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 meets the following conditions: La is less than or equal to 72 nm, and Lc is less than or equal to 15 nm; wherein La is a lattice constant of a graphite crystal in the graphite material on a 110 plane, and Lc is a lattice constant of the graphite crystal in the graphite material on a 002 plane; f is greater than or equal to 15 mN, and F is particle crushing force. An electrochemical device (especially a lithium ion battery) containing the composite material can ensure excellent first effect and fast charge performance, and also has excellent self-discharge performance, capacity performance and cycle performance.

Description

Technical Field

[0001] This invention relates to a graphite material and its preparation method, an electrochemical device, and an electronic device. Background Technology

[0002] Microcrystalline graphite is a type of natural graphite with a small cell size and abundant porosity, giving it greater kinetic advantages than conventional flake natural graphite, and higher capacity and compaction than conventional artificial graphite. Furthermore, the raw materials for microcrystalline graphite are very inexpensive, costing approximately 20-30% of the price of natural flake graphite of the same quality, thus showing promising application prospects. However, naturally mined microcrystalline graphite has an extremely high impurity content. When used as a negative electrode material in lithium-ion batteries, it requires impurity removal, but this process is complex and costs approximately 2-3 times that of natural flake graphite of the same quality. Considering all factors, its cost is not advantageous, significantly limiting the application of microcrystalline graphite.

[0003] Existing impurity removal technologies, such as Chinese patent application CN107555426A, use acid-base and high-temperature heat treatment to remove impurities from microcrystalline graphite. While claiming low energy consumption, the treatment of waste acid and alkali and the need for crucible furnaces inevitably lead to a significant increase in costs and damage the structure of the graphite material. Lithium-ion batteries containing graphite cannot guarantee excellent first-efficiency and fast-charging performance. Chinese patent application CN109616640A improves the cycle performance of microcrystalline graphite by adding inorganic salts and coating it under a nitrogen atmosphere; however, its experimental process is not suitable for large-scale factory production, and the experimental materials used are expensive, which is not conducive to cost reduction in the final product. Although the cycle performance of lithium-ion batteries using this microcrystalline graphite is improved, excellent first-efficiency and fast-charging performance cannot be guaranteed. Therefore, it is crucial to find a way to ensure excellent first-efficiency and fast-charging performance in lithium-ion batteries containing graphite materials. Summary of the Invention

[0004] To address the shortcomings of existing lithium-ion batteries containing graphite materials in guaranteeing excellent initial efficiency and fast charging performance, this invention provides a graphite material, its preparation method, an electrochemical device, and an electronic device. This graphite material possesses extremely low La and Lc values ​​and a large particle crushing force F. Electrochemical devices containing this material (especially lithium-ion batteries) can guarantee excellent initial efficiency and fast charging performance, while also achieving excellent self-discharge performance, capacity performance, and cycle performance.

[0005] To achieve the above objectives, the present invention employs the following technical solutions.

[0006] In a first aspect, the present invention provides a graphite material that satisfies the following conditions:

[0007] a. La ≤ 72 nm, Lc ≤ 15 nm; where La is the lattice constant of the graphite crystal in the 110 plane and Lc is the lattice constant of the graphite crystal in the 002 plane.

[0008] b. F ≥ 15 mN, where F is the crushing force of the particles.

[0009] Secondly, the present invention provides a method for preparing the graphite material as described above, comprising the following steps:

[0010] S1. The 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;

[0011] S2. Press the mixture to obtain a graphite blank;

[0012] S3. The graphite blank is laid on the surface of the graphitization equipment, and graphitized insulation material is laid on the graphite blank for graphitization treatment. The graphite blank is obtained by graphitization treatment.

[0013] S4. The graphitized graphite blank is crushed to obtain 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 described above.

[0016] The positive and progressive effects of this invention are as follows:

[0017] This invention provides a graphite material. By controlling and designing parameters such as lattice constants La and Lc, and particle crushing force F, electrochemical devices (especially lithium-ion batteries) using this graphite material can guarantee excellent first-cycle efficiency and fast-charging performance, while also taking into account excellent self-discharge performance, capacity performance, and cycle performance. Detailed Implementation

[0018] 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.

