Method for preparing recycled graphite material from waste graphite saggar, negative electrode material and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and discloses a method for preparing a recycled graphite material from a waste graphite sagger, a negative electrode material and a lithium ion battery. According to the method for preparing the recycled graphite material from the waste graphite saggar, the waste graphite saggar is taken and subjected to reduction and graphitization at high temperature, so that non-metal impurities containing oxygen, nitrogen, sulfur and other elements, organic impurities such as hydrocarbons and phenols and metal impurities containing alkali metal, alkaline earth metal and other elements are effectively removed; a high-temperature graphite oxide product with a certain space structure is obtained; then, an alkaline organic coating solution is taken to treat the high-temperature graphitized product by adopting a low-temperature-to-high-temperature staged treatment mode, so that impurities which are not completely removed, such as metal oxides and salts, can be further effectively removed, and meanwhile, the space structure of the high-temperature graphitized product is optimized; and finally, the recycled graphite material which is high in purity and can well meet the use requirements of the lithium ion negative electrode material is obtained.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion batteries, and particularly relates to a method for preparing recycled graphite material from waste graphite crucible, a negative electrode material and a lithium ion battery. BACKGROUND

[0002] Graphite crucible is a common material bearing container in lithium battery manufacturing, metal smelting, chemical industry, aerospace and military industry, etc. A large number of graphite crucibles are retired and abandoned due to high temperature, chemical corrosion and mechanical damage, causing great waste of resources. Graphite, as one of the most important sources of negative electrode materials for lithium batteries, plays an extremely important role in providing lithium storage sites, stabilizing battery voltage and ensuring battery cycle life. Using waste graphite crucible as raw material for preparing graphite negative electrode material can not only reduce environmental pollution and difficult treatment problems, but also realize resource recycling and utilization, thereby increasing the production of lithium battery negative electrode material and reducing production cost and promoting sustainable development.

[0003] Currently, the waste graphite crucible is mainly recycled to prepare graphite negative electrode material through purification, impurity removal and carbonization processes. The patent application with publication number CN113372121A discloses a method for preparing porous SiC from waste graphite crucible. The method includes crushing and ball milling the waste graphite crucible to prepare powder; then acid washing and drying to obtain clean carbon powder; mixing the clean carbon powder with high-purity silicon powder and placing them in a graphite crucible for sintering in an argon atmosphere to obtain a sintered body; and further sintering the sintered body to obtain porous SiC. The method has the advantages of low production cost, simple operation, easy availability of raw materials and convenient batch production. However, the method uses acid multiple times in the production process, which causes difficulties in handling and environmental pollution. The patent application with publication number CN116169273A discloses a preparation method of composite coated artificial graphite negative electrode material. The method includes coarsely and finely crushing and shaping at least one of scrap resistance material, scrap graphite crucible or scrap box plate to obtain crushed and shaped material; mixing the crushed and shaped material with liquid coating agent, and mixing the liquid phase coating precursor with pitch to obtain composite coated precursor; then performing high-temperature carbonization treatment to obtain composite coated carbonized product; and performing screening, depolymerization and magnetic removal treatment to obtain composite coated artificial graphite negative electrode material. The obtained composite coated artificial graphite negative electrode material has the advantages of high capacity, small specific surface area and excellent rate performance. However, the method fails to effectively remove impurities in the waste graphite material, and the obtained graphite material has insufficient purity, which cannot meet the use requirements of lithium battery negative electrode material.

[0004] Therefore, obtaining a recycling method capable of realizing effective removal of heavy metal ions, organic impurities and other impurities in waste graphite crucible and obtaining a recycled graphite material with ideal spatial structure is of great significance for realizing the resource utilization of waste graphite crucible. SUMMARY

[0005] The first object of the present application is to provide a method for preparing a recycled graphite material from waste graphite crucible, which can effectively remove complex impurities such as heavy metal ions, organic impurities and other impurities in the waste graphite crucible, and the obtained recycled graphite material has ideal spatial structure, excellent purity and electrical properties, and can well meet the use requirements of lithium battery negative electrode materials, and has good application prospect in realizing the resource utilization of waste graphite crucible.

[0006] The second object of the present application is to provide a recycled graphite material.

[0007] The third object of the present application is to provide a negative electrode material.

[0008] The fourth object of the present application is to provide a lithium ion battery.

[0009] Specifically, the method for preparing a recycled graphite material from waste graphite crucible provided by the present application comprises: S1, taking waste graphite crucible and crushing to obtain crucible powder, and taking the crucible powder for high-temperature graphitization treatment in a reducing atmosphere to obtain a high-temperature graphitization product; S2, taking the high-temperature graphitization product and mixing with an alkaline organic coating liquid, and performing a one-stage reaction under the conditions of 80℃-120℃ and stirring to obtain a one-stage reaction product; taking the one-stage reaction product and performing a two-stage reaction under the conditions of 600℃-800℃ and inert atmosphere to obtain a two-stage reaction product; taking the two-stage reaction product for high-temperature drying, crushing and demagnetization to obtain a recycled graphite material; wherein the alkaline graphite organic coating liquid comprises a strong base, an organic solvent and a coating agent.

[0010] Further, in step S1, the Dv50 of the crucible powder is 30-50 mu m.

[0011] Further, in step S1, the reducing atmosphere comprises inert gas and hydrogen in a volume ratio of (80-99):(1-20).

[0012] Further, in step S1, the inert gas is argon and / or nitrogen.

[0013] Further, in step S1, the temperature of the high-temperature graphitization treatment is 2500-3000℃, and the time is 30-40h.

[0014] Further, in step S2, the strong base is sodium hydroxide and / or potassium hydroxide.

[0015] Further, in step S2, the organic solvent is selected from one or more of ethylene glycol, ethylene glycol butyl ether and N-methyl pyrrolidone.

