Modified rice husk-based hard carbon material and preparation method and application thereof

Abstract

This invention discloses a modified rice husk-based hard carbon material, its preparation method, and its application, belonging to the technical field of hard carbon material preparation and application. Specifically, it includes the following steps: rice husks are washed, soaked in sodium hydroxide, and then dried to obtain pure rice husks. Next, the pure rice husks are carbonized and ball-milled to obtain rice husk-based carbon powder. Finally, the rice husk-based carbon powder is compounded with an aerogel composite to obtain the modified rice husk-based hard carbon material. This invention purifies and carbonizes rice husks and then combines them with an aerogel composite; the two work synergistically to further optimize the initial discharge specific capacity, initial coulombic efficiency, and coefficient of thermal expansion of the rice husk-based hard carbon material as a battery anode.

Description

Technical Field

[0001] This invention relates to the field of hard carbon material preparation and application technology, specifically to a modified rice husk-based hard carbon material, its preparation method, and its application. Background Technology

[0002] Currently, commercial lithium-ion battery anodes are mainly composed of graphite-based materials. However, the theoretical specific capacity of graphite needs to be improved, and lithium crystallization is prone to occur during high-rate charge and discharge, making it difficult to meet the requirements of high capacity and high safety for next-generation batteries. To address this, researchers have focused on hard carbon materials, which have a disordered graphite-like structure, a theoretical specific capacity significantly higher than that of graphite, and excellent rate performance and cycle stability. They are highly promising next-generation anode materials. Among them, biomass-based hard carbon has attracted attention due to its wide availability of raw materials, low cost, and good environmental compatibility. Rice husks, as agricultural waste, are mainly composed of cellulose, hemicellulose, and lignin. After carbonization, they can form porous hard carbon, making them an ideal raw material for preparing biomass-based hard carbon.

[0003] However, the current preparation and application of rice husk-based hard carbon faces several technical bottlenecks. First, rice husks contain impurities such as ash, silica, and lignin. If not effectively purified, these impurities can clog lithium storage channels and disrupt the uniformity of the carbon structure during carbonization, reducing active sites for lithium storage. They may also undergo irreversible reactions with lithium ions, reducing battery capacity and efficiency. Second, improper control of parameters such as carbonization temperature and atmosphere can easily lead to excessively high or low graphitization of hard carbon. The former reduces lithium storage micropores and defect sites, while the latter reduces conductivity, both affecting the initial discharge specific capacity and ion transport efficiency. Third, the thermal expansion coefficient of pure rice husk-based hard carbon is difficult to control. Temperature fluctuations during battery charging and discharging can easily cause changes in material volume, damaging the electrode structure and affecting cycle stability and safety.

[0004] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a modified rice husk-based hard carbon material, its preparation method, and its application, in order to address the technical deficiencies mentioned in the background art.

[0006] The objective of this invention can be achieved through the following technical solution: a method for preparing a modified rice husk-based hard carbon material, comprising the following steps:

[0007] S1. Wash the rice husks with deionized water and mix them with sodium hydroxide. Add the mixture to a reaction vessel containing deionized water and heat it at 65-75℃ for 3-4 hours. Then, add hydrochloric acid solution dropwise until the pH of the solution is neutral. Filter the mixture, wash it with deionized water, and dry it to obtain pure rice husks.

[0008] S2. Transfer the pure rice husks to a ceramic firing boat and place them together in a tube furnace. Keep them at 1000-1200℃ in a nitrogen atmosphere for 4-6 hours. Then, let them cool naturally to room temperature in a nitrogen atmosphere and remove them. Transfer them to a planetary ball mill and ball mill for 9-10 hours to obtain rice husk-based carbon powder.

[0009] S3. Grind the aerogel composite, pass it through a 200-mesh sieve, and add it together with rice husk-based carbon powder into ethanol and deionized water. Disperse it ultrasonically for 40-60 minutes. Add tetrabutyl titanate to the reaction system, stir for 5-10 minutes, and then transfer it to a vacuum drying oven to dry at 80°C for 6 hours to obtain modified rice husk-based hard carbon material.

[0010] Furthermore, in step S1, the ratio of rice husk, sodium hydroxide, and deionized water is 1g:1g:4mL, and the concentration of the hydrochloric acid solution is 1mol / L.

