WS2 / W composite material, preparation method thereof and application of WS2 / W composite material in sodium-sulfur battery

Abstract

The invention discloses a WS2 / W composite material, a preparation method thereof and application of the WS2 / W composite material in a sodium-sulfur battery. The preparation method comprises the following steps: uniformly stirring isopropanol and acetone to obtain a mixed solution A; weighing tungsten hexachloride, adding the tungsten hexachloride into the mixed solution A, and uniformly stirring to obtain a mixed solution B; transferring into a reaction kettle, sealing and putting into a drying oven for reaction; after the reaction is finished, carrying out suction filtration and washing on a product by using industrial alcohol, and drying in a vacuum oven to obtain W18O49 powder; the method comprises the following steps: weighing W18O49 powder and sublimed sulfur, respectively and correspondingly placing the W18O49 powder and sublimed sulfur in a first porcelain boat and a second porcelain boat, then placing the second porcelain boat in the first porcelain boat, placing the second porcelain boat in a tubular furnace, introducing argon into a furnace chamber of the tubular furnace, after the pressure of the furnace chamber is increased to 0.2-0.3 MPa, keeping the airtightness of the system, heating to 1100-1300 DEG C at the rate of 20 DEG C / min, keeping the pressure at 0.2-0.3 MPa in the heating process, and keeping the temperature for 2-3 hours; and after the temperature reaches 1100-1300 DEG C, continuously preserving heat for 2 hours, introducing argon, cooling to room temperature, and collecting to obtain WS2 / W powder. The problems of poor conductivity of the sulfur positive electrode, polysulfide shuttle effect and slow reaction kinetics are solved.

Description

A WS2 / W composite material, its preparation method, and its application in sodium-sulfur batteries. Technical Field

[0001] This invention relates to the field of functional materials technology, specifically to a WS2 / W composite material, its preparation method, and its application in sodium-sulfur batteries. Background Technology

[0002] As the global energy structure shifts towards renewable energy, large-scale electrochemical energy storage technology has become one of the key technologies supporting this transition. While lithium-ion batteries are widely used, their scarcity and high cost limit their ability to meet the long-term demand for large-scale energy storage. Room-temperature sodium-sulfur (RT Na-S) batteries, however, benefit from the high abundance of sodium and sulfur in the Earth's crust, low cost, and a theoretical specific capacity of up to 1675 mAh g⁻¹ for the sulfur cathode. -1 Its significant advantages make it an ideal candidate for the next generation of large-scale energy storage technology. Traditional high-temperature sodium-sulfur batteries need to operate at around 300°C, which poses safety risks and energy loss problems. In contrast, room-temperature sodium-sulfur batteries use liquid electrolytes to achieve room-temperature operation, which greatly improves safety and energy utilization efficiency, showing a broader application prospect.

[0003] However, the commercialization of room-temperature sodium-sulfur batteries faces three major technological bottlenecks that severely restrict their performance improvement and practical application: ① Extremely poor conductivity of the sulfur cathode: The low conductivity of sulfur and its discharge product Na2S makes the electrochemical reaction difficult to carry out efficiently, resulting in low sulfur utilization and poor battery rate performance. ② Polysulfide shuttle effect: Soluble long-chain sodium polysulfides (Na2S) generated during charge and discharge... x (4≤x≤8) These compounds readily dissolve in the electrolyte and migrate across the separator to the sodium anode, triggering side reactions and causing irreversible loss of active material, leading to rapid capacity decay and reduced coulombic efficiency. ③ Slow reaction kinetics: The conversion of polysulfides to solid Na2S has a high energy barrier, and the decomposition barrier of Na2S during charging is also high, resulting in poor reversibility of the charge-discharge reaction and low energy efficiency. The slow conversion rate of solid Na2S2 to Na2S increases charge accumulation on the electrode surface, increasing impedance and further reducing battery performance.

