WO2023092491A1 - 一种正极活性材料及其制备方法和应用 - Google Patents

一种正极活性材料及其制备方法和应用 Download PDF

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WO2023092491A1
WO2023092491A1 PCT/CN2021/133668 CN2021133668W WO2023092491A1 WO 2023092491 A1 WO2023092491 A1 WO 2023092491A1 CN 2021133668 W CN2021133668 W CN 2021133668W WO 2023092491 A1 WO2023092491 A1 WO 2023092491A1
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positive electrode
electrode active
active material
manganese oxide
lithium nickel
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PCT/CN2021/133668
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English (en)
French (fr)
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张振国
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宁德时代新能源科技股份有限公司
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Priority to PCT/CN2021/133668 priority Critical patent/WO2023092491A1/zh
Priority to CN202180090731.8A priority patent/CN116802843A/zh
Priority to EP21963473.0A priority patent/EP4231388A4/en
Priority to US18/072,809 priority patent/US20230166983A1/en
Publication of WO2023092491A1 publication Critical patent/WO2023092491A1/zh

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    • C—CHEMISTRY; METALLURGY
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    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • C01G53/40—Nickelates
    • C01G53/42—Nickelates containing alkali metals, e.g. LiNiO2
    • C01G53/44—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese
    • C01G53/54—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese of the type [Mn2O4]-, e.g. Li(NixMn2-x)O4, Li(MyNixMn2-x-y)O4
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—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
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • 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
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/30—Three-dimensional structures
    • C01P2002/32—Three-dimensional structures spinel-type (AB2O4)
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C01P2002/54—Solid solutions containing elements as dopants one element only
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/50—Agglomerated particles
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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, in particular to a positive electrode active material and its preparation method and application.
  • Lithium nickel manganese oxide material has a discharge platform as high as 4.7V (vs. Li/Li + ), which is the first choice for low-cost and high-energy-density cathode active materials.
  • LNMO Lithium nickel manganese oxide material
  • the transition metal (mainly Mn) ions in it are dissolved and diffused to the surface of the negative electrode to deposit, hindering the deintercalation of Li + in the graphite, which makes the reversible capacity of the graphite negative electrode drop rapidly.
  • the capacity fading of negative electrode graphite is the most, far exceeding the activity consumption of positive electrode and electrolyte.
  • This application is made in view of the above-mentioned problems, and its purpose is to reduce the content of Mn 3+ in the positive electrode active material, and reduce the dissolution of manganese from the source.
  • the present application provides a positive electrode active material and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device.
  • the first aspect of the present application provides a positive electrode active material, which includes a spinel lithium nickel manganese oxide material, and the spinel lithium nickel manganese oxide material has the following chemical formula: Li a Ni 0.5-x Mn 1.5 -y M x+y O 4 , wherein, M is at least one selected from Mg, Zn, Ti, Zr, W, Nb, Al, B, P, Mo, V, Cr, 0.9 ⁇ a ⁇ 1.1,- 0.2 ⁇ x ⁇ 0.2, -0.02 ⁇ y ⁇ 0.3, x+y ⁇ 0;
  • the content of Mn 3+ in the spinel lithium nickel manganese oxide material is less than or equal to 0.7wt%.
  • the present application provides a positive electrode active material with a lower Mn 3+ content, which reduces the dissolution of manganese from the source, thereby reducing the gas production of the battery and improving the cycle performance of the battery.
  • the volume median particle diameter of the primary particles of the spinel lithium nickel manganese oxide material is 0.5 ⁇ m to 16 ⁇ m, optionally 2 ⁇ m to 10 ⁇ m.
  • the volume median particle size of the primary particle of the spinel lithium nickel manganese oxide material is 0.5 ⁇ m to 16 ⁇ m, and when it can be selected as 2 ⁇ m to 10 ⁇ m, it is beneficial to reduce the specific surface area and the amount of fine powder of the material, and further improve the cycle performance of the battery. At the same time, the processing performance of the pole piece is guaranteed.
  • the spinel-type lithium nickel manganese oxide material is a quasi-single crystal or single crystal material, and the inventors have found that when the quasi-single crystal or single crystal material is used as the positive electrode active material, transition metal ions are dissolved Less, better cycle performance, less gas production.
  • the volume median particle diameter of the spinel lithium nickel manganese oxide material is 2 ⁇ m to 24 ⁇ m, optionally 5 ⁇ m to 17 ⁇ m. The inventors found that when the volume median particle size of the spinel-type lithium nickel manganese oxide material is within the above range, the dissolution of transition metal ions is less, the cycle performance is better, and the gas production is smaller.
  • the primary particle morphology of the spinel lithium nickel manganese oxide material is octahedral or polyhedral. It has a low-index crystal face, low surface energy and stable crystal face, which can effectively inhibit the dissolution of transition metal ions (especially Mn ions).
  • the molar ratio of Ni atoms and their position doping atoms to Mn atoms and their position doping atoms in the spinel lithium nickel manganese oxide material is greater than or equal to 1:3, and at this time, less manganese
  • the ions exist as trivalent Mn 3+ .
  • the positive electrode active material also includes a surface modification layer, the surface modification layer covers at least part of the surface of the spinel lithium nickel manganese oxide material, and the material of the surface modification layer is selected from Ti , at least one of oxides of Zr, W, Al, B, P or Mo.
  • the existence of the surface modification layer can further reduce the dissolution of transition metal ions (especially Mn ions) Mn 3+ , thereby reducing the gas production of the battery and improving the cycle performance of the battery.
  • the content of the surface modification layer is less than 3%. At this time, it is beneficial to reduce the dissolution of transition metal ions (especially Mn 3+ ), thereby reducing the gas production of the battery and improving the cycle performance of the battery, without significantly reducing the capacity of the battery and increasing the interface impedance.
  • the positive electrode active material is used to prepare a button-type half-battery, and the charging capacity of 3.5V-4.4V accounts for less than or equal to 2% of the charging capacity of 3.5V-4.9V during 0.01C-0.2C charging and discharging, It shows that there is a lower content of Mn 3+ in the positive electrode active material of the present application, and the secondary battery prepared by using the positive electrode active material has lower gas production and better cycle performance.
  • the second aspect of the present application also provides a method for preparing a positive electrode active material, which includes the following steps:
  • the spinel lithium nickel manganese oxide material has the following chemical formula: Li a Ni 0.5-x Mn 1.5-y M x+y O 4 , wherein M is selected from Mg, Zn, Ti, Zr, W, At least one of Nb, Al, B, P, Mo, V, Cr, 0.9 ⁇ a ⁇ 1.1, -0.2 ⁇ x ⁇ 0.2, -0.02 ⁇ y ⁇ 0.3, x+y ⁇ 0;
  • the content of Mn 3+ in the spinel lithium nickel manganese oxide material is less than or equal to 0.7wt%.
  • the third aspect of the present application provides a secondary battery, including the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared according to the method of the second aspect of the present application.
  • a fourth aspect of the present application provides a battery module including the secondary battery of the third aspect of the present application.
  • a fifth aspect of the present application provides a battery pack, including the battery module of the fourth aspect of the present application.
  • the sixth aspect of the present application provides an electric device, including at least one selected from the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application. kind.
  • the application provides a positive electrode active material and a preparation method thereof, a secondary battery, a battery module, a battery pack, and an electrical device, wherein the Mn content of the spinel lithium nickel manganese oxide material in the positive electrode active material is less than or equal to 0.7wt%, which reduces the content of Mn 3+ in the material from the source, effectively reduces the dissolution of manganese, reduces the gas production of the battery, and improves the cycle performance of the battery.
  • FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG. 1 .
  • FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.
  • FIG. 4 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 5 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of an electrical device in which a secondary battery is used as a power source according to an embodiment of the present application.
  • FIG. 7A and 7B are microscopic electron microscope (SEM) photos of the positive electrode active material of Example 1, wherein FIG. 7B is a partially enlarged view of FIG. 7A .
  • FIG. 8 is a photomicrograph of the cathode active material of Example 4.
  • FIG. 9 is a photomicrograph of the cathode active material of Example 13.
  • FIG. 10 is a photomicrograph of the cathode active material of Example 16.
  • FIG. 11A and FIG. 11B are photomicrographs of the positive electrode active material of Comparative Example 2, and FIG. 11B is a partially enlarged view of FIG. 11A .
  • FIG. 12A and FIG. 12B are photomicrographs of the cathode active material of Comparative Example 3, wherein FIG. 12B is a partially enlarged view of FIG. 12A .
  • Fig. 13 is the charging and discharging first cycle curves of Examples 4, 11 and Comparative Example 2.
  • ranges disclosed herein are defined in terms of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be combined arbitrarily, ie any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are contemplated. Additionally, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5.
  • the numerical range "a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article, and "0-5" is only an abbreviated representation of the combination of these values.
  • a certain parameter is an integer ⁇ 2
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed in sequence, and may also include steps (b) and (a) performed in sequence.
  • step (c) means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c) , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b) and so on.
  • the “comprising” and “comprising” mentioned in this application mean open or closed.
  • the “comprising” and “comprising” may mean that other components not listed may be included or included, or only listed components may be included or included.
  • the term "or” is inclusive unless otherwise stated.
  • the phrase "A or B” means “A, B, or both A and B.” More specifically, the condition "A or B” is satisfied by either of the following: 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).
  • the present application provides a positive electrode active material.
  • the present application proposes a positive electrode active material, which includes a spinel lithium nickel manganese oxide material, and the spinel lithium nickel manganese oxide material has the following chemical formula: Li a Ni 0.5 -x Mn 1.5-y M x+y O 4 , wherein, M is at least one selected from Mg, Zn, Ti, Zr, W, Nb, Al, B, P, Mo, V, Cr, 0.9 ⁇ a ⁇ 1.1, -0.2 ⁇ x ⁇ 0.2, -0.02 ⁇ y ⁇ 0.3, x+y ⁇ 0;
  • the content of Mn 3+ in the spinel lithium nickel manganese oxide material is less than or equal to 0.7wt%.
  • the spinel-type lithium nickel manganese oxide material of the present application is mainly composed of an ordered P4 3 32 structure. Since the Mn in the P4 3 32 structure is all Mn 4+ , the spinel of the present application The lithium nickel manganese oxide material has a high P4 3 32 structure content, so the content of Mn 3+ in the material is lower, and the content of Mn 3+ is less than or equal to 0.7wt%, which reduces the dissolution of the positive electrode active material Mn 3+ from the source , reducing the gas production of the battery and improving the cycle performance of the battery.
  • the volume median particle diameter (dv50) of the primary particles of the spinel lithium nickel manganese oxide material is 0.5 ⁇ m to 16 ⁇ m.
  • the inventors found that when the primary particle of the spinel lithium nickel manganese oxide material has a volume median particle diameter of the range, it has higher tap density and compaction density, lower specific surface area and micropowder Amount, using the positive electrode active material containing the spinel-type lithium nickel manganese oxide material, has lower manganese dissolution, lower gas production and higher cycle performance. Further, the inventors also found that the increase of the volume median particle size of the primary particles is beneficial to reduce the dissolution of manganese and improve the cycle performance of the battery.
  • the volume median particle size of the primary particles of the spinel-type lithium nickel manganese oxide material can be selected from 2 ⁇ m to 10 ⁇ m.
  • the primary particles of the spinel-type lithium nickel manganese oxide material are also referred to as crystal grains of the spinel-type lithium nickel manganese oxide material, and are also simply referred to as primary particles or crystal grains in the present application.
  • the volume median particle diameter (Dv50) of the spinel lithium nickel manganese oxide material is 2 ⁇ m to 24 ⁇ m, optionally 5 ⁇ m to 17 ⁇ m. The inventors found that when the volume median particle size of the spinel-type lithium nickel manganese oxide material is within the above range, the dissolution of transition metal ions is less, the gas production is smaller, and the cycle performance is better.
