Artificial graphite material, preparation method thereof, negative plate containing artificial graphite material, electrochemical device and electronic equipment

Abstract

The invention discloses an artificial graphite material, a preparation method thereof, a negative plate containing the artificial graphite material, an electrochemical device and electronic equipment. The artificial graphite material meets the following conditions: the crushing coefficient P is 0.75-0.95, P = A / B, A and B are respectively the specific surface areas of the artificial graphite material before and after powder pressing, and the powder pressing pressure is 5t; the rounding degree R ranges from 0.58 to 0.70; and the grinding convexity degree S ranges from 0.55 to 0.72. The artificial graphite material provided by the invention has excellent storage performance, and the preparation process is low in cost.

Description

Technical Field

[0001] This invention specifically relates to artificial graphite materials and their preparation methods, negative electrode sheets containing the same, electrochemical devices, and electronic devices. Background Technology

[0002] Unlike lithium-ion batteries used in traditional BEVs (Bullet Electric Vehicles), lithium-ion batteries for energy storage place greater emphasis on storage performance (primarily manifested in long lifespan) and low cost per kilowatt-hour. Therefore, developing lithium-ion batteries that offer both extremely low cost and long lifespan will significantly promote the application of lithium-ion batteries in energy storage.

[0003] Generally, the high-temperature graphitization process of artificial graphite vaporizes impurities in the raw material coke, which then adhere to the graphite surface. As the temperature cools, this deposit condenses into a thick, hard shell. This shell is highly disordered and contains various surface defects and impurities, increasing the material's specific surface area and accelerating surface degradation. Because it grows in situ on the graphite surface, it persists even after being used in batteries, significantly impacting battery lifespan. Therefore, to extend the long-term storage life of materials, proper purification is usually necessary.

[0004] Chinese patent CN114477162A uses multi-layer pre-graphitization and post-graphitization coating to cover surface defects, but the lithium-ion battery performance drops drastically in later operating conditions, failing to fundamentally solve the problem. Chinese patent CN110600715A uses strong shaping and surface crystallization treatment on artificial graphite, but this significantly increases energy consumption and reduces the material's cost competitiveness.

[0005] Therefore, how to improve the storage performance of artificial graphite materials at a low cost is a very important issue in this field. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of insufficient storage performance in existing artificial graphite materials by providing artificial graphite materials, their preparation methods, negative electrode sheets containing the same, electrochemical devices, and electronic devices. The artificial graphite materials provided by this invention exhibit excellent storage performance, and the preparation process is low-cost.

[0007] In a first aspect, the present invention provides an artificial graphite material, wherein the artificial graphite material satisfies the following conditions:

[0008] The breakage coefficient P is 0.75-0.95, P=A / B, where A and B are the specific surface areas of the artificial graphite material before and after powder pressing, and the powder pressing pressure is 5t.

[0009] The roundness R is 0.58-0.70;

[0010] The wear resistance S is 0.55-0.72.

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

[0012] S1. Graphitize the raw coke to obtain product I;

[0013] S2. Perform a first shaping on product I to obtain product II; the rotational speed R1 of the first shaping is 2500 r / min-3500 r / min;

[0014] S3. The product II is subjected to a “heating-first heat preservation-cooling-second heat preservation” cycle treatment, and then a second shaping is performed to obtain the artificial graphite material; the rotation speed R2 of the second shaping is 5000r / min-7000r / min; the cooling rate is 8-18℃ / min; the first heat preservation time is 0.5-2h.

[0015] Thirdly, the present invention provides an artificial graphite material, which is prepared by the artificial graphite material preparation method described above.

[0016] Fourthly, the present invention provides a negative electrode sheet comprising the artificial graphite material as described above.

[0017] Fifthly, the present invention provides an electrochemical device comprising the artificial graphite material as described above or the negative electrode as described above.

[0018] In a sixth aspect, the present invention provides an electronic device comprising the electrochemical device as described above.

[0019] 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.

[0020] The reagents and raw materials used in this invention are all commercially available.

[0021] The positive and progressive effects of this invention are as follows:

[0022] The artificial graphite material provided by this invention, by controlling the breakage coefficient, roundness, and roughness within a specific range, exhibits excellent storage performance and further good recycling performance. The preparation method of the artificial graphite material of this invention is simple and highly cost-competitive. Detailed Implementation

[0023] The first aspect of the present invention provides an artificial graphite material, wherein the artificial graphite material satisfies the following conditions:

[0024] The breakage coefficient P is 0.75-0.95, P=A / B, where A and B are the specific surface areas of the artificial graphite material before and after powder pressing, and the powder pressing pressure is 5t.

[0025] The roundness R is 0.58-0.70;

[0026] The wear resistance S is 0.55-0.72.

[0027] In this invention, the breakage coefficient P reflects the degree of fragmentation of the powder under extreme pressure. The closer the value is to 1.0, the less likely the material is to break. The testing method is as follows: using the ASTM D6556 multi-point BET method (77K nitrogen adsorption), the original specific surface area of ​​the artificial graphite material is first tested and recorded as A; then the powder is pressed under a pressure of 5t, and the specific surface area is tested again and recorded as B. P = A / B.

