A fast-charging graphite negative electrode material, a preparation method therefor, and an application thereof

Abstract

This invention discloses a fast-charging graphite anode material, its preparation method, and its application. The steps are as follows: Step 1, pulverizing a graphite precursor to obtain fine powder; Step 2, mixing the fine powder with a pore-forming agent, heating and reacting under an inert atmosphere, and then washing and drying to obtain a porous graphite precursor; Step 3, mixing the porous graphite precursor with a liquid granulating agent and a catalyst uniformly, solidifying and granulating under heating conditions, and then oriented under a vertical magnetic field to obtain porous secondary graphite particles; Step 4, sequentially carbonizing the porous secondary graphite particles at low and high temperatures under gas protection to obtain a fast-charging graphite anode material with a core-shell structure; its core is porous secondary graphite particles, and the shell is an amorphous carbon coating layer. By combining the synergistic process of "magnetic field oriented granulation, hierarchical pore formation, and core-shell structure regulation," the prepared fast-charging graphite anode material can simultaneously achieve high compaction density, high ion diffusion rate, and long cycle life.

Description

Technical Field

[0001] This invention relates to the technical field of graphite anode materials, specifically a fast-charging graphite anode material, its preparation method, and its application. Background Technology

[0002] With the explosive growth of the new energy vehicle industry and the urgent need to address range anxiety in consumer electronics, the ultra-fast charging experience, where "charging is like refueling," has become the high ground in the competition for lithium-ion battery technology. Graphite anode materials, with their low cost, high theoretical capacity, and excellent cycle performance, remain the preferred anode material for current commercial batteries. However, in high-rate fast charging scenarios (such as 4C and above), traditional graphite anodes face severe physicochemical bottlenecks: on the one hand, the layered structure of graphite results in a low diffusion coefficient of lithium ions between layers (typically on the order of 10⁻¹² cm² / s). During high-current charging, lithium ions cannot be intercalated in time, easily depositing on the anode surface to form lithium dendrites, which can puncture the separator and cause safety hazards. On the other hand, nano-sizing or pore-forming modifications to improve rate performance often significantly increase the specific surface area of ​​the material. An excessively large specific surface area leads to a decrease in initial coulombic efficiency, increased electrolyte consumption, and reduced cycle life. In other words, the lithium ion diffusion rate is slow during fast charging, lithium deposition is easy at high rates, and cycle stability is poor.

[0003] Existing pore-forming technologies (such as KOH activation) are mostly non-directional random pore-forming, with disordered pore structures that are prone to collapse. This makes it difficult to form a high-efficiency ion transport highway that runs through the interior of the particles. Furthermore, the granulation process relies heavily on mechanical force, which cannot achieve the ordered arrangement of graphite microcrystals inside the particles. This results in poor anisotropy of ion transport and makes it difficult to achieve both high energy density and high power density.

[0004] Existing modification methods often suffer from drawbacks: for example, while soft / hard carbon coating can improve interfacial stability, excessively thick coating layers can hinder lithium-ion transport; introducing heteroatom doping can widen interlayer spacing, but often introduces too many defects, leading to decreased electronic conductivity. Particularly for the preparation of secondary particles, traditional spray drying or mechanical fusion methods struggle to precisely control the internal microstructure of the particles, failing to construct the ideal "core-shell" synergistic configuration—that is, a high-capacity graphite core inside and a high-rate transport channel on the outside. Furthermore, while magnetic field-assisted orientation technology can theoretically induce the directional alignment of graphite microcrystals, its complexity—the difficulty in matching magnetic field strength with granulating agents—and its inability to seamlessly integrate with industrial pore-forming and carbonization processes have kept this technology largely confined to the laboratory stage, preventing low-cost, large-scale industrial applications.

