WO2023036102A1 - 正极材料及其制备方法、正极片和电池 - Google Patents

正极材料及其制备方法、正极片和电池 Download PDF

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WO2023036102A1
WO2023036102A1 PCT/CN2022/117165 CN2022117165W WO2023036102A1 WO 2023036102 A1 WO2023036102 A1 WO 2023036102A1 CN 2022117165 W CN2022117165 W CN 2022117165W WO 2023036102 A1 WO2023036102 A1 WO 2023036102A1
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positive electrode
cobalt
lithium
electrode material
compound
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PCT/CN2022/117165
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English (en)
French (fr)
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黄友元
张弘旭
罗亮
严武渭
杨顺毅
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深圳市贝特瑞纳米科技有限公司
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Priority to EP22866565.9A priority Critical patent/EP4280299A1/en
Priority to US18/283,848 priority patent/US20240162421A1/en
Publication of WO2023036102A1 publication Critical patent/WO2023036102A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C01P2002/54—Solid solutions containing elements as dopants one element only
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • 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
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C01P2004/84—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases one phase coated with the other
    • C01P2004/86—Thin layer coatings, i.e. the coating thickness being less than 0.1 time the particle radius
    • 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
    • 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 disclosure relates to the technical field of positive electrode materials, in particular to a positive electrode material, a preparation method thereof, a positive electrode sheet and a battery.
  • lithium-ion batteries have been widely used in many fields such as automobiles and mobile devices due to their high voltage, high energy density and long life, and the cathode material directly determines the main performance of lithium-ion batteries.
  • high-nickel materials have become one of the most promising cathode materials for lithium-ion batteries.
  • the present disclosure provides a positive electrode material, including lithium-nickel composite oxide particles, the outer surface of the lithium-nickel composite oxide particles is covered with a lithium cobalt oxide coating layer, and the lithium-nickel composite oxide particles are distributed inside Cobalt element; the general formula of the lithium-nickel composite oxide is Li a Ni 1-xy Co x M y O 2 ;
  • said M includes at least one of group 2 elements, group 13 elements and transition metal elements, and does not include nickel and cobalt.
  • the molar content of the cobalt element decreases gradually from the outside to the center of the lithium-nickel composite oxide particles.
  • the molar content reduction rate of cobalt element is 0.025mol%/ ⁇ m-0.3mol%/ ⁇ m.
  • the lithium-nickel composite oxide particles are distributed with divalent cobalt and trivalent cobalt, the divalent cobalt is distributed inside the lithium-nickel composite oxide particles, and the trivalent cobalt is distributed in the lithium-nickel composite oxide particles.
  • the surface of nickel composite oxide particles are distributed with divalent cobalt and trivalent cobalt, the divalent cobalt is distributed inside the lithium-nickel composite oxide particles, and the trivalent cobalt is distributed in the lithium-nickel composite oxide particles.
  • the molar content of nickel is >94%.
  • the average particle diameter of the lithium nickel composite oxide particles is 3 ⁇ m-17 ⁇ m.
  • the thickness of the lithium cobaltate coating layer is 20nm-200nm.
  • M includes at least one of Mg, Ca, Sr, Ba, B, Al, Ti, Zr, V, Nb, Ta, Y, Mo, W, La, Ce and Gd.
  • the preparation method of the cathode material provided by the present disclosure includes the following steps:
  • the cobalt compound includes a divalent cobalt compound and a trivalent cobalt compound
  • M in the M compound includes at least one of group 2 elements, group 13 elements and transition metal elements, and does not include nickel and cobalt .
  • the M compound includes at least one of M oxides, M hydroxides and M phosphates.
  • the molar content of the cobalt compound in the nickel hydroxide and the cobalt compound mixture is 0.5%-5%.
  • the molar content of the trivalent cobalt compound in the cobalt compound is 50%-85%.
  • the lithium compound includes at least one of lithium hydroxide or lithium carbonate.
  • the cobalt compound includes at least one of cobalt hydroxide, cobalt oxyhydroxide, cobalt monoxide and cobalt trioxide.
  • the lithium compound, the cobalt compound and the optional M compound are coated on the surface of the nickel hydroxide by solid phase mixing.
  • the solid-phase mixing method includes mechanical mixing.
  • the molar content ratio of the sum of the molar contents of the nickel hydroxide, cobalt compound and M compound to the lithium compound is 1:0.95-1.1.
  • the nickel hydroxide has an average particle size of 3 ⁇ m-17 ⁇ m.
  • the nickel hydroxide is spherical.
  • the aerobic condition includes an aerobic atmosphere, and the oxygen content in the aerobic atmosphere is ⁇ 98%.
  • the sintering temperature is 600°C-750°C, and the time is 8h-20h.
  • the preparation method of the positive electrode material further includes the steps of washing, drying and secondary sintering performed in sequence after sintering.
  • the temperature of the secondary sintering is 250°C-700°C, and the time is 5h-15h.
  • the secondary sintering is performed in an oxygen atmosphere.
  • the oxygen content of the aerobic atmosphere is ⁇ 90%.
  • M is selected from at least one of Mg, Ca, Sr, Ba, B, Al, Ti, Zr, V, Nb, Ta, Y, Mo, W, La, Ce and Gd.
  • the present disclosure provides a positive electrode sheet, including the positive electrode material prepared by any one of the methods described above.
  • the present disclosure also provides a lithium ion battery, including the positive electrode sheet.
  • Fig. 1 is the flow chart of the preparation process of positive electrode material provided by the present disclosure
  • Figure 2 is a schematic structural view of the cathode material provided in some embodiments of the present disclosure.
  • Example 3 is an SEM image of the positive electrode material provided by Example 1 of the present disclosure.
  • Fig. 4 is the XPS diagram of the cathode material provided by Example 1 of the present disclosure.
  • Example 5 is an EDS scan diagram of the positive electrode material provided by Example 1 of the present disclosure.
  • Fig. 7 is a capacity comparison chart of 2032-type button batteries prepared by using the positive electrode materials provided in Example 1 and Example 8 of the present disclosure, respectively;
  • FIG. 8 is a comparison diagram of impedances of 2032-type button batteries prepared by using the positive electrode materials provided in Example 1 and Example 8 of the present disclosure, respectively.
  • the particles of the positive electrode material are secondary particles, and the secondary particles are spherical particles formed by the accumulation of primary particles.
  • the electrode material with high cycle performance is often obtained by coating the positive electrode material, but this coating is generally It can only cover the surface of spherical secondary particles, but not the surface of the inner primary particles.
  • some researchers use the method of mixing and sintering precursors and lithium compounds to obtain LiNiMO 2 compounds, and then mix and coat them in liquid phase or solid phase to obtain Co-coated high-nickel cathode materials, in which the Co coating layer is mainly concentrated in Near the surface layer of lithium nickel compound, no effective coating layer is formed at the grain boundary inside the material, and it is easy to form a MO oxide coating layer on the surface of the material, which increases the material resistance, reduces the material magnification, and affects the performance and performance of the material after long cycles. Growth rate of internal resistance.
  • an embodiment of the present disclosure provides a positive electrode material, including lithium-nickel composite oxide particles, and the outer surface of the lithium-nickel composite oxide particles is coated with lithium cobalt oxide. coating, cobalt elements are distributed inside the lithium-nickel composite oxide particles; the general formula of the lithium-nickel composite oxide is Li a Ni 1-xy Co x M y O 2 ;
  • said M includes at least one of Group 2 (ie Group IIA) elements, Group 13 (ie Group IIIA) elements and transition metal elements One, excluding nickel and cobalt.
  • a is for example 0.95-1.10, 0.97-1.10, 0.99-1.10 or 0.95-1.07, such as 0.95, 0.98, 1, 1.02, 1.05, 1.08 or 1.1;
  • x is for example 0.01-0.05, 0- 0.04 or 0.01-0.04, such as 0, 0.01, 0.02, 0.03, 0.04 or 0.05;
  • y is for example 0-0.005, 0.001-0.005, 0.001-0.004 or 0-0.003, such as 0, 0.001, 0.002, 0.003, 0.004 or 0.005 .
  • M is selected from Mg, Ca, Sr, Ba, B, Al, Ga, In, Ti, V, Nb, Ta, Y, W, La, Ce, Gd, Mn, Fe, Cu, At least one of Zn, Mo, Ce and Zr.
  • the positive electrode material provided by the present disclosure is coated with lithium cobalt oxide on the surface of the lithium nickel composite oxide particles, thereby effectively inhibiting the side reaction between the lithium nickel composite oxide particles and the electrolyte, improving the lithium ion conductivity, and passing the lithium nickel
  • the cobalt element is distributed inside the composite oxide particles, and lithium cobaltate or M lithium cobaltate is formed at the grain boundary to stabilize the crystal structure of the lithium-nickel composite oxide, thereby effectively improving the rate performance and cycle stability of the positive electrode material.
  • the molar content of cobalt element gradually decreases (or the mass content of cobalt element gradually decreases), so as to facilitate the lithium-nickel composite oxidation
  • Lithium nickel cobalt oxide or lithium nickel cobalt oxide is formed near the outer layer of the particle, effectively stabilizing the crystal structure inside the lithium nickel composite oxide, inhibiting the mixing of lithium and nickel, thereby effectively improving the structural stability of the positive electrode material.
  • the molar content of the cobalt element decreases gradually, and the reduction rate is 0.025mol%/ ⁇ m-0.300mol%/ ⁇ m.
  • the calculation of the reduction rate is based on the molar content (expressed as M0) of the cobalt element on the outer surface of the lithium nickel composite oxide particle, and an arbitrary point is selected in the direction extending from the outside to the center. , Determine the molar content of cobalt element at this point (expressed as M1), the formula for calculating the reduction rate is (M0-M1)/M0 ⁇ 100%.
  • the disclosure controls the distribution of Co in the material, and the outer Ni content of the material is lower, which improves the stability; the inner Ni content is higher, and the material capacity is improved; the above-mentioned concentration gradient of the disclosure will be more conducive to stabilizing the crystal structure inside the lithium-nickel composite oxide, To improve the structural stability of the positive electrode material, if the concentration gradient is too low, the above effects will not be achieved. If the concentration gradient is too large, the material lattice will not match, resulting in stress accumulation, and the material will easily crack.
