A method for preparing a long-cycle artificial graphite anode material and the graphite anode material.

Abstract

This invention relates to the field of lithium-ion battery technology, specifically to a method for preparing a long-cycle artificial graphite anode material and the graphite anode material itself. The preparation method includes the following steps: S1. Crushing and shaping isotropic coke to obtain material A; S2. Molding material A to obtain block B; S3. Graphitizing block B to obtain graphitized block product C; S4. Releasing internal stress on graphitized block product C to obtain product D; S5. Depolymerizing and separating product D and refining it to obtain the graphite anode material. This invention introduces high-frequency vibration aging treatment and / or high-frequency ultrasonic impact treatment to release internal stress during the preparation of the graphite anode material. This not only effectively eliminates most of the internal stress in the particles but also identifies and eliminates particles with excessive internal stress in advance, thereby improving the cycle performance of the battery cell.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a method for preparing a long-cycle artificial graphite anode material and the graphite anode material itself. Background Technology

[0002] With the large-scale application of renewable energy and the rapid development of the electric vehicle industry, high-performance energy storage technology has become one of the core directions for solving energy sustainability issues. Lithium-ion batteries, due to their high energy density, long cycle life, and environmental friendliness, have become the mainstream technology in the field of electrochemical energy storage. Among the key materials of lithium-ion batteries, the performance of the anode material directly affects the battery's energy density, cycle stability, and safety. Graphite materials, due to their abundant resource reserves, high electronic conductivity, stable chemical properties, and low cost, have long been the preferred material for the anode of commercial lithium-ion batteries.

[0003] However, traditional graphite anodes still face significant challenges during long-term charge-discharge cycles. First, graphite exhibits at least a 10% volume expansion effect during lithium-ion insertion / extraction. Repeated volume changes can easily lead to contact failure between electrode material particles, peeling of active material from the electrode sheet, and cracking and pulverization of the active material particles due to internal stress accumulation, thus causing capacity decay. Second, the solid electrolyte interphase (SEI) film on the graphite surface will crack and regenerate during cycling due to expansion stress, continuously consuming electrolyte and active lithium source, resulting in decreased coulombic efficiency and increased impedance. These problems severely restrict the widespread application of graphite anodes in long-life energy storage systems (such as grid-scale energy storage).

[0004] Existing technical documents: Reference 1: Patent application CN 119361692 A discloses a high-capacity graphite anode material with long cycle life and its preparation method. First, medium-sulfur coke and commercial coke are pre-carbonized separately, and then mixed in proportion and directly graphitized to obtain an artificial graphite anode material for energy storage. The medium-sulfur coke and commercial coke can exert a synergistic effect to improve the cycle performance and processing performance of the material.

[0005] Reference 2: Patent application CN 115806289 A discloses a graphite anode material with long cycle life, its preparation method, and its application. It selects isotropic coke and, through crushing, fine powder extraction, spheroidization, carbonization, and graphitization, ultimately obtains a graphite anode material for energy storage with ultra-long cycle life and excellent high-temperature storage performance. Fine powder extraction and spheroidization improve high-temperature storage, and the rational selection of the coke structure achieves long cycle life.

[0006] Reference 3: Patent application CN 115784221 A discloses an artificial graphite anode material with better cycle performance and its preparation method. By mixing coke powder and binder, granulating, dispersing and depolymerizing, and graphitizing, a secondary particle artificial graphite anode material is finally obtained. This invention alleviates the expansion stress during cycling, reduces expansion, and improves cycle performance through the secondary particle structure. At the same time, the secondary particles can also improve the rate performance.

[0007] After in-depth research, the inventors of this invention discovered that: Reference 1 introduced medium-sulfur coke, which improved the capacity to some extent. However, the sulfides in the medium-sulfur coke will decompose and volatilize during graphitization and generate active sites on the surface of graphite particles, which will have an adverse effect on the cycling performance of the material and is not conducive to long-term cycling performance.

[0008] Reference 2 alleviates the overall expansion stress of the electrode during cycling by using isotropic coke, but does not improve the internal expansion stress of the active material particles themselves. During ultra-long cycling, the accumulation of internal stress will lead to the collapse of graphite crystals and the pulverization of active material particles.

[0009] Reference 3 alleviates the expansion stress of the electrode during cycling and improves the rate performance of the cell by granulation, but does not improve the expansion internal stress of the active material particles. The accumulation of internal stress during ultra-long cycling will lead to the collapse of graphite crystals and the pulverization of active material particles.

[0010] In view of this, the present invention is hereby proposed. Summary of the Invention

[0011] The primary objective of this invention is to provide a method for preparing long-cycle artificial graphite anode materials. The method of this invention uses high-frequency vibration aging technology or high-frequency ultrasonic impact to perform internal stress relief treatment on graphitized block products. This treatment can not only effectively eliminate most of the internal stress of the particles, but also identify those particles with excessive internal stress in advance and eliminate these problematic particles, thereby improving the cycle performance of the battery cell.

[0012] The second objective of this invention is to provide a graphite anode material, which is prepared by the long-cycle artificial graphite anode material preparation method described above.

[0013] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A method for preparing a long-cycle artificial graphite anode material includes the following steps: S1. The isotropic coke is crushed and shaped to obtain material A; S2. The material A is subjected to molding processing to obtain block B; S3. The block B is subjected to graphitization treatment to obtain graphitized blocky product C; S4. The graphitized bulk product C is subjected to stress relief treatment to obtain product D; S5. Depolymerize and separate the product D and remove the fine powder to obtain the long-cycle artificial graphite anode material.

[0014] Furthermore, by volume percentage, the isotropic focal plane contains ≥60% mosaic structure and ≤10% sheet structure.

