A method for repairing and regenerating graphite negative electrode materials of waste lithium batteries

Abstract

The invention discloses a repair and regeneration method for waste lithium battery graphite negative electrode materials, belongs to the technical field of graphite negative electrode regeneration, and is used to solve the technical problem in the prior art that the discharge specific capacity and cycle stability of regenerated graphite need to be further improved. The invention specifically comprises the following steps: performing impurity removal and purification treatment on the waste graphite material to prepare purified graphite, mixing the purified graphite, concentrated sulfuric acid and hydrogen peroxide, raising the temperature of the reaction system to 50-60°C, stirring and mixing for 60-80 minutes, and post-processing to obtain an expanded graphite precursor. The invention improves the graphite conversion rate and porosity of the graphite negative electrode material and enhances it with asphalt and graphene-modified silicon as reinforcing agents, thereby effectively improving not only the first discharge specific capacity and coulombic efficiency of the regenerated graphite negative electrode material, but also the discharge capacity retention rate and cycle stability of the regenerated graphite negative electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of graphite negative electrode regeneration, and in particular to a method for repairing and regenerating graphite negative electrode materials of waste lithium batteries. Background Art

[0002] With the widespread application of lithium-ion batteries in electric vehicles, energy storage devices and consumer electronics, the recycling and resource utilization of waste lithium batteries has become a global focus. Graphite, as a core component of lithium-ion battery negative electrode materials, has a direct impact on the battery's energy density, cycle life and safety characteristics.

[0003] Waste graphite negative electrodes usually contain electrolyte residues, binders, conductive agents and metal impurities. In existing technologies, graphite regeneration mainly relies on high-temperature calcination (>2800℃) to repair the crystal structure of graphite, but this process has extremely high energy consumption, resulting in high regeneration costs and difficulty in large-scale application. In addition, high-temperature treatment can easily lead to an increase in graphite lattice defects and irreversible expansion of interlayer spacing, reducing its conductivity and mechanical stability. The specific capacity can be increased by introducing silicon-based materials into the graphite material, but the volume expansion effect of silicon (>300%) still leads to particle pulverization and electrode shedding during the cycle. Regenerated graphite is prone to interlayer damage, surface oxidation and micropore collapse during long-term charging and discharging, resulting in a decrease in specific capacity and a shortened cycle life, making it difficult to restore its high capacity and long-cycle stability at the same time. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for repairing and regenerating graphite negative electrode materials of waste lithium batteries, which is used to solve the technical problem in the prior art that the discharge specific capacity and cycle stability of regenerated graphite need to be further improved.

[0005] The purpose of the present invention can be achieved by the following technical solution: A method for repairing and regenerating graphite negative electrode materials of waste lithium batteries, comprising the following steps:

[0006] S1, the waste graphite material is subjected to impurity purification treatment to prepare purified graphite, the purified graphite, concentrated sulfuric acid and hydrogen peroxide are mixed, the reaction system temperature is raised to 50-60 ° C, stirred and mixed for 60-80 min, and post-processed to obtain expanded graphite precursor, the expanded graphite precursor is calcined to prepare expanded graphite;

[0007] The synthetic reaction mechanism of expanded graphite is:

[0008] During the preparation process, concentrated sulfuric acid acts as a strong oxidant and intercalant, which can be inserted into the graphite interlayer to form graphite interlayer compounds. Hydrogen peroxide plays a role in assisting oxidation and promoting intercalation. The carbon atoms between the graphite layers interact with the sulfuric acid molecules, resulting in an increase in the distance between the graphite layers, forming an expanded graphite precursor. Under high temperature and argon protection, the sulfuric acid molecules in the expanded graphite precursor begin to decompose, generating gases (such as sulfur dioxide, sulfur trioxide and water vapor), which increase the pressure between the graphite layers, thereby causing the graphite layers to expand and form expanded graphite. During the high-temperature roasting process, the catalyst can dissolve the carbon. When the solubility of the disordered carbon reaches saturation, it is supersaturated for the graphite. The melted part of the carbon tends to the low-energy graphite crystal form and deposits, thereby increasing the degree of graphitization and preparing expanded graphite.

[0009] S2, using nano-silica as a matrix, coating and depositing titanium dioxide on its exterior to prepare modified silica;

[0010] S3, modifying the modified silicon dioxide by modifying graphene to prepare graphene-modified silicon;

[0011] S4. Grind and mix the asphalt, expanded graphite and graphene-modified silicon in a weight ratio of 2-3:50:7-8, and then transfer them to a tube furnace. Under an inert atmosphere, increase the temperature of the tube furnace to 780-820°C, keep the temperature and roast for 4-5 hours, cool and discharge the material to obtain regenerated graphite.

