Negative active material as well as preparation method and application thereof

Abstract

The invention discloses a negative electrode active material as well as a preparation method and application thereof, and belongs to the technical field of battery materials. Comprising graphite secondary particles formed by graphite primary particles and carbon particles located on the surfaces of the graphite secondary particles, 8 < Dv50 / P1 + Dv '50 / P2 < 14, and 0 < 10s / k < 4.5; dv50 is the corresponding particle size when the cumulative particle size distribution percentage of the graphite primary particles reaches 50%; p1 is the compaction density of the graphite primary particles; dv '50 is the corresponding particle size when the cumulative particle size distribution percentage of the carbon particles reaches 50%; p2 is the compaction density of the carbon particles; s is the specific surface area of the graphite secondary particles; k% is the weight percentage content of the carbon particles in the negative electrode active material. The negative electrode active material improves the charging capability and the energy density.

Description

Technical Field

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

[0002] Lithium-ion batteries (LIBs) have become a widely used energy device in modern portable electronic products due to their advantages such as light weight, high energy density, and long cycle life. The demand for lithium-ion batteries is increasing, especially in areas such as electronic digital products, smart devices, and power tools. However, as users place increasingly higher demands on the energy density, fast charging capability, and service life of portable devices, existing lithium-ion battery technology still faces significant technical bottlenecks in achieving high energy density and fast charging performance. The negative electrode material of a lithium-ion battery directly affects its electrochemical performance, especially during high-rate charge and discharge processes, where the stability, conductivity, and ion diffusion capacity of the negative electrode material are particularly important. Existing negative electrode materials are mostly based on graphite, which has excellent conductivity and high reversible capacity, but its structure is prone to polarization during high-rate charging, resulting in prolonged charging time. In addition, during the electrode coating process, uneven coating or surface morphology defects can easily cause localized lithium deposition, seriously affecting the battery's charge and discharge efficiency and safety.

[0003] In response to the above problems, some technical solutions have attempted to improve the conductivity and structural stability of negative electrode materials by improving the morphology of graphite particles, increasing the close contact between particles, or introducing carbon coating technology. For example, coating graphite particles with carbon materials can reduce interfacial impedance and improve the transmission efficiency of lithium ions. However, traditional carbon coating technology has the problem of uneven particle gaps and poor electrolyte permeability, which leads to limited ion transmission and difficulty in achieving fast charging. In addition, the morphology of existing graphite particles is difficult to accurately control, especially the lack of sphericity, which leads to enhanced anisotropy of the electrode, thereby exacerbating the polarization phenomenon and limiting the fast charging capability of the battery.

[0004] Therefore, it is urgent to find a negative electrode active material to solve the problems of low charging capacity and energy density in the above-mentioned prior art. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a negative electrode active material with faster charging capability and higher energy density.

[0006] The present invention also provides a method for preparing the negative electrode active material.

[0007] The present invention also provides a negative electrode sheet comprising the negative electrode active material.

[0008] The present invention also provides a secondary battery comprising the negative electrode plate.

[0009] The present invention also provides an electric device comprising the secondary battery.

[0010] According to an embodiment of the first aspect of the present invention, a negative electrode active material is provided, the negative electrode active material comprising graphite secondary particles formed from graphite primary particles and carbon particles located on surfaces of the graphite secondary particles, the negative electrode active material satisfying the following relationship: 8 < Dv50 / P1 + Dv'50 / P2 < 14, 0 < 10s / k < 4.5;

[0011] Wherein, Dv50 is the particle size corresponding to when the cumulative particle size distribution percentage of the graphite primary particles reaches 50%, in μm; P1 is the compacted density of the graphite primary particles, in g / cm 3 Dv'50 is the particle size corresponding to when the cumulative particle size distribution percentage of the carbon particles reaches 50%, in μm; P2 is the compacted density of the carbon particles, in g / cm 3 ; s is the specific surface area of ​​the graphite secondary particles, in m 2 / g; k% is the weight percentage of the carbon particles in the negative electrode active material.