[0015] Furthermore, in step S1, the particle size Dv50 of the material A is 10-20 μm.

[0016] Furthermore, in step S2, the shape of the block B includes a cylinder and / or a cuboid and / or a cube.

[0017] Furthermore, in step S2, the density of block B is 1.40-1.80 g / cm³. 3 .

[0018] Furthermore, in step S2, the weight of each block B is 10-200 kg.

[0019] Furthermore, in step S3, the graphitization process is carried out under an inert atmosphere, the graphitization temperature is 2800-3000℃, and the graphitization time is 5-15h.

[0020] Furthermore, in step S4, the method of releasing internal stress includes high-frequency vibration aging treatment and / or high-frequency ultrasonic shock treatment.

[0021] Furthermore, the frequency of the high-frequency vibration aging treatment is 20-300Hz.

[0022] Furthermore, the target amplitude of the high-frequency vibration aging treatment is 1-2 mm, the amplitude at the start of vibration is 0.3-0.7 mm, and the amplitude increases at a rate of 0.05-0.2 mm / min.

[0023] Furthermore, the duration of continuous vibration after the high-frequency vibration aging treatment reaches the target amplitude is 5-60 minutes.

[0024] Furthermore, the frequency of the high-frequency ultrasonic shock treatment is 5-60kHz.

[0025] Furthermore, the power density of the high-frequency ultrasonic shock treatment is 0.5-2.5 W / cm². 2 .

[0026] Furthermore, the amplitude of the high-frequency ultrasonic shock treatment is 10-500 μm.

[0027] Furthermore, the high-frequency ultrasonic shock treatment time is 30-60 minutes.

[0028] Furthermore, the medium subjected to the high-frequency ultrasonic shock treatment includes at least one of deionized water, ethanol, and n-propanol.

[0029] A graphite anode material is prepared by the preparation method of long-cycle artificial graphite anode material described in any of the preceding embodiments.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method of the present invention triggers local lattice slip or dislocation movement of graphite through high-frequency vibration aging treatment or high-frequency ultrasonic impact treatment. This process induces small plastic deformation on the particle surface and at the same time promotes the release of stress in the relatively concentrated areas of the particle, gradually realizing the overall stress balance of the particle. The plastic deformation caused by high-frequency vibration aging treatment will reduce the content of long dislocation lines in the particle and appropriately increase the content of short dislocation lines, which can avoid the particle from cracking and shattering during use. The short dislocation lines interlock with each other and are not easy to crack during charge and discharge cycles, which can significantly improve the structural stability of graphite particles, thereby improving the long cycle stability of the battery cell. This technology can not only effectively eliminate most of the internal stress of the particles, but also identify those particles with excessive internal stress in advance and eliminate these problematic particles, thereby further improving the cycle performance of the battery cell.

[0031] (2) This invention achieves directional expansion of energy along dislocation lines during particle expansion by controlling the directional relaxation of lattice defects, while maintaining the intrinsic structure of graphite. Macroscopically, this manifests as a "self-healing" effect. During repeated lithium-ion intercalation, the treated graphite particles can absorb volumetric strain through dislocation slip, thereby significantly improving structural durability. This characteristic is particularly crucial in long-cycle batteries, effectively suppressing the expansion stress and pulverization of negative electrode active material particles. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0033] The first aspect of this invention provides a method for preparing a long-cycle artificial graphite anode material, comprising the following steps: S1. The isotropic coke is crushed and shaped to obtain material A; S2. Material A is subjected to pressure molding to obtain block B; S3. Graphitize the bulk B to obtain graphitized bulk product C; S4. The graphitized bulk product C is subjected to stress relief treatment to obtain product D; S5. Depolymerize and separate product D and remove fine powder to obtain long-cycle artificial graphite anode material.

[0034] Currently, artificial graphite anode materials for energy storage mainly face challenges such as large accumulated stress from internal particle expansion, large accumulated stress from overall electrode expansion, and numerous active sites on particle surfaces during ultra-long cycling. These materials undergo thousands of cycles during use, with future requirements even exceeding 10,000 cycles. Although the charge-discharge rate is low, the high number of cycles leads to the accumulation of significant internal stress in both the active material particles and the electrode during their lifespan. This internal stress can cause graphite crystal collapse, graphite particle pulverization, separation between graphite particles, and peeling of the electrode from the copper foil, ultimately resulting in high polarization resistance and a series of problems such as lithium plating and cycle failure. These issues become more pronounced in the latter half of the ultra-long cycle life of the battery cell.

[0035] To address the aforementioned issues, this invention first releases the internal stress of the graphitized bulk product C during the preparation of graphite anode materials, and then performs depolymerization and separation to remove fine powder. This effectively avoids the premature accumulation of internal stress in the particles, which could lead to graphite crystal collapse, loss of active materials, and capacity drop in the latter half of long cycling cycles. The resulting graphite anode material exhibits better long-cycle stability.

[0036] In some embodiments of the present invention, fine powder refers to particles with a diameter ≤1μm. Without theoretical constraints, long-cycle samples do not ideally contain nanoscale particles, as nano-sized particles can lead to excessively high surface energy, making them prone to side reactions with the electrolyte. Methods for removing fine powder include, but are not limited to, fine powder extraction.

[0037] In some specific embodiments of the present invention, the mosaic structure content under isotropic polarized light microscopy is ≥60% by volume percentage. For example, it can be any single value or a range of any two values ​​from 60%, 70%, 80%, 90%, and 95%. The lamellar structure content is ≤10%, for example, it can be any single value or a range of any two values ​​from 10%, 8%, 6%, 3%, and 1%. In the present invention, the mosaic structure content and the lamellar structure content are obtained by polarized light microscopy testing. The polarized light microscopy determination refers to the People's Republic of China Ferrous Metallurgical Industry Standard YB / T077-2017, "Method for Determination of Optical Structure of Coke."

