A polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material and its preparation method as well as a lithium-sulfur battery positive electrode and a lithium-sulfur battery

Abstract

The present invention discloses a polyaniline-coated porous rod-shaped vanadium nitride loaded with sulfur composite material, a preparation method thereof, a lithium-sulfur battery positive electrode, and a lithium-sulfur battery. The porous rod-shaped vanadium nitride material with a high specific surface area is synthesized by calcination in an inert atmosphere using metavanadate and melamine as raw materials; a vanadium nitride / sulfur composite material is then prepared by a sulfur fumigation method, and a polyaniline conductive layer is further coated on the surface of the composite material to improve the cycle stability and rate performance of the lithium-sulfur battery; the porous structure of the vanadium nitride can adsorb and accommodate more sulfur, providing sufficient space to overcome volume changes during the cycle, and the vanadium nitride has strong adsorption characteristics for polysulfides, inhibiting the shuttle effect of polysulfides; at the same time, the polyaniline coated on the surface of the vanadium nitride can enhance the conductivity of the composite material, improve the conductivity of the lithium-sulfur battery positive electrode, and effectively inhibit the diffusion of polysulfides into the electrolyte, thereby enhancing the cycle stability and rate performance of the lithium-sulfur battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur battery positive electrode materials, and particularly relates to a polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material and a preparation method thereof, as well as a lithium-sulfur battery positive electrode and a lithium-sulfur battery. Background Art

[0002] Lead-acid batteries, as the first rechargeable batteries used on a large scale, have the advantages of low cost, high safety, and no memory effect. However, they still have certain limitations in terms of energy density, cycle life, and environmental impact. Lithium-sulfur batteries can generate up to 1675 mAh g due to their inherent two-electron reaction system. -1 Specific capacity and 2600Wh kg -1 The high specific energy density of sulfur, its abundant storage in nature, low price and non-toxicity make it a widely used battery.

[0003] However, lithium-sulfur batteries have many problems that limit their practical application, mainly manifested in the poor conductivity of sulfur and its reduction product Li2S2 / Li2S, the volume expansion of the positive electrode material during charging, the dissolution and shuttle of polysulfides, and the corrosion and dendrite formation of the lithium negative electrode. These problems lead to low sulfur utilization and poor cycle stability, and at the same time significantly reduce the coulombic efficiency of lithium-sulfur batteries, shorten their lifespan, and reduce their energy density. Therefore, the further market application of lithium-sulfur batteries is limited. Summary of the Invention

[0004] To address the aforementioned technical issues and achieve rational regulation of polysulfides, the present invention provides a polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material and its preparation method. The preparation method is simple, and the resulting composite material has a large specific surface area. Its porous structure provides ample space for accommodating polysulfides, while also promoting lithium ion transport within the positive electrode material. The vanadium nitride in the material provides numerous adsorption active sites for polysulfides, effectively mitigating the shuttling effect of polysulfides between the positive and negative electrodes. Furthermore, a polyaniline coating on the outer layer not only improves the composite material's conductivity but also further prevents the diffusion of polysulfides into the electrolyte, thereby enhancing the cycle stability and rate performance of the lithium-sulfur battery.

[0005] The present invention also provides a lithium-sulfur battery positive electrode and a lithium-sulfur battery assembled therefrom, wherein the battery capacity is still as high as 735 mAh g after 150 cycles. -1 .

[0006] The technical solution adopted by the present invention is:

[0007] A method for preparing a polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material, the preparation method comprising the following steps:

[0008] (1) mixing metavanadate and melamine, and calcining them at 600-1000° C. in an inert atmosphere to prepare a porous rod-shaped vanadium nitride material;

[0009] (2) mixing the porous rod-shaped vanadium nitride material with sulfur powder, and sealing and heating in an inert atmosphere for sulfur fumigation to obtain a vanadium nitride / sulfur composite material;

[0010] (3) dispersing the aniline monomer and the vanadium nitride / sulfur composite material in a dilute sulfuric acid solution, adding a dilute sulfuric acid solution containing an initiator, stirring in an ice-water bath for reaction, and filtering, washing, and drying after the reaction to obtain the polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material.

