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. The graphite material comprises an inner core and a shell, and the material of the inner core comprises first graphite; the material of the shell comprises second graphite; the graphite material meets the following conditions: 6 < K < = 30, and K is a shape coefficient; 1.06 < = F < = 1.12, and F is a withstand voltage coefficient; 0 < = L < = 2%, and L is bulk phase porosity. The graphite material provided by the invention has good compaction density, and has good fast charging performance and cycle performance when being applied to a battery.

Description

Technical Field

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

[0002] Artificial graphite, with its excellent cycle performance, high-rate charge-discharge efficiency, and electrolyte compatibility, is widely used in automotive power batteries and mid-to-high-end electronic products. However, the capacity of artificial graphite is difficult to exceed 360 mAh / g, and to simultaneously achieve fast-charging performance, it is difficult to exceed 355 mAh / g. Furthermore, when made into electrode sheets, its compaction is also difficult to surpass 1.70 g / cc. -1 Even if forced to achieve this, the dynamics would be extremely poor.

[0003] In existing technologies, such as CN 112582592 A, graphite is treated by liquid phase coating. Although this improves fast charging performance, it essentially deteriorates capacity, compaction and high-temperature performance. CN115621443 A improves fast charging by coating graphene, but this increases cost and processing difficulty, making it counterproductive.

[0004] Although microcrystalline graphite has good kinetic properties, it often requires ultra-high temperature treatment to overcome its poor high-temperature performance. In order to obtain suitable compaction, a large amount of fine powder needs to be removed by shaping, which reduces the yield of microcrystalline graphite and increases the cost. Therefore, it is necessary to make reasonable use of this fine powder to increase the added value of the product. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing technologies where artificial graphite, when used in batteries, struggles to simultaneously achieve good fast-charging and cycle performance. It provides graphite materials, their preparation methods, electrochemical devices, and electronic devices. The graphite material provided by this invention possesses good compaction density, resulting in excellent fast-charging and cycle performance when applied to batteries.

[0006] In a first aspect, the present invention provides a graphite material comprising a core and a shell, wherein the core is made of a first graphite and the shell is made of a second graphite.

[0007] The graphite material satisfies the following conditions:

[0008] 6 < K ≤ 30, where K is the shape factor;

[0009] 1.06≤F≤1.12, where F is the pressure resistance coefficient;

[0010] 0≤L≤2%, where L is the bulk porosity.

[0011] Secondly, the present invention provides a method for preparing the graphite material as described above, comprising the following steps:

[0012] (1) The second graphite raw material is subjected to hydroxylation treatment to obtain the second graphite matrix; the first graphite raw material is subjected to hydroxylation treatment to obtain the first graphite matrix;

[0013] (2) The mixture comprising the second graphite matrix and the first graphite matrix is ​​calcined to obtain the graphite material.

[0014] 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.

[0015] Fourthly, the present invention provides an electronic device comprising the electrochemical device as described above.

[0016] 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.

[0017] The reagents and raw materials used in this invention are all commercially available.

[0018] The positive and progressive effects of this invention are as follows:

[0019] This invention provides a graphite material with a core-shell structure, which has a low shape factor, bulk porosity, and good compressive strength. The graphite material has high compaction density, adhesion and processing properties, and exhibits good fast-charging performance and cycle performance when applied to electrochemical devices (especially lithium-ion batteries). Detailed Implementation

[0020] Graphite materials

[0021] The graphite material provided in the first aspect of the present invention includes a core and a shell, wherein the core is made of a first graphite and the shell is made of a second graphite.

[0022] The graphite material satisfies the following conditions:

[0023] 6 < K ≤ 30, where K is the shape factor;

[0024] 1.06≤F≤1.12, where F is the pressure resistance coefficient;

[0025] 0≤L≤2%, where L is the bulk porosity.

[0026] In this invention, the shape factor K can reflect the degree of similarity between the particle shape and a sphere. The shape factor of a perfect sphere is 6. The closer the shape factor is to 6, the greater the tap density. The calculation time is K=S / ρ.D[3,2], where S is the specific surface area of ​​the particle, ρ is the true density of the particle, and D[3,2] is the area average diameter of the particle.

[0027] In this invention, the compressive strength coefficient F reflects the flexibility of the material coating layer. The smaller the F value, the better the elasticity and flexibility of the coating layer. It is calculated using the formula F = P2 / P1, where P1 is the final 2T powder compaction measured using the five-point method, and P2 is the 2T powder compaction measured using the ten-point method.