[0012] The synthetic reaction mechanism of regenerated graphite is:

[0013] During the high-temperature roasting process, the carbonaceous residue produced by the pyrolysis of asphalt, the layered structure of expanded graphite and the composite effect of graphene-modified silicon jointly promote the formation of the regenerated graphite composite structure to prepare regenerated graphite.

[0014] Furthermore, in step S1, the preparation method of purified graphite is: the graphite negative electrode material is crushed and mixed with the purification liquid, the reaction system is sealed, the temperature is increased to 130-150° C., and the mixture is stirred for 3-5 hours at the same temperature, and then post-treated to obtain purified graphite.

[0015] The synthetic reaction mechanism of purified graphite is:

[0016] Sodium persulfate in the purification solution has strong oxidizing properties. Under high temperature conditions, it oxidizes metal impurities such as lithium, copper, and iron contained in the waste graphite negative electrode material, oxidizing them from low-valent metal ions to high-valent states. The high-valent metal ions are complexed with nitrate or sulfate ligands, thereby dissociating from the graphite surface and entering the solution. After washing and removal, purified graphite is prepared.

[0017] Furthermore, the amount ratio of the graphite negative electrode material and the purification liquid is 1g:20-30mL, the purification liquid is composed of sodium nitrate, sodium persulfate and deionized water in a ratio of 1g:2g:8mL, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed three times with 0.1mol / L nitric acid and then washed with purified water until neutral, the filter cake is transferred to a dryer at a temperature of 70-80°C, and dried to constant weight to obtain purified graphite.

[0018] Furthermore, in step S1, the amount ratio of purified graphite, concentrated sulfuric acid and hydrogen peroxide is 1g:6-7mL:0.8-1mL, the concentration of the concentrated sulfuric acid is 90-98wt%, and the mass fraction of the hydrogen peroxide is 28-30wt%. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water until neutral and then dried, and the filter cake is transferred to a drying oven at a temperature of 70-80°C and dried to constant weight to obtain an expanded graphite precursor.

[0019] Furthermore, in step S1, the calcination treatment method is as follows: the expanded graphite precursor and the catalyst are mixed uniformly in a weight ratio of 20:1 and then added to a tube furnace. Under the protection of an inert atmosphere, the tube furnace is heated to 400-500°C at a heating rate of 3-5°C / min, kept warm and calcined for 6-7h, and naturally cooled to room temperature. The solid is discharged, washed three times with 2-3mol / L nitric acid solution, and then washed with purified water until neutral. The filter cake is transferred to a drying oven at a temperature of 70-80°C and dried to constant weight to obtain expanded graphite, wherein the catalyst consists of cobalt oxide and nickel oxide in a weight ratio of 2:1.

[0020] Furthermore, in step S2, the preparation method of modified silica is: mixing nano-silica, anhydrous ethanol and ammonia water, ultrasonically dispersing for 30-50 minutes, raising the temperature of the reaction system to 40-45°C, adding tetrabutyl titanate to the reaction system, keeping the temperature and stirring for 26-30 hours, and post-treating to obtain modified silica.

[0021] The synthetic reaction mechanism of modified silica is:

[0022] During the reaction, tetrabutyl titanate will undergo a hydrolysis reaction under alkaline conditions to generate titanium hydroxy compounds, which will undergo a condensation reaction with the hydroxyl groups on the surface of the nano-silica to form Ti-O-Si bonds, thereby binding the titanium element to the surface of the nano-silica to form a modified structure. The ammonia water and low temperature environment reduce the titanium deposition rate, thereby forming a uniform titanium coating modification on the nano-silica particles to prepare modified silica.

[0023] Furthermore, the amount ratio of the nano-silica, anhydrous ethanol, ammonia water and tetrabutyl titanate is 1g:100mL:3mL:1.3-1.6g, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water until neutral, and the filter cake is transferred to a drying oven at a temperature of 70-80°C and dried to constant weight to obtain modified silica.

