WO2021238152A1 - 一种锂离子电池用复合正极材料、其制备方法及用途 - Google Patents

一种锂离子电池用复合正极材料、其制备方法及用途 Download PDF

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WO2021238152A1
WO2021238152A1 PCT/CN2020/135525 CN2020135525W WO2021238152A1 WO 2021238152 A1 WO2021238152 A1 WO 2021238152A1 CN 2020135525 W CN2020135525 W CN 2020135525W WO 2021238152 A1 WO2021238152 A1 WO 2021238152A1
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positive electrode
cathode material
electrode material
oxygen
lithium ion
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PCT/CN2020/135525
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English (en)
French (fr)
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许鑫培
杨红新
江卫军
乔齐齐
孙明珠
施泽涛
王鹏飞
马加力
陈思贤
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蜂巢能源科技有限公司
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Priority to US17/787,465 priority Critical patent/US20230032851A1/en
Priority to JP2022521739A priority patent/JP7389247B2/ja
Priority to EP20937875.1A priority patent/EP4024516A4/en
Priority to KR1020227034553A priority patent/KR20220150938A/ko
Publication of WO2021238152A1 publication Critical patent/WO2021238152A1/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
    • H01M4/36—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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H01M4/1315—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx containing halogen atoms, e.g. LiCoOxFy
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/582—Halogenides
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present disclosure relates to the field of battery technology, for example, to a composite positive electrode material for lithium ion batteries, a preparation method and application thereof.
  • Lithium-ion batteries have penetrated every aspect of life due to their high energy density and better cycle performance.
  • the development of cathode materials directly affects the development prospects of lithium-ion batteries.
  • they are widely used in the automotive and electronic industries.
  • NCM Ni x Co y Mn z
  • NCA Ni x Co y Al z
  • cobalt is expensive and pollutes the environment.
  • CN107546385A discloses a method for preparing LiNi x Mn 1-x O 2 binary cathode material and the prepared LiNi x Mn 1-x O 2.
  • the method includes: (1) preparing binary nickel and manganese salt aqueous solutions and Mixed alkali aqueous solution; (2) Respectively, binary nickel, manganese salt aqueous solution and mixed alkali aqueous solution were added to a microwave reactor protected by nitrogen at a certain flow rate, and stirred at a constant temperature for reaction; (3) The reactants were transferred to the hydrothermal reactor (4) Co-precipitate is filtered, washed, and dried; (5) The dried co-precipitate is mixed with lithium salt, mixed and ground, and then placed in a sintering furnace for high-temperature solid-phase reaction to obtain a binary cathode material .
  • the prepared nickel-manganese-based binary cathode material has an initial discharge capacity of more than 170 mAh/g and good cycle performance.
  • CN109811412A discloses a layered lithium nickel manganate cathode material with a single crystal morphology and a preparation method thereof.
  • the method includes: (1) a nickel salt and a manganese salt are prepared by a wet chemical method to obtain a nickel manganese precursor, wherein The molar ratio of Ni and Mn is 1:1; (2) Pre-sintering the nickel-manganese precursor to obtain a nickel-manganese oxide precursor; (3) Mixing the nickel-manganese oxide precursor with the lithium source and the M source additive, Then it is calcined to obtain a layered lithium nickel manganate cathode material with a single crystal morphology.
  • the present disclosure provides a composite positive electrode material for lithium ion batteries, a preparation method and application thereof.
  • a composite cathode material for lithium ion batteries includes a cathode material core and a halide coating layer coated on the surface of the cathode material core.
  • the halide includes Li 3 YX 6 , where X is at least one of halogens.
  • the halide-coated cathode material is coated with the halide coating layer, which greatly improves the ion conductivity and structural stability of the cathode material, and reduces the surface impedance of the material.
  • the interaction between the halogen-1 valent anion and the lithium ion in the halide provided by the present disclosure is weaker, and has better lithium ion conductivity; secondly, due to the larger halogen ion radius, it is beneficial to lithium ion Thirdly, the halide has good stability and is convenient to form a stable and firm connection with the base material; moreover, the halide coating layer has good chemical stability, which blocks the contact between the positive electrode material and the electrolyte, and reduces the side effects. The reaction occurs.
  • the combined effect of the above factors makes the obtained composite positive electrode material have extremely high ionic conductivity and structural stability, thereby improving the capacity, first effect and cycle performance of the material.
  • the sulfide solid electrolyte or the oxide solid electrolyte has good ionic conductivity, it cannot achieve the technical effect to be achieved by the present disclosure because the sulfide chemical stability is poor.
  • the reactions involved in the oxide solid electrolyte are more complicated.
  • the oxide solid electrolyte will react with air and moisture, and the cycle stability will decrease; the oxide particles are relatively hard, the solid interface contact is not good, the density is large, the mass energy density is low, and it is not suitable Large-scale production process.
  • the halide is Li 3 YCl 6 and/or Li 3 YBr 6 , for example, the halide can be Li 3 YCl 6 , or Li 3 YBr 6 , or Li 3 YCl 6 and Li 3 YBr 6 mixture.
  • the positive electrode material core includes a cobalt-free positive electrode material.
  • the positive electrode material core includes lithium nickel manganate positive electrode material.
  • the chemical formula of the lithium nickel manganese oxide cathode material is LiNi x Mn y O 2 , 0.55 ⁇ x ⁇ 0.95, 0.05 ⁇ y ⁇ 0.45, where x is for example 0.55, 0.6, 0.65, 0.7, 0.72, 0.75, 0.8, 0.9 or 0.95, etc.
  • y is, for example, 0.05, 0.08, 0.1, 0.2, 0.3, 0.35, 0.4, or 0.45.
  • halides are useful for various lithium-ion battery cathode materials commonly used in the art (for example, lithium iron phosphate, NCM ternary, NCA ternary, lithium cobaltate, lithium manganate, lithium nickel cobaltate, Lithium nickel manganese oxide, etc.) can play a role in improving ionic conductivity and stabilizing the structure.
  • lithium iron phosphate for example, lithium iron phosphate, NCM ternary, NCA ternary, lithium cobaltate, lithium manganate, lithium nickel cobaltate, Lithium nickel manganese oxide, etc.
  • the present disclosure particularly improves the performance of the cobalt-free positive electrode material by introducing a halide coating layer.
  • the cobalt-free positive electrode material is a cobalt-free positive electrode material based on a ternary material.
  • the present disclosure can also reduce the residual alkali by coating the halide coating layer on the surface of the cobalt-free positive electrode material.
  • the technical principle is: at a higher temperature (700-800°C), the halide coating layer and the cobalt-free positive electrode material Where the surface is in contact, the halogen in the halide (such as Cl) will react with a part of the lithium, forming an oxide at high temperature to be embedded in the material, reducing residual alkali and improving product performance.