[0028] In this invention, the roundness R describes the sharpness of the edges of artificial graphite material particles; a higher value indicates a smoother edge. The roundness range is typically 0 to 1, where 0 represents very sharp edges and 1 represents perfectly rounded edges. The testing method is as follows: SEM images of the artificial graphite material are obtained using a scanning electron microscope (SEM), and then the images are analyzed using the Malvern Morphologi 4 software module to obtain the roundness R.

[0029] In this invention, the roughness S describes the degree to which the particles are close to a sphere; a higher value indicates a closer approximation to a sphere, and it is used to describe the unevenness of the particle surface. The testing method is as follows: SEM images of the artificial graphite material are obtained using a scanning electron microscope (SEM), and then the images are analyzed using the Malvern Morphologi 4 software module to obtain the roughness S.

[0030] In this invention, the breakage coefficient P of the artificial graphite material can be 0.80-0.88.

[0031] In some specific embodiments, the breakage coefficient P of the artificial graphite material can be 0.75, 0.8, 0.81, 0.83, 0.85 or 0.92.

[0032] In this invention, the roundness R of the artificial graphite material can be 0.59-0.66;

[0033] In some specific implementations, the roundness R of the artificial graphite material can be 0.57, 0.58, 0.63, 0.65, 0.66 or 0.7.

[0034] In this invention, the roughness S of the artificial graphite material can be 0.65-0.70.

[0035] In some specific embodiments, the roughness S of the artificial graphite material can be 0.6, 0.62, 0.68, 0.7, 0.711 or 0.72.

[0036] In some specific embodiments, the artificial graphite material meets the following conditions: the breakage coefficient P is 0.85, the roundness R is 0.63, and the convexity S is 0.68.

[0037] In some specific embodiments, the artificial graphite material meets the following conditions: the breakage coefficient P is 0.83, the roundness R is 0.65, and the convexity S is 0.70.

[0038] In some specific embodiments, the artificial graphite material meets the following conditions: the breakage coefficient P is 0.81, the roundness R is 0.66, and the convexity S is 0.72.

[0039] In some specific embodiments, the artificial graphite material meets the following conditions: the breakage coefficient P is 0.80, the roundness R is 0.70, and the convexity S is 0.71.

[0040] In some specific embodiments, the artificial graphite material meets the following conditions: the breakage coefficient P is 0.92, the roundness R is 0.57, and the convexity S is 0.62.

[0041] In some specific embodiments, the artificial graphite material meets the following conditions: the breakage coefficient P is 0.85, the roundness R is 0.58, and the convexity S is 0.68.

[0042] In some specific embodiments, the artificial graphite material meets the following conditions: the breakage coefficient P is 0.85, the roundness R is 0.63, and the convexity S is 0.60.

[0043] In some specific embodiments, the artificial graphite material meets the following conditions: the breakage coefficient P is 0.75, the roundness R is 0.63, and the convexity S is 0.68.

[0044] In some specific embodiments, the artificial graphite material meets the following conditions: the breakage coefficient P is 0.85, the roundness R is 0.63, and the convexity S is 0.55.

[0045] In this invention, the artificial graphite material can be prepared by the method for preparing artificial graphite material described in the second aspect.

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

[0047] S1. Graphitize the raw coke to obtain product I;

[0048] S2. Perform a first shaping on product I to obtain product II; the first rotational speed R1 of the first shaping is 2500 r / min-3500 r / min;

[0049] S3. The product II is subjected to a “heating-first heat preservation-cooling-second heat preservation” cycle treatment, and then a second shaping is performed to obtain the artificial graphite material; the second rotation speed R2 of the second shaping is 5000r / min-7000r / min; the cooling rate is 8-18℃ / min; the first heat preservation time is 0.5-2h.

[0050] In this invention, the raw material coke can be any raw material conventionally used in the preparation of artificial graphite materials in the art, preferably needle coke, such as coal-based needle coke.

[0051] In this invention, the volatile matter content of the raw material coke is preferably less than 5%, for example, 3.5%; the Dv50 of the raw material coke is preferably 8μm-15μm, for example, 12μm.

[0052] In step S1, the graphitization temperature can be a temperature conventionally used in the art, preferably 2500℃-3000℃, for example 2700℃ or 3000℃.

[0053] In step S2, the first shaping can be performed in an air jet mill.

[0054] In step S2, the temperature of the first shaping can be 400℃-500℃, for example, 450℃. The main purpose of heating in the first shaping is to remove the water of crystallization adsorbed on the product I.

[0055] In step S2, the first rotational speed R1 can be 2700 r / min - 3300 r / min. The main purpose of controlling the appropriate rotational speed in the first shaping process is to remove the large, irregular edges on the surface of product I.

[0056] In some specific implementations, the first rotational speed R1 can be 2500 r / min, 3000 r / min, 3300 r / min or 3500 r / min.

[0057] In step S2, the roundness R of product II is ≥0.45.