  • volume median particle size refers to the particle size corresponding to the volume-based particle distribution of the material, starting from the small particle size and reaching 50% of the cumulative volume.
  • the physical meaning is that the volume content of particles with a particle size larger than it accounts for 50% of the total particles, and the volume content of particles smaller than it also accounts for 50% of the total particles.
  • the volume median particle size of the primary particles mentioned in the present application can be counted according to the following method: under a scanning electron microscope (SEM), choose a field of view containing tens to 100 crystal particles, find the The third largest grain (because the largest grain may be an abnormal grain, so choose the third largest grain with a lower possibility of abnormality), use the circumcircle of its shape as an approximation, and record the diameter of its circumscribed circle as Drd , use the same method to count grains with a circumscribed circle diameter ⁇ 0.1Drd, and count the volume median particle diameter dv50, which is also referred to as the grain size in this application.
  • the volume median particle size of the spinel-type lithium nickel manganese oxide material of the present application can be measured in the same manner.
  • the spinel lithium nickel manganese oxide material in this application can be polycrystalline, single crystal or single crystal, and in some optional embodiments of the present application, the spinel lithium nickel manganese oxide material is a single crystal or monocrystalline material.
  • the basis for defining single crystal, quasi-single crystal and polycrystal in this application is Dv50 of spinel-type lithium nickel manganese oxide material/primary particle dv50. The value between 1 and 2 is defined as single crystal, and 2 to 3 is defined as quasi-single crystal. Crystalline, 3 or more are defined as polycrystalline.
  • the primary particle morphology of the spinel-type lithium nickel manganese oxide material is octahedron or polyhedron, for example, octahedral polyhedron is tapered and truncated.
  • the surfaces of octahedron crystal grains are all (111) faces, and the surfaces of polyhedrons after octahedrons are sharpened and edged are (111), (100), (112), etc.
  • These low-index crystal faces have low surface energy and stable crystal faces. , can further suppress the dissolution of transition metal ions (mainly Mn 3+ ions, including a small amount of nickel ions). And other shapes, such as flake, equiaxed, massive and other irregular shapes are more prone to Mn dissolution.
  • transition metal ions mainly Mn 3+ ions, including a small amount of nickel ions.
  • other shapes such as flake, equiaxed, massive and other irregular shapes are more prone to Mn dissolution.
  • the molar ratio of Ni atoms and their positional doping atoms to Mn atoms and their positional doping atoms in the spinel lithium nickel manganese oxide material is greater than or equal to 1:3.
  • the inventors have found that when the content of Mn atoms exceeds 3 times that of Ni atoms, excess Mn can only exist as Mn 3+ . Therefore, when the molar ratio of Ni atoms and their position doping atoms to Mn atoms and their position doping atoms is greater than When it is equal to 1:3, it is beneficial to further reduce the content of Mn 3+ in the material, reduce the gas production of the battery, and improve the cycle performance of the battery.
  • the Ni atom and its position doping atom can be understood as Ni atom and the doping atom replacing the Ni atom position
  • the Mn atom and its position doping atom can be understood as the Mn atom and the doping atom replacing the Mn atom position. atom.
  • the positive electrode active material further includes a surface modification layer, the surface modification layer covers at least part of the surface of the spinel-type lithium nickel manganese oxide material, and the material of the surface modification layer At least one selected from the oxides of Ti, Zr, W, Al, B, P or Mo.
  • the material of the surface modification layer is selected from titanium oxide, zirconium oxide, tungsten oxide, aluminum oxide, oxide At least one of boron, phosphorus oxide, and molybdenum oxide.
  • the inventors have found that in the spinel-type lithium nickel manganese oxide material of the present application, during the Li + deintercalation process, the probability of positional movement and exchange between Ni and Mn atoms increases, and during the charge and discharge process, there will be a part of Mn 4 + gradually transforms into Mn 3+ .
  • the existence of the surface modification layer allows Li + to be preferentially transported through the fast ion conductor formed by it, which reduces the probability of Ni and Mn position exchange while improving the ion conductivity, further reduces the dissolution of Mn 3+ , and thus reduces the output of the battery. Gas volume and improve the cycle performance of the battery.
  • the content of the surface modification layer is less than 3%. At this time, it is beneficial to reduce the dissolution of transition metal ions, especially the dissolution of Mn3 + , thereby reducing the gas production of the battery and improving the cycle performance of the battery. Further, when the content of the surface modification layer is less than 3%, it will not be significantly reduced. The capacity of the battery increases the interface impedance.
  • the button-type half-battery is prepared with the positive electrode active material, and the charging capacity of 3.5V-4.4V accounts for less than or equal to 2% of the charging capacity of 3.5V-4.9V during 0.01C-0.2C charging and discharging. Further explanation
  • the positive electrode active material of the present application has lower Mn 3+ content, and the secondary battery prepared by using the positive electrode active material has lower gas production and better cycle performance.
  • the second aspect of the present application provides a method for preparing a positive electrode active material, which includes the following steps:
  • the spinel lithium nickel manganese oxide material has the following chemical formula: Li a Ni 0.5-x Mn 1.5-y M x+y O 4 , wherein M is selected from Mg, Zn, Ti, Zr, W, At least one of Nb, Al, B, P, Mo, V, Cr, 0.9 ⁇ a ⁇ 1.1, -0.2 ⁇ x ⁇ 0.2, -0.02 ⁇ y ⁇ 0.3, x+y ⁇ 0;
  • the content of Mn 3+ in the spinel lithium nickel manganese oxide material is less than or equal to 0.7wt%.
  • the spinel-type lithium nickel manganese oxide material prepared by the method of the present application can be directly used as a positive electrode active material.
  • the P4 3 32 structure belongs to the low-temperature phase. If a high-content P4 3 32 structure is to be obtained, it needs to be kept at low temperature for a long time, but this is not conducive to the growth of grains, and the material often basically maintains the shape of the precursor.
  • the solid density and compaction density are low, the specific surface area is large, there are many fine powders, and the surface of the grain is difficult to grow into a stable crystal plane; in order to promote the growth of the grain, the tap density and the compaction density are increased to promote the formation of a stable grain surface.
  • a specific slow cooling method can be used to obtain a spinel-type lithium nickel manganese oxide material with a high P4 3 32 structure content, so that the Mn 3+ content is less than or equal to 0.7wt%. Furthermore, after the high-temperature sintering of the present application, the specific preparation method of slow cooling method is adopted, which will not affect the growth of crystal grains, and can obtain primary particles with a larger size, so that the obtained spinel lithium nickel manganese oxide
  • the material has higher tap density and compaction density, lower specific surface area and fine powder content, and when used as a positive electrode active material, it is beneficial to further improve the cycle performance of the battery.
  • the high-temperature sintering temperature and holding time affect the upper limit and average value of the primary particle size, and the high-temperature sintering temperature is also the driving force for grain growth and deformation. If the sintering temperature is too high and the holding time is too long, primary particles tend to aggregate; The applied sintering temperature combined with the holding time can obtain primary particles with a grain size greater than 0.5 ⁇ m; however, if the sintering temperature is too low, the grains tend to maintain the shape of the precursor, making it difficult to obtain grains with octahedral or polyhedral shapes. However, with the sintering temperature of the present application, it is easy to obtain crystal grains with octahedral or polyhedral morphology, without excessive dependence on the morphology of the precursor.
  • single crystals can also be prepared by crushing and reheating after high-temperature sintering, it will add additional process steps and damage the surface of the crystal grains.
  • the optional implementation method of this application is: first determine the target grain size dv50(C) of the finished product, and then select a volume median particle size of 0.3-2.2dv50(C ) nickel source and manganese source, mixed with lithium source, and then select the sintering temperature and time matching dv50 (C) for heat treatment.
  • single crystals can also be prepared by crushing and then heat-treating after high-temperature sintering.
  • the temperature is lowered to a certain temperature by slow cooling, so that the Fd-3m structure is transformed into a P4 3 32 structure, thereby obtaining a high content P4 3 32 structure, in this application, the temperature that needs to be cooled slowly is called the lower limit temperature, and the lower limit temperature in this application is 400°C-650°C; after cooling to the lower limit temperature, step (4) continues to cool down
  • the process of cooling to room temperature may still adopt the method of slow temperature reduction in this application, or natural cooling or furnace cooling may be used, which is not limited in this application.
  • the cooling rate of natural cooling in this application is well known in the art, for example, at 700-1000°C, the cooling rate is about 10°C/min; at 300-700°C, the cooling rate is about 5-6°C/min, etc. This is not limited.
  • the average cooling rate of medium and slow cooling is ⁇ 0.7°C/min, and 0.2-0.7°C/min is optional.
  • the average temperature drop rate can be understood as the ratio of the total temperature difference from the high temperature sintering temperature to the total time until the temperature drops below the lower limit temperature. It can be understood that cooling below the lower limit temperature means that when the temperature is kept at the lower limit temperature, the holding time is included in the total time, and when the temperature is lower than the lower limit temperature, the holding time is not included in the total time.
  • the form of slow cooling described in this application may include continuous slow cooling and/or step cooling, with an average cooling rate ⁇ 0.7°C/min; the step cooling can be understood as setting a heat preservation section after cooling to a certain temperature, including every cooling Set a heat preservation section at 50°C-200°C, and the heat preservation time is 1 ⁇ 30h.
  • the lithium source is selected from but not limited to at least one of lithium-containing carbonates, hydroxides, nitrates, oxides, etc.
  • the nickel source is selected from but not limited to lithium-containing At least one of nickel oxides, hydroxides, carbonates, oxalates, nitrates, etc.
  • the manganese source is selected from but not limited to manganese-containing oxides, hydroxides, carbonates, oxalic acid at least one of salt, nitrate, and the like.
  • the lithium source, nickel source and manganese source can be weighed according to the stoichiometric ratio of each element in the desired lithium nickel manganese oxide product. This is a well-known means in the art, and this application does not make a limitation here.
  • the nickel source, manganese source, lithium source, etc. may come from the same compound or from different compounds.
  • the nickel source and the manganese source can be directly mixed with the lithium source, or the soluble nickel source and the soluble manganese source can be formed by coprecipitation to form nickel manganese hydroxide, nickel manganese carbonate, nickel manganese oxide, etc., and then Mixing with a lithium source, the co-precipitation and other methods are commonly used methods in the art to prepare nickel-manganese hydroxides.
  • nickel-manganese sulfate solution and NaOH alkali solution can be reacted under specific pH, temperature and ammonia concentration conditions to form spherical
  • the nickel-manganese hydroxide secondary particles are not limited in this application.
  • the "soluble" means that the corresponding nickel source and manganese source are soluble in water, dilute acid or organic solvents such as alcohols or ethers.
  • the inventors also found that the smaller the particles of the nickel source and the manganese source, the greater the activity, which will easily lead to serious adhesion between particles in the finished product during the sintering process, making it difficult to obtain a single crystal form.
  • the particles of the nickel source and the manganese source are too large, it will be difficult to burn through, and the sintering temperature will need to be increased, resulting in adhesion between the particles.
  • the volume median particle size of the primary particles of the spinel lithium nickel manganese oxide material can be understood as the target grain size of the primary particles. If the nickel source and the manganese source use this particle size range, it is easier to obtain a spinel-type lithium nickel manganese oxide material with a single crystal or quasi-single crystal state by sintering.
  • the nickel-manganese precursors such as nickel-manganese hydroxide, nickel-manganese carbonate, nickel-manganese oxide, etc. by co-precipitation
  • the "target volume median particle size” or “target grain size” can be understood as the volume median particle size or grain size of the expected primary particles, because the spinel obtained by the method of the present application
  • the grain size of the primary particles of the stone-type lithium nickel manganese oxide material is almost the same as the expected grain size, so in this application, it can be understood as the “target volume median particle size” or “target grain size” and the obtained The volume median diameter of the primary particles is the same.
