Graphite material and preparation method thereof, electrochemical device and electronic equipment

Abstract

The invention discloses a graphite material and a preparation method thereof, an electrochemical device and electronic equipment. Each particle of the graphite material comprises a core and a carbon coating layer, the core comprises a graphite matrix and silicon, and the silicon is located in the graphite matrix; wherein the graphite material comprises a silicon-rich region; taking the center of the section along the longest diameter of the particles of the graphite material as a circle center, extending outwards along the longest diameter direction from the circle center, and taking the area from 75% radius to 95% radius of the particles of the graphite material as a silicon-rich area; the mass ratio of the silicon element in the silicon-rich region to the total mass of the graphite material is C1, and C1 is 2-4%; and the mass ratio of the silicon element in the silicon-rich region to the total silicon element mass in the graphite material is C2: C2 > = 90%. The graphite material provided by the invention has high capacity and good structural stability, and has good cycle performance when being used as a battery negative electrode material.

Description

Technical Field

[0001] This invention specifically relates to graphite materials and their preparation methods, electrochemical devices, and electronic devices. Background Technology

[0002] Graphite is a commonly used anode material in the battery field. Microcrystalline graphite is inexpensive and has significant advantages in kinetics compared to conventional flake graphite. However, its capacity and compaction density are usually lower than those of conventional flake graphite, which limits the use of microcrystalline graphite as an anode material in lithium-ion batteries.

[0003] Existing technologies, such as CN 110416497 A, use silicon-carbon materials and microcrystalline graphite to be mixed by isostatic pressing to improve capacity. However, this method is essentially a physical composite of two materials and cannot effectively suppress the expansion of silicon materials. The cycling performance and high-temperature performance of the material are still shortcomings. CN109592677 A uses intercalation treatment to expand the lattice spacing to increase the lithium intercalation capability of microcrystalline graphite, but this treatment will significantly deteriorate the first efficiency and structural stability of the material.

[0004] Therefore, developing a microcrystalline graphite with high capacity, good structural stability, and good cycle performance is of great significance. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing microcrystalline graphite, such as low capacity and low compaction density, resulting in poor structural stability and cycle performance when used as a battery anode material. It provides graphite materials, their preparation methods, electrochemical devices, and electronic devices. The graphite material provided by this invention exhibits high capacity and good structural stability, demonstrating excellent cycle performance when used as a battery anode material.

[0006] To overcome the above-mentioned technical problems, the present invention provides the following technical solution.

[0007] In a first aspect, the present invention provides a graphite material, wherein the particles of the graphite material include a core and a carbon coating layer, the core including a graphite matrix and silicon, the silicon being located inside the graphite matrix;

[0008] The graphite material contains silicon-rich regions;

[0009] With the center of the cross-section along the longest diameter of the graphite material particle as the center, the region extending outward from the center along the longest diameter direction, from 75% to 95% of the radius of the graphite material particle, is the silicon-rich region.

[0010] The mass ratio of silicon element in the silicon-rich region to the total mass of the graphite material is C1, where C1 is 2%-4%.

[0011] The mass ratio of silicon in the silicon-rich region to the total silicon mass in the graphite material is C2:C2≥90%.

[0012] Secondly, the present invention provides a method for preparing the graphite material as described above, comprising the following steps:

[0013] (1) Pore formation is performed on the graphite raw material to obtain a graphite matrix;

[0014] (2) A silicon source is used to perform vapor deposition on the graphite matrix to obtain a graphite material precursor;

[0015] (3) Carbon coating is performed on the graphite material precursor to obtain the graphite material.

[0016] Thirdly, the present invention provides an electrochemical device comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode material layer and a negative electrode current collector, the negative electrode material layer comprising the graphite material as described above.

[0017] Fourthly, the present invention provides an electronic device comprising the electrochemical device as described above.

[0018] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0019] The reagents and raw materials used in this invention are all commercially available.

[0020] The positive and progressive effects of this invention are as follows:

[0021] This invention provides a graphite material by setting a silicon-rich region with a specific silicon distribution in a graphite matrix and combining it with a carbon coating layer. This graphite material can suppress the expansion or shedding of silicon while having a large silicon content, exhibiting good structural stability and high capacity. It greatly improves the cycle performance when used as a battery anode material, and further has good high-temperature storage performance and fast charging performance. Detailed Implementation

[0022] Graphite materials

[0023] The first aspect of the present invention provides a graphite material, wherein the particles of the graphite material include a core and a carbon coating layer, the core including a graphite matrix and silicon, and the silicon being located inside the graphite matrix;

[0024] The graphite material contains silicon-rich regions;

[0025] With the center of the cross-section along the longest diameter of the graphite material particle as the center, the region extending outward from the center along the longest diameter direction is the silicon-rich region, from 75% to 95% of the radius of the graphite material particle.

[0026] The mass ratio of silicon element in the silicon-rich region to the total mass of the graphite material is C1, where C1 is 2%-4%.

[0027] The mass ratio of silicon in the silicon-rich region to the total silicon mass in the graphite material is C2:C2≥90%.

[0028] In this invention, "the silicon is located inside the graphite matrix" means that the silicon is distributed in the pores inside the graphite particles in the graphite matrix, the gaps between different graphite particles, and the surface of the graphite particles.

[0029] In this invention, the silicon may be elemental silicon and / or silicon oxide.

[0030] In some specific embodiments, the C1 of the graphite material is preferably 2.5%-3.5%.

[0031] In some specific embodiments, the C1 of the graphite material is 2%, 2.1%, 2.8%, 2.9%, 3%, 3.1%, 3.3%, or 3.5%.

[0032] In some specific embodiments, the C2 content of the graphite material is preferably 93%-97%.

[0033] In some specific implementations, the C2 content of the graphite material is 93%, 95%, 96%, or 97%.

[0034] In some specific implementations, the crushing force F of the graphite material can satisfy: 25mN≤F≤35mN. The crushing force F is the critical pressure at which a single particle of the material will break during a compressive strength test.

[0035] In some specific embodiments, the crushing force F of the graphite material is 26 mN, 27 mN, 28 mN, 29 mN, 30 mN, 31 mN, 32 mN or 35 mN.