[0011] Furthermore, in step S3, the ratio of the aerogel composite, rice husk-based carbon powder, ethanol-deionized water, and tetrabutyl titanate is 1g:4g:50mL:5mL:0.3-0.4g.

[0012] Further, in step S3, the preparation method of the aerogel composite is as follows: the porous aerogel is added to a reaction vessel containing isopropanol and aniline, and after standing for 20-30 minutes, the excess isopropanol and aniline are poured out. Then, a mixed solution is added dropwise. After the addition is complete, the mixture is shaken for 20-30 minutes and then stood for 12 hours. The mixture is first washed with methanol solution until the solution is colorless, and then washed with deionized water until the graphite skeleton settles to the bottom. After freeze-drying for 24 hours, the mixture is taken out and placed in a tube furnace and annealed in an argon atmosphere at 600-800℃ for 1-2 hours to obtain the aerogel composite.

[0013] The reaction principle for preparing aerogel complexes is as follows:

[0014] First, utilizing the high specific surface area and three-dimensional porous structure of porous aerogels, isopropanol is used as a solvent to reduce the interfacial tension between aniline and the porous aerogel framework, facilitating the full penetration and adsorption of aniline molecules into the pores and surface of the porous aerogel. Then, a mixed solution of ammonium sulfate, phytic acid, and deionized water is added dropwise. Ammonium sulfate acts as an oxidant, initiating an oxidative polymerization reaction of aniline. Simultaneously, phytic acid acts as a dopant and crosslinking agent; its multiple phosphate groups can form hydrogen bonds with the polyaniline molecular chains, achieving doping modification of polyaniline and enhancing its bonding force with the porous aerogel framework. Next, methanol is used for washing to remove unreacted organic impurities, followed by washing with deionized water to remove water-soluble impurities. Then, freeze-drying removes moisture from the precursor while preserving its three-dimensional porous characteristics to the greatest extent. Finally, annealing is performed under an argon inert atmosphere. This process causes the phytic acid-doped polyaniline to undergo a carbonization reaction, transforming it into a structurally stable carbon-based material. Simultaneously, it promotes the formation of a tight interfacial bond between the porous aerogel framework and the carbonization product, resulting in an aerogel composite.

[0015] Furthermore, the ratio of the porous aerogel, isopropanol, aniline, and the mixed solution is 1g:3.0-3.5mL:0.08mL:4.9-5.1mL, and the mixed solution is obtained by uniformly mixing ammonium sulfate, phytic acid, and deionized water in a ratio of 0.5g:2.1-2.2mL:5mL.

[0016] Furthermore, the porous aerogel is prepared by the following steps:

[0017] B1. Mix copper nitrate aqueous solution and sodium hydroxide aqueous solution and stir until the solution color changes from colorless to blue. Add ethylenediamine and continue stirring for 3-5 minutes. Then add hydrazine hydrate and stir until the color turns milky white. Place it in a water bath at 50-60℃ and keep it warm for 3-4 hours. After the reaction is complete, take out the upper red copper-based nanoparticles and wash them with deionized water 4-5 times to obtain copper-based nanoparticles.

[0018] B2. Disperse copper-based nanoparticles in deionized water, add polyvinylpyrrolidone solution dropwise, stir evenly, pour into a mold, and place in liquid nitrogen for rapid freezing and molding. Then, freeze-dry under vacuum for 48 hours, anneal at high temperature in a hydrogen-argon mixed atmosphere at 500-600℃, transfer to ethanol for soaking for 2-3 hours, wash with deionized water until the block settles to the bottom, remove the deionized water from the surface, and obtain carbonized aerogel.

[0019] B3. Immerse the carbonized aerogel in ferric chloride hydrochloric acid solution for 24 hours, wash with deionized water 5-6 times, and freeze-dry to obtain porous aerogel.