[0004] To address these issues, researchers have developed various strategies for modifying sulfur cathodes: utilizing the high specific surface area and conductivity of porous carbon materials to improve sulfur dispersion, but non-polar carbon materials have weak adsorption capacity for polar polysulfides, making it difficult to effectively suppress the shuttle effect; anchoring polysulfides through polar metal compounds, but single adsorption is insufficient to simultaneously solve the reaction kinetics problem; introducing transition metal single atoms or nanoclusters to accelerate polysulfide conversion, but these methods suffer from complex preparation processes, high costs, and insufficient stability.

[0005] Transition metal disulfides (TMDs) such as MoS2 and WS2 have been attempted for sulfur cathode modification due to their layered structure and polar surface. However, pure WS2 suffers from limited electronic conductivity and insufficient active sites, and it is difficult to achieve efficient anchoring and synergistic catalytic conversion of polysulfides when used alone. Summary of the Invention

[0006] To address the shortcomings of the existing technology, the present invention aims to propose a WS2 / W composite material, its preparation method, and its application in sodium-sulfur batteries. Through the synergistic effect of WS2 and W, the problems of extremely poor conductivity of sulfur cathode, polysulfide shuttle effect, and slow reaction kinetics are solved simultaneously.

[0007] This invention is achieved through the following technical solution: a method for preparing WS2 / W composite material, comprising the following steps: S1. Measure 30-40 mL of isopropanol and 10-20 mL of acetone and add them to a beaker, stir evenly at room temperature to obtain mixed solution A; S2. Weigh 0.003-0.006 mol of tungsten hexachloride and add it to mixed solution A obtained in step S1, stir evenly at room temperature to obtain mixed solution B; S3. Transfer mixed solution B obtained in step S2 into a reaction vessel, seal it and place it in an oven, react at 180-200℃ for 12-24 h; S4. After the reaction in step S3 is completed, filter and wash the product with industrial alcohol, dry it in a vacuum oven, and collect W. 18 O 49 Powder; S5. According to n W :n S =0.1~0.5 is called obtaining W 18 O 49 The powder and sublimed sulfur are placed in the first and second porcelain boats respectively, and then the second porcelain boat is placed into the first porcelain boat; S6. The first and second porcelain boats are placed in a tube furnace, and argon gas is introduced into the furnace cavity. After the furnace cavity pressure rises to 0.2~0.3MPa, the system is kept airtight, and the temperature is raised to 1100~1300℃ at a rate of 20℃ / min. During the heating process, the pressure is maintained at 0.2~0.3 MPa. After reaching 1100~1300℃, the temperature is held for 2 hours. Then, argon gas is introduced to cool it to room temperature, and finally, WS2 / W powder is collected.

[0008] Furthermore, the stirring time in step S1 is 5~15 min.

[0009] Furthermore, the stirring time in step S2 is 5~15 min.

[0010] Further, in step S4, the product is dried in a vacuum oven at 60-90°C for 10-30 minutes.

[0011] WS2 / W composite material obtained according to any one of the preparation methods described.

[0012] Application of the WS2 / W composite material in sodium-sulfur batteries according to any one of the claims.

[0013] Compared with existing technologies, the beneficial effects of this invention are as follows: The WS2 / W composite material prepared by this invention provides abundant polar active sites through the layered structure of WS2, which can anchor polysulfides through strong chemisorption and inhibit their dissolution and migration; the high conductivity of metallic W constructs an efficient electron transport network, reduces reaction resistance, and accelerates the polysulfide conversion reaction rate. The synergistic effect of the WS2 and W interface can also optimize the reaction pathway, lower the energy barrier of Na2S2 / Na2S conversion, and improve reaction kinetics.

[0014] 1) This invention uses isopropanol and acetone as a mixed solvent, which can improve the controllability of the reaction. Isopropanol provides a reducing environment to promote W6. + →W n+ (n<6) controllable reduction, while acetone is optimized by adjusting solvent polarity. 18 O 49 Crystal growth kinetics to suppress agglomeration.

[0015] 2) This invention will W 18 O 49 The sulfur and sublimed sulfur were physically separated in two separate porcelain boats, avoiding direct impact from sulfur vapor and allowing the sulfidation reaction to proceed from W... 18 O 49 The process proceeds gradually from the surface inwards, forming a uniform WS2 / W interface.

