Tungsten diselenide / nitrogen-doped porous carbon composite material, modified separator and preparation method and application thereof

Abstract

The application provides a tungsten diselenide / nitrogen-doped porous carbon composite material, a modified diaphragm and a preparation method and application thereof. The tungsten diselenide / nitrogen-doped porous carbon composite material comprises nitrogen-doped porous carbon, and the pore channel of the nitrogen-doped porous carbon is filled with tungsten diselenide; wherein the mass ratio of tungsten diselenide to carbon in the nitrogen-doped porous carbon is (10-30):(90-70), and the doping amount of nitrogen in the tungsten diselenide / nitrogen-doped porous carbon composite material is 1-5 at.%. The application inhibits the shuttle effect caused by the dissolution of polysulfide into an organic electrolyte in the room-temperature sodium-sulfur battery cycle process by modifying the diaphragm with the tungsten diselenide / nitrogen-doped porous carbon composite material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage materials, in particular, to a tungsten diselenide / nitrogen-doped porous carbon composite material, a modified separator and a preparation method and application thereof. BACKGROUND

[0002] In order to alleviate the serious climate change and environmental pollution caused by the combustion of fossil fuels, it is urgent to innovate battery technology and develop advanced electrode materials. Studies have shown that room-temperature sodium-sulfur batteries have high theoretical energy density, low cost and environmental friendliness, which brings them a broad practical application prospect, and thus it is considered as the next generation of energy storage systems with great commercial value. Unfortunately, its commercialization road still faces problems such as actual energy density far lower than theoretical value, short cycle life and poor safety performance. First, the poor electrical conductivity of the positive electrode sulfur (5×10 -30 S cm -1 ) and its discharge product sodium sulfide (Na2S2 / Na2S) leads to low sodium-sulfur battery reaction activity; second, the positive electrode sulfur will have serious volume expansion during charging and discharging, which makes the base structure easy to crumble and the battery cycle stability poor; finally, the generated sodium polysulfide in the sodium-sulfur battery reaction process is easy to dissolve in the electrolyte and cause "shuttle effect", which leads to serious loss of active material and rapid decay of battery capacity. Sodium polysulfide is easy to dissolve in the electrolyte and diffuse to the sodium negative electrode to cause side reactions, causing the shuttle effect, and the irreversible loss of active material is the main reason for the above problems. Glass fiber separator has a rich pore structure and a large pore size, and has a weak inhibitory effect on the polysulfide shuttle effect. Therefore, the glass fiber separator needs to be modified to meet the needs of high specific energy and long life room-temperature sodium-sulfur batteries. The introduction of polar materials can inhibit the dissolution of soluble polysulfides in the electrolyte, i.e. reduce the content of polysulfides in the electrolyte, thereby improving the utilization rate of the positive electrode sulfur and the cycle life. From the perspective of applying physical constraints to glass fiber separators, carbon-based materials have high electrical conductivity, large specific surface area, universal porous structure and low cost, and can better play their role after being combined with polar materials.

[0003] However, the prior art inhibits the shuttle effect of polysulfides by improving the positive electrode material, and the preparation process of the positive electrode material is complex, and the performance improvement is not obvious. For example, a heterostructure is constructed to improve the redox reaction kinetics of sodium-sulfur batteries. Na2S / Na2Te@C has advantages such as rich heterojunction, high conductivity and porosity, which can promote the diffusion of electrons / ions and provide high catalytic activity. The Na2S@Na2Te heterostructure embedded in the carbon structure aims to effectively inhibit the shuttle effect of polysulfides. The prior art discloses a tantalum-based metal nitride porous carbon sphere based on defect engineering as a sulfur positive electrode material of a sodium-sulfur battery, which controllably introduces defects, and then prepares a defect tantalum nitride porous carbon sphere composite material. The prior art also discloses a cobalt-based metal compound mesoporous carbon sphere composite material and a preparation method thereof as a positive electrode material of a sodium-sulfur battery; the method uses the composite material Co-S-C@MC to prepare a positive electrode material of a sodium-sulfur battery, which has high specific discharge capacity, long cycle stability and excellent rate performance. Some methods mix treated lignin-removed tea residue powder with solid sublimed sulfur in a certain proportion, uniformly mix them, and then react at 140℃-160℃ for 10h-15h, and then heat to 180℃-300℃ to remove the surface sulfur, to obtain a positive electrode material of a sodium-sulfur battery, which can improve the specific capacity of the sodium-sulfur battery.

[0004] Currently, there are few studies on inhibiting the shuttle effect of sodium polysulfide by modifying the separator to improve the performance of the battery. Although the prior art discloses a preparation method of a separator modification material, metal sulfide particles are combined with porous carbon by loading annealing, and a separator modification layer is prepared by coating the obtained composite material on the surface of a commercial separator. In lithium-sulfur and sodium-sulfur batteries, the "shuttle effect" of polysulfides can be inhibited by capturing the catalytic conversion mechanism to improve the life of the battery, but the carbon material is a non-polar material that can only adsorb polysulfides through weak intermolecular forces, and the effect is limited.

[0005] Therefore, the present application is proposed. SUMMARY

[0006] The main purpose of the present application is to provide a tungsten diselenide / nitrogen-doped porous carbon composite material, a modified separator and a preparation method and application thereof, to solve the problem that in the prior art, the shuttle effect of polysulfides in sodium-sulfur batteries leads to serious loss of active materials and rapid decay of battery capacity.

[0007] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a tungsten diselenide / nitrogen-doped porous carbon composite material is provided, which comprises nitrogen-doped porous carbon, and tungsten diselenide is filled in the pore channels of the nitrogen-doped porous carbon; wherein the mass ratio of tungsten diselenide to carbon in the nitrogen-doped porous carbon is (10-30):(90-70), and the doping amount of nitrogen in the tungsten diselenide / nitrogen-doped porous carbon composite material is 1-5 at. %.

