WO2022100507A1 - 正极活性材料及电化学装置 - Google Patents

正极活性材料及电化学装置 Download PDF

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WO2022100507A1
WO2022100507A1 PCT/CN2021/128709 CN2021128709W WO2022100507A1 WO 2022100507 A1 WO2022100507 A1 WO 2022100507A1 CN 2021128709 W CN2021128709 W CN 2021128709W WO 2022100507 A1 WO2022100507 A1 WO 2022100507A1
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active material
positive electrode
electrode active
ratio
positive
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PCT/CN2021/128709
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English (en)
French (fr)
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吴霞
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宁德新能源科技有限公司
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Priority to JP2022522741A priority Critical patent/JP7383807B2/ja
Priority to EP21891033.9A priority patent/EP4207379A4/en
Publication of WO2022100507A1 publication Critical patent/WO2022100507A1/zh
Priority to US18/129,440 priority patent/US20230238529A1/en

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    • H—ELECTRICITY
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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    • C01G51/00—Compounds of cobalt
    • C01G51/40—Cobaltates
    • C01G51/42—Cobaltates containing alkali metals, e.g. LiCoO2
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    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G51/00—Compounds of cobalt
    • C01G51/40—Cobaltates
    • C01G51/66—Cobaltates containing alkaline earth metals, e.g. SrCoO3
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    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
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    • H01M4/00—Electrodes
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
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    • 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
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • 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
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    • C01P2002/52—Solid solutions containing elements as dopants
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    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
    • C01P2002/85—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by XPS, EDX or EDAX data
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    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • H—ELECTRICITY
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    • H01M4/00—Electrodes
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    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of positive electrode materials, in particular, to positive electrode active materials and electrochemical devices.
  • Lithium-ion batteries are widely used in portable electronic products, electric transportation, national defense aviation, energy storage and other fields due to their advantages of high energy density, good cycle performance, environmental protection, safety and no memory effect. In order to meet the needs of social development, it is an urgent problem to seek lithium-ion batteries with higher energy density and power density, which requires the cathode materials used to have higher specific capacity and higher voltage platform.
  • the cathode active material is developing towards high voltage.
  • the current cathode active material will extract a large amount of Li + , and the crystal structure of the material will undergo a series of irreversible phase transitions (O3 to H1-3, H1-3 to O1), which greatly reduces the material cycle performance and safety performance.
  • the interface side reactions are intensified at high voltage, such as the serious dissolution of Co metal in LiCoO 2 materials, and the high-voltage electrolyte technology is difficult to support.
  • the decomposition and failure of conventional electrolytes at high voltage are accelerated, so the capacity decay is very serious.
  • the irreversible phase transition can be delayed by doping with metal cations, but the effect of this method on the structure stability is not obvious at voltages higher than 4.6V.
  • the doping amount increases, the theoretical capacity loss will increase.
  • the present application proposes a positive electrode active material and an electrochemical device, the material has a P6 3 mc crystal structure, a stable crystal structure, and an HCP oxygen structure, low oxygen activity at high voltage, and can improve the capacity and cycle of lithium ion batteries. stability.
  • the present application provides a positive electrode active material, the positive electrode active material has a P6 3 mc crystal structure, and the positive electrode active material is a lithium transition metal composite oxide containing Co and R elements and optionally M elements , wherein the M element includes at least one of Al, Mg, Ti, Mn, Fe, Ni, Zn, Cu, Nb, Cr, Y or Zr, the R element includes at least one of F and Cl, and the R
  • the molar content of the elements is n R
  • the sum of the molar contents of the Co and M elements is n Co+M
  • the ratio of the n R to the n Co+M is 0 ⁇ 0.01.
  • the present application provides an electrochemical device comprising a positive electrode active material layer, the positive electrode active material layer comprising the positive electrode active material according to the first aspect of the present application, and the compaction density of the positive electrode active material layer is 3.0 g /cm 3 to 4.4 g/cm 3 , preferably 4.12 g/cm 3 to 4.22 g/cm 3 .
  • the present application at least has the following beneficial effects:
  • the positive electrode active material provided by the present application has a P6 3 mc crystal structure, which has high crystal structure stability and reduces the probability of particle breakage and crystal structure damage, thereby improving the cycle performance and thermal stability of the electrochemical device.
  • the positive active material of the present application is co-doped with anions and cations, the cations are Co element and M element, and the anion is R element, wherein M and O form an M-O bond, and the energy band structure of oxygen is lowered through the M-O bond and the anion R, which can reduce the energy band structure of oxygen. Reducing the energy band overlap between Co and oxygen, slowing down the release of oxygen from the lattice, can stabilize the oxygen in the positive active material, so that the positive active material has a higher specific capacity and voltage platform, and is also conducive to reducing the positive electrode active material under high voltage. Interface side reactions, improve interface stability.
  • the electrochemical device of the present application also has a high specific capacity, a high voltage platform, and the interface is stable at high voltage, which can improve cycle stability.
  • any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with any other lower limit to form an unspecified range, and likewise any upper limit can be combined with any other upper limit to form an unspecified range.
  • every point or single value between the endpoints of a range is included within the range, even if not expressly recited.
  • each point or single value may serve as its own lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.
  • the positive electrode active material has a P6 3 mc crystal structure, and the positive electrode active material is a lithium transition metal composite oxide containing Co and R elements and optionally M elements.
  • the M element includes at least one of Al, Mg, Ti, Mn, Fe, Ni, Zn, Cu, Nb, Cr, Y or Zr
  • the R element includes at least one of F and Cl
  • the R The molar content of the elements is n R
  • the sum of the molar contents of the Co and M elements is n Co+M
  • the ratio of the n R to the n Co+M is 0 ⁇ 0.01.
  • the positive electrode active material provided by the present application has a P6 3 mc crystal structure, specifically a hexagonal close-packed crystal structure, the crystal structure is more stable, the probability of particle breakage and crystal structure damage is lower, and the process of lithium ion deintercalation and intercalation is low.
  • the structural changes caused by the lithium ion are small, and the stability in air and water is high, which is beneficial to improve the cycle performance and thermal stability of lithium-ion batteries.
  • co-doping of anions and cations is adopted, Co element and M element are selected for the cation, and R element is selected for the anion.
  • the overlapping of the bands can slow down the release of oxygen from the lattice, which can stabilize the oxygen in the positive electrode active material during the battery cycle, stabilize the interface between the positive electrode active material and the electrolyte, thereby improving the cycle stability and making the positive electrode active material higher.
  • the specific capacity and voltage platform are also beneficial to reduce the interfacial side reactions of the positive electrode active material under high voltage and improve the interfacial stability.
  • the specific method of anion and cation co-doping is not limited, and wet doping may be performed in the co-precipitation stage of the precursor, or dry doping may be performed in the sintering stage.
  • the cationic doping element M includes at least one of Al, Mg, Ti, Mn, and Y.
  • the anion doping element R includes at least one of F and Cl, more preferably F, F can make the structure of the positive electrode active material more stable, and can stabilize the interface between the positive electrode active material and the electrolyte during the cycle of the battery, It is beneficial to improve the cycle performance of lithium-ion batteries.
  • the molar content of the M element is n M
  • the ratio of the n M to the n Co+M is 0 ⁇ y ⁇ 0.15
  • the molar content of the Co element is n Co
  • the n Co and The ratio of n Co+M is 1-y.
  • the positive electrode active material further includes Li element, the molar content of the Li element is n Li , and the ratio of the n Li to the n Co+M is 0.6 ⁇ x ⁇ 0.95.
  • the positive electrode active material further includes Na element, the molar content of the Na element is n Na , and the ratio of the n Na to the n Co+M is 0 ⁇ z ⁇ 0.03.
  • the general chemical formula of the positive electrode active material is Li x Na z Co 1-y My O 2- ⁇ R ⁇ , 0.6 ⁇ x ⁇ 0.95, 0 ⁇ y ⁇ 0.15, 0 ⁇ z ⁇ 0.03, 0 ⁇ 0.01.
  • the XPS spectrum of the positive electrode active material contains O1s peaks in the range of 530eV-535eV.
  • the characteristic peak of O moves to the high binding energy, which reduces the energy band overlap between Co and O, slows down the release of oxygen from the lattice, stabilizes the oxygen in the positive active material, and stabilizes the positive electrode.
  • the interface between the active material and the electrolyte improves cycling stability.
  • the positive active material includes, but is not limited to, Li 0.63 Na 0.019 Co 0.99 M 0.01 O 1.999 R 0.001 , Li 0.9 Na 0.015 Co 0.99 M 0.01 O 1.998 R 0.002 , Li 0.73 Na 0.012 Co 0.988 M 0.012 O 1.995 R 0.005 , li 0.73 NA 0.01 CO 0.985 M 0.015 o 1.995 R 0.005 , Li 0.73 NA 0.004 CO 0.974 M 0.026 O 1.993 R 0.007 , LI 0.002 CO 0.99 M 0.01 , LI 0.73 NA 0.012 CO.011, LI 0.73 NA 0.012 CO.012 CO.012 CO.012 CO.73 NA 0.012 NA 0.012 CO.012 CO.73 NA 0.012 CO.012 CO.73 NA 0.012 CO.73 NA 0.012 CO.73 NA 0.012 CO.73 NA 0.012 CO.73 NA 0.012 CO.73 NA 0.012 CO.73 NA 0.012 NA 0.98
  • the positive electrode active material includes, but is not limited to, Li 0.9 Na 0.015 Co 0.99 Al 0.01 O 1.998 F 0.002 , Li 0.73 Na 0.012 Co 0.988 Al 0.012 O 1.995 F 0.005 , Li 000.73 Na 0.004 Co 0.974 Al 0.026 O 0.999 Cl 0.027 O 1.99 Li 0.73 Na 0.01 Co 0.985 Mg 0.015 O 1.995 F 0.005 .
