WO2023024581A1 - 用于锂离子电池的正极材料及其制备方法 - Google Patents

用于锂离子电池的正极材料及其制备方法 Download PDF

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WO2023024581A1
WO2023024581A1 PCT/CN2022/092274 CN2022092274W WO2023024581A1 WO 2023024581 A1 WO2023024581 A1 WO 2023024581A1 CN 2022092274 W CN2022092274 W CN 2022092274W WO 2023024581 A1 WO2023024581 A1 WO 2023024581A1
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positive electrode
electrode material
lithium
formula
peak
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PCT/CN2022/092274
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French (fr)
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张航
刘亚飞
王竞鹏
张学全
陈彦彬
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北京当升材料科技股份有限公司
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Priority to JP2023553014A priority Critical patent/JP7515738B2/ja
Priority to KR1020237029803A priority patent/KR20230154306A/ko
Priority to EP22859929.6A priority patent/EP4283719A1/en
Publication of WO2023024581A1 publication Critical patent/WO2023024581A1/zh
Priority to US18/235,084 priority patent/US11984590B2/en

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    • 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
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    • 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
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    • 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
    • C01G53/50—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese of the type [MnO2]n-, e.g. Li(NixMn1-x)O2, Li(MyNixMn1-x-y)O2
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    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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    • C01P2004/00—Particle morphology
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    • 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
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    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
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    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • 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 invention relates to a positive electrode material of a lithium ion battery and a preparation method thereof.
  • Layered ternary materials are currently one of the mainstream choices for anode materials for lithium-ion batteries. Compared with components such as anodes and electrolytes, cathode materials have low capacity, a large proportion, and high cost, which restricts the overall performance of lithium-ion batteries. The key factor.
  • Patent application CN111106344A uses aluminum-magnesium phosphate composites as raw materials, and coats the surface of positive electrode materials through solid phase, liquid phase, and gas phase methods. After heat treatment, a composite positive electrode with positive electrode material-doped layer-coating layer from the inside to the outside is obtained. Materials, during the back-burning process, a small amount of lithium ions enter the coating layer to improve the ionic conductivity of the coating layer, and at the same time, some metals in the coating layer enter the positive electrode surface to stabilize the material structure, thereby obtaining a high-capacity positive electrode material with better comprehensive performance.
  • the patent application CN111217407A pre-calcined the precursor and the lithium-containing compound separately, and then mixed and sintered to improve the crystallinity of the material, reduce the residual alkali content on the surface of the material, and inhibit the occurrence of surface side reactions, thereby improving the capacity and capacity of the positive electrode material. cycle stability.
  • the present disclosure provides a positive electrode material for a lithium-ion battery, which has the following general formula I:
  • M and M' are different from each other and each independently selected from at least one of La, Cr, Mo, Ca, Fe, Ti, Zn, Y, Zr, W, Nb, V, Mg, B, Al, Sr, Ba, Ta A sort of,
  • A is at least one selected from F, Cl, Br, I, S, and
  • N of micrograin boundaries in the primary particles of the positive electrode material is about 10.5 to about 14.5, wherein N is calculated by formula I:
  • D S is the average size of the primary particles measured by the cross-sectional SEM photo of the positive electrode material
  • D X is the crystallite size in the primary particles of the positive electrode material calculated by XRD test and Scherrer formula. average size.
  • the present invention by including a controllable and specific number of micrograin boundaries in the primary particles of the positive electrode material, a path for rapid diffusion of lithium ions in the bulk phase is provided, and the diffusion coefficient of lithium ions is improved, thereby achieving excellent rate performance and capacity At the same time, it takes into account the crystallinity of the primary particles, avoiding microcracks inside the particles, especially in the primary particles, during the charge/discharge cycle of the battery, thereby improving the cycle life of the positive electrode material and lithium-ion battery.
  • the present invention also provides the preparation method of positive electrode material according to the present invention, it comprises the following steps:
  • Step i)-1 mixing a first aqueous solution containing a nickel salt, a cobalt salt, and a manganese salt, a second aqueous solution containing a sodium-containing basic compound and/or a potassium-containing basic compound, and aqueous ammonia, and adjusting the resulting mixed aqueous solution
  • the first pH value is about 9 to about 12, so that the co-precipitation reaction occurs to form crystals
  • step i)-2 when the crystal grows to a median particle diameter D50 of about 2 to about 5 ⁇ m, adjusting the second pH value of the mixed aqueous solution to about 9 to about 12, wherein the second pH value is greater than the first a pH value, and the difference is between about 0.1 to about 1.0, allowing the crystals to continue to grow to a median particle size D50 of about 9 to about 20 ⁇ m, thereby obtaining the precursor; and
  • Step ii) mixing the precursor, the lithium source and the first additive containing the element M, and sintering the resulting mixture at a constant temperature at a temperature of 650-900° C. for about 4 to about 20 hours, and naturally cooling down the sintered compound After cooling down to room temperature, crushing, sieving, and iron removal, the first positive electrode material Li 1+a Ni x Co y Mn z M c O 2 is obtained, and optionally
  • Step iii) mixing the first positive electrode material Li 1+a Ni x Co y Mnz M c O 2 and the second additive containing the element M' and/or A, and sintering at a constant temperature at a temperature of about 200 to about 700 ° C to form The resulting mixture is kept for about 3 to about 10 hours, thereby obtaining the second positive electrode material Li 1+a Ni x Co y Mnz M c M' d O 2-b A b .
  • the preparation method according to the present invention is controllable and simple and easy to operate.
  • the primary fiber morphology and crystallinity of the precursor can be controlled in a simple way, and then the primary fiber of the positive electrode material can be controlled.
  • the crystallinity of the positive electrode material and the control of the number of micrograin boundaries are realized through the selection and dosage control of the doping elements that have the effect of regulating the growth of micrograin boundaries, combined with the regulation and control of the sintering temperature.
  • Lithium-ion batteries comprising cathode materials according to the present invention can be used in electric vehicles (such as automobiles), regional power stations and portable devices.
  • FIG. 1 is a scanning electron microscope (SEM) image of the cathode material prepared in Example 1.
  • FIG. 2 is a cross-sectional SEM image of the positive electrode material prepared in Example 1.
  • FIG. 3 is an XRD test spectrum of the cathode material prepared in Example 1.
  • Figure 4 is a schematic diagram of the method for calculating the angle of repose.
  • Products and methods according to the present invention may comprise or comprise the essential technical features described in this disclosure, as well as additional and/or optional components, ingredients, steps or other limiting features described herein; The essential technical features described, as well as additional and/or optional components, ingredients, steps or other restrictive features described herein; or essentially consist of the essential technical features described in this disclosure, and additional and/or Optionally present components, ingredients, steps or other limiting features described herein.
  • the term "about” means that the numerical value it defines may have a deviation within the range of ⁇ 10% of the numerical value, for example, the term “about 300 nm” refers to the range of "300 ⁇ 30 nm”.