[0016] Further, in step S2, the carbon material coating agent is selected from one or more of low-temperature coal tar pitch, low-temperature petroleum pitch, polypyrrole and polyaniline.

[0017] Further, in step S2, the mass ratio of the strong base, the organic solvent and the carbon material coating agent in the alkaline organic coating solution is (0.05-0.1):1:(0.08-0.12).

[0018] Further, in step S2, the total solid content of the reaction solution system of the one-stage reaction is 50%-60%.

[0019] Further, in step S2, the stirring speed of the one-stage reaction is 300 rpm-500 rpm, and the reaction time is 4 h-6 h.

[0020] Further, in step S2, the time of the two-stage reaction is 6 h-8 h.

[0021] Further, in step S2, the temperature of the high-temperature drying is 280°C-320°C, and the time is 8 h-16 h.

[0022] Further, the pH value of the recycled graphite material is 6.8-7.2, the Dv50 is 8 μm-10 μm, and the water content is less than 100 ppm.

[0023] The recycled graphite material provided by the application is prepared by the method for preparing a recycled graphite material from waste graphite saggers.

[0024] Further, the impurity element content of the recycled graphite material is not higher than 6.21 ppm.

[0025] Further, the impurity element is selected from one or more of iron element, sodium element, chromium element, copper element, nickel element, aluminum element, molybdenum element, cobalt element and zinc element.

[0026] The negative electrode material provided by the application comprises the recycled graphite material.

[0027] Further, the negative electrode material comprises a graphite material, and the mass ratio of the recycled graphite material and the graphite material is (18-20):(80-82).

[0028] The lithium ion battery provided by the application comprises the recycled graphite material or the negative electrode material.

[0029] Beneficial effects: The application provides a method for preparing a recycled graphite material from waste graphite retort. The waste graphite retort is produced in the process of battery manufacturing, metal smelting, chemical industry, aerospace and military industry, etc. The waste graphite retort is first subjected to high-temperature graphitization treatment in a reducing atmosphere. Non-metallic impurities, organic impurities and metallic impurities in the waste graphite retort are removed, and a preliminary three-dimensional space structure is formed. The high-temperature graphitization product is obtained. The high-temperature graphitization product is then reacted with an alkaline organic coating solution at a low temperature of 80-120°C. The preliminary activation and etching of the high-temperature graphitization product are performed to further form a pore structure. The metallic oxides and salts in the high-temperature graphitization product are removed. The carbon material coating agent is fully coated. The one-stage reaction product is obtained. The one-stage reaction product is subjected to carbonization treatment at a high temperature of 600-800°C. The carbon material coating agent on the surface of the high-temperature graphitization product is carbonized. The impurities are further removed. The excessive porosity is filled. The new pore structure is formed. The preliminary three-dimensional space structure of the high-temperature graphitization product is optimized. Finally, the recycled graphite material with an ideal space structure, good structural stability, high purity and excellent electrical properties is obtained. The recycled graphite material can be used alone or in combination with normal graphite as a material for preparing a lithium ion battery negative electrode. The application has a good application prospect in the resource utilization of the waste graphite retort. DETAILED DESCRIPTION

[0030] The inventors of the present application take the resource utilization of a large amount of waste graphite retort generated in the production of lithium battery manufacturing, metal smelting, chemical industry, aerospace and military industry as the starting point, aiming at the problems of incomplete impurity removal, certain pollution of the recycling process and unsatisfactory electrical performance and stability of the regenerated product in the existing recycling process, through extensive and in-depth research and a large number of experiments, it is found creatively that: taking the waste graphite retort under high temperature and reducing atmosphere for graphitization treatment can effectively remove non-metallic impurities containing oxygen, nitrogen, sulfur and other elements, organic impurities such as hydrocarbons and phenols, and metal impurities containing alkali metals and alkaline earth metals, and obtain high-temperature oxidized graphite products with certain spatial structure; then using a staged treatment method from low temperature to high temperature, taking the alkaline organic coating liquid including strong alkali and carbon material coating agent to treat the high-temperature graphitized product, further remove the impurities such as metal oxides and salts that have not been completely removed, and optimize the spatial structure of the high-temperature graphitized product, improve the graphite pore structure and stabilize the structure, so as to finally obtain a recycled graphite material with high purity and good satisfaction for the use of lithium ion negative electrode material. Based on this, the technical scheme of the present application is obtained.

[0031] In the first aspect, the present application provides a method for preparing a recycled graphite material from waste graphite retort, which specifically comprises: S1, taking the waste graphite retort for crushing to obtain retort powder, and taking the retort powder for high-temperature graphitization treatment in a reducing atmosphere to obtain a high-temperature graphitized product; S2, taking the high-temperature graphitized product and an alkaline organic coating liquid for mixing and then for one-stage reaction to obtain a one-stage reaction product; taking the one-stage reaction product for two-stage reaction to obtain a two-stage reaction product; and taking the two-stage reaction product for high-temperature drying, crushing and demagnetization to obtain a recycled graphite material.

[0032] In the present application, in step S1, the waste graphite retort is a waste generated in the production process of lithium battery manufacturing, metal smelting, chemical industry, aerospace and military industry, which contains a large amount of complex impurities and is used as a raw material for preparing a recycled graphite material.

[0033] In the present application, in step S1, the waste graphite retort is crushed to increase the specific surface area, promote heat and mass transfer, and improve the consistency of graphitization. The method and instrument used for crushing are a conventional technical means in the prior art, and the person skilled in the art can make adaptive selection according to the actual use needs, and the present application does not particularly limit it.

[0034] In some embodiments, the method of crushing the spent graphite crucible specifically comprises: taking the spent graphite crucible to perform mechanical coarse crushing and fine crushing. Specific examples of instruments for achieving mechanical coarse crushing include, but are not limited to, one or more of a roller crusher, a cone crusher, and a impact crusher. Specific examples of instruments for achieving fine crushing include, but are not limited to, one or more of a jet mill, a ball mill, and a classification mechanical mill.

