Depolymerization method of carbon-coated negative electrode material

Abstract

The invention relates to the field of preparation of negative electrode materials, in particular to a depolymerization method of a carbon-coated negative electrode material, which comprises the following steps: (1) carrying out surface activation treatment on an agglomerated carbon-coated negative electrode material to reduce Van der Waals' force among particles; (2) depolymerizing the activated particles through a spinning roller mill, injecting a carbon precursor into the spinning roller mill, and primarily carbonizing the carbon precursor by using friction heat of the spinning roller mill to form a surface repairing layer; and (3) carrying out graded screening on the depolymerized particles, screening out particles with target particle sizes, and carrying out secondary high-temperature carbonization to form a complete carbon coating layer. According to the method, through three-stage process cooperation of surface activation, dynamic carbon repair and closed-loop grading, the bottlenecks of low efficiency, large damage and high cost in the traditional depolymerization technology are broken through, and the economical efficiency of large-scale production is realized while the electrochemical performance of the material is improved.

Description

Technical Field

[0001] The present invention relates to the field of negative electrode material preparation, and in particular to a method for depolymerizing a carbon-coated negative electrode material. Background Art

[0002] With the widespread application of lithium-ion batteries in new energy vehicles, energy storage systems, and portable electronic devices, the demand for high-performance negative electrode materials is becoming increasingly urgent. Carbon-coated negative electrode materials, as an important type of functional material, significantly improve the overall performance of materials by coating a uniform carbon layer on the surface of traditional negative electrode materials such as graphite, silicon-based materials, and hard carbon. The main functions of the carbon coating layer include: enhancing the conductivity of the material and promoting the rapid insertion and extraction of lithium ions; inhibiting the side reactions between the electrolyte and the active material and reducing the irreversible capacity loss; and alleviating the structural collapse caused by volume changes during charge and discharge, thereby improving cycle stability. Especially in silicon-based negative electrode materials, the volume expansion of silicon can reach 300% during the lithiation process. The carbon coating layer can effectively constrain its deformation and extend the battery life. Therefore, carbon coating technology has become a key means to optimize the performance of negative electrode materials.

[0003] However, during the preparation of carbon-coated anode materials, agglomeration has become a major bottleneck restricting their industrial application. Agglomeration typically manifests as particles clumping together due to physical or chemical forces, resulting in uneven particle size distribution, reduced specific surface area, and a reduction in active sites. The causes of this agglomeration are complex and include the following: First, the high surface energy of particles, especially nanomaterials, leads to adsorption of particles dominated by van der Waals forces; second, the high-temperature carbonization of organic precursors (such as phenolic resin and asphalt) used in the carbon coating process may produce sticky intermediates, exacerbating particle adhesion; third, mechanical treatments (such as ball milling and drying) or electrostatic effects further promote agglomeration. For example, during spray drying, rapid solvent evaporation can leave organic matter on the particle surface, forming "adhesive bridges" and leading to secondary agglomeration. This agglomeration not only reduces material processing performance but also creates localized stress concentrations during electrode coating, impacting battery rate performance and cycle life.

[0004] Existing technologies have proposed various solutions to the agglomeration problem of carbon-coated anode materials, but all have significant limitations. Mechanical disaggregation is one of the most widely used methods, such as physical dispersion of agglomerated particles through ball milling or airflow milling. However, while high-energy ball milling can effectively break up agglomerates, over-grinding can lead to rupture of the carbon coating and even damage to the matrix structure, reducing the electrochemical activity of the material. While airflow milling can reduce mechanical contact, it has low efficiency in classifying ultrafine particles (e.g., <1 μm) and results in high equipment energy consumption. Another common strategy is to introduce chemical dispersants, such as surfactants or polymers, to inhibit particle aggregation through electrostatic repulsion or steric hindrance. However, these additives may remain on the material surface, hindering lithium ion transport, or decompose during high-temperature carbonization to produce impurities, affecting material purity. Some studies have attempted to optimize carbon coating process parameters, such as using gradient temperature increases or adjusting precursor concentrations, to reduce agglomeration. However, these methods require extremely high process control precision. Even slight fluctuations in parameters can lead to uneven coating or increased agglomeration, making stability difficult to ensure in actual production.

