Preparation method of negative electrode material based on negative electrode aging hard carbon material

Abstract

The invention relates to the technical field of batteries, in particular to a negative electrode material preparation method based on a negative electrode aged hard carbon material, which comprises the following steps: firstly, crushing and grading an aged hard carbon precursor to obtain particles with a preset particle size; the preparation method comprises the following steps: performing pretreatment such as acid washing, alkali washing, water washing and ethanol washing, mixing a purified precursor with a coating material in proportion to form a uniform coating layer, pre-sintering in a protective atmosphere, and preliminarily stabilizing a material structure by controlling parameters such as a heating rate; and carrying out specific surface area detection on the pre-sintered primary product, and dynamically adjusting pre-sintering process parameters according to the specific surface area detection to ensure that the pore structure of the material reaches the standard. And performing high-temperature carbonization treatment on the material meeting the standard so as to repair the carbon layer structure and improve the conductivity. And finally, performing quality judgment by detecting the first coulombic efficiency of a finished product. According to the invention, the first coulombic efficiency, the specific capacity and the cycling stability of the regenerated hard carbon material are improved, and the recycling of the aging material is realized.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method for preparing a negative electrode material based on a negative electrode aged hard carbon material. Background Technology

[0002] Sodium-ion batteries, as a supplementary and alternative technology to lithium-ion batteries, have been under development alongside lithium batteries since the 1970s, but their development lagged behind due to insufficient performance of early electrode materials. In recent years, with the scarcity and rising costs of lithium resources, sodium-ion batteries have once again become a research hotspot in the energy storage field due to their advantages such as abundant sodium resources, low cost, and high safety. Comparable to lithium iron phosphate batteries, they show great potential in large-scale energy storage, low-speed electric vehicles, and applications in extremely cold regions, and were listed as one of the top ten emerging technologies in the field of chemistry in 2022. However, the performance bottleneck of anode materials remains a key challenge restricting their commercialization.

[0003] Hard carbon, as the preferred commercial anode material for sodium-ion batteries, boasts a disordered layered structure and abundant micropores that efficiently accommodate sodium ions, solving the problem of unstable sodium storage in graphite anodes due to their small interlayer spacing. Compared to soft carbon, titanium-based materials, and alloy anodes, hard carbon has three core advantages: high specific capacity, uniform volume expansion, outstanding fast-charging performance, and good low-temperature adaptability. Currently, mainstream preparation relies on biomass precursors, which are low-cost but subject to supply fluctuations. Novel precursors such as humic acid and citric acid are becoming key directions for industrialization due to their easily tunable molecular structures and high carbon yield.

[0004] During long-term storage, hard carbon precursors are subject to structural degradation due to environmental humidity and oxygen erosion. This degradation manifests as functional group hydrolysis and oxidation loss, pore structure collapse and defect annihilation, and ash impurity migration and accumulation. This leads to a decrease in plateau capacity, a reduction in ramp capacity, and a decrease in first-cycle coulombic efficiency, while also severely impacting cycling performance. Summary of the Invention

[0005] Therefore, the present invention provides a method for preparing anode materials based on aged hard carbon materials, in order to overcome the problem that the structure of aged hard carbon precursors cannot be efficiently utilized due to structural deterioration in the prior art.

[0006] To achieve the above objectives, the present invention provides a method for preparing a negative electrode material based on a negative electrode aged hard carbon material, comprising: Step S1: The aged hard carbon precursor is subjected to a preset number of crushing processes to obtain aged hard carbon particles of a preset particle size. Step S2: Pre-treat the aged hard carbon particles to obtain a hard carbon precursor; the pre-treatment includes acid washing, alkali washing, water washing and ethanol washing. Step S3: Mix the hard carbon precursor with the coating material to obtain the coated hard carbon material. Step S4: The coated hard carbon material is pre-fired under a protective atmosphere with a first preset flow rate to obtain a raw hard carbon material. The pre-fired parameters include a first preset temperature, a first preset holding time, and a first preset heating rate. Step S5: Detect the coated hard carbon material to obtain the specific surface area of ​​the coated hard carbon material, and determine whether the preparation of the coated hard carbon material meets the preset standard based on the specific surface area; Step S6: The coated hard carbon material that meets the preset standard is subjected to high-temperature carbonization treatment in a protective atmosphere with a second preset flow rate to obtain the repaired hard carbon material product; the high-temperature carbonization treatment parameters include a second preset temperature, a second preset holding time, and a second preset heating rate. Step S7: Obtain the first coulombic efficiency of the hard carbon material product and determine whether the preparation of the hard carbon material product meets the preset standard based on the first coulombic efficiency; Step S8: In response to the fact that the preparation of the hard carbon material product does not meet the preset standard, the preparation of the hard carbon material product is checked according to the first charge specific capacity to determine whether it meets the preset standard, or the reason why the hard carbon material product does not meet the preset standard is determined according to the content of harmful functional groups on the surface.

[0007] Furthermore, in response to the specific surface area being less than a preset specific surface area threshold, it is determined that the preparation of the coated hard carbon material does not meet the preset standard, and the first preset heating rate is reduced according to the difference between the preset specific surface area threshold and the specific surface area. In response to the specific surface area being greater than or equal to a preset specific surface area threshold, it is determined that the preparation of the coated hard carbon material meets a preset standard.

[0008] Furthermore, the decrease in the first preset heating rate is positively correlated with the difference between the preset specific surface area threshold and the specific surface area.

[0009] Furthermore, in response to the first coulombic efficiency being less than a first preset first coulombic efficiency threshold, it is determined that the preparation of the hard carbon material product does not meet the preset standard, and the reason why the hard carbon material product does not meet the preset standard is determined based on the content of harmful functional groups on the surface. In response to the first coulombic efficiency being greater than or equal to a first preset first coulombic efficiency threshold and less than a second preset first coulombic efficiency threshold, it is determined that the preparation of the hard carbon material product does not meet the preset standard, and the preparation of the hard carbon material product is verified according to the first charge specific capacity. In response to the first coulombic efficiency being greater than or equal to a second preset first coulombic efficiency threshold, it is determined that the preparation of the hard carbon material product conforms to a preset standard.

