Preparation method of high-rate graphene negative electrode material

Abstract

The invention discloses a preparation method of a high-rate graphene negative electrode material, and belongs to the technical field of battery processing. In order to solve the technical problem that the rate capability and the cycling stability of the graphene negative electrode material in the prior art need to be further improved, the preparation method of the high-rate graphene negative electrode material comprises the following steps: putting modified graphene, a modified binder and a conductive agent into a reaction kettle, and stirring for 0.5-1 hour to obtain negative electrode slurry. According to the invention, the modified graphene, the modified binder and the modified conductive agent are uniformly mixed, the aluminum foil is coated with the mixture, and the mixture is scraped by a scraper and dried to obtain the graphene negative electrode material, so that the rate capability and the cycling stability of the graphene negative electrode material are improved, and the charging specific capacity of the graphene negative electrode material is also improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery processing, and in particular to a method for preparing a high-rate graphene negative electrode material. Background Art

[0002] In recent years, graphene, a two-dimensional nanomaterial composed of a single layer of carbon atoms arranged in a honeycomb lattice, has become a global research hotspot in materials science due to its excellent electrical, mechanical, and thermal properties. Its high conductivity, large specific surface area, and excellent mechanical properties make it a key material for improving energy storage and conversion efficiency. In the field of lithium-ion batteries, graphene is used as a negative electrode material or conductive additive. Its two-dimensional sheet structure can effectively shorten the lithium ion diffusion path, and its highly conductive network can significantly increase the electron transport rate of the electrode, thereby improving the battery's rate performance and cycle stability. However, when graphene negative electrode materials are used in the preparation of lithium batteries, they often suffer from insufficient specific capacity.

[0003] In the prior art, graphene negative electrode materials contain a large number of oxygen-containing groups. During the charge and discharge process, these oxygen-containing groups will decompose or undergo irreversible side reactions with lithium ions, filling the lithium storage holes in the carbon material structure, causing the reversible capacity to decay, which greatly affects the rate performance and specific capacity of the lithium battery. In order to improve the lithium storage performance of lithium batteries, conventional modification methods such as carbon coating, metal oxide composite, surface oxidation and element doping are used. Among them, the addition of silicon to the graphene negative electrode material can improve the lithium storage capacity of the material, but silicon alloys with lithium during the charge and discharge process, and the volume expands, resulting in instability and pulverization of the electrode structure, and even detachment from the current collector, which reduces the battery cycle performance. In addition, the interface interaction between silicon and graphene is weak, and it is difficult to form a stable interface structure, which affects the transmission efficiency of lithium ions and electrons, and thus affects the overall electrochemical performance of the battery.

[0004] In view of the technical defects in this aspect, a solution is now proposed. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing a high-rate graphene negative electrode material, which is used to solve the technical problem in the prior art that the rate performance and cycle stability of graphene negative electrode materials need to be further improved.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing a high-rate graphene negative electrode material comprises the following steps: S1. Place 1,2-bis(2-aminoethoxy)ethane and N,N-dimethylformamide in a reactor under a nitrogen atmosphere, heat to 25-30°C, slowly add thiocarbonyldiimidazole, keep the mixture warm for 18-20 hours, and post-treat to obtain a modified binder precursor; The preparation reaction formula of the modified binder precursor is: The preparation reaction principle of the modified binder precursor is: During the reaction, the thiocarbonyl group in thiocarbonyldiimidazole undergoes a nucleophilic substitution reaction with the amino group in 1,2-bis(2-aminoethoxy)ethane to generate a thiocarbonyl derivative. The generated thiocarbonyl derivative molecule contains a thiocarbonyl group and an amino group, which can further react with the amino group or thiocarbonyl group of another molecule to undergo intermolecular cross-linking to form a polythiourea structure, thereby obtaining a modified binder precursor.

[0007] S2. Place the modified binder precursor and N-methylpyrrolidone in a reaction kettle, stir for 15-20 minutes, add polyacrylic acid and deionized water, heat to 75-85° C., keep the temperature for reaction for 10-12 hours, and post-treat to obtain the modified binder; The preparation reaction formula of the modified binder is: The preparation reaction principle of the modified binder is: During the reaction, the carboxylic acid groups on the polyacrylic acid molecular chain undergo condensation reaction with the amino groups in the modified binder precursor to form amide bonds, thereby obtaining the modified binder.

[0008] S3, placing the modified graphene, modified binder and modified conductive agent in a reactor and stirring for 0.5-1h to obtain a negative electrode slurry; S4. Coat the negative electrode slurry on aluminum foil, flatten it with a scraper, and dry it to obtain a graphene negative electrode material.

