Graphite negative electrode material and its preparation method and application

Abstract

The present invention relates to the field of carbon materials and discloses a graphite negative electrode material and its preparation method and application. The graphite negative electrode material has the following characteristics: (1) the total pore volume of the graphite negative electrode material is ≤0.02cm 3 / g, the pore volume of micropores with a pore diameter of ≤2nm is ≥0.00001cm 3 / g, and the pore volume of mesopores with a pore diameter of 2-50 nm is 0.0001-0.02 cm 3 / g; (2) in the graphite negative electrode material, the ratio of the specific surface area of ​​micropores to the specific surface area of ​​mesopores is 0.01-100:1; (3) the specific surface area of ​​the graphite negative electrode material is ≤5m 2 / g. (4) The thermal diffusion coefficient of the graphite negative electrode material is ≥0.2mm 2 ·s ‑1 The graphite negative electrode material has a high thermal diffusion coefficient, and a battery containing the graphite negative electrode material has a high charge and discharge capacity, an initial coulombic efficiency, and an excellent rate performance, and the preparation method is simple and low in cost.

Description

Technical Field

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

[0002] Lithium-ion battery anodes are primarily composed of carbon materials, including amorphous carbon, natural graphite, and artificial graphite. Graphite, with its regular layered structure and excellent conductivity, boasts a theoretical specific capacity of 372 mA·h / g and high efficiency, making it the current mainstream anode material. Currently, three main types of raw materials are used in the development of artificial graphite: isotropic coke, asphalt glue, and needle coke. Isotropic coke-based artificial graphite has low crystallinity, high isotropy, low capacity, and high power efficiency. Needle coke-based artificial graphite has high capacity but relatively poor rate capability, while asphalt glue generally falls between the two.

[0003] CN104681786A discloses a coal-based negative electrode material, a preparation method, and a lithium-ion battery. The coal-based negative electrode material comprises a graphitized inner layer of the coal-based material, an intermediate layer, and an outer layer distributed on the surface. The preparation method includes pulverizing the coal-based material; adding a binder, or a mixture of a binder and a modifier; and then performing pressing and high-temperature graphitization to produce the finished product.

[0004] CN111232970A discloses a graphite negative electrode material, a lithium ion battery, a preparation method and an application. The preparation method comprises the following steps: subjecting a mixture of mesophase carbon microspheres, anthracite powder and a catalyst to a high temperature graphitization treatment; wherein the mass ratio of the mesophase carbon microspheres to the anthracite powder is 1:9-8:1; the particle size D of the anthracite powder is 1:9-8:1; 50 CN111628146A discloses a process for preparing lithium-ion battery negative electrode materials from asphalt-filled microcrystalline graphite. The process comprises: using microcrystalline graphite as the raw material, adding medium-low temperature coal tar and kneading to obtain modified microcrystalline graphite; then transferring the modified microcrystalline graphite into a reactor, adding liquid medium-temperature asphalt and mixing, raising the temperature to 350-500°C, evacuating the reactor, and allowing the mixture to stand for 1-3 hours. The reactor is then filled with inert gas, pressurized, and allowed to stand for 2-5 hours. After depressurization, the asphalt-filled microcrystalline graphite is obtained; and then the asphalt-filled microcrystalline graphite is subjected to sheeting, powdering, carbonization, screening, and demagnetization to obtain the target product.

[0005] The structure and process of the negative electrode materials provided by the above-mentioned prior art are complex and costly. Although the obtained negative electrode materials can improve the charge and discharge capacity and the first coulombic efficiency of the battery, the thermal conductivity of the above-mentioned negative electrode materials is low, resulting in the battery's service life and safety failing to meet actual needs. Summary of the Invention

[0006] The purpose of the present invention is to overcome the problems of complex structure, poor thermal conductivity, complex preparation process and high cost of negative electrode materials in the prior art, and to provide a graphite negative electrode material and its preparation method and application. The graphite negative electrode material has a high thermal diffusion coefficient, and a battery containing the graphite negative electrode material has a high charge and discharge capacity, first coulombic efficiency and excellent rate performance, and the preparation method is simple and low-cost.

