意实施方式中，所述二次电池还包括负极极片，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的底涂层，所述底涂层包括碳纳米管、石墨、石墨烯、银复合碳纳米颗粒、锡复合碳纳米颗粒中的一种或多种。
上述底涂层不仅具有优异的导电性，还有利于金属离子在集流体表面的均匀沉积，提升电池的循环性能和安全性。
在任意实施方式中，所述底涂层的面密度为5g/m2～50g/m2。
面密度为5g/m2～50g/m2的底涂层有利于成核位点的均匀分布，促进金属的均匀沉积，同时也不影响电子的传输行为。
在任意实施方式中，所述底涂层的厚度为2μm～100μm。
控制底涂层的厚度为2μm～100μm，可以提供足够多的成核位点有利于金属离子的均匀沉积，抑制枝晶。
本申请的第四方面提供一种电池模块，包括本申请第三方面的二次电池。
本申请的第五方面提供一种电池包，包括本申请第三方面的二次电池或本申请第四方面的电池模块。
本申请的第六方面提供一种用电装置，包括本申请第三方面的二次电池、本申请第四方面的电池模块、本申请第五方面的电池包中的至少一种。
附图说明
图1是本申请一实施方式的二次电池的示意图；
图2是图1所示的本申请一实施方式的二次电池的分解图；
图3是本申请一实施方式的电池模块的示意图；
图4是本申请一实施方式的电池包的示意图；
图5是图4所示的本申请一实施方式的电池包的分解图；
图6是本申请一实施方式的二次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、及其制备方法、二次电池、电池模块、电池包和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。
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。
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)。
现有技术中聚阴离子化合物由于资源充足、环境友好、易于规模化生产、且具有开放的钠离子扩散通道、热稳定性及循环稳定性较好，所以成为热门的钠电池正极材料之一。但是，在实际生产过程中，研究者发现聚阴离子化合物材料表面具有较高的残碱量，在空气中的暴露也易导致材料表面残碱增加，造成克容量恶化，从而影响电池的性能。因此，需要开发一种残碱量低、具有优异的电化学性能、可用于高倍率电池的正极活性材料，以满足新一代电化学体系的应用需要。
[正极活性材料]
基于此，本申请提出了一种二次电池用正极活性材料，该正极活性材料包括碳材料复合的铁基聚阴离子化合物和含镁氧化物，铁基聚阴离子化合物具有如下通式：Na4Fe3-xMxMgy(PO4)2P2O7/C，其中，M包含过渡金属元素，0≤x≤0.5，0<y<0.18。
在本文中，术语“过渡金属元素”是指元素周期表中第ⅢB～ⅦB、Ⅷ族的元素、以及第ⅠB～ⅡB族元素。
在一些实施方式中，x可选为0、0.1、0.15、0.2、0.25、0.3、0.35、0.4、0.45或0.5。
在一些实施方式中，y可选为0.02、0.04、0.06、0.08、0.10、 0.12、0.14、0.16或0.17。
在正极活性材料中引入镁元素，一方面，部分镁元素可掺杂进入铁基聚阴离子化合物晶格内部，取代铁基聚阴离子化合物晶格中的铁元素或过渡金属元素，从而提高正极活性材料的离子电导率和电子电导率，改善正极活性材料的导离子和导电子性能。另一方面，部分镁元素以含镁氧化物的形式分布于铁基聚阴离子化合物的表面，减少正极活性材料材料表面与环境中水分直接接触，降低正极活性材料的残碱量，改善正极活性材料稳定性及可加工性能。并且，该正极活性材料还具有较高的克容量，有利于提高其电池的能量密度。
在正极活性材料中引入碳材料，可以有效提高正极活性材料的导电性和电池性能。
在本文中，术语“克容量”是指每克正极活性材料放出的电量，能够反映电池的容量，其可以通过任意公知方法进行测试。
在一些实施方式中，含镁氧化物分布于铁基聚阴离子化合物一次粒子的至少部分表面上。
在本文中，术语“一次粒子”是指铁基聚阴离子化合物未团聚之前的颗粒，铁基聚阴离子化合物的一次粒子的粒径范围为30nm～120nm。
在一些实施方式中，含镁氧化物包括氧化镁。
在一些实施方式中，含镁氧化物分布于铁基聚阴离子化合物一次粒子的部分表面上。
在一些实施方式中，含镁氧化物分布于铁基聚阴离子化合物一次粒子的全部表面上。
含镁氧化物分布于铁基聚阴离子化合物一次粒子的部分表面上或者全部表面上，可有效地减少正极活性材料与环境中水分直接接触，降低正极活性材料的残碱量，改善正极活性材料稳定性及可加工性能。
