Sulfur-doped mesoporous hard carbon material for sodium-ion batteries and preparation method and application thereof

Abstract

The application provides a sulfur-doped mesoporous hard carbon material for a sodium ion battery and a preparation method and application thereof, and the method comprises the following steps: selecting a biomass raw material, cleaning and drying the biomass raw material, and then crushing the biomass raw material to obtain a biomass powder; uniformly mixing the biomass raw material, a sulfur-containing compound and a pore structure directing agent in a liquid phase according to a mass ratio of 1:(0.6-2.5):(0.2-0.6) to obtain a mixture; stirring the mixture in deionized water to form a uniform slurry, and drying the slurry to obtain a precursor composite; performing medium-temperature decomposition on the precursor composite in a tube furnace to realize biomass pre-carbonization, preliminary doping of sulfur elements and pore structure guiding; continuing to perform high-temperature decomposition on the precursor composite to realize carbon skeleton shaping, complete doping of sulfur elements and mesoporous structure construction, and obtaining a crude hard carbon material product; and performing purification treatment on the crude hard carbon material product to obtain a sulfur-doped mesoporous hard carbon material; and the method is simple in process, low in cost and friendly to the environment.

Description

Technical Field

[0001] This invention belongs to the field of hard carbon material preparation technology, specifically relating to a sulfur-doped mesoporous hard carbon material for sodium-ion batteries, its preparation method, and its application. Background Technology

[0002] With the development of large-scale renewable energy storage and low-speed electric vehicles, sodium-ion batteries, due to their abundant sodium resources and low cost, have become an important supplement to lithium-ion batteries, demonstrating enormous application potential in the field of large-scale energy storage. The anode material is a core component of sodium-ion batteries, and hard carbon materials, with their wide interlayer spacing and amorphous structure, have become one of the most promising anode materials for sodium-ion batteries, capable of storing sodium ions through both intercalation and adsorption mechanisms.

[0003] However, commercially available hard carbon anode materials still have many problems: First, sodium ions have a larger radius than lithium ions, resulting in greater diffusion and migration resistance in hard carbon materials, leading to poor rate performance and severe capacity decay at high current densities; Second, the material surface has many defects, causing irreversible side reactions with the electrolyte, resulting in low initial charge-discharge efficiency and consuming a large amount of sodium source; Third, hard carbon materials have insufficient electronic conductivity, leading to significant battery polarization and reduced energy efficiency.

[0004] Existing technologies for modifying hard carbon anodes mainly focus on two aspects: pore structure regulation and heteroatom doping. While pore structure activation can increase sodium storage sites, it easily leads to an excessively large specific surface area, further reducing the initial efficiency. Although sulfur doping can improve the conductivity and surface sodium storage activity of the material, single doping methods cannot solve the problem of slow sodium ion diffusion in the bulk phase, resulting in limited improvement in rate performance. Existing modification methods often struggle to simultaneously achieve sodium storage capacity, initial efficiency, and rate performance.

[0005] To address the aforementioned issues, it is necessary to propose a sulfur-doped mesoporous hard carbon material for sodium-ion batteries that is rationally designed and effectively solves these problems, along with its preparation method and applications. Summary of the Invention

[0006] The present invention aims to at least solve one of the technical problems existing in the prior art, and to provide a sulfur-doped mesoporous hard carbon material for sodium-ion batteries, its preparation method, and its application.

[0007] A first aspect of the present invention provides a method for preparing a sulfur-doped mesoporous hard carbon material for sodium-ion batteries, the method comprising: Biomass raw materials are selected, washed, dried, and then pulverized to obtain biomass powder; The biomass raw material, sulfur-containing compound, and pore structure guiding agent are uniformly mixed in the liquid phase at a mass ratio of 1:(0.6-2.5):(0.2-0.6) to obtain a mixture; The mixture was stirred in deionized water to form a homogeneous slurry, and the homogeneous slurry was dried to obtain the precursor complex. The precursor composite was heated to 350°C to 550°C in a tube furnace at a heating rate of 3°C / min to 6°C / min and held for 1 to 3 hours to achieve biomass pre-carbonization, initial sulfur doping, and pore structure guidance. Continue heating at a rate of 2℃ / min~5℃ / min to 900℃~1200℃, hold for 2h~4h to achieve carbon framework shaping, complete sulfur doping and mesoporous structure construction, and obtain coarse hard carbon material product. The crude hard carbon material product was purified to obtain sulfur-doped mesoporous hard carbon material.

