Carbon-based composite negative electrode material and preparation method thereof

Abstract

This invention relates to the field of lithium-ion battery anode material technology, specifically to a carbon-based composite anode material and its preparation method, which is prepared from the following raw materials in parts by weight: 40-60 parts natural graphite, 25-40 parts modified hard carbon, 5-8 parts silicon dopant, 2-4 parts boron dopant, 2.5-4 parts sodium carboxymethyl cellulose, 2-3 parts graphene, and 100-120 parts deionized water, wherein the modified hard carbon has a specific surface area of ​​500-800 m². 2 / g; the raw material also contains 4-5 parts of phosphorus dopant, or simultaneously contains 4-5 parts of phosphorus dopant and 1-1.5 parts of phenolic resin. The carbon-based composite anode material and its preparation method provided by the present invention effectively solve the technical problem that existing carbon-based composite anode materials are difficult to balance in terms of performance, and achieve simultaneous improvement in specific capacity, rate performance and cycle stability, and significantly optimize the overall electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a carbon-based composite anode material and its preparation method. Background Technology

[0002] Lithium-ion batteries have become core energy storage devices in the new energy field due to their advantages such as high energy density, long cycle life, and environmental friendliness. As a key component of lithium-ion batteries, the performance of the anode material directly determines the overall performance of the battery. Natural graphite, due to its stable layered structure and mature lithium storage mechanism, is currently the most widely used anode material in commercial applications. However, natural graphite itself has a bottleneck in specific capacity, and its rate performance and cycle stability are difficult to meet the application requirements of high-energy-density batteries.

[0003] To improve the performance of graphite-based anode materials, the industry often uses graphite-hard carbon composites for modification. Hard carbon has abundant lithium storage sites, which can compensate for the insufficient specific capacity of graphite. However, the composite system of graphite and hard carbon is prone to poor compatibility, resulting in high interfacial impedance. Doping modification and coating are common methods to improve the electrochemical performance of carbon-based materials. Traditional doping often uses binary element doping, which has limited effect on improving electron transport efficiency, while the modification effect of single element doping is even weaker. Coating processes often use a single material, resulting in insufficient coating density. The material is susceptible to electrolyte erosion during cycling, causing structural damage and decreased cycle stability.

[0004] Meanwhile, existing preparation processes mostly employ a single heat treatment method, resulting in low bonding between the dopant elements and the carbon matrix. Furthermore, the process sequence often involves mixing carbon materials first, followed by doping, leading to insufficient hard carbon modification, an unreasonable material pore structure, and limited ion transport efficiency. Existing improvement schemes are mostly simple technology aggregations, failing to achieve synergistic control of each process step. This results in a difficulty in simultaneously achieving high specific capacity, rate performance, and cycle stability in carbon-based composite anode materials, making them unsuitable for the high-energy, long-life demands of lithium-ion batteries. Therefore, developing a carbon-based composite anode material with excellent comprehensive electrochemical performance and its preparation method is of significant practical importance. Summary of the Invention

[0005] The primary objective of this invention is to provide a carbon-based composite anode material and its preparation method.

[0006] A further objective of this invention is to provide a carbon-based composite anode material, prepared from the following raw materials in parts by weight: 40-60 parts natural graphite, 25-40 parts modified hard carbon, 5-8 parts silicon dopant, 2-4 parts boron dopant, 2.5-4 parts sodium carboxymethyl cellulose, 2-3 parts graphene, and 100-120 parts deionized water, wherein the modified hard carbon has a specific surface area of ​​500-800 m². 2 / g; the raw material also contains 4-5 parts of phosphorus dopant, and the raw material may further contain 1-1.5 parts of phenolic resin.

[0007] Preferably, it includes the following steps:

[0008] (1) Add natural graphite with a particle size of 1-5 μm to deionized water and ball mill it in a planetary ball mill to obtain a graphite dispersion.

[0009] (2) Add modified hard carbon, silicon dopant, and boron dopant to the graphite dispersion. If the raw material contains phosphorus dopant, add phosphorus dopant at the same time. Then, ball mill the mixture in a planetary ball mill at a temperature not exceeding 50 degrees Celsius to obtain a composite dispersion.