[0028] In this invention, bulk porosity reflects the structural density of graphite materials. A combined SEM-FIB test was conducted, selecting 30 typical median-sized particles (aspect ratio less than 2, Dv ± 0.5 μm). The particles were cut at their longest diameter, and the areas of these 30 cuts were rendered and statistically analyzed using Photoshop. The ratio L of the pore area to the cross-sectional area at the longest diameter (cut parallel to the plane coinciding with the longest diameter of the particle and the operator's viewpoint; after cutting, pores appear as small, dark pits on the cross-section, while the remaining area is a smooth, glossy surface) is calculated.

[0029] In this invention, the shape factor K of the graphite material can satisfy: 6 < K ≤ 20.

[0030] In some specific embodiments, the shape factor K of the graphite material is: 9.7, 13.1, 15.3, 15.5, 15.6, 21.7, 25.7 or 29.7.

[0031] In this invention, the compressive strength coefficient F of the graphite material can satisfy: 1.06≤F≤1.10.

[0032] In some specific embodiments, the compressive strength coefficient F of the graphite material is: 1.06, 1.07, 1.08, 1.09, 1.1 or 1.12.

[0033] In this invention, the bulk porosity of the graphite material can satisfy: 0≤L≤1.6%.

[0034] In some specific embodiments, the bulk porosity of the graphite material is 0.10%, 0.70%, 1.00%, 1.10%, 1.30%, 1.60%, or 2.00%.

[0035] In this invention, the particle size D of the graphite material V 50 can be 7μm-13μm.

[0036] In some specific embodiments, the particle size D of the graphite materialV 50 can be 10.3μm, 11.7μm, 11.8μm, 12.2μm, 12.4μm, 12.6μm, 12.7μm, 13.6μm or 13.7μm.

[0037] In some specific embodiments, the thickness of the outer shell in the graphite material is 50-100 nm, for example 53 nm, 57 nm, 61 nm, 64 nm, 65 nm, 67 nm, 74 nm or 89 nm.

[0038] Preparation methods of graphite materials

[0039] The second aspect of the present invention provides a method for preparing graphite material, which includes the following steps:

[0040] (1) The second graphite raw material is subjected to hydroxylation treatment to obtain the second graphite matrix; the first graphite raw material is subjected to hydroxylation treatment to obtain the first graphite matrix;

[0041] (2) The mixture comprising the second graphite matrix and the first graphite matrix is ​​calcined to obtain the graphite material.

[0042] In some specific implementations, the hydroxylation treatment can be performed by adding the first graphite raw material or the second graphite raw material to an alkaline solution and stirring.

[0043] In some specific embodiments, the treatment agent used in the hydroxylation process may be an alkaline solution.

[0044] In some specific embodiments, the treatment agent used in the hydroxylation treatment is a sodium hydroxide solution with a concentration of 3 mol / L.

[0045] In some specific embodiments, the temperature of the hydroxylation treatment may be 50-65°C, for example 60°C.

[0046] In some specific implementations, in step (2), the mixture may also include a binder, a solvent, and a surfactant.

[0047] Optionally, the binder is liquid petroleum asphalt and / or phenolic resin, wherein the coking value of the liquid petroleum asphalt is <25%.

[0048] Optionally, the volume ratio of the adhesive to the solvent may be (5-10):1, for example, 9:1.

[0049] Optionally, the mass ratio of the binder to the first graphite matrix is ​​1:(5-10), for example, 1:10 or 1:5.

[0050] Optionally, the surfactant may be dodecyltrimethylammonium bromide.

[0051] Optionally, the mass ratio of the first graphite matrix to the surfactant is 1:(0-0.002) but not 0.

[0052] In some specific embodiments, the mass ratio of the first graphite matrix to the surfactant is 1:0.001 or 1:0.002.

[0053] In some specific embodiments, in step (2), the mixture can be prepared by mixing the solvent and the binder first, and then adding the surfactant, the second graphite matrix and the first graphite matrix in sequence.

[0054] In some specific embodiments, the calcination temperature can be 900℃-1200℃, for example 1000℃.

[0055] In some specific implementations, the calcination time is 6h-8h, for example 8h.

[0056] In some specific implementations, the mass ratio of the second graphite matrix to the first graphite matrix may be (0.02-0.1):1.

[0057] In some specific implementations, the mass ratio of the second graphite matrix to the first graphite matrix is ​​0.02:1, 0.05:1, or 0.1:1.

[0058] First Graphite Raw Material

[0059] In some preferred embodiments, the first graphite raw material is artificial graphite.

[0060] In some specific implementations, the bulk porosity of the first graphite raw material is ≤0.5%.

