Evaluation method of graphite fast-filling performance and fast-filling graphite

Abstract

The invention provides a method for evaluating the rapid charging performance of graphite and rapid charging type graphite, and belongs to the technical field of lithium ion batteries. According to the evaluation method, the evaluation index P of the rapid charging performance of the graphite is provided by constructing the effective relationship among the parameters Id, Ig, Dv50, Dv100 and Dv0 of the graphite, the rapid charging capacity of the graphite can be distinguished according to the P value range, and the judgment result is accurate; in addition, the evaluation method has universality, and is beneficial for engineers to quickly screen graphite.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a method for evaluating the fast charging performance of graphite and fast-charging graphite. Background Art

[0002] As a commonly used negative electrode active material for lithium-ion batteries, the selection of graphite is crucial for the fast charging performance of lithium-ion batteries. Under the same system, when replacing graphite and testing the direct current impedance (DCIR) of the battery, the lower the direct current impedance, the better the fast charging performance of this kind of graphite. However, this evaluation method requires assembling the battery and testing the direct current impedance of the battery, which is relatively complex.

[0003] In related technologies, there are also methods for evaluating the fast charging performance by using parameters such as the particle size of the negative electrode active material or I d / I g value. For example, the patent application document CN105024075A discloses a negative electrode material for a fast-charging graphite lithium-ion battery and a preparation method thereof. The preparation method of the negative electrode material for the fast-charging graphite lithium-ion battery includes the following steps: (1) mixing, heating and kneading, and pulverizing a mixture containing a graphite precursor and pitch; wherein, the average particle size D 50 of the graphite precursor is 5-10 μm, and the mass ratio of the graphite precursor to the pitch is 50:50-90:10; (2) performing heat treatment at 300-700 °C under the protection of an inert gas; (3) graphitization; the average particle size D 50 of the prepared negative electrode material for the fast-charging graphite lithium-ion battery is between 5-15 μm, the specific surface area is below 2.0 m 2 / g, the first discharge capacity of the battery made of the negative electrode material for the fast-charging graphite lithium-ion battery is above 355 mAh / g, the first charge-discharge efficiency is above 90%, and it can reach above 80% after 45 minutes of fast charging (1.5C). The product has a high discharge capacity and charge-discharge efficiency and good rate performance.

[0004] Another example is that the patent application document CN 114094077 A discloses a negative electrode material and a negative electrode sheet including the negative electrode material. The negative electrode material is graphite coated with amorphous carbon, and the ratio ID / IG of the ID to IG of the negative electrode material is 0.15-0.3. By adjusting the process of the coating treatment to control the surface disorder degree (i.e., ID / IG is 0.15-0.3), a fast-charging negative electrode material with high safety is prepared. Summary of the Invention

[0005] The present invention is made based on the inventor's discovery and recognition of the following facts and problems: Although it has been recognized in the above related technologies that the particle size of graphite or I d / I gKey parameters such as values will affect the fast charging performance of graphite, but the comprehensive influence of key parameters such as the particle size of graphite and I d / I g values on its fast charging performance has not been recognized. Therefore, it is necessary to design an evaluation method for the fast charging performance of graphite and fast charging type graphite.

[0006] The present invention aims to solve at least one of the technical problems in the related art to some extent. For this purpose, an embodiment of the present invention provides an evaluation method for the fast charging performance of graphite, including the following steps:

[0007] S1. Test the Raman spectrum of the graphite to obtain the height of the D peak I d and the height of the G peak I g in the Raman spectrum; and test the particle sizes Dv0, Dv50, and Dv100 corresponding to when the cumulative volume distribution percentage of the graphite reaches 0%, 50%, and 100%;

[0008] S2. Calculate the evaluation index P of the fast charging performance of the graphite according to P = I d / I g × Dv50 / (Dv100 - Dv0);

[0009] S3. When 0.15 ≤ P ≤ 0.8, determine that the graphite is fast charging type graphite; when P < 0.15 or P > 0.80, determine that the graphite is non-fast charging type graphite.