[0005] In addition, existing depolymerization technologies mostly focus on improving a single link and lack consideration of the coordinated optimization of the entire process. What is more serious is that traditional methods often sacrifice material performance or economy in exchange for depolymerization effects. Therefore, how to achieve efficient depolymerization while taking into account material structure protection, process economy and environmental friendliness has become a technical problem that urgently needs to be broken through in this field. This situation highlights the necessity of developing new depolymerization technologies, and breakthroughs need to be sought in mechanism innovation and process integration to achieve efficient preparation and performance optimization of carbon-coated negative electrode materials. Summary of the Invention

[0006] The present invention aims to overcome the defects of the carbon-coated negative electrode materials in the prior art, such as agglomeration, which leads to uneven particle size distribution, decreased specific surface area and reduced active sites. The solutions proposed in the prior art often sacrifice material performance or economy in exchange for depolymerization effect. A depolymerization method for carbon-coated negative electrode materials is provided to overcome the above-mentioned shortcomings.

[0007] To achieve the above-mentioned purpose, the present invention is implemented through the following technical solutions: In a first aspect, the present invention first provides a method for depolymerizing a carbon-coated negative electrode material, comprising the following steps: (1) Surface activation treatment of agglomerated carbon-coated negative electrode materials to reduce the van der Waals force between particles; (2) The activated particles are deagglomerated by a rotary mill, and a carbon precursor is injected into the mill at the same time. The friction heat of the rotary mill is used to cause the carbon precursor to undergo preliminary carbonization to form a surface repair layer; (3) The depolymerized particles are graded and screened to select particles of target size and then subjected to secondary high-temperature carbonization to form a complete carbon coating layer.

[0008] As one of the core components of lithium-ion batteries, the performance of carbon-coated negative electrode materials directly determines the battery's energy density, cycle life and safety. With the rapid development of the new energy industry, the demand for high-capacity and high-stability negative electrode materials is becoming increasingly urgent, and carbon coating technology has significantly improved the electrochemical performance of traditional negative electrode materials through surface modification. However, in the actual preparation process, the carbon-coated materials often form agglomerates due to the interaction between particles, resulting in uneven particle size distribution, reduced active sites and deteriorated processing performance. Although existing technologies have attempted to solve the agglomeration problem through mechanical depolymerization and chemical dispersion, they often lose sight of one thing while focusing on the other: mechanical depolymerization can easily damage the carbon layer structure, and chemical dispersant residues may introduce impurities, while high-end surface modification technologies are difficult to apply on a large scale due to cost and process complexity. In addition, the depolymerized particles are prone to re-agglomeration due to surface defects in subsequent treatments, further weakening the material performance. This series of problems exposes the shortcomings of existing technologies in the coordinated optimization of depolymerization and repair. There is an urgent need for an innovative method that can both efficiently disperse agglomerates and simultaneously repair carbon layer defects.

[0009] Based on the above-mentioned technical pain points, the depolymerization method proposed in the present invention realizes the optimization of the entire process from suppressing agglomeration at the root to dynamically repairing the carbon layer through multi-step collaborative design.

[0010] Before deagglomeration, the agglomerated particles are first subjected to surface activation treatment, and the van der Waals forces between the particles are weakened by low-temperature plasma or chemical dispersants. The creativity of this step lies in that traditional deagglomeration processes mostly rely directly on mechanical force to break up agglomerates, while ignoring the active regulation of the surface energy of the particles. Surface activation treatment not only reduces the energy consumption of subsequent mechanical deagglomeration, but also reduces the possibility of secondary adhesion of particles from a physical and chemical level, providing a more stable basis for deagglomeration. For example, low-temperature plasma treatment bombards the surface of the particles to remove residual organic matter and form active sites, making the particles easier to disperse rather than reaggregate during the deagglomeration process. This pretreatment strategy is rarely mentioned in the existing technology. Its essence is to change the interaction mode of particles through interface engineering, rather than simply relying on external force destruction.

