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; (2) in the graphite negative electrode material, the ratio of the pore volume of micropores with a pore diameter of ≤2 nm to the total pore volume of the graphite negative electrode material is ≥30%; and (3) the surface silicon content of the graphite negative electrode material is 0.27-1wt%. The graphite negative electrode material has a dense structure, a low pore volume, and a high pore volume content provided by the micropores in the graphite negative electrode material. A battery containing the negative electrode material has high charge and discharge capacity, first coulombic efficiency, and excellent fast charging capability, 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 mixing a binder and a modifier; and then performing pressing and high-temperature graphitization to form a finished product. The coal-based negative electrode material has a stable graphite structure, good surface compatibility with the electrolyte, and exhibits high specific capacity, high conductivity, high rate capability, excellent liquid absorption, and cycling performance.

[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 10-20μm.

[0005] CN111628146A discloses a process for preparing lithium-ion battery negative electrode materials using asphalt-filled microcrystalline graphite. The process comprises: using microcrystalline graphite as raw material, adding medium-low temperature coal tar and kneading the mixture to obtain modified microcrystalline graphite; transferring the modified microcrystalline graphite into a reactor, adding liquid medium-temperature asphalt and mixing the mixture; heating the mixture to 350-500°C, evacuating the mixture, and allowing the mixture to stand for 1-3 hours; then filling the reaction vessel with an inert gas, pressurizing the reaction vessel, and allowing the mixture to stand for 2-5 hours; and releasing the pressure to obtain asphalt-filled microcrystalline graphite; and then subjecting the asphalt-filled microcrystalline graphite to sheeting, powdering, carbonization, screening, and demagnetization to obtain the target product.

[0006] The structure and process of the negative electrode materials provided by the above-mentioned prior art are complex and the cost is high. Although the prepared negative electrode materials can improve the charge and discharge capacity and the first coulombic efficiency of the battery, the fast charging capability of the battery is insufficient, which greatly limits the application of the negative electrode materials. Summary of the Invention

[0007] The purpose of the present invention is to overcome the problems of insufficient fast charging capacity, complex structure, 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 structure of the graphite negative electrode material is dense, the pore volume in the graphite negative electrode material is low, and the pore volume content provided by the micropores in the graphite negative electrode material is high. The battery containing the negative electrode material has high charge and discharge capacity and first coulomb efficiency and excellent fast charging capability, and the preparation method is simple and low in cost.

[0008] In order to achieve the above object, the first aspect of the present invention provides a graphite negative electrode material, characterized in that the graphite negative electrode material has the following characteristics:

[0009] (1) The total pore volume of the graphite negative electrode material is ≤0.02cm 3 / g;

[0010] (2) In the graphite negative electrode material, the ratio of the pore volume of micropores with a pore diameter of ≤2 nm to the total pore volume of the graphite negative electrode material is ≥30%;

[0011] (3) The surface silicon content of the graphite negative electrode material is 0.27-1 wt%.

[0012] A second aspect of the present invention provides a method for preparing a graphite negative electrode material, characterized in that 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) Under heating and stirring conditions, the graphitized material, the first modifier and the second modifier are mixed and modified to obtain the graphite negative electrode material.

[0016] A third aspect of the present invention provides a graphite negative electrode material prepared by the above method.

[0017] A fourth aspect of the present invention provides a use of the above-mentioned graphite negative electrode material in at least one of a secondary battery, a mechanical component material, and a heat storage material.

[0018] 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:

[0019] (1) The graphite negative electrode material provided by the present invention has a dense structure, high isotropy, and small grain size. The pore volume in the graphite negative electrode material is small, and the pore volume content provided by the micropores in the graphite negative electrode material is high, so that the battery containing the graphite negative electrode material has a high charge and discharge capacity and excellent fast charging performance.

[0020] (2) Batteries containing the graphite negative electrode material provided by the present invention not only have high charge and discharge capacity and initial coulombic efficiency, but also have excellent fast charging performance. Specifically, the graphite negative electrode material has a charge and discharge capacity of ≥340 mAh / g, an initial coulombic efficiency of ≥94%, a 2C / 0.1C capacity retention rate of ≥170 mAh / g, and a 10C / 1C constant current charge capacity ratio of ≥66%.