[0012] The negative electrode active material according to the embodiment of the present invention has at least the following beneficial effects:

[0013] The negative electrode active material of the present invention forms a uniformly distributed carbon coating layer by controlling the size of carbon particles and directly bonding the carbon particles to graphite secondary particles, thereby effectively reducing the interfacial impedance of the negative electrode material. The presence of carbon particles effectively improves the transmission efficiency of lithium ions within the negative electrode material, reduces the polarization effect during high-rate charging and discharging, and improves the fast charging performance of the battery.

[0014] This invention achieves a balance between compaction capacity and kinetic capacity by limiting the ratio of the particle size and compaction density of primary graphite particles to that of carbon particles, satisfying the equation Dv50 / P1 + Dv'50 / P2. This further enhances the charge and energy density of the negative electrode active material. By limiting the mass percentage of carbon particles in the negative electrode active material and the specific surface area of ​​secondary graphite particles, this equation ensures sufficient carbon particle coverage for optimal compatibility of the composite particles, increases particle isotropy, and prevents excessive carbon particle agglomeration, which reduces compaction and energy density. This not only improves the conductivity of the negative electrode material but also optimizes the structural stability and cycle life of the particles.

[0015] According to some embodiments of the present invention, the particle size Dv50 of the graphite primary particles is 7 to 15 μm.

[0016] According to some embodiments of the present invention, the compacted density P1 of the graphite primary particles is 1.7 to 2.1 g / cm 3 .

[0017] According to some embodiments of the present invention, the particle size Dv'50 of the carbon particles is 3-5 μm.

[0018] According to some embodiments of the present invention, the compacted density P2 of the carbon particles is 0.8 to 1.8 g / cm 3 .

[0019] According to some embodiments of the present invention, the compacted density P2 of the carbon particles is 1 to 1.8 g / cm 3 .

[0020] According to some embodiments of the present invention, the compaction density of carbon particles can be controlled by subjecting them to an oxidation treatment at 250° C.±50° C. in an air atmosphere for 0 to 24 hours.

[0021] According to some embodiments of the present invention, the specific surface area s of the graphite secondary particles is 1.0 to 1.7 m 2 / g.

[0022] According to some embodiments of the present invention, the specific surface area s of the graphite secondary particles can be controlled by subjecting the graphite secondary particles to an oxidation treatment at 300-500° C. for 5-32 hours in an air atmosphere.

[0023] According to some embodiments of the present invention, the value of k is 3-15.

[0024] According to some embodiments of the present invention, the value of k is 5 to 10. Thus, the polarization resistance is lower and the energy density is higher.

[0025] According to some embodiments of the present invention, the major diameter b and minor diameter a of the graphite secondary particles satisfy the following relationship: 1≤b / a≤2. Thus, limiting the major diameter to minor diameter ratio of the graphite secondary particles makes the particles more spherical, improves the isotropy of the electrode, reduces polarization, and increases high-rate constant-current charging time, achieving super-fast charging speeds.

[0026] According to some embodiments of the present invention, the major diameter d and minor diameter c of the carbon particles satisfy a d / c ratio of 2.5 to 4.5. This limits the aspect ratio of the carbon particles, making them closer to flakes, ensuring a sufficient bonding area to reduce interfacial impedance, promote lithium ion transport and diffusion, further reduce polarization, and increase constant current time.

[0027] According to some embodiments of the present invention, the R value of the carbon particles is 0.5 to 2.0. Wherein, R value = ID / IG. Thus, limiting the R value of the surface carbon particles ensures the disorder of the interface, is beneficial to ion diffusion, and reduces polarization. Furthermore, the R value is calculated by the following method: the Raman spectrum of the negative electrode active material is tested by a laser microconfocal Raman spectrometer (instrument model is HR Evolution, HORIBA, France), and the laser wavelength of the Raman spectrometer can be in the range of 532nm to 633nm. The powder of the negative electrode active material is taken for testing. During the test, a range of 100μm×100μm is scanned, and the particles within the area are scanned. 100 points are tested at equal intervals, and the test range of each point is 0.02cm -1 to 0.05cm -1 Between. Recorded at 1300cm -1 to 1400cm -1 The peak between the two is the D peak, at 1500 cm -1 to 1600cm -1 The peak between the two peaks is the G peak. La Spec software was used for data processing to obtain the peak intensities of the D peak and the G peak of the particle, which were recorded as ID and IG, respectively. The ID / IG intensity ratio of each point was calculated, and then the average value of 100 points was calculated as the final ID / IG intensity ratio.