  • a positive electrode material for a lithium-ion battery which has the following general formula I:
  • M and M' are different from each other and each independently selected from La, Cr, Mo, Ca, Fe, Ti, Zn, Y, Zr, W, Nb, V, Mg, B, Al, At least one of Sr, Ba, Ta, A is at least one selected from F, Cl, Br, I, S, and
  • N of micrograin boundaries in the primary particles of the positive electrode material is about 10.5 to about 14.5, wherein N is calculated by formula I:
  • D S is the average size of the primary particles measured by the cross-sectional SEM photo of the positive electrode material
  • D X is the average size of the crystallites in the primary particles of the positive electrode material calculated by the XRD test and the Scherrer formula. size.
  • the positive electrode material has the following general formula II:
  • the capacity development and rate performance of layered ternary materials are limited by the diffusion capacity of lithium ions.
  • the diffusion of lithium ions at defect sites such as micrograin boundaries is often limited neglect.
  • a certain number of microcrystals are retained inside the primary particles of the positive electrode material, and microcrystal boundaries are formed between the microcrystals.
  • a certain number of microcrystal boundaries is conducive to improving the diffusion rate of the lithium ion bulk phase, thereby improving the positive electrode material.
  • Excellent capacity and rate performance while maintaining good crystallinity, avoiding the risk of primary particle breakage during repeated charge/discharge, thereby ensuring the cycle life of the cathode material.
  • the positive electrode material has the structural characteristics of primary particles agglomerating to form secondary particles, wherein the primary particle refers to a relatively complete single particle that has a clear boundary with the surrounding positive electrode material, and the secondary particle refers to the accumulation of multiple primary particles. , large positive electrode material spheres that do not separate without external force.
  • the inside of the primary particle of the positive electrode material is not a perfect single crystal structure, but is composed of a plurality of microcrystalline regions with a short-range ordered crystal structure tightly bound together, and the boundary defining the mutual combination of the microcrystalline regions is a microcrystalline boundary, This micrograin boundary cannot be clearly identified by external observation means such as a scanning electron microscope.
  • N D S /D X Formula I.
  • DS is about 300 to about 600nm, preferably about 400 to about 550nm, more preferably about 450 to about 550nm, and DS is measured through the SEM image of the cross section of the positive electrode material.
  • Dx is about 30 to about 60 nm, preferably about 40 to about 50 nm, more preferably about 40 to about 45 nm, and Dx is calculated via Equation II:
  • D (003) represents the crystal thickness of the (003) crystal plane normal direction represented by the single (003) peak
  • D (104) represents the crystal thickness of the (104) crystal plane normal direction represented by the single (104) peak
  • D (003) and D (104) are each calculated via the Scherrer formula:
  • ⁇ is the X-ray wavelength
  • ⁇ is the full width at half maximum of diffraction peak D (003) or D (104) in the XRD pattern
  • ⁇ is the diffraction peak D (003) or D (104) Bougella diffraction angle in the XRD pattern, the 2 ⁇ range of (003) peak is about 18.5 ⁇ about 19.5 °, and the 2 ⁇ range of (104) peak is about 44.0 ⁇ about 45.0°.
  • the median diameter D 50 of the secondary particles of the cathode material is about 9 to about 20 ⁇ m, and the D 50 is measured by a laser particle size analyzer and calculated based on volume distribution.
  • the median particle diameter D 50 refers to the particle diameter value corresponding to when the volume distribution percentage of particles reaches 50%. For example, when the median diameter D 50 of secondary particles is 9 ⁇ m, it means that secondary particles larger than 9 ⁇ m account for 50% by volume, and particles smaller than 9 ⁇ m also account for 50% by volume.
  • the ratio of the compacted density PD measured at 20KN to the tapped density TD of the positive electrode material satisfies 1.1 ⁇ PD/TD ⁇ 1.3.
  • the PD/TD ratio within this value range makes the positive electrode material dense enough, which is conducive to the processing of lithium-ion battery pole pieces with high compaction density, and improves the volumetric energy density.
  • it has a suitable porosity, which helps the electrolyte Infiltrate the positive electrode material, so that the lithium-ion battery has excellent capacity and rate performance.
  • the positive electrode material has an angle of repose ⁇ 50°, preferably about 30° to about 45°, and the angle of repose ⁇ is measured according to GB/T 6609.24-2004 Test method for angle of repose of alumina powder.
  • the angle of repose ⁇ within this value range makes the positive electrode material have good fluidity, which is beneficial to the processability in actual production.
  • the present invention also provides the method for the cathode material of lithium ion, it comprises the following steps:
  • Step i)-1 mixing a first aqueous solution containing a nickel salt, a cobalt salt, and a manganese salt, a second aqueous solution containing a sodium-containing basic compound and/or a potassium-containing basic compound, and aqueous ammonia, and adjusting the resulting mixed aqueous solution
  • the first pH value is about 9 to about 12, so that the co-precipitation reaction occurs to form crystals
  • step i)-2 when the crystal grows to a median particle diameter D50 of about 2 to about 5 ⁇ m, adjusting the second pH value of the mixed aqueous solution to about 9 to about 12, wherein the second pH value is greater than the first a pH value, and the difference is between about 0.1 to about 1.0, allowing the crystals to continue to grow to a median particle size D50 of about 9 to about 20 ⁇ m, thereby obtaining the precursor; and
  • Step ii) mixing the precursor, lithium source and additives containing the element M, sintering the resulting mixture at a constant temperature at a temperature of 650-900° C. for about 4 to about 20 hours, and naturally cooling down (preferably to room temperature ) and crushing, sieving, and iron removal to obtain the first positive electrode material Li 1+a Ni x Co y Mn z M c O 2 , and optionally
  • Step iii) mixing the first positive electrode material Li 1+a Ni x Co y Mnz M c O 2 and the second additive containing the element M' and/or A, and sintering at a constant temperature at a temperature of about 200 to about 700 ° C to form The resulting mixture is kept for about 3 to about 10 hours, thereby obtaining the second positive electrode material Li 1+a Ni x Co y Mnz M c M' d O 2-b A b .
  • the preparation method according to the present invention is controllable and simple, and the nucleation process of the precursor and the pH value of the crystal growth process are controlled by the joint adjustment of the alkaline compound containing sodium/potassium and ammonia water, so as to control the pH value of the precursor
  • the primary fiber morphology and crystallinity of the body and then control the number of micrograin boundaries in the primary particles of the positive electrode material.
  • the control of the crystallinity of the positive electrode material and the number of micrograin boundaries is realized.
  • the first pH value is about 10.5 to about 11.2, and the second pH value is about 11.2 to about 11.8.
  • the nickel salt, cobalt salt and manganese salt are each independently selected from sulfate, nitrate, acetate and combinations thereof, preferably the nickel salt, cobalt salt and manganese
  • the salts are both sulfates, or both nitrates, or both acetates.
  • step i)-1 the nickel salt, cobalt salt and manganese salt are according to the nickel, cobalt, manganese in the first positive electrode material general formula Li 1+a Ni x Co y Mn z M c O 2-b The molar ratio between them is mixed.
  • step i)-1 the concentration of the first aqueous solution is 1 to 3 mol/L, the concentration of the second aqueous solution as a precipitant is 2 to 12 mol/L, and the concentration of ammonia as a complexing agent is 2 ⁇ 10mol/L.