[0021] (3) In the preparation method of the graphite negative electrode material provided by the present invention, under heating and stirring conditions, the first modifier and the second modifier are used to graphitize the coal to obtain a graphitized material for modification. The composite modification of the graphitized material using the two modifiers can complement each other and act synergistically. The composite modifier can better fill the pores of the first phase carbon than the single modifier, increase the proportion of micropores, and reduce the total pore volume to a greater extent. The graphite negative electrode material thus prepared is used in batteries, which can not only improve the battery's charge and discharge capacity and first coulomb efficiency, but also significantly improve the battery's fast charging capability. In addition, the preparation method provided by the present invention has the characteristics of low cost, strong process operability, and abundant and easily available raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a scanning electron microscope image of a slice of the graphite negative electrode material provided in Example 1. DETAILED DESCRIPTION

[0023] 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.

[0024] 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:

[0025] (1) The total pore volume of the graphite negative electrode material is ≤0.02cm 3 / g;

[0026] (2) In the graphite negative electrode material, the ratio of the pore volume of micropores with a pore diameter of ≤2 nm to the total pore volume of the graphite negative electrode material is ≥30%;

[0027] (3) The surface silicon content of the graphite negative electrode material is 0.27-1 wt%.

[0028] In the present invention, the graphite negative electrode material has a dense structure, high isotropy, and small grain size. In particular, the graphite negative electrode material has a low pore volume, and the proportion of the pore volume provided by micropores in the total pore volume of the graphite negative electrode material is relatively high, thereby enabling the battery containing the graphite negative electrode material to have a high charge and discharge capacity, first coulombic efficiency, and excellent fast charging performance.

[0029] In the present invention, the total pore volume and micropore volume of the negative electrode material are measured using a nitrogen adsorption specific surface area method.

[0030] In the present invention, the surface silicon content of the graphite negative electrode material is tested by X-ray photoelectron spectroscopy (XPS) using a Thermo Scientific MULTILAB 2000 photoelectron spectrometer.

[0031] Furthermore, when the total pore volume of the negative electrode material is 0.0001-0.02 cm 3 / g, preferably 0.0001-0.01cm 3 / g, the secondary battery containing the graphite negative electrode material has higher charge and discharge capacity and first coulomb efficiency, and has excellent fast charging capability.

[0032] Furthermore, when the ratio of the pore volume of micropores with a pore size ≤ 2 nm in the graphite negative electrode material to the total pore volume of the graphite negative electrode material is 50-100%, preferably 60-100%, the secondary battery containing the graphite negative electrode material has higher charge and discharge capacity and first coulombic efficiency, and has excellent fast charging capability.

[0033] According to the present invention, the specific surface area of ​​the graphite negative electrode material is ≤5m 2 / g, preferably 0.1-4m 2 / g, more preferably 1-3m 2 / g.

[0034] In the present invention, the specific surface area of ​​the graphite negative electrode material is measured using a nitrogen adsorption specific surface area method.

[0035] According to the present invention, the surface silicon content of the graphite negative electrode material is 0.28-1.5 wt%, preferably 0.30-1 wt%.

[0036] According to the present invention, Figure 1 As shown, Figure 1 This is a scanning electron microscope slice of the graphite negative electrode material of the present invention, Figure 1It can be seen that the graphite negative electrode material contains the first phase carbon of coal-based graphite and the second phase carbon of amorphous carbon.

[0037] According to the present invention, based on the total weight of the graphite negative electrode material, the content of the first phase carbon is 70-99 wt %, and the content of the second phase carbon is 1-30 wt %.

[0038] 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.

[0039] In the present invention, the crystallite size L in the c-axis direction of the graphite negative electrode material obtained by XRD is c and the crystallite size L in the a-axis direction a The following conditions are met:

[0040] 25nm≤L c ≤70nm, preferably 30nm≤L c ≤50nm;

[0041] 40nm≤L a ≤100nm, preferably 55nm≤L a ≤85nm;

[0042] The graphitization degree of the graphite negative electrode material satisfies the following condition: 85≤graphitization degree≤93, preferably 86≤graphitization degree≤90.

