Preparation method of battery graphite negative electrode material

Abstract

The application belongs to the field of secondary battery materials, and discloses a preparation method of a battery graphite negative electrode material, which comprises the following steps: S1, cooling and crushing spherical graphite particles obtained by two-stage temperature increasing heat treatment of natural graphite; S2, introducing the treated spherical graphite particles into precursors containing fluorine, nitrogen and sulfur to form F, N and S atom gradient doped graphite particles; S3, mixing the atom doped graphite particles with precursors sol containing a carbon source and a titanium source, spray drying and carbonizing to form a TiO2 porous carbon coating layer; and S4, grafting a crown ether derivative on the surface of the coated graphite particles; according to the method, a multi-layer and multi-functional synergistic modification layer is constructed on the surface of the natural graphite through gradient heteroatom doping, TiO2 porous carbon core-shell coating and surface crown ether derivative grafting, the graphite negative electrode performance is improved in multiple dimensions, and the ultimate performance of fast charging, long service life and high initial efficiency is realized.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery materials technology, specifically relating to a method for preparing a graphite anode material for batteries. Background Technology

[0002] Graphite, as the core substrate of lithium-ion battery anode materials, has long dominated the anode material market since the commercialization of lithium-ion batteries due to its advantages such as high theoretical lithium storage capacity (372mAh / g), stable layered crystal structure, low cost, and environmental friendliness. It is widely used in consumer electronics batteries, power batteries, and energy storage batteries. In terms of material type, existing graphite anode materials are mainly divided into two categories: natural graphite and artificial graphite. Natural graphite is prepared from natural mineral resources through purification and shaping processes, and is widely used in consumer electronics batteries and low-to-mid-range power batteries. Artificial graphite, on the other hand, is prepared from petroleum coke, needle coke, and other raw materials through complex processes such as carbonization and graphitization, and is the mainstream choice for high-end power batteries.

[0003] In recent years, with the continuous upgrading of the demand for high range, fast charging, and long life of new energy vehicles and high safety, low degradation, and high rate of energy storage batteries, the performance shortcomings of existing graphite anode materials have gradually become prominent, specifically in the following aspects: (1) Insufficient conductivity and lithium storage activity, which restricts the rate performance and capacity utilization; (2) Significant volume expansion during cycling, leading to electrode structure failure; (3) Poor electrode-electrolyte interface stability, resulting in frequent side reactions. Therefore, the inherent problems of existing graphite anode materials in terms of conductivity, volume expansion, and interface stability can no longer meet the demand for high-performance lithium-ion batteries in the fields of new energy vehicles and energy storage. Summary of the Invention

[0004] To address the shortcomings mentioned in the background art, the present invention aims to provide a method for preparing graphite anode materials for batteries. By controlling the electronic structure of graphite through elemental gradient doping, the method solves the problems of limited active sites and conductivity in traditional graphite lithium storage. By using porous carbon and TiO2 composite coating, the method solves the problem of electrode failure caused by volume expansion during cycling in traditional graphite. At the same time, the method further optimizes ion transport by using chemical grafting of (benzo-15-crown 5-ether)-4'-carboxylic acid to solve the problems of competition for intercalation between Li+ and other ions and poor wettability at the electrode-electrolyte interface. Through multi-dimensional modification, the method synergistically improves the performance of graphite anodes, making it suitable for high-energy-density and long-cycle-life power batteries and energy storage batteries.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for preparing a graphite anode material for batteries includes the following steps:

[0007] S1. Place natural graphite in a high-temperature rotary furnace, perform two-stage heating heat treatment, and then cool and crush it to obtain spherical graphite particles.

[0008] S2. The treated spherical graphite particles are placed in a high-temperature rotary furnace and heated to 800~900℃. Fluorine-containing and nitrogen-containing precursors are introduced in sequence to form a gradient doping structure with F-rich inner layer and N-rich outer layer. Then the temperature is lowered to 600℃ and sulfur-containing precursors are introduced to complete S doping.

[0009] S3. A precursor sol is prepared by mixing a polymer rich in carboxyl and hydroxyl groups with titanate and a template agent. The precursor sol is then mixed with atomically doped graphite particles and carbonized by spray drying to form a porous TiO2 carbon coating layer.

[0010] S4. Graft crown ether derivatives onto the surface of the coated graphite particles, and utilize the crown ether carboxylic acid to undergo an esterification reaction with the abundant oxygen-containing functional groups on the surface of the composite material to form covalent bonds.

[0011] Preferably, step S1 specifically includes:

[0012] S101. High-purity graphite particles are obtained by flotation of natural graphite. The graphite particles are then crushed to the micron level using an air jet mill or mechanical grinding equipment, and spherical or near-spherical particles are formed through inter-particle collisions.

[0013] S102. Place the graphite particles in a high-temperature rotary furnace and heat them to 700°C at a rate of 3°C / min under N2 atmosphere protection. Hold the temperature for 0.5~1.5h to fully remove volatiles. Then, rapidly heat the temperature to 1050°C at a rate of 15°C / min and hold for 2~3h.

