WO2021043149A1 - 正极活性材料、其制备方法、正极极片、锂离子二次电池及包含锂离子二次电池的装置 - Google Patents

正极活性材料、其制备方法、正极极片、锂离子二次电池及包含锂离子二次电池的装置 Download PDF

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WO2021043149A1
WO2021043149A1 PCT/CN2020/112914 CN2020112914W WO2021043149A1 WO 2021043149 A1 WO2021043149 A1 WO 2021043149A1 CN 2020112914 W CN2020112914 W CN 2020112914W WO 2021043149 A1 WO2021043149 A1 WO 2021043149A1
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active material
positive electrode
electrode active
optionally
particles
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PCT/CN2020/112914
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English (en)
French (fr)
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钭舒适
胡春华
蒋耀
吴奇
何金华
邓斌
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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 EP20861784.5A priority Critical patent/EP3944377A4/en
Publication of WO2021043149A1 publication Critical patent/WO2021043149A1/zh
Priority to US17/682,258 priority patent/US20220181675A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • 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
    • 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
    • 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
    • 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
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/10—Solid density
    • 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
    • C01P2006/11—Powder tap density
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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

  • This application belongs to the technical field of secondary batteries, and specifically relates to a positive electrode active material, a preparation method thereof, a positive electrode pole piece, a lithium ion secondary battery, and a device containing the lithium ion secondary battery.
  • Lithium-ion secondary battery is a kind of rechargeable battery, which mainly relies on the movement of lithium ions between the positive electrode and the negative electrode to work, and is a clean energy that is currently widely used.
  • the positive electrode active material provides lithium ions that reciprocate between the positive and negative electrodes for the battery charging and discharging process. Therefore, the positive electrode active material is very important to the performance of the battery.
  • lithium-ion secondary batteries are increasingly used in various devices such as consumer electronics and electric vehicles, people have put forward higher requirements for the energy density and high-temperature cycle performance of lithium-ion secondary batteries.
  • the first aspect of the present application to provide a positive electrode active material particles and comprising a body covering an outer surface of the body particle coating layer, the body particles including the nickel-containing lithium composite oxide and the doping element M 1 element, the cladding layer Including oxides of M 2 elements;
  • the average valence of the M 1 element When the positive electrode active material is in the 11% delithiation state, the average valence of the M 1 element is ⁇ 1 , and the average valence of the M 2 element is ⁇ 1 ; when the positive electrode active material is in the 78% delithiation state, the average valence of the M 1 element is ⁇ 2.
  • the M 1 element includes one or more of Si, Ti, Cr, Mo, V, Se, Nb, Ru, Rh, Pd, Sb, Te, Ce and W
  • the M 2 element is selected from Mg, Al, Ca, One or more of Zr, Zn, Y, and B.
  • the positive electrode active material provided in the present application includes lithium composite oxide bulk particles containing nickel and doped element M 1 , and the outer surface of the bulk particles has an oxide coating layer of M 2 element, and as the positive electrode active material is removed For lithium, the average valence of the M 1 element increases, and the average valence of the M 2 element remains constant. As a result, the capacity display of the positive electrode active material is greatly improved, and the energy density of the lithium ion secondary battery using the same can be significantly improved.
  • the structural stability of the positive electrode active material during high temperature cycling and high temperature storage is greatly improved, and the electrolyte oxidation activity on the surface of the positive electrode active material is greatly reduced, which can reduce the battery's high temperature cycle and high temperature storage process. The electrolyte decomposes and produces gas, so the high-temperature cycle performance and high-temperature storage performance of the battery are also significantly improved.
  • the ⁇ 1 and ⁇ 2 satisfy ⁇ 2 > ⁇ 1 ⁇ +3.
  • the battery has better high temperature cycle performance and high temperature storage performance.
  • the ⁇ 1 is one or more of +3, +4, +5, and +6 valences.
  • the ⁇ 1 is one or more of +3 and +4 valences.
  • the M 1 element may include one or more of Ti, Mo, V, Nb, Ru, Sb, and W; optionally, the M 1 element includes Ti, Nb, Ru, Sb, and W Or, the M 2 element includes one or more of Al, Zr, Zn, Y, and B; optionally, the M 2 element includes one of Al, Zr, Zn, and Y Or more; optionally, the M 2 element includes one or more of Al, Zr and Y.
  • Using appropriate M 1 element or M 2 element can further improve the high-temperature cycle performance and high-temperature storage performance of the battery, and can also further increase the energy density of the battery.
  • the M 1 element is uniformly doped in the bulk particles.
  • the M 1 element is uniformly doped in the bulk particles, which can further improve the energy density, high-temperature cycle performance and high-temperature storage performance of the battery.
  • the smaller the relative deviation of the local mass concentration of the M 1 element in the bulk particles the more uniform the distribution of the M 1 element in the bulk particles, and the better the overall performance of the battery.
  • the relative deviation of the local mass concentration of the M 1 element in the bulk particles is 32% or less, and optionally 20% or less.
  • the body particles are secondary particles formed by aggregating two or more primary particles.
  • the positive electrode active material can thus have higher lithium ion transport performance, thereby improving the cycle performance of the battery.
  • the lithium ion transport performance of the positive electrode active material can be further improved, and the structural stability can also be improved, so that the battery can obtain higher cycle performance.
  • the molar ratio of the M 1 element to the M 2 element is 0.09:1 to 4:1, optionally 0.1:1 to 3:1, The selection is 0.2:1 ⁇ 2.5:1, and the selection is 0.5:1 ⁇ 2:1.
  • the proper molar ratio of M 1 element to M 2 element in the positive electrode active material can further improve the high-temperature cycle performance and high-temperature storage performance of the battery.
  • the actual doping concentration of the M 1 element in the positive electrode active material is 2000 ⁇ g/cm 3 to 55000 ⁇ g/cm 3 , optionally 2300 ⁇ g/cm 3 to 49000 ⁇ g/cm 3 , optional Is 3000 ⁇ g/cm 3 ⁇ 30000 ⁇ g/cm 3 .
  • the true doping concentration of the M 1 element in the positive electrode active material is within the above range, which can well improve the energy density, high-temperature cycle performance, and high-temperature storage performance of the battery.
  • the content of the M 2 element in the positive electrode active material is 300 ppm to 6500 ppm, and optionally 500 ppm to 5000 ppm.
  • the content of the M 2 element in the positive electrode active material is within the above range, which enables the battery to have higher high-temperature cycle performance and high-temperature storage performance, and at the same time enables the battery to have a higher energy density.
  • the volume average particle diameter Dv50 of the positive electrode active material may be 8 ⁇ m to 20 ⁇ m, and optionally 9 ⁇ m to 16 ⁇ m.
  • the Dv50 of the positive electrode active material is in an appropriate range, which can improve the cycle performance and rate performance of the battery, and at the same time help the battery obtain a higher energy density.
  • the thickness T of the coating layer is 0.001 ⁇ m to 0.5 ⁇ m, optionally 0.1 ⁇ m to 0.3 ⁇ m.
  • the thickness T of the coating layer and the average particle size of the positive electrode active material Meet between: Optional, Optional, The coating layer meets the above conditions and can effectively improve the high-temperature cycle performance and high-temperature storage performance of the battery.
  • the lithium composite oxide is a compound represented by Chemical Formula 1,
  • the battery using the above-mentioned high nickel ternary material can better combine higher energy density, high temperature cycle performance and high temperature storage performance.
  • the X elements when the bulk particles are doped with X elements, the X elements are uniformly doped in the bulk particles.
  • the local mass concentration of the doped elements (including M 1 and X elements) in the bulk particles The relative deviation of X is 32% or less, optionally 30% or less, and optionally 20% or less; or, X element shows a decreasing mass concentration gradient from the outer surface of the body particle to the particle core direction; optional , X elements are doped in the outer surface of the body particles.
  • the surface of the positive electrode active material is a rough surface.
  • a specific surface area of the positive electrode active material is 0.2m 2 /g ⁇ 1.5m 2 / g, further preferably 0.3m 2 / g ⁇ 1m 2 / g. If the specific surface area of the positive electrode active material is within the above range, the capacity development and cycle life of the positive electrode active material can be improved.
  • the true density of the positive electrode active material is 4.6 g/cm 3 ⁇ 5.2 g/cm 3 , optionally 4.6 g/cm 3 ⁇ 4.9 g/cm 3 .
  • the true density of the positive electrode active material is within an appropriate range, which can increase the energy density of the battery.
  • the tap density of the positive electrode active material is 2.3 g/cm 3 to 2.8 g/cm 3 .
  • the tap density of the positive electrode active material is within an appropriate range, which can increase the energy density of the battery.
  • a second aspect of the present application provides a positive pole piece, which includes a positive current collector and a positive active material layer disposed on the positive current collector, and the positive active material layer includes the positive active material of the first aspect of the present application.
  • the positive pole piece of the present application includes the positive active material of the present application, so that the lithium ion secondary battery adopting the same can take into account higher energy density, high-temperature storage performance, and high-temperature cycle performance at the same time.
  • a third aspect of the present application provides a lithium ion secondary battery, which includes the positive pole piece of the second aspect of the present application.
  • the lithium ion secondary battery of the present application includes the positive pole piece of the present application, and thus can simultaneously take into account higher energy density, high-temperature storage performance, and high-temperature cycle performance.
  • the fourth aspect of the present application provides a device, which includes the lithium ion secondary battery of the third aspect of the present application.
  • the device of the present application includes the lithium ion secondary battery of the present application, and thus may have the same or similar beneficial effects.
  • the fifth aspect of the present application provides a method for preparing a positive electrode active material, which includes:
  • a mixture including a transition metal source containing nickel, a lithium source, and a precursor of M 1 element, and perform sintering treatment on the mixture to obtain bulk particles doped with M 1 element;
  • the body particles are mixed with the precursor of M 2 element and subjected to sintering treatment to form a coating layer containing M 2 element oxide on the outer surface of the body particles to obtain a positive electrode active material;
  • the average valence of the M 1 element When the positive electrode active material is in the 11% delithiation state, the average valence of the M 1 element is ⁇ 1 , and the average valence of the M 2 element is ⁇ 1 ; when the positive electrode active material is in the 78% delithiation state, the average valence of the M 1 element is ⁇ 2.
  • the M 1 element includes one or more of Si, Ti, Cr, Mo, V, Se, Nb, Ru, Rh, Pd, Sb, Te, Ce and W
  • the M 2 element is selected from Mg, Al, Ca, One or more of Zr, Zn, Y, and B.
  • the positive electrode active material obtained by adopting the preparation method of the present application has greatly improved its capacity and can significantly improve the energy density of the lithium ion secondary battery adopting it.
  • the structural stability of the positive electrode active material during high temperature cycling and high temperature storage is greatly improved, and the electrolyte oxidation activity on the surface of the positive electrode active material is greatly reduced, which can reduce the battery's high temperature cycle and high temperature storage process.
  • the electrolyte decomposes and produces gas, so the high-temperature cycle performance and high-temperature storage performance of the battery are also significantly improved.
  • the mixture may also include a precursor of X element, and the obtained bulk particles are also doped with X element, and the X element is selected from one of F, N, P, and S Or more; or, before mixing the bulk particles with the precursor of the M 2 element, it may further include: c) mixing the bulk particles with the precursor of the X element and performing a sintering treatment to make the X element Doped in the bulk particles, the X element is selected from one or more of F, N, P, and S.
  • the atmosphere of the sintering treatment is an oxygen-containing atmosphere; optionally, the oxygen content of the sintering atmosphere is 70% to 100%, optionally more than 85%; the temperature of the sintering treatment The temperature is 500°C to 1000°C, 700°C to 900°C is optional, and 750°C to 850°C is optional; the sintering treatment time is 5h-25h, and the optional 5h-15h.
  • the atmosphere of the sintering treatment is an oxygen-containing atmosphere; optionally, the oxygen content of the sintering atmosphere is 70%-100%, optionally more than 85%; the temperature of the sintering treatment The temperature is 100°C to 550°C, 200°C to 500°C is optional; the sintering treatment time is 3h-25h, and the optional 5h-10h.
  • the atmosphere of the sintering treatment is an oxygen-containing atmosphere; optionally, the oxygen content of the sintering atmosphere is 70%-100%, and optionally 80%-95%; the sintering treatment
  • the temperature of the sintering process is 400°C to 1000°C, 400°C to 850°C is optional, and 400°C to 750°C is optional; the sintering treatment time is 3h-25h, and the optional 5h-10h.
  • FIG. 1 is a schematic diagram of doping and coating of a positive electrode active material according to an embodiment of the present application.
  • FIG. 2 is a schematic diagram of the location of the relative deviation test of the local mass concentration of the M 1 element in the bulk particles of the positive electrode active material of Examples 1 to 28 and Comparative Examples 1 to 8.
  • FIG. 2 is a schematic diagram of the location of the relative deviation test of the local mass concentration of the M 1 element in the bulk particles of the positive electrode active material of Examples 1 to 28 and Comparative Examples 1 to 8.
  • Fig. 3 is a schematic diagram of an embodiment of a lithium ion secondary battery.
  • Fig. 4 is an exploded view of Fig. 3.
  • Fig. 5 is a schematic diagram of an embodiment of a battery module.
  • Fig. 6 is a schematic diagram of an embodiment of a battery pack.
  • Fig. 7 is an exploded view of Fig. 6.
  • FIG. 8 is a schematic diagram of an embodiment of a device in which a lithium ion secondary battery is used as a power source.
  • any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range.
  • every point or single value between the end points of the range is included in the range. Therefore, each point or single numerical value can be used as its own lower limit or upper limit, combined with any other point or single numerical value, or combined with other lower or upper limits to form an unspecified range.
  • the term "or” is inclusive. That is, the phrase “A or (or) B” means “A, B, or both A and B.” More specifically, any of the following conditions satisfy the condition "A or B”: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).
  • an embodiment of the present application provides a positive electrode active material, which includes body particles and a coating layer covering the outer surface of the body particles.
  • the body particles include a lithium composite oxide containing nickel element and doping element M 1
  • the coating layer includes an oxide of M 2 element.
  • the average valence of the M 1 element is ⁇ 1 ; when the positive electrode active material is in the 78% delithiation state, the average valence of the M 1 element is ⁇ 2 ; ⁇ 1 and ⁇ 2 satisfy ⁇ 2 > ⁇ 1 .
  • the M 1 element includes one or more of Si, Ti, Cr, Mo, V, Se, Nb, Ru, Rh, Pd, Sb, Te, Ce and W;
  • the M 2 element is selected from Mg, Al, Ca, One or more of Zr, Zn, Y, and B.
  • the body particles are nickel-based lithium composite oxide, and the body particles are doped with M 1 element.
  • M 1 element With the removal of the positive electrode active material lithium, average valence of M 1 element is increased, i.e., M 1 element can be capable of participating in a redox reaction electrons are released and the positive electrode active material during delithiation. As a result, the positive electrode active material can release more lithium ions, thereby exhibiting higher capacity performance.
  • the use of the positive electrode active material can significantly improve the energy density of the lithium ion secondary battery.
  • the M 1 element itself can effectively bind oxygen atoms.
  • the electrons contributed by the M 1 element can cause charge compensation inside the material, which further inhibits the material from releasing oxygen.
  • the structural stability of the positive electrode active material during high-temperature cycling and high-temperature storage is greatly improved.
  • the outer surface of the body particles has an oxide coating layer of the M 2 element, and with the delithiation of the positive electrode active material, the average valence of the M 2 element is constant.
  • the coating layer can form a continuous and stable strong protective effect on the body particles, effectively isolate the electrolyte from corroding the body particles, and further improve the structural stability of the positive electrode active material. Therefore, the use of the positive electrode active material can also significantly improve the high-temperature cycle performance and high-temperature storage performance of the battery.
  • the charge compensation effect of the M 1 element in the positive electrode active material can also reduce the strong oxidizing Ni 4+ in the material, and reduce the surface oxygen defects of the material, thereby effectively reducing the electrolyte oxidation activity on the surface of the material, and greatly reducing the battery's high temperature Decomposition of electrolyte during circulation and high-temperature storage to produce gas.
  • the protective effect of the coating layer on the body particles can further reduce the decomposition of the electrolyte on the surface of the material to produce gas. Therefore, the high-temperature cycle performance and high-temperature storage performance of the battery are further improved.
  • “78% delithiation state” refers to the state when the molar content of lithium extracted from the positive electrode active material accounts for 78% of the theoretical lithium content during the charging process of the battery.
  • the “11% de-lithium state” refers to the state when the molar content of lithium extracted from the positive electrode active material accounts for 11% of the theoretical lithium content during the charging process of the battery.
  • a "full discharge state” and a “full charge state” are generally set, and a “discharge cut-off voltage” and a “charge cut-off voltage” are set corresponding to the battery to ensure the battery's Safe to use.
  • the “discharge cut-off voltage” and “charge cut-off voltage” may have certain differences due to the difference in the positive electrode active material or the difference in safety requirements.
  • the delithiation state of the positive electrode active material in the "full charge state” is generally around the “11% delithiation state", and the positive electrode in the "full charge state”
  • the delithiation state of the active material is generally around "78% delithiation state”.