[0043] In the present invention, the graphite negative electrode material having the above-mentioned microstructural characteristics has high isotropy and small grain size, thereby further improving the fast charging performance of the battery containing the graphite negative electrode material.

[0044] In the present invention, the graphitization degree G of the negative electrode material is calculated according to the following formula:

[0045] G=(0.344-d 002 ) / (0.344-0.3354), where d 002 Calculated using the Bragg equation.

[0046] A second aspect of the present invention provides a method for preparing a graphite negative electrode material, characterized in that the method comprises the following steps:

[0047] (1) crushing coal to obtain coal particles;

[0048] (2) graphitizing the coal particles to obtain a graphitized material;

[0049] (3) Under heating and stirring conditions, the graphitized material, the first modifier and the second modifier are mixed and modified to obtain the graphite negative electrode material.

[0050] In the present invention, in the process of preparing the graphite negative electrode material, under heating and stirring conditions, the first modifier and the second modifier are used to jointly modify the graphitized material obtained by graphitizing coal. The two modifiers can complement and act synergistically with each other. Compared with a single modifier, the composite modifier can better fill the pores of the first phase carbon, increase the proportion of micropores in the prepared graphite negative electrode material, and reduce the total pore volume to a greater extent. As a result, the secondary battery containing the negative electrode material not only has a high charge and discharge capacity and first coulomb efficiency, but more importantly, has excellent fast charging capability.

[0051] 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.

[0052] According to the present invention, the coal meets the following conditions: vitrinite reflectance ≥ 2; volatile matter ≤ 10wt%; ash content ≤ 15wt%.

[0053] In the present invention, coal that meets the above conditions is selected as raw material for preparing graphite negative electrode material, and a graphite negative electrode material with a dense structure and small grain size can be obtained, so that the battery containing the graphite negative electrode material not only has a high charge and discharge capacity and first coulomb efficiency, but also has excellent fast charging capability.

[0054] 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.

[0055] According to the present invention, the coal meets the following conditions: vitrinite reflectance ≥ 2.3; volatile matter ≤ 10wt%; ash content ≤ 10wt%.

[0056] In the present invention, conventional equipment in the art, such as a jet mill, can be used to pulverize the coal.

[0057] 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.

[0058] According to the present invention, in step (2), the graphitization conditions include: controlling the actual maximum power transmission of the transformer in the graphitization equipment to be ≥5,000 kW, and the continuous power transmission time of the actual maximum power transmission is 0.5-100 hours.

[0059] In the present invention, the graphitization equipment can be a graphitization equipment commonly used in the art. Specifically, the graphitization equipment can be selected from at least one of an Acheson furnace, a box furnace, an inner string furnace, a vertical graphitization furnace, and a horizontal graphitization furnace.

[0060] Furthermore, the graphitization conditions include: controlling the actual maximum power transmission of the transformer in the graphitization equipment to be 5,000-50,000 kW, and the continuous power transmission time of the actual maximum power transmission is 10-80 hours.

[0061] According to the present invention, in step (3), the first modifier is selected from mesophase asphalt; the second modifier is selected from at least one of petroleum asphalt, coal asphalt, oxidized asphalt and high molecular polymer.

[0062] In the present invention, mesophase asphalt is used as the first modifier and cooperated with at least one of petroleum asphalt, coal asphalt, oxidized asphalt and high molecular polymer as the second modifier to jointly modify the graphitized material, thereby obtaining a graphite negative electrode material with a dense structure, a high proportion of micropore volume in the total pore volume and a small grain size, so that the battery containing the graphite negative electrode material not only has a high charge and discharge capacity and first coulomb efficiency, but also has excellent fast charging capability.

[0063] According to the present invention, the first modifier satisfies the following conditions: the softening point of the first modifier is ≥150°C; the mesophase content of the first modifier is ≥40wt%; the second modifier satisfies the following conditions: the softening point of the second modifier is ≥100°C.

[0064] In the present invention, the first modifier and the second modifier having the above-mentioned characteristics are used in combination to modify the graphitized material, which can further improve the charge and discharge performance, first coulomb efficiency and fast charging capability of the graphite negative electrode material.