[0009] Furthermore, in step S1, the amount ratio of the 1,2-bis(2-aminoethoxy)ethane, N,N-dimethylformamide and thiocarbonyldiimidazole is 2-4g:20-40mL:3-5g, and the post-treatment step comprises: after the reaction is completed, the reaction solution is cooled to room temperature, the reaction solution is added to 80-100mL of ethyl acetate, filtered, the filter cake is washed with ethanol 1-2 times, transferred to an oven at a temperature of 60-70°C, and dried to constant weight to obtain a modified binder precursor; in step S2, the modified binder precursor, N-methylpyrrole The amount ratio of alkanone, polyacrylic acid and deionized water is 2-4g:40-60mL:4-6g:50-60mL. The post-processing step includes: after the reaction is completed, the reaction liquid is cooled to room temperature, transferred to an oven at a temperature of 90-100°C, and dried to constant weight to obtain a modified binder; in step S3, the mass ratio of the modified graphene, modified binder and modified conductive agent is 80-100:2-3:2-3; in step S4, the coating thickness is 5-10μm, the drying temperature is 100°C, and the drying time is 6-8h.

[0010] Furthermore, in step S3, the modified graphene is prepared by the following steps: A1. Graphene oxide, amino-modified nano-silicon and deionized water are placed in a reactor, ultrasonically dispersed for 15-30 minutes, and a hot melamine solution is added. The mixture is cooled to room temperature and stirred for 18-20 hours. The modified graphene precursor is obtained by post-treatment. A2. Place the modified graphene precursor in a tube furnace, raise the temperature to 700-800°C, and keep the temperature for reaction for 2-3 hours to obtain modified graphene.

[0011] The preparation reaction principle of modified graphene is: During the reaction, graphene oxide is partially deprotonated in water and its surface is negatively charged. Melamine molecules contain multiple amino groups and can be protonated with amino-modified nano-silicon in water to be positively charged. Through electrostatic attraction, the positively charged melamine molecules and amino-modified nano-silicon are adsorbed onto the negatively charged surface of graphene oxide to form a complex of melamine and amino-modified nano-silicon uniformly distributed in the graphene oxide. After heating to 700-800°C, the graphene oxide is deoxidized at high temperature and reduced to graphene. Melamine is thermally decomposed to generate nitrogen-doped carbon. The amino-modified nano-silicon is converted into silicon nanoparticles after high-temperature treatment and is encapsulated by the graphene layer. The carbon layer wraps the silicon particles to form a core-shell structure, thereby obtaining modified graphene having, from the inside to the outside, a silicon core, a nitrogen-doped carbon layer and a graphene shell.

[0012] Furthermore, in step A1, the amount ratio of the graphene oxide, amino-modified nano-silicon, deionized water and melamine hot solution is 2-4g:4-8g:200-300mL:250-300mL, and the melamine hot solution is composed of melamine and 90-100°C deionized water in a ratio of 3g:250mL. The post-treatment step includes: after the reaction is completed, the reaction liquid is cooled to room temperature, filtered, and the filter cake is washed with deionized water 2-3 times, transferred to an oven at a temperature of 60-80°C, and dried to constant weight to obtain a modified graphene precursor; in step A2, the heating rate is 5-10°C / min.

[0013] Furthermore, the preparation method of the amino-modified nano-silicon is as follows: nano-silicon particles, deionized water, ethanol and γ-aminopropyltriethoxysilane are placed in a reaction kettle, heated to 50-60° C., kept warm for 2-4 hours, and post-treated to obtain amino-modified nano-silicon.

[0014] The preparation reaction principle of amino-modified nano-silicon is: During the reaction, γ-aminopropyltriethoxysilane is hydrolyzed under high temperature conditions to generate silanol, which then undergoes a condensation reaction with the silanols on the surface of the nano-silicon particles to obtain amino-modified nano-silicon.

[0015] Furthermore, the amount ratio of the nano-silicon particles, deionized water, ethanol and γ-aminopropyltriethoxysilane is 2-4g:5-8mL:20-30mL:0.5-1g, and the post-treatment step includes: after the reaction is completed, the reaction liquid is cooled to room temperature, filtered, the filter cake is washed 1-2 times with deionized water and ethanol, transferred to an oven at a temperature of 50-60°C, and dried to constant weight to obtain amino-modified nano-silicon.

[0016] Furthermore, in step S3, the modified conductive agent is prepared by the following steps: B1. Place carbon nanotubes and sodium citrate trihydrate in a planetary ball mill, ball mill for 1-2 hours, calcinate, and post-treat to obtain modified carbon nanotubes; The preparation reaction principle of modified carbon nanotubes is: During the reaction, sodium citrate trihydrate is calcined under argon protection, first losing its crystal water and decomposing into sodium carbonate and carbon. The generated carbon atoms are deposited on the surface of the carbon nanotubes to form a carbon-coated structure. Mechanical grinding is used to evenly mix the sodium citrate and the carbon nanotubes, promoting the attachment of the carbon source to the surface of the carbon nanotubes to obtain modified carbon nanotubes.