  • anions and cations with high electronegativity are selected for doping.
  • the ratio of the electronegativity of the M element cation to the electronegativity of the Co element cation is 1-2, preferably 1.05-1.64, and specifically, the electronegativity ratio may be, for example, 1.64 , 1.58, 1.05, 1.23, etc., which are not limited here.
  • the R element concentration on the surface of the positive electrode active material is higher than the R element concentration inside the positive electrode active material, wherein the R element concentration is n R (the molar content of the R element) and n Co The ratio of +M (the sum of the molar contents of Co and M elements).
  • the R element is enriched on the surface of the positive electrode active material, which can reduce the amount of activated oxygen on the surface of the material, reduce the amount of oxygen released, and slow down the oxidation of the positive electrode active material to the electrolyte.
  • the ratio of the R element concentration in the depth region from the surface of the positive electrode active material to 50 nm to the R element concentration in other regions of the positive electrode active material is (1-10):1. If the ratio is greater than 10:1, the doping concentration of the R element on the surface of the positive active material is much larger than the doping concentration of the internal R element, and CEI is deposited on the surface of the material or Co-R is deposited on the surface, resulting in deterioration of impedance and further deterioration of the performance of the electrochemical device.
  • the R element concentration difference at any position in other regions of the positive electrode active material is lower than 5%.
  • the R element is evenly distributed in the positive active material, so that the valence state and lithium content of each part of the transition metal are the same, which not only stabilizes the oxygen in each part, but also does not cause local overcharge or over-intercalation, so that the redox reaction of each part is carried out uniformly. , the lithium ion migration proceeds uniformly.
  • the cathode active material of the present application includes pores and/or slits.
  • the positive electrode active material includes pores and slits.
  • the pores on the surface of the positive active material particles are imaged by SEM to observe whether there are pores on the surface of the particles; the gaps inside the particles are cut by CP (cross-section polishing) technology, and then imaged by SEM. Observe whether there are gaps inside the particles.
  • the average particle size Dv50 of the positive electrode active material is 10 ⁇ m to 25 ⁇ m, the average particle size is too large, the diffusion path of lithium ions in the large particle size particles is longer, and the greater the resistance to be overcome by diffusion, The crystal deformation and volume expansion of the cathode active material caused by the intercalation process continue to accumulate, making the intercalation process gradually difficult to carry out. Controlling the particle size of the cathode active material below 25 ⁇ m can improve the electrochemical kinetic performance and rate during the charge and discharge process. performance, and reduce the polarization phenomenon, so that the battery has higher specific capacity, Coulomb efficiency and cycle performance.
  • the particle size of the positive active material is set to more than 10 ⁇ m to ensure that the particle size of the positive active material will not be too small and reduce the surface side reactions of the material. , and can effectively inhibit the agglomeration between particles of the positive electrode active material with too small particle size, so as to ensure that the battery has high rate performance and cycle performance.
  • the positive electrode active material has a specific surface area of 0.1 m 2 /g to 3 m 2 /g.
  • the specific surface area of the positive electrode active material is within the above range, the stability of the positive electrode active material to air, water and carbon dioxide can be improved, and the reactivity of the electrolyte on the surface of the positive electrode active material can be reduced, so that the above effects can be better exerted and the charging capacity of the positive electrode can be improved.
  • Discharge capacity development, cycle performance and safety performance is 0.72 m 2 /g to 2.5 m 2 /g.
  • the crystal structure of the positive electrode active material can be determined by an X-ray powder diffractometer, for example, a Brucker D8A_A25 X-ray diffractometer from Brucker AxS, Germany, with CuK ⁇ ray as the radiation source, the ray wavelength
  • the scanning 2 ⁇ angle range was from 10° to 90°, and the scanning rate was 4°/min.
  • the specific surface area of the positive active material is the meaning known in the art, and can be measured with instruments and methods known in the art, for example, it can be tested with the nitrogen adsorption specific surface area analysis test method, and calculated with the BET (Brunauer Emmett Teller) method, wherein The nitrogen adsorption specific surface area analysis test can be carried out by the TriStar II specific surface area and pore analyzer of Micromeritics Company in the United States.
  • the average particle diameter Dv50 of the positive electrode active material has a meaning known in the art, and can be measured by instruments and methods known in the art. For example, it can be conveniently measured with a laser particle size analyzer, such as a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.
  • a laser particle size analyzer such as a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.
  • the R element concentration of the positive electrode active material can be analyzed by electron energy loss spectrum known in the art, and the type and number of dopant atoms in the depth region from the surface to 50 nm are analyzed according to the electron energy loss spectrum of the positive electrode active material. In the same way, the types of dopant atoms and the number of dopant atoms in other regions are analyzed to obtain the depth longitudinal distribution of the R element in the positive electrode active material.
  • a second aspect of the present application provides a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode current collector can be made of metal foil, carbon-coated metal foil or porous metal plate, preferably aluminum foil.
  • the positive electrode active material layer includes the positive electrode active material of the first aspect of the present application.
  • the positive active material in the positive active material layer is Li x Na z Co 1-y My O 2- ⁇ R ⁇ .
  • the compaction density of the positive electrode active material layer is 3.0 g/cm 3 to 4.4 g/cm 3 , preferably, the compaction density of the positive electrode active material layer is 4.12 g/cm 3 to 4.22 g/cm 3 .
  • the compaction density of the positive electrode active material layer is within the above range, which is beneficial to improve the specific capacity and energy density of the battery, and improve the rate performance and cycle performance of the battery.
  • the compacted density of the positive electrode active material can be measured by instruments and methods known in the art, for example, it can be conveniently measured by an electronic pressure testing machine, such as a UTM7305 electronic pressure testing machine.
  • the positive electrode active material layer also includes a binder and a conductive agent.
  • the binder can be styrene-butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer
  • SBR styrene-butadiene rubber
  • CMC carboxymethyl cellulose
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA polyvinyl alcohol
  • PVA polyvinyl alcohol
  • the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the above-mentioned positive electrode sheet can be prepared according to conventional methods in the art.
  • the positive electrode active material and optional conductive agent and binder are dispersed in a solvent (such as N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode slurry, and the positive electrode slurry is coated on the positive electrode current collector , after drying, cold pressing and other processes, the positive pole piece is obtained.
  • a solvent such as N-methylpyrrolidone, abbreviated as NMP
  • the positive electrode sheet of the present application has high comprehensive electrochemical performance and safety performance.
  • a third aspect of the present application provides an electrochemical device comprising the positive electrode active material layer of the first aspect of the present application.
  • the compaction density of the positive electrode active material layer is 3.0 g/cm 3 to 4.4 g/cm 3 , preferably, the compaction density of the positive electrode active material layer is 4.12 g/cm 3 to 4.22 g/cm 3 .
  • the compaction density of the positive electrode active material layer is within the above range, which is beneficial to improve the specific capacity and energy density of the battery, and improve the rate performance and cycle performance of the battery.
  • the compacted density of the positive electrode active material can be measured by instruments and methods known in the art, for example, it can be conveniently measured by an electronic pressure testing machine, such as a UTM7305 electronic pressure testing machine.
  • the X-ray diffraction method is used to analyze the main peak in the XRD pattern of the positive electrode active material in the range of 18° to 19°.
  • the half-width of the main peak is between 0° and 0.5°.
  • the electrochemical device further includes a negative pole piece, a separator, and an electrolyte.
  • the negative pole piece may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.
  • the negative electrode current collector includes two opposite surfaces, and the negative electrode active material layer is laminated on either or both of the two surfaces of the negative electrode current collector.
  • the negative electrode current collector can be made of metal foil, carbon-coated metal foil, or porous metal plate, and copper foil is preferred.
  • the negative electrode active material layer usually includes the negative electrode active material and optional conductive agents, binders and thickeners.
  • the extremely active material can be one or more of natural graphite, artificial graphite, mesophase microcarbon balls (MCMB), hard carbon and soft carbon
  • the conductive agent can be superconducting carbon, acetylene black, carbon black, Ketjen black , one or more of carbon dots, carbon nanotubes, graphene and carbon nanofibers
  • the binder can be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin and carboxymethyl cellulose (CMC)
  • the thickener may be carboxymethyl cellulose (CMC).
  • the present application is not limited to these materials, and other materials that can be used as negative electrode active materials, conductive agents, binders, and thickeners for lithium ion batteries can also be used in the present application.
  • the above-mentioned negative pole pieces can be prepared according to conventional methods in the art.
