Negative electrode material and its preparation method and application

Abstract

The present invention relates to the field of carbon materials, and discloses a negative electrode material and its preparation method and application. The crystallite size L in the c-axis direction of the negative electrode material obtained by XRD is c and the crystallite size L in the a-axis direction a Meet the following conditions: 10nm≤L c ≤30nm formula (I); and 10nm≤L a ≤60nm formula (II); the graphitization degree of the negative electrode material satisfies the following conditions: 70≤graphitization degree≤85 formula (III). This negative electrode material can significantly improve the rate performance of the battery while maintaining high charge and discharge capacity and initial coulombic efficiency, achieving a balance between the three. The preparation method is simple and low-cost.

Description

Technical Field

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

[0002] Lithium-ion battery negative electrodes are primarily carbon materials, including amorphous carbon, natural graphite, and artificial graphite. Graphite has a regular layered structure and excellent conductivity, with a theoretical specific capacity of 372 mA·h / g and high efficiency, making it the current mainstream negative electrode material. However, during high current charge and discharge, lithium ions in graphite negative electrodes diffuse slowly, resulting in poor rate performance. Currently, the most widely used high-power negative electrode materials are lithium titanate and amorphous carbon. Lithium titanate has low energy density and high cost. Amorphous carbon, with its complex structure, allows for rapid lithium ion diffusion and high rate performance, but suffers from low capacity and initial efficiency.

[0003] CN104681786A discloses a coal-based negative electrode material. This material consists of a graphitized inner layer, an intermediate layer, and an outer layer distributed on the surface. Its 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] CN109319757A discloses a method for preparing a hollow open onion carbon negative electrode material for a lithium-ion battery. The method comprises using a coal-based material as a raw material, mixing it with a nickel salt or a nickel element as a catalyst, and heating the mixture so that the nickel salt or the nickel element is evenly distributed on the surface of the coal-based material particles. After cooling, an open graphite onion carbon layer is formed on the spherical surface. Finally, the graphite onion carbon with a hollow open spherical structure is obtained after purification through acid and alkali treatment.

[0005] CN107528053A discloses a negative electrode material for a lithium-ion secondary battery, a negative electrode for a lithium-ion secondary battery, and a lithium-ion secondary battery. The negative electrode material for a lithium-ion secondary battery contains a carbon material having an average interplanar spacing d002 of 0.335 nm to 0.340 nm as determined by X-ray diffraction, a volume average particle size (50% D) of 1 μm to 40 μm, a maximum particle size Dmax of 74 μm or less, and at least two exothermic peaks within a temperature range of 300°C to 1000°C when subjected to differential thermal analysis in an air flow.

[0006] The negative electrode materials provided by the above-mentioned prior art have complex structures and processes, high costs, and the obtained graphite-based negative electrode materials have insufficient rate performance. Summary of the Invention

[0007] The purpose of the present invention is to overcome the problems of insufficient power performance, complex preparation process and high cost of graphite negative electrode materials in the prior art, and to provide a negative electrode material and its preparation method and application. The negative electrode material can significantly improve the rate performance of the battery while maintaining a high charge and discharge capacity and first coulombic efficiency, achieving a balance between the three, and its preparation method is simple and low-cost.

[0008] In order to achieve the above object, the present invention provides a negative electrode material in the first aspect, characterized in that the crystallite size L in the c-axis direction of the negative electrode material obtained by XRD is c and the crystallite size L in the a-axis direction a The following conditions are met:

[0009] 10nm≤L c ≤30nm Formula (I); and

[0010] 10nm≤L a ≤60nm Formula (II);

[0011] The graphitization degree of the negative electrode material satisfies the following condition: 70≤graphitization degree≤85 formula (III).

[0012] A second aspect of the present invention provides a method for preparing a 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 the negative electrode material;

[0015] The coal meets the following conditions: vitrinite reflectance ≤ 2; volatile matter 10-50wt%; ash ≤ 30wt%; caking index ≤ 100;

[0016] The graphitization conditions include: a graphitization temperature of 2600° C. or higher, and a graphitization time of 0.5-100 h.