[0011] In step (1), the calcination time is 2-6 hours; the calcination conditions are preferably heating at 700-800° C. for 3-5 hours.

[0012] The metavanadate is any one or more of sodium metavanadate, potassium metavanadate, and ammonium metavanadate; and the mass ratio of the metavanadate to melamine is 1:1-3.

[0013] In step (2), the mass ratio of the porous rod-shaped vanadium nitride material to the sulfur powder is 1:2-4.

[0014] In step (2), the sulfur fumigation is carried out by heating at 140-170° C. for 12-50 hours, preferably at 150-160° C. for 35-45 hours.

[0015] The inert atmosphere is argon or nitrogen atmosphere.

[0016] In step (3), the ratio of the amount of the aniline monomer, the vanadium nitride / sulfur composite material, and the initiator is 1-5 mL: 3-10 g: 10-60 g; and the initiator is ammonium persulfate or potassium persulfate.

[0017] In step (3), the concentration of the dilute sulfuric acid is 0.1 to 0.5 M, preferably 0.2 to 0.3 M; and the reaction time in an ice-water bath with stirring is 5 to 25 hours, preferably 10 to 20 hours.

[0018] In step (3), the concentration of the vanadium nitride / sulfur composite material in the dilute sulfuric acid solution is 1 to 10 g L -1 , preferably 5-7 g L -1 .

[0019] The present invention also provides a polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material prepared by the above preparation method.

[0020] The present invention also provides a lithium-sulfur battery positive electrode, which is prepared using the polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material as an active material.

[0021] The present invention also provides a lithium-sulfur battery, which is assembled with the lithium-sulfur battery positive electrode as the positive electrode, and has good stability and the battery capacity is still as high as 735mAh g after 150 cycles. -1 .

[0022] In the preparation method of the polyaniline-coated porous rod-shaped vanadium nitride loaded sulfur composite material provided by the present invention, metavanadate and melamine are first used as raw materials, calcined in an inert atmosphere, and a porous rod-shaped vanadium nitride material with an ultra-high specific surface area (up to 222.8 m 2 g -1 ). The chemical reactions involved in the above reaction are as follows:

[0023] C3H6N6+3NaVO3→3VN+3NaOH+3CO2+NH3+N2

[0024] Then, using the sulfur fumigation method, the vanadium nitride and sulfur powder are sealed in an inert atmosphere and heated, so that the sulfur powder sublimates into sulfur vapor and is loaded on the surface of the vanadium nitride to obtain a vanadium nitride / sulfur composite material; finally, the above materials and aniline monomer are dispersed in dilute sulfuric acid. The dilute sulfuric acid solution can promote the dissolution of the aniline monomer. Then, an initiator is added, and under the conditions of an ice water bath, a layer of polyaniline is coated on the surface of the vanadium nitride / sulfur composite material to further improve its conductivity and inhibit the shuttling of lithium polysulfide, ultimately improving the cycle stability of the battery.

[0025] The synthesis method of the polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material disclosed in the present invention is simple and environmentally friendly. The porous structure of vanadium nitride can adsorb and accommodate more sulfur, thereby increasing the sulfur loading capacity. In addition, vanadium nitride has a large number of strong adsorption active sites for polysulfides, which can effectively slow down the shuttle effect of polysulfides between the positive and negative electrodes. At the same time, the surface-coated conductive polymer can enhance the conductivity of the composite material, improve the conductivity of the positive electrode of the lithium-sulfur battery, and further slow down the shuttle effect of polysulfides between the positive and negative electrodes, thereby enhancing the cycle stability and rate performance of the lithium-sulfur battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is an SEM image of vanadium nitride prepared in Example 1;

[0027] Figure 2 This is the XRD pattern of the vanadium nitride prepared in Example 1;

[0028] Figure 3 Nitrogen adsorption / desorption curve (A) and pore size distribution curve (B) of vanadium nitride prepared in Example 1;