  • the reduction rate of the molar content of cobalt is, for example, 0.03mol%/ ⁇ m-0.3mol%/ ⁇ m, 0.03mol%/ ⁇ m-0.25mol%/ ⁇ m, 0.03mol%/ ⁇ m-0.2mol%/ ⁇ m or 0.1mol%/ ⁇ m-0.3mol%/ ⁇ m, such as 0.025mol%/ ⁇ m, 0.035mol%/ ⁇ m, 0.045mol%/ ⁇ m 0.055mol%/ ⁇ m, 0.08mol%/ ⁇ m, 0.1mol%/ ⁇ m, 0.15 mol%/ ⁇ m, 0.2 mol%/ ⁇ m, 0.25 mol%/ ⁇ m or 0.30 mol%/ ⁇ m.
  • the molar content of nickel is >94%, so that the positive electrode material provided by the present disclosure has a higher capacity advantage, and the present disclosure adjusts the Ni content by controlling the content of Co , is operable.
  • the above-mentioned molar content of nickel refers to the ratio of the molar content of nickel element in the positive electrode material based on the sum of the amounts of nickel, lithium, cobalt and optional M element being 100%.
  • the molar content of nickel is, for example, 94.1%-96%, 94.5%-96% or 94.1%-95.5%, such as 94.1%, 94.2%, 94.5%, 94.8%, 95%, 95.5%, or 96%.
  • the average particle size of the lithium-nickel composite oxide particles is 3 ⁇ m-17 ⁇ m, so as to facilitate uniform distribution in the positive electrode sheet.
  • the average particle size of the lithium-nickel composite oxide particles is, for example, 5 ⁇ m-17 ⁇ m, 3 ⁇ m-15 ⁇ m or 4 ⁇ m-16 ⁇ m, such as 3 ⁇ m, 5 ⁇ m, 7 ⁇ m, 9 ⁇ m, 11 ⁇ m, 13 ⁇ m, 15 ⁇ m or 17 ⁇ m.
  • the thickness of the lithium cobalt oxide coating layer on the surface of the lithium-nickel composite oxide particles is 20nm-200nm, so as to reduce the material impedance and ensure the rate performance and cycle performance of the positive electrode material while effectively suppressing lithium.
  • the side reaction between the nickel composite oxide and the electrolyte improves the lithium ion conductivity of the positive electrode material.
  • the thickness of the lithium cobalt oxide coating layer is, for example, 30nm-200nm, 30nm-190nm or 50nm-150nm, such as 20nm, 25nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 150nm, 180nm or 200nm.
  • One embodiment of the present disclosure provides a method for preparing a positive electrode material, comprising the following steps:
  • the cobalt compound includes divalent cobalt compound and trivalent cobalt compound.
  • One embodiment of the present disclosure provides a method for preparing a positive electrode material, comprising the following steps (as shown in Figure 1):
  • the M includes at least one of group 2 elements, group 13 elements and transition metal elements, and does not include nickel and cobalt;
  • the cobalt compounds include divalent cobalt compounds and trivalent cobalt compounds.
  • M includes at least one of Group 2 elements, Group 13 elements, and transition metal elements, and excludes nickel and cobalt.
  • M can be selected from at least one of, for example, Mg, Ca, Sr, Ba, B, Al, Ti, Zr, V, Nb, Ta, Y, Mo, W, La, Ce and Gd .
  • nickel hydroxide is coated to form a lithium nickel M ternary material to further inhibit the phase transition of the material and at the same time inhibit the contraction of the unit cell, provide a stable lithium ion transmission channel, and improve the cycle stability of the material. And thermal stability, stable material structure.
  • the M compound includes but not limited to one or a mixture of M oxide, M hydroxide or M phosphate.
  • the cobalt compound includes divalent cobalt compounds and trivalent cobalt compounds.
  • the divalent cobalt compound and the trivalent cobalt compound are used to coat nickel hydroxide together.
  • the divalent cobalt has higher reactivity and is easier to diffuse into the nickel hydroxide during sintering to form lithium nickel cobalt oxide or lithium nickel cobalt oxide.
  • Solid solution oxide stabilizes the crystal structure inside the lithium-nickel composite oxide particles and inhibits the mixing of lithium and nickel, while trivalent cobalt tends to coat the surface of lithium nickelate particles to form a lithium cobaltate coating layer, which inhibits the side effects of the material. Reaction, improve the lithium ion conductivity of the positive electrode material.
  • the molar content of the trivalent cobalt compound in the cobalt compound is 50%-85%.
  • the molar content of the trivalent cobalt compound will affect the thickness of the coating layer and the stability of the crystal structure inside the lithium-nickel composite oxide particles.
  • a coating layer with a moderate thickness can be formed on the outer surface of the lithium-nickel composite oxide particles to improve the lithium ion conductivity, Reduce the material impedance; and ensure that a certain amount of Co doping enters the interior of the lithium-nickel composite oxide particles, thereby effectively promoting the formation of sufficient lithium nickel cobalt oxide or lithium nickel cobalt oxide solid solution oxides, thereby effectively inhibiting the mixing of lithium and nickel.
  • Improve the cycle stability of cathode materials improve the cycle stability of cathode materials.
  • the molar content of the trivalent cobalt compound was too low, and during the sintering process, more Co elements were doped into the lithium nickelate particles, resulting in a reduction in the coating effect of the material; the molar content of the trivalent cobalt compound If it is too high, the Co element cannot enter the interior of the lithium-nickel composite oxide particles insufficiently, and cannot form enough lithium nickel cobalt oxide or lithium nickel cobalt oxide solid solution oxide, which cannot effectively inhibit the mixing of lithium and nickel, and will also cause the coating layer to be too thick. , increasing the impedance of the material and affecting the rate capability of the material.
  • Co element is coated on the surface of lithium-nickel composite oxide particles to form a lithium cobalt oxide coating layer, which improves the lithium ion conductivity of the positive electrode material, forms a high lithium ion conductivity network, improves the rate performance of the material, and inhibits the contact between the material and the lithium ion. Electrolyte side reactions.
  • the molar content of the trivalent cobalt compound in the cobalt compound is, for example, 55%-85%, 50%-80% or 69%-85%, such as 50%, 60%, 65%, 70%, 75%, 80%, or 85%.
  • divalent cobalt compounds include but are not limited to at least one of divalent cobalt oxides, divalent cobalt hydroxides, and divalent oxyhydroxides; trivalent cobalt includes but not limited to trivalent cobalt At least one of cobalt oxide, trivalent cobalt hydroxide and trivalent cobalt oxyhydroxide.
  • the preparation method of the positive electrode material provided by the present disclosure is simple, stable and safe, and is easy for large-scale industrial production.
  • the cobalt compound, the lithium compound and the optional M compound are coated on the surface of nickel hydroxide and sintered, and the cobalt element is distributed on the surface of the lithium-nickel composite oxide particles and in a gradient distribution at the same time, and the cobalt compound
  • the dosage will affect the thickness of the coating layer and the stability of the crystal structure of lithium-nickel composite oxide particles.
  • the molar content of the cobalt compound in the mixture of nickel hydroxide and the cobalt compound is 0.5%-5%.
  • the molar content of the cobalt compound in the nickel hydroxide and the cobalt compound refers to the sum of the amount of the cobalt element in the cobalt compound and the sum of the amount of the nickel element in the nickel hydroxide and the cobalt element in the cobalt compound Ratio, abbreviated as Co/(Co+Ni).
  • Co/(Co+Ni) within the above range can not only form a coating layer with a moderate thickness on the surface of lithium nickelate particles, effectively ensure the ionic conductivity of the material, reduce the impedance of the material, but also ensure the nickel content. at a higher level, thereby increasing the capacity of the material.
  • the limited content of the Co element in the present disclosure can achieve the effect of simultaneously covering the surface of the lithium nickelate particles and doping inside the lithium nickelate particles to stabilize the crystal structure of the lithium nickelate particles.
  • Co/(Co+Ni) When Co/(Co+Ni) is higher than 5%, it will cause the coating layer on the surface of lithium nickelate particles to be too thick, reduce the electronic conductivity of the material, increase the impedance of the material, and also reduce the nickel content, resulting in a material capacity drops. And when Co/(Co+Ni) is lower than 0.5%, Co element content is too low, can't reach at the surface coating of lithium nickelate particle at the same time and doping stable lithium nickelate particle crystal structure in the interior of lithium nickelate particle Effect.
  • Co/(Co+Ni) is for example 1%-5%, 0.5%-4.5%, 1%-4.5% or 1%-4%, such as 0.5%, 0.75%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 4.5%, or 5%.
  • the Ni 2+/4+ redox pairs increase, which facilitates more Li + extraction, so the material capacity has a significant advantage.
  • lithium compounds include, but are not limited to, lithium hydroxide, lithium carbonate, and mixtures of lithium hydroxide and lithium carbonate.
  • spherical nickel hydroxide with an average particle size of 3 ⁇ m-17 ⁇ m is selected as the raw material, which is more conducive to uniformly covering the cobalt compound, lithium hydroxide and optional M compound through solid phase mixing. Coated on the surface of spherical nickel hydroxide.
  • the average particle size of the spherical sodium nickel hydroxide is, for example, 5 ⁇ m-17 ⁇ m, 3 ⁇ m-15 ⁇ m or 6 ⁇ m-17 ⁇ m, such as 3 ⁇ m, 5 ⁇ m, 8 ⁇ m, 10 ⁇ m, 12 ⁇ m, 15 ⁇ m or 17 ⁇ m.
  • step S100 the lithium compound, the cobalt compound and the optional M compound are coated on the surface of nickel hydroxide by solid phase mixing, the process is simpler and the operation is more convenient , which is more suitable for large-scale production and reduces production costs.
  • the solid-phase mixing method includes mechanical mixing, and the mechanical mixing method includes but is not limited to mixing with a high-speed mixer.
  • the aerobic condition includes an oxygen atmosphere, and the oxygen content in the aerobic atmosphere is ⁇ 98%, so as to facilitate the participation of oxygen in the reaction during the sintering process.
  • the sintering temperature is 600°C-750°C, and the time is 8h-20h, so as to facilitate the preparation of cobalt element while doping inside the lithium-nickel composite oxide particles and coating the lithium-nickel composite oxide particles.
  • the sintering temperature is, for example, 600°C-700°C, 650°C-750°C or 680°C-740°C, such as 600°C, 620°C, 650°C, 680°C, 700°C, 720°C or 750°C °C
  • the sintering time is, for example, 10h-20h, 8h-18h or 12h-20h, such as 8h, 9h, 10h, 12h, 15h, 18h or 20h.
