A method for preparing hard carbon based on biomass pyrolysis volatile circulating deposition
By using biomass pyrolysis volatile matter cyclic deposition technology, combined with composite salt solution impregnation and dynamic vapor phase deposition, the problems of high raw material ash content and strong randomness of pore structure in the preparation of biomass-based hard carbon have been solved, realizing the preparation of high-efficiency and low-cost hard carbon materials and improving electrochemical performance and safety.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Filing Date
- 2026-05-13
- Publication Date
- 2026-07-14
AI Technical Summary
In existing biomass preparation technologies, the raw materials have high ash content and inorganic impurities, leading to the following technical problems: In the existing technologies, the raw materials have high ash content and inorganic impurities, resulting in strong randomness in pore structure, a high proportion of open pores, a large specific surface area, insufficient closed pore volume, high cost of exogenous carbon sources, and safety and environmental protection issues.
A method of circulating deposition of biomass pyrolysis volatiles is adopted. Through pore conditioning, pre-carbonization, acid washing, coating and high-temperature carbonization treatment by impregnation with composite salt solution, combined with dynamic vapor deposition technology, a non-fully dense carbon layer with both pore sealing and ion transport capabilities is formed. The self-sourced pyrolysis volatiles are used as the carbon source to avoid the need for external carbon sources.
It achieves high initial coulombic efficiency and low specific surface area with low cost and green technology, significantly improves the platform capacity and electrochemical stability of hard carbon materials, reduces raw material costs and safety risks, and is suitable for large-scale production.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of carbon materials and energy storage materials preparation technology, and in particular to a method for preparing hard carbon based on the cyclic deposition of biomass pyrolysis volatiles. Specifically, it is a method for preparing high-performance hard carbon materials that combines in-situ pore expansion with composite molten salt, cyclic vapor deposition of self-sourced pyrolysis volatiles, and high-temperature dynamic pore sealing control, as well as the application of this hard carbon material in sodium-ion batteries, potassium-ion batteries, and other alkali metal-ion batteries. Background Technology
[0002] With the rapid development of the new energy storage industry, sodium-ion batteries, due to their abundant resources, low cost, and high safety, have broad application prospects in large-scale energy storage and low-speed power applications. Hard carbon materials, due to their low sodium intercalation potential, high capacity, and good cycle stability, have become one of the most promising anode materials for sodium-ion batteries for industrialization. Currently, hard carbon is mainly prepared using biomass raw materials such as coconut shells, fruit shells, wood, and straw, through carbonization and high-temperature treatment.
[0003] However, the existing biomass-based hard carbon preparation technology still has the following technical defects: (1) The raw material has high ash content and inorganic impurities, resulting in more side reactions and affecting electrochemical stability; (2) The pore structure is highly random, with a high proportion of open pores and a large specific surface area, resulting in low initial coulombic efficiency; (3) The closed pore volume is insufficient and the plateau capacity is low; (4) The existing vapor deposition sealing process relies on external carbon sources such as methane, acetylene, coke oven gas, and oil vapor, which is costly and poses safety and environmental protection problems; (5) Conventional sugar and asphalt-based coated carbon layers have low graphitization degree and generally poor interface stability.
[0004] Therefore, it is of great significance to develop a hard carbon preparation process that can construct closed-pore structures in a low-cost, green, and efficient manner without relying on exogenous carbon sources, and significantly improve the first coulombic efficiency and capacity. Summary of the Invention
[0005] To address the shortcomings of the existing technologies, this invention aims to provide a method for preparing hard carbon based on the cyclic deposition of biomass pyrolysis volatiles. This invention utilizes the synergistic deposition characteristics of multi-component carbon sources in biomass pyrolysis volatiles, and through high-temperature dynamic atmosphere control, forms a partially dense carbon layer on the hard carbon surface that combines pore sealing and ion transport capabilities, thereby achieving improved performance with high initial coulombic efficiency and low specific surface area.