[0017] B2. Place the modified carbon nanotubes, deionized water and sodium dodecyl sulfate in a reaction kettle, stir for 15-20 minutes, add the paper fiber mixture, stir for 0.5-1 hour, and post-treat to obtain a modified conductive agent.

[0018] The preparation reaction principle of the modified conductive agent is: During the reaction, sodium dodecyl sulfate acts as an anionic surfactant, with its hydrophobic end adsorbed on the surface of the modified carbon nanotube particles and the hydrophilic end facing the water phase, forming a double layer or steric hindrance layer to prevent the particles from re-aggregating, thereby stabilizing the dispersed system. After being evenly mixed with the paper fiber mixture, a wet film is formed under the suction filtration operation in the post-processing step, and the modified conductive agent is obtained after drying.

[0019] Furthermore, in step B1, the carbon nanotubes and sodium citrate trihydrate are used in an amount ratio of 1-2g:10-12g, the ball milling medium is composed of zirconium oxide with a diameter of 8-10mm, the ball milling ratio is 1:30-32, and the post-treatment step includes: after the reaction is completed, the reaction solution is cooled to room temperature, filtered, and the filter cake is washed 2-3 times with a 15-20wt% hydrochloric acid aqueous solution and deionized water, transferred to an oven at a temperature of 60-80°C, and dried to constant weight to obtain modified carbon. Nanotubes; in step B2, the amount ratio of the modified carbon nanotubes, deionized water, sodium dodecyl sulfate and paper fiber mixture is 1-2g:20-25mL:0.1-0.2g:1000-1200mL, the paper fiber mixture is composed of paper fiber and deionized water according to the amount ratio of 0.5g:1000mL, and the post-treatment step includes: after the reaction is completed, filtering, transferring the filter cake to an oven at a temperature of 60-80°C, and drying to constant weight to obtain a modified conductive agent.

[0020] The present invention has the following beneficial effects: 1. The present invention modifies nano-silicon particles with a silane coupling agent to obtain amino-modified nano-silicon, further prepares modified graphene consisting of a silicon core, a nitrogen-doped carbon layer, and a graphene shell from the inside out by electrostatic self-assembly and high-temperature calcination, mixes carbon nanotubes with paper fibers, and obtains a modified conductive agent by suction filtration, obtains a modified binder having a polysulfonylurea structure by nucleophilic reaction and amidation reaction, uniformly mixes the modified graphene, the modified binder, and the modified conductive agent, coats the mixture on aluminum foil, flattens the mixture with a scraper, and dries the mixture to obtain a graphene negative electrode material; the present invention modifies carbon nanotubes by , further mixed with paper fibers, and filtered to prepare a modified conductive agent. The carbon nanotubes and graphene in the modified conductive agent form a three-dimensional interpenetrating conductive network, shortening the lithium ion diffusion path, reducing the charge transfer impedance, and constructing a multi-dimensional electron transmission channel, thereby improving the conductive efficiency of the negative electrode material and further improving the conductivity and rate performance of the lithium battery. The paper fibers in the modified conductive agent serve as a base to provide mechanical support, enhance the flexibility and deformation resistance of the negative electrode, and the high flexibility of carbon nanotubes and graphene can withstand the volume change of silicon during the charge and discharge process, prevent the active material from falling off, and improve the cycle stability of the lithium battery.

[0021] 2. The present invention modifies nano-silicon particles with a silane coupling agent to obtain amino-modified nano-silicon, further combines negatively charged graphene oxide with positively charged amino-modified nano-silicon and melamine through electrostatic self-assembly, and deoxidizes the graphene oxide at high temperature and reduces it to graphene by high-temperature calcination. Melamine is pyrolyzed to generate nitrogen-doped carbon. The amino-modified nano-silicon is converted into silicon nanoparticles after high-temperature treatment, and the silicon particles are encapsulated by the graphene layer and the carbon layer wraps the silicon particles to form a core-shell structure, thereby obtaining modified graphene with a silicon core, a nitrogen-doped carbon layer and a graphene shell from the inside out. The silicon nanoparticles are prone to volume expansion during the charge and discharge process. The graphene shell and the nitrogen-doped carbon layer form a double elastic buffer layer. The flexibility of graphene can withstand mechanical stress. The nitrogen-doped carbon layer disperses stress through the pore structure, reducing the pulverization of silicon particles and the collapse of the electrode structure, improving the structural stability of the negative electrode material in use, and improving the cycle stability of the lithium battery. The high conductivity of graphene and the p-type doping effect of nitrogen-doped carbon work together to form a conductive path throughout the electrode, reducing the internal resistance of the negative electrode material, and improving the conductivity and rate performance of the lithium battery. In addition, the theoretical specific capacity of silicon is relatively high, which improves the lithium storage performance of the graphene negative electrode material and further improves the specific capacity of the lithium battery.