[0005] Against this backdrop, developing a fast-charging graphite anode material that can simultaneously achieve "high real density, high ion diffusion rate, and long cycle life" has become a key challenge that the industry urgently needs to overcome. Summary of the Invention

[0006] Therefore, the technical problem to be solved by this invention is to provide a fast-charging graphite anode material and its preparation method and application. By combining the synergistic preparation process of "magnetic field directional granulation, hierarchical pore formation and core-shell structure regulation", the prepared fast-charging graphite anode material can simultaneously achieve high solid density, high ion diffusion rate and long cycle life, which is of great strategic significance for promoting the commercialization of high-energy-density fast-charging lithium-ion batteries.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] A method for preparing a fast-charging graphite anode material includes the following steps:

[0009] Step 1: Pulverize the graphite precursor to obtain fine powder;

[0010] Step 2: Mix the fine powder with the pore-forming agent, heat under an inert atmosphere to carry out the pore-forming reaction, keep warm, wash and dry to obtain a porous graphite precursor;

[0011] Step 3: Mix the porous graphite precursor with liquid granulation agent and catalyst evenly, solidify and granulate under heating conditions, and use the catalyst to induce the porous graphite precursor to oriented arrangement under the action of a vertical magnetic field with an intensity of 0.5-1.5T to obtain porous graphite secondary particles.

[0012] Step 4: The porous graphite secondary particles obtained in Step 3 are subjected to low-temperature carbonization and high-temperature carbonization under gas protection to obtain a fast-charging graphite anode material with a core-shell structure; the core of the fast-charging graphite anode material is porous graphite secondary particles, and the shell is an amorphous carbon coating layer.

[0013] This invention involves creating pores in fine powder combined with a compound pore-forming agent at a specific temperature. The resulting porous graphite precursor, with its multi-level interconnected pore structure, is then granulated using a vertical magnetic field. A catalyst induces the directional growth of graphite microcrystals along specific crystal planes. The resulting porous graphite secondary particles, with their ordered internal structure, are then subjected to both low-temperature and high-temperature carbonization. Because the liquid granulating agent is uniformly coated on the porous graphite precursor, the carbonization shrinkage rate, graphitization degree, and catalyst distribution differ between the internal and surface layers of the porous graphite secondary particles. This results in a denser or more ordered surface structure, while the interior retains its porous characteristics. Consequently, a fast-charging graphite anode material with a core-shell structure exhibiting internal and external differences is naturally formed after carbonization. This not only increases the lithium-ion diffusion coefficient to 10... -10 cm 2The method achieves a high capacity retention rate (≥90%) after 100 cycles at 6C or even 10C rates, fundamentally solving the problem of lithium-ion transport lag in thick electrodes. Furthermore, by optimizing particle size distribution and tap density, it ensures that the battery's volumetric energy density is not significantly sacrificed due to fast charging requirements. In other words, through the synergistic effect of these technologies, the prepared fast-charging graphite anode material can simultaneously achieve high tap density, high ion diffusion rate, and long cycle life.

[0014] In the above-mentioned method for preparing a fast-charging graphite anode material, in step 1, the graphite precursor is selected from at least one of natural graphite, artificial graphite, and mesophase carbon microspheres;

[0015] The fine powder has an average particle size D50 of 4-8 μm, and the particle size distribution satisfies D10≥2 μm and D90≤12 μm. The small particle size design of the fine powder can shorten the lithium ion transport path, laying the foundation for subsequent granulation to form uniform porous graphite secondary particles.

[0016] In the preparation method of the above-mentioned fast-charging graphite anode material, in step 2, the mass ratio of the fine powder to the pore-forming agent is 4:1; the pore-forming agent is a compound system of ammonium bicarbonate and urea, with a mass ratio of ammonium bicarbonate to urea of ​​1:(1~3); ammonium bicarbonate and urea decompose under heating conditions to generate gas, forming a rich pore structure inside the graphite particles. Compared with a single pore-forming agent, the compound system can achieve a more uniform pore formation effect, avoiding localized through-pores or uneven pore formation.

[0017] Heating to 400-600℃ at a heating rate of 2-5℃ / min under an inert atmosphere, and holding at that temperature for 1-3 hours. The temperature setting of 400-600℃ is based on the decomposition characteristics of the ammonium bicarbonate and urea compound system and the requirement for hierarchical pore formation: below 400℃, although ammonium bicarbonate has decomposed, urea has not completely decomposed or carbonized, resulting in insufficient pore formation and insufficient gas release, making it impossible to form an effective microporous-mesoporous hierarchical structure. In addition, residual urea may block the pores, resulting in a low specific surface area and insufficient porosity. Above 600℃, excessively high temperatures may cause the formed micropores to undergo excessive sintering and collapse due to graphitization shrinkage or migration of pore wall atoms, resulting in the rupture of the mesoporous structure, leading to a sharp decrease in specific surface area and loss of hierarchical pore structure. At the same time, it may cause local structural ordering of the graphite precursor, which is not conducive to the rapid transport of subsequent ions. Therefore, 400-600℃ is just right to achieve the staged decomposition of the two pore-forming agents (ammonium bicarbonate first releases gas to form preliminary pores, and urea decomposes subsequently to expand the pores and avoid premature closure of the pore structure), thereby obtaining a hierarchical porous structure with good connectivity and reasonable pore size distribution.