  • the corresponding positive electrode active material works between 11% delithiation state and 78% delithiation state to ensure normal use.
  • the positive electrode active material is used to prepare a series of standard button half-cells, which are respectively charged to 2.8V, 2.9V, 3.0V, 3.1V, 3.2V, 3.3V,...4.0V, 4.1V, at a rate of 0.1C.
  • the positive pole piece of the battery is removed, the electrolyte is removed after washing, the positive electrode active material is digested, and the inductively coupled plasma-emission spectrometer is used (inductively coupled plasma-Optical Emission spectrometers, ICP-OES) test the mass concentration of Li element of the positive electrode active material to calculate the "delithiation state", and obtain the corresponding relationship between the charging voltage and the "delithiation state", and then get "11% The charging voltage corresponding to the "de-lithium state” and "78% de-lithium state”.
  • ICP-OES inductively coupled plasma-Optical Emission spectrometers
  • the half-cell containing the positive electrode active material is charged to the voltage U 1 corresponding to the "11% delithiation state", and the positive electrode active material in the "11% delithiation state” can be obtained by disassembling.
  • charging the half-cell containing the positive electrode active material to the voltage U 2 corresponding to the "78% delithiation state” can be disassembled to obtain the positive electrode active material in the "78% delithiation state".
  • the valences of M 1 and M 2 elements in the "11% delithiation state" positive electrode active material and the "78% delithiation state” positive electrode active material can be obtained by X-ray photoelectron spectroscopy (XPS) testing. More accurate, can be obtained through Synchrotron radiation photoelectron spectroscopy (SRPES) test.
  • XPS X-ray photoelectron spectroscopy
  • SRPES Synchrotron radiation photoelectron spectroscopy
  • the "11% delithiated state" positive electrode active material, the average valence of M 1 element ⁇ 1 and "78% delithiated state” positive electrode active material, the average valence of M 1 element is [alpha] between 2 It satisfies ⁇ 2 > ⁇ 1 ⁇ +3.
  • the average valence of the M 1 element remains above +3.
  • the high-valence M 1 element has a stronger binding ability to oxygen atoms in the material, which can further improve the structural stability of the positive electrode active material, and prevent the positive electrode active material from crystal lattice cracking during high-temperature cycling and high-temperature storage. Therefore, the battery can have better high-temperature cycle performance and high-temperature storage performance.
  • the high-valence M 1 element can contribute more electrons in the positive electrode active material, thereby further reducing the electrolyte oxidation activity on the surface of the material, and further improving the high-temperature cycle performance and high-temperature storage performance of the battery.
  • the high-valence M 1 element contributes more electrons in the positive electrode active material, which can support the positive electrode active material to release more lithium ions, thereby further increasing the energy density of the battery.
  • ⁇ 1 is one or more of +3, +4, +5, and +6 valences.
  • ⁇ 1 is one or more of +3 and +4 valences.
  • the M 1 element may include one or more of Ti, Mo, V, Nb, Ru, Sb, and W.
  • the M 1 element may include one or more of Ti, Nb, Ru, Sb, and W.
  • the M 2 element may include one or more of Al, Zr, Zn, Y, and B.
  • the M 2 element may include one or more of Al, Zr, Zn, and Y.
  • the M 2 element may include one or more of Al, Zr, and Y.
  • the M 1 element is uniformly doped in the bulk particles.
  • the uniform doping of M 1 element can keep the properties of the body particles consistent throughout, and the structural stability of each position of the body particles is improved, which improves the problem of oxygen release at various positions of the body particles, thereby further improving the high-temperature storage of the positive electrode active material And the structural stability during high-temperature cycling, which can better improve the performance of the battery.
  • the M 1 element is uniformly doped in the bulk particles, which also makes the migration and diffusion capacity of lithium ions in different areas within the bulk particles at the same level, and the structural stability and deformation resistance of the bulk particles are close to each other, making the positive electrode active material particles
  • the stress distribution is uniform, and it is not prone to cracking, preventing side reactions and performance deterioration caused by the fresh surface exposed by the cracking, thereby further improving the energy density, high-temperature cycle performance and high-temperature storage performance of the battery.
  • the relative deviation of the local mass concentration of the M 1 element in the bulk particles is 32% or less, and further is 30% or less, such as 20% or less, 15% or less, 12% or less, 11% or less, or 10%. %the following. The smaller the relative deviation of the local mass concentration of the M 1 element in the bulk particles, the more uniform the distribution of the M 1 element in the bulk particles, and the better the overall performance of the battery.
  • the mass particles localized mass concentration of M 1 element is in the body of particles within any selected location point finite volume element, M 1 element representing the concentration of all the elements, by EDX (Energy Dispersive X-Ray Spectroscopy , energy Dispersive X-ray spectrometer) or EDS element analysis combined with TEM (Transmission Electron Microscope) or SEM (Scanning Electron Microscope) single-point scanning test element concentration distribution or other similar methods.
  • EDX Electronicgy Dispersive X-Ray Spectroscopy , energy Dispersive X-ray spectrometer
  • EDS element analysis combined with TEM (Transmission Electron Microscope) or SEM (Scanning Electron Microscope) single-point scanning test element concentration distribution or other similar methods.
  • the mass concentration of M 1 element in ⁇ g/g at different positions in the bulk particle is respectively denoted as ⁇ 1 , ⁇ 2 , ⁇ 3 ,..., ⁇ n , n is a positive integer greater than or equal to 15.
  • the average mass concentration of the M 1 element in the bulk particle is the mass concentration of the M 1 element in the range of a single bulk particle, which can be obtained by EDX or EDS element analysis combined with TEM or SEM surface scanning test element concentration distribution or other similar methods.
  • the test surface includes all the points in the single-point test.
  • the average mass concentration of M 1 element in the bulk particle is denoted as The unit is ⁇ g/g.
  • the bulk particles are secondary particles formed by agglomeration of two or more primary particles.
  • the positive electrode active material can thus have higher lithium ion transport performance, thereby improving the cycle performance of the battery.
  • the lithium ion transport performance of the positive electrode active material can be further improved, and the structural stability can also be improved, so that the battery can obtain higher cycle performance.
  • the molar ratio of M 1 element to M 2 element in the positive electrode active material may be 0.09:1 to 4:1, may also be 0.1:1 to 3:1, and further be 0.2:1 to 2.5: 1. It is further 0.5:1 to 2:1.
  • the molar ratio of the M 1 element to the M 2 element in the positive electrode active material is appropriate, which can better exert the synergistic effect of the doping modification of the M 1 element and the coating modification of the oxide containing the M 2 element. Under the synergistic effect, the irreversible structural phase change of the positive electrode active material can be effectively inhibited, and the surface of the positive electrode active material can be effectively protected from corrosion by the electrolyte, and the gas production of the battery can be reduced, thereby further improving the high-temperature cycle performance and high-temperature storage performance of the battery.
  • the above-mentioned molar ratio of the M 1 element to the M 2 element in the positive electrode active material is also beneficial to improve the ion conductivity of the positive electrode active material, thereby increasing the energy density of the battery.
  • the actual doping concentration ⁇ of the M 1 element in the positive electrode active material may be 2000 ⁇ g/cm 3 to 55000 ⁇ g/cm 3 , may also be 2300 ⁇ g/cm 3 to 49000 ⁇ g/cm 3 , or may be 3000 ⁇ g/cm 3 ⁇ 30000 ⁇ g/cm 3 , 11028 ⁇ g/cm 3 ⁇ 30000 ⁇ g/cm 3 , or 11028 ⁇ g/cm 3 ⁇ 25351 ⁇ g/cm 3 .
  • the positive electrode active material, the true doping concentration ⁇ M 1 element is 2000 ⁇ g / cm 3 or more, for example 3 or more and 2300 ⁇ g / cm 3 or more, or 3000 ⁇ g / cm, g capacity and can effectively improve the structural stability of the positive electrode active material, and reduce the The electrolyte oxidation activity on the surface of the material.
  • the true doping concentration ⁇ of M 1 element in the positive electrode active material is 55000 ⁇ g/cm 3 or less, for example, 49000 ⁇ g/cm 3 or less, or 30000 ⁇ g/cm 3 or less, which can make the positive electrode active material have a good layered crystal structure and prevent M 1 Element enters the lithium layer to ensure that the positive electrode active material provides a good carrier for the deintercalation of lithium ions, facilitates the intercalation and deintercalation of lithium ions, effectively inhibits the irreversible consumption of active lithium ions, and makes the positive electrode active material have a higher initial capacity and cycle Capacity retention rate.
  • the true doping concentration ⁇ of the M 1 element in the positive electrode active material is within the above range, which can well improve the energy density, high-temperature cycle performance, and high-temperature storage performance of the battery.
  • ⁇ is the actual doping concentration of M 1 element in the positive electrode active material, and the unit is ⁇ g/cm 3 .
  • ⁇ true positive electrode active material the true density in units of g / cm 3, which is equal to the ratio of the mass and the true volume of the positive electrode active material of the positive electrode active material, wherein the true volume is the actual volume of the solid material, not including the positive electrode active material particles And the pores between each other.
  • ⁇ true can be determined by using instruments and methods known in the art, such as the gas volume method, which can be performed by a powder true density tester.
  • Concentration of active material for the positive electrode to ⁇ g / g in units of the M 1 element, i.e., the mass M 1 element per gram of the positive electrode active material contained. among them, Content of the cathode active material representative of the entire macro M 1 element, comprising a body incorporating the positive electrode active material particles M 1 element, the positive electrode active material particle surface of the body of the other phase is enriched in M 1 element, and a positive electrode active material particles is located M 1 element between. It can be obtained by the absorption spectrum of the positive electrode active material solution, such as ICP (Inductive Coupled Plasma Emission Spectrometer), XAFS (X-ray absorption fine structure spectroscopy, X-ray absorption fine structure spectroscopy) and other tests.
  • ICP Inductive Coupled Plasma Emission Spectrometer
  • XAFS X-ray absorption fine structure spectroscopy, X-ray absorption fine structure spectroscopy
  • the content of the M 2 element in the positive electrode active material may be 300 ppm to 6500 ppm.
  • the content of M 2 element in the positive electrode active material can be ⁇ 300ppm, ⁇ 500ppm, ⁇ 1000ppm, ⁇ 1500ppm, ⁇ 2000ppm, or ⁇ 2500ppm; and can be ⁇ 3000ppm, ⁇ 3500ppm, ⁇ 4000ppm, ⁇ 4500ppm, ⁇ 5000ppm, or ⁇ 6500ppm.
  • the content of the M 2 element in the positive electrode active material is 500 ppm to 5000 ppm.
  • ppm (parts per million) is the mass of the M 2 element in the positive active material to the mass of the positive active material in parts per million.
  • the content of M 2 element in the positive electrode active material is within the above range, which can make the coating layer and the body particles have a higher bonding fastness, prevent the battery from falling off the coating layer during high temperature cycling and high temperature storage, thereby effectively exerting
  • the protective effect of the coating layer on the body particles enables the battery to have higher high-temperature cycle performance and high-temperature storage performance.
  • the positive electrode active material also maintains a higher lithium ion diffusion and migration ability, so that the battery has a higher energy density.
  • the content of M 2 element in the positive electrode active material can be measured by the absorption spectrum of the positive electrode active material solution, such as ICP (Inductive Coupled Plasma Emission Spectrometer), XAFS (X-ray absorption fine structure spectroscopy, X-ray absorption fine structure spectroscopy) Spectrum) and so on.
  • ICP Inductive Coupled Plasma Emission Spectrometer
  • XAFS X-ray absorption fine structure spectroscopy, X-ray absorption fine structure spectroscopy
  • the thickness T of the coating layer can be selected from 0.001 ⁇ m to 0.5 ⁇ m, such as 0.01 ⁇ m to 0.4 ⁇ m, for example, 0.1 ⁇ m to 0.3 ⁇ m, 0.21 ⁇ m to 0.3 ⁇ m, or 0.210 ⁇ m to 0.267 ⁇ m.
  • the thickness of the coating layer is within the above range, it is not easy to fall off from the body particles during the repeated lithium removal and lithium insertion process of the positive electrode active material, which can continue to play a protective effect on the body particles, while ensuring that the positive electrode active material has high lithium ions Diffusion migration capacity and gram capacity.
  • the thickness T of the coating layer and the average particle size of the positive electrode active material Meet between: Optional, Such as In this way, the protective effect of the coating layer on the body particles can be exerted more effectively, and the positive electrode active material can be guaranteed to have a higher lithium ion diffusion and migration ability and gram capacity.
  • the thickness of the coating layer can be measured by a method known in the art.
  • a cross-section polisher such as the IB-09010CP argon ion cross-section polisher of Japan Electronics (JEOL)
  • JEOL Japan Electronics
  • EDX or EDS Elemental analysis combined with TEM or SEM (such as the X-Max EDS of the Oxford Instruments Group in the United Kingdom and the Sigma-02-33 SEM of the German ZEISS) surface scanning test to obtain the element distribution map in the cross section; the coating layer is obtained according to the element distribution of the cross section thickness of.
  • the thickness of the coating layer at multiple (more than 3, such as 5, 8, 10, 12, etc.) different positions on the cross section can be tested, and the average value is recorded as the thickness of the coating layer.
  • Average particle size of positive electrode active material It is the average value of the diameters of the positive electrode active material particles in different orientations.
  • the element distribution diagram in the cross section of the positive electrode active material particles can be obtained, and multiple (3 or more, such as 5, 8, 10) can be obtained according to the element distribution of the cross section. No., 12, etc.) Diameters of different orientations, and the average value is recorded as the average particle size of the positive electrode active material
  • the volume average particle diameter Dv50 of the positive electrode active material can be selected from 8 ⁇ m to 20 ⁇ m, for example, 9 ⁇ m to 18 ⁇ m, and for example, 9 ⁇ m to 16 ⁇ m.
  • the Dv50 of the positive electrode active material within the above range can improve the transport and diffusion performance of lithium ions and electrons in the positive electrode active material particles, and is beneficial to reduce the side reaction of the electrolyte on the surface of the particles, inhibit the agglomeration between the particles, thereby improving the battery's performance Cycle performance and rate performance.
  • the D v 50 of the positive electrode active material within the above range also enables the positive electrode active material to have a higher compaction density, and improves the energy density of the battery.
  • the surface of the positive active material may be a rough surface. This is beneficial to increase the active specific surface area of the positive electrode active material and increase the capacity of the positive electrode active material.
  • the surface area of the positive electrode active material may be 0.2m 2 /g ⁇ 1.7m 2 / g, may also be 0.2m 2 /g ⁇ 1.5m 2 / g, e.g. 0.3m 2 / g ⁇ 1m 2 /g.
  • the specific surface area of the positive electrode active material is within the above range, which ensures that the positive electrode active material has a higher active specific surface area, and at the same time helps to reduce the side reaction of the electrolyte on the surface of the positive electrode active material, thereby improving the capacity and cycle life of the positive electrode active material .
  • the tap density of the positive electrode active material may be 2.3 g/cm 3 to 2.8 g/cm 3 . This is conducive to making the battery have a higher energy density.
  • the true density of the positive electrode active material may be 4.6 g/cm 3 ⁇ 5.2 g/cm 3 , and may also be 4.6 g/cm 3 ⁇ 4.9 g/cm 3 . If the true density of the positive electrode active material is in an appropriate range, the positive electrode active material can have a higher specific capacity and energy density, thereby improving the capacity performance and energy density of the battery.
  • the molar content of nickel in the lithium composite oxide accounts for 50%-95% of the total molar content of transition metal site elements, such as 50%, 60%, 65%, 70%, 75%, 80%, 85%. %, 90%, or 95%, etc.
  • the positive electrode active material has a higher specific capacity and can further increase the energy density of the battery.
  • the lithium composite oxide has a layered structure with lithium sites, transition metal sites, and oxygen sites.
  • the M 1 element is doped at the transition metal site.
  • the aforementioned transition metal site element refers to an element located at the transition metal site.
  • the lithium composite oxide is a compound shown in Chemical Formula 1,
  • M 1 is the substitution of one or more of the nickel site, the cobalt site and the manganese site of the bulk particle;
  • the battery using the high nickel ternary material can better combine higher energy density, high temperature cycle performance and high temperature storage performance.
  • 0.6 ⁇ x ⁇ 0.9 such as 0.7 ⁇ x ⁇ 0.8.
  • X can be selected from one or more of F, N and S.
  • X includes F.
  • the X elements when the bulk particles are doped with X elements, can be uniformly doped in the bulk particles, such as the relative deviation of the local mass concentration of doping elements (including M 1 and X elements) in the bulk particles It can be 32% or less, for example 30% or less, and even 20% or less.
  • the uniformly doped positive electrode active material has better overall structural stability.
  • the X element can also have a decreasing mass concentration gradient from the outer surface of the bulk particle to the direction of the particle core.
  • the X element is doped in the outer surface layer of the bulk particles. This can reduce the surface oxygen activity of the material, and at the same time make the material have both high dynamic performance and gram capacity.
  • the volume average particle size Dv50 of the positive electrode active material has a well-known meaning in the art, and is also called the median particle size, which represents the particle size corresponding to 50% of the volume distribution of the positive electrode active material particles.