  • the sodium-containing basic compound and/or the potassium-containing basic compound are each independently selected from the group consisting of sodium or potassium hydroxide, carbonate, bicarbonate, potassium salts and their combinations.
  • step i)-1 the co-precipitation reaction is performed in the presence of an inert gas.
  • the inert gas is nitrogen.
  • step i)-1 the reaction system temperature of the co-precipitation reaction is constant temperature, preferably 50-80°C.
  • step i)-1 the reaction time of the co-precipitation reaction is 40-100 hours.
  • step i)-1 the co-precipitation reaction is performed under stirring.
  • step i)-2 crystal growth is performed under stirring.
  • step i)-2 after the co-precipitation reaction is completed, one or more operations of aging, separation, washing and drying are performed, thereby obtaining the precursor.
  • the lithium source is selected from lithium carbonate, lithium hydroxide and combinations thereof, preferably lithium hydroxide.
  • the first additive comprising element M is selected from oxides, hydroxides, halides, sulfides, phosphates, borates and combinations thereof of element M, preferably Tungsten trioxide, molybdenum trioxide, niobium pentoxide, lanthanum trioxide, and tantalum pentoxide, or combinations thereof.
  • step ii) the precursor, the lithium source and the first additive containing the element M are uniformly mixed in a high-speed mixer.
  • step ii) isothermal sintering is performed in an oxygen furnace.
  • step ii) after the sintered mixture is lowered to room temperature, it is crushed, sieved, and iron is removed, thereby obtaining the positive electrode material Li 1+a Ni x Co y Mnz M c O 2 .
  • the second additive comprising element M' and/or A is selected from oxides, hydroxides, halides, sulfides, phosphates of element M' and/or A , borates and combinations thereof, preferably alumina and/or lithium fluoride.
  • step iii) the first positive electrode material Li 1+a Ni x Co y Mnz M c O 2 and the second additive comprising elements M' and/or A are mixed in a high speed mixer uniform.
  • the second additive comprising elements M' and/or A may be a mixture of compounds each comprising element M' and a compound comprising element A, or may be a compound comprising both elements M' and A.
  • step iii) isothermal sintering is performed in an oxygen furnace.
  • the material coating methods include dry coating, coating after washing and drying, wet in-situ coating, and the like.
  • the second aqueous solution of preparation concentration is the ammoniacal liquor of 6mol/L as complexing agent solution.
  • the particle size D 50 of the nuclear particles in the reaction system grows to 3.0 ⁇ m, adjust the pH of the solution to 11.2 ⁇ 0.05, adjust the flow rate of the first aqueous solution to 500mL/h, increase the stirring speed to 700rpm, and keep the reaction temperature unchanged.
  • the particle size D 50 grows to 14 ⁇ m, it is aged for 1 h, separated, washed, and dried to obtain the precursor material Ni 0.83 Co 0.11 Mn 0.06 (OH) 2 ;
  • the above-mentioned precursor, lithium hydroxide, and tungsten trioxide were weighed at a molar ratio of 1:1.03:0.002, mixed uniformly in a mixer, and sintered at a constant temperature in an oxygen furnace with an oxygen concentration greater than 95% and a heating rate of 5 °C/min, sintering temperature 800 °C, sintering time 12h, after natural cooling to room temperature, crushing, sieving, iron removal, to obtain positive electrode material 1: Li 1.03 Ni 0.828 Co 0.110 Mn 0.060 W 0.002 O 2 .
  • FIG. 1 is a SEM image of the positive electrode material prepared in Example 1.
  • the positive electrode material was prepared according to the method of Example 1, the material composition and specific process conditions were changed as shown in Table 1, and Examples 2-5 and Comparative Examples 1-6 were respectively carried out to prepare positive electrode material 2 to positive electrode material 5, and the positive electrode Material D1 to positive electrode material D6.
  • Example 2 the first additive is niobium pentoxide.
  • Example 3 the first additive is molybdenum trioxide.
  • Example 4 the first additive is dilanthanum trioxide, and the second additive is aluminum oxide.
  • Example 5 the first additive is tantalum pentoxide, and the second additive is lithium fluoride.
  • FIG. 2 is an SEM image of a cross-section of the positive electrode material prepared in Example 1.
  • D (003) represents the crystal thickness of the (003) crystal plane normal direction represented by the single (003) peak
  • D (104) represents the crystal thickness of the (104) crystal plane normal direction represented by the single (104) peak
  • D (003) and D (104) are each calculated via Equation III:
  • ⁇ is the X-ray wavelength
  • ⁇ is the full width at half maximum of diffraction peak D (003) or D (104) in the XRD pattern
  • ⁇ is the diffraction peak D (003) or D (104) Bougella diffraction angle in the XRD pattern, the 2 ⁇ range of the (003) peak is 18.5-19.5°, and the 2 ⁇ range of the (104) peak is 44.0-45.0°.
  • FIG. 3 is an XRD test spectrum of the cathode material prepared in Example 1.
  • the median particle size D50 is measured by a laser particle size analyzer and calculated based on the volume distribution.
  • the angle of repose is measured according to GB/T 6609.24-2004 test method for angle of repose of alumina powder.
  • the measuring device includes: glass funnel (the inner diameter of the feeding port is 3mm); glass bottom plate (the surface is wiped clean, and placed horizontally under the funnel); funnel fixing bracket (solid structure, keep the center line of the funnel perpendicular to the horizontal plane); height locator (determine the funnel The height from the feed opening to the surface of the glass floor, uses 60mm among the present invention).
  • the positive electrode material, conductive carbon black and polyvinylidene fluoride (PVDF) prepared in Examples 1-5 and Comparative Examples 1-6 were weighed and mixed according to the mass ratio of 95%: 2.5%: 2.5%, and N- Methylpyrrolidone (NMP) and stirred to make the mixture form a uniform slurry, coated on the aluminum foil, scraped, dried and rolled flat, punched into a positive electrode sheet with a diameter of 12mm and a thickness of 120 ⁇ m with a pressure of 100MPa, and then placed Dry in a vacuum oven at 120°C for 12 hours.
  • PVDF polyvinylidene fluoride
  • the coin cell assembly process was carried out in an Ar gas-protected glove box, where the water content and oxygen content were both less than 5 ppm.
  • EC ethylene carbonate
  • DEC divinyl carbonate
  • Rate performance test method use the above-mentioned activated battery, under room temperature, within the voltage range of 3.0 ⁇ 4.3V, conduct charge/discharge tests at current densities of 0.1C, 0.2C, 0.33C, 0.5C, 1C, and 2C respectively. The capacity values at different rates are evaluated against the retention rate at a rate of 0.1C, and the results are shown in Table 3.
  • Cycling performance test method Use the activated battery at high temperature (50°C) with a current density of 1C and a voltage range of 3.0 to 4.3V to perform 80 cycles, and evaluate the cycle performance by its capacity retention rate. The results are shown in the table 3.