[0024] Furthermore, in step S3, the graphene-modified silicon is processed by the following steps:

[0025] A1. Graphene oxide and tetrahydrofuran were mixed, the reaction system temperature was raised to 50-60° C., isocyanatepropyltriethoxysilane was added dropwise to the reaction system, and after the addition was complete, the reaction was kept warm for 40-60 minutes, and post-processed to obtain modified graphene;

[0026] The synthetic reaction mechanism of modified graphene is:

[0027]

[0028] Wherein, GO is graphene oxide.

[0029] During the reaction, the isocyanate group on the isocyanatepropyltriethoxysilane molecule undergoes a condensation reaction with the oxygen-containing group on the graphene oxide molecule, and the triethoxysilane is modified on the graphene oxide molecule to prepare modified graphene.

[0030] A2. Modified silica, modified graphene, and anhydrous ethanol are mixed and ultrasonically dispersed for 30-50 minutes. The temperature of the reaction system is raised to 50-60°C. A catalyst is added to the reaction system, and the reaction is kept warm for 90-120 minutes. After post-treatment, graphene-modified silicon is obtained.

[0031] The synthetic reaction mechanism of graphene-modified silicon is:

[0032]

[0033] Where, It is modified silica.

[0034] During the reaction, the catalyst catalyzes the hydrolysis of triethoxysilane on the modified graphene molecule to form silanol, and the silanol reacts with the active groups on the surface of the modified silica to form a deposition coating, thereby depositing and coating the graphene on the surface of the modified silica to prepare graphene-modified silicon.

[0035] Furthermore, in step A1, the amount ratio of the graphene oxide, tetrahydrofuran and isocyanatepropyltriethoxysilane is 4g:80mL:0.8-1.2g, and the post-treatment includes: after the reaction is completed, the reaction system is kept warm at 50-60°C, and low-boiling substances are removed under reduced pressure to obtain modified graphene; in step A2, the amount ratio of the modified silica, modified graphene, anhydrous ethanol and catalyst is 7g:1-1.3g:80mL:10mL, and the catalyst is 3-5mol / L sodium hydroxide solution. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, allowed to stand, the upper suspension is removed, the lower sediment is washed with anhydrous ethanol three times and then dried, and the filter cake is transferred to a drying oven at a temperature of 60-70°C and dried to constant weight to obtain graphene-modified silicon.

[0036] The present invention has the following beneficial effects:

[0037] 1. The present invention uses graphite negative electrode as raw material, removes impurities with purified liquid, removes metal ions therein, and then expands it. Under the conditions of catalyst and high temperature, the carbonization of organic matter such as the binder in the graphite negative electrode is promoted to be converted into graphite, thereby improving the graphitization conversion rate of the graphite. High-purity graphite has a more regular crystal structure, and the expanded graphite has a larger interlayer spacing, which provides more channels and space for the insertion and removal of lithium ions, is beneficial to improving the transmission rate of lithium ions, and is beneficial to the insertion and removal of lithium ions, thereby improving the first discharge specific capacity and the first coulomb efficiency of the regenerated graphite. In addition, the material structure of high-purity graphite, expanded graphite with a large interlayer spacing and a high graphitization conversion rate improves the structural stability of the material, reduces the pulverization and shedding of the material during the charge and discharge process, thereby improving the discharge capacity retention rate and ensuring the stability of the regenerated graphite during long cycles.

[0038] 2. The present invention uses asphalt and graphene-modified silicon as reinforcing agents to reinforce expanded graphite prepared from waste graphite electrodes. High-temperature calcination promotes asphalt carbonization and graphene-modified silicon to form a continuous conductive network, promotes charge transfer of silicon particles, reduces polarization loss, and repairs the graphite microcrystalline structure, thereby improving lithium storage capacity. The specific capacity of silicon is much higher than that of graphite. The introduction of silicon significantly improves the overall capacity. The asphalt carbonization layer covers the surface defects of the graphite, reduces electrolyte decomposition and lithium loss, and improves the first discharge specific capacity and coulombic efficiency of the negative electrode material. The amorphous carbon layer formed by asphalt carbonization inhibits the structural damage of silicon and graphite during the cycle, reduces pulverization and shedding, and the porous structure of the expanded graphite accommodates the volume change of silicon, maintains the integrity of the electrode, and improves the discharge capacity retention rate and reversible specific capacity of the material.

