WO2022105421A1 - 正极活性材料以及制备方法，正极，锂离子二次电池 - Google Patents

正极活性材料以及制备方法，正极，锂离子二次电池 Download PDF

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WO2022105421A1
WO2022105421A1 PCT/CN2021/120159 CN2021120159W WO2022105421A1 WO 2022105421 A1 WO2022105421 A1 WO 2022105421A1 CN 2021120159 W CN2021120159 W CN 2021120159W WO 2022105421 A1 WO2022105421 A1 WO 2022105421A1
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positive electrode
active material
phase
electrode active
lithium nickel
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PCT/CN2021/120159
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English (en)
French (fr)
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武怿达
黄学杰
詹元杰
马晓威
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松山湖材料实验室
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Priority to EP21893572.4A priority Critical patent/EP4228027A4/en
Publication of WO2022105421A1 publication Critical patent/WO2022105421A1/zh
Priority to US18/318,375 priority patent/US20230317942A1/en

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    • 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
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    • 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
    • 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
    • C01G53/54—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese of the type [Mn2O4]-, e.g. Li(NixMn2-x)O4, Li(MyNixMn2-x-y)O4
    • H—ELECTRICITY
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    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—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
    • H01M4/36—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
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/80—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
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/04—Particle morphology depicted by an image obtained by TEM, STEM, STM or AFM
    • 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
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of positive electrode materials, in particular to positive electrode active materials and preparation methods, positive electrodes, and lithium ion secondary batteries.
  • lithium-ion secondary batteries Compared with other rechargeable battery systems, lithium-ion secondary batteries have the advantages of high operating voltage, light weight, small size, no memory effect, low self-discharge rate, long cycle life, and high energy density.
  • Mobile terminal products such as mobile phones, notebook computers, and tablet computers.
  • the surface of the cathode material loses oxygen and dissolves on the surface of the material, which eventually leads to active substances. reduce. Surface modification has become the focus of attention.
  • the surface modification method commonly used in this field is to coat the surface of the positive electrode material.
  • the surface structure can be well fixed, the stability of the positive electrode material can be maintained, and the corrosion of the electrolyte can be suppressed.
  • the surface coating can block the direct contact between the cathode material and the electrolyte, reduce the decomposition of the electrode material under high voltage, and is beneficial to the stability of the entire high-voltage interface.
  • the coating material due to the difference in the surface structure of the coating material and the material to be coated, it is difficult for the coating material to uniformly and stably coat the surface of the positive electrode material.
  • the coating material even if the material to be coated can be evenly coated on the surface of the positive electrode material, under high voltage, since the coating on the surface is gradually consumed, the positive electrode material will eventually be exposed to the electrolyte, which will still cause rapid performance degradation.
  • a positive electrode active material includes a modified material of lithium nickel manganate and a coating layer on the surface of the modified material of lithium nickel manganate.
  • the coating layer is composed of inorganic compounds.
  • the inorganic compound is selected from any one or more of oxides, fluorides, phosphides, and borides.
  • the lithium nickel manganate modified material is a primary particle with a core-shell structure including a spinel phase and a rock salt-like phase.
  • the spinel phase is an inner core, and the rock salt-like phase is distributed on the surface of the spinel phase to form an outer shell.
  • the spinel phase is lithium nickel manganate with spinel structure.
  • the rock-salt-like phase is induced by the spinel-structured lithium nickel manganate.
  • the rock-salt phase contains Mg, Zn, Ni, Mn, Fe, Co, Ti, Cr, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Ta, Sr, Al, Nb, B , Si, F and S at least one placeholder element.
  • the placeholder is located at the 16c or 8a position of the spinel structure.
  • the rock-salt-like phase is also doped with phosphorus element.
  • the phosphorus element is distributed in a concentration gradient from the outer surface of the rock-salt-like phase to the interior, forming a phosphorus gradient doping layer.
  • the inorganic compound includes Li, Mg, Zn, Ni, Mn, Fe, Co, Ti, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Ta, Al, Nb , any one or more of oxides, fluorides, phosphides and borides of any one of B, Si, F, S, P and Sr.
  • the chemical formula of the spinel-structured lithium nickel manganate is Li 1+x Ni 0.5-y Mn 1.5-z O u , wherein 0.2 ⁇ x ⁇ 0.2, -0.2 ⁇ y ⁇ 0.2 , -0.2 ⁇ z ⁇ 0.2, 3.8 ⁇ u ⁇ 4.2.
  • the chemical formula of the spinel-structured lithium nickel manganate is Li 1+x Ni 0.5-y Mn 1.5-z M s O u , wherein M is Mg, Zn, Ni, Mn, At least one of Fe, Co, Ti, Cr, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Ta, Sr, Al, Nb, B, Si, F and S, -0.2 ⁇ x ⁇ 0.2, -0.2 ⁇ y ⁇ 0.2, -0.2 ⁇ z ⁇ 0.2, 0 ⁇ s ⁇ 0.2 and 3.8 ⁇ u ⁇ 4.2.
  • the thickness of the coating layer is 2 nm ⁇ 20 nm.
  • the spinel phase has a size of 0.1 ⁇ m to 30 ⁇ m.
  • the rock-salt-like phase has a thickness of 0.5 nm to 50 nm.
  • the concentration of phosphorus element gradually decreases from the outer surface to the inner part.
  • the thickness of the phosphorus gradient doping layer is 0.5 nm ⁇ 40 nm.
  • a method for preparing a positive electrode active material comprising the following steps:
  • the coating mixture is sintered in air, oxygen or inert gas at 150°C to 550°C for 0.5 hour to 20 hours.
  • the step of providing the lithium nickel manganate modified material includes:
  • the doping mixture is sintered at 600°C to 1200°C for 0.5 hours to 20 hours.
  • the inorganic compound precursor is selected from any one or more of oxides, organic compounds, fluorides, phosphides, and borides.
  • the sintering process of the doping mixture is: heating to 600°C-1200°C at a heating rate of 0.5°C/min-10°C/min, then sintering for 0.5-20 hours, and then heating at 0.5°C/min.
  • the cooling rate of min ⁇ 10°C/min was lowered to room temperature.
  • a positive electrode of a lithium ion secondary battery includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, the positive electrode active material layer including the positive electrode active material.
  • a lithium-ion secondary battery comprising:
  • a negative electrode comprising a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector;
  • the lithium nickel manganate modified material is obtained by first inducing and doping the phosphorus element gradient on the surface of the spinel-structured lithium nickel manganate, and on the basis of which, the positive electrode active material is obtained by coating with an inorganic compound.
  • the surface of the lithium nickel manganate modified material is a rock-salt-like phase, and the surface layer of the rock-salt-like phase is conducive to the gradient doping of phosphorus elements on the surface of the lithium nickel manganate modified material.
  • the surface doping of phosphorus element can significantly improve the electrochemical performance of the positive electrode active material, including the first discharge efficiency, the average discharge efficiency and the charge-discharge cycle stability.
  • the inorganic compound coating layer can increase the interface stability, but the inorganic compound is non-conductive, which will lead to a decrease in the electronic conductivity of the surface of the positive active material.
  • Surface-graded phosphorus doping can not only increase the surface structure stability of LiMnO alone, but also improve the electronic conductance of the cathode active material surface.
  • the gradient doping of phosphorus element can change the surface energy of the surface of the positive active material.
  • a large amount of rock-salt-like phase structure is introduced on the surface of lithium nickel manganate.
  • This structure and inorganic compounds, especially the crystallinity of oxides are more matched, which is conducive to the close combination of the inorganic compound and the surface of the lithium nickel manganate modified material, making the coating more uniform and firmer, and the modification effect is better.
  • FIG. 1 is a scanning transmission electron microscope (STEM) image of the phosphorus-doped lithium nickel manganate modified material prepared in Example 1 of the present application.
  • FIG. 2A and FIG. 2B are STEM line scan images of phosphorus element on the surface of the phosphorus-doped lithium nickel manganate modified material prepared in Example 1 of the present application.
  • Example 3 is a transmission electron microscope (TEM) image of the coated lithium nickel manganate positive electrode active material prepared in Example 1 of the present application.
  • 4A and 4B are STEM images of the phosphorus-doped lithium nickel manganate modified material prepared in Example 2 of the present application.
  • FIG. 5 shows the change of the relative content of phosphorus elements on the surface obtained by X-ray photoelectron spectroscopy (XPS) characterization of the phosphorus-doped lithium nickel manganate modified material prepared in Example 2 of the present application at different etching depths.
  • XPS X-ray photoelectron spectroscopy
  • FIG. 6 is a TEM image of the coated lithium nickel manganate positive electrode active material prepared in Example 2 of the present application.
  • An embodiment of the present application provides a positive electrode active material, including a lithium nickel manganate modified material and a coating layer on the surface of the lithium nickel manganate modified material.
  • the coating layer is composed of inorganic compounds.
  • the lithium nickel manganate modified material is a primary particle with a core-shell structure including a spinel phase and a rock salt-like phase.
  • the spinel phase is an inner core, and the rock salt-like phase is distributed on the surface of the spinel phase to form an outer shell.
  • the spinel phase is lithium nickel manganate having a spinel structure.
