A high-performance sodium-ion battery hydrogen peroxide modified hard carbon negative electrode material easy to prepare and low in cost and a preparation method thereof

Abstract

The application relates to a high-performance sodium-ion battery hydrogen peroxide modified hard carbon negative electrode material which is easy to prepare and low in cost. A preparation method comprises the following steps: S1, crushing, washing, filtering and vacuum drying alfalfa to obtain a biomass precursor material; S2, low-temperature cracking, annealing under an argon atmosphere to obtain a hard carbon precursor carbon material; S3, completely dispersing the hard carbon precursor material in deionized water to obtain a hard carbon precursor material mixed solution, adding an acid solution to adjust the pH value, then adding a hydrogen peroxide aqueous solution, filtering after reaction, washing until neutral, vacuum drying to obtain an intermediate product, and vacuum drying to obtain a modified hard carbon precursor carbon material; and S4, high-temperature pyrolysis under the protection of an argon atmosphere and annealing. Compared with a traditional biomass material, the specific capacity, the first coulomb efficiency and the capacity retention rate of the hard carbon negative electrode material prepared from the biomass alfalfa are significantly improved.

Description

Technical Field

[0001] This application relates to hard carbon anode materials, and more specifically, it relates to a high-performance sodium-ion battery hydrogen peroxide-modified hard carbon anode material that is easy to prepare, low in cost, and has a preparation method thereof. Background Technology

[0002] Against the backdrop of the rapid development of the energy storage field, lithium-ion batteries have begun to be used on a large scale. However, the price of lithium carbonate and the extremely limited lithium reserves have raised concerns, making large-scale application of lithium-ion batteries a potential risk. The search for the next generation of energy storage batteries has become a research hotspot. Sodium-ion batteries, due to abundant sodium resources, lower costs, and better low-temperature performance, are considered a powerful alternative to lithium-ion batteries.

[0003] Biomass-based hard carbon materials are abundant, including coconut shells, lotus seed shells, corn stalks, and sunflower seed shells, with coconut shells currently being the primary source for commercially available hard carbon. Current biomass hard carbon anode materials generally suffer from small interlayer spacing, low degree of disorder, structural instability, insufficient conductivity, and excessive ash. Increasing the preparation temperature leads to increased graphitization, reduced defects, and decreased specific surface area in the final carbonized material, resulting in higher initial coulombic efficiency and reversible capacity. However, excessively high pyrolysis temperatures can lead to excessive graphitization, reducing the interlayer spacing and inhibiting sodium ion insertion and extraction. Over-washing of acid-hydrolyzed ash reduces material strength and yield, and the cycle capacity retention of the product does not meet requirements. Therefore, controlling the pyrolysis process and temperature within the appropriate range for the selected biomass material is a key factor determining the electrochemical performance of biomass-based hard carbon materials. At the same time, it is important to note that the interlayer spacing and structural defects of hard carbon materials, such as the degree of disorder, have a significant impact on reversible capacity and first coulombic efficiency. Therefore, for bio-based hard carbon materials, in addition to key factors such as pyrolysis temperature and raw materials, how to control the interlayer spacing, degree of disorder, and structural stability to improve reversible capacity is also a key research focus for practitioners.

[0004] Alfalfa (Alfalfa muxue) is a perennial herbaceous plant belonging to the genus Alfalfa in the family Fabaceae. It is cultivated or found semi-wild throughout China. It is drought-tolerant, high-yielding, and of excellent quality, and also improves soil. Its main uses are hay, silage, and forage. During the research and development of biomass-based hard carbon anode materials, the inventors accidentally discovered that alfalfa, with its high nitrogen content and easily controllable cellulose / lignin structure, has great potential in the preparation of hard carbon anode materials. However, there is currently no research on the targeted and effective use of alfalfa to prepare high-performance sodium-ion hard carbon anode materials. Summary of the Invention

[0005] To address the issues of small interlayer spacing, low degree of disorder, and poor cycle stability in biomass hard carbon anode materials, this application provides an easy-to-prepare, low-cost, high-performance sodium-ion battery hydrogen peroxide-modified hard carbon anode material and its preparation method.

[0006] This application provides a method for preparing a high-performance sodium-ion battery hydrogen peroxide-modified hard carbon anode material that is easy to prepare and low in cost, comprising the following steps:

[0007] S1: The biomass material is crushed, washed, filtered, and vacuum dried to obtain biomass precursor material, wherein the biomass material includes alfalfa;

[0008] S2: The biomass precursor material obtained in S1 is pyrolyzed at low temperature under the protection of argon atmosphere, and then annealed under argon atmosphere to obtain hard carbon precursor carbon material.

[0009] S3: The hard carbon precursor material in S2 is completely dispersed in deionized water to obtain a mixed solution of hard carbon precursor material. An acid solution is added dropwise to adjust the pH value, and then an aqueous solution of hydrogen peroxide is added dropwise. After the reaction, the mixture is filtered and washed until neutral to obtain an intermediate product. The intermediate product is then dried under vacuum to obtain the modified hard carbon precursor carbon material.

[0010] S4: Under argon atmosphere protection, the modified hard carbon precursor carbon material obtained in S3 is pyrolyzed at high temperature and annealed to room temperature to obtain hydrogen peroxide modified hard carbon anode material.

[0011] In step S1, crushing and proper cleaning can improve the uneven heating of uncrushed materials, increase the surface area of ​​the material under heat and the contact area with the subsequent hydrogen peroxide activator, and promote a more uniform carbonization reaction. Proper cleaning can remove most of the surface ash and some soluble sugars and lipids from the biomass materials, preventing these substances from forming soft carbon during carbonization and affecting electrochemical performance. In step S2, low-temperature pyrolysis removes volatile components, reduces structural defects, and avoids rapid temperature rise and violent gas release during high-temperature carbonization, which could lead to material cracking. It also initially forms a cross-linked carbon network, shortens the high-temperature carbonization time, and improves the final carbonization yield. In step S4, hydrogen peroxide can dissociate into hydrogen peroxide ions in an acidic environment, reacting with surface defects or sp2 hybridized carbon atoms in the carbon material. However, this reaction is relatively mild and does not destroy the carbon skeleton, only altering the carbon structure to a certain extent.