[0011] During the deagglomeration stage, this application innovatively combines mechanical deagglomeration with the introduction of a carbon precursor, utilizing the frictional heat generated by the high-speed rotation of the mill to trigger the initial carbonization of the carbon precursor. In the prior art, the mill is viewed solely as a purely mechanical deagglomeration tool, and the heat generated is often considered a negative factor that needs to be suppressed. However, this invention breaks with this stereotype by converting frictional heat into a usable energy source, simultaneously achieving deagglomeration and surface repair. Specifically, a liquid or gaseous carbon precursor (such as a phenolic resin solution) is injected into the mill cavity. While the particles are dispersed under mechanical force, frictional heat causes the precursor to partially carbonize at the damaged sites, forming an amorphous carbon layer. This process not only instantly fills the microcracks generated by deagglomeration but also restores the continuity of the carbon coating through an in-situ reaction. Compared to the traditional "deagglomeration first, then repair" step-by-step process, this method significantly shortens the production process through process integration and avoids secondary contamination or agglomeration of particles during transfer. This dynamic repair mechanism has not been reported in existing technologies. Its core lies in transforming the destructive process of depolymerization into an opportunity for surface repair, achieving a synergistic effect of "destruction and repair at the same time".

[0012] During the post-depolymerization processing, a combined strategy of graded screening and secondary high-temperature carbonization further optimizes material properties. Graded screening not only separates particles of acceptable size but also returns substandard coarse powder to the rotary mill for further processing, creating a closed-loop control system. Secondary high-temperature carbonization targets the amorphous properties of the initial carbonized layer, completing the graphitization and crystallization of the carbon layer at a higher temperature (800-900°C), improving its conductivity and structural stability. This step is innovative in two ways: First, the coarse powder recirculation mechanism of graded screening addresses the low waste utilization rate of traditional processes, reducing material waste through recycling. Second, secondary carbonization is not a simple repetition of high-temperature treatment, but rather targeted optimization of the properties of the initial carbonized layer. For example, while the amorphous carbon layer formed by the initial carbonization can immediately repair surface defects, its conductivity is still inferior to that of the graphitized carbon layer. Secondary carbonization, through precise control of temperature and time, further enhances the properties of the carbon layer on top of this repair. This staged carbonization strategy not only avoids the potential damage to the matrix material caused by a single high-temperature treatment, but also achieves a step-by-step improvement in the quality of the carbon layer through a gradient process.

[0013] From the perspective of technical results, the creative breakthrough of this method is reflected in three core advantages. First, the synergistic effect of surface activation and deagglomeration by rotary milling significantly reduces the energy consumption of deagglomeration. Traditional mechanical deagglomeration requires high rotation speed or long-term grinding to achieve the ideal dispersion effect, while surface activation pretreatment reduces the interaction force between particles, thereby effectively reducing the energy consumption of deagglomeration. Second, the in-situ carbonization repair mechanism of the carbon precursor effectively solves the problem of carbon layer damage caused by mechanical deagglomeration. In traditional deagglomeration processes, carbon layer rupture exposes the matrix material and triggers electrolyte side reactions. However, this method significantly reduces damage through instant repair, which is the first time that the Coulomb efficiency has been significantly improved. Finally, the integrated design of the process significantly improves production economy. The utilization of friction heat from rotary milling reduces the need for external heating, and the closed-loop process of graded screening and secondary carbonization reduces waste disposal costs. The overall process is compatible with existing production line equipment, and the return on investment cycle is significantly shortened compared to traditional methods. These technical effects are not achieved by the superposition of single improvements, but through the organic connection and synergy of multiple steps, forming a new process paradigm.