[0008] Optionally, the sulfur-containing compound includes one or more of thiophene, thiourea, and sodium sulfite.

[0009] Optionally, the pore structure guiding agent may be selected from one or more of polyethylene glycol, hexadecyltrimethylammonium bromide, and mesoporous silica.

[0010] Optionally, the mixture is stirred in deionized water to form a homogeneous slurry, comprising: The mixture is stirred in deionized water for 2 to 4 hours to form a uniform slurry.

[0011] Optionally, the precursor complex is obtained by drying the homogeneous slurry, comprising: The precursor complex is obtained by spray drying to remove moisture, wherein the inlet temperature is 180℃~220℃ and the outlet temperature is 80℃~100℃.

[0012] Optionally, the crude hard carbon material is purified to obtain a sulfur-doped mesoporous hard carbon material, comprising: The crude product is soaked in 1 mol / L to 4 mol / L dilute sulfuric acid or dilute hydrochloric acid for 6 h to 12 h; Wash repeatedly with deionized water until neutral; The sulfur-doped mesoporous hard carbon material is obtained by drying in a vacuum at 80℃~100℃ for 12h~24h.

[0013] Optionally, biomass raw materials are selected, washed, dried, and then pulverized to obtain biomass powder, including: Select biomass raw materials rich in cellulose, wash and dry them, and then pulverize them to 150-200 mesh to obtain the biomass powder.

[0014] Another aspect of the present invention provides a sulfur-doped mesoporous hard carbon material for sodium-ion batteries, which is prepared by the method for preparing sulfur-doped mesoporous hard carbon materials for sodium-ion batteries described above.

[0015] Optionally, the sulfur-doped mesoporous hard carbon material includes a mesoporous-dominated hierarchical pore-connected structure; wherein, The pore size distribution of the pore-connecting structure is concentrated in the range of 2 nm to 50 nm, the mesopore volume accounts for more than 60% of the total pore volume, the total pore volume is 0.8 cm³ / g to 1.5 cm³ / g, and the specific surface area is 300 m² / g to 600 m² / g. Sulfur is uniformly doped into the carbon framework in the form of CSC covalent bonds, with a total sulfur content of 3 at.% to 10 at.%.

[0016] Optionally, the sulfur-doped mesoporous hard carbon material described above for sodium-ion batteries can be used as the anode material for sodium-ion batteries.

[0017] This invention provides a sulfur-doped mesoporous hard carbon material for sodium-ion batteries, its preparation method, and its applications. The preparation method uses biomass raw materials, sulfur-containing compounds, and a pore structure guiding agent to prepare a precursor composite. The precursor composite is then subjected to staged pyrolysis to obtain the coarse hard carbon material product. Specifically, pre-carbonization of biomass, initial sulfur doping, and pore structure guiding are achieved through medium-temperature pyrolysis, and pre-carbonization of biomass, initial sulfur doping, and pore structure guiding are achieved through high-temperature pyrolysis. This preparation method employs a one-step mixing and staged pyrolysis process, eliminating the need for complex subsequent activation or secondary doping steps. It has low production costs, is easy to scale up for industrial production, and the entire process emits no toxic or harmful gases, making it environmentally friendly. It achieves synergistic regulation of mesoporous structure and sulfur doping, solving the problem that single modification methods cannot simultaneously achieve sodium storage capacity, initial efficiency, and rate performance. This provides a new technical approach and method for the rational design of hard carbon anode materials for sodium-ion batteries. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of a method for preparing a sulfur-doped mesoporous hard carbon material for sodium-ion batteries according to an embodiment of the present invention. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] like Figure 1 As shown, one aspect of the present invention provides a method S100 for preparing a sulfur-doped mesoporous hard carbon material for sodium-ion batteries, the method comprising: S110. Select biomass raw materials, wash and dry them, and then pulverize them to obtain biomass powder.

[0021] Specifically, select biomass raw materials rich in cellulose and hemicellulose, such as rice husks, corn cobs, and bamboo powder, wash and dry them, and then pulverize them to 150-200 mesh to obtain biomass powder. It should be noted that biomass raw materials are not limited to the types mentioned above, and can also be other types of biomass raw materials.

