A multi-element coated single-crystal lithium-rich manganese-based positive electrode material and a preparation method thereof

Abstract

This invention provides a multi-element coated single-crystal lithium-rich manganese-based cathode material and its preparation method, belonging to the field of single-crystal lithium-rich manganese-based cathode material preparation. This invention employs an electrospinning-solid-state sintering method to construct a multi-component coating layer on the surface of a nano / micron-scale single-crystal lithium-rich manganese-based cathode material. By coating with carbon and metal oxide layers, the cathode material and electrolyte are physically isolated, preventing the reaction of high-valence metal cations and active oxygen species on the material surface with the electrolyte, and also inhibiting the corrosion of HF in the electrolyte. The coating layer also confines the active oxygen species generated during charging within the material, preventing oxygen escape, thereby alleviating problems such as low first-cycle coulombic efficiency, poor rate performance, and poor cycle stability of lithium-rich manganese-based materials. The coated metal oxides can react with residual lithium on the surface of the lithium-rich manganese-based cathode material, reducing residual lithium on the substrate surface and improving the material's air stability and cycle stability.

Description

Technical Field

[0001] The present invention relates to the field of preparation of single crystal lithium-rich manganese-based cathode materials, and particularly to a multi-element coated single crystal lithium-rich manganese-based cathode material and a preparation method thereof. Background Art

[0002] Layered lithium-rich manganese-based materials (Li a [Ni x Co y Mn 1-x-y O 2+b , where 1.1 ≤ a ≤ 1.5, 0 < x < 0.5, 0 ≤ y < 0.2, 0 ≤ b ≤ 0.5) as cathode materials with high specific energy, high specific capacity and environmental friendliness have received more and more extensive attention and in-depth research. Polycrystalline lithium-rich manganese-based materials can activate the redox reaction in the Li2MnO3 phase only at voltages above 4.5V. The redox reaction is unstable, which will cause oxygen active substances to be irreversibly released into the electrolyte, exacerbating the interfacial side reactions between the lithium-rich manganese-based electrode and the electrolyte. Especially after long-term cycling, it will lead to electrolyte decomposition, dissolution of transition metals (TM), and irreversible loss of active lithium, resulting in morphological degradation and irreversible structural transformation, and ultimately leading to rapid deterioration of electrochemical performance. Single crystal particles exhibit unique advantages compared to polycrystalline particles, such as higher crystallinity, fewer grain boundaries, better particle integrity, higher mechanical stability, and fewer surface defects. However, as the size of layered lithium-rich manganese particles decreases, the interfacial side reactions will be more significant. Therefore, how to improve single crystal lithium-rich manganese-based materials to reduce interfacial side reactions has become an urgent technical problem in this field. Summary of the Invention

[0003] The purpose of the present invention is to provide a multi-element coated single crystal lithium-rich manganese-based cathode material and a preparation method thereof. The single crystal lithium-rich manganese-based material coated by electrospinning in the present invention can reduce interfacial side reactions and greatly improve the specific capacity.

[0004] In order to achieve the above invention purpose, the present invention provides the following technical solutions: The present invention provides a preparation method of a multi-element coated single crystal lithium-rich manganese-based cathode material, including the following steps: (1) Mix a water-soluble polymer substance, a soluble salt, water and a single crystal lithium-rich manganese-based cathode material to obtain a spinning solution; (2) Electrospin the spinning solution obtained in step (1) to obtain fibers; (3) Sinter the fibers obtained in step (2) to obtain a multi-element coated single crystal lithium-rich manganese-based cathode material.

[0005] Preferably, the water-soluble polymer substance in step (1) includes any one or more of polyvinyl alcohol, polyethylene oxide, polyacrylic acid, polyvinylpyrrolidone, polyethyleneimine, polyacrylamide, polyethylene glycol, cellulose, and ethyl cellulose; the relative molecular mass of the water-soluble polymer substance is 100 to 50,000.

[0006] Preferably, the soluble salt in step (1) is a soluble nitrate and / or a soluble phosphate.