  • the molar ratio of the nickel source to the manganese source is greater than or equal to 1:3; the spinel lithium nickel manganese oxide material obtained in this range is easier to achieve Ni atom and position doping
  • the ratio of atoms to Mn atoms and their positional doping atoms is greater than or equal to 1:3, so as to obtain a spinel-type lithium nickel manganese oxide material with lower Mn 3+ content.
  • the function of the additive is to add doping elements to the lithium nickel manganese oxide, and the dosage of the additive is determined according to the elemental stoichiometric ratio of the doped lithium nickel manganese oxide, and the present application does not repeat them here.
  • the inventors also found that the type and amount of additives will affect the phase transition temperature and atomic diffusion of the mixed material, and then affect the grain growth. Low-melting-point additives will melt at high temperatures to bond the grains into large pieces, while additives with too high melting point or too low chemical activity will inhibit the migration of grain boundaries and inhibit the growth of grains.
  • the additive is at least one selected from the oxides, hydroxides, nitrates, carbonates or ammonium salts of Mg, Zn, Ti, Zr, W, Nb, Al, B, P, Mo, V or Cr ,
  • the additive is selected from at least one of magnesium oxide, zinc oxide, titanium oxide, zirconium oxide, tungsten oxide, niobium oxide, aluminum oxide, boric acid, ammonium dihydrogen phosphate, molybdenum oxide, vanadium oxide or chromium oxide kind.
  • the inventors also found in the research that increasing the oxygen concentration in the sintering atmosphere is beneficial to obtain a higher-purity P4 3 32 structure, thereby obtaining a positive electrode active material with a lower Mn 3+ content.
  • the high-temperature sintering atmosphere is oxygen.
  • the surface modification process can be interspersed in a slow temperature drop process according to specific conditions, for example, in step (3), the temperature is slowly dropped from the high temperature sintering temperature to the surface modification layer. temperature, and then naturally cooled to room temperature, after the surface modification treatment, the temperature was raised to the surface modification temperature, kept for a period of time, such as 3-30h, and then continued to slowly cool down to 400°C-650°C, and finally naturally cooled to room temperature.
  • the surface modification temperature is related to the type of surface modification. Those skilled in the art can select a specific surface modification temperature according to the selected surface modification. This application is not limited here. For example, when aluminum oxide is selected as For surface modifiers, the surface modification temperature can be selected at about 650°C, and when boron oxide is selected as the surface modifier, the surface modification temperature is about 500°C.
  • the surface modifier is selected from at least one of oxides of Ti, Zr, W, Al, B, P or Mo. In some optional embodiments of the present application, the surface modifier is at least one selected from titanium oxide, zirconium oxide, tungsten oxide, aluminum oxide, boric acid, ammonium dihydrogen phosphate, and molybdenum oxide.
  • step (3) includes the following steps:
  • the present application does not limit the cooling process from the surface modification temperature to room temperature, for example, the slow cooling method of the present application, or the natural cooling method can be used to realize it.
  • the lower limit temperature 400°C-650°C
  • the holding time at the surface modification temperature and the cooling time between the surface modification temperature and the lower limit temperature will be included in the total cooling time. Time; if the surface modification temperature is lower than the lower limit temperature, the surface modification time will not be included in the total cooling time.
  • the ordering heat treatment temperature should not be too low, otherwise grains with satisfactory grain size and morphology cannot be obtained. From the perspective of actual production, it is impossible to keep heat indefinitely in orderly heat treatment. Therefore, the ordering heat treatment temperature should be moderate, and should also match the target grain size and high-temperature sintering temperature and time. The higher the high-temperature sintering temperature, the higher the Fd-3m content, and the longer the ordering heat treatment holding time. The larger the crystal grains, the greater the diffusion power is required, and the higher the ordering heat treatment temperature is. The ordering heat treatment temperature also affects the ordering heat treatment time.
  • a secondary battery is provided.
  • a secondary battery typically includes a positive pole piece, a negative pole piece, an electrolyte, and a separator.
  • active ions are intercalated and extracted back and forth between the positive electrode and the negative electrode.
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the separator is arranged between the positive pole piece and the negative pole piece, which mainly plays a role in preventing the short circuit of the positive and negative poles, and at the same time allows ions to pass through.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.
  • the positive electrode film layer includes the positive electrode active material of the first aspect of the application or the positive electrode active material prepared according to the method of the second aspect of the application. Material.
  • the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposing surfaces of the positive electrode current collector.
  • the positive electrode current collector can be a metal foil or a composite current collector.
  • aluminum foil can be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the composite current collector can be formed by forming metal materials (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalic acid It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene glycol ester
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the positive electrode film layer may further optionally include a binder.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • the positive electrode film layer may also optionally include a conductive agent.
  • the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode sheet can be prepared in the following manner: the above-mentioned components used to prepare the positive electrode sheet, such as positive electrode active material, conductive agent, 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 current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.
  • a solvent such as N -methylpyrrolidone
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposing surfaces of the negative electrode current collector.
  • the negative electrode current collector can use a metal foil or a composite current collector.
  • copper foil can be used as the metal foil.
  • the composite current collector may include a base layer of polymer material and a metal layer formed on at least one surface of the base material of polymer material.
  • Composite current collectors can be formed by metal materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyethylene terephthalic acid It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • the negative electrode active material can be a negative electrode active material known in the art for batteries.
  • the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and the like.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.
  • the tin-based material may be selected from at least one of simple tin, tin oxide compounds and tin alloys.
  • the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials of batteries can also be used. These negative electrode active materials may be used alone or in combination of two or more.
  • the negative electrode film layer may further optionally include a binder.
  • the binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer may also optionally include a conductive agent.
  • the conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer may optionally include other additives, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • CMC-Na sodium carboxymethylcellulose
  • the negative electrode sheet can be prepared in the following manner: the above-mentioned components used to prepare the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.
  • a solvent such as deionized water
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the present application has no specific limitation on the type of electrolyte, which can be selected according to requirements.
  • electrolytes can be liquid, gel or all solid.
  • the electrolyte is an electrolytic solution.
  • the electrolyte solution includes an electrolyte salt and a solvent.
  • the electrolyte salt may be selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium difluorooxalate borate, lithium difluorodifluorooxalatephosphate and lithium tetrafluorooxalatephosphate.
  • the solvent may be selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte may optionally include additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performances of the battery, such as additives that improve battery overcharge performance, additives that improve high-temperature or low-temperature performance of batteries, and the like.
  • a separator is further included in the secondary battery.
  • the present application has no particular limitation on the type of the isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.
  • the material of the isolation film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, and there is no particular limitation.
  • the positive pole piece, the negative pole piece and the separator can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer package.
  • the outer package can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard case, such as a hard plastic case, aluminum case, steel case, and the like.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.
  • FIG. 1 shows a square-shaped secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity.
  • the housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to close the accommodating cavity.
  • the positive pole piece, the negative pole piece and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the accommodating chamber. Electrolyte 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.
  • the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.
  • FIG. 3 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 may be fixed by fasteners.
  • the battery module 4 may also include a case having a housing space in which a plurality of secondary batteries 5 are accommodated.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.
  • 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 , the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electric device, which 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 of the electric device, and can also be used as an energy storage unit of the electric device.
  • the electric devices may include mobile devices (such as mobile phones, notebook computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, etc.) , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but not limited thereto.
  • a secondary battery, a battery module or a battery pack can be selected according to its use requirements.
  • FIG. 6 is an example of an electrical device.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • a battery pack or a battery module may be used.
  • a device may be a cell phone, tablet, laptop, or the like.
  • the device is generally required to be light and thin, and a secondary battery can be used as a power source.
  • lithium source lithium carbonate
  • the mixture was heated up to 850°C, kept at this temperature for 30 hours, and sintered at a high temperature in an air sintering atmosphere, then slowly cooled to 650°C (lower limit temperature) at a cooling rate of 0.5°C/min, and then cooled to room temperature with the furnace to obtain Crystalline Li 1.01 Ni 0.51 Mn 1.49 O 4 cathode active material.
  • Examples 2-15 were the same as Example 1, except that the corresponding preparation parameters were adjusted according to Table 1, and a positive electrode active material comprising single crystal or quasi-single crystal Li 1.01 Ni 0.51 Mn 1.49 O 4 was obtained.
  • the lithium source lithium carbonate
  • the lithium source lithium carbonate
  • Example 4 Except that the source of nickel and manganese is adjusted to be nickel oxide and manganese oxide according to Table 1, the rest of Example 4 is the same.
  • the lithium source lithium carbonate
  • the lithium source lithium carbonate
  • the lithium source lithium carbonate
  • Heat the mixture to 970°C, keep it warm for 10 hours, sinter at high temperature in an air sintering atmosphere, cool to room temperature naturally, raise the temperature to 640°C for annealing, keep it for 15 hours, and then cool with the furnace to obtain the product.
  • lithium source lithium carbonate
  • the mixture was heated up to 600°C, kept for 100 hours, sintered at a high temperature in an air sintering atmosphere, and then cooled to room temperature with the furnace to obtain a positive electrode active material containing polycrystalline Li 1.01 Ni 0.51 Mn 1.49 O 4 .
  • the temperature is lowered to 650° C. at a cooling rate of 1° C./min after high-temperature sintering, and then cooled to room temperature with the furnace, and the rest is the same as that of Example 4.
  • the temperature is lowered at a cooling rate of 3°C/min.
  • the temperature drops to 870°C and 770°C respectively, it is kept for 1 hour.
  • the temperature drops to 650°C, it is kept for 3 hours, and the room temperature is cooled with the furnace. 4 is the same.
  • a Mastersizer 3000 laser particle size analyzer was used to measure the volume median particle size Dv50 of the spinel lithium nickel manganese oxide material prepared in each example and comparative example.
  • JY/T010-1996 use a field emission scanning electron microscope (Zeiss Sigma300) to observe the grain shape of the spinel-type lithium nickel manganese oxide material, and use the circumscribed ellipsoid of the outline of the primary particle (grain) to approximate the grain statistics.
  • the volume distribution of grain size, and record the grain size the specific statistical method is: choose a photo containing dozens to one hundred grains under SEM, find the third largest grain (avoid the largest and second largest grains) Abnormal grains), the diameter of its circumscribed circle is recorded as Drd, only the grain size ⁇ 0.1Drd is counted, and the volume median grain size dv50 is calculated, which is the grain size.
  • the photomicrograph (SEM) of the positive electrode active material of Example 1 is shown in Figure 7A and Figure 7B
  • the SEM photos of the positive electrode active material of Embodiment 4, 13, and 16 are shown in Figure 8- Figure 10 respectively, for
  • the SEM photos of the positive electrode active material of Example 2 are shown in FIG. 11A and FIG. 11B
  • the SEM photos of the positive electrode active material of Comparative Example 3 are shown in FIGS. 12A and 12B .
  • the positive electrode active material of embodiment 1 is a polycrystalline material
  • the positive electrode active material of embodiment 4, 13, 16 is a single crystal, a single crystal material
  • the crystal grains in each embodiment are octahedral or The octahedral polyhedron is sharpened and edged, and the grains have a large average diameter, and the average diameter of the grains is ⁇ 0.5 ⁇ m.
  • the positive electrode active material in Comparative Example 2 has irregular crystal grains
  • the positive electrode active material in Comparative Example 3 is polycrystalline with flaky crystal grains, and the average diameter of the crystal grains is relatively small.
  • the positive electrode active materials obtained in the foregoing Examples 1-24 and Comparative Examples 1-6 were prepared into button-type half batteries, and performance tests were performed.
  • the positive electrode active material prepared in each example and comparative example was mixed with conductive carbon black and PVDF at a weight ratio of 90:5:5, an appropriate amount of N-methylpyrrolidone was added, and the mixture was evenly stirred to obtain a positive electrode slurry.