[0029] Figure 4 This is a SEM image of the vanadium nitride / sulfur composite material prepared in Example 1;

[0030] Figure 5 This is the XRD pattern of the vanadium nitride / sulfur composite material prepared in Example 1;

[0031] Figure 6 This is an SEM image of the polyaniline-coated porous rod-shaped vanadium nitride-supported sulfur composite material prepared in Example 1;

[0032] Figure 7 This is an SEM image of the porous rod-shaped vanadium nitride prepared in Example 2;

[0033] Figure 8 This is an SEM image of the porous rod-shaped vanadium nitride prepared in Example 3;

[0034] Figure 9 This is an SEM image of the porous rod-shaped vanadium nitride prepared in Example 4;

[0035] Figure 10 This is an SEM image of the porous rod-shaped vanadium nitride prepared in Example 5;

[0036] Figure 11 The mapping diagram of the polyaniline-coated porous rod-shaped vanadium nitride-supported sulfur composite material prepared in Example 5, (a) is a SEM image, (b), (c), (d), (e), and (f) are the mapping diagrams of V, N, C, S, and O, respectively;

[0037] Figure 12 TEM image of the polyaniline-coated porous rod-shaped vanadium nitride-supported sulfur composite material prepared in Example 5;

[0038] Figure 13 This is the XRD pattern of the polyaniline-coated porous rod-shaped vanadium nitride-supported sulfur composite material prepared in Example 5;

[0039] Figure 14 These are Raman images of the porous rod-shaped vanadium nitride, porous rod-shaped vanadium nitride loaded with sulfur, and polyaniline-coated porous rod-shaped vanadium nitride loaded with sulfur composite material prepared in Example 5;

[0040] Figure 15 This is an SEM image of the polyaniline-coated porous rod-shaped vanadium nitride prepared in Comparative Example 1;

[0041] Figure 16 This is an SEM image of the polyaniline-coated porous rod-shaped vanadium nitride and sulfur-loaded composite material prepared in Comparative Example 1;

[0042] Figure 17 This is an SEM image of the layered vanadium nitride material prepared in Comparative Example 2;

[0043] Figure 18 This is the XRD pattern of the layered vanadium nitride material prepared in Comparative Example 2;

[0044] Figure 19 This is an SEM image of the layered vanadium nitride / sulfur composite material prepared in Comparative Example 2;

[0045] Figure 20 This is an SEM image of the polyaniline-coated layered vanadium nitride-loaded sulfur composite material prepared in Comparative Example 2;

[0046] Figure 21 The lithium-sulfur battery made of the polyaniline-coated porous rod-shaped vanadium nitride-supported sulfur composite material prepared in Example 5 was -1 Cycling stability test results under different current densities.

[0047] Figure 22 The lithium-sulfur battery prepared by polyaniline coated porous rod-shaped vanadium nitride and loaded sulfur composite material prepared in Comparative Example 1 was -1 Cycling stability test results under different current densities.

[0048] Figure 23 The lithium-sulfur battery made of the polyaniline-coated layered vanadium nitride-supported sulfur composite material prepared in Comparative Example 2 was -1 Cycling stability test results under different current densities. DETAILED DESCRIPTION

[0049] The present invention is described in detail below with reference to the embodiments.

[0050] Example 1

[0051] A method for preparing a polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material comprises the following steps:

[0052] (1) 0.1 g of ammonium metavanadate and 0.1 g of melamine solid powder were spread on a porcelain boat and placed in a high-temperature tube furnace. The reaction was carried out at 600 ° C for 6 h in a nitrogen atmosphere. After cooling, the product was washed with deionized water and anhydrous ethanol, filtered, and dried to obtain a porous rod-shaped vanadium nitride material. The SEM image is shown in FIG. Figure 1 As shown, the XRD pattern is Figure 2 As shown, the nitrogen adsorption / desorption curve and the corresponding pore size distribution curve are shown in Figure 3 shown; from Figure 1-3 It can be seen that this step prepared a porous structure of vanadium nitride material;