  • the rock-salt-like phase is induced by the spinel-structured lithium nickel manganate.
  • the rock-salt-like phase includes nickel, manganese, lithium, and oxygen elements, and further includes a placeholder element.
  • the placeholder elements are selected from Mg, Zn, Ni, Mn, Fe, Co, Ti, Cr, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Ta, Sr, Al, Nb, B At least one of , Si, F and S, and the placeholder is located at the 16c or 8a position of the spinel structure.
  • the rock-salt-like phase is also doped with a phosphorus element, and the phosphorus element is distributed in a gradient from the outer surface of the rock-salt-like phase to the interior.
  • the lithium nickel manganate modified material is obtained by first inducing and doping the phosphorus element gradient on the surface of the spinel-structured lithium nickel manganate, and on the basis of which, the positive electrode active material is obtained by coating with an inorganic compound.
  • the surface of the lithium nickel manganate modified material is a rock-salt-like phase, and the surface layer of the rock-salt-like phase is conducive to the gradient doping of phosphorus elements on the surface of the lithium nickel manganate modified material.
  • the surface doping of phosphorus element can significantly improve the electrochemical performance of the positive electrode active material, including the first discharge efficiency, the average discharge efficiency and the charge-discharge cycle stability.
  • Inorganic compound coating can increase the interfacial stability, but inorganic compounds are non-conductive, which will lead to a decrease in the electronic conductivity of the surface of the positive active material.
  • Surface-graded phosphorus doping can not only increase the surface structure stability of LiMnO alone, but also improve the electronic conductance of the cathode active material surface.
  • the gradient doping of phosphorus element can change the surface energy of the cathode active material surface.
  • a rock-salt-like structure is introduced on the surface of lithium nickel manganate while phosphorus doping, which matches the lattice constant of inorganic compounds, especially oxides, which is beneficial to the surface of inorganic compounds and lithium nickel manganate modified materials. The tight combination makes the coating more uniform and firmer, and the modification effect is better.
  • the generally defined core-shell structure is an ordered assembly formed by one material wrapping another material through chemical bonds or other forces.
  • the primary particle is a core-like shell structure, and the defined core-like shell structure "core” and "shell” are actually integrated.
  • the "shell” is a rock-salt phase structure formed by the surface lattice reconstruction of the spinel structure.
  • the structure of the lithium nickel manganate modified material of the present application includes two phases, resulting in the crystal structure of the surface layer being different from the crystal structure inside the material.
  • the inside of the material thus formed is referred to as a "core”
  • the surface layer is referred to as a "shell”
  • a material with such a structure is defined as a material of a core-shell-like structure.
  • the primary particle refers to the smallest unit constituting the lithium nickel manganate modified material, and specifically refers to the smallest unit that can be determined based on the geometric configuration of the appearance. Aggregates of primary particles are secondary particles.
  • the primary particles have a core-shell structure. In the core-shell structure, the inner core of the spinel phase and the outer shell of the rock salt-like phase are integrated, and the spinel phase and the rock salt-like phase cannot be separated from each other through oxygen bonding.
  • the chemical formula of the spinel-structured lithium nickel manganate is Li 1+x Ni 0.5-y Mn 1.5-z O u , wherein 0.2 ⁇ x ⁇ 0.2, -0.2 ⁇ y ⁇ 0.2 , -0.2 ⁇ z ⁇ 0.2, 3.8 ⁇ u ⁇ 4.2.
  • the values of x, y, and z may vary depending on the ratio between the elements, but are all set within a range that allows the compound represented by the formula to exhibit a spinel structure.
  • the bulk phase of the spinel-structured lithium nickel manganate is uniformly doped with elements favorable for phosphorus doping
  • the chemical formula of the spinel-structured lithium nickel manganate may be Li 1+ x Ni 0.5-y Mn 1.5-z M s O u , wherein M is Mg, Zn, Ni, Mn, Fe, Co, Ti, Cr, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, At least one of Ca, Ta, Sr, Al, Nb, B, Si, F and S, -0.2 ⁇ x ⁇ 0.2, -0.2 ⁇ y ⁇ 0.2, -0.2 ⁇ z ⁇ 0.2, 0 ⁇ s ⁇ 0.2 and 3.8 ⁇ u ⁇ 4.2.
  • the values of x, y, z, s, and u may vary depending on the ratio between the elements, but are all set within a range such that the compound represented by the chemical formula can exhibit a spinel structure.
  • the place occupant element is Al
  • the Al element is more conducive to improving the structural stability of the positive electrode active material and reducing the potential barrier of phosphorus element doping into the spinel structure.
  • the size of the spinel phase core may be any value between 0.1 ⁇ m and 30 ⁇ m, for example, may be 0.5 ⁇ m, 1 ⁇ m, 2 ⁇ m, 3 ⁇ m, 4 ⁇ m, 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m , 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 15 ⁇ m, 16 ⁇ m, 17 ⁇ m, 18 ⁇ m, 19 ⁇ m, 20 ⁇ m, 21 ⁇ m, 22 ⁇ m, 23 ⁇ m, 24 ⁇ m, 25 ⁇ m, 26 ⁇ m, 27 ⁇ m, 28 ⁇ m or 29 ⁇ m.
  • the thickness of the rock-salt-like shell may be any value between 0.5 nm and 50 nm, for example, may be 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, 30nm, 31nm, 32nm, 33nm, 34nm, 35nm, 36nm, 37nm, 38nm, 39nm, 40nm, 41nm, 42nm, 43nm, 44nm, 45nm, 46nm, 47nm, 48nm, 49nm or 50nm.
  • the lithium nickel manganate modified material provided by the present application is doped with phosphorus element, but is different from the phosphate-coated positive electrode active material in the related art.
  • Phosphate-coated positive electrode active material refers to a material formed by phosphate crystal or amorphous phosphate covering the surface of spinel positive electrode material, and a phosphate coating layer can be seen on the surface of the material through transmission electron microscopy.
  • phosphorus element is doped in the primary particles, and phosphorus element is doped into the spinel structure in a concentration gradient from the surface of the primary particle to the interior.
  • Both the spinel phase and the rock-salt-like phase of the primary particles may be doped with phosphorus element, but phosphorus element is preferentially doped in the rock-salt-like phase.
  • the doping amount (concentration) of the phosphorus element in the primary particles is gradually decreased from the outside to the inside.
  • the surface is doped with phosphorus elements in a gradient, and the concentration gradient of the doping elements decreases from the outside to the inside, which can reduce the amount of doping, and at the same time ensure that the material interface in contact with the electrolyte has a higher doping concentration and higher structural stability. Gradient doping can well relieve the structural stress generated during the deintercalation process of lithium ions.
  • phosphorus element doping can significantly improve the stability of the surface of the material and increase the stability of the interface.
  • the doping of phosphorus element on the surface combined with the oxide coating process can significantly improve the stability and electronic conductivity of the material. .
  • the structure in which the phosphorus element in the primary particles is distributed in a concentration gradient can be defined as a phosphorus gradient doped layer.
  • the thickness of the phosphorus gradient doping layer may be any value between 0.5 nm and 40 nm and less than the radius of the primary particle, for example, it may also be 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm , 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, 30nm, 31nm , 32nm, 33nm, 34nm, 35nm, 36nm, 37nm, 38nm, 39nm or 40nm
  • the positive electrode active material, the rock-salt-like surface layer and the phosphorus gradient doped layer provided in this application can be characterized by common characterization methods in the art, such as scanning transmission electron microscopy (STEM), high-resolution TEM and X-ray photoelectron spectroscopy. Microscopy (XPS) was used for characterization. Among them, STEM can accurately see the distribution of the rock-salt-like phase on the surface due to part of the site-occupying elements occupying the 16c or 8a positions of the spinel octahedron. The narrow-range fine scanning of XRD shows that there are representative types between 43° and 44°. Miscellaneous peaks of rock-salt phase, STEM line scan can also prove the gradient distribution of phosphorus element.
  • STEM scanning transmission electron microscopy
  • XPS X-ray photoelectron spectroscopy
  • the etching analysis of X-ray photoelectron spectroscopy can also prove the gradient distribution of phosphorus element in the phosphorus gradient doped layer.
  • the elements contained in the surface coating can be proved by the following ways.
  • the morphology, structure and composition of the surface coating can be detected by TEM to prove its existence.
  • Raman and infrared spectroscopy can characterize the surface coating.
  • the inorganic compound may be selected from any one or more of oxides, fluorides, phosphides, and borides. In some embodiments, the inorganic compound is selected from oxides.
  • the surface lattice matching between the oxide structure and the rock-salt phase structure is higher, which is more conducive to the surface bonding of the coating layer and the lithium nickel manganate modified material, which is conducive to reducing the loss of the coating layer under high voltage and improving the positive electrode activity. Material surface stability.
  • the inorganic compound may include Li, Mg, Zn, Ni, Mn, Fe, Co, Ti, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Ta, Al, An oxide, fluoride, phosphide or boride of any one of Nb, B, Si, F, S, P and Sr.
  • the inorganic compound is an oxide, fluoride, phosphide or boride of a metal element of the above elements.