  • the positive electrode slurry is coated on the aluminum foil, and then dried to obtain the positive electrode sheet.
  • the loading capacity of the positive electrode active material on the positive electrode sheet is 0.015 g/cm 2 .
  • a mixed solution of carbonate, phosphate, etc. containing 1mol/L LiPF 6 is used as the electrolyte.
  • a polypropylene film ( ⁇ 16mm) with a thickness of 12 ⁇ m is used as a separator, and the lithium sheet, separator, and positive electrode sheet are placed in order, so that the separator is placed between the metal lithium sheet and the composite negative electrode sheet to play the role of isolation. Inject the electrolyte, assemble it into a CR2030 button cell, and let it stand for 24 hours to obtain a button half cell.
  • Li/Me 0.5, where Me represents transition metal atoms or ions, that is, atoms and ions other than Li and oxygen; and a Mn 3+
  • the charging and discharging process of /Mn 4+ corresponds to the deintercalation of a Li + ; because the charging voltage range of Mn 3+ /Mn 4+ is 4.4 ⁇ 3.5V (mainly concentrated around 4.0V), Ni 4+ /Ni 3+ , The price change voltage of Ni 3+ /Ni 2+ is between 4.8 and 4.5V, so the 4V platform is generally recognized as coming from Mn 3+ /Mn 4+ , so the deintercalation amount of Li + on the 4V platform is Mn 3+ /Mn 4+ The amount (that is, the amount of Mn 3+ in the material in the fully intercalated lithium state), and the remaining Mn is stable Mn 4+ .
  • 4V platform charging capacity ratio x Q1/Q2, in view of the fact that the battery may not be activated in the first lap, and the second lap may be affected by the discharge of the first lap, so this application x takes the average of the 4V platform charging capacity ratio of the first two laps value.
  • Table 2 shows the physical and chemical parameters of the positive electrode active materials in Examples 1-24 and Comparative Examples 1-6, and Table 3 shows the statistical results of the button half-cell.
  • the positive electrode active materials prepared in each example and comparative example were mixed with conductive carbon black and PVDF at a weight ratio of 96:2.5:1.5, and an appropriate amount of N-methylpyrrolidone was added, and stirred evenly to obtain positive electrode slurry.
  • the positive electrode slurry is coated on the aluminum foil, and then dried to obtain the positive electrode sheet.
  • the loading capacity of the positive electrode active material on the positive electrode sheet is 0.02 g/cm 2 .
  • a mixed solution of carbonate and phosphate containing 1mol/L LiPF 6 was used as the electrolyte.
  • Electrolyte solution is injected, and after packaging, it is formed into a capacity to obtain a secondary battery.
  • the target value of the positive electrode gram capacity of single-crystal nickel-manganese spinel/graphite soft-pack batteries is 130mAh/g, and 80% of it is 104mAh/g, which is more intuitive than the 80% of the capacity of each material. Reflect the overall capacity performance of the entire cycle, not just the cycle life. See Table 4 for the statistical results.
  • the fully discharged battery was disassembled, the negative electrode piece was separated, and the negative electrode piece was slightly shaken in dimethyl carbonate (DMC) solvent for 5 seconds to remove the residual electrolyte on the surface of the negative electrode, and then dried.
  • DMC dimethyl carbonate
  • the negative electrode material was scraped off from the surface of the negative electrode sheet, and the Ni content ( ⁇ g/g or ppm) and the Mn content ( ⁇ g/g or ppm) in the negative electrode material were detected by inductively coupled plasma spectroscopy.
  • the test results of gas production and ion dissolution are shown in Table 4.
  • the content of Mn in the positive electrode active materials of Examples 1 to 24 of the present application is lower than 0.7%, and further, the grain size of the positive electrode active materials of the present application is greater than 0.5 ⁇ m, optionally Greater than or equal to 2 ⁇ m.
  • the morphology of the positive electrode active material grains of the present application is octahedral or polyhedral with octahedrons sharpened and edges removed.
  • the slower the cooling rate the lower the mass content of Mn 3+ .
  • the cooling rate is lower than 0.7°C/min, positive electrode active materials with a mass content of Mn 3+ lower than 0.7% can be obtained; however, if the cooling rate is too slow, the production process will take a long time and consume a lot of energy, which is not conducive to reducing production costs. Therefore, in this application, the average cooling rate of slow cooling can be selected as 0.2-0.7° C./min.
  • Example 4 According to Example 4 and Example 11, it can be seen that increasing the content of oxygen in the sintering atmosphere is beneficial to obtain positive electrode active materials with lower Mn 3+ content.
  • Example 4 the charging and discharging first cycle curves of Example 4, Example 11 and Comparative Example 2 are shown in Figure 13. It can be seen from Figure 13 that the 4V platform of Example 4 is obviously narrower than the 4V platform of Comparative Example 2, It shows that Example 4 of the present application has a lower Mn 3+ content; while the 4V platform of Example 11 is not visible, indicating that the lithium nickel manganese oxide of Example 11 has a lower Mn 3+ content.
  • Examples 23 and 24 illustrate that the positive electrode active material of the present application can also be obtained by adopting the stepwise cooling method of the present application.
  • comparative examples 1 and 2 adopt the existing method of annealing after cooling to prepare spinel lithium nickel manganese oxide with high P4 3 32 content, which still has a relatively high Mn 3+ content, such as higher than 0.8wt%;