  • the lithium ion diffusion coefficient test is carried out on the powder material, and the EIS test method is adopted: take the unactivated half-cell prepared above, let it stand for 2 hours, and charge it with a constant current of 0.1C to the cut-off voltage of 4.3V, then keep charging at a constant voltage for 30 minutes, then discharge at a constant current of 0.1C to a cut-off voltage of 3.0V;
  • the EIS test is carried out within the frequency range of 100 kHz to 0.01 Hz, and the amplitude is 10 mV. According to the formula:
  • the slope of the fitting line between Z re and ⁇ -1/2 can be obtained, that is, ⁇ ;
  • Z re is the real part of the measured impedance spectrum
  • R s is the solution resistance
  • R ct is the charge transfer resistance
  • ⁇ is the angular frequency
  • f is the test frequency
  • ⁇ is the Warburg factor
  • the bulk Li + diffusion coefficient of the material was calculated; where R is the ideal gas constant, T is the absolute temperature, A is the cross-sectional area of the electrode, n is the number of electron transfers, F is the Faraday constant, and C is the concentration of lithium ions in the electrode.
  • Table 2 shows the physical and chemical parameters of the positive electrode materials of Examples 1-5 and Comparative Examples 1-6.
  • the positive electrode material obtained has the micrograin boundary number N in the range of 10.5 to 14.5 and excellent lithium diffusion coefficient.
  • Comparative Example 1 when the amount of additive elements that have the effect of regulating the growth of micrograin boundaries is used too much, the size of the microcrystals is significantly reduced due to the hindered growth and fusion, the number of internal micrograin boundaries is too large, and the overall crystallinity of the positive electrode material deteriorates. Lithium diffusion coefficient decreases.
  • Comparative Example 2 when no additive elements that have the effect of regulating the growth of micrograin boundaries are added, it is beneficial for the fusion and growth of microcrystals to eliminate micrograin boundaries, so that the number of micrograin boundaries is too small, and the lithium diffusion coefficient is significantly changed. Small.
  • Comparative Example 4 when the pH of the second stage is lower than that of the first stage in the precursor synthesis process, the crystallinity of the precursor becomes better, the primary particles of the positive electrode material are not easy to grow and the size is too small during the sintering process, and the crystallite size does not change relatively. As a result, the internal micrograin boundaries are reduced, and the lithium diffusion coefficient becomes significantly smaller.
  • Comparative Example 5 when the sintering temperature was too low, the fusion growth between microcrystals in the positive electrode material was insufficient, the size was significantly smaller, and the micrograin boundaries increased, but the overall crystallinity of the positive electrode material was poor, and the lithium diffusion coefficient was greatly reduced.
  • Table 3 shows the performance parameters of the positive electrode materials of the above Examples 1-5 and Comparative Examples 1-6.
