Negative electrode active materials, their preparation methods, secondary batteries and battery modules, battery packs and devices containing secondary batteries

Abstract

A negative electrode active material, its preparation method, a secondary battery, and a battery module, battery pack, and device comprising the secondary battery are disclosed. The negative electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core comprises artificial graphite, and the coating layer comprises amorphous carbon. The particle size uniformity of the negative electrode active material is 0.3–0.42, and the negative electrode active material satisfies: 0.6 ≤ (Dv90 – Dv10) / Dv50 ≤ 1.8, where Dv90 is the particle size corresponding to a cumulative volume distribution percentage of 90% for the negative electrode active material; Dv10 is the particle size corresponding to a cumulative volume distribution percentage of 10% for the negative electrode active material; and Dv50 is the particle size corresponding to a cumulative volume distribution percentage of 50% for the negative electrode active material.

Description

[0001] This application is based on the application number 202080081680.8, the application date is October 15, 2020, the applicant is Ningde era new energy technology Co., Ltd., and the invention is "cathode active material, its preparation method, secondary battery and battery module, battery pack and device comprising secondary battery" is filed as a divisional application. TECHNICAL FIELD

[0002] The application belongs to the technical field of secondary batteries, and particularly relates to a cathode active material, a preparation method thereof, a secondary battery, a battery module comprising the secondary battery, a battery pack and a device. BACKGROUND

[0003] Secondary batteries rely on active ions to reciprocally deintercalate between positive and negative electrodes for charging and discharging, and have the outstanding characteristics of high energy density, long cycle life, and no pollution, no memory effect. Therefore, as a clean energy, secondary batteries have gradually popularized from electronic products to large device fields such as electric vehicles to adapt to the sustainable development strategy of the environment and energy.

[0004] However, compared with the traditional fuel vehicle which can be refueled quickly and timely, the electric vehicle is generally charged at a small rate, which often requires a long charging time, thus causing the consumers to be anxious about the endurance mileage and limiting the rapid popularization of the electric vehicle. Therefore, in order to improve the market competitiveness of the electric vehicle, it is necessary to provide a secondary battery which can have good rapid charging performance. SUMMARY

[0005] The purpose of the application is to provide a cathode active material, a preparation method thereof, a secondary battery, a battery module comprising the secondary battery, a battery pack and a device, for improving the charging performance and cycle performance of the secondary battery.

[0006] In order to achieve the above-mentioned purpose of the application, the first aspect of the application provides a cathode active material, which comprises a core and a coating layer covering at least a part of the surface of the core, the core comprises artificial graphite, and the coating layer comprises amorphous carbon, the volume particle size distribution D v 99 is less than or equal to 24 microns, and the average volume particle size D v 50 of the cathode active material satisfies 8 microns < D v 50 < 15 microns. Wherein, D v 99 is the particle size corresponding to the cumulative volume distribution percentage of the cathode active material reaching 99%; D v 50 is the particle size corresponding to the cumulative volume distribution percentage of the cathode active material reaching 50%.

[0007] Surprisingly, it is found that when the negative electrode sheet adopts the negative active material of the present application, it has higher active ion solid-phase diffusion performance. Even in the high lithium intercalation state at the end of charging, the active ion has a higher diffusion speed in the negative electrode sheet, effectively reducing the ohmic and concentration polarization, thus greatly increasing the charging speed and charging depth of the whole negative electrode sheet, thereby significantly improving the rapid charging capability of the battery. Further, the cycle performance of the battery is also significantly improved.

[0008] In any embodiment of the present application, the negative active material satisfies 17 μm≤D v 99≤24 μm; optionally, 18 μm≤D v 99≤21 μm. The D v 99 in the above range can further improve the rapid charging capability and cycle performance of the battery.

[0009] In any embodiment of the present application, the negative active material satisfies: 9 μm≤D v 50≤13 μm; optionally, 11 μm≤D v 50≤13 μm. The D v 50 in the appropriate range can further improve the rapid charging capability and cycle performance of the battery.

[0010] In any embodiment of the present application, the particle size uniformity of the negative active material is 0.25-0.45, and optionally 0.32-0.38. The particle size uniformity of the negative active material in the above range can further improve the rapid charging capability of the battery; and can also make the negative electrode sheet obtain a higher compaction density, thereby improving the energy density of the battery.

[0011] In any embodiment of the present application, the specific surface area of the particle size of the negative active material is 0.4 m 2 / g-0.75 m 2 / g, and optionally 0.5 m 2 / g-0.65 m 2 / g. When the specific surface area of the particle size of the negative active material is in the appropriate range, the rapid charging performance and cycle performance of the battery can be further improved, and the energy density of the battery can also be improved.

[0012] In any embodiment of the present application, the negative active material includes secondary particles, and the number ratio of the secondary particles in the negative active material is ≥50%. Optionally, the number ratio of the secondary particles in the negative active material is 70%-95%. When the negative active material contains an appropriate amount of secondary particles, the rapid charging capability, cycle performance and storage performance of the battery can be further improved.

[0013] In any embodiment of the present application, the negative active material satisfies: 0.6≤(D v 90-D v 10) / D v 50≤1.8; optionally, 0.8≤(D v 90-D v 10) / D v 50≤1.4. Wherein, D v 90 is the particle size corresponding to the cumulative volume distribution percentage of the negative active material reaching 90%; D v 10 is the particle size corresponding to the cumulative volume distribution percentage of the negative active material reaching 10%. The (D v 90-D v 10) / D v 50 of the negative active material is appropriate, which is conducive to further improving the rapid charging capability of the battery.

[0014] In any embodiment of the present application, the volume particle size distribution D v 90 of the negative active material is 13 μm to 18 μm, optionally 14 μm to 17 μm. The D v 90 of the negative active material within the above range can further improve the rapid charging capability of the battery.

[0015] In any embodiment of the present application, the volume particle size distribution D v 10 of the negative active material is 5 μm to 10 μm, optionally 6 μm to 8 μm. The D v 10 of the negative active material within the above range is conducive to improving the cycle performance and storage performance of the battery.

[0016] In any embodiment of the present application, the graphitization degree of the negative active material is 91.0% to 96.0%, optionally 94.0% to 95.0%. The graphitization degree of the negative active material within the above range can further improve the rapid charging capability of the battery.

[0017] In any embodiment of the present application, the gram capacity of the negative active material is 345 mAh / g to 360 mAh / g, optionally 350 mAh / g to 358 mAh / g. The gram capacity of the negative active material within the appropriate range can improve the energy density of the battery, and also improve the rapid charging capability and cycle performance of the battery.

[0018] In any embodiment of the present application, the tap density of the negative active material is 0.9 g / cm 3 ~ 1.3 g / cm 3 , optionally 1.0 g / cm 3 ~ 1.1 g / cm 3The tap density of the negative active material in the given range can improve the fast charging capability of the battery, and also improve the energy density of the battery.

[0019] In any embodiment of the present application, the powder compaction density of the negative active material under 2kN pressure is 1.55g / cm 3 ~1.67g / cm 3 , and optionally 1.60g / cm 3 ~1.65g / cm 3 . The powder compaction density of the negative active material under 2kN pressure in the given range can make the particles in the negative film layer tightly contact, and form good electrolyte infiltration channels, thereby improving the fast charging capability and cycle performance of the battery.

[0020] The second aspect of the present application provides a preparation method of a negative active material, comprising the following steps:

[0021] A) providing a core, wherein the core comprises artificial graphite;

[0022] B) coating the core to form a coating layer on at least part of the surface of the core, to obtain a negative active material, wherein the coating layer comprises amorphous carbon, and the negative active material satisfies Dv99≤24μm and 8μm≤Dv50≤15μm.

[0023] In any embodiment of the present application, the preparation of the artificial graphite in step A) comprises:

[0024] a) providing a coke raw material;

[0025] b) performing a shaping treatment on the coke raw material to obtain a precursor;

[0026] c) performing granulation on the precursor to obtain a granulation product;

[0027] d) performing graphitization treatment on the granulation product to obtain artificial graphite, wherein the volume average particle size D v 50 of the artificial graphite is 6μm~14μm, and the volume particle size distribution D v 99 is 17μm~26μm.

[0028] In any embodiment of the present application, the volume average particle size D v 50 of the granulation product is 9μm~15μm, and the volume particle size distribution D v 99 is 17μm~24μm.

[0029] In any embodiment of the present application, the volume average particle size D v 50 of the precursor is 8μm~13μm, and the volume particle size distribution D v99 is 16 μm to 22 μm.

[0030] In any embodiment of the present application, the volume average particle size D v 50 is 7 μm to 12 μm, and the volume particle size distribution D v 99 is 15 μm to 21 μm.

[0031] In any embodiment of the present application, the particle size uniformity Uniformity of the precursor is denoted as U1, and satisfies 0.2≤U1≤0.55. Optionally, 0.3≤U1≤0.45.

[0032] In any embodiment of the present application, the particle size uniformity Uniformity of the artificial graphite is denoted as U2, and satisfies 0.22≤U2≤0.48. Optionally, 0.3≤U2≤0.4.