[0020] The reaction principle for preparing porous aerogels is as follows:

[0021] First, copper nitrate reacts with sodium hydroxide in a metathesis reaction to form a blue copper hydroxide precipitate. Then, ethylenediamine is added as a complexing agent to coordinate with the copper hydroxide, forming a stable copper-ethylenediamine complex. Next, hydrazine hydrate exerts its strong reducing properties under warm conditions in a 50-60°C water bath, converting the complexed Cu... 2+ The copper atoms are reduced to elemental copper, and under the directional guidance of ethylenediamine, copper atoms grow in a directional manner to form copper-based nanoparticles. These nanoparticles are then dispersed in deionized water. The addition of polyvinylpyrrolidone (PVP) ensures uniform dispersion of the nanoparticles through its hydrophilic groups, preventing agglomeration. Simultaneously, PPVP acts as a carbon source, coating the surface of the nanoparticles. Rapid freezing with liquid nitrogen causes the water in the system to quickly form an ice crystal framework. Vacuum freeze-drying removes the ice crystals, preserving the porous composite structure. Annealing in a hydrogen-argon mixed atmosphere causes PPVP to undergo a high-temperature carbonization reaction, forming a dense graphitic carbon coating on the surface of the copper nanoparticles, resulting in a carbonized aerogel. Finally, in a ferric chloride hydrochloric acid solution, Fe... 3+ It exhibits strong oxidizing properties in the acidic environment provided by hydrochloric acid, and undergoes a redox reaction with elemental copper inside the carbon coating layer, oxidizing Cu to water-soluble Cu. 2+ After soaking for 24 hours, the copper core was completely etched away, leaving only a porous graphite carbon nanoframework. After washing away residual ions with water and freeze-drying to retain the porous structure, a graphite carbon porous aerogel was finally obtained.

[0022] Further, in step B1, the volume ratio of copper nitrate aqueous solution, sodium hydroxide aqueous solution, ethylenediamine, and hydrazine hydrate is 30-35:650-660:4.5-5.0:0.32-0.35, the mass fraction of the sodium hydroxide solution is 37%, and the copper nitrate aqueous solution is obtained by dissolving copper nitrate trihydrate and deionized water at a ratio of 1g:32mL; in step B2, the volume ratio of copper-based nanoparticles, deionized water, and polyvinylpyrrolidone solution is 0.2g:20mL:2.4-2.6mL, the polyvinylpyrrolidone solution is obtained by dissolving polyvinylpyrrolidone and deionized water at a ratio of 1g:40mL, and the volume ratio of hydrogen to argon in the hydrogen-argon mixture is 3:17; in step B3, the concentration of the ferric chloride hydrochloric acid solution is 1mol / L.

[0023] The present invention also proposes a modified rice husk-based hard carbon material, which is prepared by the above-mentioned method for preparing a modified rice husk-based hard carbon material.

[0024] The present invention also proposes an application of a modified rice husk-based hard carbon material, wherein the modified rice husk-based hard carbon material prepared by the above-mentioned method is applied to the negative electrode material of lithium-ion batteries.

[0025] The present invention has the following beneficial effects:

[0026] 1. The rice husks of this invention are purified by alkaline washing and neutralization to remove impurities and avoid clogging the subsequent carbon skeleton channels, laying the foundation for the formation of a pure carbon matrix. High-temperature nitrogen carbonization combined with ball milling can generate a hard carbon structure with low graphitization degree. Relying on abundant micropores and mesopores, it provides basic lithium storage sites. At the same time, the carbon particle size is optimized to increase the specific surface area. The TiO2 generated by the hydrolysis of tetrabutyl titanate in ethanol and deionized water system not only has lithium intercalation and storage activity itself, but can also achieve capacity superposition through "hard carbon lithium storage and TiO2 lithium storage". Meanwhile, the aerogel composite not only expands the ion transport channels with its three-dimensional porous network, but also introduces additional defective active sites through nitrogen and phosphorus heteroatom doping to enhance the adsorption capacity of lithium ions. Finally, the uniform composite of the two makes the pore structure connected, further optimizing the ion transport path. Under the synergistic effect of multiple steps, the number of lithium storage active sites and ion transport efficiency of the material are significantly improved, thereby effectively improving the first discharge specific capacity.