[0038] In some specific embodiments of the present invention, the particle size Dv50 of the material A obtained in step S1 is 10-20 μm. For example, it can be any one value or a range of any two values ​​among 10 μm, 12 μm, 15 μm, 18 μm, and 20 μm.

[0039] In some specific embodiments of the present invention, the shape of the block B obtained in step S2 can be a cylinder and / or a cuboid and / or a cube.

[0040] In some specific embodiments of the present invention, the density of block B is 1.40-1.80 g / cm³. 3 For example, it can be 1.40 g / cm³. 3 1.50g / cm 3 1.60g / cm 3 1.70g / cm 3 1.80g / cm 3 The range of values ​​consisting of any one point value or any two point values.

[0041] In some specific embodiments of the present invention, the weight of each block B is 10-200 kg. For example, it can be any one value or a range of any two values ​​among 10 kg, 50 kg, 100 kg, 150 kg, and 200 kg.

[0042] In some specific embodiments of the present invention, the graphitization process is carried out under an inert atmosphere, for example, the inert atmosphere can be argon; the temperature of the graphitization process is 2800-3000℃, for example, it can be any one value or a range of any two values ​​among 2800℃, 2850℃, 2900℃, 2950℃, and 3000℃; the time of the graphitization process is 5-15h, for example, it can be any one value or a range of any two values ​​among 5h, 8h, 10h, 12h, and 15h.

[0043] In some specific embodiments of the present invention, step S4, the method of releasing internal stress includes high-frequency vibration aging treatment and / or high-frequency ultrasonic shock treatment. Preferably, step S4, the method of releasing internal stress includes high-frequency vibration aging treatment.

[0044] To release internal stress and identify and eliminate particles with excessive internal stress in advance, the present invention introduces high-frequency vibration aging treatment and / or high-frequency ultrasonic impact treatment during the preparation of graphite anode materials. Unconstrained by theory, a typical high-frequency vibration aging technique involves fixing a vibrator with an eccentric weight to the surface of a blocky graphite material. The motor speed is adjusted by the equipment controller to bring the blocky graphite material into a resonant state. The resonant frequency is usually dynamically adjusted according to the characteristics of the graphite material (such as mass and stiffness) to ensure energy transfer to the interior of the graphite material. The high-frequency vibration generates periodic alternating stress, which superimposes with the existing stress inside the graphite particles, triggering local lattice slip or dislocation movement in the graphite. This process induces minute plastic deformation on the particle surface and simultaneously promotes stress release in areas of relatively concentrated stress inside the particles, gradually achieving overall stress balance. Stress release inhibits particle breakage and improves battery cycle life. The plastic deformation caused by high-frequency vibration aging treatment reduces the content of long dislocation lines and appropriately increases the content of short dislocation lines, improving the structural stability of the graphite particles. Furthermore, some graphite particles develop excessive internal stress during the raw material coke crushing, shaping, and graphitization processes. Under high-frequency vibration, the induced effect of vibration can cause a small number of particles to pulverize and produce fine powder. After these high-stress particles are processed into electrodes, as the battery cell undergoes long cycles, the internal stress of the particles accumulates prematurely to the point of exceeding the cohesive force of the particles, leading to graphite crystal collapse, loss of active materials, and side reactions between the pulverized particles and the new surfaces they create and the electrolyte. This results in a significant drop in capacity in the latter half of the long cycle, failing to achieve the target of over 10,000 cycles. Therefore, high-frequency vibration can not only effectively eliminate most of the internal stress of the particles but also identify those particles with excessive internal stress in advance and eliminate these problematic particles, thereby further improving the cycle performance of the battery cell.

[0045] Compared to the limitations of existing technologies (which can only solve the problem of electrode expansion stress at a macroscopic level, mainly improving the cycle performance of the cell in the first half of its life cycle; as the internal stress of the active material particles accumulates and exceeds the cohesive force of the particles, the particles pulverize, and the cycle performance of the cell still drops), this invention not only solves the problem of electrode expansion at a macroscopic level, but also solves the problem of the internal stress of the active material particles inside the electrode accumulating too early and exceeding the cohesive force of the particles during long-term cycling. This greatly improves the crystal stability of the active material particles and also identifies particles with excessive internal stress in advance, further improving the cycle performance of the cell. It truly solves the cycle performance problem of the cell from the active material particle level.

[0046] Specifically, without being bound by theory, the explanation regarding "identifying particles with excessive internal stress in advance and eliminating these problematic particles" is as follows: Stress concentrations of varying degrees exist near the microscopic defects of graphite particles. When subjected to vibration, the alternating stress applied to the graphite particles is superimposed with the residual stress in the graphite particles. When the result of the stress superposition reaches a certain value, the stress concentration at the most severe location will exceed the yield limit of the graphite particles, resulting in slow plastic deformation (severely deformed particles will crack). This plastic deformation reduces the peak value of the residual stress at that location and strengthens the graphite matrix. Subsequently, the vibration produces the same effect at other locations with severe stress concentration, until the superposition effect of the additional stress from the vibration and the residual stress can no longer cause plastic deformation at any location.

[0047] Identification: When the vibration aging amplitude of a block made of high internal stress particles reaches a certain range of the block's yield limit, cracks will appear first, indicating that the powder particles in the block have high internal stress.

[0048] Elimination: Continue vibrating the block that has developed cracks until the block is completely cracked, thereby pulverizing the high-stress particles.

[0049] The particle size of pulverized particles decreases after the deagglomeration process, especially for Dv90 and Dv100. The degree of reduction is affected by the pulverization effect of the particles.