  • the content of Y element in the Li 3 YX 6 is 0.1%-1%, such as 0.1%, 0.3%, 0.5%, 0.7%, 0.8% , 0.9% or 1%, etc.
  • the conductivity improvement effect will be insignificant; if the content of Y element in Li 3 YX 6 is greater than 1%, it will hinder lithium The insertion and extraction of ions reduces electrochemical performance.
  • the content of the Y element in the Li 3 YX 6 is 0.1%-0.3%.
  • the particle size D50 of the core of the positive electrode material is 1 ⁇ m-5 ⁇ m, such as 1 ⁇ m, 2 ⁇ m, 2.5 ⁇ m, 3 ⁇ m, 3.5 ⁇ m, 4 ⁇ m, or 5 ⁇ m, etc.
  • the particle size D50 of the core of the positive electrode material is 1 ⁇ m-3 ⁇ m.
  • the particle size D50 of the Li 3 YX 6 is 5nm-500nm, such as 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 50nm, 65nm, 80nm, 100nm, 15nm, 130nm, 150nm, 180nm, 200nm, 230nm, 260nm, 300nm, 350nm, 375nm, 400nm, 450nm, 500nm, etc.
  • the particle size D50 of the Li 3 YX 6 is 50 nm-100 nm.
  • the core particle size D50 of the positive electrode material is 1 ⁇ m-5 ⁇ m, and the particle size D50 of Li 3 YX 6 is 5 nm-500 nm. Within this range, it can be better formed on the surface of the coated base material. Better coating.
  • the halide coating layer has good chemical stability and does not react with oxygen and water in the air.
  • the content of residual alkali and free water of the composite cathode material is low, and the material
  • the total amount of residual lithium carbonate and lithium hydroxide is less than 0.3% (wt); the free water content in the material is less than 200ppm; its specific surface area is in the range of 0.2m 2 /g-0.9m 2 /g; the pH of the material is less than 12 .
  • a method for preparing the composite cathode material for lithium ion batteries includes the following steps:
  • the coating agent is mixed with the base cathode material, and then processed at a high temperature of 400°C-800°C in an oxygen-containing atmosphere to obtain a composite cathode material, such as 400°C, 425°C, 450°C, 460°C, 480°C, 500°C, 525°C , 550°C, 580°C, 600°C, 650°C, 700°C, 730°C, 750°C or 800°C etc.
  • a composite cathode material such as 400°C, 425°C, 450°C, 460°C, 480°C, 500°C, 525°C , 550°C, 580°C, 600°C, 650°C, 700°C, 730°C, 750°C or 800°C etc.
  • the coating agent includes Li 3 YX 6 , and X is at least one of halogens.
  • high temperature treatment is performed at 400°C-800°C. If the temperature is lower than 400°C, it will cause poor bonding between the coating layer and the core of the positive electrode material; if the temperature is higher than 800°C, it will lead to halogenation.
  • the structure of the substance has undergone serious changes, and for ternary materials or cobalt-free cathode materials, the mixing of lithium and nickel will be aggravated, thereby reducing the effect of improving conductivity, and the temperature is preferably 400°C-700°C.
  • Li3YX6 when the high temperature treatment temperature is higher than 700°C and below 800°C, the structure of Li3YX6 will be slightly damaged, reducing its effect on improving ion conductivity, and at the same time, it will contact the surface of the positive electrode material, especially the cobalt-free positive electrode material.
  • the halogen (such as Cl) in Li3YX6 will react with a part of the lithium, forming an oxide at high temperature to be embedded in the material, reducing residual alkali and improving product performance.
  • the volume concentration of oxygen in the oxygen-containing atmosphere is 20%-100%, for example, 20%, 25%, 30%, 40%, 45%, 50%, 60%, 70%, 80%. %, 90% or 100% etc.
  • the volume concentration of oxygen in the oxygen-containing atmosphere is 50%-90%.
  • the mixing method is dry mixing.
  • the mixing includes: mixing the coating agent and the base cathode material in a mixing device at a rotation speed of 2000 rpm to 3000 rpm, for example, 2000 rpm, 2250 rpm, 2500 rpm, 2700 rpm, 2800 rpm, or 3000 rpm.
  • the mixing time is 10 minutes to 20 minutes, such as 10 minutes, 15 minutes, 18 minutes, or 20 minutes.
  • the temperature of the high temperature treatment is 400-700°C.
  • the high temperature treatment time is 4h-8h, such as 4h, 4.2h, 4.5h, 5h, 5.5h, 5.7h, 6h, 6.5h, 7h, 7.5h or 8h.
  • the method further includes the steps of grinding and sieving after the high temperature treatment.
  • the base cathode material is lithium nickel manganese oxide
  • the preparation method of the lithium nickel manganese oxide includes:
  • the lithium source in step (a) is LiOH.
  • the mixing in step (a) is: mixing in a high-speed mixing device at a rotation speed of 2000 rpm-3000 rpm for 10 minutes to 20 minutes.
  • the high temperature reaction time in step (b) is 8h-12h, such as 8h, 9h, 9.5h, 10h, 11h or 12h.
  • the high-temperature reaction in step (b) is performed in an oxygen-containing atmosphere with an oxygen volume concentration greater than 90%.
  • the gas flow rate of the oxygen-containing atmosphere is 2L/min-20L/min, such as 2L/min, 5L/min, 7L/min, 10L/min, 12L/min, 14L/min, 15L/min or 20L/min etc.
  • step (b) after the high temperature reaction in step (b), a step of cooling and crushing is performed.
  • the method includes the following steps:
  • the coating agent and the base cathode material are mixed in a mixing device, the coating agent is Li 3 YCl 6 and/or Li 3 YBr 6 , mixed at a speed of 2000rpm-3000rpm for 10 minutes-20 minutes, and then placed in an oxygen-containing atmosphere High temperature treatment at 400°C-700°C for 4h-8h, in the oxygen-containing atmosphere, the volume concentration of oxygen is 20%-100%, grinding, sieving with a 300-400 mesh sieve, to obtain a composite positive electrode material.
  • the composite cathode material includes lithium nickel manganate and a coating layer coated on the surface of the lithium nickel manganate, the coating layer being Li 3 YCl 6 and/or Li 3 YBr 6 ;
  • the content of the Y element in the coating layer is 0.1%-1%.
  • a positive electrode in one embodiment of the present disclosure, includes the composite positive electrode material for lithium ion batteries according to one embodiment of the present disclosure.
  • a lithium ion battery is provided, and the lithium ion battery includes the positive electrode according to an embodiment of the present disclosure.