[0008] Further, the particle size of the tungsten diselenide / nitrogen-doped porous carbon composite material is 0.5-1.0 μm.

[0009] Further, the specific surface area of the nitrogen-doped porous carbon is 100-500 m 2 / g.

[0010] Further, the pore volume of the nitrogen-doped porous carbon is 0.12 cm 3 / g-0.65 cm 3 / g.

[0011] Further, the preparation method of the nitrogen-doped porous carbon comprises the following steps: mixing the porous carbon with melamine, and performing heat treatment to obtain the nitrogen-doped porous carbon.

[0012] Further, the mass ratio of the porous carbon to the melamine is 1:1-10.

[0013] Further, the temperature of the heat treatment is 800-850 ℃, and the time of the heat treatment is 4-6 h.

[0014] According to another aspect of the present application, there is provided a preparation method of the tungsten diselenide / nitrogen-doped porous carbon composite material provided by the first aspect, comprising the following steps: providing the nitrogen-doped porous carbon, mixing the nitrogen-doped porous carbon, Na2WO4·2H2O, selenium powder, an acid solution, and an auxiliary agent, and preparing the tungsten diselenide / nitrogen-doped porous carbon composite material by a solvothermal method.

[0015] Further, the acid solution comprises at least one of a hydrochloric acid solution, an acetic acid solution, and a phosphoric acid solution, and more preferably the hydrochloric acid solution.

[0016] Further, the auxiliary agent comprises at least one of N2H4·2H2O, carbon disulfide, and quinoline, and more preferably the N2H4·2H2O.

[0017] Further, the reaction temperature of the solvothermal method is 180-250 ℃, and the reaction time of the solvothermal method is 10-16 h.

[0018] Further, the molar ratio of the Na2WO4·2H2O to the selenium powder is 1:1-5.

[0019] Further, the mass ratio of the Na2WO4·2H2O to the nitrogen-doped porous carbon is (5-10):1.

[0020] According to a third aspect of the present application, there is provided a modified separator, which comprises a separator, and a modified coating layer arranged on the side of the separator close to a positive electrode, wherein the material of the modified coating layer comprises the tungsten diselenide / nitrogen-doped porous carbon composite material provided by the first aspect or the second aspect, a conductive agent, and a binder.

[0021] Further, the loading amount of the tungsten diselenide / nitrogen-doped porous carbon composite material on the separator is 0.2-0.6 mg / cm 2 .

[0022] Further, the conductive agent includes at least one of Super P, activated carbon, acetylene black; and more further, the conductive agent is Super P.

[0023] Further, the binder includes at least one of PVDF, CMC, SBR; and more further, the binder is PVDF.

[0024] Further, the material of the separator includes at least one of glass fiber, polypropylene, polyethylene; and more further, the material of the separator is glass fiber.

[0025] Further, the mass ratio of the tungsten diselenide / nitrogen-doped porous carbon composite material, the conductive agent, and the binder is (6-8):(3-1):1.

[0026] According to a fourth aspect of the present application, a preparation method of the modified separator provided by the third aspect is provided, and the preparation method includes the following steps: mixing the tungsten diselenide / nitrogen-doped porous carbon composite material, the conductive agent, and the binder, and then grinding, and then dispersing in a solvent to obtain a modified coating slurry; coating the modified coating slurry to one side of the separator close to the positive electrode, and removing the solvent to obtain the modified separator.

[0027] Further, the solvent includes at least one of NMP, deionized water, and DMF; and more further, the solvent is NMP.

[0028] According to a fifth aspect of the present application, the tungsten diselenide / nitrogen-doped porous carbon composite material provided by the first aspect or the second aspect, or the modified separator provided by the third aspect or the fourth aspect is applied in a sodium-sulfur battery.

[0029] By using the technical solution of the present application, the sodium-sulfur battery at room temperature is inhibited from causing the shuttle effect caused by the dissolution of polysulfide into the organic electrolyte during the cycle process by modifying the separator by using the tungsten diselenide / nitrogen-doped porous carbon composite material. The tungsten diselenide / nitrogen-doped porous carbon composite material is filled with tungsten diselenide in the pore channel of the nitrogen-doped porous carbon, wherein the polar tungsten diselenide can form a bond with the soluble polysulfide to limit the shuttle of the polysulfide; at the same time, the porous carbon can adsorb the polysulfide through the van der Waals force and the active site; and the nitrogen doped in the porous carbon can provide more active sites to adsorb the polysulfide, thereby effectively inhibiting the “shuttle effect”, effectively reducing the loss of active substances, and significantly enhancing the stability of the battery.

[0030] In addition, the modified separator is obtained by coating the modified coating material containing the tungsten diselenide / nitrogen-doped porous carbon composite material on one side of the separator close to the positive electrode, and the electrochemical performance of the sodium-sulfur battery at room temperature can be significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings, which form a part of the specification, are included to provide a further understanding of the application and are incorporated herein in conjunction with the description of the application. The drawings are as follows:

[0032] Figure 1 A schematic diagram showing the position of the modified separator in the sodium-sulfur battery and the inhibition of the shuttle effect is shown;

[0033] Figure 2 A SEM diagram of the modified glass fiber separator in Example 1 is shown;

[0034] Figure 3 A SEM diagram of the glass fiber separator in Comparative Example 1 is shown. DETAILED DESCRIPTION

[0035] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0036] As analyzed in the background art of the present application, the effect of inhibiting the shuttle effect of polysulfides in the sodium-sulfur battery by improving the positive electrode material in the prior art is not good, and the effect of adsorbing polysulfides by using porous carbon to modify the separator is limited. In order to solve this problem, the present application provides a tungsten diselenide / nitrogen-doped porous carbon composite material, a modified separator and a preparation method and application thereof.

