A negative electrode material, a preparation method therefor, and an application thereof

Abstract

This invention relates to the field of battery technology, specifically to an anode material, its preparation method, and its application. The anode material comprises: a core, the core comprising graphite; and a coating layer disposed on at least a portion of the surface of the core, the coating layer comprising a carbon layer and a transition metal oxide fixed to the surface of the carbon layer near the core. Compared with existing technologies, the anode material provided by this invention, through an amorphous carbon-transition metal oxide coated graphite structure (C-MxOy@Gr), fundamentally solves the problems of low ion migration rate, slow ion diffusion, and polarization existing in traditional lithium-ion battery anode materials under low-temperature conditions, thereby improving battery capacity and charging / discharging efficiency.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a negative electrode material, its preparation method, and its application. Background Technology

[0002] To meet the ever-increasing demand for ultra-high energy density, batteries are required to have fast charging and discharging capabilities. The next generation of high-energy-density rechargeable batteries (LIBs) needs to be developed that are safe, suitable for large-scale application, and low in cost (e.g., for electric vehicles and hybrid electric vehicles). This requires electrode materials with high capacity, long cycle life, and excellent rate performance. Furthermore, lithium-ion batteries currently face severe challenges in extremely cold regions such as northern regions and high-altitude plateaus. At low temperatures, the capacity of lithium-ion batteries decreases significantly, and they may even become unchargeable. This is mainly because at low temperatures, the ion migration rate of the battery decreases, and electrode materials experience slow ion diffusion and polarization, leading to a decrease in battery capacity, reduced charging and discharging efficiency, or even complete malfunction.

[0003] Therefore, developing lithium-ion battery electrode materials that are resistant to extreme cold has significant research value and practical application value. Summary of the Invention

[0004] In view of this, the purpose of this invention is to at least partially solve one of the technical problems in the related art. To this end, this invention provides an anode material, its preparation method, and its application. By coating a graphite structure with an amorphous carbon-transition metal oxide (C-MxOy@Gr), it fundamentally solves the problems of low ion migration rate, slow ion diffusion, and polarization existing in traditional lithium-ion battery anode materials under low-temperature conditions, thereby improving battery capacity and charging / discharging efficiency.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: According to one aspect of the present invention, a negative electrode material is provided, comprising: The kernel comprises graphite; A coating layer is disposed on at least a portion of the surface of the core, the coating layer comprising a carbon layer and a transition metal oxide fixed to the surface of the carbon layer near the core.

[0006] In some embodiments, the specific surface area of ​​the negative electrode material is 0.8 m². 2 / g~2.5m 2 / g.

[0007] In some embodiments, the Dv50 particle size of the negative electrode material is 5 μm to 40 μm.

[0008] In some embodiments, the Raman spectrum of the negative electrode material satisfies: 0.5 ≤ AD / (AD+AG) ≤ 1.5, where AD is the wavenumber of the Raman spectrum at 1340 cm⁻¹. -1 ~1350cm -1 The peak area at AG represents the wavenumber of the Raman spectrum at 1580 cm⁻¹. -1 ~1590cm -1 Peak area at that location.

[0009] In some of these embodiments, the graphite has a particle size that satisfies Dv10: 4μm~7μm.

[0010] In some of these embodiments, the graphite has a particle size that satisfies Dv50: 11 μm to 18 μm.

[0011] In some of these embodiments, the graphite has a particle size that satisfies Dv90: 20 μm to 27 μm.

[0012] In some of these embodiments, the graphite has a particle size that satisfies Dv99: 32μm~39μm.

[0013] In some embodiments, the thickness of the carbon layer in the coating is 0.01 μm to 0.3 μm.

[0014] In some embodiments, the transition metal oxide in the coating layer includes one or more of niobium oxide, iron oxide, copper oxide, and manganese oxide.

[0015] In some embodiments, the particle size of the transition metal oxide in the coating layer is 0.002 μm to 0.10 μm.

[0016] According to another aspect of the present invention, the present invention provides a method for preparing the negative electrode material described in the above technical solution, comprising the following steps: a) The graphite raw material is successively crushed, shaped and graded, graphitized and demagnetized by sieving to obtain the core material; b) Mix the core material obtained in step a) with a transition metal oxide and perform physical anchoring to obtain an intermediate product; c) The intermediate product obtained in step b) is mixed with the carbon source solution and then dried, carbonized and cooled in sequence to obtain the negative electrode material.

[0017] In some of these embodiments, in step a), the graphite raw material includes one or more of needle coke, petroleum coke, anthracite, and natural graphite.

[0018] In some of these embodiments, in step a), the carbon content of the graphite raw material is ≥80%.

[0019] In some of these embodiments, in step a), the particle size of the pulverized material is 8 μm to 25 μm.

[0020] In some of these embodiments, in step a), the graphitization temperature is 2500°C to 3000°C.

[0021] In some of these embodiments, in step b), the mass ratio of the core material to the transition metal oxide is 100:(5~20).

[0022] In some of these embodiments, in step b), the physical anchoring method includes ball milling; the ball milling speed is 50 r / min to 80 r / min, and the time is 1 h to 3 h.

[0023] In some of these embodiments, in step c), the mass ratio of the intermediate product to the carbon source in the carbon source solution is 100:(5~15).

[0024] In some embodiments, in step c), the carbon source solution comprises a carbon source and a solvent, wherein the carbon source comprises one or more of asphalt, resin-based carbon source, and polyimide, and the solvent comprises one or more of tetrahydrofuran, dimethyl sulfoxide, N-methylpyrrolidone, ethylene glycol butyl ether, and acetonitrile; the mass ratio of the carbon source to the solvent is (0.5~20):100; preferably, the carbon source is a mixture of asphalt and resin-based carbon source, wherein the mass percentage of the asphalt is 60%~100%, but not 100%.