[0058] In step S2, the roughness S of product II is ≥0.55.

[0059] In step S3, the number of cycles of the "heating-first heat preservation-cooling-second heat preservation" process can be 2-3 times.

[0060] In step S3, the temperature of the first insulation can be 900℃-1100℃, for example, 1000℃.

[0061] In step S3, the first heat preservation time is preferably 1-2 hours, for example 1 hour, 1.5 hours or 2 hours.

[0062] In step S3, the heating rate can be 3-8℃ / min, for example 5℃ / min.

[0063] In step S3, the temperature of the second heat preservation can be 550℃-700℃, for example 600℃.

[0064] In step S3, the second heat preservation time is 1-3 hours, for example, 2 hours.

[0065] In step S3, the cooling method is to introduce gas for cooling. The flow rate of the introduced gas can be 15-30 L / min, preferably 20-30 L / min, for example 20 L / min, 23 L / min or 30 L / min; the gas is preferably nitrogen.

[0066] In step S3, the cooling rate can be 9-18℃ / min, preferably 10-18℃ / min, for example 10℃ / min, 15℃ / min or 18℃ / min.

[0067] In step S3, the temperature of the second shaping can be 550℃-700℃, for example 600℃.

[0068] In step S3, the second rotational speed R2 can be 6000 r / min - 7000 r / min.

[0069] In some specific implementations, the second rotational speed R2 can be 5300 r / min, 6000 r / min, 6500 r / min or 6700 r / min.

[0070] In step S3, the second shaping time can be 1-3 hours, for example, 2 hours.

[0071] In step S3, after the second shaping, the obtained material can be post-processed, including one or more of grading, washing and ultrasonic vibration.

[0072] The particle size distribution width d of the artificial graphite material obtained by grading can satisfy: d < 1.10; preferably 1.0 < d < 1.10.

[0073] The particle size of the artificial graphite material obtained by grading satisfies: (Dv90-Dv50) / (Dv50-Dv10)>1.4.

[0074] In this invention, the particle size distribution widths d, Dv10, Dv50, and Dv90 can be obtained by using a conventional laser particle size analyzer in the art.

[0075] The artificial graphite material provided in the third aspect of the present invention is prepared by the preparation method described above.

[0076] In this invention, the artificial graphite material has the same structural features as the artificial graphite material described in the first aspect.

[0077] A fourth aspect of the present invention provides a negative electrode sheet comprising the artificial graphite material as described above.

[0078] In this invention, the negative electrode sheet may include a negative electrode current collector and a negative electrode material layer, wherein the negative electrode material layer is disposed on at least one surface of the negative electrode current collector; the negative electrode material layer includes the artificial graphite material as described above.

[0079] In this invention, the negative electrode current collector can be a conventional negative electrode current collector in the art. The negative electrode current collector, serving as the substrate supporting the negative electrode material layer, is typically a metal foil with a thickness of 3-500 μm. There are no particular limitations 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.

[0080] In this invention, the negative electrode material layer may further include a conductive agent.

[0081] 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 conductive carbon black (Super P, abbreviated as SP), carbon nanotubes (CNT), 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.

[0082] In this invention, the negative electrode material layer may further include a binder.

[0083] 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 SBR.

[0084] In this invention, the negative electrode material layer may further include a thickener.

[0085] 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).

[0086] In some embodiments, the method for preparing the negative electrode sheet includes the following steps: coating a negative electrode slurry containing the artificial graphite material onto at least one surface of the negative electrode current collector, drying, cold pressing, and slitting to obtain the negative electrode sheet.

[0087] In some specific embodiments, the negative electrode slurry includes: the artificial graphite material, a conductive agent, a thickener, and a binder, wherein the conductive agent is acetylene black; the thickener is CMC; and the binder is SBR and PAA; preferably, the mass ratio of the artificial graphite material, acetylene black, CMC, SBR, and PAA is 97.4:0.4:0.4:0.5:1.3.

[0088] A fifth aspect of the present invention provides an electrochemical device comprising the artificial graphite material as described above or the negative electrode as described above.

[0089] In this invention, the electrochemical device is preferably a battery.

[0090] In some embodiments, the electrochemical device is a lithium-ion battery.

[0091] In some embodiments, the lithium-ion battery may be a liquid lithium-ion battery, an all-solid-state lithium-ion battery, or a semi-solid-state lithium-ion battery. The battery type does not limit the scope of protection of this invention.

[0092] In some specific embodiments, the liquid lithium-ion battery includes a positive electrode, a negative electrode as described above, a separator, and an electrolyte.

[0093] In some specific embodiments, the all-solid-state lithium-ion battery includes a positive electrode, a negative electrode as described above, and a solid electrolyte membrane.

[0094] In this invention, the liquid lithium-ion battery includes a positive electrode, a negative electrode as described above, and a separator.

[0095] Positive electrode film

[0096] In this invention, the positive electrode sheet may include a positive current collector and a positive electrode material layer, wherein the positive electrode material layer is disposed on at least one surface of the positive current collector; the positive electrode material layer includes a positive electrode active material.