[0037] In a first typical embodiment of the present application, a tungsten diselenide / nitrogen-doped porous carbon composite material is provided, which includes nitrogen-doped porous carbon, and tungsten diselenide is filled in the pores of the nitrogen-doped porous carbon; wherein the mass ratio of tungsten diselenide to carbon in the nitrogen-doped porous carbon is (10-30):(90-70), and the doping amount of nitrogen in the tungsten diselenide / nitrogen-doped porous carbon composite material is 1-5 at. %.

[0038] The application modifies the separator by using a tungsten diselenide / nitrogen-doped porous carbon composite material to inhibit the shuttle effect caused by the dissolution of polysulfides into the organic electrolyte during the cycling of a room-temperature sodium-sulfur battery. The tungsten diselenide / nitrogen-doped porous carbon composite material has tungsten diselenide filled in the pores of the nitrogen-doped porous carbon, wherein the polar tungsten diselenide can form bonds with the soluble polysulfides to limit the polysulfide shuttle; at the same time, the porous carbon can adsorb the polysulfides through van der Waals forces and active sites; and the nitrogen doped in the porous carbon can provide more active sites to adsorb the polysulfides, thereby effectively inhibiting the "shuttle effect", effectively reducing the loss of active materials, and significantly enhancing the stability of the battery. In addition, by coating the coating material containing the tungsten diselenide / nitrogen-doped porous carbon composite material on the side of the separator close to the positive electrode to obtain a modified separator, the electrochemical performance of the room-temperature sodium-sulfur battery can be significantly improved.

[0039] Compared with the use of a single material (such as only tungsten diselenide or only nitrogen-doped porous carbon), in the battery using the modified separator coated with the tungsten diselenide / nitrogen-doped porous carbon composite material, the sodium ion diffusion coefficient is large, and excellent adsorption performance is exhibited for sodium polysulfide.

[0040] Typically but not limitedly, in the tungsten diselenide / nitrogen-doped porous carbon composite material provided by the application, the mass ratio of tungsten diselenide to the porous carbon in the nitrogen-doped porous carbon is, for example, 10:90, 15:85, 20:80, 25:75, 30:70, or a range value composed of any two numerical values; and the doping amount of nitrogen in the tungsten diselenide / nitrogen-doped porous carbon composite material is, for example, 1 at.%, 2 at.%, 3 at.%, 4 at.%, 5 at.%, or a range value composed of any two numerical values.

[0041] In the application, "at.%" represents atomic percentage.

[0042] The porous structure of the porous carbon in the nitrogen-doped porous carbon can enable the tungsten diselenide to be filled in the pores, thereby increasing the active sites, further inhibiting the polysulfide shuttle, promoting the rapid transmission of the electrolyte and ions, and improving the electrochemical performance of the battery. In addition, the nitrogen-doped porous carbon with a larger specific surface area can provide a larger reaction interface to promote the adsorption of polysulfides, so that the battery has excellent battery capacity retention rate and cycle stability. In order to further promote the filling of the tungsten diselenide in the pores and the adsorption of the polysulfides, the specific surface area of the nitrogen-doped porous carbon is preferably 100-500 m 2 / g, the pore volume of the nitrogen-doped porous carbon is 0.12 cm 3 / g-0.65 cm 3 / g.

[0043] Typically but not limitedly, the specific surface area of the nitrogen-doped porous carbon is, for example, 100 m 2 / g, 200 m2 / g, 300 m 2 / g, 400 m 2 / g, 500 m 2 / g, or any two of the values form a range; the pore volume of the nitrogen-doped porous carbon is 0.12 cm 3 / g, 0.20 cm 3 / g, 0.30 cm 3 / g, 0.40 cm 3 / g, 0.50 cm 3 / g, 0.65 cm 3 / g, or any two of the values form a range.

[0044] Since the separator in the battery is a three-dimensional porous membrane, the pore size distribution is 0.3-10 μm. The tungsten diselenide / nitrogen-doped porous carbon composite material is coated on the side of the separator close to the positive electrode, in order to improve the stability of the separator modification material, and to avoid the battery short circuit caused by the tungsten diselenide / nitrogen-doped porous carbon composite material falling off through the pores of the separator. Preferably, the particle size of the tungsten diselenide / nitrogen-doped porous carbon composite material is 0.5-1.0 μm.

[0045] Typically but not limitedly, the particle size of the tungsten diselenide / nitrogen-doped porous carbon composite material is, for example, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, or any two of the values form a range.

[0046] In some embodiments, the method for preparing the nitrogen-doped porous carbon comprises the following steps: mixing the porous carbon with melamine, and performing a heating treatment to obtain the nitrogen-doped porous carbon. Only a small amount of nitrogen atoms is doped into the porous carbon during the preparation process.

[0047] In order to further promote the generation of the nitrogen-doped porous carbon, the mass ratio of the porous carbon to melamine is preferably 1:1-10.

[0048] Typically but not limitedly, the mass ratio of the porous carbon to melamine is, for example, 1:1, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, or any two of the values form a range.

[0049] In order to further increase the porosity of the nitrogen-doped porous carbon, the heating treatment temperature is preferably 800-850 °C, and the heating treatment time is preferably 4-6 h.

[0050] Typically but not limitedly, the heating treatment temperature is, for example, 800 °C, 810 °C, 820 °C, 830 °C, 840 °C, 850 °C, or any two of the values form a range; and the heating treatment time is, for example, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, or any two of the values form a range.

[0051] In a second typical embodiment of the present application, a preparation method of a tungsten diselenide / nitrogen-doped porous carbon composite material is provided, comprising the following steps: providing a nitrogen-doped porous carbon, mixing the nitrogen-doped porous carbon, Na2WO4·2H2O, selenium powder, an aqueous hydrochloric acid solution, and N2H4·2H2O, and preparing the tungsten diselenide / nitrogen-doped porous carbon composite material by a solvothermal method. The preparation method realizes in-situ generation of tungsten diselenide in the pore channels of the nitrogen-doped porous carbon.

