Sulfur-doped hard carbon composite material, and preparation method and application thereof

Abstract

This invention belongs to the field of electrochemical energy storage materials technology, specifically a sulfur-doped hard carbon composite material, its preparation method, and its application. Through a two-step synergistic process of "acid-induced sulfonation crosslinking-composite carbonization," using polyphenylene sulfide (PPS) plastic as a polymeric sulfur source, linear PPS is in-situ transformed into a three-dimensional crosslinked network and composited with biomass hard carbon. After carbonization, efficient and stable sulfur doping and the synergistic construction of a hierarchical porous structure are achieved. The sulfur-doped hard carbon composite material prepared by this invention, when used as a negative electrode in sodium-ion batteries, exhibits high reversible specific capacity, high initial coulombic efficiency, excellent rate performance, and outstanding cycle stability, showing broad application prospects in the field of low-cost, high-performance sodium-ion batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical energy storage materials, in particular to a sulfur-doped hard carbon composite material and a preparation method and application thereof. BACKGROUND

[0002] The increasingly severe energy crisis and environmental pollution problems have prompted human society to demand high-efficiency, clean and sustainable energy storage technologies. Among numerous electrochemical energy storage systems, lithium-ion batteries have been widely used in portable electronic devices and electric vehicles due to their high energy density and long cycle life. However, the limited crust abundance and uneven distribution of lithium resources have resulted in high costs, making it difficult to meet the requirements of low-cost and high-resource sustainability for large-scale energy storage power stations in the future. Sodium element is in the same main group as lithium element, has similar chemical properties, and is abundant in resources (crust abundance is about 2.3%), widely distributed and low in price, making sodium-ion batteries regarded as one of the most potential complementary or alternative technologies of lithium-ion batteries in the field of large-scale energy storage.

[0003] Among the key materials of sodium-ion batteries, the performance of the negative electrode material directly determines the energy density, power density and cycle life of the battery. As the current mainstream negative electrode material of lithium-ion batteries, graphite is difficult to effectively and reversibly embed and extract sodium ions due to the larger radius of sodium ions, and has very low sodium storage capacity. In contrast, hard carbon material can provide favorable paths and sites for sodium ion storage and transmission due to its large interlayer spacing, disordered turbostratic structure and rich nanopores, and is currently recognized as the most likely commercialized negative electrode material for sodium-ion batteries. Biomass resources (such as coconut shells, straws, fruit shells, etc.) are ideal precursors for preparing high-performance hard carbon negative electrodes due to their wide sources, low cost, environmental friendliness and natural multi-level structure suitable for preparing hard carbon.

[0004] However, the hard carbon material prepared by directly carbonizing biomass alone still faces many challenges in practical applications. First, its intrinsic electronic conductivity is poor, resulting in severe polarization at high current density and poor rate performance. Second, the sodium storage sites are limited, and the reversible specific capacity is usually limited to below 300 mAh / g, which is difficult to further improve to meet the demand for high energy density. In addition, uncontrollable pore development during high-temperature carbonization can easily lead to excessively high specific surface area, which exacerbates the irreversible decomposition of electrolyte in the first cycle and reduces the first coulombic efficiency.

[0005] To address these issues, researchers have widely employed heteroatom doping strategies to modify hard carbon materials. Sulfur doping, in particular, has been theoretically and experimentally proven to be a highly effective approach. On one hand, sulfur atoms possess a large atomic radius (1.02 Å) and low electronegativity (2.58). Their incorporation into the carbon lattice effectively expands the interlayer spacing, significantly reducing the diffusion barrier of sodium ions between layers, thereby improving the material's rate performance. On the other hand, the CSC covalent bonds formed between sulfur atoms and carbon can serve as additional Faraday redox active centers, providing additional surface pseudocapacitive sodium storage sites for sodium ions, thus enhancing the overall specific capacity of the material. Existing sulfur doping methods typically use small-molecule sulfur-containing compounds as dopant sources, such as elemental sulfur powder, thiourea, and hydrogen sulfide gas, which are mixed with the carbon precursor and then co-pyrolyzed at high temperatures. However, these conventional methods generally suffer from a common problem: small-molecule sulfur sources are highly susceptible to sublimation or volatilization during high-temperature carbonization (e.g., sulfur powder has a boiling point of approximately 445°C), leading to significant sulfur loss. This results in the effective sulfur content actually incorporated into the carbon framework being far lower than the theoretical value, leading to low doping efficiency. Furthermore, the rapid vaporization of the sulfur source causes uncontrollable etching of the carbon framework, resulting in disordered pore structure, numerous open pores, and excessively high specific surface area. These defects not only fail to effectively contribute to sodium storage capacity but also become active centers for electrolyte decomposition, exacerbating side reactions, reducing initial coulombic efficiency, and impairing the material's cycling stability and tap density.