[0010] The advantages and technical effects brought by the evaluation method of the embodiment of the present invention are:

[0011] (1) The evaluation method of the embodiment of the present invention only needs to test the Raman spectrum and particle size distribution of graphite, and then calculate the evaluation index P of the fast charging performance of graphite through P = I d / I g × Dv50 / (Dv100 - Dv0). Then, according to the size of P, the quality of the fast charging performance of graphite can be judged. There is no need to assemble and test the performance of lithium-ion batteries, and the judgment process is simple;

[0012] (2) Compared with the related art that only uses I d / I g or particle size to evaluate the fast charging performance of graphite, the evaluation method of the embodiment of the present invention comprehensively considers the influence of I d / I g and particle size on the fast charging performance of graphite, and the evaluation result is more accurate.

[0013] In some embodiments, when 0.28 ≤ P ≤ 0.61, it is determined that the graphite has excellent fast charging performance; when 0.15 ≤ P < 0.28, or 0.61 < P ≤ 0.80, it is determined that the graphite has good fast charging performance.

[0014] In addition, an embodiment of the present invention also provides a fast-charging type graphite. The evaluation index of the fast-charging performance of the graphite is denoted as P, and P = I d / I g × Dv50 / (Dv100 - Dv0), and 0.15 ≤ P ≤ 0.8, where I d is the height of the D peak in the Raman spectrum of the graphite, and I g is the height of the G peak in the Raman spectrum of the graphite. Dv0, Dv50, and Dv100 are the particle sizes corresponding to the cumulative volume distribution percentages of the graphite reaching 0%, 50%, and 100%, respectively.

[0015] The advantages and technical effects brought by the graphite of the embodiment of the present invention are as follows:

[0016] (1) I d represents the content of amorphous carbon in the graphite, and I g represents the content of graphitized carbon in the graphite. The ratio of the peak heights I d / I g then represents the ratio of the content of amorphous carbon to graphitized carbon in the graphite;

[0017] (2) Dv50 / (Dv100 - Dv0) represents the concentration degree of the particle size distribution of the graphite. The more concentrated the particle size distribution is, the larger this value is;

[0018] (3) By defining several parameters of the graphite, namely I d I g , Dv50, Dv100, and Dv0, and constructing an effective relationship between these parameters, the evaluation index P of the fast-charging performance of the graphite is proposed, so that P is between 0.15 and 0.8, thereby improving the fast-charging performance of the graphite.

[0019] In some embodiments, 0.28 ≤ P ≤ 0.61.

[0020] In some embodiments, Dv0 is 1 - 5 μm.

[0021] In some embodiments, Dv0 is 2 - 4 μm.

[0022] In some embodiments, Dv50 is 10 - 16 μm.

[0023] In some embodiments, Dv50 is 12 - 15 μm.

[0024] In some embodiments, Dv100 is 25 - 35 μm.

[0025] In some embodiments, Dv100 is 26 - 32 μm.

[0026] In some embodiments, Id / I g is 0.5 - 1.

[0027] In some embodiments, I d / I g is 0.7 - 0.9. Detailed implementation manners

[0028] Embodiments of the present invention will be described in detail below. The following described embodiments are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0029] Embodiments of the present invention provide a method for evaluating the fast charging performance of graphite, which is characterized by including the following steps:

[0030] S1. Test the Raman spectrum of the graphite to obtain the height I of the D peak (1280 - 1410 cm -1 ) in the Raman spectrum d and the height I of the G peak (1560 - 1600 cm -1 ) in the Raman spectrum; and test the particle sizes Dv0, Dv50, and Dv100 corresponding to when the cumulative volume distribution percentage of the graphite reaches 0%, 50%, and 100%; g

[0031] S2. Calculate the evaluation index P of the fast charging performance of the graphite according to P = I d / I g × Dv50 / (Dv100 - Dv0);

[0032] S3. When 0.15 ≤ P ≤ 0.8, determine that the graphite is fast - charging type graphite; when P < 0.15 or P > 0.80, determine that the graphite is non - fast - charging type graphite.

[0033] The evaluation method of the embodiments of the present invention only needs to test the Raman spectrum and particle size distribution of the graphite, and then calculate the evaluation index P of the fast charging performance of the graphite through P = I d / I g × Dv50 / (Dv100 - Dv0). Then, according to the size of P, the quality of the fast charging performance of the graphite can be judged. There is no need to assemble and test the performance of lithium - ion batteries, and the judgment process is simple; in addition, compared with the related technology that only uses I d / I g or particle size to evaluate the fast charging performance of graphite, the evaluation method of the embodiments of the present invention comprehensively considers the influence of I d / I g and particle size on the fast charging performance of graphite, and the evaluation result is more accurate.