  • the thickness of the cladding layer is 2 nm-20 nm. At this thickness, the cathode active material combines high activity and high stability.
  • the embodiments of the present application also provide a method for preparing the positive electrode active material, comprising the following steps:
  • the step of providing the lithium nickel manganate modified material includes:
  • the spinel-structured lithium nickel manganate can be prepared by methods known to those skilled in the art. For example, it can be prepared by a low temperature solid phase method. Specifically, a precursor can be prepared by mixing nickel salt, manganese salt, lithium hydroxide and oxalic acid by ball milling, and then the precursor is calcined at high temperature to obtain the spinel-structured lithium nickel manganate.
  • the phosphorus source may be selected from nickel phosphate, cobalt phosphate, manganese phosphate, magnesium phosphate, calcium phosphate, iron phosphate, copper phosphate, zinc phosphate, titanium phosphate, zirconium phosphate, lithium phosphate, cobalt pyrophosphate, nickel pyrophosphate, pyrophosphate Manganese, magnesium pyrophosphate, calcium pyrophosphate, iron pyrophosphate, copper pyrophosphate, zinc pyrophosphate, titanium pyrophosphate, zirconium pyrophosphate, ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, hydrogen phosphate
  • dilithium, lithium pyrophosphate, pyrophosphoric acid, phosphoric acid and phosphorus pentoxide One or more of dilithium, lithium pyrophosphate, pyrophosphoric acid, phosphoric acid and phosphorus pentoxide.
  • the rock-salt-like phase inducer may include one or more of oxides and salts of the placeholder elements.
  • the rock salt-like phase inducer may include one or more of organic acids or inorganic acids, such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, formic acid, oxalic acid, citric acid, and the like.
  • organic or inorganic acid may promote the generation of a rock salt-like phase.
  • the rock-salt-like phase inducer may be one or more of organic acids or inorganic acids alone, or may further include one or more of oxides and salts of place-occupying elements. In some embodiments, the rock-salt-like phase inducer may also be one or more of oxides and salts of place-occupying elements alone.
  • the rock salt phase inducer is Mg, Zn, Fe, Co, Ti, Cr, Y, Sc, Ru , one or more of oxides and salts of Cu, Mo, Ge, W, Zr, Ca, Ta, Sr, Al, Nb, B, Si, F and S, or organic or inorganic acids.
  • the rock-salt phase inducer can be a metal-free acidic compound, or one or more of Ni, Mn oxides or salts, or Ni, One or more of Mn oxides or salts and one or more of organic acids and inorganic acids.
  • the mass ratio of the phosphorus source, the rock salt-like phase inducer and the spinel-structured lithium nickel manganate can be any ratio between 1:1:(20-400), for example, 1:1:50, 1:1 :80, 1:1:100, 1:1:150, 1:1:200, 1:1:250, 1:1:300 or 1:1:350.
  • the phosphorus source, the rock salt-like phase inducer, and the spinel-structured lithium nickel manganate can be mixed by methods known to those skilled in the art, such as mechanical mixing, ultrasound, ball milling, and the like.
  • the sintering process of the doped mixture in step a2 is as follows: heating to 600° C. to 1200° C. at a heating rate of 0.5° C./min ⁇ 10° C./min, then sintering for 0.5 hour ⁇ 20 hours, and then heating at 0.5° C. to 20° C.
  • the cooling rate of °C/min ⁇ 10°C/min is lowered to room temperature.
  • the specific sintering temperature may be 600°C, 650°C, 700°C, 800°C, 900°C, 1000°C, 1100°C or 1200°C.
  • the sintering in step a2 can be performed in oxygen, air, an atmosphere containing a reducing gas (such as hydrogen), or an inert atmosphere (such as nitrogen or argon) and an atmosphere containing oxygen.
  • a reducing gas such as hydrogen
  • an inert atmosphere such as nitrogen or argon
  • the inorganic compound precursor is selected from any one or more of oxides, organic compounds, fluorides, phosphides, and borides.
  • Organics are sintered to form oxides.
  • the organic substance is selected from any one or a combination of any one or more of tetrabutyl titanate, polyvinylidene fluoride, tantalum ethoxide, niobium ethoxide, and phosphate.
  • the mass ratio of the sum of the mass of the inorganic compound and the inorganic compound precursor to the lithium nickel manganate modified material is (0.5-20):1000.
  • the specific sintering temperature may be 250°C, 300°C, 350°C, 400°C, 450°C, 500°C or 550°C.
  • the non-oxidizing atmosphere may be nitrogen or argon, for example.
  • the present application also provides a positive electrode of a lithium ion secondary battery, comprising a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector, wherein the positive electrode active material layer includes the above-mentioned positive electrode active material.
  • the positive electrode current collector may be selected from conductive members formed of highly conductive metals used in the positive electrode of the related art lithium ion secondary battery.
  • the positive electrode current collector may be aluminum or an alloy including aluminum as a main component.
  • the shape of the positive electrode current collector is not particularly limited because it may vary depending on the shape and the like of the lithium ion secondary battery.
  • the positive electrode current collector may have various shapes such as a rod shape, a plate shape, a sheet shape, and a foil shape.
  • the positive electrode active material layer further includes a conductive additive and a binder.
  • the conductive additive may be a conventional conductive additive in the art, which is not particularly limited in the present application.
  • the conductive additive is carbon black (eg, acetylene black or Ketjen black).
  • the adhesive may be a conventional adhesive in the art, which is not particularly limited in the present application, and may be composed of polyvinylidene fluoride (PVDF), or may be composed of carboxymethyl cellulose (CMC) and butylbenzene Made of rubber (SBR).
  • the binder is polyvinylidene fluoride (PVDF).
  • the application also provides a lithium-ion secondary battery, comprising:
  • a negative electrode comprising a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector;
  • the negative electrode, separator and electrolyte can use conventional negative electrode current collector, separator and electrolyte materials in the art, which are not particularly limited in the present application.
  • the negative electrode current collector may be copper, and the shape of the negative electrode current collector is also not particularly limited, and may be rod-shaped, plate-shaped, sheet-shaped, and foil-shaped, and may vary depending on the shape of the lithium ion secondary battery and the like.
  • the negative electrode active material layer includes a negative electrode active material, a conductive additive and a binder. Negative active materials, conductive additives and binders are also conventional materials in the art. In some embodiments, the negative active material is metallic lithium. The conductive additives and binders are as described above and will not be repeated here.
  • the separator can be selected from those commonly used in lithium ion secondary batteries, such as polyolefin films, microporous films made of polyethylene and polypropylene; porous polyethylene films and polypropylene multilayer films. ; non-woven fabrics formed of polyester fibers, aramid fibers, glass fibers, etc.; and base films made of ceramic particles such as silica, alumina, and titania adhered to their surfaces, etc.
  • the separator is a triple layer film of PP/PE/PP coated on both sides with alumina.
  • the electrolytic solution may include an electrolyte and a non-aqueous organic solvent.
  • the electrolyte is selected from, but not limited to, LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 .
  • the non-aqueous organic solvent can be carbonate, ester and ether. Among them, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) and ethylmethyl carbonate (EMC) can be used.
  • the electrolyte is an ethylene carbonate (EC)/dimethyl carbonate (DMC) non-aqueous electrolyte with a LiPF 6 concentration of 1 mol/L, wherein the volume ratio of EC to DMC is 1: 1.
  • EC ethylene carbonate
  • DMC dimethyl carbonate
  • STEM was performed with a spherical aberration-corrected scanning transmission microscope with model JEM ARM200F (JEOL, Tokyo, Japan); X-ray photoelectron spectroscopy (XPS) was performed with an ESCALAB250 X-ray photoelectron spectrometer produced by Thermo Fisher Company To study the types of elements and chemical environment on the surface of powder samples, where the X-ray radiation source is Mg K ⁇ .
  • FIG. 1 is an STEM image of the phosphorus element gradient-doped lithium nickel manganate modified material prepared in Example 1.
  • FIG. 1 It can be seen from Figure 1 that there is a rock-salt-like phase generated by the occupancy of spinel octahedron 16c atoms on the surface of the material, and the thickness of the rock-salt-like phase is about 12 nm.
  • FIG. 2A and FIG. 2B are STEM line scan images of the phosphorus element content on the surface of the phosphorus element gradient-doped lithium nickel manganate modified material prepared in Example 1.
  • FIG. 2A and Figure 2B there is no coating layer on the surface of lithium nickel manganate after doping. Combined with Figure 1, it can be seen that phosphorus is distributed in the rock-like salt phase, and the content of phosphorus gradually decreases from the surface to the interior.
  • 3 is a TEM image of the coated lithium nickel manganate positive electrode active material of the embodiment. It can be seen that a coating layer is formed on the surface of the lithium nickel manganate modified material, and the thickness of the coating layer is about 6-8 nm.
  • FIG. 4A and FIG. 4B are STEM images of the phosphorus element gradient-doped lithium nickel manganate modified material prepared in Example 2, wherein FIG. 4A and FIG. 4B are images at different magnifications, respectively. It can be seen from Fig. 4A and Fig. 4B that there is a rock-salt-like phase generated by the atomic occupation of spinel octahedron 8a on the surface of the material, and the thickness of the rock-salt-like phase is about 10 nm.