[0018] In the above-mentioned method for preparing a fast-charging graphite anode material, in step 3, the liquid granulating agent is at least one of liquid asphalt, liquid phenolic resin, liquid epoxy resin, and polyacrylonitrile solution, and the amount of the liquid granulating agent is 5-20% of the mass of the porous graphite precursor;

[0019] In this solution, the solvent is dimethylformamide, which is readily miscible with the catalyst, and the polyacrylonitrile concentration is 10%. If the concentration is too high, the solution viscosity will be too high, making it difficult to achieve a uniform thin-layer coating on the porous graphite surface, easily causing particle adhesion and pore blockage. Furthermore, during the vertical magnetic field orientation process, excessive fluid resistance will hinder the orderly arrangement of graphite sheets. If the concentration is too low, the amorphous carbon shell formed after carbonization will be too thin or discontinuous, making it difficult to effectively buffer the volume expansion during the charging and discharging process.

[0020] The catalyst is selected from at least one of metal salts or oxides of iron, cobalt, and nickel, and the amount of catalyst used is 0.01-0.1% of the mass of the porous graphite precursor. After carbonization, the liquid granulator forms an amorphous carbon coating layer on the surface of the secondary porous graphite particles, constituting a core-shell structure. Furthermore, the trace amount of catalyst promotes local graphitization of the shell carbon material during subsequent carbonization, thereby improving the electronic conductivity of the shell.

[0021] The selection of a magnetic field strength range of 0.5-1.5T aims to strike a balance between orientation effectiveness, process stability, and economic efficiency. Below 0.5T, the orientation torque provided by the magnetic field is insufficient to overcome the viscous resistance and Brownian motion of the slurry, resulting in disordered graphite particle arrangement, low orientation degree, and poor batch stability, making it difficult to achieve the expected anisotropic properties. Above 1.5T, excessive particle agglomeration or "bridging" may occur, interfering with the uniform distribution of the catalyst (especially if it contains ferromagnetic components). Simultaneously, equipment costs, eddy current heating, and process control difficulties increase dramatically, hindering stable industrial production. Therefore, 0.5-1.5T is the preferred range to ensure efficient orientation, reliable curing and locking of the graphite precursor, and engineering feasibility.

[0022] In the above-mentioned method for preparing a fast-charging graphite anode material, step 3 involves a curing and granulation heating temperature of 180-600℃ and a processing time of 1-4 hours. This heating temperature range is set to ensure that the liquid granulator reaches the minimum curing temperature to form a preliminary particle structure, avoiding insufficient fluidity due to excessively low temperature, which would prevent the porous graphite precursor from being uniformly coated. In addition, it prevents excessive pyrolysis of the granulator or damage to the graphite microcrystalline structure, and also ensures seamless integration with the subsequent carbonization process.

[0023] The average particle size D50 of the porous graphite secondary particles is 8-20 μm, the particle size distribution of the porous graphite secondary particles satisfies D10≥5 μm, D90≤25 μm, and the tap density is 0.8-1.2 g / cm³. 3 .

[0024] In the above-mentioned method for preparing a fast-charging graphite anode material, step 4, the gas is at least one of nitrogen, argon, and helium;

[0025] The conditions for low-temperature carbonization are: heating to 400-600℃ at a heating rate of 1-3℃ / min and holding for 1-2 hours; the conditions for high-temperature carbonization are: heating to 800-1200℃ at a heating rate of 3-5℃ / min and holding for 2-6 hours. The carbonization process employs a segmented heating method, which helps control the carbonization process of the liquid granulating agent, resulting in a uniform and dense coating structure of the shell carbon material.

[0026] The above-mentioned method for preparing a fast-charging graphite anode material describes a multi-level porous structure comprising micropores with a diameter <2 nm, mesopores with a diameter of 2-50 nm, and macropores with a diameter >50 nm. These multi-level channels form a continuous lithium-ion transport network within the particles. Specifically, the micropores provide active sites for lithium-ion insertion / extraction, the mesopores serve as rapid lithium-ion transport channels, and the macropores act as electrolyte reservoirs. The synergistic effect of these three components significantly shortens the lithium-ion diffusion path and enhances the lithium-ion transport rate.