[0036] In some specific implementations, the irreversible deformation Q of the graphite material can satisfy: 10% < Q ≤ 15%. The irreversible deformation Q is the amount of deformation change of a single particle of the material compared to the initial particle when the pressure is removed after the maximum deformation is reached.

[0037] In some specific embodiments, the irreversible deformation Q of the graphite material is 11.2%, 11.3%, 11.7%, 12.1%, 12.2%, 12.8%, 13%, 13.4%, 13.5% or 15%.

[0038] In some specific embodiments, the particle size Dv50 of the graphite material can be 6μm-13μm.

[0039] In some specific embodiments, the particle size Dv50 of the graphite material can be 11.2μm, 11.8μm, 12μm, 12.2μm, 12.5μm, 12.8μm, 12.9μm or 13.4μm.

[0040] In some specific embodiments, the thickness of the carbon coating layer may be less than or equal to 100 μm, preferably 10 μm to 100 μm.

[0041] In some specific embodiments, the carbon coating layer can cover more than 90% of the surface area of ​​the entire structure formed by the graphite substrate and the silicon. This essentially achieves complete coverage of the graphite substrate and silicon by the carbon coating layer, effectively suppressing silicon expansion and shedding, while also preventing direct contact between the electrolyte and the graphite material.

[0042] In this invention, the silicon can be discretely and uniformly distributed within the silicon-rich region.

[0043] In some specific embodiments, the pore density of the graphite material is 1000-20000 pores / cm³. 3 Pore ​​density refers to the density per unit volume (cm³). 3 The number of pores in the graphite material.

[0044] In some specific embodiments, the pore density of the graphite material can be 3100 pores / cm³. 3 9700 pieces / cm 3 10300 pieces / cm 3 11300 pieces / cm 3 12600 pieces / cm 3 12800 pieces / cm 3 12900 pieces / cm 3 14900 pieces / cm 3 17,300 pieces / cm 3 Or 19200 / cm 3 .

[0045] Preparation methods of graphite materials

[0046] The second aspect of the present invention provides a method for preparing graphite material, which includes the following steps:

[0047] (1) Pore formation is performed on the graphite raw material to obtain a graphite matrix;

[0048] (2) A silicon source is used to perform vapor deposition on the graphite matrix to obtain a graphite material precursor;

[0049] (3) Carbon coating is performed on the graphite material precursor to obtain the graphite material.

[0050] In some specific implementations, the mass ratio of the pore-forming agent to the graphite raw material used in pore-forming can be (0.005-0.04):1, for example, 0.005:1, 0.02:1 or 0.04:1.

[0051] In some specific embodiments, the pore-forming agent may be ZnCl2 or aluminum hydroxyaluminate.

[0052] In some specific embodiments, the pore-forming process may include the following steps: impregnating graphite raw material in a solution of a pore-forming agent, followed by heat treatment.

[0053] Preferably, the immersion time is 10-15 hours, for example, 12 hours.

[0054] Preferably, the heat treatment temperature is 400°C-600°C, for example 400°C, 500°C or 600°C.

[0055] Preferably, the heating rate of the heat treatment is 3-8°C, for example 5°C / min.

[0056] Preferably, the heat treatment time is 4-8 hours, for example, 6 hours.

[0057] Preferably, the solvent of the pore-forming agent solution is an acid solution, preferably a hydrochloric acid solution; and the concentration of the acid solution is preferably 1 mol / L.

[0058] Preferably, the heat treatment is carried out in an inert atmosphere, which may be a nitrogen atmosphere.

[0059] In some specific implementations, after the pore-forming process is completed, an alkaline solution is used for washing. The purpose of washing is to remove the pore-forming agent.

[0060] Preferably, the alkaline solution is a sodium hydroxide solution.

[0061] Preferably, the concentration of the alkaline solution is 1 mol / L.

[0062] Optionally, the washing is performed three times.

[0063] In some specific embodiments, the temperature of the vapor deposition can be 450-750°C, for example 600°C.

[0064] In some specific embodiments, the temperature of the vapor deposition can be 500°C-750°C or 450°C-700°C.

[0065] In some specific implementations, the vapor deposition time can be 6-10 hours, for example, 8 hours.

[0066] In some specific implementations, the silicon source may be silicon trichloride.

[0067] In some specific embodiments, the mass ratio of silicon element deposited in the vapor phase to the graphite matrix can be 1:(10-20), for example 1:18.

[0068] In some specific embodiments, the carbon coating temperature can be 850°C-1200°C, for example 1000°C.

[0069] In some specific implementations, the carbon coating time can be 6h-10h, for example 8h.

[0070] In some specific embodiments, the carbon coating includes the following steps: transferring the graphite material precursor to a rotary kiln, adding a carbon source, and then transferring the material to a carbonization kiln for carbon coating treatment to obtain the graphite material.

[0071] In some specific implementations, the carbon source for carbon coating may be one or more of petroleum asphalt, phenolic resin, coal tar, and coumarone resin.

[0072] In some alternative embodiments, the softening point of the petroleum asphalt is 70°C, 90°C, or 110°C.

[0073] Graphite raw materials

[0074] In some preferred embodiments, the graphite raw material is microcrystalline graphite.

[0075] In this invention, the microcrystalline graphite raw material preferably satisfies the following conditions: La≤72 nm, Lc≤15 nm; wherein, La is the lattice constant of the graphite crystal in the 110 plane of the microcrystalline graphite raw material, Lc is the lattice constant of the graphite crystal in the 002 plane of the microcrystalline graphite raw material; F1≥15 mN, F1 is the particle crushing force.

[0076] In some preferred embodiments, La ≤ 60 nm.

[0077] In some preferred embodiments, Lc ≤ 12 nm.

[0078] In some preferred embodiments, 15 mN ≤ F1 ≤ 25 mN.

[0079] In some preferred embodiments, the particle size distribution symmetry (S) of the microcrystalline graphite raw material satisfies 0 < S ≤ 0.1, preferably 0 < S ≤ 0.07.

[0080] In some preferred embodiments, the sphericity (D) of the microcrystalline graphite raw material is preferably 0.5-1.0.

[0081] In some preferred embodiments, the carbon content of the microcrystalline graphite raw material is greater than 99.9%, and the percentage is the mass percentage of the microcrystalline graphite raw material.