  • the negative electrode active material and optional conductive agent, binder and thickener are dispersed in a solvent, which can be deionized water, to form a uniform negative electrode slurry, and the negative electrode slurry is coated on the negative electrode current collector, After drying, cold pressing and other processes, the negative pole piece is obtained.
  • the above-mentioned separator is not particularly limited, and any well-known porous structure separator with electrochemical stability and chemical stability can be selected, such as glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • any well-known porous structure separator with electrochemical stability and chemical stability can be selected, such as glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • One or more of the single-layer or multi-layer films are examples of the single-layer or multi-layer films.
  • the above electrolyte includes a lithium salt and an organic solvent, wherein the specific types and compositions of the lithium salt and the organic solvent are not specifically limited, and can be selected according to actual needs.
  • the lithium salt may include one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium perchlorate
  • the organic solvent may include one or more of cyclic carbonate, chain carbonate, and carboxylate .
  • the electrolyte may also contain functional additives, such as vinylene carbonate, vinyl sulfate, propane sultone, fluoroethylene carbonate, and the like.
  • the electrochemical device of the present application has high specific capacity, high voltage platform, high cycle performance and safety, stable interface under high voltage, and reversible structure. good sex.
  • the present application further provides a method for preparing a positive electrode active material, the method comprising the following steps S10-S30:
  • the M element-doped (Co 1-y My ) 3 O 4 precursor powder is prepared by the liquid phase co-precipitation and sintering method, wherein 0 ⁇ y ⁇ 0.15, and then the precursor powder is prepared by using The solid-phase sintering method was sintered with sodium carbonate and lithium salt to obtain Nam Co 1-y My O 2- ⁇ R ⁇ with P6 3 mc crystal structure. Finally, the positive electrode with P6 3 mc crystal structure was synthesized by ion exchange method.
  • the active material Li x Na z Co 1-y My O 2- ⁇ R ⁇ the preparation process is safe and controllable, so that the prepared positive electrode active material has the specific chemical composition and structure described in this application, which can greatly improve the positive electrode activity
  • the electrochemical performance of the material makes the electrochemical device have high specific capacity, high voltage platform, high cycle performance and safety, stable interface under high voltage, and good structural reversibility.
  • step S10 the specific steps of using the cobalt salt and the salt containing the M element to obtain the coprecipitate by a liquid-phase precipitation method include:
  • the cobalt salt is at least one of cobalt nitrate, cobalt chloride, cobalt sulfate and cobalt acetate;
  • the salt containing M element is nitrate, chloride salt, At least one of sulfate and acetate.
  • the solvent is at least one of deionized water, methanol, ethanol, acetone, isopropanol and n-hexanol.
  • the precipitating agent is at least one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, potassium bicarbonate, sodium carbonate and potassium carbonate. It should be noted that, before adding the precipitating agent into the mixed solution, the precipitating agent can be pre-prepared to obtain a precipitating agent solution, and the solvent used for preparing the precipitating agent solution can be deionized water, methanol, ethanol, acetone, isopropanol and At least one of n-hexanol.
  • the concentration of the precipitant in the precipitant solution is preferably 0.1 mol/L to 3 mol/L, more preferably 1 mol/L to 3 mol/L.
  • the complexing agent is at least one of ammonia water, ammonium carbonate, ammonium bicarbonate, urea, hexamethylenetetramine, ethylenediaminetetraacetic acid, citric acid and ascorbic acid. It should be noted that, before adding the complexing agent into the mixed solution, the complexing agent can be pre-prepared to obtain a complexing agent solution, and the solvent used for preparing the complexing agent solution can be deionized water, methanol, ethanol, acetone, At least one of isopropanol and n-hexanol.
  • the concentration of the complexing agent in the complexing agent solution is preferably 0.1 mol/L to 3 mol/L, more preferably 0.5 mol/L to 1.5 mol/L.
  • the pH value of the reaction solution will affect the precipitation rate of each metal ion, thereby directly affecting the crystal nucleation and growth rate of the transition metal source, which in turn affects the chemical composition and structure of the transition metal source, and finally affects the chemical composition of the positive active material. structure.
  • the pH value of the reaction solution is controlled to be 5 to 9, for example, it can be 5, 6, 7, 8, 9, and of course other data within the above range can also be used.
  • the pH value of the reaction solution can be adjusted by adjusting the type and content of the precipitant and/or complexing agent.
  • the temperature of the reaction solution will directly affect the rate and yield of the chemical reaction, and the reaction time will affect the growth process of the reaction product, which in turn affects the chemical composition and structure of the reaction product.
  • the reaction temperature is 25°C to 100°C, and the reaction time is 2 hours to 30 hours.
  • step 10 may also include:
  • the coprecipitate was washed with an appropriate amount of detergent and dried. It should be noted that the application does not specifically limit the detergent used for washing and the number of times of washing, which can be selected according to actual needs, as long as the remaining ions on the surface of the co-precipitate are removed.
  • the detergent can be deionized water.
  • the sintering temperature and time of the coprecipitate will affect the specific surface area, particle size, morphology and crystal structure of the reaction product.
  • the sintering temperature of the coprecipitate is 400°C to 800°C, more preferably 450°C to 600°C; the sintering time of the coprecipitate is 5h ⁇ 20h, preferably 12h ⁇ 15h.
  • step S10 the sintering treatment may be performed in an air or oxygen atmosphere.
  • step S20 the molar ratio of (Co 1-y My ) 3 O 4 , Na 2 CO 3 and Li a R according to Na, Co, M, and R is 0.7: (1-y ):y: ⁇ , the molar ratio of Na to Co is (0.5-0.8):1, preferably, the molar ratio of Na to Co is 0.74:1.
  • step S20 the temperature and time of the sintering treatment will affect the specific surface area, particle size, morphology and crystal structure of the reaction product.
  • the temperature of the sintering treatment is 700°C-1000°C, more preferably 800°C-900°C; the time of the sintering treatment is preferably 36h-56h, more preferably 40h-50h.
  • the sintering treatment can be performed in an air or oxygen atmosphere.
  • the lithium-containing molten salt includes at least one of lithium nitrate, lithium chloride, and lithium hydroxide.
  • step S30 Nam Co 1-y My O 2- ⁇ R ⁇ and lithium-containing molten salt are mixed in a ratio of (0.01-0.2): 1 in the molar ratio of Na element to Li element, preferably, Na element The molar ratio to Li element is 0.03:1.
  • step S30 the temperature and time of the sintering treatment will affect the specific surface area, particle size, morphology and crystal structure of the reaction product.
  • the temperature of the sintering treatment is 200°C-400°C, more preferably 250°C-350°C; the sintering treatment time is preferably 2h-8h, more preferably 4h-6h.
  • the sintering treatment can be performed in an air or oxygen atmosphere.
  • step S30 may further include:
  • the sintered product is washed with an appropriate amount of detergent and dried.
  • the application does not specifically limit the detergent used for washing and the number of times of washing, which can be selected according to actual needs, as long as the molten salt on the surface of the sintered product is removed.
  • the detergent can be deionized water.
  • cathode active material Li x Na z Co 1-y My O 2- ⁇ R ⁇ has a P6 3 mc crystal structure, of course, the final product will also have a part of the R-3m crystal structure of the cathode active material .
  • the type and content of reactants, pH value, type and concentration of precipitant, type and concentration of complexing agent, sintering temperature and time, etc. are comprehensively regulated to make the positive electrode active
  • the material has the specific chemical composition and structure described in this application, which can greatly improve the electrochemical performance of the positive electrode active material, as well as the specific capacity, cycle performance and safety performance of the lithium ion battery.
  • the cobalt chloride and the sulfate containing M element are mixed into deionized water according to the molar ratio of Co element and M element as (1-y):y to obtain a mixed solution; the precipitating agent and the complexing agent are added Mix the solutions to obtain a reaction solution, and adjust the pH value of the reaction solution to 6, so that the reaction solution is subjected to a co-precipitation reaction under stirring to obtain a co-precipitate; the co-precipitate is sintered at 600°C to 700°C to obtain M element Doped (Co 1-y My ) 3 O 4 powder, wherein 0 ⁇ y ⁇ 0.15;
  • the positive electrode active materials of Examples 1-10 and Comparative Examples 1-6 were all prepared under the above-mentioned reaction conditions, and the obtained positive electrode active materials were shown in Table 1.
  • the above-prepared positive active material, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 95:2:3. , to form a uniform positive electrode slurry; apply the positive electrode slurry on a 12 ⁇ m aluminum foil, dry, cold-press, and then cut and weld tabs to obtain a positive electrode.
  • NMP N-methylpyrrolidone
  • the separator adopts polyethylene (PE) porous polymer film.
  • ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) were mixed in a weight ratio of 1:1:1, and LiPF 6 was added and mixed evenly to form an electrolytic solution.
  • liquid in which the concentration of LiPF 6 was 1.15 mol/L. 5
  • the above-mentioned positive pole pieces, separators and negative pole pieces are stacked, wound and placed in the outer packaging foil in order, leaving a liquid injection port.
  • the electrolyte is poured from the liquid injection port, and the lithium ion battery is prepared through the processes of chemical formation and capacity.