  • Example 1 Compared with Example 1, the capacities of the positive electrode materials in Comparative Examples 1-6 generally decreased at 0.1C. In Comparative Example 5, due to the low sintering temperature, the growth and crystallization of the positive electrode materials was insufficient, and the capacity could not be exerted.

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Abstract

本发明提供了一种用于锂离子电池的正极材料，其具有以下通式I：Li 1+aNi xCo yMn zM cM' dO 2-bA b 通式I，其中-0.05≤a≤0.3，0.8≤x≤1，0≤y≤0.2，0≤z≤0.2，0≤c≤0.01，0≤d≤0.01，x+y+z+c+d＝1，并且0≤b≤0.05；M和M'彼此不同并且各自独立地选自La、Cr、Mo、Ca、Fe、Ti、Zn、Y、Zr、W、Nb、V、Mg、B、Al、Sr、Ba、Ta中的至少一种，A为选自F、Cl、Br、I、S中的至少一种，并且所述正极材料的一次颗粒中的微晶界数量N为10.5～14.5，其中，N经由公式I计算得出：N＝D S/D X 公式I，其中，D S为通过所述正极材料的横切面SEM照片测量得到的一次颗粒的平均尺寸，并且D X为通过XRD测试及谢乐公式计算得到的所述正极材料的一次颗粒中的微晶的平均尺寸。本发明还提供了所述正极材料的制备方法。

Description

用于锂离子电池的正极材料及其制备方法 技术领域
本发明涉及一种锂离子电池的正极材料及其制备方法。
背景技术
在全球“碳达峰”、“碳中和”的时代背景下，新能源汽车和节能减排成为汽车产业的当务之急，推动着传统的内燃机汽车向更加绿色环保的新能源电动汽车转型。在电动汽车中，锂离子电池作为一种很有前景的高效环保电源受到了广泛关注。
层状三元材料是目前锂离子电池正极材料的主流选择之一，相较于负极、电解液等组分，正极材料容量低，占比大，成本高，因此成为制约锂离子电池整体性能的关键因素。
可以通过调整材料颗粒尺寸、结构形貌、掺杂以及包覆改性等手段来改善层状三元材料的容量、倍率及寿命等性能。专利申请CN111106344A以磷酸铝镁复合物为原料，通过固相、液相、气相方法包覆在正极材料表面，热处理后得到从内到外依次为正极材料-掺杂层-包覆层的复合正极材料，返烧过程中，少量锂离子进入包覆层，改善包覆层离子电导，同时包覆层中部分金属进入正极表面，稳定材料结构，从而获得综合性能更优的高容量正极材料。专利申请CN111217407A通过将前驱体和含锂化合物分别预烧处理，再混合烧结，提高了材料结晶度，降低了材料表面残碱含量，抑制了表面副反应的发生，从而提升了正极材料的容量和循环稳定性。
为满足电动汽车持续增长的续航里程、快充等需求，仍然需要持续改进锂离子电池的倍率性能、容量和循环寿命等，对层状三元材料的性能提升是其中的关键。
发明内容
为此，一方面，本公开提供了一种用于锂离子电池的正极材料，其具有以下通式I：
Li 1+aNi xCo yMn zM cM’ dO 2-bA b   通式I，
其中-0.05≤a≤0.3，0.8≤x≤1，0≤y≤0.2，0≤z≤0.2，0≤c≤0.01，0≤d≤0.01且x+y+z+c+d＝1，并且0≤b≤0.05；
M和M’彼此不同并且各自独立地选自La、Cr、Mo、Ca、Fe、Ti、Zn、Y、Zr、W、Nb、V、Mg、B、Al、Sr、Ba、Ta中的至少一种，
A为选自F、Cl、Br、I、S中的至少一种，并且
所述正极材料的一次颗粒中的微晶界数量N为约10.5～约14.5，其中，N经由公式I计算得出：
N＝D S/D X   公式I，
其中，D S为通过所述正极材料的横切面SEM照片测量得到的一次颗粒的平均尺寸，并且D X为通过XRD测试及谢乐公式计算得到的所述正极材料的一次颗粒中的微晶的平均尺寸。
根据本发明，通过在正极材料的一次颗粒中包含可控的特定数量的微晶界，提供了锂离子体相快速扩散的路径，提高了锂离子扩散系数，从而实现了优异的倍率性能和容量发挥；同时兼顾了一次颗粒的结晶性，避免了在电池充/放电循环过程中，在颗粒内部，尤其是在一次颗粒中产生微裂纹，从而改善了正极材料和锂离子电池的循环寿命。
另一方面，本发明还提供根据本发明的正极材料的制备方法，其包括以下步骤：
步骤i)-1混合含有镍盐、钴盐和锰盐的第一水溶液、含钠的碱性化合物和/或含钾的碱性化合物的第二水溶液、以及氨水，调节由此得到的混合水溶液的第一pH值为约9～约12，从而使共沉淀反应发生以形成晶体，
步骤i)-2当所述晶体生长至其中值粒径D 50为约2～约5μm时，调节所述混合水溶液的第二pH值为约9～约12，其中，第二pH值大 于第一pH值，且差值在约0.1～约1.0之间，使晶体继续生长至其中值粒径D 50为约9～约20μm，由此得到前驱体；和
步骤ii)混合前驱体、锂源和包含元素M的第一添加剂，在650～900℃的温度下，恒温烧结由此得到的混合物并持续约4～约20小时，自然降温使经烧结的化合物降至室温，经破碎、过筛、除铁后，得到第一正极材料Li 1+aNi xCo yMn zM cO 2，以及任选地
步骤iii)混合第一正极材料Li 1+aNi xCo yMn zM cO 2和包含元素M’和/或A的第二添加剂，在约200～约700℃的温度下，恒温烧结由此得到的混合物并持续约3～约10小时，由此得到第二正极材料Li 1+aNi xCo yMn zM cM’ dO 2-bA b。
根据本发明的制备方法可控而且简单易操作，通过控制前驱体的成核过程和晶体生长过程的pH值，以简单方式控制前驱体的一次纤维形貌及结晶性，进而控制正极材料的一次颗粒中的微晶界数量。而且，通过具有微晶界生长调控作用的掺杂元素的种类选择及用量控制，结合调控烧结温度，实现了对正极材料的结晶性及微晶界数量的控制。
包含根据本发明的正极材料的锂离子电池可用于电动车辆(如汽车)、区域性电站和便携式设备中。
参考以下附图，本发明的各种其它特征、方面和优点会变得更加显而易见。这些附图并非按比例绘制，旨在示意性地解释说明各种结构及位置关系，并且不应理解为限制性的。
附图说明
图1为实施例1制得的正极材料的扫描电镜(SEM)图像。
图2为实施例1制得的正极材料的横切面SEM图像。
图3为实施例1制得的正极材料的XRD测试谱图。
图4为安息角计算方法示意图。
具体实施方式
除非另外定义，本文使用的所有技术和科学术语均为与本发明所 属领域技术人员通常理解的含义。若存在不一致的地方，则以本申请提供的定义为准。
除非另外指出，本文所列出的数值范围旨在包括范围的端点，和该范围之内的所有数值和所有子范围。
本文的材料、含量、方法、设备、附图和实例均是示例性的，除非特别说明，不应理解为限制性的。
本文所用术语“包含”、“包括”和“具有”均表示可以将不影响最终效果的其他组分或其他步骤包括在内。这些术语涵盖“由......组成”和“基本上由......组成”的含义。根据本发明的产品和方法可以包含或包括本公开中描述的必要技术特征，以及额外的和/或任选存在的组分、成分、步骤或本文描述的其他限制性特征；或者可以由本公开中描述的必要技术特征，以及额外的和/或任选存在的组分、成分、步骤或本文描述的其他限制性特征组成；或者基本上由本公开中描述的必要技术特征，以及额外的和/或任选存在的组分、成分、步骤或本文描述的其他限制性特征组成。
除非另有明确说明，本公开中所用的所有材料和试剂均商购可得。
除非另外指出或者明显矛盾，本文进行的操作都可以在室温和常压下进行。