[0082] In some specific implementations, the La of the microcrystalline graphite raw material is 56 nm, 65 nm, or 67 nm.

[0083] In some specific implementations, the Lc of the microcrystalline graphite raw material is 7.1 nm, 9.4 nm, or 9.8 nm.

[0084] In some specific implementations, the particle crushing force F1 of the microcrystalline graphite raw material is 16mN, 19mN, or 20mN.

[0085] In some specific implementations, the particle size distribution symmetry S of the microcrystalline graphite raw material is 0.37, 0.52, or 0.57.

[0086] In some specific implementations, the sphericity D of the microcrystalline graphite raw material is 0.81, 0.88, or 0.89.

[0087] In some specific implementations, the microcrystalline graphite raw material satisfies the following conditions: La is 67 nm, Lc is 9.8 nm, particle crushing force F1 is 20 mN, particle size distribution symmetry S is 0.57, and sphericity D is 0.89.

[0088] In some specific implementations, the microcrystalline graphite raw material satisfies the following conditions: La is 65 nm, Lc is 9.4 nm, particle crushing force F1 is 19 mN, particle size distribution symmetry S is 0.52, and sphericity D is 0.88.

[0089] In some specific embodiments, the microcrystalline graphite raw material satisfies the following conditions: La is 56 nm, Lc is 7.1 nm, particle crushing force F1 is 16 mN, particle size distribution symmetry S is 0.37, and sphericity D is 0.81.

[0090] Wherein, La is composed of Calculated. Among them... It is 0.0027 nm. The half-width at half maximum (WHM) is θ, which is based on... Calculated; where, The specific testing method for d(110) is as follows: Add the graphite material and 50 mL of n-hexane to a beaker, ultrasonically vibrate for 5 min, then use a pipette to drop 100 μL of the solution onto a TEM observation copper grid. After rapidly drying the copper grid, observe it; use TEM for selective diffraction observation and calibration to obtain... And d(110).

[0091] Wherein, Lc is composed of Calculated. Among them... It is 0.0027 nm. The half-width at half maximum (FWHM) is θ', which is based on Calculated; where, The specific testing method for d(002) is as follows: Add the graphite material and 50 mL of n-hexane to a beaker, and ultrasonically vibrate for 5 min. Then, use a pipette to draw 100 μL of the solution and drop it onto a TEM observation copper grid. After rapidly drying the copper grid, observe it. Use TEM for selective diffraction observation and calibration to obtain the desired result. And d(002).

[0092] The particle crushing force (F1) refers to the critical pressure at which a single particle of the material breaks during a compressive strength test. The particle crushing force can be obtained using the Xiamen Yuaneng Technology Single Particle Mechanical Property Testing System (SPFT2000). The specific testing method is as follows: 0.5g of graphite material is added to a beaker containing 20ml of anhydrous ethanol and ultrasonically dispersed for 5min to obtain a dispersion; 100μL of the dispersion is dropped onto a glass slide, and the slide is transferred to the SPFT2000 sample observation stage; the single particle is positioned using the optical microscope of the SPFT2000, and the indenter is pressed down at a uniform speed. The stress abrupt change point during particle compression is recorded as the particle crushing force.

[0093] The particle size distribution symmetry (S) is calculated from [D(3,4)-Dv50] / Dv50; where D(3,4) and Dv50 are obtained according to GB / T 41949-2022. The smaller the particle size distribution symmetry, the better the particle size distribution symmetry, and the higher the peak of the differential curve of the particle size volumetric force distribution.

[0094] Sphericity (D) refers to the ratio of the surface area of ​​a sphere of the same volume as the material particle to the surface area of ​​the material particle itself. Generally, the closer a particle's morphology is to a sphere, the closer its sphericity is to 1. A sphere has a sphericity of 1, while other objects have a sphericity less than 1. Sphericity is tested according to GB / T 37406-2019.

[0095] In some specific embodiments, the preparation method of the microcrystalline graphite raw material includes the following steps:

[0096] S1. The microcrystalline graphite precursor and the binder are first mixed, and a solvent is added for a second mixing to obtain a mixture; wherein, the temperature of the first mixing is 5-20°C below the softening point of the binder;

[0097] S2. Press the mixture to obtain a microcrystalline graphite preform;

[0098] S3. The microcrystalline graphite blank is laid on the surface of the graphitization furnace, and graphitized insulation material is laid on the microcrystalline graphite blank for graphitization treatment. The microcrystalline graphite blank is obtained by graphitization treatment.

[0099] S4. The graphitized microcrystalline graphite blank is crushed to obtain microcrystalline graphite raw material.

[0100] Optionally, the temperature of the first mixing is 8-15°C below the softening point of the adhesive, for example, 10°C.

[0101] Optionally, in step S1, the sphericity D of the graphite precursor is 0.7-1.0.

[0102] Optionally, in step S1, the graphite precursor is natural microcrystalline graphite, wherein the natural microcrystalline graphite is preferably obtained by pretreatment of microcrystalline graphite ore, wherein the pretreatment includes, for example, water washing and spheroidization treatment.

[0103] Optionally, in step S1, the fixed carbon content of the microcrystalline graphite precursor is 88%-91%.

[0104] Optionally, in step S1, the Dv50 particle size of the microcrystalline graphite precursor is 6-8 μm, for example, 7 μm.

[0105] Optionally, in step S1, the mass ratio of the microcrystalline graphite precursor to the binder is (4-7):1, for example, 5:1.

[0106] Optionally, in step S1, the binder includes one or more of petroleum asphalt, phenolic resin, epoxy resin, and coal tar.

[0107] Optionally, in step S1, the softening point of the adhesive is 100-250℃, preferably 100-130℃, for example 110℃.

[0108] Optionally, in step S1, the solvent is selected from one or more of xylene, toluene, and n-hexane.

[0109] Optionally, in step S1, the solid content of the mixture is 40%-60%, for example, 45%, where the percentage is the mass percentage of the solid component of the mixture relative to the mass of the mixture.

[0110] Optionally, in step S1, the first mixing method is stirring; wherein the stirring time is preferably 0.5-2 hours, for example, 1 hour; and the stirring speed is preferably 30-90 r / min.