  • the lithium-ion batteries prepared in the examples and comparative examples were charged at a constant current of 0.1C to a voltage of 4.7V, and then charged at a constant voltage of 4.7V to a current of 0.05C.
  • the charging capacity of the lithium-ion battery is recorded as the charging capacity of the first cycle of the lithium-ion battery, after which it is left for 5 minutes, and then discharged with a constant current of 0.1C to a voltage of 3.0V, and left for 5 minutes. This is a cyclic charge-discharge process. It is the first cycle discharge capacity of the lithium-ion battery, that is, the initial capacity of the lithium-ion battery.
  • the lithium-ion battery was subjected to a 50-cycle charge-discharge test according to the above method, and the discharge capacity of the 50th cycle was detected.
  • the capacity retention rate (%) of the lithium-ion battery after 50 cycles the discharge capacity of the 50th cycle/the first cycle discharge capacity ⁇ 100%.
  • Table 2 shows the positive electrode active materials of Examples 1-10 and Comparative Examples 1-6 analyzed by X-ray photoelectron spectroscopy, the position of the main peak of O1s in the XPS spectrum of the positive electrode active material, and the positive electrode active material.
  • the performance parameters of the fabricated lithium-ion battery are shown in Table 2.
  • Comparative analysis of the data in Table 2 shows that since the positive active materials of Comparative Examples 1 to 4 are only doped with cations, such as Al and Mg, under high voltage (>4.6V), Comparative Examples 1 to 4 and Examples 3,
  • the first cycle discharge capacities of 6, 7, and 8 are similar, but pure cation doping, although they are also P6 3 mc crystal structure, due to the low peak position of its O1s main peak, that is, the oxygen structure is not stable enough, and it cannot relieve the positive electrode active material.
  • the surface phase transition under high pressure, as the phase transition continues to spread inward, causes the capacity of the lithium battery to decay rapidly.
  • Examples 3, 6, 7, and 8 which are doped with a small amount of R element, the obtained positive electrode active materials have a higher O1s main peak position, that is, the activity of oxygen can be reduced, thereby greatly improving the activity of the positive electrode Crystal stability of materials under high temperature and high pressure.
  • the amount of doping R element should not be too much, otherwise the first cycle discharge capacity at 45 °C and the capacity retention rate after 50 cycles are greatly reduced.
  • the surface exceeds a certain concentration, a large amount of active lithium will be combined to form a dense LiF layer, which will deteriorate the interface resistance and cause capacity loss.
  • Example 11, Example 12 and Comparative Example 7 were prepared according to the above preparation method, and the ratio of the electronegativity of the M element to the electronegativity of the Co element in the positive electrode active material was measured as shown in Table 3. , and the performance parameters of the lithium-ion battery made of the above positive active material are shown in Table 3.
  • the positive electrode active material has higher stability under high temperature and high pressure.
  • Examples 13-16 were prepared according to the above preparation method, wherein the components of the positive active materials prepared in Examples 3 and 13-16 were the same, namely Li 0.73 Na 0.012 Co 0.988 Al 0.012 O 1.995 F 0.005 , using XPS Analysis is carried out to test the R element concentration on the particle surface and the R element concentration inside the particle, the ratio of the R element concentration in the depth area of the particle surface to 50nm and the R element concentration in other areas, and the R element concentration at any position in other areas. Difference. And the performance parameters of the lithium ion battery made of the above positive active material are shown in Table 4.
  • the ratio of the R element concentration from the particle surface of the positive electrode active material to the depth of 50 nm to the R element concentration in other regions is (1-10):1, and any position in other regions
  • the first cycle discharge capacity and the 50 cycle capacity retention rate of the lithium battery can be maintained at a high level.
  • the particle surface of the positive electrode active material reaches a depth of 50nm
  • the ratio of the R element concentration to the R element concentration in other areas is greater than 10:1, or the difference in the R element concentration at any position in other areas is greater than 5%, the first cycle discharge capacity and the 50-cycle capacity retention rate of the lithium battery are both has declined.
  • Examples 17-19 were prepared according to the above preparation method, wherein the components of the positive active materials prepared in Example 3 and Examples 17-19 were the same, namely Li 0.73 Na 0.012 Co 0.988 Al 0.012 O 1.995 F 0.005 , The electron microscope was used to analyze the pores on the surface of the particles and the gaps inside the particles;
  • the positive active material prepared in Example 3 includes pores and gaps.
  • the first cycle discharge capacity of the battery prepared according to Example 3 can reach 235mAh/g, and the capacity retention rate after 50 cycles can reach 91%;
  • the first-cycle discharge capacity and the 50-cycle capacity retention rate of the batteries prepared according to Examples 17-19 decreased, which was due to the pore and crevice structure of the particles, which was conducive to the release of the surface and/or interior of the active material during the cycle.
  • the resulting stress strain stabilizes the interface between the cathode active material and the electrolyte, thereby improving the cycle capacity retention rate and improving the cycle stability at high voltage.
  • Examples 20 to 22 were prepared according to the above preparation method, wherein the components of the positive active materials prepared in Examples 20 to 22 were the same, namely Li 0.73 Na 0.012 Co 0.988 Al 0.012 O 1.995 F 0.005 , and the positive electrode activity was measured.
  • the specific surface area of the material is shown in Table 6, and the performance parameters of the lithium ion battery made of the above positive active material are shown in Table 6.
  • the specific surface areas of Examples 3, 20 and 21 are in the range of 0.72m 2 /g to 2.5m 2 /g, and the specific surface areas are not too large, which can improve the stability of the positive electrode active material to air, water and carbon dioxide. It can reduce the reactivity of the electrolyte on the surface of the positive electrode active material, thereby improving the cycle capacity retention rate and improving the cycle stability under high voltage; The reactivity of the surface electrolyte increases, the side reactions on the surface of the material increase, and the cycle capacity retention rate and the cycle stability under high voltage are decreased.
  • Examples 23-24 were prepared according to the above preparation method, wherein the components of the positive active materials prepared in Example 3 and Examples 23-24 were the same, namely Li 0.73 Na 0.012 Co 0.988 Al 0.012 O 1.995 F 0.005 ,
  • the performance parameters of the lithium-ion battery made of the above-mentioned positive active material are shown in Table 7.
  • the battery has a capacity of not less than 180mAh/g in a fully discharged state, it is analyzed by X-ray diffraction.
  • the main peak range and the half width of the main peak are shown in Table 7.
  • the main peaks in the XDR spectra of the positive electrode active materials of Examples 3, 23 and 24 are in the range of 18° to 19°, and the half-peak width of the main peak is in the range of 0° to 0.5°. It can be seen that the positive electrode When the half-peak width of the main peak of the active material is between 0° and 0.5°, the crystal structure of the positive active material is more stable, which can improve the stability of the positive active material to air, water and carbon dioxide, and reduce the surface electrolyte of the positive active material. Reactivity, thereby improving the cycle capacity retention rate and improving the cycle stability at high voltage.