[0012] This invention uses alfalfa as the main raw material. As a legume, alfalfa contains a relatively high amount of nitrogen, which improves conductivity. Compared to hard carbon anode materials made from mixed nitrogen sources, alfalfa exhibits more uniform conductivity and is less prone to lithium dendrite formation. The formation of CN bonds further expands the interlayer spacing and increases defects. Potassium is removed and decomposed during acid washing and pyrolysis to generate carbon dioxide, creating additional mesopores and expanding the diffusion path of diffused ions. The stem has a cylindrical hollow structure with a relatively dense arrangement of internal vascular bundles. The hollow structure generates hierarchical pores, shortening the ion diffusion path and forming relatively dense channels after carbonization. Mild oxidation can etch nanoscale pores (1-2 nm), forming a rich pore structure, increasing the specific surface area, and contributing to pseudocapacitance. The oxidation reaction can also partially destroy the carbon structure, expanding the interlayer spacing of hard carbon and facilitating sodium ion diffusion. Oxygen bubbles generated by the decomposition of hydrogen peroxide form "physical pores" inside the biomass, further increasing the specific surface area and porosity of the hard carbon material.

[0013] Furthermore, hydrogen peroxide treatment provides more reaction sites within the material, allowing calcium and sulfur amino acids within the alfalfa to generate tiny calcium sulfide particles that provide interlayer support, thus expanding the interlayer spacing. Simultaneously, the larger specific surface area can reduce irreversible reactions such as electrolyte decomposition, improving the initial coulombic efficiency to some extent and forming a more stable SEI film.

[0014] In one specific embodiment, the number of cleaning cycles in S1 is ≤3, the mass ratio of hard carbon precursor material to deionized water in S3 is 1:(3-7), the pH value is adjusted to 2-3, the concentration of hydrogen peroxide aqueous solution is 25-35wt%, the volume ratio of hydrogen peroxide aqueous solution to hard carbon precursor material mixed solution is 1:(1-5), and the reaction between hydrogen peroxide and hard carbon precursor material in S3 is a constant temperature reaction at 30-60℃ for 4-12 hours.

[0015] By adopting the above-mentioned scheme, the ash is removed through cleaning. By carefully limiting the concentration and volume ratio of the acid solution and hydrogen peroxide aqueous solution, the acidification and oxidation are relatively mild and will not damage the carbon structure too much. At the same time, the effect of expanding the interlayer spacing of hard carbon is better. It can increase the interlayer spacing without significantly blocking the ion channels, resulting in better performance of the product.

[0016] In one specific embodiment, the vacuum drying temperature in steps S1 and S3 is 90-92℃, the low-temperature pyrolysis temperature gradient in S2 is 1-5℃ / min to 300-320℃, then 1.0-1.5℃ / min to 400-600℃, and held for 1.5-2.0h, and the high-temperature pyrolysis temperature gradient in S4 is 4-5℃ / min to 900℃, then 1.0-1.5℃ / min to 1200-1400℃, and the pyrolysis time is 1.5-2.0h.

[0017] By adopting the above scheme, the oxidation is mild, the gas escape rate during the pyrolysis process is appropriate, the volatile matter residue is low, the structure is stable, the pore structure is not prone to excessive expansion and contraction during charging and discharging, which would cause the carbon skeleton to break, the calcium sulfide nucleation is uniform and the size is appropriate, and the interlayer spacing is expanded without significantly blocking the passage of ions.

[0018] In one specific embodiment, S3 further includes the following steps: preparing a glucose aqueous solution, adjusting the pH of the solution to 9–11, dispersing the washed intermediate in the glucose aqueous solution, stirring evenly, and filtering.

[0019] By adopting the above scheme, under a pH of 9-11, glucose molecules dissociate into negatively charged gluconate, which then attracts positively charged sites on the CaS surface via electrostatic attraction. 2+ The combination of these processes allows for the targeted and uniform formation of a glucose coating layer on the surface of the intermediate product. The free radicals generated during decomposition promote the reduction of sulfur, further generating calcium sulfide. Under the process settings of this invention, calcium sulfide grows more slowly, resulting in more uniform nucleation and uniform dispersion as nanoparticles. The interlayer spacing is suitable for sodium ion diffusion. Simultaneously, the glucose coating on the surface sinters to form a carbon coating layer, which not only blocks the contact between calcium sulfide and the electrolyte but also further optimizes the interlayer structure. This also makes the multilayer structure "supported" by calcium sulfide more stable, thus improving the specific capacity and capacity retention of the hard carbon anode material.

[0020] In one specific embodiment, the concentration of the glucose aqueous solution is 8-12 wt%.

[0021] The inventors discovered that at this concentration, the calcium sulfide formation rate and size are suitable, which has a good effect on improving the interlayer spacing. The carbon coating layer formed by glucose has a good blocking effect and is less likely to produce side reactions. The structure is also more stable than traditional biomass materials. At the same time, the carbon layer is not too thick and will not block the ion channels too much. The resulting hard carbon anode material has the best performance.

[0022] In one specific embodiment, S4 further includes the following steps: placing the material in a rotary tube furnace, introducing argon gas at a flow rate of 60 mL / min as a protective gas, raising the temperature to 800°C at 5°C / min, introducing acetylene gas at a flow rate of 5-10 mL / min as an active gas for chemical vapor deposition, stopping the acetylene gas flow after 30 minutes, maintaining the temperature for 90 minutes, and then cooling the temperature to room temperature at 5°C / min to obtain a hard carbon anode material.

[0023] By adopting the above scheme, after glucose is specifically coated on the calcium sulfide surface, a thin layer of carbon is then uniformly deposited on the surface of the product, resulting in richer pores, more stable strength and structure, and better product performance.

[0024] In one specific implementation, the high-temperature pyrolysis temperature gradient in S4 is 4-5℃ / min to 900℃, and then 1.5℃ / min to 1200-1400℃, with a pyrolysis time of 1.5 hours.

[0025] By adopting the above approach and further limiting the high-temperature pyrolysis process parameters at this time, the interlayer spacing is more suitable for the deposition of the carbon coating layer.

[0026] In one specific implementation, alfalfa includes purple alfalfa.

[0027] In one specific embodiment, the biomass raw material further includes a second biomass raw material of 0-40% alfalfa mass, which includes one or more of coconut shells, melon seed shells, corn stalks, reeds, bamboo, cotton, tung oil shells, giant reeds, hazelnut shells, pine cone shells, rice husks, and coffee grounds.