[0022] 3. The present invention prepares a modified binder with a polythiourea structure through nucleophilic reaction and amidation reaction. The cis and trans structures of the thiourea group in the modified binder precursor provide two hydrogen bonding modes, forming a multidimensional hydrogen bonding network with the modified graphene and the modified conductive agent. When the negative electrode produces microcracks due to volume expansion, the dynamic hydrogen bonds of the thiourea groups in the modified binder can be reformed to automatically repair the cracks, maintain the mechanical integrity of the negative electrode, enhance the mechanical properties and self-healing ability of the negative electrode material, and improve the cycle stability of the lithium battery. The ether oxygen bonds in the modified binder can serve as channels for lithium ion transmission, thereby improving the ion transmission performance of the negative electrode material, and can effectively improve the ion transmission efficiency in the electrode network structure, thereby improving the rate performance and conductivity of the lithium battery. DETAILED DESCRIPTION

[0023] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] The nano-silicon particles used in the present invention were purchased from Hebei Ruihuang Metal Materials Co., Ltd., with a particle size of 80,000 mesh and a brand name of 3939A. The polyacrylic acid used in the present invention was purchased from Shandong Xinghai Chemical Co., Ltd., with a liquid appearance, a molecular weight of 72.06n, and a brand of Xinghai Chemical. The graphene oxide used in the present invention is purchased from Lingshou County Bohan Mineral Products Co., Ltd., with a particle size of 2000 mesh and the product name is expanded graphite; The carbon nanotubes used in the present invention are purchased from Shanghai Lishuo Composite Materials Technology Co., Ltd., with a particle size of 40-200 mesh, and the product name is carbon fiber powder; The paper fiber used in the present invention was purchased from Zhejiang Zhenghe Silicon Materials Co., Ltd., with a brand number of 207-35; The aluminum foil used in the present invention is purchased from Shanghai Xingnuo Industrial Co., Ltd., the material is 8079, and the viscosity is non-glue.

[0025] Example 1 This embodiment provides a method for preparing a high-rate graphene negative electrode material, comprising the following steps: S1. Preparation of modified graphene Weigh 20 g of nanosilicon particles, 50 mL of deionized water, 200 mL of ethanol, and 5 g of γ-aminopropyltriethoxysilane into a reactor, heat to 50°C, and keep warm for 2 h. After the reaction is complete, cool the reaction solution to room temperature and filter it. Wash the filter cake once with deionized water and ethanol, transfer it to an oven at 50°C, and dry it to constant weight to obtain amino-modified nanosilicon. Weigh: 20 g of graphene oxide, 40 g of amino-modified nanosilicon and 2000 mL of deionized water into a reactor, ultrasonically disperse for 15 min, add 2500 mL of hot melamine solution, cool to room temperature, and stir for 18 h. After the reaction is completed, cool the reaction solution to room temperature, filter, wash the filter cake twice with deionized water, transfer to an oven at 60°C, and dry to constant weight to obtain a modified graphene precursor; The modified graphene precursor was weighed and placed in a tube furnace, heated to 700° C. at a heating rate of 5° C. / min, and kept at this temperature for 2 h to obtain modified graphene.

[0026] S2. Preparation of modified conductive agent Weigh: 10 g of carbon nanotubes and 100 g of sodium citrate trihydrate were placed in a planetary ball mill and ball-milled for 1 h. The mixture was calcined. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The filter cake was washed twice with a 15 wt% hydrochloric acid solution and deionized water, and then transferred to an oven at 60°C and dried to constant weight to obtain modified carbon nanotubes. Weigh: 10 g of modified carbon nanotubes, 200 mL of deionized water and 1 g of sodium dodecyl sulfate, place them in a reactor, stir for 15 minutes, add 10,000 mL of the paper fiber mixture, stir for 0.5 hours, and after the reaction is completed, filter and transfer the filter cake to an oven at 60°C and dry to constant weight to obtain a modified conductive agent.