除非另外指出或者明显矛盾，可以任何合适的次序进行本公开中的方法步骤。
如本文中所使用，术语“约”是指其所限定的数值可以具有±该数值的10％的范围内的偏差，例如，术语“约300nm”是指“300±30nm”的范围。
以下将详细描述本公开的实例。
[正极材料]
根据本公开，提供一种用于锂离子电池的正极材料，其具有以下通式I：
Li 1+aNi xCo yMn zM cM’ dO 2-bA b    通式I，
其中-0.05≤a≤0.3，0.8≤x≤1，0≤y≤0.2，0≤z≤0.2，0≤c≤0.01，0≤d≤0.01且x+y+z+c+d＝1.，并且0≤b≤0.05；M和M’彼此不同并且各自独立地选自La、Cr、Mo、Ca、Fe、Ti、Zn、Y、Zr、W、Nb、V、Mg、B、Al、Sr、Ba、Ta中的至少一种，A为选自F、Cl、Br、I、S中的至少一种，并且
所述正极材料的一次颗粒中的微晶界数量N为约10.5～约14.5，其中，N经由公式I计算得出：
N＝D S/D X    公式I，
其中，D S为通过所述正极材料的横切面SEM照片测量得到的一次颗粒的平均尺寸，D X为通过XRD测试及谢乐公式计算得到的所述正极材料的一次颗粒中的微晶的平均尺寸。
在一些实例中，当通式I中的d和b为0时，正极材料具有以下通式II：
Li 1+aNi xCo yMn zM cO 2    通式II，
其中a、x、y、z、c、M、M’和A如前面对通式I所定义。
层状三元材料的容量发挥以及倍率性能都受限于锂离子扩散能力，除锂离子的层间扩散和固-液界面交换过程外，锂离子在微晶界等缺陷位置处的扩散往往被忽略。根据本发明的正极材料的一次颗粒内部保留了一定数量的微晶，并在微晶之间形成微晶界，一定数量的微晶界有利于提升锂离子体相的扩散速率，从而提升正极材料的容量和倍率性能，同时保持了良好的结晶性，避免在重复的充/放电过程中发生一次颗粒破碎的风险，从而保证了正极材料的循环寿命。
所述正极材料具有一次颗粒团聚组成二次颗粒的结构特征，其中一次颗粒是指与周围的正极材料具有明显界线的较完整的单个颗粒，二次颗粒是指由多个上述一次颗粒相互堆积构成的，无外力作用时不会发生分离的尺寸较大的正极材料球体。所述正极材料一次颗粒内部并非完美的单晶结构，而是由多个具有短程有序的晶体结构的微晶区域紧密结合组成，定义所述微晶区域的相互结合的界线为微晶界，该微晶界无法通过扫描电镜等外部观察手段明确辨析。
微晶界数量通过公式I进行评价：
N＝D S/D X   公式I。
在一些实例中，D S为约300～约600nm，优选约400～约550nm，更优选约450～约550nm，并且D S是经由将正极材料剖开后的横切面的SEM图像测量得到的。
在一些实例中，D X为约30～约60nm，优选约40～约50nm，更优选约40～约45nm，并且D X经由公式II计算得出：
Dx＝(D (003)+D (104))/2    公式II，
其中，D (003)表示单个(003)峰所代表的(003)晶面法向的晶体厚度，D (104)表示单个(104)峰所代表的(104)晶面法向的晶体厚度，并且D (003)和D (104)各自经由谢乐公式计算得出：
D＝Kλ/(β·cosθ)    谢乐公式，
其中，
K为Sherry常数0.89，
λ为X射线波长
Figure PCTCN2022092274-appb-000001
β为XRD图谱中衍射峰D (003)或D (104)的半高宽度，以及
θ为XRD图谱中的衍射峰D (003)或D (104)布格拉衍射角，(003)峰的2θ范围为约18.5～约19.5°，并且(104)峰的2θ范围为约44.0～约45.0°。
在一些实例中，所述正极材料的二次颗粒的中值粒径D 50为约9～约20μm，并且D 50经由激光粒度仪测量并基于体积分布计算得出。
中值粒径D 50指的是，颗粒的体积分布百分数达到50％时所对应的粒径值。例如，二次颗粒的中值粒径D 50为9μm表示，大于9μm的二次颗粒占50体积％，小于9μm的颗粒也占50体积％。
在一些实例中，所述正极材料的在20KN测得的压实密度PD与振实密度TD的比值符合1.1≤PD/TD≤1.3。在该数值范围内的PD/TD比值使得正极材料足够密实，从而有利于加工得到高压实密度的锂离子电池极片，并提高体积能量密度，同时具有合适的孔隙率，有助于电解液浸润正极材料，从而使得锂离子电池具有优异的容量和倍率性能。
在一些实例中，所述正极材料的安息角α≤50°，优选为约30～ 约45°，所述安息角α是根据GB/T 6609.24-2004氧化铝粉末安息角测试方法测得的。在该数值范围内安息角α使得正极材料具有良好的流动性，有利于实际生产中的加工性。
[正极材料的制备方法]
本发明还提供用于锂离子的正极材料的方法，其包括以下步骤：
步骤i)-1混合含有镍盐、钴盐和锰盐的第一水溶液、含钠的碱性化合物和/或含钾的碱性化合物的第二水溶液、以及氨水，调节由此得到的混合水溶液的第一pH值为约9～约12，从而使共沉淀反应发生以形成晶体，
步骤i)-2当所述晶体生长至其中值粒径D 50为约2～约5μm时，调节所述混合水溶液的第二pH值为约9～约12，其中，第二pH值大于第一pH值，且差值在约0.1～约1.0之间，使晶体继续生长至其中值粒径D 50为约9～约20μm，由此得到前驱体；和
步骤ii)混合所述前驱体、锂源和包含元素M的添加剂，在650～900℃的温度下，恒温烧结由此得到的混合物并持续约4～约20小时，自然降温(优选降至室温)及破碎、过筛、除铁，得到第一正极材料Li 1+aNi xCo yMn zM cO 2，以及任选地
步骤iii)混合第一正极材料Li 1+aNi xCo yMn zM cO 2和包含元素M’和/或A的第二添加剂，在约200～约700℃的温度下，恒温烧结由此得到的混合物并持续约3～约10小时，由此得到第二正极材料Li 1+aNi xCo yMn zM cM’ dO 2-bA b。
如前所述，根据本发明的制备方法可控而且简单易行，通过含钠/钾的碱性化合物和氨水共同调节，控制前驱体的成核过程和晶体生长过程的pH值，以控制前驱体的一次纤维形貌及结晶性，进而控制正极材料一次颗粒中微晶界数量。而且，通过具有微晶界生长调控作用的掺杂元素选择及用量控制，结合调控烧结温度，实现了对正极材料结晶性及微晶界数量的控制。
在一些实例中，第一pH值为约10.5～约11.2，并且第二pH值为约11.2～约11.8。
在一些实例中，在步骤i)-1中，镍盐、钴盐和锰盐各自独立地选自硫酸盐、硝酸盐、醋酸盐和它们的组合，优选所述镍盐、钴盐和锰盐均为硫酸盐、或者均为硝酸盐、或者均为醋酸盐。
在一些实例中，在步骤i)-1中，镍盐、钴盐和锰盐按照第一正极材料通式Li 1+aNi xCo yMn zM cO 2-b中镍、钴、锰之间的摩尔比进行混合。
在一些实例中，在步骤i)-1中，第一水溶液的浓度为1～3mol/L，作为沉淀剂的第二水溶液的浓度为2～12mol/L，作为络合剂的氨水的浓度为2～10mol/L。
在一些实例中，在步骤i)-1中，含钠的碱性化合物和/或含钾的碱性化合物各自独立地选自钠或钾的氢氧化物、碳酸盐、碳酸氢盐、草酸盐和它们的组合。
在一些实例中，在步骤i)-1中，共沉淀反应在惰性气体的存在下进行。在一些实例中，惰性气体为氮气。
在一些实例中，在步骤i)-1中，共沉淀反应的反应体系温度为恒温，优选为50～80℃。
在一些实例中，在步骤i)-1中，共沉淀反应的反应时间为40～100小时。
在一些实例中，在步骤i)-1中，共沉淀反应在搅拌下进行。
在一些实例中，在步骤i)-2中，晶体生长在搅拌下进行。
在一些实例中，在步骤i)-2中，在共沉淀反应结束后，进行陈化、分离、洗涤和烘干中的一种或多种操作，由此得到前驱体。
