Preparation method of graphite and graphite

Abstract

The invention discloses a preparation method of graphite and graphite, belongs to the technical field of graphite, and overcomes the defects of multiple tests, complicated process and high cost for determining a process route in the prior art. The preparation method of the graphite comprises the following steps: S1, measuring a chromatic value of a raw material extraction liquid; s2, modifying agents with different mass ratios are added into the raw materials according to the chromatic values, then modification treatment is carried out, and when the mass ratio of the modifying agents to the mass ratio of the raw materials is 0-12%, modification treatment is not carried out; and S3, graphitizing. The additive amount of the modifier in the technological process can be judged from the raw material end, the trial and error cost of the technology is reduced, and the graphite negative electrode with high magnification and good fast charge can be rapidly obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of graphite, and in particular relates to a method for preparing graphite and graphite. Background Art

[0002] Lithium-ion batteries are widely used in new energy and other fields due to their high energy density and excellent cycle performance. Graphite, as the negative electrode material of lithium-ion batteries, currently has a very mature application market. However, with the fast-paced lifestyle of modern society, the battery industry has gradually increased its requirements for fast charging performance. The tight lattice arrangement and small interlayer spacing of graphite limit the migration channel of lithium ions, which hinders the improvement of fast charging performance. Therefore, graphite materials need to be modified in different ways.

[0003] Among them, modifying and heat treating the graphite precursor, i.e., raw materials such as petroleum coke, is an effective way to improve the fast charging performance of graphite. For raw materials of different properties, in order to improve the rate performance of graphite, multiple tests are required to determine the final method, which is complicated and costly. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art that multiple experiments are required to determine the process route for improving the rate performance of graphite, the process is complicated and the cost is high, thereby providing a method for preparing graphite and graphite.

[0005] Before graphitization, a modifier is added for low-temperature heat treatment to wrap and bond the raw material particles together to form secondary particles, which can improve the fast charging performance of graphite negative electrode materials. There are some substances inside the raw materials, which will escape to the surface of the particles under high-temperature treatment. The structural conversion mechanism of the substances that escape to the surface at the coking temperature is similar to that of the modifier. At a coking temperature greater than 500°C, a layer of disordered carbon structure will be formed. This part of the structure has a small crystal size formed in the subsequent graphitization process, and the interlayer spacing is larger than that of graphite, which is conducive to improving the transmission speed of lithium ions, thereby improving the fast charging performance of the negative electrode material. This part of the substance is dissolved, and the concentration of this part of the substance inside the raw material is quantified by the color value, and then the amount of modifier added is determined according to the size of the color value, so as to determine the process route for graphite preparation. Without multiple experiments, a graphite negative electrode material with good high-rate fast charging can be prepared.

[0006] To this end, the present invention provides the following technical solutions.

[0007] The present invention provides a method for preparing graphite, comprising the following steps:

[0008] S1. Determine the chromaticity value of the raw material extract;

[0009] S2. According to the chromaticity value, different mass ratios of modifiers are added to the raw materials, and then modification treatment is performed, wherein the mass ratio of modifier to raw material is 0-12%. When the mass ratio of modifier to raw material is 0%, no modification treatment is performed;

[0010] S3. Graphitization.

[0011] Furthermore, the preparation method of the graphite comprises the following steps: determining the A value of the raw material, where the A value is the chromaticity value of the extract obtained by mixing the raw material and the extraction solvent at a solid-liquid ratio of 1g:10ml, filtering and extracting; the chromaticity value of the extract is tested according to the method in "HJ 1182-2021";

[0012] When A≥5×10 4 When the raw material is directly graphitized;

[0013] When 0.5×10 4 <A<5×10 4 When the raw material is mixed with a modifier for modification, the raw material is graphitized, wherein 1%≤modifier mass / raw material mass≤4%;

[0014] When A≤0.5×10 4 When the raw material is mixed with a modifier for modification, the raw material is graphitized, wherein 4% < modifier mass / raw material mass ≤ 12%.