[0050] In some specific embodiments of the present invention, the frequency of the high-frequency vibration aging treatment is 20-300Hz. For example, it can be any one value or a range of any two values ​​among 20Hz, 50Hz, 100Hz, 150Hz, 200Hz, 250Hz, and 300Hz.

[0051] In some specific embodiments of the present invention, the target amplitude of the high-frequency vibration aging treatment is 1-2 mm, for example, it can be any one value or a range of any two values ​​among 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, and 2 mm; the amplitude at the start of vibration is 0.3-0.7 mm, for example, it can be any one value or a range of any two values ​​among 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, and 0.7 mm; the amplitude increase rate is 0.05-0.2 mm / min, for example, it can be any one value or a range of any two values ​​among 0.05 mm / min, 0.08 mm / min, 0.1 mm / min, 0.12 mm / min, 0.15 mm / min, 0.18 mm / min, and 0.2 mm / min. A slower rate of increase in amplitude is beneficial for the relatively uniform distribution of short dislocation lines, but too slow an increase in amplitude will prolong the production cycle, increase production costs, and is not conducive to large-scale production. If the rate of increase in amplitude is too fast, the energy accumulated inside the particle will be difficult to be uniformly transferred, resulting in too many short dislocation lines inside the particle, excessively large crystal slip steps, and easy pulverization of the particle, which is not conducive to improving cycle performance.

[0052] In some specific embodiments of the present invention, after the high-frequency vibration aging treatment reaches the target amplitude, the vibration time at the target amplitude is 5-60 min. For example, it can be any one value or a range of any two values ​​among 5 min, 15 min, 30 min, 45 min, and 60 min.

[0053] In some specific embodiments of the present invention, the frequency of the high-frequency ultrasonic shock treatment is 5-60kHz, for example, it can be any one value or a range of any two values ​​among 5kHz, 20kHz, 40kHz, and 60kHz.

[0054] In some specific embodiments of the present invention, the power density of the high-frequency ultrasonic shock treatment is 0.5-2.5 W / cm². 2 For example, it can be 0.5 W / cm 2 1W / cm 2 1.5W / cm 2 2W / cm 2 2.5W / cm 2 The range of values ​​consisting of any one point value or any two point values.

[0055] In some specific embodiments of the present invention, the amplitude of the high-frequency ultrasonic shock treatment is 10-500μm. For example, it can be any one value or a range of any two values ​​among 10μm, 100μm, 200μm, 300μm, 400μm, and 500μm.

[0056] In some specific embodiments of the present invention, the high-frequency ultrasonic shock treatment time is 30-60 minutes. For example, it can be any one value or a range of any two values ​​among 30 minutes, 40 minutes, 50 minutes, and 60 minutes.

[0057] In some specific embodiments of the present invention, the medium for high-frequency ultrasonic impact treatment includes deionized water.

[0058] A second aspect of the present invention provides a graphite anode material, which is prepared by the preparation method of the long-cycle artificial graphite anode material described in any of the foregoing embodiments.

[0059] In some specific embodiments of the present invention, the dislocation line density per unit area of ​​the prepared graphite anode material particle slices with a length <30nm is 20-60 / μm. 2 For example, it can be 20 / μm 2 30 / μm 2 40 / μm 2 50 / μm 2 60 / μm 2 The value of any one point or the range of two points in the range; the dislocation line density with a length > 50 nm is not higher than 15 / μm. 2 For example, it can be 15 / μm 2 12 / μm 2 10 / μm 2 8 / μm 2 5 / μm 2 2 / μm 2 1 / μm 2 0.5 / μm 2 The range of values ​​consisting of any one point value or any two point values.

[0060] Unconstrained by theory, in graphite anode materials, if the content of long dislocation lines is too high, cracking is likely to continue along these lines during use, leading to easy pulverization of graphite particles during charge and discharge, and a short lifespan. Conversely, if the density of short dislocation lines is too low, the density of long dislocation lines is relatively high, making graphite particles prone to cracking during charge and discharge. When the density of short dislocation lines is appropriate, the density of long dislocation lines is low, and the short dislocation lines can interlock, making them less prone to cracking during charge and discharge cycles. However, if the content of short dislocation lines is too high, pulverization will occur, producing debris. When the density of short dislocation lines exceeds a certain value, it will also cause the graphite material particles to crack and pulverize. The graphite anode material provided in this invention has a density of long dislocation lines with a length >50nm per unit area of ​​the particle slice ≤15 / μm. 2 The short dislocation linear density is 20-60 / μm. 2The graphite particles have a low content of long dislocation lines and an appropriate content of short dislocation lines. This prevents the graphite particles from cracking and shattering due to an excessive number of short dislocation lines. Furthermore, the short dislocation lines can interlock with each other, making them less prone to cracking during charge-discharge cycles. This significantly improves the structural stability of the graphite particles, thereby enhancing the cycle stability of the battery.

[0061] In some specific embodiments of the present invention, the dislocation linear density with a length >50nm per unit area of ​​the graphite anode material particle slice is 2-15 / μm. 2 If the content of long dislocation lines is too high, the graphite particles are prone to cracking and pulverization; if the content of long dislocation lines is too low, the processing is difficult and it will lead to an excessive increase in the density of short dislocation lines.

[0062] In some specific embodiments of the present invention, the average width of the slip steps on the surface of the graphite anode material particles is 0.5-1 nm. For example, it can be any one value or a range of any two values ​​from 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, and 1 nm. Plastic deformation causes slip steps to form on the surface. The average size of a single step needs to be within a certain range. If the step size is too small, the effect of improving the durability of the graphite particles is not good. If the step size is too large, it will lead to particle cracking and pulverization.