[0035] In the present application, in step S1, the Dv50 of the crucible powder is preferably 30 μm to 50 μm, such as 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, 43 μm, 45 μm, 48 μm, 50 μm, or any value therebetween. At this time, the crucible powder has a relatively ideal specific surface area, which is conducive to the reduction reaction and graphitization reaction on its surface and inside, so as to improve the quality of the obtained high-temperature graphitized product.

[0036] In the present application, in step S1, the reducing atmosphere refers to a gaseous environment with electron-donating ability or oxygen-removing ability, which at least includes a reducing gas. Specific examples of the reducing gas include, but are not limited to, hydrogen and / or methane.

[0037] In some embodiments, the reducing atmosphere preferably includes an inert gas and hydrogen, and the volume ratio of the inert gas to hydrogen is preferably (80-99):(1-20), such as 80:20, 82:18, 85:15, 89:11, 90:10, 95:5, 99:1, or any value therebetween. Specific examples of the inert gas include, but are not limited to, argon and / or nitrogen.

[0038] In the present application, in step S1, the conditions of the high-temperature graphitization treatment specifically include a temperature of preferably 2500°C to 3000°C, such as 2500°C, 2678°C, 2700°C, 2800°C, 2950°C, 3000°C, or any value therebetween; and a time of preferably 30 h to 40 h, such as 30 h, 32 h, 34 h, 35 h, 37.5 h, 39 h, 40 h, or any value therebetween.

[0039] In the present application, in step S2, the alkaline organic coating solution specifically comprises a strong base, an organic solvent and a carbon material coating agent. The strong base refers to a compound that can completely ionize hydroxyl ions in an aqueous solution, and specific examples thereof include, but are not limited to, sodium hydroxide and / or potassium hydroxide. The organic solvent refers to a class of organic compounds composed mainly of carbon and hydrogen, which is a medium for the reaction of the strong base, the carbon material coating agent and the high-temperature graphitized product, and specific examples thereof include, but are not limited to, one or more of ethylene glycol, ethylene glycol butyl ether and N-methyl pyrrolidone. The carbon material coating agent refers to a functional substance mainly composed of carbon-based substances, which can form a continuous carbon coating layer on the surface of the high-temperature graphitized product, and specific examples thereof include, but are not limited to, one or more of low-temperature coal tar pitch, low-temperature petroleum pitch, polypyrrole and polyaniline.

[0040] In some specific embodiments, in the alkaline organic coating solution, the mass ratio of the strong base, the organic solvent and the carbon material coating agent is preferably (0.05-0.1):1:(0.08-0.12), such as 0.05:1:0.08, 0.06:1:0.08, 0.075:1:0.09, 0.08:1:0.09, 0.1:1:0.1, 0.1:1:0.11, 0.1:1:0.12 or any value therebetween. At this time, the alkaline organic coating solution contains a suitable concentration of strong base and carbon material coating agent, which has a more excellent treatment effect on the high-temperature graphitized product.

[0041] In some specific embodiments, the addition amount of the high-temperature graphitized product is preferably: the total solid content of the reaction solution system of the first-stage reaction is 50%-60% of the addition amount of the high-temperature graphitized product and the alkaline organic coating solution mixed. The total solid content refers to the total mass percentage of the high-temperature graphitized product, the strong base and the carbon material coating agent in the reaction solution system.

[0042] In the present application, in step S2, the first-stage reaction is carried out under the conditions of lower temperature and stirring; wherein the temperature of the first-stage reaction is specifically 80-120℃, such as 80℃, 80.5℃, 81℃, 83℃, 85℃, 90℃, 95℃, 100℃, 110℃, 120℃ or any value therebetween.

[0043] In some specific embodiments, the conditions of the one-stage reaction specifically include that the stirring speed is preferably 300 rpm to 500 rpm, such as 300 rpm, 320 rpm, 350 rpm, 380 rpm, 400 rpm, 425 rpm, 450 rpm, 475 rpm, 500 rpm, or any value therebetween; and the reaction time is preferably 4 h to 6 h, such as 4 h, 4.1 h, 4.3 h, 4.5 h, 4.7 h, 4.9 h, 5 h, 5.2 h, 5.6 h, 6 h, or any value therebetween.

[0044] In the present application, in step S2, the two-stage reaction is performed under conditions of high temperature and inert atmosphere; wherein the temperature of the two-stage reaction is specifically 600℃ to 800℃, such as 600℃, 620℃, 640℃, 650℃, 680℃, 700℃, 730℃, 750℃, 780℃, 800℃, or any value therebetween.

[0045] In some specific embodiments, the conditions of the two-stage reaction specifically include that the reaction time is preferably 6 h to 8 h, such as 6 h, 6.3 h, 6.5 h, 6.8 h, 7 h, 7.2 h, 7.5 h, 8 h, or any value therebetween.

[0046] In the present application, in step S2, the high-temperature drying refers to a process of removing water and organic solvents in the two-stage reaction product by using high-temperature conditions, and the conditions of the high-temperature drying specifically include that the temperature is preferably 280℃ to 320℃, such as 280℃, 390℃, 300℃, 310℃, 320℃, or any value therebetween; and the time is preferably 8 h to 16 h, such as 8 h, 8.5 h, 9 h, 10 h, 12 h, 14 h, 16 h, or any value therebetween.

[0047] In the present application, in step S2, the method and instrument for crushing the two-stage reaction product after high-temperature drying are a technical means commonly used in the prior art, and the person skilled in the art can make adaptive selection according to the actual use needs, and the present application does not particularly limit it.