[0028] Secondly, the present invention provides a high-performance sodium-ion battery hydrogen peroxide modified hard carbon anode material that is easy to prepare and low in cost, and is prepared using the above-mentioned preparation method.

[0029] In summary, this application has the following beneficial effects:

[0030] Compared to the traditional process of repeatedly washing and removing ash in the preparation of hard carbon from biomass materials, this application uses a milder hydrogen peroxide oxidation process to generate gas, physically create pores, and partially disrupt the carbon structure network to expand the interlayer spacing. By targeting the structural characteristics and elemental composition of alfalfa, reaction sites are increased and process parameters are limited to uniformly generate nano-sized calcium sulfide inside the hard carbon anode material to expand the interlayer spacing. The resulting hydrogen peroxide modified hard carbon anode material has a higher specific capacity and capacity retention rate.

[0031] This application further treats the intermediate product with a glucose solution of a certain concentration to better promote the reduction and formation of calcium sulfide. After sintering, a carbon coating layer of suitable thickness is formed at the calcium sulfide sites. The thinner carbon layer further increases the strength and porosity of the multilayer structure, resulting in a hydrogen peroxide modified hard carbon anode material with better cycle stability. Attached Figure Description

[0032] Figure 1 The specific capacity curves of the hard carbon anode material prepared in Example 1 and Comparative Example 1 of this invention.

[0033] Figure 2 Scanning electron microscope (SEM) image of the hard carbon anode material prepared in Example 1 of this invention.

[0034] Figure 3 Scanning electron microscope (SEM) image of the hard carbon anode material prepared in Comparative Example 1 of this invention.

[0035] Figure 4 Transmission electron microscope image of the hard carbon anode material prepared in Comparative Example 1 of this invention.

[0036] Figure 5 Transmission electron microscopy image of the hard carbon anode material prepared in Example 1 of this invention.

[0037] Figure 6 XRD patterns of Example 1 and Comparative Example 1 of the present invention.

[0038] Figure 7 Raman spectra of Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0039] To further aid in understanding the technical solution of this invention, several specific implementation examples are provided below to describe the technical solution of this invention in more detail. All of these described embodiments are only some embodiments of this invention, and not all of them.

[0040] The following specific embodiments can be combined with each other. The same or similar concepts or processes may not be described again in some embodiments. Unless otherwise specified, the reaction devices, monomer compounds and other materials involved in the following embodiments are commercially available.

[0041] The following examples are further illustrations of the present invention, but the present invention is not limited thereto.

[0042] Example

[0043] Example 1

[0044] S1: The alfalfa raw material was crushed using a crusher, washed twice with deionized water, sieved to 100 mesh, filtered, and then vacuum dried at 90℃ to obtain alfalfa-based biomass precursor material.

[0045] S2: The alfalfa-based biomass precursor material obtained in S1 was pyrolyzed at low temperature under an argon protective atmosphere. The temperature was increased to 300℃ at a gradient of 5℃ / min, and then increased to 600℃ at a gradient of 1℃ / min. The temperature was held for 2 hours and then annealed to obtain alfalfa-based hard carbon precursor carbon material.

[0046] S3: The alfalfa-based hard carbon precursor carbon material described in S2 is completely dispersed in 5 times its volume of deionized water. A 5wt% sulfuric acid solution is prepared using 98wt% concentrated sulfuric acid. The sulfuric acid solution is added dropwise to the dispersed hard carbon precursor carbon material mixture to adjust the pH value of the solution to 2.5. An equal volume of 30wt% hydrogen peroxide aqueous solution is added dropwise to the acidic mixture of alfalfa-based hard carbon precursor carbon material in S3. The mixture is reacted in a constant temperature water bath at 40℃ for 4 hours. After filtration, the mixture is washed successively with deionized water and ethanol until neutral and tested with pH paper. The mixture is then vacuum dried at 90℃ to obtain the modified alfalfa-based hard carbon precursor carbon material.

[0047] S4: The material obtained in S4 was pyrolyzed at 1300℃ under argon atmosphere protection, with a heating gradient of 5℃ / min to 900℃, and then heated to 1300℃ at 1℃ / min, held for 2h, and annealed to room temperature at a cooling rate of 2℃ / min to obtain hydrogen peroxide modified alfalfa-based hard carbon anode material.

[0048] Example 2

[0049] S1: The alfalfa raw material was crushed using a crusher, washed twice with deionized water, sieved to 100 mesh, filtered, and then vacuum dried at 90℃ to obtain alfalfa-based biomass precursor material.

[0050] S2: The alfalfa-based biomass precursor material obtained in S1 was pyrolyzed at low temperature under an argon protective atmosphere. The temperature was increased to 300℃ at a gradient of 5℃ / min, and then increased to 600℃ at a gradient of 1℃ / min. The temperature was held for 2 hours and then annealed to obtain alfalfa-based hard carbon precursor carbon material.

[0051] S3: The alfalfa-based hard carbon precursor carbon material described in S2 is completely dispersed in 5 times its volume of deionized water. A 5wt% sulfuric acid solution is prepared using 98wt% concentrated sulfuric acid. The sulfuric acid solution is added dropwise to the dispersed hard carbon precursor carbon material mixture to adjust the pH of the solution to 2.5. An equal volume of 45wt% hydrogen peroxide aqueous solution is added dropwise to the acidic mixture of alfalfa-based hard carbon precursor carbon material in S3. The mixture is reacted in a constant temperature water bath at 40℃ for 4 hours. After filtration, the mixture is washed successively with deionized water and ethanol until neutral and tested with pH paper. The mixture is then vacuum dried at 90℃ to obtain the modified alfalfa-based hard carbon precursor carbon material.

[0052] S4: The material obtained in S4 was pyrolyzed at 1300℃ under argon atmosphere protection, with a heating gradient of 5℃ / min to 900℃, and then heated to 1300℃ at 1℃ / min, held for 2h, and annealed to room temperature at a cooling rate of 2℃ / min to obtain hydrogen peroxide modified alfalfa-based hard carbon anode material.

[0053] Example 3

[0054] S1: The alfalfa raw material was crushed using a crusher, washed twice with deionized water, sieved to 100 mesh, filtered, and then vacuum dried at 90℃ to obtain alfalfa-based biomass precursor material.