[0027] 2. The rice husk purification of this invention can remove impurities that easily undergo irreversible reactions with lithium ions, avoiding ineffective capacity consumption. High-temperature carbonization can reduce oxygen-containing functional groups on the surface of hard carbon, reducing irreversible lithium ion fixation caused by chemical adsorption. The TiO2 coating generated by the hydrolysis of tetrabutyl titanate can uniformly coat the surface of rice husk-based carbon powder, covering surface defects caused by the disordered structure of hard carbon, reducing excessive decomposition of electrolyte at defect sites. The heteroatom doping of the aerogel composite can regulate the electronic structure of the carbon material surface, promote the formation of a uniform and stable SEI film, and reduce lithium ion loss caused by excessive decomposition of electrolyte. The uniform dispersion of the two can also reduce the internal polarization of the electrode, avoiding additional irreversible capacity caused by uneven local reactions. The combined effect of multiple links can significantly reduce the irreversible consumption of lithium ions during the first charge and discharge process, and effectively improve the first coulombic efficiency.

[0028] 3. The high-temperature carbonization of this invention forms a dense and moderately ordered hard carbon structure in rice husks, which inherently possesses low thermal expansion characteristics. Simultaneously, it reduces structural defects and porosity fluctuations, preventing an increase in the coefficient of thermal expansion due to structural loosening during heating. Purification of the rice husks removes high-expansion impurities, preventing them from compromising the thermal stability of the carbon skeleton and ensuring uniform thermal expansion of the hard carbon matrix. The TiO2 generated from the hydrolysis of tetrabutyl titanate has a high melting point of 1840℃ and excellent thermal stability, serving as a rigid support phase interspersed within the network of rice husk-based carbon and aerogel composites. This suppresses volume expansion of the material during heating. The aerogel composite, with its low expansion characteristics and three-dimensional porous structure, absorbs the thermal stress generated by the carbon skeleton during heating, mitigating volume changes. Furthermore, the tight interface between the two prevents localized differences in thermal expansion. Through the synergistic effect of these multiple steps, the overall coefficient of thermal expansion of the material is optimized, providing support for the structural stability of lithium-ion batteries during long-term cycling. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] In this application, polyvinylpyrrolidone is selected from Shandong Yongbang Chemical Technology Co., Ltd., with CAS number 9003-39-8, active ingredient content of 99%, and product number 80088.

[0031] Example 1

[0032] This embodiment provides a method for preparing a modified rice husk-based hard carbon material, comprising the following steps:

[0033] S1. Preparation of pure rice husks

[0034] Weigh out 10g of rice husks, wash them with deionized water, mix them with 10g of sodium hydroxide, and add them to a reaction vessel containing 40mL of deionized water. Heat the mixture at 65℃ for 3 hours, then add 1mol / L hydrochloric acid solution dropwise until the solution pH is neutral. Filter the mixture, wash it with deionized water, and then dry it to obtain pure rice husks.

[0035] S2. Preparation of rice husk-based carbon powder

[0036] The pure rice husks were transferred to a ceramic firing boat and placed in a tube furnace. After being kept at 1000°C in a nitrogen atmosphere for 4 hours, the furnace was naturally cooled to room temperature in a nitrogen atmosphere and then transferred to a planetary ball mill for ball milling for 9 hours to obtain rice husk-based carbon powder.

[0037] S3. Preparation of porous aerogel

[0038] Weigh out 1g of copper nitrate trihydrate and dissolve it in 32mL of deionized water to obtain an aqueous solution of copper nitrate.

[0039] Weigh out 30 mL of copper nitrate aqueous solution and 650 mL of 37 wt% sodium hydroxide aqueous solution, mix and stir until the solution color changes from colorless to blue, then add 4.5 mL of ethylenediamine, continue stirring for 3 min, then add 0.35 mL of hydrazine hydrate, stir until the color turns milky white, place it in a 50℃ water bath and keep it warm for 3 h. After the reaction is complete, take out the upper red copper-based nanoparticles, wash them 4 times with deionized water to obtain copper-based nanoparticles;

[0040] Weigh out 2g of copper-based nanoparticles and disperse them in 200mL of deionized water. Add 24mL of polyvinylpyrrolidone solution to the solution, stir well, pour into a mold, and freeze-dry in liquid nitrogen for 48h. After high-temperature annealing in a hydrogen-argon mixed atmosphere at 500℃, transfer to ethanol for 2h, wash with deionized water until the block settles to the bottom, and remove the deionized water from the surface to obtain carbonized aerogel.

[0041] The carbonized aerogel was immersed in a 1 mol / L ferric chloride hydrochloric acid solution for 24 hours, then washed five times with deionized water and freeze-dried to obtain a porous aerogel.

