Graphite material and preparation method

Abstract

The invention discloses a graphite material and a preparation method thereof, wherein the preparation method comprises granulation, mixing SiO2 microspheres, a liquid coating agent and a graphite coke raw material powder, granulating to obtain graphite carbon; graphitizing the graphite carbon to obtain a graphite with a specific surface area b of 6-13m 2 / g, the total length of the channel L is 1*10 7 ‑6*10 7 m / g graphite material. This application utilizes SiO2 microspheres, which have a relatively standard spherical morphology, a relatively uniform morphology, and a relatively concentrated particle size distribution. This helps reduce agglomeration and improves the dispersibility and suspension of the SiO2 microspheres within the liquid coating agent. This results in a graphite material formed after the SiO2 overflows having a larger specific surface area and longer pore length.

Description

Technical Field

[0001] The present invention relates to the technical field of graphite negative electrode materials, and in particular to a graphite material and a preparation method thereof. Background Art

[0002] Carbon materials have the advantages of low chemical potential, good cycle performance, low price, and environmental friendliness. They are currently the most ideal and commonly used negative electrode materials for lithium-ion batteries. Among carbon materials, graphite materials have obvious advantages over soft carbon and hard carbon in terms of specific capacity, discharge platform, and cost. However, the consumer electronics and power battery fields have increasingly higher requirements for fast charging, mainly reflected in good fast charging capabilities under room and low temperature conditions. Currently, graphite negative electrode materials are usually specially designed and processed to meet the fast charging requirements. The solutions for fast charging technology are mainly: 1. Coating with an amorphous carbon layer; 2. Reducing the graphite particle size; 3. Optimizing the material structure design. Currently, the common solution to improve the fast charging capability of artificial graphite is to coat it with a layer of soft carbon or hard carbon, but conventional coating can no longer meet the growing demand for fast charging.

[0003] Prior art already uses pore-forming agents such as silicon carbide and resin to coat the surface of graphite, graphitize it in a graphitization furnace, and then coat it with the resin material to form artificial graphite, where the pore-forming additive creates pores in the artificial graphite. However, the inventors discovered that the pores in the porous graphite produced by this method only exist on the graphite surface and cannot provide rapid lithium ion migration channels within the graphite. The silicon carbide particles have irregular morphology and are prone to uneven mixing, resulting in uneven pores. Prior art methods use petroleum coke and silicon powder directly mixed and extruded into 2mm thin sheets, which are then graphitized in a graphitization furnace. The silicon powder vaporizes and escapes at high temperatures, leaving pores. This method uses a large amount of silicon powder and the particles are bonded together by extrusion, resulting in a weak bond between the particles. The graphite material is subjected to gas corrosion and pore-forming treatment, the pores are repaired by vapor deposition, and then chemically doped and granulated with silicon-based materials. The resulting negative electrode material has an irreversible effect on the energy density of the material because the crystal structure of the graphite particles is destroyed after corrosion. The preparation process is complex and closed pores are easily formed inside the graphite.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The object of the present invention is to provide a graphite material and a preparation method thereof.

[0006] The present invention is achieved in that:

[0007] In a first aspect, the present invention provides a method for preparing a graphite material, comprising the following steps:

[0008] Granulation, mixing SiO2 microspheres, liquid coating agent and graphite coke raw material powder, granulating to obtain a mixture;

[0009] Graphitization treatment: graphitizing graphite carbon to obtain graphite material.

[0010] In an optional embodiment, the SiO2 microspheres are obtained by modifying SiO2 obtained by hydrolysis of orthosilicate compounds;

[0011] Preferably, the average particle size of the SiO2 microspheres is 100-500 nm;

[0012] Preferably, the orthosilicate compound is at least one of methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, and butyl orthosilicate;

[0013] Preferably, the modification is to hydrophobically modify the SiO2 microspheres using carboxylic acid.

[0014] In an optional embodiment, the preparation method of the SiO2 microspheres is: mixing alcohol, water and ammonia water to obtain a mixed solution A, adding an orthosilicate compound to the mixed solution A for reaction to obtain SiO2 microspheres;

[0015] Preferably, the volume ratio of the alcohol, water, ammonia water and orthosilicate compound is 5-10:10-100:0.5-5:1-50;

[0016] Preferably, the alcohol in the mixed solution A is at least one of methanol, ethanol, and propanol;

[0017] Preferably, the orthosilicate compound is added dropwise to the mixed solution A, and the mixed solution A is stirred during the addition process;

[0018] Preferably, the temperature for reacting the mixed solution A with the orthosilicate compound is 18-25° C. and the time is 4-20 hours.

[0019] In an optional embodiment, after the reaction is completed, the reaction liquid is subjected to solid-liquid separation, and the separated solid is washed and dried to obtain SiO2 microspheres;

[0020] More preferably, the washing is performed by alternating between at least one of alcohol, water and an aqueous solution of alcohol or two or more thereof;

[0021] More preferably, the drying is drying the washed solid at 25-90° C. for 2-10 h.