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Abstract

本申请提供了正极活性材料及电化学装置，所述正极活性材料具有P6 3mc晶体结构，所述正极活性材料为包含Co和R元素以及可选地包含M元素的锂过渡金属复合氧化物，其中，M元素包括Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr、Y或Zr中的至少一种，R元素包括F、Cl中的至少一种，所述R元素的摩尔含量为n R，所述Co和M元素的摩尔含量之和为n Co+M，所述n R与所述n Co+M的比值为0<δ≤0.01。本申请的正极活性材料，晶体结构稳定性高，从而改善电化学装置的循环性能和热稳定性。

Description

正极活性材料及电化学装置
本申请要求于2020年11月10日提交中国专利局，申请号为202011243565.4，申请名称为“正极活性材料及电化学装置”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及正极材料技术领域，具体地讲，涉及正极活性材料及电化学装置。
背景技术
锂离子电池因其能量密度高、循环性能好、环保、安全且无记忆效应等优点，被广泛的应用于便携式电子产品、电动交通、国防航空、能源储备等领域。为了满足社会发展的需求，寻求具有更高能量密度和功率密度的锂离子电池是亟待解决的问题，这就要求所用正极材料具有更高比容量和更高电压平台。
为了获取更高比能量，正极活性材料正朝着高电压方向发展，目前的正极活性材料随着电压的升高，Li +大量脱出，材料的晶体结构将发生一系列不可逆的相变(O3到H1-3，H1-3到O1)，使得材料循环性能和安全性能大大降低。并且，在高电压下界面副反应加剧，例如LiCoO 2材料的Co金属溶出严重，而高电压电解液技术难以配套，常规电解液在高电压下分解加速、失效加快，因而容量衰减十分严重。为了提高材料的晶相结构稳定性，可以通过金属阳离子掺杂来推迟不可逆相变，但该方法在高于4.6V电压后对结构的稳定效果并不明显。此外，掺杂量增多，理论容量损失会增大。
因此，急需寻求一种具有高比容量、高电压平台、结构可逆性好且在高电压下界面稳定的正极活性材料。
申请内容
鉴于此，本申请提出了正极活性材料及电化学装置，该材料具有P6 3mc晶体结构，晶 体结构稳定，且具有HCP氧结构，高电压下氧活性低，能提高锂离子电池的容量、循环稳定性。
第一方面，本申请提供一种正极活性材料，所述正极活性材料具有P6 3mc晶体结构，所述正极活性材料为包含Co和R元素以及可选地包含M元素的锂过渡金属复合氧化物，其中，M元素包括Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr、Y或Zr中的至少一种，R元素包括F、Cl中的至少一种，所述R元素的摩尔含量为n R，所述Co和M元素的摩尔含量之和为n Co+M，所述n R与所述n Co+M的比值为0<δ≤0.01。
第二方面，本申请提供一种电化学装置，包括正极活性材料层，所述正极活性材料层包括根据本申请第一方面的正极活性材料，所述正极活性材料层的压实密度为3.0g/cm 3～4.4g/cm 3，优选为4.12g/cm 3～4.22g/cm 3。
相对于现有技术，本申请至少具有以下有益效果：
本申请提供的正极活性材料具有P6 3mc晶体结构，晶体结构稳定性高，降低颗粒破碎、晶体结构损坏的概率，从而改善电化学装置的循环性能和热稳定性。
本申请的正极活性材料采用阴阳离子共掺杂，阳离子选用Co元素与M元素，阴离子选用R元素，其中，M与O形成M-O键，通过M-O键和阴离子R拉低氧的能带结构，能够减少Co与氧的能带重叠，减缓晶格释放氧，可以稳定住正极活性材料中的氧，使得正极活性材料具有较高的比容量和电压平台，还有利于减少高电压下正极活性材料的界面副反应，提高界面稳定性。
因此，本申请的电化学装置也具有高比容量、高电压平台且在高电压下界面稳定，能够提高循环稳定性。
附图说明
图1中的(a)为对比例1和(b)为实施例3提供的正极活性材料的XPS图谱。
具体实施方式
以下所述是本申请实施例的优选实施方式，应当指出，对于本技术领域的普通技术人员来说，在不脱离本申请实施例原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也视为本申请实施例的保护范围。
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“多种”的含义是两个以上。
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
首先说明本申请第一方面提供的正极活性材料，所述正极活性材料具有P6 3mc晶体结构，所述正极活性材料为包含Co和R元素以及可选地包含M元素的锂过渡金属复合氧化物，其中，M元素包括Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr、Y或Zr中的至少一种，R元素包括F、Cl中的至少一种，所述R元素的摩尔含量为n R，所述Co和M元素的摩尔含量之和为n Co+M，所述n R与所述n Co+M的比值为0<δ≤0.01。
本申请提供的正极活性材料具有P6 3mc晶体结构，具体为六方密堆积的晶体结构，晶体结构的稳定性更高，颗粒破碎、晶体结构损坏的概率更低，锂离子脱嵌、入嵌过程中引起的结构变化较小，且在空气及水中的稳定性较高，从而对改善锂离子电池的循环性能和热稳定性有利。
在本申请的正极活性材料中，采用阴阳离子共掺杂，阳离子选用Co元素与M元素，阴离子选用R元素，通过M-O键和阴离子R拉低氧的能带结构，能够减少Co与氧的能带 重叠，减缓晶格释放氧，能够在电池循环过程中稳定住正极活性材料中的氧，稳定住正极活性材料和电解液之间的界面，从而提高循环稳定性，使得正极活性材料具有较高的比容量和电压平台，还有利于减少高电压下正极活性材料的界面副反应，提高界面稳定性。阴阳离子共掺杂的具体方法不受限制，可以在前驱体共沉淀阶段进行湿法掺杂，也可以在烧结阶段进行干法掺杂。
优选地，阳离子掺杂元素M包括Al、Mg、Ti、Mn、Y中的至少一种。阴离子掺杂元素R包括F、Cl中的至少一种，更优选为F，F可以使得正极活性材料的结构更加稳定，在电池循环使用过程中能够稳定正极活性材料与电解液之间的界面，有利于改善锂离子电池的循环性能。
优选地，所述M元素的摩尔含量为n M，所述n M与所述n Co+M的比值为0≤y<0.15，所述Co元素的摩尔含量为n Co，所述n Co与所述n Co+M的比值为1-y。
在本申请的一些实施方式中，所述正极活性材料进一步包含Li元素，所述Li元素的摩尔含量为n Li，所述n Li与所述n Co+M的比值为0.6<x<0.95。
在本申请的一些实施方式中，所述正极活性材料进一步包含Na元素，所述Na元素的摩尔含量为n Na，所述n Na与所述n Co+M的比值为0<z<0.03。
在本申请的具体实施方式中，所述正极活性材料的化学通式为Li xNa zCo 1-yM yO 2-δR δ，0.6<x<0.95，0≤y<0.15，0≤z<0.03，0<δ≤0.01。
利用X射线光电子能谱法分析，所述正极活性材料的XPS图谱中在530eV～535eV范围内含有O1s峰。如图1所示，在XPS图谱中，O特征峰向高结合能处移动，减少Co与O的能带交叠，减缓晶格释放氧，稳定住正极活性材料中的氧，从而稳定住正极活性材料和电解液之间的界面，提高循环稳定性。
在本申请的一些实施方式中，正极活性材料包括但不限于Li 0.63Na 0.019Co 0.99M 0.01O 1.999R 0.001、Li 0.9Na 0.015Co 0.99M 0.01O 1.998R 0.002、Li 0.73Na 0.012Co 0.988M 0.012O 1.995R 0.005、Li 0.73Na 0.01Co 0.985M 0.015O 1.995R 0.005、Li 0.73Na 0.004Co 0.974M 0.026O 1.993R 0.007、Li 0.73Na 0.002Co 0.97M 0.03O 1.99R 0.01、Li 0.73Na 0.012Co 0.988M 0.012O 1.998R 0.002、Li 0.73Na 0.01Co 0.985M 0.015O 1.995R 0.005、 Li 0.73Na 0.01Co 0.985M 0.015O 1.995R 0.005、Li 0.73Na 0.004Co 0.974M 0.026O 1.993R 0.007等，其中，M包括Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr、Y或Zr中的至少一种，R包括F、Cl中的至少一种。
更优选地，正极活性材料包括但不限于Li 0.9Na 0.015Co 0.99Al 0.01O 1.998F 0.002、Li 0.73Na 0.012Co 0.988Al 0.012O 1.995F 0.005、Li 0.73Na 0.004Co 0.974Al 0.026O 1.993Cl 0.007或Li 0.73Na 0.01Co 0.985Mg 0.015O 1.995F 0.005。
为了拉低O的能带，选用高电负性的阴离子、阳离子来进行掺杂。在本申请的一些实施方式中，所述M元素阳离子的电负性与Co元素阳离子的电负性的比值为1～2，优选为1.05～1.64，具体地，电负性比值例如可以是1.64、1.58、1.05、1.23等等，在此不做限定。