[0042] S4. Preparation of aerogel complex

[0043] Weigh out 5g of ammonium sulfate and 21mL of phytic acid and dissolve them in 50mL of deionized water to obtain a mixed solution;

[0044] Weigh 10g of porous aerogel and add it to a reaction vessel containing 30mL of isopropanol and 0.8mL of aniline. After standing for 20min, pour off the excess isopropanol and aniline, and then add 49mL of the mixed solution dropwise. After the addition is complete, shake for 20min and let stand for 12h. First, wash with methanol solution until the solution is colorless, and then wash with deionized water until the graphite skeleton settles to the bottom. After freeze-drying for 24h, take it out and place it in a tube furnace. Anneal it at 600℃ in an argon atmosphere for 1h to obtain the aerogel composite.

[0045] S5. Preparation of modified rice husk-based hard carbon materials

[0046] Weigh out 10g of aerogel composite, grind it, pass it through a 200-mesh sieve, and add it together with 40g of rice husk-based carbon powder into 500mL of ethanol and 100mL of deionized water. Disperse it by sonication for 40min, add 3g of tetrabutyl titanate to the reaction system, stir for 5min, and then transfer it to a vacuum drying oven to dry at 80℃ for 6h to obtain modified rice husk-based hard carbon material.

[0047] Example 2

[0048] This embodiment provides a method for preparing a modified rice husk-based hard carbon material, comprising the following steps:

[0049] S1. Preparation of pure rice husks

[0050] Weigh out 10g of rice husks, wash them with deionized water, mix them with 10g of sodium hydroxide, and add them to a reaction vessel containing 40mL of deionized water. Heat the mixture at 70℃ for 3.5h, then add 1mol / L hydrochloric acid solution dropwise until the pH of the solution is neutral. Filter the mixture, wash it with deionized water, and then dry it to obtain pure rice husks.

[0051] S2. Preparation of rice husk-based carbon powder

[0052] The pure rice husks were transferred to a ceramic firing boat and placed in a tube furnace. After being kept at 1100℃ in a nitrogen atmosphere for 4.5 hours, the furnace was naturally cooled to room temperature in a nitrogen atmosphere and then transferred to a planetary ball mill for ball milling for 9.5 hours to obtain rice husk-based carbon powder.

[0053] S3. Preparation of porous aerogel

[0054] Weigh out 1g of copper nitrate trihydrate and dissolve it in 32mL of deionized water to obtain an aqueous solution of copper nitrate.

[0055] Weigh out 32 mL of copper nitrate aqueous solution and 655 mL of 37 wt% sodium hydroxide aqueous solution, mix and stir until the solution color changes from colorless to blue, then add 4.8 mL of ethylenediamine, continue stirring for 3 min, then add 0.35 mL of hydrazine hydrate, stir until the color turns milky white, place it in a water bath at 55 ℃ and keep it warm for 3.5 h. After the reaction is completed, take out the upper red copper-based nanoparticles, wash them 4 times with deionized water to obtain copper-based nanoparticles;

[0056] Weigh out 2g of copper-based nanoparticles and disperse them in 200mL of deionized water. Add 25mL of polyvinylpyrrolidone solution to the solution, stir well, pour into a mold, and freeze-dry in liquid nitrogen for 48h. Then, anneal at high temperature in a hydrogen-argon mixed atmosphere at 550℃, transfer to ethanol for 2.5h, wash with deionized water until the block settles to the bottom, and remove the deionized water from the surface to obtain carbonized aerogel.

[0057] The carbonized aerogel was immersed in a 1 mol / L ferric chloride hydrochloric acid solution for 24 hours, then washed five times with deionized water and freeze-dried to obtain a porous aerogel.

[0058] S4. Preparation of aerogel complex

[0059] Weigh out 5g of ammonium sulfate and 21mL of phytic acid and dissolve them in 50mL of deionized water to obtain a mixed solution;

[0060] Weigh 10g of porous aerogel and add it to a reaction vessel containing 32mL of isopropanol and 0.8mL of aniline. After standing for 25min, pour off the excess isopropanol and aniline, and then add 50mL of the mixed solution dropwise. After the addition is complete, shake for 25min and let stand for 12h. First, wash with methanol solution until the solution is colorless, and then wash with deionized water until the graphite skeleton settles to the bottom. After freeze-drying for 24h, take it out and place it in a tube furnace. Anneal it at 700℃ in an argon atmosphere for 1.5h to obtain the aerogel composite.