[0027] S3. Preparation of modified binder Weigh: 20 g of 1,2-bis(2-aminoethoxy)ethane and 200 mL of N,N-dimethylformamide are placed in a reactor under a nitrogen atmosphere, the temperature is raised to 25°C, 30 g of thiocarbonyldiimidazole is slowly added, and the reaction is kept warm for 18 hours. After the reaction is completed, the reaction solution is cooled to room temperature, and the reaction solution is added to 800 mL of ethyl acetate and filtered. The filter cake is washed once with ethanol, transferred to an oven at a temperature of 60°C, and dried to constant weight to obtain a modified binder precursor; Weigh: 20 g of modified binder precursor and 400 mL of N-methylpyrrolidone are placed in a reactor, stirred for 15 minutes, 40 g of polyacrylic acid and 500 mL of deionized water are added, the temperature is raised to 75°C, and the reaction is kept warm for 10 hours. After the reaction is completed, the reaction liquid is cooled to room temperature, transferred to an oven at a temperature of 90°C, and dried to constant weight to obtain a modified binder.

[0028] S4. Preparation of graphene negative electrode material The modified graphene, modified binder and modified conductive agent were placed in a reactor at a mass ratio of 80:2:2 and stirred for 0.5 h to obtain a negative electrode slurry; The negative electrode slurry was coated on aluminum foil and flattened with a scraper to a coating thickness of 5 μm. The foil was dried at 100 °C for 6 h to obtain a graphene negative electrode material.

[0029] Example 2 This embodiment provides a method for preparing a high-rate graphene negative electrode material, comprising the following steps: S1. Preparation of modified graphene Weigh: 30 g of nanosilicon particles, 65 mL of deionized water, 250 mL of ethanol, and 7 g of γ-aminopropyltriethoxysilane into a reactor, heat to 55°C, and keep warm for 3 hours. After the reaction is complete, cool the reaction solution to room temperature and filter it. Wash the filter cake twice with deionized water and ethanol, transfer it to an oven at 55°C, and dry it to constant weight to obtain amino-modified nanosilicon. Weigh: 30 g of graphene oxide, 60 g of amino-modified nanosilicon and 2500 mL of deionized water into a reactor, ultrasonically disperse for 20 min, add 2700 mL of hot melamine solution, cool to room temperature, and stir for 19 h. After the reaction is completed, cool the reaction solution to room temperature, filter, wash the filter cake twice with deionized water, transfer to an oven at 70°C, and dry to constant weight to obtain a modified graphene precursor; The modified graphene precursor was weighed and placed in a tube furnace, heated to 750° C. at a heating rate of 7° C. / min, and kept at this temperature for 2.5 h to obtain the modified graphene.

[0030] S2. Preparation of modified conductive agent Weigh: 15 g of carbon nanotubes and 110 g of sodium citrate trihydrate were placed in a planetary ball mill and ball-milled for 1.5 h. The mixture was calcined. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The filter cake was washed twice with a 17 wt % hydrochloric acid solution and deionized water, and then transferred to an oven at 70°C and dried to constant weight to obtain modified carbon nanotubes. Weigh: 15 g of modified carbon nanotubes, 220 mL of deionized water and 1.5 g of sodium dodecyl sulfate, place them in a reactor, stir for 17 minutes, add 11000 mL of paper fiber mixture, stir for 1 hour, after the reaction is completed, filter, transfer the filter cake to an oven at 70 ° C, and dry to constant weight to obtain a modified conductive agent.

[0031] S3. Preparation of modified binder Weigh: 30 g of 1,2-bis(2-aminoethoxy)ethane and 300 mL of N,N-dimethylformamide were placed in a reactor under a nitrogen atmosphere, heated to 25°C, and 40 g of thiocarbonyldiimidazole was slowly added. The mixture was kept warm for 19 hours. After the reaction was completed, the reaction solution was cooled to room temperature and added to 900 mL of ethyl acetate. The mixture was filtered and the filter cake was washed twice with ethanol. The mixture was transferred to an oven at 65°C and dried to a constant weight to obtain a modified binder precursor. Weigh: 30 g of modified binder precursor and 500 mL of N-methylpyrrolidone are placed in a reactor, stirred for 17 minutes, 50 g of polyacrylic acid and 550 mL of deionized water are added, the temperature is raised to 80°C, and the reaction is kept warm for 11 hours. After the reaction is completed, the reaction liquid is cooled to room temperature, transferred to an oven at a temperature of 95°C, and dried to constant weight to obtain a modified binder.

[0032] S4. Preparation of graphene negative electrode material The modified graphene, modified binder, and modified conductive agent were placed in a reactor at a mass ratio of 90:2.5:2.5, and stirred for 0.5 h to obtain a negative electrode slurry; The negative electrode slurry was coated on aluminum foil and smoothed with a scraper to a coating thickness of 7 μm. The foil was dried at 100° C. for 7 h to obtain a graphene negative electrode material.