[0034] In the evaluation method of the embodiments of the present invention, when 0.15 ≤ P ≤ 0.80, it is determined that the graphite is fast-charging type graphite; when P < 0.15 or P > 0.80, it is determined that the graphite is fast-charging type graphite.

[0035] Preferably, when 0.28 ≤ P ≤ 0.61, it is determined that the graphite has excellent fast-charging performance; when 0.15 ≤ P < 0.28, or 0.61 < P ≤ 0.80. The above evaluation criteria further refine the range of 0.15 ≤ P ≤ 0.80 of the evaluation index P, which is more conducive to the sub-evaluation of fast-charging type graphite and facilitates the screening of graphite with excellent or good fast-charging performance.

[0036] A fast-charging type graphite, the evaluation index of the fast-charging performance of the graphite is denoted as P, P = I d / I g × Dv50 / (Dv100 - Dv0), and 0.15 ≤ P ≤ 0.8, where I d is the height of the D peak in the Raman spectrum of the graphite, I g is the height of the G peak in the Raman spectrum of the graphite, and Dv0, Dv50 and Dv100 are the particle sizes corresponding to the cumulative volume distribution percentages of the graphite reaching 0%, 50% and 100% respectively.

[0037] I d represents the content of amorphous carbon in the graphite, I g represents the content of graphitized carbon in the graphite, and the ratio of the peak heights I d / I g then represents the ratio of the content of amorphous carbon and graphitized carbon in the graphite; Dv50 / (Dv100 - Dv0) represents the particle size distribution concentration of the negative electrode active material, and the more concentrated the particle size distribution, the larger this value; by limiting the I d 、I g 、Dv50, Dv100 and Dv0 of these parameters, an effective relationship between these parameters is constructed, and the evaluation index P of the fast-charging performance of the graphite is proposed, so that P is between 0.15 - 0.8, such as 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, etc., thereby improving the fast-charging performance of the graphite.

[0038] In some embodiments, 0.28 ≤ P ≤ 0.61. When P is within this range, the graphite has excellent fast-charging performance.

[0039] In some embodiments, Dv0 is 1 - 5 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc., preferably 2 - 4 μm. When Dv0 is too small, P will be too small, which is not conducive to improving the fast-charging performance of the graphite. When Dv0 is too large, P will be too large, which is also not conducive to improving the fast-charging performance of the graphite.

[0040] In some embodiments, Dv50 is 10 - 16 μm, such as 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, etc., and preferably 12 - 15 μm. When Dv50 is too small, P will be too small, which is not conducive to improving the fast charging performance of graphite. When Dv50 is too large, P will be too large, which is also not conducive to improving the fast charging performance of graphite.

[0041] In some embodiments, Dv100 is 25 - 35 μm, such as 25 μm, 26 μm, 28 μm, 30 μm, 32 μm, 34 μm, 35 μm, etc., and preferably 26 - 32 μm. When Dv100 is too small, P will be too large, which is not conducive to improving the fast charging performance of graphite. When Dv100 is too large, P will be too small, which is also not conducive to improving the fast charging performance of graphite.

[0042] In some embodiments, I d / I g is 0.5 - 1, such as 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc., and preferably 0.7 - 0.9. When I d / I g is too small, P will be too small, which is not conducive to improving the fast charging performance of graphite. When I d / I g is too large, P will be too large, which is also not conducive to improving the fast charging performance of graphite.

[0043] The present invention will be described in detail below with reference to embodiments.

[0044] Example 1

[0045] A method for evaluating the fast charging performance of graphite, with graphite A as the evaluation object. This evaluation method includes the following steps:

[0046] S1. Test the Raman spectrum of graphite A to obtain the height I -1 of the D peak (1280 - 1410 cm d ) and the height I -1 of the G peak (1560 - 1600 cm g ), and I d / I g is shown in Table 1; at the same time, test the particle size values Dv0, Dv50, and Dv100 corresponding to when the cumulative volume distribution percentage of graphite A reaches 0%, 50%, and 100%, and the results are shown in Table 1;

[0047] S2. Calculate the evaluation index P = 0.07 of the fast charging performance of graphite A according to P = I d / I g × Dv50 / (Dv100 - Dv0);

[0048] S3. When 0.28 ≤ P ≤ 0.61, it is determined that the graphite has excellent fast charging performance and is fast charging type graphite; when 0.15 ≤ P < 0.28 or 0.61 < P ≤ 0.80, it is determined that the graphite has good fast charging performance and is fast charging type graphite; when P < 0.15 or P > 0.80, it is determined that the graphite has poor fast charging performance and is non-fast charging type graphite;

[0049] According to the above judgment criteria, since the fast charging performance evaluation index P of graphite A is 0.07, which satisfies the condition of P < 0.15, it is determined that the fast charging performance of graphite A is poor and it is non-fast charging type graphite.