[0065] Furthermore, the first modifier satisfies the following conditions: the softening point of the first modifier is 200-400°C; the mesophase content of the first modifier is 50-100wt%; the second modifier satisfies the following conditions: the softening point of the second modifier is 150-400°C.

[0066] According to the present invention, the amount of the graphitized material is 30-99.9wt%, the total amount of the first modifier and the second modifier is 0.1-30wt%, and the amount ratio of the first modifier to the second modifier is 0.1-10:1.

[0067] In the present invention, when the amounts of graphitized material and modifier meet the above-mentioned ranges, a graphite negative electrode material with a dense structure, a high proportion of micropore volume in the total pore volume and a small grain size can be obtained, so that the battery containing the graphite negative electrode material not only has a high charge and discharge capacity and first coulombic efficiency, but also has excellent fast charging capability.

[0068] Furthermore, the amount of the graphitized material is 20-99 wt %, the total amount of the first modifier and the second modifier is 1-20 wt %, and the amount ratio of the first modifier to the second modifier is 0.2-5:1.

[0069] According to the present invention, in step (3), the heating conditions include: heating to 400-1200° C. at a heating rate of 0.1-5° C. / min. The stirring conditions include: rotating speed of 50-3000 r / min and mixing time of 0.1-100 h.

[0070] In the present invention, under the above-mentioned slow heating conditions, the graphitized material, the first modifier and the second modifier are stirred and mixed, which can ensure that the first modifier and the second modifier are fully filled into the pores of the graphitized material, thereby making the surface modification of the first phase carbon by the modifier more uniform, thereby making the battery containing the graphite negative electrode material not only have a high charge and discharge capacity and first coulomb efficiency, but also have excellent fast charging capability.

[0071] Furthermore, the heating conditions include: heating the temperature to 400-1000° C. at a heating rate of 0.2-3° C. / min. The stirring conditions include: rotating speed of 50-1000 r / min and mixing time of 0.5-50 h.

[0072] Furthermore, the heating conditions include: heating the temperature to 500-800° C. at a heating rate of 0.5-2.5° C. / min. The stirring conditions include: rotating speed of 100-800 r / min and mixing time of 1-10 h.

[0073] According to the present invention, the method further comprises the following steps:

[0074] (3-1) mixing and modifying the graphitized material, the first modifier, and the second modifier under heating and stirring conditions to obtain an intermediate;

[0075] (3-2) Carbonizing the intermediate to obtain the graphitized negative electrode material.

[0076] In the present invention, preferably, the intermediate obtained by mixing and modifying the first modifier, the second modifier and the graphitized material is further carbonized, thereby further reducing the grain size of the negative electrode material, improving the structural density of the negative electrode material and the proportion of the pore volume of micropores in the total pore volume, thereby improving the charge and discharge capacity and the first coulombic efficiency of the battery containing the graphite negative electrode material, and having excellent fast charging capability.

[0077] According to the present invention, the carbonization conditions include: a carbonization temperature of 800-1500° C. and a carbonization time of 0.1-100 h.

[0078] Furthermore, the carbonization conditions include: a carbonization temperature of 900-1400° C., preferably 1000-1300° C.; and a carbonization time of 0.5-80 h, preferably 1-50 h.

[0079] A third aspect of the present invention provides a graphite negative electrode material obtained by the preparation method.

[0080] A fourth aspect of the present invention provides a use of the above-mentioned graphite negative electrode material in at least one of a secondary battery, a mechanical component material, and a heat storage material.

[0081] 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 ≥340 mAh / g, an initial coulombic efficiency of ≥94%, a 2C / 0.2C capacity retention rate of ≥50%, and a 10C / 1C constant current charge capacity ratio of ≥66%.

[0082] The present invention will be described in detail below through examples.

[0083] (1) Particle size (D 50 )

[0084] D50 was obtained by testing with the MalvernMastersizer 2000 laser particle size analyzer from Malvern Instruments Ltd., UK;

[0085] (2) BET and pore volume

[0086] 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.

[0087] (3) Surface silicon content:

[0088] X-ray photoelectron spectroscopy (XPS) was performed using a Thermo Scientific MULTILAB2000 photoelectron spectrometer.

[0089] (4) The morphology of the graphite negative electrode material was characterized by SEM.