[0053] (2) 0.1 g of vanadium nitride powder and 0.2 g of sulfur powder were mixed evenly, transferred to a polytetrafluoroethylene vial, and sulfurized at 140 ° C for 50 h under an argon atmosphere to obtain a vanadium nitride / sulfur composite material. The SEM image is shown in the figure. Figure 4 As shown, the XRD pattern is Figure 5 As shown;

[0054] (3) Take 0.01 mL of aniline monomer and disperse it in 60 mL of 0.1 M dilute sulfuric acid solution, then add 0.1 g of vanadium nitride / sulfur composite material, and take 0.2 g of ammonium persulfate and disperse it in 40 mL of 0.1 M dilute sulfuric acid solution. After dissolution, mix the two solutions and stir in an ice-water bath to react for 5 h. After the reaction is completed, collect the product, wash it with deionized water and anhydrous ethanol, and dry it to obtain a polyaniline-coated porous rod-shaped vanadium nitride-supported sulfur composite material, the SEM image of which is shown in the figure below. Figure 6 It can be seen from the figure that polyaniline material is coated on the surface of the vanadium nitride / sulfur composite material.

[0055] Example 2

[0056] A method for preparing a polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material comprises the following steps:

[0057] (1) 0.1 g of potassium metavanadate and 0.2 g of melamine solid powder were spread on a porcelain boat and placed in a high-temperature tube furnace. The reaction was carried out at 700°C in an argon atmosphere for 5 h. After cooling, the product was washed with deionized water and anhydrous ethanol, filtered, and dried to obtain a porous rod-shaped vanadium nitride material;

[0058] (2) 0.1 g of porous rod-shaped vanadium nitride material was mixed evenly with 0.25 g of sulfur powder, transferred to a polytetrafluoroethylene vial, and fumigated with sulfur at 145 °C for 40 h under an argon atmosphere to obtain a vanadium nitride / sulfur composite material;

[0059] (3) Take 0.02 mL of aniline monomer and disperse it in 60 mL of 0.2 M dilute sulfuric acid solution, then add 0.1 g of vanadium nitride / sulfur composite material, and take another 0.3 g of ammonium persulfate and disperse it in 40 mL of 0.2 M dilute sulfuric acid solution. After dissolution, mix the two solutions and stir in an ice-water bath to react for 10 h. After the reaction is completed, collect the product, wash it with deionized water and anhydrous ethanol, and dry it. The SEM image of the porous rod-shaped vanadium nitride is shown below. Figure 7 Show.

[0060] Example 3

[0061] A method for preparing a polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material comprises the following steps:

[0062] (1) 0.1 g of sodium metavanadate and 0.3 g of melamine solid powder were spread on a porcelain boat and placed in a high-temperature tube furnace. The mixture was reacted at 800°C for 3 h in a nitrogen atmosphere. After cooling, the product was washed with deionized water and anhydrous ethanol, filtered, and dried to obtain a porous rod-shaped vanadium nitride material.

[0063] (2) 0.1 g of porous rod-shaped vanadium nitride material was mixed evenly with 0.3 g of sulfur powder, transferred to a polytetrafluoroethylene vial, and fumigated with sulfur at 150 °C for 30 h under an argon atmosphere to obtain a vanadium nitride / sulfur composite material;

[0064] (3) Take 0.03 mL of aniline monomer and disperse it in 60 mL of 0.3 M dilute sulfuric acid solution, then add 0.1 g of vanadium nitride / sulfur composite material, and take another 0.4 g of potassium persulfate and disperse it in 40 mL of 0.3 M dilute sulfuric acid solution. After dissolution, mix the two solutions and stir in an ice-water bath to react for 15 h. After the reaction is completed, collect the product, wash it with deionized water and anhydrous ethanol, and dry it. The SEM image of the porous rod-shaped vanadium nitride is shown below. Figure 8 Show.