[0007] Preferably, the soluble nitrate is any one or more of aluminum nitrate, magnesium nitrate, zirconium nitrate, and cerium nitrate; the soluble phosphate is any one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0008] Preferably, the chemical formula of the single-crystalline lithium-rich manganese-based cathode material in step (1) is Li a [Ni x Co y Mn 1-x-y O 2+b , where 1.1 ≤ a ≤ 1.5, 0 < x < 0.5, 0 ≤ y < 0.2, 0 ≤ b ≤ 0.5; the particle size of the single-crystalline lithium-rich manganese-based cathode material is 50 nm to 15 μm.

[0009] Preferably, the mass ratio of the water-soluble polymer substance to the single-crystalline lithium-rich manganese-based cathode material in step (1) is (0.01 to 1):1, the mass ratio of the soluble salt to the single-crystalline lithium-rich manganese-based cathode material is (0.001 to 0.1):1, and the volume ratio of water to the mass of the single-crystalline lithium-rich manganese-based cathode material is 10 mL:(0.1 to 8) g.

[0010] Preferably, the mixing method of the water-soluble polymer substance, the soluble salt, water, and the single-crystalline lithium-rich manganese-based cathode material in step (1) is: adding the water-soluble polymer substance and the soluble salt into water, then stirring at a speed of 100 to 600 r / min at a temperature of 25 to 80 °C for 0.5 to 5 h until completely dissolved, and then adding the single-crystalline lithium-rich manganese-based cathode material and stirring at a speed of 700 to 1200 r / min for 0.1 to 1 h.

[0011] Preferably, in step (2), the voltage of electrospinning is 10 to 25 kV, the advancing speed of electrospinning is 0.1 to 1 mL / h, the receiving distance of electrospinning is 15 to 25 cm, and the relative humidity of electrospinning is 20 to 50%.

[0012] Preferably, in step (3), the holding temperature of sintering is 200 to 900 °C, the holding time of sintering is 60 to 600 min, and the sintering atmosphere is an air or nitrogen atmosphere.

[0013] This invention provides a multi-element coated single-crystal lithium-rich manganese-based cathode material prepared by the preparation method described in the above technical solution.

[0014] This invention provides a method for preparing a multi-element coated single-crystal lithium-rich manganese-based cathode material, comprising the following steps: (1) mixing a water-soluble polymer, a soluble salt, water, and a single-crystal lithium-rich manganese-based cathode material to obtain a spinning solution; (2) electrospinning the spinning solution obtained in step (1) to obtain fibers; and (3) sintering the fibers obtained in step (2) to obtain a multi-element coated single-crystal lithium-rich manganese-based cathode material. This invention uses a water-soluble polymer as a carrier, uniformly dispersing functional soluble salts and single-crystal lithium-rich manganese-based cathode material powder to form a spinning solution. The strong stretching effect of electrospinning allows the fiber precursor to tightly coat the surface of the single-crystal particles. Solid-state sintering then transforms the polymer carrier into carbon and the salts into composite oxides, ultimately forming a continuous, dense, and firmly bonded multi-element coating layer. This invention employs an electrospinning-solid-state sintering method to construct a multi-component coating layer on the surface of nano / micron-sized single-crystal lithium-rich manganese-based cathode material. By coating with carbon and metal oxide layers, the cathode material and electrolyte are physically isolated, preventing the reaction of high-valence metal cations and active oxygen species on the material surface with the electrolyte, and also inhibiting the corrosion of HF in the electrolyte. The coating layer also confines the active oxygen species generated during charging within the material, preventing oxygen escape and thus alleviating problems such as low first-cycle coulombic efficiency, poor rate performance, and poor cycle stability of lithium-rich manganese-based materials. The coated metal oxides can react with residual lithium on the surface of the lithium-rich manganese-based cathode material, reducing residual lithium on the substrate surface and improving the material's air stability and cycle stability. The results of the embodiments show that the specific capacity of the single-crystal lithium-rich manganese-based cathode material coated by electrospinning is greatly improved, and the first-cycle efficiency is increased by 2%, indicating that this invention can effectively reduce interfacial side reactions by coating the single-crystal lithium-rich manganese-based cathode material with multiple elements. Attached Figure Description