[0052] To further promote the reaction to generate tungsten diselenide, the acid solution preferably includes any one or more of a hydrochloric acid solution, an acetic acid solution, and a phosphoric acid solution; more preferably, the acid solution is a hydrochloric acid solution.

[0053] To further promote the dissolution of the selenium powder, the auxiliary agent preferably includes any one or more of N2H4·2H2O, carbon disulfide, and quinoline; more preferably, the auxiliary agent is N2H4·2H2O.

[0054] To better prepare the tungsten diselenide / nitrogen-doped porous carbon composite material, the reaction temperature of the solvothermal method is preferably 180-250°C, and the reaction time of the solvothermal method is preferably 10-16h.

[0055] Typically but not exclusively, the reaction temperature of the solvothermal method is, for example, 180°C, 200°C, 220°C, 240°C, 250°C, or a range defined by any two of the values; and the reaction time of the solvothermal method is, for example, 10h, 12h, 14h, 16h, 18h, or a range defined by any two of the values.

[0056] In some typical embodiments, the tungsten diselenide / nitrogen-doped porous carbon composite material is prepared by the following steps: (1) adding Na2WO4·2H2O and selenium powder to deionized water, and ultrasonic treatment to promote the dispersion of the solution, to obtain a primary mixture; (2) adding an aqueous hydrochloric acid solution, N2H4·2H2O, and nitrogen-doped porous carbon to the primary mixture, and stirring and ultrasonic treatment in cycles to obtain a secondary mixture. To further promote the reaction to generate tungsten diselenide, the concentration of the aqueous hydrochloric acid solution is preferably 36-38wt%. Multiple stirring and ultrasonic treatment can fully mix the solution, to promote uniform dispersion of the solute molecules in the pore channels of the nitrogen-doped porous carbon, and to enable the generated tungsten diselenide to be further uniformly distributed inside the nitrogen-doped porous carbon during the subsequent solvothermal process, thereby avoiding local agglomeration of the tungsten diselenide and promoting the structure of the generated tungsten diselenide / nitrogen-doped porous carbon composite material to be more stable. (3) placing the secondary mixture in a reaction kettle, and reacting in a constant-temperature oven for 10-16h, with the reaction temperature being set to 180-250°C; after the reaction is completed, performing solid-liquid separation on the generated solution, washing the precipitate with anhydrous ethanol and deionized water, vacuum drying the precipitate, with the drying temperature being 50-80°C and the drying time being 2-12h, to obtain the tungsten diselenide / nitrogen-doped porous carbon composite material.

[0057] To further improve the formation rate of tungsten diselenide, the preferred molar ratio of Na2WO4·2H2O to selenium powder is 1:1-5.

[0058] Typical, but not limiting, molar ratios of Na₂WO₄·2H₂O to selenium powder are, for example, 1:1, 1:2, 1:3, 1:4, 1:5, or any combination of the two.

[0059] To further enhance the inhibition of polysulfides by tungsten diselenide / nitrogen-doped porous carbon composite material, the preferred mass ratio of Na2WO4·2H2O to nitrogen-doped porous carbon is (5-10):1.

[0060] Typical, but not limiting, ratios of Na₂WO₄·2H₂O to nitrogen-doped porous carbon are, for example, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, or any range of two such ratios.

[0061] In a third typical embodiment of this application, a modified diaphragm is provided. The modified diaphragm includes a diaphragm and a modified coating is provided on the side of the diaphragm near the positive electrode. The material of the modified coating includes the tungsten diselenide / nitrogen-doped porous carbon composite material, conductive agent and binder provided in the first typical embodiment or the second typical embodiment.

[0062] A modified coating containing tungsten diselenide / nitrogen-doped porous carbon composite material was applied to the side of the separator near the positive electrode to obtain the modified separator. Figure 1 The diagram shows the location of the modified separator in a sodium-sulfur battery and its role in suppressing the shuttle effect. Figure 1 In the diagram, "Sodium Metal Anode" indicates that sodium metal is the negative electrode, and "CB / S" indicates that porous carbon@sulfur is the positive electrode. From... Figure 1 It can be seen that the polysulfides generated by the positive electrode are adsorbed by the modified separator, effectively suppressing the shuttle effect caused by polysulfides dissolving into the organic electrolyte during the cycling process of room-temperature sodium-sulfur batteries. Porous carbon can adsorb polysulfides through van der Waals forces and active sites. Nitrogen doping, by introducing nitrogen atoms into the carbon lattice, further improves the electronic structure and physicochemical properties of porous carbon, giving it more active sites and promoting the adsorption of more polysulfides. Furthermore, the presence of tungsten diselenide filling the pores of the nitrogen-doped porous carbon allows the polar tungsten diselenide to bond with soluble polysulfides, further suppressing polysulfide shuttle. Therefore, the abundant adsorption active sites and strong interactions with polysulfides on this modified separator effectively improve the chemical performance of the battery.

[0063] In some embodiments, the loading amount of tungsten diselenide / nitrogen-doped porous carbon composite material on the membrane is 0.2–0.6 mg / cm³. 2The loading amount of the tungsten diselenide / nitrogen-doped porous carbon composite material on the separator is too low, so the tungsten diselenide / nitrogen-doped porous carbon composite material cannot form an effective barrier layer and an adsorption layer on the separator, and cannot effectively adsorb polysulfides; and the loading amount is too high, which will make the mechanical properties of the modified separator poor, the internal resistance of the modified separator increase, and the modified coating easily fall off from the glass fiber separator, and also cannot effectively adsorb polysulfides.

[0064] Typically but not limitedly, the loading amount of the tungsten diselenide / nitrogen-doped porous carbon composite material on the separator is, for example, 0.2 mg / cm 2 , 0.3 mg / cm 2 , 0.4 mg / cm 2 , 0.5 mg / cm 2 , 0.6 mg / cm 2 , or a range value composed of any two numerical values.