[0025] In some of these embodiments, in step c), the drying temperature is 40°C to 60°C.

[0026] In some embodiments, step c) includes the carbonization process comprising: placing the dried sample into a tube furnace and heating it to 800°C to 1200°C at a rate of 2°C / min to 10°C / min under an inert gas atmosphere and holding it at that temperature for 4 to 6 hours to complete the carbonization process; the inert gas includes one or more of helium, neon, argon, krypton, xenon, and radon.

[0027] According to another aspect of the present invention, a negative electrode sheet is provided, comprising a negative electrode current collector and a negative electrode coating disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode coating comprises the negative electrode material described in the above-described technical solution or the negative electrode material prepared by the preparation method described in the above-described technical solution.

[0028] According to another aspect of the present invention, a lithium-ion battery is provided, comprising the negative electrode sheet described in the above technical solution.

[0029] Implementing the technical solution of the present invention has at least the following beneficial effects: The anode material provided by this invention utilizes an amorphous carbon-transition metal oxide-coated graphite structure (C-MxOy@Gr), which provides more diffusion channels for lithium ions, achieving a peak charge rate of 12C at room temperature. Simultaneously, the transition metal oxide is anchored to the graphite surface, strengthening the interfacial contact between the transition metal oxide and the graphite matrix, improving electrochemical reactivity, and further increasing the diffusion rate of lithium ions. During high-current charge and discharge, electrode polarization is mitigated, enhancing the lithium intercalation capability of the electrode material. Furthermore, the amorphous carbon layer coating helps absorb stress release during lithium intercalation, improving expansion and increasing battery cycle life. More importantly, the synergistic coating of the amorphous carbon layer and the transition metal oxide improves the ion diffusion efficiency of the anode material, enhancing its electrochemical lithium storage performance at low temperatures.

[0030] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0031] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0032] Figure 1 This is a schematic diagram of the structure of the negative electrode material provided in an embodiment of the present invention.

[0033] Figure 2 This is a SEM image of the negative electrode material provided in Embodiment 1 of the present invention.

[0034] Figure 3 The graph shows the full-charge expansion rate results of the negative electrode sheets in Examples 1-8 and Comparative Examples 1-3 of the present invention.

[0035] Explanation of reference numerals in the attached figures: 1-Core; 2-Carbon layer; 3-Transition metal oxide; 4-Covering layer.

[0036] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0037] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0038] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0039] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0040] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0041] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0042] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0043] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0044] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0045] Currently, lithium-ion batteries face severe challenges in operating in extremely cold regions such as northern regions and high-altitude plateaus. In low-temperature environments, the capacity of lithium-ion batteries decreases significantly, and they may even become unchargeable. This is mainly because at low temperatures, the ion migration rate of the battery decreases, and electrode materials experience slow ion diffusion and polarization, leading to reduced battery capacity, decreased charge / discharge efficiency, and even malfunction. Therefore, developing cold-resistant lithium-ion battery electrode materials has significant research importance and practical application value.

[0046] Conventional graphite anode materials possess advantages such as high theoretical specific capacity, low operating potential, low cost, and high stability, making them one of the most commonly used anode materials for lithium-ion batteries. However, graphite cannot meet the energy storage requirements under low-temperature conditions. Based on this, the inventors of this invention considered modifying graphite: on the one hand, they attempted to change the structural characteristics of graphite, such as reducing particle size, increasing interlayer spacing, creating pores, doping, and introducing defects, thereby shortening the lithium-ion diffusion path and accelerating lithium-ion diffusion efficiency; however, the inventors found that the above improvement strategies would damage the graphite structure, increase the specific surface area, and lead to instability in the cycling process and reversible capacity loss. On the other hand, attempts have been made to surface-coat graphite with materials such as carbon, metal oxides, and polymers. Metal oxides have a high theoretical specific capacity (700~1000mAh), which means that the energy density of the battery can be improved. During the charging and discharging process, in addition to the traditional intercalation / deintercalation mechanism, metal oxides also have some other reaction mechanisms, such as alloying reactions and conversion reactions. These unique reaction mechanisms enable the composite materials of metal oxides to quickly intercalate and deintercalate under high-rate charging and discharging conditions, resulting in excellent rate and low-temperature performance. However, metal oxides also have some shortcomings, such as low electronic conductivity. To address this, the inventors of this invention have enhanced their electronic conductivity through methods such as nanostructure design and multiphase system design, thereby obtaining excellent electrochemical performance.

[0047] Based on this, the inventors of this invention constructed a coating layer composed of disordered carbon layer and oxide composite on the surface of graphite particles. The amorphous carbon layer provides more diffusion channels for lithium ions, while the transition metal oxide is anchored on the graphite surface, strengthening the interfacial contact between the transition metal oxide and the graphite matrix, improving electrochemical reaction activity, increasing the diffusion rate of lithium ions, and improving the reversible specific capacity and cycle stability of the anode material.

[0048] According to one aspect of the present invention, a negative electrode material is provided, comprising: The kernel comprises graphite; A coating layer is disposed on at least a portion of the surface of the core, the coating layer comprising a carbon layer and a transition metal oxide fixed to the surface of the carbon layer near the core.

[0049] In this invention, the negative electrode material comprises a core and a coating layer, preferably consisting of a core and a coating layer; wherein the coating layer is disposed on at least a portion of the surface of the core, preferably on the entire surface of the core, thereby achieving complete coating. As an example, see [link to example]. Figure 1 As shown, Figure 1 This is a schematic diagram of the structure of the negative electrode material provided in an embodiment of the present invention, wherein 1 is the core, 2 is the carbon layer, 3 is the transition metal oxide, and 4 is the coating layer.