[0015] Figure 1 Cycle-capacity retention of CR2025 button half-cells prepared from the multi-element coated monocrystalline lithium-rich manganese-based cathode materials provided in Examples 1-5 and the monocrystalline lithium-rich manganese-based cathode materials provided in the comparative examples; Figure 2 The cycle-discharge specific capacity of CR2025 button half-cells prepared from the multi-element coated monocrystalline lithium-rich manganese-based cathode materials provided in Examples 1-5 and the monocrystalline lithium-rich manganese-based cathode materials provided in the comparative examples. Detailed Implementation

[0016] This invention provides a method for preparing a multi-element coated single-crystal lithium-rich manganese-based cathode material, comprising the following steps: (1) A spinning solution is obtained by mixing a water-soluble polymer, a soluble salt, water and a single-crystal lithium-rich manganese-based cathode material; (2) Electrospinning the spinning solution obtained in step (1) to obtain fibers; (3) The fibers obtained in step (2) are sintered to obtain a multi-element coated single-crystal lithium-rich manganese-based cathode material.

[0017] This invention mixes water-soluble polymers, soluble salts, water, and single-crystal lithium-rich manganese-based cathode materials to obtain a spinning solution.

[0018] In this invention, unless otherwise specified, the water-soluble polymers, soluble salts, water, and single-crystal lithium-rich manganese-based cathode materials used are all commercially available products well known to those skilled in the art, or articles prepared using existing methods known to those skilled in the art.

[0019] In this invention, the water-soluble polymer preferably includes any one or more of polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyacrylic acid (PAA), polyvinylpyrrolidone (PVP), polyethyleneimine (PEI), polyacrylamide (PAM), polyethylene glycol (PEG), cellulose, and ethyl cellulose (EC); the relative molecular mass of the water-soluble polymer is preferably 100-50000. As one embodiment of this invention, the relative molecular mass of the water-soluble polymer can be 100, 200, 500, 1000, 2000, 5000, 10000, 15000, 20000, 25000, 30000, 35000, 40000, 45000, or 50000. This invention, by controlling the molecular weight of the water-soluble polymer, can avoid both fiber breakage due to excessively low molecular weight and excessive viscosity of the spinning solution due to excessively high molecular weight.

[0020] In this invention, the soluble salt is preferably a soluble nitrate and / or a soluble phosphate; the soluble nitrate is preferably any one or more of aluminum nitrate, magnesium nitrate, zirconium nitrate, and cerium nitrate; the soluble phosphate is preferably any one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. By controlling the type of soluble salt, this invention allows for the coating of different types of elements onto the surface of single-crystal lithium-rich manganese-based cathode materials.

[0021] In this invention, the water is preferably deionized water. In this invention, water is used as a solvent for mixing the components.

[0022] In this invention, the preferred chemical formula of the single-crystal lithium-rich manganese-based cathode material is Li. a [Ni x Co y Mn 1-x-yO 2+b , where 1.1 ≤ a ≤ 1.5, 0 < x < 0.5, 0 ≤ y < 0.2, 0 ≤ b ≤ 0.5. As an embodiment of the present invention, a can be 1.1, 1.2, 1.3, 1.4 or 1.5; x can be 0.1, 0.2, 0.3 or 0.4; y can be 0.02, 0.05, 0.08, 0.1, 0.12, 0.15 or 0.18; b can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5.

[0023] In the present invention, the particle size of the single-crystal lithium-rich manganese-based cathode material is preferably 50 nm to 15 μm; the single-crystal lithium-rich manganese-based cathode material preferably has no agglomeration. As an embodiment of the present invention, the particle size of the single-crystal lithium-rich manganese-based cathode material can be 50 nm, 100 nm, 300 nm, 500 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm or 15 μm. By controlling the particle size and state of the single-crystal lithium-rich manganese-based cathode material, the present invention is beneficial to its sufficient coating modification.