  • the volume average particle size D v 50 of the positive electrode active material can be measured with instruments and methods known in the art, for example, it can be conveniently measured with a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Co., Ltd., UK.
  • the specific surface area of the positive electrode active material is a well-known meaning in the art, and it can be measured by instruments and methods known in the art. For example, it can be measured by the nitrogen adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method, where The nitrogen adsorption specific surface area analysis test can be carried out by the NOVA 2000e specific surface area and pore size analyzer of the United States Conta Company.
  • the test method is as follows: take 8.000g ⁇ 15.000g of positive electrode active material in a weighed empty sample tube, stir and weigh the positive electrode active material, and put the sample tube into the NOVA 2000e degassing station for degassing , Weigh the total mass of the positive electrode active material and the sample tube after degassing, and calculate the mass G of the positive electrode active material after degassing by subtracting the mass of the empty sample tube from the total mass.
  • the tap density of the positive electrode active material is a well-known meaning in the art, and can be measured with a well-known instrument and method in the art, for example, a tap density meter, such as FZS4-4B type tap density meter.
  • the preparation method includes a bulk particle preparation step S10 and a coating layer preparation step S20.
  • the aforementioned nickel-containing transition metal source is, for example, one or more of Ni-containing oxides, hydroxides, and carbonates, such as hydroxides containing Ni, Co, and Mn.
  • the hydroxides containing Ni, Co, and Mn can be obtained by methods known in the art, for example, by co-precipitation method, gel method or solid phase method.
  • the Ni source, Co source, and Mn source are dispersed in a solvent to obtain a mixed solution; the mixed solution, strong alkali solution and complexing agent solution are simultaneously pumped into a stirred reactor by means of continuous co-current reaction. , Control the pH of the reaction solution to be 10-13, the temperature in the reactor is 25°C to 90°C, and pass inert gas protection during the reaction; after the reaction is completed, it is aged, filtered, washed and vacuum dried to obtain Ni , Co and Mn hydroxides.
  • the Ni source may be a soluble nickel salt, such as one or more of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate, and another example, one or more of nickel sulfate and nickel nitrate, Another example is nickel sulfate;
  • the Co source can be a soluble cobalt salt, such as one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate, and another example is cobalt sulfate and cobalt nitrate.
  • the Mn source may be a soluble manganese salt, such as one or more of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate and manganese acetate, and another example is sulfuric acid One or more of manganese and manganese nitrate, and another example is manganese sulfate.
  • the strong base may be one or more of LiOH, NaOH, and KOH, for example, NaOH.
  • the complexing agent may be one or more of ammonia, ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium citrate, and disodium ethylenediaminetetraacetic acid (EDTA), for example, ammonia.
  • the solvents of the mixed solution, strong base solution and complexing agent solution are each independently deionized water, methanol, ethanol, acetone, and isopropyl.
  • the solvents of the mixed solution, strong base solution and complexing agent solution are each independently deionized water, methanol, ethanol, acetone, and isopropyl.
  • the inert gas introduced during the reaction is, for example, one or more of nitrogen, argon, and helium.
  • the above-mentioned lithium source may be lithium oxide (Li 2 O), lithium phosphate (Li 3 PO 4 ), lithium dihydrogen phosphate (LiH 2 PO 4 ), lithium acetate (CH 3 COOLi), lithium hydroxide (LiOH), lithium carbonate One or more of (Li 2 CO 3 ) and lithium nitrate (LiNO 3 ). Further, the lithium source is one or more of lithium carbonate, lithium hydroxide, and lithium nitrate; further, the lithium source is lithium carbonate.
  • M 1 element precursor may be an oxide of the element M 1, nitrates, carbonates, bicarbonates, sulfates, chlorides, acetates and oxyhydroxides of one or more, according to the actual Need to choose.
  • the precursor of element M 1 M 1 element oxides such as silicon oxide (e.g.
  • SiO 2, SiO, etc. titanium oxide (e.g., TiO 2, TiO, etc.), chromium oxide (e.g., CrO 3, Cr 2 O 3 etc.), molybdenum oxide (such as MoO 2 , MoO 3, etc.), vanadium oxide (such as V 2 O 5 , V 2 O 4 , V 2 O 3, etc.), selenium oxide (such as SeO 2, etc.), niobium oxide (such as Nb 2 O 5 , NbO 2, etc.), ruthenium oxide (such as RuO 2 ), palladium oxide (such as PdO, etc.), rhodium oxide (such as Rh 2 O 3, etc.), antimony oxide (such as Sb 2 O 5 , Sb 2 O 3 etc.), one or more of tellurium oxide (such as TeO 2 etc.), cerium oxide (such as CeO 2 etc.) and tungsten oxide (such as WO 2 , WO 3 etc.).
  • titanium oxide e.g., TiO 2, Ti
  • a ball mill mixer or a high-speed mixer can be used to mix the materials.
  • the transition metal source containing nickel, the lithium source and the precursor of the M 1 element are added to a high-speed mixer and mixed, and the mixing time can be 0.5h-3h.
  • the mixed materials can be added to the atmosphere sintering furnace for sintering.
  • the sintering atmosphere is an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen atmosphere.
  • the O 2 concentration of the sintering atmosphere is, for example, 70% to 100%, further 80% or more, and still further 85% or more.
  • the sintering temperature is, for example, 500°C to 1000°C, for example, 600°C to 1000°C, and for example, 700°C to 900°C, such as 750°C to 850°C. This is conducive to uniformly doping the M 1 element in the bulk particles, in particular, the M 1 element has a higher doping uniformity in the bulk particles.
  • the sintering time can be adjusted according to the actual situation, for example, 5h-25h, for example, 5h-15h.
  • the positive electrode active material there are many theoretically feasible ways to control the distribution of M 1 elements in the lithium nickel composite oxide and the valence states of different delithiation states, such as the M 1 element precursor itself The valence state, the dosage ratio of the precursors of different M 1 element valence states, the oxidability of the sintering atmosphere during doping, the number of sintering, the uniformity of mixing, the sintering temperature, the sintering time, etc.
  • methods for controlling the type, sintering time and temperature of the doping precursor in the S10 step are listed to obtain a series of positive electrode active materials.
  • the positive electrode active material has the characteristics of high energy density, thermal stability and high temperature cycle stability.
  • the positive electrode active material with the characteristics of the valence state of the M 1 element in different delithiation states has better effects.
  • the sintered product may be crushed and sieved to obtain a positive electrode active material with optimized particle size distribution and specific surface area.
  • the crushing method There are no special restrictions on the crushing method, and it can be selected according to actual needs, such as using a particle crusher.
  • Precursor elements M 2 M 2 element may be chlorides, sulfates, nitrates, oxides, hydroxides, fluorides, carbonates, bicarbonates, acetates, phosphate, dihydrogen phosphate And one or more of organic compounds, but not limited thereto.
  • step S20 a ball mill mixer or a high-speed mixer can be used to mix the materials.
  • the bulk particles and the precursor of the M 2 element are added to a high-speed mixer for mixing, and the mixing time is 0.5h-3h.
  • the mixed materials can be added to the atmosphere sintering furnace for sintering.
  • the sintering atmosphere is an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen atmosphere.
  • the O 2 concentration of the sintering atmosphere is, for example, 70% to 100%, further 80% or more, and still further 85% or more.
  • the sintering temperature is, for example, 100°C to 550°C, and further, for example, 200°C to 500°C, 240°C to 310°C, or 260°C to 310°C.
  • the sintering time can be 3h-25h, such as 5h-10h.
  • the oxide of the M 2 element is not easy to diffuse into the body particles, but forms a coating layer covering the outer surface of the body particles.
  • the M 2 element matches the surface lattice of the body particles, so that the coating layer and the body particles are closely combined, and the coating layer will not damage the structure of the body particles, so that the coating layer can reliably protect the body particles.
  • the mixture further includes a precursor of X element, and the obtained bulk particles are also doped with X element, and X element is selected from one of F, N, P, and S. Kind or more.
  • the precursor of the X element can be selected from, for example, ammonium fluoride, lithium fluoride, hydrogen fluoride, elemental phosphorus, phosphorus oxide, ammonium dihydrogen phosphate, ammonium metaphosphate, ammonium dihydrogen phosphite, ammonium nitrate, ammonium nitrite, ammonium carbonate, One or more of ammonium bicarbonate, ammonium sulfate, ammonium bisulfate, ammonium bisulfite, ammonium sulfite, ammonium bisulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur, but not limited thereto.
  • step S20 it may further include step S30: mixing the bulk particles with the precursor of the X element, and performing a sintering process, so that the X element is doped in the bulk particles.
  • step S30 the precursor of the X element as described above can be used.
  • a ball mill mixer or a high-speed mixer can be used to mix the materials.
  • the bulk particles and the precursor of the X element are added to a high-speed mixer for mixing, and the mixing time can be 0.5h-3h.
  • the mixed materials can be added to the atmosphere sintering furnace for sintering.
  • the sintering atmosphere is an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen atmosphere.
  • the O 2 concentration of the sintering atmosphere is, for example, 70% to 100%, and further 80% to 95%.
  • the sintering temperature is, for example, 400°C to 1000°C, such as 400°C to 850°C, and then 400°C to 750°C.
  • the sintering time can be 3h-25h, such as 5h-10h.
  • the X element By adjusting the sintering temperature and the sintering time, the X element can be uniformly doped into the bulk particles, or the outer surface of the X element bulk particles can have a reduced mass concentration gradient from the direction of the particle core.
  • This application also provides a positive pole piece, which includes any one or more of the above-mentioned positive electrode active materials.
  • the positive pole piece of the embodiment of the present application adopts the positive electrode active material of the embodiment of the present application, it also has the above-mentioned beneficial effects.
  • the use of the positive pole piece of the present application enables the lithium ion secondary battery to simultaneously take into account good high-temperature cycle performance, high-temperature storage performance, and higher energy density.
  • the positive pole piece includes a positive current collector and a positive active material layer provided on at least one surface of the positive current collector.
  • the positive electrode current collector includes two opposite surfaces in its thickness direction, and the positive electrode active material layer is stacked on either or both of the two surfaces of the positive electrode current collector.
  • the positive electrode active material layer includes any one or more of the positive electrode active materials mentioned in the embodiments of the present application.
  • the positive active material layer may further include a conductive agent and a binder.
  • This application does not specifically limit the types of conductive agents and binders in the positive active material layer, and can be selected according to actual needs.
  • the conductive agent may be one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers;
  • the binder may be styrene-butadiene Rubber (SBR), water-based acrylic resin, sodium carboxymethyl cellulose (CMC-Na), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butadiene Aldehyde (PVB), ethylene-vinyl acetate copolymer (EVA), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene- One or more of hexafluoropropylene copolymer, fluorine-containing acrylic resin and polyvinyl alcohol
  • the positive electrode current collector can be a metal foil or porous metal plate with good electrical conductivity and mechanical properties, such as aluminum foil.
  • the positive pole piece can be prepared according to conventional methods in the art.
  • the positive electrode active material, conductive agent, and binder are dispersed in a solvent.
  • the solvent can be N-methylpyrrolidone (NMP) to form a uniform positive electrode slurry.
  • NMP N-methylpyrrolidone
  • the positive electrode slurry is coated on the positive electrode current collector and dried. After drying and rolling, the positive pole piece is obtained.
  • the embodiments of the present application also provide a lithium ion secondary battery.
  • the lithium ion secondary battery includes a positive pole piece, a negative pole piece, a separator and an electrolyte, wherein the positive pole piece is the above-mentioned positive pole piece.
  • the lithium ion secondary battery adopts the positive pole piece of the embodiment of the present application, it can simultaneously take into account good room temperature and high temperature cycle performance, high high temperature storage performance, and high energy density.
  • the negative pole piece may be a metal lithium piece.
  • the negative pole piece may also include a negative current collector and a negative active material layer provided on at least one surface of the negative current collector.
  • the negative electrode current collector includes two opposite surfaces in the thickness direction of the negative electrode current collector, and the negative electrode active material layer is stacked on either or both of the two surfaces of the negative electrode current collector.
  • the anode active material layer includes an anode active material.
  • the embodiments of the present application do not specifically limit the types of negative electrode active materials, and can be selected according to actual needs.
  • the negative active material layer may further include a conductive agent and a binder.
  • a conductive agent is one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers
  • the binder is styrene butadiene rubber One or more of (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), and water-based acrylic resin.
  • the negative active material layer may also optionally include a thickener, such as sodium carboxymethyl cellulose (CMC-Na).
  • a thickener such as sodium carboxymethyl cellulose (CMC-Na).
  • the negative electrode current collector can be a metal foil or porous metal plate with good electrical conductivity and mechanical properties, such as copper foil.
  • the negative pole piece can be prepared according to conventional methods in the art. For example, disperse the negative electrode active material, conductive agent, binder and thickener in a solvent.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water to form a uniform negative electrode slurry, and then coat the negative electrode slurry.
  • NMP N-methylpyrrolidone
  • the electrolyte may be a solid electrolyte, such as a polymer electrolyte, an inorganic solid electrolyte, etc., but it is not limited thereto. Electrolyte can also be used as the electrolyte. As the above-mentioned electrolyte solution, a solvent and a lithium salt dissolved in the solvent are included.
  • the solvent can be a non-aqueous organic solvent, such as ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), carbonic acid Dipropyl ester (DPC), methyl propyl carbonate (MPC), ethylene propyl carbonate (EPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA) , One or more of methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) and ethyl butyrate (EB). For example, there are two or more types.
  • EC ethylene carbonate
  • PC propylene carbonate
  • EMC diethyl carbonate
  • DMC dimethyl carbonate
  • DPC carbonic acid Dipropyl ester
  • MPC methyl propyl carbon
  • the lithium salt can be LiPF 6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO 4 (lithium perchlorate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonimide), LiTFSI ( Lithium bistrifluoromethanesulfonimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium bisoxalate borate), LiPO 2 F 2 (lithium difluorophosphate), LiDFOP One or more of (lithium difluorooxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate), such as LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiBOB (lithium bis
  • the electrolyte may also optionally contain other additives, such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), three Fluoromethyl ethylene carbonate (TFPC), succinonitrile (SN), adiponitrile (ADN), glutaronitrile (GLN), hexanetrinitrile (HTN), 1,3-propane sultone (1 , 3-PS), ethylene sulfate (DTD), methylene disulfonate (MMDS), 1-propene-1,3-sultone (PST), 4-methyl ethylene sulfate (PCS), 4-ethyl ethylene sulfate (PES), 4-propyl ethylene sulfate (PEGLST), propylene sulfate (TS), 1,4-butane sultone (1,4-BS ), ethylene sulfite (DTO), dimethyl sulfite (DM
  • the lithium ion secondary battery in the embodiments of the present application has no special restrictions on the separator.
  • Any well-known separator with a porous structure with electrochemical stability and mechanical stability can be selected, such as glass fiber, non-woven fabric, polyethylene (PE ), polypropylene (PP) and polyvinylidene fluoride (PVDF) one or more of single-layer or multi-layer films.
  • PE polyethylene
  • PP polypropylene
  • PVDF polyvinylidene fluoride
  • the positive pole piece and the negative pole piece are alternately stacked, and an isolation film is arranged between the positive pole piece and the negative pole piece for isolation to obtain a battery core, which can also be obtained after winding. Placing the electric core in the casing, injecting electrolyte, and sealing to obtain a lithium ion secondary battery.
  • FIG. 3 shows a lithium ion secondary battery 5 with a square structure as an example.
  • the lithium ion secondary battery may include an outer package.
  • the outer packaging is used to encapsulate the positive pole piece, the negative pole piece and the electrolyte.
  • 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 plate enclose to form an accommodating cavity.
  • the housing 51 has an opening communicating with the containing cavity, and a cover plate 53 can cover the opening to close the containing cavity.
  • the positive pole piece, the negative pole piece, and the separator may be formed into the cell 52 through a winding process or a lamination process.
  • the battery core 52 is encapsulated in the containing cavity.
  • the electrolyte can be an electrolyte, and the electrolyte is infiltrated in the cell 52.
  • the number of battery cells 52 contained in the lithium ion secondary battery 5 can be one or several, which can be adjusted according to requirements.
  • the outer packaging of the lithium ion secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like.
  • the outer packaging of the lithium ion secondary battery may also be a soft bag, such as a pouch type soft bag.
  • the material of the soft bag can be plastic, for example, it can include one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.
  • the lithium ion secondary battery can be assembled into a battery module, and the number of lithium ion secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • Fig. 5 is a battery module 4 as an example.
  • a plurality of lithium ion secondary batteries 5 may be arranged in order along the length direction of the battery module 4. Of course, it can also be arranged in any other manner. Furthermore, the plurality of lithium ion secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having an accommodating space, and a plurality of lithium ion secondary batteries 5 are accommodated in the accommodating space.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • Fig. 6 and Fig. 7 are the battery pack 1 as an example. 6 and 7, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided 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 be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4.
  • a plurality of battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides a device, which includes at least one of the lithium ion secondary battery, battery module, or battery pack described in the present application.