在一些实施方式中，基于正极活性材料的总质量计，正极活性材料中镁元素的质量含量为0.02％～0.7％。在一些实施方式中，基于正极活性材料的总质量计，正极活性材料中镁元素的质量含量可选 为0.02％、0.05％、0.1％、0.15％、0.2％、0.25％、0.3％、0.35％、0.4％、0.45％、0.5％、0.55％、0.6％、0.65％或0.7％。
在一些实施方式中，正极活性材料中镁元素包括铁基聚阴离子化合物中的Mg和含镁氧化物中的镁。
正极活性材料中镁元素的质量含量可以采用本领域公知的任意手段进行测试。作为示例，可以参考标准YS/T 1006.2-2014、GB/T 23367.2-2009或YS/T 1028.5-2015。具体的，可以采用电感耦合等离子体发射光谱仪(Thermo，ICAP7400；PerkinElmer，Avio200)测定待测样品中镁元素的发光强度，配置不同含量的镁元素标准样品测定其发光强度作为标准曲线，根据待测样品中镁元素的发光强度在标准曲线中确定其质量含量。
基于正极活性材料的总质量计，控制正极活性材料中镁元素的质量含量为0.02％～0.7％，有利于降低正极活性材料的残碱量，改善正极活性材料稳定性及可加工性能，提高正极活性材料的克容量和其电池3C倍率下的容量保持率，提升电池的循环性能和倍率性能。
在一些实施方式中，M包含Ni、Co、Mn、Cu、V、Ti、Mo、Nb、W、Cr、Zn、Zr、Ca中的一种或多种，可选Ni、Co、Mn、Cu、V、Ca中的一种或多种。
在一些实施方式中，M包含Ni。在一些实施方式中，M包含Co。在一些实施方式中，M包含Mn。在一些实施方式中，M包含Ca。在一些实施方式中，M包含Cu。
铁基聚阴离子化合物中引入过渡金属元素的掺杂，有利于提高正极活性材料的电压平台，改善材料的离子电导率和电子电导率，降低电池的极化，提升电池循环性能和倍率性能。。
在一些实施方式中，M包含Ni、Co、Mn、Cu、V、Ca中的至少两种。
在一些实施方式中，M包含Ni和Mn。在一些实施方式中，M包含Mn和Co。在一些实施方式中，M包含Ni和Co。在一些实施方式中，M包含Ni和Ca。在一些实施方式中，M包含Mn、Ni和Co。
控制M包含Ni、Co、Mn、Cu、V、Ca中的至少两种，有利于进一步提高电池的倍率性能。
在一些实施方式中，碳材料以碳膜的形式包覆于铁基聚阴离子化合物的表面或者碳材料以颗粒的形式分布于铁基聚阴离子化合物的一次离子之间。
在一些实施方式中，碳材料以碳膜的形式包覆于铁基聚阴离子化合物的表面。
在一些实施方式中，碳材料颗粒的形式分布于铁基聚阴离子化合物的一次离子之间。
碳材料以碳膜的形式包覆于铁基聚阴离子化合物的表面或者碳材料以颗粒的形式分布于铁基聚阴离子化合物的一次离子之间，均可以有效提高正极活性材料的导电性和电池性能。
在一些实施方式中，碳材料包括无定形碳、导电炭黑、碳纳米管、石墨烯中的一种或多种。
在一些实施方式中，碳材料包括无定形碳。在一些实施方式中，碳材料包括导电炭黑。在一些实施方式中，碳材料包括石墨烯。在一些实施方式中，碳材料包括碳纳米管。
上述碳材料易与铁基聚阴离子化合物相互复合，提高正极活性材料的导电性能。其中，由于导电炭黑、碳纳米管或石墨烯的结晶度均高于无定形碳，故包括导电炭黑、碳纳米管或石墨烯的碳材料的导电性优于包括无定形碳的碳材料的导电性。
在一些实施方式中，基于正极活性材料的总质量计，碳材料的质量含量为0.5％～6％，可选为1％～3.6％。在一些实施方式中，基于正极活性材料的总质量计，碳材料的质量含量可选为0.5％、1％、1.1％、1.5％、2％、2.5％、3％、3.5％、3.6％、4％、4.5％、5％、5.5％或6％。
基于正极活性材料的总质量计，控制碳材料的质量含量为0.5％～6％，有利于达到正极活性材料的克容量与导电性之间的平衡，同时获得更高的克容量和更优的循环性能与倍率性能。避免碳材料质量含量过低导致正极活性材料导电性差，不利于正极活性材料的 容量挥发，也避免碳材料质量含量过高，导致正极活性材料的克容量降低以及压实密度的影响。基于正极活性材料的总质量计，控制碳材料的质量含量为1％～3.6％，有利于进一步提高正极活性材料的克容量，进一步提升电池的容量。
在一些实施方式中，正极活性材料的克容量为≥98mAh/g。
在一些实施方式中，正极活性材料的克容量可选为98mAh/g、100mAh/g、105mAh/g、110mAh/g、115mAh/g、120mAh/g、125mAh/g。
正极活性材料中的克容量可以采用本领域公知的任意手段进行测试。作为示例，在25℃、常压环境下，将扣式电池以0.1C倍率恒流充电至电压为4V，再以4V恒压充电至电流降到0.05C，记录此时的充电比容量，即为首次脱钠容量；之后以0.1C倍率恒流放电至电压为1.5V，记录此时的放电比容量，为首次嵌钠容量。正极活性材料的克容量即为首次嵌钠容量。
具有≥98mAh/g克容量的正极活性材料有利于提升其电池的容量，拓宽了电池的应用。
在一些实施方式中，基于正极活性材料的总质量计，正极活性材料的NaHCO3残碱量小于1.2％。