[0024] In this invention, the preferred mass ratio of the water-soluble polymer to the single-crystal lithium-rich manganese-based cathode material is (0.01~1):1; the preferred mass ratio of the soluble salt to the single-crystal lithium-rich manganese-based cathode material is (0.001~0.1):1; and the preferred volume ratio of the water to the mass of the single-crystal lithium-rich manganese-based cathode material is 10mL:(0.1~8)g. In one embodiment of the present invention, the mass ratio of the water-soluble polymer to the single-crystal lithium-rich manganese-based cathode material can be 0.01:1, 0.02:1, 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1, or 1:1; the mass ratio of the soluble salt to the single-crystal lithium-rich manganese-based cathode material can be 0.001:1, 0.002:1, 0.005:1, 0.01:1, 0.015:1, or 1:1. 1. 0.02:1, 0.025:1, 0.03:1, 0.035:1, 0.04:1, 0.045:1, 0.05:1, 0.055:1, 0.06:1, 0.065:1, 0.07:1, 0.075:1, 0.08:1, 0.085:1, 0.09:1, 0.095:1 or 0.1:1; the volume ratio of the water to the mass of the single-crystal lithium-rich manganese-based cathode material can be 10mL:0.1g, 10mL:0.5g, 10mL:1g, 10mL:2g, 10mL:3g, 10mL:4g, 10mL:5g, 10mL:6g, 10mL:7g or 10mL:8g. By controlling the specific dosage of each component, this invention can control the viscosity of the spinning solution and the thickness of the coating layer formed by water-soluble polymers and soluble salts on the surface of the single-crystal lithium-rich manganese-based cathode material, thereby achieving complete coating.

[0025] In this invention, the preferred method for mixing the water-soluble polymer, soluble salt, water, and monocrystalline lithium-rich manganese-based cathode material is as follows: the water-soluble polymer and soluble salt are added to water, and then stirred at 100-600 r / min for 0.5-5 h at a temperature of 25-80°C until completely dissolved. Then, the monocrystalline lithium-rich manganese-based cathode material is added and stirred at 700-1200 r / min for 0.1-1 h. More preferably, the water-soluble polymer and soluble salt are added to water, and then stirred at 40-70°C... The solution is stirred at 200-500 rpm for 1-4 hours at a temperature of 50-60°C until completely dissolved. Then, a single-crystal lithium-rich manganese-based cathode material is added and stirred at 800-1100 rpm for 0.2-0.8 hours. More preferably, a water-soluble polymer and a soluble salt are added to water, and then stirred at 300-400 rpm for 2-3 hours at 50-60°C until completely dissolved. Then, the single-crystal lithium-rich manganese-based cathode material is added and stirred at 900-1000 rpm for 0.5 hours. This invention, by controlling the mixing process, ensures that the components are uniformly dispersed in the spinning solution.

[0026] After obtaining the spinning solution, the present invention performs electrospinning on the spinning solution to obtain fibers.

[0027] In this invention, the voltage of the electrospinning is preferably 10~25kV; the feed speed of the electrospinning is preferably 0.1~1mL / h; the receiving distance of the electrospinning is preferably 15~25cm; and the relative humidity of the electrospinning is preferably 20~50%. In one embodiment of the present invention, the voltage of the electrospinning can be 10kV, 12kV, 14kV, 15kV, 16kV, 18kV, 20kV, 22kV, 24kV, or 25kV; the feed speed of the electrospinning can be 0.1mL / h, 0.2mL / h, 0.3mL / h, 0.4mL / h, 0.5mL / h, 0.6mL / h, 0.7mL / h, 0.8mL / h, 0.9mL / h, or 1mL / h; the receiving distance of the electrospinning can be 15cm, 16cm, 18cm, 20cm, 22cm, 24cm, or 25cm; and the relative humidity of the electrospinning can be 20%, 22%, 24%, 25%, 26%, 28%, 30%, 32%, 34%, 35%, 36%, 38%, 40%, 45%, or 50%. This invention achieves uniform spinning by controlling the voltage of electrospinning and regulating the electric field force; controlling the feed speed regulates the spinning flow rate, preventing the fibers from becoming thicker or forming beads; and controlling the receiving distance allows the fibers more time to stretch and solidify, resulting in fibers with the required diameter.