[0097] In some embodiments, the positive electrode active material may 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.

[0098] In some embodiments, the positive electrode material layer further includes a conductive agent. The conductive agent is a reagent used to ensure that the electrode has good charge-discharge performance. It can be selected from graphite materials such as natural graphite and artificial graphite; carbon black materials such as Super P, conductive carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers such as carbon nanotubes (CNTs), carbon fibers, and metal fibers; 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, for example, Super P and CNTs.

[0099] In some embodiments, the positive electrode material layer further includes a binder. The binder may be a component that facilitates bonding between the positive electrode material and the conductive agent, and also facilitates bonding between the positive electrode material and the positive electrode current collector. It can typically be selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers, such as PVDF.

[0100] In some embodiments, the positive electrode material layer includes a positive electrode active material, Super P, CNT, and PVDF.

[0101] In some specific embodiments, the mass ratio of the positive electrode active material, Super P, CNT and PVDF is 97:1.0:0.5:1.5.

[0102] In this invention, the positive electrode current collector can be a conventional positive electrode current collector in the art. For the positive electrode current collector, materials that do not cause chemical changes and have high conductivity can be used without limitation. For example, commonly used materials include stainless steel, aluminum, nickel, titanium, or calcined carbon, or aluminum or stainless steel materials surface-treated with carbon, nickel, titanium, silver, etc. To enhance adhesion, micro-embossing can be formed on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms, such as films, sheets, foils, meshes, or porous bodies.

[0103] In some alternative embodiments, the positive current collector is aluminum foil.

[0104] In this invention, the positive electrode sheet can be prepared using methods conventional in the art.

[0105] In some optional embodiments, the method for preparing the positive electrode sheet includes the following steps: mixing the positive electrode material, binder and conductive agent in a certain mass ratio, adding solvent and mixing evenly to obtain a positive electrode slurry; then uniformly coating the positive electrode slurry onto at least one surface of the positive electrode current collector; and then preparing the positive electrode sheet by drying, rolling, slitting and other processes.

[0106] electrolyte

[0107] In some embodiments, the electrolyte may be a conventional electrolyte used in batteries, typically including non-aqueous solvents and lithium salts.

[0108] In this invention, the non-aqueous solvent can be a conventional non-aqueous solvent in the art.

[0109] In some embodiments, the non-aqueous solvent preferably comprises ester solvents and / or dimethyl sulfoxide (DMSO), more preferably carbonate solvents. The carbonate solvent may optionally be one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), methyl ethyl carbonate (EMC), ethylene carbonate, propylene carbonate, and butyl carbonate (BC). The non-aqueous solvent may also include ethyl acetate.

[0110] In this invention, the lithium salt can be a conventional lithium salt in the art, preferably one or more of LiPF6, LiBF4, LiClO4, LiCF3SO3 and LiN(CF3SO2)2, for example, LiPF6; the concentration of the lithium salt is preferably 1 mol / L.

[0111] In this invention, the electrolyte may include additives, which may be conventional additives in the art, such as fluoroethylene carbonate (FEC).

[0112] In some embodiments, the electrolyte includes LiPF6, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate.

[0113] In some preferred embodiments, the electrolyte comprises EC, EMC, and DEC. The volume ratio of EC, EMC, and DEC is, for example, 1:1:1.

[0114] In some embodiments, the electrolyte can be prepared by conventional methods in the art. Optionally, it can be prepared by the following method: mixing the various non-aqueous solvents in proportion in an argon atmosphere glove box with a water content of <10 ppm, and then adding a fully dried lithium salt and mixing evenly to obtain the electrolyte.

[0115] diaphragm

[0116] In some alternative embodiments, the diaphragm may be a polypropylene membrane or a polyethylene membrane.

[0117] In some alternative embodiments, the thickness of the diaphragm may be 9 μm-18 μm, for example, 11 μm.

[0118] In some alternative embodiments, the air permeability of the diaphragm can be 180s / 100mL-380s / 100mL.

[0119] In some alternative embodiments, the porosity of the membrane may be 30%-50%.

[0120] In this invention, the method for preparing the lithium-ion battery can be a conventional method in the art. It can be that the positive electrode, separator, and negative electrode are wound in sequence to obtain the battery cell, which is then packaged in a packaging shell and injected with the electrolyte. Alternatively, the positive electrode, separator, and negative electrode are stacked in sequence to obtain the battery cell, which is then packaged in a packaging shell and injected with the electrolyte. After that, the lithium-ion battery is obtained through processes such as settling, hot and cold pressing, formation, clamping, and capacity testing.

[0121] A sixth aspect of the present invention provides an electronic device comprising the electrochemical device as described above.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] Example 1

[0126] 1. Negative electrode sheet

[0127] (1) Preparation of artificial graphite materials

[0128] S1. Coal-based needle coke (A-series needle coke, purchased from Baoshun Technology Co., Ltd., with a volatile content of 3.5%) was crushed into pieces with a Dv50 of 12μm, and then graphitized to obtain product I; the graphitization temperature was 2700℃;

[0129] S2. The product I obtained in step S1 is placed into an air jet mill and heated to 450°C. At the same time, the rotation speed of the air jet mill is kept at the first rotation speed R1, which is 3000 r / min. The first shaping is performed to obtain product II. The roundness R of the obtained product II is greater than 0.45 and the convexity S is greater than 0.55.