在一些实施方式中，基于正极活性材料的总质量计，正极活性材料的NaHCO3残碱量可选为0.01％、0.05％、0.1％、0.2％、0.3％、0.4％、0.5％、0.6％、0.7％、0.8％、0.9％、1％、1.1％或1.15％。
正极活性材料的NaHCO3残碱量可以采用本领域公知的任意手段进行测试。作为示例，通过化学试剂电位滴定法测试确定，例如可以参考标准GB/T 9725-2007。具体的，可以采用瑞士万通905Titrando电位滴定仪，将正极活性材料溶解在去离水子中，采用标准滴定溶液对正极活性材料水溶液进行滴定，每滴加0.1ml标准滴定溶液，记录其电位或pH值，滴定至电位或pH值变化不大时，停止滴定。记录滴加的标准滴定溶液的体积及测得的电位或pH值，用作图法或二级微商法确定滴定终点，确定滴定标准溶液的滴定体积。通过计算得到的NaHCO3的质量除以正极活性材料的质量，以质量含 量作为正极活性材料的NaHCO3残碱量。
基于正极活性材料的总质量计，正极活性材料的NaHCO3残碱量小于1.2％，可有效的提升其稳定性及可加工性能。
本申请还提出了一种二次电池用正极活性材料的制备方法，包括以下步骤：
将包含铁源、钠源、磷源、镁源的原料溶于水中，得到混合浆料，所述原料中可选地包括M源，所述M源包括含有过渡金属的盐；
将混合浆料干燥后进行煅烧，制备正极活性材料，所述正极活性材料包括铁基聚阴离子化合物和含镁氧化物，所述铁基聚阴离子化合物具有如下通式：
Na4Fe3-xMxMgy(PO4)2P2O7/C
其中，M包含过渡金属元素，0≤x≤0.5，0<y<0.18。
上述正极活性材料的制备方法简单，制作成本低。制备的正极活性材料具有较低的残碱量和较高的克容量，其电池具有优异的循环性能和倍率性能。
正极活性材料中过渡金属的引入，有利于改善材料的离子电导率和电子电导率，提升电池的循环性能和倍率性能。。
在一些实施方式中，原料还包括碳源。
碳源的加入有利于在正极活性材料中引入导电碳元素，提高正极活性材料的导电性。
在一些实施方式中，将混合浆料干燥后进行煅烧包括以下步骤：
将混合浆料进行干燥处理，得到前驱体粉末；
将前驱体粉末进行分步煅烧，第一步煅烧温度300℃～400℃，煅烧时间为3h～6h，第二步煅烧温度为500℃～600℃，煅烧时间为8h～15h，制备正极活性材料。
分步煅烧有利于前驱体粉末的充分反应，提升所制备正极活性材料的结晶性及物相纯度，降低正极活性材料表面的残碱量，改善正极活性材料稳定性及可加工性能，提高正极活性材料的克容量、改善电池循环性能和倍率性能。
在一些实施方式中，第二步煅烧温度为525℃～575℃，可选为 550℃～575℃。
控制第二步煅烧温度为525℃～575℃，有利于进一步降低活性材料表面的残碱量，改善材料的导电性，提升电池的循环性能和倍率性能。进一步控制第二步煅烧温度为550℃～575℃，有利于更大更大程度上提升电池的循环性能和倍率性能。
在一些实施方式中，第二步煅烧时间为10h～14h。
控制第二步煅烧时间为10h～14h，有利于获得高结晶性高纯度的正极活性材料，同时通过控制保温时间，可控制一次晶粒的粒径大小和材料表面的残碱量，进而改善材料的克容量和电池的循环倍率性能。
在一些实施方式中，M源包括硝酸镍、乙酸镍、硝酸钴、硝酸锰、乙酸钴、乙酸锰、草酸镍、草酸钴、草酸锰、氧化镍、氧化钴、氧化锰中的一种或多种。
在一些实施方式中，镁源包括硝酸镁、碳酸镁、乙酸镁、氢氧化镁、草酸镁、氧化镁中的一种或多种。
在一些实施方式中，碳源包括蔗糖、单宁酸、聚乙二醇、聚丙烯腈、纤维素、聚乙烯吡咯烷酮、蔗糖、草酸、葡萄糖、抗坏血酸、聚乙烯、柠檬酸、导电炭黑、碳纳米管、石墨烯中的一种或多种。
在一些实施方式中，碳源包括蔗糖、单宁酸、聚乙二醇、聚丙烯腈、纤维素、聚乙烯吡咯烷酮、蔗糖、草酸、葡萄糖、抗坏血酸、聚乙烯、柠檬酸中的一种或多种。
在一些实施方式中，碳源包括导电炭黑、碳纳米管、石墨烯中的一种或多种。
上述碳源在高温的煅烧下易生产碳材料包覆于铁基聚阴离子化合物的表面或者分布于铁基聚阴离子化合物的一次粒子之间，提高正极活性材料的导电性。其中，由于煅烧温度的影响，包括蔗糖、单宁酸、聚乙二醇、聚丙烯腈、纤维素、聚乙烯吡咯烷酮、蔗糖、草酸、葡萄糖、抗坏血酸、聚乙烯、柠檬酸、导电炭黑、碳纳米管、石墨烯中一种或多种的碳源形成的无定形碳的结晶度较低，而包括导电炭黑、碳纳米管、石墨烯中一种或多种的碳源生成的碳材料的 结晶度较高，故包括导电炭黑、碳纳米管、石墨烯中一种或多种的碳源生成的碳材料具有更优异的导电性能。
[正极极片]
正极极片包括正极集流体及形成于正极集流体的至少部分表面上的正极活性材料层，正极活性材料层包括一些实施方式中的正极活性材料。
正极活性材料层还可以包括导电剂，以改善正极的导电性能。导电剂可选为Super P、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨、石墨烯及碳纳米纤维中的一种或几种。