[0039] 3. The present invention uses nano-silica as a substrate, and sequentially coats modified carbon dioxide and graphene modification layers on its exterior to prepare graphene-modified silicon. After the nano-silica is modified with tetrabutyl titanate, Ti-O-Si bonds are formed on the surface, which improves the dispersibility of silicon dioxide in the graphene-modified silicon and enhances its interaction with graphene. The modified graphene has a unique two-dimensional structure, which enables the modified graphene to be evenly loaded and coated on the modified silicon dioxide, thereby effectively wrapping the modified silicon dioxide to form a modified silicon with graphene oxide as a conductive layer, preventing silicon from agglomerating during the charge and discharge process. The TiO2 coating and the excellent mechanical properties of graphene oxide buffer the volume expansion of silicon to a certain extent, maintain the stability of the regenerated graphite structure, inhibit the volume expansion of SiO2, and cooperate with the expanded graphite to maintain the structural stability of the graphite negative electrode. The amorphous TiO2 has a high Li + Diffusion coefficient, shortening Li + The diffusion distance is shortened to improve the rate performance. DETAILED DESCRIPTION

[0040] 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.

[0041] In the present invention, nano-silica is a silica microsphere with a particle size of 20nm-10um;

[0042] In the present invention, the graphene oxide is selected from multilayer graphene oxide produced by Hangzhou Zheming New Materials Co., Ltd., with an effective component content of 99.9%, an average thickness of 1-3nm, a diameter of 4-7μm, a number of layers of 2-5, and a specific surface area of ​​20-50m 2 / g;

[0043] In the present invention, the asphalt is selected from the national standard modified coal tar produced by Handan Xina Chemical Technology Co., Ltd., with a flash point of 260°C, an ash content of 0.2, a coking value of 56, and a softening point of 100-110°C.

[0044] Example 1

[0045] This embodiment provides a method for preparing graphene-modified silicon, comprising the following steps:

[0046] Step I: Preparation of modified silica

[0047] Weigh: 20 g of nano-silica, 2000 mL of anhydrous ethanol and 30 mL of 20 wt% ammonia water, add them to a reaction flask and mix, ultrasonically disperse for 30 min, raise the temperature of the reaction flask to 40°C, add 26 g of tetrabutyl titanate to the reaction flask, keep warm and stir for 26 h, lower the temperature of the reaction flask to room temperature, filter, wash the filter cake with purified water until it is neutral, transfer the filter cake to a drying oven at a temperature of 70°C, and dry to constant weight to obtain modified silica.

[0048] Step II: Preparation of modified graphene

[0049] Weigh: 20 g of graphene oxide and 4000 mL of tetrahydrofuran are added to a reaction flask and stirred. The temperature of the reaction flask is raised to 50°C. 4 g of isocyanatepropyltriethoxysilane is added dropwise to the reaction flask. After the addition is complete, the reaction is kept warm for 40 minutes. The reaction flask is kept warm at 50°C and low-boiling substances are evaporated under reduced pressure to obtain modified graphene.

[0050] Step III: Preparation of graphene-modified silicon

[0051] Weigh: 14 g of modified silica, 2 g of modified graphene, and 160 mL of anhydrous ethanol, add them to a reaction flask and mix, ultrasonically disperse for 30 minutes, raise the temperature of the reaction flask to 50°C, add 20 mL of 3 mol / L sodium hydroxide solution to the reaction flask, keep warm and react for 90 minutes, lower the temperature of the reaction flask to room temperature, let it stand for 15 minutes, remove the upper suspension, wash the lower sediment with anhydrous ethanol three times and then dry it, transfer the filter cake to a drying oven at a temperature of 60°C, and dry it to constant weight to obtain graphene-modified silicon.

[0052] Example 2

[0053] This embodiment provides a method for preparing graphene-modified silicon, comprising the following steps:

[0054] Step I: Preparation of modified silica

[0055] Weigh: 20 g of nano-silica, 2000 mL of anhydrous ethanol and 30 mL of 20 wt% ammonia water, add them to a reaction flask and mix, ultrasonically disperse for 40 minutes, raise the temperature of the reaction flask to 43°C, add 29 g of tetrabutyl titanate to the reaction flask, keep warm and stir for 28 hours, lower the temperature of the reaction flask to room temperature, filter, wash the filter cake with purified water until it is neutral, transfer the filter cake to a drying oven at a temperature of 75°C, and dry it to constant weight to obtain modified silica.

[0056] Step II: Preparation of modified graphene

[0057] Weigh: 20 g of graphene oxide and 4000 mL of tetrahydrofuran are added to a reaction flask and stirred. The temperature of the reaction flask is raised to 55° C. 5 g of isocyanatepropyltriethoxysilane is added dropwise to the reaction flask. After the addition is complete, the reaction is kept warm for 50 minutes. The reaction flask is kept warm at 55° C. and low-boiling substances are evaporated under reduced pressure to obtain modified graphene.

