Sodium-ion battery negative electrode material based on corn cob derived hard carbon, negative electrode and preparation method thereof

Abstract

The invention relates to the technical field of sodium-ion battery negative electrode materials, in particular to a sodium-ion battery negative electrode material based on corn cob derived hard carbon, a negative electrode and a preparation method of the sodium-ion battery negative electrode material. According to the preparation method of the sodium-ion battery negative electrode material based on the corn cob derived hard carbon, the problems of low specific capacity and poor first effect of the traditional biomass hard carbon are solved through acid pretreatment, pre-carbonization synergistic pore forming, alkali activation layer expansion and sodium salt-asphalt dual coating modification; the obtained material has a hierarchical porous structure and a stable surface SEI film, the first efficiency in a sodium ion battery is greater than or equal to 87%, and the specific capacity at 0.1 C is greater than or equal to 325mAh / g.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, and in particular to a sodium-ion battery anode material based on corn-derived hard carbon, the anode, and its preparation method. Background Technology

[0002] With the rapid development of renewable energy and electric vehicles, lithium-ion batteries face challenges from lithium resource scarcity and rising costs. Sodium-ion batteries, due to the abundance, wide distribution, and low cost of sodium resources, have become a research hotspot in the energy storage field. However, the ionic radius of sodium ions is significantly larger than that of lithium ions, resulting in slow insertion / extraction kinetics and low capacity in traditional graphite anodes, which fails to meet practical needs. Therefore, developing high-performance sodium-ion battery anode materials has become a key technological breakthrough.

[0003] Hard carbon materials, due to their disordered microcrystalline structure and large interlayer spacing, can achieve high sodium storage capacity through mechanisms such as adsorption, intercalation, and pore filling, making them a mainstream candidate material for sodium-ion battery anodes. Their raw material composition is mainly resin-based carbon and biomass-derived carbon. While typical polymer precursors such as phenol-formaldehyde resin, polyacrylonitrile, and starch are widely used in hard carbon preparation, these petroleum derivatives not only have high raw material costs but also pose significant environmental pollution risks during precursor preparation and high-temperature pyrolysis carbonization. In contrast, biomass-based raw materials exhibit significant advantages, with renewable, eco-friendly, and economical sources. Preparing hard carbon materials through biomass conversion can not only significantly reduce production costs but also effectively alleviate the environmental pollution problems caused by large-scale waste incineration.

[0004] Currently, biomass hard carbon feedstock systems cover categories such as coconut shells, bamboo, glucose, and straw. However, hard carbon prepared from these carbon sources generally suffers from technical bottlenecks such as low coulombic efficiency, insufficient cycle stability, and poor rate performance. Some biomass feedstocks also face problems such as drastic price fluctuations and mismatches between growth cycles and industrial production. Furthermore, the large amount of byproducts generated during processing can easily cause secondary pollution. For example, existing biomass hard carbon (coconut shells, bamboo, etc.) generally suffers from low initial efficiency (<80%), insufficient specific capacity (coconut shell-derived hard carbon 0.1C capacity is generally <300 mAh / g), and poor cycle stability, mainly due to disordered pore structure and surface defects leading to excessive SEI film growth. Summary of the Invention

[0005] The main objective of this invention is to provide a sodium-ion battery anode material based on corn-derived hard carbon, the anode itself, and a method for preparing the same, in order to solve the aforementioned technical problems. This results in the sodium-ion battery anode material based on corn-derived hard carbon exhibiting superior rate performance and cycle stability, and the prepared anode possessing high initial efficiency and high capacity.

[0006] To achieve the above objectives, this invention provides a method for preparing a sodium-ion battery anode material based on corn-derived hard carbon, comprising the following steps: S1: Acid pretreatment: The crushed corn cobs are subjected to acid treatment, and the filtered product is dried to obtain a biomass precursor. S2: Pre-carbonization treatment: The biomass precursor is pre-carbonized in an inert atmosphere and then cooled to obtain a hard carbon intermediate; S3: Crushing process: The hard carbon intermediate is crushed to obtain hard carbon powder A with a particle size D50 between 7 and 9 μm; S4: Alkali activation: Hard carbon powder A is mixed with sodium hydroxide solution, and then washed and dried in sequence to obtain hard carbon powder B; S5: Coating and high-temperature carbonization: Hard carbon powder B is mixed with sodium salt and asphalt, and then subjected to gradient calcination in an inert mixed atmosphere. After cooling and grinding, the final product is obtained, which is the sodium-ion battery anode material.

