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

Abstract

The invention discloses an artificial graphite material and a preparation method thereof, a negative plate, an electrochemical device and electronic equipment. The artificial graphite material comprises secondary particles; the artificial graphite material meets the following conditions: the crushing coefficient P is 0.5-0.7, 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 surface hydroxyl abundance N is 0.7 at%-1.8 at%; and the lattice spacing d ranges from 0.338 nm to 0.342 nm. The preparation method of the artificial graphite material provided by the invention realizes low-cost recovery of the graphite material in the waste battery, and the prepared artificial graphite material has excellent cycle performance and storage performance.

Description

Technical Field

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

[0002] Graphite is an important anode material for lithium-ion batteries, and it is generally divided into artificial graphite and natural graphite. Artificial graphite is derived from petrochemical byproducts and requires high-temperature graphitization for production. This entire process is energy-intensive and highly polluting, placing significant pressure on power supplies. Natural graphite comes from natural mineral deposits, has a relatively limited production volume, and has other important applications, such as metal smelting and nuclear energy. Therefore, the effective recycling of graphite resources has received widespread attention.

[0003] Currently, graphite resource recycling mainly refers to recovering graphite materials from the negative electrode sheets of used batteries. Recycling methods typically include acid methods and high-temperature methods (>1600℃), which are costly and highly polluting, often accompanied by a significant decline in material performance. For example, Chinese patent CN117865145 A uses secondary high-temperature graphitization and coating to repair and recycle graphite, which is extremely costly; Chinese patent CN116375022A uses an acid method, resulting in a significant increase in BET (Bio-Electro ... Summary of the Invention

[0004] This invention aims to overcome the shortcomings of existing technologies in recovering graphite materials from waste batteries, namely high costs and severe performance degradation. It provides artificial graphite materials, their preparation methods, negative electrode sheets, electrochemical devices, and electronic devices. The artificial graphite material preparation method provided by this invention achieves low-cost recovery of graphite materials from waste batteries, and the resulting artificial graphite material exhibits excellent cycle performance and storage performance.

[0005] In a first aspect, the present invention provides an artificial graphite material, wherein the artificial graphite material satisfies the following conditions:

[0006] The breakage coefficient P is 0.5-0.7, 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.

[0007] The surface hydroxyl abundance N is 0.7 at%-1.8 at%;

[0008] The lattice spacing d is 0.338-0.342 nm.

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

[0010] S1. The graphite recycled powder is subjected to a first shaping process to obtain product I; the first rotational speed R1 of the first shaping process is 600 r / min - 1200 r / min;

[0011] S2. The product I is subjected to heat treatment, rinsing and second shaping in sequence to obtain the artificial graphite material; the second rotation speed R2 of the second shaping is 2600 r / min - 3600 r / min.

[0012] Thirdly, the present invention provides an artificial graphite material, which is prepared by the artificial graphite material preparation method described above.

[0013] Fourthly, the present invention provides a negative electrode sheet comprising the artificial graphite material as described above.

[0014] Fifthly, the present invention provides an electrochemical device comprising the artificial graphite material as described above or the negative electrode as described above.

[0015] In a sixth aspect, the present invention provides an electronic device comprising the electrochemical device as described above.

[0016] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

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

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

[0019] The present invention provides a method for preparing artificial graphite materials, which recovers graphite materials from the negative electrode sheets of waste batteries. The method is simple, efficient, easy to operate, and low in cost. The artificial graphite materials recovered by the present invention have a fragmentation coefficient, surface hydroxyl abundance, and lattice spacing within a certain range, exhibiting excellent cycle performance and storage performance. Detailed Implementation

[0020] The first aspect of the present invention provides an artificial graphite material, wherein the artificial graphite material satisfies the following conditions:

[0021] The breakage coefficient P is 0.5-0.7, 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.

[0022] The surface hydroxyl abundance N is 0.7 at%-1.8 at%;

[0023] The lattice spacing d is 0.338-0.342 nm.

[0024] 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 test method is the ASTM D6556 multi-point BET method (77K nitrogen adsorption). First, the original specific surface area of ​​the artificial graphite material is measured and recorded as A; then, the powder is pressed under a pressure of 5t, and the specific surface area is measured again and recorded as B. P = A / B.