在本申请的一些实施方式中，所述正极活性材料表面的R元素浓度高于所述正极活性材料内部的R元素浓度，其中，R元素浓度为n R(R元素的摩尔含量)与n Co+M(Co和M元素的摩尔含量之和)的比值。R元素在正极活性材料表面富集，可减少材料表面活化氧的数量，降低氧的脱出量，减缓正极活性材料对电解液的氧化。
优选地，所述正极活性材料表面到50nm的深度区域内的R元素浓度与所述正极活性材料其他区域内的R元素浓度的比值为(1～10)：1。若比值大于10:1，正极活性材料表面R元素掺杂浓度远大于内部R元素掺杂浓度，材料表面CEI沉积或Co-R在表面沉积，造成阻抗恶化，进一步恶化电化学装置的性能。
优选地，所述正极活性材料其他区域内的任意位置的R元素浓度差低于5％。R元素均匀分布在正极活性材料内部，使得各部分过渡金属价态和锂含量比例相同，既均匀稳定各部分氧，也不会引起局部过充或过嵌现象，使得各个部分氧化还原反应均匀进行，锂离子迁移均匀进行。
进一步，本申请的正极活性材料包括孔和/或缝隙。优选地，正极活性材料包括孔及缝隙。正极活性材料颗粒表面的孔是采用SEM对颗粒进行成像，观察颗粒表面是否存在孔；颗粒内部的缝隙是采用CP(横截面剖光，cross-section polishing)技术切开颗粒，然后经SEM成像，观察颗粒内部是否存在缝隙。
在本申请的一些实施方式中，正极活性材料的平均粒径Dv50为10μm～25μm，平均粒径太大，锂离子在大粒径颗粒中扩散路径较长，且扩散需要克服的阻力越大，嵌入过程引起的正极活性材料晶体变形与体积膨胀不断积累，使得嵌入过程逐渐变得难以进行，将正极活性材料的粒径控制在25μm以下，可以提高充放电过程中的电化学动力学性能及倍率 性能，并减小极化现象，使电池具有较高的比容量、库伦效率及循环性能。平均粒径太小，正极活性材料的比表面积往往较大，表面副反应会增多，将正极活性材料的粒径在10μm以上，保证正极活性材料的粒径不会过小，减少材料表面副反应，并且还能有效抑制粒径过小的正极活性材料的颗粒与颗粒之间的团聚，保证电池具有较高的倍率性能和循环性能。
所述正极活性材料的比表面积为0.1m 2/g～3m 2/g。使正极活性材料的比表面积在上述范围内，能够提高正极活性材料对空气、水及二氧化碳的稳定性，降低正极活性材料表面电解液的反应活性，从而更好地发挥上述效果，提高正极的充放电容量发挥、循环性能及安全性能。优选地，本申请的正极活性材料的比表面积为0.72m 2/g～2.5m 2/g。
需要说明的是，正极活性材料的晶体结构可以采用X射线粉末衍射仪测定，例如使用德国Brucker AxS公司的Brucker D8A_A25型X射线衍射仪，以CuKα射线为辐射源，射线波长
Figure PCTCN2021128709-appb-000001
扫描2θ角范围为10°～90°，扫描速率为4°/min。
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Micromeritics公司的Tri Star Ⅱ型比表面与孔隙分析仪进行。
正极活性材料的平均粒径Dv50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R元素浓度可以用本领域公知的电子能量损失谱进行分析，根据正极活性材料的电子能量损失谱分析表面到50nm的深度区域内的掺杂原子的种类以及掺杂原子的数量。按照相同的方式分析其他区域内的掺杂原子的种类以及掺杂原子的数量，得到正极活性材料中R元素的深度纵向分布。
正极极片
本申请的第二方面提供一种正极极片，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。
正极集流体可以采用金属箔材、涂炭金属箔材或多孔金属板，优选采用铝箔。
正极活性物质层包括本申请第一方面的正极活性材料。可选地，正极活性物质层中的正极活性材料为Li xNa zCo 1-yM yO 2-δR δ。
所述正极活性材料层的压实密度为3.0g/cm 3～4.4g/cm 3，优选地，所述正极活性材料层的压实密度为4.12g/cm 3～4.22g/cm 3。正极活性材料层的压实密度在上述范围内，有利于提高电池的比容量和能量密度，并提高电池的倍率性能及循环性能。
正极活性材料的压实密度可以用本领域公知的仪器及方法进行测定，例如用电子压力试验机方便地测定，如UTM7305型电子压力试验机。
进一步地，正极活性物质层中还包括粘结剂和导电剂。
所述粘结剂可以是丁苯橡胶(SBR)、水性丙烯酸树脂、羧甲基纤维素(CMC)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)及聚乙烯醇(PVA)中的一种或多种。
所述导电剂可以是超导碳、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。
可以按照本领域常规方法制备上述正极极片。通常将正极活性材料及可选的导电剂和粘结剂分散于溶剂(例如N-甲基吡咯烷酮，简称为NMP)中，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、冷压等工序后，得到正极极片。
由于采用了本申请第一方面的正极活性材料，因此本申请的正极极片具有较高的综合电化学性能及安全性能。
电化学装置
本申请的第三方面提供一种电化学装置，包括本申请第一方面的正极活性材料层。
所述正极活性材料层的压实密度为3.0g/cm 3～4.4g/cm 3，优选地，所述正极活性材料层的压实密度为4.12g/cm 3～4.22g/cm 3。正极活性材料层的压实密度在上述范围内，有利于提高电池的比容量和能量密度，并提高电池的倍率性能及循环性能。
正极活性材料的压实密度可以用本领域公知的仪器及方法进行测定，例如用电子压力试验机方便地测定，如UTM7305型电子压力试验机。
进一步地，所述电化学装置在满放状态容量不低于180mAh/g时，利用X射线衍射法分析，所述正极活性材料的XRD图谱中的主峰在18°～19°范围内，所述主峰的半峰宽在0°～0.5°之间。正极活性材料在经过循环后，主峰位置与半高宽不变，表明正极活性材料整体的层状结构未发生明显变化，正极活性材料的结构可逆性好。
在本申请的一些实施例中，电化学装置还包括负极极片、隔离膜和电解液。
负极极片可以是包括负极集流体及设置于负极集流体上的负极活性物质层。例如负极集流体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。负极集流体可以采用金属箔材、涂炭金属箔材或多孔金属板等材料，优选采用铜箔。
负极活性物质层通常包括负极活性材料以及可选的导电剂、粘结剂和增稠剂，负
极活性材料可以是天然石墨、人造石墨、中间相微碳球(MCMB)、硬碳及软碳中的一种或多种，导电剂可以是超导碳、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，粘结剂可以是丁苯橡胶(SBR)、水性丙烯酸树脂及羧甲基纤维素(CMC)中的一种或多种，增稠剂可以是羧甲基纤维素(CMC)。但本申请并不限定于这些材料，本申请还可以使用其它可被用作锂离子电池负极活性物质、导电剂、粘结剂、增稠剂的材料。
可以按照本领域常规方法制备上述负极极片。通常将负极活性材料及可选的导电剂、粘结剂和增稠剂分散于溶剂中，溶剂可以是去离子水，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、冷压等工序后，得到负极极片。
对上述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化学稳定性的多孔结构隔离膜，例如可以是玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的一种或多种的单层或多层薄膜。
对上述电解液包括锂盐以及有机溶剂，其中锂盐和有机溶剂的具体种类及组成均不受到具体的限制，可根据实际需求进行选择。优选地，锂盐可包括六氟磷酸锂、四氟硼酸锂、高氯酸锂中的一种或几种，有机溶剂可包括环状碳酸酯、链状碳酸酯、羧酸酯中的一种或几种。所述电解液中还可含有功能添加剂，例如碳酸亚乙烯酯、硫酸乙烯酯、丙磺酸内酯、氟代碳酸乙烯酯等。
由于采用了本申请第一方面的正极活性材料，本申请的电化学装置具有较高的比容量、高电压平台，并兼具较高的循环性能及安全，在高电压下界面稳定，结构可逆性好。
第四方面，本申请还提供一种正极活性材料的制备方法，所述方法包括以下步骤S10～S30：
S10、将钴盐及含有M元素的盐采用液相沉淀法制得共沉淀物，并将共沉淀物进行烧结，得到M元素掺杂的(Co 1-yM y) 3O 4粉体，其中，0≤y<0.15；
S20、按照化学计量比将(Co 1-yM y) 3O 4、Na 2CO 3和Li aR(0<a<3)的混合粉体在氧气气氛下烧结，得到具有P6 3mc晶体结构的Na mCo 1-yM yO 2-δR δ，其中，0.6<m<1；
S30、将Na mCo 1-yM yO 2-δR δ与含锂熔盐按照Na元素与Li元素的摩尔比为0.01～0.2的比例混合，并在空气气氛中进行离子交换反应，将反应产物洗涤烘干得到正极活性材料Li xNa zCo 1-yM yO 2-δR δ，其中，M包括Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr、Y或Zr 中的至少一种，R包括F、Cl中的至少一种，0.6<x<0.95，0≤y<0.15，0≤z<0.03，0<δ≤0.01。