[0048] In the present application, in step S2, removing magnetism from the two-stage reaction product after high-temperature drying and crushing refers to a method of removing magnetic substances in the two-stage reaction product by using physical, chemical or electromagnetic means, which is a technical means commonly used in the prior art, and the person skilled in the art can make adaptive selection according to the actual use needs, and the present application does not particularly limit it.

[0049] In the present application, the pH value of the recycled graphite material is preferably 6.8-7.2, and can be 6.8, 6.9, 7, 7.1, 7.2 or any value therebetween; the Dv50 is preferably 8-10 μm, and can be 8 μm, 8.3 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm or any value therebetween; and the water content is preferably less than 100 ppm.

[0050] It should be noted that the Dv50 of each substance in the present application refers to the particle size corresponding to the cumulative particle size distribution percentage of 50% in a particle size distribution, and the test method is a conventional technical means in the prior art, which can be selected by those skilled in the art according to actual use needs, and the present application does not particularly limit it.

[0051] In some embodiments of the present application, the test method of Dv50 specifically comprises: mixing 1 g of the substance to be tested with an appropriate amount of dispersant to obtain a test solution, and testing the test solution using a laser particle size analyzer under the conditions of pump speed of 2400-2500 r / min, ultrasonic frequency of 19.5 Hz and ultrasonic time of 70 s, and taking the average value of four parallel tests.

[0052] In a second aspect, the present application further provides a recycled graphite material, which is prepared by the method for preparing a recycled graphite material from waste graphite sagger.

[0053] In the present application, the recycled graphite material can well meet the use requirements of negative electrode materials in lithium ion batteries, and can be used alone or compounded with normal graphite materials as negative electrode materials.

[0054] In the present application, the recycled graphite material has excellent purity, and the content of impurity elements is not higher than 6.21 ppm. The impurity elements specifically include but are not limited to one or more of iron element, sodium element, chromium element, copper element, nickel element, aluminum element, molybdenum element, cobalt element and zinc element.

[0055] In a third aspect, the present application further provides a negative electrode material, which comprises the recycled graphite material.

[0056] In the present application, the negative electrode material preferably further comprises a graphite material, which refers to a lithium battery negative electrode graphite material prepared from conventional raw materials such as petroleum coke and needle coke, or a commercially available lithium battery negative electrode graphite material.

[0057] In some specific embodiments, the mass ratio of the recycled graphite material and the graphite material is preferably (18-20):(80-82), such as 18:82, 18.5:81.5, 19:81, 19.9:80.1, 20:80, or any value therebetween.

[0058] In a fourth aspect, the present application also provides a lithium ion battery comprising the recycled graphite material or the negative electrode material described above.

[0059] Embodiments of the present application are described in detail below, and examples of the embodiments are intended to explain the present application, and cannot be understood as a limitation of the present application. If a specific technique or condition is not specified in the embodiments, the technique or condition described in the literature in the art or according to the product manual is used. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be obtained by purchase.

[0060] The reagents used in the following examples and their sources are specifically as follows: Commercially available graphite (China Graphite Group Co., Ltd., product code YXSG-6-9995); Low-temperature coal pitch (Handan Jinghao Chemical Co., Ltd., product code JH004); Low-temperature petroleum pitch (Tianshan Environmental Protection Kuche Petrochemical Co., Ltd., product code AH-110#); Polypyrrole (Sigma-Aldrich, product code 717300); Super-P (Tianjin Huayuan Chemical Technology Co., Ltd., product code 2020040012); Sodium carboxymethylcellulose (Nippon Soda, product code CMC1330); Styrene-butadiene rubber (Dongguan Shengli New Material Co., Ltd., product code SL-SXDJ100); Graphene@carbon nanotube composite conductive paste (Zhejiang Yipu New Material Technology Co., Ltd., product code YP5005); Polyvinylidene fluoride (Fulunolin Chemical Industry, product code FL2300).

[0061] Also, it should be noted that the waste graphite retort used in the following examples and comparative examples is consistent.

[0062] Example 1 This embodiment is used to illustrate a preparation method of a negative electrode material, which specifically comprises: S1, 20 kg of waste graphite retort was mechanically coarsely broken and finely broken to obtain retort powder (Dv50=30 μm); the retort powder was taken in a mixed gas atmosphere (V N2 :V H2=9:1) for 32 h to obtain a high-temperature graphitization product.

[0063] S2, (1) the high-temperature graphitization product was placed in a high-temperature reaction kettle, 22.6 kg of an alkaline organic coating solution (including sodium hydroxide, ethylene glycol and low-temperature coal pitch with a mass ratio of 1:20:1.6) was added, at this time the total solid content of the reaction solution was 53%, and one-stage reaction was carried out at 80°C and 300 rpm for 6 h, the solid was collected by filtration to obtain a one-stage reaction product, and the filtrate could be reused; (2) the one-stage reaction product was taken to carry out two-stage reaction under a nitrogen atmosphere at 600°C for 8 h to obtain a two-stage reaction product; (3) pure water was introduced, and the two-stage reaction product was stirred and washed at 150 rpm until the pH value was 7, then high-temperature drying was carried out at 300°C for 12 h until the water content was <100 ppm, the product was broken to Dv50 of 8 μm, and then magnetic removal was carried out to obtain a recycled graphite material.

[0064] S3, the recycled graphite material and commercially available graphite were mixed according to a mass ratio of 18:82 to obtain a negative electrode material.

[0065] Example 2 This example is used to illustrate a preparation method of a negative electrode material, which specifically comprises: S1, 20 kg of waste graphite anode was mechanically coarsely broken and finely broken to obtain anode powder (Dv50=40 μm); the anode powder was taken in a mixed gas atmosphere (V Ar :V H2 =9:1) for 32 h to obtain a high-temperature graphitization product.