  • Figure 5 shows the change of the relative content of phosphorus element on the surface of the phosphorus element gradient-doped lithium manganate modified material obtained in Example 2 by XPS characterization at different etching depths. We can see that phosphorus element changes from surface to The content of the interior decreases with the increase of the etching depth.
  • FIG. 6 is a TEM image of the coated lithium nickel manganate positive electrode active material of the embodiment. It can be seen from FIG. 6 that a coating layer is formed on the surface of the lithium nickel manganate modified material, and the thickness of the coating layer is about 2- 3nm.
  • Comparative Example 1 is basically the same as Example 1, the only difference is that no phosphorus is doped in the lithium nickel manganate modified material, that is, no phosphorus source (NH 4 ) 2 HPO 4 is added during the preparation process (without surface gradient doping). Phosphorus nickel lithium manganate direct coating).
  • Comparative Example 2 is basically the same as Example 1, except that the modified material of lithium nickel manganate is not further coated with boron oxide and aluminum oxide.
  • Comparative Example 3 is basically the same as Example 1, the only difference is that no phosphorus is doped in the lithium nickel manganate modified material, and the lithium nickel manganate modified material is not further coated with boron oxide and aluminum oxide.
  • Comparative Example 4 is basically the same as Example 2, the only difference is that no phosphorus is doped in the lithium nickel manganate modified material, that is, no phosphorus source H 3 PO 4 is added in the preparation process.
  • Comparative Example 5 is basically the same as Example 2, except that the modified material of lithium nickel manganate is not further coated with fluoride.
  • Comparative Example 6 is basically the same as Example 2, except that no phosphorus is doped in the lithium nickel manganate modified material, and the lithium nickel manganate modified material is not further coated with fluoride.
  • the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 6 were assembled into coin cells according to the following steps.
  • the positive active materials prepared in the examples and comparative examples carbon black as a conductive additive and polyvinylidene fluoride (PVDF) as a binder, were dispersed in N-methylpyrrolidone (NMP) in a weight ratio of 80:10:10. , mixed uniformly to prepare a uniform positive electrode slurry.
  • NMP N-methylpyrrolidone
  • the uniform positive electrode slurry was evenly coated on the aluminum foil current collector with a thickness of 15 ⁇ m, and dried at 55 ° C to form a pole piece with a thickness of 100 ⁇ m, and the pole piece was placed under a roller press for rolling (pressure about 1MPa). ⁇ 1.5cm 2 ), cut into a circle with a diameter of ⁇ 14mm, and then placed in a vacuum oven at 120° C. for 6 hours. After natural cooling, it was taken out and placed in a glove box to be used as a positive pole piece.
  • NMP N-methylpyrrolidone
  • metal lithium is used as the negative electrode of the battery, and a triple-layer film of PP/PE/PP coated with alumina on both sides is placed between the positive electrode and the negative electrode as a separator, and is added dropwise to conventional carbonate
  • a quasi-electrolyte solution using the positive electrode plate prepared in step (1) as the positive electrode, assembles a button-type battery with a model of CR2032.
  • the button battery After standing the prepared button battery at room temperature (25°C) for 10 hours, the button battery was activated by charging and discharging, and then the button battery prepared above was charged and discharged using a blue battery charge and discharge tester. Loop test. First, cycle at room temperature (25°C) at a rate of 0.1C for 1 week, and then continue to cycle at a rate of 0.2C for 4 weeks, wherein the charge-discharge voltage range of the control battery is 3.5V-4.9V. Then, the button battery was transferred to a high temperature environment of 55°C, and the cycle was continued for 50 cycles at a rate of 0.2C, while the charge-discharge voltage range of the control battery was still 3.5V to 4.9V.