[0050] Example 2

[0051] A method for evaluating the fast charging performance of graphite, with the evaluation object being graphite B. This evaluation method includes the following steps:

[0052] S1. Test the Raman spectrum of graphite B to obtain the height I -1 of the D peak (1280 - 1410 cm d ) and the height I -1 of the G peak (1560 - 1600 cm g ), I d / I g as shown in Table 1; at the same time, test the particle size values Dv0, Dv50, and Dv100 corresponding to when the cumulative volume distribution percentage of graphite B reaches 0%, 50%, and 100%, and the results are shown in Table 1;

[0053] S2. Calculate the evaluation index P = 0.15 of the fast charging performance of graphite B according to P = I d / I g × Dv50 / (Dv100 - Dv0);

[0054] S3. When 0.28 ≤ P ≤ 0.61, it is determined that the graphite has excellent fast charging performance and is fast charging type graphite; when 0.15 ≤ P < 0.28 or 0.61 < P ≤ 0.80, it is determined that the graphite has good fast charging performance and is fast charging type graphite; when P < 0.15 or P > 0.80, it is determined that the graphite has poor fast charging performance and is non-fast charging type graphite;

[0055] According to the above judgment criteria, since the fast charging performance evaluation index P of graphite B is 0.15, which satisfies the condition of 0.15 ≤ P < 0.28, it is determined that graphite B has good fast charging performance and is fast charging type graphite.

[0056] Example 3

[0057] A method for evaluating the fast charging performance of graphite, with the evaluation object being graphite C. This evaluation method includes the following steps:

[0058] S1. Test the Raman spectrum of graphite C to obtain the height I of the D peak (1280 - 1410 cm -1 ) in the Raman spectrum d and the height I of the G peak (1560 - 1600 cm -1 ) in the Raman spectrum g , I d / I g as shown in Table 1; At the same time, test the particle size values Dv0, Dv50, and Dv100 corresponding to when the cumulative volume distribution percentage of graphite C reaches 0%, 50%, and 100%, and the results are shown in Table 1;

[0059] S2. Calculate the evaluation index P = 0.28 of the fast charging performance of graphite C according to P = I d / I g × Dv50 / (Dv100 - Dv0);

[0060] S3. When 0.28 ≤ P ≤ 0.61, it is judged that the graphite has excellent fast charging performance and is fast charging type graphite; When 0.15 ≤ P < 0.28, or 0.61 < P ≤ 0.80, it is judged that the graphite has good fast charging performance and is fast charging type graphite; When P < 0.15 or P > 0.80, it is judged that the graphite has poor fast charging performance and is non - fast charging type graphite;

[0061] According to the above judgment criteria, since the evaluation index P of the fast charging performance of graphite C is 0.28, which satisfies the condition of 0.28 ≤ P ≤ 0.61, it is judged that graphite C has excellent fast charging performance and is fast charging type graphite.

[0062] Example 4

[0063] A method for evaluating the fast charging performance of graphite, with the evaluation object being graphite D. This evaluation method includes the following steps:

[0064] S1. Test the Raman spectrum of graphite D to obtain the height I of the D peak (1280 - 1410 cm -1 ) in the Raman spectrum d and the height I of the G peak (1560 - 1600 cm -1 ) in the Raman spectrum g , I d / I g as shown in Table 1; At the same time, test the particle size values Dv0, Dv50, and Dv100 corresponding to when the cumulative volume distribution percentage of graphite D reaches 0%, 50%, and 100%, and the results are shown in Table 1;

[0065] S2. Calculate the evaluation index P = 0.43 of the fast charging performance of graphite D according to P = I d / I g × Dv50 / (Dv100 - Dv0);

[0066] S3. When 0.28 ≤ P ≤ 0.61, it is determined that the graphite has excellent fast charging performance and is fast charging type graphite; when 0.15 ≤ P < 0.28 or 0.61 < P ≤ 0.80, it is determined that the graphite has good fast charging performance and is fast charging type graphite; when P < 0.15 or P > 0.80, it is determined that the graphite has poor fast charging performance and is non-fast charging type graphite;

[0067] According to the above judgment criteria, since the fast charging performance evaluation index P of graphite D is 0.43, which satisfies the condition of 0.28 ≤ P ≤ 0.61, it is determined that graphite D has excellent fast charging performance and is fast charging type graphite.