  • Figures 1a and 1b are SEM images of the material before coating (the positive electrode material prepared in the comparative example provided in the present disclosure) under different magnifications;
  • 2a and 2b are SEM images of the coated material (the cathode material prepared in the embodiment provided in the present disclosure) under different magnifications;
  • Figure 3 is the first charge-discharge curve of the material before and after coating.
  • the two curves indicated by arrows in the figure correspond to the composite cathode material after coating, and the two curves not indicated by arrows correspond to the positive electrode material before coating.
  • the former corresponds to the positive electrode material of the comparative example, and the composite positive electrode material of the embodiment after coating;
  • FIG. 4 is a cycle performance curve of the materials before and after coating, wherein the positive electrode material of the comparative example before coating corresponds to the composite positive electrode material of the embodiment after coating.
  • This embodiment provides a composite positive electrode material for a lithium ion battery.
  • the composite positive electrode material includes a positive electrode material core and a halide coating layer coated on the surface of the positive electrode material core.
  • the positive electrode material core is LiNi 0.75 Mn 0.25 O 2
  • the halide is Li 3 YCl 6 , based on the mass of the positive electrode material core as 100%, the content of Y element in the Li 3 YCl 6 is 0.5%, and the particle size D50 of the positive electrode material core is 3 ⁇ m .
  • This embodiment also provides a method for preparing the composite cathode material, which includes the following steps:
  • the coating agent Li 3 YCl 6 and the base cathode material are mixed in a mixing device at a rotation speed of 2200 rpm for 20 minutes, and then treated at a high temperature of 600 °C under an oxygen-containing atmosphere for 5 hours.
  • the oxygen-containing atmosphere is a combination of oxygen and nitrogen.
  • the volume concentration of nitrogen is 40%, and the volume concentration of oxygen is 60%, ground, and sieved with a 300-mesh sieve to obtain a composite positive electrode material.
  • This embodiment provides a composite positive electrode material for a lithium ion battery.
  • the composite positive electrode material includes a positive electrode material core and a halide coating layer coated on the surface of the positive electrode material core.
  • the positive electrode material core is LiNi 0.6 Mn 0.4 O 2
  • the halide is Li 3 YBr 6 , based on the mass of the positive electrode material core being 100%, the content of Y element in the Li 3 YBr 6 is 0.3%, and the particle size D50 of the positive electrode material core is 3 ⁇ m .
  • This embodiment also provides a method for preparing the composite cathode material, which includes the following steps:
  • the coating agent Li 3 YBr 6 and the base cathode material are mixed in a mixing device at a speed of 2750 rpm for 10 minutes, and then treated at a high temperature of 500° C. for 5.5 hours in an oxygen-containing atmosphere.
  • the atmosphere is a mixed atmosphere of oxygen and nitrogen, the volume concentration of nitrogen is 60%, and the volume concentration of oxygen is 40%, grinding and sieving with a 300-mesh sieve to obtain the composite positive electrode material.
  • This embodiment provides a composite positive electrode material for a lithium ion battery.
  • the composite positive electrode material includes a positive electrode material core and a halide coating layer coated on the surface of the positive electrode material core.
  • the positive electrode material core is LiNi 0.7 Mn 0.3 O 2
  • the halide is Li 3 YCl 6 , based on the mass of the positive electrode material core being 100%, the content of Y element in the Li 3 YCl 6 is 0.8%, and the particle size D50 of the positive electrode material core is 3 ⁇ m .
  • This embodiment also provides a method for preparing the composite cathode material, which includes the following steps:
  • the coating agent Li 3 YCl 6 and the base cathode material are mixed in a mixing device at a speed of 2250 rpm for 15 minutes, and then treated at a high temperature of 450 °C under an oxygen-containing atmosphere for 8 hours.
  • the oxygen-containing atmosphere is a combination of oxygen and nitrogen.
  • the volume concentration of nitrogen is 15%, and the volume concentration of oxygen is 85%, grinding, and sieving with a 400-mesh sieve to obtain a composite positive electrode material.
  • This embodiment provides a composite positive electrode material for a lithium ion battery.
  • the composite positive electrode material includes a positive electrode material core and a halide coating layer coated on the surface of the positive electrode material core.
  • the positive electrode material core is lithium iron phosphate
  • the halide is Li 3 YCl 6 , based on the mass of the positive electrode material core being 100%, the content of Y element in the Li 3 YCl 6 is 0.7%, and the particle size D50 of the positive electrode material core is 3.5 ⁇ m.
  • Coating process mix the coating agent (Li 3 YCl 6 ) and the matrix material in a mixing device, and then treat them at a high temperature of 450° C. for 8 hours under an oxygen-containing atmosphere.
  • the oxygen-containing atmosphere is a mixed atmosphere of oxygen and nitrogen.
  • the volume concentration is 15%, and the volume concentration of oxygen is 85%, ground, and sieved with a 400-mesh sieve to obtain a composite positive electrode material.
  • This embodiment provides a composite positive electrode material for a lithium ion battery.
  • the composite positive electrode material includes a positive electrode material core and a halide coating layer coated on the surface of the positive electrode material core.
  • the positive electrode material core is LiNi 0.8 Mn 0.2 O 2
  • the halide is Li 3 YCl 6 , based on the mass of the positive electrode material core being 100%, the content of Y element in the Li 3 YCl 6 is 0.15%, and the particle size D50 of the positive electrode material core is 5 ⁇ m .
  • This embodiment also provides a method for preparing the composite cathode material, which includes the following steps:
  • the coating agent Li 3 YCl 6 and the base cathode material are mixed in a mixing device at a speed of 2600 rpm for 15 minutes, and then treated at a high temperature of 550°C for 7 hours in an oxygen-containing atmosphere, the oxygen-containing atmosphere is oxygen and argon
  • the volume concentration of argon gas is 10%
  • the volume concentration of oxygen gas is 90%, ground, and sieved with a 250-mesh sieve to obtain a composite positive electrode material.
  • Example 1 Except that the mass of the core of the positive electrode material is 100%, the content of the Y element in the Li 3 YCl 6 is 0.05%, and the other preparation methods and conditions are the same as in Example 1.
  • This comparative example is the uncoated cathode material LiNi 0.75 Mn 0.25 O 2 .
  • step (2) Except that the temperature of the high-temperature treatment in step (2) is adjusted to 300° C., the other preparation methods and conditions are the same as in Example 1.
  • step (2) Except that the temperature of the high-temperature treatment in step (2) is adjusted to 820°C, the other preparation methods and conditions are the same as in Example 1.
  • Figure 1a and Figure 1b are the SEM images of the material before coating (the cathode material of Comparative Example 1) under different magnifications.
  • Figure 2a and Figure 2b are the material after coating. (Composite cathode material of Example 1) SEM images at different magnifications. It can be seen from the figure that fragmented coatings are distributed on the coated sample particles.