[0025] In this invention, the surface hydroxyl abundance reflects the number or coverage density of hydroxyl (-OH) functional groups per unit area on the surface of the artificial graphite material (the surface refers to a region with a thickness of 100 nm from the surface layer towards the center). The surface hydroxyl abundance is analyzed by XPS and expressed as the percentage (at%) of oxygen atoms in the hydroxyl groups relative to the total number of detected atoms within the analysis depth. In lithium-ion battery anodes, the presence of hydroxyl groups significantly affects interfacial reactivity, initial coulombic efficiency (ICE), and cycle stability.

[0026] In this invention, the lattice spacing reflects the ease with which lithium ions are embedded in artificial graphite materials. A smaller lattice spacing indicates poorer kinetics and higher repair costs, while a larger lattice spacing indicates more defects, which is detrimental to storage performance. The test method for lattice spacing refers to the national standard GB / T 24533-2019.

[0027] In this invention, the breakage coefficient P of the artificial graphite material can be 0.55-0.60.

[0028] In some specific implementations, the breakage coefficient P of the artificial graphite material may be 0.52, 0.55, 0.62, 0.66 or 0.7.

[0029] In this invention, the surface hydroxyl abundance N of the artificial graphite material can be 1.0at%-1.5at%.

[0030] In some specific embodiments, the surface hydroxyl abundance N of the artificial graphite material can be 0.73 at%, 0.88 at%, 0.96 at%, 1.1 at%, 1.31 at%, 1.54 at%, or 1.75 at%.

[0031] In some specific embodiments, the lattice spacing d of the artificial graphite material may be 0.3383 nm, 0.3385 nm, 0.3393 nm, 0.3395 nm, 0.3397 nm, 0.3405 nm, or 0.3413 nm.

[0032] In some specific embodiments, the artificial graphite material satisfies the following conditions: a breakage coefficient P of 0.62, a surface hydroxyl abundance N of 1.10 at%, and a lattice spacing d of 0.3393 nm.

[0033] In some specific embodiments, the artificial graphite material satisfies the following conditions: a breakage coefficient P of 0.55, a surface hydroxyl abundance N of 1.31 at%, and a lattice spacing d of 0.3405 nm.

[0034] In some specific embodiments, the artificial graphite material satisfies the following conditions: a breakage coefficient P of 0.66, a surface hydroxyl abundance N of 0.96 at%, and a lattice spacing d of 0.3385 nm.

[0035] In some specific embodiments, the artificial graphite material satisfies the following conditions: a breakage coefficient P of 0.52, a surface hydroxyl abundance N of 1.54 at%, and a lattice spacing d of 0.3413 nm.

[0036] In some specific embodiments, the artificial graphite material satisfies the following conditions: a breakage coefficient P of 0.70, a surface hydroxyl abundance N of 0.88 at%, and a lattice spacing d of 0.3383 nm.

[0037] In some specific embodiments, the artificial graphite material satisfies the following conditions: a breakage coefficient P of 0.62, a surface hydroxyl abundance N of 1.75 at%, and a lattice spacing d of 0.3395 nm.

[0038] In some specific embodiments, the artificial graphite material satisfies the following conditions: a breakage coefficient P of 0.62, a surface hydroxyl abundance N of 0.73 at%, and a lattice spacing d of 0.3397 nm.

[0039] In this invention, the artificial graphite material includes secondary particles, and the proportion of the secondary particles can be 50-100%, for example 75%.

[0040] In this invention, the artificial graphite material can be prepared by the method for preparing artificial graphite material described in the second aspect.

[0041] The second aspect of this invention provides a method for preparing artificial graphite materials, which includes the following steps:

[0042] S1. The recycled graphite powder is subjected to a first shaping process to obtain product I; the rotational speed R1 of the first shaping process is 600 r / min - 1200 r / min;

[0043] S2. The product I is subjected to heat treatment, rinsing and second shaping in sequence to obtain the artificial graphite material; the rotation speed R2 of the second shaping is 2600 r / min - 3600 r / min.

[0044] In this invention, the recycled graphite powder can be derived from the negative electrode sheet of a waste battery.

[0045] In some implementations, the method for obtaining the graphite recycled powder from the negative electrode sheet of the waste battery includes: first treating the negative electrode sheet of the waste battery with ultraviolet light, sieving, collecting the sieve material and washing it with water.

[0046] The intensity of the ultraviolet light can be 90 μW / cm²-150 μW / cm², for example 123 μW / cm².

[0047] The temperature of the irradiation treatment can be 30-45℃, for example 38℃.