[0055] S2: The alfalfa-based biomass precursor material obtained in S1 was pyrolyzed at low temperature under an argon protective atmosphere. The temperature was increased to 300℃ at a gradient of 5℃ / min, and then increased to 600℃ at a gradient of 1℃ / min. The temperature was held for 2 hours and then annealed to obtain alfalfa-based hard carbon precursor carbon material.

[0056] S3: Disperse the alfalfa-based hard carbon precursor carbon material described in S2 completely in 5 times its volume of deionized water, prepare a 5wt% sulfuric acid solution using 98wt% concentrated sulfuric acid, and add the sulfuric acid solution dropwise to the dispersed hard carbon precursor carbon material mixed solution to adjust the pH value of the solution to 2.5.

[0057] An equal volume of 30wt% hydrogen peroxide aqueous solution was added dropwise to an acidic mixed solution of alfalfa-based hard carbon precursor carbon material in S3. The mixture was reacted for 4 hours under a constant temperature water bath at 40℃. After filtration, the intermediate product was obtained by washing with deionized water and ethanol until neutral and testing with pH paper.

[0058] A 10wt% glucose aqueous solution was prepared, the pH of the solution was adjusted to 10, the washed intermediate was dispersed in the glucose aqueous solution, stirred evenly, filtered, and vacuum dried at 90℃ to obtain the modified alfalfa-based hard carbon precursor carbon material.

[0059] S4: The material obtained in S4 was pyrolyzed at 1300℃ under argon atmosphere protection, with a heating gradient of 5℃ / min to 900℃, and then heated to 1300℃ at 1℃ / min, held for 2h, and annealed to room temperature at a cooling rate of 2℃ / min to obtain hydrogen peroxide modified alfalfa-based hard carbon anode material.

[0060] Example 4

[0061] S1: The alfalfa raw material was crushed using a crusher, washed twice with deionized water, sieved to 100 mesh, filtered, and then vacuum dried at 90℃ to obtain alfalfa-based biomass precursor material.

[0062] S2: The alfalfa-based biomass precursor material obtained in S1 was pyrolyzed at low temperature under an argon protective atmosphere. The temperature was increased to 300℃ at a gradient of 5℃ / min, and then increased to 600℃ at a gradient of 1℃ / min. The temperature was held for 2 hours and then annealed to obtain alfalfa-based hard carbon precursor carbon material.

[0063] S3: Disperse the alfalfa-based hard carbon precursor carbon material described in S2 completely in 5 times its volume of deionized water, prepare a 5wt% sulfuric acid solution using 98wt% concentrated sulfuric acid, and add the sulfuric acid solution dropwise to the dispersed hard carbon precursor carbon material mixed solution to adjust the pH value of the solution to 2.5.

[0064] An equal volume of 30wt% hydrogen peroxide aqueous solution was added dropwise to an acidic mixed solution of alfalfa-based hard carbon precursor carbon material in S3. The mixture was reacted for 4 hours under a constant temperature water bath at 40℃. After filtration, the intermediate product was obtained by washing with deionized water and ethanol until neutral and testing with pH paper.

[0065] A 17wt% glucose aqueous solution was prepared, the pH of the solution was adjusted to 10, the washed intermediate was dispersed in the glucose aqueous solution, stirred evenly, filtered, and vacuum dried at 90℃ to obtain the modified alfalfa-based hard carbon precursor carbon material.

[0066] S4: The material obtained in S4 was pyrolyzed at 1300℃ under argon atmosphere protection, with a heating gradient of 5℃ / min to 900℃, and then heated to 1300℃ at 1℃ / min, held for 2h, and annealed to room temperature at a cooling rate of 2℃ / min to obtain hydrogen peroxide modified alfalfa-based hard carbon anode material.

[0067] Example 5

[0068] S1: The alfalfa raw material was crushed using a crusher, washed twice with deionized water, sieved to 100 mesh, filtered, and then vacuum dried at 90℃ to obtain alfalfa-based biomass precursor material.

[0069] S2: The alfalfa-based biomass precursor material obtained in S1 was pyrolyzed at low temperature under an argon protective atmosphere. The temperature was increased to 300℃ at a gradient of 5℃ / min, and then increased to 600℃ at a gradient of 1℃ / min. The temperature was held for 2 hours and then annealed to obtain alfalfa-based hard carbon precursor carbon material.

[0070] S3: Disperse the alfalfa-based hard carbon precursor carbon material described in S2 completely in 5 times its volume of deionized water, prepare a 5wt% sulfuric acid solution using 98wt% concentrated sulfuric acid, and add the sulfuric acid solution dropwise to the dispersed hard carbon precursor carbon material mixed solution to adjust the pH value of the solution to 2.5.

[0071] An equal volume of 30wt% hydrogen peroxide aqueous solution was added dropwise to an acidic mixed solution of alfalfa-based hard carbon precursor carbon material in S3. The mixture was reacted for 4 hours under a constant temperature water bath at 40℃. After filtration, the intermediate product was obtained by washing with deionized water and ethanol until neutral and testing with pH paper.

[0072] A 3wt% glucose aqueous solution was prepared, the pH of the solution was adjusted to 10, the washed intermediate was dispersed in the glucose aqueous solution, stirred evenly, filtered, and vacuum dried at 90℃ to obtain the modified alfalfa-based hard carbon precursor carbon material.

[0073] S4: The material obtained in S4 was pyrolyzed at 1300℃ under argon atmosphere protection, with a heating gradient of 5℃ / min to 900℃, and then heated to 1300℃ at 1℃ / min, held for 2h, and annealed to room temperature at a cooling rate of 2℃ / min to obtain hydrogen peroxide modified alfalfa-based hard carbon anode material.

[0074] Example 6

[0075] S1: The alfalfa raw material was crushed using a crusher, washed twice with deionized water, sieved to 100 mesh, filtered, and then vacuum dried at 90℃ to obtain alfalfa-based biomass precursor material.

[0076] S2: The alfalfa-based biomass precursor material obtained in S1 was pyrolyzed at low temperature under an argon protective atmosphere. The temperature was increased to 300℃ at a gradient of 5℃ / min, and then increased to 600℃ at a gradient of 1℃ / min. The temperature was held for 2 hours and then annealed to obtain alfalfa-based hard carbon precursor carbon material.

[0077] S3: Disperse the alfalfa-based hard carbon precursor carbon material described in S2 completely in 5 times its volume of deionized water, prepare a 5wt% sulfuric acid solution using 98wt% concentrated sulfuric acid, and add the sulfuric acid solution dropwise to the dispersed hard carbon precursor carbon material mixed solution to adjust the pH value of the solution to 2.5.