  • GITT constant current intermittent titration technique
  • Li3YCl6 coating increases the diffusion rate of lithium ions and improves the conductivity of the material.
  • the battery was prepared with the materials of the respective examples and comparative examples, and the first charge-discharge performance and cycle performance tests were performed.
  • Preparation of the battery First, the obtained cathode material and the conductive agent SP, polyvinylidene fluoride, and N-methylpyrrolidone are mixed to prepare a slurry.
  • the mass ratio of the cathode material, the conductive agent and the polyvinylidene fluoride is 92:4 : 4.
  • the amount of N-methylpyrrolidone added is to make the solid content of the slurry 50%; secondly, the slurry is evenly coated on the aluminum foil and dried at 100°C for 12 hours to prepare pole pieces; then the pole pieces are punched out A circular pole piece with a diameter of 14 ⁇ m was prepared and prepared into a button half-cell battery in a glove box. Finally, the button battery was put aside, charged and discharged, and the first charge-discharge performance test and cycle test were obtained under the same test process. Test conditions: 25°C constant temperature oven, the charge rate of the first effect test is 0.1C, and the discharge rate is 0.1C; the charge rate of the cycle test is 0.5C, and the discharge rate is 1C. See Table 2 for the test results.
  • Figure 3 is the first charge-discharge curve of the material before and after coating.
  • the two curves indicated by arrows in the figure correspond to the composite cathode material after coating, and the two curves not indicated by arrows correspond to the positive electrode material before coating.
  • the former corresponds to the positive electrode material of Comparative Example 1, and the composite positive electrode material of Example 1 after coating.
  • the 0.1C discharge capacity of the uncoated material is 183.4mAh/g, and the first effect is 86.7%; the 0.1C discharge capacity of the material after this solution is coated is 192.2mAh/g, and the first effect is 87.29%. Therefore, after coating Li 3 YCl 6 , the electrochemical performance of the material is improved.
  • the positive electrode material of Comparative Example 1 before coating corresponds to the composite positive electrode material of Example 1 after coating. It can be seen from the curve that the material has good cycle stability after coating.
  • the reason for the improved stability is that the halide coating layer formed on the surface of the material has good stability, forming a stable and firm connection with the base material, and blocking The contact between the positive electrode material and the electrolyte is reduced, and the occurrence of side reactions is reduced.
  • the reason for the improvement of the first effect is that the interaction between the halogen-1 valent anion and the lithium ion in the halide is weaker, which has better lithium ion conductivity and reduces the surface resistance. Moreover, due to the larger halide ion radius, it is beneficial The migration of lithium ions.
