A method for preparing a sodium-sulfur battery cathode material, the resulting material, and its applications.

Abstract

This invention discloses a method for preparing a sodium-sulfur battery cathode material, the resulting material, and its applications. The preparation method includes the following steps: dissolving lignin and an inorganic alkali in water, stirring until homogeneous, and then drying to obtain a solid precursor; heating the solid precursor to 400-500 °C in an inert gas atmosphere and holding it thereafter, then heating it to 700-800 °C and holding it thereafter to obtain a carbonized product; washing and drying the carbonized product to obtain an oxygen-rich porous carbon material; grinding the oxygen-rich porous carbon material and sublimed sulfur in equal mass until homogeneous, followed by heat treatment to obtain the sodium-sulfur battery cathode material. This invention also discloses the cathode material obtained by the above preparation method and its application in sodium-sulfur battery cathode materials. This invention achieves precise control over the composition and nucleation mode of CEI, forming a uniformly distributed micro-nano scale structure on the cathode surface; the obtained cathode material can improve the Na+... + The improved interface transport efficiency significantly enhances the electrochemical performance of the battery.

Description

Technical Field

[0001] This invention pertains to battery materials, their preparation methods and applications, specifically a method for preparing a sodium-sulfur battery cathode material, the resulting material, and its applications. Background Technology

[0002] Room temperature sodium-sulfur batteries have become an important candidate for next-generation energy storage systems due to their high theoretical capacity and abundant sodium resources. However, they are limited by chemical reactions and structural issues at the cathode-electrolyte interface. In traditional ether-based electrolytes, polysulfides are highly soluble, leading to a severe shuttle effect and rapid capacity decay. In carbonate-based electrolytes, although a CEI can be formed by reacting with polysulfides, if the composition and spatial structure of the CEI are not ideal, it can easily form large and dense inorganic aggregates. This structure hinders charge and ion transport, thus limiting the overall performance of the battery. Summary of the Invention

[0003] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing sodium-sulfur battery cathode materials with precise control over CEI composition and nucleation mode. Another purpose of this invention is to provide a sodium-sulfur battery cathode material with excellent electrochemical performance. A further purpose of this invention is to provide an application in improving the cycle life and rate performance of room temperature sodium-sulfur batteries.

[0004] Technical solution: The present invention provides a method for preparing a sodium-sulfur battery cathode material, comprising the following steps:

[0005] Step 1: Dissolve lignin and inorganic alkali in water, stir evenly, and then dry to obtain a solid precursor;

[0006] Step 2: In an inert gas atmosphere, the solid precursor is first heated to 400~500 ℃ and held at that temperature, then heated to 700~800 ℃ and held at that temperature to obtain the carbonized product.

[0007] Step 3: Wash and dry the carbonization products to obtain oxygen-rich porous carbon materials.

[0008] Step four: Grind oxygen-rich porous carbon material and sublimed sulfur of equal mass until uniform, heat to allow molten sulfur to fully penetrate into the pores of the carbon material, and then heat treat under an inert atmosphere to remove residual free sulfur on the surface, thereby obtaining sodium-sulfur battery cathode material.

[0009] Furthermore, in step one, the lignin is any one of enzymatically hydrolyzed lignin, alkali lignin, dealkali-treated lignin, sulfite lignin, and organic solvent lignin. The preferred lignin is enzymatically hydrolyzed lignin.

[0010] Furthermore, in step one, the inorganic base is any one of KOH, alkali lignin, dealkali lignin, sulfite lignin, and organic solvent lignin. KOH is preferred as the inorganic base.

[0011] Furthermore, in step one, the mass ratio of lignin to inorganic alkali is 1:2~3.

[0012] Furthermore, in step two, the heating rate is 5-10 °C / min, the holding time at 400-500 °C is 1-2 h, and the holding time at 700-800 °C is 1-2 h. Below 400 °C, the pre-carbonization process of the biomass raw material is insufficient, making it difficult to form a stable carbon framework structure, which is detrimental to the subsequent construction of the pore structure. Above 500 °C, the loss of volatiles in the biomass is too drastic, reducing the effectiveness of the activator in the pore-forming reaction. Below 700 °C, the activator reaction is insufficient, making it difficult to achieve sufficient etching and structural expansion of the carbon framework. Above 800 °C, the activation reaction is too vigorous, easily leading to the destruction of the carbon framework structure and potentially significantly reducing the oxygen content in the porous carbon material, thus hindering the maintenance of the integrity of the porous carbon structure and the material yield.