[0019] Graphite materials

[0020] The graphite material provided in the first aspect of the present invention satisfies the following conditions:

[0021] a. La ≤ 72 nm, Lc ≤ 15 nm; where La is the lattice constant of the graphite crystal in the 110 plane and Lc is the lattice constant of the graphite crystal in the 002 plane.

[0022] b. F ≥ 15 mN, where F is the crushing force of the particles.

[0023] In some preferred embodiments, La ≤ 60 nm. The La is, for example, 53 nm, 58 nm, 59 nm, 61 nm, 62 nm, 65 nm, 66 nm or 67 nm.

[0024] In some preferred embodiments, Lc ≤ 12 nm. The Lc is, for example, 8.8 nm, 9.6 nm, 10.3 nm, 10.8 nm, 10.9 nm, 11.1 nm, 12.9 nm, 13.1 nm or 13.2 nm.

[0025] In this invention, 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).

[0026] In this invention, the 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).

[0027] In this invention, the particle crushing force (F) refers to the critical pressure at which a single particle of the material breaks apart during a compressive strength test. Preferably, 15 mN ≤ F ≤ 25 mN. The particle crushing force is, for example, 15 mN, 16 mN, 17 mN, 18 mN, 19 mN, 20 mN, 21 mN, or 23 mN.

[0028] In this invention, 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 above dispersion is dropped onto a glass slide, and the glass 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 change point during the particle compression process is recorded as the particle crushing force.

[0029] In a preferred embodiment, the graphite material satisfies 0 < S ≤ 0.1, preferably 0 < S ≤ 0.07, where S represents the symmetry of particle size distribution.

[0030] In some specific implementations, the particle size distribution symmetry is, for example, 0.01, 0.035, 0.038, 0.051, 0.052, 0.056, 0.067, 0.072, 0.083, 0.096, or 0.1.

[0031] 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.

[0032] In one specific embodiment, the graphite material satisfies the following: La is 62 nm, Lc is 12 nm, the particle crushing force is 21 mN, and the particle size distribution symmetry is 0.051.

[0033] In one specific embodiment, the graphite material satisfies the following conditions: La is 58 nm, Lc is 9.6 nm, particle crushing force is 17 mN, and particle size distribution symmetry is 0.1.

[0034] In one specific embodiment, the graphite material satisfies the following conditions: La is 72 nm, Lc is 15 nm, the particle crushing force is 25 mN, and the particle size distribution symmetry is 0.01.

[0035] In one specific embodiment, the graphite material satisfies the following conditions: La is 60 nm, Lc is 11.1 nm, particle crushing force is 20 mN, and particle size distribution symmetry is 0.052.

[0036] In one specific embodiment, the graphite material satisfies the following conditions: La is 65 nm, Lc is 13.2 nm, particle crushing force is 23 mN, and particle size distribution symmetry is 0.067.

[0037] In one specific embodiment, the graphite material satisfies the following conditions: La is 61 nm, Lc is 10.9 nm, particle crushing force is 18 mN, and particle size distribution symmetry is 0.038.

[0038] In one specific embodiment, the graphite material satisfies the following conditions: La is 66 nm, Lc is 12.9 nm, particle crushing force is 23 mN, and particle size distribution symmetry is 0.067.

[0039] In one specific embodiment, the graphite material satisfies the following conditions: La is 62 nm, Lc is 12 nm, the particle crushing force is 23 mN, and the particle size distribution symmetry is 0.056.

[0040] In one specific embodiment, the graphite material satisfies the following conditions: La is 59 nm, Lc is 10.8 nm, particle crushing force is 19 mN, and particle size distribution symmetry is 0.072.

[0041] In one specific embodiment, the graphite material satisfies the following conditions: La is 53 nm, Lc is 8.8 nm, particle crushing force is 15 mN, and particle size distribution symmetry is 0.051.

[0042] In one specific embodiment, the graphite material satisfies the following conditions: La is 67 nm, Lc is 13.1 nm, particle crushing force is 23 mN, and particle size distribution symmetry is 0.083.