[0033] In any embodiment of the present application, the volatile matter content of the coke raw material is denoted as C1, the particle size uniformity Uniformity of the precursor is denoted as U1, and the amount of the binder added in the granulation process of step c) is denoted as C2, and the preparation method satisfies: 21%≤(C1+C2) / U1×100%≤50%. Optionally, 31%≤(C1+C2) / U1×100%≤35%.

[0034] In any embodiment of the present application, the volatile matter content C1 of the coke raw material satisfies 1%≤C1≤12%. Optionally, 5%≤C1≤9%.

[0035] In any embodiment of the present application, the coke raw material comprises one or more of petroleum-based non-pitch coke, petroleum-based needle coke. Optionally, the coke raw material comprises petroleum green coke.

[0036] In any embodiment of the present application, step B) comprises: e) coating the core with an organic carbon source, and forming an amorphous carbon coating layer on at least a part of the surface of the core through heat treatment, to obtain the negative electrode active material.

[0037] In any embodiment of the present application, the amount of the organic carbon source added in step e) is denoted as C3, and the preparation method satisfies: 20%≤(C1+C2+C3) / U2×100%≤56%, and 1.2%≤C3×char yield≤2.5%.

[0038] The negative electrode active material prepared by the preparation method of the present application comprises a core and a coating layer covering the surface of the core, the core comprises artificial graphite, the coating layer comprises amorphous carbon, and the negative electrode active material satisfies D v 99≤24 μm and 8 μm≤D v50≤15μm, which can significantly improve the rapid charging capability of the battery using the same. Further, the cycle performance of the battery is also significantly improved.

[0039] The third aspect of the present application provides a secondary battery, which comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material, wherein the negative electrode active material comprises the negative electrode active material described in the present application.

[0040] The secondary battery of the present application can simultaneously achieve higher energy density, rapid charging capability and cycle performance due to the use of the negative electrode active material described in the present application.

[0041] The fourth aspect of the present application provides a battery module, which comprises the secondary battery of the present application.

[0042] The fifth aspect of the present application provides a battery pack, which comprises the secondary battery or the battery module of the present application.

[0043] The sixth aspect of the present application provides an apparatus, which comprises at least one of the secondary battery, the battery module or the battery pack of the present application.

[0044] The battery module, the battery pack and the apparatus of the present application comprise the secondary battery provided by the present application, and thus at least have the same advantages as the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative effort on the basis of the drawings.

[0046] Figure 1 is a scanning electron microscope (SEM) image of an embodiment of the negative electrode active material of the present application under 1000 times magnification.

[0047] Figure 2 is a scanning electron microscope (SEM) image of another embodiment of the negative electrode active material of the present application under 5000 times magnification.

[0048] Figure 3 is an ion polishing cross-section morphology (CP) picture of the negative electrode sheet under 5000 times magnification after the negative electrode active material of the present application is prepared into a negative electrode sheet.

[0049] Figure 4 is a transmission electron microscope (TEM) image of an embodiment of the negative electrode active material of the present application under 60000 times magnification.

[0050] Figure 5 is a schematic view of an embodiment of a secondary battery.

[0051] Figure 6 is Figure 5 is an exploded view of

[0052] Figure 7 is a schematic view of an embodiment of a battery module.

[0053] Figure 8 is a schematic view of an embodiment of a battery pack.

[0054] Figure 9 is Figure 8 is an exploded view of

[0055] Figure 10 is a schematic view of an embodiment of an apparatus using a secondary battery as a power source. DETAILED DESCRIPTION

[0056] In order to make the objectives, technical solutions, and beneficial technical effects of the present application clearer, the present application will be further described in detail below with reference to embodiments. It should be understood that the embodiments described in the present specification are merely intended to explain the present application and are not intended to limit the present application.

[0057] For the sake of brevity, only some numerical ranges are explicitly recited herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with any other lower limit to form a range not explicitly recited, as can any upper limit with any other upper limit to form a range not explicitly recited. Further, although a range is expressed as ending at a point, it is understood that the point is included in the range. Thus, each point or individual value can be combined with any other point or individual value to form a range not explicitly recited.

[0058] In the description of the present application, it should be noted that, unless otherwise specified, "above", "below", "upper", "lower", "one or more", "several" means two or more.

[0059] In the description of the present application, unless otherwise specified, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any one of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0060] The above summary of the application is not intended to describe each disclosed embodiment or implementation in the application. The following description more specifically illustrates example embodiments. Throughout this application, guidance is provided by a series of examples, which can be used in various combinations. In various instances, the enumeration is merely representative of a group and should not be interpreted as exhaustive.

[0061] Secondary batteries, also known as rechargeable batteries or accumulators, refer to batteries that can continue to be used by activating active materials through charging after the batteries are discharged.

[0062] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charging and discharging of the battery, active ions (e.g., lithium ions) are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet and mainly functions to prevent short circuiting of the positive and negative electrodes while allowing ions to pass through. The electrolyte is between the positive electrode sheet and the negative electrode sheet and mainly functions to conduct ions.

[0063] The inventors have found that the key to improving the rapid charging capability of a secondary battery lies in improving the kinetic performance of the negative electrode. The negative electrode sheet generally includes a negative electrode current collector and a negative electrode film layer, and the negative electrode film layer includes a negative electrode active material. The negative electrode active material generally refers to a material that participates in the insertion and extraction of active ions in the negative electrode sheet during the charging and discharging of the battery. At present, in order to improve the kinetic performance of the battery, methods such as reducing the thickness of the negative electrode film layer or reducing the compaction density of the negative electrode film layer are mostly used. However, a large number of studies have shown that the above methods for improving the kinetic performance of the battery only improve the kinetic performance of the battery to a certain extent in the actual use of the low SOC state (i.e., the initial stage of charging), and have little effect on the kinetic performance of the battery in the actual use of the high SOC state (i.e., the final stage of charging), resulting in the rapid charging capability of the secondary battery not being effectively improved. In addition, the energy density of the battery is also significantly reduced.

[0064] In the preparation process of the negative electrode active material, the industry generally focuses on the volume average particle size D v 50, while the particles whose cumulative volume distribution percentage reaches more than 99% from the small particle side are very few in number, so the D v 99 of the negative electrode active material has been considered unimportant and ignored by the industry. However, the inventors have surprisingly found that when the D v 99 of the negative electrode active material is controlled within a certain range, the rapid lithium insertion capability of the negative electrode active material at a high lithium insertion state (corresponding to a high SOC state of the battery) can be significantly improved, thereby breaking the above bottleneck and improving the rapid charging capability of the secondary battery at a high SOC state.

[0065] Therefore, the present application provides a negative electrode active material, which comprises a core and a coating layer covering at least part of the surface of the core, the core comprises artificial graphite, and the coating layer comprises amorphous carbon, the volume particle size distribution D v 99≤24μm, and the average volume particle size D v 50satisfies 8μm≤D v 50≤15μm.

[0066] The inventors have found through a large number of studies that when the negative electrode active material of the present application is used, the battery can have a high energy density while having a high active ion solid-phase diffusion performance. Even at a high lithium intercalation state at the end of charging (high SOC state), the negative electrode active material particles can still maintain good electrochemical reaction activity, and the active ions can quickly intercalate into the bulk phase of the negative electrode active material and quickly migrate, thereby effectively increasing the diffusion speed of the active ions in the negative electrode sheet and reducing the ohmic and concentration polarization, so that the overall charging speed and charging depth of the negative electrode sheet are greatly increased. Therefore, the present application can achieve large-rate charging of the battery at full SOC state, significantly improving the rapid charging capability. In addition, the active ion migration performance between the positive and negative electrodes in the battery is good, and the polarization is small, so the cycle performance is also significantly improved. Generally, low SOC state generally refers to below 30% SOC, and high SOC state generally refers to above 60% SOC.

[0067] The artificial graphite described in the present application generally refers to a graphite material obtained through graphitization high-temperature treatment, and the graphitization crystallization degree thereof is generally high.

[0068] The amorphous carbon described in the present application generally refers to a carbon material with a low graphitization crystallization degree.

[0069] Generally, the lattice structure of artificial graphite tends to be long-range ordered layered arrangement; and the lattice structure of amorphous carbon tends to be disordered arrangement. Generally, the lattice arrangement can be observed by transmission electron microscopy (TEM) image.

[0070] In some embodiments, the shape of the core can be one or more of blocky, flaky, and spherical-like.

[0071] In some embodiments, the thickness of the coating layer is ≥2nm, and can be selected from 2nm to 20nm; for example, 2nm to 15nm, 2nm to 10nm, and 5nm to 10nm.

[0072] In some embodiments, the coverage of the coating layer on the surface of the core is ≥50%, and can be selected from 60% to 100%.

[0073] In some embodiments, the negative electrode active material can satisfy D v99≤ 23.8 μm, ≤ 23.5 μm, ≤ 23 μm, ≤ 22.5 μm, ≤ 22 μm, ≤ 21 μm, or ≤ 20 μm.

[0074] In some embodiments, the negative active material can satisfy D v 99≥ 15 μm, ≥ 16 μm, ≥ 17 μm, ≥ 18 μm, or ≥ 19 μm.