[0061] In some specific implementations, the preparation method of the first graphite raw material may include the following steps: subjecting petroleum needle coke to full forging, degassing, pressing and graphitization in sequence to obtain the first graphite raw material.

[0062] Optionally, the volatile matter V of the petroleum needle coke is less than 5%.

[0063] Optionally, the degassing time can be 1-3 hours, for example, 2 hours.

[0064] Optionally, the pressing method may be isostatic pressing, wherein the isostatic pressing pressure is 100 MPa - 300 MPa, for example 200 MPa; and the isostatic pressing time is 18h - 36h, for example 24h.

[0065] Optionally, the degassing temperature is 450℃-800℃, for example, 450℃, 600℃ or 800℃.

[0066] Second graphite raw material

[0067] In some preferred embodiments, the second graphite material is microcrystalline graphite.

[0068] In this invention, the particle size D of the second graphite raw material V 50 can be <1μm.

[0069] In this invention, the second 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 second graphite raw material on the 110 plane, Lc is the lattice constant of the graphite crystal in the second graphite raw material on the 002 plane; F1≥15 mN, F1 is the particle crushing force.

[0070] In some preferred embodiments, La ≤ 60 nm.

[0071] In some preferred embodiments, Lc ≤ 12 nm.

[0072] In some preferred embodiments, 15 mN ≤ F1 ≤ 25 mN.

[0073] In some preferred embodiments, the particle size distribution symmetry (S) of the second graphite raw material satisfies 0 < S ≤ 0.1, preferably 0 < S ≤ 0.07.

[0074] In some preferred embodiments, the sphericity (D) of the second graphite raw material is preferably 0.5-1.0, more preferably 0.85-0.92.

[0075] In some preferred embodiments, the carbon content of the second graphite raw material is greater than 99.9%, and the percentage is the mass percentage of the second graphite raw material.

[0076] In some specific implementations, the La of the second graphite raw material is 52 nm, 57 nm, or 61 nm.

[0077] In some specific implementations, the Lc of the second graphite raw material is 66.4 nm, 8.2 nm, or 9.3 nm.

[0078] In some specific implementations, the particle crushing force F1 of the second graphite raw material is 15 mN, 17 mN or 18 mN.

[0079] In some specific implementations, the particle size distribution symmetry S of the second graphite raw material is 0.041, 0.32, or 0.51.

[0080] In some specific implementations, the sphericity D of the second graphite raw material is 0.78, 0.89, or 0.9.

[0081] In some specific embodiments, the second graphite raw material satisfies the following conditions: La is 57 nm, Lc is 8.2 nm, particle crushing force F1 is 17 mN, particle size distribution symmetry S is 0.041, and sphericity D is 0.90.

[0082] In some specific embodiments, the second graphite raw material satisfies the following conditions: La is 61 nm, Lc is 9.3 nm, particle crushing force F1 is 18 mN, particle size distribution symmetry S is 0.51, and sphericity D is 0.89.

[0083] In some specific embodiments, the second graphite raw material satisfies the following conditions: La is 52 nm, Lc is 66.4 nm, particle crushing force F1 is 15 mN, particle size distribution symmetry S is 0.32, and sphericity D is 0.78.

[0084] 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).

[0085] Wherein, Lc is composed of Calculated. Among them... It is 0.0027 nm. The full 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).

[0086] 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.

[0087] 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.

[0088] 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.

[0089] In some specific implementations, the preparation method of the second graphite raw material includes the following steps:

[0090] 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;

[0091] S2. Press the mixture to obtain a microcrystalline graphite preform;

[0092] 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.

[0093] S4. The graphitized microcrystalline graphite blank is crushed to obtain the second graphite raw material.

[0094] Optionally, the temperature of the first mixing is 8-15°C below the softening point of the adhesive, for example, 10°C.

[0095] Optionally, in step S1, the sphericity D of the graphite precursor is 0.7-1.0.

[0096] Optionally, in step S1, the graphite precursor is natural microcrystalline graphite. Preferably, the natural microcrystalline graphite is obtained from microcrystalline graphite ore through pretreatment, wherein the pretreatment includes, for example, water washing and spheroidization.

[0097] Optionally, in step S1, the fixed carbon content of the microcrystalline graphite precursor is 88%-91%.

[0098] Optionally, in step S1, the Dv50 particle size of the microcrystalline graphite precursor is 6-8 μm, for example, 7 μm.

[0099] Optionally, in step S1, the mass ratio of the microcrystalline graphite precursor to the binder is (4-7):1, for example, 5:1.