[0058] Step III: Preparation of graphene-modified silicon

[0059] Weigh: 14 g of modified silica, 2.3 g of modified graphene, and 160 mL of anhydrous ethanol are added to a reaction flask and mixed, ultrasonically dispersed for 40 minutes, the temperature of the reaction flask is raised to 55°C, 20 mL of 4 mol / L sodium hydroxide solution is added to the reaction flask, and the reaction is kept warm for 105 minutes. The temperature of the reaction flask is lowered to room temperature and allowed to stand for 15 minutes. The upper suspension is removed, and the lower sediment is washed three times with anhydrous ethanol and then dried. The filter cake is transferred to a drying oven at a temperature of 65°C and dried to constant weight to obtain graphene-modified silicon.

[0060] Example 3

[0061] This embodiment provides a method for preparing graphene-modified silicon, comprising the following steps:

[0062] Step I: Preparation of modified silica

[0063] Weigh: 20 g of nano-silica, 2000 mL of anhydrous ethanol and 30 mL of 20 wt% ammonia water, add them to a reaction flask and mix, ultrasonically disperse for 50 min, raise the temperature of the reaction flask to 45°C, add 32 g of tetrabutyl titanate to the reaction flask, keep warm and stir for 30 h, lower the temperature of the reaction flask to room temperature, filter, wash the filter cake with purified water until it is neutral, transfer the filter cake to a drying oven at 80°C, and dry it to constant weight to obtain modified silica.

[0064] Step II: Preparation of modified graphene

[0065] Weigh: 20 g of graphene oxide and 4000 mL of tetrahydrofuran are added to a reaction flask and stirred. The temperature of the reaction flask is raised to 60°C. 6 g of isocyanatepropyltriethoxysilane is added dropwise to the reaction flask. After the addition is complete, the reaction is kept warm for 60 minutes. The reaction flask is kept warm at 60°C and low-boiling substances are evaporated under reduced pressure to obtain modified graphene.

[0066] Step III: Preparation of graphene-modified silicon

[0067] Weigh: 14 g of modified silica, 2.6 g of modified graphene, and 160 mL of anhydrous ethanol, add them to a reaction flask and mix, ultrasonically disperse for 50 minutes, raise the temperature of the reaction flask to 60°C, add 20 mL of 5 mol / L sodium hydroxide solution to the reaction flask, keep warm and react for 120 minutes, lower the temperature of the reaction flask to room temperature, let it stand, remove the upper suspension, wash the lower sediment with anhydrous ethanol three times and then dry it, transfer the filter cake to a drying oven at a temperature of 70°C, and dry it to constant weight to obtain graphene-modified silicon.

[0068] Example 4

[0069] This embodiment provides a method for repairing and regenerating a waste lithium battery graphite negative electrode material, comprising the following steps:

[0070] Step 1: Preparation of purified graphite

[0071] The graphite negative electrode material is crushed and passed through an 80-mesh sieve to obtain waste graphite negative electrode powder;

[0072] Mix sodium nitrate, sodium persulfate, and deionized water in a ratio of 1 g:2 g:8 mL to obtain a purified solution for later use.

[0073] The graphite negative electrode material and the purification liquid were added to the reaction flask in a dosage ratio of 1g:20mL and stirred. After the reaction flask was sealed, the temperature was raised to 130°C and stirred for 3 hours. The temperature of the reaction flask was lowered to room temperature and filtered. The filter cake was washed three times with 0.1mol / L nitric acid and then washed with purified water until neutral. The filter cake was transferred to a dryer at a temperature of 70°C and dried to constant weight to obtain purified graphite.

[0074] Step 2: Preparation of expanded graphite

[0075] Weigh: 20 g of purified graphite, 120 mL of 90 wt% concentrated sulfuric acid, and 16 mL of 28 wt% hydrogen peroxide were added to a reaction flask and stirred. The temperature of the reaction flask was raised to 50° C. and stirred for 60 min. The temperature of the reaction flask was lowered to room temperature, and the mixture was filtered. The filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at 70° C. and dried to constant weight to obtain an expanded graphite precursor.