[0028] After electrospinning, the present invention preferably further includes drying the electrospun product; the drying temperature is preferably 50~200℃; the drying time is preferably 1~24h; the drying is preferably carried out in a vacuum drying oven. As one embodiment of the present invention, the drying temperature can be 50℃, 60℃, 80℃, 100℃, 150℃ or 200℃; the drying time can be 1h, 4h, 8h, 12h, 16h, 20h or 24h. The present invention can remove excess moisture through drying.

[0029] After obtaining the fiber, the present invention sinters the fiber to obtain a multi-element coated single-crystal lithium-rich manganese-based cathode material.

[0030] In this invention, the holding temperature for sintering is preferably 200~900℃; the holding time for sintering is preferably 60~600min; the atmosphere for sintering is preferably air or nitrogen atmosphere; the heating rate to the holding temperature for sintering is preferably 1~10℃ / min; and the cooling method for sintering is preferably natural cooling. In one embodiment of the present invention, the holding temperature for sintering can be 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, or 900℃; the holding time for sintering can be 60min, 120min, 180min, 240min, 300min, 360min, 420min, 480min, 540min, or 600min; and the heating rate to the holding temperature for sintering can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min. This invention utilizes a nitrogen atmosphere for sintering, which carbonizes the polymer material to form a carbon layer on the surface of a single-crystal lithium-rich manganese base. Carbon is relatively stable and can prevent side reactions with the electrolyte, as well as inhibit local structural transformations originating from the surface and the decomposition of the electrolyte. Sintering in air, on the other hand, easily produces a surface spinel structure, thereby increasing the rate capability.

[0031] After sintering, the present invention preferably further includes grinding and sieving the sintered product. The present invention does not have specific limitations on the specific operations of grinding and sieving, as long as the particle size of the multi-element coated single-crystal lithium-rich manganese-based cathode material meets the requirements.

[0032] In this invention, the particle size of the multi-element coated single-crystal lithium-rich manganese-based cathode material is preferably ≥250 mesh.

[0033] This invention uses water-soluble polymers as carriers to uniformly disperse functional soluble salts and single-crystal lithium-rich manganese-based cathode material powders to form a spinning solution. The strong stretching effect of electrospinning is used to tightly coat the fiber precursor onto the surface of the single-crystal particles. Then, solid-state sintering is used to transform the polymer carrier into carbon and the salts into composite oxides, ultimately forming a continuous, dense, and firmly bonded multi-element coating layer.

[0034] This invention employs an electrospinning-solid-state sintering method to construct a multi-component coating layer on the surface of nano / micron-scale single-crystal lithium-rich manganese-based cathode material. By coating with carbon and metal oxide layers, the cathode material and electrolyte can be physically isolated, preventing the reaction of high-valence metal cations and active oxygen species on the material surface with the electrolyte, and also inhibiting the corrosion of HF in the electrolyte. The coating layer can also confine the active oxygen species generated during charging inside the material, preventing oxygen escape, thereby alleviating problems such as low first-cycle coulombic efficiency, poor rate performance, and poor cycle stability of lithium-rich manganese-based materials. The coated metal oxides can react with residual lithium on the surface of the lithium-rich manganese-based cathode material, reducing residual lithium on the substrate surface and improving the air stability and cycle stability of the material.

[0035] The preparation method provided by this invention is simple, easy to operate, and suitable for mass production.

[0036] This invention also provides a multi-element coated single-crystal lithium-rich manganese-based cathode material prepared by the preparation method described above. In this invention, the particle size of the multi-element coated single-crystal lithium-rich manganese-based cathode material is preferably ≥250 mesh.