[0013] Furthermore, in step three, the washing process involves first washing with a dilute hydrochloric acid solution, then washing with deionized water, and the drying temperature is 60~80 ℃.

[0014] Furthermore, in step three, the oxygen content of the oxygen-rich porous carbon material is 10-13%, and its specific surface area is greater than 700 m². 2 g -1 It is mainly composed of micropores with a pore size range of 0.6~1.5 nm.

[0015] Furthermore, in step four, the heat treatment temperature is 200~300 ℃.

[0016] The sodium-sulfur battery cathode material obtained by the above preparation method includes a porous carbon matrix and sulfur loaded on the porous carbon matrix, with the sulfur having a mass percentage of 45-48 wt%. The surface of the porous carbon matrix is ​​rich in oxygen-containing functional groups. During cycling, the sodium-sulfur battery cathode material forms a dense and uniform inorganic-organic composite interface layer in situ on the cathode surface, thereby effectively inhibiting polysulfide dissolution and promoting sodium ion transport.

[0017] This invention provides an application of a sodium-sulfur battery cathode material in improving the cycle life and rate performance of room-temperature sodium-sulfur batteries.

[0018] Furthermore, the room-temperature sodium-sulfur battery comprises a sodium metal anode, a mixed solvent electrolyte of propylene carbonate and fluoroethylene carbonate; the electrolyte has a concentration of 2 mol / L. -1An electrolyte solution in which sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) is dissolved in a mixed solvent of PC and FEC, with a volume ratio of PC to FEC of 1:1.

[0019] Preparation Principle: Using enzymatically hydrolyzed lignin as the carbon source, which is rich in oxygen-containing functional groups such as hydroxyl, carboxyl, and carbonyl groups, LDPC-O, a porous carbon material with abundant oxygen content, can be prepared after activation and carbonization with KOH. This material's surface can form various nucleation sites with moderate activity, promoting the in-situ formation of a fine and uniform inorganic-organic composite positive electrode electrolyte interphase (CEI) layer during the first discharge of the battery. The oxygen-containing functional groups weaken the electronic coupling between carbon defect sites and electrolyte components, reducing adsorption energy and enabling a "multi-point nucleation, diffusion-friendly" mechanism at the interface, preventing excessive aggregation of inorganic matter. By regulating the CEI structure through oxygen-containing functional groups, the positive electrode material forms a dense and uniform inorganic-organic composite interface layer during cycling, thereby improving the battery's cycle life and rate performance.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0021] 1. By directionally controlling the oxygen-containing functional groups on the cathode surface, this invention achieves precise control over the composition and nucleation mode of CEI, forming a high-density, micro-nano-scale uniformly distributed inorganic phase-organic polymer composite structure on the cathode surface.

[0022] 2. The obtained cathode material can not only effectively inhibit the dissolution and shuttle of polysulfides, but also improve the performance of Na. + The interface transport efficiency is improved, thus significantly enhancing the electrochemical performance of the battery. Experimental results show that the battery using this cathode material still maintains a reversible specific capacity of 694.2 mAh g⁻¹ after 500 cycles at 1C rate. -1 The average capacity decay rate per cycle is only 0.07%;

[0023] 3. The technical approach of this invention differs from existing strategies that focus on electrolyte regulation. It emphasizes optimizing CEI from the design source of the electrode surface, opening up new ideas for the positive electrode interface engineering of room temperature sodium-sulfur batteries. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope image of the LDPC-O prepared in this invention;

[0025] Figure 2 These are the BET adsorption / desorption isotherms and pore distribution diagrams of LDPC-O prepared by this invention, wherein a is the adsorption / desorption isotherm and b is the pore distribution diagram.

[0026] Figure 3This is the overall X-ray photoelectron spectrum of LDPC-O and LDPC-H prepared in this invention;

[0027] Figure 4 These are thermogravimetric analysis (TGA) diagrams of LDPC-O / S and LDPC-H / S prepared in this invention;

[0028] Figure 5 This is the cycle performance curve of the room temperature sodium-sulfur battery prepared by this invention at a 1C current density;

[0029] Figure 6 This is the rate curve of the room-temperature sodium-sulfur battery prepared according to the present invention;

[0030] Figure 7 The images show TEM images of the interface phase layer of the LDPC-O / S cathode prepared in this invention after the first discharge and the corresponding selected area electron diffraction pattern, where a is a low-magnification TEM morphology image of the interface phase and b is a high-magnification TEM morphology image of the interface phase and the corresponding selected area electron diffraction pattern.