  • the button battery After standing the prepared button battery at room temperature (25°C) for 10 hours, the button battery was activated by charging and discharging, and then the button battery prepared above was charged and discharged using a blue battery charge and discharge tester. Loop test. First, cycle at room temperature (25°C) at a rate of 0.1C for 1 week, and then continue to cycle at a rate of 0.2C for 200 cycles, wherein the charge-discharge voltage range of the control battery is 3.5V-4.9V.
  • the results show that the capacity retention rate and cycle performance of the battery are greatly improved after surface phosphorus doping compared with the non-phosphorus-doped lithium nickel manganate active material.
  • the harmful side reactions between the positive electrode active material and the electrolyte are suppressed, the decomposition of the electrolyte and the dissolution of Mn/Ni are suppressed, and the cycle stability of the battery is improved.
  • phosphorus doping can improve the coating effect, and further improve the surface stability and electronic conductivity of the surface-coated positive electrode active material.

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Abstract

本申请公开了一种正极活性材料，包括镍锰酸锂改性材料和镍锰酸锂改性材料表面的包覆层。包覆层由无机化合物组成。镍锰酸锂改性材料为包括尖晶石相和类岩盐相的具有类核壳结构的初级粒子。尖晶石相为内核，类岩盐相构成外壳。尖晶石相为尖晶石结构的镍锰酸锂；类岩盐相由尖晶石结构的镍锰酸锂诱导形成。类岩盐相中包含Mg、Zn、Ni、Mn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta、Sr、Al、Nb、B、Si、F和S中的至少一种占位元素。占位元素位于尖晶石相的16c或8a位置。类岩盐相中还掺杂有磷元素，磷元素从类岩盐相的外表面向内部呈梯度分布。本申请还公开了所述正极活性材料的制备方法、含有该正极活性材料的锂离子二次电池的正极以及锂离子二次电池。

Description

正极活性材料以及制备方法，正极，锂离子二次电池
相关申请
本申请要求2020年11月17日申请的，申请号为202011284601.1，名称为“正极活性材料以及制备方法，正极，锂离子二次电池”的中国专利申请的优先权，在此将其全文引入作为参考。
技术领域
本申请涉及正极材料技术领域，特别是涉及正极活性材料以及制备方法，正极，锂离子二次电池。
背景技术
锂离子二次电池与其他的可充电的电池体系相比，具有工作电压高、重量轻、体积小、无记忆效应、自放电率低、循环寿命长、能量密度高等优点，目前已广泛应用于手机、笔记本电脑、平板电脑等移动终端产品。在实际应用中，对于高压尖晶石正极材料来说，在循环过程中，由于传统的碳酸酯类电解液与正极材料相互作用，使正极材料表面丢氧，材料表面发生溶解，最终导致活性物质减少。表面改性成为人们的关注焦点。本领域常用的表面改性方法是对正极材料的表面进行包覆。通过表面包覆，能够很好的固定表面结构，保持正极材料的稳定性，抑制电解液的腐蚀。表面包覆能够阻隔正极材料和电解液的直接接触，减少电极材料在高电压下的分解，有利于整个高压界面的稳定性。
然而，包覆过程中，由于包覆物和待包覆材料表面结构差异，导致包覆物很难均匀、稳定的包覆在正极材料表面。同时即便待包覆物能够均匀包覆在正极材料表面，在高电压下，由于表面的包覆物被逐渐消耗，正极材料最终将暴露在电解液当中，仍会造成性能的迅速衰减。
发明内容
基于此，有必要针对正极材料表面包覆易损耗的问题，提供一种正极活性材料以及制备方法，正极，锂离子二次电池。
一种正极活性材料，包括镍锰酸锂改性材料和所述镍锰酸锂改性材料表面的包覆层。所述包覆层由无机化合物组成。所述无机化合物选自氧化物、氟化物、磷化物、硼化物中的任意一种或多种。所述镍锰酸锂改性材料为包括尖晶石相和类岩盐相的具有核壳结构的初级粒子。所述尖晶石相为内核，所述类岩盐相分布在所述尖晶石相的表面构成外壳。所述尖晶石相为尖晶石结构的镍锰酸锂。所述类岩盐相由所述尖晶石结构的镍锰酸锂诱导形 成。所述类岩盐相中包含Mg、Zn、Ni、Mn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta、Sr、Al、Nb、B、Si、F和S中的至少一种占位元素。所述占位元素位于尖晶石结构的16c或8a位置。所述类岩盐相中还掺杂有磷元素。所述磷元素从类岩盐相的外表面向内部呈浓度梯度分布，形成磷梯度掺杂层。
在一些实施例中，所述无机化合物包括Li、Mg、Zn、Ni、Mn、Fe、Co、Ti、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta、Al、Nb、B、Si、F、S、P和Sr中的任意一种元素的氧化物、氟化物、磷化物和硼化物中的任意一种或多种。
在一些实施例中，所述的尖晶石结构的镍锰酸锂的化学式为Li 1+xNi 0.5-yMn 1.5-zO u，其中，0.2≤x≤0.2，-0.2≤y≤0.2，-0.2≤z≤0.2，3.8≤u≤4.2。
在一些实施例中，所述的尖晶石结构的镍锰酸锂的化学式为Li 1+xNi 0.5-yMn 1.5-zM sO u，其中，M为Mg、Zn、Ni、Mn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta、Sr、Al、Nb、B、Si、F和S中的至少一种，-0.2≤x≤0.2，-0.2≤y≤0.2，-0.2≤z≤0.2，0＜s≤0.2且3.8≤u≤4.2。在其中一个实施例中，所述包覆层的厚度为2nm～20nm。
在一些实施例中，所述尖晶石相的尺寸为0.1μm～30μm。
在一些实施例中，所述类岩盐相的厚度为0.5nm～50nm。
在一些实施例中，在所述初级粒子中，磷元素的浓度由外表面向内部逐渐降低。
在一些实施例中，所述磷梯度掺杂层的厚度为0.5nm～40nm。
一种所述的正极活性材料的制备方法，其特征在于，包括以下步骤：
提供所述镍锰酸锂改性材料；
将无机化合物或无机化合物前驱体与所述镍锰酸锂改性材料进行混合，得到包覆混合物，所述无机化合物前驱体经烧结形成所述无机化合物；以及
将所述包覆混合物在空气，氧气或惰性气体中150℃～550℃下烧结0.5小时～20小时。
在一些实施例中，提供所述镍锰酸锂改性材料的步骤包括：
将磷源、类岩盐相诱导剂以及所述尖晶石结构的镍锰酸锂进行混合，得到掺杂混合物；以及
将所述掺杂混合物在600℃～1200℃下烧结0.5小时～20小时。
在一些实施例中，所述无机化合物前驱体选自氧化物、有机物、氟化物、磷化物、硼化物中的任意一种或多种。
在一些实施例中，掺杂混合物的烧结过程为：以0.5℃/min～10℃/min的升温速率升温至600℃～1200℃，然后经过0.5小时～20小时的烧结，随后以0.5℃/min～10℃/min的降温 速率降至室温。
一种锂离子二次电池的正极，包括正极集流体和位于所述正极集流体上的正极活性材料层，所述正极活性材料层包括所述的正极活性材料。
一种锂离子二次电池，其特征在于，包括：
所述的正极；
负极，其包括负极集流体和位于所述负极集流体上的负极活性材料层；
隔膜和电解液。
本申请通过先在尖晶石结构的镍锰酸锂表面进行诱导及磷元素梯度掺杂得到镍锰酸锂改性材料，在其基础上又进行了无机化合物包覆得到该正极活性材料。镍锰酸锂改性材料的表面为类岩盐相，类岩盐相表面层有利于磷元素在镍锰酸锂改性材料表面的梯度掺杂。磷元素表面掺杂能显著提高所述正极活性材料的电化学性能，包括首次放电效率、平均放电效率和充放电循环稳定性。无机化合物包覆层能够增加界面稳定性，但是无机化合物是不导电的，将会导致正极活性材料表面电子电导下降。表面梯度磷掺杂不仅能够单独增加镍锰酸锂表面结构稳定性，还能够提高正极活性材料表面的电子电导。同时磷元素的梯度掺杂能够改变正极活性材料表面的表面能，在磷掺杂的同时在镍锰酸锂表面大量引入了类岩盐相结构，这种结构和无机化合物，尤其是氧化物的晶格常数更加匹配，有利于无机化合物与镍锰酸锂改性材料表面的紧密结合使得包覆更均匀，更牢固，改性效果更好。
附图说明
图1为本申请实施例1制得的磷掺杂后的镍锰酸锂改性材料的扫描透射电子显微镜(STEM)图。
图2A和图2B为本申请实施例1制得的磷掺杂后的镍锰酸锂改性材料的表面磷元素的STEM线扫图。
图3为本申请实施例1制得的包覆后的镍锰酸锂正极活性材料的透射电子显微镜(TEM)图。
