A hydrothermal sulfuration modified seed coat-based hard carbon material and a preparation method and application thereof

Abstract

The present application relates to a kind of based on hydrothermal sulphidation modified seed coat hard carbon material and its preparation method and application, first to biomass precursor is pretreated to remove impurities such as low-temperature carbonization, pickling;After the pretreated material is wet ball milling treatment;Again, the material is sulphidized by hydrothermal way;The material after sulphidation is calcined at high temperature in inert atmosphere, and then it is cooled to room temperature naturally to obtain hard carbon material.The preparation method utilizes the advantage of sulfur element on microstructure and its own properties, and the target product is obtained by pre-carbonization, pickling, ball milling, sulphidation, carbonization five steps, the material yield is high, stability is good, repeatability is strong, pollution is less and meets the requirements of green chemistry, and the requirement to equipment is low, has great application potential.The hydrothermal sulphidation modified seed coat hard carbon material prepared by the above method increases the sodium storage site of hard carbon, and improves the capacity performance and rate performance of hard carbon.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery materials technology, specifically to a hydrothermal sulfidation modified seed coat-based hard carbon material, its preparation method, and its application. Background Technology

[0002] Due to global warming and fossil fuel shortages, there is an urgent need to develop environmentally friendly and sustainable new energy models. Lithium-ion batteries have become the mainstream technology for electrochemical energy storage due to their excellent electrochemical performance. However, the shortage of lithium resources and the poor low-temperature performance of lithium-ion batteries have hindered their further development. Sodium, which belongs to the same group as lithium, is abundant, with a crustal abundance of up to 2.3%. It can be obtained through low-cost methods such as seawater desalination byproducts and salt lake brine, with raw material costs only 1 / 10 of lithium, demonstrating significant economic advantages and potential for large-scale application. In the future, it is expected to form a complementary energy storage application pattern with lithium-ion batteries. However, as the requirements for energy density and cycle life of energy storage systems continue to increase, the capacity characteristics, rate performance, and cycle stability of sodium-ion batteries face higher technical challenges. Among these, the performance optimization of anode materials is the core technological breakthrough for improving the overall performance of sodium-ion batteries. Hard carbon materials have many sodium storage active sites, high specific capacity, small volume expansion after sodium intercalation, good safety, and structural stability, and are considered one of the most promising anode materials for sodium-ion batteries due to their obvious comparative advantages. However, hard carbon anode materials currently suffer from significant defects such as low initial efficiency, poor rate performance, and poor cycle performance, making it difficult to meet the needs of practical applications.

[0003] Biomass precursors possess a wide range of raw material sources and unique microstructure characteristics, whose structural features directly influence the morphology, structure, and electrochemical performance of derived hard carbon. Biomass-based hard carbon exhibits significant application potential due to its high specific surface area, excellent porosity, and the ease of carbonization and high yield of its precursors. Mesophyll biomass, with its unique natural advantages, is an excellent precursor material for hard carbon; its high oxygen content and unique microstructure endow carbon-based materials with excellent structural stability. Heteroatom doping technology can effectively regulate the electronic structure of carbon materials and increase active sites, thereby significantly improving sodium storage performance. Notably, the diffusion rate of sodium ions between layers in carbon materials is significantly lower than the diffusion coefficient within the pores, becoming a rate-controlling step in the electrode charge-discharge process and limiting the rate performance of the battery. Sulfur doping can introduce defects and improve active sites, increasing Na+ ion concentration. +Adsorption energy provides additional sodium storage capacity to carbon materials. In heteroatom doping, sulfur (S) has the most significant effect on increasing interlayer spacing because its atomic radius of 1.02 μm is larger than that of B (0.82 μm), C (0.77 μm), and N (0.75 μm). This effectively reduces the diffusion resistance of sodium ions and increases their insertion and extraction rates. Sulfur doping can also improve the electronic conductivity of carbon materials, thereby significantly improving their rate performance. Furthermore, sulfur doping can introduce defects and active sites, increasing sodium ion adsorption capacity and providing additional sodium storage capacity to carbon materials.