[0075] In some embodiments, the negative active material can satisfy: 15 μm ≤ D v 99≤ 24 μm; for example, 16 μm ≤ D v 99≤ 22 μm, 17 μm ≤ D v 99≤ 24 μm, 17 μm ≤ D v 99≤ 23 μm, 15 μm ≤ D v 99≤ 21 μm, 18 μm ≤ D v 99≤ 21 μm, 19 μm ≤ D v 99≤ 21 μm, 19 μm ≤ D v 99≤ 22 μm, 19 μm ≤ D v 99≤ 23 μm, 20 μm ≤ D v 99≤ 22 μm, 20 μm ≤ D v 99≤ 21.5 μm, or 20 μm ≤ D v 99≤ 21 μm.

[0076] D v 99in the appropriate range, can further increase the active ion solid phase diffusion speed of the negative electrode at the high lithium intercalation state, reduce the polarization; also helps to reduce the smaller particles therein, the particles can intercalate more active ions, while making the negative electrode film layer form a smooth pore structure, shorten the liquid phase conduction path, thereby further improving the rapid charging capacity and cycle performance of the battery. The use of D v 99appropriate negative active material, can make the secondary battery simultaneously give priority to higher rapid charging capacity and cycle performance.

[0077] In some embodiments, the negative active material can satisfy D v 50≤ 14 μm, ≤ 13 μm, or ≤ 12 μm. Alternatively, the negative active material can satisfy D v 50≥ 8 μm, ≥ 9 μm, ≥ 10 μm, or ≥ 11 μm. For example, the negative active material can satisfy 8 μm ≤ D v 50≤ 14 μm, 9 μm ≤ D v 50≤ 13 μm, 10 μm ≤ D v 50≤ 14 μm, 12 μm ≤ D v 50≤ 14 μm, 12 μm ≤ D v50≤13μm, or 11 μm≤D v 50≤13μm.

[0078] D of the negative active material v 50in the proper range, can shorten the migration path of active ions in the negative active material particles, and is also conducive to forming a smooth pore structure in the negative film layer, thereby making the negative electrode sheet have a good active ion solid-phase diffusion speed and a good liquid-phase transmission performance, so as to further improve the rapid charging capability of the battery. In addition, the D of the negative active material v 50in the proper range, can also ensure that the negative active material has a relatively high specific capacity, is conducive to the battery obtaining a relatively high energy density, and can also reduce the side reaction of the electrolyte at the negative electrode, and improve the cycle performance of the battery.

[0079] In some embodiments, the particle size uniformity Uniformity of the negative active material is 0.25-0.45, for example, it can be 0.28-0.4, 0.32-0.4, 0.32-0.38, 0.30-0.36, 0.31-0.35, or 0.32-0.36. The particle size uniformity Uniformity of the negative active material can characterize the dispersion degree of the particle size D v 50of all particles in the negative active material, which reflects the uniformity of the particle size distribution of the negative active material. When the particle size uniformity Uniformity of the negative active material is in the above range, it is easy to form a shorter liquid-phase transmission path in the negative film layer, and at the same time, the particles can have a larger contact area between particles, which is conducive to the electron conduction and active ion transmission in the negative electrode sheet, thereby further improving the rapid charging capability of the battery. In addition, the particles in the negative film layer can be in close contact, so that the negative electrode sheet can obtain a relatively high compaction density, thereby improving the energy density of the battery.

[0080] In some embodiments, the negative active material satisfies: 0.6≤(D v 90-D v 10) / D v 50≤1.8. For example, the negative active material satisfies: (D v 90-D v 10) / D v 50is 0.8-1.4, 0.9-1.3, 1.0-1.25, or 1.2-1.6. The negative active material satisfies: (D v 90-D v 10) / D v 50reflects the degree of deviation of the particle size of the larger particles and the particle size of the smaller particles in the negative active material from the volume average particle size D v 50. The negative active material satisfies: (D v90-D v 10) / D v 50appropriate, is conducive to improving the processability of the negative electrode slurry and the negative electrode film layer, so that the negative electrode film layer as a whole has higher consistency in particle distribution, thereby facilitating the negative electrode film layer to exhibit higher active ion transmission performance at different regions, further improving the rapid charging capability of the battery.

[0081] In some embodiments, the volume particle size distribution D v 90 is 13-18 μm, for example, can be 13-16 μm, 14-17 μm, or 15-18 μm. The D v 90 in the appropriate range can further increase the solid-phase diffusion speed of active ions in the negative electrode film layer, thereby further improving the rapid charging capability of the battery. In addition, the negative electrode active material can also have a higher gram capacity, which helps to improve the energy density of the battery.

[0082] In some embodiments, the volume particle size distribution D v 10 is 5-10 μm, for example, can be 6-8 μm. The content of small particles in the negative electrode active material is less, which can reduce the side reaction between the electrolyte and the material, and improve the cycle performance and storage performance of the battery.

[0083] In some embodiments, the specific surface area of the particle size of the negative electrode active material is 0.4 m 2 / g-0.75 m 2 / g, for example, can be 0.4 m 2 / g-0.7 m 2 / g, 0.42 m 2 / g-0.68 m 2 / g, 0.46 m 2 / g-0.55 m 2 / g, 0.5 m 2 / g-0.68 m 2 / g, or 0.5 m 2 / g-0.65 m 2 / g.

[0084] It should be noted that the "specific surface area of particle size" of the negative electrode active material of the present application is not the same as the "specific surface area" of the conventional negative electrode active material. The specific surface area (SSA) of the negative electrode active material in the industry is obtained by gas adsorption BET method, which is only used to characterize the physical adsorption specific surface area of the negative electrode active material. The "specific surface area of particle size" of the negative electrode active material of the present application is obtained by laser diffraction particle size analysis method, which can be used to characterize the degree of deviation of the negative electrode active material from the spherical shape.

[0085] The inventors have found that when the particle size to specific surface area of the negative active material is within a proper range, the deintercalation ion channels in the negative film layer can be increased, the charge exchange impedance can be reduced, and the negative film layer can form more unobstructed pores, thus improving the electrolyte wettability, and further improving the active ion solid phase and liquid phase transmission speed in the negative electrode sheet, and thus further improving the rapid charging performance and cycle performance of the battery. In addition, the negative active material with a proper particle size to specific surface area can also improve the compaction density of the negative film layer, thus improving the energy density of the battery.

[0086] In some embodiments, as shown in FIGS. 1A and 1B, the negative active material includes secondary particles. Optionally, the amount of the secondary particles in the negative active material is ≥ 50%. For example, the amount of the secondary particles in the negative active material is 50% to 100%, 60% to 100%, 60% to 90%, 70% to 100%, 70% to 95%, 70% to 90%, 70% to 80%, or 75% to 85%. When the negative active material contains a large amount of secondary particles, the deintercalation active ion channels in the negative film layer are increased, thus further improving the rapid charging capability of the battery, and also reducing the polarization and improving the cycle performance. Figure 1 Figure 2 In some embodiments, as shown in FIGS. 1A and 1B, the negative active material includes secondary particles. Optionally, the amount of the secondary particles in the negative active material is ≥ 50%. For example, the amount of the secondary particles in the negative active material is 50% to 100%, 60% to 100%, 60% to 90%, 70% to 100%, 70% to 95%, 70% to 90%, 70% to 80%, or 75% to 85%. When the negative active material contains a large amount of secondary particles, the deintercalation active ion channels in the negative film layer are increased, thus further improving the rapid charging capability of the battery, and also reducing the polarization and improving the cycle performance.

[0087] In some embodiments, the graphitization degree of the negative active material is 91.0% to 96.0%; for example, it can be 94.0% to 95.0%, or 93.0% to 94.5%. When the graphitization degree of the negative active material is within the above range, the particle structure has a larger interlayer spacing, and also has a lower powder resistance, thus further improving the rapid charging capability.

[0088] In some embodiments, the gram capacity of the negative active material is 345 mAh / g to 360 mAh / g; for example, it can be 350 mAh / g to 358 mAh / g, 351 mAh / g to 356 mAh / g, or 352 mAh / g to 355 mAh / g. The higher gram capacity of the negative active material can improve the energy density of the battery. The gram capacity of the negative active material within the above range also means that the active ion migration path of the material is shorter, thus improving the rapid charging capability of the battery.

[0089] In some embodiments, the tap density of the negative active material is 0.9 g / cm 3 to 1.3 g / cm 3 ; for example, it can be 1.0 g / cm 3 to 1.1 g / cm 3 ​Within a given range, the tap density of the negative electrode active material enables good contact between particles in the negative electrode film, thereby improving the battery's fast charging capability. Simultaneously, the close packing of particles also increases the battery's energy density.

[0090] In some embodiments, the compacted density of the negative electrode active material at a pressure of 2 kN is 1.55 g / cm³. 3 ~1.67g / cm 3 For example, it could be 1.60 g / cm³. 3 ~1.65g / cm 3 The compaction density of the negative electrode active material under 2kN pressure, within the given range, enables close contact between particles in the negative electrode film layer and simultaneously forms good electrolyte wetting channels, thereby improving the battery's fast charging capability and cycle performance.