[0010] Furthermore, in response to the first charge specific capacity being less than a preset first charge specific capacity threshold, it is verified that the preparation of the hard carbon material product does not meet the preset standard, and the second preset temperature of the high-temperature carbonization treatment is increased according to the difference between the preset first charge specific capacity threshold and the first charge specific capacity. In response to the first charge specific capacity being greater than or equal to a preset first charge specific capacity threshold, the preparation of the hard carbon material product is verified to meet the preset standard.

[0011] Furthermore, the increase in the second preset temperature is positively correlated with the difference between the preset first-cycle charging specific capacity threshold and the first-cycle charging specific capacity.

[0012] Furthermore, in response to the fact that the content of harmful functional groups on the surface is less than a preset threshold for the content of harmful functional groups on the surface, it is determined that the reason why the preparation of the hard carbon material product does not meet the preset standard is that the second preset heat preservation time of the high-temperature carbonization treatment is not up to standard, and the second preset heat preservation time is increased according to the difference between the preset threshold for the content of harmful functional groups on the surface and the content of harmful functional groups on the surface. In response to the fact that the content of harmful functional groups on the surface is greater than or equal to a preset threshold for the content of harmful functional groups on the surface, it is determined that the reason why the preparation of the finished hard carbon material does not meet the preset standard is that the preset particle size of the crushing process is not up to standard, and the preset particle size of the crushing is reduced according to the difference between the content of harmful functional groups on the surface and the preset threshold for the content of harmful functional groups on the surface.

[0013] Furthermore, the increase in the second preset heat preservation time is positively correlated with the difference between the preset threshold for the content of harmful functional groups on the surface and the content of harmful functional groups on the surface; The reduction in the preset particle size of the crushed material is positively correlated with the difference between the content of harmful functional groups on the surface and the preset threshold value of harmful functional groups on the surface.

[0014] Furthermore, the aged hard carbon precursor includes one of bamboo charcoal, coconut shell charcoal, anthracite, lignite, peanut shell, phenolic resin, epoxy resin, and corn cob.

[0015] Furthermore, the coating material includes one of alumina, titanium dioxide, cadmium oxide, asphalt, rosin resin, vinyl resin, glucose, and polyacrylonitrile.

[0016] Compared with existing technologies, the advantages of this invention are as follows: by controlling the crushing process of the aged hard carbon precursor to obtain particles of a predetermined particle size, the particle size distribution and specific surface area of ​​the material can be optimized. This helps to improve the uniformity of subsequent coating and carbonization processes, thereby enhancing the electrochemical performance of the material, such as ion diffusion rate and capacity utilization. Simultaneously, a consistent particle size distribution reduces variability during battery manufacturing, improving battery consistency and cycle stability.

[0017] Furthermore, pretreatment steps including acid washing, alkali washing, water washing, and ethanol washing effectively remove impurities, metal ions, and harmful functional groups from the surface of aged hard carbon particles, purifying the material. This reduces side reactions and irreversible capacity loss during battery charging and discharging, improving the purity and safety of the material. Pretreatment also helps improve the adhesion between the material and the coating layer, laying the foundation for subsequent steps and ultimately improving the battery's initial coulombic efficiency and lifespan.

[0018] Furthermore, mixing the hard carbon precursor with the coating material forms a uniform coating layer, which isolates the electrolyte from direct contact with the hard carbon, reducing solvent decomposition and excessive growth of the solid electrolyte interfacial film during the first charge and discharge cycle. This significantly improves the material's initial coulombic efficiency and structural stability, while also enhancing its conductivity and mechanical strength, thus extending the battery's cycle life.

[0019] Furthermore, pre-calcination under a protective atmosphere, by controlling the temperature, holding time, and heating rate, can initially stabilize the structure of the hard carbon material, remove volatile components and residual moisture, and form a porous structure. This optimizes the specific surface area and pore distribution of the material, providing an ideal precursor for subsequent high-temperature carbonization and helping to improve the electrochemical performance and consistency of the final product.

[0020] Furthermore, by real-time monitoring of the specific surface area of ​​the coated hard carbon material and comparing it with a preset threshold, the material quality can be quickly assessed. If the specific surface area does not meet the standard, the system automatically reduces the pre-sintering heating rate to adjust the material structure and avoid over-sintering or pore blockage. This feedback mechanism ensures adaptive optimization of process parameters, improves production efficiency and product qualification rate, and reduces resource waste.

[0021] Furthermore, the high-temperature carbonization process is carried out under a protective atmosphere. By controlling the temperature, holding time, and heating rate, the graphitization degree and crystal structure of the hard carbon material can be further repaired, improving conductivity and capacity. This step effectively eliminates internal defects and forms a stable carbon network, thereby improving the rate performance and cycle performance of the material, making hard carbon materials more suitable for high-energy-density battery applications.

[0022] Furthermore, by detecting the initial coulombic efficiency and performing multi-dimensional verification of parameters such as the first-charge specific capacity and the content of harmful functional groups on the surface based on the results, the root causes of problems in the preparation process can be accurately identified. For example, if the efficiency is low, the system can automatically adjust the carbonization temperature or the particle size to optimize material properties. This intelligent feedback control improves the reliability and consistency of the product.