[0043] In one specific embodiment, the graphite material satisfies the following conditions: La is 58 nm, Lc is 10.3 nm, particle crushing force is 16 mN, and particle size distribution symmetry is 0.096.

[0044] In some alternative embodiments, the Dv50 particle size of the graphite material is 10-13 μm, for example, 9.5 μm.

[0045] In this invention, the 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. The sphericity of a sphere is equal to 1, and the sphericity of other objects is less than 1. The sphericity of the graphite material is preferably 0.5-1.0, for example, 0.58, 0.59, 0.68, 0.7, 0.71, 0.73, 0.75, or 0.92.

[0046] In this invention, the sphericity can be obtained by testing according to GB / T 37406-2019.

[0047] In some alternative embodiments, the carbon content of the graphite material is 99.9% or more, and the percentage is the mass percentage of the graphite material.

[0048] In some alternative implementations, the graphite material is microcrystalline graphite.

[0049] Preparation methods of graphite materials

[0050] The method for preparing the graphite material as described above, provided in the second aspect of the present invention, includes the following steps:

[0051] S1. The 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;

[0052] S2. Press the mixture to obtain a graphite blank;

[0053] S3. The graphite blank is laid on the surface of the graphitization equipment, and graphitized insulation material is laid on the graphite blank for graphitization treatment. The graphite blank is obtained by graphitization treatment.

[0054] S4. The graphitized graphite blank is crushed to obtain graphite material.

[0055] In some preferred embodiments, the temperature of the first mixing is 8-15°C below the softening point of the adhesive, for example, 10°C.

[0056] In some alternative implementations, in step S1, the sphericity D of the graphite precursor is 0.7-1.0.

[0057] In some alternative implementations, in step S1, the graphite precursor is natural microcrystalline graphite. Preferably, the natural microcrystalline graphite is obtained from microcrystalline graphite ore through pretreatment; the pretreatment preferably includes water washing and spheroidization.

[0058] In some alternative implementations, in step S1, the fixed carbon content of the graphite precursor is 88%-91%.

[0059] In some alternative implementations, in step S1, the Dv50 particle size of the graphite precursor is 6-8 μm, for example, 7 μm.

[0060] In some alternative implementations, in step S1, the mass ratio of the graphite precursor to the binder is (4-7):1, for example, 5:1.

[0061] In some alternative embodiments, in step S1, the binder includes one or more of petroleum asphalt, phenolic resin, epoxy resin, and coal tar.

[0062] In some alternative embodiments, in step S1, the softening point of the adhesive is 100-250°C, preferably 100-130°C, for example 110°C.

[0063] In some alternative embodiments, in step S1, the solvent is selected from one or more of xylene, toluene, and n-hexane.

[0064] In some alternative embodiments, 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.

[0065] In some alternative implementations, 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.

[0066] In some alternative embodiments, 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.

[0067] In some optional embodiments, step S1, the method for preparing the graphite precursor includes the following steps: washing and flotating the graphite ore with water, and then performing 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.

[0068] In some optional embodiments, 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.

[0069] In some alternative implementations, in step S3, the temperature of the graphitization process is greater than 1600°C.

[0070] In some alternative implementations, the graphitization process in step S3 takes 18-40 hours, preferably 24-36 hours.

[0071] In some alternative implementations, in step S3, the graphitized insulation material is petroleum coke and / or pitch coke.

[0072] In some alternative implementations, in step S3, the graphitization equipment is a graphitization furnace.

[0073] In some alternative implementations, step S4 further includes sieving and magnetic impurity removal after the pulverization process.

[0074] In some alternative embodiments, in step S4, the pulverization process is to pulverize the particles to a Dv50 particle size of 10-13 μm.

[0075] Electrochemical device

[0076] In the electrochemical device provided in the third aspect of the present invention, therein is 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.

[0077] In this invention, the electrochemical device is preferably a battery.

[0078] In one alternative embodiment, the electrochemical device is a lithium-ion battery; the lithium-ion battery further includes a positive electrode, a separator, and an electrolyte.

[0079] negative electrode sheet

[0080] In this invention, the negative electrode material layer is disposed on at least one surface of the negative electrode current collector.

[0081] In some implementations, the negative electrode material layer also includes a thickener.