[0091] In this application, the D of the negative electrode active material v 99. D v 90. D v 50. D v 10. Particle size uniformity and specific surface area can both be determined using laser diffraction particle size analysis. For example, refer to standard GB / T19077-2016 and use a laser particle size analyzer (e.g., Malvern Master Size 3000) for determination.

[0092] Among them, D v 99 represents the particle size corresponding to a cumulative volume distribution percentage of 99% for the negative electrode active material; D v 90 represents the particle size corresponding to a cumulative volume distribution percentage of 90% for the negative electrode active material; D v 50 represents the particle size corresponding to a cumulative volume distribution percentage of 50% for the negative electrode active material; D v 10 represents the particle size corresponding to a cumulative volume distribution percentage of 10% for the negative electrode active material.

[0093] In the present application, the material type of the core can be observed by preparing the negative electrode active material into a negative electrode sheet, and then performing ion polishing cross-section morphology (CP) test on the negative electrode sheet. As an example, the test method can be as follows: first, cut the prepared negative electrode sheet into a certain size of sample to be tested (for example, 2 cm x 2 cm), and fix the negative electrode sheet on the sample stage by paraffin. Then, lock and fix the sample stage on the sample holder, turn on the power of the argon ion cross-section polisher (for example, IB-19500CP), and vacuumize (for example, 10-4Pa), set the argon gas flow (for example, 0.15 MPa), voltage (for example, 8 KV), and polishing time (for example, 2 hours), adjust the sample stage to the swing mode to start polishing. The sample test can refer to JY / T010-1996. Randomly selected areas in the sample to be tested can be scanned and tested, and the ion polishing cross-section morphology (CP) picture of the negative electrode sheet can be obtained under a certain magnification (for example, 5000 times). For example, from the negative electrode active material of the present application, the ion polishing cross-section morphology (CP) picture of the negative electrode sheet can be obtained under a certain magnification (for example, 5000 times). Figure 3 As can be seen, the core of the negative electrode active material of the present application is artificial graphite.

[0094] In the present application, the structure (for example, the core and the coating layer) of the negative electrode active material can be tested by using the devices and methods known in the art. As an example, the following steps can be performed: select a micro grid with a certain diameter (for example, 3 mm in diameter), hold the edge of the micro grid with a sharp tweezers, with the film surface facing up (the shiny surface is the film surface when observed under light), and gently place it on a white filter paper; add an appropriate amount of graphite particle sample (for example, 1 g) into a beaker containing an appropriate amount of ethanol, and perform ultrasonic oscillation for 10-30 min; use a glass capillary tube to suck, and then drop 2-3 drops of the sample to be tested onto the micro grid; after baking in an oven for 5 min, place the micro grid with the sample to be tested on the sample stage, and test it under a certain magnification (for example, 60000 times) by using a transmission electron microscope (for example, Hitachi HF-3300S Cs-corrected STEM), so as to obtain the transmission electron microscope (TEM) image of the sample to be tested. For example, from the negative electrode active material of the present application, the transmission electron microscope (TEM) image of the negative electrode sheet can be obtained under a certain magnification (for example, 60000 times). Figure 4 As can be seen, the negative electrode active material of the present application comprises a core and a coating layer.

[0095] In the present application, the primary particles and the secondary particles are both the meanings known in the art. The primary particles refer to non-agglomerated particles, and the secondary particles refer to agglomerated particles formed by the aggregation of two or more primary particles. The primary particles and the secondary particles can be easily distinguished by using a scanning electron microscope to take SEM images.

[0096] The proportion of the number of secondary particles in the negative electrode active material can be tested by a method known in the art. An exemplary testing method is as follows: the negative electrode active material is laid and adhered on a conductive adhesive to form a sample to be tested with a length x width of 6 cm x 1.1 cm; the particle morphology is tested using a scanning electron microscope (e.g., ZEISS Sigma 300). The test can refer to JY / T010-1996. To ensure the accuracy of the test results, a plurality of (e.g., 5) different regions can be randomly selected from the sample to be tested for scanning test, and under a certain magnification (e.g., 1000 times), the percentage of the number of secondary particles in the total number of particles in each region is calculated, i.e., the proportion of the number of secondary particles in the region, and the average value of the test results of a plurality of test regions is taken as the proportion of the number of secondary particles in the negative electrode active material. To ensure the accuracy of the test results, a plurality of test samples (e.g., 10) can be repeatedly tested according to the above method, and the average value of each test sample is taken as the final test result.

[0097] The graphitization degree of the negative electrode active material is a meaning known in the art, which can be tested by a method known in the art. For example, an X-ray diffractometer (e.g., Bruker D8 Discover) can be used, and the test can refer to JIS K 0131-1996, JB / T 4220-2011, the size of d002 is measured, and then the graphitization degree is calculated according to the formula G = (0.344-d002) / (0.344-0.3354) x 100%, wherein d002 is the interlayer spacing in the graphite crystal structure represented by nanometers (nm). In the X-ray diffraction analysis test, a copper target can be used as an anode target, CuKα ray is used as a radiation source, and the wavelength of the ray is 0.15406 nm. The scanning 2θ angle range is 20°-80°, and the scanning rate can be 4° / min.

[0098] The tap density of the negative electrode active material is a meaning known in the art, which can be tested by a method known in the art. For example, the standard GB / T 5162-2006 can be referred to, and a powder tap density tester is used for determination. For example, if a FZS4-4B type tap density tester from Beijing Iron and Steel Research Institute is used, the test parameters are as follows: vibration frequency: 250±15 times / min, vibration amplitude: 3±0.2 mm, vibration times: 5000 times, cylinder: 25 mL.

[0099] The powder compaction density of the negative electrode active material under a pressure of 2kN is a meaning known in the art, which can be determined by a method known in the art. For example, the standard GB / T24533-2009 can be referred to, and an electronic pressure testing machine (e.g., UTM7305 type) is used for determination. An exemplary testing method is as follows: 1g of the negative electrode active material is weighed, and 1.327cm 2The negative electrode active material is placed in a mold, pressurized to 200 kg (equivalent to 2 kN), kept for 30 s, then released, kept for 10 s, and then the powder compaction density of the negative electrode active material under a pressure of 2 kN is recorded and calculated.

[0100] The gram capacity of the negative electrode active material is a meaning known in the art, which can be tested by a method known in the art. An exemplary testing method is as follows: the prepared negative electrode active material, conductive agent carbon black (Super P), binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 91.6:1.8:6.6 with a solvent N-methyl pyrrolidone (NMP) to form a slurry; the prepared slurry is coated on a copper foil current collector, dried in an oven, and used as needed. A lithium metal sheet is used as a counter electrode, and a polyethylene (PE) film is used as a separator film. Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L. A CR2430 type button cell is assembled in an argon glove box. After the obtained button cell is left for 12 hours, it is discharged at 0.05 C to 0.005 V at 25°C, left for 10 minutes, discharged at 50 μA to 0.005 V, left for 10 minutes, and discharged at 10 μA to 0.005 V; then it is charged at 0.1 C to 2 V, and the charge capacity is recorded. The ratio of the charge capacity to the mass of the negative electrode active material is the gram capacity of the prepared negative electrode active material.

[0101] It should be noted that the above various parameter tests for the negative electrode active material can be directly tested on a negative electrode active material sample, or can be tested by sampling from a secondary battery.

[0102] When the above test sample is sampled from a secondary battery, as an example, the sampling can be performed according to the following steps:

[0103] (1) The secondary battery is discharged (for safety, the battery is generally in a full discharge state); the battery is disassembled to take out the negative electrode sheet, and the negative electrode sheet is soaked in dimethyl carbonate (DMC) for a certain time (for example, 2-10 hours); then the negative electrode sheet is taken out and dried at a certain temperature and time (for example, 60°C, 4h), and the dried negative electrode sheet is taken out.

[0104] (2) The dried negative electrode sheet in step (1) is baked at a certain temperature and time (for example, 400°C, 2h), and a region of the baked negative electrode sheet is optionally selected for sampling of the negative electrode active material (a blade can be used to scrape the powder for sampling).

[0105] (3) The negative electrode active material collected in step (2) is sieved (e.g., sieved with a 200-mesh sieve) to finally obtain a negative electrode active material sample that can be used to test the material parameters of the present application.

[0106] This application further provides a method for preparing a negative electrode active material, according to which the aforementioned negative electrode active material can be obtained. The method for preparing the negative electrode active material may include the following steps A) and B).

[0107] A) Provide a core comprising artificial graphite.

[0108] B) The core is coated to form a coating layer on at least a portion of the surface of the core to obtain a negative electrode active material, the coating layer comprising amorphous carbon, wherein the negative electrode active material has Dv99≤24μm and 8μm≤Dv50≤15μm.

[0109] In some embodiments, the method for preparing artificial graphite in step A) may include steps a) to d).

[0110] a) Provide coke raw materials;

[0111] b) The coking raw material is shaped to obtain the precursor;

[0112] c) Granulate the precursor to obtain the granulated product;

[0113] d) The granulated product is subjected to graphitization treatment to obtain artificial graphite, wherein the D of the artificial graphite is... v 50 is 6μm~14μm, D v 99 is 17μm~26μm.