[0006] Therefore, how to achieve efficient and stable fixation of sulfur in the hard carbon framework, while precisely controlling the evolution of pore structure to synergistically improve the sodium storage capacity, rate performance and cycle stability of the material, is a key technical problem that urgently needs to be solved in the current research field of sulfur-doped hard carbon anode materials. Summary of the Invention

[0007] The purpose of this invention is to provide a sulfur-doped hard carbon composite material, its preparation method, and its application, in order to solve the problems mentioned in the background art.

[0008] To address the aforementioned technical problems, this invention provides the following technical solution: a method for preparing a sulfur-doped hard carbon composite material, comprising the following steps: Step 1: Pre-carbonize the biomass raw material under an inert atmosphere to obtain a pre-carbonized product; then, perform high-temperature carbonization on the pre-carbonized product under an inert atmosphere to obtain biomass hard carbon. Step 2: Dissolve polyphenylene sulfide in N-methylpyrrolidone solvent to prepare PPS solution; add concentrated sulfuric acid to the PPS solution and stir to mix; then add the biomass hard carbon obtained in step 1, stir to mix and carry out sulfonation crosslinking reaction, and after drying treatment, obtain sulfonation crosslinked composite precursor; Step 3: Under an inert protective atmosphere, the sulfonated crosslinked composite precursor obtained in Step 2 is subjected to carbonization treatment. After carbonization, it is naturally cooled to room temperature to obtain the sulfur-doped hard carbon composite material.

[0009] Further, in step 1, the biomass raw material is selected from one or more of coconut shells, walnut shells, apricot shells, olive shells, rice husks, sugarcane bagasse, bamboo shavings, wood chips, and straw; preferably, the biomass raw material is coconut shells.

[0010] Furthermore, in step 1, the pre-carbonization treatment is carried out at a temperature of 300~600°C for a time of 0.5~2h.

[0011] Preferably, the pre-carbonization temperature is 400°C and the time is 1 hour.

[0012] Further, in step 1, the high-temperature carbonization treatment method is as follows: the temperature is raised to 1200~1500°C at a rate of 1~10°C / min and then held for carbonization for 1~4 hours.

[0013] Preferably, the heating rate is 5°C / min, the high-temperature carbonization temperature is 1300°C, and the holding carbonization time is 2h.

[0014] Furthermore, in step 1, the inert atmosphere is nitrogen or argon.

[0015] Further, in step 2, the preparation process of the PPS solution is as follows: PPS powder is added to NMP solvent and heated and stirred at 160~200°C until completely dissolved.

[0016] Preferably, the solution is heated and stirred at 180°C for 1 hour.

[0017] Further, in step 2, the concentrated sulfuric acid has a mass fraction of 95%~98%, and the volume-to-mass ratio of the concentrated sulfuric acid to PPS is (0.25~2) mL:1g.

[0018] Preferably, the concentrated sulfuric acid has a mass fraction of 98%, and the mass-to-volume ratio of concentrated sulfuric acid to PPS is 1 mL: 1 g.

[0019] Furthermore, in step 2, the temperature for stirring and mixing after adding concentrated sulfuric acid is 60~100°C, and the time is 0.5~2h.