[0027] The above-mentioned method for preparing a fast-charging graphite anode material, wherein the capacity retention rate of the fast-charging graphite anode material is ≥90% after 100 cycles of 6C fast charging and ≥85% after 100 cycles of 10C fast charging.

[0028] A fast-charging graphite anode material is prepared by the above-mentioned method for preparing a fast-charging graphite anode material.

[0029] An application of a fast-charging graphite anode material, wherein the fast-charging graphite anode material is prepared by the preparation method described above or the fast-charging graphite anode material described above is used as the anode material of a lithium-ion battery.

[0030] The technical solution of the present invention achieves the following beneficial technical effects:

[0031] (1) This invention involves creating pores in fine powder combined with a compound pore-forming agent at a certain temperature, then introducing a vertical magnetic field into the resulting porous graphite precursor with a multi-level interconnected channel structure within the particles during the granulation stage. A catalyst is used to induce the directional growth of graphite microcrystals along specific crystal planes. The porous graphite secondary particles, forming an ordered orientation structure within, are then subjected to low-temperature and high-temperature carbonization sequentially. Because the liquid granulating agent is uniformly coated on the porous graphite precursor and catalyst, the carbonization shrinkage rate, graphitization degree, and catalyst distribution differ between the internal and external layers of the porous graphite secondary particles. This results in a more dense or ordered surface structure, while the internal structure retains its porous characteristics. Thus, after carbonization, a fast-charging graphite anode material with a core-shell structure exhibiting internal and external differences is naturally formed. This not only increases the lithium-ion diffusion coefficient to 10... -10 cm 2 The method achieves a high capacity retention rate (≥90%) after 100 cycles at 6C or even 10C rates, fundamentally solving the problem of lithium-ion transport lag in thick electrodes. Furthermore, by optimizing particle size distribution and tap density, it ensures that the battery's volumetric energy density is not significantly sacrificed due to fast charging requirements. In other words, through the synergistic effect of these technologies, the prepared fast-charging graphite anode material can simultaneously achieve high tap density, high ion diffusion rate, and long cycle life.

[0032] (2) This invention constructs a multi-level pore structure of micropores-mesopores-macropores inside graphite particles through a pore-forming agent compound system and a pore-forming process with precise control of heating conditions, forming a continuous lithium-ion transport network. This structural design significantly shortens the solid-phase diffusion path of lithium ions and improves the transport rate of lithium ions in the graphite anode, solving the kinetic bottleneck problem in the fast charging process from the material structure level.

[0033] (3) This invention achieves preferred orientation of graphite particles by oriented granulation under the action of a vertical magnetic field, so that the (004) plane of the graphite crystal is aligned perpendicular to the current collector direction. This orientation structure further shortens the lithium ion insertion path and improves the tap density of secondary particles, thus improving fast charging performance while taking into account the volumetric energy density of the material.

[0034] (4) This invention prepares a material with a uniform core-shell structure by introducing a trace catalyst and a segmented carbonization process. The core is porous secondary graphite particles, and the shell is an amorphous carbon coating layer formed by carbonization of a granulating agent. The amorphous carbon coating layer of the shell layer inhibits the direct contact between the electrolyte and the graphite core, improves the interfacial compatibility between the graphite anode and the electrolyte, reduces irreversible capacity loss, and improves the initial coulombic efficiency and cycle stability; it also forms a local graphitized structure inside the shell layer, which improves the electronic conductivity of the composite material.

[0035] (5) The method of the present invention is simple and highly controllable. The parameters of each step are optimized in a coordinated manner. The prepared fast-charging graphite anode material has excellent comprehensive performance and can be widely used in lithium-ion batteries in electric vehicles, consumer electronics, energy storage equipment and other fields. It has important industrial application value.

[0036] This is not only a disruptive innovation to traditional graphite modification technology, but also the core material foundation to support the next generation of electric vehicles to realize the vision of "charging for 5 minutes and driving for 200 kilometers". It has profound practical significance for enhancing my country's international competitiveness in the field of high-end lithium battery materials. Attached Figure Description

[0037] Figure 1 This is a process flow diagram of the present invention;

[0038] Figure 2 In the middle: (a) is the capacity of the fast-charging graphite anode material prepared in Example 1 after 100 cycles at 6C; (b) is the capacity of the fast-charging graphite anode material prepared in Example 1 after 100 cycles at 10C.