[0100] Optionally, in step S1, the binder includes one or more of petroleum asphalt, phenolic resin, epoxy resin, and coal tar.

[0101] Optionally, in step S1, the softening point of the adhesive is 100-250℃, preferably 100-130℃, for example 110℃.

[0102] Optionally, in step S1, the solvent is selected from one or more of xylene, toluene, and n-hexane.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] Optionally, in step S3, the temperature of the graphitization treatment is greater than 1600℃.

[0109] Optionally, in step S3, the graphitization treatment time is 18-40 hours, preferably 24-36 hours.

[0110] Optionally, in step S3, the graphitized insulation material is petroleum coke and / or pitch coke.

[0111] Optionally, in step S3, the graphitization equipment is a graphitization furnace.

[0112] Optionally, in step S4, the pulverization process further includes sieving and magnetic impurity removal.

[0113] Optionally, in step S4, the pulverization process involves pulverizing the particles until the Dv50 particle size is 10-13 μm.

[0114] Electrochemical device

[0115] 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.

[0116] In this invention, the electrochemical device is preferably a battery.

[0117] 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.

[0118] negative electrode sheet

[0119] In this invention, the negative electrode material layer is disposed on at least one surface of the negative electrode current collector.

[0120] In some implementations, the negative electrode material layer also includes a thickener.

[0121] 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).

[0122] In some implementations, the negative electrode material layer further includes a conductive agent.

[0123] 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.

[0124] In some implementations, the negative electrode material layer further includes a binder.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] Positive electrode film

[0130] 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.

[0131] 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.

[0132] In some implementations, the positive electrode material layer further includes a binder.

[0133] 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.

[0134] 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.

[0135] In some embodiments, the positive electrode material layer further includes a conductive agent.

[0136] 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.

[0137] In some specific implementations, the conductive agent is conductive carbon SP.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] In some alternative embodiments, the solvent includes one or more of N-methylpyrrolidone (NMP), dimethyl carbonate, ethylene carbonate, and diethylene carbonate, for example, NMP.

[0143] diaphragm

[0144] In this invention, the diaphragm can be a diaphragm conventionally used in the art.

[0145] In some alternative embodiments, the diaphragm may be a polypropylene film or a polyethylene film.

[0146] The air permeability of the diaphragm can be 180-380 s / 100mL.

[0147] The porosity of the diaphragm can be 30%-50%.

[0148] The thickness of the diaphragm can be 9-18 μm.

[0149] 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%.

[0150] electrolyte

[0151] 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.

[0152] 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.

[0153] electronic devices

[0154] The electronic device provided in the fourth aspect of the present invention includes the electrochemical device as described above.

[0155] 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.

[0156] 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.

[0157] Example 1

[0158] (1) Preparation of the second graphite matrix:

[0159] S1. Microcrystalline graphite ore (purchased from Hunan Lutang Microcrystalline Graphite, carbon content > 85%) was subjected to preliminary water washing and flotation to achieve a fixed carbon content of 88-91%. After coarse crushing, it was spheroidized by a honeycomb mill for 24 hours to obtain a microcrystalline graphite precursor with a sphericity of 0.9. 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 5:2. 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 twice 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.

[0160] 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.

[0161] 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.

[0162] S4. The graphitized microcrystalline graphite preform described above is crushed and shaped, and the component with Dv50 < 1 μm is collected as the second graphite raw material (microcrystalline graphite). The obtained second graphite raw material has a La of 57 nm, an Lc of 8.2 nm, a particle crushing force F1 of 17 mN, a particle size distribution symmetry S of 0.041, a sphericity D of 0.90, and a carbon content greater than 99.9%.

[0163] S5. Add 0.5 kg of the above-mentioned second graphite raw material (C1) to 20 L of a 3 mol / L hot sodium hydroxide solution, stir at 60 °C for 6 h to hydroxylate the second graphite raw material, and then filter and dry to obtain the second graphite matrix.

[0164] (2) Preparation of the first graphite matrix:

[0165] Petroleum needle coke was selected as raw material (volatile matter V < 5%). After coarse crushing, it was subjected to full forging at 1100℃ for 6 hours, and then degassed by being subjected to negative pressure at 600℃ (T1) in a medium frequency furnace for 2 hours. After cooling to room temperature, it was subjected to isostatic pressing at 200 MPa for 24 hours, and then pulverized into particles with a Dv50 of 10 μm. Finally, it was graphitized to obtain graphitized powder (artificial graphite). The graphitization temperature was 2800℃ and the graphitization time was 36 hours.