[0061] S5. Preparation of modified rice husk-based hard carbon materials

[0062] Weigh out 10g of aerogel composite, grind it, pass it through a 200-mesh sieve, and add it together with 40g of rice husk-based carbon powder into 500mL of ethanol and 100mL of deionized water. Disperse it ultrasonically for 50min, add 3.5g of tetrabutyl titanate to the reaction system, stir for 8min, and then transfer it to a vacuum drying oven to dry at 80℃ for 6h to obtain modified rice husk-based hard carbon material.

[0063] Example 3

[0064] This embodiment provides a method for preparing a modified rice husk-based hard carbon material, comprising the following steps:

[0065] S1. Preparation of pure rice husks

[0066] Weigh out 10g of rice husks, wash them with deionized water, mix them with 10g of sodium hydroxide, and add them to a reaction vessel containing 40mL of deionized water. Heat the mixture at 75℃ for 4 hours, then add 1mol / L hydrochloric acid solution dropwise until the solution pH is neutral. Filter the mixture, wash it with deionized water, and then dry it to obtain pure rice husks.

[0067] S2. Preparation of rice husk-based carbon powder

[0068] The pure rice husks were transferred to a ceramic firing boat and placed in a tube furnace. After being kept at 1200℃ in a nitrogen atmosphere for 6 hours, the furnace was naturally cooled to room temperature in a nitrogen atmosphere and then transferred to a planetary ball mill for ball milling for 10 hours to obtain rice husk-based carbon powder.

[0069] S3. Preparation of porous aerogel

[0070] Weigh out 1g of copper nitrate trihydrate and dissolve it in 32mL of deionized water to obtain an aqueous solution of copper nitrate.

[0071] Weigh out 35 mL of copper nitrate aqueous solution and 660 mL of 37 wt% sodium hydroxide aqueous solution, mix and stir until the solution color changes from colorless to blue, then add 5.0 mL of ethylenediamine, continue stirring for 5 min, then add 0.35 mL of hydrazine hydrate, stir until the color turns milky white, place it in a 60℃ water bath and keep it warm for 4 h. After the reaction is complete, take out the upper red copper-based nanoparticles, wash them 5 times with deionized water to obtain copper-based nanoparticles;

[0072] Weigh out 2g of copper-based nanoparticles and disperse them in 200mL of deionized water. Add 26mL of polyvinylpyrrolidone solution to the solution, stir well, pour into a mold, and freeze-dry in liquid nitrogen for 48h. Then, anneal at high temperature in a hydrogen-argon mixed atmosphere at 600℃, transfer to ethanol and soak for 3h. Wash with deionized water until the block settles to the bottom, remove the deionized water from the surface, and obtain carbonized aerogel.

[0073] The carbonized aerogel was immersed in a 1 mol / L ferric chloride hydrochloric acid solution for 24 hours, then washed 6 times with deionized water and freeze-dried to obtain a porous aerogel.

[0074] S4. Preparation of aerogel complex

[0075] Weigh out 5g of ammonium sulfate and 22mL of phytic acid and dissolve them in 50mL of deionized water to obtain a mixed solution;

[0076] Weigh 10g of porous aerogel and add it to a reaction vessel containing 35mL of isopropanol and 0.8mL of aniline. After standing for 30min, pour off the excess isopropanol and aniline, and then add 51mL of the mixed solution dropwise. After the addition is complete, shake for 30min and let stand for 12h. First, wash with methanol solution until the solution is colorless, and then wash with deionized water until the graphite skeleton settles to the bottom. After freeze-drying for 24h, take it out and place it in a tube furnace. Anneal it at 800℃ in an argon atmosphere for 2h to obtain the aerogel composite.

[0077] S5. Preparation of modified rice husk-based hard carbon materials

[0078] Weigh 10g of aerogel composite, grind it, pass it through a 200-mesh sieve, and add it together with 40g of rice husk-based carbon powder into 500mL of ethanol and 100mL of deionized water. Disperse it by sonication for 60min. Add 4g of tetrabutyl titanate to the reaction system, stir for 10min, and then transfer it to a vacuum drying oven to dry at 80℃ for 6h to obtain modified rice husk-based hard carbon material.