[0020] Preferably, the stirring temperature is 80°C and the stirring time is 1 hour.

[0021] Further, in step 2, the mass ratio of PPS to biomass hard char is 0.25:1 to 2:1; the stirring reaction temperature after adding biomass hard char is 60 to 100°C, and the reaction time is 1 to 4 hours.

[0022] Preferably, the mass ratio of PPS to biomass hard char is 1:1, the stirring reaction temperature is 80°C, and the reaction time is 2 hours.

[0023] Further, in step 2, the drying temperature is 80~120°C and the time is 6~24h; preferably, the drying temperature is 105°C and the time is 12h.

[0024] Further, in step 3, the carbonization process involves heating the temperature to 500-800°C at a rate of 1-10°C / min, followed by holding the temperature for carbonization for 0.5-2 hours.

[0025] Preferably, the heating rate is 5°C / min, the carbonization temperature is 600°C, and the carbonization time is 1 hour.

[0026] Furthermore, in step 3, the inert atmosphere is nitrogen or argon.

[0027] On the other hand, the present invention provides a sodium-ion battery negative electrode sheet comprising the above-mentioned sulfur-doped hard carbon composite material, wherein the sulfur-doped hard carbon composite material is the only or main active material in the negative electrode sheet, and the sodium-ion battery negative electrode sheet can be used in sodium-ion batteries.

[0028] Compared with existing technologies, the beneficial effects achieved by this invention are as follows: This invention utilizes a two-step synergistic process of "acid-induced sulfonation crosslinking - composite carbonization," using polyphenylene sulfide plastic as a high-molecular sulfur source to in-situ transform linear polyphenylene sulfide into a three-dimensional crosslinked network and composite it with biomass hard carbon. After carbonization, it achieves efficient and stable doping of sulfur and the synergistic construction of a hierarchical porous structure. This invention has the following significant advantages: 1. High sulfur doping efficiency and stable active site structure. This invention uses polyphenylene sulfide (PPS) as a polymeric sulfur source and transforms linear PPS chains into a three-dimensional cross-linked network in situ through acid-induced sulfonation cross-linking pretreatment. This network exhibits higher thermal stability during carbonization, effectively suppressing random chain breakage and volatilization of sulfur-containing small molecules. It promotes the in-situ transformation of sulfur into a highly electrochemically active and structurally stable thiophene sulfur configuration within the carbon framework, significantly improving sulfur retention and effective doping levels. This overcomes the shortcomings of traditional small-molecule sulfur sources, such as low doping efficiency and unstable sulfur morphology, while also effectively increasing the carbon interlayer spacing and pseudocapacitive active sites in hard carbon materials.

[0029] 2. Constructing a multi-level pore structure with micropores and mesopores to achieve synergistic improvement in capacity and kinetics. This invention utilizes a rigid polymer network formed by sulfonation crosslinking, which acts as a skeletal support during carbonization, inhibiting disordered shrinkage and collapse of the carbon layer and promoting the formation of uniform micropores. This provides abundant active sites for sodium ion "pore-filling" at low potentials, contributing to a high plateau capacity. Simultaneously, the in-situ decomposition of sulfonic acid groups during carbonization generates a mild pore-forming effect, forming a connected mesoporous network. This effectively shortens the transport path of electrolyte ions, reduces diffusion resistance, and endows the material with excellent rate performance. This multi-level pore structure with the synergistic coexistence of micropores and mesopores achieves simultaneous optimization of sodium storage capacity and reaction kinetics.

[0030] 3. Achieving high-value utilization of polyphenylene sulfide (PPS) plastics, combining environmental protection and economic benefits. The PPS raw material used in this invention can be derived from waste PPS products generated during industrial production or use. By dissolving and regenerating it and using it for functional modification of hard carbon materials, the high-value transformation of waste engineering plastics into high-performance electrochemical energy storage materials is achieved. This method not only reduces raw material costs but also provides a new technical approach for the recycling of waste plastics and the co-processing of biomass waste, demonstrating significant environmental benefits and promising prospects for industrial application. Attached Figure Description

[0031] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a scanning electron microscope image of the hard carbon material prepared in Example 1.