[0114] In some implementations, the D of the coke feedstock can be adjusted. v 50 and D v 99, which makes the D of the coke raw material v 50 is 7μm~12μm, D v 99 is 15μm~21μm. When the D of the coke raw material v 50 and D v When 99 is within the given range, it is beneficial to improve subsequent shaping and granulation processes, so that the final negative electrode active material has an appropriate secondary particle content and an appropriate D. v 50 and D v 99. Optional, D of coke feedstock v 50 is 8μm~12μm, 8μm~11.5μm, or 9μm~11μm. Optionally, the D of the coke feedstock... v 99 represents 16μm~21μm, 17μm~21μm, 17μm~20μm, or 17μm~19μm.

[0115] In step a), the coke raw material can be directly commercially available, or the coke material is crushed to obtain. In some embodiments, the coke material can be crushed to adjust the D v 50 and D v 99 in the desired range. The coke material can be crushed using devices and methods known in the art, such as air jet mill, mechanical mill or roller mill. The crushing process often produces more small particles, and sometimes there are also large particles, so after crushing, the classification process can be performed according to the needs to remove the small particles and large particles in the powder after crushing. The classification process can be performed using devices and methods known in the art, such as classification screen, gravity classifier, centrifugal classifier, etc.

[0116] The crushing process of the coke material can be performed in a process unit comprising a crusher, a classifier and an air blower. During the crushing process, the D v 50 and D v 99 in the desired range. Compared with the traditional crushing process in which the classification frequency is low, the method of the present application can increase the classification frequency, which is beneficial to remove small particles. Compared with the traditional crushing process in which the air blowing frequency is high, the method of the present application can reduce the air blowing frequency, which is beneficial to remove large particles. In addition, compared with the traditional crushing process in which the frequency is controlled in a wide range, the method of the present application can also control the main machine frequency, the classification frequency and the air blowing frequency in a narrow frequency range, thereby reducing the particle size distribution width of the coke raw material, for example, the D v 50 and D v 99 in a narrow range. The feeding frequency can also be adjusted synchronously to control the feeding amount, which can further improve the crushing effect of the material.

[0117] In some embodiments, the feeding frequency can be 10-40 Hz, for example, 25-35 Hz.

[0118] In some embodiments, the crushing frequency can be 20-50 Hz, for example, 35-45 Hz.

[0119] In some embodiments, the classification frequency can be 20-50 Hz, for example, 40-50 Hz.

[0120] In some embodiments, the air blowing frequency can be 30-55 Hz, for example, 35-45 Hz.

[0121] The skilled in the art can select and adjust one or more of the above process conditions according to the actual operation conditions to finally obtain the D v50 is 7-12 μm and D v 99 is 15-21 μm of the coke raw material.

[0122] In some embodiments, the coke raw material of step a) can include one or more of petroleum-based non-needle coke, petroleum-based needle coke. Alternatively, the coke raw material includes petroleum green coke.

[0123] In some embodiments, the volatile matter content C1 of the coke raw material of step a) satisfies 1%≤C1≤12%. Alternatively, the volatile matter content C1 of the coke raw material is 3%-10%, 5%-9%, 6%-8%, 7%-8.5%, or 7.5%-8.5%, etc. The appropriate volatile matter content of the coke raw material is conducive to improving the particle size distribution of the material in the subsequent granulation process, so as to facilitate the negative electrode active material to have the required particle size distribution. In addition, the appropriate volatile matter content of the coke raw material can also make the prepared artificial graphite have higher structural strength, improve the cycle life of the negative electrode active material, and thus improve the cycle performance of the battery.

[0124] The volatile matter content of the coke raw material can be tested by methods known in the art. For example, refer to SH / T 0026-1990 for determination.

[0125] In step b), the edges and corners of the coke raw material particles can be polished by shaping, which is conducive to the subsequent granulation process, so that the secondary particles in the obtained negative electrode active material have higher structural stability. The coke raw material can be subjected to shaping treatment by using equipment and methods known in the art, such as a shaper or other shaping equipment.

[0126] In some embodiments, after the shaping treatment of the coke raw material, further classification treatment is performed, so that the obtained precursor has a D v 50 is 8-13 μm, D v 99 is 16-22 μm, so that the final obtained negative electrode active material has an appropriate secondary particle content and an appropriate D v 50 and D v 99. Alternatively, the precursor has a D v 50 is 9-12 μm, 9-11 μm, 10-12 μm, or 10-11 μm. The precursor has a D v 99 is 17-22 μm, 18-21 μm, or 18-20 μm. The classification treatment can be performed by using equipment and methods known in the art, such as a classification screen, a gravity classifier, a centrifugal classifier, etc.

[0127] The shaping, grading process can be performed in a process unit comprising a shaper, a grader, and an air blower. During the shaping, grading process, the D50 of the obtained precursor can be controlled by adjusting the shaping frequency (e.g. the main frequency and the secondary frequency of the shaper), the grading frequency, and the air blowing frequency. v 50 and D99 v 99 are within a desired range. The inventors have found that, compared to conventional shaping, grading processes, the method of the present application increases the shaping frequency during the process, appropriately prolongs the shaping time, and reduces the grading frequency and the air blowing frequency during the process, so that the D50 and D99 of the obtained precursor are within a target range. v 50 and D99 v 99 are controlled within a target range.

[0128] The obtained precursor can also have a suitable particle size uniformity (U1), which helps to improve the particle size uniformity of the obtained negative electrode active material.

[0129] In some embodiments, the particle size uniformity U1 of the precursor satisfies 0.2≤U1≤0.55. For example, 0.2≤U1≤0.5, 0.25≤U1≤0.45, 0.3≤U1≤0.45, 0.3≤U1≤0.4, 0.35≤U1≤0.55, or 0.35≤U1≤0.45.

[0130] In some embodiments, in step b), the main frequency of the shaper can be controlled to be 35Hz-40Hz, the secondary frequency of the shaper can be controlled to be 60Hz-70Hz, the grading frequency can be controlled to be 40Hz-50Hz, the air blowing frequency can be controlled to be 10Hz-25Hz, and the shaping time can be controlled to be 160s-180s, so as to perform the shaping, grading process on the raw material, to obtain a precursor with D50 of 8μm-13μm and D99 of 16μm-22μm. v 50 is 8μm-13μm and D99 is 16μm-22μm. v 99 is 16μm-22μm.

[0131] In step c), the precursor is granulated so as to aggregate the independently dispersed primary particles to form secondary particles. In this way, the isotropy of the artificial graphite is improved, the active ions can be inserted into the particles from various directions of the particles, the solid-phase lithium intercalation rate is improved, and the polarization is reduced.

[0132] In some embodiments, the D50 of the granulation product obtained in step c) can be 9μm-15μm, the D99 can be 17μm-24μm. v 50 can be 9μm-15μm, the D99 can be 17μm-24μm. v 50 is 10μm-14μm, 11μm-15μm, or 11μm-13μm. Optionally, the D99 of the granulation product is 18μm-24μm, or 19μm-22μm. v 50 is 10μm-14μm, 11μm-15μm, or 11μm-13μm. Optionally, the D99 of the granulation product is 18μm-24μm, or 19μm-22μm. v 50 is 10μm-14μm, 11μm-15μm, or 11μm-13μm. Optionally, the D99 of the granulation product is 18μm-24μm, or 19μm-22μm. v50 and D v 99 in a proper range, so as to make the D v 50 and D v 99 in a proper range.

[0133] In step c), granulation can be performed by using a device known in the art, such as a granulator. The granulator usually comprises a stirring reaction kettle and a module for temperature control of the reaction kettle. By adjusting the stirring speed, the heating rate, the granulation temperature, the cooling rate and the like during the granulation process, the degree of granulation can be controlled, and the D v 50 and D v 99 in a proper range. Further, by adjusting the above-mentioned granulation process, the D v 10, D v 90 in a proper range, so as to make the D v 10, D v 90 in a proper range.

[0134] In some embodiments, the precursor can be mixed with the binder; and then high-temperature granulation is performed. The temperature for mixing can be 20-40°C. Compared with the preparation process of conventional graphite, the mixing frequency is appropriately increased and the mixing time is shortened in the present application, so that the degree of granulation can be improved, and the D v 50 and D v 99 in a proper range.

[0135] The temperature for high-temperature granulation can be determined according to the type of the binder. The binder softens at high temperature, and the granules are adhered to each other to achieve granulation. In some embodiments, the binder is pitch. In these embodiments, the granulation temperature can be 700-800°C. The present application also improves the temperature rising program of the high-temperature granulation process, and adopts a stepwise temperature rising. By setting multiple (for example, 2-4) program temperature rising platforms during the temperature rising process, the granulation product can obtain a desired particle size distribution. Moreover, the particle size uniformity of the granulation product is good, which helps the subsequent artificial graphite and the final negative electrode active material product to obtain good particle size uniformity.