[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: This invention provides a method for preparing hard carbon based on the cyclic deposition of volatile matter from biomass pyrolysis, comprising the following steps: (1) After pretreatment of biomass raw materials, the raw materials are impregnated in a composite salt solution to adjust the pore size, and then dried to obtain the salt-impregnated precursor. (2) Salt impregnation of precursors is used to precarbonize precarbonized products, and the pyrolysis volatiles are cooled to remove tar, dried, and pressure stabilized before being stored in a buffer tank for later use. (3) The pre-carbonized product is acid-washed, washed with water until neutral, and dried to obtain the acid-washed product; (4) The pickling product is coated with a polymer precursor to obtain a coated product; (5) The coated product is subjected to high-temperature carbonization treatment, and the pyrolysis volatiles in the buffer tank in step (2) are circulated into the reaction zone for dynamic vapor deposition to seal the pore inlet and form a closed pore structure. (6) Cool naturally or with inert gas, crush and sieve to obtain biomass-based high closed-pore hard carbon material.
[0007] Further, in step (1), the biomass raw material is at least one of coconut shell, apricot shell, walnut shell, bamboo, wood chips, straw, and peanut shell.
[0008] Further, in step (1), the pretreatment of biomass raw materials involves crushing the biomass raw materials into 5-30 mm particles, washing them with water, and then drying them at 80-130°C to a constant weight.
[0009] Further, in step (1), the composite salt is at least two of MgCl2, AlCl3, CaCl2, ZnCl2, and FeCl3.
[0010] Further, in step (1), the total concentration of the composite salt solution is 0.5 to 4 mol / L.
[0011] Furthermore, in step (1), the temperature of the impregnation and pore-adjusting treatment is 25-90°C and the time is 4-24h.
[0012] Further, in step (2), the pre-carbonization is carried out under an inert atmosphere, with the temperature increased to 350-700℃ at a rate of 2-8℃ / min and held for 0.5-4h. During the pre-carbonization process, the biomass undergoes pyrolysis, and the composite salt melts and expands the pores in situ, inhibiting collapse and forming a primary sodium storage pore structure; the pyrolysis volatiles include CH4, CO, H2, C2-C6 hydrocarbons, oxygen-containing organic vapors, and light tar components.
[0013] Furthermore, in step (3), the acid used for pickling is selected from at least one of hydrochloric acid, oxalic acid, citric acid, and dilute hydrofluoric acid.
[0014] Further, in step (4), the polymer precursor is selected from at least one of polyimide precursor, phenolic resin, furan resin, lignin-derived resin, polysiloxane resin, and polysilazane.
[0015] Further, in step (4), the coating amount of the polymer precursor is 1% to 20% of the mass of the coated product. The pickling product and the liquid polymer precursor are impregnated, crosslinked, and cured to form a continuous coating layer.
[0016] Furthermore, in step (5), the high-temperature carbonization treatment is carried out under an inert atmosphere, with the temperature increased to 1100-1600℃ at a rate of 2-5℃ / min and held for 1-8 hours.
[0017] Preferably, in the dynamic vapor deposition process of the present invention, a graded temperature range deposition is adopted, wherein 700-850°C is a low temperature deposition stage for micropore deposition, 850-1100°C is a medium temperature sealing stage for pore sealing, the deposition rate is increased, the pore entrance gradually shrinks, and a closed pore structure is formed; 1100-1600°C is a high temperature stabilization stage for forming a non-fully dense surface carbon layer to avoid complete graphitization.
[0018] Furthermore, in step (5), the dynamic vapor deposition pressure is controlled to be 0.95 to 1.25 atm.
[0019] Preferably, in the dynamic vapor deposition process of the present invention, the pressure is controlled by dynamic adjustment. In the low-temperature deposition stage, the reaction pressure is controlled at 0.95 to 1.05 atm to promote the diffusion and deposition of pyrolysis volatiles into the internal pores of the material. In the medium-temperature sealing stage, the reaction pressure is controlled at 1.05 to 1.25 atm to increase the carbon deposition rate in the pore opening area and achieve gradual closure of the pore entrance. In the high-temperature stage above 1100°C, the material mainly undergoes carbon structure rearrangement and densification processes, and no longer undergoes significant vapor deposition reactions.
[0020] Furthermore, in step (5), the dynamic vapor deposition adopts pulsed ventilation, with a single ventilation time of 10s to 60s and an interval of 20s to 120s, to avoid continuous carbon buildup causing complete blockage of the pores.
[0021] In the dynamic vapor deposition process of the present invention, pyrolysis volatiles are deposited in a multi-component synergistic manner, wherein CH4 and C2H4 provide the main carbon source for deposition, H2 inhibits excessively rapid carbon deposition, CO promotes the formation of defective carbon, and oxygen-containing organic matter regulates the disorder of the deposition layer, thereby forming a non-completely dense closed-pore carbon layer suitable for sodium ion diffusion.