[0032] Figure 2 This is a transmission electron microscope image of the hard carbon material prepared in Example 1.

[0033] Figure 3 The X-ray diffraction patterns are those of the hard carbon materials prepared in Example 1 and Comparative Examples 1 and 2.

[0034] Figure 4 The images show the Raman spectra of the hard carbon materials prepared in Example 1 and Comparative Examples 1 and 2.

[0035] Figure 5 This is a pore size distribution diagram of the hard carbon material prepared in Example 1.

[0036] Figure 6 The first constant current charge-discharge curves are shown for the working electrodes (negative electrodes) of the hard carbon materials prepared in Example 1 and Comparative Examples 1 and 2.

[0037] Figure 7The diagram shows the rate performance of the working electrode (negative electrode) corresponding to the hard carbon materials prepared in Example 1 and Comparative Examples 1 and 2.

[0038] Figure 8 The graph shows the cycle performance of the working electrode (negative electrode) corresponding to the hard carbon material prepared in Example 1. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0040] All materials used in this invention are commercially available products. The polyphenylene sulfide is an industrially produced polyphenylene sulfide product. The biomass is coconut shell, which is crushed and repeatedly washed with deionized water to remove surface impurities. It is then dried in an oven at 105°C for 6 hours before the experiment.

[0041] Example 1: Preparation of acid-induced sulfonation treated sulfur-doped hard carbon composite material (CHC-SPPS).

[0042] Step 1: Preparation of biomass hard char: The dried coconut shell granules were placed in a tube furnace and heated to 400°C at a heating rate of 5°C / min under a high-purity nitrogen atmosphere. The mixture was then held at this temperature for 1 hour for pre-carbonization, followed by natural cooling to room temperature to obtain pre-carbonized coconut shell, denoted as CSC. The obtained CSC was then placed in a tube furnace and heated to 1300°C at a heating rate of 5°C / min under a high-purity nitrogen atmosphere. It was held at this temperature for 2 hours for carbonization, followed by natural cooling to room temperature to obtain coconut shell-based hard char, denoted as CHC.

[0043] Step 2: Sulfonation Crosslinking Treatment: Weigh 4g of polyphenylene sulfide (PPS) powder and add it to 20mL of N-methylpyrrolidone (NMP) solvent. Heat and stir at 180°C for 1 hour until the PPS is completely dissolved to form a pale yellow transparent PPS solution. Slowly add 4mL of 98% concentrated sulfuric acid to the PPS solution and stir at an 80°C constant temperature water bath for 1 hour. Weigh 4g of the prepared CHC and add it to the solution. Continue stirring and mixing at an 80°C constant temperature water bath for 2 hours to ensure the sulfonation crosslinking reaction proceeds fully. Then transfer the solution to a forced-air drying oven and dry at 105°C for 12 hours to completely evaporate the NMP solvent, obtaining the sulfonated crosslinked composite precursor.

[0044] Step 3: Carbonization treatment: The composite precursor from Step 2 is loaded into a corundum ceramic boat and placed in a tube furnace. Under a high-purity nitrogen atmosphere, the temperature is increased to 600°C at a heating rate of 5°C / min, and carbonized at this temperature for 1 hour. Afterward, it is naturally cooled to room temperature to obtain the sulfur-doped hard carbon composite material. The obtained sample is labeled CHC-SPPS.

[0045] Comparative Example 1: Preparation of sulfur-doped hard carbon composite material (CHC-PPS) with solid-phase surface sulfonation treatment.