[0022] In this embodiment, the biomass feedstock uses commonly used industrial raw materials, saving costs. Cellulose easily forms an amorphous carbon structure and wide interlayer spacing during pyrolysis, providing natural intercalation space for sodium ions and ensuring high sodium storage capacity.

[0023] S120. The biomass raw material, sulfur-containing compound, and pore structure guiding agent are uniformly mixed in the liquid phase at a mass ratio of 1:(0.6-2.5):(0.2-0.6) to obtain a mixture.

[0024] The sulfur-containing compound includes one or more of thiophene, thiourea, and sodium sulfite. The pore structure directing agent is selected from one or more of polyethylene glycol, hexadecyltrimethylammonium bromide, and mesoporous silica. A suitable biomass feedstock, sulfur-containing compound, and pore structure directing agent are selected, and the biomass feedstock, sulfur-containing compound, and pore structure directing agent are uniformly mixed in the liquid phase at a mass ratio of 1:(0.6-2.5):(0.2-0.6) to obtain a mixture.

[0025] It should be noted that, in this embodiment, the types of biomass raw materials, sulfur-containing compounds, and pore structure guiding agents are not limited to the types mentioned above, and other types can be selected according to actual needs. This embodiment does not make specific limitations.

[0026] In this embodiment, by limiting the proportion of sulfur source and the proportion of directing agent, and combining two-stage heating, the problem of excessive specific surface area caused by the activation of a single pore structure is avoided, and mesoporous-dominated interconnected channels are realized, which not only ensures ion transport but also reduces side reactions.

[0027] S130. The mixture is stirred in deionized water to form a uniform slurry, and the uniform slurry is dried to obtain the precursor complex.

[0028] Specifically, the mixture is stirred in deionized water for 2-4 hours to form a uniform slurry. The slurry is then spray-dried to remove moisture, yielding a dried precursor complex, wherein the inlet temperature is 180°C-220°C and the outlet temperature is 80°C-100°C.

[0029] In this embodiment, sufficient mixing time ensures adequate contact of the biomass powder, sulfur source, and directing agent at the molecular level, laying the foundation for uniform composition of the composite particles obtained by subsequent spray drying and avoiding performance inconsistencies and polarization caused by excessive or insufficient local doping. Spray drying at a specific temperature can quickly remove moisture, preventing component sedimentation and separation, and yielding spherical or near-spherical precursor composites with good flowability and uniform composition, which is beneficial for the uniformity of subsequent pyrolysis reactions.

[0030] S140. The precursor composite is heated to 350℃~550℃ in a tube furnace at a heating rate of 3℃ / min~6℃ / min and held for 1h~3h to achieve biomass pre-carbonization, initial sulfur doping and pore structure guidance.

[0031] Specifically, the precursor complex is heated to 350℃~550℃ in a tube furnace at a heating rate of 3℃ / min~6℃ / min and held for 1h~3h. During this mesophilic pyrolysis stage, biomass macromolecules undergo pyrolysis and cross-linking to form a primary carbon skeleton; sulfur-containing compounds decompose to produce sulfur-containing active groups, which covalently bond with the carbon skeleton, achieving initial uniform doping of sulfur; pore structure guiding agents begin to decompose or self-assemble, providing template guidance for subsequent mesopore formation; thus achieving biomass pre-carbonization, initial sulfur doping, and pore structure guidance.

[0032] S150, continue heating at a rate of 2℃ / min~5℃ / min to 900℃~1200℃, hold for 2h~4h to achieve carbon framework shaping, complete sulfur doping and mesoporous structure construction, and obtain coarse hard carbon material product.

[0033] Specifically, the material is heated to 900℃~1200℃ at a heating rate of 2℃ / min~5℃ / min and held for 2h~4h. During this high-temperature pyrolysis stage, the carbon skeleton further condenses and graphite microcrystals grow, and the structure tends to stabilize. The bonding between sulfur and the carbon skeleton is more complete, the thiophene sulfur ratio is significantly increased, and the electronic conductivity of the material is optimized. The pore structure guiding agent completely decomposes or etches the carbon skeleton, forming a mesoporous dominated interconnected pore structure, completing the final structural shaping of the material, realizing the shaping of the carbon skeleton, complete doping of sulfur, and construction of the mesoporous structure, and obtaining a coarse and hard carbon material product.