[0050] The present invention provides an amorphous carbon layer-transition metal oxide coated graphite structure (C-MxOy@Gr). The transition metal oxide has high energy density and high lithium intercalation capability. The amorphous carbon layer can provide more diffusion channels for lithium ions, while the transition metal oxide particles are coated and anchored on the graphite surface to improve electronic conductivity.

[0051] In a specific embodiment of the present invention, the specific surface area (BET) of the negative electrode material is preferably 0.8 m². 2 / g~2.5m 2 / g, for example, 0.8m 2 / g, 1.2m 2 / g, 1.6m 2 / g, 2.0m 2 / g, 2.5m 2 / g or any value between two of these. It should be noted that if the BET is too large, there will be more defect sites in the carbon layer, increasing the reactivity and side reactions; if the BET is too small, the reactivity will decrease, the charging rate will decrease, and the risk of lithium plating will increase. Therefore, this invention can ensure sufficient electrochemical reactivity and avoid the adverse effects of increased side reactions caused by an excessively large specific surface area of ​​the negative electrode material by controlling the specific surface area of ​​the negative electrode material within the above range.

[0052] In a specific embodiment of the present invention, the Dv50 particle size of the negative electrode material is preferably 5μm to 40μm, for example, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, or any value between two of these. It should be noted that when the Dv50 particle size of the negative electrode material is less than 5μm, it may accelerate the reduction and decomposition of the solvent in the electrolyte, generating a large amount of gas and causing the battery to swell. Simultaneously, when the Dv50 particle size of the negative electrode material is greater than 40μm, the long diffusion path may lead to a faster lithium-ion accumulation rate, potentially forming needle-like lithium dendrites.

[0053] In a specific embodiment of the present invention, the Raman spectrum of the negative electrode material satisfies: 0.5 ≤ AD / (AD+AG) ≤ 1.5, where AD is the wavenumber of the Raman spectrum located at 1340 cm⁻¹. -1 ~1350cm-1 The peak area at AG represents the wavenumber of the Raman spectrum at 1580 cm⁻¹. -1 ~1590cm -1 The peak area at [value missing]. It should be noted that the wavenumber of the Raman spectrum is at 1340 cm⁻¹. -1 ~1350cm -1 The presence of this peak (D band, disordered carbon or defective graphite band) reflects the degree of defect in the carbon layer structure; the peak area here is denoted as AD. Meanwhile, the wavenumber of the Raman spectrum is at 1580 cm⁻¹. -1 ~1590cm -1 The presence of the peak at point G (G-band, crystalline graphite band) reflects the degree of order in the long-range carbon layer; the peak area here is denoted as AG. Satisfying the above relationship: 0.5 ≤ AD / (AD+AG) ≤ 1.5, it can improve rate performance without losing too much active lithium. Specifically: By controlling the Raman spectrum of the negative electrode material within the aforementioned range, sufficient electronic conduction efficiency can be ensured, avoiding excessively high battery impedance. At the same time, sufficient ion insertion sites can be provided to ensure full release of battery capacity. When the Raman spectrum value of the negative electrode material is too high, the negative electrode material is prone to excessive activity and side reactions. When the Raman spectrum value of the negative electrode material is too low, the degree of graphitization of the negative electrode material increases, thereby affecting the diffusion of lithium ions and potentially leading to a deterioration in the rate performance of the battery.

[0054] The Raman spectrum of the negative electrode material provided by this invention can be obtained under the following test conditions: During the test, the laser wavelength of the Raman spectrometer is set to 532 nm, and the wavenumber range is 800 cm⁻¹. -1 ~2000cm -1 .

[0055] In a specific embodiment of the present invention, the core comprises graphite; the particle size of the graphite preferably satisfies at least one of the following conditions: Dv10: 4μm~7μm, Dv50: 11μm~18μm, Dv90: 20μm~27μm, Dv99: 32μm~39μm. It should be noted that by controlling the graphite particle size as described above, and screening out graphite particles that meet the particle size limitation parameters, it is beneficial to obtain anode materials that meet the expected performance requirements.

[0056] In a specific embodiment of the present invention, the thickness of the carbon layer in the coating layer is preferably 0.01 μm to 0.3 μm, for example, 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm or any value between two of these; by controlling the thickness of the carbon layer in the coating layer within the above range, the coating continuity can be ensured, the core exposure can be avoided, and the film density can be controlled to avoid ion transport obstruction.

[0057] In a specific embodiment of the present invention, the transition metal oxide in the coating layer preferably includes one or more of niobium oxide, iron oxide, copper oxide, and manganese oxide. By selecting the above-mentioned specific types of transition metal oxide materials (theoretical capacity greater than 500mAh), the battery capacity can be better improved, the diffusion coefficient of lithium metal can be effectively increased, the growth of lithium dendrites can be effectively suppressed, and the electrochemical performance of graphite materials can be improved. At the same time, in conjunction with the carbon layer to form a composite coating layer, the direct interaction between the electrolyte and graphite is suppressed, and the reversible specific capacity and cycle stability of the negative electrode material are improved.

[0058] In a specific embodiment of the present invention, the particle size of the transition metal oxide in the coating layer is preferably 0.002 μm to 0.10 μm, for example, 0.002 μm, 0.006 μm, 0.01 μm, 0.03 μm, 0.05 μm, 0.08 μm, 0.1 μm, or any value between two of these. By controlling the particle size of the transition metal oxide within the above range, the dispersion state of the transition metal oxide in the carbon coating layer can be ensured, the ion diffusion path can be shortened, and the ion transport efficiency can be guaranteed.