  • comparative example 3 adopts the method of low-temperature sintering, and the content of Mn 3+ in the lithium nickel manganese oxide obtained is relatively low, but still cannot reach less than 0.7%, and adopts the method of low-temperature sintering, the obtained nickel Lithium manganate is a flaky polycrystalline structure. It can also be seen from the performance data in Table 4 that although its Mn content is low, its manganese dissolution rate is high and its cycle performance is low. It is not limited to any theory.
  • the positive electrode active material of the present application is applied to secondary batteries, and it has less dissolution of transition metal ions, better cycle performance, and smaller gas production than the comparative examples; further, it has a single Compared with the positive electrode active material with polycrystalline structure, the positive electrode active material with crystal or single crystal structure has further reduced transition metal ion dissolution, gas production, and improved cycle performance; it can also be seen from the various embodiments of the present application that, Along with the reduction of Mn 3+ content, battery cycle performance is improved; In addition, according to embodiment 4 and embodiment 18-embodiment 20 can find out, when the surface modification layer is included in the positive electrode active material, the transition metal of battery Ion dissolution and gas production are further reduced, and the cycle performance is further improved.
  • the inventors have also found that single crystal or single crystal-like positive electrode active materials with small particle sizes are beneficial to the improvement of the first cycle discharge capacity of secondary batteries, and single crystal or single crystal-like positive electrode active materials with large particle sizes are conducive to the dissolution of manganese , the reduction of gas production and the improvement of battery cycle performance, so the volume median particle size of the primary particles of the optional spinel lithium nickel manganese oxide material in this application is 2 ⁇ m to 10 ⁇ m.
  • the present application is not limited to the above-mentioned embodiments.
  • the above-mentioned embodiments are merely examples, and within the scope of the technical solutions of the present application, embodiments that have substantially the same configuration as the technical idea and exert the same effects are included in the technical scope of the present application.
  • various modifications conceivable by those skilled in the art are added to the embodiments, and other forms constructed by combining some components in the embodiments are also included in the scope of the present application. .

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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和应用，所述正极活性材料包括尖晶石型镍锰酸锂材料，所述尖晶石型镍锰酸锂材料具有如下的化学式：Li aNi 0.5-xMn 1.5-yM x+yO 4，其中，M选自Mg、Zn、Ti、Zr、W、Nb、Al、B、P、Mo、V、Cr中的至少一种，0.9≤a≤1.1，-0.2≤x≤0.2，-0.02≤y≤0.3，x+y≥0；所述尖晶石型镍锰酸锂材料中Mn 3+的含量小于等于0.7wt％。

Description

一种正极活性材料及其制备方法和应用 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和应用。
背景技术
镍锰酸锂材料(LNMO)具有高达4.7V(vs.Li/Li +)的放电平台，是低成本高能量密度正极活性材料的首选。然而LNMO用于石墨全电池中时，其中的过渡金属(主要是Mn)离子溶出，扩散到负极表面沉积，阻碍Li +在石墨中的脱嵌，使得石墨负极的可逆容量急速下降。在LNMO/石墨全电池中，负极石墨的容量衰减是最多的，远远超过正极和电解质的活性消耗。
现有技术在减缓Mn溶出方面主要包括：掺杂稳定结构、包覆隔离接触、控制晶粒表面晶面、退火处理等，这些方法的最终目的主要还是阻断Mn 3+从LNMO中溶出的途径，如何从源头上减少Mn 3+含量是本申请要解决的问题。
发明内容
本申请是鉴于上述课题而进行的，其目的在于降低正极活性材料中的Mn 3+含量，从源头上减少锰溶出。
为了达到上述目的，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。
本申请的第一方面提供了一种正极活性材料，其包括尖晶石型镍锰酸锂材料，所述尖晶石型镍锰酸锂材料具有如下的化学式：Li aNi 0.5-xMn 1.5-yM x+yO 4，其中，M选自Mg、Zn、Ti、Zr、W、Nb、Al、B、P、Mo、V、Cr中的至少一种，0.9≤a≤1.1，-0.2≤x≤0.2，-0.02≤y≤0.3，x+y≥0；
所述尖晶石型镍锰酸锂材料中Mn 3+的含量小于等于0.7wt％。
由此，本申请提供了一种具有更低Mn 3+的含量的正极活性材料，从源头上减少了锰溶出，进而减少了电池的产气量以及提高电池的循环性能。
在任意实施方式中，所述尖晶石型镍锰酸锂材料的一次颗粒的体积中值粒径为0.5μm至16μm，可选为2μm至10μm。
尖晶石型镍锰酸锂材料一次颗粒的体积中值粒径在0.5μm至16μm，可选为2μm至10μm时，有利于降低材料的比表面积和微粉量，进一步提高了电池的循环性能，同时保 证极片的加工性能。
在任意实施方式中，所述尖晶石型镍锰酸锂材料为类单晶或单晶材料，发明人发现，采用所述类单晶或单晶材料作为正极活性材料时，过渡金属离子溶出更少、循环性能更优、产气更小。
在任意实施方式中，所述尖晶石型镍锰酸锂材料的体积中值粒径为2μm至24μm，可选为5μm至17μm。发明人发现，所述尖晶石型镍锰酸锂材料的体积中值粒径在所述范围内时，过渡金属离子溶出更少、循环性能更优、产气更小。
在任意实施方式中，所述尖晶石型镍锰酸锂材料的一次颗粒形貌为八面体或多面体。其具有低指数晶面，晶面表面能低，晶面稳定，可以有效抑制过渡金属离子(尤其Mn离子)溶出。
在任意实施方式中，所述尖晶石型镍锰酸锂材料中Ni原子及其位置掺杂原子与Mn原子及其位置掺杂原子的摩尔比大于等于1:3，此时更少的锰离子以三价Mn 3+形式存在。
在任意实施方式中，所述正极活性材料还包括表面修饰层，所述表面修饰层包覆所述尖晶石型镍锰酸锂材料的至少部分表面，所述表面修饰层的材料选自Ti、Zr、W、Al、B、P或Mo的氧化物中的至少一种。表面修饰层的存在可以进一步降低渡金属离子(尤其Mn离子)Mn 3+溶出，进而减少了电池的产气量以及提高电池的循环性能。
在任意实施方式中，基于所述正极活性材料的总重量，所述表面修饰层的含量小于3％。此时，有利于降低渡金属离子(尤其Mn 3+)溶出，进而减少电池的产气量以及提高电池的循环性能，还不会明显降低电池的容量、增加界面阻抗。
在任意实施方式中，以所述正极活性材料制备扣式半电池，0.01C～0.2C充放电中，3.5V～4.4V的充电容量占3.5V～4.9V充电容量的比例小于等于2％，说明本申请的正极活性材料中存在更低含量的Mn 3+，进而使用所述正极活性材料制备的二次电池具有更低的产气量和更优的循环性能。
本申请的第二方面还提供一种正极活性材料的制备方法，其包括以下步骤：
(1)提供锂源、镍源、锰源，以及任选的添加剂，球磨混粉；
(2)高温烧结：在空气、氧气或其混合气体气氛中，升温至850～1150℃保温2～50h；
(3)自高温烧结温度缓慢降温至400℃-650℃，其中，所述缓慢降温的平均降温速率≤0.7℃/min；
(4)冷却至室温，获得尖晶石型镍锰酸锂材料；
其中，所述尖晶石型镍锰酸锂材料具有如下的化学式：Li aNi 0.5-xMn 1.5-yM x+yO 4，其中，M选自Mg、Zn、Ti、Zr、W、Nb、Al、B、P、Mo、V、Cr中的至少一种，0.9≤a≤1.1，-0.2≤x≤0.2，-0.02≤y≤0.3，x+y≥0；
所述尖晶石型镍锰酸锂材料中Mn 3+的含量小于等于0.7wt％。
本申请的制备方法中，在高温烧结后，采用特定的缓慢降温的方式，获得的正极活性材料，具有更低的Mn 3+含量。
本申请的第三方面提供一种二次电池，包括本申请第一方面的正极活性材料或根据本申请第二方面的方法制备的正极活性材料。
本申请的第四方面提供一种电池模块，包括本申请的第三方面的二次电池。
本申请的第五方面提供一种电池包，包括本申请的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，包括选自本申请的第三方面的二次电池、本申请的第四方面的电池模块或本申请的第五方面的电池包中的至少一种。
本申请的有益效果：
本申请提供的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，正极活性材料中的尖晶石型镍锰酸锂材料的Mn 3+的含量小于等于0.7wt％，从源头降低了材料中Mn 3+的含量，有效减少锰溶出，降低电池的产气量，进而提高了电池的循环性能。
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。
图7A和图7B是实施例1的正极活性材料的显微电镜(SEM)照片，其中图7B为图7A的局部放大图。
图8是实施例4的正极活性材料的显微电镜照片。
图9是实施例13的正极活性材料的显微电镜照片。
图10是实施例16的正极活性材料的显微电镜照片。
图11A和图11B是对比例2的正极活性材料的显微电镜照片，其中图11B为图11A的局部放大图。
图12A和图12B是对比例3的正极活性材料的显微电镜照片，其中图12B为图12A的局部放大图。
图13是实施例4、11及对比例2的扣电充放电首圈曲线。
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、电池包和电学装置的实施方式。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，可选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
本申请人在研究锂电池的正极活性材料的过程中发现，尖晶石型镍锰酸锂材料中含有的Mn 3+在服役过程中，发生歧化反应生成Mn 2+溶解到电解液中，扩散到负极影响负极表面结构，使石墨负极容量大大下降。为了减少Mn 3+溶出，提高电池循环性能，本申请提供了一种正极活性材料。
本申请的一个实施方式中，本申请提出了一种正极活性材料，其包括尖晶石型镍锰酸锂材料，所述尖晶石型镍锰酸锂材料具有如下的化学式：Li aNi 0.5-xMn 1.5-yM x+yO 4，其中，M选自Mg、Zn、Ti、Zr、W、Nb、Al、B、P、Mo、V、Cr中的至少一种，0.9≤a≤1.1，-0.2≤x≤0.2，-0.02≤y≤0.3，x+y≥0；
所述尖晶石型镍锰酸锂材料中Mn 3+的含量小于等于0.7wt％。