[0068] Example 5

[0069] A method for evaluating the fast charging performance of graphite, with the evaluation object being graphite E. This evaluation method includes the following steps:

[0070] S1. Test the Raman spectrum of graphite E to obtain the height I -1 of the D peak (1280 - 1410 cm d ) and the height I -1 of the G peak (1560 - 1600 cm g ), I d / I g as shown in Table 1; at the same time, test the particle size values Dv0, Dv50, and Dv100 corresponding to when the cumulative volume distribution percentage of graphite E reaches 0%, 50%, and 100%, and the results are shown in Table 1;

[0071] S2. Calculate the evaluation index P = 0.61 of the fast charging performance of graphite E according to P = I d / I g × Dv50 / (Dv100 - Dv0);

[0072] S3. When 0.28 ≤ P ≤ 0.61, it is determined that the graphite has excellent fast charging performance and is fast charging type graphite; when 0.15 ≤ P < 0.28 or 0.61 < P ≤ 0.80, it is determined that the graphite has good fast charging performance and is fast charging type graphite; when P < 0.15 or P > 0.80, it is determined that the graphite has poor fast charging performance and is non-fast charging type graphite;

[0073] According to the above judgment criteria, since the fast charging performance evaluation index P of graphite E is 0.61, which satisfies the condition of 0.28 ≤ P ≤ 0.61, it is determined that graphite E has excellent fast charging performance and is fast charging type graphite.

[0074] Example 6

[0075] A method for evaluating the fast charging performance of graphite, with graphite F as the evaluation object. This evaluation method includes the following steps:

[0076] S1. Test the Raman spectrum of graphite F to obtain the height I of the D peak (1280 - 1410 cm -1 ) d and the height I of the G peak (1560 - 1600 cm -1 ) g , I d / I g as shown in Table 1; At the same time, test the particle size values Dv0, Dv50, and Dv100 corresponding to when the cumulative volume distribution percentage of graphite F reaches 0%, 50%, and 100%, and the results are shown in Table 1;

[0077] S2. Calculate the evaluation index P = 0.80 of the fast charging performance of graphite F according to P = I d / I g × Dv50 / (Dv100 - Dv0);

[0078] S3. When 0.28 ≤ P ≤ 0.61, it is judged that the graphite has excellent fast charging performance and is fast charging type graphite; When 0.15 ≤ P < 0.28, or 0.61 < P ≤ 0.80, it is judged that the graphite has good fast charging performance and is fast charging type graphite; When P < 0.15 or P > 0.80, it is judged that the graphite has poor fast charging performance and is non-fast charging type graphite;

[0079] According to the above judgment criteria, since the fast charging performance evaluation index P of graphite F = 0.80, which meets the condition of 0.61 < P ≤ 0.80, it is judged that graphite F has good fast charging performance and is fast charging type graphite.

[0080] Example 7

[0081] A method for evaluating the fast charging performance of graphite, with graphite G as the evaluation object. This evaluation method includes the following steps:

[0082] S1. Test the Raman spectrum of graphite G to obtain the height I of the D peak (1280 - 1410 cm -1 ) d and the height I of the G peak (1560 - 1600 cm -1 ) g , I d / I g as shown in Table 1; At the same time, test the particle size values Dv0, Dv50, and Dv100 corresponding to when the cumulative volume distribution percentage of graphite G reaches 0%, 50%, and 100%, and the results are shown in Table 1;

[0083] S2. According to P = I d / Ig The evaluation index P for calculating the fast charging performance of graphite G is P = 1.38 by ×Dv50 / (Dv100 - Dv0);

[0084] S3. When 0.28 ≤ P ≤ 0.61, it is determined that the graphite has excellent fast charging performance and is fast charging type graphite; when 0.15 ≤ P < 0.28 or 0.61 < P ≤ 0.80, it is determined that the graphite has good fast charging performance and is fast charging type graphite; when P < 0.15 or P > 0.80, it is determined that the graphite has poor fast charging performance and is non-fast charging type graphite;

[0085] According to the above judgment criteria, since the fast charging performance evaluation index P of graphite G is P = 1.38, which satisfies the condition of P > 0.80, it is determined that graphite G has poor fast charging performance and is fast charging type graphite.