[0066] S2, (1) the high-temperature graphitization product was placed in a high-temperature reaction kettle, 23.6 kg of an alkaline organic coating solution (including potassium hydroxide, ethylene glycol butyl ether and low-temperature petroleum pitch with a mass ratio of 1.6:20:2) was added, at this time the total solid content of the reaction solution was 54%, and one-stage reaction was carried out at 100°C and 400 rpm for 7 h, the solid was collected by filtration to obtain a one-stage reaction product, and the filtrate could be reused; (2) the one-stage reaction product was taken to carry out two-stage reaction under a nitrogen atmosphere at 700°C for 7 h to obtain a two-stage reaction product; (3) pure water was introduced, and the two-stage reaction product was stirred and washed at 100 rpm until the pH value was 7, then high-temperature drying was carried out at 300°C for 12 h until the water content was <100 ppm, the product was broken to Dv50 of 9 μm, and then magnetic removal was carried out to obtain a recycled graphite material.

[0067] S3, the recovered graphite material and the commercially available graphite were mixed according to a mass ratio of 19:81 to obtain the negative electrode material.

[0068] Example 3 This example is used to illustrate a method for preparing a negative electrode material, which specifically comprises: S1, 20 kg of waste graphite anode was mechanically coarsely broken and finely broken to obtain anode powder (Dv50 = 50 pm); the anode powder was subjected to high-temperature graphitization treatment under the condition of a mixed atmosphere of nitrogen and hydrogen (V N2 :V H2 = 9:1), 3000°C for 38h to obtain a high-temperature graphitized product.

[0069] S2, (1) the high-temperature graphitized product was placed in a high-temperature reaction kettle, 24.4 kg of alkaline organic coating solution (including potassium hydroxide, N-methyl pyrrolidone and polypyrrole at a mass ratio of 2:20:2.7) was added, at this time the total solid content of the reaction solution was 50%, and the reaction was carried out under the condition of 120°C, 500 rpm for 6h, the solid was collected by filtration to obtain a one-stage reaction product, and the filtrate could be reused; (2) the one-stage reaction product was subjected to a two-stage reaction under the condition of a nitrogen atmosphere, 800°C for 6h to obtain a two-stage reaction product; (3) pure water was introduced, and the two-stage reaction product was stirred and washed under 150 rpm until the pH value was 7, then high-temperature drying was carried out at 300°C for 12h until the water content was <100 ppm, and the product was broken to Dv50 of 10 pm before being subjected to magnetic removal to obtain a recovered graphite material.

[0070] S3, the recovered graphite material and the commercially available graphite were mixed according to a mass ratio of 20:80 to obtain the negative electrode material.

[0071] Comparative Example 1 This comparative example used the method provided in Example 1 to prepare a negative electrode material, except that in step S1, the anode powder was subjected to high-temperature graphitization treatment under the condition of a nitrogen atmosphere, 2500°C for 32h, and other conditions remained unchanged to obtain the negative electrode material.

[0072] Comparative Example 2 This comparative example used the method provided in Example 1 to prepare a negative electrode material, except that in step S2, the high-temperature graphitized product was not subjected to the treatment in (1) and (2) (one-stage reaction and two-stage reaction), but was directly broken and subjected to magnetic removal before being mixed with the commercially available graphite, and other conditions remained unchanged, which specifically comprises: S1, 20 kg of waste graphite anode was mechanically coarsely broken and finely broken to obtain anode powder (Dv50 = 30 pm); the anode powder was subjected to high-temperature graphitization treatment under the condition of a mixed atmosphere of nitrogen and hydrogen (VN2 :V H2 High-temperature graphitization was carried out at 2500℃ for 32 hours under conditions of 9:1 (ratio = 9:1) to obtain the high-temperature graphitized product.

[0073] S2. The high-temperature graphitization product is crushed to a Dv50 of 8μm and then demagnetized to obtain recycled graphite material. Then, the recycled graphite material and commercially available graphite are mixed at a mass ratio of 18:82 to obtain the negative electrode material.

[0074] Comparative Example 3 The comparative example uses the method provided in Example 1 to prepare the negative electrode material. The difference is that in step S2, only the high-temperature graphitization product is treated in (1) (one-stage reaction), and other conditions remain the same, specifically including: S1. Take 20 kg of waste graphite crucible and perform mechanical coarse and fine crushing to obtain crucible powder (Dv50=30μm); take the crucible powder and place it in a mixed atmosphere of nitrogen and hydrogen (V N2 :V H2 High-temperature graphitization was carried out at 2500℃ for 32 hours under conditions of 9:1 (ratio = 9:1) to obtain the high-temperature graphitized product.

[0075] S2. Place the high-temperature graphitization product in a high-temperature reactor and add 22.6 kg of alkaline organic coating solution (including sodium hydroxide, ethylene glycol, and low-temperature coal tar pitch in a mass ratio of 1:20:1.6). At this point, the total solid content of the reaction solution is 53%. The first-stage reaction is carried out at 80℃ and 300 rpm for 6 hours. The solid is collected by filtration to obtain the first-stage reaction product. The product is dried at 80℃ until the water content is <100 ppm. After being crushed to a Dv50 of 8 μm, it is demagnetized to obtain the recovered graphite material.

[0076] S3. Mix recycled graphite material and commercially available graphite at a mass ratio of 18:82 to obtain the negative electrode material.

[0077] Comparative Example 4 The comparative example uses the method provided in Example 1 to prepare the negative electrode material. The difference is that in step S2, only the high-temperature graphitization product is treated in (2) (two-stage reaction), and other conditions remain the same, specifically including: S1. Take 20 kg of waste graphite crucible and perform mechanical coarse and fine crushing to obtain crucible powder (Dv50=30μm); take the crucible powder and place it in a mixed atmosphere of nitrogen and hydrogen (V N2 With V H2 High-temperature graphitization was carried out at 2500℃ for 32 hours under conditions of 9:1 (ratio = 9:1) to obtain the high-temperature graphitized product.