[0059] This invention provides a high-capacity, high-rate graphite-modified anode material. By coating a graphite structure with an amorphous carbon-transition metal oxide (C-MxOy@Gr), it provides more diffusion channels for lithium ions, achieving a peak charge rate of 12C at room temperature. Simultaneously, anchoring the transition metal oxide to the graphite surface strengthens the interfacial contact between the transition metal oxide and the graphite matrix, improving electrochemical reactivity and further increasing the lithium-ion diffusion rate. During high-current charge and discharge, it weakens electrode polarization and enhances the lithium intercalation capability of the electrode material. Furthermore, the amorphous carbon layer coating helps absorb stress release during lithium intercalation, improving expansion and increasing battery cycle life. More importantly, the synergistic coating of the amorphous carbon layer and the transition metal oxide improves the ion diffusion efficiency of the anode material, enhancing its electrochemical lithium storage performance at low temperatures.

[0060] According to another aspect of the present invention, the present invention provides a method for preparing the negative electrode material described in the above-mentioned technical solution, comprising the following steps: a) The graphite raw material is successively crushed, shaped and graded, graphitized and demagnetized by sieving to obtain the core material; b) Mix the core material obtained in step a) with a transition metal oxide and perform physical anchoring to obtain an intermediate product; c) The intermediate product obtained in step b) is mixed with the carbon source solution and then dried, carbonized and cooled in sequence to obtain the negative electrode material.

[0061] The present invention first processes graphite raw materials sequentially through crushing, shaping and grading, graphitization and sieving and demagnetization to obtain core material.

[0062] In specific embodiments of the present invention, the graphite raw material preferably includes one or more of needle coke, petroleum coke, anthracite, and natural graphite; the carbon content of the graphite raw material is preferably ≥80%. In a preferred embodiment of the present invention, the graphite raw material is needle coke with a carbon content ≥88%. The present invention does not impose any special restrictions on the source of the graphite raw material, and commercially available products well known to those skilled in the art can be used.

[0063] In a specific embodiment of the present invention, the particle size of the pulverized material is preferably 8μm to 25μm, for example, 8μm, 10μm, 15μm, 18μm, 25μm, or any value between two of these. It should be noted that controlling the particle size of the pulverized graphite raw material within the above range not only provides the required regular particles for subsequent shaping and grading of the graphite raw material, but also improves the uniformity of graphitization, avoiding the phenomenon of ungraphitized cores due to excessively large particle sizes during subsequent graphitization; after pulverization, shaping and grading are performed, followed by graphitization treatment.

[0064] In a specific embodiment of the present invention, the graphitization temperature is preferably 2500℃~3000℃, for example, 2500℃, 2600℃, 2700℃, 2800℃, 2900℃, 3000℃, or any value between two of these. The present invention uses the above temperature range to remove high-melting-point impurities, avoid insufficient crystallization and impurity residue caused by excessively low temperatures, and also avoid equipment wear and increased costs caused by setting the graphitization temperature too high. Afterwards, the material is sieved and demagnetized to obtain the core material.

[0065] After obtaining the core material, the present invention mixes the obtained core material with a transition metal oxide and performs physical anchoring to obtain an intermediate product. In the present invention, the transition metal oxide is the same as that in the above-described technical solution, and will not be described again here.

[0066] In a specific embodiment of the present invention, the mass ratio of the core material to the transition metal oxide is preferably 100:(5~20), for example, 100:5, 100:8, 100:10, 100:15, 100:20, or any value between two of these. By controlling the mass ratio of the core material to the transition metal oxide within the above range, the present invention can optimize the physical anchoring effect and obtain an intermediate product that meets the requirements.

[0067] In a specific embodiment of the present invention, the physical anchoring method preferably includes ball milling; the high-energy collision and shear force of the ball milling process can cause transition metal oxide nanoparticles to embed into defects on the graphite surface, thus forming physical anchoring.

[0068] In a specific embodiment of the present invention, the preferred rotational speed of the ball mill is 50 r / min to 80 r / min, and the preferred milling time is 1 h to 3 h. It should be noted that controlling the ball milling speed within the above range ensures sufficient milling, preventing the transition metal oxides from merely adhering loosely to the surface of the core material, which could lead to subsequent failure in anchoring the transition metal oxides. It also avoids the agglomeration of transition metal oxides or damage to the core material caused by excessively high rotational speeds. Controlling the milling time to 1 h to 3 h aims to ensure sufficient anchoring and uniform dispersion of the transition metal oxides, while also avoiding material loss due to excessively long milling times.

[0069] After obtaining the intermediate product, the present invention mixes the intermediate product with a carbon source solution, and then sequentially dries, carbonizes and cools to obtain a negative electrode material.

[0070] In a specific embodiment of the present invention, the carbon source solution preferably includes a carbon source and a solvent. The carbon source preferably includes one or more of asphalt, resin-based carbon source, and polyimide. The solvent preferably includes one or more of tetrahydrofuran, dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), ethylene glycol butyl ether (Butyl cellosolve), and acetonitrile. The present invention does not impose any special restrictions on the source of the carbon source and solvent, and commercially available products well known to those skilled in the art can be used.

[0071] In a specific embodiment of the present invention, the mass ratio of the carbon source to the solvent is preferably (0.5~20):100, for example, 0.5:100, 1:100, 5:100, 10:100, 15:100, 20:100, or any value between two of these. In a preferred embodiment of the present invention, the carbon source is a mixture of asphalt and resin-based carbon source, wherein the mass percentage of the asphalt is preferably 60%~100%, but not 100%. By using a mixture of asphalt and resin-based carbon source as the carbon source, and with asphalt as the main component, the present invention can ensure the conductivity of the carbon layer. Simultaneously, the added resin-based carbon source can solve the problem of uneven coating in asphalt coating, increasing the uniformity of the carbon layer coating.

