Lithium-rich manganese-based single-crystal positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium-rich manganese-based single-crystal positive electrode material as well as a preparation method and application thereof. The preparation method comprises the following steps: obtaining a lithium-rich manganese-based precursor through a step-by-step hydrothermal reaction, mixing the lithium-rich manganese-based precursor with a lithium source and an additive, carrying out first sintering, mixing the obtained lithium-rich manganese-based positive electrode material with a coating agent, and carrying out second sintering, so as to obtain the coated lithium-rich manganese-based positive electrode material; and coating Si by vapor deposition to obtain the lithium-rich manganese-based single-crystal positive electrode material. The lithium-rich manganese-based single-crystal positive electrode material prepared by the invention has high rate performance, high cycle stability (100 cycle capacity retention ratio is greater than 108%) and high compaction density (greater than or equal to 3.16 g / cm < 3 >), and is suitable for a high-energy-density lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a lithium-rich manganese-based single-crystal cathode material, its preparation method, and its application. Background Technology

[0002] Layered lithium-rich manganese-based materials (xLi₂MnO₃·(1-x)LiTMO₂, where TM represents one or more transition metal elements) have attracted widespread attention and in-depth research as cathode materials with high specific energy, high specific capacity, environmental friendliness, and low cost. Different electrochemical performance characteristics can be obtained by adjusting the ratio of two structural elements in layered lithium-rich materials. Low-voltage lithium-rich manganese-based materials refer to materials with a voltage upper limit of less than 4.45V. Compared with other materials, their advantages include a high voltage plateau, relatively high discharge capacity, and lower cost; their disadvantages include poor rate performance, generally poor cycle stability, low compaction density, and limited volumetric energy density. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a lithium-rich manganese-based single-crystal cathode material, its preparation method, and its applications. The lithium-rich manganese-based single-crystal cathode material prepared by this invention exhibits high rate performance, high cycle stability (capacity retention > 108% after 100 cycles), and high solid density (≥ 3.16 g / cm³). 3 It is suitable for high energy density lithium-ion batteries.

[0004] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a lithium-rich manganese-based single-crystal cathode material, comprising the following steps: After adjusting the pH of the first metal salt solution to 10-12, the first hydrothermal reaction was carried out to obtain D. 50 Crystals with a particle size of 1~3μm; D 50 Crystals with a particle size of 1~3μm are mixed with a second metal salt solution and subjected to a second hydrothermal reaction to obtain a lithium-rich manganese-based precursor. The first metal salt solution contains nickel salt, cobalt salt, and manganese salt, with a molar ratio of 0.35~0.4:0~0.05:0.6. The metal salts in the second metal salt solution include nickel salt, cobalt salt, and manganese salt, and the molar ratio of nickel salt, cobalt salt, and manganese salt is 0.4:0.1:0.5; A lithium-rich manganese-based precursor, a lithium source, and additives are mixed and subjected to a first sintering process to obtain a lithium-rich manganese-based cathode material. The lithium-rich manganese-based cathode material and the coating agent are mixed and subjected to a second sintering to obtain the coated lithium-rich manganese-based cathode material. The coated lithium-rich manganese-based cathode material is coated with Si by vapor deposition to obtain a lithium-rich manganese-based single-crystal cathode material.

[0005] Preferably, the chemical formula of the lithium-rich manganese-based cathode material is Li 1+n Ni x Mn y Co z M a O2, wherein 0.02 < a < 0.1, x + y + z + a = 1, 0 < n < 0.3, 0.3 < x < 0.5, 0.4 < y < 0.7, 0 < z < 0.2, and M includes one or more of Al, K, Sr, Ce, Be, B, Co, Nb, W, P, Ti, Mg, S, Na, F, and Si; and D of the lithium-rich manganese-based cathode material. 50 Particle size is 0.7~2μm, D 10 Particle size is 0.2~1.5μm, D 90 The particle size is 2.5~4μm.

[0006] Preferably, the first sintering is carried out in a slightly oxygen-enriched atmosphere; the oxygen content in the slightly oxygen-enriched atmosphere is 30~60 vol%; the first sintering includes sequentially performing a first stage sintering, a second stage sintering, a third stage sintering, and a fourth stage sintering; the temperature of the first stage sintering is 400~600℃, and the holding time is 120~500 min; the temperature of the second stage sintering is 800~1000℃, and the holding time is 60~1200 min; the temperature of the third stage sintering is 950~1250℃, and the holding time is 0~1200 min; the temperature of the fourth stage sintering is 500~850℃, and the holding time is 0~600 min.

[0007] Preferably, the additive includes one or more of oxides, hydroxides and salts of Al, K, Sr, Ce, Be, B, Co, Nb, W, P, Ti, Mg, S, Na, F and Si.