[0034] S160. The hard carbon material product is purified to obtain sulfur-doped mesoporous hard carbon material.

[0035] Specifically, after pyrolysis, the material is naturally cooled to room temperature in a nitrogen atmosphere to obtain a black crude product. The crude product of the hard carbon material is then soaked in 1 mol / L to 4 mol / L dilute sulfuric acid or dilute hydrochloric acid for 6 h to 12 h, and stirred to remove residual pore structure guiding agent and inorganic impurities. It is then repeatedly washed with deionized water until neutral, and dried in a vacuum at 80℃ to 100℃ for 12 h to 24 h to obtain the final sulfur-doped mesoporous hard carbon material.

[0036] This invention provides a method for preparing sulfur-doped mesoporous hard carbon materials for sodium-ion batteries. The method involves preparing a precursor composite using biomass raw materials, sulfur-containing compounds, and a pore structure guiding agent. The precursor composite is then subjected to staged pyrolysis to obtain the coarse hard carbon material product. Specifically, pre-carbonization of biomass, initial sulfur doping, and pore structure guiding are achieved through medium-temperature pyrolysis, while pre-carbonization of biomass, initial sulfur doping, and pore structure guiding are achieved through high-temperature pyrolysis. This preparation method employs a one-step mixing and staged pyrolysis process, eliminating the need for complex subsequent activation or secondary doping steps. The template agent can be removed through simple acid washing, resulting in low production costs and easy industrial-scale production. Furthermore, the entire process produces no toxic or harmful gas emissions, making it environmentally friendly. It achieves synergistic regulation of mesoporous structure and sulfur doping, solving the problem that single modification methods cannot simultaneously achieve sodium storage capacity, initial efficiency, and rate performance. This provides a new technical approach and method for the rational design of hard carbon anode materials for sodium-ion batteries.

[0037] Another aspect of the present invention provides a sulfur-doped mesoporous hard carbon material for sodium-ion batteries, which is prepared using the method for preparing sulfur-doped mesoporous hard carbon materials for sodium-ion batteries described above. The specific steps of the preparation method S100 for this sulfur-doped mesoporous hard carbon material for sodium-ion batteries have been described in detail above and will not be repeated here.

[0038] Specifically, the sulfur-doped mesoporous hard carbon material for sodium-ion batteries provided by this invention has a hierarchical pore-connected structure dominated by mesopores. The pore size distribution is concentrated in the range of 2 nm to 50 nm, with mesopores of 2 nm to 10 nm being the main pore type. Mesopores account for more than 60% of the total pore volume, with a total pore volume of 0.8 cm³ / g to 1.5 cm³ / g and a specific surface area of ​​300 m² / g to 600 m² / g. This pore structure provides a fast transport path for sodium ions and electrolyte through mesoporous channels, reducing bulk diffusion resistance, while avoiding the increase in side reactions caused by excessive specific surface area, thus achieving a balance between sodium storage sites and interfacial stability.

[0039] Sulfur is uniformly doped into the carbon framework via CSC covalent bonds, with a total sulfur content of 3 at.% to 10 at.%, of which thiophene sulfur, which enhances electronic conductivity and surface sodium storage activity, accounts for no less than 50% of the total sulfur content. The material retains the natural oxygen, potassium, and other heteroatoms contained in biomass, which synergistically regulate the surface chemical properties of the material with sulfur, guiding the formation of a stable and thin SEI film and reducing irreversible capacity loss.

[0040] The material has a typical hard carbon structure, consisting of short-range ordered graphite microcrystal regions interwoven with amorphous carbon regions. X-ray diffraction measurements show that the interlayer spacing (d002) of the (002) crystal planes of the graphite microcrystals is between 0.38 and 0.42 nanometers, which is much larger than the 0.335 nanometers of graphite. This provides sufficient interlayer space for the rapid intercalation and storage of sodium ions, while the amorphous carbon regions provide a large number of surface adsorption sites for sodium ions.

[0041] In another aspect of the present invention, the sulfur-doped mesoporous hard carbon material for sodium-ion batteries described above is applied to the negative electrode material of sodium-ion batteries.