[0082] 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).

[0083] In some implementations, the negative electrode material layer further includes a conductive agent.

[0084] 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.

[0085] In some implementations, the negative electrode material layer further includes a binder.

[0086] 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.

[0087] 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.

[0088] 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 material layer, 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 does 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 negative electrode material layer 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.

[0089] 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.

[0090] Positive electrode film

[0091] 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.

[0092] 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.

[0093] In some alternative embodiments, the positive electrode material layer further includes a binder.

[0094] 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.

[0095] In some alternative 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.

[0096] In some alternative embodiments, the positive electrode material layer further includes a conductive agent.

[0097] 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.

[0098] In one specific embodiment, the conductive agent is conductive carbon SP.

[0099] In some alternative 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.

[0100] 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.

[0101] 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 material layer 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.

[0102] 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.

[0103] In some alternative embodiments, the solvent includes one or more of N-methylpyrrolidone (NMP), dimethyl carbonate, ethylene carbonate, and diethylene carbonate, for example, NMP.

[0104] diaphragm

[0105] In this invention, the diaphragm can be a diaphragm conventionally used in the art.

[0106] In some alternative embodiments, the diaphragm may be a polypropylene film or a polyethylene film.

[0107] The air permeability of the diaphragm can be 180-380 s / 100mL.

[0108] The porosity of the diaphragm can be 30%-50%.

[0109] The thickness of the diaphragm can be 9-18 μm.

[0110] 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%.

[0111] electrolyte

[0112] 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.

[0113] 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.

[0114] electronic devices

[0115] The electronic device provided in the fourth aspect of the present invention includes an electrochemical device as described above.

[0116] 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.

[0117] 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.

[0118] The reagents and raw materials used in this invention are all commercially available.

[0119] The main reagents used in the following examples and comparative examples are as follows:

[0120] The microcrystalline graphite ore was purchased from Lutang Graphite Processing Plant in Chenzhou, Hunan Province. It is grade 1 earthy graphite with a carbon content of >85% and impurities of silicon and metallic elements.

[0121] Petroleum asphalt (softening point 110℃) was purchased from Liaoning Xinde New Material Technology Co., Ltd., model XD-110;

[0122] Petroleum asphalt (softening point 130℃) was purchased from Liaoning Xinde New Material Technology Co., Ltd., model XD-130;

[0123] Petroleum asphalt (softening point 250℃) was purchased from Liaoning Xinde New Material Technology Co., Ltd., model XD-250;

[0124] Petroleum asphalt (softening point 280℃) was purchased from Liaoning Xinde New Material Technology Co., Ltd., model XD-280;

[0125] The commercially available graphite material was purchased from Shanghai Shanshan Technology Co., Ltd., model number FSN-1.

[0126] Example 1

[0127] (1) Preparation of graphite materials

[0128] S0. The microcrystalline graphite ore is initially washed and floated to remove soil, so that its fixed carbon content reaches 90%; after coarse crushing, it is spheroidized by honeycomb milling for 6 hours to obtain a graphite precursor with a sphericity of 0.83 (Dv50 particle size of 7μm).

[0129] S1. Mix the above graphite precursor with petroleum asphalt with a softening point of 110℃ at a mass ratio of 5:1. Heat the mixture to 10℃ below the softening point (100℃) and stir for 1 hour (stirring speed of 15r / min-20r / min). Then add an appropriate amount of xylene solvent to assist in the dispersion of petroleum asphalt and continue stirring for 1 hour to obtain a mixture (solid content of 45%).

[0130] S2. Then, the mixture is added to a 40×30cm×30cm rubber mold and pressed under isostatic pressure of 200MPa for 24 hours. Then, it is demolded to obtain a graphite preform.

[0131] S3. The above-mentioned graphite rough blank is used as graphitized insulation material and laid on the surface of the Atchison graphitization furnace. Then, a layer of petroleum coke is laid on top for graphitization to gasify and remove impurities. The graphitization temperature is 3000℃ and the time is 48 h. The graphite rough blank forms a graphitized blank.