[0048] The sieving can be performed using methods conventional in the art. Preferably, the sieving is a vibrating sieve. Preferably, the mesh size of the sieve used is 30 mesh.

[0049] The number of times the water is washed is preferably 3 times.

[0050] In this invention, the carbon content of the recycled graphite powder can be greater than 98%.

[0051] In this invention, the recycled graphite powder includes secondary particles; wherein the proportion of the secondary particles can be 50-100%, for example 75%.

[0052] In step S1, the first shaping can be performed in an air jet mill.

[0053] In step S1, the temperature of the first shaping can be 400℃-500℃, for example, 500℃. The main purpose of heating in the first shaping is to remove the water of crystallization adsorbed on the graphite recycled powder.

[0054] In step S1, the first shaping time can be 1 hour to 5 hours, for example, 4 hours.

[0055] In step S1, the first rotational speed R1 can be 800 r / min - 1200 r / min. The main purpose of controlling the appropriate rotational speed in the first shaping process is to remove the irregular large edges on the surface of the graphite recycled powder.

[0056] In some specific implementations, the first rotational speed R1 may be 600 r / min, 1000 r / min or 1200 r / min.

[0057] In step S1, the breakage coefficient P of product I can be 0.3 or higher.

[0058] In step S2, the temperature of the heat treatment can be 900℃-1100℃, for example, 1000℃.

[0059] In step S2, the heat treatment time can be 0.5-3 hours, for example, 2 hours.

[0060] In step S2, the heating rate of the heat treatment can be 2-5℃ / min, for example, 2℃ / min.

[0061] In step S2, the detergent used for rinsing may include subcritical water, the temperature of which is 150-200°C, for example, 200°C.

[0062] In step S2, the flow rate of the detergent used for rinsing can be 8-15 L / min, for example, 8 L / min, 10 L / min or 15 L / min.

[0063] In step S2, the rinsing time can be 0.5-3 hours, for example, 2 hours.

[0064] In step S2, the temperature of the second shaping can be 300℃-500℃, for example 400℃.

[0065] In step S2, the second rotational speed R2 can be 3000 r / min - 3600 r / min.

[0066] In some specific implementations, the second rotational speed R2 may be 2600 r / min, 3000 r / min, or 3600 r / min.

[0067] In step S2, the second shaping time can be 0.5h-3h, for example 1h.

[0068] In this invention, the artificial graphite material is further subjected to post-processing, which includes one or more of grading, washing, and demagnetization.

[0069] Preferably, the particle size distribution width d of the artificial graphite material obtained by grading satisfies: d < 1.10.

[0070] Preferably, the particle size of the artificial graphite material obtained by grading satisfies: (Dv90-Dv50 / Dv50-Dv10)>1.4.

[0071] In this invention, the particle size distribution width, Dv10, Dv50, and Dv90 can be obtained by using a conventional laser particle size analyzer in the art.

[0072] The artificial graphite material provided in the third aspect of the present invention is prepared by the artificial graphite material preparation method described above.

[0073] In this invention, the artificial graphite material has the same structural features as the artificial graphite material described in the first aspect.

[0074] The negative electrode provided in the fourth aspect of the present invention comprises the artificial graphite material as described above.

[0075] 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.

[0076] 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.

[0077] In this invention, the negative electrode material layer may further include a conductive agent.

[0078] 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.

[0079] In this invention, the negative electrode material layer may further include a binder.

[0080] 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.

[0081] In this invention, the negative electrode material layer may further include 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 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.

[0084] 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.

[0085] The electrochemical device provided in the fifth aspect of the present invention includes the artificial graphite material as described above or the negative electrode as described above.

[0086] In this invention, the electrochemical device is preferably a battery.

[0087] In some embodiments, the electrochemical device is a lithium-ion battery.

[0088] 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.

[0089] In some specific embodiments, the liquid lithium-ion battery includes a positive electrode, a negative electrode as described above, a separator, and an electrolyte.

[0090] 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.

[0091] In this invention, the liquid lithium-ion battery includes a positive electrode, a negative electrode as described above, and a separator.

[0092] Positive electrode film

[0093] 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.

[0094] 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.

[0095] 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.

[0096] In some embodiments, the positive electrode material layer further includes a binder. The binder may be a component that facilitates the bonding between the positive electrode active material and the conductive agent, and also facilitates the bonding between the positive electrode active 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.

[0097] In some embodiments, the positive electrode material layer includes a positive electrode active material, Super P, CNT, and PVDF.