[0078] An equal volume of 30wt% hydrogen peroxide aqueous solution was added dropwise to an acidic mixed solution of alfalfa-based hard carbon precursor carbon material in S3. The mixture was reacted for 4 hours under a constant temperature water bath at 40℃. After filtration, the intermediate product was obtained by washing with deionized water and ethanol until neutral and testing with pH paper.

[0079] A 10wt% glucose aqueous solution was prepared, the pH of the solution was adjusted to 10, the washed intermediate was dispersed in the glucose aqueous solution, stirred evenly, filtered, and vacuum dried at 90℃ to obtain the modified alfalfa-based hard carbon precursor carbon material.

[0080] S4: The material obtained in S4 was pyrolyzed at 1300℃ under an argon atmosphere. The temperature was increased to 900℃ at a rate of 5℃ / min, and then increased to 1300℃ at a rate of 1℃ / min. The temperature was held for 2 hours, and then annealed to room temperature at a rate of 2℃ / min. The material was placed in a rotary tube furnace, and argon gas was introduced at a flow rate of 60 mL / min. The temperature was increased to 800℃ at a rate of 5℃ / min. Acetylene gas was introduced at a flow rate of 10 mL / min for chemical vapor deposition. After holding for 30 minutes, the acetylene gas was stopped. The reaction was held at 90 minutes, and then the temperature was lowered to room temperature at a rate of 5℃ / min to obtain hydrogen peroxide modified alfalfa-based hard carbon anode material.

[0081] Example 7

[0082] S1: The alfalfa raw material was crushed using a crusher, washed twice with deionized water, sieved to 100 mesh, filtered, and then vacuum dried at 90℃ to obtain alfalfa-based biomass precursor material.

[0083] S2: The alfalfa-based biomass precursor material obtained in S1 was pyrolyzed at low temperature under an argon protective atmosphere. The temperature was increased to 300℃ at a gradient of 5℃ / min, and then increased to 600℃ at a gradient of 1℃ / min. The temperature was held for 2 hours and then annealed to obtain alfalfa-based hard carbon precursor carbon material.

[0084] S3: Disperse the alfalfa-based hard carbon precursor carbon material described in S2 completely in 5 times its volume of deionized water, prepare a 5wt% sulfuric acid solution using 98wt% concentrated sulfuric acid, and add the sulfuric acid solution dropwise to the dispersed hard carbon precursor carbon material mixed solution to adjust the pH value of the solution to 2.5.

[0085] An equal volume of 30wt% hydrogen peroxide aqueous solution was added dropwise to an acidic mixed solution of alfalfa-based hard carbon precursor carbon material in S3. The mixture was reacted for 4 hours under a constant temperature water bath at 40℃. After filtration, the intermediate product was obtained by washing with deionized water and ethanol until neutral and testing with pH paper.

[0086] A 10wt% glucose aqueous solution was prepared, the pH of the solution was adjusted to 10, the washed intermediate was dispersed in the glucose aqueous solution, stirred evenly, filtered, and vacuum dried at 90℃ to obtain the modified alfalfa-based hard carbon precursor carbon material.

[0087] S4: The material obtained in S4 was pyrolyzed at 1300℃ under argon atmosphere protection, with a temperature gradient of 5℃ / min to 900℃, and then increased to 1300℃ at 1℃ / min. It was held at this temperature for 2 hours, then annealed to room temperature at a rate of 2℃ / min. The material was then placed in a rotary tube furnace, and argon gas was introduced at a flow rate of 60 mL / min. The temperature was increased to 800℃ at a rate of 5℃ / min, and acetylene gas was introduced at a flow rate of 20 mL / min for chemical vapor deposition. After holding for 30 minutes, the acetylene gas was stopped, and the reaction was maintained at this temperature for 90 minutes. The temperature was then reduced to room temperature at a rate of 5℃ / min to obtain hydrogen peroxide modified alfalfa-based hard carbon anode material.

[0088] Example 8

[0089] S1: The alfalfa raw material was crushed using a crusher, washed twice with deionized water, sieved to 100 mesh, filtered, and then vacuum dried at 90℃ to obtain alfalfa-based biomass precursor material.

[0090] S2: The alfalfa-based biomass precursor material obtained in S1 was pyrolyzed at low temperature under an argon protective atmosphere. The temperature was increased to 300℃ at a gradient of 5℃ / min, and then increased to 600℃ at a gradient of 1℃ / min. The temperature was held for 2 hours and then annealed to obtain alfalfa-based hard carbon precursor carbon material.

[0091] S3: Disperse the alfalfa-based hard carbon precursor carbon material described in S2 completely in 5 times its volume of deionized water, prepare a 5wt% sulfuric acid solution using 98wt% concentrated sulfuric acid, and add the sulfuric acid solution dropwise to the dispersed hard carbon precursor carbon material mixed solution to adjust the pH value of the solution to 2.5.

[0092] An equal volume of 30wt% hydrogen peroxide aqueous solution was added dropwise to an acidic mixed solution of alfalfa-based hard carbon precursor carbon material in S3. The mixture was reacted for 4 hours under a constant temperature water bath at 40℃. After filtration, the intermediate product was obtained by washing with deionized water and ethanol until neutral and testing with pH paper.

[0093] The material was vacuum dried at 90℃ and placed in a rotary tube furnace. Argon gas was introduced at a flow rate of 60 mL / min to raise the temperature to 800℃ at 5℃ / min. Acetylene gas was introduced at a flow rate of 10 mL / min to carry out chemical vapor deposition. After 30 minutes, the acetylene gas was stopped and the reaction was maintained at this temperature for 90 minutes. The temperature was then lowered to room temperature at 5℃ / min to obtain the modified alfalfa-based hard carbon precursor carbon material.

[0094] S4: Under argon atmosphere protection, the material obtained in S4 was pyrolyzed at 1300℃, with a temperature gradient of 5℃ / min to 900℃, and then increased to 1300℃ at 1℃ / min, held for 2h, and annealed to room temperature at a cooling rate of 2℃ / min. A 10wt% glucose aqueous solution was prepared, and the pH of the solution was adjusted to 10. The annealed modified alfalfa-based hard carbon precursor carbon material was dispersed in the glucose aqueous solution, stirred evenly, and filtered to obtain hydrogen peroxide modified alfalfa-based hard carbon anode material.