[0014] S103, cooled to 800℃ in the furnace, then rapidly cooled to room temperature by introducing N2, and then mechanically dispersed and sieved to obtain spherical graphite particles with a D50 of 10~20μm.

[0015] Preferably, in step S101, the natural graphite raw material D50 has a particle size of 5-25 μm, a carbon content of ≥99.9%, and an ash content of ≤0.1%.

[0016] Preferably, step S2 specifically includes:

[0017] S201. Reload the spherical graphite particles into the high-temperature rotary furnace, raise the temperature to 850℃ under N2 protection and stabilize it. After turning off N2, introduce a mixed gas of CF4 and NH3 and react for 30~50 minutes. After the reaction is completed, switch to pure N2 and lower the furnace temperature to 600℃.

[0018] S202, at 600℃, a mixture of H2S and N2 is introduced and treated for 20~40 minutes. After treatment, the pipes and furnace are purged with a large amount of N2 until cooled to room temperature. F, N and S atomic gradient doped graphite particles.

[0019] Preferably, the volume ratio of CF4 to NH3 in step 201 is 1:2.

[0020] Preferably, the volume ratio of H2S to N2 in step 202 is 1:19.

[0021] Preferably, step S3 specifically includes:

[0022] S301. Dissolve block copolymer F127 in anhydrous ethanol and stir magnetically until completely dissolved to obtain solution A. Add citric acid and tetrabutyl titanate to anhydrous ethanol and stir until clear to obtain solution B. Under vigorous stirring, slowly add solution B to solution A. After the addition is complete, continue stirring for 3-5 hours to form a precursor sol.

[0023] S302. The gradient-doped graphite particles and the above sol are mixed at low speed in a planetary ball mill for 30 minutes to make the sol uniformly adhere to the graphite surface. The mixed wet material is transferred to a spray dryer and spray dried at an inlet temperature of 200℃ to obtain a dry composite powder with the precursor uniformly coated.

[0024] S303. Under N2 atmosphere, the composite powder uniformly coated with the precursor is heated to 550℃ at a rate of 6~8℃ / s, held for 4~6min, and cooled to room temperature to obtain TiO2 porous carbon-coated graphite particles.

[0025] Preferably, the mass ratio of block copolymer F127, citric acid, tetrabutyl titanate and atomically doped graphite particles is 1:2:3~4:100.

[0026] Preferably, step S4 specifically includes:

[0027] S401. Dissolve (benzo-15-crown-5-ether)-4'-carboxylic acid in N,N-dimethylformamide, add a small amount of 4-dimethylaminopyridine, and stir until fully dissolved;

[0028] S402. Disperse TiO2 porous carbon-coated graphite particles in the above solution, heat to 120°C under nitrogen protection, and reflux with magnetic stirring for 8-12 hours.

[0029] S403. After the reaction is complete, cool to room temperature and wash repeatedly by centrifugation with anhydrous ethanol and deionized water until the physically adsorbed free crown ether molecules and solvent are completely removed. Dry the washed material in a vacuum oven at 80°C for 8-12 hours to obtain the graphite anode material of the battery.

[0030] Preferably, the mass ratio of (benzo-15-crown-5-ether)-4'-carboxylic acid, 4-dimethylaminopyridine, and TiO2 porous carbon-coated graphite particles is 1~2:0.5:100.

[0031] The beneficial effects of this invention are:

[0032] This invention addresses the problems of limited active sites and conductivity in traditional graphite lithium storage by controlling the electronic structure of graphite through elemental gradient doping. The N atom is Li. + Providing additional adsorption sites enhances the lithium storage capacity of the material. Simultaneously, nitrogen (N) embedding in the graphite lattice lowers the electron transport activation energy, further improving conductivity. The high electronegativity of sulfur (F) atoms allows them to form strong polar CF bonds with carbon (C) atoms on the graphite surface. The presence of these bonds alters the electron cloud distribution on the graphite surface, reducing the adsorption and decomposition of solvent molecules in the electrolyte, decreasing the amount of SEI film formed, and resulting in a denser SEI film. This prevents repeated rupture and regeneration of the SEI film during cycling, reducing the formation of dead lithium. The larger radius of sulfur (S) atoms, compared to carbon (C) atoms, slightly widens the interlayer spacing of graphite. + Reduced spatial resistance during insertion / extraction increases diffusion rate, mitigating the problem of rapid capacity drop at high rates; widened interlayer spacing allows graphite to accommodate Li. + The spatial elasticity is enhanced, and the volume expansion rate of the first cycle is reduced.

[0033] This invention addresses the problem of electrode failure caused by volume expansion in traditional graphite cycling through a composite coating of porous carbon and TiO2, while further optimizing ion transport. The TiO2 layer suppresses volume expansion and stabilizes the structure; the TiO2 generated from the decomposition of tetrabutyl titanate exhibits zero-strain characteristics, and Li... + Embedding to generate Li4Ti5O 12 At this time, the volume change is less than 1%, forming a rigid shell on the graphite surface, directly restricting the expansion of graphite particles and preventing electrode cracking caused by inter-particle compression; furthermore, TiO2 itself has a certain lithium storage capacity and can be used as an auxiliary active material to synergistically store lithium with graphite, further improving the overall capacity of the material. The porous carbon layer generated by citric acid carbonization has high conductivity and high specific surface area, which can construct a continuous conductive network to encapsulate TiO2 and graphite particles, solving the problem of poor conductivity of TiO2, preventing the coating layer from becoming a conductive barrier, and providing fast ion channels; at the same time, the porous structure can store electrolyte, Li + It can reach the graphite surface without long-distance diffusion, thus improving the capacity retention of the material at high rates of 5C.