[0072] In a specific embodiment of the present invention, the mass ratio of the intermediate product to the carbon source in the carbon source solution is 100:(5~15), for example, 100:5, 100:6, 100:7, 100:8, 100:10, 100:12, 100:15, or any value between two of these. By controlling the mass ratio of the intermediate product to the carbon source within the above range, the present invention can ensure the formation of effective coating, prevent the electrolyte from penetrating into the core and causing side reactions, and also prevent the carbon layer from being too thick, which would increase the resistance to electron and lithium-ion transport and lead to a degradation in the rate performance of the negative electrode.

[0073] In a specific embodiment of the present invention, the drying temperature is preferably 40°C to 60°C, for example, 40°C, 45°C, 50°C, 60°C, or any value between two of these. By controlling the drying temperature within the above range, the present invention ensures that only solvent evaporation occurs, without triggering changes in the chemical structure of the carbon source, thus ensuring that the performance of the core material is not damaged.

[0074] In a specific embodiment of the present invention, the carbonization process preferably includes: placing the dried sample into a tube furnace, heating it to 800℃~1200℃ at a rate of 2℃ / min~10℃ / min under an inert gas atmosphere, and holding it at that temperature for 4h~6h to complete the carbonization process; the inert gas preferably includes one or more of helium, neon, argon, krypton, xenon, and radon. It should be noted that the role of adding inert gas during the carbonization process is to isolate oxidation, ensure the purity and structural integrity of the material, and at the same time, by controlling the heating rate, it can avoid the rapid decomposition of the carbon source, which may lead to cracking of the carbon layer. The slow heating and holding reaction for 4h~6h can provide sufficient pyrolysis reaction time for the carbon source, ensuring the orderly arrangement of the carbon skeleton, and at the same time, it can avoid the possibility of slight sintering of the carbon layer due to excessive holding time, which would reduce the uniformity of the carbon layer coating.

[0075] After final cooling, the negative electrode material is obtained. The preparation method provided by this invention uses a liquid-phase coating reagent to construct a composite coating layer of disordered carbon and transition metal oxides on the surface of graphite particles. First, through mechanical mixing, the transition metal oxides are physically anchored on the graphite surface. Compared with the technical solution where the transition metal oxides are disorderedly dispersed in the coated carbon layer, this invention brings the two into close contact, which can strengthen the interfacial contact between the transition metal oxides and graphite, increase the reactive sites, improve the electrochemical reaction activity, increase the diffusion rate of lithium ions, weaken the electrode polarization problem during high current charging and discharging, and improve the lithium intercalation capability of the electrode material. In addition, since the particle size of graphite is large and the particle size of transition metal oxides is small, and the amount of graphite used in the mixing is greater than that of transition metal oxides, there are voids between the transition metal oxides on the graphite surface, which can accommodate some of the pitch precursor. This allows the carbon layer generated after carbonization to fill the voids between the transition metal oxides. On this basis, it can both limit the expansion problem of graphite material and effectively improve the conductivity of the material.

[0076] According to another aspect of the present invention, a negative electrode sheet is provided, comprising a negative electrode current collector and a negative electrode coating disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode coating comprises the negative electrode material described in the above-described technical solutions or the negative electrode material prepared by the preparation method described in the above-described technical solutions. Thus, the negative electrode sheet possesses all the features and advantages of the negative electrode material described in the above-described technical solutions, which will not be repeated here.

[0077] In this invention, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode coating is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0078] In a specific embodiment of the present invention, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil; the composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0079] In specific embodiments of the present invention, the negative electrode coating may also include a negative electrode binder, a negative electrode conductive agent, and other optional additives. For example, the negative electrode binder may include at least one selected from polyacrylonitrile (PAN), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethyl methacrylate (PMAA), and carboxymethyl chitosan (CMCS); the negative electrode conductive agent may include at least one selected from superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers; other optional additives include thickeners (such as sodium carboxymethyl cellulose (CMC-Na)). These materials are all commercially available.

[0080] In a specific embodiment of the present invention, the method for preparing the negative electrode sheet adopts a method well known to those skilled in the art: first, the raw materials are mixed in a solvent in a certain proportion to form a slurry, and then the negative electrode slurry is coated on the negative electrode current collector. After cold rolling and drying, the negative electrode sheet can be obtained.

[0081] According to another aspect of the present invention, a lithium-ion battery is provided, comprising the negative electrode sheet described in the above-described technical solution. Thus, the lithium-ion battery possesses all the features and advantages of the negative electrode sheet described in the above-described technical solution, which will not be repeated here.

[0082] In a specific embodiment of the present invention, the lithium-ion battery further includes basic structural and component units such as a positive electrode, a separator, an electrolyte, and outer packaging. The positive electrode, separator, and negative electrode can be formed into a cell by a winding process or a stacking process, and then assembled into a lithium-ion battery using an assembly method well known to those skilled in the art. The present invention does not impose any special limitations on this.

[0083] In a specific embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector along the thickness direction; wherein, the positive current collector may be a metal foil, a foamed metal, or a composite current collector. For example, as a metal foil, silver-surfaced aluminum or stainless steel, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, or titanium, etc., may be used; the foamed metal may be foamed nickel, foamed copper, foamed aluminum, foamed alloy, etc.; the composite current collector may include a polymer material base layer and a metal layer, and the composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0084] In a specific embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material. The present invention does not impose any particular limitation on the specific type of the positive electrode active material; any active material known in the art that can be used as the positive electrode of a battery cell can be used. Those skilled in the art can select according to actual needs. Specifically, the positive electrode active material may include, but is not limited to, at least one of lithium transition metal oxides, lithium phosphates with an olivine structure, and their respective modified compounds; examples of lithium transition metal oxides may include, but are not limited to, at least one 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 their modified compounds; examples of lithium phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. These materials are all commercially available.