  • the molar ratio of the sum of the nickel hydroxide, the cobalt compound and the optional M compound to the lithium compound is 1:0.95-1.1.
  • the sum of the amount of substance of the above-mentioned nickel hydroxide, cobalt compound and optional M compound refers to nickel element in nickel hydroxide, cobalt element in cobalt compound (comprising divalent cobalt and trivalent cobalt) and optional M compound
  • the sum of the amount of matter of the M element referred to as the sum of the amount of matter of Ni, Co and optional M for short.
  • the amount of substance of the above-mentioned lithium compound refers to the amount of substance of lithium element in the lithium compound, referred to as the amount of substance of Li for short.
  • the prepared positive electrode material has a higher nickel content and a more stable structure.
  • the molar ratio of the sum of the amounts of Ni, Co and optional M to Li is, for example, 1:0.98-1.1, 1:1-1.1 or 1:0.95-1.09, such as 1:0.95, 1:0.98, 1:1, 1:1.02, 1:1.05, 1:1.08, or 1:1.1.
  • the nickel hydroxide is spherical and has an average particle size of 3 ⁇ m-17 ⁇ m.
  • the preparation method of the positive electrode material further includes the steps of washing, drying and secondary sintering in sequence after sintering, wherein the temperature of the secondary sintering is 250°C-700°C, and the time is 5h- 15h.
  • the lithium element and impurities remaining on the surface of the positive electrode material obtained after sintering are removed by washing to avoid affecting the high temperature safety of the material due to the lithium element remaining on the surface of the material, and the structural stability of the material is further improved by secondary sintering.
  • the sintered material is washed with distilled water, deionized water, or purified water.
  • the secondary sintering temperature is, for example, 260°C-700°C, 300°C-700°C, 250°C-600°C or 300°C-600°C, such as 250°C, 300°C, 350°C, 450°C , 500°C, 550°C, 600°C, 650°C or 700°C
  • the time for secondary sintering is, for example, 5h-12h, 6h-15h or 6h-12h, such as 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h.
  • the secondary sintering is also performed under aerobic conditions, and the aerobic conditions are such that the oxygen content is ⁇ 90%.
  • FIG. 2 a schematic structural view of the positive electrode material provided by the present disclosure is shown in Figure 2. It can be seen from Figure 2 that the positive electrode material provided by the present disclosure has a core-shell structure, and the inner core is Li a Ni 1-xy Co x M y O 2 , the shell is lithium cobaltate.
  • An embodiment of the present disclosure provides a positive electrode material prepared by the method described above.
  • An embodiment of the present disclosure provides a positive electrode sheet or a battery comprising the positive electrode material provided above or the positive electrode material obtained by the preparation method provided above.
  • the positive electrode material provided by the present disclosure is coated with a lithium cobaltate coating layer on the outer surface of the lithium-nickel composite oxide particles, and cobalt element is distributed inside, so that it can not only stabilize the crystal structure of the lithium-nickel composite oxide, but also inhibit The side reaction between the material and the electrolyte significantly improves the rate performance and cycle stability while improving the lithium ion conductivity.
  • the cathode material provided by the disclosure has the advantages of good cycle performance and high safety performance.
  • a part of the cobalt element coated on the nickel hydroxide is obtained by coating the divalent cobalt compound, the trivalent cobalt compound, lithium hydroxide and the optional M compound on the surface of the nickel hydroxide through high-temperature sintering.
  • a uniform lithium cobaltate coating layer is formed on the surface of lithium particles, and part of the cobalt element is distributed in the lithium-nickel composite oxide particle. The change and the side reaction with the electrolyte significantly improve the rate performance and cycle stability of the material while improving the lithium ion conductivity.
  • the preparation method of the cathode material provided by the present disclosure is simple, stable and safe, and is easy for large-scale industrial production.
  • This embodiment provides a positive electrode material, which is prepared according to the following steps:
  • Ni(OH) 2 , Co(OH) 2 , CoOOH, LiOH ⁇ H 2 O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co being 1.05, where Co occupies the mole of Ni+Co 0.015 of the total amount, CoOOH accounts for 65% of the total molar amount of Co(OH) 2 and CoOOH, and Ni(OH) 2 is spherical nickel hydroxide with a particle size of 10-15 ⁇ m;
  • the dried material is subjected to secondary sintering at 600°C in an atmosphere with an oxygen content ⁇ 90%, and the sintering time is 8 hours to obtain the positive electrode material.
  • This embodiment provides a positive electrode material, which is prepared according to the following steps:
  • Ni(OH) 2 , CoO, Co 2 O 3 , LiOH ⁇ H 2 O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co being 1.05, where Co occupies the total molar amount of Ni+Co
  • the amount of 0.015, Co 2 O 3 accounts for 65% of the total molar amount of CoO and Co 2 O 3
  • Ni(OH) 2 is spherical nickel hydroxide, and the particle size is 3-10 ⁇ m;
  • the dried material is subjected to secondary sintering at 650° C. for 5 hours in an atmosphere with an oxygen content ⁇ 90%, to obtain the positive electrode material.
  • This embodiment provides a positive electrode material, which is prepared according to the following steps:
  • Ni(OH) 2 , Co(OH) 2 , CoOOH, LiOH ⁇ H 2 O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co being 1.05, where Co occupies the mole of Ni+Co
  • the total amount is 0.015, CoOOH accounts for 85% of the total molar amount of Co(OH) 2 and CoOOH, and Ni(OH) 2 is spherical nickel hydroxide with a particle size of 12-17 ⁇ m;
  • the dried material is subjected to secondary sintering at 550° C. for 12 hours in an atmosphere with an oxygen content ⁇ 90%, to obtain the positive electrode material.
  • This embodiment provides a positive electrode material, which is prepared according to the following steps:
  • the dried material is subjected to secondary sintering at 600° C. for 10 hours in an atmosphere with an oxygen content ⁇ 90%, to obtain the positive electrode material.
  • This embodiment provides a positive electrode material, which is prepared according to the following steps:
  • Ni(OH) 2 , Co(OH) 2 , CoOOH and LiOH ⁇ H 2 O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co being 1.05, wherein Co occupies the mole of Ni+Co
  • the total amount is 0.035, CoOOH accounts for 65% of the total molar amount of Co(OH) 2 and CoOOH, and Ni(OH) 2 is spherical nickel hydroxide with a particle size of 10-15 ⁇ m;
  • the dried material is subjected to secondary sintering at 600° C. for 10 hours in an atmosphere with an oxygen content ⁇ 90%, to obtain the positive electrode material.
  • This embodiment provides a positive electrode material, which is prepared according to the following steps:
  • Ni(OH) 2 , Co(OH) 2 , CoOOH, Sr(OH) 2 and LiOH ⁇ H 2 O according to the ratio of the molar weight of Li to the sum of the molar weights of Ni and Co being 1.05, where Co Occupies 0.035 of the total molar amount of Ni+Co, CoOOH accounts for 50% of the total molar amount of Co(OH) 2 and CoOOH, and Ni(OH) 2 is spherical nickel hydroxide with a particle size of 10-15 ⁇ m;
  • the dried material is subjected to secondary sintering at 600° C. for 10 hours in an atmosphere with an oxygen content ⁇ 90%, to obtain the positive electrode material.
  • This embodiment provides a positive electrode material, which is prepared according to the following steps:
  • Ni(OH) 2 , Co(OH) 2 , CoOOH, LiOH ⁇ H 2 O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co is 1.1, where Co occupies the mole of Ni+Co 0.015 of the total amount, CoOOH accounts for 65% of the total molar amount of Co(OH) 2 and CoOOH, and Ni(OH) 2 is spherical nickel hydroxide with a particle size of 10-15 ⁇ m;
  • the dried material is subjected to secondary sintering at 600° C. for 10 hours in an atmosphere with an oxygen content ⁇ 90%, to obtain the positive electrode material.
  • This embodiment provides a positive electrode material, the difference between its preparation method and embodiment 1 is that in step (1), Co accounts for 10% of the total molar amount of Ni+Co, and the rest of the steps are the same as in embodiment 1. This will not be repeated here.
  • This embodiment provides a positive electrode material, which is prepared according to the following steps:
  • Ni(OH) 2 , Co(OH) 2 , CoOOH, LiOH ⁇ H 2 O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co being 0.95, wherein Co occupies the mole of Ni+Co 0.015 of the total amount, CoOOH accounts for 65% of the total molar amount of Co(OH) 2 and CoOOH, and Ni(OH) 2 is spherical nickel hydroxide with a particle size of 10-15 ⁇ m;
  • This embodiment provides a positive electrode material, which is prepared according to the following steps:
  • Ni(OH) 2 , Co(OH) 2 , CoOOH, LiOH ⁇ H 2 O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co being 1.0, wherein Co occupies the mole of Ni+Co 0.015 of the total amount, CoOOH accounts for 65% of the total molar amount of Co(OH) 2 and CoOOH, and Ni(OH) 2 is spherical nickel hydroxide with a particle size of 10-15 ⁇ m;
  • This comparative example provides a kind of positive electrode material, and the difference of its preparation method and embodiment 1 is, in step (1), CoOOH accounts for Co(OH) 10 % of the total molar amount of CoOOH, all the other steps are all the same as embodiment 1 Same, no more details here.
  • This comparative example provides a kind of cathode material, and the difference of its preparation method and embodiment 1 is, in step (1), CoOOH accounts for Co(OH) 95 % of the total molar amount of CoOOH, all the other steps are all the same as embodiment 1 Same, no more details here.
  • This comparative example provides a positive electrode material, the difference between its preparation method and Example 1 is that in step (1), the Co compound in the raw material is Co(OH) 2 , no trivalent cobalt compound is used in the raw material, and the rest The steps are the same as those in Embodiment 1, and will not be repeated here.
  • This comparative example provides a kind of positive electrode material, and its preparation method differs from Example 1 in that, in step (1), the Co compound in the raw material is CoOOH, and divalent cobalt compound is not used in the raw material, and the remaining steps are all the same as those in the implementation Example 1 is the same and will not be repeated here.
  • This comparative example provides a positive electrode material.
  • the difference between its preparation method and Example 1 is that in step (1), no cobalt compound is used in the raw material, and the ratio of the molar weight of Li to the sum of the molar weight of Ni is 1.05. Ni(OH) 2 and LiOH ⁇ H 2 O, and other steps are the same as in Example 1, and will not be repeated here.