[0098] 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.

[0099] 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.

[0100] In some alternative embodiments, the positive current collector is aluminum foil.

[0101] In this invention, the positive electrode sheet can be prepared using methods conventional in the art.

[0102] In some optional embodiments, the method for preparing the positive electrode sheet includes the following steps: mixing the positive electrode active 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.

[0103] electrolyte

[0104] In some embodiments, the electrolyte may be a conventional electrolyte used in batteries, typically including non-aqueous solvents and lithium salts.

[0105] In this invention, the non-aqueous solvent can be a conventional non-aqueous solvent in the art.

[0106] 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.

[0107] 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.

[0108] In this invention, the electrolyte may include additives, which may be conventional additives in the art, such as fluoroethylene carbonate (FEC).

[0109] In some embodiments, the electrolyte includes LiPF6, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate.

[0110] 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.

[0111] 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.

[0112] diaphragm

[0113] In some alternative embodiments, the diaphragm may be a polypropylene membrane or a polyethylene membrane.

[0114] In some alternative embodiments, the thickness of the diaphragm may be 9 μm-18 μm, for example, 11 μm.

[0115] In some alternative embodiments, the air permeability of the diaphragm can be 180s / 100mL-380s / 100mL.

[0116] In some alternative embodiments, the porosity of the membrane may be 30%-50%.

[0117] 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.

[0118] The electronic device provided in the sixth aspect of the present invention includes the electrochemical device as described above.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] Example 1

[0123] 1. Negative electrode plate

[0124] (1) Preparation of artificial graphite materials

[0125] S0. Preparation of recycled graphite powder: Disassemble waste batteries to obtain waste negative electrode sheets. First, treat the waste negative electrode sheets under ultraviolet light with an intensity of 123 W / cm² and a treatment temperature of 38℃. Then, vibrate and sieve the powder through a 30-mesh screen to collect the sieve material and obtain primary recycled graphite powder. Then, wash the powder three times with water to obtain recycled graphite powder with a carbon content greater than 98% and a secondary particulate graphite content of 75%.

[0126] S1. The obtained recycled graphite powder is fed into an air jet mill and heated to 500℃. At the same time, the rotation speed of the air jet mill is kept at the first rotation speed R1, where R1 is 1000 r / min. The first shaping is carried out for 4 hours to obtain product I. The breakage coefficient of product I is greater than 0.3.

[0127] S2. The product I obtained in step S1 is heated to 1000℃ at a rate of 2℃ / min and held for 2 hours for heat treatment. Then, the air jet mill is vacuumed to maintain an internal pressure of less than 0.1 atmospheres. It is then rinsed with preheated and pressurized subcritical water at 200℃ at a flow rate of 10L / min for 2 hours. The temperature is then maintained at 400℃, and the speed of the splitter is adjusted to the second speed R2, which is 3000r / min. The second shaping is then performed for 1 hour. The resulting material has a breakage coefficient greater than 0.5 and a hydroxyl abundance less than 3.0. 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. Finally, it is washed with water, dried, and demagnetized to obtain artificial graphite material.

[0128] (2) Preparation of negative electrode

[0129] 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.

[0130] 2. Positive electrode plate

[0131] Lithium iron phosphate (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) was added as a solvent. The mixture was stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry was coated onto a positive electrode current collector aluminum foil, and the positive electrode sheet was prepared by drying, cold pressing, and slitting.

[0132] 3. Diaphragm

[0133] A porous PE membrane with a thickness of 11 μm was used as the separator.

[0134] 4. Electrolyte

[0135] 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.

[0136] 5. Lithium-ion batteries

[0137] 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 injected with the electrolyte prepared above. 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.

[0138] Examples 2-7 and Comparative Examples 1-5

[0139] Some process parameters of each embodiment and comparative example are shown in Table 1. Other unlisted process parameters and preparation methods are the same as in Example 1.

[0140] Examples 2, 3, 1, and 2 differ from Example 1 in that the first rotational speed R1 is the same as that in Example 1, while the other steps and process conditions are the same.

[0141] Examples 4, 5, 3, and 4 differ from Example 1 in that the second rotational speed R2 is the same as in Example 1, while the other steps and process conditions are the same.

[0142] Examples 6 and 7 differ from Example 1 in that the flow rate of subcritical water, other steps, and process conditions are the same as in Example 1.