[0063] In some specific embodiments of the present invention, the average internal stress of the graphite anode material particles is 60-200 MPa. For example, it can be any single value or a range of any two values ​​from 60 MPa, 80 MPa, 100 MPa, 120 MPa, 150 MPa, 180 MPa, and 200 MPa. By using lattice slip and dislocation movement, the peak internal stress generated during particle processing can be reduced and controlled within a suitable range. If the internal stress is too high, as the cell undergoes long-term cycling, the internal stress of the particles will accumulate prematurely to exceed the cohesive force of the particles, leading to graphite crystal collapse, loss of active material, and particle pulverization, which creates new surfaces that react with the electrolyte, resulting in a drop in capacity in the latter half of the long-cycle period and affecting the long-cycle stability of the battery. Conversely, if the internal stress is too low, the graphite particles have poor compressive strength and are easily deformed or broken under pressure. Controlling the internal stress within the above-mentioned range yields better overall results.

[0064] In some specific embodiments of the present invention, the particle size Dv50 of the graphite anode material is 11-21 μm, for example, it can be any one value or a range of any two values ​​among 11 μm, 13 μm, 15 μm, 18 μm, and 21 μm; the particle size distribution (Dv90-Dv10) / Dv50 = 0.7-1.1, for example, it can be any one value or a range of any two values ​​among 0.7, 0.8, 0.9, 1.0, and 1.1.

[0065] In some specific embodiments of the present invention, the tap density of the graphite anode material is 1.2-1.5 g / cm³. 3 For example, it could be 1.2 g / cm³. 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 The range of values ​​formed by any one point or any two points in the range; due to the release of internal stress in the particles, the internal grains of the particles are densely packed, the surface morphology is regular, and the tap density is improved.

[0066] The embodiments of the present invention will be described in detail below with reference to specific examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0067] Example 1 S1. The isotropic focal oxide (with a mosaic structure content of 90% and a sheet structure content of 3% under a polarizing microscope) is crushed and shaped to obtain material A with a particle size Dv50 of 10μm; S2. Material A is subjected to pressure molding to form a cylindrical block with a density of 1.5 g / cm³. 3 Each piece weighs 10kg, resulting in block B; S3. Graphitization treatment was carried out on block B under argon atmosphere. The holding temperature of graphitization treatment was 2800℃ and the holding time was 15h to obtain graphitized block product C. S4. The graphitized bulk product C was subjected to internal stress relief treatment using high-frequency vibration aging technology. The vibration frequency was 300 Hz and the vibration amplitude was 2 mm. The amplitude was 0.7 mm at the beginning of the vibration and the amplitude increased at a rate of 0.2 mm / min. As the vibration time was extended, the amplitude gradually increased to 2 mm. After reaching the target amplitude, the vibration was continued for 5 min to obtain product D. S5. The product D block material is depolymerized, separated, and finely powdered to finally obtain a long-cycle artificial graphite anode material.

[0068] Example 2 S1. The isotropic focal oxide (with a mosaic structure content of 70% and a sheet structure content of 6% under a polarizing microscope) was crushed and shaped to obtain material A with a particle size Dv50 of 15μm; S2. Material A is subjected to pressure molding to form a rectangular block with a density of 1.6 g / cm³. 3Each piece weighs 100kg, resulting in block B; S3. Graphitization treatment was carried out on block B under argon atmosphere. The holding temperature for graphitization treatment was 2900℃ and the holding time was 10h to obtain graphitized block product C. S4. The graphitized bulk product C was subjected to internal stress relief treatment using high-frequency vibration aging technology. The vibration frequency was 200 Hz and the vibration amplitude was 1.5 mm. The amplitude was 0.5 mm at the beginning of the vibration and the amplitude increased at a rate of 0.15 mm / min. As the vibration time was extended, the amplitude gradually increased to 1.5 mm. After reaching the target amplitude, the vibration was continued for 30 min to obtain product D. S5. The product D block material is depolymerized, separated, and finely powdered to finally obtain a long-cycle artificial graphite anode material.

[0069] Example 3 S1. The isotropic focal oxide (with a mosaic structure content of 60% and a sheet structure content of 10% under a polarizing microscope) was crushed and shaped to obtain material A with a particle size Dv50 of 20μm; S2. Material A is subjected to pressure molding to form a cube with a density of 1.8 g / cm³. 3 Each piece weighs 200 kg, resulting in piece B; S3. Graphitization treatment was carried out on block B under argon atmosphere. The holding temperature for graphitization treatment was 3000℃ and the holding time was 5h to obtain graphitized block product C. S4. The graphitized bulk product C was subjected to internal stress relief treatment using high-frequency vibration aging technology. The vibration frequency was 20 Hz and the vibration amplitude was 1 mm. The amplitude was 0.3 mm at the beginning of vibration and the amplitude increased at a rate of 0.1 mm / min. As the vibration time increased, the amplitude gradually increased to 1 mm. After reaching the target amplitude, the vibration was continued for 60 min to obtain product D. S5. The product D block material is depolymerized, separated, and finely powdered to finally obtain a long-cycle artificial graphite anode material.

[0070] Example 4 Example 4 is similar to Example 2, except that in step S4, the vibration frequency of the high-frequency vibration aging treatment is 10Hz.

[0071] Example 5 Example 5 is similar to Example 2, except that in step S4, the vibration frequency of the high-frequency vibration aging treatment is 350Hz.

[0072] Example 6 Example 6 is similar to Example 2, except that in step S4, the vibration time after the high-frequency vibration aging treatment reaches the target amplitude is 2 minutes.

[0073] Example 7 Example 7 is similar to Example 2, except that in step S4, the vibration time after the high-frequency vibration aging treatment reaches the target amplitude is 70 minutes.

[0074] Example 8 Example 8 is similar to Example 2, except that in step S4, the target amplitude of the high-frequency vibration aging treatment is 0.8 mm.