[0031] Figure 8 The images show TEM images of the interface phase layer of the LDPC-H / S cathode prepared in this invention after the first discharge and the corresponding selected area electron diffraction pattern, where a is a low-magnification TEM morphology image of the interface phase and b is a high-magnification TEM morphology image of the interface phase and the corresponding selected area electron diffraction pattern.

[0032] Figure 9 This is an X-ray photoelectron spectrum of the interface phase layer of the positive electrode prepared by the present invention after the first discharge, where a is the O 1s spectrum and b is the F 1s spectrum. Detailed Implementation

[0033] Unless otherwise specified, all materials and reagents used in the following examples are commercially available. Experimental methods not specifically described in the examples are generally performed under standard conditions or as recommended by the manufacturer. Enzymatic hydrolysis of lignin, obtained from corn cobs through enzyme catalysis, was purchased from Linyi Senhe Biomaterials Co., Ltd.

[0034] Example 1

[0035] A method for preparing a sodium-sulfur battery cathode material includes the following steps:

[0036] (1) Dissolve 1.0 g of enzymatically hydrolyzed lignin and 2.0 g of KOH in 50 mL of deionized water and stir for 1 hour to fully dissolve and mix them. Then evaporate the solvent in a 90 °C drying pot to obtain a uniform solid precursor.

[0037] (2) The obtained precursor was placed in a tube furnace and subjected to two-stage pyrolysis under argon protection: first at 5 °C min -1The temperature was raised to 500 °C and held for 1 hour, then raised to 800 °C at the same rate and held for 1 hour. After pyrolysis, the mixture was allowed to cool naturally to room temperature to obtain the carbonized product.

[0038] (3) The carbonized product was thoroughly washed with 1 M hydrochloric acid solution to remove unreacted KOH and other inorganic impurities, then washed with deionized water until neutral, and finally dried in a drying oven at 60 °C to obtain LDPC-O powder. The morphology of LDPC-O is shown in its scanning electron microscope image. Figure 1 The porosity of LDPC-O is shown in its BET adsorption / desorption isotherm and pore distribution diagram. Figure 2 ).

[0039] (4) LDPC-O and sublimed sulfur were ground evenly at a mass ratio of 1:1. The physical mixture was placed in a stainless steel sealed container and heated at 155 °C for 12 hours to allow the molten sulfur to fully penetrate into the pores of the carbon material. Subsequently, under an inert atmosphere, the sample was treated at 200 °C for 30 minutes to remove the free sulfur remaining on the surface, and finally the LDPC-O / S cathode material was obtained.

[0040] Comparative Example 1

[0041] A method for preparing a positive electrode material includes the following steps:

[0042] (1) Dissolve 1.0 g of enzymatically hydrolyzed lignin and 2.0 g of KOH in 50 mL of deionized water and stir for 1 hour to fully dissolve and mix them. Then evaporate the solvent in a 90 °C drying pot to obtain a uniform solid precursor.

[0043] (2) The obtained precursor was placed in a tube furnace and subjected to two-stage pyrolysis under argon protection: first at 5 °C min -1 The temperature was raised to 500 °C and held for 1 hour, then raised to 800 °C at the same rate and held for 1 hour. After pyrolysis, the mixture was allowed to cool naturally to room temperature to obtain the carbonized product.

[0044] (3) The carbonized product was thoroughly washed with 1 M hydrochloric acid solution to remove unreacted KOH and other inorganic impurities, then washed with deionized water until neutral, and finally dried in a drying oven at 60 °C to obtain LDPC-O powder.

[0045] (4) Place the above LDPC-O powder in a tube furnace and heat it at 5 °C for 5 min in a hydrogen (5% H2) / argon mixed atmosphere. -1 The temperature was raised to 800 ℃ and held for 1 hour to obtain LDPC-H with a significantly reduced oxygen functional group content.

[0046] (4) LDPC-H and sublimed sulfur were ground evenly at a mass ratio of 1:1. The physical mixture was placed in a stainless steel sealed container and heated at 155 °C for 12 hours to allow the molten sulfur to fully penetrate into the pores of the carbon material. Subsequently, under an inert atmosphere, the sample was treated at 200 °C for 30 minutes to remove the free sulfur remaining on the surface, and finally the LDPC-H / S cathode material was obtained.