[0017] The third aspect of the present invention provides a negative electrode material prepared by the above preparation method.

[0018] A fourth aspect of the present invention provides use of the above-mentioned negative electrode material in a lithium-ion battery.

[0019] Through the above technical solution, the negative electrode material provided by the present invention and its preparation method and application achieve the following beneficial effects:

[0020] (1) The negative electrode material provided by the present invention has the characteristics of low graphitization degree and small grain size, thereby enabling the battery containing the negative electrode material to have moderate charge and discharge capacity and first coulombic efficiency and excellent rate performance. Specifically, the charge and discharge capacity of the battery containing the negative electrode material is ≥270mAh / g, the first coulombic efficiency is ≥88%, and the 2C / 0.2C capacity retention rate is ≥45%.

[0021] (2) The negative electrode material provided by the present invention has a low degree of graphitization, a small grain size and a high density, so that the battery containing the negative electrode material has a more excellent rate performance.

[0022] (3) In the preparation method of the negative electrode material provided by the present invention, coal is used as raw material. The raw material is abundant and easy to obtain, and the process is simple and easy to implement, which can significantly reduce the preparation cost of the negative electrode material. The negative electrode material prepared by this method can achieve excellent rate performance while maintaining a high charge and discharge capacity and first coulombic efficiency. 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] The first aspect of the present invention provides a negative electrode material, characterized in that the crystallite size L in the c-axis direction of the negative electrode material obtained by XRD is c and the crystallite size L in the a-axis direction a The following conditions are met:

[0025] 10nm≤L c ≤30nm Formula (I); and

[0026] 10nm≤L a ≤60nm Formula (II);

[0027] The graphitization degree of the negative electrode material satisfies the following condition: 70≤graphitization degree≤85 formula (III).

[0028] In the present invention, the negative electrode material that meets the above conditions has the characteristics of dense structure and small grain size, thereby making the channels for lithium ion insertion and extraction more numerous and shorter, and can significantly improve the rate performance of the battery including the negative electrode material while maintaining a high charge and discharge capacity and first coulombic efficiency.

[0029] In the present invention, the graphitization degree G of the negative electrode material is calculated according to the following formula:

[0030] G=(0.344-d 002 ) / (0.344-0.3354), where d 002 The value is calculated using the Bragg equation.

[0031] Furthermore, when 12nm≤L c ≤28nm, 15nm≤L a When the particle size is ≤55 nm, the grain size of the negative electrode material is further reduced, so that the rate performance of the battery containing the negative electrode material is further improved.

[0032] Furthermore, when the degree of graphitization is 72≤≤84, the battery containing the negative electrode material can maintain a high charge and discharge capacity and a high first coulombic efficiency while improving the rate performance.

[0033] According to the present invention, the interlayer spacing d of the (002) crystal plane of the negative electrode material obtained by XRD is 002 The following conditions are met:

[0034] 0.3340nm≤d 002 ≤0.3400nm Formula (IV).

[0035] Furthermore, the interlayer spacing d of the (002) crystal plane of the negative electrode material obtained by XRD is 002 The following conditions are met:

[0036] 0.33669nm≤d 002 ≤0.33798nm, preferably 0.33678nm≤d 002 ≤0.33781nm.

[0037] In the present invention, the negative electrode material is prepared from a single raw material and is homogeneous.

[0038] According to the present invention, the true density of the negative electrode material is ≥2g / cm 3 , preferably 2-3g / cm 3 , more preferably 2-2.5 g / cm 3 .

[0039] In the present invention, the true density of the negative electrode material is measured using a true density meter from Micromeritics Instrument Corp. II 1340 measured at 25°C.

[0040] According to the present invention, the ash content of the negative electrode material is ≤2000 ppm, preferably ≤500 ppm.

[0041] In the present invention, the ash content of the negative electrode material is measured using the GB / T3521 method.