  • the lithium ion secondary battery, battery module or battery pack can be used as a power source of the device, and can also be used as an energy storage unit of the device.
  • the device can be, but is not limited to, consumer electronic products, electric vehicles, and the like.
  • the device may be a mobile device (such as a mobile phone, a tablet computer, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric pedal Vehicles, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • a mobile device such as a mobile phone, a tablet computer, a notebook computer, etc.
  • an electric vehicle such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric pedal Vehicles, electric golf carts, electric trucks, etc.
  • electric trains ships and satellites, energy storage systems, etc.
  • the device can select a lithium ion secondary battery, battery module, or battery pack according to its usage requirements.
  • Fig. 8 is a device as an example.
  • the device is an electric vehicle, which can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • a battery pack or a battery module can be used.
  • the sintering temperature is 825°C
  • the sintering atmosphere is an oxygen-containing atmosphere with an O 2 concentration of 90%
  • the sintering time is 15 hours.
  • the bulk particles can be obtained after crushing and sieving, in which the Sb is uniform. Doped in the bulk structure of the bulk particles.
  • the positive pole piece, the isolation film and the metal lithium piece are stacked in sequence, and the above-mentioned electrolyte is injected to assemble the button battery.
  • the positive electrode active material, the conductive agent acetylene black and the binder PVDF prepared above are dispersed in the solvent NMP at a weight ratio of 94:3:3 and mixed uniformly to obtain the positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector After drying and cold pressing on the aluminum foil, a positive pole piece is obtained.
  • the negative active material artificial graphite, hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR), thickener sodium carbon methyl cellulose (CMC) are dispersed in a weight ratio of 90:5:2:2:1 Mixing evenly in deionized water to obtain negative electrode slurry; uniformly coating the negative electrode slurry on the negative electrode current collector aluminum foil, drying and cold pressing, to obtain a negative electrode pole piece.
  • PE Polyethylene
  • Example 1 The difference from Example 1 is that the relevant parameters in the preparation steps of the positive electrode active material are changed to obtain the positive electrode active material with predetermined parameter characteristics, as shown in Table 1-1 to Table 1-2 for details.
  • the positive electrode active material precursors of Examples 2-25 and Comparative Examples 1-5 are all [Ni 0.8 Co 0.1 Mn 0.1 ](OH) 2 ; the positive electrode active material precursors of Examples 26-28 and Comparative Examples 6-8
  • the body is [Ni 0.5 Co 0.2 Mn 0.3 (OH) 2 .
  • the precursor of the element M 1 in Example 2 is TiO; the precursor of the element M 1 in Examples 3, 20, 21, 24, and 25 is NbO 2 ; the precursor of the element M 1 in Example 4 is MoO 2 ; implementation Example 5 precursor elements is M 1 RuO 2; M 1 element in embodiment 6 of the precursor of Example V 2 O 3; Example M 1 element is a precursor 7,22,23,27 WO 2; embodiment The precursor of M 1 element in Example 8 is Sb 2 O 3 and WO 2 , and the content of each precursor is basically the same; the precursor of M 1 element in Comparative Example 4 is Y 2 O 3 ; the M 1 element in Comparative Example 5 The precursor of is MgO;
  • the remaining precursors of M 2 elements that are different from those in Example 1 are selected from B 2 O 3 , ZrO 2 , ZnO, and Y 2 O 3 ;
  • the sintering temperature is 615°C and the sintering time is 5h; the step (2) the sintering temperature is 305°C, and the sintering time is 8h;
  • Step (1) the sintering temperature of Example 21 is 550°C, and the sintering time is 2h; Step (2) the sintering temperature is 290°C, and the sintering time is 9h;
  • the step (1) the sintering temperature of Example 22 is 810°C, and the sintering time is 15h; the step (2) the sintering temperature is 110°C, and the sintering time is 3h;
  • the step (1) the sintering temperature of Example 23 is 830°C, and the sintering time is 15h; the step (2) the sintering temperature is 550°C, and the sintering time is 20h;
  • Step (1) the sintering temperature of Example 24 is 770°C, and the sintering time is 16h; Step (2) the sintering temperature is 310°C, and the sintering time is 7h;
  • Step (1) the sintering temperature of Example 25 is 750°C, and the sintering time is 17h; Step (2) the sintering temperature is 260°C, and the sintering time is 9h;
  • Steps (1) of Examples 26, 27 and Comparative Example 7 are sintering temperature of 790°C and sintering time of 12h; Step (2) sintering temperature of 280°C and sintering time of 7h;
  • Step (1) the sintering temperature of Example 28 is 500°C, and the sintering time is 2h; Step (2) the sintering temperature is 240°C, and the sintering time is 6h;
  • Comparative Example 1 and Comparative Example 6 were not doped and coated, and both were sintered once; the sintering temperature of Comparative Example 1 was 825°C, and the sintering time was 15h; the sintering temperature of Comparative Example 6 was 790°C, and the sintering time was 12h ;
  • Comparative Example 2 and Comparative Example 7 are not doped with M 1 element
  • Comparative Example 3 and Comparative Example 8 are not coated with M 2 element, and both are sintered once; the sintering temperature of Comparative Example 3 is 825° C. and the sintering time is 15 h; the sintering temperature of Comparative Example 8 is 790° C. and the sintering time is 12 h.
  • ⁇ represents the relative deviation of the local mass concentration of M 1 element in the bulk particle
  • the concentration of the element M 1 is true doping concentration of the element M 1 in the positive electrode active material
  • the content of M 2 element is the content of M 2 element in the positive electrode active material
  • the molar ratio represents the molar ratio of M 1 element to M 2 element in the positive electrode active material
  • charge 18 button batteries with a constant current of 1C to the upper limit of the charge and discharge cut-off voltage, then charge at a constant voltage until the current is less than or equal to 0.05mA, then leave it aside for 2 minutes, and then discharge at a constant current of 1C until the charge and discharge cut-off Lower voltage limit.
  • the 18 button batteries after the above charge and discharge were charged to 2.8V, 2.9V, 3.0V, 3.1V, 3.2V, 3.3V,...4.0V, 4.1V, 4.2V, at a rate of 0.1C, respectively.
  • 4.3V, 4.4V, 4.5V that is, the charging voltage interval is 0.1V).
  • the corresponding battery voltage is 2.8V.
  • the chemical formula of the positive electrode active material is Li 0.22 Ni 0.8 Co 0.1 Mn 0.1 O 2 converted by the ICP-OES test, the corresponding voltage is the voltage corresponding to the 78% delithiation state.
  • the pole pieces containing the positive electrode active material to be tested are taken, and the button cell is fabricated according to the above method.
  • FIG. 2 shows the 17 positions of the particle cross section, each with an area of 20nm ⁇ 20nm, using the X-Max energy spectrometer (EDS) of the Oxford Instruments Group in the United Kingdom and the Sigma-02-33 scanning of the German ZEISS The electron microscope (SEM) tests the mass concentration of M 1 elements at the 17 sites.
  • EDS X-Max energy spectrometer
  • SEM electron microscope
  • the test method is as follows: select Li, O, Ni, Co, Mn and doping elements for the detection elements, set the SEM parameters to 20kV acceleration voltage, 60 ⁇ m aperture , 8.5mm working distance, 2.335A current, when performing EDS test, it is necessary to stop the test when the spectrum area reaches more than 250,000 cts (controlled by acquisition time and acquisition rate), and collect data to obtain the mass concentration of M 1 element at each point. Denoted as ⁇ 1 , ⁇ 2 , ⁇ 3 ,..., ⁇ 17 respectively .