[0022] In an optional embodiment, before the reaction solution is subjected to solid-liquid separation, carboxylic acid is added to the reaction solution to hydrophobically modify the SiO2 microspheres;

[0023] Preferably, the carboxylic acid is formic acid or acetic acid;

[0024] Preferably, the mass ratio of the carboxylic acid to the orthosilicate compound is 1:(5-10).

[0025] In an optional embodiment, the liquid coating agent includes at least one of liquid asphalt, liquid phenolic resin and liquid epoxy resin;

[0026] Preferably, the residual carbon content of the liquid coating agent is 5%-30%.

[0027] In an optional embodiment, the granulation is to mix SiO2 microspheres with a liquid coating agent to obtain a mixed coating agent, and then mix the mixed coating agent with graphite coke raw material powder and granulate to obtain a mixture;

[0028] Preferably, in the mixed coating agent, the mass ratio of SiO2 microspheres to asphalt is 1:(10-100);

[0029] Preferably, in the mixture, the mass ratio of the mixed coating agent to the graphite coke raw material is (2-10): (90-100);

[0030] Preferably, the graphite coke raw material is green coke or cooked coke;

[0031] Preferably, the graphite coke raw material D50 is 5-10 μm.

[0032] In an optional embodiment, the granulation comprises:

[0033] Set the fusion machine thermal oil temperature to 100-300℃;

[0034] Add graphite coke raw materials into the fusion machine, adjust the fusion machine speed to 20-300rpm, and when the material temperature rises to 50-100℃, add the mixed coating agent;

[0035] Adjust the fusion machine speed to 200-500rpm. When the material temperature rises to 100-300℃, fuse for 10-60min to obtain a mixed material.

[0036] In an optional embodiment, the temperature of the graphitization treatment is 2800-3000°C;

[0037] Preferably, the graphitization treatment equipment is one of an inner string graphitization furnace, a box-type graphitization furnace, and an Acheson graphitization furnace.

[0038] In a second aspect, the present invention provides a graphite material obtained by the method for preparing a graphite material according to any one of the aforementioned embodiments, wherein pores exist in the graphite material and the specific surface area b of the graphite material is 6-13 m 2 / g, the total length L of the duct is 1*10 7 -6*107 m / g, where L = b / 2πr, r is the average pore size;

[0039] Preferably, the pores exist on the surface and inside of the graphite negative electrode material;

[0040] More preferably, the pores of the graphite negative electrode material decrease in diameter from the surface to the inside, and the number of pores increases from small to large.

[0041] Preferably, the average pore diameter is 50-200 nm.

[0042] The present invention has the following beneficial effects:

[0043] The method of the present application does not have the problems of large amount of silicon powder used in existing silicon powder pore making, particles are bonded together by extrusion force, the bonding between particles is not strong, and gas corrosion and pore making treatment of graphite material affects the energy density of the material.

[0044] Generally, silicon oxide pore-forming agents are prone to agglomeration during mixing, resulting in uneven distribution of the pore-forming agent and, consequently, uneven pore distribution. This application utilizes SiO2 microspheres, which have a relatively standard spherical morphology, a relatively uniform morphology, and a relatively concentrated particle size distribution. This helps reduce agglomeration and improves the dispersibility and suspension of the SiO2 microspheres within the liquid coating agent. This results in the graphite material formed after the SiO2 overflows having a larger specific surface area and a longer pore length, which can significantly increase lithium ion migration channels and shorten the lithium ion diffusion distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0046] Figure 1 The electron microscope image of SiO2 microspheres obtained in the examples of this application;

[0047] Figure 2 The particle size changes of the graphite materials obtained in Example 1, Example 2 and Comparative Example 1 after compaction and rolling. DETAILED DESCRIPTION

[0048] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0049] This embodiment provides a method for preparing a graphite material, comprising the following steps:

[0050] Hydrophobic modification of SiO2 microspheres: using carboxylic acid to hydrophobically modify SiO2 microspheres to obtain modified SiO2 microspheres;

[0051] Granulation, mixing and granulating the modified SiO2 microspheres, the liquid coating agent and the graphite coke raw material powder to obtain a mixture;

[0052] Graphitization treatment: graphitizing graphite carbon to obtain graphite material.

[0053] Generally, silicon oxide pore-forming agents are crushed particles with irregular morphology, which easily agglomerate during mixing, resulting in uneven distribution. This application uses SiO2 microspheres, which have a relatively standard spherical morphology, a relatively uniform morphology, and a relatively concentrated particle size distribution, which helps reduce agglomeration. As a result, the graphite material formed after the SiO2 overflows has a larger specific surface area and longer pore length.