[0008] Preferably, the coating agent comprises one or more oxides, hydroxides, and salts of Al, K, Sr, Ce, Be, B, Co, Nb, W, P, Ti, Mg, S, Na, F, Si, and C.

[0009] Preferably, the second sintering is carried out in an air atmosphere; the temperature of the second sintering is 100~900℃, and the holding time is 60~700min.

[0010] Preferably, the conditions for vapor deposition coating of Si include: the silicon source gas is silane; the carrier gas is argon or nitrogen; the volume percentage of the silicon source gas in the total gas mixture is 1-10%; the fluidization rate is 0.5-2 cm / s; the processing temperature is 300-800℃; and the processing time is 1-5 h.

[0011] Preferably, the thickness of the Si layer formed by vapor deposition coating Si is 2~5 nm.

[0012] The present invention also provides a lithium-rich manganese-based single-crystal cathode material prepared by the preparation method described above, comprising a lithium-rich manganese-based cathode material and a coating agent and a Si layer sequentially coated on the surface of the lithium-rich manganese-based cathode material.

[0013] This invention also provides the application of the lithium-rich manganese-based single-crystal cathode material described above in lithium-ion batteries.

[0014] This invention provides a method for preparing a lithium-rich manganese-based single-crystal cathode material, comprising the following steps: After adjusting the pH of the first metal salt solution to 10-12, the first hydrothermal reaction was carried out to obtain D. 50 Crystals with a particle size of 1~3μm; D 50 Crystals with a particle size of 1~3μm are mixed with a second metal salt solution and subjected to a second hydrothermal reaction to obtain a lithium-rich manganese-based precursor. The first metal salt solution contains nickel salt, cobalt salt, and manganese salt, with a molar ratio of 0.35~0.4:0~0.05:0.6. The metal salts in the second metal salt solution include nickel salt, cobalt salt, and manganese salt, and the molar ratio of nickel salt, cobalt salt, and manganese salt is 0.4:0.1:0.5; A lithium-rich manganese-based precursor, a lithium source, and additives are mixed and subjected to a first sintering process to obtain a lithium-rich manganese-based cathode material. The lithium-rich manganese-based cathode material and the coating agent are mixed and subjected to a second sintering to obtain the coated lithium-rich manganese-based cathode material. The coated lithium-rich manganese-based cathode material is coated with Si by vapor deposition to obtain a lithium-rich manganese-based single-crystal cathode material.

[0015] The lithium-rich manganese-based precursor prepared by this invention has a cobalt-rich surface, resulting in high porosity and more ample space for the growth of individual primary grains. This is beneficial for the growth of primary grains and promotes the formation of single-crystal morphology, leading to higher single-crystal density. 50The cathode material has a size of 0.6~1μm, or exists as a single-crystal aggregate of 1.5~3μm. During charge and discharge, the surface of the lithium-rich manganese-based cathode material undergoes side reactions with the electrolyte, leading to structural collapse. In this invention, the coating agent can enhance the rate performance of the material, and the silicon coating can effectively isolate the cathode material itself from the electrolyte reaction. By sacrificing some initial efficiency through single crystallization, the probability of structural collapse of the cathode material is reduced by decreasing the phase transition tendency of the cathode material, thereby optimizing cycle stability and rate performance. Moreover, the single-crystal particles can fill the voids more efficiently under pressure, increasing the compaction density of the cathode material and avoiding limitations on volumetric energy density. This results in a low-voltage, high-compact lithium-rich manganese-based single-crystal cathode material with excellent cycle performance and rate performance, and a capacity retention of >108% after 100 cycles. The preparation method used in this invention is green and environmentally friendly, without molten salt, and suitable for industrial production. Attached Figure Description

[0016] Figure 1 A scanning electron microscope image of the lithium-rich manganese-based precursor prepared in Example 1; Figure 2 This is a scanning electron microscope image of the lithium-rich manganese-based single-crystal cathode material prepared in Example 1; Figure 3 A scanning electron microscope image of the lithium-rich manganese-based cathode material prepared in Comparative Example 1; Figure 4 Comparison of 0.1C charge-discharge curves of the lithium-rich manganese-based single-crystal cathode material prepared in Example 1 and the lithium-rich manganese-based cathode material prepared in Comparative Example 1; Figure 5 The graph shows a comparison of the cycle discharge capacity of the lithium-rich manganese-based single-crystal cathode material prepared in Example 1 and the lithium-rich manganese-based cathode material prepared in Comparative Example 1. Detailed Implementation