[0042] Specifically, the sulfur-doped mesoporous hard carbon material prepared for sodium-ion batteries is mixed with conductive agents (acetylene black, Ketjen black) and binders (polyvinylidene fluoride, sodium carboxymethyl cellulose) at a mass ratio of 8:1:1. N-methylpyrrolidone or deionized water is added to form a slurry, which is then coated onto a copper foil current collector. After drying and rolling, it is formed into a sodium-ion battery negative electrode. Sodium-ion batteries assembled with this electrode exhibit excellent sodium storage capacity, initial efficiency, and rate cycle performance, and can be widely used in sodium-ion battery systems for large-scale energy storage power stations, low-speed electric vehicles, and portable electronic devices.

[0043] The sulfur-doped mesoporous hard carbon material prepared in this invention, when used as a negative electrode for sodium-ion batteries, achieves a first-cycle coulombic efficiency of 82%~90%, a reversible specific capacity of 300 mAh / g~380 mAh / g at a current density of 0.1 A / g, a capacity retention rate of over 65% at a high rate of 5 A / g, and a capacity retention rate of over 80% after 2000 cycles. Its overall electrochemical performance is significantly better than that of existing sulfur-doped hard carbon materials.

[0044] The synergistic effect of the mesoporous structure and sulfur doping (especially high proportion of thiophene sulfur) in the sulfur-doped mesoporous hard carbon material of this invention significantly improves the overall performance of sodium-ion battery anodes. Specifically, the mesoporous channels reduce the bulk diffusion resistance of sodium ions and improve rate performance; thiophene sulfur optimizes the electronic conductivity of the material and reduces battery polarization; sulfur and biomass natural heteroatoms synergistically regulate surface chemistry, guiding the formation of a stable SEI film and improving initial efficiency; the wide interlayer spacing hard carbon structure provides sodium ions with dual sodium storage sites for intercalation and adsorption, ensuring high sodium storage capacity. Multiple factors work together to improve the overall performance of the material.

[0045] The following examples illustrate the specific process of preparing sulfur-doped mesoporous hard carbon materials for sodium-ion batteries provided by this invention.

[0046] Example 1 This embodiment provides a method for preparing sulfur-doped mesoporous hard carbon materials for sodium-ion batteries, specifically using cellulose-rich coconut shells as biomass raw materials. First, the coconut shells are washed, dried, and pulverized to 180 mesh to obtain biomass powder. The biomass raw materials, a sulfur-containing compound (thiophene), and a pore structure guiding agent (polyethylene glycol) are uniformly mixed in a liquid phase at a mass ratio of 1:1.5:0.4 to obtain a mixture. This mixture is stirred in deionized water for 3 hours to form a homogeneous slurry, which is then spray-dried to remove moisture, yielding a dried precursor composite. The spray drying inlet temperature is 200°C, and the outlet temperature is 90°C. The precursor composite is placed in a tube furnace and heated to 450°C at a heating rate of 4.5°C / min, and held for 2 hours to achieve pre-carbonization of the biomass, initial sulfur doping, and pore structure guidance. Heating continues at a heating rate of 3.5°C / min to 1050°C, and held for 3 hours to achieve carbon framework shaping, complete sulfur doping, and mesoporous structure construction, yielding a coarse hard carbon material product. The crude hard carbon material product was purified by soaking it in 2.5 mol / L dilute hydrochloric acid for 9 hours, washing it repeatedly with deionized water until neutral, and then drying it in vacuum at 90℃ for 18 hours to obtain sulfur-doped mesoporous hard carbon material.

[0047] Testing revealed that the sulfur-doped mesoporous hard carbon material obtained in this embodiment has a specific surface area of ​​452 m² / g, a total pore volume of 1.21 cm³ / g, a mesoporous pore volume accounting for 72% of the total pore volume, and a total sulfur content of 6.8 at.%, with sulfur uniformly doped into the carbon framework via CSC covalent bonds. Electrochemical performance tests were conducted using this material as a sodium-ion battery anode material. At a current density of 0.1 A / g, the initial reversible specific capacity was 386 mAh / g, and the first-cycle coulombic efficiency was 84.2%. Rate performance testing showed that even at a high rate of 5 A / g, the reversible specific capacity still reached 251 mAh / g, with a capacity retention rate of 65.0%. Cycle stability testing indicated that after 2000 cycles at a current density of 1 A / g, the reversible specific capacity retention rate was 81.5%. The sulfur-doped mesoporous hard carbon material prepared in this embodiment exhibits significantly better overall electrochemical performance than existing sulfur-doped hard carbon materials, demonstrating synergistic advantages of high capacity, high initial efficiency, excellent rate performance, and ultra-long cycle life.