[0090] (5) XRD analysis

[0091] The interlayer spacing d of the negative electrode material 002 、L a 、L c All were tested and analyzed by a D8Advance X-ray diffractometer from Bruker AXS GmbH, Germany; calibration was performed using the silicon internal standard method. 002 The value is calculated by the Bragg formula, L a 、L c Calculated by Scherrer formula;

[0092] (6) Graphitization degree G

[0093] The graphitization degree G of the negative electrode material is calculated according to the following formula:

[0094] G=(0.344-d 002 ) / (0.344-0.3354), where d 002 Calculated using the Bragg equation.

[0095] (7) 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.

[0096] (8) Softening point of modifier

[0097] The softening point of the modifier was tested by titration using Mettler.

[0098] (9) Mesophase content of mesophase asphalt

[0099] Measured using the national standard GB / T38396-2019 method.

[0100] (10) Battery performance

[0101] a. The charge and discharge capacity, initial coulombic efficiency and rate performance of the battery were tested using the 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.

[0102] b. Prepare a soft-pack battery by matching the negative electrode sheet with the ternary positive electrode. Use the Xinwei battery tester to measure the 1C and 10C constant current charging capacities in the voltage range of 2.5-4.2V, and calculate the 10C / 1C constant current charging capacity ratio.

[0103] Example 1

[0104] (1) Coal (vitrinite reflectance 2.445; volatile matter 7.7 wt%; ash 2.6 wt%) was pulverized by a jet mill to obtain coal particles with a D50 of 10 μm;

[0105] (2) graphitizing the coal particles in a graphitization furnace, wherein the actual maximum power transmission of the transformer in the graphitization furnace is 20,000 kW and the actual maximum power transmission time is 22 hours, to obtain a graphitized material;

[0106] (3-1) adding a graphitized material, a first modifier which is mesophase pitch (softening point of 240°C, mesophase content of 70 wt%), and a second modifier which is petroleum asphalt (softening point of 260°C) in a mass ratio of 92:5:5 to a high-temperature coating machine with stirring, heating the mixture to 700°C at a heating rate of 2°C / min, heating the mixture while stirring, and maintaining the temperature in the high-temperature coating machine for 5 h under stirring (rotation speed of 180 rpm) to obtain an intermediate;

[0107] (3-2) The intermediate was carbonized at 1000°C for 2 h in an inert atmosphere and sieved to obtain graphite negative electrode material A1.

[0108] SEM images of graphite negative electrode material A1 are shown in the following figure: Figure 1 As shown, from Figure 1 It can be seen that the surface of the first phase carbon coal-based graphite is evenly covered with a layer of second phase carbon of amorphous carbon, and the material structure is dense.

[0109] In the graphite negative electrode material A1, the content of the first phase carbon is 94.1 wt %, and the content of the second phase carbon is 5.9 wt %.

[0110] Example 2

[0111] (1) Coal (vitrinite reflectance 2.445; volatile matter 7.7 wt%; ash 2.6 wt%) was pulverized by a jet mill to obtain coal particles with a D50 of 10 μm;

[0112] (2) graphitizing the coal particles in a graphitization furnace, wherein the actual maximum power transmission of the transformer in the graphitization furnace is 20,000 kW and the actual maximum power transmission time is 22 hours, to obtain a graphitized material;

[0113] (3-1) adding a graphitized material, a first modifier which is mesophase pitch (softening point of 240°C, mesophase content of 70 wt%), and a second modifier which is petroleum asphalt (softening point of 260°C) in a mass ratio of 97:1:2 to a high-temperature coating machine with stirring, heating the mixture to 700°C at a heating rate of 2°C / min, heating the mixture while stirring, and maintaining the temperature in the high-temperature coating machine for 5 h under stirring (rotation speed of 180 rpm) to obtain an intermediate;

[0114] (3-2) The intermediate is carbonized at 1000°C for 2 h in an inert atmosphere and sieved to obtain graphite negative electrode material A2.

[0115] In the graphite negative electrode material A2, the content of the first phase carbon is 98.3 wt %, and the content of the second phase carbon is 1.7 wt %.