[0166] Then, 10 kg of the above graphitized powder was added to 20 L of a 3 mol / L hot sodium hydroxide solution, stirred at 60 °C for 6 h to perform hydroxylation treatment, filtered, and dried to obtain the first graphite matrix.

[0167] (3) Coating treatment

[0168] Prepare a 20L mixed solution with ethanol and liquid petroleum asphalt (coking value <25%, purchased from Xinde New Materials, model L-80) in a mass ratio of 9:1. Add 0.02kg of dodecyltrimethylammonium bromide (C2, DTAB). Then add 0.5kg of the second graphite matrix obtained in step (1) into the above mixed solution and stir at high speed for 0.5h. Then add 10kg of the first graphite matrix prepared in step (2), wherein the mass ratio of liquid petroleum asphalt to the first graphite matrix is ​​1:10. After stirring at high speed for 2h, filter and dry. Place the resulting mixture in a rotary kiln and calcine at 1000℃ for 8h under a nitrogen atmosphere to obtain the graphite material.

[0169] Example 2

[0170] The difference from Example 1 is that the amount of the second graphite raw material C1 added in S5 above is changed to 1 kg, while other experimental conditions remain unchanged.

[0171] Example 3

[0172] The difference from Example 1 is that the amount of the second graphite raw material C1 added in S5 above is changed to 0.2 kg, while other experimental conditions remain unchanged.

[0173] Example 4

[0174] The difference from Example 1 is that the temperature T1 of the degassing treatment in step (2) is changed to 450℃, while other experimental conditions remain unchanged.

[0175] Example 5

[0176] The difference from Example 1 is that the temperature T1 of the degassing treatment in step (2) is changed to 800℃, while other experimental conditions remain unchanged.

[0177] Example 6

[0178] The difference from Example 1 is that the amount of dodecyltrimethylammonium bromide added in step (3) is changed to 0.01 kg, while other experimental conditions remain unchanged.

[0179] Example 7

[0180] The difference from Example 1 is that the liquid petroleum asphalt in step (3) is replaced with phenolic resin (purchased from Jinan Shengquan Group Coating Phenolic Resin).

[0181] Example 8

[0182] The difference from Example 1 is that DTAB in step (3) is replaced with triethanolamine oleic acid soap (purchased from Qingdao Ruinuo Chemical Co., Ltd.).

[0183] Example 9

[0184] The difference from Example 1 is that the mass ratio of liquid petroleum asphalt to the first graphite matrix in step (3) is changed to 1:5, while other experimental conditions remain unchanged.

[0185] Example 10

[0186] 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 second graphite raw material had a La of 61 nm, an Lc of 9.3 nm, a particle crushing force F1 of 18 mN, a particle size distribution symmetry S of 0.51, a sphericity D of 0.89, and a carbon content greater than 99.9%.

[0187] Example 11

[0188] 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 second graphite raw material had a La of 52 nm, an Lc of 6.4 nm, a particle crushing force F1 of 15 mN, a particle size distribution symmetry S of 0.32, a sphericity D of 0.78, and a carbon content greater than 99.9%.

[0189] Comparative Example 1

[0190] The difference from Example 1 is that the amount of the second graphite raw material added in S5 above is changed to 1.5 kg, while other experimental conditions remain unchanged.

[0191] Comparative Example 2

[0192] The difference from Example 1 is that step S5 is omitted.

[0193] Comparative Example 3

[0194] The difference from Example 1 is that the temperature T1 of the degassing treatment in step (2) is changed to 400℃, while other experimental conditions remain unchanged.

[0195] Comparative Example 4

[0196] The difference from Example 1 is that the temperature T1 of the degassing treatment in step (2) is changed to 900℃, while other experimental conditions remain unchanged.

[0197] Comparative Example 5

[0198] The difference from Example 1 is that the amount of dodecyltrimethylammonium bromide added in step (3) is changed to 0 kg, while other experimental conditions remain unchanged.

[0199] Comparative Example 6

[0200] The difference from Example 1 is that the amount of dodecyltrimethylammonium bromide added in step (3) is changed to 0.05 kg, while other experimental conditions remain unchanged.

[0201] Comparative Example 7

[0202] The difference from Example 1 is that in step (2), commercially available graphite (purchased from Shangtai Graphite, model R-30) was used as the first graphite raw material for hydroxylation treatment, while other experimental conditions remained unchanged.

[0203] Comparative Example 8

[0204] The difference from Example 1 is that the mass ratio of the second graphite matrix to the first graphite matrix in step (3) is changed to 0.01:1.

