Method for acquiring negative electrode active material, and negative electrode active material and use thereof

Abstract

A method for acquiring a negative electrode active material, and a negative electrode active material and the use thereof. The method for acquiring a negative electrode active material comprises the following steps: (a) providing negative electrode active materials to be screened, which negative electrode active materials are of a core-shell structure, wherein a core layer is graphite, and a shell layer is amorphous carbon; and (b) acquiring the coating rates A of the amorphous carbon of the negative electrode active materials to be screened in step (a) on the surface of the graphite, the mass contents B of the amorphous carbon in the negative electrode active materials and the specific surface areas S of the negative electrode active materials, and screening a negative electrode active material having A*B / S greater than or equal to 0.005, but less than or equal to 0.075. The negative electrode active material acquired by using the method can improve the charging capacity of a lithium-ion battery, and ensures that the lithium-ion battery still has very good cycle life and safety when having been subjected to quick charging and use for a long period of time.

Description

Method for obtaining negative electrode active material, negative electrode active material and application thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application number CN202310706036.0, filed with the Patent Office of China on June 14, 2023, entitled “A method for obtaining negative electrode active materials, negative electrode active materials and their applications,” the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present disclosure relates to the field of battery technology, and in particular to a method for obtaining a negative electrode active material, the negative electrode active material, and applications thereof. Background Art

[0004] Lithium-ion battery safety incidents are common. Anode active materials are key components of lithium-ion batteries, playing a crucial role in their cycling, fast-charging, and high- and low-temperature performance. Developing safe anode materials is crucial to improving overall battery safety. Currently, with increasing market demand for lithium-ion batteries, especially to meet the low temperatures of northern winters, higher demands are being placed on their low-temperature performance. Therefore, lithium-ion batteries that combine excellent safety, high- and low-temperature discharge performance, and cycling performance are becoming the preferred choice. Graphite has a layered structure, resulting in slow lithium-ion insertion and removal. Amorphous carbon coating its surface not only enhances the lithium-ion insertion and removal rate by leveraging its high diffusion rate during charge and discharge (approximately 10 times that of graphite), but also effectively reduces the DCR (delayed charge / discharge ratio) and improves kinetic performance. However, excessive carbon coating can degrade the battery's high-temperature performance, posing a safety risk. The large specific surface area of ​​graphite means smaller particles, more channels for lithium ion migration, shorter paths, and better rate performance. However, due to the large contact area with the electrolyte, the area of ​​the SEI film formed is also large, the irreversible capacity is large, and the initial efficiency will be reduced. In addition, more binder will be added, making processing difficult and the slurry viscosity relatively high, resulting in increased internal resistance and reduced cycle performance, which in turn reduces its safety performance.

[0005] Existing technologies mostly involve carbon coating graphite, which can increase the lithium ion insertion and extraction rate and effectively reduce the DCR, improving low-temperature performance while reducing high-temperature performance. Small particles and large specific surface area are beneficial for improving rate performance, but excessive surface area means a large contact area with the electrolyte, which increases side reactions and is detrimental to battery cycling.

[0006] Therefore, it is crucial to overcome the above-mentioned defects and obtain a method for obtaining anode active materials with balanced fast charging, high safety and low-temperature performance to ensure that the lithium-ion battery negative electrode has a high charging capacity at low temperatures, while ensuring that the lithium-ion battery has good safety during long-term fast charging use.

[0007] Application Contents

[0008] One object of the present disclosure is to provide a method for obtaining a negative electrode active material, wherein the negative electrode active material obtained by this method can achieve a balance between cycle performance, low temperature performance and rate performance, and has excellent comprehensive performance.

[0009] Another object of the present disclosure is to provide a negative electrode active material that can ensure that the battery has a high charging capacity at low temperatures, while ensuring that the battery has good safety during long-term rapid charging use.

[0010] Another object of the present disclosure is to provide a negative electrode sheet.

[0011] Another object of the present disclosure is to provide a lithium ion battery.

[0012] Another object of the present disclosure is to provide an application of the lithium-ion battery in consumer electronics, power tools and electric vehicles.