[0007] In order to achieve the above object, the present invention provides a graphite negative electrode material, characterized in that the graphite negative electrode material has the following characteristics:

[0008] (1) The total pore volume of the graphite negative electrode material is ≤0.02cm 3 / g, micropore volume with pore diameter ≤ 2nm ≥ 0.00001cm 3 / g, the mesopore volume with a pore size of 2-50 nm is 0.0001-0.02 cm 3 / g;

[0009] (2) In the graphite negative electrode material, the ratio of the specific surface area of ​​micropores to the specific surface area of ​​mesopores is 0.01-100:1;

[0010] (3) The specific surface area of ​​the graphite negative electrode material is ≤5m 2 / g;

[0011] (4) The thermal diffusion coefficient of the powder of the graphite negative electrode material is ≥0.2 mm 2 ·s -1 .

[0012] A second aspect of the present invention provides a method for preparing a graphite negative electrode material, wherein the method comprises the following steps:

[0013] (1) crushing coal to obtain coal particles;

[0014] (2) graphitizing the coal particles to obtain a graphitized material;

[0015] (3) mixing the graphitized material with a modifier to obtain a mixture;

[0016] (4) The mixed material is subjected to two-stage carbonization to obtain the graphite negative electrode material;

[0017] The modifier is mesophase asphalt.

[0018] A third aspect of the present invention provides a graphite negative electrode material prepared by the above method.

[0019] A fourth aspect of the present invention provides an application of the above-mentioned graphite negative electrode material in at least one of a lithium-ion battery, a mechanical component material, and a thermally conductive material.

[0020] Through the above technical solution, the graphite negative electrode material provided by the present invention and its preparation method and application achieve the following beneficial effects:

[0021] (1) The graphite negative electrode material provided by the present invention has a small pore content, a dense structure, and a small grain size. In addition, the specific surface area provided by the micropores in the graphite negative electrode material is moderate, so that the graphite negative electrode material has a high charge and discharge capacity and a high thermal diffusion coefficient.

[0022] (2) The graphite negative electrode material provided by the present invention not only has excellent electrochemical properties, but also has a high thermal diffusion coefficient. Specifically: the charge and discharge capacity of the graphite negative electrode material is ≥350mAh / g, and the thermal diffusion coefficient is ≥0.2mm 2 ·s -1 , the first coulombic efficiency is ≥93%, and the 2C / 0.2C capacity retention rate is ≥45%.

[0023] (4) The method for preparing a graphite negative electrode material provided by the present invention significantly reduces the pore volume and specific surface area of ​​the graphite negative electrode material by performing a two-stage carbonization on a mixture of a modifier and a graphitized material, thereby improving the density of the negative electrode material and, at the same time, reducing the grain size, so that the prepared graphite negative electrode material has a high thermal diffusion coefficient, and improves the charge and discharge capacity, first coulomb efficiency, and rate performance of a lithium-ion battery containing the negative electrode material. In particular, the preparation method is low in cost, has strong process operability, and uses abundant and readily available raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a TEM image of the graphite negative electrode material prepared in Example 1. DETAILED DESCRIPTION

[0025] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0026] A first aspect of the present invention provides a graphite negative electrode material, characterized in that the graphite negative electrode material has the following characteristics:

[0027] (1) The total pore volume of the graphite negative electrode material is ≤0.02cm 3 / g, micropore volume with pore diameter ≤ 2nm ≥ 0.00001cm 3 / g, the mesopore volume with a pore size of 2-50 nm is 0.0001-0.02 cm 3 / g;

[0028] (2) In the graphite negative electrode material, the ratio of the specific surface area of ​​micropores to the specific surface area of ​​mesopores is 0.01-100:1;

[0029] (3) The specific surface area of ​​the graphite negative electrode material is ≤5m 2 / g;

[0030] (4) The thermal diffusion coefficient of the graphite negative electrode material is ≥0.2 mm 2 ·s -1 .

[0031] In the present invention, the graphite negative electrode material has a relatively small total pore volume and specific surface area. In particular, in the graphite negative electrode material, the specific surface area provided by the micropores accounts for a moderate proportion, thereby improving the structural density of the graphite negative electrode material. The modification of the modifier can reduce the grain size of the graphite negative electrode material, thereby making the graphite negative electrode material have a high thermal diffusion coefficient, and the battery containing the graphite negative electrode material has a high charge and discharge capacity.

[0032] In the present invention, the total pore volume, micropore volume, and mesopore volume of the graphite anode material were measured according to standard GB / T19587. The sample pretreatment conditions were: 350°C for 6 hours. The pore volume was calculated using the DFT model.