[0007] Preferably, step S1 specifically includes: soaking the crushed corn cobs in a mixed acid solution for acid treatment, ultrasonically vibrating them at room temperature, washing them with deionized water after filtration until the pH of the filtrate is 6-7, and then drying them in a vacuum drying oven at 80°C for 12 hours to obtain the biomass precursor.

[0008] Preferably, the acid solution is a binary mixture of nitric acid and hydrochloric acid.

[0009] Preferably, the concentration of nitric acid in the mixed acid is 6-9 mol / L, the concentration of hydrochloric acid is 6-9 mol / L, and the volume ratio of nitric acid to hydrochloric acid is 1:1-5.

[0010] Preferably, in step S2, the pre-carbonization temperature is 300℃~450℃, the pre-carbonization time is 8-10 h, and the inert atmosphere is a mixture of argon and carbon dioxide with a flow rate of 1~5 L / min.

[0011] Preferably, in step S4, the concentration of sodium hydroxide is 3~5 mol / L, the mass ratio of hard carbon powder to sodium hydroxide is 1:2, the mixing temperature is 60℃~80℃, and the mixing and stirring time is 6~8 h.

[0012] Preferably, in step S5, the sodium salt is at least one of sodium carbonate, sodium nitrate or sodium acetate, the asphalt is asphalt with a softening point of 270°C to 280°C, the mass ratio of sodium salt to hard carbon powder is 5wt% to 10wt%, and the mass ratio of asphalt to hard carbon powder is 1wt% to 5wt%.

[0013] Preferably, in step S5, the mixing time of hard carbon powder B with sodium salt and asphalt is 3~5 h. The gradient calcination includes a first gradient, a second gradient and a third gradient. The calcination temperature of the first gradient is 350℃ and held for 2 h. The calcination temperature of the second gradient is the melting temperature or decomposition temperature of sodium salt. The calcination temperature of the third gradient is 1150℃~1350℃ and held for 4~6 h.

[0014] The present invention also provides a negative electrode material, including a sodium-ion battery negative electrode material prepared by the preparation method described above.

[0015] The present invention also provides a negative electrode, which is prepared using the negative electrode material described above.

[0016] The present invention also provides an application of the sodium-ion battery anode material prepared according to the above preparation method as a sodium-ion battery anode material.

[0017] This invention uses large-scale artificially cultivated corn as the core raw material, leveraging its abundant renewable resource reserves to construct a novel preparation system with a stable and reliable raw material source and significantly lower overall production costs than traditional petrochemical raw materials. Through innovative technological pathways, it achieves a breakthrough in the efficient conversion of artificially cultivated biomass resources into high-value-added products, providing a sustainable raw material solution for the industrialization of bio-based materials. Attached Figure Description

[0018] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the preparation process of the sodium-ion battery anode material in this invention.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] The following is in conjunction with the appendix Figure 1 The present invention provides a clear and complete description of the technical problems solved by the embodiments, the technical solutions adopted, and the technical effects achieved. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other equivalent or obvious variations of embodiments obtained by those skilled in the art without creative effort fall within the protection scope of this invention. The embodiments of this invention can be embodied in various different ways as defined and covered by the claims.

[0021] It should be noted that many specific details are given in the following description for ease of understanding. However, it is obvious that the present invention may be implemented without these specific details.

[0022] It should be noted that, in the absence of explicit limitations or conflicts, the various embodiments and their technical features in this invention can be combined with each other to form a technical solution.