[0130] S3. The product II obtained in step S2 is heated to 1000℃ at a rate of 5℃ / min and held for 1h (first holding). Then, nitrogen is introduced at a flow rate of 20L / min to cool it down to 600℃ (cooling rate of 10℃ / min) and held for 2h (second holding). The above "heating-first holding-cooling-second holding" cycle is repeated twice. Then, the temperature is maintained at 600℃, and the rotation speed of the separator is adjusted to the second rotation speed R2, which is 6000r / min, for the second shaping, which takes 2h. The material obtained from the second shaping is then naturally cooled and then graded to control its particle size distribution width d to be less than 1.10 and (Dv90-Dv50) / (Dv50-Dv10)>1.4. Then, it is washed with water and ultrasonically vibrated to obtain artificial graphite material.

[0131] (2) Preparation of negative electrode

[0132] The prepared artificial graphite material was used as the negative electrode material, acetylene black as the conductive agent, CMC as the thickener, and SBR and PAA as the binder. They were mixed in a mass ratio of 97.4:0.4:0.4:0.5:1.3, and deionized water was added as a solvent. The mixture was stirred thoroughly to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on one surface of the negative electrode current collector copper foil. After drying, cold pressing, and slitting, a negative electrode sheet was prepared.

[0133] 2. Positive electrode plate

[0134] Lithium iron phosphate cathode material (LFP), Super P, CNT, and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97:1.0:0.5:1.5, and N-methylpyrrolidone (NMP) solvent was added. The mixture was stirred thoroughly to obtain a cathode slurry. The cathode slurry was coated on one surface of the cathode current collector aluminum foil, and the cathode sheet was prepared by drying, cold pressing, and slitting.

[0135] 3. Diaphragm

[0136] A porous PE membrane with a thickness of 11 μm was used as the separator.

[0137] 4. Electrolyte

[0138] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0139] 5. Lithium-ion batteries

[0140] The positive electrode, separator, and negative electrode prepared in the aforementioned steps are stacked sequentially, with the separator positioned between the positive and negative electrode to act as a separator. Then, an aluminum-plastic film is wrapped around the separator, dried, and the electrolyte prepared above is injected. After encapsulation, settling, and formation processes, a soft-pack battery with a designed capacity of 1 Ah, i.e., a lithium-ion battery, is finally prepared.

[0141] Examples 2-9 and Comparative Examples 1-7

[0142] The process parameters for each embodiment and comparative example are shown in Table 1. Other unlisted process parameters and preparation methods are the same as in Example 1.

[0143] Example 2 differs from Example 1 in that the first rotational speed R1 is adjusted to 3300 r / min, while the other steps and process conditions are the same as in Example 1.

[0144] Example 3 differs from Example 1 in that the second rotational speed R2 is adjusted to 6700 r / min, while the other steps and process conditions are the same as in Example 1.

[0145] Example 4 differs from Example 1 in that the nitrogen flow rate is adjusted to 30 L / min (cooling rate is 18 °C / min), while the other steps and process conditions are the same as in Example 1.

[0146] Example 5 differs from Example 1 in that the first heat preservation time is adjusted to 2 hours, while the other steps and process conditions are the same as in Example 1.

[0147] Example 6 differs from Example 1 in that the first rotational speed R1 is adjusted to 2500 r / min, the first holding time is adjusted to 2h, the number of cycles is 3, and the second rotational speed R2 is adjusted to 5300 r / min; other steps and process conditions are the same as in Example 1.

[0148] Example 7 differs from Example 1 in that the graphitization temperature is adjusted to 3000℃ and the first holding time is adjusted to 1.5h, while the other steps and process conditions are the same as in Example 1.

[0149] Example 8 differs from Example 1 in that the first rotational speed R1 is adjusted to 3500 r / min, the nitrogen flow rate is adjusted to 30 L / min (cooling rate is 18℃ / min), and the second rotational speed R2 is adjusted to 6500 r / min; other steps and process conditions are the same as in Example 1.

[0150] Example 9 differs from Example 1 in that the first rotation speed R1 is adjusted to 3100 r / min, the first holding time is adjusted to 1.8h, and the second rotation speed R2 is adjusted to 6700 r / min; the other steps and process conditions are the same as in Example 1.

[0151] The difference between Comparative Example 1 and Example 1 is that the first rotational speed R1 is adjusted to 2000 r / min, while the other steps and process conditions are the same as in Example 1.

[0152] The difference between Comparative Example 2 and Example 1 is that the second rotational speed R2 is adjusted to 7500 r / min, while the other steps and process conditions are the same as in Example 1.