[0076] Cobalt oxide and nickel oxide are mixed uniformly in a weight ratio of 2:1 to obtain a catalyst;

[0077] The expanded graphite precursor and the catalyst were mixed uniformly in a weight ratio of 20:1 and added into a tube furnace. Under argon protection, the tube furnace was heated to 400°C at a heating rate of 3°C / min, kept warm for 6 hours, and naturally cooled to room temperature. The material was discharged, and the solid was washed three times with 2mol / L nitric acid solution and then washed with purified water until neutral. The filter cake was transferred to a drying oven at a temperature of 70°C and dried to constant weight to obtain expanded graphite.

[0078] Step 3: Preparation of regenerated graphite

[0079] Weigh by weight: 2 parts of asphalt, 50 parts of expanded graphite and 7 parts of graphene-modified silicon prepared in Example 1 and add them to a ball mill. Set the ball milling rate to 500 r / min and ball mill mixing for 50 minutes. Then transfer it to a tube furnace. Under an argon atmosphere, the temperature of the tube furnace is increased to 780°C, kept warm and calcined for 4 hours, and then cooled and discharged to obtain regenerated graphite.

[0080] Example 5

[0081] This embodiment provides a method for repairing and regenerating a waste lithium battery graphite negative electrode material, comprising the following steps:

[0082] Step 1: Preparation of purified graphite

[0083] The graphite negative electrode material is crushed and passed through an 80-mesh sieve to obtain waste graphite negative electrode powder;

[0084] Mix sodium nitrate, sodium persulfate, and deionized water in a ratio of 1 g:2 g:8 mL to obtain a purified solution for later use.

[0085] The graphite negative electrode material and the purification liquid were added to the reaction flask in a ratio of 1 g: 25 mL and stirred. After the reaction flask was sealed, the temperature was raised to 140 ° C. and the mixture was stirred for 4 hours. The temperature of the reaction flask was lowered to room temperature and filtered. The filter cake was washed with 0.1 mol / L nitric acid three times and then washed with purified water until neutral. The filter cake was transferred to a dryer at a temperature of 75 ° C. and dried to constant weight to obtain purified graphite.

[0086] Step 2: Preparation of expanded graphite

[0087] Weigh: 20 g of purified graphite, 130 mL of 94 wt% concentrated sulfuric acid, and 18 mL of 29 wt% hydrogen peroxide were added to a reaction flask and stirred. The temperature of the reaction flask was raised to 55° C. and stirred for 70 minutes. The temperature of the reaction flask was lowered to room temperature and filtered. The filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at 75° C. and dried to constant weight to obtain an expanded graphite precursor.

[0088] Cobalt oxide and nickel oxide are mixed uniformly in a weight ratio of 2:1 to obtain a catalyst;

[0089] The expanded graphite precursor and the catalyst were mixed uniformly in a weight ratio of 20:1 and added to a tube furnace. Under argon protection, the tube furnace was heated to 450°C at a heating rate of 4°C / min, kept warm and calcined for 6.5 hours, and naturally cooled to room temperature. The material was discharged, and the solid was washed three times with 2.5 mol / L nitric acid solution and then washed with purified water until neutral. The filter cake was transferred to a drying oven at a temperature of 75°C and dried to constant weight to obtain expanded graphite.

[0090] Step 3: Preparation of regenerated graphite

[0091] Weigh by weight: 2.5 parts of asphalt, 50 parts of expanded graphite and 7.5 parts of graphene-modified silicon prepared in Example 2 and add them to a ball mill. Set the ball milling rate to 500 r / min and ball mill mixing for 50 minutes. Then transfer it to a tubular furnace. Under an argon atmosphere, the temperature of the tubular furnace is increased to 800°C, kept warm and calcined for 4.5 hours, and then cooled and discharged to obtain regenerated graphite.

[0092] Example 6

[0093] This embodiment provides a method for repairing and regenerating a waste lithium battery graphite negative electrode material, comprising the following steps:

[0094] Step 1: Preparation of purified graphite

[0095] The graphite negative electrode material is crushed and passed through an 80-mesh sieve to obtain waste graphite negative electrode powder;

[0096] Mix sodium nitrate, sodium persulfate, and deionized water in a ratio of 1 g:2 g:8 mL to obtain a purified solution for later use.

[0097] The graphite negative electrode material and the purification liquid were added to the reaction flask in a dosage ratio of 1g:30mL and stirred. After the reaction flask was sealed, the temperature was raised to 150°C and stirred for 5 hours. The temperature of the reaction flask was lowered to room temperature and filtered. The filter cake was washed three times with 0.1mol / L nitric acid and then washed with purified water until neutral. The filter cake was transferred to a dryer at a temperature of 80°C and dried to constant weight to obtain purified graphite.