[0143] The difference between Comparative Example 5 and Example 1 is that subcritical water rinsing is not performed, while other steps and process conditions are the same as in Example 1.

[0144] Table 1

[0145] P N(at%) d(nm) R1(r / min) Subcritical water flow rate (L / min) R2(r / min) Example 1 0.62 1.10 0.3393 1000 10 3000 Example 2 0.55 1.31 0.3405 600 10 3000 Example 3 0.66 0.96 0.3385 1200 10 3000 Example 4 0.52 1.54 0.3413 1000 10 2600 Example 5 0.70 0.88 0.3383 1000 10 3600 Example 6 0.62 1.75 0.3395 1000 8 3000 Example 7 0.62 0.73 0.3397 1000 15 3000 Comparative Example 1 0.45 1.43 0.3398 500 10 3000 Comparative Example 2 0.76 0.92 0.3381 1400 10 3000 Comparative Example 3 0.49 1.61 0.3415 1000 10 2400 Comparative Example 4 0.73 0.84 0.3382 1000 10 4000 Comparative Example 5 0.62 3.56 0.3393 1000 / 3000

[0146] Example 1: Material Characterization

[0147] The artificial graphite materials and intermediate products obtained in Examples 1-7 and Comparative Examples 1-5 were characterized as follows:

[0148] 1. Crushing coefficient P

[0149] The ASTM D6556 multi-point BET method (77K nitrogen adsorption) was used. First, the original specific surface area of ​​the sample was tested and recorded as A. Then, the powder was pressed at a pressure of 5t (held for 30s), and the specific surface area was tested again and recorded as B. P=A / B. The results are recorded in Table 1.

[0150] 2. Surface hydroxyl abundance N

[0151] (1) Sample preparation: The powder compression method was used for sample preparation.

[0152] Artificial graphite material is ultrasonically dispersed in high-purity anhydrous ethanol to form a uniform suspension. A small amount of the suspension is taken with a dropper and dropped onto a clean substrate of a silicon wafer. The substrate is then thoroughly dried in a vacuum drying oven to remove all ethanol solvent. A small amount of dried artificial graphite material is taken and evenly spread on gold foil. Another flat foil or glass plate is used to gently press the powder from above to form a flat, dense sheet with good contact with the foil. The prepared sample is then dried in a vacuum drying oven at 60-80°C for at least 12 hours to remove physically adsorbed water and solvent to the maximum extent.

[0153] (2) Sample loading into the preparation chamber for pretreatment

[0154] After drying, place the sample into the rapid injection chamber of the XPS instrument as soon as possible to prevent re-adsorption of water and contaminants from the air. Allow the sample to stand in the rapid injection chamber (vacuum of approximately 10⁻⁵ Pa) for a period of time, or subject it to gentle heating (e.g., 80°C) to further remove adsorbed gases from the sample surface. Once the required vacuum level is achieved, transfer the sample to an ultra-high vacuum analysis chamber (vacuum level typically better than 5 × 10⁻⁵ Pa). -8 Pa).

[0155] (3) Data acquisition and analysis

[0156] First, a low-resolution, fast, broad-spectrum scan is performed in the range of 0-1100 eV or 0-1400 eV to identify all elements present on the sample surface (such as C, O, N, Si, etc.) and to check for any obvious contaminants; then, a high-resolution, slow scan is performed on the C 1s and O 1s orbitals.

[0157] Key parameters: Power: 20-40 eV (to ensure sufficient resolution and signal-to-noise ratio), Step size: 0.05-0.1 eV, Number of scans: Multiple scans are stacked to improve the signal-to-noise ratio (usually 5-20 times).

[0158] Based on the collected data, XPS processing software (such as CasaXPS, Avantage) automatically processes and calculates the surface hydroxyl abundance N, and the results are recorded in Table 1.

[0159] 3. Lattice spacing d

[0160] Referring to the national standard GB / T 24533-2019, the results are recorded in Table 1.

[0161] 4. Percentage of secondary particles

[0162] (1) Wet dispersion:

[0163] Disperse a small amount of recycled graphite powder in anhydrous ethanol using ultrasonication (power should not be too high, and the time should be short, such as 30-60 seconds, to prevent breakage of secondary particles). Place 1-2 drops of this suspension onto a silicon wafer or polished aluminum foil and allow it to dry naturally. If the subsequent SEM image quality is poor, a very thin layer of gold or platinum can be sputtered onto it to enhance the signal.