[0028] According to some embodiments of the present invention, the carbon particles are soft carbon particles or hard carbon particles.

[0029] According to an embodiment of the second aspect of the present invention, a method for preparing the negative electrode active material is provided, the steps of the preparation method comprising:

[0030] S1. Mixing graphite primary particles with a first binder to form graphite secondary particles;

[0031] S2, mixing the carbon particles, the second binder and the graphite secondary particles, and graphitizing them to obtain composite particles;

[0032] S3. Mixing the composite particles with a coating agent and performing carbonization treatment to obtain the negative electrode active material.

[0033] According to some embodiments of the present invention, the graphite primary particles are natural graphite or artificial graphite.

[0034] According to some embodiments of the present invention, in step S1, the mass ratio of the graphite primary particles to the first binder is 7-9:1-2.

[0035] According to some embodiments of the present invention, in steps S1 and S2, the first binder and the second binder are independently selected from at least one of coal tar, coal pitch, and petroleum pitch.

[0036] According to some embodiments of the present invention, in step S3, the coating agent includes at least one of asphalt, epoxy resin, polyester resin, and polyurethane resin.

[0037] According to some embodiments of the present invention, in step S1, the temperature of the mixing treatment is 250-550°C.

[0038] According to some embodiments of the present invention, in step S1, the mixing treatment time is 5 to 48 hours.

[0039] According to some embodiments of the present invention, in step S2, the temperature of the graphitization treatment is 2800-3500°C.

[0040] According to some embodiments of the present invention, in step S2, the graphitization treatment time is 10 to 200 hours.

[0041] According to some embodiments of the present invention, in step S3, the temperature of the carbonization treatment is 700-1200°C.

[0042] According to some embodiments of the present invention, in step S3, the carbonization treatment time is 12 to 48 hours.

[0043] According to an embodiment of the third aspect of the present invention, there is provided a negative electrode plate comprising the above-mentioned negative electrode active material.

[0044] According to an embodiment of the fourth aspect of the present invention, there is provided a secondary battery comprising the above-mentioned negative electrode plate.

[0045] According to an embodiment of a fifth aspect of the present invention, there is provided an electrical device comprising the above-mentioned secondary battery of the present invention.

[0046] Unless otherwise specified, “between” in the present invention includes the number itself, for example, “between 2 and 3” includes the endpoint values ​​2 and 3.

[0047] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0049] Figure 1 Schematic diagram of the structure of the negative electrode active material in Example 1 of the present invention. DETAILED DESCRIPTION

[0050] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0051] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0052] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, and connecting should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0053] In the description of the present invention, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0054] The test method of each parameter in the present invention is:

[0055] 1) Powder compaction P1 and P2 test methods:

[0056] The powder compaction density is tested using methods known in the art. Refer to GB / T 24533-2009 and use an electronic pressure testing machine (UTM7305) to test: place a certain amount of powder on a compaction die, set a pressure of 5 tons, and read the thickness of the powder at this pressure on the device to calculate the powder compaction density P.

[0057] 2) Dv50 and Dv'50 of graphite primary particles and carbon particles were measured using a laser diffraction particle size distribution analyzer (Malvern Mastersizer 3000) according to the particle size distribution laser diffraction method GB / T19077-2016 to obtain Dv50 and Dv'50;

[0058] 3) Test method for specific surface area of ​​graphite secondary particles: The specific surface area of ​​the negative electrode active material was measured using a specific surface area analyzer (Tristar II 3020M) by the nitrogen adsorption / desorption method: the negative electrode active material sample was dried in a vacuum drying oven, then placed in a sample tube and measured in the analyzer.