[0111] Optionally, in step S1, the second mixing method is stirring; wherein the stirring time is preferably 0.5-2 hours, for example 1 hour; the stirring speed is preferably 60-120 r / min; and the stirring temperature is preferably room temperature.

[0112] Optionally, in step S1, the preparation method of the microcrystalline graphite precursor includes the following steps: washing and flotation of microcrystalline graphite ore with water, followed by coarse crushing and spheroidization treatment to obtain the graphite precursor; wherein, the spheroidization treatment time is preferably 4-24 hours; the spheroidization treatment is preferably carried out using a honeycomb mill.

[0113] Optionally, in step S2, the pressing is isostatic pressing; wherein the isostatic pressing time is preferably 18-30 hours, for example 24 hours; and the isostatic pressing pressure is preferably 150-300 MPa, for example 200 MPa.

[0114] Optionally, in step S3, the temperature of the graphitization treatment is greater than 1600℃.

[0115] Optionally, in step S3, the graphitization treatment time is 18-40 hours, preferably 24-36 hours.

[0116] Optionally, in step S3, the graphitized insulation material is petroleum coke and / or pitch coke.

[0117] Optionally, in step S3, the graphitization equipment is a graphitization furnace.

[0118] Optionally, in step S4, the pulverization process further includes sieving and magnetic impurity removal.

[0119] Optionally, in step S4, the pulverization process involves pulverizing the particles until the Dv50 particle size is 10-13 μm.

[0120] Electrochemical device

[0121] The electrochemical device provided in the third aspect of the present invention includes a negative electrode sheet, the negative electrode sheet including a negative electrode material layer and a negative electrode current collector, the negative electrode material layer including the graphite material as described above.

[0122] In this invention, the electrochemical device is preferably a battery.

[0123] In some alternative embodiments, the electrochemical device is a lithium-ion battery; the lithium-ion battery further includes a positive electrode, a separator, and an electrolyte.

[0124] negative electrode sheet

[0125] In this invention, the negative electrode material layer is disposed on at least one surface of the negative electrode current collector.

[0126] In some implementations, the negative electrode material layer also includes a thickener.

[0127] The addition of the thickener can increase the viscosity of the system of each component in the negative electrode slurry. It can be a thickener commonly used in the art to prepare negative electrode sheets, such as sodium carboxymethyl cellulose (CMC).

[0128] In some implementations, the negative electrode material layer further includes a conductive agent.

[0129] The conductive agent is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, specific materials that can be used include: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black (Super P), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives, etc.

[0130] In some implementations, the negative electrode material layer further includes a binder.

[0131] The type of adhesive is not particularly limited and can be selected from polyvinylidene fluoride, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfonates, styrene-butadiene rubber (SBR), fluororubber and various copolymers, such as PAA and SBR.

[0132] In some specific embodiments, the mass ratio of the graphite material, conductive agent, binder and thickener in the negative electrode material layer is 97.2:0.5:1.8:0.5.

[0133] In this invention, the negative electrode current collector can be a conventional negative electrode current collector in the art. As a substrate supporting the negative electrode active material, the negative electrode current collector is typically a metal foil with a thickness of 3-500 micrometers. There are no particular restrictions on the material, as long as it has high conductivity and will not produce a chemical reaction in the secondary battery system. For example, it can be a foil formed by surface treatment of nickel, titanium, aluminum, silver, stainless steel, carbon, etc. The negative electrode current collector usually has a smooth surface, but fine textures can also be formed on its surface to improve the adhesion between the positive electrode active material and the current collector. Besides foil, the negative electrode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or non-woven fabric. Generally, the negative electrode current collector is copper foil.

[0134] In some embodiments, the method for preparing the negative electrode sheet includes the following steps: coating the negative electrode slurry obtained by thoroughly mixing the components of the negative electrode material layer in a solvent onto at least one surface of the negative electrode current collector, drying, cold pressing, and slitting to obtain the final product.

[0135] Positive electrode film

[0136] In this invention, the positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector.

[0137] In this invention, the positive electrode active material in the positive electrode material layer can be a positive electrode active material conventionally used in the art, such as one or more of lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium cobalt oxide.

[0138] In some implementations, the positive electrode material layer further includes a binder.

[0139] The type of adhesive is not particularly limited and can be selected from polyvinylidene fluoride, polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfonates, styrene-butadiene rubber (SBR), fluororubber and various copolymers, such as PVDF.

[0140] In some embodiments, the binder content is 1%-10%, for example 1.8%, which is a percentage of the total mass of the positive electrode material layer.

[0141] In some embodiments, the positive electrode material layer further includes a conductive agent.

[0142] The type of conductive agent is not particularly limited; it is a reagent used to ensure that the electrode has good charge and discharge performance. It can be selected from graphite materials such as natural graphite and artificial graphite; carbon black materials such as SP, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; conductive fibers such as carbon fiber and metal fiber; metal powders such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; and conductive metal oxides or polyphenylene derivatives such as titanium dioxide.

[0143] In some specific implementations, the conductive agent is conductive carbon SP.

[0144] In some embodiments, the content of the conductive agent is 0.2%-3%, for example 1.2%, which is a percentage of the total mass of the positive electrode material layer.

[0145] In some specific embodiments, the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer is 97:1.2:1.8.

[0146] In this invention, the positive electrode current collector can be a conventional positive electrode current collector in the art. As a substrate supporting the positive electrode material layer, the positive electrode current collector is typically a metal foil with a thickness of 3-500 micrometers. There are no particular limitations on the material, as long as it has high conductivity and will not produce a chemical reaction in the secondary battery system. For example, it can be a foil formed by surface treatment of nickel, titanium, aluminum, silver, stainless steel, carbon, etc. The positive electrode current collector usually has a smooth surface, but fine textures can also be formed on its surface to improve the adhesion between the positive electrode active material and the current collector. Besides foil, the positive electrode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or non-woven fabric. Generally, the positive electrode current collector is aluminum foil.

[0147] In some embodiments, the method for preparing the positive electrode sheet includes: coating a positive electrode slurry obtained by thoroughly mixing the components of the positive electrode material layer in a solvent onto at least one surface of the positive electrode current collector, drying, and rolling to compact it, thereby obtaining the positive electrode sheet.