  • Example 1 By comparing Example 1 with Comparative Example 2, the coating is an oxide solid electrolyte, which has poor ionic conductivity, resulting in a decrease in the electrochemical performance of the material.
  • Example 1 By comparing Example 1 with Comparative Example 3, the coating is a sulfide solid electrolyte, which has poor stability during the cycle, resulting in a decrease in the cycle performance of the material.
  • Example 1 By comparing Example 1 with Comparative Example 4, when the coating temperature is 300° C., the coating material and the matrix material are not tightly combined, resulting in a decrease in the cycle stability of the material.
  • the coating temperature is 820°C, and the structure of the coating material may change, which affects the cycle stability of the material.
  • Example 1 By comparing Example 1 with Example 6, the thickness of the coating layer is increased, which makes it difficult for lithium ions to deintercalate during charging and discharging.
  • Example 7 has a smaller halide coating amount, and the improvement in ion conductivity is lower.

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Abstract

一种锂离子电池用复合正极材料、其制备方法及用途，所述复合正极材料包括正极材料内核及包覆在所述正极材料内核表面的卤化物包覆层，所述卤化物包括Li 3YX 6，其中，X为卤素中的至少一种。经卤化物包覆层的包覆，极大地提升了正极材料的离子导电性和结构稳定性，降低了材料的表面阻抗。

Description

一种锂离子电池用复合正极材料、其制备方法及用途 技术领域
本公开涉及电池技术领域，例如涉及一种锂离子电池用复合正极材料、其制备方法及用途。
背景技术
锂离子电池由于具有高能量密度、较好的循环性能已经渗透到生活中的方方面面。作为锂离子电池的核心，正极材料的发展直接影响了锂离子电池的发展前景，由于三元正极材料的高密度、较好的循环寿命，因而被广泛应用于汽车、电子行业。其中较为熟知的有NCM(Ni xCo yMn z)，NCA(Ni xCo yAl z)等，但是钴元素价格昂贵且对环境有污染，这些不利因素限制了三元材料的发展。
无钴正极材料具有较高的可逆比容量、价格低廉等优势受到研发人员的广泛关注。
CN107546385A公开了一种制备LiNi xMn 1-xO 2二元正极材料的方法及制备得到的LiNi xMn 1-xO 2，所述方法包括：(1)配制二元镍、锰盐水溶液和混合碱水溶液；(2)分别二元镍、锰盐水溶液和混合碱水溶液以一定的流速加入通有氮气保护的微波反应器中，并恒温搅拌反应；(3)反应物转移至水热反应釜中进行水热反应；(4)共沉淀物过滤、洗涤，干燥；(5)干燥后的共沉淀物配入锂盐混合研磨后，置于烧结炉中高温固相反应，得到二元正极材料。其制备得到的镍锰基二元正极材料起始放电容量高达170mAh/g以上，循环性能良好。
CN109811412A公开了一种单晶形貌的层状镍锰酸锂正极材料及其制备方法，所述方法包括：(1)将镍盐和锰盐通过湿化学法，制备得到镍锰前驱体，其中Ni和Mn的摩尔比为1:1；(2)将镍锰前驱体进行预烧结，得到镍锰氧化物 前驱体；(3)将镍锰氧化物前驱体与锂源、M源添加剂混合，然后煅烧，得到单晶形貌的层状镍锰酸锂正极材料。
但是，由于其中钴元素的缺失，使其导电性较低，相对于传统的NCM和NCA等三元材料，导电性能和结构稳定性差是较大的问题，进而在电化学性能方面受到一定的制约。
发明内容
本公开提供一种锂离子电池用复合正极材料、其制备方法及用途。
本公开在一实施例中提供一种锂离子电池用复合正极材料，所述复合正极材料包括正极材料内核及包覆在所述正极材料内核表面的卤化物包覆层，所述卤化物包括Li 3YX 6，其中，X为卤素中的至少一种。
本公开提供的一实施例中，卤化物包覆正极材料，经卤化物包覆层的包覆，极大了提升了正极材料的离子导电性和结构稳定性，降低了材料的表面阻抗，其技术原理如下：首先，本公开提供的卤化物中的卤素-1价阴离子和锂离子的相互作用较弱，具有更好的锂离子传导能力；其次，由于卤素离子半径较大，有利于锂离子的迁移；再次，该卤化物的稳定性好，便于与基体材料形成稳定牢固的连接；而且，该卤化物包覆层的化学稳定性好，阻隔了正极材料和电解液的接触，降低了副反应的发生。上述因素综合作用，使所得复合正极材料具有极高的离子导电性和结构稳定性，从而提升材料的容量、首效和循环性能。
对于包覆层的化学组成，硫化物固态电解质或氧化物固态电解质虽然具有较好的离子电导率，但是无法实现本公开所要达到的技术效果，因为，硫化物化学稳定性较差。氧化物固态电解质涉及的反应较为复杂，氧化物固态电解质与空气和水分接触会发生反应，循环稳定性下降；氧化物颗粒比较硬，固态界面接触不好，密度大，质量能量密度低，不适合规模性生产过程。
在一实施例中，所述卤化物为Li 3YCl 6和/或Li 3YBr 6，例如卤化物可以是Li 3YCl 6，也可以是Li 3YBr 6，还可以是Li 3YCl 6和Li 3YBr 6的混合物。
在一实施例中，所述正极材料内核包括无钴正极材料。
在一实施例中，所述正极材料内核包括镍锰酸锂正极材料。
在一实施例中，所述镍锰酸锂正极材料的化学式为LiNi xMn yO 2， 0.55≤x≤0.95，0.05≤y≤0.45，其中，x例如0.55、0.6、0.65、0.7、0.72、0.75、0.8、0.9或0.95等。y例如0.05、0.08、0.1、0.2、0.3、0.35、0.4或0.45等。
本公开提供的一实施例中，卤化物对于本领域常用的多种锂离子电池正极材料(例如磷酸铁锂、NCM三元、NCA三元、钴酸锂、锰酸锂、镍钴酸锂、镍锰酸锂等)均能起到提升离子导电性和稳定结构的作用。
本公开通过引入卤化物包覆层，对于无钴正极材料性能改善尤为突出，所述的无钴正极材料是基于三元材料的无钴正极材料。
本公开通过在无钴正极材料表面包覆卤化物包覆层，还可以降低残碱，其技术原理是：在较高温度下(700-800℃)，卤化物包覆层与无钴正极材料表面接触的位置，卤化物中的卤素(例如Cl)会反应掉一部分锂，在高温下形成氧化物嵌入到材料内部，降低残碱的同时提升产品性能。
在一实施例中，以正极材料内核的质量为100％计，所述Li 3YX 6中Y元素的含量为0.1％-1％，例如0.1％、0.3％、0.5％、0.7％、0.8％、0.9％或1％等。