[0034] This invention addresses the problems of Li+ competing with other ions for insertion and poor wettability at the electrode and electrolyte interfaces through chemical grafting of (benzo-15-crown 5-ether)-4'-carboxylic acid. The 15-crown 5-ether structure of the crown ether molecule is compatible with Li+. + Radius highly matched, capable of specifically binding Li + This forms a host-guest complex, preventing impurity ions in the electrolyte from embedding into the graphite interlayer, thus avoiding the decrease in lithium storage capacity caused by ion occupancy and reducing Li... + The residence time at the interface improves the initial coulombic efficiency. Simultaneously, the carboxylic acid groups at the ends of the crown ether molecules are chemically grafted onto the hydroxyl groups on the coating surface via esterification, rather than through physical adsorption, allowing for long-term stability. The ether oxygen bond of the crown ether is hydrophilic, reducing the contact angle between the electrolyte and the electrode and improving electrolyte wetting efficiency. The grafted surface is smoother, resulting in a more uniform and thinner SEI film, reduced SEI film impedance, and decreased polarization loss during charge and discharge.

[0035] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1

[0038] A method for preparing a graphite anode material for batteries includes the following steps:

[0039] S1. Natural graphite with a D50 of 5-25 μm, a carbon content ≥99.9%, and an ash content ≤0.1% is obtained by flotation to obtain high-purity graphite particles. The graphite particles are then pulverized to the micron level using an air jet mill or mechanical grinding equipment, and spherical or near-spherical particles are formed through inter-particle collisions. The graphite particles are placed in a high-temperature rotary furnace and heated to 700℃ at a rate of 3℃ / min under N2 atmosphere protection, and held at that temperature for 1.5h to fully remove volatiles. Then, the temperature is rapidly increased to 1050℃ at a rate of 15℃ / min and held for 2h. The furnace is then cooled to 800℃, and then rapidly cooled to room temperature by introducing N2. After removal, the particles are mechanically dispersed and sieved to obtain spherical graphite particles with a D50 of 10~20μm.

[0040] S2. The spherical graphite particles are reloaded into the high-temperature rotary furnace and heated to 850°C under N2 protection and stabilized. After the N2 is turned off, a mixed gas of CF4 and NH3 in a volume ratio of 1:2 is introduced and reacted for 50 minutes. After the reaction is completed, pure N2 is switched and the furnace temperature is lowered to 600°C. At 600°C, a mixed gas of H2S and N2 in a volume ratio of 1:19 is introduced and treated for 20 minutes. After treatment, the pipes and furnace body are purged with a large amount of N2 until cooled to room temperature. The graphite particles are then atomically doped with F, N, and S.

[0041] S3. Dissolve 1g of block copolymer F127 in 15mL of anhydrous ethanol and stir magnetically until completely dissolved to obtain solution A. Add 2g of citric acid and 4g of tetrabutyl titanate to 30mL of anhydrous ethanol and stir until clear to obtain solution B. Under vigorous stirring, slowly add solution B dropwise to solution A. After the addition is complete, continue stirring for 3h to form a precursor sol. Mix 100g of gradient-doped graphite particles with the above sol at low speed in a planetary ball mill for 30min to make the sol uniformly adhere to the graphite surface. Transfer the mixed wet material to a spray dryer and spray dry at an inlet temperature of 200℃ to obtain a dry composite powder with uniform precursor coating. Under N2 atmosphere, heat the composite powder with uniform precursor coating to 550℃ at a rate of 6~8℃ / s, hold for 4min, and cool to room temperature to obtain TiO2 porous carbon-coated graphite particles.

[0042] S4. Dissolve 2g of (benzo-15-crown 5-ether)-4'-carboxylic acid in 20mL of N,N-dimethylformamide, add 0.5g of 4-dimethylaminopyridine, and stir until fully dissolved; disperse 100g of TiO2 porous carbon-coated graphite particles in the above solution, heat to 120℃ under nitrogen protection, and magnetically stir under reflux for 8h; after the reaction is completed, cool to room temperature, and repeatedly centrifuge and wash with anhydrous ethanol and deionized water until the physically adsorbed free crown ether molecules and solvent are completely removed. Dry the washed material in a vacuum oven at 80℃ for 12h to obtain the graphite anode material for the battery.