[0023] Example 1: Preparation method of corn-derived hard carbon anode material, the specific steps are as follows: S1: Crush 1 kg of corn cob with a small crusher, pass it through a 50-mesh sieve, and continue crushing if it does not pass through the sieve. Take the sieved material and soak it in a mixture of nitric acid (6 mol / L) and hydrochloric acid (6 mol / L) in a volume ratio of 1:3. Sonicate for 3 hours with the ultrasonic frequency set to 40 kHz and the power density controlled at 0.8 W / cm². After filtration through a Buchner funnel, wash with deionized water until the pH of the filtrate is 6.8. Then dry it in a vacuum drying oven at 80°C for 12 hours to obtain the biomass precursor. S2: The precursor is placed in a graphite crucible and heated to 350°C at a heating rate of 10°C / min under an inert atmosphere of argon (10%) and carbon dioxide. The temperature is held for 8 hours and then naturally cooled to obtain a hard carbon intermediate. S3: Hard carbon powder A is obtained by crushing the hard carbon precursor to a particle size D50 of 8μm using an air jet mill; S4: Hard carbon powder A and sodium hydroxide (3mol / L) were mixed and stirred at a mass ratio of 1:2. The mixture was heated to 80℃, stirred at 500r / min for 6 hours, washed and dried to obtain hard carbon powder B. S5: Mix hard carbon powder B, sodium acetate, and pitch (softening point 275℃) in a mixer at a ratio of 85:10:5 for 5 hours. After mixing, place the mixture in a ceramic crucible and heat it in a nitrogen atmosphere from room temperature to 300℃ at a rate of 10℃ / h, hold for 2 hours, then heat it to 350℃ at a rate of 10℃ / h, hold for 2 hours, then heat it to 1250℃ at a rate of 2℃ / min, hold for 6 hours, and after naturally cooling to room temperature, grind it in an agate mortar and pestle and pass it through a 250-mesh sieve. The material passing through the sieve is the final product.

[0024] Manufacturing method of negative electrode sheet: The final products were mixed in a mass ratio of 85:5:10 (hard carbon: SuperP: PVDF) and stirred evenly to form a slurry; The slurry was uniformly coated onto the surface of the aluminum foil current collector using a 200mm scraper, and then placed in an 80℃ vacuum drying oven for 24 hours to dry completely. The resulting disc electrode was then precisely punched to obtain a diameter of 12mm.

[0025] Electrical performance testing: A CR2032 coin cell was assembled in an argon-filled glove box using a sodium metal sheet as the counter electrode and a 1M NaPF6 / ethylene glycol dimethyl ether electrolyte. Test results showed that the specific capacity of this electrode during the first charge cycle was 336 mAh g. -1 The initial Coulomb efficiency was 89.3%.

[0026] Example 2: The only difference between Example 2 and Example 1 is that the volume ratio of nitric acid to hydrochloric acid is 1:5; the other operating steps are the same as in Example 1.

[0027] Electrical performance testing: A CR2032 coin cell was assembled in an argon-filled glove box using a sodium metal sheet as the counter electrode and a 1M NaPF6 / ethylene glycol dimethyl ether electrolyte. Test results showed that the specific capacity of this electrode during the first charge cycle was 339 mAhg. -1 The initial Coulomb efficiency was 90%.

[0028] Example 3: S1: Crush 1 kg of corn cob with a small crusher, pass it through a 50-mesh sieve, and continue crushing if it does not pass through the sieve. Take the sieved material and soak it in a mixture of nitric acid (9 mol / L) and hydrochloric acid (9 mol / L) in a volume ratio of 1:3. Sonicate for 3 hours with the ultrasonic frequency set to 40 kHz and the power density controlled at 0.8 W / cm². After filtration through a Buchner funnel, wash with deionized water until the pH of the filtrate is 6.8. Then dry it in a vacuum drying oven at 80 ℃ for 12 hours to obtain the biomass precursor. S2: The precursor is placed in a graphite crucible and heated to 350°C at a heating rate of 10°C / min under an inert atmosphere of argon (10%) and carbon dioxide. The temperature is held for 8 hours and then naturally cooled to obtain a hard carbon intermediate. S3: Hard carbon powder A is obtained by crushing the hard carbon precursor to a particle size D50 of 8μm using an air jet mill; S4: Hard carbon powder A and sodium hydroxide (3mol / L) were mixed and stirred at a mass ratio of 1:2. The mixture was heated to 80℃, stirred at 500r / min for 6 hours, washed and dried to obtain hard carbon powder B. S5: Mix hard carbon powder B, sodium nitrate, and pitch (softening point 275℃) in a mixer at a ratio of 85:10:5 for 5 hours. After mixing, place the mixture in a ceramic crucible and heat it in a nitrogen atmosphere from room temperature to 300℃ at a rate of 10℃ / h and hold for 2 hours. Then, heat it to 350℃ at a rate of 10℃ / h and hold for 2 hours. Finally, heat it to 1250℃ at a rate of 2℃ / min and hold for 6 hours. After naturally cooling to room temperature, grind the mixture in an agate mortar and pestle and pass it through a 250-mesh sieve. The material passing through the sieve is the final product.