[0037] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0038] Example 1 A method for preparing a multi-element coated single-crystal lithium-rich manganese-based cathode material comprises the following steps: (1) Add 2g of water-soluble polymer and 0.2g of soluble salt to 20mL of water, and then stir at 500r / min for 1h at 50℃ until completely dissolved. Then add 4g of single-crystal lithium-rich manganese-based cathode material and stir at 1000r / min for 0.5h to obtain spinning solution; the water-soluble polymer is PAA with a molecular weight of 5000, the soluble salt is aluminum nitrate, and the water is deionized water; the chemical formula of the single-crystal lithium-rich manganese-based cathode material is Li 1.3 [Ni 0.35 Mn 0.65 O2.3 The particle size of the single-crystal lithium-rich manganese-based cathode material is 700 nm; (2) The spinning solution obtained in step (1) is electrospun and dried in a vacuum drying oven at 60°C for 12 hours to obtain fibers; the voltage of electrospinning is 15kV, the feed speed of electrospinning is 0.5mL / h, the receiving distance of electrospinning is 18cm, and the relative humidity of electrospinning is 45%; (3) In air, the fiber obtained in step (2) is heated to 500°C at a heating rate of 3°C / min and sintered for 300 min. After naturally cooling to room temperature, it is ground to pass through a 250-mesh sieve to obtain a multi-element coated single-crystal lithium-rich manganese-based cathode material.

[0039] Example 2 A method for preparing a multi-element coated single-crystal lithium-rich manganese-based cathode material comprises the following steps: (1) Add 2g of water-soluble polymer and 0.2g of soluble salt to 20mL of water, and then stir at 500r / min for 1h at 50℃ until completely dissolved. Then add 4g of single-crystal lithium-rich manganese-based cathode material and stir at 1000r / min for 0.5h to obtain spinning solution; the water-soluble polymer is PAA with a molecular weight of 5000, the soluble salt is aluminum nitrate, and the water is deionized water; the chemical formula of the single-crystal lithium-rich manganese-based cathode material is Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The particle size of the single-crystal lithium-rich manganese-based cathode material is 700 nm; (2) The spinning solution obtained in step (1) is electrospun and dried in a vacuum drying oven at 60°C for 12 hours to obtain fibers; the voltage of electrospinning is 15kV, the feed speed of electrospinning is 0.5mL / h, the receiving distance of electrospinning is 18cm, and the relative humidity of electrospinning is 45%; (3) In a nitrogen atmosphere, the fiber obtained in step (2) is heated to 500°C at a heating rate of 3°C / min and sintered for 300 min. After naturally cooling to room temperature, it is ground to pass through a 250-mesh sieve to obtain a multi-element coated single-crystal lithium-rich manganese-based cathode material.

[0040] Example 3 A method for preparing a multi-element coated single-crystal lithium-rich manganese-based cathode material comprises the following steps: (1) Add 2g of water-soluble polymer and 0.2g of soluble salt to 20mL of water, and then stir at 500r / min for 1h at 50℃ until completely dissolved. Then add 4g of single-crystal lithium-rich manganese-based cathode material and stir at 1000r / min for 0.5h to obtain spinning solution. The water-soluble polymer is PAA with a molecular weight of 5000, the soluble salt is cerium nitrate, and the water is deionized water. The chemical formula of the single-crystal lithium-rich manganese-based cathode material is Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The particle size of the single-crystal lithium-rich manganese-based cathode material is 700 nm; (2) The spinning solution obtained in step (1) is electrospun and dried in a vacuum drying oven at 60°C for 12 hours to obtain fibers; the voltage of electrospinning is 15kV, the feed speed of electrospinning is 0.5mL / h, the receiving distance of electrospinning is 18cm, and the relative humidity of electrospinning is 45%; (3) In a nitrogen atmosphere, the fiber obtained in step (2) is heated to 500°C at a heating rate of 3°C / min and sintered for 300 min. After naturally cooling to room temperature, it is ground to pass through a 250-mesh sieve to obtain a multi-element coated single-crystal lithium-rich manganese-based cathode material.