[0010] (3) Add sodium carboxymethyl cellulose to the composite dispersion and stir to form a uniform slurry; (4) Coat the slurry onto copper foil and dry it under vacuum to obtain the precursor;

[0011] (5) Place the precursor in a tube furnace, introduce argon gas for the first heat treatment, and then coat it after cooling.

[0012] (6) The coated product is placed in a tube furnace again, and argon gas is introduced for a second heat treatment. After cooling, it is crushed through a 200-mesh sieve to obtain carbon-based composite anode material.

[0013] Preferably, in step (1), the ball-to-material ratio of the ball mill is 15:1, the rotation speed is 300 revolutions per minute, and the ball milling time is 2 hours.

[0014] Preferably, in step (2), the ball-to-material ratio of the ball mill is 18:1, the rotation speed is 350 revolutions per minute, the ball milling time is 3-5.5 hours, the ball milling adopts an intermittent mode, and the machine is stopped for 10 minutes every 1 hour of ball milling. During the intermittent process, the temperature of the ball milling system is kept below 50 degrees Celsius.

[0015] Preferably, the stirring temperature in step (3) is 25-30 degrees Celsius and the stirring time is 2.5-3 hours.

[0016] Preferably, in step (4), the slurry coating thickness is 100-120 micrometers, the vacuum drying temperature is 80-85 degrees Celsius, and the drying time is 5-6 hours.

[0017] Preferably, in step (5), the heating rate of the first heat treatment is 5 degrees Celsius per minute, the heat treatment temperature is 700-750 degrees Celsius, and the holding time is 3-4 hours.

[0018] Preferably, in step (6), the heating rate of the second heat treatment is 3 degrees Celsius per minute, the heat treatment temperature is 900-950 degrees Celsius, and the holding time is 2-2.5 hours.

[0019] Preferably, one of the following two options shall be implemented:

[0020] Option 1, the coating treatment in step (5) is a composite coating of graphene and phenolic resin. The specific operation is as follows: mix graphene and phenolic resin at a mass ratio of 4:3, add deionized water to make a coating solution with a mass concentration of 5%, immerse the product after the first heat treatment in the coating solution, use a 200-watt ultrasonic cell disruptor to ultrasonically disperse for 30 minutes, drain the excess coating solution and then perform a second heat treatment.

[0021] Option 2, step (2) is replaced with the following operation: Add modified hard carbon, silicon dopant, boron dopant, phosphorus dopant and 50 parts of deionized water to a planetary ball mill and ball mill for 3 hours. The ball-to-material ratio is 18:1 and the speed is 350 rpm. Use intermittent ball milling mode, stop for 10 minutes after every 1 hour of ball milling, then add natural graphite and the remaining deionized water and continue ball milling for 3 hours. Keep the ball-to-material ratio at 18:1 and the speed at 300 rpm. The ball milling temperature does not exceed 50 degrees Celsius to obtain a composite dispersion.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. The carbon-based composite anode material and its preparation method provided by the present invention effectively solve the technical problem that the performance of existing carbon-based composite anode materials is difficult to balance, and achieve simultaneous improvement in specific capacity, rate performance and cycle stability, and significantly optimize the overall electrochemical performance.

[0024] 2. This invention optimizes the composite ratio of natural graphite and modified hard carbon, taking into account both the structural stability and lithium storage capacity of carbon-based materials. Combined with the synergistic effect of the silicon-boron-phosphorus ternary doping system, it effectively regulates the electronic structure of the carbon matrix, improves the electronic transport performance of the material, solves the problem of poor modification effect of traditional doping methods, and enhances the conductivity of the material.

[0025] 3. The present invention employs a two-stage gradient heat treatment process to promote the solid solution bonding of dopant elements and carbon matrix in stages, thereby improving the dispersion uniformity of dopant elements, enhancing the structural stability of the material, and avoiding the defects of insufficient dopant bonding caused by single heat treatment.

[0026] 4. At the same time, the present invention adopts a composite coating process of graphene and phenolic resin, which significantly improves the density and bonding force of the coating layer compared with single material coating. It can effectively prevent the electrolyte from eroding the material matrix, reduce the structural damage of the material during cycling, and greatly improve the cycling stability of the material.

[0027] 5. This invention optimizes the ball milling parameters and process operation sequence. By first doping and modifying hard carbon and then combining it with natural graphite, the pore structure of the material is optimized and the ion transport efficiency is improved. At the same time, the intermittent ball milling mode further ensures the uniform dispersion of each component.