[0164] (2) SEM image acquisition

[0165] Images were acquired using a scanning electron microscope (SEM, manufactured by Nippon Electron, model JSM-7610FPlus).

[0166] Low-magnification observation: First, scan the entire sample stage at a low magnification (500-2000) to find statistically representative areas (i.e., uniformly dispersed particles without large-area aggregation or blank areas). Multi-area sampling: Randomly select 30 such representative fields of view at different locations on the sample for photography;

[0167] High magnification confirmation: Switch the magnification to 5000-20000x or even higher to clearly distinguish the primary particle structure on the surface of secondary particles and confirm the particle types that are difficult to identify at low magnification.

[0168] The key points for identifying single particles and secondary particles are: single particles have clear and independent boundaries; secondary particles have relatively blurred boundaries and can be seen to be "bonded" together by smaller units.

[0169] (3) Statistical analysis

[0170] Print the SEM image or open it in image software. Use a counter to manually classify and count all particles in a single image. To ensure statistical significance, at least 300 particles need to be counted in total (counting all particles in 30 sampling areas).

[0171] Calculation ratio:

[0172] Percentage of secondary particles = (Number of secondary particles / Total number of particles) × 100%

[0173] The 1Ah lithium-ion pouch batteries prepared in each embodiment and comparative example were activated and capacity-graded, followed by various tests. The activation and capacity-graded process included cycling the prepared lithium-ion battery three times at a current of 0.5Ah within a voltage range of 2.5-3.65V, and taking the average discharge capacity of the three cycles as C.

[0174] Example 2: Cyclic Performance Test

[0175] 1. Capacity retention rate during room temperature cycling

[0176] The lithium-ion batteries prepared in Examples 1-7 and Comparative Examples 1-5 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.

[0177] 2. High-temperature cycling capacity retention rate

[0178] The lithium-ion batteries prepared in Examples 1-7 and Comparative Examples 1-5 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.

[0179] Example 3: Storage Performance Test

[0180] At 25°C, the lithium-ion batteries prepared in Examples 1-7 and Comparative Examples 1-5 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.

[0181] Table 2

[0182] Implementation Room temperature cycling capacity retention (%) High-temperature cycling capacity retention (%) Storage days (days) Example 1 97.6 96.2 427 Example 2 96.9 94.7 399 Example 3 97.5 95.6 420 Example 4 96.0 94.3 385 Example 5 96.4 94.5 399 Example 6 96.6 93.1 371 Example 7 96.1 95.2 406 Comparative Example 1 93.2 90.1 322 Comparative Example 2 94.6 91.2 350 Comparative Example 3 95.1 93.1 343 Comparative Example 4 95.6 93.6 357 Comparative Example 5 95.8 91.2 308

[0183] As can be seen from the data in the table above, the lithium-ion battery made from the artificial graphite material recovered from waste batteries in this invention has excellent storage and cycle performance. Specifically, it can be stored for more than 370 days at a high temperature of 60°C; the capacity retention rate during room temperature cycling is more than 95%, and the capacity retention rate during high temperature cycling is more than 93%. Furthermore, the recycling method of this invention is simple and easy to implement.

[0184] Compared with Example 1, Comparative Example 1 differs in that R1 is lower than the scope of the present invention, the breakage coefficient P of the prepared artificial graphite material is lower than the scope of the present invention, and its cycle capacity retention rate and storage performance are significantly deteriorated, especially the storage performance, which is reduced by about 25%.

[0185] Compared with Example 1, Comparative Example 2 differs in that R1 is higher than the scope of the present invention, the breakage coefficient P of the prepared artificial graphite material is higher than the scope of the present invention, and its cycle capacity retention rate and storage performance are reduced to varying degrees, with the storage performance reduced by about 18%.

[0186] Compared with Example 1, Comparative Example 3 differs in that R2 in Comparative Example 1 is lower than the scope of the present invention, and the breakage coefficient P of the artificial graphite material obtained is lower than the scope of the present invention. Its cycle capacity retention rate and storage performance are significantly deteriorated, especially the storage performance, which is reduced by about 20%.

[0187] Compared with Example 1, Comparative Example 4 differs in that R2 in Comparative Example 2 is higher than the scope of the present invention, the breakage coefficient P of the prepared artificial graphite material is higher than the scope of the present invention, and its cycle capacity retention rate and storage performance are reduced to varying degrees, with the storage performance reduced by about 16%.