在本申请中，采用液相共沉淀加烧结法制备M元素掺杂的(Co 1-yM y) 3O 4前驱体粉体，其中，0≤y<0.15，再将前驱体粉体采用固相烧结法与、碳酸钠、锂盐进行烧结，得到具有P6 3mc晶体结构的Na mCo 1-yM yO 2-δR δ，最后采用离子交换法合成P6 3mc晶体结构的正极活性材料Li xNa zCo 1-yM yO 2-δR δ，制备过程安全可控，使得制备得到的正极活性材料具有本申请所述的特定化学组成和结构，能够大幅度提高正极活性材料的电化学性能，进而使得电化学装置具有较高的比容量、高电压平台，并兼具较高的循环性能及安全，在高电压下界面稳定，结构可逆性好。
具体地，步骤S10、将钴盐及含有M元素的盐采用液相沉淀法制得共沉淀物的具体步骤包括：
S11、将钴盐及含有M元素的盐按照Co元素与M元素的摩尔比为(1-y)：y的比例混合加入溶剂中，得到混合溶液；
S12、将沉淀剂和络合剂加入混合溶液，得到反应溶液，并调节反应溶液的pH值至预设范围，使反应溶液在预定的温度和搅拌速率下进行共沉淀反应，得到共沉淀物。
在一些优选的实施例中，步骤S10中，钴盐为硝酸钴、氯化钴、硫酸钴及醋酸钴中的至少一种；含有M元素的盐为含有M元素的硝酸盐、氯化盐、硫酸盐、醋酸盐中的至少一种。
溶剂为去离子水、甲醇、乙醇、丙酮、异丙醇及正己醇中的至少一种。
在一些优选的实施例中，步骤S12中，沉淀剂为氢氧化钠、氢氧化钾、碳酸氢钠、碳酸氢钾、碳酸钠及碳酸钾中的至少一种。需要说明的是，在将沉淀剂加入混合溶液中前，可以将沉淀剂预配制得到沉淀剂溶液，用于配制沉淀剂溶液的溶剂可以为去离子水、甲醇、乙醇、丙酮、异丙醇及正己醇中的至少一种。
进一步地，沉淀剂溶液中沉淀剂的浓度优选为0.1mol/L～3mol/L，更优选为1mol/L～3mol/L。
在一些优选的实施例中，步骤S12中，络合剂为氨水、碳酸铵、碳酸氢铵、尿素、六亚甲基四胺、乙二胺四乙酸、柠檬酸及抗坏血酸中的至少一种。需要说明的是，在将络合剂加入混合溶液中前，可以将络合剂预配制得到络合剂溶液，用于配制络合剂溶液的溶剂可以为去离子水、甲醇、乙醇、丙酮、异丙醇及正己醇中的至少一种。
进一步地，络合剂溶液中络合剂的浓度优选为0.1mol/L～3mol/L，更优选为0.5mol/L～1.5mol/L。
反应溶液的pH值会影响各金属离子的沉淀速率，从而对过渡金属源的晶体成核及生长速率产生直接影响，进而影响过渡金属源的化学组成及结构，最终影响正极活性材料的化学组成及结构。为了实现本申请的正极活性材料，在步骤S12中，反应溶液的pH值控制5～9，例如可以是5、6、7、8、9，当然也可以是上述范围内的其他数据。在具体实施方式中，可以通过调节沉淀剂和/或络合剂的种类及含量来调节反应溶液的pH值。
另外，反应溶液的温度会直接影响化学反应的速率和反应产率，反应时间会影响反应产物的生长过程，进而影响反应产物的化学组成及结构。作为优选地，步骤S12中，反应温度为25℃～100℃，反应时间为2小时～30小时。
可选地，步骤10还可以包括：
采用适量的洗涤剂对共沉淀物进行洗涤并烘干。需要说明的是，本申请对洗涤所用的洗涤剂及洗涤的次数没有特别地限制，可以根据实际需求进行选择，只要将共沉淀物表面的剩余离子除去即可。例如，洗涤剂可以为去离子水。
在步骤S10中，所述共沉淀物的烧结温度及时间会影响反应产物的比表面积、粒径、形貌和晶体结构。作为优选地，步骤S13中，所述共沉淀物的烧结温度为400℃～800℃， 更优选地为450℃～600℃；所述共沉淀物的烧结时间为5h～20h，优选为12h～15h。
在步骤S10中，烧结处理可以在空气或氧气气氛中进行。
在一些优选的实施例中，步骤S20中，(Co 1-yM y) 3O 4、Na 2CO 3和Li aR按照Na、Co、M、R的摩尔比为0.7：(1-y)：y：δ，Na与Co的摩尔比值为(0.5～0.8)：1，优选地，Na与Co的摩尔比值为0.74：1。
在步骤S20中，烧结处理的温度及时间会影响反应产物的比表面积、粒径、形貌和晶体结构。作为优选地，步骤S20中，烧结处理的温度为700℃～1000℃，更优选地为800℃～900℃；烧结处理的时间优选为36h～56h，更优选地为40h～50h。烧结处理可以在空气或氧气气氛中进行。
在一些优选的实施例中，步骤S30中，含锂熔盐包括硝酸锂、氯化锂、氢氧化锂中的至少一种。
在步骤S30中，Na mCo 1-yM yO 2-δR δ与含锂熔盐按照Na元素与Li元素的摩尔比为(0.01～0.2)：1的比例混合，优选地，Na元素与Li元素的摩尔比值为0.03:1。
在步骤S30中，烧结处理的温度及时间会影响反应产物的比表面积、粒径、形貌和晶体结构。作为优选地，步骤S30中，烧结处理的温度为200℃～400℃，更优选地为250℃～350℃；烧结处理的时间优选为2h～8h，更优选地为4h～6h。烧结处理可以在空气或氧气气氛中进行。
可选地，步骤S30还可以包括：
采用适量的洗涤剂对烧结产物进行洗涤并烘干。需要说明的是，本申请对洗涤所用的洗涤剂及洗涤的次数没有特别地限制，可以根据实际需求进行选择，只要将烧结产物表面的熔盐除去即可。例如，洗涤剂可以为去离子水。
需要说明的是，最终产物正极活性材料Li xNa zCo 1-yM yO 2-δR δ具有P6 3mc晶体结构，当 然，最终产物也会存在部分R-3m晶体结构的正极活性材料。
本申请的正极活性材料制备过程中，通过对反应物的种类及含量、pH值、沉淀剂的种类及浓度、络合剂的种类及浓度、烧结温度及时间等进行综合地调控，使正极活性材料具有本申请所述的特定化学组成和结构，能够大幅度提高正极活性材料的电化学性能，以及提高锂离子电池的比容量、循环性能及安全性能。
下面结合具体实施例，进一步阐述本申请。应理解，这些实施例仅用于说明本申请而不用于限制本申请的范围。
正极活性材料的制备
S10、将氯化钴及含有M元素的硫酸盐按照Co元素与M元素的摩尔比为(1-y)：y的比例混合加入去离子水中，得到混合溶液；将沉淀剂和络合剂加入混合溶液，得到反应溶液，并调节反应溶液的pH值至6，使反应溶液在搅拌下进行共沉淀反应，得到共沉淀物；将共沉淀物置于600℃～700℃下进行烧结，得到M元素掺杂的(Co 1-yM y) 3O 4粉体，其中，0≤y<0.15；
S20、将(Co 1-yM y) 3O 4粉体、Na 2CO 3粉末和Li aR粉末按照Na、Co、M、R的摩尔比为0.7：(1-y)：y：δ进行混合得到混合粉体，将混合粉体在氧气气氛下置于800℃～900℃进行烧结48h，得到具有P6 3mc晶体结构的Na mCo 1-yM yO 2-δR δ，其中，0.6<m<1；
S30、将Na mCo 1-yM yO 2-δR δ与氯化锂按照Na元素与Li元素的摩尔比为0.01～0.2的比例混合，并在空气气氛中加热至250℃～350℃，进行离子交换反应6h，将反应产物洗涤烘干得到正极活性材料Li xNa zCo 1-yM yO 2-δR δ，其中，M包括Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr、Y或Zr中的至少一种，R包括F、Cl中的至少一种，0.6<x<0.95，0≤y<0.15，0≤z<0.03，0<δ≤0.01。
实施例1-10和对比例1-6的正极活性材料均按照上述的反应条件下进行制备，制得的 正极活性材料如表1所示。
表1
Figure PCTCN2021128709-appb-000002
锂离子电池的制备
1)正极极片的制备
将上述制备的正极活性材料、导电炭黑(Super P)、粘结剂聚偏二氟乙烯(PVDF)按95：2：3重量比在适量的N-甲基吡咯烷酮(NMP)中充分搅拌混合，使其形成均匀的正极浆料；将该正极浆料涂布在12μm的铝箔上，干燥，冷压，再经过裁片、焊接极耳，得到正极。
2)负极极片的制备
将人造石墨、丁苯橡胶和羧甲基纤维素钠按照96:2:2的重量比与去离子水混合，搅拌均匀，得到负极浆料。将该负极浆料涂布在12μm的铜箔上。干燥，冷压，再经过裁片、焊接极耳，得到负极。
3)隔离膜采用聚乙烯(PE)多孔聚合物薄膜。
4)电解液的制备
在干燥氩气环境下，将碳酸亚乙酯(EC)、碳酸亚丙酯(PC)和碳酸二乙酯(DEC)按照1:1:1的重量比混合，加入LiPF 6混合均匀，形成电解液，其中LiPF 6的浓度为1.15mol/L。5)将上述正极极片、隔离膜、负极极片按次序叠放、卷绕、置于外包装箔中，留下注液口。从注液口灌注电解液，封装，再经过化成、容量等工序制得锂离子电池。
性能测试：
(1)容量发挥及循环性能测试
在45℃、常压(0.1MPa)下，将实施例和对比例制备得到的锂离子电池以0.1C恒流充电至电压为4.7V，然后4.7V恒压充电至电流为0.05C，此时的充电容量记为锂离子电池的首圈充电容量，之后静置5min，再以0.1C恒流放电至电压为3.0V，静置5min，此为一个循环充放电过程，此次的放电容量记为锂离子电池首圈放电容量，也即为锂离子电池的初始容量。将锂离子电池按照上述方法进行50圈循环充放电测试，检测得到第50圈循环的放电容量。锂离子电池循环50圈后的容量保持率(％)＝第50圈循环的放电容量/首圈放电容量×100％。
表2为实施例1-10和对比例1-6的正极活性材料利用X射线光电子能谱法分析，上述正极活性材料的XPS图谱中的O1s主峰峰位的所处位置，并且上述正极活性材料制成的锂离子电池的性能参数如表2所示。
表2
Figure PCTCN2021128709-appb-000003
Figure PCTCN2021128709-appb-000004