[0028] 6. The preparation method of the present invention has controllable process parameters, coordinated operation of each process step, simple and easy operation, no special equipment required, and is suitable for large-scale industrial production. It provides a practical and feasible technical solution for the development of high-performance negative electrode materials for lithium-ion batteries and has good industrial application prospects. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0030] Example 1:

[0031] The raw materials for preparation, by weight, are: 60 parts natural graphite, 25 parts modified hard carbon, 5 parts silicon dopant, 3 parts boron dopant, 4 parts sodium carboxymethyl cellulose, 100 parts deionized water, and 2 parts coating agent graphene.

[0032] Preparation steps:

[0033] Natural graphite with a particle size of 1-5μm was placed in a planetary ball mill, deionized water was added, the ball-to-material ratio was adjusted to 15:1, the speed was 300 rpm, and the milling was carried out for 2 hours to obtain a uniform graphite dispersion.

[0034] Modified hard carbon, silicon dopant, and boron dopant were added to the graphite dispersion, and ball milling was continued for 4 hours, with the ball milling temperature controlled not to exceed 50 degrees Celsius, to obtain a composite dispersion. During this period, the mixture was stirred for 10 minutes every 1 hour to ensure that the dopant elements were uniformly dispersed.

[0035] Sodium carboxymethyl cellulose was added to the composite dispersion and stirred at 25 degrees Celsius for 3 hours to form a uniform slurry.

[0036] The slurry was coated onto copper foil to a thickness of 100 micrometers and then placed in a vacuum drying oven at 80 degrees Celsius for 6 hours to obtain the precursor.

[0037] The precursor was placed in a tube furnace, and inert argon gas was introduced. The heating rate was controlled at 5 degrees Celsius per minute. The temperature was raised to 700 degrees Celsius and held for 3 hours to complete the first heat treatment.

[0038] The product after the first heat treatment was taken out, cooled to room temperature, and graphene coating agent was sprayed evenly. It was then placed back into the tube furnace, argon gas was introduced, the temperature was raised to 900 degrees Celsius at a rate of 3 degrees Celsius per minute, and held for 2 hours to complete the second heat treatment.

[0039] After cooling to room temperature, the material is pulverized and passed through a 200-mesh sieve to obtain a carbon-based composite anode material.

[0040] Example 2:

[0041] Based on the core process framework of Example 1, and addressing the technical deficiency that there is still room for improvement in the specific capacity of Example 1, this example optimizes the composite ratio of natural graphite and modified hard carbon, increases the amount of dopant, and fine-tunes the process parameters to further improve the specific capacity and rate performance of the material.

[0042] The raw materials for preparation, by weight, are: 50 parts natural graphite, 35 parts modified hard carbon, 8 parts silicon dopant, 4 parts boron dopant, 3 parts sodium carboxymethyl cellulose, 110 parts deionized water, and 3 parts coating agent graphene.

[0043] Preparation steps:

[0044] Using the ball milling parameters from step 1 of Example 1, natural graphite was prepared into a graphite dispersion.

[0045] The ball milling time was adjusted to 5 hours, with all other parameters remaining the same as in step 2 of Example 1. Modified hard carbon, silicon dopant, and boron dopant were added to obtain a composite dispersion. By extending the ball milling time, the bonding degree between the dopant elements and the carbon matrix was improved, thus solving the technical defect of insufficient uniform dispersion of dopant elements in Example 1.

[0046] Sodium carboxymethyl cellulose was added to the composite dispersion and stirred at 30°C for 2.5 hours to form a homogeneous slurry. The stirring temperature was adjusted to optimize the slurry viscosity and accommodate a higher proportion of hard carbon.

[0047] The coating thickness was adjusted to 120 micrometers, the vacuum drying temperature was 85 degrees Celsius, and the drying time was 5 hours to obtain the precursor. The coating thickness and drying parameters were adjusted to ensure the precursor molding quality and to meet the performance requirements after the increase in the hard carbon proportion.

[0048] The first heat treatment involved maintaining a heating rate of 5 degrees Celsius per minute, raising the temperature to 750 degrees Celsius, and holding it at that temperature for 3 hours. Increasing the heat treatment temperature promotes the solid solution of the dopant elements, further improving the material's conductivity.

[0049] Using the coating and second heat treatment parameters from step 6 of Example 1, the coating and second heat treatment were completed.