本公开提供的一实施例中，Li 3YX 6中Y元素的含量若小于0.1％，会导致导电性提升效果不明显；Li 3YX 6中Y元素的含量若大于1％，会导致阻碍锂离子的嵌入和脱出，降低电化学性能。
在一实施例中，以正极材料内核的质量为100％计，所述Li 3YX 6中Y元素的含量为0.1％-0.3％。
在一实施例中，所述正极材料内核的粒径D50为1μm-5μm，例如1μm、2μm、2.5μm、3μm、3.5μm、4μm或5μm等
在一实施例中，所述正极材料内核的粒径D50为1μm-3μm。
在一实施例中，所述Li 3YX 6的粒径D50为5nm-500nm，例如5nm、10nm、15nm、20nm、25nm、30nm、35nm、40nm、50nm、65nm、80nm、100nm、15nm、130nm、150nm、180nm、200nm、230nm、260nm、300nm、350nm、375nm、400nm、450nm或500nm等。
在一实施例中，所述Li 3YX 6的粒径D50为50nm-100nm。
本公开提供的一实施例中，正极材料内核粒径D50为1μm-5μm，Li 3YX 6的粒径D50为5nm-500nm，在此范围内，可以更好地在包覆的基体材料表面形成较好的包覆层。本公开一实施例提供的复合正极材料中，卤化物包覆层具有很好的化学稳定性，不和空气中的氧和水发生反应，复合正极材料的残余碱和游 离水的含量低，材料的残余碳酸锂和氢氧化锂总量低于0.3％(wt)；材料中的游离水含量低于200ppm；其比表面积范围在0.2m 2/g-0.9m 2/g；材料的pH≤12。
本公开在一实施例中提供一种所述的锂离子电池用复合正极材料的制备方法，所述方法包括以下步骤：
将包覆剂与基体正极材料混合，然后在含氧气氛下400℃-800℃高温处理，得到复合正极材料，例如400℃、425℃、450℃、460℃、480℃、500℃、525℃、550℃、580℃、600℃、650℃、700℃、730℃、750℃或800℃等。
其中，所述包覆剂包括Li 3YX 6，X为卤素中的至少一种。
本公开提供的一实施例中，在400℃-800℃下进行高温处理，若温度低于400℃，会导致包覆层和正极材料内核的结合性差；若温度高于800℃，会导致卤化物的结构发生严重变化，而且对于三元材料或者无钴正极材料会加剧锂镍混排，从而降低提升导电性的效果，优选为400℃-700℃。
需要说明的是，高温处理的温度高于700℃且在800℃以下时，Li3YX6的结构发生轻微破坏，降低其对离子导电性的改进效果，同时，与正极材料尤其是无钴正极材料表面接触的位置，Li3YX6中的卤素(例如Cl)会反应掉一部分锂，在高温下形成氧化物嵌入到材料内部，降低残碱的同时提升产品性能。
在一实施例中，所述含氧气氛中，氧气的体积浓度为20％-100％，例如20％、25％、30％、40％、45％、50％、60％、70％、80％、90％或100％等。
在一实施例中，所述含氧气氛中，氧气的体积浓度为50％-90％。
在一实施例中，所述混合的方式为干法混合。
在一实施例中，所述混合包括：将包覆剂与基体正极材料在混合设备中，以2000rpm-3000rpm的转速混合，例如2000rpm、2250rpm、2500rpm、2700rpm、2800rpm或3000rpm等。
在一实施例中，所述混合的时间为10分钟-20分钟，例如10分钟、15分钟、18分钟或20分钟等。
在一实施例中，所述高温处理的温度为400-700℃。
在一实施例中，所述高温处理的时间为4h-8h，例如4h、4.2h、4.5h、5h、5.5h、5.7h、6h、6.5h、7h、7.5h或8h等。
在一实施例中，所述方法还包括在高温处理后进行研磨和筛分的步骤。
在一实施例中，所述基体正极材料为镍锰酸锂，所述镍锰酸锂的制备方法包括：
(a)将锂源和前驱体Ni xMn y(OH) 2，0.55≤x≤0.95，0.05≤y≤0.45混合均匀；
(b)于800℃-1000℃高温反应，得到镍锰酸锂，例如800℃、820℃、850℃、900℃、950℃、970℃或1000℃等。
在一实施例中，步骤(a)所述锂源为LiOH。
在一实施例中，步骤(a)所述混合为：在高速混合设备中，于2000rpm-3000rpm的转速混合10分钟-20分钟。
在一实施例中，步骤(b)所述高温反应的时间为8h-12h，例如8h、9h、9.5h、10h、11h或12h等。
在一实施例中，步骤(b)所述高温反应在氧气体积浓度大于90％的含氧气氛下进行。
在一实施例中，含氧气氛的气体流量为2L/min-20L/min，例如2L/min、5L/min、7L/min、10L/min、12L/min、14L/min、15L/min或20L/min等。
在一实施例中，步骤(b)所述高温反应之后进行降温冷却并破碎的步骤。
在一实施例中，所述方法包括以下步骤：
(1)制备基体正极材料镍锰酸锂：
(a)将LiOH和前驱体Ni xMn y(OH) 2在高速混合设备中，于2000rpm-3000rpm的转速混合10分钟-20分钟，0.55≤x≤0.95，0.05≤y≤0.45；
(b)于氧气体积浓度大于90％的含氧气氛下，800℃-1000℃高温反应8h-12h，含氧气氛的气体流量为2L/min-20L/min，得到镍锰酸锂，降温冷却并破碎，备用；
(2)将包覆剂与基体正极材料在混合设备中，包覆剂为Li 3YCl 6和/或Li 3YBr 6，以2000rpm-3000rpm的转速混合10分钟-20分钟，然后在含氧气氛下400℃-700℃高温处理4h-8h，所述含氧气氛中，氧气的体积浓度为20％-100％，研磨，采用300目-400目筛进行筛分，得到复合正极材料，所述复合正极材料包括镍锰酸锂及包覆在所述镍锰酸锂表面的包覆层，所述包覆层为Li 3YCl 6和/或Li 3YBr 6；
以正极材料内核的质量为100％计，所述包覆层中Y元素的含量为0.1％-1％。
本公开在一实施例中提供一种正极，所述正极包括本公开一实施例所述的 锂离子电池用复合正极材料。
本公开在一实施例中提供一种锂离子电池，所述锂离子电池包括本公开一实施例所述的正极。
附图说明
附图用来提供对本公开技术方案的进一步理解，并且构成说明书的一部分，与本申请的实施例一起用于解释本公开的技术方案，并不构成对本公开技术方案的限制。
图1a和图1b是包覆前材料(本公开提供的对比例制备得到的正极材料)在不同倍数下的SEM图；
图2a和图2b是包覆后材料(本公开提供的实施例制备得到的正极材料)在不同倍数下的SEM图；
图3是包覆前后材料的首次充放电曲线，其中，图中箭头标示的两条曲线对应包覆后的复合正极材料，未用箭头标示的两条曲线对应包覆前的正极材料，包覆前对应对比例的正极材料，包覆后对应实施例的复合正极材料；
图4是包覆前后材料的循环性能曲线，其中，包覆前对应对比例的正极材料，包覆后对应实施例的复合正极材料。
具体实施例
下面结合附图并通过具体实施方式来进一步说明本公开的技术方案。
实施例1
本实施例提供一种锂离子电池用复合正极材料，所述复合正极材料包括正极材料内核及包覆在所述正极材料内核表面的卤化物包覆层，所述正极材料内核为LiNi 0.75Mn 0.25O 2，所述卤化物为Li 3YCl 6，以正极材料内核的质量为100％计，所述Li 3YCl 6中Y元素的含量为0.5％，所述正极材料内核的粒径D50为3μm。
本实施例还提供了所述复合正极材料的制备方法，包括以下步骤：
(1)制备基体正极材料镍锰酸锂