[0033] In the present invention, the specific surface area, the specific surface area of ​​the micropores and the specific surface area of ​​the mesopores of the graphite negative electrode material are measured using a nitrogen adsorption specific surface area method.

[0034] In the present invention, the thermal diffusion coefficient of the graphite negative electrode material powder is measured using an LFA467 flash thermal conductivity instrument manufactured by NETZSCH Group of Germany, using the flash method.

[0035] Furthermore, when the total pore volume of the graphite negative electrode material is 0.0001-0.02 cm 3 / g, the volume of micropores with a pore size of ≤2nm is 0.0001-0.001cm 3 / g, and the mesopore volume with a pore size of 2-50 nm is 0.0001-0.0115 cm 3 / g, the graphite negative electrode material has a more excellent thermal diffusion coefficient, and the battery containing the graphite negative electrode material has a higher charge and discharge capacity and a more excellent rate performance.

[0036] Furthermore, the total pore volume of the graphite negative electrode material is 0.0001-0.01 cm 3 / g, and the pore volume of micropores with a pore diameter of ≤2nm is 0.0001-0.001cm3 / g, and the pore volume of mesopores with a pore diameter of 2-50 nm is 0.0001-0.01 cm 3 / g.

[0037] Furthermore, in the graphite negative electrode material, the ratio of the specific surface area of ​​micropores to the specific surface area of ​​mesopores is 0.01-50:1, preferably 0.02-10:1, and more preferably 0.05-1:1.

[0038] Furthermore, the specific surface area of ​​the graphite negative electrode material is 0.1-5m 2 / g, preferably 0.5-3m 2 / g, more preferably 1-2.5m 2 / g.

[0039] According to the present invention, the specific surface area of ​​the micropores in the graphite negative electrode material is 0.01-2m 2 / g, preferably 0.05-1.5m 2 / g, more preferably 0.1-1m 2 / g.

[0040] According to the present invention, the specific surface area of ​​the mesopores in the graphite negative electrode material is 0.01-3m 2 / g, preferably 0.05-2m 2 / g, more preferably 0.5-1.5m 2 / g.

[0041] Furthermore, the thermal diffusion coefficient of the powder of the graphite negative electrode material is ≥0.9 mm 2 ·s -1 , preferably ≥1.0mm 2 ·s -1 .

[0042] According to the present invention, the graphite negative electrode material comprises a first phase carbon of coal-based graphite and a second phase carbon of amorphous carbon;

[0043] Part or all of the surface of the first phase carbon is covered with the second phase carbon;

[0044] Alternatively, the second phase carbon is dispersed in the first phase carbon.

[0045] In the present invention, the graphite negative electrode material has a two-phase carbon structure, specifically, including a first phase carbon of coal-based graphite and a second phase carbon of amorphous carbon, and part or all of the surface of the first phase carbon is covered by the second phase carbon or the second phase carbon is uniformly dispersed in the first phase carbon. Specifically, the TEM image of the graphite negative electrode material of the present invention is as follows: Figure 1 As shown by Figure 1It can be seen that the graphite negative electrode material of the present invention comprises a two-phase carbon structure of coal-based graphite and amorphous carbon. In the present invention, the graphite negative electrode material having this two-phase carbon structure has a dense structure, small grain size, low pore content, and a moderate specific surface area provided by the micropores. This gives the graphite negative electrode material a high thermal diffusivity and enables batteries containing this graphite negative electrode material to have excellent charge and discharge capacity, first coulombic efficiency, and rate performance.

[0046] According to the present invention, based on the total weight of the negative electrode material, the content of the first phase carbon is 70-99.9 wt %, and the content of the second phase carbon is 0.1-30 wt %.

[0047] In the present invention, the contents of the first phase carbon and the second phase carbon in the negative electrode material are calculated based on the feed amount of the raw materials and the residual carbon rate.

[0048] Further preferably, based on the total weight of the negative electrode material, the content of the first phase carbon is 80-99.9 wt %, and the content of the second phase carbon is 0.1-20 wt %.

[0049] A second aspect of the present invention provides a method for preparing a graphite negative electrode material, wherein the method comprises the following steps:

[0050] (1) crushing coal to obtain coal particles;

[0051] (2) graphitizing the coal particles to obtain a graphitized material;

[0052] (3) mixing the graphitized material with a modifier to obtain a mixture;

[0053] (4) performing two-stage carbonization on the mixture to obtain the graphite negative electrode material;

[0054] The modifier is mesophase asphalt.