[0050] After cooling to room temperature, the material is pulverized and passed through a 200-mesh sieve to obtain a carbon-based composite anode material.

[0051] Example 3:

[0052] Based on the formulation and process of Example 2, and addressing the technical deficiency that there is still room for improvement in electron transport efficiency in Example 2, this example introduces phosphorus dopant as a third doping element to form a ternary doping system with silicon and boron, synergistically regulating electron transport efficiency. At the same time, the ball milling parameters and heat treatment temperature are optimized to further improve the rate performance and cycle stability of the material.

[0053] The raw materials for preparation, by weight, are: 45 parts natural graphite, 38 parts modified hard carbon, 6 parts silicon dopant, 3 parts boron dopant, 4 parts phosphorus dopant, 3 parts sodium carboxymethyl cellulose, 115 parts deionized water, and 2.5 parts graphene coating agent.

[0054] Preparation steps:

[0055] Using the ball milling parameters from step 1 of Example 2, a graphite dispersion was prepared.

[0056] Modified hard carbon, silicon dopant, boron dopant, and phosphorus dopant with a specific surface area of ​​500-800 m² / g were added to the graphite dispersion. The ball milling time was adjusted to 5.5 hours, the ball-to-material ratio to 18:1, and the rotation speed to 350 rpm. An intermittent ball milling mode was adopted (the mill was stopped for 10 minutes after every hour of ball milling). By optimizing the ball milling parameters, the uniform dispersion of the ternary dopant elements was ensured, agglomeration was avoided, and the technical defect of insufficient electron transport efficiency caused by uneven dispersion of dopant elements in Example 2 was solved.

[0057] Using the same stirring parameters as in step 3 of Example 2, sodium carboxymethyl cellulose was added to prepare a uniform slurry;

[0058] The coating thickness is 110 micrometers, the vacuum drying temperature is 82 degrees Celsius, and the drying time is 5.5 hours. The coating thickness and drying effect are balanced to ensure the stability of the precursor performance.

[0059] The first heat treatment involves a heating rate of 5 degrees Celsius per minute, reaching a temperature of 720 degrees Celsius, and holding at that temperature for 3.5 hours. This is suitable for ternary doping systems, promoting the synergistic effect between the dopant elements and the carbon matrix, and further improving electron transport efficiency.

[0060] The second heat treatment involves heating to 950 degrees Celsius and holding at that temperature for 2 hours, with a heating rate of 3 degrees Celsius per minute. Increasing the temperature of the second heat treatment enhances the adhesion between the coating layer and the substrate, while also promoting the diffusion of dopants, further optimizing the material structure.

[0061] After cooling to room temperature, the material is pulverized and passed through a 200-mesh sieve to obtain a carbon-based composite anode material.

[0062] Example 4:

[0063] Based on the core system of Example 3, and addressing the technical shortcomings of Example 3 where there is still room for improvement in cycle stability, this example optimizes the coating process by using a composite coating of graphene and phenolic resin instead of single graphene coating, further reducing electrolyte erosion, improving the cycle stability of the material, and expanding the protection range of the coating agent.

[0064] The raw materials for preparation are as follows (by weight): 40 parts natural graphite, 40 parts modified hard carbon, 7 parts silicon dopant, 3 parts boron dopant, 5 parts phosphorus dopant, 2.5 parts sodium carboxymethyl cellulose, 120 parts deionized water, 2 parts graphene coating agent, and 1.5 parts phenolic resin.

[0065] Preparation steps:

[0066] Using the ball milling parameters from step 1 of Example 3, a graphite dispersion was prepared.

[0067] Using the same ball milling parameters as in step 2 of Example 3, modified hard carbon and ternary dopant were added to obtain a composite dispersion;

[0068] Sodium carboxymethyl cellulose was added to the composite dispersion and stirred at 28 degrees Celsius for 3 hours to prepare a uniform slurry;

[0069] The precursor was obtained by coating a thickness of 115 micrometers, vacuum drying at a temperature of 83 degrees Celsius, and drying for 5 hours.

[0070] The parameters for the first heat treatment are the same as those in step 5 of Example 3, and the first heat treatment is completed.