[0023] Furthermore, this invention utilizes aged hard carbon materials as precursors, achieving the recycling of waste resources, reducing raw material costs, and alleviating environmental burden. The entire method, through multi-step coordination and parameter optimization, ensures high initial coulombic efficiency, high capacity, and long lifespan of the final product. Simultaneously, real-time monitoring and feedback mechanisms enable the process to be adaptive, adapting to aged materials from different sources and improving production flexibility. Attached Figure Description

[0024] Figure 1 This is a flowchart of the anode material preparation method based on the anode aging hard carbon material according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating the process of determining whether the preparation of the coated hard carbon material conforms to a preset standard based on the specific surface area, as described in this embodiment of the invention. Figure 3 This is a flowchart illustrating the process of determining whether the preparation of the hard carbon material product conforms to a preset standard based on the initial coulombic efficiency, as described in this embodiment of the invention. Figure 4 This is a flowchart illustrating the process of verifying whether the preparation of the hard carbon material product conforms to a preset standard based on the first charge specific capacity in an embodiment of the present invention. Figure 5 This is a flowchart illustrating the reasons why the finished hard carbon material does not meet the preset standard according to the surface functional group content in an embodiment of the present invention. Figure 6 The image shows the microstructure of the hard carbon prepared from aged bamboo charcoal in an embodiment of the present invention. Figure 7 This is a microscopic morphology diagram of hard carbon prepared from unaged bamboo charcoal in an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0026] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0027] Please see Figure 1-7The diagrams shown are, respectively, a flowchart of a method for preparing a negative electrode material based on aged hard carbon material according to an embodiment of the present invention; a flowchart of determining whether the preparation of the coated hard carbon material meets a preset standard based on the specific surface area; a flowchart of determining whether the preparation of the finished hard carbon material meets a preset standard based on the first coulombic efficiency; a flowchart of verifying whether the preparation of the finished hard carbon material meets a preset standard based on the first charge specific capacity; a flowchart of the reasons why the finished hard carbon material does not meet the preset standard based on the surface functional group content; a microscopic morphology diagram of hard carbon prepared from aged bamboo charcoal according to an embodiment of the present invention; and a microscopic morphology diagram of hard carbon prepared from unaged bamboo charcoal according to an embodiment of the present invention.

[0028] This invention provides a method for preparing a negative electrode material based on aged hard carbon material, comprising: Step S1: The aged hard carbon precursor is subjected to a preset number of crushing processes to obtain aged hard carbon particles of a preset particle size. Step S2: Pre-treat the aged hard carbon particles to obtain a hard carbon precursor; the pre-treatment includes acid washing, alkali washing, water washing and ethanol washing. Step S3: Mix the hard carbon precursor with the coating material to obtain the coated hard carbon material. Step S4: The coated hard carbon material is pre-fired under a protective atmosphere with a first preset flow rate to obtain a raw hard carbon material. The pre-fired parameters include a first preset temperature, a first preset holding time, and a first preset heating rate. Step S5: Detect the coated hard carbon material to obtain the specific surface area of ​​the coated hard carbon material, and determine whether the preparation of the coated hard carbon material meets the preset standard based on the specific surface area; Step S6: The coated hard carbon material that meets the preset standard is subjected to high-temperature carbonization treatment in a protective atmosphere with a second preset flow rate to obtain the repaired hard carbon material product; the high-temperature carbonization treatment parameters include a second preset temperature, a second preset holding time, and a second preset heating rate. Step S7: Obtain the first coulombic efficiency of the hard carbon material product and determine whether the preparation of the hard carbon material product meets the preset standard based on the first coulombic efficiency; Step S8: In response to the fact that the preparation of the hard carbon material product does not meet the preset standard, the preparation of the hard carbon material product is checked according to the first charge specific capacity to determine whether it meets the preset standard, or the reason why the hard carbon material product does not meet the preset standard is determined according to the content of harmful functional groups on the surface.

[0029] Specifically, the preset number of crushing cycles is set to 1-5 times, with 3 cycles selected in this embodiment; the crushing time per cycle is set to 1-3 minutes; the pretreatment includes acid washing, alkali washing, water washing, and ethanol washing, with acid washing and alkali washing selected in this embodiment. The acid concentration for acid washing is 1 mol / L-2 mol / L, the alkali concentration for alkali washing is 1 mol / L-2 mol / L, and the duration is 1-2 hours, with 1 hour selected in this embodiment; the first preset flow rate is set to 500 mL / min-1500 mL / min; the first preset temperature is set to 600℃-800℃; the first preset holding time is set to 2 hours-4 hours; and the first preset heating rate is set to 5℃ / min-10℃ / min, with 8℃ / min selected in this embodiment. Through the coordinated setting of the above parameters, impurities and some surface defects in the aged hard carbon material can be effectively removed, laying a good foundation for subsequent coating treatment.

[0030] Specifically, the second preset flow rate is set to 800 mL / min-2000 mL / min, and 1500 mL / min is selected in this embodiment; the second preset temperature is set to 1300℃-1500℃, and 1400℃ is selected in this embodiment; the second preset holding time is set to 4h-6h, and 5h is selected in this embodiment; the second preset heating rate is set to 3℃ / min-8℃ / min, and 5℃ / min is selected in this embodiment. By precisely controlling the protective atmosphere flow rate and temperature change parameters during the high-temperature carbonization stage, the ordered arrangement of graphite microcrystals inside the hard carbon material can be promoted, lattice defects can be repaired, and the collapse of the pore structure caused by excessive graphitization can be suppressed, thereby balancing the material's capacity and cycle stability.

[0031] Specifically, in response to the specific surface area being less than a preset specific surface area threshold, it is determined that the preparation of the coated hard carbon material does not meet the preset standard, and the first preset heating rate is reduced according to the difference between the preset specific surface area threshold and the specific surface area. In response to the specific surface area being greater than or equal to a preset specific surface area threshold, it is determined that the preparation of the coated hard carbon material meets a preset standard.

[0032] Specifically, the preset specific surface area threshold is set to 12 m² / g-18 m² / g, and 15 m² / g is selected in this embodiment. Specific surface area is chosen as the evaluation criterion because it directly affects the contact area between the hard carbon material and the electrolyte, as well as the ion transport path. When the specific surface area is too low, there are insufficient active sites on the material surface, resulting in decreased ion adsorption and diffusion efficiency, thus limiting capacity utilization. By controlling the specific surface area at around 15 m² / g, sufficient active sites can be ensured to achieve high capacity, while stability issues caused by excessive surface exposure can be avoided, thereby balancing the electrochemical performance and cycle life of the material.

[0033] Specifically, the decrease in the first preset heating rate is positively correlated with the difference between the preset specific surface area threshold and the specific surface area. It is understood that the positive correlation can be linear or nonlinear, and there is no specific limitation. The slope of the linear positive correlation is also not specifically limited and can be set according to the actual preparation conditions, as long as the larger the difference between the preset specific surface area threshold and the specific surface area, the greater the decrease in the first preset heating rate. For example, the decrease in the first preset heating rate can be set to... The difference between the preset specific surface area threshold and the specific surface area is set to... ,but γ is the heating rate adjustment coefficient, set to γ=1.06, and μ0 is a constant.