[0086] The following uses graphite A - G as the negative electrode active material to assemble the negative electrode sheet and the coin - type lithium - ion battery respectively, and then conducts the electrode sheet level test and the coin - cell level test respectively to verify the evaluation results of Examples 1 - 7. The specific operations are as follows:

[0087] (1) Electrode sheet preparation:

[0088] Positive electrode sheet: According to the weight ratio of NCM811, Super - P, and polyvinylidene fluoride (PVDF) of 8:1:1 (the weight of NCM811 is 10 g), an appropriate amount of N - methyl - 2 - pyrrolidone (NMP) is added to make a slurry with a solid content of 65 wt%. The slurry is evenly coated on the aluminum foil with a 250 - μm fixed - thickness scraper at a constant speed. The aluminum foil is taken out after being placed in an 80°C forced - air drying oven for 2 hours, cut into circular electrode sheets with a diameter of 14 mm, and then dried in a 120°C vacuum drying oven for 5 hours.

[0089] Negative electrode sheet: Graphite is mixed with Super - P, binder CMC, and binder SBR according to a weight ratio of 96:1:1:2 (the weight of graphite is 10 g). An appropriate amount of water is added to make a slurry with a solid content of 45 wt%. The slurry is ultrasonicated for 20 min and then placed on a magnetic stirrer and stirred for 10 min at a stirring rate of 500 r / min; then the slurry is taken out and evenly coated on the copper foil with a 250 - μm fixed - thickness scraper at a constant speed. The copper foil is taken out after being placed in an 80°C forced - air drying oven for 2 hours, cut into circular electrode sheets with a diameter of 14 mm, and then dried in a 120°C vacuum drying oven for 5 hours.

[0090] (2) Electrode sheet level test:

[0091] The negative electrode sheets assembled with different graphites are tested for sheet resistance and porosity. The methods for testing sheet resistance and porosity are not limited here, but the following methods can be referred to:

[0092] ① Sheet resistance: The testing equipment is HIOKI, an electrode resistance testing system; the negative electrode sheet is cut into about 100 mm in length and 100 mm in width, placed under the probe, the probe is pressed down to fit the sheet, the computer software RM2612A is opened, relevant parameters are input, such as the dressing layer thickness [=(sheet thickness - current collector thickness) / 2], and then the test can be carried out. The results are shown in Table 2.

[0093] ② Porosity: The negative electrode sheet is cut into 60 mm in width and 100 mm in length, the sheet thickness and copper foil thickness are measured with a micrometer to calculate the external volume of the sheet; the weight of the sheet is measured with a balance with a precision of one hundred-thousandth, and then the sheet is placed in the test chamber of a true density meter to test the volume of the sheet excluding pores. The porosity = 1 - volume of the sheet excluding pores / external volume of the sheet. The results are shown in Table 2.

[0094] (3) Preparation of coin cell:

[0095] The positive electrode case, positive electrode sheet, separator, negative electrode sheet, nickel foam, and negative electrode case are assembled in sequence, and an appropriate amount of electrolyte is dropped during the process. The electrolyte contains 1 mol / L LiPF6 as the electrolyte, and the solvent used in the electrolyte is a mixed solution of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) with a volume ratio of 1:1:1, to obtain a coin-type lithium-ion battery.

[0096] (4) Coin cell hierarchical testing:

[0097] ① The prepared coin cell is cycled 3 times at 0.33C (1C = 190 mA / g) and 2.5 - 4.25V, and the charging capacity of the third cycle is taken as the constant volume capacity C0 of the battery; the battery is charged at a constant current and constant voltage at a rate of 4C to 4.25V, and then discharged at a rate of 1C to 2.5V. This charge-discharge process is repeated 10 times, and the charging capacity of the 10th time is recorded as C10. After that, the battery is charged at a constant current and constant voltage at a rate of 4C to 4.25V again, and then disassembled to observe the lithium deposition situation on the negative electrode sheet. The results are shown in Table 2.

[0098] ② Impedance testing method: 1) Adjust the state of charge (SOC) of the battery to 50% SOC at a rate of 0.33C; 2) Leave it standing at 25°C for 1 h, and test the direct current resistance (DCIR) during charging for 10 s at a rate of 4C. The results are shown in Table 2.