[0071] The product after the first heat treatment was removed and cooled to room temperature. Graphene and phenolic resin were mixed evenly at a mass ratio of 4:3, and an appropriate amount of deionized water was added to prepare a coating solution with a mass concentration of 5%. The product was immersed in the coating solution and ultrasonically dispersed for 30 minutes using an ultrasonic cell disruptor with a power of 200 watts to ensure uniform coating. Immersion coating was used instead of single spray coating to optimize the coating effect and solve the technical defect of insufficient density of single graphene coating in Example 3.

[0072] The soaked product was removed, excess coating liquid was drained, and it was placed in a tube furnace. Argon gas was introduced, and the temperature was raised to 920 degrees Celsius at a rate of 3 degrees Celsius per minute. The temperature was held for 2.5 hours to complete the second heat treatment. By extending the holding time, the carbonization of the phenolic resin was promoted, forming a dense composite coating layer that effectively prevented electrolyte corrosion.

[0073] After cooling to room temperature, the material is pulverized and passed through a 200-mesh sieve to obtain a carbon-based composite anode material.

[0074] Example 5:

[0075] Based on the raw material system and process of Example 4, and addressing the technical deficiency that there is still room for improvement in ion transport efficiency in Example 4, this example adjusts the order of ball milling and doping. First, the modified hard carbon and dopant are ball-milled and modified, and then combined with natural graphite to optimize the pore structure of the material, improve the ion transport efficiency, and expand the protection range of the process sequence.

[0076] The raw materials for preparation, by weight, are: 55 parts natural graphite, 30 parts modified hard carbon, 6 parts silicon dopant, 2 parts boron dopant, 4 parts phosphorus dopant, 3.5 parts sodium carboxymethyl cellulose, 105 parts deionized water, 2 parts graphene coating agent, and 1 part phenolic resin.

[0077] Preparation steps:

[0078] Modified hard carbon with a specific surface area of ​​500-800 m² / g, silicon dopant, boron dopant, and phosphorus dopant were placed in a planetary ball mill, along with 50 parts of deionized water. The ball-to-material ratio was 18:1, and the milling speed was 350 rpm for 3 hours using an intermittent milling mode (stopping for 10 minutes after every hour of milling). This process first modifies the hard carbon by doping, improving its electronic conductivity and ion adsorption capacity, thus addressing the technical defect in Example 4 where insufficient modification of the hard carbon led to inadequate ion transport efficiency.

[0079] Add natural graphite and the remaining 55 parts of deionized water to the above ball-milled product, and continue ball milling for 3 hours, maintaining a ball-to-material ratio of 18:1, a rotation speed of 300 rpm, and controlling the ball milling temperature to not exceed 50 degrees Celsius to obtain a composite dispersion. This ensures the uniform composite of natural graphite and modified hard carbon, optimizing the pore structure of the material.

[0080] Sodium carboxymethyl cellulose was added to the composite dispersion and stirred at 25 degrees Celsius for 3 hours to form a uniform slurry;

[0081] The precursor was obtained by coating a thickness of 105 micrometers, vacuum drying at 80 degrees Celsius, and drying for 6 hours.

[0082] The first heat treatment involved a heating rate of 5 degrees Celsius per minute, reaching a temperature of 700 degrees Celsius, and holding at that temperature for 4 hours. Extending the holding time promoted the formation and optimization of the pore structure, further improving ion transport efficiency.

[0083] Using the coating and second heat treatment parameters from steps 6 to 7 of Example 4, the composite coating and second heat treatment are completed.

[0084] After cooling to room temperature, the material is pulverized and passed through a 200-mesh sieve to obtain a carbon-based composite anode material.

[0085] Comparative Example 1:

[0086] The raw materials for preparation, by weight, are: 85 parts natural graphite, 5 parts silicon dopant, 3 parts boron dopant, 4 parts sodium carboxymethyl cellulose, 100 parts deionized water, and 2 parts graphene coating agent.

[0087] Preparation steps: completely consistent with Example 1, except for the absence of modified hard carbon component, while the other raw material ratios and process parameters remain unchanged.

[0088] Comparative Example 2:

[0089] The raw materials for preparation, by weight, are: 60 parts natural graphite, 25 parts modified hard carbon, 4 parts sodium carboxymethyl cellulose, 100 parts deionized water, and 2 parts coating agent graphene.

[0090] Preparation steps: completely consistent with Example 1, except for the absence of silicon dopant and boron dopant, while the other raw material ratios and process parameters remain unchanged.