[0095] Example 9

[0096] S1: The alfalfa raw material was crushed using a crusher, washed twice with deionized water, sieved to 100 mesh, filtered, and then vacuum dried at 90℃ to obtain alfalfa-based biomass precursor material.

[0097] S2: The alfalfa-based biomass precursor material obtained in S1 was pyrolyzed at low temperature under an argon protective atmosphere. The temperature was increased to 300℃ at a gradient of 5℃ / min, and then increased to 600℃ at a gradient of 1℃ / min. The temperature was held for 2 hours and then annealed to obtain alfalfa-based hard carbon precursor carbon material.

[0098] S3: Disperse the alfalfa-based hard carbon precursor carbon material described in S2 completely in 5 times its volume of deionized water, prepare a 5wt% sulfuric acid solution using 98wt% concentrated sulfuric acid, and add the sulfuric acid solution dropwise to the dispersed hard carbon precursor carbon material mixed solution to adjust the pH value of the solution to 2.5.

[0099] An equal volume of 30wt% hydrogen peroxide aqueous solution was added dropwise to an acidic mixed solution of alfalfa-based hard carbon precursor carbon material in S3. The mixture was reacted for 4 hours under a constant temperature water bath at 40℃. After filtration, the intermediate product was obtained by washing with deionized water and ethanol until neutral and testing with pH paper.

[0100] A 10wt% glucose aqueous solution was prepared, and the washed intermediate was dispersed in the glucose aqueous solution, stirred evenly, filtered, and vacuum dried at 90℃ to obtain the modified alfalfa-based hard carbon precursor carbon material.

[0101] S4: The material obtained in S4 was pyrolyzed at 1300℃ under an argon atmosphere. The temperature was increased to 900℃ at a rate of 5℃ / min, and then increased to 1300℃ at a rate of 1℃ / min. The temperature was held for 2 hours, and then annealed to room temperature at a rate of 2℃ / min. The material was placed in a rotary tube furnace, and argon gas was introduced at a flow rate of 60 mL / min. The temperature was increased to 800℃ at a rate of 5℃ / min. Acetylene gas was introduced at a flow rate of 10 mL / min for chemical vapor deposition. After holding for 30 minutes, the acetylene gas was stopped. The reaction was held at 90 minutes, and then the temperature was lowered to room temperature at a rate of 5℃ / min to obtain hydrogen peroxide modified alfalfa-based hard carbon anode material.

[0102] Example 10

[0103] S1: The raw material of alfalfa was crushed using a crusher, washed twice with deionized water, sieved to 100 mesh, filtered, and then vacuum dried at 90℃ to obtain alfalfa-based biomass precursor material.

[0104] S2: The alfalfa-based biomass precursor material obtained in S1 was pyrolyzed at low temperature under an argon protective atmosphere. The temperature was increased to 300℃ at a gradient of 5℃ / min, and then increased to 600℃ at a gradient of 1℃ / min. The temperature was held for 2 hours and then annealed to obtain the alfalfa-based hard carbon precursor carbon material.

[0105] S3: Disperse the alfalfa-based hard carbon precursor carbon material described in S2 completely in 5 times its volume of deionized water, prepare a 5wt% sulfuric acid solution using 98wt% concentrated sulfuric acid, and add the sulfuric acid solution dropwise to the dispersed hard carbon precursor carbon material mixed solution to adjust the pH value of the solution to 2.5.

[0106] An equal volume of 30wt% hydrogen peroxide aqueous solution was added dropwise to the acidic mixed solution of alfalfa-based hard carbon precursor carbon material in S3. The mixture was reacted for 4 hours under constant temperature water bath at 40℃. After filtration, the mixture was washed with deionized water and ethanol until neutral and tested with pH paper. The mixture was then dried under vacuum at 90℃ to obtain the modified alfalfa-based hard carbon precursor carbon material.

[0107] S4: The material obtained in S4 was pyrolyzed at 1300℃ under argon atmosphere protection, with a heating gradient of 5℃ / min to 900℃, and then heated to 1300℃ at 1℃ / min, held for 2h, and annealed to room temperature at a cooling rate of 2℃ / min to obtain hydrogen peroxide modified alfalfa-based hard carbon anode material.

[0108] Comparative Example

[0109] Comparative Example 1

[0110] S1: The alfalfa raw material was crushed using a crusher, sieved to 100 mesh, washed twice with deionized water, filtered, and then vacuum dried at 90℃ to obtain alfalfa-based biomass precursor material.

[0111] S2: The alfalfa-based biomass precursor material obtained in S1 was pyrolyzed at low temperature under an argon protective atmosphere. The temperature was increased to 300℃ at a gradient of 5℃ / min, and then increased to 600℃ at a gradient of 1℃ / min. The temperature was held for 2 hours and then annealed to obtain alfalfa-based hard carbon precursor carbon material.

[0112] S3: The alfalfa-based hard carbon precursor carbon material described in S2 was completely dispersed in 5 times its volume of deionized water. A 5wt% sulfuric acid solution was prepared using 98wt% concentrated sulfuric acid. The sulfuric acid solution was added dropwise to the dispersed hard carbon precursor carbon material mixture to adjust the pH value of the solution to 2.5. The acidic mixture of alfalfa-based hard carbon precursor carbon material was placed in a constant temperature water bath at 40℃ for 4 hours. After filtration, it was washed with deionized water and ethanol in sequence until neutral and tested with pH paper. It was then vacuum dried at 90℃ to obtain the comparative alfalfa-based hard carbon precursor carbon material.

[0113] S4: The material obtained in S4 was pyrolyzed at 1300℃ under argon atmosphere protection, with a temperature gradient of 5℃ / min to 900℃, and then increased to 1300℃ at 1℃ / min, held for 2 hours, and annealed to room temperature to obtain the comparative alfalfa-based hard carbon anode material.

[0114] Comparative Example 2

[0115] S1: Use a crusher to crush the reed raw material, sieve it to 100 mesh, wash it twice with deionized water, filter it and vacuum dry it at 90℃ to obtain reed-based biomass precursor material.