[0013] In order to achieve the above-mentioned purpose of the present disclosure, the following technical solutions are adopted:

[0014] A method for obtaining a negative electrode active material comprises the following steps:

[0015] (a) providing a negative electrode active material to be screened, wherein the negative electrode active material to be screened has a core-shell structure, wherein the core layer is graphite and the shell layer is amorphous carbon;

[0016] (b) Obtaining the coverage rate A of amorphous carbon on the graphite surface, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S of the negative electrode active material to be screened in step (a), and screening out the negative electrode active material whose relationship among A, B, and S satisfies 0.005≤A*B / S≤0.075.

[0017] In one embodiment, the relationship between A, B and S satisfies: 0.013≤A*B / S≤0.06.

[0018] In one embodiment, the relationship between A, B and S satisfies: 0.02≤A*B / S≤0.04.

[0019] In one embodiment, the range of A is 30% to 100%, the range of B is 0.5% to 6%, and the range of S is 0.8 to 2 m2 / g.

[0020] In one embodiment, the method for obtaining the mass content B of the amorphous carbon in the negative electrode active material includes:

[0021] (a1) drying a plurality of negative electrode active material standard samples having a known mass content of amorphous carbon, wherein the mass content of amorphous carbon in the negative electrode active material standard samples is B1;

[0022] (b1) performing thermogravimetric testing on the negative electrode active material standard samples to obtain the thermal weight loss rate y1 of the amorphous carbon of the different negative electrode active material standard samples; the temperature range of the thermal weight loss rate is 200-620°C;

[0023] The thermogravimetric test includes a first heat treatment and a second heat treatment, wherein the temperature of the first heat treatment is 25-400°C, the heating rate is 5-8°C / min, and the temperature of the second heat treatment is 400-800°C, the heating rate is 2-4°C / min; the oxygen flow rate of the first heat treatment and the second heat treatment is 10-100 mL / min;

[0024] (c1) Linear fitting analysis was performed with the mass content of amorphous carbon in the negative electrode active material B1 as the horizontal axis and the thermal weight loss rate y1 as the vertical axis, and the relationship equation was obtained: y = 1.9343x + 0.1317;

[0025] (d1) Drying the negative electrode active material to be tested under the same conditions as step (a1), performing a thermogravimetric test under the same conditions as step (b1) to obtain its thermal weight loss rate y2, and obtaining the mass content B of amorphous carbon in the negative electrode active material to be tested according to the relationship curve equation in step (c1).

[0026] In one embodiment, the method for obtaining the specific surface area S of the negative electrode active material includes: performing a test using a specific surface area tester.

[0027] A negative electrode active material is obtained by the method for obtaining the negative electrode active material.

[0028] A negative electrode sheet comprises the negative electrode active material or the negative electrode active material obtained by the method for obtaining the negative electrode active material.

[0029] A lithium-ion battery comprises the negative electrode sheet.

[0030] The lithium-ion battery is used in consumer electronics, power tools and electric vehicles.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The present invention discloses a method for obtaining a negative electrode active material, obtaining the coverage rate A of amorphous carbon on the graphite surface, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S of the negative electrode active material, and screening a negative electrode active material that satisfies 0.005≤A*B / S≤0.075. The obtained negative electrode active material can balance the kinetic performance, cycle performance, and high and low temperature performance of the negative electrode sheet.

[0033] (2) The battery obtained from the negative electrode active material disclosed in the present invention has a high charging capacity and also has a good cycle life and safety when used for a long time with fast charging, with significant effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific embodiments of the present disclosure or the technical solutions in the prior art, the drawings required for use in the specific embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] FIG1 is a fitted line graph of a standard sample of the negative electrode active material disclosed in the present invention. DETAILED DESCRIPTION

[0036] According to one aspect of the present disclosure, the present disclosure relates to a method for obtaining a negative electrode active material, comprising the following steps:

[0037] (a) providing a negative electrode active material to be screened, wherein the negative electrode active material to be screened has a core-shell structure, wherein the core layer is graphite and the shell layer is amorphous carbon;

[0038] (b) Obtaining the coverage rate A of amorphous carbon on the graphite surface, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S of the negative electrode active material to be screened in step (a), and screening out the negative electrode active material whose relationship among A, B, and S satisfies 0.005≤A*B / S≤0.075.

[0039] The coverage rate in the present disclosure is defined as: the percentage of the coverage area of ​​amorphous carbon on the graphite (particle) surface to the total surface area of ​​the graphite (particle).

[0040] In one embodiment, the graphite comprises artificial graphite.