[0078] S2, the high-temperature graphitization product was placed in a nitrogen atmosphere at 600°C for 8h to obtain a two-stage reaction product, which was broken to Dv50 of 8pm and then subjected to magnetic removal to obtain a recycled graphite material.

[0079] S3, the recycled graphite material and commercially available graphite were mixed in a mass ratio of 18:82 to obtain a negative electrode material.

[0080] Comparative Example 5 This comparative example used the method provided in Example 1 to prepare a negative electrode material, except that in step S2, the high-temperature graphitization product and the alkaline organic coating solution were mixed and then directly subjected to the treatment in (2) and (3), and other conditions remained unchanged, specifically including: S1, 20kg of waste graphite anode was mechanically coarsely broken and finely broken to obtain anode powder (Dv50=30pm); the anode powder was subjected to high-temperature graphitization treatment at 2500°C for 32h under a mixed gas atmosphere of nitrogen and hydrogen (V N2 :V H2 =9:1) to obtain a high-temperature graphitization product.

[0081] S2, (1) the high-temperature graphitization product was placed in a high-temperature reaction kettle and 22.6kg of alkaline organic coating solution (including sodium hydroxide, ethylene glycol and low-temperature coal tar pitch in a mass ratio of 1:20:1.6) was added and mixed uniformly, and then subjected to two-stage reaction at 600°C for 8h under a nitrogen atmosphere to obtain a two-stage reaction product; (2) pure water was introduced and the two-stage reaction product was stirred and washed at 150rpm until the pH value was 7, followed by high-temperature drying at 300°C for 12h until the water content was <100ppm, and then broken to Dv50 of 8pm and subjected to magnetic removal to obtain a recycled graphite material.

[0082] S3, the recycled graphite material and commercially available graphite were mixed in a mass ratio of 18:82 to obtain a negative electrode material.

[0083] Comparative Example 6 This comparative example used the method provided in Example 1 to prepare a negative electrode material, except that in step S2, only the high-temperature graphitization product was subjected to the treatment in (3), and other conditions remained unchanged, specifically including: S1, 20kg of waste graphite anode was mechanically coarsely broken and finely broken to obtain anode powder (Dv50=30pm); the anode powder was subjected to high-temperature graphitization treatment at 2500°C for 32h under a mixed gas atmosphere of nitrogen and hydrogen (V N2 :V H2 =9:1) to obtain a high-temperature graphitization product.

[0084] S2, pure water was introduced, and the high-temperature graphitization product was stirred and washed at 150 rpm until the pH value was 7, followed by high-temperature drying at 300°C for 12 h until the water content was <100 ppm, crushing to Dv50 of 8 μm, and then removing the magnetism to obtain a recovered graphite material.

[0085] S3, the recovered graphite material and commercially available graphite were mixed according to a mass ratio of 18:82 to obtain a negative electrode material.

[0086] Example 4 This example is used to illustrate the preparation of a lithium ion battery, which specifically comprises: 1. Preparation of a negative electrode sheet: (1) the negative electrode material provided in Example 1, Super-P, sodium carboxymethyl cellulose, and butadiene-styrene rubber were mixed according to a mass ratio of 93.5:1.5:3:2, and then a proper amount of deionized water was added and stirred to obtain a negative electrode slurry; (2) the negative electrode slurry was evenly applied to both sides of a copper foil (the area density was 180 g / cm 2 ), and then dried, rolled, and die-cut to obtain a negative electrode sheet of 62 mm x 52 mm x 90 μm (±2 μm).

[0087] 2. Preparation of a positive electrode sheet: (1) lithium iron phosphate, graphene@carbon nanotube composite conductive slurry, Super-P, and polyvinylidene fluoride were mixed according to a mass ratio of 94:3:1:2, and then a proper amount of N-methylpyrrolidone was added and stirred to obtain a positive electrode slurry; (2) the positive electrode slurry was evenly applied to both sides of a carbon-coated aluminum foil (the area density was 350 g / cm 2 ), and then dried, rolled, and die-cut to obtain a positive electrode sheet of 60 mm x 50 mm x 120 μm (±2 μm).

[0088] 3. Preparation of an electrolyte: in a dry room with an air dew point of -50°C, propylene carbonate, dimethyl carbonate, and diethyl carbonate were mixed according to a volume ratio of 1:1:1, and then sodium hexafluorophosphate, ethylene sulfate, and fluoroethylene carbonate were added according to a final concentration of 1 mol / L, 1 wt%, and 2% (v / v) of the additive amount, and stirred to obtain an electrolyte.

[0089] 4. Assembly of a lithium ion battery: the negative electrode sheet, the positive electrode sheet, and a ceramic aluminum oxide-coated polypropylene separator (Hangzhou Jiupeng New Material Co., Ltd., product number CY-L500G) were dried until the water content was <200 ppm, and then stacked into a bare cell through a lamination process, and then welded into an aluminum-plastic film battery shell after the positive and negative electrode tabs were welded, and then the electrolyte was injected and sealed, and then high-temperature standing and formation were performed to obtain a lithium ion battery, and the capacity of the lithium ion battery was about 10 Ah.

[0090] Example 5 The lithium ion battery was prepared by the method provided in Example 4, except that in the step "1, preparation of negative electrode sheet", the negative electrode material provided in Example 1 was replaced by the recycled graphite material provided in Example 1 in equal mass, and other conditions remained unchanged, to obtain the lithium ion battery.

[0091] Example 6 The lithium ion battery was prepared by the method provided in Example 4, except that in the step "1, preparation of negative electrode sheet", the negative electrode material provided in Example 1 was replaced by the negative electrode material provided in Example 2 in equal mass, and other conditions remained unchanged, to obtain the lithium ion battery.