[0015] When A≥5×10 4 When the material is treated with high temperature, it means that there are enough substances similar to the modifier inside the raw material. During high temperature treatment, these substances will escape and bond the raw materials together, achieving self-bonding of the raw materials, forming secondary particles, and achieving self-modification effect. No additional modifier is needed. If additional modifier is added at this time, the material will be severely agglomerated, the particle size will be too large, and subsequent processing and application will be affected.

[0016] 0.5×10 4 <A<5×10 4 It means that there is a certain amount of substances similar to the modifier inside the raw material, and the raw material can also form secondary particles, but because there are too few such substances, the structure of the formed secondary particles is unstable. Therefore, a small amount of modifier needs to be added at this time to form stable secondary particles, and the particle size of the secondary particles can be controlled at the same time by controlling the amount of the added binder.

[0017] A≤0.5×10 4 This indicates that there are few substances similar to the modifier in the raw material, and the raw material tends to form single particles. The content of the modifier needs to be increased to achieve the modification effect, and the particle size of the secondary particles can be controlled at the same time by controlling the amount of the added binder.

[0018] Furthermore, the modification treatment includes two-stage heating: stirring at 280℃~400℃ for 2~3h, and then heating to 550℃~600℃ for 2~3h. Stirring at 280℃~400℃ dissolves the modifier and mixes it evenly with the raw material; stirring at 550℃~600℃, the modifier eliminates volatiles at this temperature and begins to coke to form a disordered carbon structure, thereby improving the fast charging performance of the negative electrode material.

[0019] Further, the raw material is green coke. Optionally, the raw material is at least one of petroleum coke, needle coke and asphalt coke; preferably, the raw material contains at least one of petroleum coke or asphalt coke.

[0020] Furthermore, the D50 of the raw material is 1 to 100 μm.

[0021] Furthermore, the volatile matter of the raw material is less than 14%. The volatile matter test of the raw material refers to "SHT0026-1990-Method for Determination of Volatile Matter of Petroleum Coke".

[0022] Further, the modifier is a binder; preferably, the modifier includes a high molecular polymer;

[0023] More preferably, the modifier includes at least one of asphalt, petroleum resin, biomass resin, phenolic resin, epoxy resin, polyvinyl pyrrolidone (PVP), polyacrylamide (PAM), polyacrylic acid (PAA), polycaprolactone (PCL), polyvinyl alcohol (PVA), and polyethylene glycol (PEG).

[0024] Furthermore, the method for determining the A value of the raw material includes: drying and grinding the raw material, adding it to an extraction solvent for extraction, with a solid-liquid ratio of 1g:10mL, filtering, and testing the obtained extract with reference to "HJ 1182-2021".

[0025] Furthermore, after grinding, the product is sieved through a 200-325 mesh sieve, and the product under the sieve is added to the extraction solvent.

[0026] Furthermore, the extraction solvent is a polar solvent; optionally, the polarity of the extraction solvent is 4.0 to 4.5.

[0027] Furthermore, the extraction solvent is at least one of chloroform, ethyl acetate and tetrahydrofuran.

[0028] Furthermore, the graphitization condition is to keep the temperature at 2900-3100° C. for 2-4 hours.

[0029] The present invention also provides graphite prepared by the above preparation method.

[0030] The technical solution of the present invention has the following advantages:

[0031] 1. The preparation method of graphite of the present invention comprises the following steps: S1, measuring the chromaticity value of the raw material extract; S2, adding modifiers of different mass ratios to the raw material according to the size of the chromaticity value, and then performing modification treatment, wherein the mass of the modifier / the mass of the raw material is 0-12%, and when the mass of the modifier / the mass of the raw material is 0%, no modification treatment is performed; S3, graphitization.

[0032] By first testing the chromaticity value of the raw material extract and then regulating the subsequent process based on the chromaticity value of the raw material extract, it is possible to judge the process from the raw material end, reduce the trial and error cost of the process, and quickly obtain a graphite negative electrode with good high-rate fast charging performance.