[0022] This invention also provides a biomass-based high-closed-pore hard carbon material prepared by the above method, with a BET specific surface area ≤5m². 2 / g.
[0023] Furthermore, the initial coulombic efficiency of the biomass-based high closed-pore hard carbon material is ≥90%.
[0024] The present invention also provides the application of the biomass-based high closed-pore hard carbon material prepared by the above method in the negative electrode of sodium-ion battery, potassium-ion battery or other alkali metal-ion battery.
[0025] Compared with the prior art, the beneficial technical effects of the present invention are as follows: (1) Self-generated carbon source closed-loop cycle: The pyrolysis volatiles generated by the biomass itself during the pre-carbonization stage are used as the carbon source for gas phase deposition, eliminating the need for external carbon sources such as methane, acetylene, and coke oven gas, which significantly reduces raw material costs and safety risks. (2) Significant improvement in closed-pore structure: Through the synergistic effect of pulsed ventilation, staged temperature range deposition and dynamic pressure control, the in-situ deposition of homologous pyrolysis volatiles is used to realize the transformation from open pore to closed pore and improve the platform capacity; (3) Low specific surface area: The BET specific surface area of the hard carbon material obtained by this invention can be as low as 4.7 m². 2 / g; (4) High initial coulombic efficiency: The initial coulombic efficiency of the hard carbon material obtained by this invention can reach 92.2%; (5) High reversible capacity: The hard carbon material obtained in this invention has a reversible capacity of up to 322.6 mAh / g in sodium-ion batteries; (6) Green and environmentally friendly process: This invention realizes the resource utilization of pyrolysis by-products, which is in line with the concepts of green chemical industry and circular economy and is suitable for large-scale production. Attached Figure Description
[0026] Figure 1 This is a graph showing the electrochemical performance of the hard carbon material in Example 1 of the present invention.
[0027] Figure 2 This is a graph showing the electrochemical performance of the hard carbon material in Example 2 of the present invention.
[0028] Figure 3 This is a graph showing the electrochemical performance of the hard carbon material in Example 3 of the present invention.
[0029] Figure 4 This is a graph showing the electrochemical performance of the hard carbon material of Comparative Example 1 in this invention.
[0030] Figure 5 This is a graph showing the electrochemical performance of the hard carbon material in Comparative Example 2 of this invention.
[0031] Figure 6 This is a graph showing the electrochemical performance of the hard carbon material of Comparative Example 3 in this invention.
[0032] Figure 7 This is a graph showing the electrochemical performance of the hard carbon material in Comparative Example 4 of this invention. Detailed Implementation
[0033] The technical solutions 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.
[0034] Example 1 The fruit shells were crushed into 10mm particles, washed three times with deionized water, and dried at 105℃ for 12 h. A composite salt solution of MgCl2 and AlCl3 with a total concentration of 2mol / L was prepared by mixing them in a 1:1 molar ratio. The dried fruit shell particles were then impregnated at 25℃ for 12 h, and subsequently dried at 110℃ to obtain the salt-impregnated precursor. The salt-impregnated precursor was placed in a tube furnace and heated to 500℃ at a rate of 5℃ / min under a nitrogen atmosphere, and held at that temperature for 2 h. During the pre-carbonization process, a condenser for removing tar, a drying tube, and a buffer tank were connected to the outlet of the tube furnace to collect the pyrolysis volatiles. The main components of the pyrolysis volatiles were CH4, CO, H2, and a small amount of C2H4. The pre-carbonization product was washed with 1mol / L hydrochloric acid at 60℃ for 2 h, then washed with deionized water until neutral, and dried at 105℃. The obtained carbon powder was mixed with a polyimide precursor solution with a solid content of 10% at a mass ratio of 1:0.5, stirred and impregnated for 1 hour, and then crosslinked and cured at 120℃ for 2 hours. The coated product was placed in a high-temperature furnace and heated to 1450℃ at a rate of 3℃ / min under a nitrogen atmosphere. During the heating process, the collected pyrolysis volatiles were introduced in two stages: a low-temperature deposition stage (700–850℃) and a medium-temperature sealing stage (850–1100℃) using a pulsed method of 30s introduction followed by 60s stop, for a total deposition time of 1.5 hours. During the low-temperature deposition stage (700–850℃), the control system pressure was set at 0.98–1.02 atm; during the medium-temperature sealing stage (850–1100℃), the control system pressure was set at 1.10–1.18 atm. The mixture was then held at this temperature for 3 hours. After natural cooling to room temperature, the material was pulverized and passed through a 200-mesh sieve to obtain a biomass-based high-closed-pore hard carbon material.