[0065] Example 4

[0066] A method for preparing a polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material comprises the following steps:

[0067] (1) 0.2 g of ammonium metavanadate and 0.2 g of melamine solid powder were spread on a porcelain boat and placed in a high-temperature tube furnace. The reaction was carried out at 900 ° C for 2 h in an argon atmosphere. After cooling, the product was washed with deionized water and anhydrous ethanol, filtered, and dried to obtain a porous rod-shaped vanadium nitride material;

[0068] (2) 0.1 g of porous rod-shaped vanadium nitride material was mixed evenly with 0.35 g of sulfur powder, transferred to a polytetrafluoroethylene vial, and fumigated with sulfur at 160 °C for 20 h under an argon atmosphere to obtain a vanadium nitride / sulfur composite material;

[0069] (3) Take 0.04 mL of aniline monomer and disperse it in 60 mL of 0.4 M dilute sulfuric acid solution, then add 0.1 g of vanadium nitride / sulfur composite material, and take another 0.5 g of ammonium persulfate and disperse it in 40 mL of 0.4 M dilute sulfuric acid solution. After dissolution, mix the two solutions and stir in an ice-water bath to react for 20 h. After the reaction is completed, collect the product, wash it with deionized water and anhydrous ethanol, and dry it. The SEM image of the porous rod-shaped vanadium nitride is shown below. Figure 9 Show.

[0070] Example 5

[0071] A method for preparing a polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material comprises the following steps:

[0072] (1) 0.2 g of sodium metavanadate and 0.6 g of melamine solid powder were spread on a porcelain boat and placed in a high-temperature tube furnace. The mixture was reacted at 1000° C. for 2 hours in a nitrogen atmosphere. After cooling, the product was washed with deionized water and anhydrous ethanol, filtered, and dried to obtain a porous rod-shaped vanadium nitride material.

[0073] (2) 0.1 g of porous rod-shaped vanadium nitride material was mixed evenly with 0.4 g of sulfur powder, transferred to a polytetrafluoroethylene vial, and fumigated with sulfur at 170 °C for 12 h under an argon atmosphere to obtain a vanadium nitride / sulfur composite material;

[0074] (3) Take 0.02 mL of aniline monomer and disperse it in 60 mL of 0.5 M dilute sulfuric acid solution, then add 0.1 g of vanadium nitride / sulfur composite material, and take another 0.6 g of potassium persulfate and disperse it in 40 mL of 0.5 M dilute sulfuric acid solution. After dissolution, mix the two solutions and stir in an ice-water bath to react for 25 hours. After the reaction is completed, collect the product, wash it with deionized water and anhydrous ethanol, and dry it to obtain a polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material. The SEM image of the obtained porous rod-shaped vanadium nitride is shown as follows: Figure 10 The mapping diagram is as follows Figure 11 As shown in the TEM image Figure 12 As shown, the XRD pattern is Figure 13 The Raman images of vanadium nitride, vanadium nitride / sulfur and polyaniline coated porous rod-shaped vanadium nitride loaded sulfur composites are shown in Figure 2. Figure 14 shown.

[0075] Comparative Example 1

[0076] A method for preparing a polyaniline-coated porous rod-shaped vanadium nitride and sulfur-loaded composite material comprises the following steps:

[0077] (1) 0.2 g of sodium metavanadate and 0.6 g of melamine solid powder were spread on a porcelain boat and placed in a high-temperature tube furnace. The mixture was reacted at 1000° C. for 2 hours in a nitrogen atmosphere. After cooling, the product was washed with deionized water and anhydrous ethanol, filtered, and dried to obtain a porous rod-shaped vanadium nitride material.

[0078] (2) Take 0.02 mL of aniline monomer and disperse it in 60 mL of 0.5 M dilute sulfuric acid solution, then add 0.1 g of porous rod-shaped vanadium nitride material, and take another 0.6 g of potassium persulfate and disperse it in 40 mL of 0.5 M dilute sulfuric acid solution. After dissolution, mix the two solutions and stir in an ice-water bath to react for 25 hours. After the reaction is completed, collect the product, wash it with deionized water and anhydrous ethanol, and dry it to obtain a polyaniline-coated porous rod-shaped vanadium nitride material. The SEM image of the obtained polyaniline-coated porous rod-shaped vanadium nitride is shown as follows: Figure 15 Show.