[0055] In the present invention, in the process of preparing the graphite negative electrode material, after mixing the modifier with the graphitized material obtained by graphitizing coal, the obtained mixture is subjected to two-stage carbonization, which can significantly reduce the pore volume and specific surface area of ​​the graphite negative electrode material and improve the density of the negative electrode material. The modifier can generate some micropores while reducing the total pore volume. Some micropores become new active sites for lithium ion insertion and extraction, thereby significantly improving the charge and discharge capacity of the battery. At the same time, the graphite negative electrode material is prepared according to the above method, which can reduce the grain size while improving the density of the negative electrode material, so that the prepared graphite negative electrode material has a high thermal diffusion coefficient, and the charge and discharge capacity, first coulomb efficiency and rate performance of the lithium ion battery containing the negative electrode material are improved.

[0056] In the present invention, preferably, the mixture is carbonized in the first stage under slowly rising temperature conditions and in the second stage at high temperature, thereby enabling the modifier to better fill the pores of the first phase carbon and modify its surface, bonding particles with high surface energy together, reducing surface defects of the obtained negative electrode material, improving the structural density of the negative electrode material, and achieving regulation of the specific surface area content provided by the micropores in the negative electrode material, so that the specific surface area provided by the micropores in the negative electrode material is moderate, and the second stage carbonization enables the modifier to be converted into the second phase carbon of the graphite negative electrode material.

[0057] Specifically, the conditions for the second-stage carbonization include: heating the mixture to 200-600°C at a heating rate of 0.01-5°C / min and keeping it warm for 1-20 hours for the first stage carbonization, and then continuing to heat it to 800-1500°C and keeping it warm for 0.1-100 hours for the second stage carbonization.

[0058] Furthermore, the conditions for the second-stage carbonization include: heating the mixture to 300-600°C at a heating rate of 0.1-3°C / min and keeping it warm for 1-15 hours for the first stage carbonization, and then continuing to heat it to 900-1400°C and keeping it warm for 0.5-80 hours for the second stage carbonization.

[0059] Furthermore, the conditions for the second-stage carbonization include: heating the mixture to 300-500°C at a heating rate of 0.5-2.5°C / min and keeping it warm for 1-10 hours for the first stage carbonization, and then heating it to 1000-1300°C and keeping it warm for 1-50 hours for the second stage carbonization.

[0060] Furthermore, the present invention uses coal as raw material, and when the above method is used to prepare the negative electrode material, it can not only significantly reduce the preparation cost of the negative electrode material, but also achieve high value-added utilization and clean and efficient conversion of coal.

[0061] According to the present invention, the coal meets the following conditions: vitrinite reflectance ≥ 2; volatile matter ≤ 10wt%; ash content ≤ 15wt%.

[0062] In the present invention, coal that meets the above conditions is selected as a raw material for preparing a graphite negative electrode material, and a graphite negative electrode material with moderate crystallinity, graphitization degree, small grain size and high isotropy can be obtained, so that the graphite negative electrode material has a high thermal diffusion coefficient, and the battery containing the graphite negative electrode material has improved charge and discharge capacity, first coulomb efficiency and rate performance.

[0063] In the present invention, the vitrinite reflectance of the coal is measured using the national standard GB / T 6948 method, and the volatile matter content and ash content of the coal are both measured using the national standard GB / T 30732 method.

[0064] According to the present invention, the coal meets the following conditions: vitrinite reflectance ≥ 2.3; volatile matter ≤ 10wt%; ash content ≤ 10wt%.

[0065] In the present invention, conventional equipment in the art, such as a jet mill, can be used to pulverize the coal.

[0066] In the present invention, in step (1), the particle size D of the coal particles is 50 It is 1-100 μm, preferably 2-50 μm.

[0067] According to the present invention, in step (2), the graphitization conditions include: a graphitization temperature of 3000° C. or higher, and a graphitization time of 0.5-100 h.

[0068] According to the present invention, the graphitization conditions include: a graphitization temperature of 3000-3500° C., and a graphitization time of 1-80 h.

[0069] In the present invention, the graphitized material is modified using mesophase asphalt as a modifier, which can significantly reduce the pore volume and specific surface area of ​​the prepared graphite negative electrode material, improve the density of the graphite negative electrode material, and at the same time generate some active micropores, thereby increasing the thermal diffusion coefficient of the graphite negative electrode material and improving the charge and discharge capacity of the battery containing the graphite negative electrode material.