[0091] Comparative Example 3:

[0092] The raw materials used in the preparation were exactly the same as those in Example 1.

[0093] Preparation steps: Following steps 1 to 4 of Example 1, after obtaining the precursor, only one heat treatment is performed. Argon gas is introduced, the temperature is raised at a rate of 5 degrees Celsius per minute, the temperature is raised to 800 degrees Celsius, and held for 5 hours. After cooling, graphene is coated, and no second heat treatment is performed. The remaining steps remain unchanged.

[0094] Comparative Example 4:

[0095] The raw materials for preparation, by weight, are: 40 parts natural graphite, 40 parts modified hard carbon, 7 parts silicon dopant, 3 parts boron dopant, 5 parts phosphorus dopant, 2.5 parts sodium carboxymethyl cellulose, 120 parts deionized water, and 3.5 parts phenolic resin coating agent.

[0096] Preparation steps: completely consistent with Example 4, except that a single phenolic resin is used instead of graphene and phenolic resin composite coating, and the other raw material ratios and process parameters remain unchanged.

[0097] Comparative Example 5:

[0098] The raw materials used in the preparation were exactly the same as those in Example 5.

[0099] Preparation steps: exactly the same as in Example 1, using the traditional process sequence of first mixing natural graphite and modified hard carbon, then adding dopants and ball milling, with the remaining process parameters unchanged.

[0100] Comparative Example 6:

[0101] Carbon-based composite anode materials were prepared by referring to the combination schemes of graphite and hard carbon composite, binary doping, single heat treatment, and single coating disclosed in the prior art.

[0102] The raw materials for preparation, by weight, are: 55 parts natural graphite, 30 parts modified hard carbon, 5 parts silicon dopant, 3 parts boron dopant, 3 parts sodium carboxymethyl cellulose, 105 parts deionized water, and 2 parts coating agent graphene.

[0103] Preparation steps: First, mix natural graphite and modified hard carbon, add deionized water and ball mill for 3 hours, then add silicon dopant and boron dopant and continue ball milling for 3 hours, add sodium carboxymethyl cellulose and stir for 3 hours, after coating and drying, perform a heat treatment, heat to 800 degrees Celsius and hold for 4 hours, after cooling, spray graphene coating to obtain carbon-based composite anode material.

[0104] To make the technical solution of this invention clearer and more complete, and to facilitate implementation by those skilled in the art, the specific specifications, preparation methods, and vague terms related to the core raw materials involved in this invention are hereby clarified as follows:

[0105] (1) Preparation of modified hard carbon: Coconut shell is used as raw material. It is carbonized in an inert atmosphere at 600-650 degrees Celsius for 2 hours, and then activated with KOH at 800-850 degrees Celsius for 1.5 hours. The liquid-solid ratio of activation is 3:1. After washing with water, drying and pulverizing, modified hard carbon with a specific surface area of ​​500-800 m² / g is obtained.

[0106] (2) Specific forms of dopants: silicon suboxide (SiO) is used as silicon dopant, boron acid (H3BO3) is used as boron dopant, and ammonium dihydrogen phosphate (NH4H2PO4) is used as phosphorus dopant.

[0107] (3) Specifications of sodium carboxymethyl cellulose: molecular weight 80,000-100,000, degree of substitution 0.7-0.9;

[0108] (4) Quantitative calculation of “appropriate amount of deionized water” in the preparation of coating solution: The mass concentration of coating solution is 5% as the percentage of the total mass of graphene and phenolic resin to the total mass of coating solution. The mass of deionized water added = (total mass of graphene + phenolic resin) / 5% - (total mass of graphene + phenolic resin).

[0109] (5) Graphene coating agent spraying process: The amount of graphene coating agent sprayed in Examples 1-3 is consistent with the mass ratio of graphene in the raw material components of the present invention. Atomizing spray gun with an air pressure of 0.2MPa is used for uniform spraying. During the spraying process, the product is kept flat and the thickness does not exceed 5mm.

[0110] Performance testing and results analysis:

[0111] Test sample:

[0112] The carbon-based composite anode materials prepared in Examples 1 to 5 and Comparative Examples 1 to 6 were selected and coin cells were fabricated accordingly. Using lithium metal as the counter electrode, a 1 mol / L LiPF6 EC / DMC / EMC solution as the electrolyte (volume ratio 1:1:1), and a Celgard 2400 polypropylene membrane as the separator, the coin cells were assembled in a glove box and subjected to performance testing after standing for 24 hours.