正极活性材料层还可以包括粘结剂，以将正极活性材料和可选的导电剂牢固地粘结在正极集流体上。粘结剂可选为聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚丙烯酸(PAA)、聚乙烯醇(PVA)、乙烯-醋酸乙烯酯共聚物(EVA)、丁苯橡胶(SBR)、羧甲基纤维素(CMC)、海藻酸钠(SA)、聚甲基丙烯酸(PMA)及羧甲基壳聚糖(CMCS)中的至少一种。
正极集流体可以采用导电碳片、金属箔材、涂炭金属箔材、多孔金属板或复合集流体。导电碳片的导电碳材质可选为Super P、炭黑、科琴黑、碳点、碳纳米管、石墨、石墨烯及碳纳米纤维中的一种或几种，金属箔材、涂炭金属箔材和多孔金属板的金属材质各自独立地选自铜、铝、镍及不锈钢中的至少一种，复合集流体可以为金属箔材与高分子基膜复合形成的复合集流体。
在一些实施方式中，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、粘结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。
[隔离膜]
在一些实施方式中，二次电池中还包括隔离膜。本申请对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，隔离膜的材质可选自聚乙烯、聚丙烯、聚偏氟乙烯、芳纶、聚对苯二甲酸乙二醇酯、聚四氟乙烯、聚丙烯腈、聚酰亚胺，聚酰胺、聚酯和天然纤维中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜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，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，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
[二次电池]
二次电池，包括正极极片，正极极片包括一些实施方式中的正极活性材料或者一些实施方式中的制备方法制备的正极活性材料。
在一些实施方式中，二次电池还包括负极极片、隔离膜和电解液。
在一些实施方式中，二次电池为无负极钠电池。
无负极钠电池中不预沉积负极活性材料，仅包含负极集流体。首次充电时，钠离子在阳极侧得到电子以金属钠在集流体表面沉积形成钠金属相，放电时，金属钠能够转变为钠离子回到正极，实现循环充放。相比于其他钠二次电池，无负极钠电池由于不受负极材料的限制，可以获得更高的能量密度。无负极钠电池中没有足够的钠金属作为负极材料，向电池中提供足够的钠元素。因此，本申请提供的正极活性材料的应用能够更有效地提高二次电池的循环性能和高倍率性能。
在一些实施方式中，无负极钠电池的CB值小于等于0.1。
CB值为二次电池中负极极片的单位面积容量除以正极极片的单位面积容量。由于无负极电池中，不包含负极活性材料，因此负极 极片的单位面积容量较小，二次电池的CB值小于等于0.1。
在一些实施方式中，二次电池包括负极极片，负极极片可以仅包括负极集流体，不包含负极活性材料。在一些实施方式中，负极极片也可以在负极集流体上预沉积金属相。
在一些实施方式中，负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铝箔或铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(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)等的基材)上而形成。
在一些实施方式中，负极极片包括负极集流体以及设置在负极集流体至少一个表面的底涂层，底涂层包括碳纳米管、石墨、石墨烯、银复合碳纳米颗粒、锡复合碳纳米颗粒中的一种或多种。
上述底涂层不仅具有优异的导电性，还有利于金属离子在无负极电池集流体表面的均匀沉积，提升电池的循环性能和安全性。
在一些实施方式中，底涂层的面密度为5g/m2～50g/m2。
在一些实施方式中，底涂层的面密度可选为5g/m2、10g/m2、15g/m2、20g/m2、25g/m2、30g/m2、35g/m2、40g/m2、45g/m2或50g/m2。
面密度为5g/m2～50g/m2的底涂层有利于无负极电池中负极成核位点的均匀分布，促进金属的均匀沉积，同时也不影响电子的传输行为。
在一些实施方式中，底涂层的厚度为2μm～100μm。
在一些实施方式中，底涂层的厚度可选为2μm、5μm、10μm、15μm、20μm、25μm、30μm、35μm、40μm、45μm、50μm、55μm、60μm、65μm、70μm、75μm、80μm、85μm、90μm、95μm或100μm。