[0132] S4. Take out the graphitized preform obtained in step S3, crush it, sieve it and remove impurities magnetically to obtain graphite material (Dv50 particle size is 10μm, sphericity is 0.73, carbon content is 99.9%).

[0133] (2) Preparation of lithium-ion batteries

[0134] 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.

[0135] The preparation of the negative electrode sheet includes the following steps: the obtained graphite material, conductive agent (SP), binder (PAA and SBR, with a mass ratio of 1.3:0.5) and 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.

[0136] 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.

[0137] 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%.

[0138] The electrolyte used is a commercially available electrolyte (manufacturer: Xinya Shanshan New Material Technology (Quzhou) Co., Ltd., model: E3).

[0139] Example 2

[0140] The only difference between Example 2 and Example 1 is that in the preparation of graphite material, the spheroidization treatment time in step S0 is 4 hours, and the sphericity of the obtained graphite precursor is 0.7. The other conditions are the same as in Example 1.

[0141] Example 3

[0142] The only difference between Example 3 and Example 1 is that in the preparation of graphite material, the sphericity treatment time in step S0 is 24 hours, and the sphericity of the obtained graphite precursor is 0.98. The other conditions are the same as in Example 1.

[0143] Example 4

[0144] The only difference between Example 4 and Example 1 is that in the preparation of graphite material, in step S1, the softening point of petroleum asphalt is 130°C, and it is heated to 120°C. The other conditions are the same as in Example 1.

[0145] Example 5

[0146] The only difference between Example 5 and Example 1 is that in the preparation of graphite material, in step S1, the softening point of petroleum asphalt is 100°C, and it is heated to 90°C, while the other conditions are the same as in Example 1.

[0147] Example 6

[0148] The only difference between Example 6 and Example 1 is that in the preparation of the graphite material, the graphitization temperature in step S3 is 2800℃, and the other conditions are the same as in Example 1.

[0149] Example 7

[0150] The only difference between Example 7 and Example 1 is that in the preparation of the graphite material, the graphitization temperature in step S3 is 3200℃, and the other conditions are the same as in Example 1.

[0151] Example 8

[0152] The only difference between Example 8 and Example 1 is that in the preparation of graphite material, in step S4, the graphitized preform is crushed, sieved and magnetically cleaned to control the Dv50 particle size to 13 μm, and the other conditions are the same as in Example 1.

[0153] Example 9

[0154] The only difference between Example 9 and Example 1 is that in the preparation of the graphite material, in step S1, the softening point of the petroleum asphalt is 250°C, and it is heated to 240°C. The other conditions are the same as in Example 1.

[0155] Example 10

[0156] The only difference between Example 10 and Example 1 is that in the preparation of the graphite material, in step S1, the mass ratio of graphite precursor to petroleum pitch is 4:1, and the other conditions are the same as in Example 1.

[0157] Example 11

[0158] The only difference between Example 11 and Example 1 is that in the preparation of graphite material, in step S1, the mass ratio of graphite precursor to petroleum pitch is 7:1. At the same time, in step S4, the graphitized preform is crushed, sieved and magnetically cleaned to control the Dv50 particle size to be 9.5 μm. The other conditions are the same as in Example 1.

[0159] Example 12

[0160] The only difference between Example 12 and Example 1 is that in the preparation of the graphite material, the graphitization temperature in step S3 is 1700℃, and the other conditions are the same as in Example 1.

[0161] Comparative Example 1

[0162] The only difference between this comparative example and Example 1 is that in the preparation of the graphite material, the sphericity treatment time in step S0 is 2 hours, and the sphericity of the obtained graphite precursor is 0.6. The other conditions are the same as in Example 1.

[0163] Comparative Example 2

[0164] The only difference between this comparative example and Example 1 is that in the preparation of the graphite material, in step S1, the softening point of the petroleum asphalt is 280°C, and it is heated to 270°C. The other conditions are the same as in Example 1.

[0165] Comparative Example 3

[0166] The only difference between this comparative example and Example 1 is that in the preparation of the graphite material, the graphitization temperature in step S3 is 3500℃, and the other conditions are the same as in Example 1.