发明人意外地发现：本申请的尖晶石型镍锰酸锂材料以有序的P4 332结构为主，由于P4 332结构中，其Mn均为Mn 4+，本申请的尖晶石型镍锰酸锂材料具有高的P4 332结构含量，因而材料中Mn 3+的含量更低，Mn 3+的含量小于等于0.7wt％，从源头上降低了正极活性材料Mn 3+的溶出，降低了电池的产气量，提高电池的循环性能。
在本申请的一些实施方式中，所述尖晶石型镍锰酸锂材料的一次颗粒的体积中值粒径(dv50)为0.5μm至16μm。发明人发现，当所述尖晶石型镍锰酸锂材料的一次颗粒具有所述范围的体积中值粒径，其具有更高的振实密度和压实密度、更低的比表面积和微粉量，采用包含所述尖晶石型镍锰酸锂材料的正极活性材料，具有更低的锰溶出、更低的产气量 和更高的循环性能。进一步，发明人还发现，一次颗粒的体积中值粒径增大有利于降低锰溶出，提高电池循环性能，然而粒径过大会引起首圈放电容量的下降，以及造成工艺成本增加、极片加工性能变差等问题，因此在本申请的一些实施方式中，所述尖晶石型镍锰酸锂材料的一次颗粒的体积中值粒径可选为2μm至10μm。
本申请中，所述尖晶石型镍锰酸锂材料的一次颗粒也称为尖晶石型镍锰酸锂材料的晶粒，本申请中也简称为一次颗粒或晶粒。
在本申请的一些实施方式中，所述尖晶石型镍锰酸锂材料的体积中值粒径(Dv50)为2μm至24μm，可选为5μm至17μm。发明人发现，所述尖晶石型镍锰酸锂材料的体积中值粒径在所述范围内时，过渡金属离子溶出更少、产气更小、循环性能更优。
本申请中，“体积中值粒径”、“dv50”、“Dv50”是指材料在体积基准的颗粒分布中，从小粒径测起、达到体积累积50％时所对应的粒径。物理意义是粒径大于它的颗粒体积含量占总颗粒的50％，小于它的颗粒体积含量也占总颗粒的50％。
示例性的，本申请所说的一次颗粒的体积中值粒径可以按如下方法做统计：在扫描电子显微镜(SEM)下任选一个含几十到100个晶体颗粒的视野，找到范围内的第三大晶粒(因为最大的晶粒可能是异常晶粒，所以选择异常的可能性较低的第三大晶粒)，用其外形的外接圆做近似，将其外接圆直径记为Drd，用相同的方法统计外接圆直径≥0.1Drd的晶粒，统计体积中值粒径dv50，本申请中也称为晶粒尺寸。本申请的尖晶石型镍锰酸锂材料的体积中值粒径可采用相同的方式测得。
本申请中的尖晶石型镍锰酸锂材料可以为多晶、类单晶或单晶，在本申请的一些可选的实施方式中，所述尖晶石型镍锰酸锂材料为类单晶或单晶材料。发明人在研究中发现，相比于多晶，具有类单晶和单晶结构的尖晶石型镍锰酸锂材料作为电池的正极活性材料，过渡金属离子溶出更少、循环性能更优、产气更小。本申请定义单晶、类单晶与多晶的依据是尖晶石型镍锰酸锂材料Dv50/一次颗粒dv50，该值在1～2之间定义为单晶，2～3定义为类单晶、3以上定义为多晶。
发明人在研究中发现，过渡金属离子的溶出与晶粒表面稳定性相关，过渡金属离子溶出与晶粒表面原子不断反应消耗关系密切，所以稳定的晶面作为晶粒表面时，过渡金属离子溶出会显著减少。在本申请的一些实施方式中，所述尖晶石型镍锰酸锂材料的一次颗粒形貌为八面体或多面体，例如八面体削尖去棱多面体。其中，八面体晶粒表面均为(111)面，八面体削尖去棱后的多面体表面为(111)、(100)、(112)等，这些低指数晶面表面能 低，晶面稳定，可以进一步抑制过渡金属离子(主要为Mn 3+离子，还包括少量的镍离子)溶出。而其他形貌，例如片状、等轴状、块状及其他不规则外形均更容易发生Mn溶出。
在本申请的一些实施方式中，所述尖晶石型镍锰酸锂材料中Ni原子及其位置掺杂原子与Mn原子及其位置掺杂原子的摩尔比大于等于1:3。发明人发现，当Mn原子含量超过Ni原子的3倍，多余的Mn只能以Mn 3+存在，因此，当Ni原子及其位置掺杂原子与Mn原子及其位置掺杂原子的摩尔比大于等于1:3时，有利于进一步减少材料中Mn 3+的含量，减少电池产气量，提高电池循环性能。
本申请中，所述Ni原子及其位置掺杂原子可以理解为Ni原子及替代Ni原子位置的掺杂原子，Mn原子及其位置掺杂原子可以理解为Mn原子及替代Mn原子位置的掺杂原子。
在本申请的一些实施方式中，所述正极活性材料还包括表面修饰层，所述表面修饰层包覆所述尖晶石型镍锰酸锂材料的至少部分表面，所述表面修饰层的材料选自Ti、Zr、W、Al、B、P或Mo的氧化物中的至少一种，示例性地，所述表面修饰层的材料选自氧化钛、氧化锆、氧化钨、氧化铝、氧化硼、氧化磷、氧化钼中的至少一种。发明人发现，本申请的尖晶石型镍锰酸锂材料中，在Li +脱嵌过程中，Ni和Mn原子发生位置移动交换的概率增大，在充放电过程中，会有一部分Mn 4+逐渐转变为Mn 3+。而表面修饰层的存在使得Li +优先通过其形成的快离子导体传递，在提高离子导电性的同时降低了Ni和Mn位置交换的概率，进一步降低了Mn 3+溶出，进而减少了电池的产气量以及提高电池的循环性能。
在本申请一些实施方式中，基于所述正极活性材料的总重量，所述表面修饰层的含量小于3％。此时，有利于降低过渡金属离子溶出，尤其是Mn 3+的溶出，进而减少电池的产气量以及提高电池的循环性能，进一步地，所述表面修饰层的含量小于3％时不会明显降低电池的容量、增加界面阻抗。
发明人发现，尖晶石镍锰酸锂的有序程度可由扣电充放电曲线衡量，因为该材料中，Ni 4+/Ni 3+，Ni 3+/Ni 2+变价的电压均在4.8～4.5V之间，而Mn 4+/Mn 3+的变价主要发生在4.4V以下、4.0V附近。所以，以包含尖晶石镍锰酸锂的正极活性材料制备扣式半电池，4.4V～3.5V的充放电容量几乎全部来自Mn 3+/Mn 4+。Mn 3+含量越低，扣式半电池中4.4V～3.5V的充放电容量越低，无Mn 3+时，扣电中4.4V～3.5V的充放电容量接近0；在本申请的一些实施方式中，以所述正极活性材料制备扣式半电池，0.01C～0.2C充放电中，3.5V～4.4V的充电容量占3.5V～4.9V充电容量的比例小于等于2％，进一步说明本申请的正极活性材料具有更低的Mn 3+含量，进而使用所述正极活性材料制备的二次电池具有更低的产气量和更优的循 环性能。
本申请第二方面提供了一种正极活性材料的制备方法，其包括以下步骤：
(1)提供锂源、镍源、锰源，以及任选的添加剂，球磨混粉；
(2)高温烧结：在空气、氧气或其混合气体气氛中，升温至850～1150℃保温2～50h；
(3)自高温烧结温度缓慢降温至400℃-650℃，其中，所述缓慢降温的平均降温速率≤0.7℃/min；
(4)冷却至室温，获得尖晶石型镍锰酸锂材料；
其中，所述尖晶石型镍锰酸锂材料具有如下的化学式：Li aNi 0.5-xMn 1.5-yM x+yO 4，其中，M选自Mg、Zn、Ti、Zr、W、Nb、Al、B、P、Mo、V、Cr中的至少一种，0.9≤a≤1.1，-0.2≤x≤0.2，-0.02≤y≤0.3，x+y≥0；
所述尖晶石型镍锰酸锂材料中Mn 3+的含量小于等于0.7wt％。
采用本申请的方法制备的尖晶石型镍锰酸锂材料可以直接用作正极活性材料。
发明人发现，P4 332结构属于低温相，如果要得到高含量P4 332结构，就需要长时间低温保温，但这样不利于晶粒的生长，材料往往还是基本保持前驱体的形貌，振实密度和压实密度低、比表面积大、微粉多、且晶粒表面也很难生长成稳定晶面；而为了促进晶粒生长，提高振实密度和压实密度、促进晶粒表面形成稳定的晶面，就需要高温热处理，这又会导致大量镍锰无序的Fd-3m结构的形成，降低P4 332结构含量，从而使材料中具有较高含量的Mn 3+。现有制备高含量P4 332结构的尖晶石型镍锰酸锂材料，通常采用高温烧结后再在较低温度(通常是600～700℃)退火处理，以得到P4 332含量较高的材料，但获得的材料中仍含有相当量的Fd-3m结构，Mn 3+含量仍然较高。而本申请通过高温烧结后，采用特定的缓慢降温方式，可以获得高P4 332结构含量的尖晶石型镍锰酸锂材料，使其Mn 3+的含量小于等于0.7wt％。更进一步地，本申请的高温烧结后，采用特定的缓慢降温方式的制备方法，不会影响晶粒的生长，能够获得具有较大尺寸的一次颗粒，使获得的尖晶石型镍锰酸锂材料具有更高的振实密度和压实密度、更低的比表面积和微粉量，用作正极活性材料时，有利于进一步提高电池的循环性能。
发明人还发现，高温烧结的温度和保温时间影响一次颗粒尺寸的上限和平均值，高温烧结的温度也是晶粒长大和变形的驱动力。烧结温度过高，保温时间过长，一次颗粒易发生聚集，烧结温度过低，或保温时间太短，晶粒生长不充分，易保留前驱体形貌，难以形成大尺寸晶粒；当采用本申请的烧结温度结合保温时间，能够获得晶粒尺寸大于0.5μm的 一次颗粒；而烧结温度过低，晶粒易保持前驱体形貌，从而难以获得具有八面体或多面体形貌的晶粒。而采用本申请的烧结温度，易获得具有八面体或多面体形貌的晶粒，而不过分依赖于前驱体的形貌。
此外，用高温烧结后破碎再热处理的方式虽然也能制备单晶，但其会增加额外的工艺环节，破坏晶粒表面。为了合成粒径外形更规则的单晶或类单晶，本申请可选实施方法为：首先确定成品的目标晶粒尺寸dv50(C)，然后选择体积中值粒径为0.3～2.2dv50(C)的镍源和锰源，与锂源混合后，再选择与dv50(C)匹配的烧结温度和时间进行热处理。当然，用高温烧结后破碎再热处理的方式也能制备单晶。
进一步地，本申请经过高温烧结获得富含Fd-3m结构的镍锰酸锂晶粒后，通过缓慢降温的方式降温到一定温度，使Fd-3m结构转化为P4 332结构，从而获得高含量P4 332结构，本申请中的需要以缓慢降温的方式降温达到的温度称为下限温度，本申请中的下限温度为400℃-650℃；当降温至下限温度之后，步骤(4)继续降温冷却至室温的过程可以仍旧采用本申请的缓慢降温的方式，也可以采用自然冷却或称随炉冷却等降温方式，本申请在此不做限定。本申请中自然冷却的降温速率为本领域公知，例如在700-1000℃，降温速率约为10℃/min；在300-700℃，降温速率约为5-6℃/min等，本申请对此不做限定。
发明人发现，缓慢降温过程中，降温速率越慢，越有利于P4 332结构含量的提高，但是降温速率过慢会造成生产过程耗时长，能量损耗大，不利于降低生产成本，因此本申请中缓慢降温的平均降温速率≤0.7℃/min，可选0.2-0.7℃/min。
本申请中，所述平均降温速率可以理解为自高温烧结温度开始降温，截至降温至下限温度以下的总温差与总时间之比。降温至下限温度以下可以理解为，在下限温度进行保温时，保温时间计入总时间，在低于下限温度的温度进行保温，保温时间不计入总时间。本申请中所述缓慢降温的形式可以包括连续缓慢降温和/或阶梯式降温，平均降温速率≤0.7℃/min；所述阶梯式降温可以理解为降温一定温度后设置一个保温段，包括每降温50℃-200℃设置一保温段，保温时间为1～30h。
在本申请的一些实施方式中，所述锂源选自但不限于含锂的碳酸盐、氢氧化物、硝酸盐、氧化物等的至少一种；所述镍源选自但不限于含镍的氧化物、氢氧化物、碳酸盐、草酸盐、硝酸盐等的至少一种；所述锰源选自但不限于含锰的氧化物、氢氧化物、碳酸盐、草酸盐、硝酸盐等的至少一种。
本申请中，可以根据所需镍锰酸锂产物中各元素的化学计量比相应称取锂源、镍源和锰源，此为本领域所公知的手段，本申请在此不做限定。
本申请中，所述的镍源、锰源、锂源等可来自于同一化合物或来自不同化合物。例如，镍源和锰源可以直接与锂源混合，也可以先将可溶性镍源和可溶性锰源通过共沉淀等方式形成镍锰氢氧化物、镍锰碳酸盐、镍锰氧化物等，再与锂源混合，所述共沉淀等方法是本领域常用的制备镍锰氢氧化物的方法，例如可以将硫酸镍锰盐溶液与NaOH碱溶液在特定pH、温度、氨浓度条件下反应生成球形镍锰氢氧化物二次颗粒，本申请在此不做限定，所述“可溶性”是指相应的镍源和锰源可溶于水、稀酸或诸如醇类或醚类等有机溶剂。
发明人还发现，镍源、锰源的颗粒越小，活性越大，在烧结过程中容易导致成品中颗粒间粘连严重，难以获得单晶形态。而镍源、锰源的颗粒太大又会出现烧透困难，也会需要提高烧结温度，导致颗粒间粘连，因此，在本申请的一些可选的实施方式中，镍源和锰源的体积中值粒径Dv50(P)与尖晶石型镍锰酸锂材料一次颗粒的目标体积中值粒径dv50(C)之比各自独立地满足：Dv50(P)/dv50(C)＝0.3～2.2，此处尖晶石型镍锰酸锂材料一次颗粒的体积中值粒径可以理解为一次颗粒的目标晶粒尺寸。镍源和锰源采用此粒径范围，烧结更易获得具有单晶或类单晶状态的尖晶石型镍锰酸锂材料。在另一些实施方式中，当先将可溶性镍源和可溶性锰源通过共沉淀等方式形成镍锰氢氧化物、镍锰碳酸盐、镍锰氧化物等镍锰前驱体时，镍锰前驱体的体积中值粒径Dv50(P)与尖晶石型镍锰酸锂材料一次颗粒的目标体积中值粒径dv50(C)也满足Dv50(P)/dv50(C)＝0.3～2.2。
本申请中，所述“目标体积中值粒径”或“目标晶粒尺寸”可以理解为期望得到的一次颗粒的体积中值粒径或晶粒尺寸，由于采用本申请的方法获得的尖晶石型镍锰酸锂材料的一次颗粒的晶粒尺寸与期望得到的晶粒尺寸几乎相同，因此在本申请中，可以理解为“目标体积中值粒径”或“目标晶粒尺寸”与获得的一次颗粒的体积中值粒径相同。
在本申请的一些实施方式中，所述镍源与所述锰源摩尔比大于等于1:3；此范围内获得的尖晶石型镍锰酸锂材料中更易实现Ni原子及其位置掺杂原子与Mn原子及其位置掺杂原子的比例大于等于1:3，从而获得Mn 3+含量更低的尖晶石型镍锰酸锂材料。
本申请中，所述添加剂的作用是向镍锰酸锂中添加掺杂元素，添加剂的用量根据掺杂的镍锰酸锂的元素化学计量比确定，本申请在此不做赘述。发明人还发现，添加剂的种类和用量会影响混合材料的相变温度、原子扩散，进而影响到晶粒生长。低熔点添加剂会在高温时熔化将晶粒粘结成大块，而添加剂熔点过高或化学活性过低又会抑制晶界迁移，抑制晶粒长大，因此在本申请的一些实施方式中，所述添加剂选自Mg、Zn、Ti、Zr、W、Nb、Al、B、P、Mo、V或Cr的氧化物、氢氧化物、硝酸盐、碳酸盐或铵盐等的至少一种， 可选地，所述添加剂选自氧化镁、氧化锌、氧化钛、氧化锆、氧化钨、氧化铌、氧化铝、硼酸、磷酸二氢铵、氧化钼、氧化钒或氧化铬中的至少一种。
发明人在研究中还发现，提高烧结气氛中的氧浓度有利于获得更高纯度的P4 332结构，进而获得具有更低Mn 3+含量的正极活性材料。在本申请的一些实施方式中，高温烧结的气氛为氧气。