[0029] Manufacturing method of negative electrode sheet: The final products were mixed in a mass ratio of 85:5:10 (hard carbon: SuperP: PVDF) and stirred evenly to form a slurry; The slurry was uniformly coated onto the surface of the aluminum foil current collector using a 200mm scraper, and then placed in an 80℃ vacuum drying oven for 24 hours to dry completely. The resulting disc electrode was then precisely punched to obtain a diameter of 12mm.

[0030] Electrical performance testing: A CR2032 coin cell was assembled in an argon-filled glove box using a sodium metal sheet as the counter electrode and a 1M NaPF6 / ethylene glycol dimethyl ether electrolyte. Test results showed that the specific capacity of this electrode during the first charge cycle was 340 mAh g. -1 The initial Coulomb efficiency was 91.3%.

[0031] Example 4: S1: Crush 1 kg of corn cob with a small crusher, pass it through a 50-mesh sieve, and continue crushing if it does not pass through the sieve. Take the sieved material and soak it in a mixture of nitric acid (6 mol / L) and hydrochloric acid (6 mol / L) in a volume ratio of 1:3. Sonicate for 3 hours with the ultrasonic frequency set to 40 kHz and the power density controlled at 0.8 W / cm². After filtration through a Buchner funnel, wash with deionized water until the pH of the filtrate is 6.8. Then dry it in a vacuum drying oven at 80°C for 12 hours to obtain the biomass precursor. S2: The precursor is placed in a graphite crucible and heated to 350°C at a heating rate of 10°C / min under an inert atmosphere of argon (10%) and carbon dioxide. The temperature is held for 8 hours and then naturally cooled to obtain a hard carbon intermediate. S3: Hard carbon powder A is obtained by crushing the hard carbon precursor to a particle size D50 of 8μm using an air jet mill; S4: Hard carbon powder A and sodium hydroxide (3mol / L) were mixed and stirred at a mass ratio of 1:2. The mixture was heated to 80℃, stirred at 500r / min for 6 hours, washed and dried to obtain hard carbon powder B. S5: Mix hard carbon powder B, sodium acetate, and pitch (softening point 275℃) in a mixer at a ratio of 85:10:5 for 5 hours. After mixing, place the mixture in a ceramic crucible and heat it in a nitrogen atmosphere from room temperature to 300℃ at a rate of 10℃ / h, hold for 2 hours, then heat it to 350℃ at a rate of 10℃ / h, hold for 2 hours, then heat it to 1250℃ at a rate of 2℃ / min, hold for 6 hours, and after naturally cooling to room temperature, grind it in an agate mortar and pestle and pass it through a 250-mesh sieve. The material passing through the sieve is the final product.

[0032] Manufacturing method of negative electrode sheet: The final products were mixed in a mass ratio of 85:5:10 (hard carbon: SuperP: PVDF) and stirred evenly to form a slurry; The slurry was uniformly coated onto the surface of the aluminum foil current collector using a 200mm scraper, and then placed in an 80℃ vacuum drying oven for 24 hours to dry completely. The resulting disc electrode was then precisely punched to obtain a diameter of 12mm.

[0033] Electrical performance testing: A CR2032 coin cell was assembled in an argon-filled glove box using a sodium metal sheet as the counter electrode and a 1M NaPF6 / ethylene glycol dimethyl ether electrolyte. Test results showed that the specific capacity of this electrode during the first charge cycle was 343 mAh g. -1 The initial Coulomb efficiency was 90.5%.