上述底涂层厚度薄，无法作为负极活性材料使用，而在无负极钠电池中作为底涂层降低钠的成核过电势，有利于金属离子的均匀 沉积，抑制枝晶。
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。例如，图1是作为一个示例的方形结构的二次电池5，图2是二次电池5的分解图。
在一些实施方式中，参照图2，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。非牛顿流体电解质组合物浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，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3是作为一个示例的电池模块3。参照图3，在电池模块3中，多个二次电池5可以是沿电池模块3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3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4和图5是作为一个示例的电池包1。参照图4和图5，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。
[用电装置]
本申请的一个实施方式中，提供一种用电装置，包括任意实施方式的二次电池、任意实施方式的电池模块或任意实施方式的电池包中的至少一种。
用电装置包括本申请提供的二次电池、电池模块、或电池包中的至少一种。二次电池、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。
作为用电装置，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。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二次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。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。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。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。
一、制备方法
实施例1
1)正极活性材料的制备
将0.1mol焦磷酸钠、0.3mol草酸亚铁、0.2mol磷酸二氢铵、0.01mol葡萄糖和0.006mol乙酸镁加入200ml去离子水中，采用砂磨机研磨10h，得到混合浆料；将混合浆料通过喷雾干燥设备进行 干燥处理，得到干燥的前驱体粉末；将前驱体放入管式炉中，通氮气作为保护气体，进行第一步煅烧，升温至300℃保温4h，再进行第二步煅烧，升温至550℃保温12h，得到正极活性材料。
2)正极极片的制备
将10wt％聚偏氟乙烯粘结剂充分溶解于N‐甲基吡咯烷酮(NMP)中，再加入10wt％炭黑导电剂与80wt％上述正极活性材料搅拌混合均匀，得到正极浆料。将浆料均匀涂敷在集流体铝箔表面，然后转移到真空干燥箱中完全干燥。将干燥后的极片进行辊压、冲切，得到正极极片。
3)负极极片的制备
将碳纳米管和羧甲基纤维素(CMC)按照1:0.4的质量比加入到去离子水中搅拌成均匀的浆料，使浆料涂覆在负极集流体铜箔表面上形成底涂层，之后转移到真空干燥箱中完全干燥，再进行冲切，底涂层的厚度为20μm，面密度为25g/m2。得到无负极结构的负极极片。
4)电解液
在氩气气氛手套箱中(H2O<0.1ppm，O2<0.1ppm)，将钠盐六氟磷酸钠NaPF6溶解于有机溶剂乙二醇二甲醚(DME)中，搅拌均匀，得到钠盐浓度1mol/L的电解液。
5)隔离膜
以聚丙烯膜作为隔离膜。
6)扣式电池的制备
以金属钠片作为对电极，采用Celgard 2400隔离膜，并注入电解液，组装得到扣式电池。
7)全电池的制备
将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极片之间起到隔离的作用，加入上述电解液组装成叠片电池。获得实施例1的无负极钠电池产品。
实施例2～6
实施例2～6的电池与实施例1的电池制备方法相似，但是调整 了正极活性材料中碳元素的质量含量，具体参数如表1所示。
实施例7
实施例7的电池与实施例1的电池制备方法相似，但是调整了正极活性材料的制备方法，具备制备方法如下：
将0.1mol焦磷酸钠、0.28mol草酸亚铁、0.2mol磷酸二氢铵、0.04mol葡萄糖、0.02mol草酸锰(M源)和0.006mol乙酸镁加入200ml去离子水中，采用砂磨机研磨10h，得到混合浆料；将混合浆料通过喷雾干燥设备进行干燥处理，得到干燥的前驱体粉末；将前驱体粉末放入管式炉中，通氮气作为保护气体，升温至300℃保温4h，再升温至550℃保温12h，得到正极活性材料。