[0047] The oxygen contents of LDPC-O and LDPC-H were 12.9% and 3.7%, respectively, indicating a significant difference in their surface polarity. Figure 3 As shown, the sulfur loadings of LDPC-O / S and LDPC-H / S are 46.9 wt% and 46.5 wt%, respectively, indicating that both have good loading capacity for active substances, such as... Figure 4 As shown.

[0048] Application Example 1

[0049] A slurry was prepared by uniformly mixing the LDPC-O / S cathode material (70 wt%) obtained in Example 1, conductive carbon black (20 wt%), and PVDF binder (10 wt%) in NMP. The slurry was coated onto carbon-coated aluminum foil and dried overnight under vacuum at 60 °C to obtain a cathode sheet. Circular electrode sheets with a diameter of 12 mm (active material loading approximately 1.0 mg cm⁻¹) were then punched. -2 The components were placed in a glove box and assembled into CR2032 coin cells. During assembly, sodium foil was used as the negative electrode, and a glass fiber separator separated the positive and negative electrodes. The electrolyte was a mixed solvent of 2.0 M NaTFSI dissolved in PC and FEC (volume ratio 1:1), with an electrolyte-to-sulfur volume ratio of approximately 70 μL mg / mg. -1 .

[0050] Application Comparative Example 1

[0051] A slurry was prepared by uniformly mixing the LDPC-H / S cathode material (70 wt%) obtained in Comparative Example 1, conductive carbon black (20 wt%), and PVDF binder (10 wt%) in NMP. The slurry was coated onto carbon-coated aluminum foil and dried overnight under vacuum at 60 °C to obtain a cathode sheet. Circular electrode sheets with a diameter of 12 mm (active material loading approximately 1.0 mg cm⁻¹) were then punched. -2 The components were placed in a glove box and assembled into CR2032 coin cells. During assembly, sodium foil was used as the negative electrode, and a glass fiber separator separated the positive and negative electrodes. The electrolyte was a mixed solvent of 2.0 M NaTFSI dissolved in PC and FEC (volume ratio 1:1), with an electrolyte-to-sulfur volume ratio of approximately 70 μL mg / mg. -1 .

[0052] I. Electrochemical Testing:

[0053] All batteries operate at a current of 0.1C (1C = 1675 mAh g). -1 After two charge-discharge cycles for activation, cycling tests were conducted at a 1C current density (voltage range 0.5–2.8 V). Electrochemical test results showed that the LDPC-O / S electrode exhibited significantly better cycling performance than the LDPC-H / S electrode. After 500 cycles at 1C, the reversible specific capacity of LDPC-O / S remained as high as 694.2 mAh g⁻¹. -1 The capacity of LDPC-H / S is only 554.1 mAh g. -1 In contrast, LDPC-O / S exhibits an average capacity decay rate as low as 0.07% per cycle, and its coulombic efficiency remains consistently above 99%. Figure 5 Furthermore, in rate testing, LDPC-O / S also exhibited a high reversible capacity. Figure 6 The improved performance is attributed to the uniform and dense CEI structure formed on the oxygen-rich cathode surface, which effectively suppresses polysulfide dissolution and shuttle loss, while improving the interfacial transport of sodium ions.

[0054] II. Interface Morphology and Composition Analysis:

[0055] Characterization of the CEI layer on the positive electrode surface after the first discharge using XPS and TEM revealed that the oxygen-rich LDPC-O / S electrode interface layer exhibits a unique organic-inorganic composite structure, with nano-sized Na₂CO₃ and NaF crystals uniformly distributed within a dense organic polymer matrix. TEM images showed that the layer was continuous and smooth, and the electron diffraction pattern showed only diffuse diffraction rings, indicating that the inorganic phase belongs to low-crystallinity nanocrystals. Figure 7 Conversely, the CEI layer of LDPC-H / S is a distinctly rough and discontinuous coating layer, containing a large number of aggregated granular inorganic crystals and strong diffraction spots, indicating that the inorganic phase has high crystallinity and large particle size. Figure 8 XPS quantitative results further support the above observations: the proportion of organic components in the LDPC-O / S interface layer is significantly higher than that in LDPC-H / S, while the latter has a higher proportion of NaF inorganic components (…). Figure 9 ).