[0041] Example 4 A method for preparing a multi-element coated single-crystal lithium-rich manganese-based cathode material comprises the following steps: (1) Add 2g of water-soluble polymer and 0.2g of soluble salt to 20mL of water, and then stir at 500r / min for 1h at 50℃ until completely dissolved. Then add 4g of single-crystal lithium-rich manganese-based cathode material and stir at 1000r / min for 0.5h to obtain spinning solution. The water-soluble polymer is PAA with a molecular weight of 5000, the soluble salt is a complex of zirconium nitrate and ammonium dihydrogen phosphate (the atomic ratio of Zr and P in the complex is 1:1), and the water is deionized water. The chemical formula of the single-crystal lithium-rich manganese-based cathode material is Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The particle size of the single-crystal lithium-rich manganese-based cathode material is 700 nm; (2) The spinning solution obtained in step (1) is electrospun and dried in a vacuum drying oven at 60°C for 12 hours to obtain fibers; the voltage of electrospinning is 15kV, the feed speed of electrospinning is 0.5mL / h, the receiving distance of electrospinning is 18cm, and the relative humidity of electrospinning is 45%; (3) In a nitrogen atmosphere, the fiber obtained in step (2) is heated to 500°C at a heating rate of 3°C / min and sintered for 300 min. After naturally cooling to room temperature, it is ground to pass through a 250-mesh sieve to obtain a multi-element coated single-crystal lithium-rich manganese-based cathode material.

[0042] Example 5 A method for preparing a multi-element coated single-crystal lithium-rich manganese-based cathode material comprises the following steps: (1) Add 4g of water-soluble polymer and 0.2g of soluble salt to 20mL of water, and then stir at 500r / min for 1h at 50℃ until completely dissolved. Then add 4g of single-crystal lithium-rich manganese-based cathode material and stir at 1000r / min for 0.5h to obtain spinning solution. The water-soluble polymer is PAA with a molecular weight of 5000, the soluble salt is aluminum nitrate, and the water is deionized water. The chemical formula of the single-crystal lithium-rich manganese-based cathode material is Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The particle size of the single-crystal lithium-rich manganese-based cathode material is 700 nm; (2) The spinning solution obtained in step (1) is electrospun and dried in a vacuum drying oven at 60°C for 12 hours to obtain fibers; the voltage of electrospinning is 20kV, the feed speed of electrospinning is 0.5mL / h, the receiving distance of electrospinning is 18cm, and the relative humidity of electrospinning is 45%; (3) In a nitrogen atmosphere, the fiber obtained in step (2) is heated to 500°C at a heating rate of 3°C / min and sintered for 300 min. After naturally cooling to room temperature, it is ground to pass through a 250-mesh sieve to obtain a multi-element coated single-crystal lithium-rich manganese-based cathode material.

[0043] Comparative Example Single-crystal lithium-rich manganese-based cathode material, with the chemical formula Li 1.3 [Ni 0.35 Mn 0.65 O 2.3 The particle size of the single-crystal lithium-rich manganese-based cathode material is 700 nm.

[0044] The electrochemical performance of the multi-element coated monocrystalline lithium-rich manganese-based cathode materials provided in Examples 1-5 and the monocrystalline lithium-rich manganese-based cathode materials provided in the comparative examples was tested. The test method was as follows: the cathode material, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in N-methylpyrrolidone at a mass ratio of 92:4:4 to obtain a uniform mixture. The uniform mixture was then coated onto aluminum foil, dried under vacuum, rolled, and cut into circular electrode sheets. Finally, the sheets were assembled into CR2025 button half-cells in an argon-filled glove box. After standing, the cells were tested on a Xinwei battery tester. The test voltage range was 2.3~4.52V. The results are as follows. Figures 1-2 As shown in Table 1: Table 1 shows the electrochemical performance of CR2025 button half-cells prepared from the multi-element coated monocrystalline lithium-rich manganese-based cathode materials provided in Examples 1-5 and the monocrystalline lithium-rich manganese-based cathode materials provided in the comparative examples.