[0041] In the negative electrode active material disclosed herein, the coated amorphous carbon, on the one hand, relies on the high diffusion rate of amorphous carbon during the charge and discharge process (the diffusion rate is about 10 times that of graphite) to increase the insertion and extraction rate of lithium ions; on the other hand, it can effectively reduce the DCR and improve the kinetic performance; wherein the greater the coating rate A and the mass content B of amorphous carbon in the negative electrode active material, the more effectively the DCR is reduced, the kinetic performance is improved, and the low temperature performance is good; however, if the mass content B of amorphous carbon in the negative electrode active material is too large (i.e., too much coating), the high temperature performance of the battery will be reduced, and the safety will be reduced. A large specific surface area often means that its cycle storage performance is reduced. Therefore, the values ​​of A, B and S mentioned above play an important role in the kinetic performance, cycle performance, power and high and low temperature performance of the battery; wherein, a large value of A and a large value of B (high residual carbon content) have poor high temperature performance, but good low temperature storage performance; and the cycle performance is related to the specific surface area. How to comprehensively control the cycle performance, high and low temperature storage performance and rate performance to achieve a balance is the focus and difficulty of the screening of negative electrode materials. The present disclosure can comprehensively realize the regulation of cycle performance, low temperature performance and rate performance by controlling A*B / S within a specific range of values. In particular, when the value of A*B / S is controlled within the range of 0.005 to 0.075, the cycle performance and high and low temperature performance can reach more than 88%, and the rate performance can also reach more than 89%, and the safety performance is also relatively stable, thereby achieving a balance between cycle performance, high and low temperature storage performance and rate performance.

[0042] In summary, the present disclosure innovatively controls the coverage A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S to satisfy the relationship 0.005≤A*B / S≤0.075, thereby screening out the negative electrode active material. The negative electrode sheet prepared using the negative electrode active material can achieve a balance between fast charging, cycling, and low-temperature performance.

[0043] In one embodiment, A, B and S satisfy the relationship: 0.013≤A*B / S≤0.06.

[0044] In one embodiment, A, B and S satisfy the relationship: 0.02≤A*B / S≤0.04.

[0045] In one embodiment, the range of A is 30% to 100%, for example, 30%, 40%, 45%, 50%, 55%, 60%, 70%, 80%, 90%, 95%, 100%; the range of B is 0.5% to 6%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, etc.; the range of S is 0.8 to 2m 2 / g, for example 0.8m 2 / g, 0.9m 2 / g、1m2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g or 2m 2 / g, etc.

[0046] In one embodiment, the negative electrode active material of the present disclosure is obtained by purchase. The coverage rate A of amorphous carbon on the graphite surface is obtained through the supplier. In one embodiment, the negative electrode active material is derived from Guangdong Kaijin New Energy Technology Co., Ltd. In one embodiment, the negative electrode active material is derived from Hunan Zhongke Xingcheng Graphite Co., Ltd. In one embodiment, the negative electrode active material is derived from Hebei Kuntian New Energy Co., Ltd. In one embodiment, the negative electrode active material is derived from Zhejiang Carbon One New Energy Co., Ltd. In one embodiment, the negative electrode active material is derived from Shanghai Shanshan Technology Co., Ltd.

[0047] In one embodiment, the value of the coating amount B of the amorphous carbon is obtained by performing a TG test. In one embodiment, the method for obtaining the mass content B of the amorphous carbon in the negative electrode active material includes:

[0048] (a1) drying a plurality of negative electrode active material standard samples having known amorphous carbon content by mass at a drying temperature of 60 to 80° C. (e.g., 65° C., 70° C., etc.), wherein the amorphous carbon content by mass in the negative electrode active material standard samples is B1;

[0049] (b1) performing thermogravimetric testing on the negative electrode active material standard samples to obtain the thermal weight loss rate y1 of the amorphous carbon of the different negative electrode active material standard samples; the temperature range of the thermal weight loss rate is 200-620°C;

[0050] The thermogravimetric test includes a first heat treatment and a second heat treatment, wherein the temperature of the first heat treatment is 25-400°C, the heating rate is 5-8°C / min, and the temperature of the second heat treatment is 400-800°C, the heating rate is 2-4°C / min; the oxygen flow rate of the first heat treatment and the second heat treatment is 10-100 mL / min;

[0051] (c1) Linear fitting analysis was performed with the mass content of amorphous carbon in the negative electrode active material B1 as the horizontal axis and the thermal weight loss rate y1 as the vertical axis, and the relationship equation was obtained: y = 1.9343x + 0.1317;

[0052] (d1) Drying the negative electrode active material to be tested under the same conditions as step (a1), performing a thermogravimetric test under the same conditions as step (b1) to obtain its thermal weight loss rate y2, and obtaining the mass content B of amorphous carbon in the negative electrode active material to be tested according to the relationship curve equation in step (c1).