[0148] In some alternative embodiments, the solvent includes one or more of N-methylpyrrolidone (NMP), dimethyl carbonate, ethylene carbonate, and diethylene carbonate, for example, NMP.

[0149] diaphragm

[0150] In this invention, the diaphragm can be a diaphragm conventionally used in the art.

[0151] In some alternative embodiments, the diaphragm may be a polypropylene film or a polyethylene film.

[0152] The air permeability of the diaphragm can be 180-380 s / 100mL.

[0153] The porosity of the diaphragm can be 30%-50%.

[0154] The thickness of the diaphragm can be 9-18 μm.

[0155] In one specific embodiment, the diaphragm is a polyethylene film; the thickness of the diaphragm is 11 μm; the air permeability of the diaphragm is 230 s / 100 mL; and the porosity of the diaphragm is 40%.

[0156] electrolyte

[0157] In some embodiments, the electrolyte may be a conventional electrolyte used in batteries in the art, generally including non-aqueous solvents, lithium salts, and additives.

[0158] In some embodiments, the method for preparing the lithium-ion battery includes the following steps: stacking the positive electrode, separator, and negative electrode in sequence, with the separator positioned between the positive and negative electrodes to act as a separator; then wrapping with an aluminum-plastic film, drying, and injecting the electrolyte; and finally preparing a soft-pack battery through processes such as encapsulation, settling, and formation.

[0159] electronic devices

[0160] The electronic device provided in the fourth aspect of the present invention includes the electrochemical device as described above.

[0161] For example, the electronic devices described in this invention may be, but are not limited to, mobile devices (such as mobile phones, tablets, laptops, video recorders, portable printers / copiers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems and backup power supplies, etc.

[0162] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0163] Example 1

[0164] (1) Preparation of graphite matrix

[0165] S1. Microcrystalline graphite ore (purchased from Hunan Lutang Microcrystalline Graphite, with a carbon content >85% in the raw ore) was subjected to preliminary water washing and flotation to reduce its fixed carbon content to 88-91%. After coarse crushing, it was spheroidized by a honeycomb mill for 6 hours to obtain a microcrystalline graphite precursor with a sphericity of 0.83. The above microcrystalline graphite precursor was mixed with petroleum asphalt (purchased from Xinde New Materials, model XD-110) with a softening point of 110℃ at a mass ratio of 5:1. The mixture was then heated to 10℃ below the softening point of the petroleum asphalt and stirred at low speed for 1 hour. Then, xylene solvent with a mass of 2 times the mass of the obtained material was added to assist in the dispersion of the petroleum asphalt, and stirring was continued for 1 hour to obtain a semi-solid mixture.

[0166] S2. After adding the above semi-solid mixture into a 40×30cm×30cm rubber mold, press it under isostatic pressure of 200Mpa for 24h, and then demold it to obtain a microcrystalline graphite preform.

[0167] S3. The above-mentioned microcrystalline graphite blank is laid on the surface of a conventional Atchison graphitization furnace, and then a layer of conventional graphitization insulation material is laid on it before graphitization. The graphitization temperature is 3000℃ and the graphitization time is 36h.

[0168] S4. The graphitized microcrystalline graphite preform described above is pulverized, sieved, and magnetically purified. The fraction with a Dv50 of 10 μm is collected as the microcrystalline graphite raw material with a carbon content >99.9%. The obtained microcrystalline graphite raw material has a La of 67 nm, an Lc of 9.8 nm, a particle crushing force F1 of 20 mN, a particle size distribution symmetry S of 0.57, a sphericity D of 0.89, and a carbon content greater than 99.9%.

[0169] S5. Prepare 50L of HCl solution with a concentration of 1mol / L, add 0.2kg (W1) of ZnCl2 and stir evenly, then add 10kg of the above microcrystalline graphite raw material, fully impregnate for 12h, filter and collect the dried powder, and then perform heat treatment under N2 atmosphere. The specific operation is as follows: heat up to T1 at 5℃ / min, T1 is 500℃, and then hold for 6h to obtain graphite matrix;

[0170] (2) Preparation of graphite material precursors

[0171] The graphite matrix was washed three times with 1 mol / L NaOH solution and dried to obtain powder. Then, 10 kg of the powder was calcined at 800°C for 2 h at 0.1 atm in an argon atmosphere under negative pressure vacuum calcination. The powder was then directly transferred to an FBCVD-100 fluidized bed for CVD deposition in an inert gas atmosphere. Trichlorosilane was selected as the silicon source, and the deposition amount W2 was 2.67 kg. The mass ratio of silicon to graphite matrix was 1:18. The deposition time was 8 h and the deposition temperature was 600°C. The powder was then cooled to room temperature to obtain the graphite material precursor.

[0172] (3) Carbon coating

[0173] The graphite precursor was transferred to a rotary kiln via a pipe, and 4% petroleum asphalt (softening point T2 of 90℃, purchased from Xinde New Materials, model XD-90) by weight of the graphite precursor was added and mixed. The mixture was then transferred to a carbonization kiln and carbonized at 1000℃ for 8 hours to obtain the graphite material.

[0174] Example 2

[0175] The difference from Example 1 is that the amount of ZnCl2 added in S5 is changed to 0.4 kg, while other experimental conditions remain unchanged.

[0176] Example 3

[0177] The difference from Example 1 is that the amount of ZnCl2 added in S5 is changed to 0.05 kg, while other experimental conditions remain unchanged.

[0178] Example 4

[0179] The difference from Example 1 is that the temperature T1 in S5 is changed to 400℃, while other experimental conditions remain unchanged.

[0180] Example 5

[0181] The difference from Example 1 is that the temperature T1 in S5 is changed to 600℃, while other experimental conditions remain unchanged.

[0182] Example 6

[0183] The difference from Example 1 is that the mass ratio of silicon to graphite matrix in step (2) is 0.1:100, while other experimental conditions remain unchanged.

[0184] Example 7

[0185] The difference from Example 1 is that the softening point of petroleum asphalt in step (3) (purchased from Xinde New Materials, model XD-70) is changed to 70℃, while other experimental conditions remain unchanged.

[0186] Example 8

[0187] The difference from Example 1 is that the softening point of petroleum asphalt (purchased from Xinde New Materials, model XD-110) in step (3) is changed to 110℃, while other experimental conditions remain unchanged.