在本申请的一些实施方式中，当所述正极活性材料包含表面修饰层时，表面修饰过程可根据具体情况穿插在缓慢降温过程中，例如步骤(3)中自高温烧结温度缓慢降温至表面修饰温度，然后自然冷却到室温，在进行表面修饰处理后，再升温至表面修饰温度，保温一段时间，例如3-30h，随后继续缓慢降温至400℃-650℃，最后自然冷却到室温。
本申请中，所说表面修饰温度与表面修饰物的种类相关，本领域技术人员可根据所选择的表面修饰物选择具体的表面修饰温度，本申请在此不做限定，例如当选择氧化铝作为表面修饰物时，表面修饰温度可选在650℃左右，当选择氧化硼作为表面修饰物时，表面修饰温度为500℃左右。
在本申请一些实施方式中，所述表面修饰物选自Ti、Zr、W、Al、B、P或Mo的氧化物中的至少一种。在本申请一些可选的实施方式中，所述表面修饰物选自氧化钛、氧化锆、氧化钨、氧化铝、硼酸、磷酸二氢铵、氧化钼中的至少一种。
在本申请的一些实施方式中，步骤(3)包括以下步骤：
自高温烧结温度缓慢降温至表面修饰温度，然后自表面修饰温度降温至室温，与表面修饰物进行混粉后，升温至表面修饰温度，保温一段时间，例如3-30h；随后继续缓慢降温至400℃-650℃。
其中，本申请对自表面修饰温度降温至室温的过程不做限定，例如可选择采用本申请的缓慢降温的方式，或者采用自然降温等方式实现。在计算平均降温速率时，表面修饰温度高于或等于下限温度(400℃-650℃)，则表面修饰温度下的保温时间和表面修饰温度至所述下限温度之间的降温时间计入降温总时间；若表面修饰温度低于所述下限温度，则表面修饰时间不计入降温总时间。
现有方法中，为了增加P4 332含量，会在高温烧结后，再连接或单独进行一次有序化热处理，以使高温烧结获得Fd-3m结构转变为P4 332结构，常见的有序化热处理工艺为600～700℃保温一定时间。因为P4 332属低温相，所以从热力学角度温度越低越趋向于P4 332结构，即理论上为了获得足够纯的P4 332结构，可在足够低的温度保温足够长时间即可。但从动力学角度温度越低越不利于原子扩散而进行相变，所以有序化热处理温度不能太低， 否则无法获得满意的晶粒尺寸和形貌的晶粒。从实际生产角度，有序化热处理也不可能无限期保温。所以有序化热处理温度要适中，且还应与目标晶粒大小及高温烧结温度、时间匹配。高温烧结温度越高，则Fd-3m含量越高，则有序化热处理保温时间需越长。晶粒越大，越需要较大的扩散动力，则有序化热处理温度越高。有序化热处理温度同样影响有序化热处理时间。发明人在研究中发现，本申请通过缓慢降温或者阶梯式降温，其效果相当于提高了有序化热处理的平均温度，加强了有序化的动力学过程；但最终的有序化热处理温度较低，在400～650℃，所以最终的P4 332含量高。
另外，以下适当参照附图对本申请的二次电池、电池模块、电池包和用电装置进行说明。
本申请的一个实施方式中，提供一种二次电池。
通常情况下，二次电池包括正极极片、负极极片、电解质和隔离膜。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。电解质在正极极片和负极极片之间起到传导离子的作用。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使离子通过。
[正极极片]
正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，所述正极膜层中包括本申请第一方面的正极活性材料或根据本申请第二方面的方法制备的正极活性材料。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极膜层设置在正极集流体相对的两个表面的其中任意一者或两者上。
在一些实施方式中，所述正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。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层至少一个表面上的金属层。复合集流体可通过将金属材料(铝、铝合金、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，正极膜层还可选地包括粘结剂。作为示例，所述粘结剂可以包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物及含氟丙烯酸酯树脂中的至少一种。
在一些实施方式中，正极膜层还可选地包括导电剂。作为示例，所述导电剂可以包括 超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
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。
[负极极片]
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上的负极膜层，所述负极膜层包括负极活性材料。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极膜层设置在负极集流体相对的两个表面中的任意一者或两者上。
在一些实施方式中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。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，负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，负极活性材料可包括以下材料中的至少一种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，负极膜层还可选地包括粘结剂。所述粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，负极膜层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组 分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解质盐和溶剂。
在一些实施方式中，电解质盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、三氟甲磺酸锂、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂、二氟二草酸磷酸锂及四氟草酸磷酸锂中的至少一种。
在一些实施方式中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。
在一些实施方式中，所述电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
[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玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。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。
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。
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能够盖设于所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，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4。参照图3，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以为一个或多个，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。
另外，本申请还提供一种用电装置，所述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。所述二次电池、电池模块、或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以包括移动设备(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。
作为所述用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
图6是作为一个示例的用电装置。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。
正极活性材料制备
实施例1
将镍锰源(球形镍锰氢氧化物，Dv50(P)＝4.1μm)按目标化学式Li 1.0Ni 0.51Mn 1.49O 4的化学计量配比，锂源(碳酸锂)按Li/Me＝1.02添加，其中Me为目标化学式中除Li和O之外的元素摩尔数，混合球磨4h。将混合物升温至850℃，保温30小时，在空气的烧结气氛中进行高温烧结，随后以0.5℃/min的降温速率，缓慢降温至650℃(下限温度)，然后随炉冷却室温，获得包含多晶Li 1.01Ni 0.51Mn 1.49O 4的正极活性材料。
实施例2～15除了按照表1调整对应的制备参数以外，其余与实施例1相同，获得包含单晶或类单晶Li 1.01Ni 0.51Mn 1.49O 4的正极活性材料。
实施例16
除将镍锰源和添加剂B 2O 3按目标化学式Li 1.03Ni 0.49Mn 1.48O 4B 0.03的化学计量比配比，其余与实施例4相同，获得Li 1.01Ni 0.49Mn 1.48O 4B 0.03正极活性材料。
实施例17
除将镍锰源和添加剂MgO按目标化学式Li 1.01Ni 0.48Mn 1.49O 4Mg 0.03的化学计量比配比，其余与实施例4相同，获得Li 1.01Ni 0.48Mn 1.49O 4Mg 0.03正极活性材料。
实施例18
将锂源(碳酸锂)、镍锰源(球形镍锰氢氧化物，Dv50(P)＝4.1μm)按化学计量配比混合球磨4h。将混合物升温至970℃，保温10小时，在空气的烧结气氛中进行高温烧结，随后以0.5℃/min的降温速率，缓慢降温至650℃，随炉冷却至室温，将其与表面修饰物氧 化铝按混合球磨3h，再将其升温至650℃，保温20小时后，随炉冷却室温，获得包含表面修饰层的Li 1.01Ni 0.51Mn 1.49O 4的正极活性材料。
实施例19
将锂源(碳酸锂)、镍锰源(球形镍锰氢氧化物，Dv50(P)＝4.1μm)按化学计量配比混合球磨4h。将混合物升温至970℃，保温10小时，在空气的烧结气氛中进行高温烧结，随后以0.5℃/min的降温速率，缓慢降温至500℃，随炉冷却至室温，将其与表面修饰物B 2O 3按混合球磨3h，再将其升温至500℃，保温5小时后，随炉冷却室温，获得包含表面修饰层的Li 1.01Ni 0.51Mn 1.49O 4的正极活性材料。
实施例20
除将在表面修饰热处理后继续以0.5℃/min的降温速率缓慢降温至500℃，其余与实施例18相同。
实施例21
除了按照表1调整镍锰源为氧化镍与氧化锰外，其余实施例4相同。
实施例22
除将锂源替换为氢氧化锂外，其余与实施例4相同。
实施例23
将锂源(碳酸锂)、镍锰源(球形镍锰氢氧化物，Dv50(P)＝4.1μm)按化学计量配比混合球磨4h。将混合物升温至970℃，保温10小时，在空气的烧结气氛中进行高温烧结，以1℃/min的降温速率降温，并在温度降至770℃时，保温5小时，再继续温度降至650℃时，保温5h，随后随炉冷却室温，获得包含单晶Li 1.01Ni 0.51Mn 1.49O 4的正极活性材料。
实施例24
将锂源(碳酸锂)、镍锰源(球形镍锰氢氧化物，Dv50(P)＝4.1μm)按化学计量配比混合球磨4h。将混合物升温至970℃，保温10小时，在空气的烧结气氛中进行高温烧结，以3℃/min的降温速率降温，并分别在温度降至920、870、820、770、720℃时，保温2小时，再继续温度降至650℃时，保温5h，随后随炉冷却室温，获得包含单晶或类单晶Li 1.01Ni 0.51Mn 1.49O 4的正极活性材料。
对比例1
将锂源(碳酸锂)、镍锰源(球形镍锰氢氧化物，Dv50(P)＝4.1μm)按化学计量配比混合球磨4h。将混合物升温至970℃，保温10小时，在空气的烧结气氛中进行高温烧结， 自然冷却至室温后，升温至640℃退火，保温15h，然后再随炉冷却获得产品。
对比例2
除按表1所示，将镍锰源替换为氧化镍和氧化锰，其余与对比例1相同。
对比例3
将镍锰源(球形镍锰氢氧化物，Dv50(P)＝4.1μm)按目标化学式Li 1.0Ni 0.51Mn 1.49O 4的化学计量配比，锂源(碳酸锂)按Li/Me＝1.02添加，其中Me为目标化学式中除Li和O之外的元素摩尔数，混合球磨4h。将混合物升温至600℃，保温100小时，在空气的烧结气氛中进行高温烧结，随后随炉冷却室温，获得包含多晶Li 1.01Ni 0.51Mn 1.49O 4的正极活性材料。
对比例4
除高温烧结后以1℃/min的降温速率，降温至650℃，然后随炉冷却室温，其余与实施例4相同。
对比例5
除缓慢降温至700℃以外，然后随炉冷却室温，其余与实施例4相同。
对比例6
除高温烧结后，以3℃/min的降温速率降温，分别在温度降至870℃、770℃时，保温1小时，温度降至650℃后，保温3h，随炉冷却室温，其余与实施例4相同。
上述实施例1～24、对比例1～6的正极活性材料的合成工艺相关参数如下述表1所示。
Figure PCTCN2021133668-appb-000001
Figure PCTCN2021133668-appb-000002
参照GB/T 19077-2016粒度分析激光衍射法，使用Mastersizer 3000激光粒度仪测量各实施例和对比例制备的尖晶石型镍锰酸锂材料的体积中值粒径Dv50。
参照JY/T010-1996，使用场发射扫描电镜(蔡司Sigma300)观察尖晶石型镍锰酸锂材料的晶粒外形，以一次颗粒(晶粒)的轮廓的外接椭球近似代替晶粒统计晶粒大小的体积分布，并记录晶粒尺寸，具体统计方法为：SEM下任选一个含有几十到一百个晶粒的照片，找出其第三大晶粒(避免最大和第二大为异常晶粒)，将其外接圆直径记为Drd，只统计≥0.1Drd的晶粒大小，并计算其体积中值粒径dv50，即为晶粒尺寸。