[0116] Example 3

[0117] Graphite negative electrode material A3 was prepared according to the method of Example 1, except that in step (3-1), the ratio of the graphitizing material, the first modifier, and the second modifier was 82:10:8. Graphite negative electrode material A3 was obtained. The first phase carbon content in graphite negative electrode material A3 was 88.7 wt%, and the second phase carbon content was 11.3 wt%.

[0118] Example 4

[0119] Graphite negative electrode material A4 was prepared according to the method of Example 1, except that in step (3-1), the ratio of the graphitizing material, the first modifier, and the second modifier was 70:15:15. Graphite negative electrode material A4 was obtained. The first phase carbon content in graphite negative electrode material A4 was 80.2 wt %, and the second phase carbon content was 19.8 wt %.

[0120] Example 5

[0121] Graphite negative electrode material A5 was prepared according to the method of Example 1, except that a mesophase pitch with a softening point of 330°C and a mesophase content of 90 wt% was used instead of the mesophase pitch with a softening point of 240°C and a mesophase content of 70 wt% in Example 1. Graphite negative electrode material A5 had a first-phase carbon content of 93.6 wt%, and a second-phase carbon content of 6.4 wt%.

[0122] Example 6

[0123] Graphite negative electrode material A6 was prepared according to the method of Example 1, except that petroleum pitch with a softening point of 160°C was used instead of the petroleum pitch with a softening point of 260°C in Example 1. Graphite negative electrode material A6 had a first-phase carbon content of 94.4 wt %, and a second-phase carbon content of 5.6 wt %.

[0124] Example 7

[0125] Graphite negative electrode material A7 was prepared according to the method of Example 1, except that in step (3-1), the temperature was raised to 550°C at a heating rate of 2°C / min with stirring, and the temperature was maintained in a high-temperature coating machine with stirring (rotation speed of 180 rpm) for 8 hours to obtain an intermediate, thereby obtaining graphite negative electrode material A7. The content of first-phase carbon in graphite negative electrode material A7 was 94.1 wt%, and the content of second-phase carbon was 5.9 wt%.

[0126] Example 8

[0127] Graphite negative electrode material A8 was prepared according to the method of Example 1, except that in step (3-1), the temperature was increased to 700°C at a rate of 4°C / min, the temperature was increased while stirring, and the temperature was maintained in a high-temperature coating machine for 5 hours with stirring (at a speed of 180 rpm) to obtain an intermediate, thereby obtaining graphite negative electrode material A8. The first phase carbon content of graphite negative electrode material A8 was 94.1 wt%, and the second phase carbon content was 5.9 wt%.

[0128] Example 9

[0129] Negative electrode material A9 was prepared according to the method of Example 1, except that in step (3-1), the temperature was raised to 300°C at a heating rate of 2°C / min with stirring, and the temperature was maintained in a high-temperature coating machine with stirring (rotation speed of 180 rpm) for 10 hours to obtain an intermediate, namely, graphite negative electrode material A9. The graphite negative electrode material A9 had a first-phase carbon content of 94.1 wt %, and a second-phase carbon content of 5.9 wt %.

[0130] Example 10

[0131] Graphite negative electrode material A10 was prepared according to the method of Example 1, except that in step (3-1), the temperature was raised to 700°C at a heating rate of 2°C / min while stirring, and the temperature was maintained in a high-temperature coating machine for 5 hours while stirring (at a speed of 300 rpm) to obtain an intermediate, thereby obtaining graphite negative electrode material A10. The first-phase carbon content of graphite negative electrode material A10 was 94.1 wt%, and the second-phase carbon content was 5.9 wt%.

[0132] Example 11

[0133] Graphite negative electrode material A11 was prepared according to the method of Example 1, except that step (3-2) was omitted. Graphite negative electrode material A11 had a first-phase carbon content of 93.9 wt % and a second-phase carbon content of 6.1 wt %.

[0134] Comparative Example 1

[0135] A negative electrode material was prepared according to the method of Example 1, except that steps (3-1) and (3-2) were omitted to obtain negative electrode material D1. In the graphite negative electrode material D1, the content of the first phase carbon was 100 wt%, and the content of the second phase carbon was 0 wt%.