[0116] S2: The reed-based biomass precursor material obtained in S1 was pyrolyzed at low temperature under an argon protective atmosphere. The temperature gradient was increased to 300℃ at 5℃ / min, and then increased to 600℃ at 1℃ / min. The temperature was held for 2 hours and annealed to obtain the reed-based hard carbon precursor carbon material. S3: The reed-based hard carbon precursor carbon material described in S2 was completely dispersed in 5 times its volume of deionized water. A 5wt% sulfuric acid solution was prepared using 98wt% concentrated sulfuric acid. The sulfuric acid solution was added dropwise to the dispersed hard carbon precursor carbon material mixture to adjust the pH value of the solution to 2.5. The acidic mixture of reed-based hard carbon precursor carbon material was placed in a constant temperature water bath at 40℃ for 4 hours. After filtration, the mixture was washed with deionized water and ethanol until neutral and tested with pH paper. The mixture was then vacuum dried at 90℃ to obtain the comparative reed-based hard carbon precursor carbon material.

[0117] S4: The material obtained in S4 was pyrolyzed at 1300℃ under argon atmosphere protection, with a temperature gradient of 5℃ / min to 900℃, and then increased to 1300℃ at 1℃ / min, held at that temperature for 2 hours, and annealed to room temperature to obtain the comparative reed-based hard carbon anode material.

[0118] Performance testing

[0119] The hard carbon anode material samples prepared in each embodiment and comparative example were assembled into batteries according to the following steps:

[0120] S1: The hard carbon material samples, Super P, and PVDF prepared in the examples and comparative examples were ground and mixed in a mass ratio of 8:1:1, and then mixed evenly in NMP to prepare a hard carbon negative electrode slurry.

[0121] S2: The hard carbon negative electrode slurry from S1 is evenly coated onto carbon-coated aluminum foil using a 100mm scraper. It is then vacuum-dried in a 110℃ oven for 8 hours. The electrode is then cut into 10mm diameter circular sheets using a cutting machine. The active material mass is approximately 1.0-1.5 mg / cm³. 2 ;

[0122] S3: Assemble the coin cell. In a glove box filled with a protective atmosphere, use metallic sodium as the counter electrode, and the electrolyte is 1.5 mol / L NaPF6 in DMC:EC:DEC = 2:1:2. Use glass fiber as the separator, add 160 mL of electrolyte to form a CR-2032 coin cell. After the voltage is tested and found to be qualified, conduct electrochemical performance tests.

[0123] S4: The installed button cells were tested using the Xinwei BTS-610 multi-channel battery testing system. The battery operating voltage range was set to 3-0.01V, and the operating current density was 0.02A / g. Electrochemical tests were then conducted.

[0124] The specific capacity (mAh / g) and initial coulombic efficiency (%) of the hard carbon anode materials prepared by each embodiment and comparative example were tested. The capacity retention rate (%) was tested by 100 charge-discharge cycles at a working voltage of 2V and a working current density of 0.02A / g.

[0125] The test results are summarized in Table 1.

[0126] Table 1

[0127] Specific capacity (mAh / g) First-time coulomb efficiency (%) Capacity retention rate (%) Example 1 374.33 76.22 91.2 Example 2 361.21 73.10 87.4 Example 3 385.11 79.51 91.4 Example 4 379.73 78.34 91.3 Example 5 381.98 78.55 91.3 Example 6 391.42 81.58 92.1 Example 7 389.02 79.01 92.1 Example 8 381.17 79.10 90.8 Example 9 378.01 78.11 91.4 Example 10 358.30 70.82 88.7 Comparative Example 1 309.66 68.67 78.8 Comparative Example 2 247.87 43.51 66.5

[0128] Included in the instruction manual Figure 1 Example 1 achieved a reversible specific capacity of 374.33 mAh / g and a first-efficiency of 76.22% under a working current density of 0.02 A / g. In comparison, Comparative Example 1 only achieved a reversible specific capacity of 309.66 mAh / g and a first-efficiency of 68.67%. This shows that the hard carbon anode material prepared by the present invention has better performance than the unmodified hard carbon anode material.

[0129] Included in the instruction manual Figure 2 As shown in the scanning electron microscope (SEM) image of Example 1, the hydrogen peroxide-modified hard carbon anode material consists mostly of micron-sized irregular particles, arranged in a sheet-like stack, compared to the material in the instruction manual. Figure 3 The scanning electron microscope (SEM) image of Comparative Example 1 shows that the surface structure of Example 1 was destroyed, forming more pores and reaction sites.

[0130] Included in the instruction manual Figure 4 The transmission electron microscope image of Comparative Example 1 shows that the sample of Comparative Example 1 is composed of a lamellar disordered structure. Most of the irregular graphite-like regions are stacked together with a small part of the ordered graphite domain structure to form a hard carbon structure.

[0131] Included in the instruction manual Figure 5 The transmission electron microscope image of Example 1 is similar to that of Comparative Example 1, but the more obvious layered structure shows a larger interlayer spacing.

[0132] Included in the instruction manual Figure 6As can be seen from the XRD patterns of Example 1 and Comparative Example 1, according to the Bragg equation, the average interlayer spacing of the (002) crystal plane of the hard carbon material at a 2θ angle of 22.874° in Example 1 is 0.388 nm, while the (002) crystal plane of Comparative Example 1 corresponds to an angle of 2θ = 23.926°, corresponding to an average interlayer spacing of 0.371 nm. It can be seen that the hydrogen peroxide modified hard carbon anode material prepared by the present invention has the general hard carbon structural characteristics. The increase in interlayer spacing in Example 1 can be attributed to the effects of hydrogen peroxide modification and the control of calcium sulfide size. The small part of the destroyed carbon structure network expands the interlayer spacing, and the peak is attributed to CaS. This is naturally formed during the sintering process using the unique elemental composition of alfalfa. Compared with the influence of raw materials with excessive ash content or excessive washing of ash on the capacity retention of hard carbon anode materials, the process control allows the uniformly distributed sulfur and calcium elements to form a support of a certain size to expand the interlayer spacing. The hard carbon anode material prepared by the present invention has a higher specific capacity and capacity retention.

[0133] Included in the instruction manual Figure 7 As can be seen from the Raman spectra of Example 1 and Comparative Example 1, ID / IG is used to measure the disorder of carbon materials. The ID / IG value of Example 1 is 1.049, while that of Comparative Example 1 is 1.035. That is, the more disordered structure of Example 1 improves the electrical conductivity of the material and achieves better electrochemical performance.