  • the positive electrode materials provided in Examples 1-10 and Comparative Examples 1-5 were respectively tested by Hitachi S4800 scanning electron microscope (SEM) for surface morphology, and the particle size and the thickness of the surface coating layer of the positive electrode material were measured. The results are shown in Table 1 below. Show.
  • Example 1 10.2 27
  • Example 2 4.5 52
  • Example 3 13.5
  • Example 4 10.3 36
  • Example 5 10.5 67
  • Example 6 10.2 58
  • Example 7 10.7
  • Example 8 10.4 143
  • Example 9 10.6 29
  • Example 10 10.5 31
  • Comparative example 1 10.4 9 Comparative example 2 10.2 42 Comparative example 3 10.5 11 Comparative example 4 10.8 49 Comparative example 5 10.3 /
  • Figure 3 is an SEM image of the positive electrode material provided in Example 1, as can be seen from Figure 3, the particle size of the positive electrode material provided in Example 1 is 3-17 ⁇ m, and the thickness of the coating layer is about 27 nm .
  • the cathode materials provided by Examples 1-10 and Comparative Examples 1-5 are respectively subjected to X-ray photoelectron spectroscopy (XPS) testing, as can be seen from the XPS spectrogram, the positive electrode materials provided by Examples 1-10 and Comparative Examples 1-5
  • the outer coating layer of the positive electrode material is lithium cobalt oxide.
  • Figure 4 is the XPS diagram of the positive electrode material provided in Example 1. It can be seen from Figure 4 that the 2p3/2 peak of Co appears at the position where the binding energy is 780eV, and at the same time, at the position where the binding energy is 529eV position, the 1s peak of Co-O appears. Therefore, it shows that there is a Li-Co-O compound on the surface of the material, and the coating layer on the surface of the positive electrode material provided in Example 1 is mainly composed of lithium cobaltate.
  • the positive electrode materials provided in Examples 1-10 and Comparative Examples 1-5 were tested by X-ray Energy Scattering Spectroscopy (EDS), and the results are shown in Table 2. Among them, starting from the lithium-nickel composite oxide, extending from the outside to the inside, the Co content at 0 ⁇ m, 1 ⁇ m, 2 ⁇ m, 4 ⁇ m and 8 ⁇ m inside the lithium-nickel composite was tested respectively. In view of the fact that the particle size of the lithium-nickel composite oxide inside some positive electrode materials is less than 16 ⁇ m, this test selects the lithium-nickel composite oxide with a particle size of 16 ⁇ m or more for the internal Co content test.
  • EDS X-ray Energy Scattering Spectroscopy
  • Figure 5 is the EDS diagram of the positive electrode material provided by Example 1. It can be seen from Figure 5 that the Co element is distributed with cobalt elements inside the positive electrode material, and the content of cobalt elements gradually decreases from the outside to the inside. Similarly, Examples 2-10 also have similar technical effects, and the content of the cobalt element distributed inside the positive electrode material also decreases gradually from the outside to the inside.
  • FIG. 6 is the EDS diagram of the positive electrode material provided by Comparative Example 1.
  • the positive electrode material provided by Comparative Example 1 has cobalt elements distributed inside, and the content of cobalt elements remains constant from the outside to the inside. Stablize.
  • the content of the cobalt element distributed inside the positive electrode material remains basically stable from the outside to the inside, or in the innermost layer, the content of the cobalt element suddenly decreases.
  • the cathode materials provided by Examples 1-10 and Comparative Examples 1-5 are respectively used as cathode materials to prepare 2032 type button batteries, and the specific preparation method is as follows: the cathode materials, conductive carbon SP, PVDF (polyvinylidene fluoride) are prepared according to 96: Add NMP (N-methylpyrrolidone) at a mass ratio of 2:2, stir to obtain a slurry, coat the slurry on an aluminum foil and dry it as a positive electrode sheet, and use a lithium sheet as a negative electrode sheet to prepare a 2032 button-type Battery.
  • NMP N-methylpyrrolidone
  • the positive electrode materials provided in Examples 1-10 and Comparative Examples 1-5 were tested for Ni content.
  • the test procedure was as follows: Weigh 1 g of positive electrode materials, digest them with nitric acid, dilute them to 100 mL, then dilute them 200 times, and pass the PE8000S type reaction
  • the coupled plasma instrument was used to test the element content, and the results are shown in Table 1.
  • the positive electrode materials provided by Examples 1-10 and Comparative Examples 1-5 were used as positive electrode materials to prepare 2032-type button batteries, and then the above-mentioned 2032-type button batteries were respectively subjected to 0.1C first-week gram capacity, rate and 50-cycle cycle retention