[0153] The difference between Comparative Example 3 and Example 1 is that the nitrogen flow rate was adjusted to 40 L / min (the cooling rate was 32 °C / min), while the other steps and process conditions were the same as in Example 1.

[0154] The difference between Comparative Example 4 and Example 1 is that the first heat preservation time was adjusted to 3 hours, while the other steps and process conditions were the same as in Example 1.

[0155] The difference between Comparative Example 5 and Example 1 is that the first heat preservation time is adjusted to 0h (that is, after heating, no heat preservation is performed, and cooling begins directly), while the other steps and process conditions are the same as in Example 1.

[0156] The difference between Comparative Example 6 and Example 1 is that the first rotational speed R1 is adjusted to 3300 r / min and the second rotational speed R2 is adjusted to 7200 r / min. Other steps and process conditions are the same as in Example 1.

[0157] The difference between Comparative Example 7 and Example 1 is that the first rotation speed R1 was adjusted to 2000 r / min, the first holding time was adjusted to 2h, the number of cycles was adjusted to 3, the nitrogen flow rate was adjusted to 23L / min (the cooling rate was 12℃ / min), and the second rotation speed R2 was adjusted to 5200 r / min; the other steps and process conditions were the same as in Example 1.

[0158] Table 1

[0159] serial number P R S Graphitization temperature (°C) R1 (r / min) First heat preservation time t (h) Loop count Nitrogen flow rate (L / min) Cooling rate ℃ / min R2 (r / min) Example 1 0.85 0.63 0.68 2700 3000 1 2 20 10 6000 Example 2 0.83 0.65 0.70 2700 3300 1 2 20 10 6000 Example 3 0.81 0.66 0.72 2700 3000 1 2 20 10 6700 Example 4 0.80 0.70 0.71 2700 3000 1 2 30 18 6000 Example 5 0.92 0.57 0.62 2700 3000 2 2 20 10 6000 Example 6 0.85 0.58 0.68 2700 2500 2 3 20 10 5300 Example 7 0.85 0.63 0.60 3000 3000 1.5 2 20 10 6000 Example 8 0.75 0.63 0.68 2700 3500 1 2 30 18 6500 Example 9 0.85 0.63 0.55 2700 3100 1.8 2 20 10 6700 Comparative Example 1 0.96 0.51 0.55 2700 2000 1 2 20 10 6000 Comparative Example 2 0.78 0.55 0.52 2700 3000 1 2 20 10 7500 Comparative Example 3 0.75 0.53 0.5 2700 3000 1 2 40 32 6000 Comparative Example 4 0.99 0.52 0.45 2700 3000 3 2 20 10 6000 Comparative Example 5 0.79 0.54 0.53 2700 3000 0 2 20 10 6000 Comparative Example 6 0.72 0.63 0.68 2700 3300 1 2 20 10 7200 Comparative Example 7 0.85 0.55 0.68 2700 2000 2 3 23 12 5200

[0160] Example 1: Material Characterization

[0161] The artificial graphite materials obtained in Examples 1-9 and Comparative Examples 1-7 were characterized as follows:

[0162] (1) Crushing coefficient P

[0163] The ASTM D6556 multi-point BET method (77K nitrogen adsorption) was used to first test the original specific surface area of ​​the artificial graphite material, denoted as A; then, the powder was pressed at a pressure of 5t (holding pressure for 30s), and the specific surface area was tested again, denoted as B. The breakage coefficient P = A / B.

[0164] (2) Roundness R

[0165] SEM images of the artificial graphite material were acquired using a scanning electron microscope (SEM, JSM-7610FPlus, NEC). The images were then analyzed using the Malvern Morphologi 4 software module. At least 30 particles were selected from different regions of the SEM images, and each particle was tested individually. The average value was taken as the final roundness R.

[0166] (3) Grinding convexity S

[0167] SEM images of the artificial graphite material were acquired using a scanning electron microscope (SEM, JSM-7610FPlus, NEC). The images were then analyzed using the Malvern Morphologi 4 software module. At least 30 particles were selected from different regions of the SEM images, and each particle was tested individually. The average value was taken as the final abrasion degree, S.

[0168] The test results are shown in Table 1.

[0169] After preparing 1Ah lithium-ion pouch batteries using the examples and comparative examples, activation and capacity testing were performed. The activation and capacity testing process included cycling the prepared lithium-ion batteries three times at a current of 0.5Ah within a voltage range of 2.5-3.65V, and recording the average discharge capacity of the three cycles as C. Then, the following tests were performed:

[0170] Example 2: Cyclic Performance Test

[0171] (1) Capacity retention rate during ambient temperature cycling

[0172] The lithium-ion batteries prepared in Examples 1-9 and Comparative Examples 1-7 were cycled at 25°C using a charge-discharge cycle of 0.5C and 2.5-3.65V. After 3000 cycles, the discharge capacity of the battery at this point was divided by the discharge capacity of the first cycle to obtain the battery's capacity retention rate after 3000 cycles. The results are recorded in Table 2.