[0205] Comparative Example 9

[0206] The difference from Example 1 is that the mass ratio of the second graphite matrix to the first graphite matrix in step (3) is changed to 0.2:1.

[0207] Comparative Example 10

[0208] The difference from Example 1 is that commercially available graphite (purchased from Lutang Graphite Processing Plant in Chenzhou, Hunan Province, Grade I earthy graphite) was used as the second graphite raw material, and the hydroxylation treatment in step S5 of Example 1 was carried out, while other experimental conditions remained unchanged.

[0209] Table 1 shows the types, performance parameters, and amounts of raw materials used in the preparation of graphite materials in Examples 1-11 and Comparative Examples 1-10, as well as the specific process parameters:

[0210] Example 1

[0211] 1. Shape factor K:

[0212] K = S / [ρ·D[3,2]], where S is the specific surface area of ​​graphite, ρ is the true density of graphite, and D[3,2] is the area-average diameter of graphite.

[0213] 2. Bulk porosity L

[0214] Using SEM-FIB for linkage, 30 typical median particle sizes (aspect ratio less than 2, Dv±0.5μm) were selected. The particles were cut from their longest diameter, and the areas of the 30 cuts were then rendered and statistically analyzed using Photoshop. The ratio L of the pore area to the cross-sectional area was calculated at the longest diameter section of the particle (the cut is made at a plane parallel to the operator's viewpoint and coincident with the longest diameter of the particle; after the pores are cut, they appear as small black pits on the cross-section, while the rest is a smooth, shiny surface).

[0215] Table 1

[0216]

[0217] 3. Pressure resistance coefficient F

[0218] F=P2 / P1

[0219] Among them: (1) Test of P1 (five-point method)

[0220] A powder compaction tester (manufacturer: Yuaneng, model: PRCD1100) was used. First, the upper and lower metal shims were placed in the empty mold and put together, aligned with the base and fixed. Baseline initialization and thickness reset were performed. An appropriate amount of graphite material was weighed, its mass was recorded, and then added to the empty mold. After pre-vibration, the pressing pressure was 1T to perform the test and obtain the powder compaction. After the test, the pressure was released, and the above steps were repeated. The pressing pressures were 2T, 3T, 4T, 5T and 2T in sequence. P1 is the last 2T powder compaction measured by the five-point method.

[0221] (2) P2 test (ten-point method)

[0222] A powder compaction tester (manufacturer: Yuaneng, model: PRCD1100) was used. First, the upper and lower metal gaskets were placed in the empty mold and placed together, aligned with the base and fixed. Baseline initialization and thickness reset were performed. An appropriate amount of composite negative electrode material was weighed, its mass was recorded, and then added to the empty mold. After pre-vibration, the compaction was performed at a pressure of 0.5T to obtain the powder compaction. After the test, the pressure was released, and the above steps were repeated. The compaction was performed at pressures of 1T, 1.5T, 2T, 2.5T, 3T, 3.5T, 4T, 4.5T, 5T and 2T in sequence. P2 is the last 2T powder compaction measured by the ten-point method.

[0223] Example 2

[0224] (1) Thickness of the outer shell

[0225] S1. Sampling: Samples were taken from 25kg bags of graphite materials and their uncoated products prepared in the examples and comparative examples. Using a sampling spoon, 50g samples were taken from nine equally spaced locations: center, upper center, lower center, left center, right center, upper left, lower left, upper right, and lower right. The 450g powder samples were then thoroughly shaken and mixed to form test standard samples, named M1 (graphite material) and M2 (uncoated product; M1 was calcined at 450℃ under vacuum for 4 hours).

[0226] S2. True density test: Referring to the national standard GB / T 24533-2009, take 5g of test standard samples M1 and M2 respectively and test them with a TD-2200 true density tester. The true density of samples M1 and M2 is obtained by testing three times and the average true density is ρ1 and ρ2.

[0227] S3. Determination of Shell Content and Type: The heat absorption values ​​of raw material samples M1 and M2 were measured using a DSC differential scanning calorimeter. Each sample was tested three times, and the average value was recorded as sample H1 and H2. The mass percentage of the shell was denoted as x. The formula for calculating x is:

[0228] x = (H2 - H1) / H2 × 100%

[0229] The relationship between x and the true density ρ3 of the shell can be established as follows:

[0230] ρ1=ρ2(1-x)+ρ3x

[0231] ρ3=(ρ1-ρ2(1-x)) / x

[0232] ρ3 = ρ2 - (ρ2 - ρ1)H2 / (H2 - H1)

[0233] According to industry standards, a true density greater than 1.9 indicates that the shell is soft carbon coated, otherwise it is hard carbon coated. This can be used to determine the shell type and the stability of shells from different batches.