实施例8～12
实施例8～12的电池与实施例7的电池制备方法相似，但是调整了铁基聚阴离子化合物中Mn元素的x值，具体参数如表1所示。
实施例13～17
实施例13～17的电池与实施例7的电池制备方法相似，但是调整了正极活性材料中镁元素的质量含量，具体参数如表1所示。
实施例18～25
实施例18～25的电池与实施例7的电池制备方法相似，但是分别调整了第二步煅烧温度和煅烧时间，具体参数如表1所示。
实施例26～31
实施例26～31的电池与实施例7的电池制备方法相似，但是调整了铁基聚阴离子化合物中过渡金属元素种类和组合，具体参数如表1所示。
对比例1
对比例1的电池与实施例1的电池制备方法相似，但是调整了正极活性材料的制备方法，具备制备方法如下：
将0.1mol焦磷酸钠、0.3mol草酸亚铁和0.2mol磷酸二氢铵加入200ml水中，采用砂磨机研磨10h，得到混合浆料；将混合浆料通过喷雾干燥设备进行干燥处理，得到干燥的前驱体粉末；将前驱体放入管式炉中，通氮气作为保护气体，进行第一步煅烧，升温至 300℃保温4h，再进行第二步煅烧，升温至550℃保温12h，得到正极活性材料。
对比例2
对比例2的电池与对比例1的电池制备方法相似，但是正极活性材料中引入了碳材料，具体参数如表1所示。
对比例3
对比例3的电池与对比例2的电池制备方法相似，但是正极活性材料中引入了镁元素，具体参数如表1所示。
对比例4～5
对比例4～5的电池与对比例1的电池制备方法相似，但是正极活性材料中引入了不同x值的Mn元素，具体参数如表1所示。
二、性能测试
1、正极活性材料性能测试
1)镁元素含量测试
正极活性材料的成分是通过电感耦合等离子体(ICP)光谱法分析确定的，例如可以参考标准YS/T 1006.2-2014、GB/T 23367.2-2009或YS/T 1028.5-2015。具体的，可以采用电感耦合等离子体发射光谱仪(Thermo，ICAP7400；PerkinElmer，Avio200)测定待测样品中镁元素的发光强度，配置不同含量的镁元素标准样品测定其发光强度作为标准曲线，根据待测样品中镁元素的发光强度在标准曲线中确定其质量含量。
2)NaHCO3残碱量测试
对制备好的正极活性材料进行残碱量测试。本申请中NaHCO3残碱量是指测得的NaHCO3的质量占正极活性材料的质量含量。通过化学试剂电位滴定法测试确定，例如可以参考标准GB/T 9725-2007。具体的，可以采用瑞士万通905Titrando电位滴定仪，将正极活性材料溶解在去离水子中，采用标准滴定溶液对正极活性材料水溶液进行滴定，每滴加0.1ml标准滴定溶液，记录其电位或pH值，滴定至电位或pH值变化不大时，停止滴定。记录滴加的标准滴定溶液的体积及测得的电位或pH值，用作图法或二级微商法确定滴定终 点，确定滴定标准溶液的滴定体积。通过计算得到的NaHCO3的质量除以正极活性材料的质量，以质量含量作为正极活性材料的NaHCO3残碱量。
2、电池性能测试
1)扣式电池克容量测试
扣式电池克容量测试过程如下：在25℃、常压环境下，将扣式电池以0.1C倍率恒流充电至电压为4V，再以4V恒压充电至电流降到0.05C，记录此时的充电比容量，即为首次脱钠容量；之后以0.1C倍率恒流放电至电压为1.5V，记录此时的放电比容量，为首次嵌钠容量。正极活性材料的克容量即为首次嵌钠容量。
2)全电池循环容量保持率测试
全电池容量保持率测试过程如下：在25℃下，将制备的全电池，以1C恒流充电至3.7V，再以3.7V恒定电压充电至电流降到0.05C，再以1C放电至1.5V，所得容量记为初始容量(C0)。对上述同一个全电池重复以上步骤，并同时记录循环第n次后全电池的放电容量(Cn)，则每次循环后全电池容量保持率Pn＝Cn/C0×100％，以P1、P2……200这200个点值为纵坐标，以对应的循环次数为横坐标，得到全电池容量保持率与循环次数的曲线图。该测试过程中，第一次循环对应n＝1、第二次循环对应n＝2、……第200次循环对应n＝200，表1中实施例或对比例对应的全电池容量保持率数据是在上述测试条件下循环200次之后测得的数据，即P200的值。对比例以及其他实施例的测试过程同上。
3)倍率性能测试
倍率性能测试过程如下：在25℃下，将制备的电池置于25℃恒温箱中，静置30分钟，使电池达到恒温，将达到恒温的电池在25℃下以0.33C恒流充电至3.7V，3.7V下恒压充电至0.05C，静置5分钟，再以0.33C恒流放电至1.5V，静置5min，获得0.33C放电的容量C1；然后以0.33C恒流充电至3.7V，3.7V下恒压充电至0.05C，静置5分钟，再以3C恒流放电至1.5V，静置5min，获得3C放电的容量C2，则在3C倍率下的容量保持率为R＝C2/C1×100％。对比例 以及其他实施例的测试过程同上。