[0075] Example 9 Example 9 is similar to Example 2, except that in step S4, the target amplitude of the high-frequency vibration aging treatment is 2.5 mm.

[0076] Example 10 Example 10 is similar to Example 2, except that in step S4, the amplitude increases at a rate of 0.05 mm / min during the high-frequency vibration aging treatment.

[0077] Example 11 Example 11 is similar to Example 2, except that in step S4, the amplitude increases at a rate of 0.3 mm / min during the high-frequency vibration aging treatment.

[0078] Example 12 Example 12 is similar to Example 2, except that in step S4, high-frequency ultrasonic impaction technology is used to relieve the internal stress of the graphitized bulk product C. The frequency of the high-frequency ultrasonic impaction treatment is 5 kHz, and the power density of the high-frequency ultrasonic impaction treatment is 0.5 W / cm². 2 The amplitude of the high-frequency ultrasonic shock treatment was 10 μm, the treatment time was 60 min, and the medium for the high-frequency ultrasonic shock treatment was deionized water, resulting in product D; all other conditions were the same as in Example 2.

[0079] Example 13 Example 13 is similar to Example 2, except that in step S4, high-frequency ultrasonic shock technology is used to relieve the internal stress of the graphitized bulk product C. The frequency of the high-frequency ultrasonic shock treatment is 35 kHz, and the power density of the high-frequency ultrasonic shock treatment is 1.5 W / cm². 2 The amplitude of the high-frequency ultrasonic shock treatment was 300 μm, the treatment time was 40 min, and the medium for the high-frequency ultrasonic shock treatment was an aqueous solution containing 30% ethanol, to obtain product D; all other conditions were the same as in Example 2.

[0080] Example 14 Example 14 is similar to Example 2, except that in step S4, high-frequency ultrasonic shock technology is used to relieve the internal stress of the graphitized bulk product C. The frequency of the high-frequency ultrasonic shock treatment is 60 kHz, and the power density of the high-frequency ultrasonic shock treatment is 2.5 W / cm². 2 The amplitude of the high-frequency ultrasonic shock treatment was 500 μm, the treatment time was 30 min, and the medium for the high-frequency ultrasonic shock treatment was n-propanol, resulting in product D; all other conditions were the same as in Example 2.

[0081] Example 15 Example 15 is similar to Example 13, except that in step S4, the power density of the high-frequency ultrasonic shock treatment is 0.3 W / cm². 2 .

[0082] Example 16 Example 16 is similar to Example 13, except that in step S4, the power density of the high-frequency ultrasonic shock treatment is 3 W / cm². 2 .

[0083] Example 17 Example 17 is similar to Example 13, except that in step S4, the amplitude of the high-frequency ultrasonic shock treatment is 5 μm.

[0084] Example 18 Example 18 is similar to Example 13, except that in step S4, the amplitude of the high-frequency ultrasonic shock treatment is 600 μm.

[0085] Example 19 Example 19 is similar to Example 13, except that in step S4, the high-frequency ultrasonic shock treatment time is 5 minutes.

[0086] Example 20 Example 20 is similar to Example 13, except that in step S4, the high-frequency ultrasonic shock treatment time is 90 minutes.

[0087] Comparative Example 1 S1. The isotropic focal oxide (with a mosaic structure content of 70% and a sheet structure content of 6% under a polarizing microscope) was crushed and shaped to obtain material A with a particle size Dv50 of 15μm; S2. Material A is subjected to pressure molding to form a rectangular block with a density of 1.6 g / cm³. 3 Each piece weighs 100kg, resulting in block B; S3. Graphitization treatment was carried out on block B under argon atmosphere. The holding temperature for graphitization treatment was 2900℃ and the holding time was 10h to obtain graphitized block product C. S4. The graphitized bulk product C is depolymerized, separated, and finely powdered to finally obtain a long-cycle artificial graphite anode material.

[0088] Comparative Example 2 S1. The isotropic focal oxide (with a mosaic structure content of 70% and a sheet structure content of 6% under a polarizing microscope) was crushed and shaped to obtain material A with a particle size Dv50 of 15μm; S2. Material A was graphitized under an argon atmosphere. The holding temperature for graphitization was 2900℃ and the holding time was 10h to obtain graphitized product B. S3. The graphitized product B is depolymerized, separated, and finely extracted to finally obtain a long-cycle artificial graphite anode material.

[0089] Comparative Example 3 S1. The isotropic focal oxide (with a mosaic structure content of 70% and a sheet structure content of 6% under a polarizing microscope) was crushed and shaped to obtain material A with a particle size Dv50 of 17μm; S2. Material A was graphitized under an argon atmosphere. The holding temperature for graphitization was 2900℃ and the holding time was 10h to obtain graphitized product B. S3. The graphitized product B is sieved to obtain a long-cycle artificial graphite anode material.

[0090] Experimental Example 1 The dislocation linear density, particle surface slip step width, internal stress, tap density, and particle size distribution of the artificial graphite anode materials prepared in each embodiment and comparative example were tested respectively. The test methods are as follows: (1) Dislocation line density test method 1. Place 2 grams of sample in 10 ml of anhydrous ethanol and sonicate for 10 minutes, then vacuum dry after sonication; 2. After drying, the sample was sequentially transferred into ethanol / epoxy resin mixtures with volume ratios of 3:1, 1:1, and 1:3 for gradient permeation, with each step lasting 1 hour. 3. Transfer the gradient permeation sample into a silica gel mold, inject pure epoxy resin, vacuum for 10 minutes, and then dry at 60°C for 48 hours; 4. Trim the block first, then use an ultrathin slicer to cut the sample into thin slices with a thickness of 70 nm, and transfer them to a copper mesh for drying; 5. HRTEM parameters: accelerating electric field 100kV, electron dose 6 e - / Å 2The objective aperture (OL) is 24 μm; 6. First, use the low magnification mode (8Kx) to randomly select 20 particles, then switch to the high magnification mode (1Mx) to accurately focus on and photograph 4 random areas within the particles. The photo size is 200nm×200nm. 7. Process the HRTEM images obtained in step 6 using ImageJ software. First, identify the dislocation line structures, and then use the software to count the number of dislocation lines with lengths <30nm and >50nm. Process 80 images sequentially and calculate the unit area (μm). 2 The average number of dislocation lines with lengths <30nm and >50nm.