[0017] This invention provides a method for preparing a lithium-rich manganese-based single-crystal cathode material, comprising the following steps: After adjusting the pH of the first metal salt solution to 10-12, the first hydrothermal reaction was carried out to obtain D. 50 Crystals with a particle size of 1~3μm; D 50 Crystals with a particle size of 1~3μm are mixed with a second metal salt solution and subjected to a second hydrothermal reaction to obtain a lithium-rich manganese-based precursor. The first metal salt solution contains nickel salt, cobalt salt, and manganese salt, with a molar ratio of 0.35~0.4:0~0.05:0.6. The metal salts in the second metal salt solution include nickel salt, cobalt salt, and manganese salt, and the molar ratio of nickel salt, cobalt salt, and manganese salt is 0.4:0.1:0.5; A lithium-rich manganese-based precursor, a lithium source, and additives are mixed and subjected to a first sintering process to obtain a lithium-rich manganese-based cathode material. The lithium-rich manganese-based cathode material and the coating agent are mixed and subjected to a second sintering to obtain the coated lithium-rich manganese-based cathode material. The coated lithium-rich manganese-based cathode material is coated with Si by vapor deposition to obtain a lithium-rich manganese-based single-crystal cathode material.

[0018] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0019] In this invention, the pH value of the first metal salt solution is adjusted to 10-12, and then a first hydrothermal reaction is carried out to obtain D. 50 Crystals with a particle size of 1~3μm.

[0020] In one embodiment, the first metal salt solution contains nickel salt, cobalt salt, and manganese salt, with a molar ratio of 0.35~0.4:0~0.05:0.6, specifically 0.4:0:0.6 or 0.35:0.05:0.6. The nickel salt includes one or more of nickel sulfate, nickel acetate, and nickel oxalate, specifically nickel sulfate. The cobalt salt includes one or more of cobalt sulfate, cobalt acetate, and cobalt oxalate, specifically cobalt sulfate. The manganese salt includes one or more of manganese sulfate, manganese acetate, and manganese oxalate, specifically manganese sulfate. The pH value is adjusted to 10~12, specifically 11.2. The reagent used for pH adjustment is an alkaline solution, comprising sodium salt and water. The sodium salt is sodium oxalate or sodium carbonate, specifically sodium carbonate. The total concentration of nickel salt, cobalt salt, and manganese salt in the first metal salt solution is 1~4 mol / L, specifically 2~3 mol / L.

[0021] In one embodiment, the temperature of the first hydrothermal reaction is 40~70℃, specifically 50~65℃; the first hydrothermal reaction is carried out under stirring conditions; the stirring speed is 300~1200 rpm, specifically 1000 rpm; the first hydrothermal reaction is carried out in a stirred tank filled with nitrogen; when the D crystals obtained from the first hydrothermal reaction... 50 When the particle size is 1~3μm, the first hydrothermal reaction is stopped. In a specific embodiment, this is when the D crystals obtained from the first hydrothermal reaction are... 50 When the particle size is 2 μm, the first hydrothermal reaction is stopped; after the first hydrothermal reaction, the process further includes: performing solid-liquid separation on the first hydrothermal reaction product to obtain D. 50 Crystals with a particle size of 1~3μm; the solid-liquid separation is performed by vacuum filtration.

[0022] The D is obtained 50 After crystallization with a particle size of 1~3μm, the present invention will... 50 Crystals with a particle size of 1~3μm are mixed with a second metal salt solution and subjected to a second hydrothermal reaction to obtain a lithium-rich manganese-based precursor.

[0023] In one embodiment, the metal salts in the second metal salt solution include nickel salt, cobalt salt, and manganese salt, and the molar ratio of nickel salt, cobalt salt, and manganese salt is 0.3~0.4:0.05~0.15:0.5~0.55, with a specific embodiment being 0.4:0.1:0.5; the total concentration of nickel salt, cobalt salt, and manganese salt in the second metal salt solution is 1~4 mol / L, with a specific embodiment being 2~3 mol / L.

[0024] As one implementation method, the D 50 Crystals with a particle size of 1~3μm are mixed with a second metal salt solution to form: in the D 50 A second metal salt solution is pumped into crystals with a particle size of 1-3 μm; the pumping rate is 3-8 L / min, specifically 5 L / min in this embodiment; the second hydrothermal reaction is carried out under stirring; the stirring rate is 300-1200 rpm, specifically 1000 rpm in this embodiment; the second hydrothermal reaction is stopped when the D50 particle size of the crystals obtained from the second hydrothermal reaction is 1-5 μm; the temperature of the second hydrothermal reaction is 40-70℃, specifically 65℃ in this embodiment; the second hydrothermal reaction is carried out under stirring; the stirring speed is 300-1200 rpm, specifically 1000 rpm in this embodiment; the second hydrothermal reaction is carried out in a stirred tank filled with nitrogen; when the D50 particle size of the crystals obtained from the second hydrothermal reaction is 1-3 μm... 50 When the particle size is 1~5μm, the second hydrothermal reaction is stopped. In a specific embodiment, this is when the D crystals obtained from the second hydrothermal reaction are... 50 When the particle size is 2.5 μm, the second hydrothermal reaction is stopped.