[0188] Example 9

[0189] The difference from Example 1 is that ZnCl2 in step S5 is replaced with aluminum hydroxide.

[0190] Example 10

[0191] The difference from Example 1 is that the carbon source in step (3) is replaced with phenolic resin (purchased from Jinan Shengquan, phenolic resin for coatings).

[0192] Example 11

[0193] The difference from Example 1 is that petroleum asphalt with a softening point of 130℃ (purchased from Xinde New Materials, model XD-130) was used in S1 above, while other experimental conditions remained unchanged. The obtained microcrystalline graphite raw material had a La of 65 nm, an Lc of 9.4 nm, a particle crushing force F1 of 19 mN, a particle size distribution symmetry S of 0.52, a sphericity D of 0.88, and a carbon content greater than 99.9%.

[0194] Example 12

[0195] The difference from Example 1 is that in S1 above, the sphericification treatment time was 4 hours, the sphericity of the obtained graphite precursor was 0.7, and other experimental conditions remained unchanged. The obtained microcrystalline graphite raw material had a La of 56 nm, an Lc of 7.1 nm, a particle crushing force F1 of 16 mN, a particle size distribution symmetry S of 0.37, a sphericity D of 0.81, and a carbon content greater than 99.9%.

[0196] Comparative Example 1

[0197] The difference from Example 1 is that the amount of ZnCl2 added in S5 is changed to 1 kg, while other experimental conditions remain unchanged.

[0198] Comparative Example 2:

[0199] The difference from Example 1 is that the amount of ZnCl2 added in S5 is changed to 0, while other experimental conditions remain unchanged.

[0200] Comparative Example 3

[0201] The difference from Example 1 is that the temperature T1 in S5 is changed to 800℃, while other experimental conditions remain unchanged.

[0202] Comparative Example 4

[0203] The difference from Example 1 is that the amount of trichlorosilane deposited in step (2) is changed to 0, while other experimental conditions remain unchanged.

[0204] Comparative Example 5

[0205] The difference from Example 1 is that the mass ratio of silicon to graphite matrix in step (2) is 2.5:100, while other experimental conditions remain unchanged.

[0206] Comparative Example 6

[0207] The difference from Example 1 is that the mass ratio of silicon to graphite matrix in step (2) is 2:100, while other experimental conditions remain unchanged.

[0208] Comparative Example 7

[0209] The difference from Example 1 is that the softening point of petroleum asphalt (Xinde New Materials, XD-150) in step (3) is changed to 150℃, while other experimental conditions remain unchanged.

[0210] Comparative Example 8

[0211] The difference from Example 1 is that commercially available microcrystalline graphite raw material (purchased from Lutang Graphite Processing Plant in Chenzhou, Hunan Province, Grade I earthy graphite) was used to perform the same pore-forming process as in Step S5 of Example 1, while other experimental conditions remained unchanged.

[0212] Table 1 shows the types, performance parameters, amounts, and specific process parameters of each raw material used in the preparation of graphite materials in Examples 1-12 and Comparative Examples 1-8.

[0213] Table 1

[0214]

[0215] Example 1

[0216] (1) Test method for C1

[0217] Referring to GB / T 27788-2011, a cross-section along the longest diameter of the graphite material is taken and scanned using a scanning electron microscope to test the mass of silicon in the silicon-rich region and the total mass of all elements in the graphite material. The mass ratio of the two is C1.

[0218] (2) Test method for C2

[0219] Referring to GB / T 27788-2011, a cross-section along the longest diameter of the graphite material is taken and scanned using a scanning electron microscope to test the mass of silicon in the silicon-rich region and the total mass of silicon in the graphite material. The mass ratio of the two is C2.

[0220] (3) Test method for F

[0221] The crushing force of particles was tested using the Xiamen Yuaneng Technology Single Particle Mechanical Property Testing System (SPFT2000), as detailed below:

[0222] Add 0.5g of graphite material to a beaker containing 20ml of anhydrous ethanol and sonicate for 5min to obtain a dispersion. Take 100μL of the dispersion and drop it onto a glass slide. Transfer the glass slide to the SPFT2000 sample observation stage. Use the SPFT2000 optical microscope to locate a single particle and control the indenter to press down at a uniform speed. The stress change point during the particle compression process is recorded as the particle crushing force.

[0223] (4) Test method for Q

[0224] The irreversible deformation of particles was tested using the Xiamen Yuaneng Technology Single Particle Mechanical Property Testing System (SPFT2000), as detailed below:

[0225] Add 0.5g of graphite material to a beaker containing 20ml of anhydrous ethanol and sonicate for 5min to obtain a dispersion. Take 100μL of the dispersion and drop it onto a glass slide. Transfer the glass slide to the SPFT2000 sample observation stage. Use the SPFT2000 optical microscope to locate a single particle and control the indenter to press down at a constant speed. When the pressure reaches a certain level, the maximum deformation occurs. The amount of deformation change of the material compared to the initial particle when the pressure is removed is the irreversible deformation.

[0226] (5) Pore density

[0227] Referring to GB / T19587-2004, the graphite materials of the examples and comparative examples were tested, and the total pore volume was read. The volume of a single pore was calculated with a radius of 1 nm (assuming uniform pore size). The ratio of the total pore volume to the volume of a single pore is the pore density.

[0228] (6) Test method for the thickness of carbon coating

[0229] ① Sampling: Samples were taken from 25kg bags of graphite materials and uncoated products prepared in the examples and comparative examples. Using a sampling spoon, 50g samples were taken from nine equally spaced locations: center, top center, bottom center, left center, right center, top left, bottom left, top right, and bottom right. These 450g samples were then thoroughly shaken and mixed to form test standard samples, named M1 (graphite material) and M2 (uncoated product, obtained by calcining M1 at 450℃ under vacuum for 4 hours).

[0230] ② True density test: Referring to the national standard GB / T 24533-2009, 5g of test standard samples M1 and M2 were taken and tested with a TD-2200 true density tester. The true density of samples M1 and M2 was obtained by testing three times and the average true density of samples M1 and M2 was ρ1 and ρ2, respectively.