[0034] Specifically, in response to the first coulombic efficiency being less than a first preset first coulombic efficiency threshold, it is determined that the preparation of the hard carbon material product does not meet the preset standard, and the reason why the hard carbon material product does not meet the preset standard is determined based on the content of harmful functional groups on the surface. In response to the first coulombic efficiency being greater than or equal to a first preset first coulombic efficiency threshold and less than a second preset first coulombic efficiency threshold, it is determined that the preparation of the hard carbon material product does not meet the preset standard, and the preparation of the hard carbon material product is verified according to the first charge specific capacity. In response to the first coulombic efficiency being greater than or equal to a second preset first coulombic efficiency threshold, it is determined that the preparation of the hard carbon material product conforms to a preset standard.

[0035] Specifically, the first preset initial coulombic efficiency threshold is set to 79%, and the second preset initial coulombic efficiency threshold is set to 86%. The reason for choosing initial coulombic efficiency as the core evaluation indicator is that it directly reflects the ratio of reversible capacity to irreversible capacity during the first charge and discharge process, and is one of the key parameters for measuring the electrochemical performance of hard carbon materials. When the initial coulombic efficiency is below 79%, it indicates that there are a large number of irreversible reactions in the material during the first cycle, which may be due to side reactions caused by surface residual impurities, functional groups, or structural defects. In this case, it is necessary to prioritize the analysis of the content of harmful functional groups on the surface to locate the root cause of the problem. When the efficiency is in the range of 79%-86%, the overall performance of the material is close to the qualified standard. The difference may be caused by the difference in the internal structure of the particles or the ion diffusion path. By verifying the specific capacity of the first charge, it can be further determined whether the insufficient capacity is caused by uneven particle size distribution or abnormal pore structure, thereby achieving accurate classification and targeted adjustment of process defects.

[0036] Specifically, in response to the fact that the first charge specific capacity is less than a preset first charge specific capacity threshold, the preparation of the hard carbon material product is verified to be inconsistent with the preset standard, and the second preset temperature of the high-temperature carbonization treatment is increased according to the difference between the preset first charge specific capacity threshold and the first charge specific capacity. In response to the first charge specific capacity being greater than or equal to a preset first charge specific capacity threshold, the preparation of the hard carbon material product is verified to meet the preset standard.

[0037] Specifically, the preset first-cycle charge specific capacity threshold is set to 320 mAh / g. This threshold is based on a balance between the theoretical capacity of hard carbon materials in lithium-ion batteries and the actual application requirements. When the first-cycle charge specific capacity is lower than 320 mAh / g, it indicates that the material has insufficient lithium storage active sites or limited ion diffusion channels, which may be related to the temperature parameters not reaching the optimal level during the high-temperature carbonization stage. By increasing the second preset temperature, the disordered carbon structure inside the hard carbon material can be promoted to transform into a graphite-like microcrystalline structure, increasing lithium-ion intercalation sites and optimizing pore connectivity, thereby improving the material's capacity utilization. For example, when the first-cycle charge specific capacity is detected to be 305 mAh / g, the system can automatically increase the second preset temperature from 1400℃ to 1450℃, while maintaining the holding time and heating rate unchanged, to improve the material's lithium storage performance through structural rearrangement at a higher temperature. This capacity feedback-based temperature regulation mechanism can maximize the electrochemical capacity potential while ensuring the material's structural stability.

[0038] Specifically, the increase in the second preset temperature is positively correlated with the difference between the preset first-cycle charge specific capacity threshold and the first-cycle charge specific capacity. It is understood that the positive correlation can be linear or non-linear, and there is no specific limitation. The slope of the linear positive correlation is also not specifically limited and can be set according to the actual manufacturing conditions, as long as the difference between the preset first-cycle charge specific capacity threshold and the first-cycle charge specific capacity is larger, the greater the increase in the second preset temperature. For example, the increase in the second preset temperature can be set as follows: The difference between the preset first-cycle charging specific capacity threshold and the first-cycle charging specific capacity is set as follows: ,but α is the temperature adjustment coefficient, λ is set to 1.12, and λ0 is a constant.

[0039] Specifically, in response to the fact that the content of harmful functional groups on the surface is less than a preset threshold for the content of harmful functional groups on the surface, it is determined that the reason why the preparation of the hard carbon material product does not meet the preset standard is that the second preset heat preservation time of the high-temperature carbonization treatment is not up to standard, and the second preset heat preservation time is increased according to the difference between the preset threshold for the content of harmful functional groups on the surface and the content of harmful functional groups on the surface. In response to the fact that the content of harmful functional groups on the surface is greater than or equal to a preset threshold for the content of harmful functional groups on the surface, it is determined that the reason why the preparation of the finished hard carbon material does not meet the preset standard is that the preset particle size of the crushing process is not up to standard, and the preset particle size of the crushing is reduced according to the difference between the content of harmful functional groups on the surface and the preset threshold for the content of harmful functional groups on the surface.

[0040] Specifically, the preset threshold for harmful surface functional groups is set at 0.8 mmol / g. These harmful surface functional groups include carboxyl, hydroxyl, and carbonyl groups, which are prone to side reactions with the electrolyte during charge and discharge, generating irreversible products and consuming lithium ions, leading to a decrease in initial coulombic efficiency and deterioration of cycle performance. When the detected content of harmful surface functional groups is below 0.8 mmol / g, it indicates that the temperature during the high-temperature carbonization stage has not effectively decomposed or removed these functional groups. In this case, it is necessary to increase the second preset temperature to enhance the pyrolysis effect, for example, increasing the original 1400℃ to 1450℃, to promote the decomposition and volatilization of functional groups at a higher temperature. If the content is above 0.8 mmol / g, it indicates that the particle size after crushing is too large, making it difficult to completely remove the harmful functional groups remaining inside the material in subsequent processing. In this case, it is necessary to reduce the preset crushing particle size, such as adjusting from the original 3 crushing cycles to 4 crushing cycles, controlling the particle size within a smaller range to increase the specific surface area and reaction contact area of ​​the material, thereby improving the removal efficiency of functional groups during subsequent acid washing, alkali washing, and carbonization processes. This differentiated adjustment strategy based on functional group content enables precise control of the chemical state of the material surface, further ensuring the electrochemical stability of hard carbon materials.