对比分析表2中的数据可见，由于对比例1～4的正极活性材料仅掺杂了阳离子，例如Al、Mg，在高电压(>4.6V)下，对比例1～4与实施例3、6、7、8的首圈放电容量相差不多，但是单纯的阳离子掺杂，虽然同样均为P6 3mc晶体结构，由于其O1s主峰峰位较低，即氧结构不够稳定，不能缓解正极活性材料高压下的表层相变，随着相变不断向内蔓延，造成锂电池容量快速衰减。相比之下，实施例3、6、7、8，其掺杂了少量的R元素，所得的正极活性材料具有较高的O1s主峰峰位，即能够降低氧的活性，从而大幅提高正极活性材料在高温高压下的晶体稳定性。然而，通过对比例5-6可以看出，掺杂R元素的量不宜过多，否则其45℃首圈放电容量和循环50圈容量保持率均大幅降低，这是由于R元素在正极活性材料表面超过一定浓度时，会大量结合活性锂，形成致密LiF层，恶化界面阻抗，进而造成容量损失。
进一步地，根据上述制备方法制得实施例11、实施例12及对比例7，测得所述正极活性材料中的M元素的电负性与Co元素的电负性的比值如表3所示，并且上述正极活性材料制成的锂离子电池的性能参数如表3所示。
表3
Figure PCTCN2021128709-appb-000005
Figure PCTCN2021128709-appb-000006
对比分析表3中的数据可见，实施例3中的阳离子M为Al 3+，实施例11中的阳离子M为Mg 2+，实施例12中的阳离子M为Ti 3+，阳离子M元素与Co 3+的电负性比例在1～2之间，而对比例7中的阳离子M为Sr 2+，Sr 2+与Co 3+的电负性比值仅为0.57，根据对比例21制备得到的电池的首圈放电容量及循环50圈容量保持率均明显下降，并且循环稳定性急剧恶化。这是由于具有比Co更高电负性的M元素阳离子形成的M-O键能够进一步拉低氧的能带结构，减少Co与氧的能带重叠，进而减小氧的活性，稳定住氧，从而使得正极活性材料在高温高压下具有更高的稳定性。
进一步地，根据上述制备方法制得实施例13～16，其中实施例3、13～16制得的正极活性材料的组分相同，为Li 0.73Na 0.012Co 0.988Al 0.012O 1.995F 0.005，利用XPS进行分析，测试颗粒表面的R元素浓度与颗粒内部的R元素浓度，颗粒表面到50nm的深度区域内的R元素浓度与其他区域内的R元素浓度的比值及其他区域内任意位置的R元素浓度差。并且上述正极活性材料制成的锂离子电池的性能参数如表4所示。
表4
Figure PCTCN2021128709-appb-000007
Figure PCTCN2021128709-appb-000008
对比分析表4中的数据可见，正极活性材料的颗粒表面到50nm的深度区域内的R元素浓度与其他区域内的R元素浓度的比值在(1～10):1，以及其他区域内任意位置的R元素浓度差低于5％范围内时，锂电池的首圈放电容量及循环50圈容量保持率均能维持在较高的水平，当正极活性材料的颗粒表面到50nm的深度区域内的R元素浓度与其他区域内的R元素浓度的比值大于10:1，或其他区域内任意位置的R元素浓度差高于5％时，锂电池的首圈放电容量及循环50圈容量保持率均有所下降。这是由于正极活性材料表面R元素掺杂浓度远大于内部R元素掺杂浓度，表面材料表面CEI沉积或Co-R在表面沉积，造成阻抗恶化，所述正极活性材料内的R元素浓度不均匀，容易引起局部过充或者过嵌现象，影响锂电池的首圈放电容量及循环容量保持率。
进一步地，根据上述制备方法制得实施例17～19，其中实施例3及实施例17～19制得的正极活性材料的组分相同，为Li 0.73Na 0.012Co 0.988Al 0.012O 1.995F 0.005，利用电子显微镜进行分析，查看颗粒表面的孔及内部的缝隙；并且上述正极活性材料制成的锂离子电池的性能参数如表5所示。
表5
Figure PCTCN2021128709-appb-000009
Figure PCTCN2021128709-appb-000010
根据表5可知，实施例3制得的正极活性材料包括孔及缝隙，根据实施例3制备得到的电池的首圈放电容量可以达到235mAh/g，循环50圈容量保持率可以达到91％；而根据实施例17～19制备得到的电池的首圈放电容量及循环50圈容量保持率均有所下降，这是由于颗粒的孔及缝隙结构，有利于释放循环过程中活性材料表面和/或内部产生的应力应变，稳定住正极活性材料和电解液之间的界面，从而提高循环容量保持率，提高高电压下的循环稳定性。
进一步地，根据上述制备方法制得实施例20～22，其中实施例20～22制得的正极活性材料的组分相同，为Li 0.73Na 0.012Co 0.988Al 0.012O 1.995F 0.005，测得正极活性材料的比表面积如表6所示，并且上述正极活性材料制成的锂离子电池的性能参数如表6所示。
表6
Figure PCTCN2021128709-appb-000011
根据表6可知，实施例3、20及21的比表面积在0.72m 2/g至2.5m 2/g范围内，比表面积不会过大，可以提高正极活性材料对空气、水及二氧化碳的稳定性，降低正极活性材料表面电解液的反应活性，从而提高循环容量保持率，提高高电压下的循环稳定性；实施例22 的比表面积达到3.2m 2/g，比表面积过大，正极活性材料表面电解液的反应活性增大，材料表面副反应增多，循环容量保持率以及高电压下的循环稳定性均有所下降。
进一步地，根据上述制备方法制得实施例23～24，其中实施例3及实施例23～24制得的正极活性材料的组分相同，为Li 0.73Na 0.012Co 0.988Al 0.012O 1.995F 0.005，上述正极活性材料制成的锂离子电池的性能参数如表7所示，电池在满放状态容量不低于180mAh/g时，利用X射线衍射法分析，所述正极活性材料的XRD图谱中的主峰范围及主峰的半峰宽如表7所示。
表7
Figure PCTCN2021128709-appb-000012
根据表7可知，实施例3、23及24的正极活性材料的XDR图谱中的主峰在18°～19°范围内，所述主峰的半峰宽在0°～0.5°之间，可见，正极活性材料的主峰的半峰宽在0°～0.5°之间时，正极活性材料的晶体结构更加稳定，可以提高正极活性材料对空气、水及二氧化碳的稳定性，降低正极活性材料表面电解液的反应活性，从而提高循环容量保持率，提高高电压下的循环稳定性。
本申请虽然以较佳实施例公开如上，但并不是用来限定权利要求，任何本领域技术人员在不脱离本申请构思的前提下，都可以做出若干可能的变动和修改，因此本申请的保护范围应当以本申请权利要求所界定的范围为准。

Claims (11)

  1. 一种正极活性材料，其特征在于，
    所述正极活性材料具有P6 3mc晶体结构，所述正极活性材料为包含Co和R元素以及可选地包含M元素的锂过渡金属复合氧化物，其中，M元素包括Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr、Y或Zr中的至少一种，R元素包括F、Cl中的至少一种，所述R元素的摩尔含量为n R，所述Co和M元素的摩尔含量之和为n Co+M，所述n R与所述n Co+M的比值为0<δ≤0.01。
  2. 根据权利要求1所述的正极活性材料，其特征在于，其满足以下条件的至少一者：
    a.所述正极活性材料进一步包含Li元素，所述Li元素的摩尔含量为n Li，所述n Li与所述n Co+M的比值为0.6<x<0.95；
    b.所述正极活性材料进一步包含Na元素，所述Na元素的摩尔含量为n Na，所述n Na与所述n Co+M的比值为0<z<0.03；
    c.所述M元素的摩尔含量为n M，所述n M与所述n Co+M的比值为0≤y<0.15，所述Co元素的摩尔含量为n Co，所述n Co与所述n Co+M的比值为1-y。
  3. 根据权利要求1所述的正极活性材料，其特征在于，利用X射线光电子能谱法分析，所述正极活性材料的XPS图谱中在530eV～535eV范围内含有O1s峰。
  4. 根据权利要求1所述的正极活性材料，其特征在于，所述M元素阳离子的电负性与Co元素阳离子的电负性的比值为1～2，优选为1.05～1.64。
  5. 根据权利要求1所述的正极活性材料，其特征在于，
    所述正极活性材料表面的R元素浓度高于所述正极活性材料内部的R元素浓度，其中，R元素浓度为所述n R与所述n Co+M的比值。
  6. 根据权利要求5所述的正极活性材料，其特征在于，所述正极活性材料表面到50nm 的深度区域内的R元素浓度与所述正极活性材料其他区域内的R元素浓度的比值为(1～10)：1。
  7. 根据权利要求6所述的正极活性材料，其特征在于，所述正极活性材料其他区域内的任意位置的R元素浓度差低于5％。
  8. 根据权利要求1所述的正极活性材料，其特征在于，满足以下条件的至少一者：
    d.所述正极活性材料包括孔和/或缝隙；
    e.所述正极活性材料的平均粒径Dv50为10μm至25μm；
    f.所述正极活性材料的比表面积为0.1m 2/g至3m 2/g，优选为0.72m 2/g至2.5m 2/g。
  9. 根据权利要求2所述的正极活性材料，其特征在于，所述正极活性材料的化学通式为Li xNa zCo 1-yM yO 2-δR δ，其中，0.6<x<0.95，0≤y<0.15，0≤z<0.03，0<δ≤0.01。
  10. 一种电化学装置，包括正极活性材料层，其特征在于，所述正极活性材料层包括权利要求1-9中任一项所述的正极活性材料。
  11. 根据权利要求10所述的电化学装置，其特征在于，所述电化学装置在满放状态容量不低于180mAh/g时，利用X射线衍射法分析，所述正极活性材料的XRD图谱中的主峰在18°～19°范围内，所述主峰的半峰宽在0°～0.5°之间。
PCT/CN2021/128709 2020-11-10 2021-11-04 正极活性材料及电化学装置 WO2022100507A1 (zh)

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