[0042] A second aspect of the present invention provides a method for preparing a negative electrode material, characterized in that the method comprises the following steps:

[0043] (1) crushing coal to obtain coal particles;

[0044] (2) graphitizing the coal particles to obtain the negative electrode material;

[0045] The coal meets the following conditions: vitrinite reflectance ≤ 2; volatile matter 10-37wt%; ash ≤ 35wt%; caking index ≤ 100;

[0046] The graphitization conditions include: a graphitization temperature of 2600° C. or higher, and a graphitization time of 0.5-100 h.

[0047] In the present invention, after the above-mentioned coal that meets specific conditions is crushed and subjected to high-temperature graphitization treatment, a graphite material with a dense structure and small grain size can be obtained, so that the battery including this negative electrode material can significantly improve the battery's rate performance while maintaining a high charge and discharge capacity and first coulomb efficiency.

[0048] Furthermore, the present invention uses coal as raw material to develop low-cost graphite negative electrode materials with unique micro-nanostructures. When the negative electrode materials are prepared according to the method provided by the present invention, high value-added utilization and clean and efficient conversion of coal can be achieved.

[0049] In the present invention, when coal that meets the above conditions is selected as raw material and used to prepare negative electrode materials, the prepared negative electrode materials can have the characteristics of low graphitization degree and small grain size, thereby significantly improving the rate performance, charge and discharge capacity and first coulombic efficiency of the battery containing the negative electrode material.

[0050] In the present invention, the vitrinite reflectance of the coal is measured using the national standard GB / T 6948, the volatile matter content and ash content of the coal are both measured using the national standard GB / T30732; and the caking index of the coal is measured using the national standard GB / T 5447-2014.

[0051] Furthermore, the coal meets the following conditions: vitrinite reflectance is 0.1-2; volatile matter is 10-37wt%; ash content is ≤30wt%; and caking index is ≤30.

[0052] In the present invention, conventional equipment in the art, such as a jet mill, can be used to pulverize the coal.

[0053] According to the present invention, in step (1), the particle size D of the coal particles is 50 2-50 μm, preferably 5-25 μm.

[0054] According to the present invention, the method further comprises the step of shaping and / or classifying the coal particles.

[0055] According to the present invention, the graphitization conditions include: 2800-3600° C., and graphitization time of 1-60 h.

[0056] According to the present invention, the method further comprises: carbonizing the coal particles before step (2).

[0057] In the present invention, before step (2), the coal particles are carbonized to remove volatile matter from the coal particles, making the coal particles easier to graphitize, thereby ultimately increasing the graphitization degree of the negative electrode material, thereby further improving the charge and discharge capacity and the first coulombic efficiency of the battery containing the negative electrode material.

[0058] In the present invention, the carbonization conditions include: a carbonization temperature of 700-1800° C. and a carbonization time of 1-100 h.

[0059] A third aspect of the present invention provides a negative electrode material obtained by the above preparation method.

[0060] A fourth aspect of the present invention provides use of the above-mentioned negative electrode material in a lithium-ion battery.

[0061] In the present invention, the lithium-ion battery containing the above-mentioned negative electrode material has excellent electrochemical performance. Specifically, the lithium-ion battery containing the negative electrode material has a charge and discharge capacity of ≥270 mAh / g, an initial coulombic efficiency of ≥88%, and a 2C / 0.2C capacity retention rate of ≥45%.

[0062] The present invention will be described in detail below through examples.

[0063] (1) XRD analysis

[0064] The interlayer spacing d of the negative electrode material 002 , L a , L c All the results were obtained by using a D8Advance X-ray diffractometer from Bruker AXS GmbH, Germany. XRD was calibrated by the silicon internal standard method. 002 The Bragg formula Calculated, L a , L c Calculated by Scherrer formula;

[0065] (2) Particle size (D 10、D 50 、D 90 )

[0066] D 10 、D 50 、D 90 The data were obtained by testing with Malvern Mastersizer 2000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0067] (3) Graphitization degree

[0068] The graphitization degree G of the negative electrode material is calculated according to the following formula:

[0069] G=(0.344-d 002 ) / (0.344-0.3354), where d 002 The value is calculated using the Bragg equation.

[0070] (4) True density

[0071] True density was measured by Micromeritics Instrument Corp. II 1340 was measured at 25°C.