其中，实施例1的正极活性材料的显微电镜(SEM)照片如图7A和图7B所示，实施例4、13、16的正极活性材料SEM照片分别如图8-图10所示，对比例2的正极活性材料的SEM照片如图11A和图11B所示，对比例3的正极活性材料的SEM照片如图12A和图12B所示。从图中可以看出实施例1的正极活性材料为多晶材料，实施例4、13、16的正极活性材料为单晶、类单晶材料，各实施例中的晶粒呈八面体形或八面体削尖去棱的多面体形，晶粒具有较大的平均直径，晶粒平均直径≥0.5μm。对比例2的正极活性材料为不规则晶粒，对比例3的正极活性材料为片状晶粒的多晶，其晶粒平均直径较小。
另外，将上述实施例1～24和对比例1～6中得到的正极活性材料制备成扣式半电池，进行性能测试。
扣式半电池电池的组装
将各实施例和对比例制备获得的正极活性材料与导电炭黑、PVDF按重量比90：5：5混合，加入适量N-甲基吡咯烷酮，搅拌均匀，获得正极浆料。将正极浆料涂布在铝箔上，涂布后烘干，获得正极极片。正极极片上正极活性材料的负载量为0.015g/cm 2。
以含有1mol/L LiPF 6的碳酸酯、磷酸酯等的混合溶液作为电解液。
以厚度12μm的聚丙烯薄膜(Φ16mm)作为隔离膜，将锂片、隔离膜、正极片按顺序放好，使隔离膜处于金属锂片与复合负极极片中间起到隔离的作用。注入电解液，组装成CR2030扣式电池，静置24h，得扣式半电池。
Mn 3+含量测试
根据本领域所公知的，在LiNi 0.5Mn 1.5O 4中，Li/Me＝0.5，其中，Me代表过渡金属原子或离子，即除了Li和氧之外的其他原子和离子；而一个Mn 3+/Mn 4+充放电过程就对应一个Li +的脱嵌；因为Mn 3+/Mn 4+的充电电压区间为4.4～3.5V(主要集中在4.0V附近)，Ni 4+/Ni 3+，Ni 3+/Ni 2+变价的电压均在4.8～4.5V之间，因此4V平台公认是来自Mn 3+/Mn 4+， 所以4V平台Li +的脱嵌量就是Mn 3+/Mn 4+的量(即完全嵌锂状态下材料中的Mn 3+数量)，其余的Mn均为稳定的Mn 4+。以x代表4V平台Li +脱嵌量占比，也即代表4V平台充电容量占比。因此，以扣式半电池为测试对象，测试其4.4～3.5V的充电容量(Q1)和4.95～3.5V充电容量(Q2)，计算4V平台充电容量占比x＝Q1/Q2，则Mn 3+占总过渡金属原子/离子的摩尔占比为r＝0.5x。
Mn 3+占比测试具体的测试方法如下：
在25℃下，将各实施例和对比例的正极活性材料制备的扣式半电池以0.1C恒流充电至电压为4.95V，然后以4.95V恒压充电至电流为0.05C，静置5min之后，将扣式半电池以0.1C恒流放电至电压为3.5V，此为一个充放电循环，静置5min后再重复一次。从两次充放电循环的原始充放电数据中截取4.4～3.5V的充电平均容量(Q1)和4.95～3.5V充电平均容量(Q2)。
4V平台充电容量占比x＝Q1/Q2，鉴于第一圈可能会存在电池未活化、第二圈又受第一圈放电影响，所以本申请x取前两圈4V平台充电容量占比的平均值。根据Mn 3+占总过渡金属原子/离子的摩尔占比r＝0.5x计算可得Mn 3+在所述尖晶石型镍锰酸锂材料中的质量含量。
上述实施例1～24、对比例1～6的正极活性材料的物化参数如表2所示，扣式半电池统计结果详见表3。
Figure PCTCN2021133668-appb-000003
Figure PCTCN2021133668-appb-000004
表3 扣式半电0.1C充电容量4V平台占比计算
Figure PCTCN2021133668-appb-000005
另外，将上述实施例1～24和对比例1～6中得到的正极活性材料制备成二次电池，进行性能测试，测试结果如下表4所示。
二次电池的制作
分别将各实施例和对比例制备的正极活性材料与导电炭黑、PVDF按重量比96：2.5： 1.5混合，加入适量N-甲基吡咯烷酮，搅拌均匀，获得正极浆料。将正极浆料涂布在铝箔上，涂布后烘干，获得正极极片。正极极片上正极活性材料的负载量为0.02g/cm 2。
将石墨与导电炭黑、羧甲基纤维素按重量比96：1：3混合，加入适量纯水，搅拌均匀，获得负极浆料。将负极浆料涂布在铜箔上，涂布后烘干，获得负极极片。负极极片上石墨的负载量为0.008g/cm 2。
以含有1mol/L LiPF 6的碳酸脂、磷酸酯的混合溶液作为电解液。
以厚度12μm的聚丙烯薄膜(Φ16mm)作为隔离膜，将上述制得的正极极片、隔离膜，负极极片按顺序放好，使隔离膜处于正负极片中间起到隔离的作用，卷绕成型，用铝塑袋包装。注入电解液，封装后进行化成容量，制得二次电池。
电池性能测试：
1、二次电池循环性能测试
以各实施例和对比例制备的正极活性材料制备的二次电池为测试对象。
在25℃下，将二次电池以0.3C恒流充电至电压为4.9V，然后以4.9V恒压充电至电流为0.05C，静置5min之后，将二次软包电池以0.33C恒流放电至电压为3.5V，此为一个充放电循环过程，此次的放电容量为首圈放电容量。将全电池按上述方法进行多次循环充放电测试，直至全电池的放电容量衰减至104mAh/g，记录全电池的循环次数。当前阶段类单晶镍锰尖晶石/石墨软包电池的正极克容量目标值130mAh/g，其80％即为104mAh/g，相比于各材料自身容量值的80％，更能够直观得反映整个循环周期的总体容量表现，而不单单是循环寿命。统计结果详见表4。
2、产气和离子溶出测试
以各实施例和对比例制备的正极活性材料制备的二次电池为测试对象。
在25℃下，将二次电池以0.3C恒流充电至电压为4.9V，然后以4.9V恒压充电至电流为0.05C。将此满充态电池放置在25℃恒温厂房内，过程中每隔10天利用排水法测一次软包电芯体积，增加的体积即为产气体积，产气量(ml/Ah)＝产气体积/首圈放电容量。100天后，获得100天存储产气数据，测试结束后将电池以0.33C恒流放电至3.5V，然后以0.05C恒流放电至3.0V，即获得充分放电(满放)的电池。
将充分放电的电池拆解，分离负极极片，将负极极片在碳酸二甲酯(DMC)溶剂中轻微晃动5s，以除去负极表面残留电解液，然后晾干。从负极极片的表面刮下负极材料，采用电感耦合等离子光谱技术检测负极材料中的Ni含量(μg/g或ppm)和Mn含量(μg/g 或ppm)。产气和离子溶出的测试结果详见表4。
表4 二次电池全电性能
Figure PCTCN2021133668-appb-000006
从表2中可以看出，本申请实施例1～24的正极活性材料Mn 3+含量均低于0.7％，进一步的，本申请的正极活性材料的晶粒尺寸均大于0.5μm，可选地大于等于2μm。此外可 以看出，本申请的正极活性材料晶粒形貌为八面体或八面体削尖去棱的多面体形。
从实施例1～6及实施例12～15中可以看出，通过调整镍锰源粒径、高温烧结温度以及保温时间，可以获得不同形貌的正极活性材料的一次颗粒，其中，当镍锰源粒径Dv50(P)与产物目标粒径Dv50(C)满足Dv50(P)＝0.3～2.2Dv50(C)，且高温烧结温度、保温时间以及镍锰源粒径与产物目标晶粒尺寸匹配时，更易获得具有单晶或类单晶形貌的一次颗粒。此外，发明人研究发现，高温烧结温度越高，保温时间越长，对应晶粒尺寸越大。
根据实施例4、7、8与对比例4的比较可以看出，降温速率越慢，Mn 3+的质量含量越低。当降温速率低于0.7℃/min，可以获得Mn 3+的质量含量均低于0.7％的正极活性材料；然而降温速率过慢会造成生产过程耗时长，能量损耗大，不利于降低生产成本，因此本申请中缓慢降温的平均降温速率可选0.2-0.7℃/min。
根据实施例4和实施例11可以看出，提高烧结氛围中氧气的含量有利于获得具有更低Mn 3+含量的正极活性材料。
其中，实施例4、实施例11及对比例2的充放电首圈曲线如图13所示，从图13中可以看出，实施例4的4V平台明显比对比例2的4V平台要窄，说明本申请实施例4中具有更低的Mn 3+含量；而实施例11的4V平台不可见，说明实施例11的镍锰酸锂中具有更低的Mn 3+含量。
根据实施例16～22可以看出加入不同的掺杂元素或表面修饰或采用不同的锂源、镍源、锰源，均能够获得本申请的正极活性材料。
实施例23、24说明采用本申请的阶梯式降温的方式，也能够获得本申请的正极活性材料。
而相对于此，对比例1、2采用是使用了现有的降温后退火的方式制备高P4 332含量的尖晶石镍锰酸锂，其仍具有较高的Mn 3+的含量，如高于0.8wt％；对比例3采用低温烧结的方式，获得的镍锰酸锂中Mn 3+的含量相对较低，但仍不能达到低于0.7％，而且采用低温烧结的方式，获得的镍锰酸锂为片状多晶结构，从表4的性能数据中也可以看出，虽然其Mn 3+含量低，但是其锰溶出量高，循环性能低，不限于任何理论，发明人认为这是由于其晶粒形貌为片状，晶粒表面不是稳定晶面造成的；对比例4、5、6在高温烧结后，采用了本申请范围之外的降温条件，可以看出，其Mn 3+的含量均高于0.7wt％。
从表3中可以看出，以实施例1-实施例24的正极活性材料制备的扣式半电池，根据其4V平台充电容量占比均小于等于2％。
从表4中可以看出，本申请的正极活性材料应用于二次电池，其相比于各对比例，过渡金属离子溶出更少、循环性能更优、产气更小；进一步地，具有单晶或类单晶结构的正极活性材料相比于具有多晶结构的正极活性材料，过渡金属离子溶出、产气量进一步减少，循环性能进一步升高；从本申请各实施例中还可以看出，随着Mn 3+含量的降低，电池循环性能得到提升；此外，根据实施例4以及实施例18-实施例20可以看出，当所述正极活性材料中包含表面修饰层时，电池的过渡金属离子溶出、产气量进一步减少，循环性能进一步升高。
进一步地，发明人还发现，颗粒尺寸小的单晶、类单晶正极活性材料有利于二次电池首圈放电容量的提高，颗粒尺寸大的单晶、类单晶正极活性材料有利于锰溶出、产气量的减少和电池循环性能的提升，因此本申请可选的尖晶石型镍锰酸锂材料的一次颗粒的体积中值粒径为2μm至10μm。
需要说明的是，由于单晶、类单晶材料比多晶材料具有更好的性能，因此本申请中的比较均以同种形貌间进行比较，即单晶材料与单晶材料比较，多晶材料与多晶材料比较。
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 (18)

  1. 一种正极活性材料，其包括尖晶石型镍锰酸锂材料，所述尖晶石型镍锰酸锂材料具有如下的化学式：Li aNi 0.5-xMn 1.5-yM x+yO 4，其中，M选自Mg、Zn、Ti、Zr、W、Nb、Al、B、P、Mo、V、Cr中的至少一种，0.9≤a≤1.1，-0.2≤x≤0.2，-0.02≤y≤0.3，x+y≥0；
    所述尖晶石型镍锰酸锂材料中Mn 3+的含量小于等于0.7wt％。
  2. 根据权利要求1所述的正极活性材料，其中，所述尖晶石型镍锰酸锂材料的一次颗粒的体积中值粒径为0.5μm至16μm，可选为2μm至10μm。
  3. 根据权利要求1或2所述的正极活性材料，其中，所述尖晶石型镍锰酸锂材料的体积中值粒径为2μm至24μm，可选为5μm至17μm。
  4. 根据权利要求1至3中任一项所述的正极活性材料，其中，所述尖晶石型镍锰酸锂材料为类单晶或单晶材料。
  5. 根据权利要求1至4中任一项所述的正极活性材料，其中，所述尖晶石型镍锰酸锂材料的一次颗粒形貌为八面体或多面体。
  6. 根据权利要求1至5中任一项所述的正极活性材料，其中，所述尖晶石型镍锰酸锂材料中Ni原子及其位置掺杂原子与Mn原子及其位置掺杂原子的摩尔比大于等于1:3。
  7. 根据权利要求1至6中任一项所述的正极活性材料，其还包括表面修饰层，所述表面修饰层包覆所述尖晶石型镍锰酸锂材料的至少部分表面，所述表面修饰层的材料选自Ti、Zr、W、Al、B、P或Mo的氧化物中的至少一种。
  8. 根据权利要求7所述的正极活性材料，其中，基于所述正极活性材料的总重量，所述表面修饰层的含量小于3％。
  9. 根据权利要求1所述的正极活性材料，其中，以所述正极活性材料制备扣式半电池，0.01C～0.2C充放电中，3.5V～4.4V的充电容量占3.5V～4.9V充电容量的比例小于等于2％。
  10. 一种正极活性材料的制备方法，其包括以下步骤：
    (1)提供锂源、镍源、锰源，以及任选的添加剂，球磨混粉；
    (2)高温烧结：在空气、氧气或其混合气体气氛中，升温至850～1150℃保温2～50h；
    (3)自高温烧结温度缓慢降温至400℃-650℃，其中，所述缓慢降温的平均降温速率≤0.7℃/min；
    (4)冷却至室温，获得尖晶石型镍锰酸锂材料；
    其中，所述尖晶石型镍锰酸锂材料具有如下的化学式：Li aNi 0.5-xMn 1.5-yM x+yO 4，其中，M选自Mg、Zn、Ti、Zr、W、Nb、Al、B、P、Mo、V、Cr中的至少一种，0.9≤a≤1.1，-0.2≤x≤0.2，-0.02≤y≤0.3，x+y≥0；
    所述尖晶石型镍锰酸锂材料中Mn 3+的含量小于等于0.7wt％。
  11. 根据权利要求10所述的方法，其中，所述缓慢降温的形式包括阶梯式降温；所述阶梯式降温包括每降温50℃-200℃设置一保温段，保温时间为1～30h。
  12. 根据权利要求10所述的方法，其中，所述镍源与所述锰源的摩尔比大于等于1:3。
  13. 根据权利要求10所述的方法，其中，所述镍源和所述锰源的体积中值粒径与所述尖晶石型镍锰酸锂材料一次颗粒的目标体积中值粒径之比各自独立地为0.3～2.2。
  14. 根据权利要求10所述的方法，其中，所述添加剂选自Mg、Zn、Ti、Zr、W、Nb、Al、B、P、Mo、V或Cr的氧化物、氢氧化物、硝酸盐、碳酸盐或铵盐中的至少一种。
  15. 一种二次电池，其包括权利要求1-9中任一项所述的正极活性材料或权利要求10-14中任一项所述的方法制备的正极活性材料。
  16. 一种电池模块，其包括权利要求15所述的二次电池。
  17. 一种电池包，其包括权利要求16所述的电池模块。
  18. 一种用电装置，其包括权利要求15所述的二次电池、权利要求16所述的电池模块或权利要求17所述的电池包中的至少一种。
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