(a)将LiOH和前驱体Ni 0.75Mn 0.25(OH) 2在高速混合设备中，于2500rpm的转速混合15分钟；
(b)于氧气气氛下，900℃高温反应10h，氧气的气体流量为10L/min，得 到镍锰酸锂LiNi 0.75Mn 0.25O 2，降温冷却并破碎，备用；
(2)将包覆剂Li 3YCl 6与基体正极材料在混合设备中，以2200rpm的转速混合20分钟，然后在含氧气氛下600℃高温处理5h，所述含氧气氛为氧气和氮气的混合气氛，氮气的体积浓度为40％，氧气的体积浓度为60％，研磨，采用300目筛进行筛分，得到复合正极材料。
实施例2
本实施例提供一种锂离子电池用复合正极材料，所述复合正极材料包括正极材料内核及包覆在所述正极材料内核表面的卤化物包覆层，所述正极材料内核为LiNi 0.6Mn 0.4O 2，所述卤化物为Li 3YBr 6，以正极材料内核的质量为100％计，所述Li 3YBr 6中Y元素的含量为0.3％，所述正极材料内核的粒径D50为3μm。
本实施例还提供了所述复合正极材料的制备方法，包括以下步骤：
(1)制备基体正极材料镍锰酸锂
(a)将LiOH和前驱体Ni 0.6Mn 0.4(OH) 2在高速混合设备中，于2000rpm的转速混合20分钟；
(b)于氧气气氛下，1000℃高温反应8h，氧气的气体流量为5L/min，得到镍锰酸锂LiNi 0.6Mn 0.4O 2，降温冷却并破碎，备用；
(2)将包覆剂Li 3YBr 6与基体正极材料在混合设备中，以2750rpm的转速混合10分钟，然后在含氧气氛下500℃高温处理5.5h，所述含氧气氛所述含氧气氛为氧气和氮气的混合气氛，氮气的体积浓度为60％，氧气的体积浓度为40％，研磨，采用300目筛进行筛分，得到复合正极材料。
实施例3
本实施例提供一种锂离子电池用复合正极材料，所述复合正极材料包括正极材料内核及包覆在所述正极材料内核表面的卤化物包覆层，所述正极材料内核为LiNi 0.7Mn 0.3O 2，所述卤化物为Li 3YCl 6，以正极材料内核的质量为100％计，所述Li 3YCl 6中Y元素的含量为0.8％，所述正极材料内核的粒径D50为3μm。
本实施例还提供了所述复合正极材料的制备方法，包括以下步骤：
(1)制备基体正极材料镍锰酸锂
(a)将Li 2CO 3和前驱体Ni 0.7Mn 0.3(OH) 2在高速混合设备中，于2800rpm的转速混合16分钟；
(b)于氧气气氛下，800℃高温反应12h，氧气的气体流量为15L/min，得 到镍锰酸锂LiNi 0.7Mn 0.3O 2，降温冷却并破碎，备用；
(2)将包覆剂Li 3YCl 6与基体正极材料在混合设备中，以2250rpm的转速混合15分钟，然后在含氧气氛下450℃高温处理8h，所述含氧气氛为氧气和氮气的混合气氛，氮气的体积浓度为15％，氧气的体积浓度为85％，研磨，采用400目筛进行筛分，得到复合正极材料。
实施例4
本实施例提供一种锂离子电池用复合正极材料，所述复合正极材料包括正极材料内核及包覆在所述正极材料内核表面的卤化物包覆层，所述正极材料内核为磷酸铁锂，所述卤化物为Li 3YCl 6，以正极材料内核的质量为100％计，所述Li 3YCl 6中Y元素的含量为0.7％，所述正极材料内核的粒径D50为3.5μm。
基体材料磷酸铁锂的制备：
(1)将磷酸和硫酸亚铁加入到三口烧瓶中进行搅拌，300rpm转速搅拌约15min，然后加入过量双氧水，用氨水调节溶液pH直至出现白色沉淀；(2)将白色沉淀进行过滤，洗涤，60℃真空干燥得到磷酸铁(FePO 4·2H 2O)粉末；(3)将白色粉末，氢氧化锂，乙炔黑在混合设备中进行混合，于氮气气氛下600℃高温反应12h，氮气气体流量为15L/min，得到磷酸铁锂粉末基体材料，降温冷却并粉碎，备用；
包覆过程：将包覆剂(Li 3YCl 6)和基体材料在混合设备中混合，然后在含氧气氛下450℃高温处理8h，所述含氧气氛为氧气和氮气的混合气氛，氮气的体积浓度为15％，氧气的体积浓度为85％，研磨，采用400目筛进行筛分，得到复合正极材料。
实施例5
本实施例提供一种锂离子电池用复合正极材料，所述复合正极材料包括正极材料内核及包覆在所述正极材料内核表面的卤化物包覆层，所述正极材料内核为LiNi 0.8Mn 0.2O 2，所述卤化物为Li 3YCl 6，以正极材料内核的质量为100％计，所述Li 3YCl 6中Y元素的含量为0.15％，所述正极材料内核的粒径D50为5μm。
本实施例还提供了所述复合正极材料的制备方法，包括以下步骤：
(1)制备基体正极材料镍锰酸锂
(a)将LiOH和前驱体Ni 0.8Mn 0.2(OH) 2在高速混合设备中，于2000rpm的转速混合20分钟；
(b)于氧气气氛下，950℃高温反应9h，氧气的气体流量为12L/min，得到镍锰酸锂LiNi 0.8Mn 0.2O 2，降温冷却并破碎，备用；
(2)将包覆剂Li 3YCl 6与基体正极材料在混合设备中，以2600rpm的转速混合15分钟，然后在含氧气氛下550℃高温处理7h，所述含氧气氛为氧气和氩气的混合气氛，氩气的体积浓度为10％，氧气的体积浓度为90％，研磨，采用250目筛进行筛分，得到复合正极材料。
实施例6
除了以正极材料内核的质量为100％计，所述Li 3YCl 6中Y元素的含量为1.5％，其他制备方法和条件与实施例1相同。
实施例7
除了以正极材料内核的质量为100％计，所述Li 3YCl 6中Y元素的含量为0.05％，其他制备方法和条件与实施例1相同。
对比例1
本对比例为未包覆的正极材料LiNi 0.75Mn 0.25O 2。
对比例2
除了将Li 3YCl 6替换为氧化物固态电解质LLZO(Li 7La 3Zr 2O 12)，其他制备方法和条件与实施例1相同。
对比例3
除了将Li 3YCl 6替换为硫化物固态电解质LGPS(Li 10GeP 2S 12)，其他制备方法和条件与实施例1相同。
对比例4
除了将步骤(2)高温处理的温度调整为300℃，其他制备方法和条件与实施例1相同。
对比例5
除了将步骤(2)高温处理的温度调整为820℃，其他制备方法和条件与实施例1相同。
检测：
采用扫描电镜对包覆前后材料的形貌进行分析，图1a和图1b是包覆前材料(对比例1的正极材料)在不同倍数下的SEM图，图2a和图2b是包覆后材料(实施例1的复合正极材料)在不同倍数下的SEM图。有图可知看出，包覆 后的样品颗粒上分布碎片状包覆物。
采用恒电流间歇滴定技术(GITT)计算材料的锂离子扩散系数，数据参见表1。
表1
序号 样品 D(cm2/s)
对比例1 包覆前 1.32*10-8
实施例1 包覆后 1.65*10-7
对比例2 氧化物电解质替代 0.93*10-7
对比例3 硫化物电解质替代 1.33*10-7
由表1可知，Li3YCl6包覆后增大了锂离子的扩散速率，提高了材料的导电性。
采用各实施例和对比例的材料制备电池并进行首次充放电性能和循环性能测试。电池的制备：首先，将得到的正极材料和导电剂SP，聚偏氟乙烯、N-甲基吡咯烷酮进行混合制备成浆料，正极材料、导电剂和聚偏氟乙烯的质量比为92:4:4，N-甲基吡咯烷酮的加入量为使浆料的固含量为50％；其次，将浆料均匀涂到铝箔上，进行100℃烘干12h制备成极片；然后将极片冲裁成直径为14μm圆形极片，并在手套箱中制备成纽扣半电池；最后，对纽扣电池进行搁置、充放电测试，首次充放电性能测试和循环测试在同一个测试工步下得出。测试条件：25℃恒温箱，首效测试的充电倍率为0.1C，放电倍率为0.1C；循环测试的充电倍率为0.5C，放电倍率为1C。测试结果参见表2。
表2