[0033] 2. The preparation method of graphite of the present invention comprises: determining the A value of the raw material; the A value is the chromaticity value of the extract obtained by extracting the raw material and the extraction solvent at a solid-liquid ratio of 1g:10ml; the chromaticity value of the extract is tested according to the method in "HJ 1182-2021"; when A≥5×10 4 When 0.5×10 4 <A<5×10 4 When the raw material is mixed with the modifier and modified, the graphitization is performed, wherein 1%≤modifier mass / raw material mass≤4%; when A≤0.5×10 4 When the raw material is mixed with a modifier for modification, the raw material is graphitized, wherein 4% < modifier mass / raw material mass ≤ 12%.

[0034] The process can be quickly judged by the A value of the raw material, the dosage of the modifier can be adjusted, and the content of the modifying substance in the system can be balanced while avoiding the increase of material cost and serious agglomeration of materials caused by excessive addition of modifier, excessive particle size, poor modification effect, affecting subsequent processing and application, and increasing the difficulty of process processing.

[0035] 3. The modification treatment in the preparation method of graphite of the present invention includes two-stage heating, which can slow down the reaction process of the modifier to eliminate volatiles and coke, avoid heating too quickly and causing the modifier to coke before being evenly mixed, affecting the modification effect, causing the modifier to coke alone and agglomerate together, unable to be evenly dispersed on the surface of the masterbatch, and at the same time avoid the particle size after modification cannot be controlled, and fail to achieve the expected particle size result. DETAILED DESCRIPTION

[0036] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0037] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0038] The method for preparing graphite comprises the following steps:

[0039] Determine the A value of the raw material. The A value is the chromaticity of the extract obtained after the raw material and the extraction solvent are mixed at a solid-liquid ratio of 1g:10ml and filtered;

[0040] When A≥5×10 4 When the raw material is directly graphitized;

[0041] When 0.5×10 4 <A<5×10 4 When the raw material and the modifier are mixed and heated and stirred, graphitization is performed, wherein 1%≤modifier mass / raw material mass≤4%;

[0042] When A≤0.5×10 4 When the raw material is mixed with the modifier and heated and stirred, graphitization is performed, wherein 4% < modifier mass / raw material mass ≤ 12%.

[0043] The test method of the raw material A value in Examples 1-6 is as follows: the raw coke is dried at 105°C for 3 hours, ground through a 200-mesh sieve, 10 g of the sieve material is added to 100 mL of tetrahydrofuran solvent, ultrasonically extracted for 1 hour, and filtered to obtain an extract.

[0044] Refer to "HJ 1182-2021" to test the chromaticity value of the extract. The specific test process is: take 10mL of the extract in a 100mL volumetric flask, add tetrahydrofuran (when other solvents are used for extraction, the dilution solvent and the control colorimetric solvent here are consistent with the extraction solvent) and dilute to the scale line. After mixing, take 50mL of the dilution and 50mL of tetrahydrofuran and add them to 50mL colorimetric tubes respectively. Place the colorimetric tube vertically on a piece of white paper, observe the liquid column vertically downward, and compare the colors of the dilution and tetrahydrofuran. If there is still a color difference, continue to repeat the above steps to dilute until the color of the dilution and tetrahydrofuran cannot be distinguished. Record the number of dilutions n. Take the dilution n-1 times in the previous step, dilute step by step according to the dilution multiples of 2, 3...9, and observe each time using the above method until it cannot be distinguished from tetrahydrofuran. Record the dilution multiple D1 at this time. The chromaticity value is expressed as the dilution multiple, chromaticity = D1×10 (n-1) .

[0045] D50: The particle size corresponding to when the cumulative particle size distribution percentage of the sample reaches 50%. According to the provisions of GB / T19077-2016, the particle size D50 is tested by Malvern laser particle size analyzer.

[0046] Volatile matter: The mass loss after moisture correction in the presence of air in a sealed container under specified conditions is the volatile matter. Refer to "SHT0026-1990-Determination of Volatile Matter in Petroleum Coke" for testing.

[0047] Sulfur content: refers to the total sulfur content of all sulfur-containing organic and inorganic compounds in coke; tested using a sulfur meter and coulometric titration method.

[0048] The A values ​​of Examples 1-6 are shown in Table 1.