  • the test results are shown in Table 3 below.
  • test method for the first week capacity of 0.1C is: charge and discharge the 2032-type button battery at 25°C, between 3.0V and 4.3V at 0.1C/0.1C, and test the capacity in the first week;
  • the test method of magnification is:
  • test method for the 50-week cycle retention rate is: charge and discharge the 2032-type button battery at 25°C, 3.0V to 4.3V at 0.5C/1C, and test the cycle performance.
  • the test method is: 2032 type button cell is tested at 25 °C, between 3.0V to 4.3V after the first week, 0.1C charges to 50% SOC, removes The battery is tested by IviumStat electrochemical workstation at -5°C, the test frequency is 0.03-105Hz, and the test amplitude is 5mV.
  • Example 8 From the comparison of the data of Examples 1-7 and 9-10 with Example 8, it can be seen that when the molar content of the cobalt compound in the nickel hydroxide and the cobalt compound mixture is 0.5-5%, the prepared positive electrode Material impedance Ni content is higher, the impedance is smaller, and the capacity is higher.
  • Figure 7 is a capacity comparison chart of 2032-type button cells prepared using the positive electrode materials provided in Example 1 and Example 8 of the present disclosure as positive electrode materials;
  • the positive electrode material provided by the disclosure significantly improves the rate performance and cycle stability while improving the lithium ion conductivity, and has the advantages of good cycle performance and high safety performance.
  • the preparation method of the positive electrode material provided by the present disclosure realizes the doping of cobalt element inside the material and the coating of the surface, effectively inhibits the phase transition of the material and the side reaction with the electrolyte, and significantly improves the lithium ion conductivity while improving the lithium ion conductivity.
  • the rate performance and cycle stability of the material are improved.
  • the method is simple, stable, safe, and easy for large-scale industrial production, and has broad application prospects.

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Abstract

本公开提供了一种正极材料及其制备方法、正极片和电池，涉及正极材料技术领域，所述制备方法包括以下步骤：将锂化合物、二价钴化合物、三价钴化合物和任选的M化合物包覆于球形氢氧化镍的表面，然后将包覆后的材料在有氧条件下进行一次烧结；其中，三价钴化合物在所述钴化合物中的摩尔含量为50％-85％。该制备方法采用二价钴化合物和三价钴化合物共同包覆球形氢氧化镍后烧结的方案，不仅能在镍酸锂颗粒的表面形成均匀的钴酸锂包覆层，而且能够在镍酸锂颗粒的内部形成钴掺杂，在保证材料超高镍含量的同时，能够有效抑制材料相变和与电解液的副反应，显著提升材料的倍率性能、循环稳定性和容量优势。

Description

正极材料及其制备方法、正极片和电池
相关申请的交叉引用
本公开要求于2021年9月9日提交中国专利局的申请号为“CN202111052713.9”名称为“正极材料及其制备方法、正极片和电池”的中国专利申请的优先权，其全部内容通过引用结合在本公开中。
技术领域
本公开涉及正极材料技术领域，尤其是涉及一种正极材料及其制备方法、正极片和电池。
背景技术
近年来，锂离子电池由于具有高电压、高能量密度以及长寿命而在汽车和移动设备等多个领域得到广泛应用，而正极材料直接决定了锂离子电池的主要性能。随着市场对于电池能量密度的要求越来越高，高镍材料已经成为最具有发展前景的锂离子电池正极材料之一。
但是高镍材料往往存在循环性差和安全性低的缺点，因此，开发一种长循环、高安全的高镍正极材料成为本领域技术人员亟需解决的任务。
发明内容
本公开提供了一种正极材料，包括锂镍复合氧化物颗粒，所述锂镍复合氧化物颗粒的外表面包覆有钴酸锂包覆层，所述锂镍复合氧化物颗粒的内部分布有钴元素；所述锂镍复合氧化物通式为Li aNi 1-x-yCo xM yO 2；
其中，0.95≤a≤1.10，0<x≤0.05，0≤y≤0.005，所述M包括第2族元素、第13族元素以及过渡金属元素中的至少一种，且不包括镍和钴。
可选地，所述锂镍复合氧化物颗粒的内部，从外至中心，钴元素的摩尔含量逐渐降低。
可选地，以所述锂镍复合氧化物颗粒的外表面为起点，从外至中心延伸，钴元素的摩尔含量降低率为0.025mol％/μm-0.3mol％/μm。
可选地，所述锂镍复合氧化物颗粒分布有二价钴和三价钴，所述二价钴分布在所述锂镍复合氧化物颗粒的内部，所述三价钴分布在所述锂镍复合氧化物颗粒的表面。
可选地，所述正极材料中，镍的摩尔含量＞94％。
可选地，所述锂镍复合氧化物颗粒的平均粒径为3μm-17μm。
可选地，所述钴酸锂包覆层的厚度为20nm-200nm。
可选地，M包括Mg、Ca、Sr、Ba、B、Al、Ti、Zr、V、Nb、Ta、Y、Mo、W、La、Ce和Gd中的至少一种。
本公开提供的正极材料的制备方法，包括以下步骤：
将含有锂化合物、钴化合物和M化合物的复合物包覆于氢氧化镍的表面，以及将包覆后的材料在有氧条件下进行烧结，得到正极材料；
其中，所述钴化合物包括二价钴化合物和三价钴化合物，所述M化合物中的M包括第2族元素、第13族元素以及过渡金属元素中的至少一种，且不包括镍和钴。
可选地，所述M化合物包括M的氧化物、M的氢氧化物及M的磷酸盐中的至少一种。
可选地，所述钴化合物在所述氢氧化镍和所述钴化合物混合物中的摩尔含量为0.5％-5％。
可选地，所述三价钴化合物在所述钴化合物中的摩尔含量为50％-85％。
可选地，所述锂化合物包括氢氧化锂或碳酸锂中的至少一种。
可选地，所述钴化合物包括氢氧化钴、羟基氧化钴、一氧化钴及三氧化二钴中的至少一种。
可选地，所述锂化合物、钴化合物和任选的M化合物通过固相混合的方式包覆于氢氧化镍的表面。
可选地，所述固相混合的方式包括机械混合。
可选地，所述氢氧化镍、钴化合物以及M化合物的摩尔含量之和与所述锂化合物的摩尔含量比为1:0.95-1.1。
可选地，所述氢氧化镍的平均粒径为3μm-17μm。
可选地，所述氢氧化镍呈球形。
可选地，所述有氧条件包括有氧气氛，所述有氧气氛中氧气含量≥98％。
可选地，所述烧结的温度为600℃-750℃，时间为8h-20h。
可选地，所述正极材料的制备方法还包括在烧结后依次进行的洗涤、干燥和二次烧结步骤。
可选地，二次烧结的温度为250℃-700℃，时间为5h-15h。
可选地，二次烧结在有氧气氛中进行。
可选地，所述有氧气氛的氧含量≥90％。
可选地，M选自Mg、Ca、Sr、Ba、B、Al、Ti、Zr、V、Nb、Ta、Y、Mo、W、La、Ce和Gd中的至少一种。
本公开提供一种正极片，包括上文任一项所述的方法制备获得的正极材料。
本公开还提供一种锂离子电池，包括所述正极片。
附图说明
为了更清楚地说明本公开具体实施方式或现有技术中的技术方案，下面将对具体实施方式或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的 附图是本公开的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为本公开提供的正极材料制备工艺流程图；
图2为本公开一些实施方式中提供的正极材料的结构示意图；
图3为本公开实施例1提供的正极材料的SEM图；
图4为本公开实施例1提供的正极材料的XPS图；
图5为本公开实施例1提供的正极材料的EDS扫描图；
图6为本公开对比例1提供的正极材料的EDS扫面图；
图7为分别采用本公开实施例1和实施例8提供的正极材料制备得到的2032型扣式电池的容量对比图；
图8为分别采用本公开实施例1和实施例8提供的正极材料制备得到的2032型扣式电池的阻抗对比图。
具体实施方式
下面将结合实施方式和实施例对本公开的技术方案进行清楚、完整地描述，显然，所描述的实施方式和实施例是本公开一部分实施方式和实施例，而不是全部的实施方式和实施例。基于本公开中的实施方式和实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施方式和实施例，都属于本公开保护的范围。
众所周知，正极材料的颗粒是二次颗粒，二次颗粒是由一次颗粒堆积构成的球形颗粒，在常规技术中，往往通过包覆正极材料以获得高循环性能的电极材料，但这种包覆一般仅能包覆在球形二次颗粒的表面，而包覆不到内部的一次颗粒表面。目前一些研发人员采用前驱体与锂化合物混合烧结的方法得到LiNiMO 2化合物，再通过液相或固相方式进行混合包覆，得到Co包覆的高镍正极材料，其中Co包覆层主要集中在锂镍化合物表层附近，而材料内部晶界处并未形成有效的包覆层，且易于在材料表面形成MO氧化物包覆层，增加材料阻抗，降低材料倍率，影响材料长循环后的性能和内阻增长率。为了降低材料的阻抗，改善材料的倍率性能，本公开一实施方式提供了一种正极材料，包括锂镍复合氧化物颗粒，所述锂镍复合氧化物颗粒的外表面包覆有钴酸锂包覆层，所述锂镍复合氧化物颗粒的内部分布有钴元素；所述锂镍复合氧化物通式为Li aNi 1-x-yCo xM yO 2；