[0054] SiO2 microspheres, a liquid coating agent, and graphite coke raw material powder are mixed and heated to form granules. The granulated material is then graphitized in a graphitization furnace. At high temperatures, the SiO2 microspheres vaporize and overflow, leaving channels within the secondary particles. The SiO2 microspheres, evenly dispersed in the liquid coating agent, are evenly distributed across the surface of the graphite particles. During the graphitization heating process, as the SiO2 vaporizes and escapes, interconnected, evenly distributed channels are formed between the graphite particles. These evenly distributed, interconnected channels, with pore sizes ranging from 50 to 200 nm, effectively increase lithium ion migration channels and shorten lithium ion diffusion distances.

[0055] The silica added during the preparation process is evenly distributed on the surface of the primary particles. However, during the granulation process, the particles will adhere to each other, and silica will also exist inside the secondary particles formed. The evenly distributed silica will evaporate and escape during the graphitization process. During the escape process, different silica gases will gather and escape from a few holes. The overall shape is similar to that of a tree root, and channels are generated on the surface and inside the secondary particles: from the surface to the inside, the pore size of the channels decreases from large to small, the number of channels increases from small to large, and the internal channels are staggered. The spherical silica evenly distributed in the graphite can form an interconnected pore network inside the secondary particles. Compared with general pore-forming agents, the created pores are more conducive to the transmission of lithium ions.

[0056] In addition to improving rate performance, the pore network also reduces cyclic expansion of the material. During cycling, lithium ion insertion causes graphite expansion, and the internal pore network effectively mitigates this expansion. Silicon dioxide catalyzes graphite during the graphitization process, increasing its degree of graphitization and resulting in higher capacity. This increased degree of graphitization increases the electronic conduction of the graphite material, improving the conductivity of the graphite anode, reducing anode impedance, and improving kinetic performance.

[0057] In other optional embodiments of the present application, the SiO2 microspheres are obtained by modifying SiO2 obtained by hydrolysis of orthosilicate compounds.

[0058] In other optional embodiments of the present application, the average particle size of the SiO2 microspheres is 100-500 nm;

[0059] In other optional embodiments of the present application, the orthosilicate compound is at least one of methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, and butyl orthosilicate.

[0060] Nano-SiO2 microspheres are prepared by hydrolysis of orthosilicate compounds, which can directly prepare SiO2 microspheres with regular morphology, uniform particle size and high purity. Modification is beneficial to obtain good dispersibility and suspension in liquid coating agents, and SiO2 microspheres with a particle size of 100-500nm can be prepared by adjusting parameters, and pores with an average pore size of 50-200nm can be obtained.

[0061] In this application, since the SiO2 microspheres have a relatively standard spherical morphology, a relatively uniform morphology, and a relatively concentrated distribution of particle sizes, the particle size of the SiO2 microspheres and the pore size of the obtained graphite particle material can be one-to-one corresponded, that is, by adjusting the particle size of the SiO2 microspheres, the graphite particle material with the composite pore size requirements can be obtained.

[0062] In other optional embodiments of the present application, the modification is to hydrophobically modify the SiO2 microspheres using carboxylic acid.

[0063] Since the SiO2 microspheres obtained by hydrolysis have hydroxyl groups on their surfaces and have a certain degree of hydrophilicity, they are hydrophobically modified before being mixed with the liquid coating agent to further improve the dispersibility of the SiO2 microspheres in the liquid coating agent.

[0064] In other optional embodiments of the present application, the preparation method of the SiO2 microspheres is: mixing alcohol, water and ammonia water to obtain a mixed solution A, adding an orthosilicate compound to the mixed solution A to react, and obtaining SiO2 microspheres.

[0065] In other optional embodiments of the present application, the volume ratio of the alcohol, water, ammonia water and orthosilicate compound is 5-10:10-100:0.5-5:1-50.

[0066] In other optional embodiments of the present application, the alcohol in the mixed solution A is at least one of methanol, ethanol, and propanol.

[0067] In other optional embodiments of the present application, the orthosilicate compound is added dropwise to the mixed liquid A, and the mixed liquid A is stirred during the addition process, which helps to evenly disperse the generated SiO2 microspheres in the reaction liquid.

[0068] In other optional embodiments of the present application, the temperature for reacting the mixed solution A with the orthosilicate compound is 18-25° C., and the time is 4-20 hours.

[0069] In other optional embodiments of the present application, after the reaction is completed, the reaction liquid is subjected to solid-liquid separation, and the separated solid is washed and dried to obtain SiO2 microspheres;

[0070] In other optional embodiments of the present application, the washing is performed alternately using at least one of alcohol, water, and an aqueous solution of alcohol, or two or more thereof, and the washing is stopped after the filtrate is colorless;

[0071] In other optional embodiments of the present application, the drying is to dry the washed solid at 25-90° C. for 2-10 h.