[0079] Comparative Example 1

[0080] The difference between this comparative example and Example 3 is that step S1 is omitted, and the rice husks in step S1 are used instead of the pure rice husks in step S2.

[0081] Comparative Example 2

[0082] The difference between this comparative example and Example 3 is that step S4 is omitted, and in step S5, porous aerogel is used instead of the aerogel composite.

[0083] Comparative Example 3

[0084] The difference between this comparative example and Example 3 is that steps S3, S4 and S5 are omitted.

[0085] Performance testing:

[0086] The modified rice husk-based hard carbon materials prepared in Examples 1-3 and Comparative Examples 1-3 were used to make electrode sheets, which were then assembled with other components of the battery to obtain the test sample.

[0087] The initial discharge specific capacity and initial coulombic efficiency of the test sample were determined in accordance with the standard GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries".

[0088] The coefficient of thermal expansion (CTE) of the test sample was determined according to standard GB / T 3074.4-2016 "Determination of Coefficient of Thermal Expansion (CTE) of Graphite Electrodes". The specific test results are shown in Table 1 below:

[0089] Table 1 - Basic Performance Test Data of the Samples

[0090]

[0091] Data Analysis:

[0092] Comparative analysis of the data in Table 1 shows that the modified rice husk-based hard carbon material prepared in this invention, when used as a negative electrode material for lithium-ion batteries, exhibits an initial discharge specific capacity of 770 mAh / g, an initial coulombic efficiency of 92.5%, and a coefficient of thermal expansion of 1.5 × 10⁻⁶. -6 / ℃;

[0093] Because the carbonization temperature, carbonization holding time, and ball milling time of rice husk in Example 3 were all higher than those in Example 1, and the amount of isopropanol used in the preparation of the aerogel composite was greater than that in Example 1, and the annealing temperature was higher than that in Example 1, the higher temperature and longer carbonization time made the hard carbon skeleton denser and the micropores more uniform. The longer ball milling optimized the carbon particle size to increase the specific surface area. More isopropanol facilitated aniline penetration, and the higher annealing temperature strengthened the interfacial bonding. Therefore, the initial discharge specific capacity of Example 3 was 770 mAh / g, and the initial coulombic efficiency was 92.5%, which was slightly higher than that of Examples 1 and 2. The coefficient of thermal expansion was 1.5 × 10⁻⁶. -6 / ℃;

[0094] Because Comparative Example 1 omits the rice husk purification step, residual impurities clog lithium storage channels, consume lithium ions, and damage structural stability. Comparative Example 2 omits the aerogel composite preparation step, lacking N / P heteroatom doped lithium storage sites and a stable SEI film, and has weak buffering thermal expansion capacity. Comparative Example 3 completely omits the preparation steps of porous aerogel, aerogel composite, and composite, lacking additional ion transport paths and lithium storage sites. Therefore, the initial discharge specific capacity and initial coulombic efficiency of all three are lower than those of Example 3, while the coefficients of thermal expansion are higher than those of Example 3.

[0095] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a modified rice husk-based hard carbon material, characterized in that, Includes the following steps: S1. Wash the rice husks with deionized water and mix them with sodium hydroxide. Add the mixture to a reaction vessel containing deionized water and heat it at 65-75℃ for 3-4 hours. Then, add hydrochloric acid solution dropwise until the pH of the solution is neutral. Filter the mixture, wash it with deionized water, and dry it to obtain pure rice husks. S2. Transfer the pure rice husks to a ceramic firing boat and place them together in a tube furnace. Keep them at 1000-1200℃ in a nitrogen atmosphere for 4-6 hours. Then, let them cool naturally to room temperature in a nitrogen atmosphere and remove them. Transfer them to a planetary ball mill and ball mill for 9-10 hours to obtain rice husk-based carbon powder. S3. Grind the aerogel composite, pass it through a 200-mesh sieve, and add it together with rice husk-based carbon powder into ethanol and deionized water. Disperse it ultrasonically for 40-60 minutes. Add tetrabutyl titanate to the reaction system, stir for 5-10 minutes, and then transfer it to a vacuum drying oven to dry at 80°C for 6 hours to obtain modified rice husk-based hard carbon material. The preparation method of the aerogel composite is as follows: porous aerogel is added to a reaction vessel containing isopropanol and aniline. After standing for 20-30 minutes, excess isopropanol and aniline are poured out. Then, a mixed solution is added dropwise. After the addition is complete, the mixture is shaken for 20-30 minutes and then allowed to stand for 12 hours. The mixture is first washed with methanol solution until the solution is colorless, and then washed with deionized water until the graphite skeleton settles to the bottom. After freeze-drying for 24 hours, the mixture is taken out and placed in a tube furnace. It is then annealed in an argon atmosphere at 600-800℃ for 1-2 hours to obtain the aerogel composite. The mixed solution is obtained by mixing ammonium sulfate, phytic acid and deionized water in a ratio of 0.5g:2.1-2.2mL:5mL.