[0059] Example 1

[0060] This embodiment provides a negative electrode active material, and the negative electrode active material has the following characteristics:

[0061] The primary graphite particles are artificial graphite, and the short diameter a and long diameter b of the secondary graphite particles satisfy b / a of 2.0;

[0062] The surface of the graphite secondary particles is bonded with hard carbon particles, with a short diameter c and a long diameter d, satisfying d / c = 2.5;

[0063] The graphite primary particle size Dv50 is 15 μm and the compacted density P1 is 2.1 g / cm 3 The hard carbon particles Dv′50 is 5 μm and the compacted density P2 is 1.2 g / cm 3 , and the four parameters satisfy the relationship: 8<Dv50 / P1+Dv′50 / P2<14.

[0064] The graphite secondary particle size is 1.1m 2 / g, the R value of the hard carbon particles is 1, the mass ratio k is 5wt%, and the relationship between k and s satisfies: 10s / k<4.5. The structure of the negative electrode active material is as follows Figure 1 As shown, the yellow circles are hard carbon particles.

[0065] This embodiment also provides a method for preparing the above-mentioned negative electrode active material, comprising uniformly mixing artificial graphite and a binder, high-temperature asphalt (Handan Yeneng Chemical Technology Co., Ltd., model G8054) in a mass ratio of 8:2, then placing the mixture into a horizontal reactor, heating it to 300° C., and maintaining the temperature for 24 hours to obtain secondary graphite particles;

[0066] The graphite secondary particles were oxidized at 350 °C in air atmosphere for 16 h;

[0067] The hard carbon particles were oxidized at 250 °C in air atmosphere for 12 h;

[0068] Graphite secondary particles, resin hard carbon (STY-1 from Kuraray) and high-temperature asphalt (Handan Yeneng Chemical Technology Co., Ltd., model G8054) were mixed in a mass ratio of 1:0.02:0.02 and subjected to high-temperature graphitization treatment at a graphitization temperature of 3000°C and a graphitization time of 100 hours to obtain composite particles. During the process, the hard carbon can be bonded to the secondary graphite particles, and the binder is partially converted into a graphite-like structure.

[0069] The composite particles and a resin coating agent (FJ-03 from Jinan Shengquan Group) were mixed in a mass ratio of 1:0.02, and carbonized at 1000° C. for 24 hours to obtain the negative electrode active material.

[0070] This embodiment also provides a negative electrode sheet, the specific preparation method of which includes:

[0071] The negative electrode active material, binder styrene-butadiene rubber, and dispersant sodium carboxymethyl cellulose are dispersed in deionized water at a mass ratio of 98:1:1. The mixture is thoroughly stirred and mixed to obtain the negative electrode slurry. After drying, the slurry is cold pressed, trimmed, cut, and slit to produce the negative electrode sheets for lithium-ion batteries.

[0072] This embodiment also provides a lithium-ion battery, the specific preparation method of which includes:

[0073] The positive electrode active material NCM523, the conductive agent acetylene black, and the binder PVDF were mixed in a mass ratio of 97:2:1, the solvent NMP was added, and the mixture was stirred under the action of a vacuum mixer until the system became uniform to obtain a positive electrode slurry; the positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying, and then cold pressed and cut to obtain positive electrode sheets.

[0074] Preparation of electrolyte:

[0075] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0076] Preparation of isolation membrane:

[0077] Polyethylene film was selected as the isolation film.

[0078] Preparation of lithium-ion batteries:

[0079] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation, and then wound to obtain a bare cell; the bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0080] The only difference between the negative electrode active materials of Examples 2 to 17 and Comparative Examples 1 to 4 and Example 1 is the parameters listed in Table 1. The rest are the same as Example 1.