[0072] (5) Ash content of negative electrode materials

[0073] The ash content of the negative electrode material is measured using the GB / T3521 method.

[0074] (6) The vitrinite reflectance of coal was measured according to the national standard GB / T6948, the volatile matter content and ash content of coal were measured according to the national standard GB / T30732; the caking index of coal was measured according to the national standard GB / T5447-2014.

[0075] (7) Battery performance

[0076] The battery charge and discharge capacity and the first coulombic efficiency were tested by using a 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 of 0-3V.

[0077] Example 1

[0078] (1) Coal (vitrinite reflectance 0.550; volatile matter 30.6 wt %, ash 7.4 wt %, caking index 0.4) was pulverized by a jet mill to obtain coal particles with D50 = 12 μm;

[0079] (2) The coal particles were graphitized at 3000°C for 15 h and sieved to obtain the negative electrode material A1.

[0080] Example 2

[0081] (1) Coal (vitrinite reflectance 1.897; volatile matter 12.5 wt %, ash 10.4 wt %, caking index 6) was pulverized by a jet mill to obtain coal particles with a D50 of 12 μm;

[0082] (2) The coal particles were graphitized at 3000°C for 15 h and sieved to obtain the negative electrode material A2.

[0083] Example 3

[0084] A negative electrode material was prepared according to the method of Example 1, except that in step (1), the vitrinite reflectance of the coal was 1.25, the volatile matter was 24.6 wt %, the ash content was 10.3 wt %, and the bonding index was 75. Thus, negative electrode material A3 was obtained.

[0085] Example 4

[0086] A negative electrode material was prepared according to the method of Example 1, except that in step (2), the graphitization temperature was 3200° C. and the time was 30 h, thereby obtaining negative electrode material A4.

[0087] Comparative Example 1

[0088] (1) Coal (vitrinite reflectance 1.897; volatile matter 12.5 wt %, ash 10.4 wt %, caking index 6) was pulverized by a jet mill to obtain coal particles with D50 = 12 μm;

[0089] (2) Carbonizing the coal particles at 1100°C for 15 h; sieving to obtain the negative electrode material D1.

[0090] Comparative Example 2

[0091] (1) Coal (vitrinite reflectance 0.550; volatile matter 30.6 wt %, ash 7.4 wt %, caking index 0.4) was pulverized by a jet mill to obtain coal particles with D50 = 12 μm;

[0092] (2) Carbonizing the coal particles at 1100°C for 15 h; sieving to obtain the negative electrode material D2.

[0093] Comparative Example 3

[0094] (1) Coal (vitrinite reflectance 2.445; volatile matter 7.7 wt%; ash 2.6 wt%; caking index 0) was pulverized by a jet mill to obtain coal particles with a D50 of 12 μm;

[0095] (2) The coal particles were graphitized at 3000°C for 15 h and sieved to obtain the negative electrode material D3.

[0096] Comparative Example 4

[0097] A negative electrode material was prepared according to the method of Example 1, except that in step (2), the graphitization temperature was 2800° C. and the time was 15 h, thereby obtaining negative electrode material D4.

[0098] Comparative Example 5

[0099] A negative electrode material was prepared according to the method of Example 1, except that pitch coke was used instead of coal, to obtain negative electrode material D5.

[0100] The negative electrode materials obtained in the examples and comparative examples were characterized, and the results are shown in Table 1.

[0101] Table 1

[0102]

[0103] Test Case

[0104] 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, and assembled into a button cell. The electrochemical performance of the button cell was tested, and the test results are shown in Table 2.

[0105] Table 2

[0106] 0.1C charge and discharge capacity (mAh / g) First coulombic efficiency (%) 2C / 0.2C capacity retention rate (%) Example 1 286 89.9 66.0 Example 2 291 89.2 55.0 Example 3 289 88.4 48.6 Example 4 325 91.8 56.0 Comparative Example 1 260 81.3 55.4 Comparative Example 2 270 83.4 63.4 Comparative Example 3 345 93.6 42.9 Comparative Example 4 280 87.8 48.0 Comparative Example 5 350 94.5 13.8

[0107] It can be seen from the results in Table 1 and Table 2 that the negative electrode material provided by the embodiment of the present invention has a high structural density and a small grain size, so that the battery containing the above negative electrode material has a significantly improved rate performance while maintaining a high charge and discharge capacity and first coulombic efficiency.