[0035] Example 2 The fruit shells were crushed into 10mm particles, washed three times with deionized water, and dried at 105℃ for 12h. A composite salt solution with a MgCl2 to CaCl2 molar ratio of 1:1 and a total concentration of 2mol / L was prepared. The dried fruit shell particles were impregnated at 25℃ for 12h, then removed and dried at 110℃ to obtain the salt-impregnated precursor. The salt-impregnated precursor was placed in a tube furnace and heated to 500℃ at a rate of 5℃ / min under a nitrogen atmosphere, and held at that temperature for 2h. During the pre-carbonization process, a condenser for removing tar, a drying tube, and a buffer gas tank were connected to the outlet of the tube furnace to collect the pyrolysis volatiles. The main components of the pyrolysis volatiles were CH4, CO, H2, and a small amount of C2H4. The pre-carbonization product was washed with 2mol / L hydrochloric acid at 60℃ for 2h, then washed with deionized water until neutral, and dried at 105℃. The obtained carbon powder was mixed with a phenolic resin precursor solution with a solid content of 10% at a mass ratio of 1:0.5, stirred and impregnated for 1 hour, and then crosslinked and cured at 120℃ for 2 hours. The coated product was placed in a high-temperature furnace and heated to 1400℃ at a rate of 3℃ / min under a nitrogen atmosphere. During the heating process, the collected pyrolysis volatiles were introduced in two stages: a low-temperature deposition stage (700–850℃) and a medium-temperature sealing stage (850–1100℃), using a pulsed method of 30s introduction followed by 60s stop, for a total deposition time of 1.5 hours. During the low-temperature deposition stage (700–850℃), the control system pressure was set at 0.99–1.04 atm; during the medium-temperature sealing stage (850–1100℃), the control system pressure was set at 1.15–1.23 atm. The mixture was then held at these temperatures for 3 hours. After natural cooling to room temperature, the material was pulverized and passed through a 200-mesh sieve to obtain a biomass-based high-closed-pore hard carbon material.
[0036] Example 3 The fruit shells were crushed into 10mm particles, washed three times with deionized water, and dried at 105℃ for 12h. A composite salt solution with a 1:1 molar ratio of AlCl3 to CaCl2 and a total concentration of 2mol / L was prepared. The dried fruit shell particles were impregnated at 25℃ for 12h, then removed and dried at 110℃ to obtain the salt-impregnated precursor. The salt-impregnated precursor was placed in a tube furnace and heated to 500℃ at a rate of 5℃ / min under a nitrogen atmosphere, and held at that temperature for 2h. During the pre-carbonization process, a condenser for removing tar, a drying tube, and a buffer gas tank were connected to the outlet of the tube furnace to collect the pyrolysis volatiles. The main components of the pyrolysis volatiles were CH4, CO, H2, and a small amount of C2H4. The pre-carbonization product was washed with 1.5 mol / L hydrochloric acid at 60℃ for 2h, then washed with deionized water until neutral, and dried at 105℃. The obtained carbon powder was mixed with a furan resin precursor solution with a solid content of 10% at a mass ratio of 1:0.5, stirred and impregnated for 1 hour, and then crosslinked and cured at 120℃ for 2 hours. The coated product was placed in a high-temperature furnace and heated to 1350℃ at a rate of 3℃ / min under a nitrogen atmosphere. During the heating process, the collected pyrolysis volatiles were introduced in two stages: a low-temperature deposition stage (700–850℃) and a medium-temperature sealing stage (850–1100℃) using a pulsed method of 30s introduction followed by 60s stop, for a total deposition time of 1.5 hours. During the low-temperature deposition stage (700–850℃), the control system pressure was 0.97–1.01 atm; during the medium-temperature sealing stage (850–1100℃), the control system pressure was 1.06–1.12 atm. The mixture was then held at these temperatures for 3 hours. After natural cooling to room temperature, the material was pulverized and passed through a 200-mesh sieve to obtain a biomass-based high-closed-pore hard carbon material.