[0081] Table 1 Characteristics of negative electrode active materials of Examples 1 to 17 and Comparative Examples 1 to 4

[0082]

[0083]

[0084] Performance testing:

[0085] (1) Dynamic performance test: At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were fully charged at 5C and fully discharged at 1C for 50 times, then fully charged at 5C. The negative electrode plates were then disassembled and the lithium deposition on the surface of the negative electrode plates was observed. A lithium deposition area of ​​less than 5% on the negative electrode surface was considered mild, a lithium deposition area of ​​5% to 40% on the negative electrode surface was considered moderate, and a lithium deposition area of ​​more than 40% on the negative electrode surface was considered severe.

[0086] (2) Energy density (Wh / kg) = discharge capacity (Wh) / mass of lithium-ion secondary battery (kg);

[0087] (3) Constant current time test method: At 25°C, the lithium ion batteries prepared in the examples and comparative examples were discharged at a constant current of 1C to 3.0V and charged at a constant current and constant voltage of 5C to 4.5V. The constant current charging time was the required constant current time.

[0088] (4) Polarization impedance test method:

[0089] Charge the lithium-ion battery to 4.5V at a constant current of 1.5C, and then charge it to 0.05C at a constant voltage. Let it stand for 30 minutes; discharge it for 10 seconds at a current of 0.1C (take a point once every 0.1 seconds and record the corresponding voltage value U1), and discharge it for 360 seconds at a current of 1C (take a point once every 0.1 seconds and record the corresponding voltage value U2). Repeat the charge and discharge steps 5 times. "1C" is the current value that completely discharges the battery capacity within 1 hour. The DC resistance (DCR) is calculated according to the following formula: R = (U2-U1) / (1C-0.1C). The obtained DCR is the concentration polarization resistance of this application, which is the value under 50% SOC (state of charge) state.

[0090] The performance test results of the negative electrode active materials of Examples 1 to 17 and Comparative Examples 1 to 4 are shown in Table 2;

[0091] Table 2 Test results of negative electrode active material properties of Examples 1 to 17 and Comparative Examples 1 to 4

[0092]

[0093]

[0094] From the data in Table 2, it can be seen that according to Examples 2 and 3, the smaller the ratio of the major diameter b to the minor diameter a of the graphite secondary particles, the more round the graphite secondary particles are, the lower the OI value and the lower the impedance; according to Examples 4 to 7, the particle size of the graphite primary particles is reduced, the ion transmission distance is shortened, the polarization is reduced, and the charging is improved. According to Examples 8 and 9, when the ratio of the major diameter d to the minor diameter c of the carbon particles increases, the carbon particles tend to be more flaky and the carbon particles are more attached to the secondary particles, which promotes the transmission and diffusion of lithium ions and further reduces polarization. According to Examples 10 and 11, the ratio increases, the electrolyte contact area increases, and the polarization is reduced. According to Examples 12 and 13, the carbon particle compaction P2 decreases, the disorder decreases, the polarization increases, and the interface deteriorates. According to Example 14, the carbon particle size is reduced, the bonding distribution on the graphite secondary particles is more uniform, the isotropy is better, and at the same time, the energy density is guaranteed by increasing the powder pressure through oxidation treatment.

[0095] Examples 15, 16 and 17 show changes in the k-value content. As the proportion of carbon particles increases, the carbon particles covering the surface of the secondary particles become increasingly dense, the particle isotropy increases, and the polarization decreases. However, if there are too many, the carbon particles will stack on themselves, the lithium ion conduction path will increase, and the corresponding polarization will increase. In addition, since the carbon particles themselves have a low compaction, the energy density loss increases accordingly as the composite ratio increases.