[0041] Specifically, the increase in the second preset heat preservation time is positively correlated with the difference between the preset threshold for the content of harmful functional groups on the surface and the content of harmful functional groups on the surface. It is understood that the positive correlation can be linear or nonlinear, and is not specifically limited. The slope of the linear positive correlation is also not specifically limited and can be set according to the actual preparation conditions. It is only necessary to satisfy the requirement that the greater the difference between the preset threshold for the content of harmful functional groups on the surface and the content of harmful functional groups on the surface, the greater the increase in the second preset heat preservation time. For example, the increase in the second preset heat preservation time is set as follows: The difference between the preset first-cycle charging specific capacity threshold and the first-cycle charging specific capacity is set as follows: ,but β is the heat preservation time adjustment coefficient, σ is set to 0.96, and σ0 is a constant.

[0042] The reduction in the preset particle size of the crushed particles is positively correlated with the difference between the content of harmful surface functional groups and a preset threshold value for harmful surface functional group content. It is understood that the positive correlation can be linear or nonlinear, and is not specifically limited. The slope of the linear positive correlation is also not specifically limited and can be set according to the actual preparation conditions. The only requirement is that the greater the difference between the content of harmful surface functional groups and the preset threshold value for harmful surface functional group content, the greater the reduction in the preset particle size of the crushed particles. For example, the reduction in the preset particle size of the crushed particles can be set as follows: The difference between the content of harmful functional groups on the surface and a preset threshold value for the content of harmful functional groups on the surface is set as follows: ,but φ is the particle size adjustment coefficient, η is set to 1.24, and η0 is a constant.

[0043] Specifically, the aging hard carbon precursors include bamboo charcoal, coconut shell charcoal, anthracite, lignite, peanut shell, phenolic resin, epoxy resin, and corn cob. The coating materials include alumina, titanium dioxide, cadmium oxide, asphalt, rosin resin, vinyl resin, glucose, and polyacrylonitrile; The mixing process can be one of the following: hand milling, low-speed ball milling, stirring in water, or stirring in ethanol. This setup allows for flexible selection of appropriate coating materials and mixing methods based on the different sources and characteristics of the aged hard carbon precursor, optimizing the interfacial compatibility between the coating layer and the hard carbon matrix. For example, for bamboo charcoal precursors with high surface porosity, using asphalt as the coating material and employing low-speed ball milling allows the asphalt to form a uniform molten coating layer on the surface of the hard carbon particles, filling some of the surface micropores. For resin-based aged hard carbon such as phenolic resin, polyacrylonitrile is preferentially chosen as the coating material. Stirring in ethanol promotes the directional adsorption of polymer molecular chains on the hard carbon surface, forming a carbon coating network with good conductivity after subsequent carbonization. The combination of different coating materials and mixing processes can specifically improve the surface energy, ion transport resistance, and structural stability of the hard carbon material, thereby enhancing the overall electrochemical performance of the repaired product.

[0044] The present invention will be further explained and described below with reference to the accompanying drawings, but not in a way that limits the invention.

[0045] Comparative Example 1 The comparative example of this invention provides a method for preparing aged hard carbon, the steps of which include: Step 1: Place the aged bamboo charcoal into a crusher for three crushing processes, with each crushing process taking 1 minute.

[0046] Step 2: Soak the bamboo charcoal powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0047] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0048] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0049] Step 4: Place the dried bamboo charcoal powder into a tube furnace for pre-firing.

[0050] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0051] Step 5: Place the pre-burned bamboo charcoal into a high-temperature tube furnace for high-temperature carbonization.

[0052] Specifically, the sintering atmosphere is argon, the temperature is 1500℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0053] Step 6: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0054] Step 7: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 273.4 mAh / g, and the first-cycle coulombic efficiency is 80.4%.

[0055] Comparative Example 2 The comparative example of this invention provides a method for preparing aged hard carbon, the steps of which include: Step 1: Place the aged coconut shell charcoal into a crusher for three crushing processes, with each crushing process taking 1 minute.

[0056] Step 2: Soak the coconut shell charcoal powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0057] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0058] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0059] Step 4: Place the dried coconut shell charcoal powder into a tube furnace for pre-firing.

[0060] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0061] Step 5: Place the pre-burned coconut shell charcoal into a high-temperature tube furnace for high-temperature carbonization.

[0062] Specifically, the sintering atmosphere is argon, the temperature is 1500℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0063] Step 6: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0064] Step 7: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 283.36 mAh / g, and the first-cycle coulombic efficiency is 82.3%.

[0065] Comparative Example 3 The comparative example of this invention provides a method for preparing aged hard carbon, the steps of which include: Step 1: Place the aged anthracite into a crusher for three crushing processes, with each crushing process taking 1 minute.

[0066] Step 2: Soak the anthracite powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0067] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0068] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0069] Step 4: Place the dried anthracite powder into a tubular furnace for pre-firing.

[0070] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0071] Step 5: Place the pre-burned anthracite into a high-temperature tubular furnace for high-temperature carbonization.

[0072] Specifically, the sintering atmosphere is argon, the temperature is 1300℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0073] Step 6: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0074] Step 7: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 225.83 mAh / g, and the first-cycle coulombic efficiency is 73.53%.

[0075] Comparative Example 4 The comparative example of this invention provides a method for preparing aged hard carbon, the steps of which include: Step 1: Place the aged resin carbon into a crusher for three crushing processes, with each crushing process lasting 1 minute.

[0076] Step 2: Soak the resin carbon powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0077] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0078] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0079] Step 4: Place the dried resin carbon powder into a tube furnace for pre-firing.

[0080] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0081] Step 5: Place the pre-burned resin char into a high-temperature tube furnace for high-temperature carbonization.