[0016] 3) The WS2 / W composite catalyst improves reaction kinetics through a dual mechanism of accelerated electron transport and enhanced catalytic activity. The high conductivity of metallic W reduces the charge transfer resistance of the electrode, promoting the electron transfer reaction of polysulfides. The electron spillover effect at the WS2 / W interface increases the electron cloud density of S atoms, which can lower the activation energy of the polysulfide redox reaction and increase the conversion rate of S8→Na2S.

[0017] 4) This invention employs a high-pressure, closed-gas system to suppress sulfur volatilization and promote uniform reaction. Argon pressure of 0.2~0.3 MPa significantly reduces the vapor pressure of sulfur at high temperatures, preventing excessive WS2 formation due to an excess sulfur source during synthesis. Simultaneously, the high-pressure environment ensures uniform sulfur partial pressure in the reaction system, guaranteeing consistent powder composition. Furthermore, the high-pressure conditions promote close contact between reactant particles, reducing interfacial energy and facilitating the formation of a tight interfacial bond between WS2 and W, creating conditions for rapid electron transport. Moreover, compared to atmospheric pressure synthesis, the high-pressure environment reduces particle surface energy, effectively preventing the stacking and aggregation of WS2 nanosheets at high temperatures, maintaining a high specific surface area and abundant active sites.

[0018] 5) This invention uses a rapid heating rate of 20℃ / min to avoid premature reduction of the W precursor to metallic W, ensuring the synchronization of WS2 crystal nucleation and growth; at the same time, it can also form a defect-enriched WS2 structure, increase sulfur vacancies and edge active sites, enhance polysulfide adsorption and catalytic activity, inhibit excessive crystal growth, obtain nanoscale WS2 sheets and W particles, and shorten the ion transport path. Attached Figure Description

[0019] Figure 1 shows the XRD pattern of the WS2 / W composite material prepared in Example 3.

[0020] Figure 2 shows the SEM image of the WS2 / W composite material prepared in Example 3.

[0021] Figure 3 shows the cycling performance of the WS2 / W composite material prepared in Example 3.

[0022] Figure 4 shows the rate performance of the WS2 / W composite material prepared in Example 3. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0024] Example 1: The technical solution of the present invention is as follows: 1) Measure 30 mL of isopropanol and 20 mL of acetone and add them to a beaker, stir for 5 min; 2) Weigh 0.003 mol of tungsten hexachloride and add it to the above solution, stir at room temperature for 5 min; 3) Transfer the mixed solution to a 100 mL reaction vessel, seal it and place it in an oven, react at 180 °C for 24 h; 4) After the reaction is completed, filter and wash the product with industrial alcohol, dry it in a vacuum oven at 60 °C for 30 min, and collect W. 18 O 49 Powder; 5) According to n W :n S =0.1 means W is obtained 18 O 49 The powder and sublimed sulfur were placed in a large porcelain boat (60x30x30mm, 30mL) and a small porcelain boat (50x25x20mm, 14mL), respectively. The small porcelain boat was then placed on top of the large porcelain boat. The porcelain boat was placed in a tube furnace, and argon gas was introduced until the pressure reached 0.2MPa. The furnace was then closed and heated to 1100℃ at a rate of 20℃ / min. The temperature was maintained at 0.2MPa for 2 hours. Then, argon gas was introduced to cool the furnace to room temperature. Finally, the WS2 / W powder was collected.

[0025] Example 2: The technical solution of the present invention is as follows: 1) Measure 35 mL of isopropanol and 15 mL of acetone and add them to a beaker, and stir for 10 min; 2) Weigh 0.004 mol of tungsten hexachloride and add it to the above solution, and stir at room temperature for 10 min; 3) Transfer the mixed solution to a 100 mL reaction vessel, seal it and place it in an oven, and react at 190 °C for 12 h; 4) After the reaction is completed, filter and wash the product with industrial alcohol, dry it in a vacuum oven at 70 °C for 20 min, and collect W. 18 O 49 Powder; 5) According to n W :n S =0.2 means W is obtained 18 O 49 The powder and sublimed sulfur were placed in a large porcelain boat (60x30x30mm, 30mL) and a small porcelain boat (50x25x20mm, 14mL), respectively. The small porcelain boat was then placed on top of the large porcelain boat. The porcelain boat was placed in a tube furnace, and argon gas was introduced until the pressure reached 0.25MPa. The furnace was then closed, and the temperature was increased to 1200℃ at a rate of 20℃ / min. The temperature was maintained at 0.25MPa for 2 hours. Then, argon gas was introduced to cool the furnace to room temperature. Finally, the WS2 / W powder was collected.