在一些实例中，在步骤ii)中，所述锂源选自碳酸锂、氢氧化锂和它们的组合，优选氢氧化锂。
在一些实例中，在步骤ii)中，所述包含元素M的第一添加剂选自元素M的氧化物、氢氧化物、卤化物、硫化物、磷酸盐、硼酸盐和它们的组合，优选三氧化钨、三氧化钼、五氧化二铌、三氧化二镧和五氧化二钽或它们的组合。
在一些实例中，在步骤ii)中，在高速混料机中将前驱体、锂源和包含元素M的第一添加剂混合均匀。
在一些实例中，在步骤ii)中，在氧气炉中进行恒温烧结。
在一些实例中，在步骤ii)中，在使经烧结的混合物降至室温后，进行破碎、过筛、除铁，由此得到正极材料Li 1+aNi xCo yMn zM cO 2。
在一些实例中，在步骤iii)中，所述包含元素M’和/或A的第二添加剂选自元素M’和/或A的氧化物、氢氧化物、卤化物、硫化物、磷酸盐、硼酸盐和它们的组合，优选氧化铝和/或氟化锂。
在一些实例中，在步骤iii)中，在高速混料机中将第一正极材料Li 1+aNi xCo yMn zM cO 2和包含元素M’和/或A的第二添加剂混合均匀。
在一些实例中，包含元素M’和/或A的第二添加剂可以是各自包含元素M’的化合物与包含元素A的化合物的混合物，也可以是包含元素M’和A两者的化合物。
在一些实例中，在步骤iii)中，在氧气炉中进行恒温烧结。
在一些实例中，在步骤iii)中，材料包覆方式包括干法包覆、水洗烘干后包覆和湿法原位包覆等。
实施例
实施例1
将硫酸镍、硫酸钴、硫酸锰按照摩尔比83∶11∶6溶解于纯水中，得到浓度为2mol/L的第一水溶液，配制浓度为8mol/L的氢氧化钠溶液作为用作沉淀剂的第二水溶液，配制浓度为6mol/L的氨水作为络合剂溶液。
向反应釜中加入氢氧化钠和氨水的混合水溶液，调整pH至10.9，通入氮气保护，反应体系温度控制在60℃，将第一水溶液、氢氧化钠溶液和氨水分别从进液管道加入反应釜中，搅拌转速保持500rpm，第一水溶液进液量控制在200mL/h，调节氢氧化钠溶液和氨水的流速，以保持反应体系pH稳定在10.9±0.05。
待反应体系中核颗粒的粒度D 50生长至3.0μm后，调整溶液pH至11.2±0.05，第一水溶液流速调整至500mL/h，搅拌转速提高至700rpm，反应温度保持不变，待溶液中颗粒平均粒度D 50生长至14μm后，陈化1h，分离、洗涤、烘干得到前驱体材料Ni 0.83Co 0.11Mn 0.06(OH) 2；
将上述前驱体、氢氧化锂、三氧化钨以摩尔比1∶1.03∶0.002分别 称量后，在混料机中混合均匀，在氧气炉中恒温烧结，氧气浓度大于95％，升温速率为5℃/min，烧结温度800℃，烧结时间12h，自然冷却至室温后，经破碎、过筛、除铁，得到正极材料1∶Li 1.03Ni 0.828Co 0.110Mn 0.060W 0.002O 2。
图1为实施例1制得的正极材料的SEM图像。
实施例2-5和对比例1-6
按照实施例1的方法制备正极材料，材料组成及具体工艺条件如表1所示进行变化，分别进行实施例2-5和对比例1-6，制备得到正极材料2至正极材料5、以及正极材料D1至正极材料D6。
在实施例2中，第一添加剂为五氧化二铌。
在实施例3中，第一添加剂为三氧化钼。
在实施例4中，第一添加剂为三氧化二镧，第二添加剂为氧化铝。
在实施例5中，第一添加剂为五氧化二钽，第二添加剂为氟化锂。
Figure PCTCN2022092274-appb-000002
[正极材料性能测试]
对实施例1-5与对比例1-6中制备的制备的正极材料进行以下测试，测试结果记录在表2中。
D S是经由将正极材料剖开后的横切面的SEM图像测得的。图2为实施例1制得的正极材料的横切面的SEM图像。
D X经由公式II计算得出：
(D (003)+D (104))/2   公式II，
其中，D (003)表示单个(003)峰所代表的(003)晶面法向的晶体厚度，D (104)表示单个(104)峰所代表的(104)晶面法向的晶体厚度，并且D (003)和D (104)各自经由公式III计算得出：
D＝Kλ/(β·cosθ)   公式III，
其中，
K为Sherry常数0.89，
λ为X射线波长
Figure PCTCN2022092274-appb-000003
β为XRD图谱中衍射峰D (003)或D (104)的半高宽度，以及
θ为XRD图谱中的衍射峰D (003)或D (104)布格拉衍射角，(003)峰的2θ范围为18.5～19.5°，并且(104)峰的2θ范围为44.0～45.0°。
图3为实施例1制得的正极材料的XRD测试谱图。
中值粒径D 50经由激光粒度仪测量并基于体积分布计算得出。
安息角根据GB/T 6609.24-2004氧化铝粉末安息角测试方法进行测量。测量装置包括：玻璃漏斗(下料口内径3mm)；玻璃底板(表面擦拭干净，水平安置于漏斗下方)；漏斗固定支架(结构坚固，保持漏斗中心线垂直于水平面)；高度定位器(确定漏斗下料口到玻璃地板表面的高度，本发明中使用60mm)。测试过程中，取正极材料15g，匀速加入玻璃下料漏斗中，控制加料速度，避免粉体材料堵塞下料口，下料完成后，测量粉体形成的锥体的底面圆形直径d和高度h，根据反三角函数α＝arctan(2h/d)，得到粉体材料安息角α，如图4所示。
[扣式电池的制备]
将实施例1-5与对比例1-6中制备的正极材料、导电炭黑及聚偏 二氟乙烯(PVDF)按照质量比95％∶2.5％∶2.5％分别称量后混合，加N-甲基吡咯烷酮(NMP)并搅拌使混合物形成均匀浆料，涂覆于铝箔上，刮平，烘干处理后辊压平整，以100MPa的压力冲压成直径12mm、厚120μm的正极极片，然后置于真空烘箱中120℃烘干12h。
扣式电池组装过程在Ar气保护的手套箱中进行，其中水含量和氧含量均小于5ppm。使用上述获得的极片作为正极，使用直径为17mm，厚度为1mm的Li金属片作为负极；使用厚度为25μm的聚乙烯多孔膜作为隔膜，使用溶解有1mol/L的LiPF 6的碳酸乙烯酯(EC)和碳酸二乙烯酯(DEC)体积比1∶1的混合液作为电解液，使用型号为2025的扣式电池壳作为电池壳。组装完成后，获得未活化的半电池。
[扣式电池的性能评价]
扣式电池组装完成后，静置2h，待其开路电压稳定后，以0.1C(1C＝200mA/g)电流进行恒流充电至截止电压4.3V，然后保持恒压充电30min，随后以0.1C电流恒流放电至截止电压3.0V；随后再以同样的方式充/放电循环一次，将此时的电池作为已活化电池。
倍率性能测试方法：使用上述已活化电池，室温条件下，在3.0～4.3V电压范围内，分别以0.1C、0.2C、0.33C、0.5C、1C、2C电流密度进行充/放电测试，以不同倍率下的容量值相对于0.1C倍率下的保持率进行倍率性能评价，结果如表3所示。
循环性能测试方法：使用已活化电池，在高温(50℃)条件下，以1C电流密度，在3.0～4.3V电压范围内，进行80次循环，以其容量保持率评价循环性能，结果如表3所示。
[锂离子扩散系数测试]
为说明本发明所述特征材料性能提升的原因，对粉体材料进行锂离子扩散系数测试，采用EIS测试方法：取前面制备的未活化半电池，静置2h，以0.1C电流进行恒流充电至截止电压4.3V，然后保持恒压充电30min，随后以0.1C电流恒流放电至截止电压3.0V；随后再以0.1C电流恒流充电至截止电压4.3V，取下满电态半电池，在100 kHz～0.01Hz频率范围内进行EIS测试，振幅10mV。根据公式：
Z re＝R s+R ct+σω -1/2，以及
ω＝2πf，
可得Z re与ω -1/2拟合直线斜率，即σ；
其中，Z re为测试所得阻抗谱的实部，R s为溶液电阻，R ct为电荷转移电阻，ω为角频率，f为测试频率，σ为Warburg因子；
再根据锂离子扩散系数计算公式：
D Li +＝R 2T 2/(2A 2n 4F 4C 2σ 2)