[0134] In conjunction with Examples 1-2, 10, Comparative Examples 1-2 and Table 1, the hard carbon anode material prepared by using alfalfa as raw material and first treating it in a 25-35 wt% hydrogen peroxide aqueous solution and then pyrolyzing it at high temperature under certain process conditions exhibits good performance. Compared to reeds, alfalfa and yellow alfalfa have higher carbon and lignin content, and significantly higher nitrogen content. After sintering and carbonization, they form more micropores and mesopores, have lower ash content, and better electrical conductivity. Compared to yellow alfalfa, alfalfa has higher carbon, nitrogen, and lignin content, and its calcium is mainly carbonate and its protein contains sulfur-containing amino acids, while the calcium in yellow alfalfa is mainly inorganic salt and has a lower sulfur content. The inventors speculate that this may result in the CaS generated by alfalfa being uniformly dispersed in the carbon skeleton micropores as nano-sized particles. When calcium carbonate is carbonized, carbon dioxide gas escapes, forming a rich pore network and providing dispersion sites. The CaS distribution is more uniform and reasonable, and the ion channels are more unobstructed. At the same time, CaS plays a certain role in expanding the interlayer spacing, thus resulting in better performance of various electrochemical properties of the product.

[0135] In conjunction with Examples 1, 3-5 and Table 1, this application demonstrates that by immersing the intermediate product in a glucose solution of a certain concentration and pH value, the negatively charged gluconate is selectively enriched at calcium sulfide sites through electrostatic attraction. After sintering to form a thin carbon layer, the interlayer spacing of calcium sulfide is further enhanced and its stability is improved, and more pores are added.

[0136] In conjunction with Examples 3, 6-9 and Table 1, this application demonstrates that by first assembling gluconate and then depositing a thin carbon layer, the capacity retention of the product is more stable without significantly reducing the interlayer spacing.

[0137] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a high-performance sodium-ion battery hydrogen peroxide-modified hard carbon anode material that is easy to prepare and has low cost, characterized in that: The preparation method of the material includes the following steps: S1: crushing, washing, filtering, and vacuum drying the biomass material to obtain a biomass precursor material, wherein the biomass material includes alfalfa; S2: pyrolyzing the biomass precursor material obtained in S1 at low temperature under argon atmosphere protection, and annealing it under argon atmosphere to obtain hard carbon precursor carbon material; S3: completely dispersing the hard carbon precursor material in S2 in deionized water to obtain a mixed solution of hard carbon precursor material, adding acid solution to adjust the pH value, then adding hydrogen peroxide aqueous solution, filtering after reaction, washing to neutrality to obtain an intermediate product, vacuum drying to obtain modified hard carbon precursor carbon material; S4: pyrolyzing the modified hard carbon precursor carbon material obtained in S3 at high temperature under argon atmosphere protection, and annealing to room temperature to obtain hydrogen peroxide modified hard carbon anode material; In S1, the number of cleaning cycles is ≤3. In S3, the mass ratio of hard carbon precursor material to deionized water is 1:(3-7), the pH value is adjusted to 2-3, the concentration of hydrogen peroxide aqueous solution is 25-35wt%, and the volume ratio of hydrogen peroxide aqueous solution to hard carbon precursor material mixed solution is 1:(1-5). In S3, the reaction between hydrogen peroxide and hard carbon precursor material is a constant temperature reaction at 30-60℃ for 4-12 hours.

2. The method for preparing a high-performance sodium-ion battery hydrogen peroxide-modified hard carbon anode material that is easy to prepare and has low cost according to claim 1, characterized in that: The vacuum drying temperature in steps S1 and S3 is 90-92℃. The low-temperature pyrolysis temperature gradient in S2 is 1-5℃ / min to 300-320℃, then 1.0-1.5℃ / min to 400-600℃, and held for 1.5-2.0 hours. The high-temperature pyrolysis temperature gradient in S4 is 4-5℃ / min to 900℃, then 1.0-1.5℃ / min to 1200-1400℃, and the pyrolysis time is 1.5-2.0 hours.

3. The method for preparing a high-performance sodium-ion battery hydrogen peroxide-modified hard carbon anode material that is easy to prepare and has low cost according to claim 2, characterized in that: The S3 further includes the following steps: preparing a glucose aqueous solution, adjusting the pH of the solution to 9-11, dispersing the washed intermediate in the glucose aqueous solution, stirring evenly, and filtering.

4. The method for preparing a high-performance sodium-ion battery hydrogen peroxide-modified hard carbon anode material that is easy to prepare and has low cost according to claim 3, characterized in that: The concentration of the glucose aqueous solution is 8-12 wt%.

5. The method for preparing a high-performance sodium-ion battery hydrogen peroxide-modified hard carbon anode material that is easy to prepare and has low cost according to claim 3, characterized in that: The S4 process also includes the following steps: placing the material in a rotary tube furnace, introducing argon gas at a flow rate of 60 mL / min as a protective gas, raising the temperature to 800°C at 5°C / min, introducing acetylene gas at a flow rate of 5-10 mL / min as an active gas for chemical vapor deposition, holding the temperature for 30 minutes, stopping the introduction of acetylene gas, maintaining the temperature for 90 minutes, and then cooling the temperature to room temperature at 5°C / min to obtain a hard carbon anode material.

6. The method for preparing a high-performance sodium-ion battery hydrogen peroxide-modified hard carbon anode material that is easy to prepare and has low cost according to claim 5, characterized in that: The high-temperature pyrolysis temperature gradient in S4 is 4-5℃ / min to 900℃, and then 1.5℃ / min to 1200-1400℃, with a pyrolysis time of 1.5 hours.

7. The method for preparing a high-performance sodium-ion battery hydrogen peroxide-modified hard carbon anode material that is easy to prepare and has low cost according to claim 1, characterized in that: The biomass raw materials also include a second biomass raw material of 0-40% alfalfa mass, which includes one or more of the following: coconut shell, melon seed shell, corn stalk, reed, bamboo, cotton, tung oil shell, giant reed, hazelnut shell, pine cone shell, rice husk, and coffee grounds.

8. A high-performance sodium-ion battery hydrogen peroxide-modified hard carbon anode material that is easy to prepare and has low cost, characterized in that... The material is prepared using the method described in any one of claims 1-7, which provides an easy-to-prepare, low-cost, high-performance sodium-ion battery hydrogen peroxide-modified hard carbon anode material.

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