[0043] Example 2

[0044] A method for preparing a graphite anode material for batteries includes the following steps:

[0045] S1. Natural graphite with a D50 of 5-25 μm, a carbon content ≥99.9%, and an ash content ≤0.1% is obtained by flotation to obtain high-purity graphite particles. The graphite particles are then pulverized to the micron level using an air jet mill or mechanical grinding equipment, and spherical or near-spherical particles are formed through inter-particle collisions. The graphite particles are placed in a high-temperature rotary furnace and heated to 700℃ at a rate of 3℃ / min under N2 atmosphere protection, and held at that temperature for 0.5h to fully remove volatiles. Subsequently, the temperature is rapidly increased to 1050℃ at a rate of 15℃ / min and held for 3h. The furnace is then cooled to 800℃, and then rapidly cooled to room temperature by introducing N2. After removal, the particles are mechanically dispersed and sieved to obtain spherical graphite particles with a D50 of 10~20μm.

[0046] S2. The spherical graphite particles are reloaded into the high-temperature rotary furnace and heated to 850°C under N2 protection and stabilized. After the N2 is turned off, a mixed gas of CF4 and NH3 in a volume ratio of 1:2 is introduced and reacted for 30 minutes. After the reaction is completed, pure N2 is switched and the furnace temperature is lowered to 600°C. At 600°C, a mixed gas of H2S and N2 in a volume ratio of 1:19 is introduced and treated for 40 minutes. After treatment, the pipes and furnace body are purged with a large amount of N2 until cooled to room temperature. The graphite particles are then atomically doped with F, N, and S.

[0047] S3. Dissolve 1g of block copolymer F127 in 15mL of anhydrous ethanol and stir magnetically until completely dissolved to obtain solution A. Add 2g of citric acid and 3g of tetrabutyl titanate to 30mL of anhydrous ethanol and stir until clear to obtain solution B. Under vigorous stirring, slowly add solution B dropwise to solution A. After the addition is complete, continue stirring for 5h to form a precursor sol. Mix 100g of gradient-doped graphite particles with the above sol at low speed in a planetary ball mill for 20min to make the sol uniformly adhere to the graphite surface. Transfer the mixed wet material to a spray dryer and spray dry at an inlet temperature of 200℃ to obtain a dry composite powder with uniform precursor coating. Under N2 atmosphere, heat the composite powder with uniform precursor coating to 550℃ at a rate of 6~8℃ / s, hold for 6min, and cool to room temperature to obtain TiO2 porous carbon-coated graphite particles.

[0048] S4. Dissolve 1g of (benzo-15-crown 5-ether)-4'-carboxylic acid in 20mL of N,N-dimethylformamide, add 0.5g of 4-dimethylaminopyridine, and stir until fully dissolved; disperse 100g of TiO2 porous carbon-coated graphite particles in the above solution, heat to 120℃ under nitrogen protection, and reflux with magnetic stirring for 12h; after the reaction is completed, cool to room temperature, and repeatedly centrifuge and wash with anhydrous ethanol and deionized water until the physically adsorbed free crown ether molecules and solvent are completely removed. Dry the washed material in a vacuum oven at 80℃ for 8h to obtain the graphite anode material for the battery.

[0049] Example 3

[0050] A method for preparing a graphite anode material for batteries includes the following steps:

[0051] S1. Natural graphite with a D50 of 5-25 μm, a carbon content ≥99.9%, and an ash content ≤0.1% is obtained by flotation to obtain high-purity graphite particles. The graphite particles are then pulverized to the micron level using an air jet mill or mechanical grinding equipment, and spherical or near-spherical particles are formed through inter-particle collisions. The graphite particles are placed in a high-temperature rotary furnace and heated to 700℃ at a rate of 3℃ / min under N2 atmosphere protection, and held at that temperature for 1 hour to fully remove volatiles. Then, the temperature is rapidly increased to 1050℃ at a rate of 15℃ / min and held for 2.5 hours. The furnace is then cooled to 800℃, and then rapidly cooled to room temperature by introducing N2. After removal, the particles are mechanically dispersed and sieved to obtain spherical graphite particles with a D50 of 10~20 μm.

[0052] S2. The spherical graphite particles are reloaded into the high-temperature rotary furnace and heated to 850°C under N2 protection and stabilized. After the N2 is turned off, a mixed gas of CF4 and NH3 in a volume ratio of 1:2 is introduced and reacted for 40 minutes. After the reaction is completed, pure N2 is switched and the furnace temperature is lowered to 600°C. At 600°C, a mixed gas of H2S and N2 in a volume ratio of 1:19 is introduced and treated for 30 minutes. After treatment, the pipes and furnace body are purged with a large amount of N2 until cooled to room temperature. The graphite particles are then atomically doped with F, N, and S.

[0053] S3. Dissolve 1g of block copolymer F127 in 15mL of anhydrous ethanol and stir magnetically until completely dissolved to obtain solution A. Add 2g of citric acid and 3.5g of tetrabutyl titanate to 30mL of anhydrous ethanol and stir until clear to obtain solution B. Under vigorous stirring, slowly add solution B dropwise to solution A. After the addition is complete, continue stirring for 4h to form a precursor sol. Mix 100g of gradient-doped graphite particles with the above sol at low speed in a planetary ball mill for 30min to make the sol uniformly adhere to the graphite surface. Transfer the mixed wet material to a spray dryer and spray dry at an inlet temperature of 200℃ to obtain a dry composite powder with uniform precursor coating. Under N2 atmosphere, heat the composite powder with uniform precursor coating to 550℃ at a rate of 6~8℃ / s, hold for 5min, and cool to room temperature to obtain TiO2 porous carbon-coated graphite particles.