[0004] Similar types of sulfidation generally involve cross-linking sulfidation. For example, Chinese patent CN117550582A discloses a hard carbon composite material for sodium-ion batteries and its preparation method, and Chinese patent CN118125414A discloses a phosphorus-sulfur co-doped modified hard carbon anode material and its preparation method. However, neither of these methods achieves the uniformity and simplicity of hydrothermal elemental doping. In hydrothermal elemental doping synthesis, heteroatoms covalently bond with the carbon framework through hydrothermal reactions, forming a stable doped structure. Hydrothermal sulfidation is characterized by one-step synthesis, mild reaction conditions, and uniform heteroatom distribution.

[0005] Based on this, the present invention uses seed coat as a hard carbon precursor and employs an inorganic sulfur source to prepare high-performance sulfur-modified seed coat-based hard carbon materials through low-temperature hydrothermal sulfidation. The incorporation of sulfur improves the microstructure of hard carbon, increases the concentration of defects and active sites, and enhances the diffusion rate of sodium ions, thereby improving the sodium storage performance of hard carbon anode materials for sodium-ion batteries. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a hydrothermal sulfurization-modified seed coat-based hard carbon material, its preparation method, and its application. The hydrothermal sulfur doping enhances the structure and properties of the seed coat-based hard carbon material, thereby improving the electrochemical performance of the hard carbon anode material, including its sodium affinity, conductivity, mass transfer properties, specific capacity, cycle stability, and rate performance of sodium-ion batteries.

[0007] The present invention provides a method for preparing a seed coat-based hard carbon material based on hydrothermal sulfidation modification, which specifically includes the following steps: (1) Place the cleaned and dried seed coat into a muffle furnace and pre-carbonize it in an air atmosphere, then cool it naturally to room temperature to obtain the pre-carbonized seed coat. (2) The pre-carbonized seed coat is acid washed, then washed with water multiple times until the washing solution is neutral, and then the obtained seed coat is dried. (3) Grind the dried seed coat, add water and ball mill, centrifuge the mixture after ball milling, dry the solid obtained by centrifugation, and obtain solid material A; (4) Dissolve the sulfur source in water and mix well to prepare a solution. Mix the solution with the ball-milled and dried solid material A obtained in step (3). Perform hydrothermal treatment on the mixed solution and then cool it to room temperature. Centrifuge the mixture obtained from the reaction and dry the solid obtained from the centrifugation to obtain solid material B. (5) The solid material B obtained in step (4) is calcined at high temperature in an inert atmosphere and then naturally cooled to room temperature to obtain a hard carbon material based on hydrothermal sulfidation modification of seed coat.

[0008] Furthermore, in step (1), the seed coat is any one of peony shell, cottonseed shell, almond shell, or seed coat of other Paeoniaceae plants.

[0009] Furthermore, in step (1), the pre-carbonization temperature is 400-600℃, the heating rate is 2-5℃ / min, and the air pressure is 0.8-1.2atm.

[0010] Furthermore, in step (2), hydrochloric acid is used for pickling, with a concentration of 0.8-1.2 mol / L. The mass ratio of the pre-carbonized seed coat to hydrochloric acid is 1:4-1:6. The pickling time is 20-28 h. Drying is carried out using a forced-air drying oven at a temperature of 60-80℃ for a drying time of not less than 12 h.

[0011] Furthermore, in step (3), the dried seed coat is crushed, and then water and agate balls are added for ball milling.

[0012] Furthermore, in step (3), the mass ratio of the crushed seed coat, water, and agate balls is 1:(5-10):(20-30), the ball milling time is 1-6 hours, and the ball milling direction is changed every 20-30 minutes during the ball milling process. The centrifugal separation speed is 8000-10000 rpm; and the drying is carried out in a vacuum drying oven at 60-80℃ for no less than 24 hours.

[0013] Furthermore, in step (4), the centrifugation speed is 8000-10000 rpm; and the product is dried in a vacuum drying oven at 60-80℃ for no less than 24 hours.

[0014] Furthermore, in step (4), a sulfur source is used to perform hydrothermal treatment on solid material A. The amount of sulfur source added is 4-6 wt% of the added solid material A, the hydrothermal temperature is 100-150℃, and the hydrothermal time is 2-4h.