[0099] Table 1. Parameters of Graphite A - G and Fast Charging Performance Evaluation Index P

[0100] Graphite model Dv0 (μm) Dv50 (μm) Dv100 (μm) <![CDATA[I d / I g > P value A 1 9 38 0.3 0.07 B 1 10 35 0.5 0.15 C 2 12 32 0.7 0.28 D 3 14 29 0.8 0.43 E 4 15 26 0.9 0.61 F 5 16 25 1 0.80 G 6 18 23 1.3 1.38

[0101] Table 2. Performance of the negative electrode sheets and button lithium-ion batteries assembled with Graphite A-G

[0102]

[0103] From Table 1, the P values of Graphite A and G are not within the range of good or excellent fast charging, while the values of Graphite B, C, D, E, and F are within the range of good or excellent fast charging. Therefore, it can be considered that Graphite B, C, D, E, and F are fast-charging graphites, and A and G are non-fast-charging graphites.

[0104] From Table 2, the C0, C10, and charging efficiency of Graphite A and G are all lower than those of other graphites, and the corresponding lithium deposition on the negative electrode is lithium deposition in all cases, while other graphites do not deposit lithium. Therefore, it can be considered that Graphite B, C, D, E, and F are fast-charging graphites, and A and G are non-fast-charging graphites. Moreover, combined with the results of the sheet resistance and porosity of the electrode sheet, the fast-charging graphites have small sheet resistance and high porosity, which can effectively reduce Rct and Rb, thereby reducing the DCIR at the button cell level.

[0105] It should be understood that judging whether the graphite is a fast-charging graphite according to the P value in Table 1, and the button cell test in Table 2 is a corroboration of the fast-charging performance of the graphite. From the results of Table 1 and Table 2, the embodiments of the present invention define the evaluation index P for graphite fast charging and limit the range. The fast-charging ability of graphite can be distinguished according to the P value, and the judgment result is accurate; in addition, this evaluation method has universality and helps engineers quickly screen graphites.

[0106] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0107] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. An evaluation method for the fast charging performance of graphite, characterized in that, Including the following steps: S1. Test the Raman spectrum of the graphite to obtain the height ID of the D peak in the Raman spectrum d and the height IG of the G peak g ; and test the particle sizes Dv0, Dv50, and Dv100 corresponding to when the cumulative volume distribution percentage of the graphite reaches 0%, 50%, and 100%; S2. According to P = I d / I g × Dv50 / (Dv100 - Dv0), calculate the evaluation index P of the fast charging performance of the graphite; S3. When 0.15 ≤ P ≤ 0.80, it is determined that the graphite is fast-charging type graphite; when P < 0.15 or P > 0.80, it is determined that the graphite is non-fast-charging type graphite.

2. The evaluation method according to claim 1, wherein When 0.28 ≤ P ≤ 0.61, it is determined that the graphite has excellent fast-charging performance; when 0.15 ≤ P < 0.28 or 0.61 < P ≤ 0.80, it is determined that the graphite has good fast-charging performance.

3. A fast-charging graphite, characterized in that, The evaluation index of the fast charging performance of the graphite is denoted as P, and P = I d / I g × Dv50 / (Dv100 - Dv0), and 0.15 ≤ P ≤ 0.8, where I d is the height of the D peak in the Raman spectrum of the graphite, and I g is the height of the G peak in the Raman spectrum of the graphite. Dv0, Dv50, and Dv100 are the particle sizes corresponding to the cumulative volume distribution percentages of the graphite reaching 0%, 50%, and 100% respectively.

4. The fast-charging graphite according to claim 3, wherein 0.28≤P≤0.61。 5. The fast-charging graphite according to claim 3, wherein, Dv0 is 1 - 5 μm.

6. The fast-charging graphite according to claim 5, wherein Dv0 is 2 - 4 μm.

7. The fast-charging graphite according to claim 3, wherein Dv50 is 10 - 16 μm.

8. The fast-charging graphite according to claim 3, characterized in that, Dv50 is 12 - 15 μm.

9. The fast-charging graphite according to claim 3, characterized in that, Dv100 is 25 - 35 μm, preferably 26 - 32 μm.

10. The fast-charging graphite according to claim 3, wherein, I d / I g is 0.5 - 1, preferably 0.7 - 0.9.

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