[0025] In one embodiment, after the second hydrothermal reaction, the process further includes: separating the product obtained from the second hydrothermal reaction into solid and liquid components, and washing and drying the resulting solid sequentially to obtain a lithium-rich manganese-based precursor; the solid-liquid separation is performed by vacuum filtration; the washing is performed by sequential alkaline washing and water washing; the reagent used for alkaline washing is NaOH solution; the concentration of the NaOH solution is 0.5~2 mol / L, specifically 1 mol / L in this embodiment; the reagent used for water washing is pure water; the number of alkaline washings is 2~5 times, specifically 3 times in this embodiment; the number of water washings is 2~5 times, specifically 3 times in this embodiment; the drying temperature is 60~90℃, specifically 80~90℃ in this embodiment, and the time is 6~12h, specifically 8h in this embodiment; the drying is performed by vacuum drying; the vacuum degree of the vacuum drying is 10~10 5 MPa, specifically 10 MPa in this embodiment. 3 MPa.

[0026] In one embodiment, the tap density of the lithium-rich manganese-based precursor is 0.4~1.2 g / cm³. 3 In the specific embodiment, it is 0.8 g / cm³. 3 BET has a specific surface area of ​​20~50m². 2 / g, specifically 45m in the embodiment. 2 / g, the primary particle thickness is 20~60nm, and in the specific embodiment it is 25. The primary particle thickness refers to the thickness of a single crystal.

[0027] After obtaining the lithium-rich manganese-based precursor, the present invention mixes the lithium-rich manganese-based precursor, lithium source and additives, and performs a first sintering to obtain a lithium-rich manganese-based cathode material.

[0028] In one embodiment, the lithium source includes lithium carbonate and / or lithium hydroxide, specifically lithium carbonate in this embodiment; the additive includes one or more oxides, hydroxides, and salts of Al, K, Sr, Ce, Be, B, Co, Nb, W, P, Ti, Mg, S, Na, F, and Si, specifically tungsten oxide and aluminum oxide in this embodiment; the mass of the additive is 1-10% of the mass of the lithium-rich manganese-based precursor, specifically 5% in this embodiment; the particle size of the additive is 20-500 nm, specifically 30 nm in this embodiment.

[0029] In one embodiment, the lithium-rich manganese-based precursor, lithium source, and additives are mixed and subjected to ball milling; the ball milling is a wet ball milling process; the reagent used in the wet ball milling is anhydrous ethanol; the mass of the reagent used in the wet ball milling is 5-15% of the total mass of the lithium-rich manganese-based precursor, lithium source, and additives, specifically 10% in this embodiment; the grinding balls used in the ball milling process are made of zirconium oxide with a particle size of 3-5 mm, specifically 3 mm in this embodiment; the ball-to-material ratio in the ball milling process is 6-12:1, specifically 8:1 in this embodiment; the rotation speed of the ball milling process is 300-900 rpm, specifically 600 rpm in this embodiment; the ball milling time is 1-12 hours, specifically 8 hours in this embodiment; and the equipment used for the ball milling process is a planetary ball mill.

[0030] In one embodiment, the first sintering is carried out in a slightly oxygen-enriched atmosphere; the oxygen content in the slightly oxygen-enriched atmosphere is 30-60 vol%, specifically 35-50 vol% in this embodiment; the first sintering includes sequentially performing a first stage sintering, a second stage sintering, a third stage sintering, and a fourth stage sintering; the temperature of the first stage sintering is 400-600℃, specifically 550℃ in this embodiment, and the holding time is 120-500 min, specifically 500 min in this embodiment; the heating rate to the temperature of the first stage sintering is 1-10℃ / min, specifically 2℃ / min in this embodiment; the temperature of the second stage sintering is 800-1000℃, specifically 900-1000℃ in this embodiment, and the holding time is 60-1200 min, specifically 360-720 min in this embodiment; the heating rate to the second stage sintering is 1-10℃ / min, specifically 2℃ / min in this embodiment; the temperature of the second stage sintering is 800-1000℃, specifically 900-1000℃ ... heating rate to the fourth stage sintering is 1-10℃ / min, specifically 900-1000℃, and The heating rate of the sintering temperature is 1~10℃ / min, specifically 1℃ / min in this embodiment; the temperature of the third stage sintering is 950~1250℃, specifically 1000~1100℃ in this embodiment, and the holding time is 0~1200min, specifically 60~120min in this embodiment; the heating rate to the third stage sintering temperature is 1~10℃ / min, specifically 1℃ / min in this embodiment; the temperature of the fourth stage sintering is 500~850℃, specifically 600~700℃ in this embodiment, and the holding time is 0~600min, specifically 300~500min in this embodiment; the cooling rate to the fourth stage sintering temperature is 1~10℃ / min, specifically 3℃ / min in this embodiment; after the first sintering, the process further includes: naturally cooling the first sintered product to room temperature. This invention employs a four-stage high-temperature sintering process: a three-stage gradient heating to 950~1250℃, followed by annealing at 500~850℃, which promotes single-crystal exfoliation and densification.