[0072] In other optional embodiments of the present application, before the reaction solution is subjected to solid-liquid separation, carboxylic acid is added to the reaction solution to perform hydrophobic modification on the SiO2 microspheres;

[0073] Preferably, the carboxylic acid is formic acid or acetic acid;

[0074] Preferably, the mass ratio of the carboxylic acid to the orthosilicate compound is 1:(5-10).

[0075] The density of hydroxyl groups on the SiO2 surface obtained by the method of the present application is 5-10 / nm 2The hydroxyl groups on the surface of SiO2 are hydrophilic, and such materials cannot be dispersed in liquid asphalt. By adding carboxylic acid to the prepared SiO2 sample, ester bonds are generated with the hydroxyl groups. Due to the reduction of hydroxyl groups and the increase of ester bonds, the hydrophilicity of SIO2 decreases and the lipophilicity increases.

[0076] Formic acid or acetic acid is volatile. When using formic acid or acetic acid to modify the surface of SiO2 microspheres, even if the formic acid or acetic acid is excessive, it will not affect subsequent operations.

[0077] In other optional embodiments of the present application, the liquid coating agent includes at least one of liquid asphalt, liquid phenolic resin and liquid epoxy resin;

[0078] In other optional embodiments of the present application, the residual carbon content of the liquid coating agent is 5%-30%.

[0079] In other optional embodiments of the present application, the granulation is to mix SiO2 microspheres with a liquid coating agent to obtain a mixed coating agent, and then mix the mixed coating agent with graphite coke raw material powder and granulate to obtain a mixture.

[0080] In other optional embodiments of the present application, in the mixed coating agent, the mass ratio of SiO2 microspheres to asphalt is 1:(10-100). Below this ratio range, the pores generated by SiO2 cannot improve the performance of the material. Above this ratio, the pores in the graphite material become more and the adhesion of the mixed coating agent will be slightly reduced.

[0081] In other optional embodiments of the present application, in the mixture, the mass ratio of the mixed coating agent to the graphite coke raw material is (2-10): (90-100).

[0082] In other optional embodiments of the present application, the graphite coke raw material is green coke or cooked coke.

[0083] In other optional embodiments of the present application, the graphite coke raw material D50 is 5-10 μm.

[0084] In other optional embodiments of the present application, the granulation comprises:

[0085] Set the fusion machine thermal oil temperature to 100-300℃;

[0086] Add graphite coke raw materials into the fusion machine, adjust the fusion machine speed to 20-300rpm, and when the material temperature rises to 50-100℃, add the mixed coating agent;

[0087] Adjust the fusion machine speed to 200-500rpm. When the material temperature rises to 100-300℃, fuse for 10-60min to obtain a mixed material.

[0088] Set the heat transfer oil of the fusion machine at 100-300℃, add the mixed coating agent at the appropriate time, and stir at a specified speed so that the mixed coating agent can be evenly coated on the surface of the graphite coke raw material.

[0089] In other optional embodiments of the present application, the temperature of the graphitization treatment is 2800-3000°C.

[0090] In other optional embodiments of the present application, the graphitization treatment equipment is one of an internal string graphitization furnace, a box-type graphitization furnace, and an Acheson graphitization furnace.

[0091] The embodiment of the present application can also provide a graphite material obtained by the preparation method of the graphite material of any of the above embodiments, wherein the graphite material has pores and the specific surface area b of the graphite material is 6-16m 2 / g, the total length L of the duct is 1*10 7 -6*10 7 m / g, where L = b / 2πr, and r is the average pore size.

[0092] Preferably, the pores exist on the surface and inside of the graphite negative electrode material;

[0093] More preferably, the pores of the graphite negative electrode material decrease in diameter from the surface to the inside, and the number of pores increases from small to large.

[0094] Preferably, the average pore diameter is 50-200 nm.

[0095] The pore diameter of the graphite material obtained in this embodiment is 50-200 nm, and pores are generated on the surface and inside. Moreover, from the surface to the inside, the pore diameter of the pores changes from large to small, and the number changes from small to many. The overall shape is similar to a tree root, which is interconnected and relatively evenly distributed. It has a large specific surface area and a large pore length, which can greatly increase the lithium ion migration channel and shorten the lithium ion diffusion distance. The internal pore network also helps to alleviate the expansion of graphite caused by lithium ion embedding and improve the cycle performance.

[0096] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0097] Example 1

[0098] 1. Add 5ml of alcohol solution and 100ml of deionized water to container A, then slowly add 1.5ml of ammonia water to the above uniform dispersion, stir for 10min, then slowly add 2ml of orthosilicate compound, and stir at room temperature for 12h. After the reaction is completed, add 1ml of acetic acid to the reaction solution, stir evenly and react for 5min, then use alcohol solution and deionized water to rinse alternately under vacuum filtration, and alternately wash the components soluble in water or alcohol. After the solution is colorless, collect the product and dry the product in an oven at 65℃ for 6h to obtain SiO2 microspheres. Figure 1 shown.