[0046] This comparative example aims to illustrate the performance differences between the material prepared by the solid-phase surface sulfonation process and the liquid-phase homogeneous sulfonation crosslinking process of the present invention. The preparation steps are basically the same as in Example 1, except that the order of operations in step 2 is different. Specifically: 4g of PPS powder was weighed and added to 20mL of NMP solvent. The mixture was heated and stirred at 180°C for 1 hour until the PPS was completely dissolved, forming a pale yellow transparent PPS solution. 4g of the prepared CHC hard carbon was weighed and added to the PPS solution. The mixture was stirred and mixed for 2 hours under constant temperature water bath conditions at 80°C. The mixture was then transferred to a forced-air drying oven and dried at 105°C for 12 hours to obtain a PPS-coated composite precursor. The dried solid composite precursor was placed in a flask, and 4mL of 98% concentrated sulfuric acid was slowly added. The mixture was mechanically stirred in a constant temperature water bath at 80°C for 1 hour to perform solid-phase surface sulfonation crosslinking. After the reaction, the product was dried in an oven at 105°C for 12 hours to obtain the sulfonated crosslinked composite precursor. The obtained sample was labeled CHC-PPS.

[0047] Comparative Example 2: Preparation of coconut shell-derived hard carbon material (CHC).

[0048] This comparative example aims to illustrate the performance differences between raw biomass hard char without any subsequent treatment and the material of this invention. The preparation steps only include step (1) in Example 1, that is, coconut shells are pre-carbonized at 400°C for 1 hour to obtain CSC, and then carbonized at 1300°C for 2 hours to obtain biomass hard char. The obtained sample is labeled CHC.

[0049] Experiment 1: Physical Characterization Figure 1 This is a scanning electron microscope (SEM) image of the acid-induced sulfonated sulfur-doped hard carbon composite material (CHC-SPPS) prepared in Example 1. The image shows that the CHC-SPPS particles have a relatively smooth surface, and the interparticle interfaces are continuous and dense, without obvious macropores or cracks. This indicates that the three-dimensional rigid network formed by the sulfonation crosslinking treatment effectively inhibits excessive shrinkage and cracking during carbonization, resulting in a more complete and dense surface morphology for the hard carbon, which is beneficial for electron conduction and interfacial stability.

[0050] Figure 2 This is a transmission electron microscope (TEM) image of the acid-induced sulfonation-treated sulfur-doped hard carbon composite material (CHC-SPPS) prepared in Example 1. The image shows a continuous, uniform carbon coating layer with a thickness of approximately 8–10 nm formed on the surface of the CHC-SPPS particles. The carbon layer and the hard carbon matrix have a tight interfacial bond with no obvious delamination or pores. This indicates that the sulfonation crosslinking pretreatment successfully constructed a rigid polymer network, effectively suppressing the melt loss of polyphenylene sulfide and skeletal collapse during carbonization, thereby obtaining a dense and complete sulfur-rich carbon coating layer, which is beneficial for efficient sulfur anchoring and improved electrochemical performance.

[0051] Figure 3 The X-ray diffraction patterns of the hard carbon materials prepared in Example 1 (CHC-SPPS), Comparative Example 1 (CHC-PPS), and Comparative Example 2 (CHC) of this invention are shown. All samples exhibit two broadened diffraction peaks near approximately 22.5° and 43.6°, corresponding to the (002) and (100) crystal planes of the disordered carbon layers, respectively, indicating that the obtained materials are all amorphous hard carbon structures. The (002) diffraction peak of Example 1 (CHC-SPPS) shows the most significant shift to lower angles, with the carbon interlayer spacing expanding to 0.389 nm, which is beneficial for the reversible insertion and extraction of sodium ions, indicating that the incorporation of sulfur atoms effectively expands the carbon interlayer spacing. Peak fitting results show that the disordered carbon ratio in Example 1 is lower than that in Comparative Example 2, but similar to that in Comparative Example 1, indicating that the sulfonation crosslinking treatment effectively suppresses structural collapse and defect generation during the carbonization process.