[0015] Furthermore, the sulfur source mentioned in step (4) includes any one of sodium thiosulfate, sodium persulfate, sodium persulfate, sodium sulfate, sodium sulfite, and sodium polythionate.

[0016] Furthermore, in step (5), the calcination temperature is 1100-1300℃, the calcination time is 2-4h, the heating rate is 2-5℃ / min, and the working pressure of the inert gas is 0.8-1.2atm.

[0017] The present invention also provides a hydrothermal sulfidation modified seed coat-based hard carbon material obtained according to the above preparation method and its application as a negative electrode material for sodium-ion batteries.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The preparation method of the present invention utilizes the large atomic radius and strong electronegativity of sulfur atoms to obtain the target product through five steps: pre-carbonization, acid washing, ball milling, sulfidation and carbonization. The material obtained has high yield, good stability, strong repeatability, low pollution and meets the requirements of green chemistry. It has low equipment requirements and great application potential. (2) The hydrothermal sulfidation modified seed coat hard carbon material prepared in this invention improves the sodium affinity of the material, the diffusion rate of sodium ions, increases the sodium storage sites of hard carbon, improves the overall structure and electronic arrangement of hard carbon, and thus effectively improves the electrochemical performance of the material. (3) When the hydrothermally sulfidated modified seed coat hard carbon material prepared in this invention is used as a negative electrode material for sodium-ion batteries, the initial discharge specific capacity reaches 296 mAh / g, and the discharge specific capacity is still 286 mAh / g after 100 cycles, as tested at a current density of 0.1C. In the rate performance test at different current densities from low to high, the material has a good capacity retention rate under different current densities. The aforementioned test results show that the hydrothermally sulfidated modified seed coat hard carbon material has excellent high capacity and high rate performance characteristics, and is a potential application material for high energy density and high power density sodium-ion batteries. Attached Figure Description

[0019] Figure 1 SEM image of the hydrothermal sulfidation modified seed coat-based hard carbon material prepared in Example 1; Figure 2 SEM image of the seed coat-based hard carbon material prepared in Comparative Example 1; Figure 3 EDS image of the hydrothermal sulfidation modified seed coat-based hard carbon material prepared in Example 1; Figure 4 EDS image of the seed coat-based hard carbon material prepared in Comparative Example 1; Figure 5 Cycling performance curves of sodium-ion batteries using hydrothermal sulfidation modified seed coat hard carbon material prepared in Example 1 and seed coat hard carbon material prepared in Comparative Example 1 as negative electrodes at a current density of 0.1C. Figure 6Rate performance curves of sodium-ion batteries using hydrothermal sulfidation modified seed coat hard carbon material prepared in Example 1 and seed coat hard carbon material prepared in Comparative Example 1 as negative electrodes. Figure 7 The CV test curves of sodium-ion batteries using hydrothermal sulfidation modified seed coat hard carbon material prepared in Example 1 and seed coat hard carbon material prepared in Comparative Example 1 as negative electrodes at a scan rate of 0.1 mV / s are shown. Figure 8 The CV test curves of the sodium-ion battery prepared in Example 1 based on hydrothermal sulfidation modified seed coat hard carbon material as the negative electrode at different scan rates. Figure 9 The CV test curves of a sodium-ion battery using seed coat-based hard carbon material prepared for Comparative Example 1 as the negative electrode at different scan rates. Figure 10 EIS test curves of sodium-ion batteries after different cycles using hydrothermal sulfidation modified seed coat-based hard carbon material prepared in Example 1 as the negative electrode. Figure 11 EIS test curves of sodium-ion batteries using the seed coat-based hard carbon material prepared in Comparative Example 1 as the negative electrode after different cycles. Detailed Implementation

[0020] To better understand the content of this invention, it will be further described below with reference to specific embodiments and accompanying drawings. The following embodiments are based on the technology of this invention and provide detailed implementation methods and operating steps, but the scope of protection of this invention is not limited to the following embodiments.