[0031] As one implementation method, the chemical formula of the lithium-rich manganese-based cathode material is Li. 1+n Ni x Mny Co z M a O2, wherein 0.02 < a < 0.1, x + y + z + a = 1, 0 < n < 0.3, 0.3 < x < 0.5, 0.4 < y < 0.7, 0 < z < 0.2, and in a specific embodiment, a = 0.03, n = 0.1, x = 0.40, y = 0.54, z = 0.03; M includes one or more of Al, K, Sr, Ce, Be, B, Co, Nb, W, P, Ti, Mg, S, Na, F, and Si, and in a specific embodiment, W; the D of the lithium-rich manganese-based cathode material 50 The particle size is 0.7~2μm, and in the specific embodiment it is 1.92μm. D 10 The particle size is 0.2~1.5μm, and in the specific embodiment it is 0.34μm. D 90 The particle size is 2.5~4μm, and in the specific embodiment it is 3.31μm.

[0032] After obtaining the lithium-rich manganese-based cathode material, the present invention mixes the lithium-rich manganese-based cathode material with a coating agent and performs a second sintering to obtain the coated lithium-rich manganese-based cathode material.

[0033] In one embodiment, the coating agent includes one or more of oxides, hydroxides, and salts of Al, K, Sr, Ce, Be, B, Co, Nb, W, P, Ti, Mg, S, Na, F, Si, and C, specifically aluminum oxide, boron oxide, and cobalt tetroxide; the mass of the coating agent is 0.1-5% of the mass of the lithium-rich manganese-based cathode material, specifically 0.7-3% in this embodiment; the particle size of the coating agent is 10-200 nm, specifically 30 nm in this embodiment; the thickness of the coating layer formed by the coating agent is 20-100 nm, specifically 50 nm in this embodiment.

[0034] In one embodiment, the lithium-rich manganese-based cathode material and the coating agent are mixed under ball milling conditions; the ball milling is a wet ball milling; the reagent used in the wet ball milling is anhydrous ethanol; the mass of the reagent used in the wet ball milling is 5-15% of the total mass of the lithium-rich manganese-based cathode material and the coating agent, specifically 10% in this embodiment; the grinding balls used in the ball milling are made of zirconium oxide, with a particle size of 10mm and 5mm mixed; the ratio of the number of grinding balls with a particle size of 10mm to the number of grinding balls with a particle size of 5mm is 1-3:7-9, specifically 2:7 in this embodiment; the ball-to-material ratio in the ball milling is 6-12:1, specifically 8:1 in this embodiment; the rotation speed of the ball milling is 200-500 rpm, specifically 300 rpm in this embodiment; the ball milling time is 1-6 hours, specifically 4 hours in this embodiment; the equipment used in the ball milling is a ball mill.

[0035] In one embodiment, the second sintering is carried out in an air atmosphere; the temperature of the second sintering is 100~900℃, specifically 600~700℃ in this embodiment, and the holding time is 60~700min, specifically 180~360min in this embodiment; the heating rate to the temperature of the second sintering is 1~10℃ / min, specifically 5℃ / min in this embodiment; after the second sintering, the method further includes: cooling the product of the second sintering to room temperature; the cooling rate is 2~5℃ / min, specifically 3℃ / min in this embodiment.

[0036] After obtaining the coated lithium-rich manganese-based cathode material, the present invention performs vapor deposition coating of the coated lithium-rich manganese-based cathode material with Si to obtain a lithium-rich manganese-based single crystal cathode material.