[0234] S4. Determination of shell thickness: Referring to GB / T 24533-2009, take 5g of test standard sample M1 and test it with Mastersizer 3000 particle size analyzer. Measure the average volume diameter three times and obtain the average volume diameter of sample M1 as D. Record the shell thickness as d. Then we have the following equation.

[0235] 1 / 6·πD^3 ρ1x=1 / 6·π[(D-2d)]^3]ρ2+1 / 6 π[D^3-(D-2d)^3]ρ3

[0236] 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:

[0237] d=Dρ1x / 6ρ3=(Dρ1[(H2-H1)]^2) / (6H2(ρ1H2-ρ2H1))

[0238] The obtained results have an error of less than 1% compared with the formula method, and the range of d obtained is below 50nm-100nm.

[0239] (2) 5T powder compaction density

[0240] A powder compaction density tester (manufacturer: Yuaneng, model: PRCD1100) was used. First, the upper and lower metal shims were placed in the empty mold and placed together, aligned with the base and fixed. Baseline initialization and thickness reset were performed. An appropriate amount of graphite material was weighed, its mass was recorded, and then added to the empty mold. After pre-vibration, the compaction pressure was 0.5T, and the powder compaction was tested. After the test, the pressure was released, and the above steps were repeated. Tests were performed in sequence at compaction pressures of 1T, 1.5T, 2T, 2.5T, 3T, 3.5T, 4T, 4.5T, and 5T.

[0241] Example 3

[0242] Assembly of lithium-ion batteries:

[0243] 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.

[0244] 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.

[0245] 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.

[0246] 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%.

[0247] The electrolyte used is a commercially available electrolyte (manufacturer: Xinya Shanshan New Material Technology (Quzhou) Co., Ltd., model: E3).

[0248] The lithium-ion batteries assembled using the above method were subjected to the following electrical performance tests, and the results are recorded in Table 2.

[0249] (1) First-efficiency of all-cell battery

[0250] Full battery charging capacity: Charge the lithium-ion battery with a 1C current to 4.35V and record the charging capacity of this stage as C1. Then charge at a constant voltage until the cutoff current is 0.05C and record the charging capacity of this stage as C2. The full battery charging capacity is the sum of C1 and C2.

[0251] Full battery discharge capacity: After fully charging the cell and resting for 30 minutes, discharge it to 2.8V with a 1C current. Record the discharge capacity C3 at this stage, which is the full battery discharge capacity.

[0252] First-time efficiency = Total battery discharge capacity C3 / Total battery charge capacity (C1 + C2) × 100%.

[0253] (2) Fast charging time

[0254] The battery was directly charged to 8% SOC using a 0.33C current. Then, based on the measured three-electrode windows of the battery, the charging windows for 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% were tested, corresponding to C1, C2, C3, C4, C5, C6, C7, and C8 respectively. Step charge was used to charge to 80%, i.e., C1 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:

[0255] 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;

[0256] (3) Number of cycles at room temperature

[0257] 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.

[0258] (4) Storage days

[0259] 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.

[0260] The graphite material provided by this invention has a low shape factor, low bulk porosity, and good compressive strength, thus exhibiting high compaction density, good bonding properties, and good processability. Therefore, when applied to electrochemical devices, it improves fast-charging and cycling performance, while also providing excellent initial efficiency and high-temperature storage performance. When the graphite materials prepared in Examples 1-11 are applied to lithium-ion batteries, the charging time from 8% to 80% SOC is only 19.8 minutes or less; the number of cycles to 80% initial capacity at room temperature is 3630 or more; furthermore, the initial efficiency is 91.3% or more, and the storage time at 60°C reaches 371 days or more.

[0261] The comparison of Examples 1-11 shows that the shape factor K, compressive strength F, and bulk porosity L of different graphite materials all affect the particle size and compaction density of the graphite materials themselves, thereby affecting their electrical performance in application. Graphite materials with K, F, and L within the scope of this invention have high compaction density, and when applied to lithium-ion batteries, they exhibit good fast-charging performance, cycle performance, first-efficiency performance, and high-temperature storage performance.