[0048] Example 2 The difference between this embodiment and Example 1 is that the mass ratio of biomass raw material to sulfur-containing compound is adjusted to 1:0.6, while the remaining steps and parameters are exactly the same as in Example 1. Specifically, coconut shells are used as raw material and pulverized to 180 mesh. Biomass raw material, thiophene, and polyethylene glycol are mixed in the liquid phase at a mass ratio of 1:0.6:0.4 and stirred for 3 hours to form a uniform slurry. The slurry is then spray-dried (inlet 200℃, outlet 90℃) to obtain the precursor composite. The slurry is heated to 450℃ at 4.5℃ / min and held for 2 hours in a tube furnace, then heated to 1050℃ at 3.5℃ / min and held for 3 hours. After soaking in 2.5mol / L dilute hydrochloric acid for 9 hours, washing until neutral, and vacuum drying at 90℃ for 18 hours, sulfur-doped mesoporous hard carbon material is obtained.

[0049] Testing revealed that the material obtained in this embodiment had a specific surface area of ​​387 m² / g, a total pore volume of 0.96 cm³ / g, a mesoporous pore volume ratio of 63%, and a total sulfur content of 3.2 at.%. Electrochemical performance tests showed that at a current density of 0.1 A / g, the initial reversible specific capacity was 312 mAh / g, with a first-cycle coulombic efficiency of 78.5%; at a high rate of 5 A / g, the reversible specific capacity was 180 mAh / g, with a capacity retention of 57.7%; and after 2000 cycles, the capacity retention was 73.2%. Compared to Example 1, the insufficient amount of sulfur-containing compounds resulted in lower sulfur doping and incomplete mesoporous structure development, leading to a slight decrease in electrochemical performance, but it is still superior to some existing reports.

[0050] Example 3 The difference between this embodiment and Example 1 is that the mass ratio of biomass raw material to pore structure guiding agent is adjusted to 1:0.6, while the remaining steps and parameters are exactly the same as in Example 1. Specifically, coconut shells are used as raw material and pulverized to 180 mesh. Biomass raw material, thiophene, and polyethylene glycol are mixed in the liquid phase at a mass ratio of 1:1.5:0.6 and stirred for 3 hours to form a uniform slurry. The slurry is then spray-dried (inlet temperature 200°C, outlet temperature 90°C) to obtain the precursor complex. Subsequent carbonization and purification steps are the same as in Example 1.

[0051] Testing revealed that the material obtained in this embodiment had a specific surface area of ​​542 m² / g, a total pore volume of 1.48 cm³ / g, a mesoporous pore volume ratio of 81%, and a total sulfur content of 6.5 at.%. Electrochemical performance tests showed that at a current density of 0.1 A / g, the initial reversible specific capacity was 412 mAh / g, with a first-cycle coulombic efficiency of 86.1%; at a high rate of 5 A / g, the reversible specific capacity was 276 mAh / g, with a capacity retention of 67.0%; and after 2000 cycles, the capacity retention was 83.2%. Compared to Example 1, appropriately increasing the amount of pore structure guiding agent is beneficial for the full development of the mesoporous structure, providing more sodium ion storage sites, and improving both capacity and rate performance.

[0052] Example 4 The difference between this embodiment and Example 1 is that the final carbonization temperature is adjusted to 1200℃, while the remaining steps and parameters are exactly the same as in Example 1. Specifically, coconut shells are used as raw material and pulverized to 180 mesh. Biomass raw materials, thiophene, and polyethylene glycol are mixed at a mass ratio of 1:1.5:0.4, stirred for 3 hours, and spray-dried to obtain the precursor complex. The mixture is heated to 450℃ at 4.5℃ / min and held for 2 hours in a tube furnace, then heated to 1200℃ at 3.5℃ / min and held for 3 hours. Subsequent purification steps are the same as in Example 1.