[0034] Example 5: S1: Crush 1 kg of corn cob with a small crusher, pass it through a 50-mesh sieve, and continue crushing if it does not pass through the sieve. Take the sieved material and soak it in a mixture of nitric acid (6 mol / L) and hydrochloric acid (6 mol / L) in a volume ratio of 1:3. Sonicate for 3 hours with the ultrasonic frequency set to 40 kHz and the power density controlled at 0.8 W / cm². After filtration through a Buchner funnel, wash with deionized water until the pH of the filtrate is 6.8. Then dry it in a vacuum drying oven at 80°C for 12 hours to obtain the biomass precursor. S2: The precursor is placed in a graphite crucible and heated to 350°C at a heating rate of 10°C / min under an inert atmosphere of argon (10%) and carbon dioxide. The temperature is held for 8 hours and then naturally cooled to obtain a hard carbon intermediate. S3: Hard carbon powder A is obtained by crushing the hard carbon precursor to a particle size D50 of 8μm using an air jet mill; S4: Hard carbon powder A and sodium hydroxide (3mol / L) were mixed and stirred at a mass ratio of 1:2. The mixture was heated to 80℃, stirred at 500r / min for 6 hours, washed and dried to obtain hard carbon powder B. S5: Mix hard carbon powder B, sodium acetate, and pitch (softening point 275℃) in a mixer at a ratio of 92:5:3 for 5 hours. After mixing, place the mixture in a ceramic crucible and heat it in a nitrogen atmosphere from room temperature to 300℃ at a rate of 10℃ / h and hold for 2 hours. Then, heat it to 350℃ at a rate of 10℃ / h and hold for 2 hours. Finally, heat it to 1250℃ at a rate of 2℃ / min and hold for 6 hours. After naturally cooling to room temperature, grind the mixture in an agate mortar and pestle and pass it through a 250-mesh sieve. The material passing through the sieve is the final product.

[0035] Manufacturing method of negative electrode sheet: The final products were mixed in a mass ratio of 85:5:10 (hard carbon: SuperP: PVDF) and stirred evenly to form a slurry; The slurry was uniformly coated onto the surface of the aluminum foil current collector using a 200mm scraper, and then placed in an 80℃ vacuum drying oven for 24 hours to dry completely. The resulting disc electrode was then precisely punched to obtain a diameter of 12mm.

[0036] Electrical performance testing: A CR2032 coin cell was assembled in an argon-filled glove box using a sodium metal sheet as the counter electrode and a 1M NaPF6 / ethylene glycol dimethyl ether electrolyte. Test results showed that the specific capacity of this electrode during the first charge cycle was 325 mAh g. -1 The initial Coulomb efficiency was 87%.

[0037] Comparative Example 1: S1: Crush 1 kg of corn cob with a small crusher, pass it through a 50-mesh sieve, and continue crushing if it does not pass through the sieve. Take the sieved material and soak it in a mixture of nitric acid (6 mol / L) and hydrochloric acid (6 mol / L) in a volume ratio of 1:3. Sonicate for 3 hours with the ultrasonic frequency set to 40 kHz and the power density controlled at 0.8 W / cm². After filtration through a Buchner funnel, wash with deionized water until the pH of the filtrate is 6.8. Then dry it in a vacuum drying oven at 80°C for 12 hours to obtain the biomass precursor. S2: The precursor is placed in a graphite crucible and heated to 350°C at a heating rate of 10°C / min under an inert atmosphere of argon (10%) and carbon dioxide. The temperature is held for 8 hours and then naturally cooled to obtain a hard carbon intermediate. S3: Hard carbon powder A is obtained by crushing the hard carbon precursor to a particle size D50 of 8μm using an air jet mill; S4: Hard carbon powder A and sodium hydroxide (3mol / L) were mixed and stirred at a mass ratio of 1:2. The mixture was heated to 80℃, stirred at 500r / min for 6 hours, washed and dried to obtain hard carbon powder B. S5: Mix hard carbon powder B, sodium acetate, and pitch (softening point 275℃) in a mixer at a ratio of 92:5:3 for 5 hours. After mixing, place the mixture in a ceramic crucible and heat it in a nitrogen atmosphere from room temperature to 300℃ at a rate of 10℃ / h and hold for 2 hours. Then, heat it to 350℃ at a rate of 10℃ / h and hold for 2 hours. Finally, heat it to 1250℃ at a rate of 2℃ / min and hold for 6 hours. After naturally cooling to room temperature, grind the mixture in an agate mortar and pestle and pass it through a 250-mesh sieve. The material passing through the sieve is the final product.