[0026] Example 3: The technical solution of the present invention is as follows: 1) Measure 35 mL of isopropanol and 15 mL of acetone and add them to a beaker, stir for 5 min; 2) Weigh 0.005 mol of tungsten hexachloride and add it to the above solution, stir at room temperature for 10 min; 3) Transfer the mixed solution to a 100 mL reaction vessel, seal it and place it in an oven, react at 200 °C for 16 h; 4) After the reaction is completed, filter and wash the product with industrial alcohol, dry it in a vacuum oven at 75 °C for 15 min, and collect W. 18 O 49 Powder; 5) According to n W :n S =0.3 means W is obtained 18 O 49 The powder and sublimed sulfur were placed in a large porcelain boat (60x30x30mm, 30mL) and a small porcelain boat (50x25x20mm, 14mL), respectively. The small porcelain boat was then placed on top of the large porcelain boat. The porcelain boat was placed in a tube furnace, and argon gas was introduced until the pressure reached 0.3MPa. The furnace was then closed, and the temperature was increased to 1150℃ at a rate of 20℃ / min. The temperature was maintained at 0.3MPa for 2 hours. Then, argon gas was introduced to cool the furnace to room temperature. Finally, the WS2 / W powder was collected.

[0027] Example 4: The technical solution of the present invention is as follows: 1) Measure 40 mL of isopropanol and 10 mL of acetone and add them to a beaker, and stir for 15 min; 2) Weigh 0.006 mol of tungsten hexachloride and add it to the above solution, and stir at room temperature for 15 min; 3) Transfer the mixed solution to a 100 mL reaction vessel, seal it and place it in an oven, and react at 190 °C for 20 h; 4) After the reaction is completed, filter and wash the product with industrial alcohol, dry it in a vacuum oven at 80 °C for 15 min, and collect W. 18 O 49 Powder.

[0028] 5) Press n W :n S =0.4 means W is obtained 18 O 49 The powder and sublimed sulfur were placed in a large porcelain boat (60x30x30mm, 30mL) and a small porcelain boat (50x25x20mm, 14mL), respectively. The small porcelain boat was then placed on top of the large porcelain boat. The porcelain boat was placed in a tube furnace, and argon gas was introduced until the pressure reached 0.3MPa. The furnace was then closed, and the temperature was increased to 1250℃ at a rate of 20℃ / min. The temperature was maintained at 0.3MPa for 2 hours. Then, argon gas was introduced to cool the furnace to room temperature. Finally, the WS2 / W powder was collected.

[0029] Example 5: The technical solution of the present invention is as follows: 1) Measure 40 mL of isopropanol and 10 mL of acetone and add them to a beaker, and stir for 15 min; 2) Weigh 0.006 mol of tungsten hexachloride and add it to the above solution, and stir at room temperature for 15 min; 3) Transfer the mixed solution to a 100 mL reaction vessel, seal it and place it in an oven, and react at 180 °C for 24 h; 4) After the reaction is completed, filter and wash the product with industrial alcohol, dry it in a vacuum oven at 90 °C for 10 min, and collect W. 18 O 49 Powder; 5) According to n W :n S =0.5 means W is obtained 18 O 49 The powder and sublimed sulfur were placed in a large porcelain boat (60x30x30mm, 30mL) and a small porcelain boat (50x25x20mm, 14mL), respectively. The small porcelain boat was then placed on top of the large porcelain boat. The porcelain boat was placed in a tube furnace, and argon gas was introduced until the pressure reached 0.3MPa. The furnace was then closed, and the temperature was increased to 1300℃ at a rate of 20℃ / min. The temperature was maintained at 0.3MPa for 2 hours. Then, argon gas was introduced to cool the furnace to room temperature. Finally, the WS2 / W powder was collected.