[0054] S4. Dissolve 1.5g of (benzo-15-crown 5-ether)-4'-carboxylic acid in 20mL of N,N-dimethylformamide, add 0.5g of 4-dimethylaminopyridine, and stir until fully dissolved; disperse 100g of TiO2 porous carbon-coated graphite particles in the above solution, heat to 120℃ under nitrogen protection, and magnetically stir under reflux for 10h; after the reaction is completed, cool to room temperature, and repeatedly centrifuge and wash with anhydrous ethanol and deionized water until the physically adsorbed free crown ether molecules and solvent are completely removed. Dry the washed material in a vacuum oven at 80℃ for 10h to obtain the graphite anode material for the battery.

[0055] Comparative Example 1

[0056] A method for preparing a graphite anode material for batteries includes the following steps:

[0057] S1. Natural graphite with a D50 of 5-25 μm, a carbon content ≥99.9%, and an ash content ≤0.1% is obtained by flotation to obtain high-purity graphite particles. The graphite particles are then pulverized to the micron level using an air jet mill or mechanical grinding equipment, and spherical or near-spherical particles are formed through inter-particle collisions. The graphite particles are placed in a high-temperature rotary furnace and heated to 700℃ at a rate of 3℃ / min under N2 atmosphere protection, and held at that temperature for 1 hour to fully remove volatiles. Then, the temperature is rapidly increased to 1050℃ at a rate of 15℃ / min and held for 2.5 hours. The furnace is then cooled to 800℃, and then rapidly cooled to room temperature by introducing N2. After removal, the particles are mechanically dispersed and sieved to obtain spherical graphite particles with a D50 of 10~20 μm.

[0058] S2. Dissolve 1g of block copolymer F127 in 15mL of anhydrous ethanol and stir magnetically until completely dissolved to obtain solution A. Add 2g of citric acid and 3.5g of tetrabutyl titanate to 30mL of anhydrous ethanol and stir until clear to obtain solution B. Under vigorous stirring, slowly add solution B dropwise to solution A. After the addition is complete, continue stirring for 4h to form a precursor sol. Mix 100g of spherical graphite particles obtained in S1 with the above sol at low speed in a planetary ball mill for 30min to make the sol uniformly adhere to the graphite surface. Transfer the mixed wet material to a spray dryer and spray dry at an inlet temperature of 200℃ to obtain a dry composite powder with uniform precursor coating. Under N2 atmosphere, heat the composite powder with uniform precursor coating to 550℃ at a rate of 6~8℃ / s, hold for 5min, and cool to room temperature to obtain TiO2 porous carbon-coated graphite particles.

[0059] S3. Dissolve 1.5g of (benzo-15-crown 5-ether)-4'-carboxylic acid in 20mL of N,N-dimethylformamide, add 0.5g of 4-dimethylaminopyridine, and stir until fully dissolved; disperse 100g of TiO2 porous carbon-coated graphite particles in the above solution, heat to 120℃ under nitrogen protection, and magnetically stir under reflux for 10h; after the reaction is completed, cool to room temperature, and repeatedly centrifuge and wash with anhydrous ethanol and deionized water until the physically adsorbed free crown ether molecules and solvent are completely removed. Dry the washed material in a vacuum oven at 80℃ for 10h to obtain the graphite anode material for the battery.

[0060] Comparative Example 2

[0061] A method for preparing a graphite anode material for batteries includes the following steps:

[0062] S1. Natural graphite with a D50 of 5-25 μm, a carbon content ≥99.9%, and an ash content ≤0.1% is obtained by flotation to obtain high-purity graphite particles. The graphite particles are then pulverized to the micron level using an air jet mill or mechanical grinding equipment, and spherical or near-spherical particles are formed through inter-particle collisions. The graphite particles are placed in a high-temperature rotary furnace and heated to 700℃ at a rate of 3℃ / min under N2 atmosphere protection, and held at that temperature for 1 hour to fully remove volatiles. Then, the temperature is rapidly increased to 1050℃ at a rate of 15℃ / min and held for 2.5 hours. The furnace is then cooled to 800℃, and then rapidly cooled to room temperature by introducing N2. After removal, the particles are mechanically dispersed and sieved to obtain spherical graphite particles with a D50 of 10~20 μm.

[0063] S2. The spherical graphite particles are reloaded into the high-temperature rotary furnace and heated to 850°C under N2 protection and stabilized. After the N2 is turned off, a mixed gas of CF4 and NH3 in a volume ratio of 1:2 is introduced and reacted for 40 minutes. After the reaction is completed, pure N2 is switched and the furnace temperature is lowered to 600°C. At 600°C, a mixed gas of H2S and N2 in a volume ratio of 1:19 is introduced and treated for 30 minutes. After treatment, the pipes and furnace body are purged with a large amount of N2 until cooled to room temperature. The graphite particles are then atomically doped with F, N, and S.