[0065] In the present application, the material of the separator is a commonly used material in the art, including but not limited to any one or more of glass fiber, polypropylene, and polyethylene. In some embodiments, the material of the separator is glass fiber, and the modified glass fiber separator has a modified coating on the side close to the positive electrode.

[0066] In order to further inhibit the shuttle effect of polysulfides by the modified separator, it is preferred to add a conductive agent to the modified coating; the conductive agent includes any one or more of Super P (conductive carbon black), activated carbon, and acetylene black, and it is further preferred that the conductive agent is Super P.

[0067] In order to further enable the modified coating to be better coated on one side of the modified separator, it is preferred to add a binder to the modified coating; the binder includes any one or more of PVDF (polyvinylidene fluoride), CMC (sodium carboxymethyl cellulose), and SBR (styrene butadiene rubber), and it is further preferred that the binder is PVDF (polyvinylidene fluoride).

[0068] In order to further improve the properties of the modified separator, it is preferred that the material of the separator includes at least one of glass fiber, polypropylene, and polyethylene, and it is further preferred that the material of the separator is glass fiber.

[0069] In some embodiments, the mass ratio of the tungsten diselenide / nitrogen-doped porous carbon composite material, the conductive agent, and the binder in the material of the modified coating is (6-8):(1-3):1, so as to further improve the performance of the modified coating and the adhesion of the modified coating on the separator.

[0070] Typically but not limitedly, the mass ratio of the tungsten diselenide / nitrogen-doped porous carbon composite material, the conductive agent, and the binder in the material of the modified coating is, for example, 6:3:1, 7:2:1, 8:1:1, or a range value composed of any two numerical values.

[0071] In a fourth typical embodiment of the present application, a preparation method of a modified separator is provided. The tungsten diselenide / nitrogen-doped porous carbon composite material, the conductive agent, and the binder are mixed and ground, and then dispersed in a solvent to obtain a modified coating slurry. The modified coating slurry is coated on one side of the separator close to the positive electrode, and the solvent is removed to obtain a modified separator. The preparation method of the modified separator is simple to operate and suitable for industrial production. The solvent removal method includes but is not limited to vacuum drying, and any commonly used solvent removal method in the art can be used. In the present application, the solvent is preferably evaporated and removed by vacuum drying.

[0072] To better dissolve and prepare the tungsten diselenide / nitrogen-doped porous carbon composite material, the conductive agent, and the binder to form a slurry, the solvent preferably includes any one or more of NMP (N-methyl pyrrolidone), deionized water, and DMF (dimethylformamide), and is further preferably NMP (N-methyl pyrrolidone).

[0073] In a fifth typical embodiment of the present application, the tungsten diselenide / nitrogen-doped porous carbon composite material provided in the first typical embodiment or the second typical embodiment, or the modified separator provided in the third typical embodiment or the fourth typical embodiment is applied in a sodium-sulfur battery.

[0074] The beneficial effects of the present application will be further illustrated below with examples and comparative examples.

[0075] Example 1

[0076] (1) Preparation of nitrogen-doped porous carbon:

[0077] The activated carbon was heated to 800°C under the protection of argon for 1 h. Then, the activated carbon was mixed with potassium hydroxide (mass ratio of 1:1), deionized water was added, and the mixture was stirred and mixed uniformly. The mixture was dried in an 80°C oven to remove water, and a mixture was obtained. The mixture was placed in a tube furnace for activation treatment, i.e., the temperature was increased to 700°C at a rate of 2°C / min under Ar atmosphere, and the temperature was maintained for 2 h. Then, the temperature was cooled to room temperature. A 2 mol / L hydrochloric acid solution was slowly added to the cooled product to remove alkaline substances remaining on the surface. The product was washed with deionized water until it was neutral. Then, the product was placed in an 80°C oven for drying treatment, and nitrogen-doped porous carbon was obtained.

[0078] The nitrogen-doped porous carbon and melamine were placed in a magnetic boat at a weight ratio of 1:5, sealed, and then placed in the middle position of a first tube furnace for first heating treatment (the temperature was increased at a rate of 2°C / min, and the temperature was maintained at 850°C for 5 h after reaching 850°C). The temperature was cooled to room temperature, and nitrogen-doped porous carbon was obtained. The specific surface area of the nitrogen-doped porous carbon was 269.5 m 2 / g, and the pore volume was 0.36 cm 3 / g.

[0079] (2) Preparation of tungsten diselenide / nitrogen-doped porous carbon composite material:

[0080] 0.528 g of Na2WO4·2H2O and 0.256 g of selenium powder were added to deionized water, and ultrasonic treatment was performed for 30 min to obtain a first mixed solution; 10 mL of a 36.28 wt% hydrochloric acid aqueous solution, 7.35 mL of N2H4·2H2O, and 60 mg of nitrogen-doped porous carbon were added to the first mixed solution, stirring was performed for 30 min, and ultrasonic treatment was performed for 5 min for four cycles to obtain a second mixed solution; the second mixed solution was placed in a reaction kettle, and reaction was performed in a 200°C constant-temperature oven for 12 h; the generated solution was subjected to centrifugal treatment, and the precipitate was washed with anhydrous ethanol and deionized water, followed by drying of the precipitate at 60°C for 10 h; and screening was performed to obtain a tungsten diselenide / nitrogen-doped porous carbon composite material with a particle size range of 0.5-1.0 μm.

[0081] (3) Preparation of modified separator:

[0082] The tungsten diselenide / nitrogen-doped porous carbon composite material, Super P, and PVDF were mixed in a mass ratio of 7:2:1, and then grinding was performed; 10 mL of NMP was added, and stirring and mixing were performed to obtain a modified coating slurry. The modified coating slurry was coated on one side of the glass fiber separator close to the positive electrode, the loading amount of the tungsten diselenide / nitrogen-doped porous carbon composite material on the glass fiber separator was 0.4 mg / cm 2 , and the glass fiber separator was placed in a vacuum drying oven for drying treatment at a drying temperature of 80°C for 6 h to obtain a modified glass fiber separator. The modified glass fiber separator was cut into a disc for standby use. An SEM image of the modified glass fiber separator is shown in Figure 2 .