[0070] Furthermore, the mesophase content of the mesophase asphalt is 40 wt%, preferably 50-99 wt%.

[0071] According to the present invention, the mesophase pitch satisfies the following condition: the softening point of the mesophase pitch is ≥150°C.

[0072] In the present invention, the graphitized material is modified by using a mesophase pitch with a softening point of ≥150° C., which can further improve the thermal diffusion coefficient of the graphite negative electrode material and the electrochemical performance of the graphite negative electrode material.

[0073] Furthermore, the softening point of the mesophase pitch is 200-400°C.

[0074] According to the present invention, the usage ratio of the graphitized material to the modifier is 1-99.9:1.

[0075] In the present invention, when the amounts of the graphitized material and the modifier meet the above ranges, the structure of the resulting graphite negative electrode material can be made more uniform, thereby improving the thermal diffusivity of the graphite negative electrode material and the electrochemical performance of the battery containing the negative electrode material. The inventors have found that when the amount of the modifier is too high, the charge and discharge capacity of the battery containing the negative electrode material will be significantly reduced; when the amount of the modifier is too low, the pore structure of the negative electrode material will not be sufficiently reduced, the structural density will be reduced, and the thermal diffusivity and electrochemical performance of the negative electrode material will be reduced.

[0076] Furthermore, the usage ratio of the graphitized material to the modifier is 2-99:1, preferably 4-99:1.

[0077] A third aspect of the present invention provides a graphite negative electrode material obtained by the preparation method.

[0078] A fourth aspect of the present invention provides a use of the above-mentioned graphite negative electrode material in at least one of a lithium-ion battery, a mechanical component material, and a thermally conductive material.

[0079] In the present invention, the graphite negative electrode material has excellent thermal conductivity. Specifically, the thermal diffusion coefficient of the graphite negative electrode material is ≥0.2 mm 2 ·s -1 .

[0080] Furthermore, in the present invention, a lithium-ion battery containing the graphite negative electrode material has excellent electrochemical performance. Specifically, the lithium-ion battery containing the graphite negative electrode material of the present invention has a charge and discharge capacity of ≥350 mAh / g, an initial coulombic efficiency of ≥93%, and a 2C / 0.2C capacity retention rate of ≥45%.

[0081] The present invention will be described in detail below through examples.

[0082] (1) BET and pore volume

[0083] Pore ​​volume was measured using a Micromeritics 3flex N2 adsorption-desorption instrument. The test method was performed in accordance with the national standard GB / T19587. Sample pretreatment conditions were: 350°C for 6 hours. The pore volume was calculated using the DFT model.

[0084] (2) The vitrinite reflectance of coal was measured using the national standard GB / T 6948 method, and the volatile matter content and ash content of coal were measured using the national standard GB / T 30732 method.

[0085] (3) Softening point of modifier: The softening point of asphalt was tested by Mettler titration.

[0086] (4) Thermal diffusion coefficient of graphite negative electrode material

[0087] Thermal diffusivity was measured using the flash method using an LFA467 flash thermal conductivity instrument from the German NETZSCH Group. The specific test method involved weighing 100.5 grams of sample and using a powder sample preparation device to form a circular disc with a diameter of 12.7 mm and a thickness of 0.5 mm. The sample was then sealed in a sample cell between two metal sheets. The test conditions were: nitrogen at 20 mL / min, in an aluminum crucible with a punctured lid, and maintained at -5°C for 10 minutes, followed by a temperature increase of 10°C / min to 60°C.

[0088] (5) Battery performance

[0089] The charge and discharge capacity, first coulombic efficiency and rate performance of the battery were tested by using the battery test system CT2001A battery tester of Wuhan Blue Electric Electronics Co., Ltd., with a current of 0.1C (1C=350mAh / g) and a voltage range of 0-3V.

[0090] Example 1

[0091] (1) Coal (vitrinite reflectance 2.445; volatile matter 7.7 wt%; ash 2.6 wt%) was crushed by a mechanical crusher to obtain D 50 =10μm coal particles;

[0092] (2) graphitizing the coal particles at 3000°C for 25 hours to obtain a graphitized material;

[0093] (3) 92 parts of the graphitized material and 8 parts of the mesophase pitch (softening point of 300°C, mesophase content of 80 wt%) were mixed to obtain a mixture, wherein the mass ratio of the graphitized material to the modifier mesophase pitch was 11.5:1;

[0094] (4) Under inert gas, the mixture was heated to 500°C at a heating rate of 2°C / min and kept at that temperature for 2 h for the first stage of carbonization, and then continued to be heated to 1000°C at a heating rate of 5°C / min and kept at that temperature for 5 h for the second stage of carbonization. The mixture was sieved to obtain the graphite negative electrode material A1.