三、各实施例、对比例测试结果分析
按照上述方法分别制备各实施例和对比例的电池，并测量各项性能参数，结果见下表1。
表1

根据上述结果可知，实施例1～31均为二次电池用正极活性材料，包括铁基聚阴离子化合物和含镁氧化物，铁基聚阴离子化合物具有如下通式：Na4Fe3-xMxMgy(PO4)2P2O7/C，其中，M包含过渡金属元素，0≤x≤0.5，0<y<0.18。
从实施例1～31与对比例1～2的对比可见，镁元素在铁基聚阴离 子化合物中的掺杂以及镁源衍生的氧化物在铁基聚阴离子化合物表面的残留有效地降低了正极活性材料的残碱量、提高正极活性材料的克容量、提高电池高倍率下的容量保持率。
从实施例1～31与对比例3的对比可见，控制正极活性材料中的y值大于0小于0.18，方能提高正极活性材料的克容量、提高电池循环200圈的容量保持率和3C倍率下的容量保持率。
从实施例7～31与对比例4～5的对比可见，相比于仅含有过渡金属元素的传统正极活性材料，包括含镁氧化物和Mg掺杂的铁基聚阴离子化合物的正极活性材料，有利于降低正极活性材料的残碱量、提高正极活性材料的克容量、提高电池循环200圈的容量保持率和3C倍率下的容量保持率。
从实施例1～6与对比例1的对比可见，基于正极活性材料的总质量计，控制碳材料的质量含量为0.5％～6％，有利于提高正极活性材料的导电性、提高正极活性材料的克容量、提高电池循环200圈的容量保持率和3C倍率下的容量保持率。从实施例2～4与实施例1、5～6的对比可见，基于正极活性材料的总质量计，控制碳材料的质量含量为1％～3.6％，有利于进一步提高正极活性材料的克容量。
从实施例7～12与对比例4～5的对比可见，控制过渡金属元素的x值小于等于0.5，有利于降低正极活性材料的残碱量、提高正极活性材料的克容量、提高电池循环200圈的容量保持率和3C倍率下的容量保持率。
从实施例7、13～17与对比例2的对比可见，正极活性材料引入镁元素和含镁氧化物，基于正极活性材料的总质量计，控制正极活性材料中镁元素的总质量含量为0.02％～0.7％，有利于降低正极活性材料的残碱量、提高正极活性材料的克容量、提高电池3C倍率下的容量保持率。
从实施例7、18～21与对比例2的对比可见，控制煅烧温度为500℃～600℃，有利于降低正极活性材料的残碱量、提高正极活性材料的克容量、提高电池循环200圈的容量保持率和3C倍率下的容量保持率。从实施例7、19～20与实施例18、21的对比可见，控制 煅烧温度为525℃～575℃，有利于进一步提高正极活性材料的克容量、提高电池循环200圈的容量保持率和3C倍率下的容量保持率。从实施例7、20与实施例18～19、21的对比可见，控制煅烧温度为550℃～575℃，有利于更大程度上提高电池循环200圈的容量保持率和3C倍率下的容量保持率。
从实施例7、22～25与对比例2的对比可见，控制煅烧时间为8h～15h，有利于降低正极活性材料的残碱量、提高正极活性材料的克容量、提高电池循环200圈的容量保持率和3C倍率下的容量保持率。从实施例7、23～24与对比例22、25的对比可见，控制煅烧时间为10h～14h，有利于进一步提高正极活性材料的克容量、提高电池循环200圈的容量保持率和3C倍率下的容量保持率。
从实施例7、26～31与对比例4～5的对比可见，控制正极活性材料中的过渡金属元素包含Ni、Co、Mn、Ca中的一种或多种，有利于降低正极活性材料的残碱量、提高正极活性材料的克容量、提高电池循环200圈的容量保持率和3C倍率下的容量保持率。
从实施例26与实施例7、29，实施例27与实施例7、30的对比可见，相比于正极活性材料中的过渡金属元素仅包含Ni、Co、Mn中的一种，控制正极活性材料中的过渡金属元素包含Ni、Co、Mn中的两种，有利于进一步提高电池3C倍率下的容量保持率。从实施例28与实施例26～27的对比可见，相比于正极活性材料中的过渡金属元素仅包含Ni、Co、Mn中的两种，控制正极活性材料中的过渡金属元素包含Ni、Co、Mn三种，有利于更大程度上提高电池3C倍率下的容量保持率。
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 (26)

  1. 一种二次电池用正极活性材料，其特征在于，所述正极活性材料包括碳材料复合的铁基聚阴离子化合物和含镁氧化物，所述铁基聚阴离子化合物具有如下通式：
    Na4Fe3-xMxMgy(PO4)2P2O7/C
    其中，M包含过渡金属元素，0≤x≤0.5，0<y<0.18。
  2. 根据权利要求1所述的正极活性材料，其特征在于，所述含镁氧化物分布于所述铁基聚阴离子化合物的一次粒子的至少部分表面上。