[0053] In one embodiment, the negative electrode active material standard sample is sourced from Hebei Kuntian New Energy Co., Ltd., and the mass content of the amorphous carbon in the standard sample is provided by the supplier.

[0054] In one embodiment, the method for obtaining the specific surface area S of the negative electrode active material includes: testing with a specific surface area tester. In one embodiment, the specific surface area S of the negative electrode active material is tested using conventional methods in the prior art.

[0055] In one embodiment, the method for obtaining the specific surface area S of the negative electrode active material comprises the following steps:

[0056] (1) Open the protective gas valve, turn on the power of the equipment, and preheat for 30 minutes before starting the test;

[0057] (2) Carefully check whether the U-shaped sample tube and the glass funnel have cracks or gaps, and whether the tube body and inner wall are clean. Only after confirming that they are intact can the empty sample tube be weighed and recorded as m1 (mg);

[0058] (3) Use a sample loading funnel to load the sample. The sample weight is 1000 ± 50 mg.

[0059] (4) Place the sample tube steadily in a beaker and weigh it. Record the mass of the sample before purging and the mass of the empty sample tube. This mass is only used as a reference for comparison with the total mass after purging.

[0060] (5) Purge: Before testing, control the inlet flow rate to 80 mL / min and the total outlet flow rate to 80 mL / min; it can clearly tell the operator whether the gas is turned on, and can check whether the sample tube is installed properly and whether the instrument is airtight; remove the physically adsorbed substances on the sample surface by degassing, while avoiding irreversible changes on the surface; control the heating temperature to 200 °C and the heating time to 65 min;

[0061] (6) After the purge is completed, weigh the total mass of the sample tube m2 (mg), and the net weight of the sample m3 = m2 - m1;

[0062] (7) Add liquid nitrogen: fill the sample cup with liquid nitrogen to 2 / 3 and the cold trap constant temperature cup to 1 / 3;

[0063] (8) Set the storage path, sample name, sample net weight and other parameters in the software interface to start the test; the instrument uses the direct comparison method to measure the sample adsorption amount, that is, a mixture of a certain proportion of carrier gas (He) and adsorbate gas (N2) flows through the sample to be tested, and the adsorption amount of the sample to be tested is obtained based on the concentration change before and after adsorption;

[0064] (9) After the experiment, record the experimental values ​​and confirm whether the main power of the instrument is turned off, whether the main valve of the cylinder is closed, and whether the cold trap constant temperature cup is taken out. After checking that everything is correct, tidy up the experimental table and clean the sample tube and funnel.

[0065] According to another aspect of the present disclosure, the present disclosure relates to a negative electrode active material obtained by using the above method for obtaining the negative electrode active material.

[0066] According to another aspect of the present disclosure, the present disclosure also relates to a negative electrode sheet, comprising the negative electrode active material as described above or the negative electrode active material obtained by the method for preparing the negative electrode active material as described above.

[0067] According to another aspect of the present disclosure, the present disclosure also relates to a lithium-ion battery, comprising the negative electrode sheet.

[0068] The battery disclosed herein can achieve a balance between fast charging, cycling and low-temperature performance.

[0069] According to another aspect of the present disclosure, the present disclosure also relates to applications of the lithium-ion battery in consumer electronics, power tools, and electric vehicles.

[0070] The following is further explained with reference to specific embodiments and comparative examples.

[0071] Example 1

[0072] The method for obtaining the negative electrode active material comprises the following steps:

[0073] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 50%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 2%, obtain the specific surface area S of the negative electrode active material, S is 1.8m 2 / g; A*B / S=0.0056, which is the negative electrode active material;

[0074] The method for obtaining the mass content B of amorphous carbon in the negative electrode active material includes:

[0075] (a1) drying a plurality of negative electrode active material standard samples having a known mass content of amorphous carbon, wherein the mass content of amorphous carbon in the negative electrode active material standard samples is B1;

[0076] (b1) performing multiple thermogravimetric tests on the negative electrode active material standard sample to obtain the thermal weight loss rate y1 of the amorphous carbon of different negative electrode active material standard samples; the temperature range of the thermal weight loss rate is 200 to 620°C;

[0077] Each thermogravimetric test includes a first heat treatment and a second heat treatment. The temperature of the first heat treatment is 25-400°C (increasing from 25°C to 400°C) with a heating rate of 5°C / min. The temperature of the second heat treatment is 400-800°C (increasing from 400°C to 800°C) with a heating rate of 4°C / min. The oxygen flow rate of the first heat treatment and the second heat treatment is 20 mL / min.