[0085] In specific embodiments of the present invention, the positive electrode active material layer may also include a positive electrode binder, a positive electrode conductive agent, and other optional additives (such as dispersants). For example, the positive electrode binder may include at least one of styrene-butadiene rubber (SBR), waterborne acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB); the positive electrode conductive agent may include at least one of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, SuperP (SP), graphene, and carbon nanofibers. These materials are all commercially available.

[0086] In a specific embodiment of the present invention, the preparation method of the positive electrode sheet adopts a method well known to those skilled in the art: first, the raw materials are mixed in a solvent in a certain proportion to form a slurry, and then the positive electrode slurry is coated on the positive electrode current collector. After drying, pressing and other processes, the positive electrode sheet can be obtained.

[0087] In a specific embodiment of the present invention, the separator is a separator material known to those skilled in the art for preparing batteries, such as polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers, or one or more combinations thereof; the present invention does not have any special restrictions on its type and source, and conventional commercially available products can be used.

[0088] In a specific embodiment of the present invention, the electrolyte acts as a conductor of ions between the positive and negative electrode plates. The present invention does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0089] In a specific embodiment of the present invention, the electrolyte is an electrolyte solution; the electrolyte solution comprises an electrolyte salt and a solvent; wherein, the electrolyte salt preferably comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate, more preferably lithium hexafluorophosphate; the solvent preferably comprises one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), more preferably a mixed solvent of EC, DMC, and EMC. The present invention does not impose any special restrictions on the source of the solvent; commercially available products of the above-mentioned cyclic and chain carbonates well known to those skilled in the art can be used.

[0090] In a specific embodiment of the present invention, the electrolyte preferably further includes film-forming additives, such as negative electrode film-forming additives and positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance and additives that improve battery high-temperature or low-temperature performance.

[0091] This invention does not impose any particular limitation on the preparation method of the electrolyte; conventional methods well-known to those skilled in the art can be used. In a preferred embodiment of this invention, the electrolyte is obtained by uniformly mixing the various components. As an example, the preparation method of the electrolyte includes the following steps: in an argon glove box, the solvent components are first mixed to form a homogeneous solvent system, and then a lithium salt electrolyte is slowly added to avoid local overheating and decomposition of the lithium salt; after complete dissolution, trace particulate impurities are removed by pressure filtration through a 0.2 μm PTFE filter membrane to obtain the electrolyte.

[0092] In a specific embodiment of the present invention, the battery may include an outer packaging that can be used to encapsulate the aforementioned battery cell and electrolyte. The outer packaging of the battery may be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. Specifically, the hard shell may include a housing and a cover plate. The housing may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing has an opening communicating with the receiving cavity, and the cover plate can be placed over the opening to close the receiving cavity. The battery cell is encapsulated within the receiving cavity and immersed in electrolyte. Alternatively, it may be a soft pack, such as a pouch-type soft pack. The material of the soft pack may be plastic, including, for example, polypropylene, polybutylene terephthalate, and polybutylene succinate. The present invention does not impose any particular limitation on the shape of the battery; it may be cylindrical, square, or any other arbitrary shape, which can be selected by those skilled in the art according to specific practical needs.

[0093] The present application will be described in detail below with reference to the accompanying drawings and embodiments. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0094] Example 1 (1) Preparation of core material artificial graphite (Gr): Using needle coke (carbon content ≥88%) as raw material, it is first crushed to a particle size of 15μm, then shaped and graded to remove fine powder, obtaining uniformly sized coke particles. Then, it undergoes a graphitization reaction at 2700℃ to obtain the finished graphite product. Finally, the finished graphite product is sieved and demagnetized to obtain a mixed-form graphite product, i.e., the core material; its particle size distribution is Dv10: 5μm; Dv50: 15μm; Dv90: 25μm; Dv99: 38μm.

[0095] (2) Preparation of negative electrode material: 2.0g of the core material artificial graphite (Gr) obtained in step (1) and 0.25g of CuO nanoparticles (20nm~50nm) were mechanically mixed in a ball mill at a speed of 60r / min for 2h. The high-energy collision and shear force during the ball milling process will cause the copper oxide nanoparticles to embed into the surface defects of Gr, forming a physical anchor, and thus obtaining the intermediate product (Gr-CuO).

[0096] Dissolve 1g of asphalt (C) in 100mL of tetrahydrofuran solution and stir at 50℃ until completely dissolved to obtain a carbon source solution; then add Gr-CuO obtained in the above steps to the above carbon source solution, continue stirring until completely mixed, and stir at 50℃ until the solvent completely evaporates to obtain a mixture sample.

[0097] The above mixture sample was placed in a tube furnace and heated to 900℃ at a rate of 5℃ / min under an argon atmosphere, and held at that temperature for 5 hours for carbonization. It was then cooled to room temperature to obtain the anode material (C-CuO@Gr). Its SEM image is shown below. Figure 2 As shown.

[0098] Tests showed that the specific surface area of ​​the negative electrode material obtained in Example 1 of this invention was 1.55 m². 2 / g, Dv50 particle size is 15μm.