[0231] ③ Determination of carbon coating content and type: The heat absorption values ​​of M1 and M2 were measured using a DSC differential scanning calorimeter, three times for each sample, and the average value was recorded as sample H1 and H2. The mass percentage of the carbon coating was denoted as x. The formula for calculating x is:

[0232] x = (H2 - H1) / H2 × 100%

[0233] The relationship between x and the true density ρ3 of the carbon coating can be established as follows:

[0234] ρ1=ρ2(1-x)+ρ3x

[0235] ρ3=(ρ1-ρ2(1-x)) / x

[0236] ρ3 = ρ2 - (ρ2 - ρ1)H2 / (H2 - H1)

[0237] According to industry standards, a carbon coating with a true density greater than 1.9 is considered soft carbon coating, while a carbon coating with a true density greater than 1.9 is considered hard carbon coating. This can help determine the type of carbon coating and the stability of different batches of carbon coating.

[0238] ④ Determination of carbon coating thickness: Referring to GB / T 24533-2009, 5g of test standard sample M1 was taken and tested with a Mastersizer 3000 particle size analyzer. The average volume diameter of sample M1 was obtained by testing three times and the average volume diameter was D. The thickness of carbon coating was denoted as d. Then the following equation is given.

[0239] 1 / 6·πD^3 ρ1x=1 / 6·π[(D-2d)]^3]ρ2+1 / 6 π[D^3-(D-2d)^3]ρ3

[0240] Solving directly using Cardan's method for cubic equations, we find that d differs from D by four orders of magnitude. Therefore, we can directly ignore the second and third powers of d in the equation and solve for the following:

[0241] d=Dρ1x / 6ρ3=(Dρ1[(H2-H1)]^2) / (6H2(ρ1H2-ρ2H1))

[0242] The obtained results have an error of less than 1% compared with the solution obtained by the formula method, and the range of d obtained is less than 10μm-100μm.

[0243] The test results are shown in Table 2.

[0244] Table 2

[0245]

[0246] Example 2

[0247] Preparation of lithium-ion batteries

[0248] The positive electrode, separator, and negative electrode are wound together to form a battery cell, which is then packaged in a casing and injected with electrolyte to produce a soft-pack battery.

[0249] The preparation of the negative electrode sheet includes the following steps: the graphite material obtained in the examples or comparative examples, the conductive agent (SP), the binder (PAA and SBR, with a mass ratio of 1.3:0.5) and the thickener carboxymethyl cellulose (CMC) are mixed in a mass ratio of 97.2:0.5:1.8:0.5 (100 parts by mass in total), and then 82 parts by mass of deionized water are added and mixed evenly to obtain a negative electrode slurry; then the negative electrode slurry is evenly coated on copper foil; and then the negative electrode sheet is prepared by drying, rolling, cutting and other processes.

[0250] The preparation of the positive electrode sheet includes the following steps: mixing positive electrode active materials NCM622, PVDF and SP in a mass ratio of 97:1.8:1.2 (100 parts by mass in total), adding 82 parts by mass of NMP to obtain a positive electrode slurry; coating the obtained positive electrode slurry onto at least one surface of an aluminum foil, drying, and rolling to compact it, thus obtaining the positive electrode sheet.

[0251] The diaphragm is a polyethylene film with a thickness of 11 μm, an air permeability of 230 s / 100 mL, and a porosity of 40%.

[0252] The electrolyte used is a commercially available electrolyte (manufacturer: Xinya Shanshan New Material Technology (Quzhou) Co., Ltd., model: E3).

[0253] The lithium-ion batteries assembled using the above method were subjected to the following electrical performance tests, and the results are recorded in Table 3.

[0254] 1. First-time effect of all-battery

[0255] Full battery charging capacity: Charge the lithium-ion battery with a 1C current to 4.35V and record the charging capacity at this stage as c1. Then charge at a constant voltage until the cutoff current is 0.05C and record the charging capacity at this stage as c2. The full battery charging capacity is the sum of c1 and c2.

[0256] Full battery discharge capacity: After fully charging the cell and resting for 30 minutes, discharge it to 2.8V with a 1C current and record the discharge capacity c3 at this stage, which is the full battery discharge capacity.

[0257] First-time efficiency = Total battery discharge capacity c3 / Total battery charge capacity (c1+c2) × 100%.

[0258] 2. Fast charging time

[0259] The battery was directly charged to 8% SOC using a 0.33C current. Then, based on actual measurements of the three electrode windows of the battery cell, the charging windows for 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% were determined as C1, C2, C3, C4, C5, C6, C7, and C8, respectively. Step charge was used to charge to 80%, i.e., C1 was used for 8%-10%, C2 for 10%-20%, and so on. The charging time from 8% to 80% SOC was recorded as a standard for measuring fast charging capability. The calculation formula is as follows:

[0260] T （8%-80%） =(0.02 / c1+0.1 / c2+0.1 / c3+0.1 / c4+0.1 / c5+0.1 / c6+0.1 / c7+0.1 / c8)*60.

[0261] 3. Number of cycles at room temperature

[0262] The material was cycled at 25°C with a charge-discharge cycle of 0.21 A / g (calculated by the mass of the positive electrode active material) and 2.8-4.25V. The number of cycles until 80% of the initial capacity was recorded as the material's cycle performance.

[0263] 4. Number of high-temperature cycles

[0264] The material was cycled at 45°C with a charge-discharge cycle of 2.8-4.25V at a rate of 0.21A / g (calculated by the mass of the positive electrode active material). The number of cycles until 80% of the initial capacity was recorded as the material's cycle performance.

[0265] 5. Storage days

[0266] At 25℃, the cell is calibrated with a current of 0.33C and denoted as C0. Then, the cell is stored at a high temperature of 60℃. Every 7 days, the cell is taken out and its capacity is tested at room temperature and denoted as C1, C2, ..., Cn. The number of days until Cn is less than or equal to 80% of C0 is used as the standard for measuring storage capacity and is denoted as storage days.

[0267] Table 3

[0268]

[0269] The graphite material provided by this invention can suppress silicon expansion or shedding while having a high silicon content, exhibiting good structural stability and high capacity, significantly improving its cycle performance as a battery anode material. Furthermore, it also possesses excellent high-temperature storage performance and fast-charging performance. When the graphite materials prepared in Examples 1-12 are applied to lithium-ion batteries, the number of cycles to 80% of the initial capacity at room temperature is 2854 or more; the number of cycles to 80% of the initial capacity at high temperature is 1627 or more; furthermore, the initial efficiency is 90.5% or more, the storage time at 60°C reaches 280 days or more; and the charging time from 8% to 80% SOC is only 14.2 minutes or less.