[0082] Specifically, the sintering atmosphere is argon, the temperature is 1300℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0083] Step 6: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0084] Step 7: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 201.94 mAh / g, and the first-cycle coulombic efficiency is 73.86%.

[0085] Comparative Example 5 The comparative example of this invention provides a method for preparing a hard carbon material, the steps of which include: Step 1: Place the freshly burned bamboo charcoal into a crusher for three crushing processes, with each crushing process taking 1 minute.

[0086] Step 2: Soak the bamboo charcoal powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0087] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0088] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0089] Step 4: Place the dried bamboo charcoal powder into a tube furnace for pre-firing.

[0090] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0091] Step 5: Place the pre-burned bamboo charcoal into a high-temperature tube furnace for high-temperature carbonization.

[0092] Specifically, the sintering atmosphere is argon, the temperature is 1500℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0093] Step 6: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0094] Step 7: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 322.26 mAh / g, and the first-cycle coulombic efficiency is 86.8%.

[0095] Comparative Example 6 The comparative example of this invention provides a method for preparing a hard carbon material, the steps of which include: Step 1: Place the freshly burned coconut shell charcoal into a crusher for three crushing processes, with each crushing process taking 1 minute.

[0096] Step 2: Soak the coconut shell charcoal powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0097] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0098] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0099] Step 4: Place the dried coconut shell charcoal powder into a tube furnace for pre-firing.

[0100] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0101] Step 5: Place the pre-burned coconut shell charcoal into a high-temperature tube furnace for high-temperature carbonization.

[0102] Specifically, the sintering atmosphere is argon, the temperature is 1500℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0103] Step 6: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0104] Step 7: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 327.02 mAh / g, and the first-cycle coulombic efficiency is 82.4%.

[0105] Comparative Example 7 The comparative example of this invention provides a method for preparing a hard carbon material, the steps of which include: Step 1: Put the newly purchased anthracite into the crusher for three crushing processes, with each crushing process taking 1 minute.

[0106] Step 2: Soak the anthracite powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0107] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0108] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0109] Step 4: Place the dried anthracite powder into a tubular furnace for pre-firing.

[0110] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0111] Step 5: Place the pre-burned anthracite into a high-temperature tubular furnace for high-temperature carbonization.

[0112] Specifically, the sintering atmosphere is argon, the temperature is 1300℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0113] Step 6: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0114] Step 7: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. As can be seen from the table, the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 277.93 mAh / g, and the first-cycle coulombic efficiency is 81.87%.

[0115] Comparative Example 8 The comparative example of this invention provides a method for preparing a hard carbon material, the steps of which include: Step 1: Place the freshly burned resin charcoal into a crusher for three crushing processes, with each crushing process lasting 1 minute.

[0116] Step 2: Soak the resin carbon powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0117] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0118] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0119] Step 4: Place the dried resin carbon powder into a tube furnace for pre-firing.

[0120] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0121] Step 5: Place the pre-burned resin char into a high-temperature tube furnace for high-temperature carbonization.

[0122] Specifically, the sintering atmosphere is argon, the temperature is 1300℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0123] Step 6: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0124] Step 7: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. As can be seen from the table, the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 288.56 mAh / g, and the first-cycle coulombic efficiency is 78.97%. Example 1:

[0125] An embodiment of the present invention provides a method for coating and repairing aged hard carbon anodes, the steps of which include: Step 1: Place the aged bamboo charcoal into a crusher for three crushing processes, with each crushing process taking 1 minute.

[0126] Step 2: Soak the bamboo charcoal powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0127] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0128] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0129] Step 4: Dissolve rosin resin in ethanol, then add bamboo charcoal and stir well. Place the mixture in an oven to dry the ethanol.

[0130] Specifically, the ratio of bamboo charcoal to rosin resin is 5:1, the drying temperature is 70℃, and the drying time is 12 hours.

[0131] Step 5: Place the dried bamboo charcoal powder into a tube furnace for pre-firing.

[0132] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0133] Step 6: Place the pre-burned bamboo charcoal into a high-temperature tube furnace for high-temperature carbonization.

[0134] Specifically, the sintering atmosphere is argon, the temperature is 1500℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0135] Step 7: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0136] Step 8: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 311.46 mAh / g, and the first-cycle coulombic efficiency is 85.3%. Example 2:

[0137] An embodiment of the present invention provides a method for coating and repairing aged hard carbon anodes, the steps of which include: Step 1: Place the aged bamboo charcoal into a crusher for three crushing processes, with each crushing process taking 1 minute.

[0138] Step 2: Soak the bamboo charcoal powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0139] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0140] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0141] Step 4: Dissolve rosin resin in ethanol, then add bamboo charcoal and stir well. Place the mixture in an oven to dry the ethanol.

[0142] Specifically, the ratio of bamboo charcoal to rosin resin is 10:1, the drying temperature is 70℃, and the drying time is 12 hours.

[0143] Step 5: Place the dried bamboo charcoal powder into a tube furnace for pre-firing.

[0144] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0145] Step 6: Place the pre-burned bamboo charcoal into a high-temperature tube furnace for high-temperature carbonization.

[0146] Specifically, the sintering atmosphere is argon, the temperature is 1500℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0147] Step 7: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0148] Step 8: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 318.85 mAh / g, and the first-cycle coulombic efficiency is 85.42%. Example 3:

[0149] An embodiment of the present invention provides a method for coating and repairing aged hard carbon anodes, the steps of which include: Step 1: Place the aged bamboo charcoal into a crusher for three crushing processes, with each crushing process taking 1 minute.

[0150] Step 2: Soak the bamboo charcoal powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0151] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0152] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0153] Step 4: Dissolve rosin resin in ethanol, then add bamboo charcoal and stir well. Place the mixture in an oven to dry the ethanol.

[0154] Specifically, the ratio of bamboo charcoal to rosin resin is 20:1, the drying temperature is 70℃, and the drying time is 12 hours.

[0155] Step 5: Place the dried bamboo charcoal powder into a tube furnace for pre-firing.