[0014] This method demonstrates significant technical scalability: by adjusting the carbon precursor type (e.g., using a bio-based dispersant or a silicon-carbon composite precursor), it can be adapted to new systems such as silicon-based anodes and hard carbon materials. By optimizing grading parameters and carbonization conditions, the differentiated requirements for particle size distribution and carbon layer performance can be met in different application scenarios. This flexibility makes it applicable not only to current mainstream graphite anodes but also provides technical reserves for future applications in emerging fields such as sodium-ion batteries and solid-state batteries.

[0015] In summary, the creativity of this depolymerization method stems from a profound insight into the limitations of existing technologies and the reintegration of cross-disciplinary technical elements. Through the three-step synergy of surface activation pretreatment, in-situ repair driven by rotary friction heat, and graded-carbonization closed-loop control, it breaks through the conflicting relationship between depolymerization and repair in traditional processes, achieving efficient preparation and performance improvement of carbon-coated negative electrode materials. This technical solution not only solves the industry's long-standing agglomeration problem, but also provides a new technical path for upgrading lithium-ion battery negative electrode materials through process innovation.

[0016] Preferably, the surface activation treatment in step (1) is low-temperature plasma treatment.

[0017] Low-temperature plasma treatment effectively removes residual organic matter or impurities by bombarding the particle surface with high-energy particles, preventing these contaminants from becoming binding agents for secondary agglomeration in subsequent processes, thereby fundamentally reducing unintended interparticle adhesion. Secondly, plasma treatment can reduce the particle surface energy through physical etching and chemical modification. For example, by forming micro- and nano-scale rough structures on the material surface or introducing oxygen-containing polar groups, it significantly weakens the van der Waals forces that dominate agglomeration and reduces the interaction forces between particles. This surface energy manipulation not only reduces the energy consumption required for mechanical deagglomeration (for example, the rotary milling speed can be reduced to 6000-8000 rpm) but also improves dispersion efficiency, making it easier for deagglomerated particles to maintain a monodisperse state. Furthermore, the active sites generated by plasma treatment (such as free radicals or defects) enhance the binding ability of the carbon precursor to the particle surface. In particular, during the subsequent in situ carbonization step, the amorphous carbon layer can be more uniformly anchored to the activated surface, filling the microcracks generated by deagglomeration, thereby improving the continuity and conductivity of the carbon coating. Compared to chemical dispersant treatment, plasma treatment requires no exogenous additives, avoiding the negative impact of residues on electrode performance (such as sodium ion contamination or increased interfacial impedance), while also avoiding the environmental issues associated with solvent use. More importantly, this technology precisely controls the depth of surface activation through parameter optimization, avoiding substrate damage caused by overtreatment while ensuring consistent activation results, providing a reliable technical path for industrial large-scale production.

[0018] Preferably, the low-temperature plasma treatment uses an Ar / N2 mixed gas with a power of 200-800 W and a treatment time of 5-15 minutes.

[0019] Preferably, the rotation speed of the rotary mill in step (2) is 6000-10000 rpm, and an inert gas is introduced to isolate oxygen.

[0020] Preferably, the inert gas includes any one of nitrogen, helium and argon.

[0021] Preferably, in step (2), the carbon precursor is injected in the form of a solution, including any one of a phenolic resin solution, a polyvinyl alcohol solution, a glucose solution, and a sucrose solution.

[0022] Preferably, the concentration of the carbon precursor solution is 5-15 wt %, and the injection amount of the carbon precursor solution is 0.5-2 wt % of the mass of the particles.

[0023] Preferably, the target particle size range of 1-20 μm is obtained by screening in step (3), and the particles with a particle size range greater than 20 μm are returned to step (2) for re-deagglomeration.

[0024] Preferably, the secondary high-temperature carbonization in step (2) is carried out in a fluidized bed carbonization furnace at a temperature of 800-900° C. for 30-60 minutes.

[0025] Preferably, the carbon-coated negative electrode material includes any one of a carbon-coated graphite material, a carbon-coated silicon-carbon composite material, a carbon-coated hard carbon material or a carbon-coated sodium ion battery negative electrode material.