  3. 根据权利要求1或2所述的正极活性材料，其特征在于，基于所述正极活性材料的总质量计，所述正极活性材料中镁元素的质量含量为0.02％～0.7％。
  4. 根据权利要求1至3中任一项所述的正极活性材料，其特征在于，所述M包含Ni、Co、Mn、Cu、V、Ti、Mo、Nb、W、Cr、Zn、Zr、Ca中的一种或多种，可选Ni、Co、Mn、Cu、V、Ca中的一种或多种。
  5. 根据权利要求1至4中任一项所述的正极活性材料，其特征在于，所述M包含Ni、Co、Mn、Cu、V、Ca中的至少两种。
  6. 根据权利要求1至5中任一项所述的正极活性材料，其特征在于，所述碳材料以碳膜的形式包覆于所述铁基聚阴离子化合物的表面或者所述碳材料以颗粒的形式分布于所述铁基聚阴离子化合物的一次离子之间。
  7. 根据权利要求1至6中任一项所述的正极活性材料，其特征在于，所述碳材料包括无定形碳、导电炭黑、碳纳米管、石墨烯中的一种或多种。
  8. 根据权利要求1至7中任一项所述的正极活性材料，其特征在于，基于所述正极活性材料的总质量计，所述碳材料的质量含量为0.5％～6％，可选为1％～3.6％。
  9. 根据权利要求1至8中任一项所述的正极活性材料，其特征在于，所述正极活性材料的克容量为≥98mA·h/g。
  10. 根据权利要求1至9中任一项所述的正极活性材料，其特征在于，基于所述正极活性材料的总质量计，所述正极活性材料的NaHCO3残碱量小于1.2％。
  11. 一种二次电池用正极活性材料的制备方法，其特征在于，包括以下步骤：
    将包含铁源、钠源、磷源、镁源、碳源的原料溶于水中，得到混合浆料，所述原料中可选地包括M源，所述M源包括含有过渡金属的盐；
    将混合浆料干燥后进行煅烧，制备所述正极活性材料，所述正极活性材料包括铁基聚阴离子化合物和含镁氧化物，所述铁基聚阴离子化合物具有如下通式：
    Na4Fe3-xMxMgy(PO4)2P2O7/C
    其中，M包含过渡金属元素，0≤x≤0.5，0<y<0.18。
  12. 根据权利要求11所述的制备方法，其特征在于，所述将混合浆料干燥后进行煅烧包括以下步骤：
    将混合浆料进行干燥处理，得到前驱体粉末；
    将前驱体粉末进行分步煅烧，第一步煅烧的温度300℃～400℃， 时间为3h～6h，第二步煅烧的温度为500℃～600℃，时间为8h～15h，制备所述正极活性材料。
  13. 根据权利要求12所述的制备方法，其特征在于，所述第二步煅烧的温度为525℃～575℃，可选为550℃～575℃。
  14. 根据权利要求12或13所述的制备方法，其特征在于，所述第二步煅烧的时间为10h～14h。
  15. 根据权利要求11至14中任一项所述的制备方法，其特征在于，所述M源包括硝酸镍、乙酸镍、硝酸钴、硝酸锰、乙酸钴、乙酸锰、草酸镍、草酸钴、草酸锰、氧化镍、氧化钴、氧化锰中的一种或多种。
  16. 根据权利要求11至15中任一项所述的制备方法，其特征在于，所述镁源包括硝酸镁、碳酸镁、乙酸镁、氢氧化镁、草酸镁、氧化镁中的一种或多种。
  17. 根据权利要求11至16中任一项所述的制备方法，其特征在于，所述碳源包括蔗糖、单宁酸、聚乙二醇、聚丙烯腈、纤维素、聚乙烯吡咯烷酮、蔗糖、草酸、葡萄糖、抗坏血酸、聚乙烯、柠檬酸、导电炭黑、碳纳米管、石墨烯中的一种或多种。
  18. 一种二次电池，其特征在于，包括正极极片，所述正极极片包括权利要求1至10中任一项所述的正极活性材料或权利要求11至17中任一项所述的制备方法制备所得的正极活性材料。
  19. 根据权利要求18所述的二次电池，其特征在于，所述二次电池包括钠电池。
  20. 根据权利要求18或19所述的二次电池，其特征在于，所述二次电池是无负极钠电池。
  21. 根据权利要求18至20中任一项所述的二次电池，其特征在于，所述二次电池还包括负极极片，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的底涂层，所述底涂层包括碳纳米管、石墨、石墨烯、银复合碳纳米颗粒、锡复合碳纳米颗粒中的一种或多种。
  22. 根据权利要求21所述的二次电池，其特征在于，所述底涂层的面密度为5g/m2～50g/m2。
  23. 根据权利要求21或22所述的二次电池，其特征在于，所述底涂层的厚度为2μm～100μm。
  24. 一种电池模块，其特征在于，包括权利要求18至23中任一项所述的二次电池。
  25. 一种电池包，其特征在于，包括权利要求18至23中任一项所述的二次电池或权利要求24所述的电池模块。
  26. 一种用电装置，其特征在于，包括权利要求18至23中任一项所述的二次电池、权利要求24所述的电池模块或权利要求25所述的电池包中的至少一种。
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