[0113] Test items and methods:

[0114] Specific capacity test: A charge-discharge tester was used with a voltage range of 0.01 to 3.0 volts and a current density of 0.1C to test the specific capacity during the first charge-discharge cycle and the specific capacity retention rate after 500 cycles.

[0115] Cyclic stability test: At a current density of 0.5C and a voltage range of 0.01 to 3.0 volts, 1000 cycles are performed. The specific capacity is tested for each charge and discharge cycle, and the specific capacity retention rate is calculated after 1000 cycles.

[0116] Rate performance test: The charge and discharge specific capacity was tested at current densities of 0.1C, 0.2C, 0.5C, 1C, 2C and 5C respectively. The specific capacity ratio of 5C to 0.1C was calculated. The higher the ratio, the better the rate performance.

[0117] AC impedance testing: An electrochemical workstation with a frequency range of 10 mHz to 100 kHz is used to test the charge transfer impedance of the battery. The lower the impedance value, the higher the electron and ion transport efficiency.

[0118] The test results are shown in Table 1 below:

[0119] Table 1:

[0120] sample First discharge specific capacity (mAh per gram) Specific capacity retention rate after 500 cycles (%) Specific capacity retention rate after 1000 cycles (%) 5C / 0.1C specific capacity ratio (%) Charge transfer impedance (ohms) Example 1 482 89.6 82.3 68.5 35.2 Example 2 526 91.2 84.7 72.3 32.8 Example 3 548 93.5 87.9 78.6 28.5 Example 4 553 95.1 90.2 80.1 26.3 Example 5 567 96.4 92.5 83.8 23.7 Comparative Example 1 378 75.3 68.9 52.1 58.6 Comparative Example 2 412 78.5 71.2 56.8 52.4 Comparative Example 3 465 82.1 75.6 63.2 43.8 Comparative Example 4 531 88.7 81.3 70.5 38.5 Comparative Example 5 512 87.9 80.1 73.2 34.9 Comparative Example 6 498 85.2 78.5 69.3 39.7

[0121] Test Result Analysis:

[0122] Example 2 optimizes the composite ratio and doping amount based on Example 1, increasing the specific capacity from 482 mAh / g to 526 mAh / g, and the specific capacity ratio of 5C to 0.1C from 68.5% to 72.3%. This demonstrates that optimizing the ratio of natural graphite to modified hard carbon and adjusting the doping amount can effectively improve the specific capacity and rate performance of the material. Moreover, this optimization scheme is specific and operable, and those skilled in the art can repeat it according to the parameters in the specification.

[0123] Example 3 introduces a phosphorus dopant to form a ternary doped system. Combined with ball milling parameter optimization, the charge transfer impedance decreased from 32.8 ohms to 28.5 ohms. After 1000 cycles, the specific capacity retention increased from 84.7% to 87.9%, proving that the ternary doped system can significantly optimize electron transport efficiency. Moreover, the relevant process parameters are clear, and there are no problems that cannot be achieved.

[0124] Example 4 employs a graphene and phenolic resin composite coating process, which further enhances cycle stability. After 1000 cycles, the specific capacity retention rate reaches 90.2%, and the charge transfer impedance drops to 26.3 ohms, indicating that the composite coating process can effectively block electrolyte erosion. Details such as the coating solution concentration and ultrasonic parameters are clearly defined, ensuring that those skilled in the art can repeat the preparation.

[0125] Example 5 adjusts the process sequence by first doping and modifying hard carbon before combining it with natural graphite, thereby optimizing the overall performance of the material. The initial discharge specific capacity increases to 567 mA / g, the 5C to 0.1C specific capacity ratio reaches 83.8%, the specific capacity retention rate reaches 92.5% after 1000 cycles, and the charge transfer impedance decreases to 23.7 ohms. This demonstrates that adjusting the process sequence can optimize the pore structure of the material and improve ion transport efficiency. Furthermore, the process steps are clear, the parameters are well-defined, and there are no ambiguous descriptions.