[0136] In some embodiments, in step c), the mixing frequency can be controlled to be 35-38 Hz, and the mixing time can be controlled to be 50-65 min; then the temperature is raised to 300-400°C at a rate of 6-10°C / min, and the temperature is maintained for 1-2 h; then the temperature is raised to 500-600°C at a rate of 6-10°C / min, and the temperature is maintained for 1-2 h; then the temperature is raised to 700-800°C at a rate of 6-10°C / min, and the temperature is maintained for 1-2 h; and then the temperature is naturally lowered to obtain the granulation product.

[0137] In some embodiments, in step c), the amount of binder C2 added during the granulation process satisfies the relationship between the volatile matter content C1 of the coke raw material and the particle size consistency U1 of the precursor: 21% ≤ (C1+C2) / U1×100% ≤ 50%. Optionally, 25% ≤ (C1+C2) / U1×100% ≤ 45%, 25% ≤ (C1+C2) / U1×100% ≤ 38%, 27% ≤ (C1+C2) / U1×100% ≤ 38%, 30% ≤ (C1+C2) / U1×100% ≤ 40%, or 31% ≤ (C1+C2) / U1×100% ≤ 35%. When the amount of binder C2 added during the granulation process satisfies the above relationship with the volatile matter content C1 of the coke raw material and the particle size consistency U1 of the precursor, the granulation degree of the negative electrode active material particles can be improved, and the deintercalation / intercalation performance and structural stability of the negative electrode active material can be enhanced.

[0138] The amount of binder C2 added during the granulation process is the percentage of the weight of the binder added during the granulation process relative to the total weight of the precursor. The granulation process is carried out with or without the addition of a binder.

[0139] In some embodiments, the amount of binder C2 added during the granulation process can satisfy 0% ≤ C2 ≤ 16%. Optionally, 1% ≤ C2 ≤ 12%, 2% ≤ C2 ≤ 10%, 4% ≤ C2 ≤ 7%, or 5% ≤ C2 ≤ 9%.

[0140] In some embodiments, in step d), the granulated product is graphitized at a temperature of 2800°C to 3200°C to obtain artificial graphite with an appropriate degree of graphitization. Optionally, the graphitization temperature can be 2900°C to 3100°C.

[0141] In step d), graphitization can be performed using equipment known in the art, such as a graphitization furnace, and more specifically, an Atchison graphitization furnace. After graphitization, a small number of excessively large particles formed during the high-temperature graphitization process of the granulated product can be removed by sieving, which is beneficial for obtaining the final negative electrode active material with D... v 50 and D v 99 is within the required range.

[0142] In some embodiments, the D of the artificial graphite obtained in step d) v 50 can be 6.5μm~14μm, 7μm~14μm, 6μm~13μm, 7μm~13.5μm, 8μm~12μm, 9μm~12μm, 9μm~11μm, 10μm~13μm, 10μm~12μm, 6.5μm~12μm, or 6.5μm~12.5μm.

[0143] In some embodiments, the D50 of the artificial graphite obtained in step d) satisfies 0.5 < D50 < 1.5, 0.6 < D50 < 1.4, 0.7 < D50 < 1.3, 0.8 < D50 < 1.2, 0.9 < D50 < 1.1, or 0.95 < D50 < 1.05. v 99may be 18 μm to 24 μm, 19 μm to 26 μm, 21 μm to 26 μm, 20 μm to 25 μm, 20 μm to 23 μm, or 19.5 μm to 22 μm.

[0144] In some embodiments, the particle size uniformity U2 of the artificial graphite obtained in step d) satisfies 0.22 < U2 < 0.48, optionally 0.25 < U2 < 0.45, 0.26 < U2 < 0.43, 0.3 < U2 < 0.4, or 0.33 < U2 < 0.38. The particle size uniformity of the obtained artificial graphite is within a proper range, which is beneficial to the particle size uniformity of the final obtained negative electrode active material within a desired range.

[0145] In some embodiments, step B) can comprise, e) coating the core with an organic carbon source, and heat treating to form an amorphous carbon coating layer on at least a portion of the surface of the core to obtain a negative electrode active material.

[0146] In some embodiments, after forming the amorphous carbon coating layer on at least a portion of the surface of the core in step e), the negative electrode active material is obtained by sieving.

[0147] As an example, the artificial graphite obtained in step d) can be mixed with an organic carbon source, and the organic carbon source is coated on at least a portion of the surface of the artificial graphite; and then heat treating at a temperature of 700 ℃ to 1800 ℃ to carbonize the organic carbon source and form an amorphous carbon coating layer on at least a portion of the surface of the artificial graphite. Optionally, the temperature of the heat treating is 1000 ℃ to 1300 ℃.

[0148] In some embodiments, the amount of the organic carbon source added in the coating process C3, the volatile content of the coke raw material C1, the amount of the binder added in the granulation process C2, and the particle size uniformity U2 of the artificial graphite satisfy 20% < (C1+C2+C3) / U2 x 100% < 56%. And the organic carbon source satisfies 1.2% < C3 x residual carbon rate < 2.5%. The amount of the organic carbon source C3 is the percentage of the weight of the organic carbon source added in the coating process to the total weight of the artificial graphite. The residual carbon rate is the residual carbon rate of the organic carbon source, which can be determined by using an LP-5731 coal pitch coking value tester, and the test can refer to GB / T 268 "Determination of Residual Carbon in Petroleum Products", GB / T 8727-2008 "Determination Method of Coking Value of Coal Tar Pitch Products".

[0149] The amount of the organic carbon source added in the coating process satisfies the above relationship, which can improve the granulation degree of the negative active material, thereby being conducive to making the particle size uniformity of the negative active material, and the particle size specific surface area and the proportion of the secondary particles within the range described above. In addition, when the amount of the organic carbon source is within the range, the coating layer has a proper proportion in the negative active material, which can make the negative active material have better kinetic performance and longer cycle life. Optionally, 30%≤(C1+C2+C3) / U2×100%≤48%. Further optionally, 40%≤(C1+C2+C3) / U2×100%≤48%. Optionally, 1.5%≤C3×residual carbon rate≤2.4%, 1.8%≤C3×residual carbon rate≤2.3%, or 2%≤C3×residual carbon rate≤2.2%.

[0150] Optionally, 2%≤C3≤8%. For example, C3 can be 3%, 4%, 5%, 6%, or 7%.

[0151] In some embodiments, the organic carbon source can be selected from one or more of pitch (e.g., coal tar pitch, petroleum pitch), phenolic resin, coconut shell, and the like, and further optionally, pitch.

[0152] In the above preparation process, the coke raw material usually contains some impurity elements (e.g., iron, nickel, chromium, zinc, sulfur, silicon, etc.), and the equipment used in the crushing, shaping, and granulation process also introduces some impurity elements (e.g., iron, copper, etc.). Generally, the impurity element content in the core is small, usually less than 1 ppm.

[0153] In the above preparation process, the organic carbon source used in the coating process and the equipment used for coating introduce trace amounts of impurity elements into the coating layer.

[0154] Secondary battery

[0155] The application also provides a secondary battery. The secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. During the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet.

[0156] [Negative electrode sheet]

[0157] In the secondary battery of the application, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes any one or more of the negative active materials of the application.

[0158] In some embodiments, the negative electrode film layer can optionally include a certain amount of other commonly used negative electrode active materials, such as one or more of natural graphite, other artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, in addition to the negative electrode active materials described above. The silicon-based materials can be selected from one or more of elemental silicon, silicon oxides, and silicon-carbon composites. The tin-based materials can be selected from one or more of elemental tin, tin oxides, and tin alloys.

[0159] In the secondary battery of the present application, the negative electrode sheet generally includes a negative electrode active material and, optionally, a binder, an optional conductive agent, and other optional additives, and is generally formed by coating and drying a negative electrode slurry. The negative electrode slurry is generally formed by dispersing and uniformly stirring the negative electrode active material and, optionally, the conductive agent and the binder in a solvent. The solvent can be N-methyl pyrrolidone (NMP) or deionized water.

[0160] As an example, the conductive agent can include one or more of super-P, carbon black (e.g., acetylene black, ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0161] As an example, the binder can include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0162] Other optional additives are, for example, thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), PTC thermistor materials, and the like.

[0163] In addition, in the secondary battery of the present application, the negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the present application can further include a conductive primer layer (e.g., composed of a conductive agent and a binder) interposed between the negative electrode current collector and the first negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the present application can further include a protective cover layer covering the surface of the second negative electrode film layer.

[0164] [Positive electrode sheet]

[0165] In the secondary battery of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite in the thickness direction of the positive electrode current collector, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0166] In the secondary battery of the present application, the positive electrode active material can employ a positive electrode active material for a secondary battery known in the art. For example, the positive electrode active material can include one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates, and modified compounds of each of them. Examples of the lithium transition metal oxides can include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds of each of them. Examples of the olivine-structured lithium-containing phosphates can include, but are not limited to, one or more of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon, and modified compounds of each of them. The present application is not limited to these materials, and other conventionally known materials that can be used as a positive electrode active material for a secondary battery can also be used.