[0038] Manufacturing method of negative electrode sheet: The final products were mixed in a mass ratio of 85:5:10 (hard carbon: SuperP: PVDF) and stirred evenly to form a slurry; The slurry was uniformly coated onto the surface of the aluminum foil current collector using a 200mm scraper, and then placed in an 80℃ vacuum drying oven for 24 hours to dry completely. The resulting disc electrode was then precisely punched to obtain a diameter of 12mm.

[0039] Electrical performance testing: A CR2032 coin cell was assembled in an argon-filled glove box using a sodium metal sheet as the counter electrode and a 1M NaPF6 / ethylene glycol dimethyl ether electrolyte. Test results showed that the specific capacity of this electrode during the first charge cycle was 290 mAh g. -1 The initial Coulomb efficiency was 83%.

[0040] Comparative Example 2: S1: Crush 1 kg of corn cobs with a small crusher, pass through a 50-mesh sieve, and continue crushing if the cob does not pass through the sieve. Take the material that passes through the sieve to obtain the precursor. S2: The precursor is placed in a graphite crucible and heated to 350°C at a heating rate of 10°C / min under an inert atmosphere of argon (10%) and carbon dioxide. The temperature is held for 8 hours and then naturally cooled to obtain a hard carbon intermediate. S3: Hard carbon powder A is obtained by crushing the hard carbon precursor to a particle size D50 of 8μm using an air jet mill; S4: Hard carbon powder A and sodium hydroxide (3mol / L) were mixed and stirred at a mass ratio of 1:2. The mixture was heated to 80℃, stirred at 500r / min for 6 hours, washed and dried to obtain hard carbon powder B. S5: Place hard carbon powder B into a ceramic crucible and heat it from room temperature to 300℃ at 10℃ / h under a nitrogen atmosphere, hold for 2h, heat it to 350℃ at 10℃ / h, hold for 2h, heat it to 1250℃ at 2℃ / min, hold for 6h, and then cool it to room temperature naturally. Grind it in an agate mortar and pestle and pass it through a 250-mesh sieve. The material passing through the sieve is the final product. Manufacturing method of negative electrode sheet: The final products were mixed in a mass ratio of 85:5:10 (hard carbon: SuperP: PVDF) and stirred evenly to form a slurry; The slurry was uniformly coated onto the surface of the aluminum foil current collector using a 200mm scraper, and then placed in an 80℃ vacuum drying oven for 24 hours to dry completely. The resulting disc electrode was then precisely punched to obtain a diameter of 12mm.

[0041] Electrical performance testing: A CR2032 coin cell was assembled in an argon-filled glove box using a sodium metal sheet as the counter electrode and a 1M NaPF6 / ethylene glycol dimethyl ether electrolyte. Test results showed that the specific capacity of this electrode during the first charge cycle was 312 mAh g. -1 The initial Coulomb efficiency was 85%.

[0042] Table 1. Electrochemical performance of Examples 1-5 and Comparative Examples 1-2

[0043] As shown in Table 1, the hard carbon anode materials prepared in Examples 1-5, when used as anode active materials for sodium-ion batteries, all resulted in a first-charge specific capacity of over 325 mAh g⁻¹ for the corresponding sodium-ion batteries. -1 The initial coulombic efficiency is higher than 87%. Compared with the hard carbon anode materials prepared in Comparative Examples 1-2 as anode active materials for sodium-ion batteries, the sodium-ion batteries prepared with the hard carbon anode materials prepared in Examples 1-5 of this invention all have significantly improved discharge specific capacity and initial coulombic efficiency.

[0044] As shown in Table 1, the initial discharge specific capacity and coulombic efficiency of Comparative Example 1 were significantly lower than those of Example 1. In Example 1, sodium acetate decomposed at high temperature to generate sodium oxide, and the simultaneously released etching gas achieved initial pore formation on the carbon matrix. When the temperature rose to 600°C, sodium and lithium salts began to participate in the etching reaction of the carbon matrix, constructing a rich microporous network. With the gradual increase in temperature and reaction time, the microporous structure gradually evolved into mesopores and macropores, eventually forming a connected hierarchical porous system. During this process, the reduced metallic sodium was vaporized and escaped along with the lithium components. Notably, high-temperature sodium vapor can selectively react with the defect sites and oxygen-containing functional groups on the hard carbon surface, effectively repairing surface defects. At the same time, sodium oxide completely decomposed into gaseous products at ultra-high temperatures, ensuring that no residual impurities interfered with the sodium storage performance. Trace amounts of sodium selectively accumulated on the hard carbon surface during high-temperature migration, significantly improving cycle stability by inducing the formation of a thin, dense SEI film. The continuous conductive network constructed from high softening point asphalt (270-280℃) provides an ideal carrier for the above reactions.