[0156] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0157] Step 6: Place the pre-burned bamboo charcoal into a high-temperature tube furnace for high-temperature carbonization.

[0158] Specifically, the sintering atmosphere is argon, the temperature is 1500℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0159] Step 7: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0160] Step 8: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 315.65 mAh / g, and the first-cycle coulombic efficiency is 81.68%. Example 4:

[0161] An embodiment of the present invention provides a method for preparing hard carbon materials, the steps of which include: Step 1: Place the freshly burned bamboo charcoal into a crusher for three crushing processes, with each crushing process taking 1 minute.

[0162] Step 2: Soak the bamboo charcoal powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0163] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0164] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0165] Step 4: Dissolve rosin resin in ethanol, then add bamboo charcoal and stir well. Place the mixture in an oven to dry the ethanol.

[0166] Specifically, the ratio of bamboo charcoal to rosin resin is 10:1, the drying temperature is 70℃, and the drying time is 12 hours.

[0167] Step 5: Place the dried bamboo charcoal powder into a tube furnace for pre-firing.

[0168] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0169] Step 6: Place the pre-burned bamboo charcoal into a high-temperature tube furnace for high-temperature carbonization.

[0170] Specifically, the sintering atmosphere is argon, the temperature is 1500℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0171] Step 7: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0172] Step 8: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 320.3 mAh / g, and the first-cycle coulombic efficiency is 86.6%. Example 5:

[0173] An embodiment of the present invention provides a method for coating and repairing aged hard carbon anodes, the steps of which include: Step 1: Place the aged coconut shell charcoal into a crusher for three crushing processes, with each crushing process taking 1 minute.

[0174] Step 2: Soak the coconut shell charcoal powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0175] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0176] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0177] Step 4: Dissolve rosin resin in ethanol, then add coconut shell charcoal and stir well. Place the mixture in an oven to dry the ethanol.

[0178] Specifically, the ratio of coconut shell charcoal to rosin resin is 10:1, the drying temperature is 70℃, and the drying time is 12 hours.

[0179] Step 5: Place the dried coconut shell charcoal powder into a tube furnace for pre-firing.

[0180] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0181] Step 6: Place the pre-burned coconut shell charcoal into a high-temperature tube furnace for high-temperature carbonization.

[0182] Specifically, the sintering atmosphere is argon, the temperature is 1500℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0183] Step 7: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0184] Step 8: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 320.23 mAh / g, and the first-cycle coulombic efficiency is 83.2%. Example 6:

[0185] An embodiment of the present invention provides a method for coating and repairing aged hard carbon anodes, the steps of which include: Step 1: Place the aged anthracite into a crusher for three crushing processes, with each crushing process taking 1 minute.

[0186] Step 2: Soak the anthracite powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0187] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0188] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0189] Step 4: Dissolve rosin resin in ethanol, then add anthracite and stir well. Place the mixture in an oven to dry the ethanol.

[0190] Specifically, the ratio of anthracite to rosin is 10:1, the drying temperature is 70℃, and the drying time is 12 hours.

[0191] Step 5: Place the dried anthracite powder into a tubular furnace for pre-firing.

[0192] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0193] Step 6: Place the pre-burned anthracite into a high-temperature tubular furnace for high-temperature carbonization.

[0194] Specifically, the sintering atmosphere is argon, the temperature is 1300℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0195] Step 7: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0196] Step 8: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 274.21 mAh / g, and the first-cycle coulombic efficiency is 82.7%. Example 7:

[0197] An embodiment of the present invention provides a method for coating and repairing aged hard carbon anodes, the steps of which include: Step 1: Place the aged resin carbon into a crusher for three crushing processes, with each crushing process lasting 1 minute.

[0198] Step 2: Soak the resin carbon powder in 1 mol / L hydrochloric acid for 2 hours to remove impurities and ash.

[0199] Step 3: Wash the acid-washed material in deionized water until the water is neutral, and then dry it in an oven.

[0200] Specifically, the drying time is 12 hours and the temperature is 80℃.

[0201] Step 4: Dissolve rosin resin in ethanol, then add resin charcoal and stir well. Place the mixture in an oven to dry the ethanol.

[0202] Specifically, the ratio of resin charcoal to rosin resin is 10:1, the drying temperature is 70℃, and the drying time is 12 hours.

[0203] Step 5: Place the dried resin carbon powder into a tube furnace for pre-firing.

[0204] Specifically, the sintering atmosphere is argon, the carbonization temperature is 600℃, the holding time is 2h, and the heating rate is 5℃ / min.

[0205] Step 6: Place the pre-burned resin char into a high-temperature tube furnace for high-temperature carbonization.

[0206] Specifically, the sintering atmosphere is argon, the temperature is 1300℃, the holding time is 2h, and the heating rate is 3℃ / min.

[0207] Step 7: Use the cooled hard carbon material as the negative electrode material for sodium-ion batteries. Weigh the prepared hard carbon material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 92:4:4 and mix them evenly in an agate mortar. Add an appropriate amount of N-methylpyrrolidone and stir until a uniform slurry is formed. Use a scraper to evenly coat the slurry onto the surface of copper foil and dry it at 80°C under vacuum for 12 hours. Cut the Cu foil with active material into circular negative electrode sheets with a diameter of 11 mm and transfer them to a glove box for later use.

[0208] Step 8: In an argon-filled glove box, using the prepared hard carbon material as the negative electrode, a sodium sheet as the counter electrode, and NaPF6 in DIGLYME as the electrolyte, a button cell was assembled. After the assembled button cell was left to stand for 12 hours, it was placed in a 25°C constant temperature testing system and charged and discharged within a voltage range of 0-2.5V. The electrochemical test results are shown in Table 1. The table shows that the first-cycle specific capacity of the hard carbon negative electrode in this electrolyte is 287.37 mAh / g, and the first-cycle coulombic efficiency is 78.8%.