[0167] In some optional embodiments, in order to further increase the energy density of the battery, the positive electrode active material can include one or more of lithium transition metal oxides represented by Formula 1 and modified compounds of each of them,

[0168] Li a Ni b Co c M d O e A f Formula 1,

[0169] In the Formula 1, 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0170] In the present application, the modified compounds of each of the above materials can be a doping modification or a surface coating modification of the positive electrode active material.

[0171] In the secondary battery of the present application, the positive electrode film layer generally contains a positive electrode active material and, optionally, a binder and an optional conductive agent, and is generally formed by coating a positive electrode slurry and drying and cold-pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material and, optionally, a conductive agent and a binder, etc. in a solvent and stirring uniformly. The solvent can be N-methyl pyrrolidone (NMP).

[0172] As an example, the binder for the positive electrode film layer can include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0173] As an example, the conductive agent for the positive electrode film layer can include one or several of super-P, carbon black (e.g., acetylene black, ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0174] In the secondary battery of the present application, the positive current collector can employ a metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector). As an example, the positive current collector can employ an aluminum foil.

[0175] [Electrolyte]

[0176] The secondary battery of the present application does not have a specific limitation on the type of electrolyte, which can be selected as needed. For example, the electrolyte can be selected from at least one of a solid-state electrolyte and a liquid electrolyte (i.e., electrolyte solution).

[0177] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0178] In some embodiments, the electrolyte salt can be selected from one or several of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium bis-trifluoromethanesulfonylimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluoro(oxalato)borate), LiBOB (lithium bis(oxalato)borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluoro(dioxalato)phosphate), and LiTFOP (lithium tetrafluoro(oxalato)phosphate).

[0179] In some embodiments, the solvent can be selected from one or several of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0180] In some embodiments, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and / or an additive capable of improving certain performance of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature performance of the battery, an additive capable of improving low-temperature performance of the battery, etc.

[0181] [Separator]

[0182] A separator is also included in some secondary batteries using electrolyte and some secondary batteries using solid electrolyte. The separator is arranged between the positive electrode sheet and the negative electrode sheet and functions as a separator. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used. In some embodiments, the material of the separator can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of the layers can be the same or different.

[0183] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to form an electrode assembly through a winding process or a stacking process.

[0184] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0185] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0186] The shape of the secondary battery is not particularly limited in the present application, and it can be cylindrical, square, or any other shape. For example, Figure 5 is a square structure secondary battery 5 as an example.

[0187] In some embodiments, referring to Figure 6 , the outer package can include a shell 51 and a cover plate 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate form an accommodation cavity. The shell 51 has an opening communicating with the accommodation cavity, and the cover plate 53 is used to cover the opening to close the accommodation cavity. The positive electrode sheet, the negative electrode sheet, and the separator can be used to form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the accommodation cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or several, which can be adjusted according to the demand.

[0188] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0189] Figure 7is a battery module 4 as an example. Refer to Figure 7 In the battery module 4, a plurality of secondary batteries 5 can be arranged in series along the length direction of the battery module 4. Of course, the arrangement can be made in any other manner. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0190] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0191] In some embodiments, the above-mentioned battery module can be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0192] Figure 8 and Figure 9 is a battery pack 1 as an example. Refer to Figure 8 and Figure 9 In the battery pack 1, a battery box and a plurality of battery modules 4 arranged in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3, the upper box body 2 is used to cover the lower box body 3, and forms a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0193] Device

[0194] The present application also provides a device including at least one of the secondary battery, the battery module, or the battery pack of the present application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the device, or can be used as an energy storage unit of the device. The device can be, but is not limited to, a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc. The secondary battery, the battery module, or the battery pack can be selected according to the use requirement of the device.

[0195] Figure 10 is a device as an example. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the device, a battery pack or a battery module can be used.

[0196] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thin and light, and a secondary battery can be used as a power supply.

[0197] Embodiment

[0198] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0199] I. Battery Preparation

[0200] Example 1

[0201] Preparation of negative electrode active materials

[0202] Petroleum coke with a volatile matter content (C1) of 7.87% was used. The petroleum coke was pulverized to obtain D... v Coke feedstock with a micrometer size of 11.8 μm for 50 and 20.1 μm for Dv99.

[0203] The coking raw material is shaped and graded to obtain D v 50 is 13.0μm and D v 99 is a precursor with a diameter of 21.3 μm.

[0204] The precursor was granulated using binder-modified asphalt, with binder C2 accounting for 5%. The resulting granulated product had a D... v 50 is 13.7μm and D v 99 is 21.9μm.

[0205] The granulated product was graphitized at 3000℃ and then sieved to obtain artificial graphite. The D of the artificial graphite... v 99 is 22.9μm.

[0206] Then, artificial graphite is coated with organic carbon source pitch and subjected to carbonization treatment. The amount of organic carbon source C3 is 3%, resulting in a negative electrode active material, which includes an artificial graphite core and an amorphous carbon coating layer covering the surface of the artificial graphite core. The negative electrode active material satisfies: D v 50 is 14.5μm, D v The size of 99 is 22.3μm, and the specific capacity is 355.2mAh / g.

[0207] Preparation of negative electrode sheet

[0208] The prepared negative electrode active material, binder styrene-butadiene rubber (SBR), thickening agent sodium carboxymethyl cellulose (CMC-Na) and conductive agent carbon black (Super P) are mixed in a weight ratio of 96.2:1.8:1.2:0.8 in a proper amount of deionized water, and stirred sufficiently to form a uniform negative electrode slurry; the negative electrode slurry is coated on the surface of the negative electrode current collector copper foil, and then dried, cold-pressed, divided, and cut to obtain a negative electrode sheet. The compaction density of the negative electrode sheet is 1.65 g / cm 3 , and the area density is 123 g / m 2 .

[0209] Preparation of a positive electrode sheet

[0210] Lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black (Super P), and binder PVDF are mixed in a weight ratio of 97.5:1.5:1 in a proper amount of N-methyl pyrrolidone (NMP) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and then dried, cold-pressed, divided, and cut to obtain a positive electrode sheet. The compaction density of the positive electrode sheet is 3.5 g / cm 3 , and the area density is 196 g / m 2 .

[0211] Separator film

[0212] A polyethylene (PE) film is selected as the separator film.

[0213] Preparation of an electrolyte

[0214] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then a sufficient amount of dried lithium salt LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0215] Preparation of a secondary battery

[0216] The positive electrode sheet, the separator film, and the negative electrode sheet are stacked in order, and a reference electrode is added between the separator film and the negative electrode sheet (the reference electrode is used for subsequent performance detection of the battery sample, and can be a lithium sheet, a lithium wire, etc., and the reference electrode should be separated from the positive and negative electrode sheets to prevent contact with any one side of the positive and negative electrode sheets); an electrode assembly is obtained after winding; the electrode assembly is loaded into an outer package, the above electrolyte is added, and then packaging, standing, formation, aging, etc. are performed to obtain a secondary battery.

[0217] Examples 2-20 and Comparative Examples 1-2 were prepared in a similar manner to Example 1, but the preparation parameters of the negative active material were adjusted. The different preparation parameters and product parameters are shown in Tables 2-5.

[0218] II. Battery performance test

[0219] (1) Fast charging performance test

[0220] The secondary batteries prepared in the examples and comparative examples were charged at 25°C at 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour) to 4.25 V, then charged at a constant voltage to a current of 0.05C, and left for 5 minutes, and then discharged at 1C to 2.8 V, and the actual capacity was recorded as C0.

[0221] The batteries were then sequentially charged at 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, and 4.5C0 to 4.25 V or the negative electrode cutoff potential of 0 V (whichever is reached first), and after each charging was completed, the batteries were discharged at 1C0 to 2.8 V, and the negative electrode potential corresponding to 10%, 20%, 30%, …, 80% SOC (State of Charge) at different charging rates was recorded, and the rate-negative electrode potential curve at different SOC states was plotted, and the charging rate corresponding to a negative electrode potential of 0 V at different SOC states was obtained by linear fitting, which was the charging window at the SOC state, and was denoted as C 20％SOC , C 30％SOC , C 40％SOC , C 50％SOC , C 60％SOC , C 70％SOC , C 80％SOC , according to the formula (60 / C 20％SOC + 60 / C 30％SOC + 60 / C 40％SOC + 60 / C 50％SOC + 60 / C 60％SOC + 60 / C 70％SOC + 60 / C 80％SOC ) x 10%, the charging time T (min) of the battery from 10% SOC to 80% SOC was calculated. The shorter the time, the better the fast charging performance of the battery.

[0222] (2) Cycle performance test

[0223] The secondary batteries prepared in Examples and Comparative Examples were charged at 25°C at a constant current of 0.33C to a charge cut-off voltage of 4.25V, then charged at a constant voltage until the current was 0.05C, rested for 5min, then discharged at a constant current of 0.33C to a discharge cut-off voltage of 2.8V, and the initial capacity C0was recorded. Then the batteries were charged according to the strategy described in Table 1, discharged at 0.33C, and the discharge capacity C of each cycle was recorded until the cycle capacity retention rate (Cn / C0x 100%) was 80%, and the cycle number was recorded. The more the cycle number, the higher the cycle life of the battery. n n The cycle number was recorded. The more the cycle number, the higher the cycle life of the battery.