图4A和图4B为本申请实施例2制得的磷掺杂后的镍锰酸锂改性材料的STEM图。
图5为本申请实施例2制得的磷掺杂后的镍锰酸锂改性材料在不同刻蚀深度下用X射线光电子能谱学(XPS)表征得到的表面磷元素的相对含量变化。
图6为本申请实施例2制得的包覆后的镍锰酸锂正极活性材料的TEM图。
具体实施方式
为了便于理解本申请，下面将参照相关附图对本申请进行更全面的描述。附图中给出了本申请的较佳实施例。但是，本申请可以以许多不同的形式来实现，并不限于本文所描述的实施例。相反地，提供这些实施例的目的是使对本申请的公开内容的理解更加透彻全面。
除非另有定义，本文所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同。本文中在本申请的说明书中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请。本文所使用的术语“和/或”包括一个或多个相关的所列项目的任意的和所有的组合。
除了在操作实施例中所示以外或另外表明之外，所有在说明书和权利要求中表示成分的量、物化性质等所使用的数字理解为在所有情况下通过术语“约”来调整。例如，因此，除非有相反的说明，否则上述说明书和所附权利要求书中列出的数值参数均是近似值，本领域的技术人员能够利用本文所公开的教导内容寻求获得的所需特性，适当改变这些近似值。用端点表示的数值范围的使用包括该范围内的所有数字以及该范围内的任何范围，例如，1至5包括1、1.1、1.3、1.5、2、2.75、3、3.80、4和5等等。
本申请实施例提供一种正极活性材料，包括镍锰酸锂改性材料和所述镍锰酸锂改性材料表面的包覆层。所述包覆层由无机化合物组成。所述镍锰酸锂改性材料为包括尖晶石相和类岩盐相的具有核壳结构的初级粒子。所述尖晶石相为内核，所述类岩盐相分布在所述尖晶石相的表面构成外壳。
所述尖晶石相为具有尖晶石结构的镍锰酸锂。所述类岩盐相由尖晶石结构的镍锰酸锂诱导形成。所述类岩盐相中包含镍、锰、锂及氧元素，且进一步包含占位元素。所述占位元素选自Mg、Zn、Ni、Mn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta、Sr、Al、Nb、B、Si、F和S中的至少一种，所述占位元素位于尖晶石结构的16c或8a位置。
所述类岩盐相中还掺杂有磷元素，所述磷元素从类岩盐相的外表面向内部呈梯度分布。
本申请通过先在尖晶石结构的镍锰酸锂表面进行诱导及磷元素梯度掺杂得到镍锰酸锂改性材料，在其基础上又进行了无机化合物包覆得到该正极活性材料。镍锰酸锂改性材料的表面为类岩盐相，类岩盐相表面层有利于磷元素在镍锰酸锂改性材料表面的梯度掺杂。磷元素表面掺杂能显著提高所述正极活性材料的电化学性能，包括首次放电效率、平均放电效率和充放电循环稳定性。无机化合物包覆层能够增加界面稳定性，但是无机化合物是 不导电的，将会导致正极活性材料表面电子电导下降。表面梯度磷掺杂不仅能够单独增加镍锰酸锂表面结构稳定性，还能够提高正极活性材料表面的电子电导。同时磷元素的梯度掺杂能够改变正极活性材料表面的表面能。在磷掺杂的同时在镍锰酸锂表面引入了类岩盐相结构，这种结构和无机化合物，尤其是氧化物的晶格常数更加匹配，有利于无机化合物与镍锰酸锂改性材料表面的紧密结合使得包覆更均匀，更牢固，改性效果更好。
一般定义的核壳结构是由一种材料通过化学键或其他作用力将另一种材料包覆起来形成的有序组装结构。本申请中初级粒子为类核壳结构，定义的类核壳结构“核”与“壳”实际上是一体的。“壳”是通过尖晶石结构的表面晶格重构形成的岩盐相结构。本申请的镍锰酸锂改性材料结构包括两种相，导致表面层的晶体结构与材料内部的晶体结构不同。本申请中将这样形成的材料的内部称为“核”，表面层称为“壳”，并将这样结构的材料定义为类核壳结构的材料。
所述初级粒子是指构成镍锰酸锂改性材料的最小单元，并且具体是指可基于外观的几何构造确定的最小单元。初级粒子的聚集体是二级粒子。所述初级粒子具有类核壳结构。所述类核壳结构中的尖晶石相内核与类岩盐相外壳是一体的，且尖晶石相与类岩盐相之间通过氧键合而不能互相分开。
在一些实施例中，所述的尖晶石结构的镍锰酸锂的化学式为Li 1+xNi 0.5-yMn 1.5-zO u，其中，0.2≤x≤0.2，-0.2≤y≤0.2，-0.2≤z≤0.2，3.8≤u≤4.2。x、y和z的值可取决于各元素之间的比率而变化，但都设定在使该化学式所代表的化合物可呈现尖晶石结构的范围内。
在一些实施例中，尖晶石结构的镍锰酸锂的体相中均匀掺杂有有利于磷掺杂的元素，所述的尖晶石结构的镍锰酸锂的化学式可以为Li 1+xNi 0.5-yMn 1.5-zM sO u，其中，M为Mg、Zn、Ni、Mn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta、Sr、Al、Nb、B、Si、F和S中的至少一种，-0.2≤x≤0.2，-0.2≤y≤0.2，-0.2≤z≤0.2，0＜s≤0.2且3.8≤u≤4.2。x、y、z、s、u的值可取决于各元素之间的比率而变化，但都设定在使该化学式所代表的化合物可呈现尖晶石结构的范围内。
在一些实施例中，所述占位元素为Al，Al元素更有利于提高所述正极活性材料的结构稳定性和降低磷元素掺杂入尖晶石结构的势垒。
在一些实施例中，所述尖晶石相内核的尺寸可以为0.1μm～30μm之间的任意值，例如可以为0.5μm、1μm、2μm、3μm、4μm、5μm、6μm、7μm、8μm、9μm、10μm、11μm、12μm、13μm、14μm、15μm、16μm、17μm、18μm、19μm、20μm、21μm、22μm、23μm、24μm、25μm、26μm、27μm、28μm或29μm。
在一些实施例中，所述类岩盐相外壳的厚度可以为0.5nm～50nm之间的任意值，例如可以为0.5nm、1nm、2nm、3nm、4nm、5nm、6nm、7nm、8nm、9nm、10nm、11nm、12nm、13nm、14nm、15nm、16nm、17nm、18nm、19nm、20nm、21nm、22nm、23nm、24nm、25nm、26nm、27nm、28nm、29nm、30nm、31nm、32nm、33nm、34nm、35nm、36nm、37nm、38nm、39nm、40nm、41nm、42nm、43nm、44nm、45nm、46nm、47nm、48nm、49nm或50nm。
本申请提供的镍锰酸锂改性材料中掺杂有磷元素，但不同于相关技术中的磷酸盐包覆的正极活性材料。磷酸盐包覆的正极活性材料是指磷酸盐晶体的或者非晶态的磷酸盐覆盖在尖晶石正极材料表面所形成的材料，通过透射电镜能够看到材料表面有一层磷酸盐包覆层。而本申请提供的改性正极活性材料中磷元素掺杂在所述初级粒子中，磷元素从所述初级粒子颗粒表面向内部呈浓度梯度变化地掺杂到尖晶石结构内部。
所述初级粒子的尖晶石相和类岩盐相中可均掺杂有磷元素，但磷元素优先掺杂在所述类岩盐相中。所述磷元素在所述初级粒子中的掺杂量(浓度)由外向内梯度递减。表面梯度掺杂磷元素，掺杂元素从外到内浓度梯度减少，能够减少掺杂用量，同时保证和电解液接触的材料界面有更高的掺杂浓度和更高的结构稳定性，同时表面梯度掺杂能够很好的缓解锂离子在脱嵌过程中产生的结构应力。在高价元素当中，我们发现磷元素掺杂能够显著提高材料表面的稳定性，增加界面的稳定性，同时将表面磷元素掺杂结合氧化物包覆工艺，能够显著提高材料的稳定性和电子电导。
所述初级粒子中磷元素呈浓度梯度分布的结构可以定义为磷梯度掺杂层。在一些实施例中，所述磷梯度掺杂层的厚度可以为0.5nm～40nm之间且小于初级粒子半径的任意值，例如还可以为0.5nm、1nm、2nm、3nm、4nm、5nm、6nm、7nm、8nm、9nm、10nm、11nm、12nm、13nm、14nm、15nm、16nm、17nm、18nm、19nm、20nm、21nm、22nm、23nm、24nm、25nm、26nm、27nm、28nm、29nm、30nm、31nm、32nm、33nm、34nm、35nm、36nm、37nm、38nm、39nm或40nm。
本申请提供的正极活性材料，类岩盐相表面层和磷梯度掺杂层可以用本领域常用的表征方法进行表征，例如可以采用扫描透射电子显微镜(STEM)，高分辨TEM和X射线光电子能谱显微镜(XPS)进行表征。其中利用STEM能够精确的看到表面由于部分占位元素占据尖晶石八面体16c或8a位置产生的类岩盐相分布，通过XRD窄范围精细扫描看出在43°和44°之间有代表类岩盐相的杂峰，STEM线扫也能够证明磷元素的梯度分布。同时利用X射线光电子能谱的刻蚀分析也可以证明磷梯度掺杂层中磷元素的梯度分布。对 于表面无机物的包覆可以通过以下方式证明表面包覆层中含有的元素，利用TEM探测表面包覆层的形态，结构和成分以证明其存在，拉曼和红外光谱能够表征表面包覆物的化学键以证明表面包覆物的存在，通过以上方式但不仅限于以上方式的表征能够确定正极材料是否在该专利保护范围。
在一些实施例中，所述无机化合物可选自氧化物、氟化物、磷化物、硼化物中的任意一种或多种。在一些实施例中，所述无机化合物选自氧化物。氧化物结构与岩盐相结构的表面晶格匹配性更高，更有利于包覆层与镍锰酸锂改性材料的表面结合，有利于降低包覆层在高电压下的损耗，提高正极活性材料表面稳定性。
在一些实施例中，所述无机化合物可包括Li、Mg、Zn、Ni、Mn、Fe、Co、Ti、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta、Al、Nb、B、Si、F、S、P和Sr中的任意一种元素的氧化物、氟化物、磷化物或硼化物。在一些实施例中，所述无机化合物为以上元素中的金属元素的氧化物、氟化物、磷化物或硼化物。
在一些实施例中，所述包覆层的厚度为2nm-20nm。在该厚度下，该正极活性材料兼顾高活性和高稳定性。
本申请实施例还提供一种所述的正极活性材料的制备方法，包括以下步骤：
a、提供所述镍锰酸锂改性材料；