[0078] (c1) A linear fitting analysis was performed with the mass content of amorphous carbon in the negative electrode active material B1 as the horizontal axis and the thermal weight loss rate y1 as the vertical axis. The fitting line is shown in Figure 1, and the relationship equation is obtained: y = 1.9343x + 0.1317;

[0079] The specific values ​​of the mass content B1 of amorphous carbon in the negative electrode active material and the thermal weight loss rate y1 of each standard sample are shown in Table 1.

[0080] Table 1 B1 and thermal weight loss rate y1 of each standard sample

[0081] (d1) Drying the negative electrode active material to be tested under the same conditions as step (a1), and performing a thermogravimetric test under the same conditions as step (b1) to obtain its thermal weight loss rate y2. According to the relationship curve equation in step (c1), the mass content B of amorphous carbon in the negative electrode active material to be tested is obtained to be 2%.

[0082] The method for obtaining the specific surface area comprises the following steps:

[0083] (1) Open the protective gas valve, turn on the power of the equipment, and preheat for 30 minutes before starting the test;

[0084] (2) Carefully check whether the U-shaped sample tube and the glass funnel have cracks or gaps, and whether the tube body and inner wall are clean. Only after confirming that they are intact can the empty sample tube be weighed and recorded as m1 (mg);

[0085] (3) Use a sample loading funnel to load the sample. The sample weight is 1000 ± 50 mg.

[0086] (4) Place the sample tube steadily in a beaker and weigh it. Record the mass of the sample before purging and the mass of the empty sample tube. This mass is only used as a reference for comparison with the total mass after purging.

[0087] (5) Purge: Before testing, control the inlet flow rate to 80 mL / min and the total outlet flow rate to 80 mL / min; check whether the sample tube is installed properly and whether the instrument is airtight; remove the physically adsorbed substances on the sample surface by degassing, while avoiding irreversible changes on the surface; control the heating temperature to 200 °C and the heating time to 65 min;

[0088] (6) After the purge is completed, weigh the total mass of the sample tube m2 (mg), and the net weight of the sample m3 = m2 - m1;

[0089] (7) Add liquid nitrogen: fill the sample cup with liquid nitrogen to 2 / 3 and the cold trap constant temperature cup to 1 / 3;

[0090] (8) Set the storage path, sample name, sample net weight and other parameters in the software interface to start the test; the instrument uses the direct comparison method to measure the sample adsorption amount, that is, a mixture of a certain proportion of carrier gas (He) and adsorbate gas (N2) flows through the sample to be tested, and the adsorption amount of the sample to be tested is obtained based on the concentration change before and after adsorption;

[0091] (9) After the experiment, record the experimental values ​​and confirm whether the main power of the instrument is turned off, whether the main valve of the cylinder is closed, and whether the cold trap constant temperature cup is taken out. After checking that everything is correct, tidy up the experimental table and clean the sample tube and funnel.

[0092] Example 2

[0093] The method for obtaining the negative electrode active material comprises the following steps:

[0094] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 50%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 3%, obtain the specific surface area S of the negative electrode active material, S is 1.5m 2 / g; A*B / S=0.0100;

[0095] The methods for obtaining the coverage A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this embodiment are the same as those in Example 1.

[0096] Example 3

[0097] The method for obtaining the negative electrode active material comprises the following steps:

[0098] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 50%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 4%, obtain the specific surface area S of the negative electrode active material, S is 1.5m 2 / g; A*B / S=0.0133;

[0099] The methods for obtaining the coverage A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this embodiment are the same as those in Example 1.

[0100] Example 4

[0101] The method for obtaining the negative electrode active material comprises the following steps:

[0102] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 70%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 2%, obtain the specific surface area S of the negative electrode active material, S is 1.4m 2 / g; A*B / S=0.0093;

[0103] The methods for obtaining the coverage A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this embodiment are the same as those in Example 1.