[0026] Therefore, the present invention has the following beneficial effects: This invention utilizes a three-stage process—surface activation, dynamic carbon repair, and closed-loop fractionation—to overcome the bottlenecks of low efficiency, high damage, and high cost associated with traditional depolymerization techniques. This technology improves the electrochemical performance of the material while achieving the economic feasibility of large-scale production. By transforming "destructive depolymerization" into "restorative processing," it provides an industrially feasible technical path for the development of next-generation high-capacity anode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an electron microscope image of the depolymerized carbon-coated graphite particles in Example 1 of the present application. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below generally represent only a portion of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0029] Example 1 A method for depolymerizing a carbon-coated negative electrode material comprises the following steps: Step (1) Surface activation treatment: The agglomerated carbon-coated graphite material was placed in a low-temperature plasma treatment device, and an Ar / N2 mixed gas (volume ratio 8:2) was introduced. The power was set to 200 W and the treatment time was 5 minutes. After plasma bombardment, the residual organic matter on the particle surface was removed.

[0030] Step (2) Depolymerization and Preliminary Carbonization in a Rotary Mill: The activated particles were placed in a rotary mill at a speed of 6000 rpm. Argon was introduced to isolate oxygen, and a phenolic resin solution (5 wt% concentration, 0.5 wt% of the activated particles) was simultaneously injected in the form of a spray. The frictional heat of the rotary mill caused the resin to coat the particle surface and preliminarily carbonize, forming an amorphous carbon layer with a thickness of approximately 5 nm.

[0031] Step (3) Classification and screening and secondary carbonization: The depolymerized particles are passed through a centrifugal airflow classifier to screen out qualified particles with a particle size of 1-20 μm, and the coarse powder (>20 μm) is returned to the rotary mill. The qualified particles are fed into the fluidized bed carbonization furnace at a feeding rate of 30 kg / h. Ar gas is introduced from the bottom of the bed at a gas supply rate of 300 L / min to form a gas-solid fluidized state. The temperature rise curve of the fluidized bed carbonization furnace is as follows: preheating stage: from room temperature to 400 ° C at a rate of 12 ° C / min; medium temperature carbonization stage: heating to 800 ° C at a rate of 8 ° C / min; constant temperature stage: maintain the target temperature (800 ° C) for 30 minutes to suspend the particles and heat them evenly. The final coating thickness is 20 nm. Figure 1 This is an electron microscope image of the depolymerized carbon-coated graphite particles prepared in this application.

[0032] Example 2 A method for depolymerizing a carbon-coated negative electrode material comprises the following steps: Step (1) Surface activation treatment: The agglomerated carbon-coated silicon-carbon composite material was placed in a low-temperature plasma treatment device, and an Ar / N2 mixed gas (volume ratio 7:3) was introduced at a power of 800 W for 15 minutes. After the treatment, a micron-scale rough structure was formed on the surface of the particles.

[0033] Step (2) Depolymerization and Preliminary Carbonization by Rotary Milling: The activated particles were placed in a rotary mill at a speed of 10,000 rpm. A nitrogen atmosphere was introduced and a glucose solution (15 wt% concentration, equivalent to 2 wt% of the activated particles) was injected as a spray. Frictional heat (local temperature 400°C) caused the glucose to coat the particle surface and partially carbonize, forming a 10 nm amorphous carbon layer.

[0034] Step (3) Classification and secondary carbonization: The depolymerized particles are screened by a centrifugal airflow classifier to obtain particles with a particle size of 1-20 μm, and the coarse powder is refluxed. The qualified particles are fed into a fluidized bed carbonization furnace at a feeding rate of 30 kg / h. Ar gas is introduced from the bottom of the bed at a gas supply rate of 400 L / min to form a gas-solid fluidized state. The temperature rise curve of the fluidized bed carbonization furnace is as follows: preheating stage: from room temperature to 450°C at a rate of 15°C / min; medium temperature carbonization stage: heating to 900°C at a rate of 5°C / min; constant temperature stage: maintaining the target temperature (900°C) for 60 minutes to suspend the particles and heat them evenly. The final coating thickness is 50 nm.