[0033] Example 3 This embodiment provides a method for preparing a high-rate graphene negative electrode material, comprising the following steps: S1. Preparation of modified graphene Weigh: 40 g of nanosilicon particles, 80 mL of deionized water, 300 mL of ethanol, and 10 g of γ-aminopropyltriethoxysilane are placed in a reactor, heated to 60°C, and kept warm for 4 hours. After the reaction is completed, the reaction solution is cooled to room temperature and filtered. The filter cake is washed twice with deionized water and ethanol, transferred to an oven at 60°C, and dried to constant weight to obtain amino-modified nanosilicon; Weigh: 40 g of graphene oxide, 80 g of amino-modified nanosilicon and 3000 mL of deionized water into a reactor, ultrasonically disperse for 30 min, add 3000 mL of hot melamine solution, cool to room temperature, and stir for 20 h. After the reaction is completed, cool the reaction solution to room temperature, filter, wash the filter cake with deionized water three times, transfer to an oven at 80°C, and dry to constant weight to obtain a modified graphene precursor; The modified graphene precursor was weighed and placed in a tube furnace, heated to 800° C. at a heating rate of 10° C. / min, and kept at this temperature for 3 h to obtain modified graphene.

[0034] S2. Preparation of modified conductive agent Weigh 20 g of carbon nanotubes and 120 g of sodium citrate trihydrate and place them in a planetary ball mill. Mill for 2 h and calcine. After the reaction is complete, cool the reaction solution to room temperature and filter it. Wash the filter cake three times with a 20 wt% hydrochloric acid solution and deionized water, transfer it to an oven at 80°C, and dry it to constant weight to obtain modified carbon nanotubes. Weigh: 20 g of modified carbon nanotubes, 250 mL of deionized water and 2 g of sodium dodecylsulfonate, place them in a reactor, stir for 20 minutes, add 12000 mL of paper fiber mixture, stir for 1 hour. After the reaction is completed, filter, transfer the filter cake to an oven at 80°C, and dry to constant weight to obtain a modified conductive agent.

[0035] S3. Preparation of modified binder Weigh: 40 g of 1,2-bis(2-aminoethoxy)ethane and 400 mL of N,N-dimethylformamide were placed in a reactor under a nitrogen atmosphere, heated to 30°C, and 50 g of thiocarbonyldiimidazole was slowly added. The mixture was kept warm for 20 hours. After the reaction was completed, the reaction solution was cooled to room temperature and added to 1000 mL of ethyl acetate. The mixture was filtered and the filter cake was washed twice with ethanol. The mixture was transferred to an oven at 70°C and dried to constant weight to obtain a modified binder precursor. Weigh: 40 g of modified binder precursor and 600 mL of N-methylpyrrolidone are placed in a reactor, stirred for 20 min, 60 g of polyacrylic acid and 600 mL of deionized water are added, the temperature is raised to 85°C, and the reaction is kept warm for 12 h. After the reaction is completed, the reaction liquid is cooled to room temperature, transferred to an oven at a temperature of 100°C, and dried to constant weight to obtain a modified binder.

[0036] S4. Preparation of graphene negative electrode material The modified graphene, modified binder and modified conductive agent were placed in a reactor at a mass ratio of 100:3:3 and stirred for 1 hour to obtain a negative electrode slurry; The negative electrode slurry was coated on aluminum foil and smoothed with a scraper to a coating thickness of 7 μm. The foil was dried at 100° C. for 8 h to obtain a graphene negative electrode material.

[0037] Comparative Example 1 The difference between this comparative example and Example 2 is that, when preparing the modified graphene precursor in step S1, an equal amount of graphene oxide is used to replace the modified graphene.

[0038] Comparative Example 2 The difference between this comparative example and Example 2 is that, when preparing the graphene negative electrode material in step S4, an equal amount of aluminum foil is used to replace the modified conductive agent.

[0039] Comparative Example 3 The difference between this comparative example and Example 2 is that, when preparing the graphene negative electrode material in step S4, the use of the modified binder is omitted.

[0040] Performance testing: Referring to GB / T 44027.1-2024 “Determination of carbon material methods - Part 1: Determination of initial discharge specific capacity, initial coulombic efficiency, and retention of discharge capacity at different rates”, the graphene negative electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 were prepared into button-type lithium batteries. The rate performance and charge capacity of button-type lithium batteries prepared with the graphene negative electrode materials prepared in Examples 10-12 and Comparative Examples 1-3 were tested in accordance with the standard SJ / T 11793-2022 "Test Methods for Electrochemical Properties of Lithium-ion Battery Electrode Materials"; The conductivity of button-type lithium batteries prepared with the graphene negative electrode materials prepared in Examples 10-12 and Comparative Examples 1-3 was tested in accordance with the standard SJ / T 11792-2022 "Test method for conductivity of lithium-ion battery electrode materials"; The cycle performance test method of the button-type lithium battery prepared with the graphene negative electrode material is as follows: charging to 4.1V at 0.5C, then charging at 4.1V constant voltage with a cut-off current of 0.02C, and discharging to 3.0V at 0.5C. The discharge capacity is used as the cycle discharge capacity for comparison, and the highest discharge capacity among the first three cycle discharge capacities is set as 100%; The specific test results are shown in Table 1.