[0092] Example 7 The lithium ion battery was prepared by the method provided in Example 4, except that in the step "1, preparation of negative electrode sheet", the negative electrode material provided in Example 1 was replaced by the negative electrode material provided in Example 3 in equal mass, and other conditions remained unchanged, to obtain the lithium ion battery.

[0093] Comparative Example 7 The lithium ion battery was prepared by the method provided in Example 4, except that in the step "1, preparation of negative electrode sheet", the negative electrode material provided in Example 1 was replaced by the commercially available graphite in equal mass, and other conditions remained unchanged, to obtain the lithium ion battery.

[0094] Comparative Example 8 The lithium ion battery was prepared by the method provided in Example 4, except that in the step "1, preparation of negative electrode sheet", the negative electrode material provided in Example 1 was replaced by the negative electrode material provided in Comparative Example 1 in equal mass, and other conditions remained unchanged, to obtain the lithium ion battery.

[0095] Comparative Example 9 The lithium ion battery was prepared by the method provided in Example 4, except that in the step "1, preparation of negative electrode sheet", the negative electrode material provided in Example 1 was replaced by the negative electrode material provided in Comparative Example 2 in equal mass, and other conditions remained unchanged, to obtain the lithium ion battery.

[0096] Comparative Example 10 The lithium ion battery was prepared by the method provided in Example 4, except that in the step "1, preparation of negative electrode sheet", the negative electrode material provided in Example 1 was replaced by the negative electrode material provided in Comparative Example 3 in equal mass, and other conditions remained unchanged, to obtain the lithium ion battery.

[0097] Comparative Example 11 The lithium ion battery was prepared by the method provided in Example 4, except that in the step "1, preparation of negative electrode sheet", the negative electrode material provided in Comparative Example 4 was used to replace the negative electrode material provided in Example 1 in equal mass, and other conditions were kept unchanged, to obtain the lithium ion battery.

[0098] Comparative Example 12 The lithium ion battery was prepared by the method provided in Example 4, except that in the step "1, preparation of negative electrode sheet", the negative electrode material provided in Comparative Example 5 was used to replace the negative electrode material provided in Example 1 in equal mass, and other conditions were kept unchanged, to obtain the lithium ion battery.

[0099] Comparative Example 13 The lithium ion battery was prepared by the method provided in Example 4, except that in the step "1, preparation of negative electrode sheet", the negative electrode material provided in Comparative Example 6 was used to replace the negative electrode material provided in Example 1 in equal mass, and other conditions were kept unchanged, to obtain the lithium ion battery.

[0100] Test Example This test example is used to illustrate the related performance of the recycled graphite material and the lithium ion battery provided in the above examples and comparative examples, and the test specifically includes: 1. Purity of the recycled graphite material (1) Magnetic impurity content: a. Accurately weigh 200 g (accurate to 0.01 g) of the recycled graphite material and commercially available graphite into a clean sample jar, respectively, add 300 mL of anhydrous ethanol and a clean magnetic bar, tightly cover the jar, shake well, then place the sample jar on a rolling device, and roll at 70 rpm for 30 min, and shake at least 3 times during the rolling process; b. After rolling, the magnetic bar is taken out and loaded into a conical flask, the magnetic bar is washed with water, then 50 mL of anhydrous ethanol is added, and ultrasonic cleaning is performed for 20 s on an ultrasonic cleaning instrument, repeated three times, and the magnetic bar and the conical flask are washed with water three times; c. Add 1.5 mL of nitric acid (15.6 mol / L) and 4.5 mL of hydrochloric acid (1.19 mol / L) to the conical flask containing the magnetic bar, and add water to make up to a total volume of about 50 mL, place on an electric heating plate, heat and ensure micro-boiling for 30 min, and the solution is not dry, shake at least 3 times during heating, try to cover the surface of the magnetic bar with acid solution during shaking, after heating, cool naturally to room temperature, move the cooled solution to a 50 mL volumetric flask, wash the conical flask and the magnetic bar with a small amount of water 4 times, add the washed solution to the volumetric flask, and dilute to 50 mL to obtain the test solution; d. The magnetic analyzer was used to determine the test solution under the selected optimal working conditions, and the standard curve was drawn according to the series of standard solutions for calculation, and the magnetic impurity content of each test solution was obtained, and the results are shown in Table 1.

[0101] (2) Impurity element content: a. Accurately take 0mL, 0.2mL, 0.5mL, 1.0mL, 2.0mL and 5.0mL of each storage mixed standard solution into 6 100mL volumetric flasks, respectively, add 5mL of nitric acid to each, dilute to the calibration line, shake well, prepare calibration blank and series of mixed standard solutions with iron, sodium, chromium, copper, nickel, aluminum, molybdenum, cobalt and zinc element concentrations of 0mg / L, 0.1mg / L, 0.25mg / L, 0.5mg / L, 1.0mg / L and 2.5mg / L, respectively, test by inductively coupled plasma atomic emission spectrometer, and draw the standard curve; b. Accurately weigh 0.4g of recovered graphite material and commercially available graphite into a clean digestion tank, add 3mL of nitric acid (15.6mol / L) and 9mL of hydrochloric acid (1.19mol / L), shake well, tighten the sample cover, use a microwave digestion instrument to digest at 180℃ for 15min, cool to room temperature, filter, dilute to 100mL, obtain the test solution, test by inductively coupled plasma atomic emission spectrometer, and calculate the impurity element content of each test solution according to the standard curve, and the results are shown in Table 1.

[0102] Table 1.

[0103] As shown by the results in Table 1, compared with Comparative Examples 1-6, the method provided by the present application Examples 1-3 is used to treat the waste graphite anode, by introducing a reducing gas in the graphitization high-temperature treatment, and cooperating with the alkaline organic coating liquid to carry out low-temperature one-stage reaction and high-temperature two-stage reaction, the heavy metal ions, organic impurities and other impurities in the waste graphite anode can be effectively removed, the magnetic impurity content in the recovered graphite material is not higher than 0.25ppm, and the impurity element content is not higher than 6.21ppm, which has a more excellent purity than the commercially available graphite negative material.