[0056] Example 2

[0057] A method for preparing a sodium-sulfur battery cathode material includes the following steps:

[0058] (1) Dissolve 1.0 g of alkali lignin and 3.0 g of KCO3 in 50 mL of deionized water and stir for 1 hour to fully dissolve and mix them. Then evaporate the solvent in a 90 °C drying pot to obtain a uniform solid precursor.

[0059] (2) The obtained precursor was placed in a tube furnace and subjected to two-stage pyrolysis under argon protection: first at 5 °C min -1 The temperature was raised to 400 °C and held for 2 hours, then raised to 700 °C at the same rate and held for 2 hours. After pyrolysis, the mixture was allowed to cool naturally to room temperature to obtain the carbonized product.

[0060] (3) The carbonized product was thoroughly washed with 1 M hydrochloric acid solution to remove unreacted KOH and other inorganic impurities, then washed with deionized water until neutral, and finally dried in a drying oven at 80 °C to obtain LDPC-O powder. The oxygen content of LDPC-O was 10.2%.

[0061] (4) LDPC-O and sublimed sulfur were ground uniformly at a mass ratio of 1:1. The physical mixture was placed in a stainless steel sealed container and heated at 155 °C for 12 hours to allow the molten sulfur to fully penetrate into the pores of the carbon material. Subsequently, under an inert atmosphere, the sample was treated at 250 °C for 30 minutes to remove residual free sulfur on the surface, and finally the LDPC-O / S cathode material was obtained with a sulfur mass percentage of 45 wt%.

[0062] Example 3

[0063] A method for preparing a sodium-sulfur battery cathode material includes the following steps:

[0064] (1) Dissolve 1.0 g of dealkalized lignin and 2.5 g of KC2O4 in 50 mL of deionized water and stir for 1 hour to fully dissolve and mix them. Then evaporate the solvent in a 90 °C drying pot to obtain a uniform solid precursor.

[0065] (2) The obtained precursor was placed in a tube furnace and subjected to two-stage pyrolysis under argon protection: first at 10 °C min -1 The temperature was raised to 450 °C and held for 1.5 hours, then raised to 750 °C at the same rate and held for 1.5 hours. After pyrolysis, the mixture was allowed to cool naturally to room temperature to obtain the carbonized product.

[0066] (3) The carbonized product was thoroughly washed with 1 M hydrochloric acid solution to remove unreacted KOH and other inorganic impurities, then washed with deionized water until neutral, and finally dried in a drying oven at 70 °C to obtain LDPC-O powder. The oxygen content of LDPC-O was 12.1%.

[0067] (4) LDPC-O and sublimed sulfur were ground evenly at a mass ratio of 1:1. The physical mixture was placed in a stainless steel sealed container and heated at 155 °C for 12 hours to allow the molten sulfur to fully penetrate into the pores of the carbon material. Subsequently, under an inert atmosphere, the sample was treated at 300 °C for 30 minutes to remove residual free sulfur on the surface, and finally the LDPC-O / S cathode material was obtained with a sulfur mass percentage of 48 wt%.

[0068] Example 4

[0069] A method for preparing a sodium-sulfur battery cathode material includes the following steps:

[0070] (1) Dissolve 1.0 g of sulfite lignin and 2.2 g of KCl in 50 mL of deionized water and stir for 1 hour to fully dissolve and mix them. Then evaporate the solvent in a 90 °C drying pot to obtain a uniform solid precursor.

[0071] (2) The obtained precursor was placed in a tube furnace and subjected to two-stage pyrolysis under argon protection: first at 10 °C min -1 The temperature was raised to 420 °C and held for 1 hour, then raised to 710 °C at the same rate and held for 1 hour. After pyrolysis, the mixture was allowed to cool naturally to room temperature to obtain the carbonized product.

[0072] (3) The carbonized product was thoroughly washed with 1 M hydrochloric acid solution to remove unreacted KOH and other inorganic impurities, then washed with deionized water until neutral, and finally dried in a drying oven at 65 °C to obtain LDPC-O powder. The oxygen content of LDPC-O was 11.3%.

[0073] (4) LDPC-O and sublimed sulfur were ground evenly at a mass ratio of 1:1. The physical mixture was placed in a stainless steel sealed container and heated at 155 °C for 12 hours to allow the molten sulfur to fully penetrate into the pores of the carbon material. Subsequently, under an inert atmosphere, the sample was treated at 220 °C for 30 minutes to remove residual free sulfur on the surface, and finally the LDPC-O / S cathode material was obtained with a sulfur mass percentage of 46.4 wt%.