[0021] Example 1: (1) Place 15g of cleaned and dried peony seed shells into a porcelain boat, heat them to 500°C in a muffle furnace at a heating rate of 5°C / min, and keep them in flowing air at 1 atm for 2 hours. Then let them cool naturally to room temperature to obtain pre-carbonized peony seed shells. (2) Place 4.19g of the pre-carbonized peony seed shells from step (1) into a 100mL beaker, add 21.00mL of 1mol / L hydrochloric acid and soak and wash for 24h. Then wash with deionized water multiple times until the washing solution is neutral. Then dry the obtained peony seed shells in a forced-air drying oven at 60℃ for 12h. (3) Grind the dried peony seed shells from step (2) into powder using a mortar and pestle to obtain 3.17g of peony seed shell powder. Add the powder to a ball mill jar, add 15.85g of deionized water and 79.25g of agate balls to the ball mill jar, and change the direction of ball milling every 30 minutes for 3 hours. After ball milling, centrifuge the mixture after ball milling at 8000 rpm for 5 minutes. Then dry the solid obtained by centrifugation in a vacuum drying oven at 60℃ for 24 hours to obtain 2.92g of solid. (4) First, add 30 mL of deionized water to the 50 mL reactor liner, then add 0.103 g of sodium thiosulfate with a purity of 97% to prepare a solution. Then take 2 g of the solid obtained in step (3) and add it to the 50 mL reactor liner. Mix well, cover and place in the reactor. Keep in the oven at 120°C for 3 h, then cool to room temperature. Centrifuge the mixture after reaction at 8000 rpm for 5 min, and then dry in a vacuum drying oven at 60°C for 24 h to obtain 1.88 g of solid material. (5) The solid material obtained in step (4) is placed in a ceramic boat, which is then placed in a tube furnace and heated to 1300°C at a heating rate of 5°C / min. The material is then kept in flowing Ar at 1 atm for 2 hours and then naturally cooled to room temperature to obtain a hydrothermal sulfidation modified seed coat-based hard carbon material.

[0022] SEM (Surface Electron Microscopy) was performed using a Zeiss EM5000X ultra-high resolution field emission scanning electron microscope. Powdered or bulk material samples were coated onto a black conductive adhesive and then sputtered with gold. SEM was used to characterize the surface morphology and dimensions of the samples.

[0023] Please see Figure 1 , 2 SEM analysis showed that the hydrothermal sulfidation modified seed coat hard carbon material prepared in this embodiment exhibited a smooth, irregular blocky structure before and after sulfidation, and the sulfidation process did not cause significant changes in morphology.

[0024] EDS measurements were performed using an Oxford Xplore 30 energy dispersive spectrometer from Oxford Instruments. Please refer to [reference needed]. Figure 3 , 4 EDS analysis showed that hydrothermal sulfidation increased the sulfur content in the material.

[0025] The hydrothermal sulfidation modified seed coat-based hard carbon material prepared in this embodiment was passed through a 300-mesh sieve, and the battery performance of the sodium-ion battery negative electrode was measured using CR2025 coin-type battery test material. First, a slurry was prepared by mixing the hydrothermal sulfidation modified seed coat-based hard carbon material, a CMC binder solution (prepared with water as a solvent to a mass fraction of 1.5 wt%), a SBR binder, and a conductive material (super-P-Li) to prepare the working electrode. The hydrothermal sulfidation modified seed coat-based hard carbon material accounted for 95 wt% of the slurry, the CMC solution accounted for 1.5 wt% of the slurry, the SBR accounted for 2.5 wt% of the slurry, and the conductive material accounted for 1 wt% of the slurry. Then, the slurry was coated on copper foil and dried at 60°C for 24 h. The battery was assembled in a glove box, using a glass fiber separator and a Na sheet as the counter electrode, and DIGLYME containing 1.0 M NaPF6 as the electrolyte. The battery was tested on a NEWARE battery testing system (CT2001A, Wuhan, China) within a voltage window of 0.01–3 V (relative to Na). + / Na) to perform battery charge / discharge tests.