[0052] Figure 4 The Raman spectral peak fitting results are for the hard carbon materials prepared in Example 1 (CHC-SPPS), Comparative Example 1 (CHC-PPS), and Comparative Example 2 (CHC) of this invention. Compared with Comparative Example 2, the peak fitting results for the hard carbon materials prepared in Example 1 are shown. I D1 / I G and I D4 / I G The value decreased significantly, indicating that sulfonation crosslinking treatment effectively reduced edge defects and sp in the carbon skeleton. 3 Irregular sites such as hybrid carbon; I D2 / I G and I D3 / I G The value also decreased, indicating enhanced ordered stacking of graphitized domains and a reduction in amorphous carbon regions. These results demonstrate that the sulfonation crosslinking strategy not only mitigates defect formation but also promotes ordered carbon layer growth, thereby improving the material's conductivity and structural stability.

[0053] Figure 5 This is a pore size distribution diagram of the acid-induced sulfonated crosslinked sulfur-doped hard carbon composite material (CHC-SPPS) prepared in Example 1 of this invention. As can be seen from the figure, CHC-SPPS exhibits typical microporous-mesoporous composite characteristics: a concentrated, uniformly distributed micropore peak exists at ~0.5 nm, while a significant mesoporous distribution appears in the 2~10 nm range. The uniform micropores originate from the supporting effect of the sulfonated crosslinked network on the carbon skeleton, providing abundant sites for low-potential "pore filling" sodium storage; the mesopores are formed by the in-situ pore-forming effect generated by the decomposition of sulfonic acid groups, which helps to shorten the ion transport path and reduce diffusion resistance. This hierarchical pore structure with micropore-mesoporous synergy is the key structural basis for achieving high plateau capacity and excellent rate performance.

[0054] Experiment 2: Electrochemical Performance Testing Electrode preparation: The hard carbon material prepared in the above examples and comparative examples was used as the active material and mixed with conductive carbon black (Super P), sodium carboxymethyl cellulose (CMC, binder), and styrene-butadiene rubber (SBR, binder) at a mass ratio of 96:1:1:2. Using deionized water as the solvent, the mixture was stirred in a homogenizer to prepare a uniform negative electrode slurry. The slurry was uniformly coated onto a 100 μm thick aluminum foil current collector using a scraper, and then dried in a vacuum oven at 120°C for 6 hours. After drying, the slurry was compacted using a roller press and then punched into circular electrode sheets with a diameter of 16 mm using a punching machine.

[0055] Battery assembly: The prepared electrode sheet was used as the working electrode (negative electrode), a sodium metal sheet as the counter electrode and reference electrode, glass fiber filter paper as the separator, and a mixed solution of 1.5M NaPF6 dissolved in ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (volume ratio 1:2:2) as the electrolyte. All battery assembly was completed in a glove box filled with high-purity argon gas, and the battery casing model was CR2032. The assembled batteries were allowed to stand for 6 hours to allow the electrolyte to fully impregnate them.

[0056] Performance testing: The Blue Battery test system was used to conduct constant current charge and discharge tests in a 25°C constant temperature chamber, with a voltage window of 0.01-2.0 V (vs. Na / Na⁺) and a current of 0.1C (30mA / g).

[0057] Figure 6The figures show the initial galvanostatic charge-discharge curves of the hard carbon materials prepared in Example 1 (CHC-SPPS), Comparative Example 1 (CHC-PPS), and Comparative Example 2 (CHC) at a current density of 30 mA / g. As can be seen from the figures, Example 1 (CHC-SPPS) exhibits a flatter and longer low-potential discharge plateau, with a plateau capacity contribution of approximately 252 mAh / g, accounting for 74% of the total capacity. Its initial reversible specific capacity is 341 mAh / g, and its initial coulombic efficiency reaches 74%. In comparison, Comparative Example 1 (CHC-PPS) has a reversible capacity of approximately 290 mAh / g and an initial coulombic efficiency of 68%; Comparative Example 2 (CHC) has a reversible capacity of approximately 275 mAh / g and an initial coulombic efficiency of approximately 65%. This indicates that the optimized pore structure constructed by sulfonation crosslinking and the stable thiophene sulfur doping synergistically improve the plateau capacity and initial coulombic efficiency of the materials.