[0064] S3. Dissolve 1.5g of (benzo-15-crown 5-ether)-4'-carboxylic acid in 20mL of N,N-dimethylformamide, add 0.5g of 4-dimethylaminopyridine, and stir until fully dissolved; disperse 100g of gradient-doped graphite particles in the above solution, heat to 120℃ under nitrogen protection, and reflux with magnetic stirring for 10h; after the reaction is completed, cool to room temperature, and repeatedly centrifuge and wash with anhydrous ethanol and deionized water until the physically adsorbed free crown ether molecules and solvent are completely removed. Dry the washed material in a vacuum oven at 80℃ for 10h to obtain the graphite anode material of the battery.

[0065] Comparative Example 3

[0066] A method for preparing a graphite anode material for batteries includes the following steps:

[0067] S1. Natural graphite with a D50 of 5-25 μm, a carbon content ≥99.9%, and an ash content ≤0.1% is obtained by flotation to obtain high-purity graphite particles. The graphite particles are then pulverized to the micron level using an air jet mill or mechanical grinding equipment, and spherical or near-spherical particles are formed through inter-particle collisions. The graphite particles are placed in a high-temperature rotary furnace and heated to 700℃ at a rate of 3℃ / min under N2 atmosphere protection, and held at that temperature for 1 hour to fully remove volatiles. Then, the temperature is rapidly increased to 1050℃ at a rate of 15℃ / min and held for 2.5 hours. The furnace is then cooled to 800℃, and then rapidly cooled to room temperature by introducing N2. After removal, the particles are mechanically dispersed and sieved to obtain spherical graphite particles with a D50 of 10~20 μm.

[0068] S2. The spherical graphite particles are reloaded into the high-temperature rotary furnace and heated to 850°C under N2 protection and stabilized. After the N2 is turned off, a mixed gas of CF4 and NH3 in a volume ratio of 1:2 is introduced and reacted for 40 minutes. After the reaction is completed, pure N2 is switched and the furnace temperature is lowered to 600°C. At 600°C, a mixed gas of H2S and N2 in a volume ratio of 1:19 is introduced and treated for 30 minutes. After treatment, the pipes and furnace body are purged with a large amount of N2 until cooled to room temperature. The graphite particles are then atomically doped with F, N, and S.

[0069] S3. Dissolve 1g of block copolymer F127 in 15mL of anhydrous ethanol and stir magnetically until completely dissolved to obtain solution A. Add 2g of citric acid and 3.5g of tetrabutyl titanate to 30mL of anhydrous ethanol and stir until clear to obtain solution B. Under vigorous stirring, slowly add solution B dropwise to solution A. After the addition is complete, continue stirring for 4h to form a precursor sol. Mix 100g of gradient-doped graphite particles with the above sol at low speed in a planetary ball mill for 30min to make the sol uniformly adhere to the graphite surface. Transfer the mixed wet material to a spray dryer and spray dry at an inlet temperature of 200℃ to obtain a dry composite powder uniformly coated with the precursor. Under N2 atmosphere, heat the composite powder uniformly coated with the precursor to 550℃ at a rate of 6~8℃ / s, hold for 5min, and cool to room temperature to obtain the graphite anode material of the battery.

[0070] Performance testing

[0071] I. Electrochemical Performance Testing

[0072] Weigh out 80 mg of the graphite anode material samples prepared in Example 3 and Comparative Examples 1-3, 10 mg of acetylene black (conductive agent), and 10 mg of PVDF, respectively. Add N-methylpyrrolidone to make a paste, and coat it evenly on a 12 μm copper foil (coating area 1.13 cm²). 2 After vacuum drying at 60℃ for 12 hours, the product was compressed into tablets using a tablet press at a pressure of 10 MPa, with the active substance loading controlled at 1.0-1.2 mg / cm³. 2 The negative electrode was obtained. A CR2032 button half-cell was assembled in an argon glove box (H2O, O2 < 0.1ppm), using a lithium metal sheet as the positive electrode, Celgard 2400 as the separator, a 1 mol / L LiPF6 solution as the electrolyte, and EC, DMC, and EMC mixed in a 1:1:1 volume ratio as the solvent. The following performance tests were then performed:

[0073] (1) Initial charge and discharge capacity and coulombic efficiency, 0.1C rate (1C=372mA / g), voltage range 0.01-2.0V, record the initial charge capacity (lithium insertion capacity) and discharge capacity (lithium removal capacity), and calculate the coulombic efficiency (discharge capacity / charge capacity×100%).

[0074] (2) Cyclic performance test: Charge and discharge cycle test is performed at 1C rate in the voltage range of 0.01-2.0V. The discharge capacity of each cycle is recorded, and the capacity retention rate (nth discharge capacity / first discharge capacity × 100%) is calculated for different number of cycles (100 times, 1000 times).