[0099] 2. The obtained SiO2 microspheres were evenly mixed in a ratio of SiO2: asphalt (residual carbon 15%) = 1:50 to obtain mixed asphalt B. Granulation was carried out in a ratio of mixed asphalt B: green coke (D50 = 7.5 μm) = 5:95: After the green coke was added to the fusion machine, the heat transfer oil temperature was set to 280°C, and the temperature was first raised at a speed of 300 rpm to a material temperature of 80°C. Then, mixed asphalt B was added and the temperature was continued to be raised at a speed of 300 rpm to a material temperature of 150°C. The mixture was fused for 30 minutes, and then the heating was stopped and the material was discharged to obtain graphite C.

[0100] 3. The obtained graphite C is sent to a graphitization furnace for graphitization to obtain graphite material.

[0101] The pore diameter of the graphite material obtained in this embodiment is 50-200nm, and pores are generated on the surface and inside. From the surface to the inside, the pore diameter of the pores decreases from large to small, and the number increases from small to large. The overall shape is similar to a tree root, which is interconnected and relatively evenly distributed.

[0102] Example 2

[0103] Add 10ml of anhydrous ethanol and 100ml of deionized water to container A. Then slowly add 4ml of ammonia water dropwise to the above uniform dispersion and stir for 10 minutes. Then slowly add 10ml of ethyl orthosilicate dropwise and stir at room temperature for 12 hours. After the reaction is complete, add 1ml of acetic acid to the reaction solution, stir evenly, and react for 5 minutes. Then, rinse alternately with anhydrous ethanol and deionized water under vacuum filtration. After the solution becomes colorless, collect the product and dry it in an oven at 65°C for 6 hours to obtain SiO2 microspheres.

[0104] The obtained SiO2 microspheres were evenly mixed in a ratio of SiO2: asphalt (residual carbon 15%) = 1:50 to obtain mixed asphalt B. Granulation was performed in a ratio of mixed asphalt B: green coke (D50 = 7.5 μm) = 5:95: after the green coke was added to the fusion machine, the heat transfer oil temperature was set to 280°C, and the temperature was first raised at a speed of 300 rpm to a material temperature of 80°C. Then, mixed asphalt B was added and the temperature was continued to be raised at a speed of 300 rpm to a material temperature of 150°C. The mixture was fused for 30 minutes, and then the heating was stopped and the material was discharged to obtain graphite C.

[0105] The obtained graphite C is sent to a graphitization furnace for graphitization to obtain graphite material.

[0106] Example 3

[0107] Add 5ml of methanol and 100ml of deionized water to container A. Then, slowly add 1.5ml of ammonia water dropwise to the above uniform dispersion and stir for 10 minutes. Then, slowly add 2ml of propyl orthosilicate dropwise and stir at room temperature for 12 hours. After the reaction is complete, add 1ml of acetic acid to the reaction solution, stir evenly, and react for 5 minutes. Then, under vacuum filtration, alternately rinse with alcohol solution and deionized water. After the solution becomes colorless, collect the product and dry it in a 70°C oven for 6 hours to obtain SiO2 microspheres.

[0108] The obtained SiO2 microspheres were evenly mixed in a ratio of SiO2: asphalt (residual carbon 15%) = 1:30 to obtain mixed asphalt B. Granulation was performed in a ratio of mixed asphalt B: green coke (D50 = 7.5 μm) = 5:95: after the green coke was added to the fusion machine, the heat transfer oil temperature was set to 280°C, and the temperature was first raised at a speed of 300 rpm to a material temperature of 80°C. Then, mixed asphalt B was added and the temperature was continued to be raised at a speed of 300 rpm to a material temperature of 150°C. The mixture was fused for 30 minutes, and then the heating was stopped and the material was discharged to obtain graphite C.

[0109] The obtained graphite C is sent to a graphitization furnace for graphitization to obtain graphite material.

[0110] Example 4

[0111] 1. Add 5 ml of alcohol solution and 100 ml of deionized water to container A. Then slowly add 1.5 ml of ammonia water dropwise to the above uniform dispersion and stir for 10 minutes. Then slowly add 2 ml of orthosilicate compound dropwise and stir at room temperature for 12 hours. After the reaction is completed, add 1 ml of acetic acid to the reaction solution, stir evenly and react for 5 minutes. Then, rinse alternately with alcohol solution and deionized water under vacuum filtration. Collect the product after the solution becomes colorless and dry it in an oven at 65 ° C for 6 hours to obtain SiO2 microspheres.

[0112] 2. The obtained SiO2 microspheres were evenly mixed in a ratio of SiO2: asphalt (residual carbon 15%) = 1:70 to obtain mixed asphalt B. Granulation was carried out in a ratio of mixed asphalt B: green coke (D50 = 7.5 μm) = 5:95: After the green coke was added to the fusion machine, the heat transfer oil temperature was set to 280°C, and the temperature was first raised at a speed of 300 rpm to a material temperature of 80°C. Then, mixed asphalt B was added and the temperature was continued to be raised at a speed of 300 rpm to a material temperature of 150°C. The mixture was fused for 30 minutes, and then the heating was stopped and the material was discharged to obtain graphite C.