b、将无机化合物或无机化合物前驱体与所述镍锰酸锂改性材料进行混合，得到包覆混合物，所述无机化合物前驱体经烧结形成所述无机化合物；以及
c、将所述包覆混合物在250℃～550℃下烧结0.5小时～20小时。
在一些实施例中，提供所述镍锰酸锂改性材料的步骤包括：
a1、将磷源、类岩盐相诱导剂以及尖晶石结构的镍锰酸锂进行混合，得到掺杂混合物；以及
a2、将所述掺杂混合物在600℃～1200℃下烧结0.5小时～20小时。
所述尖晶石结构的镍锰酸锂可以由本领域技术人员习知的方法进行制备。例如可以通过低温固相法进行制备。具体的，可以将镍盐、锰盐、氢氧化锂以及草酸混合球磨制备前驱体，再将前驱体高温煅烧得到所述尖晶石结构的镍锰酸锂。
所述磷源可以选自磷酸镍、磷酸钴、磷酸锰、磷酸镁、磷酸钙、磷酸铁、磷酸铜、磷酸锌、磷酸钛、磷酸锆、磷酸锂、焦磷酸钴、焦磷酸镍、焦磷酸锰、焦磷酸镁、焦磷酸钙、焦磷酸铁、焦磷酸铜、焦磷酸锌、焦磷酸钛、焦磷酸锆、磷酸铵、磷酸二氢铵、磷酸氢二铵、磷酸二氢锂、磷酸氢二锂、焦磷酸锂、焦磷酸、磷酸和五氧化二磷中的一种或多种。
在一些实施例中，所述类岩盐相诱导剂可以包括所述占位元素的氧化物、盐中的一种或多种。例如，MgO、ZnO、Fe 2O 3、CoO、TiO、Cr 2O 3、Y 2O 3、Sc 2O 3、RuO 2、CuO、MoO 3、GeO 2、WO 3、ZrO 2、CaO、Ta2O5、Al 2O 3、Nb 2O、Nb 2O 5、B 2O 3、SiO 2、Al(OH) 3、H3BO3、NaAlO 2、Na 2SiO 3中的一种或多种。
在另一些实施例中，所述类岩盐相诱导剂可以包括有机酸或无机酸中的一种或多种，例如盐酸、硝酸、硫酸、磷酸、乙酸、甲酸、草酸和柠檬酸等。所述有机酸或无机酸可以促进类岩盐相的产生。
类岩盐相诱导剂既可单独为有机酸或无机酸中的一种或多种，也可以进一步包括占位元素的氧化物、盐中的一种或多种。在一些实施例中，类岩盐相诱导剂也可单独为占位元素的氧化物、盐中的一种或多种。
具体的，当占位元素为除Ni、Mn以外的其他元素时，如Mg、Zn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta、Sr、Al、Nb、B、Si、F和S等中的一种或多种，在这种情况下岩盐相诱导剂为Mg、Zn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta、Sr、Al、Nb、B、Si、F和S的氧化物和盐中的一种或多种，或者还包括有机酸或无机酸。当占位元素由Ni、Mn组成，在这种情况下岩盐相诱导剂可以为不含金属的酸性化合物，或者为Ni、Mn的氧化物或盐中的一种或多种，或者为Ni、Mn的氧化物或盐中的一种或多种以及有机酸、无机酸中的一种或多种。
所述磷源、类岩盐相诱导剂和尖晶石结构的镍锰酸锂的质量比可以为1:1：(20～400)之间的任意比值，例如1:1:50，1:1:80，1:1:100，1:1:150，1:1:200，1：1:250，1:1:300或1:1:350。
步骤a1中，所述磷源、类岩盐相诱导剂以及所述尖晶石结构的镍锰酸锂可以由本领域技术人员习知的方法进行混合，例如机械混合、超声、球磨等。
在一些实施例中，步骤a2掺杂混合物的烧结过程为：以0.5℃/min～10℃/min的升温速率升温至600℃～1200℃，然后经过0.5小时～20小时的烧结，随后以0.5℃/min～10℃/min的降温速率降至室温。具体的烧结温度可以为600℃、650℃、700℃、800℃、900℃、1000℃、1100℃或1200℃。
步骤a2中所述烧结可以在氧气、空气、含有还原性气体(如氢气)的气氛或惰性气氛(如氮气或氩气)且含有氧气的气氛下进行。
在一些实施例中，所述无机化合物前驱体选自氧化物、有机物、氟化物、磷化物、硼化物中的任意一种或多种。有机物通过烧结形成氧化物。有机物例如选自钛酸四丁酯、聚 偏氟乙烯、乙醇钽、乙醇铌、磷酸酯的任意一种或多种的组合。
在一些实施例中，所述无机化合物和无机化合物前驱体质量之和与镍锰酸锂改性材料的质量比为(0.5～20):1000。
步骤c中，具体的烧结温度可以为250℃、300℃、350℃、400℃、450℃、500℃或550℃。所述非氧化气氛例如可以为氮气或氩气。
本申请还提供一种锂离子二次电池的正极，包括正极集流体和位于所述正极集流体上的正极活性材料层，所述正极活性材料层包括上述的正极活性材料。
正极集流体可以选自相关技术的锂离子二次电池的正极中所用的由高导电金属形成的导电元件。例如，正极集流体可以为铝或包括铝作为主要组分的合金。正极集流体的形状不受特别限制，因为其可取决于锂离子二次电池的形状等而变化。例如，正极集流体可具有各种形状，如杆形、板形、片形和箔形。
所述正极活性材料层还包括导电添加剂和粘结剂。
所述导电添加剂可以是本领域中常规的导电添加剂，本申请对其没有特别限制。例如，在一些实施方案中，所述导电添加剂为炭黑(例如乙炔黑或Ketjen黑)。
所述粘合剂可以是本领域中常规的粘合剂，本申请对其没有特别限制，可以由聚偏二氟乙烯(PVDF)构成，也可以由羧甲基纤维素(CMC)和丁苯橡胶(SBR)构成。在一些实施方案中，所述粘合剂为聚偏二氟乙烯(PVDF)。
本申请还提供一种锂离子二次电池，包括：
如上所述的正极；
负极，其包括负极集流体和位于所述负极集流体上的负极活性材料层；
隔膜和电解液。
作为负极集流体，
所述负极、隔膜和电解液可以采用本领域中常规的负极集流体、隔膜和电解液材料，本申请对它们没有特别限制。
作为负极集流体可以为铜，负极集流体的形状同样不受特别限制，可以为杆形、板形、片形和箔形，可取决于锂离子二次电池的形状等而变化。所述负极活性材料层包括负极活性材料、导电添加剂和粘结剂。负极活性材料、导电添加剂和粘结剂同样为本领域的常规材料。在一些实施方案中，负极活性材料为金属锂。导电添加剂和粘结剂如上所述，在此不再赘述。
所述隔膜可以选用通常锂离子二次电池中使用的隔膜，如聚烯烃类薄膜，可列举出聚 乙烯、聚丙烯制膜的微多孔膜；多孔性的聚乙烯膜与聚丙烯的多层膜；由聚酯纤维、芳纶纤维、玻璃纤维等形成的无纺布；以及在它们的表面附着有二氧化硅、氧化铝、二氧化钛等陶瓷微粒而成的基底膜等。在一些实施方案中，隔膜为双面涂覆有氧化铝的PP/PE/PP的三层膜。
所述电解液可以包括电解质和非水有机溶剂。所述电解质选自但不限于LiPF 6、LiBF 4、LiSbF 6、LiAsF 6。所述非水有机溶剂，可以为碳酸酯、酯和醚。其中，可采用碳酸酯，如碳酸亚乙酯(EC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)和碳酸乙基甲基酯(EMC)。在一些实施方案中，所述电解液是LiPF 6的浓度为1mol/L的碳酸乙烯酯(EC)/碳酸二甲酯(DMC)非水系电解液，其中，EC与DMC的体积比为1:1。
以下为具体实施例，旨在对本申请做进一步的详细说明，以帮助本领域技术及研究人员进一步理解本申请，有关技术条件等并不构成对本申请的任何限制。在本申请权利要求范围内所做的任何形式的修改，均在本申请权利要求的保护范围之内。
以下实施例中，STEM采用型号为JEM ARM200F(JEOL，Tokyo，Japan)的球差矫正扫描透射显微镜进行；X射线光电子能谱(XPS)采用Thermo Fisher公司生产的ESCALAB250型号的X射线光电子能谱仪来研究粉末样品表面元素的种类和化学环境，其中，X射线辐射源是Mg Kα。
实施例1
将18g的LiNi 0.5Mn 1.5O 4材料(山东齐兴能源材料有限公司)、0.54g CuO和0.267g(NH 4) 2HPO 4均匀混合，将所得混合物在氧气中600℃煅烧5h，升温速率为3℃/分钟，降温速率为5℃/分钟，得到磷元素梯度掺杂的镍锰酸锂改性材料。取10g该改性材料，0.05g氧化硼和0.1g氧化铝进行均匀固相混合，然后在空气中450℃烧结10h，最终得到氧化硼氧化铝共包覆、表面梯度磷掺杂的镍锰酸锂正极活性材料。
图1为实施例1制得的磷元素梯度掺杂的镍锰酸锂改性材料的STEM图。从图1可以看到，材料表面有尖晶石八面体16c原子占位产生的类岩盐相，类岩盐相的厚度约为12nm。
图2A和图2B为实施例1制得的磷元素梯度掺杂的镍锰酸锂改性材料表面的磷元素含量的STEM线扫图。从图2A和图2B可以看出掺杂后镍锰酸锂表面没有包覆层，结合图1可以看出磷元素分布在类岩盐相中，并且磷元素的含量从表面到内部逐渐递减。
图3为实施例的包覆后的镍锰酸锂正极活性材料的TEM图，可以看出，镍锰酸锂改性材料表面形成包覆层，包覆层的厚度约为6-8nm。
实施例2
将18g的LiNi 0.4Mn 1.6O 4材料(山东齐兴能源材料有限公司)、0.54gH 3PO 4和1g草酸均匀混合将所得混合物在氧气中600℃煅烧5h，升温速率为3℃/分钟，降温速率为5℃/分钟，得到磷元素梯度掺杂的镍锰酸锂改性材料。取10g该改性材料，0.1g聚偏二氟乙烯进行均匀固相混合，然后在真空中250℃烧结15h，最终得到氟化物包覆、表面梯度磷掺杂的镍锰酸锂正极活性材料。
图4A和图4B为实施例2制得的磷元素梯度掺杂的镍锰酸锂改性材料的STEM图，其中图4A和图4B分别为不同倍率下的图像。从图4A和图4B可以看到，材料表面有尖晶石八面体8a原子占位产生的类岩盐相，类岩盐相的厚度约为10nm。
图5为实施例2制得的磷元素梯度掺杂的镍锰酸锂改性材料在不同刻蚀深度下用XPS表征得到的表面磷元素的相对含量变化，我们可以看出磷元素从表面到内部随着刻蚀深度的增加含量不断减少。
图6为实施例的包覆后的镍锰酸锂正极活性材料的TEM图，从图6可以看出，镍锰酸锂改性材料表面形成包覆层，包覆层的厚度约为2-3nm。
实施例3
将180g的LiNi 0.5Mn 1.5O 4材料(山东齐兴能源材料有限公司)、5.4g Cr 2O 3和2.67g(NH 4) 2HPO 420ml的去离子水加入烧杯中均匀混合，将烧杯置于120℃的油浴锅搅拌加热5h获得干燥混合物。将所得混合物在空气中725℃煅烧5h，升温速率为3℃/分钟，降温速率为5℃/分钟，得到磷元素梯度掺杂的镍锰酸锂改性材料。取100g该改性材料，0.2g纳米氧化钨进行均匀固相混合，然后在空气气氛550℃烧结1h，最终得到氧化钨包覆、表面梯度磷掺杂的镍锰酸锂正极活性材料。