[0075] (3) Rate performance test: The button batteries assembled above were used to conduct charge and discharge tests at 0.2C, 0.5C, 1C, 2C and 5C rates respectively. Each rate was cycled 5 times, and the discharge capacity at different rates was recorded. The ratio of the 5C rate capacity to the 0.2C rate capacity (5C capacity retention rate) was calculated.

[0076] II. Physical Performance Testing

[0077] (1) Volume expansion rate: A button half-cell was used in the electrochemical performance test. After 100 cycles, the cell was disassembled, the electrode plates were removed, cleaned with anhydrous ethanol, and then vacuum dried. The volume (Archimedes method) and thickness (SEM observation) of the electrode plates before and after cycling were measured respectively. The calculation method was: Volume expansion rate = (volume after cycling - volume before cycling) / volume before cycling × 100%;

[0078] (2) Electronic conductivity: Graphite powder was pressed into a disc with a diameter of 10 mm and a thickness of 1-2 mm (pressure 10 MPa). The conductivity was measured using the four-probe method. Test conditions: At room temperature, a current of 10 mA was applied, the voltage value was recorded, and the conductivity was calculated.

[0079] (3) The alternating impedance method (EIS) was used, with a test frequency range of 10. 5 -10 -2 The charge transfer resistance (Rct) of the SEI film was obtained by fitting the impedance spectrum using ZsimpWin software at a frequency of Hz and an amplitude of 5mV.

[0080] The obtained data is shown in Table 1 below:

[0081] Table 1 Performance test results of graphite anode materials for lithium-ion batteries

[0082] Performance indicators Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Initial discharge capacity (0.1C, mAh / g) 368 342 355 365 First-time Coulomb efficiency (%) 91.5 87.2 89.3 88.6 Capacity retention rate after 100 cycles (%) 96.2 88.5 82.3 92.1 Capacity retention rate after 1000 cycles (%) 86.8 72.3 58.6 81.5 5C high-rate capacity retention (%) 83.5 62.1 55.7 76.3 Volume expansion rate (%) 2.5 6.8 9.7 3.2 Electron conductivity (S / m) <![CDATA[1.4×10 4 ]]> <![CDATA[0.9×10 4 ]]> <![CDATA[1.1×10 4 ]]> <![CDATA[1.3×10 4 ]]> SEI film impedance (Ω) 256 685 523 412

[0083] As can be seen from the data in Table 1, compared with Example 3, the initial discharge capacity and initial coulombic efficiency of Comparative Example 1 both decreased. This is because the lack of additional lithium storage sites introduced by N and S doping, coupled with the absence of F doping to stabilize the interface, led to an increase in side reactions. The capacity retention rate after 1000 cycles was also lower, mainly because the absence of S doping to widen the interlayer spacing resulted in increased volume expansion, causing repeated rupture of the SEI film. The 5C capacity retention rate decreased significantly due to the lack of N doping to improve conductivity, which hindered electron transport. The SEI film impedance increased significantly because F doping effectively stabilized the SEI film structure.

[0084] Comparative Example 2 showed the most significant decrease in cycling stability, with a capacity retention of only 58.6% after 1000 cycles. This was mainly due to the lack of TiO2 protection, resulting in a high volume expansion rate of 9.7% and causing electrode structure damage. The 5C capacity retention was also the worst, due to the lack of a porous carbon layer providing fast ion / electron transport channels. + Diffusion is hindered, and the porous carbon coating of TiO2 is a key step in suppressing volume expansion and improving cycle life. Its absence has the greatest impact on the long-term stability of the material.

[0085] The initial coulombic efficiency of Comparative Example 3 decreased by 2.9%, mainly due to the lack of crown ethers for Li. + The selective transport effect increases the intercalation of impurity ions; the SEI membrane impedance increases by 60.9%, indicating that crown ether modification can effectively reduce interfacial impedance and improve electrolyte wettability; the capacity retention rate decreases by 5.3% after 1000 cycles and the 5C capacity retention rate decreases by 7.2%, which is less than the first two comparative groups, but still significantly affects the interfacial performance.

[0086] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0087] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing a battery graphite negative electrode material, characterized by, The method comprises the following steps: S1, placing natural graphite in a high-temperature rotary furnace, first heating to 700 DEG C under N2 atmosphere protection, treating for 0.5-1.5 h, then rapidly heating to 1050 DEG C, treating for 2-3 h, cooling and crushing to obtain spherical graphite particles; S2, placing the treated spherical graphite particles into a high-temperature rotary furnace, heating to 800-900 DEG C, introducing CF4 and NH3, reacting for 30-50 min, then switching to pure N2, reducing the furnace temperature to 600 DEG C, forming a gradient doping structure with F-rich inner layer and N-rich outer layer, then introducing H2S and N2 at 600 DEG C, treating for 20-40 min to complete S doping; S3, mixing block copolymer F127, citric acid and tetrabutyl titanate to prepare a precursor sol, then mixing the precursor sol with the atom-doped graphite particles, and forming a TiO2 porous carbon coating layer through spray drying and carbonization; S4, grafting (benzo-15-crown-5-ether)-4'-carboxylic acid on the surface of the coated graphite particles, and forming covalent bonds through esterification reaction between (benzo-15-crown-5-ether)-4'-carboxylic acid and the abundant oxygen-containing functional groups on the surface of the composite material.