[0045] Figure 1 Cycle-capacity retention of CR2025 button half-cells prepared from the multi-element coated monocrystalline lithium-rich manganese-based cathode materials provided in Examples 1-5 and the monocrystalline lithium-rich manganese-based cathode materials provided in the comparative examples; Figure 2 The cycle-discharge specific capacity of CR2025 button half-cells prepared from the multi-element coated monocrystalline lithium-rich manganese-based cathode materials provided in Examples 1-5 and the monocrystalline lithium-rich manganese-based cathode materials provided in the comparative examples is shown in Table 1. Figures 1-2 The comparison shows that the specific capacity of the monocrystalline lithium-rich manganese-based cathode material coated by electrospinning in this invention is greatly improved, and the first efficiency is increased by 2%. This indicates that by coating the monocrystalline lithium-rich manganese-based cathode material with multiple elements, this invention can effectively reduce interfacial side reactions.

[0046] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a multi-element coated single-crystal lithium-rich manganese-based cathode material, comprising the following steps: (1) A spinning solution is obtained by mixing a water-soluble polymer, a soluble salt, water and a single-crystal lithium-rich manganese-based cathode material; (2) Electrospinning the spinning solution obtained in step (1) to obtain fibers; (3) The fibers obtained in step (2) are sintered to obtain a multi-element coated single-crystal lithium-rich manganese-based cathode material.

2. The preparation method according to claim 1, characterized in that, The water-soluble polymer in step (1) includes any one or more of polyvinyl alcohol, polyethylene oxide, polyacrylic acid, polyvinylpyrrolidone, polyethyleneimine, polyacrylamide, polydiethanol, cellulose, and ethyl cellulose; the relative molecular mass of the water-soluble polymer is 100 to 50,000.

3. The preparation method according to claim 1, characterized in that, The soluble salt in step (1) is a soluble nitrate and / or a soluble phosphate.

4. The preparation method according to claim 3, characterized in that, The soluble nitrate is any one or more of aluminum nitrate, magnesium nitrate, zirconium nitrate, and cerium nitrate; the soluble phosphate is any one or more of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

5. The preparation method according to claim 1, characterized in that, The chemical formula of the single-crystalline lithium-rich manganese-based cathode material in the step (1) is Li a [Ni x Co y Mn 1-x-y O 2+b , where 1.1 ≤ a ≤ 1.5, 0 < x < 0.5, 0 ≤ y < 0.2, 0 ≤ b ≤ 0.5; the particle size of the single-crystalline lithium-rich manganese-based cathode material is 50 nm to 15 μm.

6. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of water-soluble polymer to monocrystalline lithium-rich manganese-based cathode material is (0.01~1):1, the mass ratio of soluble salt to monocrystalline lithium-rich manganese-based cathode material is (0.001~0.1):1, and the volume ratio of water to the mass of monocrystalline lithium-rich manganese-based cathode material is 10mL:(0.1~8)g.

7. The preparation method according to claim 1, characterized in that, The mixing method of water-soluble polymer, soluble salt, water and single-crystal lithium-rich manganese-based cathode material in step (1) is as follows: add water-soluble polymer and soluble salt to water, and then stir at 100-600 r / min at a temperature of 25-80°C for 0.5-5 hours until completely dissolved. Then add single-crystal lithium-rich manganese-based cathode material and stir at 700-1200 r / min for 0.1-1 hours.

8. The preparation method according to claim 1, characterized in that, In step (2), the electrospinning voltage is 10~25kV, the electrospinning propulsion speed is 0.1~1mL / h, the electrospinning receiving distance is 15~25cm, and the electrospinning relative humidity is 20~50%.

9. The preparation method according to claim 1, characterized in that, In step (3), the sintering holding temperature is 200~900℃, the sintering holding time is 60~600min, and the sintering atmosphere is air or nitrogen atmosphere.

10. The multi-element coated single-crystal lithium-rich manganese-based cathode material prepared by the preparation method according to any one of claims 1 to 9.

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