[0049] Table 1 Raw material parameters and A values ​​of Examples 1-6

[0050]

[0051]

[0052] Example 1

[0053] The present embodiment provides a method for preparing graphite, comprising: powdering and shaping the petroleum coke in sequence, adding 10% of the mass of petroleum coke asphalt, stirring at 400°C for 2 hours, then heating to 550°C and maintaining for 3 hours, and graphitizing at 3090°C for 2 hours to obtain a graphite product.

[0054] Example 2

[0055] The present embodiment provides a method for preparing graphite, comprising: powdering and shaping the petroleum coke in sequence, adding 6% asphalt by mass of the petroleum coke, stirring at 280°C for 3 hours, then heating to 600°C for 2 hours, and graphitizing at 3000°C for 2 hours to obtain a graphite product.

[0056] Example 3

[0057] The present embodiment provides a method for preparing graphite, comprising: powdering and shaping the petroleum coke in sequence, adding 4% asphalt by mass of the petroleum coke, stirring at 400°C for 2 hours, then heating to 550°C and maintaining for 3 hours, and graphitizing at 2900°C for 4 hours to obtain a graphite product.

[0058] Example 4

[0059] The present embodiment provides a method for preparing graphite, comprising: powdering and shaping the petroleum coke in sequence, adding 2% asphalt of the petroleum coke quality, stirring at 280°C for 2 hours, then heating to 600°C for 3 hours, and graphitizing at 2950°C for 2 hours to obtain a graphite product.

[0060] Example 5

[0061] The present embodiment provides a method for preparing graphite, comprising: sequentially pulverizing and shaping the petroleum coke, and graphitizing the petroleum coke at 3090° C. for 2 hours to obtain a graphite product.

[0062] Example 6

[0063] The present embodiment provides a method for preparing graphite, comprising: powdering and shaping the asphalt coke in sequence, adding 4% asphalt by mass of petroleum coke, stirring at 400°C for 2 hours, then heating to 550°C and maintaining for 3 hours, and graphitizing at 3090°C for 2 hours to obtain a graphite product.

[0064] Example 7

[0065] The present embodiment provides a method for preparing graphite, comprising: using the same raw materials as those in Example 2 to perform powdering and shaping in sequence, adding phenolic resin with a mass percentage of 6% by mass of petroleum coke, stirring at 350° C. for 2 h, then heating to 550° C. and maintaining the temperature for 3 h, and graphitizing at 3090° C. for 2 h to obtain a graphite product.

[0066] Example 8

[0067] This embodiment provides a method for preparing graphite. The raw materials and process are basically the same as those in Example 1, except that after adding 10% of asphalt, the mixture is kept at 550°C for 5 hours and graphitized at 3090°C for 2 hours to obtain a graphite product.

[0068] Comparative Example 1

[0069] This comparative example provides a method for preparing graphite, comprising: using the same raw material petroleum coke as in Example 1 to perform pulverization and shaping in sequence, adding 2% asphalt by mass of the petroleum coke, stirring at 400°C for 2 hours, then heating to 550°C and maintaining for 3 hours, and graphitizing at 3090°C for 2 hours to obtain a graphite product.

[0070] Comparative Example 2

[0071] This comparative example provides a method for preparing graphite, comprising: using the same raw material petroleum coke as in Example 4 to successively perform pulverization and shaping, and graphitizing at 2950° C. for 2 hours to obtain a graphite product.

[0072] Test example

[0073] The graphites obtained in Examples 1-8 and Comparative Examples 1-2 were made into negative electrode sheets, which were then assembled into batteries to verify their electrochemical properties.

[0074] Graphitization degree: Graphitization degree is an indicator to measure the degree to which carbon atoms form a close-packed hexagonal graphite crystal structure. Use XRD to test the 004 interplanar spacing d 004 , calculated according to the following formula: Graphitization degree = (3.440-d 004×2) / (3.440-3.354)×100%.

[0075] The specific method of making graphite into batteries is: mix graphite with SBR (styrene-butadiene rubber), CMC (sodium carboxymethyl cellulose), and SP (conductive carbon black) in a mass ratio of 95.5:2:1.5:1, apply it on copper foil, and prepare it into pole pieces through drying and rolling, and assemble it into button batteries with metal lithium sheets.