[0037] In one implementation method, the equipment used for vapor deposition coating of Si is a vapor deposition fluidized bed. The conditions for vapor deposition coating of Si include: the silicon source gas is silane; the carrier gas is argon or nitrogen, specifically nitrogen in this embodiment; the volume percentage of the silicon source gas in the total silicon source gas and carrier gas is 1-10%, specifically 5% in this embodiment; the fluidization velocity is 0.5-2 cm / s, specifically 0.8 cm / s in this embodiment; the processing temperature is 300-800℃, specifically 600℃ in this embodiment; the processing time is 1-5 h, specifically 1.5 h in this embodiment; and the thickness of the Si layer formed by vapor deposition coating is 2-5 nm, specifically 4 nm in this embodiment. This invention uses vapor deposition for silicon coating, avoiding excessively thick silicon coating from affecting conductivity.

[0038] The present invention also provides a lithium-rich manganese-based single-crystal cathode material prepared by the preparation method described above, comprising a lithium-rich manganese-based cathode material and a coating agent and a Si layer sequentially coated on the surface of the lithium-rich manganese-based cathode material.

[0039] As one embodiment, the compaction density of the lithium-rich manganese-based single-crystal cathode material is ≥3.16 g / cm³. 3 In the specific embodiment, it is 3.16 g / cm³. 3 .

[0040] This invention also provides the application of the lithium-rich manganese-based single-crystal cathode material described above in lithium-ion batteries.

[0041] The present invention does not impose any special limitations on the application of the lithium-rich manganese-based single-crystal cathode material in lithium-ion batteries; any application method known in the art can be used.

[0042] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof, but they should not be construed as limiting the scope of protection of the present invention.

[0043] Example 1 Nickel salt (nickel sulfate), cobalt salt (cobalt sulfate), and manganese salt (manganese sulfate) were dissolved in deionized water at a molar ratio of 0.4:0:0.6 to form a first metal salt solution. Nickel salt, cobalt salt, and manganese salt were dissolved in deionized water at a molar ratio of 0.4:0.1:0.5 to form a second metal salt solution. A 3 mol / L solution of the first metal salt was pumped into a 100L stirred tank filled with nitrogen, while simultaneously adding sodium carbonate aqueous solution to adjust the pH to 11.2. The mixture was stirred at 1000 rpm at 65°C, and particle growth was observed. The synthesis time was controlled to control the D... 50 Once the particle size approaches 2 μm, a 3 mol / L second metal salt solution is slowly pumped in at a flow rate of 5 L / min to control D. 50 The particle size approached 2.5 μm, and after filtration, washing three times with 1 mol / L NaOH solution and three times with pure water, it was then subjected to a vacuum of 10 at 90℃. 3 Vacuum drying at MPa for 8 h yielded a lithium-rich manganese-based precursor (Q). 前 The compacted density is 3.16 g / cm³. 3 The specific surface area of ​​BET is 0.77 m². 2 / g, with a single particle thickness of 600~1200nm; 1000g of lithium-rich manganese-based precursor, 500g of lithium carbonate, 0.5% (by weight of the precursor) of tungsten oxide (30nm particle size), and 0.1% (by weight of the precursor) of alumina (30nm particle size) were wet-milled in anhydrous ethanol for 8 hours using a planetary ball mill. The milling speed was 600 rpm, the ball-to-material ratio was 8:1, and the mass of anhydrous ethanol was 10% of the total mass of the lithium-rich manganese-based precursor, lithium carbonate, tungsten oxide, and alumina. The grinding balls were made of zirconium oxide with a particle size of 3mm. The mixed material was then placed in a muffle furnace. Sintering was performed in a furnace under a slightly oxygen-enriched atmosphere with an oxygen content of 35 vol%. The first stage involved heating to 550℃ at a rate of 2℃ / min and holding for 500 min. The second stage involved heating to 1000℃ at a rate of 1℃ / min and holding for 360 min. The third stage involved heating to 1100℃ at a rate of 1℃ / min and holding for 60 min. The fourth stage involved cooling to 700℃ at a rate of 3℃ / min and holding for 300 min, followed by natural cooling to room temperature. This yielded a lithium-rich manganese-based cathode material (Q1) with the chemical formula Al. 0.01 W 0.02 Li 1.1 Ni 0.4 Mn 0.03 Co 0.54 O2, D 50 The particle size is 1.92 μm, D 10 The particle size is 0.34 μm, D 90 The particle size is 3.31 μm; The weighed lithium-rich manganese-based cathode material was mixed with alumina (0.1% of the mass of the lithium-rich manganese-based cathode material, particle size 30 nm), boron oxide (0.1% of the mass of the lithium-rich manganese-based cathode material, particle size 30 nm), and cobalt tetroxide (0.5% of the mass of the lithium-rich manganese-based cathode material, particle size 30 nm) by wet ball milling in anhydrous ethanol for 4 hours. The ball milling speed was 300 rpm, and the mass of anhydrous ethanol was equal to the mass of the lithium-rich manganese-based cathode material, alumina, boron oxide, and cobalt tetroxide. The total mass of cobalt trioxide is 12%. The grinding balls are made of zirconium oxide. The ratio of grinding balls with a particle size of 10 mm to those with a particle size of 5 mm is 2:7, and the ball-to-material ratio is 8:1. The mixed material is placed in a tube furnace and heated to 700°C at a rate of 5°C / min in an air atmosphere. After holding at this temperature for 180 min, it is cooled to room temperature at a rate of 3°C / min to obtain the coated lithium-rich manganese-based cathode material (Q2). The thickness of the coating layer formed by the coating agent is 50 nm. The coated lithium-rich manganese-based cathode material sample was placed in a vapor deposition fluidized bed. The silicon source gas was silane, and the carrier gas was nitrogen. The volume ratio of the silicon source gas in the silicon source gas and the carrier gas was controlled at 5%. The fluidization velocity was controlled at 0.8 cm / s, the processing temperature was controlled at 600℃, and the processing time was controlled at 180 min. Si was coated by vapor deposition with a thickness of 4 nm, and the final lithium-rich manganese-based single crystal cathode material (Q3) was obtained.