[0113] 3. The obtained graphite C is sent to a graphitization furnace for graphitization to obtain graphite material.

[0114] Example 5

[0115] 1. Add 10ml of alcohol solution and 100ml of deionized water to container A. Then slowly add 3ml of ammonia water dropwise to the above uniform dispersion and stir for 10 minutes. Then slowly add 10ml of orthosilicate compound dropwise and stir at room temperature for 12 hours. After the reaction is completed, add 1ml of acetic acid to the reaction solution, stir evenly and react for 5 minutes. Then, rinse alternately with alcohol solution and deionized water under vacuum filtration. Collect the product after the solution becomes colorless and dry it in an oven at 65°C for 6 hours to obtain SiO2 microspheres.

[0116] 2. The obtained SiO2 microspheres were evenly mixed in a ratio of SiO2: asphalt (residual carbon 15%) = 1:50 to obtain mixed asphalt B. Granulation was carried out in a ratio of mixed asphalt B: green coke (D50 = 7.5 μm) = 4:98: After the green coke was added to the fusion machine, the heat transfer oil temperature was set to 280°C, and the temperature was first raised at a speed of 300 rpm to a material temperature of 80°C. Then, mixed asphalt B was added and the temperature was continued to be raised at a speed of 300 rpm to a material temperature of 150°C. The mixture was fused for 30 minutes, and then the heating was stopped and the material was discharged to obtain graphite C.

[0117] 3. The obtained graphite C is sent to a graphitization furnace for graphitization to obtain graphite material.

[0118] Example 6

[0119] 1. Add 10ml of alcohol solution and 100ml of deionized water to container A. Then slowly add 3ml of ammonia water dropwise to the above uniform dispersion and stir for 10 minutes. Then slowly add 10ml of orthosilicate compound dropwise and stir at room temperature for 12 hours. After the reaction is completed, add 1ml of acetic acid to the reaction solution, stir evenly and react for 5 minutes. Then, rinse alternately with alcohol solution and deionized water under vacuum filtration. Collect the product after the solution becomes colorless and dry it in an oven at 65°C for 6 hours to obtain SiO2 microspheres.

[0120] 2. The obtained SiO2 microspheres were evenly mixed in a ratio of SiO2: asphalt (residual carbon 15%) = 1:50 to obtain mixed asphalt B. Granulation was carried out in a ratio of mixed asphalt B: green coke (D50 = 7.5 μm) = 10:90: After the green coke was added to the fusion machine, the heat transfer oil temperature was set to 280°C, and the temperature was first raised at a speed of 300 rpm to a material temperature of 80°C. Then, mixed asphalt B was added and the temperature was continued to be raised at a speed of 300 rpm to a material temperature of 150°C. The mixture was fused for 30 minutes, and then the heating was stopped and the material was discharged to obtain graphite C.

[0121] 3. The obtained graphite C is sent to a graphitization furnace for graphitization to obtain graphite material.

[0122] Example 7

[0123] Compared with Example 1, only the type of asphalt was changed, and the asphalt used was liquid asphalt with a residual carbon content of 10%.

[0124] Example 8

[0125] Compared with Example 1, only the type of asphalt was changed, that is, liquid asphalt with a residual carbon content of 25%.

[0126] Example 9

[0127] Compared with Example 2, only the particle size of the graphite coke raw material was changed, and the graphite coke raw material D50 was 9 μm.

[0128] Example 10

[0129] Compared with Example 1, only the particle size of the graphite coke raw material was changed, and the graphite coke raw material D50 was 6.5 μm.

[0130] Comparative Example 1

[0131] 1. Granulate according to the ratio of pitch (residual carbon 15%): cooked coke (D50=7.5μm)=5:95: After the cooked coke is put into the fusion machine, set the heat transfer oil temperature to 280℃, first heat it up to 80℃ at a speed of 300rpm, add pitch, continue to heat it up to 150℃ at a speed of 300rpm, fuse for 30min, stop heating and discharge the material to obtain graphite C.

[0132] 2. The obtained graphite C is sent to a graphitization furnace for graphitization to obtain the negative electrode graphite material.

[0133] Comparative Example 2

[0134] 1. Granulate according to the ratio of pitch (residual carbon 25%): cooked coke (D50=7.5μm)=5:95: After the cooked coke is put into the fusion machine, set the heat transfer oil temperature to 280℃, first heat it up to 80℃ at a speed of 300rpm, add pitch, continue to heat it up to 150℃ at a speed of 300rpm, fuse for 30min, stop heating and discharge the material to obtain graphite C.

[0135] 2. The obtained graphite C is sent to a graphitization furnace for graphitization to obtain the negative electrode graphite material.