[0104] Example 5

[0105] The method for obtaining the negative electrode active material comprises the following steps:

[0106] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 70%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 3%, obtain the specific surface area S of the negative electrode active material, S is 1.35m 2 / g; A*B / S=0.0150;

[0107] The methods for obtaining the coverage A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this embodiment are the same as those in Example 1.

[0108] Example 6

[0109] The method for obtaining the negative electrode active material comprises the following steps:

[0110] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 70%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 4%, obtain the specific surface area S of the negative electrode active material, S is 1.3m 2 / g; A*B / S=0.0207;

[0111] The methods for obtaining the coverage A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this embodiment are the same as those in Example 1.

[0112] Example 7

[0113] The method for obtaining the negative electrode active material comprises the following steps:

[0114] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 100%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 1%, obtain the specific surface area S of the negative electrode active material, S is 1.6m 2 / g; A*B / S=0.0063;

[0115] The methods for obtaining the coverage A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this embodiment are the same as those in Example 1.

[0116] Example 8

[0117] The method for obtaining the negative electrode active material comprises the following steps:

[0118] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 100%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 2%, obtain the specific surface area S of the negative electrode active material, S is 1.6m 2 / g; A*B / S=0.0125;

[0119] The methods for obtaining the coverage A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this embodiment are the same as those in Example 1.

[0120] Example 9

[0121] The method for obtaining the negative electrode active material comprises the following steps:

[0122] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 100%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 3%, obtain the specific surface area S of the negative electrode active material, S is 1.3m 2 / g; A*B / S=0.0231;

[0123] The methods for obtaining the coverage A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this embodiment are the same as those in Example 1.

[0124] Example 10

[0125] The method for obtaining the negative electrode active material comprises the following steps:

[0126] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 100%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 4%, obtain the specific surface area S of the negative electrode active material, S is 1.2m 2 / g; A*B / S=0.0333;

[0127] The methods for obtaining the coverage A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this embodiment are the same as those in Example 1.

[0128] Example 11

[0129] The method for obtaining the negative electrode active material comprises the following steps:

[0130] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 100%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 5%, obtain the specific surface area S of the negative electrode active material, S is 1.0m 2 / g; A*B / S=0.0500;

[0131] The methods for obtaining the coverage A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this embodiment are the same as those in Example 1.

[0132] Example 12

[0133] The method for obtaining the negative electrode active material comprises the following steps:

[0134] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 100%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 6%, obtain the specific surface area S of the negative electrode active material, S is 0.8m 2 / g; A*B / S=0.0750;

[0135] The methods for obtaining the coverage A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this embodiment are the same as those in Example 1.

[0136] Comparative Example 1

[0137] The method for obtaining the negative electrode active material comprises the following steps:

[0138] The coverage rate A of amorphous carbon in graphite on the graphite surface is 0, the mass content B of amorphous carbon in the negative electrode active material is 0, and the specific surface area S of the negative electrode active material is 1.8 m 2 / g; A*B / S=0;

[0139] The methods for obtaining the coverage ratio A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this comparative example are the same as those in Example 1.

[0140] Comparative Example 2

[0141] The method for obtaining the negative electrode active material comprises the following steps:

[0142] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 30%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 1%, obtain the specific surface area S of the negative electrode active material, S is 1.7m 2 / g; A*B / S=0.0017;

[0143] The methods for obtaining the coverage ratio A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this comparative example are the same as those in Example 1.

[0144] Comparative Example 3

[0145] The method for obtaining the negative electrode active material comprises the following steps:

[0146] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 100%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 8%, obtain the specific surface area S of the negative electrode active material, S is 1.0m 2 / g; A*B / S=0.08;

[0147] The methods for obtaining the coverage ratio A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this comparative example are the same as those in Example 1.

[0148] Comparative Example 4

[0149] The method for obtaining the negative electrode active material comprises the following steps:

[0150] Obtain the coverage rate A of the amorphous carbon on the graphite surface in the composite material, A is 100%, obtain the mass content B of the amorphous carbon in the negative electrode active material, B is 10%, obtain the specific surface area S of the negative electrode active material, S is 0.8m 2 / g; A*B / S=0.1000;

[0151] The methods for obtaining the coverage ratio A, the mass content B of amorphous carbon in the negative electrode active material, and the specific surface area S in this comparative example are the same as those in Example 1.