[0108] 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 method for preparing a negative electrode material, characterized in that: The method comprises the following steps: (1) Crushing coal to obtain coal particles; (2) graphitizing the coal particles to obtain the negative electrode material; The coal meets the following conditions: vitrinite reflectance ≤ 2; volatile matter 10-50wt%; ash ≤ 35wt%; and caking index ≤ 100; The graphitization conditions include: graphitization temperature above 3000°C, graphitization time of 0.5-100h; The crystallite size L in the c-axis direction of the negative electrode material obtained by XRD c and the crystallite size L in the a-axis direction a The following conditions are met: 10nm≤L c ≤30nm formula (I); and 10nm≤L a ≤60nm formula (II); The graphitization degree of the negative electrode material satisfies the following condition: 70≤graphitization degree≤85 formula (III).

2. The preparation method according to claim 1, wherein The coal meets the following conditions: vitrinite reflectance is 0.1-2; volatile matter is 10-37wt%; ash content is ≤30wt%; and caking index is ≤30.

3. The preparation method according to claim 1 or 2, wherein The particle size D of the coal particles 50 2-50μm.

4. The preparation method according to claim 1 or 2, wherein The particle size D of the coal particles 50 5-25μm.

5. The preparation method according to claim 1 or 2, wherein The method further comprises the step of shaping and / or classifying the coal particles.

6. The preparation method according to claim 1 or 2, wherein The graphitization conditions include: graphitization temperature of 3000-3600° C., and graphitization time of 1-60 h.

7. The preparation method according to claim 1 or 2, wherein The method further comprises: prior to step (2), carbonizing the coal particles.

8. The preparation method according to claim 7, wherein The carbonization conditions include: a carbonization temperature of 700-1800° C. and a carbonization time of 1-100 h.

9. The preparation method according to claim 1 or 2, wherein The crystallite size L in the c-axis direction of the negative electrode material obtained by XRD c Meet the following conditions: 12nm≤L c ≤28nm.

10. The preparation method according to claim 1 or 2, wherein The crystallite size L in the a-axis direction of the negative electrode material obtained by XRD a Meet the following conditions: 15nm≤L a ≤55nm.

11. The preparation method according to claim 1 or 2, wherein The graphitization degree of the negative electrode material satisfies the following condition: 72≤graphitization degree≤84.

12. The preparation method according to claim 1 or 2, wherein The interlayer spacing d of the (002) crystal plane of the negative electrode material obtained by XRD 002 The following conditions are met: 0.3340nm≤d 002 ≤0.3400nm Formula (IV).

13. The preparation method according to claim 12, wherein The interlayer spacing d of the (002) crystal plane of the negative electrode material obtained by XRD 002 The following conditions are met: <h2 style=";text-align:left;direction:ltr">0.33669nm≤d<h2 style=";text-align:left;direction:ltr"> 002 <h2 style=";text-align:left;direction:ltr"> ≤0.33798nm.

14. The preparation method according to claim 13, wherein The interlayer spacing d of the (002) crystal plane of the negative electrode material obtained by XRD 002 The following conditions are met: <h2 style=";text-align:left;direction:ltr">0.33678nm≤d<h2 style=";text-align:left;direction:ltr"> 002 <h2 style=";text-align:left;direction:ltr"> ≤0.33781nm.

15. The preparation method according to claim 1 or 2, wherein The true density of the negative electrode material is ≥2g / cm 3 .

16. The preparation method according to claim 15, wherein The true density of the negative electrode material is 2-3 g / cm 3 .

17. The preparation method according to claim 16, wherein The true density of the negative electrode material is 2-2.5 g / cm 3 .

18. The preparation method according to claim 1 or 2, wherein The ash content of the negative electrode material is ≤2000ppm.

19. The preparation method according to claim 18, wherein The ash content of the negative electrode material is ≤500ppm.

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