  • the average mass concentration of M 1 element in the bulk particle Measurement method The above-mentioned EDS-SEM testing method is adopted, as shown by the dashed frame in Figure 2, the test area covers all the points scanned by the above-mentioned body particle point and does not exceed the cross section of the body particle.
  • the test method is as follows: Take the pole piece containing the positive electrode active material and punch it into a disc with a total mass greater than 0.5g or take at least 5g of the positive electrode active Material powder sample, weigh and record the quality of the sample, put it into the digestion tank, slowly add 10mL of aqua regia as a digestion reagent, and then put it into the Mars5 microwave digestion instrument of CEM Company in the United States, and perform digestion at 2450Hz microwave emission frequency; after digestion The sample solution was transferred to a volumetric flask and shaken well, the sample was put into the ICP-OES sampling system, and the content of M 1 element and M 2 element in the positive electrode active material was tested with 0.6 MPa argon pressure and 1300 W radio frequency power.
  • the TD2400 powder true density tester of Beijing Biode Electronic Technology Co., Ltd. is used to determine the true density ⁇ true of the positive electrode active material.
  • the charge-discharge cut-off voltage of the button cell is 2.8V-4.35V
  • the charge-discharge cut-off voltage of the full battery is 2.8V-4.3V.
  • the channels and barriers for lithium ion diffusion inside the cathode active material particles are inconsistent, and the structural stability and deformation resistance of each region are different, resulting in the material
  • the internal stress is unevenly distributed, and areas with high internal stress are prone to cracks, which exposes a fresh surface of the positive electrode active material, increases impedance, and deteriorates capacity performance, high-temperature cycle performance, and high-temperature storage performance.

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Abstract

本申请公开一种正极活性材料、其制备方法、正极极片、锂离子二次电池及包含锂离子二次电池的装置。正极活性材料包括本体颗粒和包覆在本体颗粒外表面的包覆层，本体颗粒包括含镍元素及掺杂元素M 1的锂复合氧化物，包覆层包括M 2元素的氧化物；正极活性材料在11％脱锂态时，M 1元素的平均化合价为α 1，M 2元素的平均化合价为β 1；正极活性材料在78％脱锂态时，M 1元素的平均化合价为α 2，M 2元素的平均化合价为β 2；α 2＞α 1且β 1＝β 2；M 1元素包括Si、Ti、Cr、Mo、V、Se、Nb、Ru、Rh、Pd、Sb、Te、Ce及W中的一种或多种，M 2元素选自Mg、Al、Ca、Zr、Zn、Y及B中的一种或多种。

Description

正极活性材料、其制备方法、正极极片、锂离子二次电池及包含锂离子二次电池的装置
相关申请的交叉引用
本申请要求享有于2019年09月02日提交的名称为“正极活性材料、其制备方法、正极极片及锂离子二次电池”的中国专利申请201910825311.4的优先权，该申请的全部内容通过引用并入本文中。
技术领域
本申请属于二次电池技术领域，具体涉及一种正极活性材料、其制备方法、正极极片、锂离子二次电池及包含锂离子二次电池的装置。
背景技术
锂离子二次电池是一种充电电池，它主要依靠锂离子在正极和负极之间移动来工作，是当前被广泛应用的清洁能源。正极活性材料作为锂离子二次电池的重要组成部分，为电池充放电过程提供在正负极往复移动的锂离子，因此正极活性材料对电池性能的发挥至关重要。
随着锂离子二次电池被越来越多地应用于消费类电子产品、电动汽车等各类装置中，人们对锂离子二次电池的能量密度及高温循环性能也提出了更高的要求。
发明内容
本申请第一方面提供一种正极活性材料，其包括本体颗粒和包覆在本体颗粒外表面的包覆层，本体颗粒包括含镍元素及掺杂元素M 1的锂复合氧化物，包覆层包括M 2元素的氧化物；
正极活性材料在11％脱锂态时，M 1元素的平均化合价为α 1，M 2元素的平均化合价为β 1；正极活性材料在78％脱锂态时，M 1元素的平均化合价为α 2，M 2元素的平均化合价为β 2；α 1和α 2满足α 2＞α 1，且β 1和β 2满足β 1＝β 2；
M 1元素包括Si、Ti、Cr、Mo、V、Se、Nb、Ru、Rh、Pd、Sb、Te、Ce及W中的一种或多种，M 2元素选自Mg、Al、Ca、Zr、Zn、Y及B中的一种或多种。
本申请提供的正极活性材料包括含镍元素及掺杂元素M 1的锂复合氧化物本体颗粒，在本体颗粒的外表面具有M 2元素的氧化物包覆层，且随着正极活性材料的脱锂，M 1元素的平均化合价升高，M 2元素的平均化合价恒定不变。由此，该正极活性材料的容量发挥得到大幅度提高，能使采用其的锂离子二次电池的能量密度得到显著提升。同时，该正极活性材料在高温循环及高温存储过程中的结构稳定性得到大幅度提高，且该正极活性材料表面的电解液氧化活性大幅度降低，能减少电池在高温循环及高温存储过程中的电解液分解产气量，因此使得电池的高温循环性能和高温存储性能也得到显著提高。
在上述任意实施方式中，可选的，所述α 1和α 2满足α 2＞α 1≥+3。电池具有更好的高温循环性能和高温存储性能。
在上述任意实施方式中，可选的，所述α 1为+3、+4、+5和+6价中的一种或多种。可选的，所述α 1为+3和+4价中的一种或多种。α 1满足上述条件，能进一步提高电池的高温循环性能和高温存储性能，还可以进一步提高电池的能量密度。
在上述任意实施方式中，M 1元素可包括Ti、Mo、V、Nb、Ru、Sb和W中的一种或多种；可选的，M 1元素包括Ti、Nb、Ru、Sb和W中的一种或多种；或，M 2元素包括Al、Zr、Zn、Y及B中的一种或多种；可选的，M 2元素包括Al、Zr、Zn和Y中的一种或多种；可选的，M 2元素包括Al、Zr和Y中的一种或多种。采用合适的M 1元素或M 2元素，能进一步改善电池的高温循环性能和高温存储性能，还可以进一步提高电池的能量密度。
在上述任意实施方式中，可选的，M 1元素在所述本体颗粒中均匀掺杂。M 1元素均匀掺杂于本体颗粒中，能进一步提高电池的能量密度、高温循环性能和高温存储性能。本体颗粒中M 1元素的局部质量浓度的相对偏差越小，则本体颗粒中M 1元素的分布越均匀，电池的综合性能越好。可选的，所述本体颗粒中M 1元素的局部质量浓度的相对偏差为32％以下，可选的为20％以下。
在上述任意实施方式中，所述本体颗粒为两个以上一次颗粒聚集而成的二次颗粒。正极活性材料由此能具有较高的锂离子传输性能，从而改善电池的循环性能。尤其是，当M 1元素在二次颗粒中均匀掺杂时，能进一步改善正极活性材料的锂离子传输性能，并且还能提高结构稳定性，从而使电池获得更高的循环性能。
在上述任意实施方式中，所述正极活性材料中，所述M 1元素与所述M 2元素的摩尔比为0.09∶1～4∶1，可选的为0.1∶1～3∶1，可选的为0.2∶1～2.5∶1，可选的为0.5∶1～ 2∶1。正极活性材料中M 1元素与M 2元素的摩尔比适当，能进一步提高电池的高温循环性能及高温存储性能。
在上述任意实施方式中，所述正极活性材料中所述M 1元素的真实掺杂浓度为2000μg/cm 3～55000μg/cm 3，可选的为2300μg/cm 3～49000μg/cm 3，可选的为3000μg/cm 3～30000μg/cm 3。正极活性材料中M 1元素的真实掺杂浓度在上述范围内，能很好地提升电池的能量密度、高温循环性能和高温存储性能。
在上述任意实施方式中，所述正极活性材料中所述M 2元素的含量为300ppm～6500ppm，可选的为500ppm～5000ppm。正极活性材料中M 2元素的含量在上述范围内，能使电池具有较高的高温循环性能和高温存储性能，同时使电池具有较高的能量密度。
在上述任意实施方式中，所述正极活性材料的体积平均粒径Dv50可以为8μm～20μm，可选的为9μm～16μm。正极活性材料的Dv50在适当范围内，能提高电池的循环性能及倍率性能，同时有利于使电池获得较高的能量密度。
在上述任意实施方式中，所述包覆层的厚度T为0.001μm～0.5μm，可选的为0.1μm～0.3μm。可选的，所述包覆层的厚度T与所述正极活性材料的平均颗粒粒径
Figure PCTCN2020112914-appb-000001
之间满足：
Figure PCTCN2020112914-appb-000002
可选的，
Figure PCTCN2020112914-appb-000003
可选的，
Figure PCTCN2020112914-appb-000004
Figure PCTCN2020112914-appb-000005
包覆层满足上述条件，能有效提高电池的高温循环性能和高温存储性能。
在上述任意实施方式中，所述锂复合氧化物为化学式1所示的化合物，
Li 1+a[Ni xCo yMn zM 1 b]O 2-pX p      化学式1
所述化学式1中，X选自F、N、P及S中的一种或多种，0.5≤x＜1，0≤y＜0.3，0≤z＜0.3，-0.2＜a＜0.2，0＜b＜0.2，0≤p＜0.2，x+y+z+b＝1。
采用上述高镍三元材料的电池能更好地兼具较高的能量密度、高温循环性能和高温存储性能。
在上述任意实施方式中，当本体颗粒掺杂有X元素时，X元素均匀掺杂于本体颗粒中，可选的，本体颗粒中掺杂元素(含M 1元素和X元素)的局部质量浓度的相对偏差为32％以下，可选的为30％以下，还可选的为20％以下；或，X元素由本体颗粒的外表面至颗粒核心方向呈减小的质量浓度梯度；可选的，X元素掺杂于本体颗粒的外表层。
在上述任意实施方式中，所述正极活性材料的表面为粗糙表面。可选的，所述正极活性材料的比表面积为0.2m 2/g～1.5m 2/g，还可选为0.3m 2/g～1m 2/g。正极活性材 料的比表面积在上述范围内，能提高正极活性材料的容量发挥和循环寿命。
在上述任意实施方式中，所述正极活性材料的真密度为4.6g/cm 3～5.2g/cm 3，可选为4.6g/cm 3～4.9g/cm 3。正极活性材料的真密度在适当范围内，能提高电池的能量密度。
在上述任意实施方式中，所述正极活性材料的振实密度为2.3g/cm 3～2.8g/cm 3。正极活性材料的振实密度在适当范围内，能提高电池的能量密度。
本申请第二方面提供一种正极极片，其包括正极集流体以及设置于正极集流体上的正极活性物质层，正极活性物质层包括本申请第一方面的正极活性材料。
本申请的正极极片包括本申请的正极活性材料，因而能使采用其的锂离子二次电池同时兼顾较高的能量密度、高温存储性能和高温循环性能。
本申请第三方面提供一种锂离子二次电池，其包括本申请第二方面的正极极片。
本申请的锂离子二次电池包括本申请的正极极片，因而能同时兼顾较高的能量密度、高温存储性能和高温循环性能。
本申请第四方面提供一种装置，其包括本申请第三方面的锂离子二次电池。
本申请的装置包括本申请的锂离子二次电池，因而可具有相同或类似的有益效果。
本申请第五方面提供一种正极活性材料的制备方法，其包括：
提供包括含镍的过渡金属源、锂源及M 1元素的前驱体的混合料，并对混合料进行烧结处理，得到掺杂有M 1元素的本体颗粒；
将本体颗粒与M 2元素的前驱体混合，并进行烧结处理，以在本体颗粒的外表面形成含M 2元素氧化物的包覆层，得到正极活性材料；其中，
正极活性材料在11％脱锂态时，M 1元素的平均化合价为α 1，M 2元素的平均化合价为β 1；正极活性材料在78％脱锂态时，M 1元素的平均化合价为α 2，M 2元素的平均化合价为β 2；α 1和α 2满足α 2＞α 1，且β 1和β 2满足β 1＝β 2；
M 1元素包括Si、Ti、Cr、Mo、V、Se、Nb、Ru、Rh、Pd、Sb、Te、Ce及W中的一种或多种，M 2元素选自Mg、Al、Ca、Zr、Zn、Y及B中的一种或多种。
采用本申请的制备方法得到的正极活性材料，其容量发挥得到大幅度提高，能使采用其的锂离子二次电池的能量密度得到显著提升。同时，该正极活性材料在高温循环及高温存储过程中的结构稳定性得到大幅度提高，且该正极活性材料表面的电解液氧 化活性大幅度降低，能减少电池在高温循环及高温存储过程中的电解液分解产气量，因此使得电池的高温循环性能和高温存储性能也得到显著提高。
在上述任意实施方式中，所述混合料中还可包括X元素的前驱体，得到的本体颗粒中还掺杂有X元素，所述X元素选自F、N、P及S中的一种或多种；或，在将所述本体颗粒与M 2元素的前驱体混合之前，还可包括：c)将所述本体颗粒与X元素的前驱体混合，并进行烧结处理，以使X元素掺杂于所述本体颗粒，所述X元素选自F、N、P及S中的一种或多种。
在上述任意实施方式中，步骤a)中：烧结处理的气氛为含氧气氛；可选的，烧结气氛的含氧量为70％～100％，可选的为85％以上；烧结处理的温度为500℃～1000℃，可选的为700℃～900℃，还可选的为750℃～850℃；烧结处理的时间为5h～25h，可选的为5h～15h。
在上述任意实施方式中，步骤b)中：烧结处理的气氛为含氧气氛；可选的，烧结气氛的含氧量为70％～100％，可选的为85％以上；烧结处理的温度为100℃～550℃，可选的为200℃～500℃；烧结处理的时间为3h～25h，可选的为5h～10h。
在上述任意实施方式中，步骤c)中：烧结处理的气氛为含氧气氛；可选的，烧结气氛的含氧量为70％～100％，可选的为80％～95％；烧结处理的温度为400℃～1000℃，可选的为400℃～850℃，可选的为400℃～750℃；烧结处理的时间为3h～25h，可选的为5h～10h。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍，显而易见地，下面所描述的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1为根据本申请实施例的一种正极活性材料的掺杂及包覆示意图。
图2为实施例1至28及对比例1至8的正极活性材料的本体颗粒中M 1元素局部质量浓度的相对偏差测试的取点位置示意图。
图3是锂离子二次电池的一实施方式的示意图。
图4是图3的分解图。
图5是电池模块的一实施方式的示意图。
图6是电池包的一实施方式的示意图。
图7是图6的分解图。
图8是锂离子二次电池用作电源的装置的一实施方式的示意图。
具体实施方式
为了使本申请的发明目的、技术方案和有益技术效果更加清晰，以下结合实施例对本申请进行进一步详细说明。应当理解的是，本说明书中描述的实施例仅仅是为了解释本申请，并非为了限定本申请。
为了简便，本文仅明确地公开了一些数值范围。然而，任意下限可以与任何上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，尽管未明确记载，但是范围端点间的每个点或单个数值都包含在该范围内。因而，每个点或单个数值可以作为自身的下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包含本数，“一种或多种”中的“多种”的含义是两种以上，“一个或多个”中的“多个”的含义是两个以上。
在本文的描述中，除非另有说明，术语“或(or)”是包括性的。也就是说，短语“A或(or)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)。
本申请的上述发明内容并不意欲描述本申请中的每个公开的实施方式或每种实现方式。如下描述更具体地举例说明示例性实施方式。在整篇申请中的多处，通过一系列实施例提供了指导，这些实施例可以以各种组合形式使用。在各个实例中，列举仅作为代表性组，不应解释为穷举。
正极活性材料
如图1所示，本申请实施例提供一种正极活性材料，其包括本体颗粒和包覆在本体颗粒外表面的包覆层。本体颗粒包括含镍元素及掺杂元素M 1的锂复合氧化物，包覆层包括M 2元素的氧化物。
正极活性材料在11％脱锂态时，M 1元素的平均化合价为α 1；正极活性材料在78％脱锂态时，M 1元素的平均化合价为α 2；α 1和α 2满足α 2＞α 1。
且正极活性材料在11％脱锂态时，M 2元素的平均化合价为β 1；正极活性材料在78％脱锂态时，M 2元素的平均化合价为β 2；β 1和β 2满足β 1＝β 2。
M 1元素包括Si、Ti、Cr、Mo、V、Se、Nb、Ru、Rh、Pd、Sb、Te、Ce及W中的一种或多种；M 2元素选自Mg、Al、Ca、Zr、Zn、Y及B中的一种或多种。
本申请实施例提供的正极活性材料中，本体颗粒采用镍基锂复合氧化物，且本体颗粒中掺杂有M 1元素。随着正极活性材料的脱锂，M 1元素的平均化合价升高，即M 1元素能够在正极活性材料脱锂过程中能够参与氧化还原反应并释放电子。由此，正极活性材料能释放更多的锂离子，从而表现出更高的容量发挥。采用该正极活性材料能使锂离子二次电池的能量密度得到显著提升。
正极活性材料中，M 1元素本身能够有效束缚氧原子。同时，M 1元素贡献的电子能使材料内部发生电荷补偿，进一步抑制材料释氧。由此，正极活性材料在高温循环及高温存储过程中的结构稳定性得到大幅度提高。此外，本体颗粒外表面具有M 2元素的氧化物包覆层，且随着正极活性材料的脱锂，M 2元素的平均化合价恒定不变。该包覆层能对本体颗粒形成持续稳定的强保护作用，有效隔绝电解液对本体颗粒的腐蚀，进一步提高正极活性材料的结构稳定性。因此，采用该正极活性材料还能显著提升电池的高温循环性能及高温存储性能。