[0083] Example 2

[0084] Example 2 differs from Example 1 in that the mass ratio of the porous carbon to melamine was set to 1:10 in step (1).

[0085] Example 3

[0086] Example 3 differs from Example 1 in that the mass ratio of the porous carbon to melamine was set to 1:1 in step (1).

[0087] Example 4

[0088] Example 4 differs from Example 1 in that the mass ratio of Na2WO4·2H2O to nitrogen-doped porous carbon was set to 5:1 in step (2).

[0089] Example 5

[0090] Example 5 differs from Example 1 in that the mass ratio of Na2WO4 2H2O to nitrogen-doped porous carbon is set to 10:1 in step (2).

[0091] Example 6

[0092] Example 6 differs from Example 1 in that the mass ratio of porous carbon to melamine, the mass ratio of Na2WO4 2H2O to nitrogen-doped porous carbon are adjusted so that the mass ratio of tungsten diselenide to carbon in the nitrogen-doped porous carbon is 10:90, and the doping amount of nitrogen in the porous carbon composite is 5 at. %.

[0093] Example 7

[0094] Example 7 differs from Example 1 in that the mass ratio of porous carbon to melamine, the mass ratio of Na2WO4 2H2O to nitrogen-doped porous carbon are adjusted so that the mass ratio of tungsten diselenide to carbon in the nitrogen-doped porous carbon is 30:70, and the doping amount of nitrogen in the porous carbon composite is 1 at. %.

[0095] Example 8

[0096] Example 8 differs from Example 1 in that the loading amount of the tungsten diselenide / nitrogen-doped porous carbon composite on the glass fiber separator is adjusted in step (3) so that the loading amount is 0.2 mg / cm 2 .

[0097] Example 9

[0098] Example 9 differs from Example 1 in that the loading amount of the tungsten diselenide / nitrogen-doped porous carbon composite on the glass fiber separator is adjusted in step (3) so that the loading amount is 0.6 mg / cm 2 .

[0099] Example 10

[0100] Example 10 differs from Example 1 in that the loading amount of the tungsten diselenide / nitrogen-doped porous carbon composite on the glass fiber separator is adjusted in step (3) so that the loading amount is 0.05 mg / cm 2 .

[0101] Example 11

[0102] Example 11 differs from Example 1 in that the loading amount of the tungsten diselenide / nitrogen-doped porous carbon composite on the glass fiber separator is adjusted in step (3) so that the loading amount is 1.0 mg / cm 2 .

[0103] Example 12

[0104] Example 12 differs from Example 1 in that the mass ratio of the tungsten diselenide / nitrogen-doped porous carbon composite, Super P and PVDF is adjusted in step (3) so that the mass ratio of the three is 6:3:1.

[0105] Example 13

[0106] Example 13 differs from Example 1 in that the mass ratio of the tungsten diselenide / nitrogen-doped porous carbon composite, Super P and PVDF is adjusted in step (3) so that the mass ratio of the three is 8:1:1.

[0107] Example 14

[0108] Example 14 differs from Example 1 in that no conductive agent is added when preparing the modified coating slurry in step (3), and the tungsten diselenide / nitrogen-doped porous carbon composite and PVDF are mixed in a mass ratio of 7:1 before being ground, and then NMP is added and stirred to obtain the modified coating slurry.

[0109] Example 15

[0110] Example 15 differs from Example 1 in that the amount of potassium hydroxide is adjusted in the preparation of the nitrogen-doped porous carbon in step (1) so that the surface area of the nitrogen-doped porous carbon is 100 m 2 / g, and the pore volume is 0.12 cm 3 / g.

[0111] Example 16

[0112] Example 16 differs from Example 1 in that the amount of potassium hydroxide is adjusted in the preparation of the nitrogen-doped porous carbon in step (1) so that the surface area of the nitrogen-doped porous carbon is 500 m 2 / g, and the pore volume is 0.65 cm 3 / g.

[0113] Example 17

[0114] Example 17 differs from Example 1 in that the amount of potassium hydroxide is adjusted in the preparation of the nitrogen-doped porous carbon in step (1) so that the surface area of the nitrogen-doped porous carbon is 50.5 m 2 / g, and the pore volume is 0.10 cm 3 / g.

[0115] Example 18

[0116] Example 18 differs from Example 1 in that the amount of potassium hydroxide is adjusted in the preparation of the nitrogen-doped porous carbon in step (1) so that the surface area of the nitrogen-doped porous carbon is 700 m 2 / g, and the pore volume is 0.85 cm3 / g.

[0117] Comparative Example 1

[0118] Comparative Example 1 differs from Example 1 in that the glass fiber separator in Comparative Example 1 is not coated with the modified coating slurry, and the SEM image of the glass fiber separator is shown in FIG. 1. Figure 3

[0119] Comparative Example 2

[0120] Comparative Example 2 differs from Example 1 in that the composite material prepared in Comparative Example 2 contains only nitrogen-doped porous carbon, and does not contain tungsten diselenide.

[0121] Comparative Example 3

[0122] Comparative Example 3 differs from Example 1 in that the composite material prepared in Comparative Example 3 contains only tungsten diselenide, and does not contain nitrogen-doped porous carbon.

[0123] Comparative Example 4

[0124] Comparative Example 4 differs from Example 1 in that nitrogen doping is not introduced into the porous carbon in Comparative Example 4.

[0125] Comparative Example 5

[0126] Comparative Example 5 differs from Example 1 in that the mass ratio of the porous carbon to melamine and the mass ratio of Na2WO4·2H2O to nitrogen-doped porous carbon are adjusted in step (2) in Comparative Example 5, so that the mass ratio of carbon in tungsten diselenide and nitrogen-doped porous carbon is 45:55, and the doping amount of nitrogen in the porous carbon composite material is 3.3 at. %.