[0152] Experimental example

[0153] 1. The negative electrode active materials in the embodiment and the comparative example are respectively prepared into soft-pack batteries, and the specific method includes:

[0154] The negative electrode active material, conductive agent SP, CMC and SBR were evenly mixed to obtain a negative electrode slurry, wherein the mass ratio of the negative electrode active material, conductive agent SP, CMC and SBR was 95:1.5:1.5:2.0. The negative electrode slurry was coated on a 6μm copper foil of the negative electrode by a coater, and a negative electrode sheet was prepared by a roller press. Lithium iron phosphate was used as the positive electrode, a lithium salt LiPF6 solution (concentration 1 mol / L), EC (ethylene carbonate) and DEC (diethyl carbonate) with a volume ratio of 1:1 as the solvent were used as the electrolyte, and Celgard 2400 was used as the separator to prepare a 5Ah soft-pack battery.

[0155] The soft-pack batteries prepared in the examples and comparative examples were tested for cycle performance, rate performance, and high-temperature storage performance. The specific test parameters were set as follows:

[0156] 1. Cycle performance: 1C / 1C, 2.5□3.65V, 25±3℃.

[0157] 2. Rate performance: 2C constant current ratio, constant current capacity / (constant current capacity + constant voltage capacity).

[0158] 3. Low temperature storage performance: The lithium-ion battery is charged to 3.65V at a rate of 0.1C, and its capacity is tested as A0. It is then placed at a temperature of -20±3℃ for 7 days. After that, its capacity A1 is tested at room temperature. Then, it is charged to 3.65V and its capacity A2 is tested. The capacity recovery is then calculated as A2 / A0*100%, which is the low temperature storage performance.

[0159] 4. High-temperature storage performance: The lithium-ion battery is charged to 3.65V at a rate of 0.1C, and its capacity is tested as A0. It is then placed at a temperature of 60±3℃ for 7 days. After that, its capacity A1 is tested at room temperature. Then, it is charged to 3.65V and its capacity A2 is tested. The capacity recovery is then calculated as A2 / A0*100%, which is the high-temperature storage performance.

[0160] The negative electrode active materials in the embodiment and the comparative example are respectively prepared into button batteries, and the specific method includes:

[0161] The negative electrode active material, conductive agent SP, CMC and SBR were evenly mixed to obtain a negative electrode slurry, wherein the mass ratio of the negative electrode active material, conductive agent SP, CMC and SBR was 95:1.5:1.5:2.0. The negative electrode slurry was coated on the negative electrode current collector by a coater, and the negative electrode sheet was prepared by a roller press. A lithium salt LiPF6 solution (concentration 1 mol / L) and a solvent EC (ethylene carbonate) + DEC (diethyl carbonate) with a volume ratio of 1:1 were used as the electrolyte, a lithium sheet was used as the positive electrode, and Celgard 2400 was used as the separator to assemble a button half-cell.

[0162] The button cells obtained in the embodiment and the comparative example were cycled twice and then fully charged and sampled for DSC testing. The specific test parameter settings are shown in Table 2 below:

[0163] Table 2 Detection parameter settings

[0164] DSC test: After fully charged and disassembled, the electrode is cleaned with DMC and dried before DSC test. The temperature range is 20-450℃ and the heating rate is 5℃ / min.

[0165] The performance test results of the above soft pack batteries and button batteries are shown in Table 3.

[0166] Table 3 Battery performance test results

[0167] As shown in Table 3, when the value of A*B / S is controlled within the range of 0.005 to 0.0075 for Examples 1 to 12 of the present disclosure compared with Comparative Examples 1 to 4, not only can the rate performance be controlled to above 85%, but the cycle performance can also be made to above 90%, and the high and low temperature performance can reach above 88%, which can effectively achieve a balance between fast charging, cycling, and high and low temperature performance of the negative electrode sheets prepared by the negative electrode active material group. However, Comparative Examples 1 and 2 have low coverage, low mass content of amorphous carbon, poor kinetic performance, low temperature difference, and large specific surface area, resulting in deviations in their cycle performance; Comparative Examples 3 and 4 have high coverage, high mass content of amorphous carbon, good kinetics, good low temperature performance, but small specific surface area, poor rate performance, and poor safety performance.