M 1元素在正极活性材料中的电荷补偿作用还能减少材料中强氧化性的Ni 4+，并减少材料的表面氧缺陷，从而有效降低材料表面的电解液氧化活性，大幅度减少电池在高温循环及高温存储过程中的电解液分解产气量。同时，包覆层对本体颗粒的保护作用能进一步减少电解液在材料表面的分解产气。因此，电池的高温循环性能及高温存储性能得到进一步提升。
在本文中，“78％脱锂态”是指电池在充电过程中，从正极活性材料中脱出的锂的摩尔含量占理论锂含量为78％时的状态。同理，“11％脱锂态”是指电池在充电过程中，从正极活性材料中脱出的锂的摩尔含量占理论锂含量为11％时的状态。锂离子二次电池在实际使用过程中，一般会设定一个“满放状态”和一个“满充状态”，对应电池设置一个“放电截止电压”和一个“充电截止电压”，以保证电池的安全使用。该“放电截止电压”和“充电截止电压”因正极活性材料的不同或安全性要求的差异，会存在一定的差异。对于含镍的锂复合氧化物正极活性材料制备的二次电池，其“满放状态” 时正极活性材料的脱锂状态一般在“11％脱锂态”左右，其“满充状态”时正极活性材料的脱锂状态一般在“78％脱锂态”左右，电池充放电使用时对应正极活性材料在11％脱锂态～78％脱锂态之间工作以保证正常使用。
在本文中，结合“脱锂态”和“电压”的对应关系，以获得处于“11％脱锂态”和“78％脱锂态”的正极活性材料进行研究。具体的，使用该正极活性材料制备一系列标准扣式半电池，分别以0.1C倍率充电至2.8V、2.9V、3.0V、3.1V、3.2V、3.3V、…、4.0V、4.1V、4.2V、4.3V、4.4V、4.5V(即充电电压间隔为0.1V)，随后拆出电池的正极极片，经洗涤除去电解液，消解正极活性材料，用电感耦合等离子体-发射光谱仪(inductively coupled plasma-Optical Emission spectrometers，ICP-OES)测试正极活性材料的Li元素质量浓度，以计算“脱锂态”，并获得充电电压与“脱锂态”的对应关系，进而得到“11％脱锂态”和“78％脱锂态”所对应的充电电压。
然后，将包含所述正极活性材料的半电池充电至“11％脱锂态”所对应的电压U 1，即可拆解获得处于“11％脱锂态”的正极活性材料。同样地，将包含所述正极活性材料的半电池充电至“78％脱锂态”所对应的电压U 2，即可拆解获得处于“78％脱锂态”的正极活性材料。
“11％脱锂态”正极活性材料和“78％脱锂态”正极活性材料中M 1元素和M 2元素的化合价可通过X射线光电子能谱分析(XPS)测试得到。更精确的，可通过同步辐射光电子能谱分析(Synchrotron radiation photoelectron spectroscopy，SRPES)测试获得。
在一些可选的实施方式中，“11％脱锂态”正极活性材料中M 1元素的平均化合价α 1与“78％脱锂态”正极活性材料中M 1元素的平均化合价α 2之间满足α 2＞α 1≥+3。正极活性材料充放电过程中，M 1元素的平均化合价保持在+3价以上。高价态的M 1元素对材料中氧原子的束缚能力更强，能够更加提高正极活性材料的结构稳定性，防止正极活性材料在高温循环过程和高温存储过程中发生晶格开裂。因此，电池能具有更好的高温循环性能和高温存储性能。
高价态的M 1元素能在正极活性材料中贡献更多的电子，从而进一步降低材料表面的电解液氧化活性，使电池的高温循环性能和高温存储性能得到进一步提高。
高价态的M 1元素在正极活性材料中贡献的电子更多，能支持正极活性材料释放出更多的锂离子，从而进一步提升电池的能量密度。
可选的，α 1为+3、+4、+5及+6价中的一种或多种。可选的，α 1为+3和+4价 中的一种或多种。
在一些实施例中，M 1元素可包括Ti、Mo、V、Nb、Ru、Sb和W中的一种或多种。可选的，M 1元素可包括Ti、Nb、Ru、Sb和W中的一种或多种。
在一些实施例中，M 2元素可包括Al、Zr、Zn、Y及B中的一种或多种。可选的，M 2元素可包括Al、Zr、Zn和Y中的一种或多种。可选的，M 2元素可包括Al、Zr和Y中的一种或多种。
在一些可选的实施方式中，M 1元素在本体颗粒中均匀掺杂。M 1元素均匀掺杂能使本体颗粒内部各处的性质保持一致，本体颗粒各个位置的结构稳定性均得到提升，改善了本体颗粒各个位置的释氧问题，从而更加提高正极活性材料在高温存储及高温循环过程中的结构稳定性，更好地提升电池的性能。
M 1元素均匀掺杂于本体颗粒中，还使得锂离子在本体颗粒内部不同区域的迁移扩散能力处于同一水平，本体颗粒各处的结构稳定性及抗变形能力接近，使得正极活性材料颗粒内的应力分布均匀，不易发生破裂，防止因破裂暴露出的新鲜表面引起的副反应及性能的恶化，从而进一步提高电池的能量密度、高温循环性能及高温存储性能。
在一些实施方式中，本体颗粒中M 1元素的局部质量浓度的相对偏差为32％以下，进一步地为30％以下，例如20％以下，15％以下，12％以下，11％以下，或10％以下。本体颗粒中M 1元素的局部质量浓度的相对偏差越小，则本体颗粒中M 1元素的分布越均匀，电池的综合性能越好。
在本文中，本体颗粒中M 1元素的局部质量浓度为在本体颗粒中任意选定位点的有限体积元内，M 1元素占所有元素的质量浓度，可由EDX(Energy Dispersive X-Ray Spectroscopy，能量色散X射线光谱仪)或EDS元素分析结合TEM(Transmission Electron Microscope，透射电子显微镜)或SEM(Scanning Electron Microscope，扫描电子显微镜)单点扫描测试元素浓度分布或其它类似方式得到。其中以EDX或EDS元素分析结合TEM或SEM单点扫描测试时，本体颗粒中不同位点处以μg/g计的M 1元素的质量浓度分别记作η 1、η 2、η 3、…、η n，n为大于等于15的正整数。
本体颗粒中M 1元素的平均质量浓度为在单个本体颗粒范围内M 1元素占所有元素的质量浓度，可由EDX或EDS元素分析结合TEM或SEM面扫描测试元素浓度分布或其它类似方式得到。其中以EDX或EDS元素分析结合TEM或SEM面扫描测试元素浓度分布的方式测试时，测试面包括上述单点测试中的所有点。本体颗粒中M 1元素的平均质量浓度记作
Figure PCTCN2020112914-appb-000006
单位为μg/g。
本体颗粒中M 1元素的局部质量浓度的相对偏差σ根据下式(1)计算得到：
Figure PCTCN2020112914-appb-000007
在一些实施方式中，本体颗粒为两个以上一次颗粒聚集而成的二次颗粒。正极活性材料由此能具有较高的锂离子传输性能，从而改善电池的循环性能。尤其是，当M 1元素在二次颗粒中均匀掺杂时，能进一步改善正极活性材料的锂离子传输性能，并且还能提高结构稳定性，从而使电池获得更高的循环性能。
在一些实施方式中，正极活性材料中M 1元素与M 2元素的摩尔比可以为0.09∶1～4∶1，还可以为0.1∶1～3∶1，进一步地为0.2∶1～2.5∶1，更进一步地为0.5∶1～2∶1。
正极活性材料中M 1元素与M 2元素的摩尔比适当，能更好地发挥M 1元素掺杂改性及含M 2元素氧化物包覆改性的协同作用。在该协同作用下，能有效抑制正极活性材料发生不可逆结构相变，并有效保护正极活性材料表面不被电解液侵蚀，减少电池产气量，从而进一步提高电池的高温循环性能及高温存储性能。
正极活性材料中M 1元素与M 2元素的上述摩尔比还有利于提高正极活性材料的导离子性能，从而能提升电池的能量密度。
在一些实施方式中，正极活性材料中M 1元素的真实掺杂浓度ω可以为2000μg/cm 3～55000μg/cm 3，还可以为2300μg/cm 3～49000μg/cm 3，还可以为3000μg/cm 3～30000μg/cm 3，11028μg/cm 3～30000μg/cm 3，或11028μg/cm 3～25351μg/cm 3。
正极活性材料中M 1元素的真实掺杂浓度ω为2000μg/cm 3以上，例如2300μg/cm 3以上，或3000μg/cm 3以上，能有效提升正极活性材料的克容量及结构稳定性，并降低材料表面的电解液氧化活性。正极活性材料中M 1元素的真实掺杂浓度ω为55000μg/cm 3以下，例如49000μg/cm 3以下，或30000μg/cm 3以下，能使正极活性材料具有良好的层状晶体结构，并且防止M 1元素进入锂层，保证正极活性材料为锂离子的脱嵌提供良好载体，有利于锂离子的嵌入及脱出，有效抑制活性锂离子的不可逆消耗，使正极活性材料具有较高的初始容量及循环容量保持率。
因此，正极活性材料中M 1元素的真实掺杂浓度ω在上述范围内，能够很好地提升电池的能量密度、高温循环性能及高温存储性能。
在本文中，正极活性材料中M 1元素的真实掺杂浓度ω由式(2)计算所得：
Figure PCTCN2020112914-appb-000008
式(2)中，ω为正极活性材料中M 1元素的真实掺杂浓度，单位为μg/cm 3。
ρ 真为正极活性材料真密度，单位为g/cm 3，其等于正极活性材料的质量与正极活性材料的真体积的比值，其中真体积是固体物质的实际体积，不包括正极活性材料颗粒内部和相互之间的孔隙。ρ 真可以用本领域公知的仪器及方法进行测定，如气体容积法，可以采用粉末真密度测试仪进行。
Figure PCTCN2020112914-appb-000009
为正极活性材料中以μg/g为单位的M 1元素的质量浓度，即每克正极活性材料中所含M 1元素的质量。其中，
Figure PCTCN2020112914-appb-000010
代表宏观正极活性材料整体中M 1元素的含量，包括掺入正极活性材料本体颗粒中的M 1元素、在正极活性材料本体颗粒表面其他相中富集的M 1元素、以及位于正极活性材料颗粒间的M 1元素。
Figure PCTCN2020112914-appb-000011
可通过正极活性材料溶液吸收光谱，如ICP(Inductive Coupled Plasma Emission Spectrometer，电感耦合等离子光谱发生仪)、XAFS(X-ray absorption fine structure spectroscopy，X射线吸收精细结构谱)等测试得到。
在一些实施方式中，正极活性材料中M 2元素的含量可以为300ppm～6500ppm。正极活性材料中M 2元素的含量可以为≥300ppm，≥500ppm，≥1000ppm，≥1500ppm，≥2000ppm，或≥2500ppm；并且可以为≤3000ppm，≤3500ppm，≤4000ppm，≤4500ppm，≤5000ppm，或≤6500ppm。可选的，正极活性材料中M 2元素的含量为500ppm～5000ppm。ppm(parts per million)是正极活性材料中M 2元素的质量占正极活性材料的质量的百万分比。
正极活性材料中M 2元素的含量在上述范围内，能使包覆层与本体颗粒间具有较高的结合牢度，防止电池在高温循环及高温存储过程中发生包覆层脱落，从而有效发挥包覆层对本体颗粒的保护作用，使电池具有较高的高温循环性能和高温存储性能。同时，正极活性材料还保持较高的锂离子扩散迁移能力，使电池具有较高的能量密度。
正极活性材料中M 2元素的含量可通过正极活性材料溶液吸收光谱，如ICP(Inductive Coupled Plasma Emission Spectrometer，电感耦合等离子光谱发生仪)、XAFS(X-ray absorption fine structure spectroscopy，X射线吸收精细结构谱)等测试得到。
在一些实施方式中，包覆层的厚度T可选为0.001μm～0.5μm，例如0.01μm～0.4μm，再例如0.1μm～0.3μm，0.21μm～0.3μm，或0.210μm～0.267μm。包覆层的厚度在上述范围内，在正极活性材料反复脱锂及嵌锂过程中不易从本体颗粒上脱落，能持续发挥对本体颗粒的保护作用，同时保证正极活性材料具有较高的锂离子扩散迁移能力及克容量。
在一些可选的实施方式中，包覆层的厚度T与正极活性材料的平均颗粒粒径
Figure PCTCN2020112914-appb-000012
之间满足：
Figure PCTCN2020112914-appb-000013
可选的，
Figure PCTCN2020112914-appb-000014
如
Figure PCTCN2020112914-appb-000015
Figure PCTCN2020112914-appb-000016
这样能更有效地发挥包覆层对本体颗粒的保护作用，并且保证正极活性材料具有较高的锂离子扩散迁移能力及克容量。
包覆层的厚度可以采用本领域公知的方法进行测定。作为示例，可以采用截面抛光仪(如日本电子(JEOL)公司的IB-09010CP型氩离子截面抛光仪)制备正极活性材料颗粒的截面，该截面经过正极活性材料颗粒的核心；然后由EDX或EDS元素分析结合TEM或SEM(如英国牛津仪器集团的X-Max型EDS结合德国ZEISS的Sigma-02-33型SEM)面扫描测试得到截面中的元素分布图；根据截面的元素分布得到包覆层的厚度。更精确地，可以测试截面上多个(3个以上，如5个、8个、10个、12个等)不同位置处包覆层的厚度值，取平均值记为包覆层的厚度。
正极活性材料的平均颗粒粒径
Figure PCTCN2020112914-appb-000017
是正极活性材料颗粒多个不同取向的直径的平均值。例如，可以根据上述EDX或EDS元素分析结合TEM或SEM面扫描测试得到正极活性材料颗粒截面中的元素分布图，根据截面的元素分布得到多个(3个以上，如5个、8个、10个、12个等)不同取向的直径，取平均值记为正极活性材料的平均颗粒粒径
Figure PCTCN2020112914-appb-000018
在一些实施例中，正极活性材料的体积平均粒径Dv50可选为8μm～20μm，例如9μm～18μm，再例如9μm～16μm。正极活性材料的Dv50在上述范围内，能提高正极活性材料颗粒中锂离子和电子的传输扩散性能，并有利于减少电解液在颗粒表面的副反应，抑制颗粒之间的团聚，从而提高电池的循环性能及倍率性能。此外，正极活性材料的D v50在上述范围内，还使正极活性材料具有较高的压实密度，提升电池的能量密度。
在一些实施方式中，正极活性材料的表面可选为粗糙表面。这样有利于提高正极活性材料的活性比表面积，提高正极活性材料的容量发挥。
在一些实施方式中，正极活性材料的比表面积可以为0.2m 2/g～1.7m 2/g，还可以为0.2m 2/g～1.5m 2/g，例如0.3m 2/g～1m 2/g。正极活性材料的比表面积在上述范围内，保证了正极活性材料具有较高的活性比表面积，同时有利于减少电解液在正极活性材料表面的副反应，从而提高正极活性材料的容量发挥及循环寿命。
在一些实施方式中，正极活性材料的振实密度可选为2.3g/cm 3～2.8g/cm 3。这样有利于使电池具有较高的能量密度。
在一些实施方式中，正极活性材料的真密度可以为4.6g/cm 3～5.2g/cm 3，还可 以为4.6g/cm 3～4.9g/cm 3。正极活性材料的真密度在适当范围内，能使正极活性材料具有较高的比容量及能量密度，从而提高电池的容量性能及能量密度。
在一些实施方式中，锂复合氧化物中镍的摩尔含量占过渡金属位元素总摩尔含量的50％～95％，如50％、60％、65％、70％、75％、80％、85％、90％、或95％等。该正极活性材料具有较高的比容量，能进一步提高电池的能量密度。
锂复合氧化物为层状结构，具有锂位点、过渡金属位点及氧位点。M 1元素掺杂于过渡金属位点。上述过渡金属位元素指的是位于过渡金属位点的元素。
在一些实施方式中，锂复合氧化物为化学式1所示的化合物，
Li 1+a[Ni xCo yMn zM 1 b]O 2-pX p      化学式1
化学式1中，M 1为对本体颗粒的镍位、钴位及锰位中的一个或多个掺杂取代；X为对本体颗粒的氧位取代，X可选自F、N、P及S中的一种或多种；并且，0.5≤x＜1，0≤y＜0.3，0≤z＜0.3，-0.2＜a＜0.2，0＜b＜0.2，0≤p＜0.2，x+y+z+b＝1。采用该高镍三元材料的电池能更好地兼具较高的能量密度、高温循环性能及高温存储性能。
可选的，0.6≤x≤0.9，如0.7≤x≤0.8。
可选的，X可选自F、N和S中的一种或多种。可选的，X包括F。
在一些实施例中，当本体颗粒掺杂有X元素时，X元素可以均匀掺杂于本体颗粒中，如本体颗粒中掺杂元素(含M 1元素和X元素)的局部质量浓度的相对偏差可以为32％以下，例如30％以下，再如20％以下。均匀掺杂的正极活性材料整体的结构稳定性更好。
X元素还可以是由本体颗粒的外表面至颗粒核心方向呈减小的质量浓度梯度。例如，X元素掺杂于本体颗粒的外表层。这能降低材料的表面氧活性，同时使材料兼具较高的动力学性能和克容量。
正极活性材料的体积平均粒径Dv50为本领域公知的含义，又称为中值粒径，表示正极活性材料颗粒的体积分布50％对应的粒径。正极活性材料的体积平均粒径D v50可以用本领域公知的仪器及方法进行测定，例如可以用激光粒度分析仪方便地测定，如英国马尔文仪器有限公司的Mastersizer 3000型激光粒度分析仪。
正极活性材料的比表面积为本领域公知的含义，可以用本领域公知的仪器及方法进行测定，例如可以用氮气吸附比表面积分析测试方法测试，并用BET(Brunauer Emmett Teller)法计算得出，其中氮气吸附比表面积分析测试可以是通过美国康塔公司的 NOVA 2000e型比表面积与孔径分析仪进行。作为具体的示例，测试方法如下：用称重后的空样品管取8.000g～15.000g正极活性材料，将正极活性材料搅拌均匀并称重，把样品管放入NOVA 2000e脱气站中脱气，称量脱气后的正极活性材料和样品管总质量，用总质量减去空样品管的质量计算得到脱气后正极活性材料的质量G。将样品管放入NOVA 2000e，测定不同相对压力下的氮气在正极活性材料表面的吸附量，基于布朗诺尔-埃特-泰勒多层吸附理论及其公式求得单分子层吸附量，进而计算出正极活性材料总表面积A，通过A/G计算得到正极活性材料的比表面积。
正极活性材料的振实密度为本领域公知的含义，可以用本领域公知的仪器及方法进行测定，例如用振实密度测定仪方便地测定，如FZS4-4B型振实密度测定仪。
接下来示意性地说明一种正极活性材料的制备方法。根据该制备方法能制备得到上述任意一种正极活性材料。制备方法包括本体颗粒制备步骤S10及包覆层制备步骤S20。
S10，提供包括含镍的过渡金属源、锂源及M 1元素的前驱体的混合料，并对混合料进行烧结处理，得到掺杂有M 1元素的本体颗粒。
上述含镍的过渡金属源例如为含Ni的氧化物、氢氧化物及碳酸盐中的一种或多种，例如为含有Ni、Co及Mn的氢氧化物。
含有Ni、Co及Mn的氢氧化物可以通过本领域已知的方法获得，例如通过共沉淀法、凝胶法或固相法制备获得。
作为一个示例，将Ni源、Co源及Mn源分散在溶剂中得到混合溶液；采用连续并流反应的方式，将混合溶液、强碱溶液和络合剂溶液同时泵入带搅拌的反应釜中，控制反应溶液的pH值为10～13，反应釜内的温度为25℃～90℃，反应过程中通惰性气体保护；反应完成后，经陈化、过滤、洗涤和真空干燥，得到含有Ni、Co及Mn的氢氧化物。