[0091] (2) Test method for the width of slip steps on particle surface 1. Wet the clean silicon wafer substrate with a trace amount of ethanol, add graphite suspension, and let it stand to dry naturally; 2. AFM uses the tapping mode, with a silicon probe elastic constant of 20 N / m, a tip curvature radius of 1 nm, a scanning range of 1 × 1 μm, a scanning rate of 0.6 Hz, and a resolution of 512 × 512 pixels; 3. Locate the target particles at low magnification, gradually reduce the scanning area to high magnification (1×1μm), and focus on the dense area of ​​slip steps; 4. Use the section line tool in NanoScope Analysis of AFM software to draw a section line perpendicular to the step direction; 5. Measure the average width of the steps. In the 3D topographic map, measure the width along the extension direction of the steps. 6. Measure the width at 3 random locations on the same particle. Measure 10 random particles and calculate the average step width of the 10 particles.

[0092] (3) XRD method for measuring internal stress in graphite particles 1. Fill the groove of the XRD sample holder with the powder sample that has passed through 200 mesh, and press the surface flat with a glass slide to ensure that the sample surface is flat and without gaps; 2. A copper target was selected, with a wavelength of λ=1.5406nm, a voltage of 40kV, a current of 40mA, a scanning range of 2θ=20-30°, a step size of 0.02°, and a scanning speed of 1° / min. After scanning, the baseline background noise was removed using the Jade software, the (002) diffraction peak was identified, and the diffraction peak angle 2θ was determined by software fitting. 3. Calculate the measured interplanar spacing: dψ = λ / (2sinθ).

[0093] 4. Internal stress calculation: σ -=E / (1+v)× ε, ε=∣(dψ-d0) / d0∣, internal stress σ - The unit is MPa, and the elastic modulus of graphite is E = 6 × 10⁻⁶. 4 MPa, Poisson's ratio v=0.16, d0 is the interlayer spacing of ideal plastic graphite, taken as 0.3354nm, and dψ is the interlayer spacing of graphite actually measured (unit: nm).

[0094] (4) Tap density test The particle tap density is determined using a tap density tester, such as the Anton Paar Ultratap 500 series tap density tester, which can withstand 3000 vibrations.

[0095] (5) Particle size distribution test Particle size is measured using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0096] The test results are shown in Tables 1 and 2.

[0097] Table 1

[0098] Table 2

[0099] Experimental Example 2 Electrical performance testing The negative electrode materials obtained in each embodiment and comparative example were mixed with CMC, SP, and SBR in a mass ratio of 95:2:1:2 in a pure aqueous solution to prepare slurries. The slurries were then coated onto the surface of copper foil to obtain negative electrode sheets. The positive electrode sheet had a mass ratio of lithium iron phosphate: SP: PVDF = 90:5:5. The separator was a microporous polypropylene membrane. The electrolyte composition was 1.1M LiPF6 dissolved in a mixed solution of EC, DMC, and EMC, with a volume ratio of EC, DMC, and EMC of 1:1:1. The mixed solution also contained 2% VC by mass. The negative electrode sheet, positive electrode sheet, separator, and electrolyte were assembled into a lithium-ion battery with a charge / discharge cutoff voltage of 2.5~3.65V.

[0100] The battery performance tests included: 1) 1000 cycles at 25℃ and 0.25C, with the graphite electrode expansion rate tested after disassembly; 2) 3000 cycles at 25℃ and 0.25C. The test results are shown in Tables 3 and 4.

[0101] Table 3

[0102] Table 4

[0103] Comparative Examples 1-3 represent the conventional long-cycle artificial graphite preparation methods currently available on the market. After graphitization, no internal stress reduction treatment is performed on the material. The material has a high long dislocation linear density, high internal stress in the particles, no plastic deformation, and no slip steps in the crystals, resulting in an excessively high electrode expansion rate and poor cycle performance.

[0104] Examples 1-3 employ high-frequency vibration aging technology to reduce internal stress in graphitized bulk materials. This significantly reduces the linear density of long dislocations in the particles and significantly increases the linear density of short dislocations, thereby reducing internal stress in the particles. The crystal slip steps on the particle surface become more pronounced, resulting in plastic deformation and high powder tap density. Consequently, the electrode expansion rate of the material decreases, and the cycle performance is greatly improved.

[0105] In Examples 4-5, when high-frequency vibration aging technology is used to reduce internal stress in graphitized bulk materials, the effect of reducing internal stress is weak when the frequency of high-frequency vibration aging technology is too low; when the frequency is too high, it will lead to excessive energy application, resulting in too many short dislocation lines, excessive crystal slip steps, and easy pulverization of particles. Compared with Example 2, the electrode expansion rate increases and the cycle performance decreases, but both are better than the comparative example without internal stress reduction treatment.

[0106] In Examples 6-7, when high-frequency vibration aging technology was used to reduce internal stress in graphitized blocks, the vibration time after reaching the target amplitude was too short, resulting in a weak stress reduction effect; the vibration time was too long, which would generate too many short dislocation lines inside the particles, resulting in excessive crystal slip steps and easy pulverization of the particles. Compared with Example 2, the electrode expansion rate increased and the cycle performance decreased, but both were better than the comparative example without stress reduction treatment.