[0098] Step 2: Preparation of expanded graphite

[0099] Weigh: 20 g of purified graphite, 140 mL of 98 wt% concentrated sulfuric acid, and 20 mL of 30 wt% hydrogen peroxide were added to a reaction flask and stirred. The temperature of the reaction flask was raised to 60 ° C. and stirred for 80 minutes. The temperature of the reaction flask was lowered to room temperature, filtered, and the filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at a temperature of 80 ° C and dried to constant weight to obtain an expanded graphite precursor;

[0100] Cobalt oxide and nickel oxide are mixed uniformly in a weight ratio of 2:1 to obtain a catalyst;

[0101] The expanded graphite precursor and the catalyst were mixed uniformly in a weight ratio of 20:1 and added into a tube furnace. Under argon protection, the tube furnace was heated to 500°C at a rate of 5°C / min, kept warm and calcined for 7 hours, and naturally cooled to room temperature. The material was discharged, and the solid was washed three times with 3 mol / L nitric acid solution and then washed with purified water until neutral. The filter cake was transferred to a drying oven at a temperature of 80°C and dried to constant weight to obtain expanded graphite.

[0102] Step 3: Preparation of regenerated graphite

[0103] Weigh 3 parts of asphalt, 50 parts of expanded graphite and 8 parts of graphene-modified silicon prepared in Example 3 in parts by weight and add them to a ball mill. Set the ball milling rate to 500 r / min and ball mill mixing for 50 minutes. Then transfer it to a tube furnace. Under an argon atmosphere, the temperature of the tube furnace is increased to 820°C, kept warm and calcined for 5 hours, and then cooled and discharged to obtain regenerated graphite.

[0104] Comparative Example 1

[0105] The difference between this comparative example and Example 6 is that, when preparing the graphene-modified silicon used, step I is omitted, and the modified silicon dioxide in step III is replaced by the nano-silica in step I.

[0106] Comparative Example 2

[0107] The difference between this comparative example and Example 6 is that in step 3, nano-silicon dioxide is used instead of graphene-modified silicon.

[0108] Comparative Example 3

[0109] The difference between this comparative example and Example 6 is that in step 2, purified graphite is used instead of the expanded graphite precursor to prepare the expanded graphite.

[0110] Comparative Example 4

[0111] The difference between this comparative example and Example 6 is that in step 2, no catalyst is added to the expanded graphite.

[0112] Performance testing:

[0113] The first discharge specific capacity, first coulombic efficiency, and discharge capacity retention rate of the battery samples prepared with the regenerated graphite prepared in Examples 4-6 and Comparative Examples 1-4 were measured with reference to the standard GB / T 44027.1-2024 "Determination of carbon material methods - Part 1: Determination of initial discharge specific capacity, initial coulombic efficiency, and discharge capacity retention rate". During the preparation of the battery samples, the slurry of the negative electrode material was obtained by mixing a mixture of regenerated graphite, a binder sodium carboxymethyl cellulose, and conductive carbon black in a weight ratio of 93:3:6 with ultrapure water to prepare a slurry, with a mass fraction of 45%;

[0114] The battery sample prepared above was cycled 800 times at a current density of 1 A / g to test the reversible specific capacity of the sample. The specific test results are shown in Table 1 below.

[0115] Table 1-Performance test data of the sample

[0116]

[0117] Data Analysis:

[0118] A comparative analysis of the data in Table 1 above shows that the lithium battery sample prepared using the regenerated graphite prepared by the present invention has an initial discharge capacity of 1270.5 mAh / g, an initial coulombic efficiency of 94.8%, a discharge capacity retention rate of 59.1%, and a reversible capacity of 1086.5 mAh / g after 800 cycles. All performance test data are superior to those of the comparative example, indicating that the present invention not only effectively improves the initial discharge capacity and coulombic efficiency of the regenerated graphite negative electrode material, but also improves its discharge capacity retention rate and reversible capacity by recycling the graphite negative electrode material, improving its graphite conversion rate and porosity, and enhancing it with asphalt and graphene-modified silicon as reinforcing agents.