[0079] (3) 0.1 g of polyaniline-coated porous rod-shaped vanadium nitride material was mixed evenly with 0.4 g of sulfur powder, transferred to a polytetrafluoroethylene vial, and sulfurized at 170 ° C for 12 h under an argon atmosphere to obtain a polyaniline-coated porous rod-shaped vanadium nitride and sulfur-loaded composite material. The SEM image of the obtained polyaniline-coated porous rod-shaped vanadium nitride and sulfur-loaded composite material is shown in FIG. Figure 16 Show.

[0080] Comparative Example 2

[0081] A method for preparing a polyaniline-coated layered vanadium nitride-loaded sulfur composite material comprises the following steps:

[0082] (1) 0.27 g of vanadium pentoxide and 0.25 g of Vc powder were dissolved in 40 mL of deionized water and transferred to a reactor. The mixture was reacted at 120° C. in an oven for 24 hours. After cooling, the product was filtered, washed, and dried with deionized water and anhydrous ethanol. The dried vanadium dioxide was spread on a porcelain boat and placed in a high-temperature tube furnace. The mixture was reacted at 600° C. in an ammonia atmosphere for 2 hours. After cooling, a porous layered vanadium nitride material was obtained. The SEM image of the obtained layered vanadium nitride material is shown in FIG. Figure 17 As shown, the XRD pattern is Figure 18 As shown;

[0083] (2) 0.1 g of porous layered vanadium nitride material was mixed evenly with 0.4 g of sulfur powder, and transferred to a polytetrafluoroethylene vial. The mixture was sulfurized at 170 ° C for 12 h under an argon atmosphere to obtain a layered vanadium nitride / sulfur composite material. The SEM image of the obtained layered vanadium nitride / sulfur composite material is shown in FIG. Figure 19 As shown;

[0084] (3) Take 0.02 mL of aniline monomer and disperse it in 60 mL of 0.5 M dilute sulfuric acid solution, then add 0.1 g of layered vanadium nitride / sulfur composite material, and take another 0.6 g of potassium persulfate and disperse it in 40 mL of 0.5 M dilute sulfuric acid solution. After dissolution, mix the two solutions and stir in an ice-water bath to react for 25 hours. After the reaction is completed, collect the product, wash it with deionized water and anhydrous ethanol, and dry it to obtain a polyaniline-coated layered vanadium nitride-supported sulfur composite material. The SEM image of the obtained polyaniline-coated layered vanadium nitride-supported sulfur composite material is shown as follows: Figure 20 Show.

[0085] Application Examples

[0086] Application of polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composites in lithium-sulfur batteries

[0087] The final products obtained in Example 5 and Comparative Examples 1 and 2 were used as the positive electrode active material of the lithium-sulfur battery. They were mixed with acetylene black and polyvinylidene fluoride (PVDF) in a ratio of 7:2:1, respectively, and prepared into a uniform slurry using N-methylpyrrolidone (NMP) as a solvent. The slurry was coated on aluminum foil, and the prepared coating was transferred to an oven and dried at 60°C for 6 hours. The sample was then transferred to a vacuum drying oven and vacuum dried at 60°C for 12 hours. It was then rolled with a tablet press and cut into pieces. The lithium sheet was used as the counter electrode, the electrolyte was a mixed organic solvent containing 1M lithium bis(trifluoromethanesulfonyl)imide (LITFSI), and the mixed organic solvent was a mixed solvent consisting of 1,3-dioxolane (DOL) and dimethyl ether (DME) in a volume ratio of 1:1. LiNO3 was added with a mass fraction of 2% as an electrolyte additive. A polypropylene film (Celgard 240) was used as a battery separator. The lithium-sulfur battery was assembled under an argon atmosphere.