[0037] Comparative Example 1 (Pore adjustment without composite salt pre-carbonization) The difference from Example 1 is that: no composite salt impregnation and pore-conditioning treatment is performed, and the biomass raw material is directly subjected to subsequent pre-carbonization treatment after pretreatment.
[0038] Comparative Example 2 (Deposition of volatiles without pyrolysis) The difference from Example 1 is that no volatiles are introduced during the high-temperature carbonization process, i.e. there is no vapor deposition process.
[0039] Comparative Example 3 (without polymer precursor coating) The difference from Example 1 is that the pickling product is not coated with a polymer precursor, but is directly subjected to high-temperature carbonization treatment.
[0040] Comparative Example 4 (using acetylene gas instead of pyrolysis volatiles for deposition) The difference from Example 1 is that: no volatiles are collected during the pre-carbonization process, and high-purity acetylene gas is introduced in a pulse manner during vapor deposition.
[0041] Test case The hard carbon materials prepared in Examples 1-3 and Comparative Examples 1-4 were characterized and their electrochemical performance was tested. Electrochemical performance testing used a CR2025 coin cell system with sodium metal as the counter electrode and a 1.5M NaPF6 mixed solution of DMC / EC / EMC as the electrolyte. The volume ratio of DMC:EC:EMC was 2:1:2. Constant current charge-discharge tests were performed within a voltage range of 0.001–2 V and a current density of 0.1C. Material characterization was performed using the nitrogen adsorption BET method (determined according to GB / T19587) to measure the specific surface area. The results are shown in Table 1 and Appendix. Figure 1-7 .
[0042] Table 1. Comparison of main electrochemical performance parameters of each embodiment and comparative example.
[0043] Table 1 and Figure 1-7 The results show that: Compared to Examples 1-3, Comparative Example 1 (without composite salt pre-carbonization and pore-conditioning) showed an increased specific surface area of 21.3 m² for its hard carbon material. 2 The initial coulombic efficiency dropped to 88.5%, and the reversible specific capacity decreased to 278.0 mAh / g. This indicates that the absence of the composite salt impregnation process leads to a reduction in interlayer spacing and capacity in hard carbon materials, proving that the composite salt impregnation process plays a crucial role in in-situ pore expansion and increasing interlayer spacing in this invention.
[0044] Compared to Examples 1-3, Comparative Example 2 (deposition of volatile matter without pyrolysis) showed a significantly increased specific surface area of its hard carbon material to 78.6 m². 2 / g, the initial coulombic efficiency decreased to 85.1%, and the reversible specific capacity decreased slightly. This indicates that the lack of volatile matter deposition leads to a significant increase in the specific surface area of hard carbon materials and a decrease in the initial coulombic efficiency, proving that the closed-loop deposition of self-generated pyrolytic volatile matter in this invention plays a key role in the construction of the closed-pore structure.
[0045] Compared to Examples 1-3, Comparative Example 3 (without polymer precursor coating) showed a significantly increased specific surface area of its hard carbon material to 86.8 m². 2 The initial coulombic efficiency decreased to 83.3% and the reversible specific capacity decreased to 298.3 mAh / g. This indicates that the absence of polymer precursor coating leads to a significant increase in specific surface area and a decrease in initial coulombic efficiency. This demonstrates that polymer precursor coating in this invention can effectively reduce specific surface area, improve initial coulombic efficiency, and form a synergistic effect with subsequent vapor deposition.
[0046] The specific surface area of the hard carbon material obtained in Comparative Example 4 (deposition using high-purity acetylene gas instead of pyrolysis volatiles) was 4.5 m². 2 / g, initial coulombic efficiency of 92.7%, and reversible specific capacity of 318.7 mAh / g. Compared with Example 1 (specific surface area 4.7 m² / g). 2 Compared to Comparative Example 4, which has a similar specific surface area and initial coulombic efficiency (92.2% mAh / g, 322.6 mAh / g), Comparative Example 4 uses exogenous high-purity acetylene gas as the carbon source, resulting in significantly higher raw material costs than the present invention's method using self-produced pyrolysis volatiles, and a slight decrease in reversible specific capacity. This indicates that the present invention uses self-produced pyrolysis volatiles from the biomass pre-carbonization stage as the carbon source for vapor-phase deposition, achieving low-cost and green technical effects while ensuring excellent electrochemical performance.