[0045] As shown in Table 1, the initial discharge specific capacity and initial coulombic efficiency in Comparative Example 2 were significantly lower than the corresponding electrochemical performance parameters in Example 1. Nitric acid and hydrochloric acid synergistically corroded the lignin in corn cobs, removing metallic impurities and forming a micro-mesoporous composite structure, forming interconnected pores and increasing the sodium ion diffusion rate.

[0046] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for preparing a sodium-ion battery anode material based on hard carbon derived from corn cob, characterized in that, The method comprises the steps of: S1: acid pretreatment: the crushed corn cob is subjected to acid treatment, and the obtained object product is dried to obtain a biomass precursor; S2: pre-carbonization treatment: the biomass precursor is subjected to pre-carbonization in an inert atmosphere, and then cooled to obtain a hard carbon intermediate; S3: crushing treatment: the hard carbon intermediate is crushed to obtain hard carbon powder A with a particle size D50 of 7-9 μm; S4: alkali activation: the hard carbon powder A is mixed with a sodium hydroxide solution, and then subjected to washing and drying in sequence to obtain hard carbon powder B; S5: coating and high-temperature carbonization: the hard carbon powder B is mixed with a sodium salt and pitch, and subjected to gradient calcination in an inert mixed gas atmosphere, and then cooled and ground to obtain a final product, i.e., a sodium ion battery negative electrode material.

2. The production method according to claim 1, characterized by, The step S1 specifically comprises: the crushed corn cob is soaked in a mixed acid solution for acid treatment, and subjected to ultrasonic oscillation treatment at room temperature, and then washed with deionized water until the pH value of the filtrate is 6-7, and then dried in a vacuum drying box at 80°C for 12 hours to obtain the biomass precursor.

3. The preparation method according to claim 2, characterized in that, The acid solution is a binary mixed system of nitric acid and hydrochloric acid.

4. The production method according to claim 3, characterized by, The concentration of the nitric acid in the mixed acid is 6-9 mol / L, the concentration of the hydrochloric acid is 6-9 mol / L, and the volume ratio of the nitric acid to the hydrochloric acid is 1:1-5.

5. The preparation method according to claim 1, characterized in that, In the step S2, the pre-carbonization temperature is 300°C-450°C, and the pre-carbonization time is 8-10 h; the inert atmosphere is a mixed gas atmosphere of argon and carbon dioxide, and the flow rate is 1-5 L / min.

6. The method of claim 1, wherein, In the step S4, the concentration of the sodium hydroxide is 3-5 mol / L, the mass ratio of the hard carbon powder to the sodium hydroxide is 1:2, the mixing temperature is 60°C-80°C, and the mixing and stirring time is 6-8 h.

7. The preparation method according to claim 1, characterized in that, In the step S5, the sodium salt is at least one of sodium carbonate, sodium nitrate or sodium acetate, the pitch is pitch with a softening point of 270°C to 280°C, the mass ratio of the sodium salt to the hard carbon powder is 5wt%-10wt%, and the mass ratio of the pitch to the hard carbon powder is 1wt%-5wt%.

8. The preparation method according to claim 7, characterized in that, In the step S5, the mixing time of the hard carbon powder B, the sodium salt and the pitch is 3-5 h, the gradient calcination comprises a first gradient, a second gradient and a third gradient, the calcination temperature of the first gradient is 350°C for 2 h, the calcination temperature of the second gradient is the melting temperature or the decomposition temperature of the sodium salt, and the calcination temperature of the third gradient is 1150°C-1350°C for 4-6 h.

9. A negative electrode material, characterized by, The sodium ion battery negative electrode material prepared by the method according to any one of claims 1-8.

10. A negative electrode characterized by comprising: The negative electrode material according to claim 9 is used for preparation.

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