[0088] The charge and discharge performance test was carried out using a battery tester. The positive electrode material of the lithium-sulfur battery of the polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material obtained in Example 5 was 0.5A g -1 The results of the cycling stability test at the current density are shown in the attached Figure 21 As shown, the battery capacity is still as high as 735mAh g after 150 cycles. -1 The positive electrode material of lithium-sulfur battery obtained in Comparative Example 1, which is a porous rod-shaped vanadium nitride coated with polyaniline and loaded with sulfur composite material, is 0.5A g -1 The results of the cycling stability test at the current density are shown in the attached Figure 22 As shown, the battery capacity is 446 mAh g after 150 cycles. -1 The porous rods coated with polyaniline lose their porous properties and cannot provide enough space to alleviate the volume expansion effect. In addition, the polyaniline is wrapped in the inner layer, so that the sulfur is exposed on the surface of the material, and the reaction also proceeds on the surface, which cannot achieve the effect of inhibiting the polysulfide shuttle, so the cycle stability is poor. The lithium-sulfur battery positive electrode material of the polyaniline-coated layered vanadium nitride-loaded sulfur composite material obtained in Comparative Example 2 has a low cycling stability at 0.5A g -1 The results of the cycling stability test at the current density are shown in the attached Figure 23 As shown, the battery capacity is 622 mAh g after 150 cycles. -1 It can be seen that the porous rod-shaped VN prepared in the embodiment of the present invention has a larger specific surface area than the layered vanadium nitride, and can adsorb and accommodate more sulfur, making the specific capacity higher than that of comparative example 2. Figure 21-23 It can be seen that only the polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material prepared according to the method of the present invention has the best cycle stability of the lithium-sulfur battery.

[0089] The detailed description of a polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material, its preparation method, lithium-sulfur battery positive electrode, and lithium-sulfur battery described above with reference to the embodiments is illustrative rather than restrictive. Several embodiments may be enumerated within the limited scope. Therefore, changes and modifications that do not depart from the overall concept of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material, characterized in that: The preparation method comprises the following steps: (1) mixing metavanadate and melamine, and calcining them at 600-1000° C. in an inert atmosphere to prepare a porous rod-shaped vanadium nitride material; (2) mixing the porous rod-shaped vanadium nitride material with sulfur powder, and sealing and heating in an inert atmosphere for sulfur fumigation to obtain a vanadium nitride / sulfur composite material; (3) dispersing the aniline monomer and the vanadium nitride / sulfur composite material in a dilute sulfuric acid solution, adding a dilute sulfuric acid solution containing an initiator, stirring in an ice-water bath for reaction, and filtering, washing, and drying after the reaction to obtain the polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material.

2. The preparation method according to claim 1, characterized in that In step (1), the calcination time is 2-6 hours.

3. The preparation method according to claim 1, characterized in that The metavanadate is any one or more of sodium metavanadate, potassium metavanadate, and ammonium metavanadate; and the mass ratio of the metavanadate to melamine is 1:1-3.

4. The preparation method according to claim 1, characterized in that In step (2), the mass ratio of the porous rod-shaped vanadium nitride material to the sulfur powder is 1:2-4.

5. The preparation method according to claim 1, characterized in that In step (2), the sulfur fumigation condition is heating at 140-170° C. for 12-50 hours.

6. The preparation method according to claim 1, characterized in that In step (3), the ratio of the amount of the aniline monomer, the vanadium nitride / sulfur composite material, and the initiator is 1-5 mL: 3-10 g: 10-60 g; and the initiator is ammonium persulfate or potassium persulfate.

7. The preparation method according to claim 1, characterized in that In step (3), the concentration of the dilute sulfuric acid is 0.1 to 0.5 M; and the reaction time in an ice-water bath with stirring is 5 to 25 hours.

8. The polyaniline-coated porous rod-shaped vanadium nitride-supported sulfur composite material prepared by the preparation method according to any one of claims 1 to 7.

9. A lithium-sulfur battery positive electrode, characterized in that: The lithium-sulfur battery positive electrode is prepared using the polyaniline-coated porous rod-shaped vanadium nitride-loaded sulfur composite material as the active material.

10. A lithium-sulfur battery, characterized in that: The positive electrode of the lithium-sulfur battery according to claim 9 is assembled as the positive electrode.

Images