[0044] Example 2 The difference from Example 1 is that, by controlling the Co salt concentration in the second metal salt solution in the precursor, the Co content in the lithium-rich manganese-based single crystal cathode material is controlled to be 0.06% of the total molar content of transition metals Ni and Mn.

[0045] Example 3 The difference from Example 1 is that the additives are changed to 0.5% strontium oxide and 0.3% titanium oxide by the precursor mass.

[0046] Comparative Example 1 1000g of lithium-rich manganese-based precursor and 500g of lithium carbonate were mixed by ball milling at 600rpm for 8h. The mixed material was then placed in a muffle furnace for sintering. In the first stage, the temperature was increased to 500℃ at 2℃ / min and held for 300min. In the second stage, the temperature was increased to 850℃ at 5℃ / min and held for 800min. After pulverization, the lithium-rich manganese-based cathode material (Q4) was obtained.

[0047] Comparative Example 2 The difference from Example 1 is that the surface cobalt enrichment treatment is not performed using a second metal salt solution.

[0048] Performance testing (1) Figure 1 The image shows a scanning electron microscope (SEM) image of the lithium-rich manganese-based precursor prepared in Example 1.

[0049] from Figure 1 It can be seen that the plate-like or thin prismatic primary grains in the lithium-rich manganese-based precursor prepared by this invention are orderly aggregated, which will provide a certain structural guidance for the growth of single crystals during subsequent processing such as high-temperature sintering.

[0050] (2) Figure 2 This is a scanning electron microscope image of the lithium-rich manganese-based single-crystal cathode material prepared in Example 1.

[0051] from Figure 2 As can be seen, the lithium-rich manganese-based single-crystal cathode material particles prepared by this invention exhibit relatively regular blocky and polygonal shapes, which conforms to the ideal morphology of single-crystal cathode materials. The core advantage of single-crystal cathode materials is the absence of internal grain boundaries, which avoids side reactions at polycrystalline grain boundaries (such as electrolyte decomposition and impurity phase formation). The regular particle morphology is a direct manifestation of the single-crystal structure at the microscale, indicating that the precursor prepared by this invention and the preparation method of the lithium-rich manganese-based single-crystal cathode material provide favorable conditions for single-crystal growth.

[0052] (3) Figure 3 The image shows a scanning electron microscope (SEM) image of the lithium-rich manganese-based cathode material prepared in Comparative Example 1.

[0053] from Figure 3 It can be seen that the primary particles of the lithium-rich manganese-based cathode material prepared in Comparative Example 1 are 200~500nm in size and exhibit a polycrystalline morphology.

[0054] (4) The charge-discharge and cycle performance of the lithium-rich manganese-based single-crystal cathode material prepared in Example 1 and the lithium-rich manganese-based cathode material prepared in Comparative Example 1 were tested, and the results are shown in Table 1. Figure 4 and Figure 5 As shown.

[0055] The test method involves mixing the positive electrode material, PVDF, and conductive agent at a mass ratio of 8:1:1, homogenizing the sample for 36 minutes, applying a 300D thickness with a scraper onto the current collector to form the positive electrode sheet, and then assembling it into a battery. The assembly sequence is as follows: negative electrode shell cover, 1 drop of electrolyte, positive electrode sheet, 2 drops of electrolyte, separator, 2 drops of electrolyte, lithium sheet, gasket, spring, positive electrode shell cover, nominal specific capacity 1C = 140mA / g, activation at 0.1C (2.5~4.4V constant current) for two cycles, and cycling at 1C (2.5~4.4V constant current) for 200 cycles.