Ni源可以为可溶性的镍盐，例如为硫酸镍、硝酸镍、氯化镍、草酸镍及醋酸镍中的一种或多种，再例如为硫酸镍及硝酸镍中的一种或多种，再例如为硫酸镍；Co源可以为可溶性的钴盐，例如为硫酸钴、硝酸钴、氯化钴、草酸钴及醋酸钴中的一种或多种，再例如为硫酸钴及硝酸钴中的一种或多种，再例如为硫酸钴；Mn源可以为可溶性的锰盐，例如为硫酸锰、硝酸锰、氯化锰、草酸锰及醋酸锰中的一种或多种，再例如为硫酸锰及硝酸锰中的一种或多种，再例如为硫酸锰。
强碱可以为LiOH、NaOH及KOH中的一种或多种，例如为NaOH。络合剂可 以为氨水、硫酸铵、硝酸铵、氯化铵、柠檬酸铵及乙二胺四乙酸二钠(EDTA)中的一种或多种，例如为氨水。
对混合溶液、强碱溶液和络合剂溶液的溶剂均没有特别的限制，例如混合溶液、强碱溶液和络合剂溶液的溶剂各自独立地为去离子水、甲醇、乙醇、丙酮、异丙醇及正己醇中的一种或多种，如为去离子水。
反应过程中通入的惰性气体例如为氮气、氩气、氦气中的一种或多种。
上述锂源可以为氧化锂(Li 2O)、磷酸锂(Li 3PO 4)、磷酸二氢锂(LiH 2PO 4)、醋酸锂(CH 3COOLi)、氢氧化锂(LiOH)、碳酸锂(Li 2CO 3)及硝酸锂(LiNO 3)中的一种或多种。进一步地，锂源为碳酸锂、氢氧化锂及硝酸锂中的一种或多种；更进一步地，锂源为碳酸锂。
M 1元素的前驱体可以为M 1元素的氧化物、硝酸盐、碳酸盐、碳酸氢盐、硫酸盐、氯化物、氢氧化合物及醋酸盐中的一种或多种，可以根据实际需求进行选择。例如，M 1元素的前驱体为M 1元素的氧化物，例如为氧化硅(如SiO 2、SiO等)、氧化钛(如TiO 2、TiO等)、氧化铬(如CrO 3、Cr 2O 3等)、氧化钼(如MoO 2、MoO 3等)、氧化钒(如V 2O 5、V 2O 4、V 2O 3等)、氧化硒(如SeO 2等)、氧化铌(如Nb 2O 5、NbO 2等)、氧化钌(如RuO 2等)、氧化钯(如PdO等)、氧化铑(如Rh 2O 3等)、氧化锑(如Sb 2O 5、Sb 2O 3等)、氧化碲(如TeO 2等)、氧化铈(如CeO 2等)及氧化钨(如WO 2、WO 3等)中的一种或多种。
在步骤S10，可以采用球磨混合机或高速混合机来进行物料混合。例如，将含镍的过渡金属源、锂源及M 1元素的前驱体加入高速混合机中混合，混料时间可以为0.5h～3h。
在步骤S10，可以将混合后的物料加入气氛烧结炉中进行烧结。烧结气氛为含氧气氛，例如为空气气氛或氧气气氛。烧结气氛的O 2浓度例如为70％～100％，进一步地为80％以上，更进一步地为85％以上。烧结温度例如为500℃～1000℃，再例如为600℃～1000℃，再例如为700℃～900℃，如750℃～850℃。这有利于使M 1元素均匀掺杂于本体颗粒中，特别地，使M 1元素在本体颗粒中具有较高的掺杂均匀性。烧结时间可根据实际情况进行调节，例如为5h～25h，再例如为5h～15h。
需要说明的是，在正极活性材料制备时，具有多种理论可行的方式可以调控锂镍复合氧化物中M 1元素的分布情况和不同脱锂态下的化合价态，如M 1元素前驱体自身的价态、不同M 1元素价态前驱体的用量比例、掺杂时的烧结气氛的氧化性、烧结次数、 混合均匀性、烧结温度、烧结时间等。在本申请文件中，列举了在S10步骤中控制掺杂前驱体种类、烧结时间和温度的方式，获得一系列正极活性材料。该正极活性材料具有高能量密度、热稳定性和高温循环稳定性的特点。可选的，经进一步控制M 1元素掺杂均相、处于不同脱锂态下M 1元素化合价态特征的正极活性材料，具有更佳的效果。
在一些实施例中，在步骤S10的烧结处理之后，还可以将烧结产物进行破碎处理并筛分，以获得具有优化的粒径分布及比表面积的正极活性材料。其中对破碎的方式并没有特别的限制，可根据实际需求进行选择，例如使用颗粒破碎机。
S20，将本体颗粒与M 2元素的前驱体混合，并进行烧结处理，以在本体颗粒的外表面形成含M 2元素氧化物的包覆层，得到正极活性材料。
M 2元素的前驱体可以为M 2元素的氯化物、硫酸盐、硝酸盐、氧化物、氢氧化物、氟化物、碳酸盐、碳酸氢盐、醋酸盐、磷酸盐、磷酸二氢盐及有机化合物中的一种或多种，但并不限于此。
在步骤S20，可以采用球磨混合机或高速混合机来进行物料混合。例如，将本体颗粒与M 2元素的前驱体加入高速混合机中进行混合，混料时间为0.5h～3h。
在步骤S20，可以将混合后的物料加入气氛烧结炉中进行烧结。烧结气氛为含氧气氛，例如为空气气氛或氧气气氛。烧结气氛的O 2浓度例如为70％～100％，进一步地为80％以上，更进一步地为85％以上。烧结温度例如为100℃～550℃，再例如为200℃～500℃，240℃～310℃，或260℃～310℃。烧结时间可以为3h～25h，如5h～10h。由于烧结温度较低，M 2元素的氧化物不易扩散至本体颗粒内部，而是形成包覆在本体颗粒外表面的包覆层。M 2元素与本体颗粒的表面晶格相匹配，使得包覆层与本体颗粒之间的结合紧密，且包覆层不会损害本体颗粒的结构，实现包覆层对本体颗粒形成可靠的保护。
在一些可选的实施方式中，在步骤S10，混合料中还包括X元素的前驱体，得到的本体颗粒中还掺杂有X元素，X元素选自F、N、P及S中的一种或多种。
X元素的前驱体例如可以选自氟化铵、氟化锂、氟化氢、单质磷、氧化磷、磷酸二氢铵、偏磷酸铵、亚磷酸二氢铵、硝酸铵、亚硝酸铵、碳酸铵、碳酸氢铵、硫酸铵、硫酸氢铵、亚硫酸氢铵、亚硫酸铵、硫化氢铵、硫化氢、硫化锂、硫化铵及单质硫中的一种或多种，但并不限于此。
在另一些可选的实施方式中，在步骤S20之前，还可以包括步骤S30：将本体颗粒与X元素的前驱体混合，并进行烧结处理，以使X元素掺杂于本体颗粒。
在步骤S30，可以采用如前文所述X元素的前驱体。
在步骤S30，可以采用球磨混合机或高速混合机来进行物料混合。例如，将本体颗粒与X元素的前驱体加入高速混合机中进行混合，混料时间可以为0.5h～3h。
在步骤S30，可以将混合后的物料加入气氛烧结炉中进行烧结。烧结气氛为含氧气氛，例如为空气气氛或氧气气氛。烧结气氛的O 2浓度例如为70％～100％，进一步地为80％～95％。烧结温度例如为400℃～1000℃，如400℃～850℃，再如400℃～750℃。烧结时间可以为3h～25h，如5h～10h。
通过调控烧结温度和烧结时间，能使X元素均匀掺杂于本体颗粒，或者使X元素本体颗粒的外表面至颗粒核心方向呈减小的质量浓度梯度。
正极极片
本申请还提供一种正极极片，该正极极片包括上述任意一种或几种正极活性材料。
本申请实施例的正极极片由于采用了本申请实施例的正极活性材料，因而也具有上述的有益效果。采用本申请的正极极片能使锂离子二次电池同时兼顾良好的高温循环性能及高温存储性能和较高的能量密度。
作为示例，正极极片包括正极集流体以及设置于正极集流体至少一个表面上的正极活性物质层。例如，正极集流体在自身厚度方向上包括相对的两个表面，正极活性物质层层叠设置于正极集流体的两个表面中的任意一者或两者上。
正极活性物质层包括本申请实施例上述任意一种或几种正极活性材料。
正极活性物质层中还可以包括导电剂和粘结剂。本申请对正极活性物质层中的导电剂及粘结剂的种类不做具体限制，可以根据实际需求进行选择。
作为示例，导电剂可以为石墨、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一种或多种；粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、羧甲基纤维素钠(CMC-Na)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚乙烯醇缩丁醛(PVB)、乙烯-醋酸乙烯酯共聚物(EVA)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物、含氟丙烯酸树脂及聚乙烯醇(PVA)中的一种或多种。
正极集流体可以采用具有良好导电性能及力学性能的金属箔材或多孔金属板，例如铝箔。
正极极片可以按照本领域常规方法制备。例如将正极活性材料、导电剂及粘结 剂分散于溶剂中，溶剂可以是N-甲基吡咯烷酮(NMP)，形成均匀的正极浆料，将正极浆料涂覆在正极集流体上，经烘干、辊压等工序后，得到正极极片。
锂离子二次电池
本申请实施例还提供一种锂离子二次电池，锂离子二次电池包括正极极片、负极极片、隔离膜和电解质，其中正极极片为上述的正极极片。
锂离子二次电池由于采用了本申请实施例的正极极片，因而能同时兼顾良好的常温及高温循环性能、较高的高温存储性能及较高的能量密度。
负极极片可以是金属锂片。
负极极片还可以是包括负极集流体以及设置于负极集流体至少一个表面上的负极活性物质层。例如，负极集流体在自身厚度方向上包括相对的两个表面，负极活性物质层层叠设置于负极集流体的两个表面中的任意一者或两者上。
负极活性物质层包括负极活性材料。本申请实施例对负极活性材料的种类不做具体地限制，可以根据实际需求进行选择。作为示例，负极活性材料可以是天然石墨、人造石墨、中间相微碳球(MCMB)、硬碳、软碳、硅、硅-碳复合物、SiO m(0＜m＜2，如m＝1)、Li-Sn合金、Li-Sn-O合金、Sn、SnO、SnO 2、尖晶石结构的钛酸锂Li 4Ti 5O 12、Li-Al合金及金属锂中的一种或多种。
负极活性物质层还可以包括导电剂和粘结剂。本申请实施例对负极活性物质层中的导电剂和粘结剂的种类不做具体限制，可以根据实际需求进行选择。作为示例，导电剂为石墨、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一种或多种；粘结剂为丁苯橡胶(SBR)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚乙烯醇缩丁醛(PVB)、水性丙烯酸树脂中的一种或多种。
负极活性物质层还可选地包括增稠剂，例如羧甲基纤维素钠(CMC-Na)。
负极集流体可以采用具有良好导电性能及力学性能的金属箔材或多孔金属板，例如铜箔。
负极极片可以按照本领域常规方法制备。例如将负极活性材料、导电剂、粘结剂及增稠剂分散于溶剂中，溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水，形成均匀的负极浆料，将负极浆料涂覆在负极集流体上，经烘干、辊压等工序后，得到负极极片。
本申请实施例的锂离子二次电池，电解质可以采用固体电解质，如聚合物电解质、无机固态电解质等，但并不限于此。电解质也可以采用电解液。作为上述电解液， 包括溶剂和溶解于溶剂中的锂盐。
溶剂可以为非水有机溶剂，例如碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)及丁酸乙酯(EB)中的一种或多种。例如为两种以上。
锂盐可以为LiPF 6(六氟磷酸锂)、LiBF4(四氟硼酸锂)、LiClO 4(高氯酸锂)、LiAsF 6(六氟砷酸锂)、LiFSI(双氟磺酰亚胺锂)、LiTFSI(双三氟甲磺酰亚胺锂)、LiTFS(三氟甲磺酸锂)、LiDFOB(二氟草酸硼酸锂)、LiBOB(双草酸硼酸锂)、LiPO 2F 2(二氟磷酸锂)、LiDFOP(二氟草酸磷酸锂)及LiTFOP(四氟草酸磷酸锂)中的一种或多种，例如为LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiBOB(双草酸硼酸锂)、LiDFOB(二氟草酸硼酸锂)、LiTFSI(双三氟甲磺酰亚胺锂)及LiFSI(双氟磺酰亚胺锂)中的一种或多种。
电解液中还可选地含有其它添加剂，例如碳酸亚乙烯酯(VC)、碳酸乙烯亚乙酯(VEC)、氟代碳酸亚乙酯(FEC)、二氟碳酸亚乙酯(DFEC)、三氟甲基碳酸亚乙酯(TFPC)、丁二腈(SN)、己二腈(ADN)、戊二腈(GLN)、己烷三腈(HTN)、1，3-丙烷磺内酯(1，3-PS)、硫酸亚乙酯(DTD)、甲基二磺酸亚甲酯(MMDS)、1-丙烯-1，3-磺酸内酯(PST)、4-甲基硫酸亚乙酯(PCS)、4-乙基硫酸亚乙酯(PES)、4-丙基硫酸亚乙酯(PEGLST)、硫酸丙烯酯(TS)、1，4-丁烷磺内酯(1，4-BS)、亚硫酸亚乙酯(DTO)、二甲基亚硫酸酯(DMS)、二乙基亚硫酸酯(DES)、磺酸酯环状季铵盐、三(三甲基硅烷)磷酸酯(TMSP)及三(三甲基硅烷)硼酸酯(TMSB)中的一种或多种，但并不限于此。
本申请实施例的锂离子二次电池对隔离膜没有特别的限制，可以选用任意公知的具有电化学稳定性和机械稳定性的多孔结构隔离膜，例如玻璃纤维、无纺布、聚乙烯(PE)、聚丙烯(PP)及聚偏二氟乙烯(PVDF)中的一种或多种的单层或多层薄膜。
将正极极片和负极极片交替层叠设置，并在正极极片与负极极片之间设置隔离膜以起到隔离的作用，得到电芯，也可以是经卷绕后得到电芯。将电芯置于外壳中，注入电解液，并封口，得到锂离子二次电池。
本申请对锂离子二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图3是作为一个示例的方形结构的锂离子二次电池5。
在一些实施例中，锂离子二次电池可包括外包装。该外包装用于封装正极极片、负极极片和电解质。
在一些实施例中，参照图4，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芯52。电芯52封装于所述容纳腔。电解质可采用电解液，电解液浸润于电芯52中。锂离子二次电池5所含电芯52的数量可以为一个或几个，可根据需求来调节。
在一些实施例中，锂离子二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。锂离子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，如可包括聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的一种或几种。
在一些实施例中，锂离子二次电池可以组装成电池模块，电池模块所含锂离子二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图5是作为一个示例的电池模块4。参照图5，在电池模块4中，多个锂离子二次电池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锂离子二次电池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，多个锂离子二次电池5容纳于该容纳空间。
在一些实施例中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图6和图7是作为一个示例的电池包1。参照图6和图7，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。
本申请还提供一种装置，所述装置包括本申请所述的锂离子二次电池、电池模块、或电池包中的至少一种。所述锂离子二次电池、电池模块或电池包可以用作所述装置的电源，也可以作为所述装置的能量存储单元。所述装置可以但不限于是消费类电子产品、电动汽车等。作为具体的示例，所述装置可以是移动设备(例如手机、平板电脑、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电 动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
所述装置可以根据其使用需求来选择锂离子二次电池、电池模块或电池包。
图8是作为一个示例的装置。该装置为电动汽车，其可以是纯电动车、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。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比、和比值都是基于重量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
实施例1
正极活性材料的制备
(1)将镍钴锰三元材料前驱体[Ni 0.8Co 0.1Mn 0.1](OH) 2、氢氧化锂LiOH及三氧化二锑Sb 2O 3加入高速混料机中进行混料1h，得到混合料，其中，镍钴锰三元材料前驱体与氢氧化锂的摩尔比Li/Me为1.05，Me表示镍钴锰三元材料前驱体中Ni、Co、Mn的总摩尔量；Sb 2O 3的加入量使得正极活性材料中Sb的真实掺杂浓度为25050μg/cm 3。将混合料放入气氛烧结炉中烧结，烧结温度为825℃，烧结气氛为O 2浓度为90％的含氧气氛，烧结时间为15h，经破碎、过筛即可得到本体颗粒，其中Sb均匀掺杂于本体颗粒的体相结构。
(2)将本体颗粒与氧化铝Al 2O 3加入高速混料机中进行混料1h，其中Al 2O 3的加入量使得包覆层中Al的含量为3002ppm，该含量为在正极活性材料中的含量。将混合后的物料放入气氛烧结炉中烧结，烧结温度为310℃，烧结气氛为O 2浓度为90％的含氧气氛，烧结时间为8h，在本体颗粒的外表面形成Al 2O 3包覆层，得到正极活性材料，其中正极活性材料的平均粒径D v50为14μm，包覆层的厚度T为0.243μm。
电解液的制备
将EC、DEC、DMC按照体积比1∶1∶1进行混合后，得到溶剂，再将锂盐LiPF 6溶解于上述溶剂中，获得电解液，其中LiPF 6的浓度为1mol/L。
扣式电池的制备
将上述制备的正极活性材料、导电炭黑及粘结剂PVDF按照重量比90∶5∶5分散至溶剂N-甲基吡咯烷酮(NMP)中进行混合均匀，得到正极浆料；将正极浆料均匀涂布于正极集流体铝箔上，经烘干、冷压后，得到正极极片。
在扣电箱中，将正极极片、隔离膜及金属锂片依次层叠设置，并注入上述电解液，组装得到扣式电池。
全电池的制备
将上述制备的正极活性材料、导电剂乙炔黑及粘结剂PVDF按照重量比94∶3∶3分散至溶剂NMP中进行混合均匀，得到正极浆料；将正极浆料均匀涂布于正极集流体铝箔上，经烘干、冷压后，得到正极极片。
将负极活性材料人造石墨、硬碳、导电剂乙炔黑、粘结剂丁苯橡胶(SBR)、增稠剂碳甲基纤维素钠(CMC)按照重量比90∶5∶2∶2∶1分散至去离子水中进行混合均匀，得到负极浆料；将负极浆料均匀涂布于负极集流体铝箔上，经烘干、冷压后，得到负极极片。
以聚乙烯(PE)多孔聚合薄膜作为隔离膜。将正极极片、隔离膜、负极极片按顺序叠好得到裸电芯，将裸电芯置于外包装中，注入上述电解液并封装，经化成等工序后，得到全电池。
实施例2～28及对比例1～8
与实施例1不同的是，改变正极活性材料的制备步骤中的相关参数，获得具有预定参数特性的正极活性材料，详见表1-1至表1-2。
其中，实施例2～25及对比例1～5的正极活性材料前驱体均为[Ni 0.8Co 0.1Mn 0.1](OH) 2；实施例26～28及对比例6～8的正极活性材料前驱体均为[Ni 0.5Co 0.2Mn 0.3(OH) 2。
实施例2中M 1元素的前驱体为TiO；实施例3、20、21、24、25中M 1元素的前驱体为NbO 2；实施例4中M 1元素的前驱体为MoO 2；实施例5中M 1元素的前驱体为RuO 2；实施例6中M 1元素的前驱体为V 2O 3；实施例7、22、23、27中M 1元素的前驱体为WO 2；实施例8中M 1元素的前驱体为Sb 2O 3和WO 2，且各前驱体的含量基本相同；对比例4中M 1元素的前驱体为Y 2O 3；对比例5中M 1元素的前驱体为MgO；
其余涉及的与实施例1不同的M 2元素的前驱体选自B 2O 3、ZrO 2、ZnO、Y 2O 3；
实施例20的步骤(1)烧结温度为615℃，烧结时间为5h；步骤(2)烧结温 度为305℃，烧结时间为8h；
实施例21的步骤(1)烧结温度为550℃，烧结时间为2h；步骤(2)烧结温度为290℃，烧结时间为9h；