[0095] TEM image of graphite negative electrode material A1 Figure 1 As shown by Figure 1 It can be seen that the graphite negative electrode material A1 contains the first phase carbon of coal-based graphite obtained by graphitization of coal and the second phase carbon of amorphous carbon obtained from the intermediate phase asphalt. In the graphite negative electrode material A1, the content of the first phase carbon is 95wt%, and the content of the second phase carbon is 5wt%.

[0096] Example 2

[0097] (1) Coal (vitrinite reflectance 2.445; volatile matter 7.7 wt%; ash 2.6 wt%) was crushed by a mechanical crusher to obtain D 50 =10μm coal particles;

[0098] (2) graphitizing the coal particles at 3000°C for 25 hours to obtain a graphitized material;

[0099] (3) 97 parts of the graphitized material and 3 parts of coal-based mesophase pitch (softening point of 300° C., mesophase content of 80 wt%) were mixed to prepare a mixture, wherein the weight ratio of the graphitized material to the modifier coal-based mesophase pitch was 32.3:1;

[0100] (4) Under inert gas, the mixture was heated to 500°C at a rate of 2°C / min and kept at that temperature for 2 h for the first stage of carbonization, and then continued to be heated to 1000°C at a rate of 5°C / min and kept at that temperature for 5 h for the second stage of carbonization; and the graphite negative electrode material A2 was obtained by sieving.

[0101] In the graphite negative electrode material A2, the content of the first phase carbon is 98.2 wt %, and the content of the second phase carbon is 1.8 wt %.

[0102] Example 3

[0103] Negative electrode material A3 was prepared according to the method of Example 1, except that the amount of graphitized material was 83 parts and the amount of modifier was 17 parts, with a mass ratio of 4.88:1. This produced graphite negative electrode material A3. The first-phase carbon content in graphite negative electrode material A3 was 89.1 wt%, and the second-phase carbon content was 10.9 wt%.

[0104] Example 4

[0105] Negative electrode material A4 was prepared according to the method of Example 1, except that the amount of graphitized material was 65 parts and the amount of modifier was 35 parts, with a mass ratio of 1.86:1. Graphite negative electrode material A4 was obtained. The first-phase carbon content in graphite negative electrode material A4 was 75.6 wt%, and the second-phase carbon content was 24.4 wt%.

[0106] Example 5

[0107] The negative electrode material A5 was prepared according to the method of Example 1, except that: in step (4), under inert gas, the mixture was heated to 550°C at 3°C / min and kept warm for 5h to perform the first stage of carbonization; and the graphite negative electrode material A5 was obtained by sieving.

[0108] In the graphite negative electrode material A5, the content of the first phase carbon is 95 wt %, and the content of the second phase carbon is 5 wt %.

[0109] Example 6

[0110] Anode material A6 was prepared according to the method of Example 1, except that in step (4), the heating rate of the first carbonization stage was 4°C / min, to obtain graphite anode material A6. The graphite anode material A6 had a first-phase carbon content of 95 wt% and a second-phase carbon content of 5 wt%.

[0111] Comparative Example 1

[0112] Anode material D1 was prepared according to the method of Example 1, except that steps (3) and (4) were not performed, to obtain anode material D1. In graphite anode material D1, the content of first phase carbon was 100 wt%, and the content of second phase carbon was 0 wt%.

[0113] Comparative Example 2

[0114] Negative electrode material D2 was prepared according to the method of Example 1, except that oxidized pitch with a softening point of 180°C was used instead of mesophase pitch. The resulting negative electrode material D2 had a first-phase carbon content of 95.4 wt% and a second-phase carbon content of 4.6 wt%.

[0115] Comparative Example 3

[0116] A negative electrode material was prepared according to the method of Example 1, except that the coal and the modifier were directly mixed and graphitized to obtain negative electrode material D3. In graphite negative electrode material D3, the modifier was completely graphitized, and the content of the second phase carbon in graphite negative electrode material D3 was 0 wt%.

[0117] The graphite negative electrode materials obtained in the examples and comparative examples were characterized, and the results are shown in Table 1.