[0056] Table 1. Test results of Example 1 and Comparative Example 1 (2.5~4.4V constant current charge and discharge).

[0057] As can be seen from Table 1, the lithium-rich manganese-based single-crystal cathode material prepared in Example 1 achieved a significant improvement in cycle performance under the condition of a certain capacity loss, and the compaction density of the material was improved through morphology and process design.

[0058] from Figure 4 It can be seen that, compared with Comparative Example 1, the charge-discharge efficiency of Example 1 is reduced due to the single crystallization of the material.

[0059] from Figure 5 It can be seen that, compared with Comparative Example 1, Example 1 has a 1C 200-cycle retention rate that is improved by about 15%.

[0060] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a lithium-rich manganese-based single-crystal cathode material, characterized in that, The method comprises the following steps: After adjusting the pH value of the first metal salt solution to 10-12, the first hydrothermal reaction is performed to obtain D 50 crystals having a particle size of 1-3 μm; The D 50 The crystalline and the second metal salt solution with a particle size of 1-3 μm are mixed, a second hydrothermal reaction is performed, and a lithium-rich manganese-based precursor is obtained. The metal salts in the first metal salt solution comprise nickel salt, cobalt salt and manganese salt, and the molar ratio of the nickel salt, the cobalt salt and the manganese salt is 0.35-0.4:0-0.05:0.6; The metal salts in the second metal salt solution comprise nickel salt, cobalt salt and manganese salt, and the molar ratio of the nickel salt, the cobalt salt and the manganese salt is 0.4:0.1:0.5; The lithium-rich manganese-based precursor, a lithium source and an additive are mixed to perform first sintering, thereby obtaining a lithium-rich manganese-based positive electrode material; The lithium-rich manganese-based positive electrode material and a coating agent are mixed to perform second sintering, thereby obtaining a coated lithium-rich manganese-based positive electrode material; The coated lithium-rich manganese-based positive electrode material is subjected to gas-phase deposition coating of Si, thereby obtaining a lithium-rich manganese-based single-crystal positive electrode material.

2. The production method according to claim 1, characterized by, The chemical formula of the lithium-rich manganese-based positive electrode material is Li 1+n Ni x Mn y Co z M a O2, wherein, 0.02 50 The particle size of the lithium-rich manganese-based positive electrode material is 0.7~2μm, D 10 The particle size of the lithium-rich manganese-based positive electrode material is 0.2~1.5μm, D 90 The particle size of the lithium-rich manganese-based positive electrode material is 2.5~4μm.

3. The preparation method according to claim 1, characterized in that, The first sintering is performed in a micro-oxygen-rich atmosphere; the oxygen content in the micro-oxygen-rich atmosphere is 30-60 vol%; the first sintering comprises sequentially performing first-stage sintering, second-stage sintering, third-stage sintering and fourth-stage sintering; the temperature of the first-stage sintering is 400-600℃, and the holding time is 120-500 min; the temperature of the second-stage sintering is 800-1000℃, and the holding time is 60-1200 min; the temperature of the third-stage sintering is 950-1250℃, and the holding time is 0-1200 min; the temperature of the fourth-stage sintering is 500-850℃, and the holding time is 0-600 min.

4. The production method according to claim 1, characterized by, The additive comprises one or more of oxides, hydroxides and salts of Al, K, Sr, Ce, Be, B, Co, Nb, W, P, Ti, Mg, S, Na, F and Si.

5. The preparation method according to claim 1, characterized in that, The coating agent comprises one or more of oxides, hydroxides and salts of Al, K, Sr, Ce, Be, B, Co, Nb, W, P, Ti, Mg, S, Na, F, Si and C.

6. The method of claim 1, wherein, The second sintering is performed in an air atmosphere; the temperature of the second sintering is 100-900℃, and the holding time is 60-700 min.

7. The preparation method according to claim 1, characterized in that, The conditions for the gas-phase deposition coating of Si comprise: the silicon source gas is silane; the carrier gas is argon or nitrogen; the volume ratio of the silicon source gas in the total gas of the silicon source gas and the carrier gas is 1-10%; the fluidization speed is 0.5-2 cm / s; the processing temperature is 300-800℃; and the processing time is 1-5 h.

8. The production method according to claim 1 or 7, characterized by, The thickness of the Si layer formed by the gas-phase deposition coating of Si is 2-5 nm.

9. The lithium-rich manganese-based single-crystal cathode material prepared by the preparation method according to any one of claims 1-8, characterized in that, The lithium-rich manganese-based positive electrode material and the coating agent and the Si layer sequentially coated on the surface of the lithium-rich manganese-based positive electrode material.

10. The lithium-rich manganese-based single-crystal positive electrode material according to claim 9 is applied in a lithium ion battery.

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