[0136] Comparative Example 3

[0137] 1. Granulate according to the ratio of pitch (residual carbon 15%): cooked coke (D50=9μm)=5:95: After the cooked coke is put into the fusion machine, set the heat transfer oil temperature to 280℃, first heat it up to 80℃ at a speed of 300rpm, add pitch, continue to heat it up to 150℃ at a speed of 300rpm, fuse for 30min, stop heating and discharge the material to obtain graphite C.

[0138] 2. The obtained graphite C is sent to a graphitization furnace for graphitization to obtain the negative electrode graphite material.

[0139] Comparative Example 4

[0140] The SiO2 particles were ball-milled to a particle size similar to that of the SiO2 microspheres described in Example 1, approximately 150 nm, to obtain SiO2 powder;

[0141] The obtained SiO2 powder was evenly mixed in a ratio of SiO2: pitch (residual carbon 15%) = 1:50 to obtain mixed pitch B. Granulation was performed in a ratio of mixed pitch B: green coke (D50 = 7.5 μm) = 5:95: after the green coke was added to the fusion machine, the heat transfer oil temperature was set to 280°C, and the temperature was first raised at a speed of 300 rpm to a material temperature of 80°C. Then, mixed pitch B was added and the temperature was continued to be raised at a speed of 300 rpm to a material temperature of 150°C. The mixture was fused for 30 minutes, and then the heating was stopped and the material was discharged to obtain graphite C.

[0142] 3. The obtained graphite C is sent to a graphitization furnace for graphitization to obtain graphite material.

[0143] The present application studies the relationship between the average particle size of SiO2 microspheres and the average pore diameter r inside the graphite material, and obtains the following table, which shows that the average diameter of the pores inside the graphite material increases with the increase of the diameter of the SiO2 microspheres.

[0144]

[0145] The graphite negative electrode materials obtained in the above examples and comparative examples were tested, and the results are shown in the table below.

[0146] The testing method of the porous negative electrode graphite obtained in the above embodiment is as follows: particle size analysis is performed using a laser particle size analyzer, and the specific surface area test is performed using a nitrogen adsorption-desorption test (BET method); the rate discharge test is performed by assembling a button battery (CR2016) on an American Arbin instrument. The above testing methods are familiar to professional and technical engineers and will not be described in detail.

[0147] The data in the table show that the specific surface area of the graphite materials obtained in Examples 1-10 is 4-5 times greater than that in the comparative example, providing more Li + Diffusion channel, shortening the Li + Diffusion distance has a huge contribution to the improvement of the material's rate performance. Through the comparison between the embodiments, we can see that when the pore length L is similar, increasing the diameter of the SiO2 microspheres, expanding the pore diameter, and increasing the specific surface area can improve the negative electrode rate performance; with the increase in the proportion of SiO2 microspheres added, the rate performance of the graphite negative electrode has also increased significantly. By replacing different asphalts, the embodiment also has a significant improvement in rate performance compared to the control. By changing the aggregate particle size, the rate performance of the graphite negative electrode varies greatly, but all are better than the performance of the control. It can be seen that the graphite negative electrode with the addition of SiO2 microspheres has been significantly improved in rate performance.

[0148] In addition, the particle size of the original powder samples obtained in Example 1, Example 2 and Comparative Example 1 of the present application, the samples compacted at 2T, the original powder samples coated with the electrode sheet but not rolled, and the samples after rolling were measured. The specific sample preparation steps are as follows:

[0149] Weigh 1.0±0.05g of sample, place the sample in a metal sleeve, and maintain it under a pressure of 2T for 30s to obtain a 2T compacted sample;

[0150] The sample, CMC and SBR were mixed evenly in a ratio of 96.5:1.5:2. The mixed slurry was coated on the copper foil using a 200 μm coater on an automatic coating machine. The coated electrode was placed in a 95°C oven and dried for 0.5 h to obtain the coated but unrolled sample.

[0151] Adjust the roller spacing of the roller machine for the dried electrode to 60 μm. After rolling, the electrode compaction is 1.45 g / cc, and the coated rolled sample is obtained.

[0152] The particle size test results of the above samples are as follows Figure 2 As shown, there is no significant difference in the particle size changes between the embodiment and the comparative example, indicating that the amount of SiO2 microspheres added in this method is appropriate and the generated pores will not affect the bonding strength between the secondary graphite particles.

[0153] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a graphite material, characterized in that: The following steps are involved: Granulation, mixing SiO2 microspheres, a liquid coating agent and graphite coke raw material powder, and granulating to obtain a mixture; the SiO2 microspheres are obtained by modifying SiO2 obtained by hydrolyzing an orthosilicate compound, and the modification is to hydrophobically modify the SiO2 microspheres using carboxylic acid; Graphitization treatment: The mixed material is graphitized to obtain a graphite material, wherein the graphite material has pores and a specific surface area b of 6-13m 2 / g, the total length L of the duct is 1*10 7 -6*10 7 m / g, where L = b / 2πr, and r is the average pore size.