实施例22的步骤(1)烧结温度为810℃，烧结时间为15h；步骤(2)烧结温度为110℃，烧结时间为3h；
实施例23的步骤(1)烧结温度为830℃，烧结时间为15h；步骤(2)烧结温度为550℃，烧结时间为20h；
实施例24的步骤(1)烧结温度为770℃，烧结时间为16h；步骤(2)烧结温度为310℃，烧结时间为7h；
实施例25的步骤(1)烧结温度为750℃，烧结时间为17h；步骤(2)烧结温度为260℃，烧结时间为9h；
实施例26、27和对比例7的步骤(1)烧结温度为790℃，烧结时间为12h；步骤(2)烧结温度为280℃，烧结时间为7h；
实施例28的步骤(1)烧结温度为500℃，烧结时间为2h；步骤(2)烧结温度为240℃，烧结时间为6h；
对比例1及对比例6未进行掺杂和包覆，且均为一次烧结；对比例1的烧结温度为825℃、烧结时间为15h；对比例6的烧结温度为790℃，烧结时间为12h；
对比例2及对比例7未掺杂M 1元素；
对比例3及对比例8未包覆M 2元素，且均为一次烧结；对比例3的烧结温度为825℃、烧结时间为15h；对比例8的烧结温度为790℃，烧结时间为12h。
其余参数见表1-1及表1-2。在表1-1及表1-2中：
σ表示本体颗粒中M 1元素的局部质量浓度的相对偏差；
M 1元素的浓度为M 1元素在正极活性材料中的真实掺杂浓度；
M 2元素的含量为M 2元素在正极活性材料中的含量；
摩尔比表示正极活性材料中M 1元素与M 2元素的摩尔比；
Figure PCTCN2020112914-appb-000019
表示包覆层的厚度T与正极活性材料的平均颗粒粒径
Figure PCTCN2020112914-appb-000020
之比。
测试部分
1)正极活性材料在不同脱锂态下M 1元素、M 2元素的平均化合价测定
在25℃下，将18个扣式电池分别以1C恒流充电至充放电截止电压上限，再恒压充电至电流小于等于0.05mA，之后搁置2分钟，然后以1C恒流放电至充放电截止 电压下限。
之后，将上述充放电后的18个扣式电池，分别以0.1C倍率充电到2.8V、2.9V、3.0V、3.1V、3.2V、3.3V、…、4.0V、4.1V、4.2V、4.3V、4.4V、4.5V(即充电电压间隔为0.1V)。取每个充电后的扣式电池，在干燥房中拆解出正极极片作为样品，称取记录样品质量后放入消解罐中，缓慢加入10mL王水作为消解试剂，之后放入美国CEM公司的Mars5微波消解仪中，以2450Hz微波发射频率进行消解；将消解后的样品溶液转移到容量瓶中摇匀，取样放入美国铂金埃尔默(PE)公司的7000DV型电感耦合等离子体-发射光谱仪(ICP-OES)的进样系统，以0.6MPa氩气压力，1300W射频功率对正极活性材料进行Li、O、Ni、Co、Mn和掺杂元素质量浓度测试，基于各个元素的质量浓度换算得到每个电压下的化学式，进而得到每个电压下的脱锂态。如2.8V电压下换算得到的正极活性材料化学式为Li 0.89Ni 0.8Co 0.1Mn 0.1O 2，则对应的脱锂态为(1-0.89)×100％＝11％，也即11％脱锂态对应的电池电压为2.8V。同理，当用ICP-OES测试换算得到正极活性材料的化学式为Li 0.22Ni 0.8Co 0.1Mn 0.1O 2时，对应的电压即为78％脱锂态对应的电压。
获得11％脱锂态和78％脱锂态对应的电压后，取含有待测正极活性材料的极片，按照上述方法制作出扣式电池。将扣式电池在25℃下，以0.1C倍率分别充电到11％脱锂态和78％脱锂态所对应的电压，再分别进行如下操作：
①在干燥房中用剪刀拆开扣式电芯，取出整个正极极片放入烧杯中，倒入适量高纯无水碳酸二甲酯(DMC)，每8h更换一次DMC，连续清洗3次，然后放入干燥房的真空静置箱中，保持抽真空状态为-0.096MPa，干燥12h；将干燥完成的正极极片，用刀片在干燥房中刮粉并研磨，称取约50mg正极活性材料粉末。
②将一片约2cm×2cm的铝箔表面用丙酮擦拭干净，裁剪约1cm×1cm的双面胶带贴在铝箔中心位置，将粉末样品铺在双面胶带上，用干净的不锈钢取样勺将粉末均匀铺满整个胶带。取另一片用丙酮擦拭干净的铝箔覆盖住样品，并整体放置于两块平整的不锈钢模块中间，之后使用压片机进行压片，加压压力约10MPa，保持15秒。
③采用美国赛默飞世尔(Thermo)科技公司的escalab 250Xi型X射线光电子能谱仪，将压片样品放入样品腔，设置单色Al Kα(hv＝1486.6eV)激发源，X射线功率150W，聚焦斑点500μm，采集M 1元素、M 2元素的2p或3d谱并用XPSpeak软件分峰处理，测定M 1元素、M 2元素的价态分布，并分别计算M 1元素、M 2元素的平均化合价。
2)本体颗粒中M 1元素的局部质量浓度的相对偏差测试
称取2g正极活性材料粉末样品，将样品均匀洒落在粘有导电胶的样品台上，再轻压使粉末固定，或者从电池正极极片中裁剪出1cm×1cm的极片，粘贴到样品台上作为待测样品。将样品台装入真空样品仓内并固定好，采用日本电子(JEOL)公司的IB-09010CP型截面抛光仪制备正极活性材料颗粒的截面，即得到本体颗粒的截面，如图2所示；参照图2所示颗粒截面的17个位置取点，每个点的面积为20nm×20nm，采用英国牛津仪器集团的X-Max型能谱仪(EDS)结合德国ZEISS的Sigma-02-33型扫描电子显微镜(SEM)测试该17个位点M 1元素的质量浓度，测试方法如下：检测元素选择Li、O、Ni、Co、Mn和掺杂元素，设置SEM参数为20kV加速电压，60μm光栏，8.5mm工作距离，2.335A电流，进行EDS测试时需待谱图面积达到250000cts以上(通过采集时间和采集速率来控制)时停止测试，并采集数据，得到各位点M 1元素的质量浓度，分别记为η 1、η 2、η 3、…、η 17。
本体颗粒中M 1元素的平均质量浓度
Figure PCTCN2020112914-appb-000021
测定方法：采取上述EDS-SEM测试方法，如图2中的虚线框所示，测试面积覆盖上述本体颗粒点扫描的所有点，且不超出该本体颗粒的截面。
之后根据前文所述式(1)计算得到本体颗粒中M 1元素的局部质量浓度的相对偏差σ。
3)正极活性材料中M 1元素、M 2元素的含量
采用PE 7000DV型ICP-OES测试正极活性材料中M 1元素、M 2元素的含量，测试方法如下：取包含正极活性材料的极片冲成总质量大于0.5g的圆片或取至少5g正极活性材料粉末样品，称取并记录样品质量后放入消解罐中，缓慢加入10mL王水作为消解试剂，之后放入美国CEM公司的Mars5微波消解仪中，以2450Hz微波发射频率进行消解；将消解后的样品溶液转移到容量瓶中摇匀，取样放入ICP-OES进样系统，以0.6MPa氩气压力，1300W射频功率进行正极活性材料中M 1元素、M 2元素含量测试。
其中，采用北京彼奥德电子技术有限公司的TD2400型粉末真密度测试仪测定正极活性材料的真密度ρ 真，测试方法如下：25℃下取一定质量的正极活性材料置于样品杯中，记录正极活性材料的质量m；把装有正极活性材料的样品杯放入真密度仪测试腔中，密闭测试系统，通入氦气或氮气等小分子直径的惰性气体，通过检测样品室和膨胀室中的气体的压力，再根据玻尔定律PV＝nRT测量被测材料的真体积V，通过m/V计算得到二次颗粒的真密度ρ 真。其中n为样品杯中气体的摩尔量；R为理想气体常数，取8.314；T为环境温度，为298.15K。之后根据前文所述式(2)计算得到正极活性材料中M 1 元素的真实掺杂浓度ω。
4)扣式电池的初始克容量测试
在25℃下，将电池以0.1C恒流充电至充放电截止电压上限，再恒压充电至电流小于等于0.05mA，之后搁置2分钟，然后以0.1C恒流放电至充放电截止电压下限，此次的放电容量即为扣式电池的初始克容量。
5)全电池的初始克容量测试
在25℃下，将电池以1/3C恒流充电至充放电截止电压上限，再恒压充电至电流小于等于0.05mA，之后搁置5分钟，然后以1/3C恒流放电至充放电截止电压下限，此次的放电容量即为全电池的初始克容量。
6)全电池的高温循环性能测试
在45℃下，将电池以1C恒流充电至充放电截止电压上限，再恒压充电至电流小于等于0.05mA，之后搁置5分钟，再以1C恒流放电至充放电截止电压下限，此为一个充放电循环，此次的放电容量记为第1次循环的放电比容量D 1。将电池按照上述方法进行400次循环充放电测试，记录第400次循环的放电比容量D 400。
全电池45℃、1C/1C循环400次容量保持率(％)＝D 400/D 1×100％
7)全电池的高温存储性能测试
在25℃下，将电池以1C倍率恒流充电至充放电截止电压上限，再恒压充电至电流小于等于0.05mA，此时测试电池的体积并记为V 0；然后将电池放入80℃的恒温箱中，测试存储10天后电池的体积并记为V 1。在本测试中，采用排水法测试电池的体积。
全电池80℃存储10天后体积膨胀率ΔV(％)＝(V 1-V 0)/V 0×100％
在测试1)、4)～7)中，
在实施例1～25及对比例1～5，扣式电池的充放电截止电压为2.8V～4.25V，全电池的充放电截止电压为2.8V～4.2V；
在实施例26～28及对比例6～8，扣式电池的充放电截止电压为2.8V～4.35V，全电池的充放电截止电压为2.8V～4.3V。
实施例1～28和对比例1～8的测试结果示于表2中。
Figure PCTCN2020112914-appb-000022
Figure PCTCN2020112914-appb-000023
表2
Figure PCTCN2020112914-appb-000024
由实施例1～25与对比例1～5、实施例26～28与对比例6～8的比较可以看出，通过使含镍的锂复合氧化物本体颗粒中掺杂有M 1元素，在本体颗粒的外表面还包覆有含M 2元素氧化物的包覆层；且随着正极活性材料的脱锂，M 1元素的平均化合价升高，M 2元素的平均化合价恒定不变；以及M 1元素和M 2元素各自选自特定的元素种类，能够使锂离子二次电池具有较高的初始克容量，并兼具较高的高温循环性能及高温存储性能。
由实施例1、9～19的结果可以看出，使正极活性材料中M 1元素、M 2元素的含量及它们的摩尔比在适当范围内，能更有效地改善电池的克容量、高温循环性能及高温存储性能。
由实施例3、20、21以及实施例26、28的结果可以看出，本体颗粒中M 1元素的局部质量浓度的相对偏差为20％以下时，M 1元素均匀掺杂性更好，正极活性材料颗粒内部各处的性质保持一致，锂离子在颗粒内部不同区域的迁移扩散能力处于同一水平；同时，M 1元素均匀掺杂的正极活性材料的整体结构稳定性更好，其中的内应力分布均匀，不易发生破裂。因此电池的性能提升效果显著。本体颗粒中掺杂元素的局部质量浓度的相对偏差大于20％时，正极活性材料颗粒内部各处锂离子扩散的通道和势垒不一致，各区域的结构稳定性和抗变形能力存在差异，导致材料内部应力分布不均，内应力大的区域易出现破裂，使得正极活性材料暴露出新鲜表面，增大阻抗，进而恶化容量性能、高温循环性能及高温存储性能。
由实施例7、22、23的结果可以看出，包覆层的厚度与正极活性材料的平均颗粒粒径
Figure PCTCN2020112914-appb-000025
之比适当，有利于使电池同时兼顾较高的克容量、高温循环性能及高温存储性能。
由实施例3和24的结果可以看出，正极活性材料的比表面积适当，有利于使电池同时兼顾较高的克容量、高温循环性能及高温存储性能。
由实施例3和25的结果可以看出，正极活性材料的真密度适当，有利于使电池同时兼顾较高的克容量、高温循环性能及高温存储性能。
以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到各种等效的修改或替换，这些修改或替换都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。

Claims (20)

  1. 一种正极活性材料，包括本体颗粒和包覆在所述本体颗粒外表面的包覆层，所述本体颗粒包括含镍元素及掺杂元素M 1的锂复合氧化物，所述包覆层包括M 2元素的氧化物；
    所述正极活性材料在11％脱锂态时，所述M 1元素的平均化合价为α 1，所述M 2元素的平均化合价为β 1；
    所述正极活性材料在78％脱锂态时，所述M 1元素的平均化合价为α 2，所述M 2元素的平均化合价为β 2；
    所述α 1和α 2满足α 2＞α 1，且所述β 1和β 2满足β 1＝β 2；
    所述M 1元素包括Si、Ti、Cr、Mo、V、Se、Nb、Ru、Rh、Pd、Sb、Te、Ce及W中的一种或多种，所述M 2元素选自Mg、Al、Ca、Zr、Zn、Y及B中的一种或多种。
  2. 根据权利要求1所述的正极活性材料，其中，所述α 1和α 2满足α 2＞α 1≥+3。
  3. 根据权利要求1-2任一项所述的正极活性材料，其中，所述α 1为+3、+4、+5和+6价中的一种或多种；可选的，所述α 1为+3和+4价中的一种或多种。
  4. 根据权利要求1-3任一项所述的正极活性材料，其中，M 1元素包括Ti、Mo、V、Nb、Ru、Sb和W中的一种或多种；可选的，M 1元素包括Ti、Nb、Ru、Sb和W中的一种或多种；或，
    M 2元素包括Al、Zr、Zn、Y及B中的一种或多种；可选的，M 2元素包括Al、Zr、Zn和Y中的一种或多种；可选的，M 2元素包括Al、Zr和Y中的一种或多种。
  5. 根据权利要求1-4任一项所述的正极活性材料，其中，所述M 1元素在所述本体颗粒中均匀掺杂；可选的，所述本体颗粒中M 1元素的局部质量浓度的相对偏差为32％以下，可选的为20％以下；
    可选的，所述本体颗粒为两个以上一次颗粒聚集而成的二次颗粒。
  6. 根据权利要求1-5任一项所述的正极活性材料，其中，所述正极活性材料中，所述M 1元素与所述M 2元素的摩尔比为0.09∶1～4∶1，可选的为0.1∶1～3∶1，可选的为0.2∶1～2.5∶1，可选的为0.5∶1～2∶1。
  7. 根据权利要求1-6任一项所述的正极活性材料，其中，
    所述正极活性材料中所述M 1元素的真实掺杂浓度为2000μg/cm 3～55000μg/cm 3，可选的为2300μg/cm 3～49000μg/cm 3，可选的为3000μg/cm 3～30000μg/cm 3；或，
    所述正极活性材料中所述M 2元素的含量为300ppm～6500ppm，可选的为500ppm～5000ppm。
  8. 根据权利要求1-7任一项所述的正极活性材料，其中，所述正极活性材料的体积平均粒径Dv50为8μm～20μm，可选的为9μm～16μm。
  9. 根据权利要求1-8任一项所述的正极活性材料，其中，所述包覆层的厚度T为0.001μm～0.5μm，可选的为0.1μm～0.3μm；
    可选的，所述包覆层的厚度T与所述正极活性材料的平均颗粒粒径
    Figure PCTCN2020112914-appb-100001
    之间满足：
    Figure PCTCN2020112914-appb-100002
    可选的，
    Figure PCTCN2020112914-appb-100003
    可选的，
    Figure PCTCN2020112914-appb-100004
  10. 根据权利要求1-9任一项所述的正极活性材料，其中，所述锂复合氧化物为化学式1所示的化合物，
    Li 1+a[Ni xCo yMn zM 1 b]O 2-pX p    化学式1
    所述化学式1中，X选自F、N、P及S中的一种或多种，0.5≤x＜1，0≤y＜0.3，0≤z＜0.3，-0.2＜a＜0.2，0＜b＜0.2，0≤p＜0.2，x+y+z+b＝1。
  11. 根据权利要求10所述的正极活性材料，其中，当本体颗粒掺杂有X元素时，X元素均匀掺杂于本体颗粒中，可选的，本体颗粒中掺杂元素(含M 1元素和X元素)的局部质量浓度的相对偏差为32％以下，可选的为30％以下，还可选的为20％以下；或，
    X元素由本体颗粒的外表面至颗粒核心方向呈减小的质量浓度梯度；可选的，X元素掺杂于本体颗粒的外表层。
  12. 根据权利要求1-11任一项所述的正极活性材料，其中，所述正极活性材料还满足如下(1)～(3)中的一个或多个：
    (1)所述正极活性材料的表面为粗糙表面，可选的，所述正极活性材料的比表面积为0.2m 2/g～1.5m 2/g，还可选为0.3m 2/g～1m 2/g；
    (2)所述正极活性材料的真密度为4.6g/cm 3～5.2g/cm 3，可选为4.6g/cm 3～4.9g/cm 3；
    (3)所述正极活性材料的振实密度为2.3g/cm 3～2.8g/cm 3。
  13. 一种正极极片，包括正极集流体以及设置于所述正极集流体上的正极活性物质层，所述正极活性物质层包括根据权利要求1-12任一项所述的正极活性材料。
  14. 一种锂离子二次电池，包括根据权利要求13所述的正极极片。
  15. 一种装置，包括根据权利要求14所述的锂离子二次电池。
  16. 一种正极活性材料的制备方法，包括：
    a)提供包括含镍的过渡金属源、锂源及M 1元素的前驱体的混合料，并对所述混合料进行烧结处理，得到掺杂有M 1元素的本体颗粒；
    b)将所述本体颗粒与M 2元素的前驱体混合，并进行烧结处理，以在所述本体颗粒的外表面形成含M 2元素氧化物的包覆层，得到正极活性材料；其中，
    所述正极活性材料在11％脱锂态时，所述M 1元素的平均化合价为α 1，所述M 2元素的平均化合价为β 1；
    所述正极活性材料在78％脱锂态时，所述M 1元素的平均化合价为α 2，所述M 2元素的平均化合价为β 2；
    所述α 1和α 2满足α 2＞α 1，且所述β 1和β 2满足β 1＝β 2；
    所述M 1元素包括Si、Ti、Cr、Mo、V、Se、Nb、Ru、Rh、Pd、Sb、Te、Ce及W中的一种或多种，所述M 2元素选自Mg、Al、Ca、Zr、Zn、Y及B中的一种或多种。
  17. 根据权利要求16所述的制备方法，其中，
    所述混合料中还包括X元素的前驱体，得到的本体颗粒中还掺杂有X元素，所述X元素选自F、N、P及S中的一种或多种；或，
    在将所述本体颗粒与M 2元素的前驱体混合之前，还包括：
    c)将所述本体颗粒与X元素的前驱体混合，并进行烧结处理，以使X元素掺杂于所述本体颗粒，所述X元素选自F、N、P及S中的一种或多种。
  18. 根据权利要求16-17任一项所述的方法，其中，步骤a)中：烧结处理的气氛为含氧气氛；可选的，烧结气氛的含氧量为70％～100％，可选的为85％以上；烧结处理的温度为500℃～1000℃，可选的为700℃～900℃，还可选的为750℃～850℃；烧结处理的时间为5h～25h，可选的为5h～15h。
  19. 根据权利要求16-18任一项所述的方法，其中，步骤b)中：烧结处理的气氛为含氧气氛；可选的，烧结气氛的含氧量为70％～100％，可选的为85％以上；烧结处理的温度为100℃～550℃，可选的为200℃～500℃；烧结处理的时间为3h～25h，可选的为5h～10h。
  20. 根据权利要求17所述的方法，其中，步骤c)中：烧结处理的气氛为含氧气氛；可选的，烧结气氛的含氧量为70％～100％，可选的为80％～95％；烧结处理的温度为400℃～1000℃，可选的为400℃～850℃，可选的为400℃～750℃；烧结处理的时间为3h～25h，可选的为5h～10h。
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