[0026] Figure 5 This indicates that the hydrothermal sulfidation modified seed coat-based hard carbon material prepared in this embodiment, when used as a sodium-ion battery anode material, exhibits an initial discharge specific capacity of 296 mAh / g under a low current density of 0.1C, and still maintains a discharge specific capacity of 286 mAh / g after 100 cycles. Figure 5 It is evident that the capacity is significantly improved after sulfur doping, and it also exhibits excellent cycling performance.

[0027] Figure 6 The results show that in rate performance tests at varying current densities from low to high, the hydrothermally sulfidated modified seed coat hard carbon material prepared in this embodiment exhibits excellent capacity retention under different current densities. This demonstrates that the hydrothermally sulfidated modified seed coat hard carbon material possesses excellent high capacity and high rate performance characteristics, making it a potential material for high-energy-density and high-power-density sodium-ion batteries.

[0028] from Figure 7 It can be seen that both the hydrothermal sulfidation modified seed coat-based hard carbon material prepared in this embodiment and the seed coat-based hard carbon material prepared in the control group (corresponding to Comparative Example 1) exhibit a pair of highly symmetrical redox peaks at around 0.01 V, corresponding to the insertion and extraction of sodium ions in the hard carbon. Furthermore, the higher redox peaks after sulfur doping indicate the presence of more active sites, suggesting a more robust reaction for sodium ion insertion and extraction.

[0029] from Figure 8 , 9It can be seen that when the scan rate increases, the redox peak current of the hydrothermal sulfidation modified seed coat hard carbon material prepared in this embodiment as the negative electrode increases, but the overall shape does not change much. This indicates that the polarization degree of the hydrothermal sulfidation modified seed coat hard carbon material is small, which is more conducive to the migration of sodium ions.

[0030] from Figure 10 It can be seen that the semi-circular diameter of the high-frequency region of the hydrothermal sulfidation-modified seed coat-based hard carbon material prepared in this embodiment is significantly smaller after the first cycle of activation, indicating that the material has a smaller charge transfer impedance. In contrast, Figure 11 It can be observed that the charge transfer impedance of the vulcanized material is lower than that of the unvulcanized material. The results indicate that this hydrothermal vulcanization-modified seed coat-based hard carbon material possesses excellent electrochemical and kinetic properties.

[0031] Comparative Example 1: (1) Place 15g of cleaned and dried peony seed shells into a porcelain boat, heat them to 500°C in a muffle furnace at a heating rate of 5°C / min, and keep them in flowing air at 1 atm for 2 hours. Then let them cool naturally to room temperature to obtain pre-carbonized peony seed shells. (2) Place 4.36g of the pre-carbonized peony seed shells from step (1) into a 100mL beaker, add 21.8mL of 1mol / L hydrochloric acid and soak for 24h. Then wash with deionized water multiple times until the washing solution is neutral. After that, dry the obtained peony seed shells in a forced-air drying oven at 60℃ for 12h. (3) Grind the dried peony seed shells from step (2) into powder using a mortar and pestle to obtain 3.22g of peony seed shell powder. Divide the powder into two equal parts and add them into a ball mill jar. Add 16.10g of deionized water and 80.50g of agate balls to each part. Change the direction of the ball mill every 30 minutes and mill for 3 hours. Centrifuge the mixture after milling at 8000 rpm for 5 minutes. Then dry the solid obtained by centrifugation in a vacuum drying oven at 60℃ for 24 hours to obtain 2.99g of solid. (4) Take 2g of the solid obtained in step (3) and add it to the lining of a 50mL reactor. Add 30mL of deionized water to the lining of the reactor, mix well, cover and place in the reactor. Keep it in the oven at 120℃ for 3h, then cool to room temperature. Centrifuge the mixture obtained from the reaction at 8000rpm for 5min, and then dry it in a vacuum drying oven at 60℃ for 24h to obtain 1.78g of solid material. (5) The solid material obtained in step (4) is placed in a ceramic boat, which is then placed in a tube furnace and heated to 1300°C at a heating rate of 5°C / min. The material is then kept in flowing Ar at 1 atm for 2 hours and then naturally cooled to room temperature to obtain seed coat-based hard carbon material (referred to as the control group).