[0167] Comparative Example 4

[0168] The only difference between this comparative example and Example 1 is that in the preparation of the graphite material, in step S4, the graphitized preform is crushed, sieved, and magnetically cleaned to control the Dv50 particle size to be 7 μm. The other conditions are the same as in Example 1.

[0169] Comparative Example 5

[0170] The only difference between this comparative example and Example 1 is that no graphite material was prepared. In the preparation of the lithium-ion battery, commercial graphite material (FSN-1) was used as the negative electrode active material. All other conditions were the same as in Example 1.

[0171] Comparative Example 6

[0172] The only difference between this comparative example and Example 1 is that in the preparation of the graphite material, in step S3, no layer of petroleum coke was laid, and in step S4, the graphitized preform was crushed, sieved, and magnetically cleaned to control the Dv50 particle size to be 11.5 μm. The other conditions are the same as in Example 1.

[0173] Comparative Example 7

[0174] The only difference between this comparative example and Example 1 is that in the preparation of the graphite material, in step S1, the temperature is heated to 4°C below the softening point (106°C), while the other conditions are the same as in Example 1.

[0175] Comparative Example 8

[0176] The only difference between this comparative example and Example 1 is that in the preparation of the graphite material, steps S2-S3 are replaced with the following steps:

[0177] S2. Heat treat the mixture (temperature 700℃, time 3 h).

[0178] S3. Perform graphitization treatment (temperature 3000℃, time 48 h).

[0179] The remaining conditions are the same as in Example 1.

[0180] Comparative Example 9

[0181] The only difference between this comparative example and Example 1 is that in the preparation of the graphite material, step S3 is replaced by the following steps:

[0182] S3-1. Perform acid and alkali treatment: First, treat with aqua regia (30% by mass) and hydrofluoric acid (40% by mass) in sequence, and then treat with sodium hydroxide solution (40% by mass).

[0183] S3-2, then perform high-temperature purification (temperature 1200℃, time 6 h).

[0184] Meanwhile, in step S4, the graphitized preform is crushed, sieved, and magnetically cleaned to control the Dv50 particle size to 6.3 μm.

[0185] The remaining conditions are the same as in Example 1.

[0186] Example 1

[0187] The lattice constant La, Lc, particle crushing force F, particle size distribution symmetry S, and sphericity D of the graphite materials obtained in Examples 1-12 and Comparative Examples 1-9 were tested.

[0188] (1) Lattice constants La and Lc:

[0189] The obtained graphite material was used as a test sample. The graphite material and 50 mL of n-hexane were added to a beaker and ultrasonically vibrated for 5 min. Then, 100 μL of the solution was pipetted onto the copper grid for TEM observation. The copper grid was quickly dried before observation.

[0190] The sample's d(110) and full width at half maximum (FWHM) were obtained by selective diffraction observation and calibration using TEM. Then according to ,in Since the value is 0.0027 nm, θ can be calculated; then... ;

[0191] The d(002) and half-maximum width of the sample were obtained by selective diffraction observation and calibration using TEM. Then according to ,in Since the value is 0.0027 nm, θ' can be calculated. .

[0192] (2) Particle crushing force F

[0193] The crushing force of particles was tested using the Xiamen Yuaneng Technology Single Particle Mechanical Property Testing System (SPFT2000), as detailed below:

[0194] 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.

[0195] (3) Particle size distribution symmetry S

[0196] Referring to GB / T 41949-2022, a laser particle size diffractometer (Malvin 3000) was used to test the graphite material. The particle size data of D(3,4) and Dv50 were directly read from the test results. Then, S was calculated according to S=[D(3,4)-Dv50] / Dv50.

[0197] (4) Sphericity D

[0198] Sphericity was tested according to GB / T 37406-2019.

[0199] (5) 2T powder compaction density (2T powder compaction)

[0200] The compaction density of graphite powder was tested using the national standard GB / T 24533-2019.

[0201] The test results are shown in Table 1.

[0202] Example 2

[0203] The following electrochemical performance tests were performed on the lithium-ion batteries prepared in Examples 1-12 and Comparative Examples 1-9:

[0204] Before testing, the prepared lithium-ion battery was activated by charging and discharging it at 0.1C at 25°C within the battery's operating voltage range of 2.8V (discharge cutoff voltage) to 4.35V (charge cutoff voltage) for one cycle. Then, the following tests were performed.