[0136] Comparative Example 2

[0137] A negative electrode material was prepared according to the method of Example 1, except that in step (3-1), an equal weight portion of the second modifier was used instead of the first modifier to obtain negative electrode material D2. In graphite negative electrode material D2, the first phase carbon content was 94.4 wt %, and the second phase carbon content was 5.6 wt %.

[0138] Comparative Example 3

[0139] A negative electrode material was prepared according to the method of Example 1, except that in step (3-1), the graphitized material, the first modifier, and the second modifier were mixed at 25°C and 180 rpm to obtain negative electrode material D3. The graphite negative electrode material D3 had a first-phase carbon content of 94.1 wt %, and a second-phase carbon content of 5.9 wt %.

[0140] Comparative Example 4

[0141] A negative electrode material was prepared according to the method of Example 1, except that stirring was not performed in step (3-1), to obtain negative electrode material D4. In the graphite negative electrode material D4, the content of the first phase carbon was 94.1 wt %, and the content of the second phase carbon was 5.9 wt %.

[0142] The graphite negative electrode materials obtained in the examples and comparative examples were characterized, and the results are shown in Table 1.

[0143] Table 1

[0144]

[0145]

[0146] V1 refers to the total pore volume of the negative electrode material; V2 refers to the micropore volume of the negative electrode material.

[0147] Test Case

[0148] (1) Half-cell performance test:

[0149] 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 a copper 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.

[0150] (2) Full battery performance test

[0151] The negative electrode materials prepared in the examples and comparative examples were mixed as active materials with conductive carbon black Super P, binder polyvinylidene fluoride (PVDF), and thickener CMC in a mass ratio of 94:2:3:1. Deionized water was added and a slurry mixer was used to adjust the negative electrode slurry to a uniform state with a solid content of 40-50%. The negative electrode slurry was evenly coated on copper foil using a coating machine, dried, and cut to obtain a negative electrode sheet. The ternary positive electrode material NCM523 was matched, and an electrolyte and a separator were added to assemble a soft-pack battery. The fast charging capability of the soft-pack battery was tested, and the test results are shown in Table 2.

[0152] Table 2

[0153]

[0154]

[0155] It can be seen from the results in Table 1 and Table 2 that the graphite negative electrode material prepared by the embodiment of the present invention has a dense structure, high isotropy, small grain size, and an appropriate surface silicon content. In particular, the graphite negative electrode material has a low pore volume, and the proportion of the pore volume provided by micropores in the total pore volume of the graphite negative electrode material is relatively high, thereby enabling the battery containing the graphite negative electrode material to have a high charge and discharge capacity, first coulombic efficiency and excellent fast charging performance.

[0156] 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 ≤0.02cm 3 / g; (2) In the graphite negative electrode material, the ratio of the pore volume of micropores with a pore diameter of ≤2 nm to the total pore volume of the graphite negative electrode material is ≥30%; (3) The surface silicon content of the graphite negative electrode material is 0.27-1wt%; The crystallite size Lc of the graphite negative electrode material in the c-axis direction obtained by XRD satisfies the following conditions: 25nm≤Lc≤70nm; The graphitization degree of the graphite negative electrode material meets the following condition: 85≤graphitization degree≤93.

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 cm 3 / 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 0.0001-0.01cm 3 / g.

4. The graphite negative electrode material according to claim 1 or 2, wherein In the graphite negative electrode material, the ratio of the pore volume of micropores with a pore diameter of ≤2 nm to the total pore volume of the graphite negative electrode material is 50-100%.

5. The graphite negative electrode material according to claim 1, wherein In the graphite negative electrode material, the ratio of the pore volume of micropores with a pore diameter of ≤2 nm to the total pore volume of the graphite negative electrode material is 60-100%.

6. The graphite negative electrode material according to claim 1, wherein The specific surface area of ​​the graphite negative electrode material is ≤5m 2 / g.

7. The graphite negative electrode material according to claim 1, wherein The specific surface area of ​​the graphite negative electrode material is 0.1-4m 2 / g.

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

9. The graphite negative electrode material according to claim 1, wherein The surface silicon content of the graphite negative electrode material is 0.28-1.5 wt%.

10. The graphite negative electrode material according to claim 9, wherein The surface silicon content of the graphite negative electrode material is 0.30-1 wt%.