2. The method for preparing the graphite material according to claim 1, wherein The average particle size of the SiO2 microspheres is 100-500nm.

3. The method for preparing the graphite material according to claim 1, wherein The orthosilicate compound is at least one of methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, and butyl orthosilicate.

4. The method for preparing graphite material according to claim 1, wherein: The preparation method of the SiO2 microspheres comprises the following steps: mixing alcohol, water and ammonia water to obtain a mixed solution A, and adding an orthosilicate compound to the mixed solution A for reaction to obtain SiO2 microspheres.

5. The method for preparing the graphite material according to claim 4, wherein: The volume ratio of the alcohol, water, ammonia water and orthosilicate compound is 5-10:10-100:0.5-5:1-50.

6. The method for preparing the graphite material according to claim 4, wherein: The alcohol in the mixed solution A is at least one of methanol, ethanol and propanol.

7. The method for preparing a graphite material according to claim 4, wherein: The orthosilicate compound is added dropwise to the mixed solution A, and the mixed solution A is stirred during the adding process.

8. The method for preparing a graphite material according to claim 4, wherein: The temperature for reacting the mixed solution A with the orthosilicate compound is 18-25° C. and the time is 4-20 hours.

9. The method for preparing a graphite material according to claim 4, wherein: After the reaction is completed, the reaction liquid is subjected to solid-liquid separation, and the separated solid is washed and dried to obtain SiO2 microspheres.

10. The method for preparing a graphite material according to claim 9, wherein: The washing is performed by using at least one of alcohol, water and an aqueous solution of alcohol or two or more of them alternately.

11. The method for preparing a graphite material according to claim 9, wherein: The drying step is to dry the washed solid at 25-90° C. for 2-10 hours.

12. The method for preparing a graphite material according to claim 9, wherein: Before solid-liquid separation of the reaction liquid, carboxylic acid is added to the reaction liquid to perform hydrophobic modification on the SiO2 microspheres.

13. The method for preparing a graphite material according to claim 12, wherein: The carboxylic acid is formic acid or acetic acid.

14. The method for preparing a graphite material according to claim 12, wherein: The mass ratio of the carboxylic acid to the orthosilicate compound is 1:(5-10).

15. The method for preparing a graphite material according to claim 1, wherein: The liquid coating agent includes at least one of liquid asphalt, liquid phenolic resin and liquid epoxy resin.

16. The method for preparing a graphite material according to claim 15, wherein: The residual carbon content of the liquid coating agent is 5%-30%.

17. The method for preparing a graphite material according to claim 1, wherein: The granulation is to mix SiO2 microspheres with a liquid coating agent to obtain a mixed coating agent, and then mix the mixed coating agent with graphite coke raw material powder and granulate to obtain a mixture.

18. The method for preparing a graphite material according to claim 17, wherein: In the mixed coating agent, the mass ratio of SiO2 microspheres to asphalt is 1:(10-100).

19. The method for preparing a graphite material according to claim 17, wherein: In the mixture, the mass ratio of the mixed coating agent to the graphite coke raw material is (2-10): (90-100).

20. The method for preparing a graphite material according to claim 17, wherein: The graphite coke raw materials are green coke and cooked coke.

21. The method for preparing a graphite material according to claim 17, wherein: The graphite coke raw material D50 is 5-10 μm.

22. The method for preparing a graphite material according to claim 17, wherein: The granulation comprises: Set the fusion machine thermal oil temperature to 100-300℃; Add graphite coke raw materials into the fusion machine, adjust the fusion machine speed to 20-300rpm, and when the material temperature rises to 50-100℃, add the mixed coating agent; Adjust the fusion machine speed to 200-500rpm. When the material temperature rises to 100-300℃, fuse for 10-60min to obtain a mixed material.

23. The method for preparing a graphite material according to claim 1, wherein: The temperature of the graphitization treatment is 2800-3000°C.

24. The method for preparing a graphite material according to claim 1, wherein: The graphitization treatment equipment is one of an inner string graphitization furnace, a box-type graphitization furnace, and an Acheson graphitization furnace.

25. A graphite material obtained by the method for preparing a graphite material according to any one of claims 1 to 24, characterized in that: There are pores in the graphite material, and the specific surface area b of the graphite material is 6-13m 2 / g, the total length L of the duct is 1*10 7 -6*10 7 m / g, where L = b / 2πr, and r is the average pore size.

26. The graphite material according to claim 25, characterized in that The pores exist on the surface and inside of the graphite negative electrode material.

27. The graphite material according to claim 25, characterized in that The pores of the graphite negative electrode material decrease in diameter from the surface to the inside, and in number from small to large.

28. The graphite material according to claim 25, characterized in that The average pore diameter is 50-200 nm.

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