[0035] Example 3 A method for depolymerizing a carbon-coated negative electrode material comprises the following steps: Step (1) Surface activation treatment: Step (1) Surface activation treatment: The agglomerated carbon-coated graphite material is placed in a low-temperature plasma treatment device, and an Ar / N2 mixed gas (volume ratio 8:2) is introduced. The power is set to 200 W and the treatment time is 5 minutes. After plasma bombardment, the residual organic matter on the particle surface is removed.

[0036] Step (2) Depolymerization and Preliminary Carbonization by Rotary Milling: The activated particles were placed in a rotary mill at a speed of 8000 rpm. Helium was introduced and a sucrose solution (10 wt% concentration, 1.25 wt% of the activated particles) was injected as a spray. The frictional heat from the rotary milling caused the sucrose to coat the particle surface and undergo preliminary carbonization, forming an amorphous carbon layer approximately 15 nm thick, repairing surface microcracks.

[0037] Step (3) Classification and secondary carbonization: The depolymerized particles are passed through a centrifugal airflow classifier to screen out particles with a particle size of 10 μm, and the coarse powder is returned to the rotary mill. The qualified particles are fed into the fluidized bed carbonization furnace at a feeding rate of 30 kg / h. Ar gas is introduced from the bottom of the bed at a gas supply rate of 400 L / min to form a gas-solid fluidized state. The temperature rise curve of the fluidized bed carbonization furnace is as follows: preheating stage: from room temperature to 450°C at a rate of 15°C / min; medium temperature carbonization stage: from room temperature to 850°C at a rate of 10°C / min; constant temperature stage: maintain the target temperature (850°C) for 60 minutes to suspend the particles and heat them evenly. The final coating thickness is 30 nm.

[0038] Example 4 A method for depolymerizing a carbon-coated negative electrode material comprises the following steps: Step (1) Surface activation treatment: The agglomerated carbon-coated graphite material is placed in a low-temperature plasma treatment device, and an Ar / N2 mixed gas (Ar / N2=6:4) is introduced at a power of 500 W for 10 minutes. After plasma bombardment, the residual organic matter on the particle surface is removed.

[0039] Step (2) Depolymerization and preliminary carbonization in a rotary mill: The activated particles were placed in a rotary mill with a rotation speed of 7000 rpm. Argon was introduced and a phenolic resin solution (concentration 8 wt%, injection amount 1.0 wt% of the activated particles) was injected in the form of a spray. The friction heat of the rotary mill caused the resin to coat the surface of the particles and undergo preliminary carbonization, forming an amorphous carbon layer with a thickness of about 8 nm.

[0040] Step (3) Classification and secondary carbonization: The deagglomerated particles are passed through a centrifugal airflow classifier to screen out particles with a particle size of 5 μm and enter the fluidized bed furnace. The coarse powder (>20 μm) is returned to the rotary mill. The qualified particles are fed into the fluidized bed carbonization furnace at a feeding rate of 30 kg / h. Ar gas is introduced from the bottom of the bed at a gas supply rate of 400 L / min to form a gas-solid fluidized state. The temperature rise curve of the fluidized bed carbonization furnace is as follows: preheating stage: from room temperature to 450°C at a rate of 15°C / min; medium temperature carbonization stage: heating to 820°C at a rate of 5°C / min; constant temperature stage: maintaining the target temperature (820°C) for 40 minutes to suspend the particles and heat them evenly. The carbon layer thickness is 25 nm.

[0041] Example 5 A method for depolymerizing a carbon-coated negative electrode material comprises the following steps: Step (1) Surface activation treatment: The agglomerated carbon-coated graphite material is placed in a low-temperature plasma treatment device, and an Ar / N2 mixed gas (Ar / N2=9:1) is introduced. The power is set to 300 W and the time is 8 minutes. After plasma bombardment, the residual organic matter on the surface of the particles is removed.