[0099] (3) Preparation of negative electrode sheet: The negative electrode material (96wt%) obtained in step (2) is mixed with 1wt% sodium carboxymethyl cellulose (CMC-Na), 1.5wt% styrene-butadiene rubber (SBR), and 1.5wt% conductive carbon black, dissolved in water and stirred evenly. The mixture is then coated onto the surface of copper foil, and cold-rolled and dried to form a negative electrode sheet.

[0100] (4) Battery fabrication: Positive electrode sheet: Using NMC (nickel-cobalt-manganese 613 series) as the positive electrode active material, 95wt% NMC, 3wt% polyvinylidene fluoride (PVDF) and 2wt% conductive carbon black are dissolved in NMP, stirred evenly, coated on aluminum foil, and then cold-rolled and dried to form a sheet, thus obtaining the positive electrode sheet.

[0101] Separator: PE polymer porous membrane is used as the separator.

[0102] Electrolyte: In a 1M LiPF6 system, a mixed solution of EC, DMC and EMC in a volume ratio of 1:1:1 was used as the electrolyte.

[0103] The positive electrode, separator, and negative electrode obtained in step (3) are sequentially stacked and wound together, electrolyte is added, and they are assembled into a 3Ah soft-pack lithium-ion battery.

[0104] Example 2 The preparation method provided in Example 1 is used, except that CuO nanoparticles are replaced with Nb2O5 nanoparticles.

[0105] Example 3 The preparation method provided in Example 1 is used, except that CuO nanoparticles are replaced with Fe3O4 nanoparticles.

[0106] Example 4 The preparation method provided in Example 1 is used, except that asphalt is replaced with phenolic resin.

[0107] Example 5 The preparation method provided in Example 1 is used, except that asphalt is replaced with a mixture of asphalt and phenolic resin, wherein the mass ratio of asphalt is 60%.

[0108] Example 6 The preparation method provided in Example 1 is used, except that asphalt is replaced with a mixture of asphalt and phenolic resin, wherein the mass ratio of asphalt is 70%.

[0109] Example 7 The preparation method provided in Example 1 is used, except that asphalt is replaced with a mixture of asphalt and phenolic resin, wherein the mass of asphalt accounts for 80%.

[0110] Example 8 The preparation method provided in Example 1 is used, except that asphalt is replaced with a mixture of asphalt and phenolic resin, wherein the mass of asphalt accounts for 90%.

[0111] Comparative Example 1 The preparation method provided in Example 1 is used, except that no asphalt is added in the preparation of the negative electrode material, and the negative electrode material (CuO@Gr) is obtained.

[0112] Comparative Example 2 The preparation method provided in Example 1 is used, except that CuO nanoparticles are not added in the preparation of the negative electrode material to obtain the negative electrode material (C@Gr).

[0113] Comparative Example 3 The preparation method provided in Example 1 was adopted, with the difference being that: 0.2g of asphalt, 2g of artificial graphite (Gr) and 0.25g of CuO nanoparticles were directly dissolved in 20mL of tetrahydrofuran solution and stirred at 50°C until the solvent was completely evaporated to obtain a mixture sample; the obtained mixture sample was then placed in a tube furnace and heated to 900°C at a heating rate of 5°C / min under an argon atmosphere and held at that temperature for 5h for carbonization treatment, and then cooled to room temperature to obtain the negative electrode material (C-Cu-Gr), that is, without the physical anchoring step of Gr and transition metal oxides.

[0114] Test method: Full-charge expansion test of negative electrode sheet: The thickness of the negative electrode sheet of the batteries prepared in each embodiment and comparative example was measured at 100% SOC using a charge-discharge test cabinet. The expansion rate of the negative electrode sheet was calculated as (thickness of negative electrode sheet at 100% SOC - thickness of negative electrode sheet at compressive stress) / thickness of negative electrode sheet at compressive stress × 100%. The test results are as follows. Figure 3 As shown.

[0115] First discharge capacity test: At 25℃, the voltage range is 2.8V~4.25V. Charge to 4.25V with 1C, then charge at 4.25V constant voltage until the current decreases to 0.05C. Discharge to 2.8V with 0.1C. Record the discharge capacity at 25℃. The test results are shown in Table 1.

[0116] Capacity retention test: At 25℃, 0℃, and 60℃, with a voltage range of 2.8V~4.25V, the battery was charged at 1C to 4.25V, then charged at a constant voltage of 4.25V until the current decreased to 0.05C, and then discharged at 0.1C to 2.8V. The number of cycles corresponding to 80% capacity retention at different temperatures was recorded. The test results are shown in Table 1. Room temperature fast charging lithium plating test: The criterion is the appearance of lithium plating on 5% of the electrode area. The battery was first fully discharged at 1C to 2.8V, left to stand for 30 minutes, and then discharged at 0.1C to 2.8V. Then, it was charged at a constant current of 4C~9C to 4.25V, and then charged at a constant voltage of 4.25V with a cutoff current of 0.05C. The test results are shown in Table 1.

[0117] Raman test procedure: (1) Instrument calibration: Shimadzu RM-3000 portable Raman spectrometer; using 520.7cm -1 Using a silicon wafer as a standard, and selecting 532nm as the excitation wavelength, the peak position and optical path were calibrated to ensure stable instrument resolution and laser power.

[0118] (2) Sample loading: Place the prepared graphite sample stably on the sample stage, align it with the laser spot, and ensure that the laser irradiates the test area vertically.

[0119] (3) Parameter settings: Referring to the optimized parameters in the patent, the excitation wavelength is 532nm, the laser power is 2mW, and the spectral resolution is 2cm. -1 Scanning range: 1000~3000cm -1 Each scan takes 10-30 seconds, and 3-5 scans are performed cumulatively to improve the signal-to-noise ratio.