[0058] Figure 7 The chart shows the 45-cycle charge-discharge rate performance of the hard carbon materials prepared in Example 1 (CHC-SPPS), Comparative Example 1 (CHC-PPS), and Comparative Example 2 (CHC) of this invention. The charge-discharge currents for cycles 1-5, 6-10, 11-15, 16-20, 21-25, 26-30, 31-35, and 36-45 are 0.2C (60 mA / g), 0.5C (150 mA / g), 1C (300 mA / g), 3C (900 mA / g), 5C (1500 mA / g), 10C (3000 mA / g), 15C (4500 mA / g), and 0.2C (60 mA / g), respectively. The results show that, at increasing current densities from 0.2C to 15C, the capacity decay of Example 1 (CHC-SPPS) is significantly less than that of the comparative example at all current densities. At current densities as high as 4500 mA / g, CHC-SPPS maintained a high reversible capacity, while the capacity of the comparative model decreased significantly. When the current density was reduced back to 0.2C, the capacity of CHC-SPPS rapidly recovered to approximately 330 mAh / g, demonstrating excellent structural stability and reversible reaction. This indicates that the hierarchical porous structure constructed by sulfonation crosslinking effectively shortens the ion transport path, endowing the material with superior rate performance.

[0059] Figure 8 This is a cycling stability graph of the acid-induced sulfonated crosslinked sulfur-doped hard carbon composite material (CHC-SPPS) prepared in Example 1 of this invention at a current density of 1 A / g. As can be seen from the graph, after 150 cycles, the specific capacity of CHC-SPPS hardly decreased, remaining at approximately 260 mAh / g, and the coulombic efficiency remained close to 100%, indicating that the material has a robust framework structure and a stable electrode / electrolyte interface, exhibiting excellent long-term working durability.

[0060] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0061] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a sulfur-doped hard carbon composite material, characterized in that: Includes the following steps: Step 1: Pre-carbonize the biomass raw material under an inert atmosphere to obtain a pre-carbonized product; then, perform high-temperature carbonization on the pre-carbonized product under an inert atmosphere to obtain biomass hard carbon. Step 2: Dissolve polyphenylene sulfide in N-methylpyrrolidone solvent to prepare PPS solution; add concentrated sulfuric acid to the PPS solution and stir to mix; then add the biomass hard carbon obtained in step 1, stir to mix and carry out sulfonation crosslinking reaction, and after drying treatment, obtain sulfonation crosslinked composite precursor; Step 3: Under an inert protective atmosphere, the sulfonated crosslinked composite precursor obtained in Step 2 is carbonized. After carbonization, it is naturally cooled to obtain the sulfur-doped hard carbon composite material.

2. The preparation method according to claim 1, characterized in that: In step 1, the biomass raw materials are selected from one or more of the following: coconut shells, walnut shells, apricot shells, olive shells, rice husks, sugarcane bagasse, bamboo shavings, wood chips, and straw.

3. The preparation method according to claim 1, characterized in that: In step 1, the pre-carbonization temperature is 400°C and the time is 1 hour.

4. The preparation method according to claim 1, characterized in that: In step 1, the high-temperature carbonization process involves heating to 1300°C at a rate of 5°C / min and then holding the temperature at 1300°C for 2 hours.

5. The preparation method according to claim 1, characterized in that: In step 2, the volume-to-mass ratio of concentrated sulfuric acid to PPS is 1 mL: 1 g.

6. The preparation method according to claim 5, characterized in that: The mass fraction of concentrated sulfuric acid is 98%.

7. The preparation method according to claim 1, characterized in that: In step 2, the mass ratio of PPS to biomass hard char is 1:1, the reaction temperature is 80°C, and the reaction time is 2 hours.

8. The preparation method according to claim 1, characterized in that: In step 3, the carbonization process involves heating to 600°C at a rate of 5°C / min and holding at 600°C for 1 hour.

9. The sulfur-doped hard carbon composite material prepared by any one of claims 1 to 8.

10. An application of the sulfur-doped hard carbon composite material as described in claim 9, characterized in that: Sulfur-doped hard carbon composite materials are used as active materials in the anode of sodium-ion batteries.

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