[0205] (1) Charging capacity and discharging capacity

[0206] The lithium-ion battery was connected to the Blue Electric Charge-Discharge Tester and subjected to long-cycle charge-discharge to measure its charging and discharging capacity. The working voltage range of the battery test was 2.8V (discharge cut-off voltage) to 4.35V (charging cut-off voltage), and the test rate was 0.3C.

[0207] First-time efficiency = Discharge capacity / Charge capacity × 100%.

[0208] (2) Fast charging time

[0209] The battery cell was directly charged to 8% SOC state at a current of 0.33C. Then, based on the actual measured three-electrode window of the battery cell, the charging windows for 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% were C1, C2, C3, C4, C5, C6, C7, and C8, respectively. Gradual charging to 80% was adopted, that is, C1 was used for 8%-10%, C2 was used for 10%-20%, and so on. The charging time from 8% to 80% SOC state was recorded as a standard for measuring fast charging capability. The calculation formula is T = (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.

[0210] (3) Number of cycles

[0211] Connect the lithium-ion battery to the Blue Electric charge-discharge tester, and then perform long-term cycling at a rate of 0.3C until the ratio of the capacity of the nth cycle to the capacity of the first cycle at 0.3C is less than 80%. Define the capacity retention rate of the (n-1)th cycle as 80%, and record the number of cycles as n-1. Stop the test.

[0212] (4) Storage days

[0213] At 25℃, the cell was calibrated with a current of 0.33C and recorded as C0. The cell was then stored at 60℃. Every 7 days, the cell was removed and its capacity was tested at room temperature and recorded as C1, C2…C… n , to C n The storage time is the number of days when the value of C0 is first less than or equal to 80%.

[0214] (5) Self-discharge performance

[0215] At 25℃, it is fully charged to constant volume with a current of 0.33C and recorded as C0. The voltage at this time is recorded as V1. After 90 days of storage, the voltage is measured as V2. Then the self-discharge voltage is V1-V2.

[0216] The test results are shown in Table 2.

[0217]

[0218]

[0219] According to Tables 1 and 2, the La of the graphite materials prepared in Examples 1-12 is between 53-72 nm, Lc is between 8.8-15 nm, particle crushing force F is between 15-25 mN, particle size distribution symmetry S is between 0.01-0.1, Dv50 particle size is between 9.5-13 μm, sphericity D is between 0.58-0.92, and 2T powder compaction is between 1.59-1.75 gcc. -1 The lithium-ion battery made from this graphite material as the negative electrode material can guarantee excellent initial efficiency and fast charging performance, while also taking into account excellent self-discharge performance, capacity performance, and cycle performance. Specifically, the initial efficiency can reach over 90%, and the fast charging time can be less than 30 seconds, or even less than 15 seconds; on this basis, the discharge capacity can reach over 355 mAh / g, the cycle count can reach over 1700 cycles, the storage days can reach over 180 days, and the self-discharge voltage can be less than 0.7V.

[0220] The inventors discovered that when La and Lc are too small, compaction and capacity problems worsen, and when the particle crushing force F is too small, cycle performance is poor. Only under the specific La, Lc, and particle crushing force F specified in this invention can the aforementioned electrochemical performance be balanced.

[0221] Compared to Example 1, Comparative Examples 1, 3, and 6-9 have excessively high La and Lc values ​​in the graphite material and excessively low particle crushing force F. The resulting lithium-ion batteries exhibit significantly reduced discharge capacity, poor initial efficiency, longer fast-charging time, and significantly worse cycle count, storage days, and self-discharge voltage.

[0222] Compared to Example 1, Comparative Example 5 differs in that the La and Lc values ​​of the graphite material are too large, and the particle crushing force F is too small. Although the resulting lithium-ion battery has higher initial efficiency, higher cycle count and storage days, and lower self-discharge voltage, the discharge capacity of the lithium-ion battery is reduced, and the fast charging time is greatly extended, making it impossible to achieve both excellent initial efficiency and fast charging performance.