[0120] (4) Signal acquisition: Start the instrument to scan and acquire Raman spectrum. Confirm that the baseline is stable, the characteristic peaks D and G are clear, and there are no obvious impurities.

[0121] (5) Repeated verification: Repeated testing in different areas of the sample to ensure data repeatability.

[0122] (6) Test completion: Turn off the laser, cool down and disconnect the power supply, clean the sample stage and experimental area, organize the spectral data for analysis, calculate the peak area ratio of D peak and G peak, evaluate the amorphous degree of the sample, and the calculation results are shown in Table 1.

[0123] Table 1 From Table 1 and Figure 3 The test results show that the synergistic effect of transition metal oxides and disordered carbon layers effectively balances high-rate charging and cycle performance. The results from Examples 1-3 show that the introduction of different transition metal oxides significantly increases fast-charging capability and cycle life. The results from Examples 4-8 show that with different types of coating reagents, as the content of phenolic resin increases, the AD / AG ratio increases, carbon layer defects increase, and cycle life deteriorates. Comparative Example 1 lacks carbon layer coating; the transition metal oxides and graphite particles only have physical contact, without a carbon layer as a connection, leading to a significant decrease in the battery's reversible specific capacity and a reduced charging rate. Furthermore, the absence of a carbon layer as a stress release buffer also results in increased electrode rebound. Comparative Example 2, due to the lack of transition metal oxides in the carbon layer, shows a 23.6% full-charge rebound expansion of the negative electrode, indicating that even with a carbon layer, without the addition of transition metal oxides, the expansion of the negative electrode during lithium insertion / extraction cannot be effectively mitigated. Comparative Example 3, due to the lack of physical anchoring between graphite and transition metal oxides, also fails to balance high-rate charging and cycle performance.

[0124] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0125] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0126] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode material, characterized in that, include: The kernel comprises graphite; A coating layer is disposed on at least a portion of the surface of the core, the coating layer comprising a carbon layer and a transition metal oxide fixed to the surface of the carbon layer near the core.

2. The negative electrode material according to any one of claims 1, characterized in that, The specific surface area of the negative electrode material is 0.8 m 2 / g ~ 2.5 m 2 / g; And / or, the Dv50 particle size of the negative electrode material is 5μm~40μm; And / or, the Raman spectrum of the negative electrode material satisfies: 0.5 ≤ AD / (AD+AG) ≤ 1.5, where AD is the wavenumber of the Raman spectrum at 1340 cm⁻¹. -1 ~1350cm -1 The peak area at AG represents the wavenumber of the Raman spectrum at 1580 cm⁻¹. -1 ~1590cm -1 Peak area at that location.

3. The negative electrode material according to any one of claims 1, characterized in that, The particle size of the graphite satisfies at least one of the following characteristics (1) to (4): (1) The particle size of the graphite satisfies Dv10: 4μm~7μm; (2) The particle size of the graphite satisfies Dv50: 11μm~18μm; (3) The particle size of the graphite satisfies Dv90: 20μm~27μm; (4) The particle size of the graphite satisfies Dv99: 32μm~39μm.

4. The negative electrode material according to any one of claims 1, characterized in that, The thickness of the carbon layer in the coating is 0.01 μm to 0.3 μm; And / or, the transition metal oxide in the coating layer includes one or more of niobium oxide, iron oxide, copper oxide, and manganese oxide; And / or, the particle size of the transition metal oxide in the coating layer is 0.002 μm to 0.10 μm.

5. A method for preparing the negative electrode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: a) The graphite raw material is successively crushed, shaped and graded, graphitized and demagnetized by sieving to obtain the core material; b) Mix the core material obtained in step a) with a transition metal oxide and perform physical anchoring to obtain an intermediate product; c) The intermediate product obtained in step b) is mixed with the carbon source solution and then dried, carbonized and cooled in sequence to obtain the negative electrode material.

6. The preparation method according to claim 5, characterized in that, In step a): The graphite raw materials include one or more of needle coke, petroleum coke, anthracite, and natural graphite. And / or, the carbon content of the graphite raw material is ≥80%; And / or, the particle size of the pulverized material is 8μm~25μm; And / or, the graphitization temperature is 2500℃~3000℃.

7. The preparation method according to claim 5, characterized in that, In step b): The mass ratio of the core material to the transition metal oxide is 100:(5~20). And / or, the physical anchoring method includes ball milling; the ball milling speed is 50 r / min to 80 r / min, and the time is 1 h to 3 h.

8. The preparation method according to claim 5, characterized in that, In step c): The mass ratio of the intermediate product to the carbon source in the carbon source solution is 100:(5~15). And / or, the carbon source solution comprises a carbon source and a solvent, wherein the carbon source comprises one or more of asphalt, resin-based carbon source, and polyimide, and the solvent comprises one or more of tetrahydrofuran, dimethyl sulfoxide, N-methylpyrrolidone, ethylene glycol butyl ether, and acetonitrile; the mass ratio of the carbon source to the solvent is (0.5~20):100; preferably, the carbon source is a mixture of asphalt and resin-based carbon source, wherein the mass percentage of the asphalt is 60%~100%, but not 100%; And / or, the drying temperature is 40°C to 60°C; And / or, the carbonization process includes: placing the dried sample into a tube furnace, heating it to 800℃~1200℃ at a rate of 2℃ / min~10℃ / min under an inert gas atmosphere, and holding it at that temperature for 4h~6h to complete the carbonization process; the inert gas includes one or more of helium, neon, argon, krypton, xenon, and radon.

9. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode coating disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode coating comprises the negative electrode material according to any one of claims 1 to 4 or the negative electrode material prepared by the preparation method according to any one of claims 5 to 8.

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

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