其中，0.95≤a≤1.10，0＜x≤0.05，0≤y≤0.005，所述M包括第2族(即IIA族)元素、第13族(即IIIA族)元素以及过渡金属元素中的至少一种，且不包括镍和钴。典型但非限制性的，a例如为0.95-1.10、0.97-1.10、0.99-1.10或0.95-1.07，诸如0.95、0.98、1、1.02、1.05、1.08或1.1；x例如为0.01-0.05、0-0.04或0.01-0.04，诸如0、0.01、0.02、0.03、0.04或0.05；y例如为0-0.005、0.001-0.005、0.001-0.004或0-0.003，诸如0、0.001、0.002、0.003、0.004或0.005。
典型但非限制性的，M选自Mg、Ca、Sr、Ba、B、Al、Ga、In、Ti、V、Nb、Ta、Y、W、La、Ce、Gd、Mn、Fe、Cu、Zn、Mo、Ce和Zr中的至少一种。
本公开提供的正极材料通过在锂镍复合氧化物颗粒的表面包覆有钴酸锂，从而有效抑制锂镍复合氧化物颗粒与电解液之间的副反应，提高锂离子电导率，通过锂镍复合氧化物颗粒的内部分布有钴元素，在晶界处形成钴酸锂或钴酸M锂，稳定锂镍复合氧化物晶体结构，从而有效提高了正极材料的倍率性能和循环稳定性。
在本公开的一种可选实施方式中，锂镍复合氧化物颗粒的内部，从外至中心，钴元素的摩尔含量逐渐降低(或者钴元素的质量含量逐渐降低)，以利于锂镍复合氧化物颗粒的外表层附近形成镍钴酸锂或镍钴M酸锂，有效稳定锂镍复合氧化物内部的晶体结构，抑制锂镍混排，从而有效提高正极材料的结构稳定性。
在本公开的一种实施方式中，以锂镍复合氧化物颗粒的外表面为起点，从外至中心延伸，钴元素的摩尔含量逐渐降低，降低率为0.025mol％/μm-0.300mol％/μm。
据信，不受理论的约束，降低率的计算是以锂镍复合氧化物颗粒的外表面的钴元素的摩尔含量(以M0表示)为基点，以从外至中心延伸的方向选择任意选一点，确定此点钴元素的摩尔含量(以M1表示)，计算降低率的公式为(M0-M1)/M0×100％。
本公开控制材料Co的分布，材料外部Ni含量较低，提高稳定性；内部Ni含量较高，提高材料容量；本公开上述的浓度梯度会更有利于稳定锂镍复合氧化物内部的晶体结构，提高正极材料的结构稳定性，如果浓度梯度过低则起不到上述效果，浓度梯度过大会造成材料晶格不匹配，导致应力累计，材料容易开裂。
典型但非限制性的，钴元素的摩尔含量降低率例如为0.03mol％/μm-0.3mol％/μm、0.03mol％/μm-0.25mol％/μm、0.03mol％/μm-0.2mol％/μm或0.1mol％/μm-0.3mol％/μm，诸如0.025mol％/μm、0.035mol％/μm、0.045mol％/μm 0.055mol％/μm、0.08mol％/μm、0.1mol％/μm、0.15mol％/μm、0.2mol％/μm、0.25mol％/μm或0.30mol％/μm。
在本公开的一种可选实施方式中，在正极材料中，镍的摩尔含量＞94％，以利于本公开提供的正极材料具有更高的容量优势，本公开通过控制Co的含量调整Ni含量，具备可操作性。
上述镍的摩尔含量指的是正极材料中，以镍、锂、钴以及任选的M元素的物质的量之和为100％计，镍元素的摩尔含量占比。
典型但非限制性的，在本公开提供的正极材料中，镍的摩尔含量例如为94.1％-96％、94.5％-96％或94.1％-95.5％，诸如94.1％、94.2％、94.5％、94.8％、95％、95.5％或96％。
在本公开的一种实施方式中，锂镍复合氧化物颗粒的平均粒径为3μm-17μm，以利于在正极片中分布均匀。
典型但非限制性的，锂镍复合氧化物颗粒的平均粒径例如为5μm-17μm、3μm-15μm或4μm-16μm，诸如3μm、5μm、7μm、9μm、11μm、13μm、15μm或17μm。
在本公开的一种实施方式中，锂镍复合氧化物颗粒表面的钴酸锂包覆层的厚度为20nm-200nm，以在降低材料阻抗，保证正极材料倍率性能和循环性能的同时有效抑制锂镍复合氧化物与电解液之间的副反应，提高正极材料的锂离子电导率。
典型但非限制性的，钴酸锂包覆层的厚度例如为30nm-200nm、30nm-190nm或50nm-150nm，诸如20nm、25nm、30nm、40nm、50nm、60nm、70nm、80nm、90nm、100nm、120nm、150nm、180nm或200nm。
本公开一实施方式提供了一种正极材料的制备方法，包括以下步骤：
将锂化合物、钴化合物和任选的M化合物包覆于氢氧化镍的表面，及将包覆后的材料在有氧条件下进行烧结，得到正极材料；
其中，所述钴化合物包括二价钴化合物和三价钴化合物。
本公开一实施方式提供了一种正极材料的制备方法，包括以下步骤(如图1所示)：
S100、将锂化合物、钴化合物和任选的M化合物包覆于氢氧化镍的表面；
S200、将包覆后的材料在有氧条件下进行烧结，得到正极材料；
其中，所述M包括第2族元素、第13族元素以及过渡金属元素中的至少一种，且不包括镍和钴；
所述钴化合物包括二价钴化合物和三价钴化合物。
[M化合物]
在本公开中，M包括第2族元素、第13族元素以及过渡金属元素中的至少一种，且不包括镍和钴。
典型但非限制性的，M可以选自例如Mg、Ca、Sr、Ba、B、Al、Ti、Zr、V、Nb、Ta、Y、Mo、W、La、Ce和Gd中的至少一种。
本公开通过在原料中加入M化合物对氢氧化镍进行包覆形成锂镍M三元材料进一步抑制材料相变的同时抑制与晶胞收缩，提供稳定的锂离子传输通道，改善材料的循环稳定性和热稳定性，稳定材料结构。
在本公开的一种实施方式中，M化合物包括但不限于M氧化物、M氢氧化物或M磷酸盐中的一种或几种的混合物。
[钴化合物]
在本公开中，所述钴化合物包括二价钴化合物和三价钴化合物。
本公开通过二价钴化合物和三价钴化合物共同包覆氢氧化镍，二价钴反应活性更高，在烧结过程中更易扩散至氢氧化镍内部，形成镍钴酸锂或镍钴M酸锂固溶体氧化物，稳定锂镍复合氧化物颗粒内部的晶体结构，抑制锂镍混排，而三价钴更倾向于包覆在镍酸锂颗粒的表面形成钴酸锂包覆层，抑制材料的副反应，提高正极材料的锂离子电导率。
在本公开的一些实施方式中，三价钴化合物在钴化合物中的摩尔含量为50％-85％。
三价钴化合物的摩尔含量会影响包覆层的厚度以及锂镍复合氧化物颗粒内部的晶体结构稳定性。在本公开中，三价钴化合物在钴化合物中的摩尔含量为50％-85％时，既 能够在锂镍复合氧化物颗粒的外表面形成厚度适中的包覆层，提高锂离子电导率，降低材料阻抗；又能够保证一定量的Co掺杂进入锂镍复合氧化物颗粒内部，从而有效促进形成足够的镍钴酸锂或镍钴M酸锂固溶体氧化物，从而有效抑制锂镍混排，提高正极材料的循环稳定性。
本申请人发现，三价钴化合物的摩尔含量过低，在烧结过程中，Co元素更多的掺杂进入镍酸锂颗粒的内部，导致材料的包覆效果降低；三价钴化合物的摩尔含量过高，Co元素进入锂镍复合氧化物颗粒内部不足，无法形成足够的镍钴酸锂或镍钴M酸锂固溶体氧化物，无法有效抑制锂镍混排，同时还会导致包覆层过厚，增加材料的阻抗，影响材料的倍率性能。
本公开通过Co元素在锂镍复合氧化物颗粒的表面包覆形成钴酸锂包覆层，提高正极材料的锂离子电导率，形成高锂离子电导率网络，提升材料倍率性能，并抑制材料与电解液的副反应。
典型但非限制性的，在本公开中，三价钴化合物在钴化合物中的摩尔含量例如为55％-85％、50％-80％或69％-85％，诸如50％、60％、65％、70％、75％、80％或85％。
在本公开的一种实施方式中，二价钴化合物包括但不限于二价钴氧化物、二价钴氢氧化物和二价羟基氧化物中的至少一种；三价钴包括但不限于三价钴氧化物、三价钴氢氧化物和三价钴羟基氧化物中的至少一种。
本公开提供的正极材料的制备方法简单、稳定安全，易于大规模工业化生产，该制备方法提供的二价钴化合物和三价钴化合物共同包覆球形氢氧化镍后再烧结的实施方式，不仅能在镍酸锂颗粒的表面形成均匀的钴酸锂包覆层，而且能够在镍酸锂颗粒的内部形成钴掺杂，能够有效抑制材料相变和与电解液的副反应，显著提升材料的倍率性能、循环稳定性和容量优势。
[钴化合物的用量]
在本公开中，钴化合物、锂化合物以及任选的M化合物包覆于氢氧化镍表面后进行烧结，钴元素同时在锂镍复合氧化物颗粒的表面包覆及内部呈梯度分布，钴化合物的用量会影响包覆层的厚度以及锂镍复合氧化物颗粒晶体结构的稳定性。
在本公开的一种可选实施方式中，钴化合物在所述氢氧化镍和钴化合物的混合物中的摩尔含量为0.5％-5％。
在本公开中，钴化合物在氢氧化镍和钴化合物中的摩尔含量指的是钴化合物中钴元素的物质的量与氢氧化镍中镍元素与钴化合物中钴元素的物质的量之和的比值，简写为Co/(Co+Ni)。
本公开中，Co/(Co+Ni)在上述范围内，不仅可以在镍酸锂颗粒表面形成厚度适中的包覆层，有效保证材料的离子电导率，降低材料的阻抗，同时还保证镍含量处于较高水平，从而提高材料的容量。同时，本公开中的Co元素的含量限定，可以达到同时在镍酸锂颗粒的表面包覆以及在镍酸锂颗粒的内部掺杂稳定镍酸锂颗粒晶体结构的效果。
当Co/(Co+Ni)高于5％时，会导致镍酸锂颗粒表面的包覆层过厚，降低材料的电子电导率，增加材料的阻抗，同时还会使得镍含量降低，导致材料的容量下降。而当Co/(Co+Ni)低于0.5％时，Co元素含量过低，无法达到同时在镍酸锂颗粒的表面包覆以及在镍酸锂颗粒的内部掺杂稳定镍酸锂颗粒晶体结构的效果。
典型但非限制性的，Co/(Co+Ni)例如为1％-5％、0.5％-4.5％、1％-4.5％或1％-4％，诸如0.5％、0.75％、0.1％、0.2％、0.5％、0.8％、1％、1.5％、2％、3％、4％、4.5％或5％。
相对于三元材料，随着Ni含量的提升，Ni 2+/4+氧化还原对增加，便于更多的Li +脱出，因此材料容量具有显著优势。
[锂化合物]
在本公开的一种实施方式中，锂化合物包括但不限于氢氧化锂、碳酸锂以及氢氧化锂和碳酸锂的混合物。
[氢氧化镍]
在本公开的一种实施方式中，选用平均粒径为3μm-17μm的球形氢氧化镍为原料，以更利于通过固相混合的方式将钴化合物、氢氧化锂以及任选的M化合物均匀包覆在球形氢氧化镍表面。
典型但非限制性的，球形氢氧化钠镍的平均粒径例如为5μm-17μm、3μm-15μm或6μm-17μm，诸如3μm、5μm、8μm、10μm、12μm、15μm或17μm。
[包覆方式]
在本公开的一种实施方式中，在步骤S100中，锂化合物、钴化合物和任选的M化合物通过固相混合的方式包覆于氢氧化镍的表面，工艺更为简单，操作更为方便，更适于进行规模化生产，降低生产成本。
在一些实施方式中，固相混合的方式包括机械混合，机械混合的方式包括但不限于采用高混机混合。
[有氧条件]
在本公开的一种实施方式中，有氧条件包括有氧气氛，有氧气氛中氧气含量≥98％，以利于在烧结过程中，氧气参与反应。
[烧结条件]
在本公开的一种实施方式中，烧结的温度为600℃-750℃，时间为8h-20h，以利于制备得到钴元素同时掺杂在锂镍复合氧化物颗粒内部以及包覆在锂镍复合氧化物颗粒表面的正极材料。
典型但非限制性的，烧结的温度例如为600℃-700℃、650℃-750℃或680℃-740℃，诸如600℃、620℃、650℃、680℃、700℃、720℃或750℃，烧结时间例如为10h-20h、8h-18h或12h-20h，诸如8h、9h、10h、12h、15h、18h或20h。