[0053] Testing revealed that the material obtained in this embodiment had a specific surface area of ​​489 m² / g, a total pore volume of 1.26 cm³ / g, a mesoporous pore volume ratio of 74%, and a total sulfur content of 5.2 at.%. Electrochemical performance tests showed that at a current density of 0.1 A / g, the initial reversible specific capacity was 371 mAh / g, with a first-cycle coulombic efficiency of 83.6%; at a high rate of 5 A / g, the reversible specific capacity was 234 mAh / g, with a capacity retention rate of 63.1%; and after 2000 cycles, the capacity retention rate was 80.2%. Compared to Example 1, increasing the carbonization final temperature is beneficial for improving the graphitization degree of the carbon material, but it leads to the pyrolysis and escape of some sulfur, resulting in a slight decrease in capacity.

[0054] Example 5 This embodiment provides a sulfur-doped mesoporous hard carbon material for sodium-ion batteries, which is prepared using the preparation method described in any one of Examples 1 to 7 above. The material comprises a hierarchical pore-connected structure dominated by mesopores. The pore size distribution of the pore-connected structure is concentrated in the range of 2 nm to 50 nm. The mesopore volume accounts for more than 60% of the total pore volume, with a total pore volume of 0.8 cm³ / g to 1.5 cm³ / g and a specific surface area of ​​300 m² / g to 600 m² / g. Sulfur is uniformly doped into the carbon framework in the form of CSC covalent bonds, with a total sulfur content of 3 at.% to 10 at.%.

[0055] Electrochemical performance tests were conducted on this material as a sodium-ion battery anode material. The results showed that the initial coulombic efficiency reached 82%–90%, and the reversible specific capacity at a current density of 0.1 A / g reached 300 mAh / g–380 mAh / g. Excellent rate performance was demonstrated, with a reversible specific capacity retention exceeding 65% at a high rate of 5 A / g. Outstanding cycle stability was also observed, with the capacity retention remaining above 80% after 2000 cycles at a current density of 1 A / g. The sulfur-doped mesoporous hard carbon material prepared in this invention achieves synergistic optimization of high capacity, high initial efficiency, excellent rate performance, and ultra-long cycle life through the synergistic regulation of sulfur doping and mesoporous structure. Its overall electrochemical performance is significantly superior to existing sulfur-doped hard carbon materials.

[0056] Comparative Example 1 This comparative example provides a method for preparing sulfur-doped mesoporous hard carbon materials for sodium-ion batteries. Compared with Example 1, this comparative example does not use the preferred range of the present invention for several key process parameters, in order to illustrate the technical advantages of the present invention. Specifically, coconut shells are used as biomass raw materials, which are washed, dried, and pulverized to 180 mesh. The biomass raw materials, sulfur-containing compounds (thiophene), and pore structure directing agents (polyethylene glycol) are mixed in the liquid phase at a mass ratio of 1:0.2:0.1 (the amounts of sulfur-containing compounds and pore structure directing agents are far below the limits specified in the present invention), and stirred for 1 hour to form a slurry. The slurry is dried in a conventional oven (without spray drying) to obtain a precursor composite. The precursor composite is placed in a tube furnace and directly heated to 800°C at a heating rate of 10°C / min (the heating rate is too fast, and a two-stage heating method is not used, resulting in a carbonization temperature lower than the 900°C~1200°C range specified in the present invention), and held for 1 hour (insufficient holding time) to obtain a coarse hard carbon material product. The crude hard carbon material product was purified by soaking it in 0.5 mol / L dilute hydrochloric acid for 3 hours (the acid concentration was lower than the 1 mol / L to 4 mol / L limit specified in this invention, and the soaking time was insufficient), washing it with deionized water, and drying it in vacuum at 60°C for 6 hours to obtain the hard carbon material.

[0057] Testing revealed that the material obtained in this comparative example had a specific surface area of ​​185 m² / g, a total pore volume of 0.42 cm³ / g, a mesoporous pore volume ratio of only 32%, and a total sulfur content of 1.1 at.%. Electrochemical performance tests were conducted on this material as a sodium-ion battery anode material. The results showed that at a current density of 0.1 A / g, the initial reversible specific capacity was only 156 mAh / g, with a first-cycle coulombic efficiency of 62.3%; at a high rate of 5 A / g, the reversible specific capacity was 62 mAh / g, with a capacity retention rate of only 39.7%; and after 2000 cycles, the capacity retention rate was only 51.2%. Compared with Example 1 of this invention (initial reversible specific capacity 386 mAh / g, first-cycle coulombic efficiency 84.2%, capacity retention rate at 5 A / g 65.0%, and capacity retention rate after 2000 cycles 81.5%), the capacity of this comparative example decreased by approximately 60%, the coulombic efficiency was significantly reduced, and the rate performance and cycle stability were severely deteriorated. The results show that when key parameters such as the amount of sulfur-containing compound, the amount of pore structure guiding agent, the drying method, the carbonization process, and the purification conditions all deviate from the preferred range of this invention, the amount of sulfur doping is seriously insufficient, the mesoporous structure cannot be effectively constructed, resulting in a lack of sodium ion storage sites, serious deterioration of electrochemical performance, and inability to meet the application requirements of sodium-ion battery anode materials.