[0173] (2) High-temperature cycling capacity retention

[0174] The lithium-ion batteries prepared in Examples 1-9 and Comparative Examples 1-7 were cycled at 45°C using a charge-discharge cycle of 1C and 2.5-3.65V. After 2000 cycles, the discharge capacity of the battery at this point was divided by the discharge capacity of the first cycle to obtain the battery's capacity retention rate after 2000 cycles. The results are recorded in Table 2.

[0175] Example 3: Storage Performance Test

[0176] At 25°C, the lithium-ion batteries prepared in Examples 1-9 and Comparative Examples 1-7 were subjected to a 0.33C current for capacity determination, denoted as C0. The batteries were then stored at a high temperature of 60°C. Every 7 days thereafter, the batteries were taken out and their capacity was tested at room temperature, denoted as C1, C2, ..., Cn. The number of days until Cn first fell below 80% of C0 was used as the standard for measuring storage capacity. The results are recorded in Table 2.

[0177] Table 2

[0178] Room temperature cycling capacity retention (%) High-temperature cycling capacity retention (%) Storage days (days) Example 1 99.1 97.3 616 Example 2 98.7 97.2 595 Example 3 97.4 96.5 574 Example 4 97.2 96.6 588 Example 5 97.1 95.1 609 Example 6 97.3 95.3 574 Example 7 97.5 95.4 595 Example 8 97.6 96.4 588 Example 9 96.6 93.4 532 Comparative Example 1 96.6 94.2 490 Comparative Example 2 96.4 94.5 462 Comparative Example 3 95.4 93.7 441 Comparative Example 4 96.1 95.1 476 Comparative Example 5 96.5 94.7 427 Comparative Example 6 96.6 92.7 476 Comparative Example 7 96.3 93.1 504

[0179] As can be seen from the data in the table above, the lithium-ion battery made of the artificial graphite material provided by this invention has good storage performance, and can be stored for more than 570 days at a high temperature of 60°C. At the same time, it also has excellent cycle performance, with a capacity retention rate of more than 97% at room temperature (3000 cycles) and a capacity retention rate of more than 95% at high temperature (2000 cycles).

[0180] In Comparative Examples 1-7, some process parameters during the preparation of artificial graphite materials were outside the scope of this invention, and the resulting artificial graphite materials could not simultaneously meet the requirements of this invention in terms of breakage coefficient P, roundness R, and roughness S. When the artificial graphite materials in Comparative Examples 1-7 were applied to lithium-ion batteries, their storage performance deteriorated significantly, with storage days decreasing by more than 7%, and their cycle performance at both room temperature and high temperature also declined.

[0181] In Comparative Example 1, the first rotational speed R1 was too low, resulting in the artificial graphite material having a breakage coefficient P, roundness R, and roughness S that were all outside the scope of this invention. Specifically, the breakage coefficient P was too large, while the roundness R and roughness S were both too small. In Comparative Example 7, the first rotational speed R1 was too low, resulting in the artificial graphite material having a roundness R that was too small and outside the scope of this invention.

[0182] In Comparative Example 2, the second rotational speed R2 was too high, resulting in excessively small roundness R and roughness S of the prepared artificial graphite material. In Comparative Example 6, the second rotational speed R2 was too high, resulting in an excessively small breakage coefficient P of the prepared artificial graphite material, which is outside the scope of this invention.

[0183] In Comparative Example 3, the cooling rate was too high, resulting in excessively small roundness R and roughness S of the artificial graphite material.

[0184] In Comparative Examples 4 and 5, if the first holding time is too high or too low, the breakage coefficient P, roundness R, and roughness S of the resulting artificial graphite materials do not simultaneously fall within the range of this invention. Specifically, in Comparative Example 4, the first holding time is too long, resulting in an excessively large breakage coefficient P and excessively small roundness R and roughness S. In Comparative Example 5, the first holding time is 0, meaning no holding is performed after heating, resulting in artificial graphite materials with excessively small roundness R and roughness S.

[0185] A high breakage coefficient P indicates that the surface of the artificial graphite material still retains the hard shell material generated during graphitization, which will worsen the material's compaction and result in more amorphous defects. A low breakage coefficient P indicates poor sphericity, easy stress concentration, easy breakage, and weak resistance to deformation. Both excessively high and low coefficients are detrimental to the storage and cycle performance of lithium-ion batteries.

[0186] A roundness R that is too low indicates that the surface of the artificial graphite material has too many sharp edges and corners, resulting in more defects and worsening storage conditions; while a roundness R that is too high will lead to extremely low particle yield, increasing costs, and excessive surface treatment will increase the number of dangling bonds on the surface, resulting in an increase in specific surface area and deteriorating performance.

[0187] If the roughness S is too low, it means that there are too many pits on the surface of the graphite particles, which will increase the consumption of electrolyte and binder and is not conducive to cycle performance. On the other hand, if the roughness S is too high, it will lead to extremely low particle yield and increase costs.

[0188] Therefore, for artificial graphite materials, the breakage coefficient P, roundness R, and roughness S must simultaneously meet the corresponding ranges in order to achieve good storage and recycling performance.