[0127] Comparative Example 6

[0128] Comparative Example 6 differs from Example 1 in that the mass ratio of the porous carbon to melamine and the mass ratio of Na2WO4·2H2O to nitrogen-doped porous carbon are adjusted in step (2) in Comparative Example 6, so that the mass ratio of carbon in tungsten diselenide and nitrogen-doped porous carbon is 3:97, and the doping amount of nitrogen in the porous carbon composite material is 6 at. %.

[0129] Test Example 1

[0130] The tungsten diselenide / nitrogen-doped porous carbon composite materials of the examples and comparative examples are subjected to XPS elemental analysis (instrument: Thermo ESCALAB 250Xi Spectrophotometer), and the contents of tungsten diselenide, nitrogen, and carbon are tested, and the results are shown in Table 1.

[0131] ​The specific surface area and pore volume of the nitrogen-doped porous carbon were tested by BET method on an ASAP 2020 nitrogen adsorption-desorption instrument.

[0132] Test Example 2

[0133] The modified separator samples provided by the examples and comparative examples were used for performance testing of sodium-sulfur batteries. Their cycle performance indicators were tested to evaluate their performance in sodium-sulfur battery applications.

[0134] Porous carbon@ sulfur (sulfur to porous carbon mass ratio of 70:30, porous carbon pore size of 8 nm, pore volume of 1.3 cm 3 / g) as the positive electrode, sodium metal as the negative electrode, and the electrolyte composition of 1M NaClO4 in EC (ethylene carbonate): PC (propylene carbonate) = 1:1 Vol% with 5% FEC (fluoroethylene carbonate) were assembled into room temperature sodium-sulfur batteries with the above modified separator samples. The obtained room temperature sodium-sulfur batteries were subjected to 100 charge-discharge cycle tests at a current density of 0.1C or 0.5C, respectively, to obtain the initial discharge specific capacity at a current density of 0.1C, the discharge specific capacity after 100 cycles at a current density of 0.1C, the initial discharge specific capacity at a current density of 0.5C, and the discharge specific capacity after 100 cycles at a current density of 0.5C. The results are shown in Table 2.

[0135] Test Example 3

[0136] The SEM images of the modified glass fiber separator in Example 1 and the glass fiber separator without coating the modified coating slurry in Comparative Example 1 were observed by scanning electron microscopy, and the results are shown in Figure 2 , Figure 3 From Figure 2 and Figure 3 , it can be seen that, compared with the unmodified glass fiber separator, the surface of the modified glass fiber separator becomes more dense, which is beneficial to hinder the passage of polysulfides and thus inhibit the shuttle effect.

[0137] Table 1

[0138]

[0139]

[0140] In Table 1, “--” indicates that the content of tungsten diselenide, nitrogen, and carbon was not detected.

[0141] Table 2

[0142]

[0143]

[0144] From the above description, it can be seen that the above-mentioned embodiments of the present application achieve the following technical effects:

[0145] From the experimental data of examples 1-7, comparative examples 1-6, it can be seen that when the mass ratio of tungsten diselenide and carbon in the nitrogen-doped porous carbon is (10-30):(90-70), and the doping amount of nitrogen in the tungsten diselenide / nitrogen-doped porous carbon composite material is 1-5 at.%, the modified separator sample coated with the tungsten diselenide / nitrogen-doped porous carbon composite material is assembled into a sodium-sulfur battery, and it is tested to have a higher specific discharge capacity, indicating that by modifying the separator with the tungsten diselenide / nitrogen-doped porous carbon composite material, the shuttle effect caused by the dissolution of polysulfides into the organic electrolyte during the cycle of the room-temperature sodium-sulfur battery can be inhibited, and the electrochemical performance of the room-temperature sodium-sulfur battery can be significantly improved. When the content of the components in the composite material is changed or any component is missing, the specific discharge capacity is significantly reduced, and the electrochemical performance of the sodium-sulfur battery is reduced.

[0146] From the experimental data of examples 8-11, it can be seen that when the loading amount of the tungsten diselenide / nitrogen-doped porous carbon composite material on the separator is 0.2-0.6 mg / cm 2 When the loading amount is changed, the specific discharge capacity is reduced, and the electrochemical performance of the room-temperature sodium-sulfur battery is reduced.

[0147] From the experimental data of examples 12-14, it can be seen that when the mass ratio of the tungsten diselenide / nitrogen-doped porous carbon composite material, the conductive agent, and the binder is (6-8):(3-1):1, the obtained modified separator sample is assembled into a sodium-sulfur battery, and it is tested to have a higher specific discharge capacity, and the electrochemical performance of the room-temperature sodium-sulfur battery is excellent. When the mass ratio of the components is changed, the specific discharge capacity is reduced, and the electrochemical performance of the room-temperature sodium-sulfur battery is reduced.

[0148] From the experimental data of examples 15-18, it can be seen that when the specific surface area of the nitrogen-doped porous carbon is 100-500 m 2 / g; and the pore volume of the nitrogen-doped porous carbon is 0.12 cm 3 / g-0.65 cm 3 / g, the modified separator sample coated with the tungsten diselenide / nitrogen-doped porous carbon composite material is assembled into a sodium-sulfur battery, and it is tested to have a higher specific discharge capacity, and the electrochemical performance of the room-temperature sodium-sulfur battery is excellent. When the specific surface area and / or the pore volume of the nitrogen-doped porous carbon is changed, the specific discharge capacity is reduced, and the electrochemical performance of the room-temperature sodium-sulfur battery is reduced.