[0032] The electrochemical performance testing method was the same as that used in Example 1. Figure 7 , Figure 9 and Figure 10 It is clear that the rate performance and long-cycle stability of the material in this comparative example are significantly worse than those of the material in Example 1 at different current densities.

[0033] Example 2: (1) Place the cleaned and dried peony seed shells into a porcelain boat, heat them to 500°C in a muffle furnace at a heating rate of 5°C / min, and keep them in flowing air at 1 atm for 2 hours. Then cool them naturally to room temperature to obtain pre-carbonized peony seed shells. (2) Place 4.3g of pre-carbonized peony seed shells into a 100mL beaker, add 21.50mL of 1mol / L hydrochloric acid and soak for 24h. Then wash with deionized water several times until neutral, and then dry in a forced-air drying oven at 60℃ for 12h. (3) The dried peony seed shells were crushed in a mortar to obtain 3.20g of peony seed shell powder. The powder was added to a ball mill jar, along with 16.00mL of deionized water and 80.00g of agate balls. The ball milling direction was changed every 30min for 3h. The mixture after ball milling was centrifuged at 8000rpm for 5min and then dried in a vacuum drying oven at 60℃ for 24h to obtain 2.86g of solid. (4) First, add 30 mL of deionized water to the liner of the reactor, then add 0.154 g of sodium thiosulfate with a purity of 97% to prepare a solution. Then take the solid obtained in step (3), add it to 50 mL of the liner of the reactor, mix well, cover the lid, put it into the reactor, keep it in the oven at 120°C for 3 h, cool it to room temperature, centrifuge the hydrothermal mixture at 8000 rpm for 5 min, and then dry it in a vacuum drying oven at 60°C for 24 h to obtain solid material. (5) The solid material obtained in step (4) is placed in a ceramic boat, which is then placed in a tube furnace and heated to 1300°C at a heating rate of 5°C / min. The mixture is then kept in flowing argon at 1 atm for 2 h and then naturally cooled to room temperature to obtain a hydrothermal sulfidation modified seed coat-based hard carbon material.

[0034] Example 3: (1) Place the cleaned and dried peony seed shells into a porcelain boat, heat them to 500°C in a muffle furnace at a heating rate of 5°C / min, and keep them in flowing air at 1 atm for 2 hours. Then cool them naturally to room temperature to obtain pre-carbonized peony seed shells. (2) Place 4.7g of pre-carbonized peony seed shells into a 100mL beaker, add 23.50mL of 1mol / L hydrochloric acid and soak for 24h, then wash with deionized water several times until neutral, and then dry in a forced-air drying oven at 60℃ for 12h. (3) Grind the dried peony seed shells from step (2) into powder using a mortar and pestle to obtain 2.65g of peony seed shell powder. Add the powder to a ball mill jar, add 13.25g of deionized water and 66.25g of agate balls to the ball mill jar, and change the direction of ball milling every 30 minutes for 3 hours. Centrifuge the mixture after ball milling at 8000 rpm for 5 minutes, and then dry the solid obtained by centrifugation in a vacuum drying oven at 60℃ for 24 hours to obtain 2.36g of solid. (4) First, add 30 mL of deionized water to the 50 mL reactor liner, then add 0.120 g of sodium thiosulfate with a purity of 97% to prepare a solution. Then take the solid obtained in step (3), add it to the reactor liner, mix well, cover the reactor, put it in the reactor, keep it in the oven at 120 °C for 3 h, cool it to room temperature, centrifuge the mixture after hydrothermal reaction at 8000 rpm for 5 min, and then dry it in a vacuum drying oven at 60 °C for 24 h to obtain solid material. (5) The solid material obtained in step (4) is placed in a ceramic boat, which is then placed in a tube furnace and heated to 1300°C at a heating rate of 4°C / min. The material is then kept in flowing Ar at 1 atm for 3 hours and then naturally cooled to room temperature to obtain a hydrothermal sulfidation modified seed coat-based hard carbon material.