[0209]

[0210] As shown in Table 1, the specific capacity and first-cycle coulombic efficiency of biochar, coal-based char, and resin char precursors all decreased after aging. After coating with rosin resin, their performance was restored to the same level as unaged materials. However, direct coating on unaged materials did not improve performance. This is because the unaged materials have insufficient surface hydroxyl groups, preventing the carboxyl groups of the rosin resin from effectively undergoing esterification cross-linking, resulting only in a physical coating layer. This coating layer cannot reconstruct the pore structure or enhance interfacial reactivity and may even hinder ion diffusion pathways, thus failing to improve performance. Therefore, the rosin resin coating method has a significant repair effect on aged hard carbon materials.

[0211] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0212] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing anode materials based on aged hard carbon materials, characterized in that, It includes: Step S1: The aged hard carbon precursor is subjected to a preset number of crushing processes to obtain aged hard carbon particles of a preset particle size. Step S2: Pre-treat the aged hard carbon particles to obtain a hard carbon precursor. The pretreatment includes acid washing, alkali washing, water washing and ethanol washing; Step S3: Mix the hard carbon precursor with the coating material to obtain the coated hard carbon material. Step S4: The coated hard carbon material is pre-fired under a protective atmosphere with a first preset flow rate to obtain a raw hard carbon material. The pre-fired parameters include a first preset temperature, a first preset holding time, and a first preset heating rate. Step S5: Detect the coated hard carbon material to obtain the specific surface area of ​​the coated hard carbon material, and determine whether the preparation of the coated hard carbon material meets the preset standard based on the specific surface area; Step S6: The coated hard carbon material that meets the preset standard is subjected to high-temperature carbonization treatment in a protective atmosphere with a second preset flow rate to obtain the repaired hard carbon material product; the high-temperature carbonization treatment parameters include a second preset temperature, a second preset holding time, and a second preset heating rate. Step S7: Obtain the first coulombic efficiency of the hard carbon material product and determine whether the preparation of the hard carbon material product meets the preset standard based on the first coulombic efficiency; Step S8: In response to the fact that the preparation of the hard carbon material product does not meet the preset standard, the preparation of the hard carbon material product is checked according to the first charge specific capacity to determine whether it meets the preset standard, or the reason why the hard carbon material product does not meet the preset standard is determined according to the content of harmful functional groups on the surface.

2. The method for preparing anode materials based on aged hard carbon materials according to claim 1, characterized in that, In response to the specific surface area being less than a preset specific surface area threshold, it is determined that the preparation of the coated hard carbon material does not meet the preset standard, and the first preset heating rate is reduced according to the difference between the preset specific surface area threshold and the specific surface area. In response to the specific surface area being greater than or equal to a preset specific surface area threshold, it is determined that the preparation of the coated hard carbon material meets a preset standard.

3. The method for preparing anode materials based on aged hard carbon materials according to claim 2, characterized in that, The decrease in the first preset heating rate is positively correlated with the difference between the preset specific surface area threshold and the specific surface area.

4. The method for preparing anode materials based on aged hard carbon materials according to claim 3, characterized in that, In response to the first coulombic efficiency being less than a first preset first coulombic efficiency threshold, it is determined that the preparation of the hard carbon material product does not meet the preset standard, and the reason why the hard carbon material product does not meet the preset standard is determined based on the content of harmful functional groups on the surface. In response to the first coulombic efficiency being greater than or equal to a first preset first coulombic efficiency threshold and less than a second preset first coulombic efficiency threshold, it is determined that the preparation of the hard carbon material product does not meet the preset standard, and the preparation of the hard carbon material product is verified according to the first charge specific capacity. In response to the first coulombic efficiency being greater than or equal to a second preset first coulombic efficiency threshold, it is determined that the preparation of the hard carbon material product conforms to a preset standard.

5. The method for preparing anode materials based on aged hard carbon materials according to claim 4, characterized in that, In response to the fact that the specific capacity of the first charge is less than the preset specific capacity threshold of the first charge, the preparation of the hard carbon material product is verified to be inconsistent with the preset standard, and the second preset temperature of the high-temperature carbonization treatment is increased according to the difference between the preset specific capacity threshold of the first charge and the specific capacity of the first charge. In response to the first charge specific capacity being greater than or equal to a preset first charge specific capacity threshold, the preparation of the hard carbon material product is verified to meet the preset standard.

6. The method for preparing anode materials based on aged hard carbon materials according to claim 5, characterized in that, The increase in the second preset temperature is positively correlated with the difference between the preset first-cycle charging specific capacity threshold and the first-cycle charging specific capacity.

7. The method for preparing anode materials based on aged hard carbon materials according to claim 6, characterized in that, In response to the fact that the content of harmful functional groups on the surface is less than the preset threshold for the content of harmful functional groups on the surface, it is determined that the reason why the preparation of the hard carbon material product does not meet the preset standard is that the second preset heat preservation time of the high-temperature carbonization treatment is not up to standard, and the second preset heat preservation time is increased according to the difference between the preset threshold for the content of harmful functional groups on the surface and the content of harmful functional groups on the surface. In response to the fact that the content of harmful functional groups on the surface is greater than or equal to a preset threshold for the content of harmful functional groups on the surface, it is determined that the reason why the preparation of the finished hard carbon material does not meet the preset standard is that the preset particle size of the crushing process is not up to standard, and the preset particle size of the crushing is reduced according to the difference between the content of harmful functional groups on the surface and the preset threshold for the content of harmful functional groups on the surface.

8. The method for preparing anode materials based on aged hard carbon materials according to claim 7, characterized in that, The increase in the second preset heat preservation time is positively correlated with the difference between the preset threshold for the content of harmful functional groups on the surface and the content of harmful functional groups on the surface; The reduction in the preset particle size of the crushed material is positively correlated with the difference between the content of harmful functional groups on the surface and the preset threshold value of harmful functional groups on the surface.

9. The method for preparing anode materials based on aged hard carbon materials according to claim 8, characterized in that, The aged hard carbon precursor includes one of the following: bamboo charcoal, coconut shell charcoal, anthracite, lignite, peanut shell, phenolic resin, epoxy resin, and corn cob.

10. The method for preparing anode materials based on aged hard carbon materials according to claim 9, characterized in that, The coating material includes one of alumina, titanium dioxide, cadmium oxide, asphalt, rosin resin, vinyl resin, glucose, and polyacrylonitrile.

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