[0039] Figure 3 In the middle: (a) is the capacity of the fast-charging graphite anode material prepared in Example 2 after 100 cycles at 6C; (b) is the capacity of the fast-charging graphite anode material prepared in Example 2 after 100 cycles at 10C.

[0040] Figure 4 In the middle: (a) is the capacity of the fast-charging graphite anode material prepared in Example 3 after 100 cycles at 6C; (b) is the capacity of the fast-charging graphite anode material prepared in Example 3 after 100 cycles at 10C.

[0041] Figure 5 In the middle: (a) is the capacity of the fast-charging graphite anode material prepared in Example 4 after 100 cycles at 6C; (b) is the capacity of the fast-charging graphite anode material prepared in Example 4 after 100 cycles at 10C.

[0042] Figure 6 In the middle: (a) is the pore size distribution curve of the fast-charging graphite anode material prepared in Example 1 obtained by BET nitrogen adsorption-desorption test; (b) is the pore size distribution curve of the fast-charging graphite anode material prepared in Example 2 obtained by BET nitrogen adsorption-desorption test. Detailed Implementation

[0043] Example 1: Preparation method of fast-charging graphite anode material using natural graphite as graphite precursor

[0044] Materials: Natural graphite (graphite precursor), pore-forming agent is a compound system of ammonium bicarbonate and urea (mass ratio of ammonium bicarbonate to urea is 1:2), liquid granulation agent is liquid phenolic resin, and catalyst is nickel nitrate.

[0045] The specific steps of the preparation method are as follows:

[0046] Step 1, pulverization: Natural graphite is pulverized by air jet milling to obtain fine powder with an average particle size D50 of 6.0 μm, and particle size distribution D10=2.5 ​​μm, D90=11.0 μm.

[0047] Step 2, Pore Formation: Mix the fine powder and the pore-forming agent at a mass ratio of 4:1, and carry out the pore-forming reaction at 500℃ under a nitrogen atmosphere at a rate of 3℃ / min. Keep warm for 2 hours, and after washing and drying, obtain the porous graphite precursor.

[0048] Step 3, Magnetic Field Granulation: The porous graphite precursor obtained in Step 2 is mixed evenly with liquid phenolic resin (the amount of liquid phenolic resin is 10 wt% of the mass of the porous graphite precursor) and nickel nitrate (the amount of nickel nitrate is 0.05 wt% of the mass of the porous graphite precursor). The mixture is then placed in a vertical magnetic field with a strength of 1.0 T for directional alignment and granulation at 350℃ for 3 hours to obtain porous secondary graphite particles with an average particle size D50 of 15 μm (D10=6 μm, D90=22 μm) and a tap density of 1.0 g / cm³. 3 .

[0049] Step 4, carbonization: The porous graphite secondary particles are carbonized in stages under argon protection: first, the temperature is increased to 550℃ at 2℃ / min and held for 1.5 hours, then increased to 1000℃ at 4℃ / min and held for 4 hours to obtain a core-shell structured fast-charging graphite anode material.

[0050] Effect verification:

[0051] Structure: such as Figure 6 As shown, the material has a complete multi-level pore structure (micropores <2nm, mesopores 2-50nm, macropores >50nm), that is, the three types of pore structures of micropores, mesopores and macropores coexist, among which the macropore content is relatively low, and the pores can form a through lithium-ion transport network inside the particles.

[0052] Performance: Assembled half-cell testing, such as Figure 2 As shown, at a 6C charge / 1C discharge rate, the initial coulombic efficiency is 92%, and the capacity retention rate after 100 cycles is 92%; at a 10C charge rate, the capacity retention rate after 100 cycles is 88%.

[0053] Example 2: Preparation method of fast-charging graphite anode material using artificial graphite as graphite precursor

[0054] Materials: Artificial graphite (graphite precursor), pore-forming agent is ammonium bicarbonate and urea (mass ratio of ammonium bicarbonate to urea is 1:3), liquid granulation agent is liquid epoxy resin, and catalyst is cobalt acetate.

[0055] The specific steps of the preparation method are as follows:

[0056] Step 1, Crushing: Artificial graphite is mechanically crushed to obtain fine powder with an average particle size D50 of 7.5 μm, and particle size distribution D10=3.0 μm, D90=11.5 μm.