[0149] The application modifies the di-selenium tungsten / nitrogen-doped porous carbon composite material to inhibit the shuttle effect caused by the dissolution of polysulfides into the organic electrolyte during the room-temperature sodium-sulfur battery cycle process. The di-selenium tungsten / nitrogen-doped porous carbon composite material is filled with di-selenium tungsten in the pore channel of the nitrogen-doped porous carbon, wherein the polar di-selenium tungsten can bond with the soluble polysulfides to limit the polysulfide shuttle; at the same time, the porous carbon can adsorb the polysulfides through the van der Waals force and active sites; and the nitrogen doped in the porous carbon can provide more active sites to adsorb the polysulfides, thereby effectively inhibiting the "shuttle effect", effectively reducing the loss of active substances, and significantly enhancing the stability of the battery. By coating the coating material containing the di-selenium tungsten / nitrogen-doped porous carbon composite material on the side of the separator close to the positive electrode to obtain a modified separator, the electrochemical performance of the room-temperature sodium-sulfur battery can be significantly improved.

[0150] The preferred embodiments of the application have been described above with the specific examples, but the application is not limited to the above examples, and various modifications and changes can be made by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A tungsten diselenide / nitrogen-doped porous carbon composite material, characterized in that, The tungsten diselenide / nitrogen-doped porous carbon composite material comprises nitrogen-doped porous carbon, and pores of the nitrogen-doped porous carbon are filled with tungsten diselenide; wherein a mass ratio of the tungsten diselenide to carbon in the nitrogen-doped porous carbon is (10-30):(90-70), and a doping amount of nitrogen in the tungsten diselenide / nitrogen-doped porous carbon composite material is 1-5 at.%. 2.The tungsten diselenide / nitrogen-doped porous carbon composite material of claim 1, wherein, The particle size of the tungsten diselenide / nitrogen-doped porous carbon composite material is 0.5-1.0 μm. And / or, the specific surface area of the nitrogen-doped porous carbon is 100-500 m 2 / g; the pore volume of the nitrogen-doped porous carbon is 0.12 cm 3 / g-0.65 cm 3 / g. 3.The tungsten diselenide / nitrogen-doped porous carbon composite material of claim 1, wherein, The preparation method of the nitrogen-doped porous carbon comprises the following steps: mixing porous carbon and melamine, and performing heat treatment to obtain the nitrogen-doped porous carbon.

4. The tungsten diselenide / nitrogen-doped porous carbon composite of claim 3, wherein, A mass ratio of the porous carbon to the melamine is 1:1-10. And / or, a temperature of the heat treatment is 800-850 ℃, and a time of the heat treatment is 4-6 h.

5. The method for preparing a tungsten diselenide / nitrogen-doped porous carbon composite according to any one of claims 1 to 4, characterized by, The method comprises the following steps: nitrogen-doped porous carbon is provided, the tungsten diselenide / nitrogen-doped porous carbon composite material is prepared by mixing the nitrogen-doped porous carbon, Na2WO4·2H2O, selenium powder, an acid solution, and an auxiliary agent through a solvothermal method.

6. The method for preparing a tungsten diselenide / nitrogen-doped porous carbon composite according to claim 5, characterized by, The acid solution comprises at least one of a hydrochloric acid solution, an acetic acid solution, and a phosphoric acid solution. 7.The method of claim 5, wherein the method further comprises a step of mixing the tungsten diselenide and the nitrogen-doped porous carbon. The acid solution is a hydrochloric acid solution. 8.The method of claim 5, wherein the method is characterized by, The auxiliary agent comprises at least one of N2H4·2H2O, carbon disulfide, and quinoline. 9.The method of claim 5, wherein the method further comprises a step of mixing the tungsten diselenide and the nitrogen-doped porous carbon. The auxiliary agent is N2H4·2H2O. 10.The method of claim 5, wherein the method is characterized by, A reaction temperature of the solvothermal method is 180-250 ℃, and a reaction time of the solvothermal method is 10-16 h. 11.The method of claim 5, wherein the method is characterized by, A molar ratio of Na2WO4·2H2O to the selenium powder is 1:1-5. And / or, a mass ratio of Na2WO4·2H2O to the nitrogen-doped porous carbon is (5-10):

1.

12. A modified separator, characterized by, The modified separator comprises a separator, a modified coating layer is arranged on a side of the separator close to a positive electrode, and a material of the modified coating layer comprises the tungsten diselenide / nitrogen-doped porous carbon composite material, a conductive agent, and a binder.

13. The modified separator of claim 12, wherein, The loading amount of the tungsten diselenide / nitrogen-doped porous carbon composite on the separator is 0.2-0.6 mg / cm 2 .

14. The modified separator of claim 12, wherein The conductive agent comprises at least one of Super P, activated carbon, and acetylene black. And / or, the binder comprises at least one of PVDF, CMC, and SBR. And / or, a material of the separator comprises at least one of glass fiber, polypropylene, and polyethylene. And / or, a mass ratio of the tungsten diselenide / nitrogen-doped porous carbon composite material, the conductive agent, and the binder is (6-8):(3-1):

1.

15. The modified separator of claim 12, wherein, The conductive agent is Super P.

16. The modified separator of claim 12, wherein The binder is PVDF.

17. The modified separator of claim 12, wherein The material of the separator is glass fiber.

18. The method of producing a modified separator according to any one of claims 12 to 17, characterized in that, The preparation method comprises the following steps: The modified coating layer slurry is obtained by mixing the tungsten diselenide / nitrogen-doped porous carbon composite material, the conductive agent, and the binder, grinding, and then dispersing in a solvent; the modified coating layer slurry is coated on the side of the separator close to the positive electrode, and the solvent is removed to obtain the modified separator.

19. The method of claim 18, wherein the modified separator is prepared by a process comprising: The solvent comprises at least one of NMP, deionized water, and DMF.

20. The method of claim 18, wherein the modified separator is prepared by the steps of: The solvent is NMP.

21. Application of the tungsten diselenide / nitrogen-doped porous carbon composite material in any one of claims 1-11 or the modified separator in any one of claims 12-20 in a sodium-sulfur battery.

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