[0270] The comparison of Examples 1-12 shows that the silicon distribution in graphite materials, combined with the carbon coating layer, has a significant impact on the particle size DV50, particle crushing force, and irreversible deformation of the graphite materials. It can suppress silicon expansion or shedding while maintaining a high silicon content, thereby improving its cycle performance as a battery anode material. Furthermore, it also exhibits good high-temperature storage performance and fast-charging performance.

[0271] In Comparative Example 1, the mass ratio of silicon in the silicon-rich region to the total mass of the graphite material is within the range of this invention, but the mass ratio of silicon in the silicon-rich region to the total mass of silicon in the graphite material is slightly less than that of this invention. In Comparative Examples 2-4, the mass ratios of silicon in the silicon-rich region to the total mass of the graphite material and the mass ratios of silicon in the silicon-rich region to the total mass of silicon in the graphite material are both less than the range of this invention. In Comparative Examples 5-8, the mass ratios of silicon in the silicon region to the total mass of the graphite material are all greater than the range of this invention, while the mass ratios of silicon in the silicon-rich region to the total mass of silicon in the graphite material are all less than the range of this invention. The materials obtained in Comparative Examples 1-10 show deterioration in both their own properties and their application. It can be seen that if the mass ratio of silicon in the silicon-rich region to the total mass of the graphite material is too large or too small, or if the mass ratio of silicon in the silicon-rich region to the total mass of silicon in the graphite material is too small, the effects of this invention cannot be achieved.

[0272] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A graphite material, characterized in that, The graphite material particles include a core and a carbon coating layer, the core comprising a graphite matrix and silicon, the silicon being located inside the graphite matrix; The graphite material contains silicon-rich regions; With the center of the cross-section along the longest diameter of the graphite material particle as the center, the region extending outward from the center along the longest diameter direction, from 75% to 95% of the radius of the graphite material particle, is the silicon-rich region. The mass ratio of silicon element in the silicon-rich region to the total mass of the graphite material is C1, where C1 is 2%-4%. The mass ratio of silicon in the silicon-rich region to the total silicon mass in the graphite material is C2:C2≥90%.

2. The graphite material as described in claim 1, characterized in that, The graphite material satisfies one or both of the following conditions (a)-(d): (a) 25mN≤F≤35mN, where F is the crushing force; (b) 10% < Q ≤ 15%, where Q is an irreversible deformation; (c) C1 is 2.5%-3.5%; (d) C2 is 93%-97%.

3. The graphite material as described in claim 1, characterized in that, The graphite material satisfies one or more of the following conditions (a)-(c): (a) The particle size of the graphite material is 6μm-13μm; (b) The thickness of the carbon coating layer is 10 μm - 100 μm; (c) The graphite material has a pore density of 1000-20000 pores / cm³. 2 .

4. A method for preparing a graphite material as described in any one of claims 1-3, characterized in that, It includes the following steps: (1) Pore formation is performed on the graphite raw material to obtain a graphite matrix; (2) A silicon source is used to perform vapor deposition on the graphite matrix to obtain a graphite material precursor; (3) Carbon coating is performed on the graphite material precursor to obtain the graphite material.

5. The method for preparing graphite material as described in claim 4, characterized in that, The method for preparing the graphite material satisfies one or more of the following conditions (a)-(d): (a) The mass ratio of the pore-forming agent to the graphite raw material used in the pore-forming process is (0.005-0.04):1; (b) The pore-forming agent used in the pore-forming process is ZnCl2 and / or aluminum hydroxide; (c) The pore-forming step includes: heat-treating the mixture of the graphite raw material and the pore-forming agent; the heat treatment temperature is 500℃-600℃; (d) After the pore-forming process is completed, the pores are washed with an alkaline solution.

6. The method for preparing graphite material as described in claim 4, characterized in that, The graphite raw material is microcrystalline graphite raw material, and the microcrystalline graphite raw material satisfies one or two of the following conditions (a)-(b): (a) La≤72 nm, Lc≤15 nm; where La is the lattice constant of the graphite crystal in the microcrystalline graphite raw material on the 110 plane, and Lc is the lattice constant of the graphite crystal in the microcrystalline graphite raw material on the 002 plane; F1≥15 mN, where F1 is the particle crushing force; (b) The microcrystalline graphite raw material is obtained by the following method: S1. The microcrystalline graphite precursor and the binder are first mixed, and a solvent is added for a second mixing to obtain a mixture; wherein, the temperature of the first mixing is 5-20°C below the softening point of the binder; S2. Press the mixture to obtain a microcrystalline graphite preform; S3. The microcrystalline graphite blank is laid on the surface of the graphitization furnace, and graphitized insulation material is laid on the microcrystalline graphite blank for graphitization treatment. The microcrystalline graphite blank is obtained by graphitization treatment. S4. The graphitized microcrystalline graphite blank is crushed to obtain microcrystalline graphite raw material.

7. The method for preparing graphite material as described in claim 4, characterized in that, Step (2) satisfies one or more of the following conditions (a)-(d): (a) The temperature of the vapor deposition is 450℃-750℃; (b) The vapor deposition time is 6-10 hours. (c) The silicon source is silicon trichloride; (d) The mass ratio of silicon in the vapor-deposited material to the graphite matrix is ​​1:(10-20).

8. The method for preparing graphite material as described in claim 4, characterized in that, Step (3) satisfies one or more of the following conditions (a)-(c): (a) The carbon source for carbon coating is one or more of petroleum asphalt, phenolic resin, coal tar and coumarone resin; (b) The carbon coating temperature is 850℃-1200℃; (c) The carbon coating time is 6h-10h.

9. An electrochemical device comprising a negative electrode, characterized in that, The negative electrode sheet includes a negative electrode material layer and a negative electrode current collector, wherein the negative electrode material layer includes graphite material as described in any one of claims 1-3.

10. An electronic device, characterized in that, It includes the electrochemical device as described in claim 9.

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