2. The method of claim 1, wherein the battery graphite negative electrode material is prepared by the steps of: The step S1 specifically comprises: ​ S101, using high-purity graphite particles obtained after flotation of natural graphite, crushing the graphite particles to micron level by using an air flow mill or a mechanical grinding device, and forming spherical or spherical-like particles through particle collision; S102, placing the graphite particles in a high-temperature rotary furnace, heating to 700 DEG C at a rate of 3 DEG C / min under N2 atmosphere protection, and treating for 0.5-1.5 h to remove volatile components, then rapidly heating to 1050 DEG C at a rate of 15 DEG C / min, and treating for 2-3 h; S103, cooling in the furnace to 800 DEG C, then rapidly cooling to room temperature by introducing N2, taking out, mechanically dispersing and sieving to obtain spherical graphite particles with D50 of 10-20 μm.

3. The method of claim 2, wherein the battery graphite negative electrode material is prepared by the steps of: mixing the natural graphite and the artificial graphite to obtain a mixture; and mixing the mixture with the binder to obtain the battery graphite negative electrode material. The natural graphite raw material in the step S101 has a D50 particle size of 5-25 um, a carbon content of ≥99.9%, and an ash content of ≤0.1%.

4. The method of claim 1, wherein the battery graphite negative electrode material is prepared by the steps of: The step S2 specifically comprises: ​ S201, re-feeding the spherical graphite particles into a high-temperature rotary furnace, heating to 850 DEG C under N2 protection, introducing a mixed gas of CF4 and NH3 after closing N2, reacting for 30-50 min, switching to pure N2 after the reaction, and reducing the furnace temperature to 600 DEG C; S202, introducing a mixed gas of H2S and N2 at 600 DEG C, treating for 20-40 min, and purging the pipeline and furnace body with a large amount of N2 until cooling to room temperature, to obtain F, N and S atom gradient-doped graphite particles.

5. The method of claim 4, wherein the battery graphite negative electrode material is prepared by the steps of: mixing the graphite powder with the binder to form a mixture; and mixing the mixture with the conductive agent to form the battery graphite negative electrode material. The volume ratio of CF4 to NH3 in the step S201 is 1:

2.

6. The method of claim 4, wherein the battery graphite negative electrode material is prepared by the steps of: mixing the graphite powder with the binder to form a mixture; and mixing the mixture with the conductive agent to form the battery graphite negative electrode material. The volume ratio of H2S to N2 in the step S202 is 1:

19.

7. The method of claim 1, wherein the battery graphite negative electrode material is prepared by the steps of: mixing a graphite powder with a binder and a solvent to form a mixture; and drying the mixture to form the battery graphite negative electrode material. The step S3 specifically comprises: S301, dissolve the block copolymer F127 in anhydrous ethanol, magnetically stir until completely dissolved to obtain solution A, add citric acid and tetrabutyl titanate to anhydrous ethanol, stir until clear to obtain solution B, slowly drop solution B into solution A under vigorous stirring, continue stirring for 3-5h after dropping is completed, form a precursor sol; S302, mix the gradient doped graphite particles with the above sol in a planetary ball mill at low speed for 30min, so that the sol is uniformly attached to the surface of the graphite, transfer the mixed wet material to a spray dryer, and spray dry at an inlet temperature of 200℃ to obtain a dry, precursor uniformly coated composite powder; S303, under N2 atmosphere, heat the precursor uniformly coated composite powder to 550℃ at a rate of 6-8℃ / s, keep for 4-6min, cool to room temperature, obtain TiO2 porous carbon coated graphite particles.

8. The method of claim 7, wherein the battery graphite negative electrode material is prepared by the steps of: mixing the graphite powder with the binder to form a mixture; and mixing the mixture with the conductive agent to form the battery graphite negative electrode material. The mass ratio of the block copolymer F127, citric acid, tetrabutyl titanate and atomically doped graphite particles is 1:2:3-4:

100.

9. The method of claim 1, wherein the battery graphite negative electrode material is prepared by the steps of: The step S4 specifically comprises: ​ S401, dissolve (benzo-15-crown-5-ether)-4'-carboxylic acid in N,N-dimethylformamide, add a small amount of 4-dimethylaminopyridine, stir until completely dissolved; S402, disperse the TiO2 porous carbon coated graphite particles in the above solution, heat to 120℃ under nitrogen protection, magnetically stir reflux reaction for 8-12h; S403, after the reaction is completed, cool to room temperature, use anhydrous ethanol and deionized water to repeatedly centrifugal wash for several times until the physically adsorbed free crown ether molecules and solvents are completely removed, dry the washed material in a vacuum oven at 80℃ for 8-12h to obtain the battery graphite negative electrode material.

10. The method of claim 9, wherein the battery graphite negative electrode material is prepared by the steps of: The mass ratio of the (benzo-15-crown-5-ether)-4'-carboxylic acid, 4-dimethylaminopyridine and TiO2 porous carbon coated graphite particles is 1-2:0.5:

100. ​