Claims
1. A method for preparing hard char based on the cyclic deposition of volatile matter from biomass pyrolysis, characterized in that, Includes the following steps: (1) After pretreatment of biomass raw materials, the raw materials are impregnated in a composite salt solution to adjust the pore size, and then dried to obtain the salt-impregnated precursor. (2) Salt impregnation of the precursor is used to precarbonize the product, and the pyrolysis volatiles are cooled to remove tar, dried, and pressure stabilized before being stored in a buffer tank for later use. (3) The pre-carbonized product is acid-washed, washed with water until neutral, and dried to obtain the acid-washed product; (4) The pickling product is coated with a polymer precursor to obtain a coated product; (5) The coated product is subjected to high-temperature carbonization treatment, and the pyrolysis volatiles in the buffer tank in step (2) are circulated into the reaction zone for dynamic vapor deposition to seal the pore inlet and form a closed pore structure. (6) Cool naturally or with inert gas, crush and sieve to obtain biomass-based high closed-pore hard carbon material.
2. The method for preparing hard carbon based on the cyclic deposition of biomass pyrolysis volatiles according to claim 1, characterized in that: In step (1), the biomass raw material is at least one of coconut shell, apricot shell, walnut shell, bamboo, wood chips, straw, and peanut shell; the pretreatment of the biomass raw material is to crush the biomass raw material into 5-30 mm particles, wash it with water, and dry it at 80-130℃ to constant weight; the composite salt is at least two of MgCl2, AlCl3, CaCl2, ZnCl2, and FeCl3, and the total concentration of the composite salt solution is 0.5-4 mol / L; the temperature of the impregnation and pore-conditioning treatment is 25-90℃ and the time is 4-24 h.
3. The method for preparing hard carbon based on the cyclic deposition of biomass pyrolysis volatiles according to claim 1, characterized in that: In step (2), the pre-carbonization is carried out under an inert atmosphere by heating to 350-700°C at a rate of 2-8°C / min and holding at that temperature for 0.5-4 hours.
4. The method for preparing hard carbon based on the cyclic deposition of biomass pyrolysis volatiles according to claim 1, characterized in that: In step (3), the acid used for pickling is selected from at least one of hydrochloric acid, oxalic acid, citric acid, and dilute hydrofluoric acid.
5. The method for preparing hard carbon based on the cyclic deposition of biomass pyrolysis volatiles according to claim 1, characterized in that: In step (4), the polymer precursor is selected from at least one of polyimide precursor, phenolic resin, furan resin, lignin-derived resin, polysiloxane resin, and polysilazane; the coating amount of the polymer precursor is 1% to 20% of the mass of the coated product.
6. The method for preparing hard carbon based on the cyclic deposition of biomass pyrolysis volatiles according to claim 1, characterized in that: In step (5), the high-temperature carbonization treatment is carried out in an inert atmosphere, with the temperature increased to 1100-1600℃ at a rate of 2-5℃ / min and held for 1-8 hours; the dynamic vapor deposition pressure is controlled at 0.95-1.25 atm and pulsed ventilation is used, with a single ventilation time of 10-60s and an interval of 20-120s.
7. The method for preparing hard char based on the cyclic deposition of biomass pyrolysis volatiles according to claim 6, characterized in that: In step (5), the dynamic vapor deposition adopts a graded temperature range deposition, wherein 700-850℃ is the low temperature deposition stage, in which micropore deposition is carried out; 850-1100℃ is the medium temperature sealing stage, in which the pore openings are sealed to form a closed pore structure; and 1100-1600℃ is the high temperature stabilization stage, in which no significant vapor deposition reaction is carried out, and a non-completely dense surface carbon layer is formed.
8. The method for preparing hard carbon based on the cyclic deposition of biomass pyrolysis volatiles according to claim 7, characterized in that: In step (5), the dynamic vapor deposition adopts a dynamic adjustment method to control the pressure. In the low temperature deposition stage, the reaction pressure is controlled at 0.95 to 1.05 atm; in the medium temperature sealing stage, the reaction pressure is controlled at 1.05 to 1.25 atm.
9. A biomass-based high-closed-cell hard carbon material prepared by the method according to any one of claims 1-8, wherein the initial coulombic efficiency of the biomass-based high-closed-cell hard carbon material is ≥90%, and the BET specific surface area is ≤5m². 2 / g.
10. The application of the biomass-based high-closed-pore hard carbon material prepared by the method according to any one of claims 1-8 in the negative electrode of sodium-ion batteries, potassium-ion batteries or other alkali metal-ion batteries.