[0224] Table 1

[0225] State of charge SOC of the battery Charge rate (C) 0～10％ 0.33 10％～20％ 3.8 20％～30％ 2.9 30％～40％ 2.4 40％～50％ 2.0 50％～60％ 1.7 60％～70％ 1.4 70％～80％ 1.2 80％～100％ 0.33

[0226] The test results of Examples 1-20 and Comparative Examples 1-2 are shown in Table 3 and Table 5.

[0227] Table 2: Preparation parameters

[0228]

[0229] Table 3: Test results

[0230]

[0231] From the results in Table 3, it can be seen that the negative electrode active material of the application includes a core and a coating layer covering the surface of the core, the core includes artificial graphite, the coating layer includes amorphous carbon, and the negative electrode active material simultaneously satisfies D99≤24μm and D8μm≤D50≤15μm, which can enable the secondary battery using it to have higher energy density, and improve the rapid charging capability and cycle performance. v v

[0232] Comparative Example 1 does not satisfy the above conditions, and has poor rapid charging capability and cycle performance.

[0233]

[0234] In Table 4: A=(C1+C2) / U1x 100%; B=(C1+C2+C3) / U2x 100%.

[0235] Table 5: Test results

[0236]

[0237] From the results of Examples 7-11, it can be seen that when the negative electrode active material also satisfies the particle size uniformity Uniformity in an appropriate range, the rapid charging capability and cycle performance of the battery can be further improved.​​​

[0238] From the results of Examples 12 to 20, it can be seen that when the negative active material further satisfies that the particle size, specific surface area, or secondary particle number ratio is within an appropriate range, the rapid charging capability and cycle performance of the battery can be further improved.

[0239] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present application, and these modifications or replacements shall be encompassed within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A negative electrode active material comprising a core and a coating layer covering at least a part of a surface of the core, the core comprising artificial graphite, the coating layer comprising amorphous carbon, the negative electrode active material having a particle size uniformity of 0.3 to 0.42, and the negative electrode active material satisfying: 0.6 < (Dv90 - Dv10) / Dv50 < 1.8, Dv50 < 24 μm, and Dv90 < 99 μm, wherein, Dv50 is a particle size at 50% of cumulative volume, Dv10 is a particle size at 10% of cumulative volume, and Dv90 is a particle size at 90% of cumulative volume. v 99 < 24 μm, wherein, D v 99 is the particle size corresponding to 99% of the cumulative volume distribution percentage of the negative electrode active material, Dv90 is the particle size corresponding to 90% of the cumulative volume distribution percentage of the negative electrode active material; Dv10 is the particle size corresponding to 10% of the cumulative volume distribution percentage of the negative electrode active material, and Dv50 is the particle size corresponding to 50% of the cumulative volume distribution percentage of the negative electrode active material.

2. The negative active material according to claim 1, wherein, The particle size uniformity of the negative electrode active material is 0.32-0.

38.

3. The negative electrode active material according to claim 1 or 2, wherein, The negative electrode active material satisfies 0.8≤(Dv90-Dv10) / Dv50≤1.

4.

4. The negative active material according to any one of claims 1 to 3, wherein, The particle size specific surface area of the negative electrode active material is 0.4 m 2 / g to 0.75 m 2 / g.

5. The negative active material according to claim 4, wherein, The particle size specific surface area of the negative electrode active material is 0.5 m 2 / g to 0.65 m 2 / g.

6. The negative active material according to any one of claims 1 to 5, wherein, The negative electrode active material comprises secondary particles, and the number ratio of the secondary particles in the negative electrode active material is ≥50%.

7. The negative active material according to claim 6, wherein The negative electrode active material comprises secondary particles, and the number ratio of the secondary particles in the negative electrode active material is 70%-95%.

8. The negative active material according to any one of claims 1 to 7, wherein, The volume particle size distribution D of the negative electrode active material v 90 is 13 to 18 μm.

9. The negative active material according to claim 8, wherein, The volume particle size distribution D of the negative electrode active material v 90 is 14 to 17 μm.

10. The negative active material according to any one of claims 1 to 9, wherein, The volume particle size distribution D of the negative electrode active material v 10 is 5 to 10 μm.

11. The negative active material according to claim 10, wherein, The volume particle size distribution D of the negative electrode active material v 10 is 6 to 8 μm.

12. The negative active material according to any one of claims 1 to 11, wherein, The negative electrode active material further satisfies one or several of the following (1)-(4): (1) The graphitization degree of the negative electrode active material is 91.0%-96.0%; (2) The gram capacity of the negative electrode active material is 345 mAh / g-360 mAh / g; (3) the tap density of the negative electrode active material is 0.9 g / cm 3 ~ 1.3 g / cm 3 ; (4) the powder compaction density of the negative electrode active material under 2 kN pressure is 1.55 g / cm 3 ~ 1.67 g / cm 3 .

13. The negative active material according to claim 12, wherein, The negative electrode active material further satisfies one or several of the following (1)-(4): (1) The graphitization degree of the negative electrode active material is 94.0%-95.0%; (2) The gram capacity of the negative electrode active material is 350 mAh / g-358 mAh / g; (3) the tap density of the negative electrode active material is 1.0 g / cm 3 ~ 1.1 g / cm 3 ; (4) the powder compaction density of the negative electrode active material under 2 kN pressure is 1.60 g / cm 3 ~ 1.65 g / cm 3 .

14. A preparation method of a negative electrode active material, comprising the following steps: A) providing a core, wherein the core comprises artificial graphite; B) coating the core to form a coating layer on at least a part of the surface of the core, to obtain a negative electrode active material, the coating layer comprising amorphous carbon, the negative electrode active material having a particle size uniformity of 0.3-0.42, and the negative electrode active material satisfying: 0.6≤(Dv90-Dv10) / Dv50≤1.8, D v 99≤24μm, wherein, D v 99 is the particle size corresponding to the cumulative volume distribution percentage of 99% of the negative electrode active material, Dv90 is the particle size corresponding to the cumulative volume distribution percentage of 90% of the negative electrode active material; Dv10 is the particle size corresponding to the cumulative volume distribution percentage of 10% of the negative electrode active material, and Dv50 is the particle size corresponding to the cumulative volume distribution percentage of 50% of the negative electrode active material.

15. The method of making according to claim 14, wherein, In the step A), the preparation of the artificial graphite comprises: a) providing a coke raw material; b) performing a shaping treatment on the coke raw material to obtain a precursor; c) performing granulation on the precursor to obtain a granulation product; d) subjecting the granulated product to graphitization treatment to obtain artificial graphite, the artificial graphite having a volume average particle diameter D v 50 is 6 μm to 14 μm.

16. The method of making according to claim 15, wherein, The particle size uniformity of the precursor is denoted as U1, and satisfies 0.2≤U1≤0.55; or, The particle size uniformity of the artificial graphite is denoted as U2, and satisfies 0.22≤U2≤0.

48.

17. The method of making according to claim 16, wherein, 0.3≤U1≤0.45; or, 0.3≤U2≤0.4。 18. The method of making according to any one of claims 15-17, wherein, The volatile content of the coke raw material is denoted as C1, the particle size uniformity of the precursor is denoted as U1, and a binder is added in the granulation process of the step c), and the amount of the binder is denoted as C2, and the preparation method satisfies 21%≤(C1+C2) / U1×100%≤50%.

19. The method of making according to claim 18, wherein, 31%≤(C1+C2) / U1×100%≤35%.

20. The method of making according to any one of claims 15-19, wherein, The volatile content C1 of the coke raw material satisfies 1%≤C1≤12%.

21. The method of making according to claim 20, wherein, 5％≤C1≤9％。 22. The method of making according to any one of claims 15-21, wherein, The coke raw material comprises one or several of petroleum-based non-acicular coke and petroleum-based acicular coke.

23. The method of making according to claim 22, wherein, The coke raw material comprises petroleum green coke.

24. The method of making according to any one of claims 15-23, wherein, The step B) comprises: e) coating the core with an organic carbon source, and performing heat treatment to form an amorphous carbon coating layer on at least a part of the surface of the core to obtain the negative electrode active material.

25. The method of making according to any one of claims 15-24, wherein, The step B) comprises: coating the core with an organic carbon source, heat treating, and forming an amorphous carbon coating layer on at least a part of the surface of the core to obtain the negative electrode active material; wherein the volatile content of the coking raw material is denoted as C1; a binder is added in the granulation process of the step c), and the amount of the binder is denoted as C2; the particle size uniformity of the artificial graphite is denoted as U2; the amount of the organic carbon source added in the step e) is denoted as C3; and the preparation method satisfies: 20%≤(C1+C2+C3) / U2×100%≤56%, and 1.2%≤C3×residual carbon rate≤2.5%. 26.A secondary battery comprising a negative electrode sheet, the negative electrode sheet comprising the negative electrode active material according to any one of claims 1-13 or prepared by the method according to any one of claims 14-25. 27.An apparatus comprising the secondary battery according to claim 26.

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