[0118] Table 1

[0119]

[0120] V1 refers to the total pore volume of the graphite negative electrode material; V2 refers to the micropore volume of the graphite negative electrode material; V3 refers to the mesopore volume of the graphite negative electrode material; BET-1 is the specific surface area of ​​the graphite negative electrode material; BET-2 is the specific surface area of ​​the micropores of the graphite negative electrode material; BET-3 is the specific surface area of ​​the mesopores of the graphite negative electrode material.

[0121] Test Case

[0122] The negative electrode materials prepared in the examples and comparative examples were mixed with conductive carbon black Super P and binder polyvinylidene fluoride (PVDF) in a mass ratio of 92:3:5. N-methylpyrrolidone (NMP) was added as a solvent and stirred to form a uniform negative electrode slurry. The negative electrode slurry was evenly coated on aluminum foil with a scraper and dried to obtain a negative electrode sheet. After cutting, the sheet was transferred to an MBraun 2000 glove box (Ar atmosphere, H2O and O2 concentrations less than 0.1×10 -6 Volume %), with a metal lithium sheet as the reference electrode, a button cell was assembled. The charge and discharge capacity, initial coulombic efficiency, and rate performance of the button cell were tested. The test results are shown in Table 2.

[0123] Table 2

[0124]

[0125] It can be seen from the results in Table 1 and Table 2 that the graphite negative electrode material prepared in the embodiment of the present invention has a small total pore volume and specific surface area, the material structure is highly dense, and the grain size of the material is moderately reduced by modification with a modifier, thereby generating partially active micropores, thereby making the graphite negative electrode material have a high thermal diffusion coefficient, and the battery containing the graphite negative electrode material has a high charge and discharge capacity and high rate performance.

[0126] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A graphite negative electrode material, characterized in that The graphite negative electrode material has the following characteristics: (1) The total pore volume of the graphite negative electrode material is ≤0.02 cm³ / g, the pore volume of micropores with a pore diameter of ≤2 nm is ≥0.00001 cm³ / g, and the pore volume of mesopores with a pore diameter of 2-50 nm is 0.0001-0.02 cm³ / g; (2) In the graphite negative electrode material, the ratio of the specific surface area of ​​micropores to the specific surface area of ​​mesopores is 0.23-0.46:1; (3) The specific surface area of ​​the graphite negative electrode material is 0.1-2.02m 2 / g; (4) The thermal diffusion coefficient of the graphite negative electrode material is ≥0.2 mm 2 ·s -1 ; In the graphite negative electrode material, the specific surface area of ​​the micropores is 0.01-2m 2 / g; The graphite negative electrode material comprises a first phase carbon of coal-based graphite and a second phase carbon of amorphous carbon obtained from mesophase pitch; Part or all of the surface of the first phase carbon is covered with the second phase carbon; Alternatively, the second phase carbon is dispersed in the first phase carbon; Based on the total weight of the negative electrode material, the content of the first phase carbon is 70-99.9wt%, and the content of the second phase carbon is 0.1-30wt%; The method for preparing the graphite negative electrode material comprises the following steps: (1) Grinding coal to obtain coal particles; (2) graphitizing the coal particles to obtain a graphitized material; (3) mixing the graphitized material and the modifier to obtain a mixture; (4) performing a two-stage carbonization on the mixture to obtain the graphite negative electrode material; The modifier is mesophase asphalt; The coal meets the following conditions: vitrinite reflectance ≥ 2; volatile matter ≤ 10wt%; ash content ≤ 15wt%; In step (4), the conditions for the second-stage carbonization include: heating the mixture to 200-600°C at a heating rate of 0.01-5°C / min and keeping it warm for 1-20 hours for the first-stage carbonization, and then continuing to heat it to 800-1500°C and keeping it warm for 0.1-100 hours for the second-stage carbonization.

2. The graphite negative electrode material according to claim 1, wherein The total pore volume of the graphite negative electrode material is 0.0001-0.02 cm³ / g, the pore volume of micropores with a pore diameter of ≤2 nm is 0.0001-0.001 cm³ / g, and the pore volume of mesopores with a pore diameter of 2-50 nm is 0.0001-0.0115 cm³ / g.