[0262] Table 2

[0263]

[0264] In Comparative Examples 1 and 6, K, F, and L are all greater than the scope of the present invention; in Comparative Examples 2, 4, and 5, although L is within the scope of the present invention, K is greater than the scope of the present invention, and F is less than the scope of the present invention; in Comparative Examples 3, 8, and 10, K and L are both greater than the scope of the present invention, and F is less than the scope of the present invention; in Comparative Example 7, F and L are both within the scope of the present invention, but K is much greater than the scope of the present invention; in Comparative Example 9, although F is within the scope of the present invention, K and L are both greater than the scope of the present invention; the materials obtained in Comparative Examples 1-10 show deterioration in both their own properties and their application. It can be seen that K, F, and L being too large or too small will prevent the achievement of the effects of the present invention.

[0265] This is likely because the shape factor K reflects the approximation of graphite particles to spheres, the pressure resistance factor F reflects the flexibility of the coating layer, and the bulk porosity F reflects the density of the material. A smaller shape factor K indicates less difficulty in coating the first graphite, better coating uniformity and degree, resulting in better flexibility of the graphite coating layer and higher bulk porosity. When the shape factor K is within the range of this invention, it indicates that the graphite material's geometry is close to spherical, ensuring good processability and adhesion, which is beneficial for coating layer formation. A pressure resistance factor F within the range of this invention ensures good elasticity of the graphite material, allowing it to maintain its shape within the electrode, resulting in richer electrode pores and ensuring fast-charging performance. A bulk porosity within the range of this invention signifies a dense graphite structure, contributing significantly to cycle performance. Therefore, any value outside the range of this invention will prevent the achievement of the technical effects of this invention.

[0266] 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, It includes a core and a shell, wherein the core is made of a first type of graphite and the shell is made of a second type of graphite; The graphite material satisfies the following conditions: 6 < K ≤ 30, where K is the shape factor; 1.06≤F≤1.12, where F is the pressure resistance coefficient; 0≤L≤2%, where L is the bulk porosity.

2. 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) 6 < K ≤ 20; (b) 0 ≤ L ≤ 1.6%; and, (c) 1.06≤F≤1.

10.

3. The graphite material as described in claim 1, characterized in that, The graphite material satisfies one or both of the following conditions (a)-(b): (a) The particle size D of the graphite material V 50 is 7μm-13μm; and, (b) The thickness of the outer shell is 50nm-100nm.

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) The second graphite raw material is subjected to hydroxylation treatment to obtain the second graphite matrix; the first graphite raw material is subjected to hydroxylation treatment to obtain the first graphite matrix; (2) The mixture comprising the second graphite matrix and the first graphite matrix is ​​calcined 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 second graphite raw material satisfies the following conditions: La≤72 nm, Lc≤15 nm; where La is the lattice constant of the graphite crystal in the second graphite raw material on the 110 plane, Lc is the lattice constant of the graphite crystal in the second graphite raw material on the 002 plane; F1≥15 mN, where F1 is the particle crushing force; (b) The second 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 the second graphite raw material; (c) The first graphite raw material satisfies the following conditions: bulk porosity ≤ 0.5%; and, (d) The preparation method of the first graphite raw material includes the following steps: petroleum needle coke is subjected to full forging, degassing, pressing and graphitization treatment in sequence to obtain the first graphite raw material.

6. The method for preparing graphite material as described in claim 5, characterized in that, The method for preparing the first graphite matrix satisfies one or more of the following conditions (a)-(d): (a) The volatile matter V of the petroleum needle coke is less than 5%; (b) The degassing time is 1-3 hours; (c) The pressing method is isostatic pressing, the isostatic pressing pressure is 100 MPa - 300 MPa, and the isostatic pressing time is 18h - 36h; and, (d) The degassing temperature is 450℃-800℃.

7. 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)-(f): (a) The treatment agent used in the hydroxylation treatment is an alkaline solution; (b) The hydroxylation treatment is performed at a temperature of 50-65°C; (c) The mass ratio of the second graphite matrix to the first graphite matrix is ​​(0.02-0.1):1; (d) The calcination temperature is 900℃-1200℃; (e) The calcination time is 6h-10h; and, (f) In step (2), the mixture further includes a binder, a solvent and a surfactant.

8. The method for preparing graphite material as described in claim 7, characterized in that, In step (2), the mixture satisfies one or more of the following conditions (a)-(e): (a) The binder is liquid petroleum asphalt and / or phenolic resin, wherein the coking value of the liquid petroleum asphalt is <25%; (b) The volume ratio of the adhesive to the solvent is (5-10):1; (c) The mass ratio of the binder to the first graphite matrix is ​​(3-10):100; (d) The surfactant is dodecyltrimethylammonium bromide; (e) The mass ratio of the first graphite matrix to the surfactant is 1:(0-0.002) and is not 0.

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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