[0104] 2. Electrical performance of lithium ion battery The star cloud test system was used to test each lithium ion battery, specifically including: (1) First coulomb efficiency test (25℃±2℃), conditions including constant current charging to 3.7V at 0.1C, cutoff current 0.05C, standing for 10min; constant current discharging to 2.5V at 0.1C, cutoff current 0.05C, recording the first discharge capacity and first coulomb efficiency in the charging and discharging process; (2) Cycle test (25℃±2℃), conditions including constant current charge to 3.7V at 1C, cut-off current 0.05C, rest for 10min; constant current discharge to 2.5V at 1C, cut-off current 0.05C, rest for 10min, record the discharge capacity at 500th cycle and 1000th cycle and the cycle capacity retention rate, the results are shown in Table 2.

[0105] Table 2.

[0106] From the results shown in Table 2, compared with Comparative Examples 8-13, the lithium ion battery provided by Inventive Examples 4-7 has more excellent charge-discharge efficiency and cycle life. In addition, although the lithium ion battery prepared by using the recycled graphite material as the raw material provided by Inventive Example 5 has a lower initial discharge specific capacity and a lower initial coulombic efficiency than the lithium ion battery prepared by using the commercially available graphite as the negative electrode material (Comparative Example 7), it shows more excellent cycle stability in the cycle test, that is, the recycled graphite material has better structural stability than the commercially available graphite. The lithium ion batteries provided by Inventive Examples 4, 6 and 7 have a 0.1C discharge specific capacity increased by about 2%-3%, a 500th cycle capacity retention rate increased by about 1.7%-3.3%, and a 1000th cycle capacity retention rate increased by about 1.4%-3.7% compared with Comparative Example 7, indicating that the introduction of the recycled graphite material can enhance the electrical conductivity and structural stability of the negative electrode material, reduce the resistance of the electrode material and optimize the interface performance, thereby improving the charge-discharge efficiency and cycle life of the lithium ion battery.

[0107] Although the embodiments of the present application have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and should not be construed as limiting the present application, and those of ordinary skill in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments without departing from the principles and spirit of the present application within the scope of the present application.

Claims

1. A method for preparing recycled graphite materials from waste graphite saggers, characterized in that, The method includes: S1. Take a waste graphite sagger and crush it to obtain sagger powder. Take the sagger powder and perform high-temperature graphitization treatment in a reducing atmosphere to obtain high-temperature graphitization product. S2. The high-temperature graphitization product and the alkaline organic coating liquid are mixed and subjected to a first-stage reaction at 80℃~120℃ with stirring to obtain a first-stage reaction product; the first-stage reaction product is subjected to a second-stage reaction at 600℃~800℃ with an inert atmosphere to obtain a second-stage reaction product; the second-stage reaction product is subjected to high-temperature drying, crushing and demagnetization to obtain recycled graphite material. The alkaline graphite organic coating solution includes a strong alkali, an organic solvent, and a carbon material coating agent.

2. The method for preparing recycled graphite materials from waste graphite saggers according to claim 1, characterized in that, In step S1, the Dv50 of the crucible powder is 30μm~50μm; Optionally, the reducing atmosphere comprises an inert gas and hydrogen in a volume ratio of (80~99):(1~20); Optionally, the inert gas is argon and / or nitrogen; Optionally, the high-temperature graphitization treatment is carried out at a temperature of 2500℃~3000℃ for a time of 30h~40h.

3. The method for preparing recycled graphite materials from waste graphite saggers according to claim 1, characterized in that, In step S2, the strong base is sodium hydroxide and / or potassium hydroxide; Optionally, the organic solvent is selected from one or more of ethylene glycol, ethylene glycol butyl ether, and N-methylpyrrolidone; Optionally, the carbon material coating agent is selected from one or more of low-temperature coal tar pitch, low-temperature petroleum pitch, polypyrrole, and polyaniline; Optionally, in the alkaline organic coating solution, the mass ratio of the strong alkali, organic solvent and carbon material coating agent is (0.05~0.1):1:(0.08~0.12).

4. The method for preparing recycled graphite materials from waste graphite saggers according to claim 1, characterized in that, In step S2, the total solid content of the reaction solution system in the first stage reaction is 50%~60%; Optionally, the stirring speed of the first-stage reaction is 300 rpm to 500 rpm, and the reaction time is 4 h to 6 h. Optionally, the duration of the second-stage reaction is 6 to 8 hours; Optionally, the high-temperature drying temperature is 280℃~320℃, and the time is 8h~16h.

5. The method for preparing recycled graphite materials from waste graphite saggers according to claim 1, characterized in that, The recycled graphite material has a pH value of 6.8~7.2, a Dv50 of 8μm~10μm, and a water content of less than 100ppm.

6. A recycled graphite material, characterized in that, The recycled graphite material is prepared by the method for preparing recycled graphite material from waste graphite saggers as described in any one of claims 1 to 5.

7. The recycled graphite material according to claim 6, characterized in that, The impurity element content of the recycled graphite material is no higher than 6.21 ppm; Optionally, the impurity element is selected from one or more of the elements iron, sodium, chromium, copper, nickel, aluminum, molybdenum, cobalt, and zinc.

8. A negative electrode material, characterized in that, The negative electrode material includes the recycled graphite material as described in claim 6 or 7.

9. The negative electrode material according to claim 8, characterized in that, The negative electrode material includes graphite material, and the mass ratio of the recycled graphite material to the graphite material is (18~20):(80~82).

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the recycled graphite material as described in claim 6 or 7, or the negative electrode material as described in claim 8 or 9.

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