2. The method for preparing a modified rice husk-based hard carbon material according to claim 1, characterized in that, In step S1, the ratio of rice husk, sodium hydroxide, and deionized water is 1g:1g:4mL, and the concentration of the hydrochloric acid solution is 1mol / L.

3. The method for preparing a modified rice husk-based hard carbon material according to claim 1, characterized in that, In step S3, the ratio of the aerogel composite, rice husk-based carbon powder, ethanol, deionized water and tetrabutyl titanate is 1g:4g:50mL:5mL:0.3-0.4g.

4. The method for preparing a modified rice husk-based hard carbon material according to claim 1, characterized in that, The ratio of the porous aerogel, isopropanol, aniline, and mixed solution is 1g:3.0-3.5mL:0.08mL:4.9-5.1mL.

5. The method for preparing a modified rice husk-based hard carbon material according to claim 1, characterized in that, The porous aerogel was prepared by the following steps: B1. Mix copper nitrate aqueous solution and sodium hydroxide aqueous solution and stir until the solution color changes from colorless to blue. Add ethylenediamine and continue stirring for 3-5 minutes. Then add hydrazine hydrate and stir until the color turns milky white. Place it in a water bath at 50-60℃ and keep it warm for 3-4 hours. After the reaction is complete, take out the upper red copper-based nanoparticles and wash them with deionized water 4-5 times to obtain copper-based nanoparticles. B2. Disperse copper-based nanoparticles in deionized water, add polyvinylpyrrolidone solution dropwise, stir evenly, pour into a mold, and place in liquid nitrogen for rapid freezing and molding. Then, freeze-dry under vacuum for 48 hours, anneal at high temperature in a hydrogen-argon mixed atmosphere at 500-600℃, transfer to ethanol for soaking for 2-3 hours, wash with deionized water until the block settles to the bottom, remove the deionized water from the surface, and obtain carbonized aerogel. B3. Immerse the carbonized aerogel in ferric chloride hydrochloric acid solution for 24 hours, wash with deionized water 5-6 times, and freeze-dry to obtain porous aerogel.

6. The method for preparing a modified rice husk-based hard carbon material according to claim 5, characterized in that, In step B1, the volume ratio of copper nitrate aqueous solution, sodium hydroxide aqueous solution, ethylenediamine, and hydrazine hydrate is 30-35:650-660:4.5-5.0:0.32-0.35, the mass fraction of the sodium hydroxide solution is 37%, and the copper nitrate aqueous solution is obtained by dissolving copper nitrate trihydrate and deionized water at a ratio of 1g:32mL; in step B2, the volume ratio of copper-based nanoparticles, deionized water, and polyvinylpyrrolidone solution is 0.2g:20mL:2.4-2.6mL, the polyvinylpyrrolidone solution is obtained by dissolving polyvinylpyrrolidone and deionized water at a ratio of 1g:40mL, and the volume ratio of hydrogen to argon in the hydrogen-argon mixture is 3:17; in step B3, the concentration of the ferric chloride hydrochloric acid solution is 1mol / L.

7. A modified rice husk-based hard carbon material, characterized in that, The modified rice husk-based hard carbon material is prepared using the preparation method of the modified rice husk-based hard carbon material as described in any one of claims 1-6.

8. The application of a modified rice husk-based hard carbon material, characterized in that, The modified rice husk-based hard carbon material prepared by the method described in any one of claims 1-6 is applied to the negative electrode material of a lithium-ion battery.

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