[0096] The difference between Comparative Example 1 and Example 1 is that no carbon particles are added, there is no carbon particle layer, and the impedance is large; the difference between Comparative Example 2 is that the values ​​are all within the range, but do not satisfy the relationship: 8 < Dv50 / P1 + Dv'50 / P2 < 14, that is, the compaction of secondary particles and carbon particles is small at the same time and the secondary particle size is large, more binder is used, and the loss ED is large; Comparative Example 3 does not satisfy the relationship: 0 < 10s / k < 4.5, indicating that the mass ratio of carbon particles does not match the secondary particle ratio, and sufficient carbon particle coating cannot be guaranteed, resulting in a large impedance. Comparative Example 4 has 10s / k = 5.7, which is not within the scope of the present invention, cannot guarantee sufficient carbon particle coating, and cannot guarantee effective impedance reduction, resulting in lithium precipitation.

[0097] While the embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A negative electrode active material, characterized in that The negative electrode active material includes graphite secondary particles formed from graphite primary particles and carbon particles located on the surface of the graphite secondary particles, and the negative electrode active material satisfies the following relationship: 8<Dv50 / P1+Dv'50 / P2<14, 0<10s / k<4.5; Wherein, Dv50 is the particle size corresponding to when the cumulative particle size distribution percentage of the graphite primary particles reaches 50%, in μm; P1 is the compacted density of the graphite primary particles, in g / cm 3 Dv'50 is the particle size corresponding to when the cumulative particle size distribution percentage of the carbon particles reaches 50%, in μm; P2 is the compacted density of the carbon particles, in g / cm 3 ; s is the specific surface area of ​​the graphite secondary particles, in m 2 / g; k% is the weight percentage of the carbon particles in the negative electrode active material.

2. The negative electrode active material according to claim 1, characterized in that Satisfy at least one of the following (1) to (6): (1) The particle size Dv50 of the graphite primary particles is 7 to 15 μm; (2) The compacted density P1 of the graphite primary particles is 1.7 to 2.1 g / cm 3 ; (3) The particle size Dv'50 of the carbon particles is 3 to 5 μm; (4) The compacted density P2 of the carbon particles is 0.8 to 1.8 g / cm 3 ; (5) The specific surface area s of the graphite secondary particles is 1.0 to 1.7 m 2 / g; (6) The value of k is 3 to 15.

3. The negative electrode active material according to claim 1 or 2, characterized in that Satisfy at least one of the following (7) to (10): (7) The major diameter b and minor diameter a of the graphite secondary particles satisfy the following conditions: 1≤b / a≤2; (8) The major diameter d and minor diameter c of the carbon particles satisfy d / c of ​​2.5 to 4.5; (9) The R value of the carbon particles is 0.5 to 2.0; (10) The carbon particles are soft carbon particles or hard carbon particles.

4. A method for preparing a negative electrode active material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: S1. Mixing graphite primary particles with a first binder to form graphite secondary particles; S2, mixing the carbon particles, the second binder and the graphite secondary particles, and graphitizing them to obtain composite particles; S3. Mixing the composite particles with a coating agent and performing carbonization treatment to obtain the negative electrode active material.

5. The preparation method according to claim 4, characterized in that The graphite primary particles are natural graphite or artificial graphite; and / or, in step S1, the mass ratio of the graphite primary particles to the first binder is 7-9:1-2.

6. The preparation method according to claim 4, characterized in that In steps S1 and S2, the first binder and the second binder are independently selected from at least one of coal tar, coal pitch, and petroleum pitch; and / or, in step S3, the coating agent includes at least one of asphalt, epoxy resin, polyester resin, and polyurethane resin.

7. The preparation method according to claim 4, characterized in that In step S1, the mixing treatment temperature is 250-550° C., and the treatment time is 5-48 hours; And / or, in step S2, the temperature of the graphitization treatment is 2800-3500° C., and the time is 10-200 hours; And / or, in step S3, the temperature of the carbonization treatment is 700-1200° C., and the time is 12-48 hours.

8. A negative electrode plate, characterized in that: The negative electrode active material comprises the negative electrode active material according to any one of claims 1 to 3.

9. A secondary battery, characterized in that: Comprising the negative electrode sheet as claimed in claim 8.

10. An electrical device, characterized in that: Comprising the secondary battery as claimed in claim 9.

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