[0042] Step (2) Depolymerization and preliminary carbonization by rotary milling: The activated particles were put into a rotary mill at a speed of 9000 rpm, nitrogen was introduced, and polyvinyl alcohol solution (concentration 12 wt%, injection amount 1.5 wt% of the activated particles) was injected in the form of a spray. The friction heat of the rotary milling caused the polyvinyl alcohol to coat the surface of the particles and preliminarily carbonize, forming an amorphous carbon layer with a thickness of about 5 nm.

[0043] Step (3) Classification and screening and secondary carbonization: The depolymerized particles are passed through a centrifugal airflow classifier to screen out particles with a particle size of 15 μm, and the coarse powder is refluxed. The qualified particles are fed into a fluidized bed carbonization furnace at a feeding rate of 50 kg / h. Ar gas is introduced from the bottom of the bed at a gas supply rate of 500 L / min to form a gas-solid fluidized state. The temperature rise curve of the fluidized bed carbonization furnace is as follows: preheating stage: heating from room temperature to 400°C at a rate of 10°C / min; medium temperature carbonization stage: heating to 880°C at a rate of 5°C / min; constant temperature stage: maintaining the target temperature (880°C) for 50 minutes to suspend the particles and heat them evenly, and finally obtaining a carbon coating with a thickness of 40 nm.

[0044] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the surface activation treatment is skipped, and the agglomerated carbon-coated graphite material is directly subjected to rotary milling for depolymerization, and no phenolic resin solution is injected during the depolymerization process.

[0045] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the surface activation treatment is skipped, and the agglomerated carbon-coated graphite material is directly subjected to rotary milling for deagglomeration, and the phenolic resin solution is injected during the deagglomeration process.

[0046] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that no phenolic resin solution is injected during the deagglomeration process of the agglomerated carbon-coated graphite material by rotary milling.

[0047] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that in step (3), no classification and screening is performed, and all particles are directly subjected to secondary carbonization.

[0048] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that in step (1), a sodium polyacrylate solution (concentration 1 wt%) was used for immersion treatment for 30 min, and no plasma activation was performed.

[0049] The carbon-coated negative electrode materials obtained after depolymerization in Examples 1-5 and Comparative Examples 1-5 were tested, and the testing methods are as follows.

[0050] 1. Particle size distribution Testing instrument: laser particle size analyzer (Malvern Mastersizer 3000); Method: 0.2 g of material was dispersed in ethanol and ultrasonicated for 10 minutes, and the D50 value was determined.

[0051] 2. Integrity of carbon coating Testing instrument: transmission electron microscope (TEM, JEOL JEM-2100F); Methods: 300 particles were randomly selected to calculate the carbon layer damage rate (percentage of damaged particles).

[0052] 3. First Coulombic Efficiency (ICE) Battery assembly: CR2032 button cell (active material: acetylene black: binder = 8:1:1, lithium sheet as counter electrode, electrolyte: 1M LiPF6 in EC / DEC); Test conditions: 0.1 C charge and discharge (0.005-2 V), calculate the first discharge / charge capacity ratio.

[0053] 4. Cyclic stability Test: Record the capacity retention of the battery after 300 cycles at 1 C.

[0054] 5. 3C double charge capacity retention rate Test: Record the capacity retention of the battery after 100 cycles at 3 C.

[0055] 6. Compaction density Method: The negative electrode material, acetylene black, and binder (PVDF) were mixed in a mass ratio of 90:5:5, NMP solvent was added to prepare the slurry, and the mixture was coated on a copper foil. The mixture was vacuum dried at 120 ° C for 12 hours, and cut into electrodes with a diameter of 10 mm. The electrode mass (m) and thickness (initial thickness h0) were recorded. A fixed pressure (usually 10-20 MPa) was applied to the electrode using a tablet press (such as MTI MSK-110). The pressure was maintained for 30 seconds, and the thickness of the electrode after compaction (h1) was measured. The compaction density = m / (πr 2 h1) (where r is the pole piece radius, unit: cm; h1 is the thickness after compaction, unit: cm).