在本公开的一种实施方式中，所述氢氧化镍、钴化合物以及任选的M化合物质的量之和与锂化合物的摩尔比为1:0.95-1.1。
上述氢氧化镍、钴化合物以及任选的M化合物的物质量之和指的是氢氧化镍中镍元素、钴化合物中钴元素(包括二价钴和三价钴)以及任选的M化合物中M元素的物质量之和，简称为Ni、Co以及任选的M的物质量之和。
上述锂化合物的物质的量指的是锂化合物中锂元素的物质的量，简称为Li的物质的量。
通过控制Ni、Co以及任选的M的物质量之和与Li的摩尔比为1:0.95-1.1，以使得制备得到的正极材料具有更高的镍含量和更为稳定的结构。
典型但非限制性的，Ni、Co以及任选的M的物质量之和与Li的摩尔比例如为1:0.98-1.1、1:1-1.1或1:0.95-1.09，诸如1:0.95、1:0.98、1:1、1:1.02、1:1.05、1:1.08或1:1.1。
在本公开的一种实施方式中，氢氧化镍呈球形，平均粒径为3μm-17μm。
在本公开的一种实施方式中，正极材料的制备方法还包括在烧结后依次进行洗涤、干燥和二次烧结的步骤，其中，二次烧结的温度为250℃-700℃，时间为5h-15h。
通过洗涤将烧结后得到的正极材料表面残留的锂元素以及杂质去除，避免由于锂元素残留在材料表面影响材料的高温安全性，通过二次烧结以进一步提高材料的结构稳定性。
在一些实施方式中，采用蒸馏水、去离子水或纯净水对烧结后的材料进行洗涤。
典型但非限制性的，二次烧结的温度例如为260℃-700℃、300℃-700℃、250℃-600℃或300℃-600℃，诸如250℃、300℃、350℃、450℃、500℃、550℃、600℃、650℃或700℃，二次烧结的时间例如为5h-12h、6h-15h或6h-12h，诸如5h、6h、7h、8h、9h、10h、11h、12h、13h、14h或15h。
在一些实施方式中，二次烧结也在有氧条件下进行，其有氧条件为氧气含量≥90％。
在一些实施方式中，本公开提供的正极材料的结构示意图如图2所示，从图2可以看出，本公开提供的正极材料为核壳结构，内核为Li aNi 1-x-yCo xM yO 2，壳层为钴酸锂。
本公开一实施方式提供了一种正极材料，由上文所述的方法制备获得。
本公开一实施方式提供了包括上述提供的正极材料或由上述提供的制备方法得到的正极材料的正极片或电池。
本公开提供的正极材料在锂镍复合氧化物颗粒的外表面包覆有钴酸锂包覆层，并在内部分布有钴元素，从而不仅能够稳定锂镍复合氧化物的晶体结构，而且能够抑制材料与电解液之间的副反应，在提高锂离子电导率的同时显著提升了倍率性能和循环稳定性。本公开提供的正极材料具有循环性能好，安全性能高等优点。
本公开提供的正极材料制备方法，通过将二价钴化合物、三价钴化合物、氢氧化锂以及任选的M化合物包覆在氢氧化镍表面，经过高温烧结得到部分钴元素包覆在镍酸锂颗粒表面形成均匀的钴酸锂包覆层，部分钴元素分布在锂镍复合氧化物颗粒内部的正极材料，同时实现了钴元素在材料内部的掺杂和表面的包覆，有效抑制材料相变以及与 电解液的副反应，在提高锂离子电导率的同时显著提升了材料的倍率性能和循环稳定性。
此外，本公开提供的正极材料的制备方法简单、稳定、安全，易于大规模工业化生产。
为了便于本领域技术人员理解，下面结合实施例和对比例对本公开提供的技术实施方式做进一步的描述。
实施例
实施例1
本实施例提供了一种正极材料，其按照以下步骤制备得到：
(1)按Li的摩尔量与Ni和Co摩尔量之和的比例为1.05称量Ni(OH) 2、Co(OH) 2、CoOOH、LiOH·H 2O，其中Co占据Ni+Co的摩尔总量的0.015，CoOOH占Co(OH) 2与CoOOH摩尔总量的65％，Ni(OH) 2为球形氢氧化镍，粒径为10-15μm；
(2)采用高混机混合Ni(OH) 2、Co(OH) 2、CoOOH和LiOH·H 2O，在氧气含量≥98％的气氛下，680℃烧结混合物，烧结时间10h，得到钴包覆的超高镍锂镍钴复合氧化物；
(3)将钴包覆的超高镍锂镍钴复合氧化物采用去离子水洗涤后，压滤，将滤饼置于真空烘干箱中200℃下烘干12h；
(4)将烘干后的材料在氧气含量≥90％的气氛下，600℃进行二次烧结，烧结时间为8h，得到正极材料。
实施例2
本实施例提供了一种正极材料，其按照以下步骤制备得到：
(1)按Li的摩尔量与Ni和Co摩尔量之和的比例为1.05称量Ni(OH) 2、CoO、Co 2O 3、LiOH·H 2O，其中Co占据Ni+Co的摩尔总量的0.015，Co 2O 3占CoO与Co 2O 3摩尔总量的65％，Ni(OH) 2为球形氢氧化镍，粒径为3-10μm；
(2)采用高混机混合Ni(OH) 2、CoO、Co 2O3和LiOH·H 2O，在氧气含量≥98％的气氛下，650℃烧结混合物，烧结时间12h，得到钴包覆的超高镍锂镍钴复合氧化物。
(3)将钴包覆的超高镍锂镍钴复合氧化物采用去离子水进行洗涤、然后压滤，将滤饼置于真空烘箱200℃烘干12h。
(4)将烘干后的材料在氧气含量≥90％的气氛下，650℃进行二次烧结，烧结时间为5h，得到正极材料。
实施例3
本实施例提供了一种正极材料，其按照以下步骤制备得到：
(1)按Li的摩尔量与Ni和Co摩尔量之和的比例为1.05称量Ni(OH) 2、Co(OH) 2、CoOOH、LiOH·H 2O，其中Co占据Ni+Co的摩尔总量的0.015，CoOOH占Co(OH) 2与CoOOH摩尔总量的85％，Ni(OH) 2为球形氢氧化镍，粒径为12-17μm；
(2)采用高混机混合Ni(OH) 2、Co(OH) 2、CoOOH和LiOH·H 2O，在氧气含量≥98％的气氛下，700℃烧结混合物，烧结时间10h，得到钴包覆的超高镍锂镍钴复合氧化物。
(3)将钴包覆的超高镍锂镍钴复合氧化物采用去离子水洗涤后压滤，将滤饼置于真空烘箱200℃烘干12h。
(4)将烘干后的材料在氧气含量≥90％的气氛下，550℃进行二次烧结，烧结时间为12h，得到正极材料。
实施例4
本实施例提供了一种正极材料，其按照以下步骤制备得到：
(1)按Li的摩尔量与Ni和Co摩尔量之和的比例为1.05称量Ni(OH) 2、Co(OH) 2、CoOOH、Al(OH) 3、LiOH·H 2O，其中Co占据Ni+Co的摩尔总量的0.015，CoOOH占Co(OH) 2与CoOOH摩尔总量的65％，Ni(OH) 2为球形氢氧化镍，粒径为10-15μm，Al含量为原料总质量的0.1％；
(2)采用高混机混合Ni(OH) 2、Co(OH) 2、CoOOH、Al(OH) 3和LiOH·H 2O，在氧气含量≥98％的气氛下，680℃烧结混合物，烧结时间10h，得到钴包覆的超高镍锂镍钴复合氧化物。
(3)将钴包覆的超高镍锂镍钴复合氧化物采用去离子水洗涤后压滤，将滤饼置于真空烘箱200℃烘干12h。
(4)将烘干后的材料在氧气含量≥90％的气氛下，600℃进行二次烧结，烧结时间为10h，得到正极材料。
实施例5
本实施例提供了一种正极材料，其按照以下步骤制备得到：
(1)按Li的摩尔量与Ni和Co摩尔量之和的比例为1.05称量Ni(OH) 2、Co(OH) 2、CoOOH和LiOH·H 2O，其中Co占据Ni+Co的摩尔总量的0.035，CoOOH占Co(OH) 2与CoOOH摩尔总量的65％，Ni(OH) 2为球形氢氧化镍，粒径为10-15μm；
(2)采用高混机混合Ni(OH) 2、Co(OH) 2、CoOOH和LiOH·H 2O，在氧气含量≥98％的气氛下，680℃烧结混合物，烧结时间10h，得到钴包覆的超高镍锂镍钴复合氧化物。
(3)将钴包覆的超高镍锂镍钴复合氧化物采用去离子水洗涤后压滤，将滤饼置于真空烘箱200℃烘干12h。
(4)将烘干后的材料在氧气含量≥90％的气氛下，600℃进行二次烧结，烧结时间为10h，得到正极材料。
实施例6
本实施例提供了一种正极材料，其按照以下步骤制备得到：
(1)按Li的摩尔量与Ni和Co摩尔量之和的比例为1.05称量Ni(OH) 2、Co(OH) 2、CoOOH、Sr(OH) 2和LiOH·H 2O，其中Co占据Ni+Co的摩尔总量的0.035，CoOOH占Co(OH) 2与CoOOH摩尔总量的50％，Ni(OH) 2为球形氢氧化镍，粒径为10-15μm；
(2)采用高混机混合Ni(OH) 2、Co(OH) 2、CoOOH、Sr(OH) 2和LiOH·H 2O，在氧气含量≥98％的气氛下，680℃烧结混合物，烧结时间10h，得到钴包覆的超高镍锂镍钴复合氧化物。
(3)将钴包覆的超高镍锂镍钴复合氧化物采用去离子水洗涤后压滤，将滤饼置于真空烘箱200℃烘干12h。
(4)将烘干后的材料在氧气含量≥90％的气氛下，600℃进行二次烧结，烧结时间为10h，得到正极材料。
实施例7
本实施例提供了一种正极材料，其按照以下步骤制备得到：
(1)按Li的摩尔量与Ni和Co摩尔量之和的比例为1.1称量Ni(OH) 2、Co(OH) 2、CoOOH、LiOH·H 2O，其中Co占据Ni+Co的摩尔总量的0.015，CoOOH占Co(OH) 2与CoOOH摩尔总量的65％，Ni(OH) 2为球形氢氧化镍，粒径为10-15μm；
(2)采用高混机混合Ni(OH) 2、Co(OH) 2、CoOOH和LiOH·H 2O，在氧气含量≥98％的气氛下，680℃烧结混合物，烧结时间10h，得到钴包覆的超高镍锂镍钴复合氧化物。
(3)将钴包覆的超高镍锂镍钴复合氧化物采用去离子水洗涤后压滤，将滤饼置于真空烘箱200℃烘干12h。
(4)将烘干后的材料在氧气含量≥90％的气氛下，600℃进行二次烧结，烧结时间为10h，得到正极材料。
实施例8
本实施例提供了一种正极材料，其制备方法与实施例1的区别在于，步骤(1)中，Co占据Ni+Co的摩尔总量的10％，其余步骤均与实施例1相同，在此不再赘述。
实施例9
本实施例提供了一种正极材料，其按照以下步骤制备得到：
(1)按Li的摩尔量与Ni和Co摩尔量之和的比例为0.95称量Ni(OH) 2、Co(OH) 2、CoOOH、LiOH·H 2O，其中Co占据Ni+Co的摩尔总量的0.015，CoOOH占Co(OH) 2与CoOOH摩尔总量的65％，Ni(OH) 2为球形氢氧化镍，粒径为10-15μm；
(2)采用高混机混合Ni(OH) 2、Co(OH) 2、CoOOH和LiOH·H 2O，在氧气含量≥98％的气氛下，680℃烧结混合物，烧结时间10h，得到正极材料。
实施例10
本实施例提供了一种正极材料，其按照以下步骤制备得到：
(1)按Li的摩尔量与Ni和Co摩尔量之和的比例为1.0称量Ni(OH) 2、Co(OH) 2、CoOOH、LiOH·H 2O，其中Co占据Ni+Co的摩尔总量的0.015，CoOOH占Co(OH) 2与CoOOH摩尔总量的65％，Ni(OH) 2为球形氢氧化镍，粒径为10-15μm；
(2)采用高混机混合Ni(OH) 2、Co(OH) 2、CoOOH和LiOH·H 2O，在氧气含量≥98％的气氛下，680℃烧结混合物，烧结时间10h，得到正极材料。
对比例1
本对比例提供了一种正极材料，其制备方法与实施例1的区别在于，步骤(1)中，CoOOH占Co(OH) 2与CoOOH摩尔总量的10％，其余步骤均与实施例1相同，在此不再赘述。
对比例2
本对比例提供了一种正极材料，其制备方法与实施例1的区别在于，步骤(1)中，CoOOH占Co(OH) 2与CoOOH摩尔总量的95％，其余步骤均与实施例1相同，在此不再赘述。
对比例3
本对比例提供了一种正极材料，其制备方法与实施例1的区别在于，步骤(1)中，原料中的Co化合物均为Co(OH) 2，原料中未采用三价钴化合物，其余步骤均与实施例1相同，在此不再赘述。