11. The graphite negative electrode material according to claim 1, wherein The graphite negative electrode material comprises a first phase carbon of coal-based graphite and a second phase carbon of amorphous carbon.

12. The graphite negative electrode material according to claim 11, wherein Based on the total weight of the graphite negative electrode material, the content of the first phase carbon is 70-99 wt %, and the content of the second phase carbon is 1-30 wt %.

13. A method for preparing the graphite negative electrode material according to any one of claims 1 to 12, characterized in that: 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 and modifying the graphitized material, the first modifier, and the second modifier under heating and stirring conditions to obtain the graphite negative electrode material; In step (3), the heating conditions include: heating to 400-1200°C at a heating rate of 0.1-5°C / min; In step (3), the stirring conditions include: a rotation speed of 50-3000 r / min; a mixing time of 0.1-100 h; In step (3), the first modifier is mesophase asphalt; the second modifier is at least one selected from petroleum asphalt, coal asphalt, oxidized asphalt and high molecular polymer; Wherein, the first modifier satisfies the following conditions: the softening point of the first modifier is ≥150°C; the mesophase content of the first modifier is ≥40wt%; The second modifier meets the following condition: the softening point of the second modifier is ≥100°C.

14. The method according to claim 13, wherein The coal meets the following conditions: vitrinite reflectance ≥ 2, volatile matter ≤ 10 wt %; ash content ≤ 15 wt %.

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

16. The method according to claim 13 or 14, wherein: In step (2), the graphitization conditions include: controlling the actual maximum power transmission of the transformer in the graphitization equipment to be ≥5,000kW, and the continuous power transmission time of the actual maximum power transmission is 0.5-100h.

17. The method according to claim 13 or 14, wherein: In step (2), the graphitization conditions include: controlling the actual maximum power transmission of the transformer in the graphitization equipment to be 5,000-50,000 kW, and the continuous power transmission time of the actual maximum power transmission is 10-80 hours.

18. The method according to claim 13 or 14, wherein The first modifier satisfies the following conditions: the softening point of the first modifier is 200-400° C.; and the mesophase content of the first modifier is 50-100 wt %.

19. The method according to claim 13 or 14, wherein: The second modifier meets the following conditions: the softening point of the second modifier is 150-400°C.

20. The method according to claim 13 or 14, wherein The amount of the graphitized material is 30-99.9wt%, the total amount of the first modifier and the second modifier is 0.1-30wt%, and the amount ratio of the first modifier to the second modifier is 0.1-10:

1.

21. The method according to claim 13 or 14, wherein The amount of the graphitized material is 20-99wt%, the total amount of the first modifier and the second modifier is 1-20wt%, and the amount ratio of the first modifier to the second modifier is 0.2-5:

1.

22. The method according to claim 13 or 14, wherein In step (3), the heating conditions include: heating to 400-1000°C at a heating rate of 0.2-3°C / min; In step (3), the stirring conditions include: a rotation speed of 50-1000 r / min; and a mixing time of 0.5-50 h.

23. The method according to claim 13 or 14, wherein In step (3), the heating conditions include: heating to 500-800°C at a heating rate of 0.5-2.5°C / min; In step (3), the stirring conditions include: a rotation speed of 100-800 r / min; and a mixing time of 1-10 h.

24. The method according to claim 13, wherein The method further comprises the following steps: (3-1) mixing and modifying the graphitized material, the first modifier, and the second modifier under heating and stirring conditions to obtain an intermediate; (3-2) Carbonizing the intermediate to obtain the graphitized negative electrode material.

25. The method according to claim 24, wherein The carbonization conditions include: a carbonization temperature of 800-1500° C. and a carbonization time of 0.1-100 h.

26. The method according to claim 25, wherein The carbonization conditions include: a temperature of 900-1400° C. and a carbonization time of 0.5-80 hours.

27. The method according to claim 26, wherein The carbonization conditions include: a temperature of 1000-1300° C. and a carbonization time of 1-50 hours.

28. A graphite negative electrode material prepared by the preparation method according to any one of claims 13 to 27.

29. Use of the graphite negative electrode material according to any one of claims 1 to 12 and 28 in a secondary battery.

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