[0168] By comparing Examples 3 to 6, Examples 8 to 11 with Examples 1, 2, and 12, it can be seen that when the value of A*B / S is controlled within the range of 0.013 to 0.05, the balance of high and low temperature performance can be taken into account, and the rate performance, cycle performance, and safety performance can be comprehensively improved.

[0169] Comparison of Examples 9-10 with Examples 1-8 and Examples 11-12 shows that when the A*B / S value is controlled within the range of 0.02-0.04, not only can the rate performance, cycle performance, and low-temperature performance be achieved above 92%, but high-temperature performance can also be achieved above 93%. The decomposition temperature and energy of the fully charged electrode in the DSC test are also relatively moderate, while also taking into account battery safety. In other words, while having relatively excellent fast-charging performance, the negative electrode active material that can simultaneously improve the cycle and high- and low-temperature performance of the negative electrode is effectively screened. Industrial Applicability

[0170] The present disclosure provides a method for obtaining a negative electrode active material, a negative electrode active material, and its application. The negative electrode active material obtained by the method disclosed herein can improve the charging capacity of lithium-ion batteries while ensuring that the lithium-ion batteries have a long cycle life and safety during long-term rapid charging use, achieving significant results.

Claims

1. A method for obtaining a negative electrode active material, characterized in that: The following steps are involved: (a) providing a negative electrode active material to be screened, wherein the negative electrode active material to be screened is a core-shell structure, wherein the core layer is graphite and the shell layer is amorphous carbon; (b) Obtaining the coverage rate A of amorphous carbon on the graphite surface, the mass content B of amorphous carbon in the negative electrode active material and the specific surface area S of the negative electrode active material to be screened in step (a), and screening out the negative electrode active material whose relationship among A, B and S satisfies 0.005≤A*B / S≤0.

075.

2. The method for obtaining negative electrode active material according to claim 1, characterized in that: The relationship between A, B and S satisfies: 0.013≤A*B / S≤0.

06.

3. The method for obtaining negative electrode active material according to claim 2, characterized in that: The relationship between A, B and S satisfies: 0.02≤A*B / S≤0.

04.

4. The method for obtaining negative electrode active material according to claim 1, characterized in that: The range of A is 30% to 100%, the range of B is 0.5% to 6%, and the range of S is 0.8 to 2 m 2 / g.

5. The method for obtaining negative electrode active material according to claim 1, characterized in that: The method for obtaining the mass content B of the amorphous carbon in the negative electrode active material comprises: (a1) drying a plurality of negative electrode active material standard samples with known amorphous carbon mass content, wherein the mass content of amorphous carbon in the negative electrode active material standard sample is B1; (b1) performing thermogravimetric tests on the negative electrode active material standards respectively to obtain the thermal weight loss rates y1 of the amorphous carbon of the different negative electrode active material standards; the temperature range of the thermal weight loss rates is 200 to 620° C.; The thermogravimetric test includes a first heat treatment and a second heat treatment, wherein the temperature of the first heat treatment is 25-400°C, the heating rate is 5-8°C / min, the temperature of the second heat treatment is 400-800°C, the heating rate is 2-4°C / min; the oxygen flow rate of the first heat treatment and the second heat treatment is 10-100 mL / min; (c1) A linear fitting analysis was performed with the mass content of amorphous carbon in the negative electrode active material B1 as the horizontal coordinate and the thermal weight loss rate y1 as the vertical coordinate, and the relationship equation was obtained: y=1.9343x+0.1317; (d1) Drying the negative electrode active material to be tested under the same conditions as step (a1), performing a thermogravimetric test under the same conditions as step (b1) to obtain its thermal weight loss rate y2, and obtaining the mass content B of amorphous carbon in the negative electrode active material to be tested according to the relationship curve equation in step (c1).

6. The method for obtaining negative electrode active material according to claim 1, characterized in that: The method for obtaining the specific surface area S of the negative electrode active material comprises: testing with a specific surface area tester.

7. A negative electrode active material, characterized in that: The negative electrode active material is obtained by the method for obtaining the negative electrode active material according to any one of claims 1 to 6.

8. A negative electrode sheet, characterized in that: The invention comprises the negative electrode active material as claimed in claim 7 or the negative electrode active material obtained by the method for obtaining the negative electrode active material as claimed in any one of claims 1 to 6.

9. A lithium ion battery, characterized in that: Includes the negative electrode sheet as described in claim 8.

10. Application of the lithium-ion battery according to claim 9 in consumer electronics, electric tools and electric vehicles.

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