[0030] The product obtained in Example 3 was analyzed, and its XRD pattern is shown in Figure 1. The peak positions are consistent with the standard card, and no impurity peaks appeared, indicating that the WS2 / W composite material was successfully prepared. The sharp XRD diffraction peaks indicate good crystallinity of the material, which is beneficial for electron transport. The sample was observed under a scanning electron microscope. As shown in Figure 2, the product has a nanosheet structure accompanied by nanoparticles, corresponding to WS2 and W, respectively. The nanosheets and nanoparticles have a large specific surface area, which can expose more reactive sites.

[0031] The obtained product was used to prepare a button-type sodium-sulfur battery. The specific encapsulation steps are as follows: Active powder, Ketjen black, carbon nanotubes, and binder (polyvinylidene fluoride PVDF) were ground evenly in a mass ratio of 7:1:1:1 to form a slurry. The slurry was then evenly coated onto copper foil using a coating machine and dried in a vacuum drying oven at 80℃ for 24 hours. Afterwards, the electrode sheets were assembled into a sodium-sulfur battery. A constant current charge-discharge test was performed on the battery using a Blue Electric electrochemical workstation, with a test voltage of 0.2-3.0V.

[0032] As shown in Figure 3, the horizontal axis represents the number of cycles, the left vertical axis represents the specific capacity, and the right vertical axis represents the coulombic efficiency. The pink curve represents the specific capacity of the battery at 0.5 A g. -1 After 150 cycles at a current density, the capacity is approximately 1400 mAh g. -1 It exhibits excellent cycle stability, with the coulombic efficiency remaining stable in the range of 98% to 100% in the vast majority of cycles, indicating that the material has excellent charge-discharge reversibility.

[0033] As shown in Figure 4, the horizontal axis represents the number of cycles and the vertical axis represents the specific capacity. The battery shows a small capacity difference under different current densities, and the capacity remains stable. When the battery returns to a low current density, the capacity can be maintained, indicating that its rate performance and stability are good.

Claims

1. A method for preparing a WS2 / W composite material, characterized in that, Includes the following steps: S1. Measure 30-40 mL of isopropanol and 10-20 mL of acetone and add them to a beaker. Stir well at room temperature to obtain mixed solution A. S2. Weigh 0.003-0.006 mol of tungsten hexachloride and add it to mixed solution A obtained in step S1. Stir well at room temperature to obtain mixed solution B. S3. Transfer mixed solution B obtained in step S2 into a reaction vessel, seal it, and place it in an oven. React at 180-200℃ for 12-24 h. S4. After the reaction in step S3 is complete, the product is washed with industrial alcohol by filtration, dried in a vacuum oven, and W is collected. 18 O 49 Powder; S5. According to n W :n S =0.1~0.5 is called obtaining W 18 O 49 The powder and sublimed sulfur are placed in the first and second porcelain boats respectively, and then the second porcelain boat is placed into the first porcelain boat; S6. The first and second porcelain boats are placed in a tube furnace, and argon gas is introduced into the furnace cavity. After the furnace cavity pressure rises to 0.2~0.3MPa, the system is kept airtight, and the temperature is raised to 1100~1300℃ at a rate of 20℃ / min. During the heating process, the pressure is maintained at 0.2~0.3MPa. After reaching 1100~1300℃, the temperature is held for 2 hours, and then argon gas is introduced to cool it to room temperature. Finally, WS2 / W powder is collected.

2. The method for preparing a WS2 / W composite material according to claim 1, characterized in that, The stirring time in step S1 is 5-15 minutes.

3. The method for preparing a WS2 / W composite material according to claim 1, characterized in that, The stirring time in step S2 is 5-15 minutes.

4. The method for preparing a WS2 / W composite material according to claim 1, characterized in that, In step S4, the product is dried in a vacuum oven at 60-90°C for 10-30 minutes.

5. The WS2 / W composite material obtained by the preparation method according to any one of claims 1-4.

6. The application of the WS2 / W composite material according to claim 5 in sodium-sulfur batteries.

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