[0057] Step 2, Pore Formation: The fine powder and pore-forming agent are mixed at a mass ratio of 4:1, and the mixture is heated to 480℃ at 5℃ / min under an argon atmosphere to carry out the pore-forming reaction. The mixture is kept at this temperature for 2.5 hours, and after washing and drying, a porous graphite precursor is obtained.

[0058] Step 3, Magnetic Field Granulation: The porous graphite precursor obtained in Step 2 is mixed evenly with liquid epoxy resin (the amount of liquid epoxy resin is 15 wt% of the mass of the porous graphite precursor) and cobalt acetate (the amount of cobalt nitrate is 0.08 wt% of the mass of the porous graphite precursor), and then cured and granulated under a 0.8T vertical magnetic field at 200℃ for 2 hours to obtain porous secondary graphite particles with an average particle size D50 of 12 μm and a tap density of 0.9 g / cm³. 3 .

[0059] Step 4, carbonization: The porous graphite secondary particles are carbonized in stages under nitrogen protection: first, the temperature is increased to 400℃ at 1℃ / min and held for 2 hours, then the temperature is increased to 1200℃ at 5℃ / min and held for 2 hours to obtain a core-shell structured fast-charging graphite anode material.

[0060] Effect verification:

[0061] Structure: such as Figure 6 The material exhibits a complete multi-level pore structure (micropores <2nm, mesopores 2-50nm, macropores >50nm), meaning that micropores, mesopores, and macropores coexist, with macropores having a relatively low content. The pores form a continuous lithium-ion transport network inside the particles.

[0062] Performance: Assembled half-cell testing, such as Figure 3 As shown, after 100 cycles of 6C fast charging, the capacity retention rate is 91%, and after 100 cycles of 10C fast charging, the capacity retention rate is 86%.

[0063] Example 3: Preparation method of fast-charging graphite anode material using mesophase carbon microspheres

[0064] Materials: Mesophase carbon microspheres (MCMB), pore-forming agent is a compound system of ammonium bicarbonate and urea (mass ratio of ammonium bicarbonate to urea is 1:1), liquid granulation agent is polyacrylonitrile (PAN) solution with a polyacrylonitrile concentration of 10%, and catalyst is iron oxide.

[0065] The specific steps of the preparation method are as follows:

[0066] Step 1: Pulverization: Pulverize MCMB to obtain fine powder with an average particle size D50 of 5.0 μm, and particle size distribution D10=2.0 μm, D90=9.0 μm.

[0067] Step 2, Pore Formation: The fine powder and pore-forming agent are mixed at a mass ratio of 4:1, and the mixture is heated to 520℃ at a rate of 2℃ / min under a nitrogen atmosphere to carry out the pore-forming reaction. The mixture is kept at this temperature for 1.5 hours, and after washing and drying, a porous graphite precursor is obtained.

[0068] Step 3, Magnetic Field Granulation: The porous graphite precursor obtained in Step 2 is mixed evenly with PAN solution (the amount of PAN solution is 5 wt% of the mass of the porous graphite precursor) and iron oxide (the amount of iron oxide is 0.02 wt% of the mass of the porous graphite precursor). Granulation is carried out under a strong vertical magnetic field of 1.5T and at 600℃ for 1 hour to obtain porous secondary graphite particles with an average particle size D50 of 18 μm and a tap density of 1.1 g / cm³. 3 .

[0069] Step 4, carbonization: The porous graphite secondary particles are carbonized in stages under helium protection: first, the temperature is increased to 600℃ at 3℃ / min and held for 1 hour, then increased to 900℃ at 3℃ / min and held for 6 hours to obtain a core-shell structured fast-charging graphite anode material.

[0070] Effect verification:

[0071] Structure: Tap density reaches 1.15 g / cm³ 3 Specific surface area 8m² 2 / g.

[0072] Performance: Assembled half-cell testing, such as Figure 4 As shown, after 100 cycles at 6C fast charging, the capacity retention rate is 90%; after 100 cycles at 10C, the capacity retention rate is 85%.

[0073] Example 4: Preparation method of fast-charging graphite anode material using natural graphite (verification of synergistic effect of compound liquid granulation agent (asphalt + resin))

[0074] Materials: Natural graphite (graphite precursor), pore-forming agent is a compound system of ammonium bicarbonate and urea (mass ratio of ammonium bicarbonate to urea is 1:2.5), liquid granulation agent is a compound of liquid asphalt and liquid phenolic resin (1:1), and catalyst is nickel chloride.