[0035] The above description is merely an embodiment of the present invention and is not intended to limit the present invention in any way. The present invention can also have other embodiments based on the above structure and function, which will not be listed hereafter. Therefore, any simple modifications, equivalent changes, and alterations made by those skilled in the art to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing seed coat-based hard carbon materials based on hydrothermal sulfidation modification, characterized in that, Specifically, the following steps are included: (1) Place the cleaned and dried seed coat into a muffle furnace and pre-carbonize it in an air atmosphere, then cool it naturally to room temperature to obtain the pre-carbonized seed coat. (2) The pre-carbonized seed coat is acid washed, then washed with water multiple times until the washing solution is neutral, and then the obtained seed coat is dried. (3) Grind the dried seed coat, add water and ball mill, centrifuge the mixture after ball milling, dry the solid obtained by centrifugation, and obtain solid material A; (4) Dissolve the sulfur source in water and mix well to prepare a solution. Mix the solution with the ball-milled and dried solid material A obtained in step (3). Perform hydrothermal treatment on the mixed solution and then cool it to room temperature. Centrifuge the mixture obtained from the reaction and dry the solid obtained from the centrifugation to obtain solid material B. (5) The solid material B obtained in step (4) is calcined at high temperature in an inert atmosphere and then naturally cooled to room temperature to obtain a hard carbon material based on hydrothermal sulfidation modification of seed coat.

2. The preparation method of seed coat-based hard carbon material based on hydrothermal sulfidation modification as described in claim 1, characterized in that, In step (1), the seed coat is any one of peony shell, cottonseed shell, almond shell, or seed coat of other Paeoniaceae plants; the pre-carbonization temperature is 400-600℃, the heating rate is 2-5℃ / min, and the air pressure is 0.8-1.2atm.

3. The preparation method of seed coat-based hard carbon material based on hydrothermal sulfidation modification as described in claim 1, characterized in that, In step (2), hydrochloric acid is used for pickling. The concentration of hydrochloric acid is 0.8-1.2 mol / L. The mass ratio of pre-carbonized seed coat to hydrochloric acid is 1:4-1:

6. The pickling time is 20-28 h. Drying is carried out in a forced-air drying oven at a temperature of 60-80℃ for a time of not less than 12 h.

4. The preparation method of seed coat-based hard carbon material based on hydrothermal sulfidation modification as described in claim 1, characterized in that, In step (3), the dried seed coat is crushed, and then water and agate balls are added for ball milling.

5. The preparation method of seed coat-based hard carbon material based on hydrothermal sulfidation modification as described in claim 4, characterized in that, In step (3), the mass ratio of the crushed seed coat, water, and agate ball is 1:(5-10):(20-30), the ball milling time is 1-6 hours, and the ball milling direction is changed every 20-30 minutes during the ball milling process; the centrifugal separation speed is 8000-10000 rpm; and the drying is carried out in a vacuum drying oven at 60-80℃ for no less than 24 hours.

6. The preparation method of seed coat-based hard carbon material based on hydrothermal sulfidation modification as described in claim 1, characterized in that, The sulfur source mentioned in step (4) includes any one of sodium thiosulfate, sodium persulfate, sodium persulfate, sodium sulfate, sodium sulfite, and sodium polythionate.

7. The preparation method of seed coat-based hard carbon material based on hydrothermal sulfidation modification as described in claim 1, characterized in that, In step (4), a sulfur source is used to perform hydrothermal treatment on solid material A. The amount of sulfur source added is 4-6 wt% of the added solid material A. The hydrothermal temperature is 100-150℃ and the hydrothermal time is 2-4h. The centrifugal separation speed is 8000-10000 rpm. The material is dried in a vacuum drying oven at 60-80℃ for no less than 24h.

8. The method for preparing seed coat-based hard carbon material based on hydrothermal sulfidation modification as described in claim 1, characterized in that, In step (5), the calcination temperature is 1100-1300℃, the calcination time is 2-4h, the heating rate is 2-5℃ / min, and the working pressure of the inert gas is 0.8-1.2atm.

9. A hydrothermal sulfidation modified seed coat-based hard carbon material obtained by any of the preparation methods described in claims 1-8.

10. The application of hydrothermal sulfidation modified seed coat-based hard carbon material as described in claim 9 as a negative electrode material for sodium-ion batteries.

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