[0126] As can be seen from the comparison of Comparative Examples 1 to 6, the material performance will be significantly reduced if any of the core technical means of the present invention is missing. Among them, Comparative Example 6, as a combination of existing technologies, has a comprehensive performance that is far lower than that of the embodiments of the present invention, further proving that the technical solution of the present invention is not a simple combination of existing technologies and has significant inventiveness.

[0127] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A carbon-based composite anode material, characterized in that, is prepared from the following raw materials by mass: natural graphite 40-60 parts, modified hard carbon 25-40 parts, silicon dopant 5-8 parts, boron dopant 2-4 parts, sodium carboxymethyl cellulose 2.5-4 parts, graphene 2-3 parts, deionized water 100-120 parts, the specific surface area of the modified hard carbon being 500-800 m 2 / g; the raw materials further comprising phosphorus dopant 4-5 parts, the raw materials further possibly comprising phenolic resin 1-1.5 parts.

2. The method for preparing the carbon-based composite anode material according to claim 1, characterized in that, Includes the following steps: (1) Add natural graphite with a particle size of 1-5 μm to deionized water and ball mill it in a planetary ball mill to obtain a graphite dispersion. (2) Add modified hard carbon, silicon dopant, and boron dopant to the graphite dispersion. If the raw material contains phosphorus dopant, add phosphorus dopant at the same time. Then, ball mill the mixture in a planetary ball mill at a temperature not exceeding 50 degrees Celsius to obtain a composite dispersion. (3) Add sodium carboxymethyl cellulose to the composite dispersion and stir to form a uniform slurry; (4) Coat the slurry onto copper foil and dry it under vacuum to obtain the precursor; (5) Place the precursor in a tube furnace, introduce argon gas for the first heat treatment, and then coat it after cooling. (6) The coated product is placed in a tube furnace again, and argon gas is introduced for a second heat treatment. After cooling, it is crushed through a 200-mesh sieve to obtain carbon-based composite anode material.

3. The preparation method according to claim 2, characterized in that, In step (1), the ball-to-material ratio of the ball mill is 15:1, the rotation speed is 300 revolutions per minute, and the ball milling time is 2 hours.

4. The preparation method according to claim 2, characterized in that, In step (2), the ball-to-material ratio of the ball mill is 18:1, the rotation speed is 350 rpm, the ball milling time is 3-5.5 hours, the ball milling adopts an intermittent mode, and the machine is stopped for 10 minutes every 1 hour of ball milling. During the intermittent process, the temperature of the ball milling system is kept below 50 degrees Celsius.

5. The preparation method according to claim 2, characterized in that, In step (3), the stirring temperature is 25-30 degrees Celsius and the stirring time is 2.5-3 hours.

6. The preparation method according to claim 2, characterized in that, In step (4), the slurry coating thickness is 100-120 micrometers, the vacuum drying temperature is 80-85 degrees Celsius, and the drying time is 5-6 hours.

7. The preparation method according to claim 2, characterized in that, In step (5), the heating rate of the first heat treatment is 5 degrees Celsius per minute, the heat treatment temperature is 700-750 degrees Celsius, and the holding time is 3-4 hours.

8. The preparation method according to claim 2, characterized in that, In step (6), the heating rate of the second heat treatment is 3 degrees Celsius per minute, the heat treatment temperature is 900-950 degrees Celsius, and the holding time is 2-2.5 hours.

9. The preparation method according to claim 2, characterized in that, Choose one of the following two options to implement: Option 1, the coating treatment in step (5) is a composite coating of graphene and phenolic resin. The specific operation is as follows: mix graphene and phenolic resin at a mass ratio of 4:3, add deionized water to make a coating solution with a mass concentration of 5%, immerse the product after the first heat treatment in the coating solution, use a 200-watt ultrasonic cell disruptor to ultrasonically disperse for 30 minutes, drain the excess coating solution and then perform a second heat treatment. Option 2, step (2) is replaced with the following operation: Add modified hard carbon, silicon dopant, boron dopant, phosphorus dopant and 50 parts of deionized water to a planetary ball mill and ball mill for 3 hours. The ball-to-material ratio is 18:1 and the speed is 350 rpm. Use intermittent ball milling mode, stop for 10 minutes after every 1 hour of ball milling, then add natural graphite and the remaining deionized water and continue ball milling for 3 hours. Keep the ball-to-material ratio at 18:1 and the speed at 300 rpm. The ball milling temperature does not exceed 50 degrees Celsius to obtain a composite dispersion.