[0058] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a sulfur-doped mesoporous hard carbon material for sodium-ion batteries, characterized in that, The preparation method includes: Biomass raw materials are selected, washed, dried, and then pulverized to obtain biomass powder; The biomass raw material, sulfur-containing compound, and pore structure guiding agent are uniformly mixed in the liquid phase at a mass ratio of 1:(0.6-2.5):(0.2-0.6) to obtain a mixture; The mixture was stirred in deionized water to form a homogeneous slurry, and the homogeneous slurry was dried to obtain the precursor complex. The precursor composite was heated to 350°C to 550°C in a tube furnace at a heating rate of 3°C / min to 6°C / min and held for 1 to 3 hours to achieve biomass pre-carbonization, initial sulfur doping, and pore structure guidance. Continue heating at a rate of 2℃ / min~5℃ / min to 900℃~1200℃, hold for 2h~4h to achieve carbon framework shaping, complete sulfur doping and mesoporous structure construction, and obtain coarse hard carbon material product. The crude hard carbon material product was purified to obtain sulfur-doped mesoporous hard carbon material.

2. The preparation method according to claim 1, characterized in that, The sulfur-containing compound includes one or more of thiophene, thiourea, and sodium sulfite.

3. The preparation method according to claim 1, characterized in that, The pore structure guiding agent is selected from one or more of polyethylene glycol, hexadecyltrimethylammonium bromide, and mesoporous silica.

4. The preparation method according to claim 1, characterized in that, The mixture is stirred in deionized water to form a homogeneous slurry, comprising: The mixture is stirred in deionized water for 2 to 4 hours to form a uniform slurry.

5. The preparation method according to claim 1, characterized in that, The precursor complex is obtained by drying the homogeneous slurry, comprising: The precursor complex is obtained by spray drying to remove moisture, wherein the inlet temperature is 180℃~220℃ and the outlet temperature is 80℃~100℃.

6. The preparation method according to claim 1, characterized in that, The crude hard carbon material is purified to obtain a sulfur-doped mesoporous hard carbon material, comprising: The crude product of the hard carbon material is soaked in 1 mol / L to 4 mol / L dilute sulfuric acid or dilute hydrochloric acid for 6 h to 12 h. Wash repeatedly with deionized water until neutral; The sulfur-doped mesoporous hard carbon material is obtained by drying in a vacuum at 80℃~100℃ for 12h~24h.

7. The preparation method according to claim 1, characterized in that, Biomass raw materials are selected, washed, dried, and then pulverized to obtain biomass powder, including: Select biomass raw materials rich in cellulose, wash and dry them, and then pulverize them to 150-200 mesh to obtain the biomass powder.

8. A sulfur-doped mesoporous hard carbon material for sodium-ion batteries, characterized in that, The sulfur-doped mesoporous hard carbon material for sodium-ion batteries is prepared using the preparation method described in any one of claims 1 to 7.

9. The sulfur-doped mesoporous hard carbon material according to claim 8, characterized in that, The sulfur-doped mesoporous hard carbon material comprises a mesoporous-dominated hierarchical pore interconnection structure; wherein, The pore size distribution of the pore-connecting structure is concentrated in the range of 2 nm to 50 nm, the mesopore volume accounts for more than 60% of the total pore volume, the total pore volume is 0.8 cm³ / g to 1.5 cm³ / g, and the specific surface area is 300 m² / g to 600 m² / g. Sulfur is uniformly doped into the carbon framework in the form of CSC covalent bonds, with a total sulfur content of 3 at.% to 10 at.%.

10. The sulfur-doped mesoporous hard carbon material for sodium-ion batteries as described in claim 8 or 9 is used as a negative electrode material for sodium-ion batteries.

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