[0188] The difference between Comparative Example 5 and Example 1 is that Comparative Example 5 did not undergo the subcritical water rinsing step, resulting in a decrease in its cycle performance, especially its high-temperature cycle performance, which decreased significantly; while its storage performance was greatly reduced, by approximately 28%.

[0189] Compared with Examples 1-3, the only difference is R1. It can be seen that increasing R1 within a certain range can improve the breakage coefficient P and surface hydroxyl abundance N of artificial graphite materials. When R1 is in the range of 1000-1200 r / min, the lithium-ion battery can obtain better cycle performance and storage performance.

[0190] Compared with Examples 1, 4 and 5, the difference lies in the different values ​​of R2. It can be seen that increasing R2 within a certain range can improve the breakage coefficient P and reduce the abundance of surface hydroxyl groups N. When R2 is in the range of 3000-3600, the lithium-ion battery prepared has high cycle performance and storage performance.

[0191] Compared with Examples 1, 6 and 7, the difference lies in the flow rate of subcritical water. It can be seen that when the flow rate of subcritical water increases from 8 L / min to 15 L / min, the cycle performance and storage performance of lithium-ion batteries both show an initial increase followed by a decrease. When the flow rate is in the range of 10-15 L / min, the lithium-ion batteries obtained can achieve better cycle performance and storage performance.

[0192] 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 synthetic graphite material, characterized by, The artificial graphite material satisfies the following conditions: a broken coefficient P of 0.5-0.7, P=A / B, where A and B are specific surface areas of the artificial graphite material before and after powder pressing, respectively, and the powder pressing pressure is 5 t; a surface hydroxyl abundance N of 0.7 at%-1.8 at%; a lattice spacing d of 0.338-0.342 nm.

2. The artificial graphite material according to claim 1, characterized by The artificial graphite material satisfies one or more of the following conditions a-c: a. a broken coefficient P of 0.55-0.60; b. a surface hydroxyl abundance N of 1.0 at%-1.5 at%; c. the artificial graphite material comprising secondary particles.

3. A method for producing an artificial graphite material, characterized by, It comprises the following steps: S1. First shaping of a graphite recovery powder to obtain product I; the first rotation speed R1 of the first shaping is 600 r / min-1200 r / min; S2. Sequentially performing heat treatment, leaching and second shaping on the product I to obtain the artificial graphite material; the second rotation speed R2 of the second shaping is 2600 r / min-3600 r / min.

4. The method for producing an artificial graphite material according to claim 3, characterized by, Step S1 satisfies one or more of the following conditions a-c: a. the first rotation speed R1 is 800 r / min-1200 r / min; b. the temperature of the first shaping is 400℃-500℃; c. the broken coefficient P of the product I is 0.3 or more.

5. The method of producing an artificial graphite material according to claim 3, characterized by, Step S2 satisfies one or more of the following conditions a-i: a. the temperature of the heat treatment is 900℃-1100℃; b. the time of the heat treatment is 0.5-3 h; c. the heating rate of the heat treatment is 2-5℃ / min; d. the washing agent of the leaching comprises subcritical water, and the temperature of the subcritical water is 150-200℃; e. the flow rate of the washing agent of the leaching is 8-15 L / min; f. the time of the leaching is 0.5-3 h; g. the temperature of the second shaping is 300℃-500℃; h. the second rotation speed R2 is 3000 r / min-3600 r / min; i. the time of the second shaping is 0.5 h-3 h.

6. The method of producing an artificial graphite material according to claim 3, characterized by, It satisfies one or more of the following conditions a-c: a. the preparation method of the graphite recovery powder comprises: first irradiation treatment of the negative electrode sheet of the waste battery under ultraviolet light, sieving, and collecting the undersize material for water washing; wherein the intensity of the ultraviolet light is 90 μW / cm²-150 μW / cm², and the temperature of the irradiation treatment is 30-45℃; b. the graphite recovery powder comprises secondary particles; c. the post-treatment after the second shaping comprises one or more of grading, washing and demagnetization.

7. An artificial graphite material, characterized by, It is prepared by the preparation method of the artificial graphite material according to any one of claims 3-6.

8. A negative electrode sheet characterized by comprising: It comprises the artificial graphite material according to any one of claims 1-2 and 7.

9. An electrochemical device, characterized by, It comprises the artificial graphite material according to any one of claims 1-2 and 7 or the negative electrode sheet according to claim 8.

10. An electronic device, comprising: It comprises the electrochemical device according to claim 9.