[0075] The specific steps of the preparation method are as follows:

[0076] Step 1, Crushing: Crush the natural graphite to obtain fine powder with an average particle size D50 of 8.0 μm, and particle size distribution D10=4.0 μm, D90=12.0 μm.

[0077] Step 2, Pore Formation: Mix the fine powder and the pore-forming agent at a mass ratio of 4:1, and carry out the pore-forming reaction at 500℃ under a nitrogen atmosphere at a rate of 3℃ / min. Keep warm for 2 hours, and after washing and drying, obtain the porous graphite precursor.

[0078] Step 3, Magnetic field granulation: The porous graphite precursor obtained in Step 2 is mixed evenly with liquid granulation agent (the mass ratio of asphalt to liquid phenolic resin in the liquid granulation agent is 1:1, and the amount of liquid granulation agent is 20wt% of the mass of porous graphite precursor) and nickel chloride (the amount of nickel chloride is 0.1wt% of the mass of porous graphite precursor). The mixture is then cured and granulated for 4 hours under a vertical magnetic field of 0.5T and at 400℃ to obtain porous graphite secondary particles with an average particle size D50 of 20μm.

[0079] Step 4, carbonization: The porous graphite secondary particles are carbonized in stages under nitrogen protection: first, the temperature is increased to 500℃ at 2.5℃ / min and held for 2 hours, then the temperature is increased to 1100℃ at 4.5℃ / min and held for 2 hours to obtain a core-shell structured fast-charging graphite anode material.

[0080] Effect verification:

[0081] Performance: Assembled half-cell testing, such as Figure 5 As shown, the capacity retention rate is 93% after 100 cycles at 6C fast charging; and 89% after 100 cycles at 10C.

[0082] Because the carbon shell formed by the compound liquid granulator combines the flexibility of soft carbon with the support of hard carbon, it has excellent cycle stability.

[0083] Comparative Example 1: Directional granulation without magnetic field (conventional mechanical stirring)

[0084] Deviation point: In step 3, no vertical magnetic field was applied; granulation was performed solely by high-speed mechanical stirring. Specifically, the porous graphite precursor was mixed with liquid phenolic resin and nickel nitrate, and then granulated by mechanical stirring at 350°C without magnetic field assistance. Other parameters were the same as in Example 1. The results are as follows:

[0085] Structure: The graphite microcrystals inside the obtained secondary particles are arranged in a disordered manner, with poor channel connectivity, exhibiting the characteristics of "dead pores".

[0086] Performance: Under 6C fast charging, the capacity retention rate is only 75% after 100 cycles, and under 10C fast charging, the capacity retention rate is only 60%. Due to the lack of magnetic field-induced anisotropic transport channels, lithium-ion transport within the particles is hindered, resulting in severe polarization at high rates.

[0087] Comparative Example 2: Single Pore-Forming Agent

[0088] Deviation point: In step (2), only ammonium bicarbonate was used as the single pore-forming agent (without urea compound), and the other parameters were the same as in Example 2. The results are as follows:

[0089] Structure: A single pore-forming agent can only form pores of a single size or shape, without an effective hierarchical pore structure.

[0090] Performance: 84% capacity retention after 100 cycles of 6C fast charging, and 75% capacity retention after 100 cycles of 10C fast charging.

[0091] Comparative Example 3: Temperature Runaway

[0092] Deviation point: The pore-forming temperature in step (2) was raised to 700℃ (exceeding the range of 400-600℃). Specifically, in step (2), the fine powder was mixed with the pore-forming agent (ammonium bicarbonate and urea compound), and the mixture was heated to 700℃ at a rate of 5℃ / min under a nitrogen atmosphere to carry out the pore-forming reaction. The remaining parameters were the same as in Example 2. The results are as follows:

[0093] Structure: The high temperature of 700℃ caused excessive ablation and collapse of the micropores, resulting in the rupture of the mesopore walls and a sharp decrease in specific surface area to 2m². 2 / g, the hierarchical pore structure may also be lost.

[0094] Performance: 80% capacity retention after 100 cycles of 6C fast charging, and 70% capacity retention after 100 cycles of 10C fast charging.