Figure PCTCN2020135525-appb-000001
Figure PCTCN2020135525-appb-000002
图3是包覆前后材料的首次充放电曲线，图中箭头标示的两条曲线对应包覆后的复合正极材料，未用箭头标示的两条曲线对应包覆前的正极材料，其中，包覆前对应对比例1的正极材料，包覆后对应实施例1的复合正极材料。从图中可以看出不包覆的材料0.1C放电容量为183.4mAh/g，首效为86.7％；本方案包覆以后材料的0.1C放电容量为192.2mAh/g，首效为87.29％。因此，包覆Li 3YCl 6之后，提高了材料的电化学性能。
图4是包覆前后材料的循环性能曲线，其中，包覆前对应对比例1的正极材料，包覆后对应实施例1的复合正极材料。通过曲线可以看出，经过包覆后材料有着较好的循环稳定性，稳定性提高的原因是在材料表面形成的卤化物包覆层的稳定性好，与基体材料形成稳定牢固的连接，阻隔了正极材料和电解液的接触，降低了副反应的发生。首效提高的原因是：卤化物中的卤素-1价阴离子和锂离子的相互作用较弱，具有更好的锂离子传导能力，降低了表面阻抗，而且，由于卤素离子半径较大，有利于锂离子的迁移。
通过实施例1与对比例2对比，包覆物为氧化物固态电解质，离子导电性较差，导致材料的电化学性能降低。
通过实施例1与对比例3对比，包覆物为硫化物固态电解质，在循环过程中稳定性较差，导致材料的循环性能降低。
通过实施例1与对比例4对比，当包覆温度为300℃，包覆物质和基体材料结合不紧密，导致材料的循环稳定性降低。
通过实施例1与对比例5对比，包覆温度为820℃，包覆物质结构可能发生变化，影响了材料的循环稳定性。
通过实施例1与实施例6对比，包覆层厚度增加，使锂离子在充放电过程中脱嵌困难。
通过实施例1与实施例7对比，实施例7的卤化物包覆量较少，对离子导电性的提升较低。

Claims (30)

  1. 一种锂离子电池用复合正极材料，所述复合正极材料包括正极材料内核及包覆在所述正极材料内核表面的卤化物包覆层，所述卤化物包括Li 3YX 6，其中，X为卤素中的至少一种。
  2. 根据权利要求1所述的锂离子电池用复合正极材料，其中，所述卤化物为Li 3YCl 6和/或Li 3YBr 6。
  3. 根据权利要求1或2所述的锂离子电池用复合正极材料，其中，所述正极材料内核包括无钴正极材料。
  4. 根据权利要求1-3任一项所述的锂离子电池用复合正极材料，其中，所述正极材料内核包括镍锰酸锂正极材料。
  5. 根据权利要求4所述的锂离子电池用复合正极材料，其中，所述镍锰酸锂正极材料的化学式为LiNi xMn yO 2，0.55≤x≤0.95，0.05≤y≤0.45。
  6. 根据权利要求1-5任一项所述的锂离子电池用复合正极材料，其中，以正极材料内核的质量为100％计，所述Li 3YX 6中Y元素的含量为0.1％-1％。
  7. 根据权利要求1-6任一项所述的锂离子电池用复合正极材料，其中，以正极材料内核的质量为100％计，所述Li 3YX 6中Y元素的含量为0.1％-0.3％。
  8. 根据权利要求1-7任一项所述的锂离子电池用复合正极材料，其中，所述正极材料内核的粒径D50为1μm-5μm。
  9. 根据权利要求1-8任一项所述的锂离子电池用复合正极材料，其中，所述正极材料内核的粒径D50为1μm-3μm。
  10. 根据权利要求1-9任一项所述的锂离子电池用复合正极材料，其中，所述Li 3YX 6的粒径D50为5nm-500nm。
  11. 根据权利要求1-10任一项所述的锂离子电池用复合正极材料，其中，所述Li 3YX 6的粒径D50为50nm-100nm。
  12. 一种权利要求1-11任一项所述的锂离子电池用复合正极材料的制备方法，所述方法包括以下步骤：
    将包覆剂与基体正极材料混合，然后在含氧气氛下400℃-800℃高温处理，得到复合正极材料；
    其中，所述包覆剂包括Li 3YX 6，X为卤素中的至少一种。
  13. 根据权利要求12所述的方法，其中，所述含氧气氛中，氧气的体积浓度为20％-100％。
  14. 根据权利要求12或13所述的方法，其中，所述含氧气氛中，氧气的体积浓度为50％-90％。
  15. 根据权利要求12-14任一项所述的方法，其中，所述混合的方式为干法混合。
  16. 根据权利要求12-15任一项所述的方法，其中，所述混合包括：将包覆剂与基体正极材料在混合设备中，以2000rpm-3000rpm的转速混合。
  17. 根据权利要求12-16任一项所述的方法，其中，所述混合的时间为10分钟-20分钟。
  18. 根据权利要求12-17任一项所述的方法，其中，所述高温处理的温度为400-700℃。
  19. 根据权利要求12-18任一项所述的方法，其中，所述高温处理的时间为4h-8h。
  20. 根据权利要求12-19任一项所述的方法，其中，所述方法还包括在高温处理后进行研磨和筛分的步骤。
  21. 根据权利要求12-20任一项所述的方法，其中，所述基体正极材料为镍锰酸锂，所述镍锰酸锂的制备方法包括：
    (a)将锂源和前驱体Ni xMn y(OH) 2，0.55≤x≤0.95，0.05≤y≤0.45混合均匀；
    (b)于800℃-1000℃高温反应，得到镍锰酸锂。
  22. 根据权利要求21所述的方法，其中，步骤(a)所述锂源为LiOH。
  23. 根据权利要求21或22所述的方法，其中，步骤(a)所述混合为：在高速混合设备中，于2000rpm-3000rpm的转速混合10分钟-20分钟。
  24. 根据权利要求21-23任一项所述的方法，其中，步骤(b)所述高温反应的时间为8h-12h。
  25. 根据权利要求21-24任一项所述的方法，其中，步骤(b)所述高温反应在氧气体积浓度大于90％的含氧气氛下进行。
  26. 根据权利要求25所述的方法，其中，含氧气氛的气体流量为2L/min-20L/min。
  27. 根据权利要求21-26任一项所述的方法，其中，步骤(b)所述高温反应之后进行降温冷却并破碎的步骤。
  28. 根据权利要求12-27任一项所述的方法，其中，所述方法包括以下步骤：
    (1)制备基体正极材料镍锰酸锂：
    (a)将LiOH和前驱体Ni xMn y(OH) 2在高速混合设备中，于2000rpm-3000rpm的转速混合10分钟-20分钟，0.55≤x≤0.95，0.05≤y≤0.45；
    (b)于氧气体积浓度大于90％的含氧气氛下，800℃-1000℃高温反应8h-12h，含氧气氛的气体流量为2L/min-20L/min，得到镍锰酸锂，降温冷却并破碎，备用；
    (2)将包覆剂与基体正极材料在混合设备中，包覆剂为Li 3YCl 6和/或Li 3YBr 6，以2000rpm-3000rpm的转速混合10分钟-20分钟，然后在含氧气氛下400℃-700℃高温处理4h-8h，所述含氧气氛中，氧气的体积浓度为20％-100％，研磨，采用300目-400目筛进行筛分，得到复合正极材料，所述复合正极材料包括镍锰酸锂及包覆在所述镍锰酸锂表面的包覆层，所述包覆层为Li 3YCl 6和/或Li 3YBr 6；
    以正极材料内核的质量为100％计，所述包覆层中Y元素的含量为0.1％-1％。
  29. 一种正极，所述正极包括权利要求1-11任一项所述的锂离子电池用复合正极材料。
  30. 一种锂离子电池，所述锂离子电池包括权利要求29所述的正极。
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