[0107] In Examples 8-9, when high-frequency vibration aging technology is used to reduce internal stress in graphitized blocks, the effect of reducing internal stress is weak when the target amplitude is too small; when the target amplitude is too large, too many short dislocation lines will be generated inside the particles, the crystal slip steps will be too large, and the particles will be easy to pulverize. Compared with Example 2, the electrode expansion rate increases and the cycle performance decreases, but both are better than the comparative example without internal stress reduction treatment.

[0108] In Examples 10-11, when high-frequency vibration aging technology is used to reduce internal stress in graphitized blocks, if the rate of increase of the target amplitude is too low, it will not affect the reduction of internal stress in the particles, but it will prolong the production cycle and increase production costs. If the rate of increase of the target amplitude is too high, the energy accumulated inside the particles will be difficult to be uniformly transferred, resulting in too many short dislocation lines in the particles, excessive crystal slip steps, and easy pulverization of the particles. Compared with Example 2, the electrode expansion rate increases and the cycle performance decreases, but it is better than the control example without internal stress reduction treatment.

[0109] Examples 12-14 show that high-frequency ultrasonic impact technology was used to reduce the internal stress of graphitized bulk materials. The long dislocation linear density of the particles was significantly reduced, while the short dislocation linear density was significantly increased. The internal stress of the particles was reduced, and the crystal slip steps on the particle surface were obvious, resulting in plastic deformation and high powder tap density. This led to a lower electrode expansion rate and a significant improvement in cycle performance.

[0110] In Examples 15-16, when high-frequency ultrasonic impact technology was used to reduce internal stress in graphitized blocks, the ultrasonic power density was too low, resulting in a weak stress reduction effect; if the ultrasonic power density was too high, too many short dislocation lines would be generated inside the particles, the crystal slip steps would be too large, and the particles would be prone to pulverization. Compared with Example 13, the electrode expansion rate increased and the cycle performance decreased, but both were better than the control examples that did not undergo stress reduction treatment.

[0111] In Examples 17-18, when high-frequency ultrasonic impact technology was used to reduce internal stress in graphitized blocks, the stress reduction effect was weak when the ultrasonic amplitude was too small; when the ultrasonic amplitude was too large, too many short dislocation lines were generated inside the particles, the crystal slip steps were too large, and the particles were easy to pulverize. Compared with Example 13, the electrode expansion rate increased and the cycle performance decreased, but both were better than the control example without stress reduction treatment.

[0112] In Examples 19-20, when high-frequency ultrasonic impact technology was used to reduce internal stress in graphitized blocks, a short ultrasonic impact time resulted in a weak stress reduction effect; a long ultrasonic impact time would generate too many short dislocation lines inside the particles, resulting in excessively large crystal slip steps and easy pulverization of the particles. Compared with Example 13, the electrode expansion rate increased and the cycle performance decreased, but both were better than the control example without stress reduction treatment.

[0113] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a long-cycle artificial graphite anode material, characterized in that, Includes the following steps: S1. The isotropic coke is crushed and shaped to obtain material A; S2. The material A is subjected to molding processing to obtain block B; S3. The block B is subjected to graphitization treatment to obtain graphitized blocky product C; S4. The graphitized bulk product C is subjected to stress release treatment to obtain product D; the stress release method includes high-frequency vibration aging treatment and / or high-frequency ultrasonic shock treatment; the frequency of the high-frequency vibration aging treatment is 20-300Hz; the frequency of the high-frequency ultrasonic shock treatment is 5-60kHz. S5. Depolymerize and separate the product D and remove the fine powder to obtain the long-cycle artificial graphite anode material.

2. The method for preparing the long-cycle artificial graphite anode material according to claim 1, characterized in that, By volume percentage, the isotropic focal plane contains ≥60% of the mosaic structure and ≤10% of the sheet structure.

3. The method for preparing the long-cycle artificial graphite anode material according to claim 1, characterized in that, In step S1, the particle size Dv50 of material A is 10-20 μm.

4. The method for preparing the long-cycle artificial graphite anode material according to claim 1, characterized in that, In step S2, at least one of the following characteristics is satisfied: (1) The shape of the block B includes a cylinder and / or a cuboid and / or a cube; (2) The density of block B is 1.40-1.80 g / cm³. 3 ; (3) The weight of each block B is 10-200 kg.

5. The method for preparing the long-cycle artificial graphite anode material according to claim 1, characterized in that, In step S3, the graphitization process is carried out under an inert atmosphere, the temperature of the graphitization process is 2800-3000℃, and the time of the graphitization process is 5-15h.

6. The method for preparing the long-cycle artificial graphite anode material according to claim 1, characterized in that, The target amplitude of the high-frequency vibration aging treatment is 1-2 mm, the amplitude at the start of vibration is 0.3-0.7 mm, and the amplitude increases at a rate of 0.05-0.2 mm / min. And / or, the duration of vibration after reaching the target amplitude is 5-60 minutes.

7. The method for preparing the long-cycle artificial graphite anode material according to claim 1, characterized in that, It meets at least one of the following characteristics: (1) The power density of the high-frequency ultrasonic shock treatment is 0.5-2.5 W / cm². 2 ; (2) The amplitude of the high-frequency ultrasonic shock treatment is 10-500 μm; (3) The duration of the high-frequency ultrasonic shock treatment is 30-60 min; (4) The medium for high-frequency ultrasonic shock treatment includes at least one of deionized water, ethanol, and n-propanol.

8. A graphite anode material, characterized in that, It is prepared by the method for preparing long-cycle artificial graphite anode material according to any one of claims 1-7.

Images