计算得到材料体相Li +扩散系数；其中R为理想气体常数，T为绝对温度，A为电极横截面积，n为电子转移数，F为法拉第常数，C为电极中锂离子浓度。
实施例1-5和对比例1-6的正极材料的物化参数如表2所示。
Figure PCTCN2022092274-appb-000004
从表1和表2可以看出，在根据本发明的实施例1-5中，通过在前驱体晶体生长过程中调控反应体系的pH，以及选择具有微晶界生长调控作用的掺杂元素及其用量，以及调控烧结温度，获得的正极材料具有在10.5～14.5范围内的微晶界数量N和优异的锂扩散系数。
在对比例1中，当具有调控微晶界生长效果的添加剂元素使用量过多时，微晶因生长融合受阻而尺寸明显变小，内部微晶界数量过多，正极材料整体结晶性变差，锂扩散系数降低。
在对比例2中，当不加入具有调控微晶界生长效果的添加剂元素时，有利于微晶间相互融合长大而消除微晶界，从而使微晶界数量过少，锂扩散系数明显变小。
在对比例3中，当前驱合成过程中第二阶段pH过高时，前驱体结晶性会变差，烧结过程中正极材料一次颗粒更易长大，微晶尺寸相对变化不大，从而内部微晶界增加，前驱体结晶性差的特点会延续到正极材料，导致锂扩散系数变小。
在对比例4中，当前驱合成过程中第二阶段pH低于第一阶段时，前驱体结晶性变好，烧结过程中正极材料一次颗粒不易长大而尺寸偏小，微晶尺寸相对变化不大，从而内部微晶界减少，锂扩散系数明显变小。
在对比例5中，当烧结温度过低时，正极材料内部微晶间融合生长不足，尺寸明显偏小，微晶界增加，但正极材料整体结晶性差，锂扩散系数大幅减小。
在对比例6中，烧结温度过高，正极材料内部微晶间过度融合生长，尺寸明显偏大，微晶界减少，锂扩散系数减小。
上述实施例1-5和对比例1-6的正极材料的性能参数如表3所示。
表3正极材料的性能参数
Figure PCTCN2022092274-appb-000005
从上表3可以看出，根据本发明的实施例1-5的正极材料表现出优异的容量、倍率保持率和循环保持率。
相对于实施例1，对比例1-6的正极材料在0.1C下容量普遍降低，对比例5因烧结温度过低，正极材料生长结晶不充分，容量无法发挥。同时可以看出，当正极材料微晶界数量过高时，倍率保持率降低，并且循环保持率明显变差，主要是由于一次颗粒内微晶界过多，易在循环过程中出现破裂；而微晶界数量N较小时，倍率性能明显变差，和前述结论一致，说明将正极材料的微晶界数量N控制在10.5～14.5的范围内，有利于同时实现高倍率性能和长循环寿命。

Claims (11)

  1. 用于锂离子电池的正极材料，其具有以下通式I：
    Li 1+aNi xCo yMn zM cM’ dO 2-bA b  通式I，
    其中-0.05≤a≤0.3，0.8≤x≤1，0≤y≤0.2，0≤z≤0.2，0≤c≤0.01，0≤d≤0.01，x+y+z+c+d＝1，并且0≤b≤0.05；
    M和M’彼此不同并且各自独立地选自La、Cr、Mo、Ca、Fe、Ti、Zn、Y、Zr、W、Nb、V、Mg、B、Al、Sr、Ba、Ta中的至少一种，
    A为选自F、Cl、Br、I、S中的至少一种，并且
    所述正极材料的一次颗粒中的微晶界数量N为约10.5～约14.5，其中，N经由公式I计算得出：
    N＝D S/D X  公式I，
    其中，D S为通过所述正极材料的横切面SEM照片测量得到的一次颗粒的平均尺寸，并且D X为通过XRD测试及谢乐公式计算得到的所述正极材料的一次颗粒中的微晶的平均尺寸。
  2. 根据权利要求1所述的正极材料，其中，D S为约300～约600nm，优选约400～约550nm，更优选约450～约550nm。
  3. 根据权利要求1或2所述的正极材料，其中，D X经由公式II计算得出：
    Dx＝(D (003)+D (104))/2  公式II，
    其中，D (003)表示单个(003)峰所代表的(003)晶面法向的晶体厚度，D (104)表示单个(104)峰所代表的(104)晶面法向的晶体厚度，并且D (003)和D (104)各自经由谢乐公式计算得出：
    D＝Kλ/(β·cosθ)  谢乐公式，
    其中，
    K为Sherry常数0.89，
    λ为X射线波长
    Figure PCTCN2022092274-appb-100001
    β为XRD图谱中衍射峰D (003)或D (104)的半高宽度，以及
    θ为XRD图谱中衍射峰D (003)或D (104)的布格拉衍射角，(003)峰 的2θ范围为约18.5～约19.5°，并且(104)峰的2θ范围为约44.0～约45.0°；
    优选D X为约30～约60nm，更优选约40～约50nm，进一步优选约40～约45nm。
  4. 根据权利要求1-3中任一项所述的正极材料，其中，所述正极材料的二次颗粒的中值粒径D 50为约9～约20μm。
  5. 根据权利要求1-4中任一项所述的正极材料，其中，所述正极材料的在20KN测得的压实密度PD与振实密度TD的比值符合1.1≤PD/TD≤1.3。
  6. 根据权利要求1-5中任一项所述的正极材料，其中，所述正极材料的安息角α≤50°，优选为约30～约45°。
  7. 制备根据权利要求1-6中任一项所述的正极材料的方法，其包括以下步骤：
    步骤i)-1混合含有镍盐、钴盐和锰盐的第一水溶液、含钠的碱性化合物和/或含钾的碱性化合物的第二水溶液、以及氨水，调节由此得到的混合水溶液的第一pH值为约9～约12，从而使共沉淀反应发生以形成晶体，
    步骤i)-2当所述晶体生长至其中值粒径D 50为约2-约5μm时，调节所述混合水溶液的第二pH值为约9～约12，其中，第二pH值大于第一pH值，且差值在约0.1～约1.0之间，使晶体继续生长至约9～约20μm，由此得到前驱体；
    步骤ii)混合所述前驱体、锂源和包含元素M的添加剂，在约650～约900℃的温度下，恒温烧结由此得到的混合物并持续约4～约20小时，经自然降温及破碎、过筛、除铁，得到第一正极材料Li 1+aNi xCo yMn zM cO 2，以及任选地
    步骤iii)混合第一正极材料Li 1+aNi xCo yMn zM cO 2和包含元素M’和/或A的第二添加剂，在约200～约700℃的温度下，恒温烧结由此得到的混合物并持续约3～约10小时，由此得到第二正极材料Li 1+aNi xCo yMn zM cM’ dO 2-bA b。
  8. 根据权利要求7所述的方法，其中，第一pH值为约10.5～约 11.2，并且第二pH值为约11.2～约11.8。
  9. 根据权利要求7或8所述的方法，其中，在步骤i)-1中，所述镍盐、钴盐和锰盐各自独立地选自硫酸盐、硝酸盐、醋酸盐和它们的组合，优选所述镍盐、钴盐和锰盐均为硫酸盐、或者均为硝酸盐、或者均为醋酸盐；和/或
    所述含钠的碱性化合物和/或含钾的碱性化合物各自独立地选自钠和钾的氢氧化物、碳酸盐、碳酸氢盐、草酸盐和它们的组合。
  10. 根据权利要求7-9中任一项所述的方法，其中，在步骤ii)中，所述锂源选自碳酸锂、氢氧化锂和它们的组合；和/或
    所述包含元素M的第一添加剂选自元素M的氧化物、氢氧化物、卤化物、硫化物、磷酸盐、硼酸盐和它们的组合，优选三氧化钨、三氧化钼、五氧化二铌、三氧化二镧和五氧化二钽或它们的组合。
  11. 根据权利要求7-10中任一项所述的方法，其中，在步骤iii)中，所述包含元素M’的第二添加剂选自元素M’的氧化物、氢氧化物、卤化物、硫化物、磷酸盐、硼酸盐和它们的组合，优选氧化铝和/或氟化锂。
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