[0074] Example 5

[0075] A method for preparing a sodium-sulfur battery cathode material includes the following steps:

[0076] (1) Dissolve 1.0 g of organic solvent lignin and 2.4 g of KOH in 50 mL of deionized water and stir for 1 hour to fully dissolve and mix them. Then evaporate the solvent in a 90 °C drying pot to obtain a uniform solid precursor.

[0077] (2) The obtained precursor was placed in a tube furnace and subjected to two-stage pyrolysis under argon protection: first at 10 °C min -1 The temperature was raised to 480 °C and held for 2 hours, then raised to 790 °C at the same rate and held for 2 hours. After pyrolysis, the mixture was allowed to cool naturally to room temperature to obtain the carbonized product.

[0078] (3) The carbonized product was thoroughly washed with 1 M hydrochloric acid solution to remove unreacted KOH and other inorganic impurities, then washed with deionized water until neutral, and finally dried in a drying oven at 75 °C to obtain LDPC-O powder. The oxygen content of LDPC-O was 10.7%.

[0079] (4) LDPC-O and sublimed sulfur were ground uniformly at a mass ratio of 1:1. The physical mixture was placed in a stainless steel sealed container and heated at 155 °C for 12 hours to allow the molten sulfur to fully penetrate into the pores of the carbon material. Subsequently, under an inert atmosphere, the sample was treated at 280 °C for 30 minutes to remove residual free sulfur on the surface, and finally the LDPC-O / S cathode material was obtained with a sulfur mass percentage of 47.1 wt%.

[0080] Of the above embodiments, the preferred embodiment is Embodiment 1.

Claims

1. A method for preparing a sodium-sulfur battery cathode material, characterized in that, Includes the following steps: Step 1: Dissolve lignin and inorganic alkali in water, stir evenly, and then dry to obtain a solid precursor; Step 2: In an inert gas atmosphere, the solid precursor is first heated to 400~500 ℃ and held at that temperature, then heated to 700~800 ℃ and held at that temperature to obtain the carbonized product. Step 3: Wash and dry the carbonization products to obtain oxygen-rich porous carbon materials. Step four: Grind oxygen-rich porous carbon material and sublimed sulfur of equal mass until uniform, heat to allow molten sulfur to fully penetrate into the pores of the carbon material, and then heat treat under an inert atmosphere to remove residual free sulfur on the surface, thereby obtaining sodium-sulfur battery cathode material.

2. The method for preparing a sodium-sulfur battery cathode material according to claim 1, characterized in that: In step one, the lignin is any one of enzymatic lignin, alkali lignin, dealkali lignin, sulfite lignin, or organic solvent lignin.

3. The method for preparing a sodium-sulfur battery cathode material according to claim 1, characterized in that: In step one, the inorganic base is any one of KOH, KCO3, KC2O4, and KCl.

4. The method for preparing a sodium-sulfur battery cathode material according to claim 1, characterized in that: In step one, the mass ratio of lignin to inorganic alkali is 1:2~3.

5. The method for preparing a sodium-sulfur battery cathode material according to claim 1, characterized in that: In step two, the heating rate is 5~10 ℃ / min, the holding time at 400~500 ℃ is 1~2 h, and the holding time at 700~800 ℃ is 1~2 h.

6. The method for preparing a sodium-sulfur battery cathode material according to claim 1, characterized in that: In step three, the washing process involves first washing with a dilute hydrochloric acid solution, then washing with deionized water, and the drying temperature is 60-80 ℃.

7. The method for preparing a sodium-sulfur battery cathode material according to claim 1, characterized in that: In step three, the oxygen-rich porous carbon material has an oxygen content of 10-13% and a specific surface area greater than 700 m². 2 g -1 .

8. The method for preparing a sodium-sulfur battery cathode material according to claim 1, characterized in that: In step four, the heat treatment temperature is 200~300 ℃.

9. A sodium-sulfur battery cathode material obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The material includes a porous carbon matrix and sulfur loaded on the porous carbon matrix, wherein the sulfur has a mass percentage of 45-48 wt%; the surface of the porous carbon matrix is ​​rich in oxygen-containing functional groups; and the sodium-sulfur battery cathode material forms a dense and uniform inorganic-organic composite interface layer in situ on the cathode surface during cycling.

10. The application of the sodium-sulfur battery cathode material according to claim 9 in improving the cycle life and rate performance of a room-temperature sodium-sulfur battery.

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