[0041] Table 1. Test results of samples Data Analysis: By analyzing the data in Table 1, it can be found that the conductivity of the button lithium battery prepared by using the graphene negative electrode material prepared in this experiment is 0.0140S·cm -1 , the capacity retention rate after 100 cycles is 94.9%, the rate performance is 93.5% and the charge capacity is 366.2mAh·g -1 ; Comparative analysis of the tabular data of Example 2 and Comparative Example 1 shows that the conductivity, capacity retention rate after 100 cycles, rate performance and charge specific capacity of Comparative Example 1 are significantly reduced, indicating that the present invention obtains amino-modified nano-silicon by modifying nano-silicon particles with a silane coupling agent, further combining negatively charged graphene oxide and positively charged amino-modified nano-silicon and melamine through electrostatic self-assembly, and deoxidizing the graphene oxide at high temperature and reducing it to graphene by high-temperature calcination, pyrolyzing melamine to generate nitrogen-doped carbon, and converting the amino-modified nano-silicon into silicon nanoparticles after high-temperature treatment, and encapsulating the silicon particles with a graphene layer and a carbon layer to form a core-shell structure, obtaining a silicon core, a nitrogen-doped carbon layer and a graphite core from the inside out. Modified graphene with a carbon shell, silicon nanoparticles are prone to volume expansion during the charge and discharge process, and the graphene shell and the nitrogen-doped carbon layer form a double elastic buffer layer. The flexibility of graphene can withstand mechanical stress, and the nitrogen-doped carbon layer disperses stress through the pore structure, reducing silicon particle pulverization and electrode structure collapse, improving the structural stability of the negative electrode material during use, and improving the cycle stability of the lithium battery. The high conductivity of graphene and the p-type doping effect of nitrogen-doped carbon work synergistically to form a conductive path throughout the electrode, reducing the internal resistance of the negative electrode material, and improving the conductivity and rate performance of the lithium battery. In addition, the theoretical specific capacity of silicon is relatively high, which improves the lithium storage performance of the graphene negative electrode material and further improves the specific capacity of the lithium battery; A comparative analysis of the tabular data of Example 2 and Comparative Example 2 shows that the conductivity, capacity retention rate after 100 cycles, and rate performance of Comparative Example 2 are significantly reduced, indicating that the present invention prepares a modified conductive agent by modifying the carbon nanotubes, further mixing them with paper fibers, and filtering them. The carbon nanotubes and graphene in the modified conductive agent form a three-dimensional interpenetrating conductive network, shortening the lithium ion diffusion path, reducing the charge transfer impedance, and constructing a multi-dimensional electron transmission channel, thereby improving the conductive efficiency of the negative electrode material and further improving the conductivity and rate performance of the lithium battery. The paper fibers in the modified conductive agent provide mechanical support as a substrate, enhance the flexibility and deformation resistance of the negative electrode, and the high flexibility of the carbon nanotubes and graphene can withstand the volume change of silicon during the charge and discharge process, prevent the active material from falling off, and improve the cycle stability of the lithium battery. A comparative analysis of the tabular data of Example 2 and Comparative Example 3 shows that the conductivity, capacity retention rate after 100 cycles and rate performance of Comparative Example 3 are significantly reduced, indicating that the present invention prepares a modified binder with a polysulfonylurea structure through nucleophilic reaction and amidation reaction, and the cis and trans structures of the thiourea group in the modified binder precursor provide two hydrogen bonding modes, forming a multidimensional hydrogen bond network with the modified graphene and the modified conductive agent. When the negative electrode produces microcracks due to volume expansion, the dynamic hydrogen bonds of the thiourea groups in the modified binder can be reformed to automatically repair the cracks and maintain the mechanical integrity of the negative electrode, thereby enhancing the mechanical properties and self-repairing ability of the negative electrode material and improving the cycle stability of the lithium battery. The ether oxygen bonds in the modified binder can serve as channels for lithium ion transmission, thereby improving the ion transmission performance of the negative electrode material, and can effectively improve the ion transmission efficiency in the electrode network structure, thereby improving the rate performance and conductivity of the lithium battery.