[0095] Although the pore-forming temperature of Comparative Example 3 was higher than that of Example 2, the structure was damaged due to excessive temperature, and the fast-charging performance was significantly reduced. Comparative Examples 2 and 3 proved the necessity of compound pore-forming agents and specific temperature control windows (400-600°C).

[0096] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for preparing a fast-charging graphite anode material, characterized in that, Includes the following steps: Step 1: Pulverize the graphite precursor to obtain fine powder; Step 2: Mix the fine powder with the pore-forming agent, heat under an inert atmosphere to carry out the pore-forming reaction, keep warm, wash and dry to obtain a porous graphite precursor; Step 3: Mix the porous graphite precursor with liquid granulation agent and catalyst evenly, solidify and granulate under heating conditions, and use the catalyst to induce the porous graphite precursor to oriented arrangement under the action of a vertical magnetic field with an intensity of 0.5-1.5T to obtain porous graphite secondary particles. Step 4: The porous graphite secondary particles obtained in Step 3 are subjected to low-temperature carbonization and high-temperature carbonization under gas protection to obtain a fast-charging graphite anode material with a core-shell structure; the core of the fast-charging graphite anode material is porous graphite secondary particles, and the shell is an amorphous carbon coating layer.

2. The method for preparing a fast-charging graphite anode material according to claim 1, characterized in that, In step 1, the graphite precursor is selected from at least one of natural graphite, artificial graphite, and mesophase carbon microspheres; The average particle size D50 of the fine powder is 4-8 μm, and the particle size distribution satisfies D10≥2 μm and D90≤12 μm.

3. The method for preparing a fast-charging graphite anode material according to claim 1, characterized in that, In step 2, the mass ratio of the fine powder to the pore-forming agent is 4:1; the pore-forming agent is a compound system of ammonium bicarbonate and urea, and the mass ratio of ammonium bicarbonate to urea is 1:(1~3). The heating conditions are as follows: heat to 400-600℃ at a heating rate of 2-5℃ / min under an inert atmosphere, and hold for 1-3 hours.

4. The method for preparing a fast-charging graphite anode material according to claim 1, characterized in that, In step 3, the liquid granulating agent is at least one of liquid asphalt, liquid phenolic resin, liquid epoxy resin, and polyacrylonitrile solution, and the amount of the liquid granulating agent is 5-20% of the mass of the porous graphite precursor; The catalyst is selected from at least one of the metal salts or oxides of iron, cobalt, and nickel, and the amount of the catalyst is 0.01-0.1% of the mass of the porous graphite precursor.

5. The method for preparing a fast-charging graphite anode material according to claim 1, characterized in that, In step 3, the heating temperature for curing and granulation is 180-600℃, and the processing time is 1-4 hours; The average particle size D50 of the porous graphite secondary particles is 8-20 μm, the particle size distribution of the porous graphite secondary particles satisfies D10≥5 μm, D90≤25 μm, and the tap density is 0.8-1.2 g / cm³. 3 .

6. The method for preparing a fast-charging graphite anode material according to claim 1, characterized in that, In step 4, the gas is at least one of nitrogen, argon, and helium; The conditions for low-temperature carbonization are: heating to 400-600℃ at a heating rate of 1-3℃ / min and holding at that temperature for 1-2 hours; The conditions for high-temperature carbonization are: heating to 800-1200℃ at a heating rate of 3-5℃ / min, and holding at that temperature for 2-6 hours.

7. A fast-charging graphite anode material, characterized in that, It is prepared by the method for preparing a fast-charging graphite anode material according to any one of claims 1 to 6.

8. The fast-charging graphite anode material according to claim 7, characterized in that, The fast-charging graphite anode material has a multi-level pore structure, including micropores with a pore size of <2nm, mesopores with a pore size of 2-50nm, and macropores with a pore size of >50nm; the multi-level pores form a through-hole lithium-ion transport network inside the particles.

9. The fast-charging graphite anode material according to claim 7, characterized in that, The fast-charging graphite anode material retains ≥90% capacity after 100 cycles of 6C fast charging and ≥85% capacity after 100 cycles of 10C fast charging.

10. An application of a fast-charging graphite anode material, characterized in that, The fast-charging graphite anode material prepared by any one of claims 1 to 6 or the fast-charging graphite anode material prepared by any one of claims 7 to 9 is used as the anode material of a lithium-ion battery.

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