[0056] 7. Specific surface area test: Method: Take 50-100 mg of material powder and place it in a vacuum degassing station (such as Micromeritics VacPrep 061) for 6 hours at 200°C to remove surface adsorbents. Then use a specific surface area analyzer (such as Micromeritics ASAP2460) to perform nitrogen adsorption-desorption tests at liquid nitrogen temperature (77 K).

[0057] The test results of the carbon-coated negative electrode materials obtained after depolymerization in Examples 1-5 and Comparative Examples 1-5 are shown in Table 1 below.

[0058] Table 1 Comparing the data in Table 1, Examples 1-5 employing the present invention demonstrate comprehensive performance advantages over Comparative Examples 1-5: The integrity of the carbon coating is significantly improved, achieving both high initial Coulombic efficiency and excellent cycling stability. Benefiting from the dense conductive network formed by dynamic repair through rotary milling and gradient carbonization, the Examples demonstrate high rate performance, with capacity retention rates reaching 30.6%-32.9% after 100 cycles at 3C (exceeding that of the Comparative Example by over 40%). Furthermore, through a coordinated strategy of particle size optimization and pore control, the Examples achieve a balance between high compaction density and a moderate specific surface area, avoiding side reactions associated with high specific surface area while ensuring efficient ion diffusion. Uncontrolled surface energy in Comparative Example 1 (no activation and repair) and Comparative Example 5 (chemical immersion pretreatment) leads to carbon layer fragmentation and excessive electrolyte infiltration, fully demonstrating the technical necessity of plasma activation and in-situ carbon repair, and demonstrating the irreplaceable nature of the three-step synergistic process for depolymerization, repair, and densification, providing a reliable path for the industrialization of high-energy, fast-charging lithium battery anode materials.

[0059] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A method for depolymerizing a carbon-coated negative electrode material, characterized in that: The following steps are involved: (1) Surface activation treatment of agglomerated carbon-coated negative electrode materials to reduce the van der Waals force between particles; (2) The activated particles are deagglomerated by a rotary mill, and a carbon precursor is injected into the mill at the same time. The friction heat of the rotary mill is used to cause the carbon precursor to undergo preliminary carbonization to form a surface repair layer; (3) The depolymerized particles are graded and screened to select particles of target size and then subjected to secondary high-temperature carbonization to form a complete carbon coating layer.

2. The method according to claim 1, characterized in that The surface activation treatment in step (1) is low-temperature plasma treatment.

3. The method according to claim 2, characterized in that The low-temperature plasma treatment uses Ar / N2 mixed gas with a power of 200-800 W and a treatment time of 5-15 minutes.

4. The method according to claim 1, wherein In step (2), the rotation speed of the rotary mill is 6000-10000 rpm, and an inert gas is introduced to isolate oxygen.

5. The method according to claim 1, wherein The inert gas includes any one of nitrogen, helium and argon.

6. The method according to claim 1, characterized in that In step (2), the carbon precursor is injected in the form of a solution, including any one of a phenolic resin solution, a polyvinyl alcohol solution, a glucose solution, and a sucrose solution.

7. The method according to claim 1 or 6, characterized in that The concentration of the carbon precursor solution is 5-15 wt %, and the injection amount of the carbon precursor solution is 0.5-2 wt % of the particle mass.

8. The method according to claim 1, characterized in that In the step (3), target particles with a particle size range of 1-20 μm are obtained by screening, and particles with a particle size range of more than 20 μm are returned to the step (2) for re-deagglomeration.

9. The method according to claim 1 or 8, characterized in that The secondary high-temperature carbonization in step (2) is carried out in a fluidized bed carbonization furnace at a temperature of 800-900° C. for 30-60 minutes.

10. The method according to claim 1, characterized in that The carbon-coated negative electrode material includes any one of a carbon-coated graphite material, a carbon-coated silicon-carbon composite material, a carbon-coated hard carbon material or a carbon-coated sodium ion battery negative electrode material.

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