[0042] The above contents are merely examples and explanations of the structure of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they shall fall within the scope of protection of the present invention.

[0043] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these 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 any one or more embodiments or examples.

[0044] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a high-rate graphene negative electrode material, characterized in that: The method comprises the following preparation steps: S1. Place 1,2-bis(2-aminoethoxy)ethane and N,N-dimethylformamide in a reactor under a nitrogen atmosphere, heat to 25-30°C, slowly add thiocarbonyldiimidazole, keep the mixture warm for 18-20 hours, and post-treat to obtain a modified binder precursor; S2. Place the modified binder precursor and N-methylpyrrolidone in a reaction kettle, stir for 15-20 minutes, add polyacrylic acid and deionized water, heat to 75-85° C., keep the temperature for reaction for 10-12 hours, and post-treat to obtain the modified binder; S3, placing the modified graphene, modified binder and modified conductive agent in a reactor and stirring for 0.5-1h to obtain a negative electrode slurry; S4. Coat the negative electrode slurry on aluminum foil, flatten it with a scraper, and dry it to obtain a graphene negative electrode material.

2. The method for preparing a high-rate graphene negative electrode material according to claim 1, wherein: In step S1, the amount ratio of the 1,2-bis(2-aminoethoxy)ethane, N,N-dimethylformamide and thiocarbonyldiimidazole is 2-4g:20-40mL:3-5g; in step S2, the amount ratio of the modified binder precursor, N-methylpyrrolidone, polyacrylic acid and deionized water is 2-4g:40-60mL:4-6g:50-60mL; in step S3, the mass ratio of the modified graphene, modified binder and modified conductive agent is 80-100:2-3:2-3; in step S4, the coating thickness is 5-10μm, the drying temperature is 100°C, and the drying time is 6-8h.

3. The method for preparing a high-rate graphene negative electrode material according to claim 1, wherein: In step S3, the modified graphene is prepared by the following steps: A1. Graphene oxide, amino-modified nano-silicon and deionized water are placed in a reactor, ultrasonically dispersed for 15-30 minutes, and a hot melamine solution is added. The mixture is cooled to room temperature and stirred for 18-20 hours. The modified graphene precursor is obtained by post-treatment. A2. Place the modified graphene precursor in a tube furnace, raise the temperature to 700-800°C, and keep the temperature for reaction for 2-3 hours to obtain modified graphene.

4. The method for preparing a high-rate graphene negative electrode material according to claim 3, wherein: In step A1, the graphene oxide, amino-modified nano-silicon, deionized water and melamine hot solution are used in a ratio of 2-4 g:4-8 g:200-300 mL:250-300 mL, and the melamine hot solution is composed of melamine and 90-100° C. deionized water in a ratio of 3 g:250 mL; in step A2, the heating rate is 5-10° C. / min.

5. The method for preparing a high-rate graphene negative electrode material according to claim 3, wherein: The preparation method of the amino-modified nano-silicon is as follows: nano-silicon particles, deionized water, ethanol and γ-aminopropyltriethoxysilane are placed in a reaction kettle, the temperature is raised to 50-60° C., the reaction is kept at this temperature for 2-4 hours, and the amino-modified nano-silicon is obtained by post-processing.

6. The method for preparing a high-rate graphene negative electrode material according to claim 5, wherein: The usage ratio of the nano-silicon particles, deionized water, ethanol and γ-aminopropyltriethoxysilane is 2-4 g: 5-8 mL: 20-30 mL: 0.5-1 g.

7. The method for preparing a high-rate graphene negative electrode material according to claim 1, wherein: In step S3, the modified conductive agent is prepared by the following steps: B1. Place carbon nanotubes and sodium citrate trihydrate in a planetary ball mill, ball mill for 1-2 hours, calcinate, and post-treat to obtain modified carbon nanotubes; B2. Place the modified carbon nanotubes, deionized water and sodium dodecyl sulfate in a reaction kettle, stir for 15-20 minutes, add the paper fiber mixture, stir for 0.5-1 hour, and post-treat to obtain a modified conductive agent.

8. The method for preparing a high-rate graphene negative electrode material according to claim 7, wherein: In step B1, the carbon nanotubes and sodium citrate trihydrate are used in a ratio of 1-2g:10-12g, the ball milling medium is composed of zirconium oxide with a diameter of 8-10mm, and the ball milling ratio is 1:30-32; in step B2, the modified carbon nanotubes, deionized water, sodium dodecyl sulfate and paper fiber mixture are used in a ratio of 1-2g:20-25mL:0.1-0.2g:1000-1200mL, and the paper fiber mixture is composed of paper fiber and deionized water in a ratio of 0.5g:1000mL.

Images