3. The graphite negative electrode material according to claim 1 or 2, wherein The total pore volume of the graphite negative electrode material is 0.0001-0.01 cm³ / g, the pore volume of micropores with a pore diameter of ≤2 nm is 0.0001-0.001 cm³ / g, and the pore volume of mesopores with a pore diameter of 2-50 nm is 0.0001-0.01 cm³ / g.

4. The graphite negative electrode material according to claim 1, wherein The specific surface area of ​​the graphite negative electrode material is 1-2.02m 2 / g.

5. The graphite negative electrode material according to claim 1, wherein In the graphite negative electrode material, the specific surface area of ​​the micropores is 0.05-1.5m 2 / g.

6. The graphite negative electrode material according to claim 1, wherein In the graphite negative electrode material, the specific surface area of ​​the micropores is 0.1-1 m 2 / g.

7. The graphite negative electrode material according to claim 1, wherein In the graphite negative electrode material, the specific surface area of ​​the mesopores is 0.01-3m 2 / g.

8. The graphite negative electrode material according to claim 1, wherein In the graphite negative electrode material, the specific surface area of ​​the mesopores is 0.05-2m 2 / g.

9. The graphite negative electrode material according to claim 1, wherein In the graphite negative electrode material, the specific surface area of ​​the mesopores is 0.5-1.5 m 2 / g.

10. The graphite negative electrode material according to claim 1, wherein The thermal diffusion coefficient of the graphite negative electrode material is ≥0.9 mm 2 ·s -1 .

11. The graphite negative electrode material according to claim 1, wherein The thermal diffusion coefficient of the graphite negative electrode material is ≥1 mm 2 ·s -1 .

12. The graphite negative electrode material according to claim 1, wherein Based on the total weight of the graphite negative electrode material, the content of the first phase carbon is 80-99.9 wt %, and the content of the second phase carbon is 0.1-20 wt %.

13. A method for preparing the graphite negative electrode material according to any one of claims 1 to 12, wherein: The method comprises the following steps: (1) Crushing coal to obtain coal particles; (2) graphitizing the coal particles to obtain a graphitized material; (3) mixing the graphitized material and the modifier to obtain a mixture; (4) performing a two-stage carbonization on the mixture to obtain the graphite negative electrode material; The modifier is mesophase asphalt; The coal meets the following conditions: vitrinite reflectance ≥ 2; volatile matter ≤ 10wt%; ash content ≤ 15wt%; In step (4), the conditions for the second-stage carbonization include: heating the mixture to 200-600°C at a heating rate of 0.01-5°C / min and keeping it warm for 1-20 hours for the first-stage carbonization, and then continuing to heat it to 800-1500°C and keeping it warm for 0.1-100 hours for the second-stage carbonization.

14. The method according to claim 13, wherein The coal meets the following conditions: vitrinite reflectance ≥ 2.3; volatile matter ≤ 10 wt%; ash content ≤ 10 wt%.

15. The method according to claim 13 or 14, wherein: In step (2), the graphitization conditions include: graphitization temperature is above 3000°C, and graphitization time is 0.5-100h.

16. The method according to claim 13 or 14, wherein: In step (2), the graphitization conditions include: graphitization temperature of 3000-3500°C, and graphitization time of 1-80h.

17. The method according to claim 13 or 14, wherein: The mesophase asphalt meets the following conditions: the softening point of the mesophase asphalt is ≥150°C.

18. The method according to claim 13, wherein The mesophase pitch meets the following conditions: the softening point of the mesophase pitch is 200-400°C.

19. The method according to claim 13, wherein The mass ratio of the graphitized material to the modifier is 1-99.9:

1.

20. The method according to claim 13, wherein The mass ratio of the graphitized material to the modifier is 2-99:

1.

21. The method according to claim 13, wherein The mass ratio of the graphitized material to the modifier is 4-99:

1.

22. The method according to claim 13, wherein The mixture is heated to 300-600° C. at a heating rate of 0.1-3° C. / min and kept warm for 1-15 hours for the first stage of carbonization, and then further heated to 900-1400° C. and kept warm for 0.5-80 hours for the second stage of carbonization.

23. The method according to claim 13, wherein The mixture is heated to 300-500° C. at a heating rate of 0.5-2.5° C. / min and kept warm for 1-10 hours for a first stage of carbonization, and then heated to 1000-1300° C. and kept warm for 1-50 hours for a second stage of carbonization.

24. Use of the graphite negative electrode material according to any one of claims 1 to 12 in at least one of a lithium ion battery, a mechanical component material, and a thermal conductive material.

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