对比例1
对比例1与实施例1基本相同，区别仅在于，镍锰酸锂改性材料中没有掺杂磷，即，制备过程中不加入磷源(NH 4) 2HPO 4(在未表面梯度掺杂磷的镍锰酸锂直接包覆)。
对比例2
对比例2与实施例1基本相同，区别仅在于，镍锰酸锂改性材料外没有进一步包覆氧化硼和氧化铝。
对比例3
对比例3与实施例1基本相同，区别仅在于，镍锰酸锂改性材料中没有掺杂磷，镍锰酸锂改性材料外也没有进一步包覆氧化硼和氧化铝。
对比例4
对比例4与实施例2基本相同，区别仅在于，镍锰酸锂改性材料中没有掺杂磷，即，制备过程中不加入磷源H 3PO 4。
对比例5
对比例5与实施例2基本相同，区别仅在于，镍锰酸锂改性材料外没有进一步包覆氟化物。
对比例6
对比例6与实施例2基本相同，区别仅在于，镍锰酸锂改性材料中没有掺杂磷，镍锰酸锂改性材料外也没有进一步包覆氟化物。
将实施例1～3和对比例1～6中制备的正极活性材料按照如下的步骤装配成扣式电池。
(1)制备正极极片
将实施例、对比例中制备的正极活性材料、炭黑作为导电添加剂和聚偏二氟乙烯(PVDF)作为粘结剂，按照重量比80:10:10分散于N-甲基吡咯烷酮(NMP)中，混合均匀，制备成均匀的正极浆料。将均匀的正极浆料均匀涂覆在厚度为15μm的铝箔集流体上，在55℃下烘干，形成厚度为100μm的极片，将极片置于辊压机下辊压(压力约为1MPa×1.5cm 2)，裁剪成直径为φ14mm的圆片，然后置于真空烘箱中于120℃下烘6小时，自然冷却后，取出置于手套箱中用作正极极片。
(2)装配锂离子二次电池
在充满惰性气氛的手套箱中，以金属锂作为电池的负极，双面涂覆氧化铝的PP/PE/PP的三层膜作为隔膜放在正极和负极之间，滴加到常规的碳酸脂类电解液，以步骤(1)制备的正极极片为正极，装配成型号为CR2032的扣式电池。
循环测试
(1)高温循环：
将制备的扣式电池在室温(25℃)条件下静置10个小时后，然后对扣式电池进行充放电活化，随后采用蓝电电池充放电测试仪对上述制备的扣式电池进行充放电循环测试。首先在室温条件下(25℃)，以0.1C的倍率循环1周，然后以0.2C的倍率继续循环4周，其中，控制电池的充放电电压范围为3.5V～4.9V。然后，将扣式电池转移至55℃的高温环境中，以0.2C的倍率继续循环50周，同时控制电池的充放电电压范围仍为3.5V～4.9V。
(2)室温循环：
将制备的扣式电池在室温(25℃)条件下静置10个小时后，然后对扣式电池进行充放电活化，随后采用蓝电电池充放电测试仪对上述制备的扣式电池进行充放电循环测试。 首先在室温条件下(25℃)，以0.1C的倍率循环1周，然后以0.2C的倍率继续循环200周，其中，控制电池的充放电电压范围为3.5V～4.9V。
实验数据列于表1和表2中。
表1.本申请各实施例的正极活性材料的电化学性能
样品 实施例1 实施例2 实施例3
测试温度℃ 55 55 55
初始可逆容量mAh/g 132.2 131.5 133.5
50次循环后可逆容量mAh/g 129 129.5 130.2
50次循环后库伦效率％ 99.05 99.15 99.21
电阻率(KΩ/cm) 550 515 539
表2.本申请各对比例的正极活性材料的电化学性能
Figure PCTCN2021120159-appb-000001
结果表明，与未掺杂磷元素的镍锰酸锂活性材料相比，表面磷掺杂之后，电池的容量保持率、循环性能都得到较大提高，这是由于经过磷梯度掺杂后，缓解了正极活性材料与电解液之间的有害副反应，抑制了电解液分解以及Mn/Ni的溶解，从而使电池的循环稳定性提高。并且，磷掺杂能够提高包覆效果，进一步提高表面包覆后的正极活性材料的表面稳定性的和电子电导率。
以上所述实施例的各技术特征可以进行任意的组合，为使描述简洁，未对上述实施例中的各个技术特征所有可能的组合都进行描述，然而，只要这些技术特征的组合不存在矛盾，都应当认为是本说明书记载的范围。
以上所述实施例仅表达了本申请的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对申请专利范围的限制。应当指出的是，对于本领域的普通技术人员来说， 在不脱离本申请构思的前提下，还可以做出若干变形和改进，这些都属于本申请的保护范围。因此，本申请专利的保护范围应以所附权利要求为准。

Claims (19)

  1. 一种正极活性材料，其特征在于，包括镍锰酸锂改性材料和所述镍锰酸锂改性材料表面的包覆层；
    所述包覆层由无机化合物组成，所述无机化合物选自氧化物、氟化物、磷化物、硼化物中的任意一种或多种；
    所述镍锰酸锂改性材料为包括尖晶石相和类岩盐相的具有类核壳结构的初级粒子，所述尖晶石相为内核，所述类岩盐相分布在所述尖晶石相的表面构成外壳；
    所述尖晶石相为尖晶石结构的镍锰酸锂；
    所述类岩盐相由尖晶石结构的镍锰酸锂诱导形成，所述类岩盐相中包含Mg、Zn、Ni、Mn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta、Sr、Al、Nb、B、Si、F和S中的至少一种占位元素，所述占位元素位于尖晶石结构的16c或8a位置；
    所述类岩盐相中还掺杂有磷元素，所述磷元素从类岩盐相的外表面向内部呈浓度梯度分布形成磷梯度掺杂层。
  2. 根据权利要求1所述的正极活性材料，其特征在于，所述无机化合物包括Li、Mg、Zn、Ni、Mn、Fe、Co、Ti、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta、Al、Nb、B、Si、F、S、P和Sr中的任意一种元素的氧化物、氟化物、磷化物和硼化物中的任意一种或多种。
  3. 根据权利要求1或2所述的正极活性材料，其特征在于，所述的尖晶石结构的镍锰酸锂的化学式为Li 1+xNi 0.5-yMn 1.5-zM sO u，其中，M为Mg、Zn、Ni、Mn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta、Sr、Al、Nb、B、Si、F和S中的至少一种，-0.2≤x≤0.2，-0.2≤y≤0.2，-0.2≤z≤0.2，0≤s≤0.2且3.8≤u≤4.2。
  4. 根据权利要求1～3任一项所述的正极活性材料，其特征在于，所述包覆层的厚度为2nm～20nm。
  5. 根据权利要求1～4任一项所述的正极活性材料，其特征在于，所述尖晶石相的尺寸为0.1μm～30μm。
  6. 根据权利要求1～5任一项所述的正极活性材料，其特征在于，所述类岩盐相的厚度为0.5nm～50nm。
  7. 根据权利要求1～6任一项所述的正极活性材料，其特征在于，在所述初级粒子中，磷元素的浓度由外表面向内部逐渐降低。
  8. 根据权利要求1～7任一项所述的正极活性材料，其特征在于，所述磷梯度掺杂层的 厚度为0.5nm～40nm。
  9. 一种如权利要求1～8任一项所述的正极活性材料的制备方法，其特征在于，包括以下步骤：
    提供所述镍锰酸锂改性材料；
    将所述无机化合物或无机化合物前驱体与所述镍锰酸锂改性材料进行混合，得到包覆混合物，所述无机化合物前驱体经烧结形成所述无机化合物；以及
    将所述包覆混合物在空气，氧气或惰性气体中150℃～550℃下烧结0.5小时～20小时。
  10. 根据权利要求9所述的正极活性材料的制备方法，其特征在于，提供所述镍锰酸锂改性材料的步骤包括：
    将磷源、类岩盐相诱导剂以及尖晶石结构的镍锰酸锂进行混合，得到掺杂混合物；以及
    将所述掺杂混合物在600℃～1200℃下烧结0.5小时～20小时。
  11. 根据权利要求10所述的正极活性材料的制备方法，其特征在于，所述磷源、类岩盐相诱导剂和尖晶石结构的镍锰酸锂的质量比为1:1：(20～400)。
  12. 根据权利要求10所述的正极活性材料的制备方法，其特征在于，所述类岩盐相诱导剂为所述占位元素的氧化物、盐中的一种或多种。
  13. 根据权利要求12所述的正极活性材料的制备方法，其特征在于，所述类岩盐相诱导剂还包括有机酸或无机酸中的一种或多种。
  14. 根据权利要求10所述的正极活性材料的制备方法，其特征在于，所述占位元素为Ni、Mn或其组合，所述岩盐相诱导剂仅为有机酸、无机酸或其组合。
  15. 根据权利要求10所述的正极活性材料的制备方法，其特征在于，所述类岩盐相诱导剂包括MgO、ZnO、Fe 2O 3、CoO、TiO、Cr 2O 3、Y 2O 3、Sc 2O 3、RuO 2、CuO、MoO 3、GeO 2、WO 3、ZrO 2、CaO、Ta2O5、Al 2O 3、Nb 2O、Nb 2O 5、B 2O 3、SiO 2、Al(OH) 3、H 3BO 3、NaAlO 2、Na 2SiO 3中的一种或多种。
  16. 根据权利要求10所述的正极活性材料的制备方法，其特征在于，所述掺杂混合物的烧结过程为：以0.5℃/min～10℃/min的升温速率升温至600℃～1200℃，然后经过0.5小时～20小时的烧结，随后以0.5℃/min～10℃/min的降温速率降至室温。
  17. 根据权利要求9所述的正极活性材料的制备方法，其特征在于，所述无机化合物前驱体选自氧化物、有机物、氟化物、磷化物、硼化物中的任意一种或多种。
  18. 一种锂离子二次电池的正极，其特征在于，包括正极集流体和位于所述正极集流 体上的正极活性材料层，所述正极活性材料层包括如权利要求1～8任一项所述的正极活性材料。
  19. 一种锂离子二次电池，其特征在于，包括：
    如权利要求18所述的正极；
    负极，其包括负极集流体和位于所述负极集流体上的负极活性材料层；
    隔膜和电解液。
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