[0189] The only difference between Example 1 and Example 2 is the first rotational speed R1. It can be seen that choosing a lower first rotational speed R1 will increase the breakage coefficient P of the artificial graphite material, slightly reduce the roundness R and the convexity S, and improve the storage performance and cycle performance.

[0190] The only difference between Example 1 and Example 3 is the second rotation speed R2. It can be seen that choosing a lower second rotation speed R2 will increase the breakage coefficient P of the artificial graphite material, slightly reduce the roundness R and the convexity S, and improve the storage performance and cycle performance, especially the storage performance.

[0191] The only difference between Example 1 and Example 4 is the cooling rate. Within a certain range, a smaller cooling rate will increase the breakage coefficient P of the artificial graphite material, slightly reduce the roundness R and convexity S, and improve the storage performance and cycle performance.

[0192] The difference between Example 1 and Example 5 lies in the holding time after heating. Extending the holding time increases the breakage coefficient P, while slightly decreasing the roundness R and roughness S, significantly impacting cycle performance. This is likely because the holding time after heating primarily causes different thermal expansion effects between the artificial graphite and its surface hard shell, creating a differential effect. The surface hard shell has a lower expansion rate, and combined with the cooling operation, this causes the hard shell to crack and be removed. Changing the holding time affects the degree of thermal expansion, influencing the removal of the hard shell and thus affecting cycle performance.

[0193] Compared to Example 1, Example 6 changed several process parameters, and the results showed that the artificial graphite material had only a lower roundness R compared to Example 1. Similarly, Example 7, compared to Example 1, changed several process parameters, and the results showed that the artificial graphite material had only a lower roughness S compared to Example 1. Example 8, compared to Example 1, changed several process parameters, and the results showed that the artificial graphite material had only a lower breakage coefficient P compared to Example 1. Example 9, compared to Example 1, changed several process parameters, and the results showed that the artificial graphite material had a lower roughness S. The resulting lithium-ion batteries exhibited different storage and cycle performance. Within a certain range, higher breakage coefficient P, roundness R, and roughness S are beneficial for improving storage performance.

[0194] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A type of artificial graphite material, characterized in that, The artificial graphite material meets the following conditions: The breakage coefficient P is 0.75-0.95, P=A / B, where A and B are the specific surface areas of the artificial graphite material before and after powder pressing, and the powder pressing pressure is 5t. The roundness R is 0.58-0.70; The wear resistance S is 0.55-0.

72.

2. The artificial graphite material according to claim 1, characterized in that, The artificial graphite material satisfies one or more of the following conditions: a. The breakage coefficient P is 0.80-0.88; b. The roundness R is 0.59-0.66; c. The roughness S is 0.65-0.

70.

3. A method for preparing an artificial graphite material, characterized in that, It includes the following steps: S1. Graphitize the raw coke to obtain product I; S2. Perform a first shaping on product I to obtain product II; the first rotational speed R1 of the first shaping is 2500 r / min-3500 r / min; S3. The product II is subjected to a "heating-first heat preservation-cooling-second heat preservation" cycle treatment, and then a second shaping is performed to obtain the artificial graphite material; the second rotation speed R2 of the second shaping is 5000r / min-7000r / min; the cooling rate is 8-18℃ / min; the first heat preservation time is 0.5-2h.

4. The method for preparing artificial graphite material according to claim 3, characterized in that, Step S2 satisfies one or more of the following conditions ad: a. The rotational speed R1 of the first shaping is 2700 r / min - 3300 r / min; b. The temperature of the first shaping is 400℃-500℃; c. The roundness R of product II is ≥0.45; d. The roughness S of product II is ≥0.

55.

5. The method for preparing artificial graphite material according to claim 3, characterized in that, The "heating-first heat preservation-cooling-second heat preservation" cycle in step S3 satisfies one or more of the following conditions: a. The "heating-first heat preservation-cooling-second heat preservation" cycle is repeated 2-3 times; b. The temperature of the first insulation is 900℃-1100℃; c. The first heat preservation time is 1-2 hours; d. The heating rate is 3-8℃ / min; e. The temperature of the second insulation is 550℃-700℃; f. The second heat preservation time is 1-3 hours; g. The cooling method is to introduce gas for cooling, and the flow rate of the introduced gas is 15-30 L / min; h. The cooling rate is 10-18℃ / min.

6. The method for preparing artificial graphite material according to claim 3, characterized in that, The second shaping in step S3 satisfies one or more of the following conditions ac: a. The temperature for the second shaping is 550℃-700℃; b. The second rotational speed R2 for the second shaping is 6000 r / min - 7000 r / min; c. The second shaping procedure takes 1-3 hours.

7. A type of artificial graphite material, characterized in that, It is prepared using the method for preparing artificial graphite materials as described in any one of claims 3-6.

8. A negative electrode sheet, characterized in that, It includes artificial graphite materials as described in any one of claims 1-2 and 7.

9. An electrochemical device, characterized in that, It includes the artificial graphite material as described in any one of claims 1-2 and 7 or the negative electrode sheet as described in claim 8.

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