[0076] The specific method of electrochemical performance test is: 0.1C constant current charge and discharge, under the condition of charge and discharge voltage of 0.05~2.0V, test the first charge and discharge capacity and the first coulomb efficiency (first charge capacity / first discharge capacity) of the button battery; the rate performance is the ratio of the capacity under 3C and 0.5C currents.

[0077] Table 2 Parameters and electrochemical performance test results of graphite of Examples 1-8 and Comparative Examples 1-2

[0078]

[0079] As shown in Table 1, by testing the A value of the raw material, Examples 1-8 adjust the amount of the modifier added according to the A value, balance the content of the modifying substance in the system, and the obtained graphite products can all obtain good fast charging performance. As shown in Examples 1 and 8, the use of two-stage heating after adding the modifier can further improve the rate performance of the graphite product.

[0080] Comparative Example 1-2 did not make corresponding process adjustments according to the A value, and too little modifier was added. Although the capacity and initial efficiency of the obtained graphitized product were slightly improved, the rate performance was significantly reduced. From the above, it can be seen that by testing the A value of the raw material and making corresponding process adjustments, the fast charging performance of the modified graphitized product can be significantly improved.

[0081] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A method for preparing graphite, It is characterized in that The following steps are involved: S1. Determine the chromaticity value of the raw material extract; S2. According to the chromaticity value, different mass ratios of modifiers are added to the raw materials, and then modification treatment is performed, wherein the mass ratio of modifier to raw material is 0-12%. When the mass ratio of modifier to raw material is 0%, no modification treatment is performed; S3. Graphitization.

2. The method for preparing graphite according to claim 1, It is characterized in that The following steps are involved: S1. Determine the A value of the raw material; the A value is the chromaticity value of the extract obtained by extracting the raw material and the extraction solvent at a solid-liquid ratio of 1g:10ml; the chromaticity value of the extract is tested according to the method in "HJ 1182-2021"; S2, when A≥5×10 4 When the raw materials are not modified; When 0.5×10 4 <A<5×10 4 When the raw material is mixed with a modifier for modification, 1%≤modifier mass / raw material mass≤4%; When A≤0.5×10 4 When the raw material is mixed with a modifier for modification, 4% < modifier mass / raw material mass ≤ 12%; S3. Graphitization.

3. The method for preparing graphite according to claim 1 or 2, It is characterized in that The modification treatment includes two-stage heating: stirring treatment at 280°C to 400°C for 2 to 3 hours, and then heating to 550°C to 600°C and stirring treatment for 2 to 3 hours.

4. The method for preparing graphite according to claim 1 or 2, It is characterized in that The raw material is raw coke; Optionally, the raw material is at least one of petroleum coke, needle coke, and pitch coke; Optionally, the D50 of the raw material is 1 to 100 μm.

5. The method for preparing graphite according to claim 1 or 2, It is characterized in that The volatile matter of the raw material is less than 14%.

6. The method for preparing graphite according to claim 1 or 2, It is characterized in that The modifier is a binder; Preferably, the modifier comprises a high molecular polymer; More preferably, the modifier includes at least one of asphalt, petroleum resin, biomass resin, phenolic resin, epoxy resin, polyvinyl pyrrolidone, polyacrylamide, polyacrylic acid, polycaprolactone, polyvinyl alcohol, and polyethylene glycol.

7. A method for preparing graphite according to any one of claims 2 to 6, It is characterized in that When determining the A value of the raw material, the raw material is first ground and then sieved through a 200-325 mesh sieve to obtain the sieve undersize, and then mixed with the extraction solvent.

8. A method for preparing graphite according to any one of claims 2 to 6, It is characterized in that The extraction solvent is a polar solvent; Preferably, the extraction solvent is at least one of chloroform, ethyl acetate and tetrahydrofuran.

9. A method for preparing graphite according to any one of claims 1 to 6, It is characterized in that The graphitization conditions are to keep the temperature at 2900-3100°C for 2-4 hours.

10. A graphite, It is characterized in that The graphite is prepared by the preparation method described in any one of claims 1 to 9.

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