对比例4
本对比例提供了一种正极材料，其制备方法与实施例1的区别在于，步骤(1)中，原料中的Co化合物均为CoOOH，原料中未采用二价钴化合物，其余步骤均与实施例1相同，在此不再赘述。
对比例5
本对比例提供了一种正极材料，其制备方法与实施例1的区别在于，步骤(1)中，原料中未采用钴化合物，按照Li的摩尔量与Ni摩尔量之和的比例为1.05称量Ni(OH) 2与LiOH·H 2O，其余步骤均与实施例1相同，在此不再赘述。
试验例1
将实施例1-10和对比例1-5提供的正极材料分别采用Hitachi S4800扫描电子显微镜(SEM)测试表面形貌，测定正极材料的粒径以及表面包覆层的厚度，结果如下表1所示。
表1
  粒径分布D50(μm) 包覆层厚度(nm)
实施例1 10.2 27
实施例2 4.5 52
实施例3 13.5 31
实施例4 10.3 36
实施例5 10.5 67
实施例6 10.2 58
实施例7 10.7 30
实施例8 10.4 143
实施例9 10.6 29
实施例10 10.5 31
对比例1 10.4 9
对比例2 10.2 42
对比例3 10.5 11
对比例4 10.8 49
对比例5 10.3 /
以实施例1为例，图3为实施例1提供的正极材料的SEM图，从图3可以看出，实施例1提供的正极材料的粒径为3-17μm，包覆层厚度为约27nm。
试验例2
将实施例1-10和对比例1-5提供的正极材料分别进行X射线光电子能谱分析(XPS)测试，通过XPS谱图可以看出，实施例1-10和对比例1-5提供的正极材料外部的包覆层均为钴酸锂。
以实施例1为例，图4为实施例1提供的正极材料的XPS图，从图4可以看出，在结合能为780eV位置，出现Co的2p3/2峰，同时，在结合能为529eV位置，出现Co-O的1s峰。因此，说明材料表面存在Li-Co-O化合物，实施例1提供的正极材料表面的包覆层以钴酸锂为主。
试验例3
将实施例1-10以及对比例1-5提供的正极材料进行X射线能量散射谱(EDS)测试，结果如表2所示。其中，以锂镍复合氧化物为起点，从外至内延伸，分别测试锂镍复合物内部0μm、1μm、2μm、4μm和8μm处的Co含量。鉴于有些正极材料内部的锂镍复合氧化物的粒径不足16μm，本测试均挑选粒径为16μm以上的锂镍复合氧化物进行内部Co含量测试。
表2
Figure PCTCN2022117165-appb-000001
Figure PCTCN2022117165-appb-000002
以实施例1为例，图5为实施例1提供正极材料的EDS图，从图5可以看出，Co元素在正极材料内部分布有钴元素，且从外至内，钴元素含量逐渐降低。同样，实施例2-10中也具有相近的技术效果，正极材料内部分布的钴元素从外至内的含量也是逐渐降低。
以对比例1为例，图6为对比例1提供正极材料的EDS图，从图6可以看出，对比例1提供的正极材料内部分布有钴元素，从外至内，钴元素的含量保持稳定。同样，对比例2-4中的，正极材料内部分布的钴元素从外至内的含量基本保持稳定，或者在最内层，出现钴元素含量的陡然降低。
试验例4
分别将实施例1-10和对比例1-5提供的正极材料作为正极材料制备2032型扣式电池，具体制备方法如下：将正极材料、导电碳SP、PVDF(聚偏氟乙烯)按照96:2:2的质量比加入NMP(N-甲基吡咯烷酮)中，搅拌得到浆料，将浆料涂布在铝箔上烘干之后作为正极片，采用锂片作为负极片，制备得到2032型扣式电池。
将实施例1-10和对比例1-5提供的正极材料进行Ni含量测试，测试步骤为：称取1g的正极材料，用硝酸消解后定容至100mL，再稀释200倍，通过PE8000S型反应耦合等离子体仪器进行元素含量测试，结果如表1所示。
将实施例1-10和对比例1-5提供的正极材料作为正极材料分别制备2032型扣式电池，然后将上述2032型扣式电池分别进行0.1C首周克容量、倍率和50周循环保持率测试，结果如下表3所示。
其中，0.1C首周客容量测试方法为：将2032型扣式电池在25℃，3.0V至4.3V之间以0.1C/0.1C对电池进行充电和放电，测试首周克容量；
倍率的测试方法为：
将2032型扣式电池在25℃，3.0V至4.3V之间测试首周之后，进行0.5C/0.5C、0.5C/1C、0.5C/2C充电/放电，各充放电一周，测定倍率性能。
50周循环保持率测试方法为：将2032型扣式电池在25℃，3.0V至4.3V之间以0.5C/1C对电池进行充电和放电，测试循环性能。
同时对实施例1和8制备的材料进行阻抗测试，测试方法为：将2032型扣式电池在25℃，3.0V至4.3V之间测试首周之后，0.1C充电至50％SOC，取下电池，采用IviumStat电化学工作站，在-5℃下进行阻抗测试，测试频率为0.03～105Hz，测试振幅为5mV。
表3
Figure PCTCN2022117165-appb-000003
从表3中实施例1-10的数据可以看出，采用本公开提供的制备方法制备得到的正极材料具有优异倍率性能和良好的循环性能。
从实施例1-7以及9-10与实施例8的数据对比可以看出，钴化合物在所述氢氧化镍和所述钴化合物混合物中的摩尔含量为0.5-5％时，制备得到的正极材料阻抗Ni含量更高，阻抗更小，容量更高。
图7为分别采用本公开实施例1和实施例8提供的正极材料作为正极材料制备得到的2032型扣式电池的容量对比图；图8为分别采用本公开实施例1和实施例8提供的正极材料作为正极材料制备得到的2032型扣式电池的阻抗对比图；从实施例1和实施例8的数据结合图7及图8的分析对比可知，Ni含量的下降使得材料的容量降低，同时Co含量的增加导致包覆层过厚，降低了材料的电子电导，增加了材料的阻抗，降低了材料的倍率和循环性能。
从实施例1和对比例1的数据对比可知，原料中三价钴含量降低会导致更多的钴元素掺杂进入材料的内部，材料表面包覆层不足，不利于抑制材料与电解液的副反应，降低了材料的循环稳定性。
从实施例1和对比例5的数据对比可知，无钴包覆的正极材料具有更高的容量，但由于缺少钴的掺杂和包覆作用，材料的倍率和循环性能显著降低。
最后应说明的是：以上各实施例仅用以说明本公开的技术方案，而非对其限制；尽管参照前述各实施例对本公开进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分或者全部技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本公开各实施例技术方案的范围。
工业实用性
本公开提供的正极材料在提高锂离子电导率的同时显著提升了倍率性能和循环稳定性，并且具有循环性能好，安全性能高等优点。同时，本公开提供的正极材料制备方法同时实现了钴元素在材料内部的掺杂和表面的包覆，有效抑制材料相变以及与电解液的副反应，在提高锂离子电导率的同时显著提升了材料的倍率性能和循环稳定性，该方法简单、稳定、安全，易于大规模工业化生产，具有广泛的应用前景。

Claims (14)

  1. 一种正极材料，其特征在于，包括锂镍复合氧化物颗粒，所述锂镍复合氧化物颗粒的外表面包覆有钴酸锂包覆层，所述锂镍复合氧化物颗粒的内部分布有钴元素；所述锂镍复合氧化物通式为Li aNi 1-x-yCo xM yO 2；
    其中，0.95≤a≤1.10，0＜x≤0.05，0≤y≤0.005，所述M包括第2族元素、第13族元素以及过渡金属元素中的至少一种，且不包括镍和钴。
  2. 根据权利要求1所述的正极材料，其特征在于，所述正极材料满足以下条件a-c中的至少一个：
    a.所述锂镍复合氧化物颗粒内部，从外至中心，钴元素的摩尔含量逐渐降低；
    b.以所述锂镍复合氧化物颗粒的外表面为起点，从外至中心延伸，钴元素的摩尔含量降低率为0.025mol％/μm-0.3mol％/μm；
    c.所述锂镍复合氧化物颗粒分布有二价钴和三价钴，所述二价钴分布在所述锂镍复合氧化物颗粒的内部，所述三价钴分布在所述锂镍复合氧化物颗粒的表面。
  3. 根据权利要求1或2所述的正极材料，其特征在于，所述正极材料满足以下条件a-c中的至少一个：
    a.所述正极材料中，镍的摩尔含量＞94％；
    b.所述锂镍复合氧化物颗粒的平均粒径为3μm-17μm；
    c.所述钴酸锂包覆层的厚度为20nm-200nm。
  4. 根据权利要求1-3中任一项所述的正极材料，其特征在于，M包括Mg、Ca、Sr、Ba、B、Al、Ti、Zr、V、Nb、Ta、Y、Mo、W、La、Ce和Gd中的至少一种。
  5. 一种正极材料的制备方法，其特征在于，包括以下步骤：
    将含有锂化合物、钴化合物和M化合物的复合物包覆于氢氧化镍的表面，以及将包覆后的材料在有氧条件下进行烧结，得到正极材料；
    其中，所述钴化合物包括二价钴化合物和三价钴化合物，所述M化合物中的M包括第2族元素、第13族元素以及过渡金属元素中的至少一种，且不包括镍和钴。
  6. 根据权利要求5所述的正极材料的制备方法，其特征在于，所述M化合物包括M的氧化物、M的氢氧化物及M的磷酸盐中的至少一种。
  7. 根据权利要求5或6所述的正极材料的制备方法，其特征在于，所述正极材料满足以下条件a-d中的至少一个：
    a.所述钴化合物在所述氢氧化镍和所述钴化合物的混合物中的摩尔含量为0.5％-5％；
    b.所述三价钴化合物在所述钴化合物中的摩尔含量为50％-85％；
    c.所述锂化合物包括氢氧化锂或碳酸锂中的至少一种；
    d.所述钴化合物包括氢氧化钴、羟基氧化钴、一氧化钴及三氧化二钴中的至少一种。
  8. 根据权利要求5-7任一项所述的正极材料的制备方法，其特征在于，所述正极材料满足以下条件a-b中的至少一个：
    a.所述锂化合物、钴化合物和任选的M化合物通过固相混合的方式包覆于氢氧化镍的表面；
    b.所述固相混合的方式包括机械混合。
  9. 根据权利要求5-8中任一项所述的正极材料的制备方法，其特征在于，所述方法满足以下条件a-c中的至少一个：
    a.所述氢氧化镍、钴化合物以及M化合物的摩尔含量之和与所述锂化合物的摩尔含量比为1:0.95-1.1；
    b.所述氢氧化镍的平均粒径为3μm-17μm；
    c.所述氢氧化镍呈球形。
  10. 根据权利要求5-9中任一项所述的正极材料的制备方法，其特征在于，所述正极材料满足以下条件a-b中的至少一个：
    a.所述有氧条件包括有氧气氛，所述有氧气氛中氧气含量≥98％；
    b.所述烧结的温度为600℃-750℃，时间为8h-20h。
  11. 根据权利要求5-10中任一项所述的正极材料的制备方法，其特征在于，所述方法满足以下条件a～d的至少一个：
    a.所述方法还包括在烧结后依次进行的洗涤、干燥和二次烧结步骤；
    b.二次烧结的温度为250℃-700℃，时间为5h-15h；
    c.二次烧结在有氧气氛中进行；
    d.所述有氧气氛的氧含量≥90％。
  12. 根据权利要求5-11中任一项所述的正极材料的制备方法，其特征在于，M选自Mg、Ca、Sr、Ba、B、Al、Ti、Zr、V、Nb、Ta、Y、Mo、W、La、Ce和Gd中的至少一种。
  13. 一种正极片，其特征在于，包括权利要求1～4或由权利要求5-12中任一项所述的方法制备获得的正极材料。
  14. 一种锂离子电池，包括权利要求13所述的正极片。
PCT/CN2022/117165 2021-09-09 2022-09-06 正极材料及其制备方法、正极片和电池 WO2023036102A1 (zh)

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