[0223] Compared with Example 1, the difference between Comparative Examples 2 and 7 is that although the particle crushing force of the graphite material is large, La and Lc are too large; the discharge capacity of the resulting lithium-ion battery is significantly reduced, the initial efficiency is poor, the fast charging time is long, and the number of cycles, storage days and self-discharge voltage are significantly worse.

[0224] Compared with Example 1, the difference in Comparative Example 4 is that although the La and Lc of the graphite material are similar, the particle crushing force F is too small; although the fast charging time of the resulting lithium-ion battery is shorter, the discharge capacity, first efficiency, number of cycles, storage days and self-discharge voltage are significantly worse, and it is impossible to achieve both excellent fast charging time and first efficiency.

[0225] 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 by, It meets the following conditions: a. La ≤ 72 nm, Lc ≤ 15 nm; where La is the lattice constant of the graphite crystal in the 110 plane and Lc is the lattice constant of the graphite crystal in the 002 plane. b. F ≥ 15 mN, where F is the crushing force of the particles.

2. The graphite material of claim 1, wherein, It satisfies one or more of the following conditions: a. La≤60 nm; b, Lc≤12 nm; c. 15 mN ≤ F ≤ 25 mN; d, 0 < S ≤ 0.1, where S is the symmetry of particle size distribution.

3. The graphite material of claim 1, wherein, It satisfies one or more of the following conditions: a. The Dv50 particle size of the graphite material is 10-13 μm; b. The sphericity of the graphite material is 0.5-1.0; c. The carbon content of the graphite material is 99.9% or more, and the percentage is the mass percentage of the graphite material. d. The graphite material is microcrystalline graphite.

4. A method of producing the graphite material according to any one of claims 1 to 3, characterized by, It includes the following steps: S1. The 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 graphite blank; S3. The graphite blank is laid on the surface of the graphitization equipment, and graphitized insulation material is laid on the graphite blank for graphitization treatment. The graphite blank is obtained by graphitization treatment. S4. The graphitized graphite blank is crushed to obtain graphite material.

5. The method for preparing graphite material as described in claim 4, characterized in that, In step S1, the temperature of the first mixing is 8-15°C below the softening point of the adhesive.

6. The method for preparing graphite material as described in claim 4, characterized in that, Step S1 satisfies one or more of the following conditions ai: a. In step S1, the sphericity of the graphite precursor is 0.7-1.0; b. In step S1, the graphite precursor is natural microcrystalline graphite; c. In step S1, the fixed carbon content of the graphite precursor is 88%-91%, and the percentage is the mass percentage of the graphite precursor. d. In step S1, the Dv50 particle size of the graphite precursor is 6-8 μm; e. In step S1, the mass ratio of the graphite precursor to the binder is (4-7):1; f. In step S1, the binder includes one or more of petroleum asphalt, phenolic resin, epoxy resin, and coal tar. g. In step S1, the softening point of the adhesive is 100-250℃; h. In step S1, the solvent is selected from one or more of xylene, toluene, and n-hexane; i. In step S1, the solid content of the mixture is 40%-60%, and the percentage is the mass percentage of the solid component of the mixture relative to the mass of the mixture.

7. The method for preparing graphite material as described in claim 4, characterized in that, Steps S1 and S2 satisfy one or more of the following conditions: a. In step S1, the first mixing method is stirring; b. In step S1, the second mixing method is stirring; c. In step S1, the preparation method of the graphite precursor includes the following steps: water washing and flotation of graphite ore, followed by coarse crushing and spheroidization treatment to obtain the graphite precursor; d. In step S2, the pressing is isostatic pressing.

8. The method for preparing graphite material as described in claim 4, characterized in that, Steps S3 and S4 satisfy one or more of the following conditions af: a. In step S3, the temperature of the graphitization treatment is greater than 1600℃; b. In step S3, the graphitization treatment time is 18-40 hours; c. In step S3, the graphitized insulation material is petroleum coke and / or pitch coke; d. In step S3, the graphitization equipment is a graphitization furnace; e. In step S4, the pulverization process further includes sieving and magnetic impurity removal; f. In step S4, the pulverization process involves pulverizing the particles until the Dv50 particle size is 10-13 μm.

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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