[0119] 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 repairing and regenerating graphite negative electrode materials of waste lithium batteries, characterized in that: The following steps are involved: S1, the waste graphite material is subjected to impurity purification treatment to prepare purified graphite, the purified graphite, concentrated sulfuric acid and hydrogen peroxide are mixed, the reaction system temperature is raised to 50-60 ° C, stirred and mixed for 60-80 min, and post-processed to obtain expanded graphite precursor, the expanded graphite precursor is calcined to prepare expanded graphite; S2, using nano-silica as a matrix, coating and depositing titanium dioxide on its exterior to prepare modified silica; S3, modifying the modified silicon dioxide by modifying graphene to prepare graphene-modified silicon; S4, grinding and mixing the asphalt, expanded graphite and graphene-modified silicon in a weight ratio of 2-3:50:7-8, and then transferring them to a tube furnace. In an inert atmosphere, the temperature of the tube furnace is raised to 780-820 ° C., and the mixture is kept at this temperature for 4-5 hours. The mixture is cooled and discharged to obtain regenerated graphite; Graphene-modified silicon is processed by the following steps: A1. Graphene oxide and tetrahydrofuran were mixed, the reaction system temperature was raised to 50-60° C., isocyanatepropyltriethoxysilane was added dropwise to the reaction system, the addition was completed, the reaction was kept warm for 40-60 min, and post-processed to obtain modified graphene, wherein the amount ratio of the graphene oxide, tetrahydrofuran and isocyanatepropyltriethoxysilane was 4 g:80 mL:0.8-1.2 g; A2. Modified silica, modified graphene, and anhydrous ethanol are mixed and ultrasonically dispersed for 30-50 minutes. The temperature of the reaction system is raised to 50-60°C, a catalyst is added to the reaction system, and the reaction is kept warm for 90-120 minutes. After post-treatment, graphene-modified silicon is obtained, wherein the amount ratio of the modified silica, modified graphene, anhydrous ethanol, and catalyst is 7g:1-1.3g:80mL:10mL, and the catalyst is 3-5mol / L sodium hydroxide solution.

2. The method for repairing and regenerating a waste lithium battery graphite negative electrode material according to claim 1, wherein: In step S1, the preparation method of purified graphite is as follows: the graphite negative electrode material is crushed and mixed with the purification liquid, the reaction system is sealed, the temperature is increased to 130-150°C, the mixture is stirred at this temperature for 3-5 hours, and the purified graphite is obtained by post-processing.

3. The method for repairing and regenerating a waste lithium battery graphite negative electrode material according to claim 2, wherein: The usage ratio of the graphite negative electrode material and the purification liquid is 1g:20-30mL, and the purification liquid is composed of sodium nitrate, sodium persulfate and deionized water in the ratio of 1g:2g:8mL.

4. The method for repairing and regenerating a waste lithium battery graphite negative electrode material according to claim 1, wherein: In step S1, the usage ratio of purified graphite, concentrated sulfuric acid and hydrogen peroxide is 1 g: 6-7 mL: 0.8-1 mL, the concentration of the concentrated sulfuric acid is 90-98 wt %, and the mass fraction of the hydrogen peroxide is 28-30 wt %.

5. The method for repairing and regenerating a waste lithium battery graphite negative electrode material according to claim 1, wherein: In step S1, the calcination treatment method is as follows: the expanded graphite precursor and the catalyst are mixed uniformly in a weight ratio of 20:1 and then added to a tube furnace. Under the protection of an inert atmosphere, the tube furnace is heated to 400-500°C at a heating rate of 3-5°C / min, kept warm and calcined for 6-7h, and naturally cooled to room temperature. The solid is discharged, washed three times with 2-3mol / L nitric acid solution, and then washed with purified water until neutral. The filter cake is transferred to a drying oven at a temperature of 70-80°C and dried to constant weight to obtain expanded graphite, wherein the catalyst is composed of cobalt oxide and nickel oxide in a weight ratio of 2:

1.

6. The method for repairing and regenerating a waste lithium battery graphite negative electrode material according to claim 1, characterized in that: In step S2, the modified silica is prepared by mixing nano-silica, anhydrous ethanol and ammonia water, ultrasonically dispersing for 30-50 minutes, raising the temperature of the reaction system to 40-45° C., adding tetrabutyl titanate to the reaction system, stirring at this temperature for 26-30 hours, and post-treating to obtain the modified silica.

7. The method for repairing and regenerating a waste lithium battery graphite negative electrode material according to claim 6, characterized in that: The usage ratio of the nano-silicon dioxide, anhydrous ethanol, ammonia water and tetrabutyl titanate is 1g:100mL:3mL:1.3-1.6g.

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