F-CoSe2 nanoflower material with high specific surface area and preparation method thereof

Abstract

The invention discloses an F-CoSe2 nanoflower material with a high specific surface area and a preparation method of the F-CoSe2 nanoflower material. The method comprises the following steps: mixing polyimide powder, cobalt nitrate and polyvinylpyrrolidone, performing ultrasonic treatment, evaporation and grinding, and sintering in a nitrogen atmosphere to prepare a C / Co / CoO composite material; calcining the composite material and selenium powder in argon-hydrogen mixed gas to obtain a CoSe2 / C material; finally, the material and ammonium fluoride are subjected to a fluorination reaction in the argon atmosphere, and the CoSe2 nanoflower material is prepared. The invention also relates to the material prepared by the method. The F-CoSe2 nanoflower material has a flower-like structure assembled by nanosheets, has high specific surface area and abundant pores, optimizes the electronic structure of the material through F doping, exposes more active sites, has strong physical adsorption and efficient chemical catalytic conversion capabilities on polysulfide in a lithium-sulfur battery, can significantly inhibit a shuttle effect, and has a good application prospect in the field of lithium-sulfur batteries. The battery performance is improved.

Description

Technical Field

[0002] This invention relates to a method for preparing catalyst materials, and more particularly to a high specific surface area F-CoSe2 nanoflower material and its preparation method. Background Technology

[0004] Lithium-sulfur batteries are considered strong candidates for the next generation of high-energy storage systems due to their high theoretical specific capacity and high energy density. However, their practical application is still limited by several key challenges: (1) the "shuttle effect" of soluble long-chain polysulfides between the positive and negative electrodes leads to loss of active materials and rapid capacity decay; (2) the slow conversion reaction kinetics of polysulfides results in high reaction overpotential and low sulfur utilization; (3) the insulating properties of sulfur and its discharge products lead to severe electrochemical polarization.

[0005] To suppress the shuttle effect, researchers have developed various functional membrane modification layers. Among them, transition metal selenides such as CoSe2, due to their strong chemisorption of polysulfides and excellent catalytic activity, can promote the efficient conversion of polysulfides, thereby significantly improving the cycle performance of batteries. However, traditional CoSe2 materials still suffer from problems such as limited specific surface area, insufficient exposure of active sites, and insufficient intrinsic conductivity, which limit further improvement in their catalytic efficiency.

[0006] Therefore, developing a novel membrane modification material that combines high specific surface area, abundant active sites, and optimized electronic structure is of great significance for improving the overall electrochemical performance of lithium-sulfur batteries. Summary of the Invention

[0008] This application provides a high specific surface area F-CoSe2 nanoflower material and its preparation method, which solves the technical problems of limited specific surface area and insufficient exposure of active sites in traditional CoSe2 materials in the prior art, and achieves simultaneous improvement of the material's physical adsorption capacity and chemical catalytic activity for polysulfides.

[0009] This application provides a method for preparing F-CoSe2 nanoflower materials with high specific surface area, characterized by the following steps:

[0010] (1) Polyimide powder, cobalt nitrate and polyvinylpyrrolidone are mixed in ultrapure water at a mass ratio of 8~10:1:1. After ultrasonic dispersion, the mixture is stirred at 70~90℃ until the solvent is completely evaporated to obtain a solid mixture. The solid mixture is ground and then sintered at high temperature under a nitrogen atmosphere to obtain a C / Co / CoO composite material. (2) Selenium powder and the C / Co / CoO composite material are loaded into a ceramic boat at a mass ratio of 4~6:1 and placed in the downstream and upstream of a tube furnace, respectively. After high-temperature calcination in an argon-hydrogen mixture for 5~7 hours, CoSe2 / C material is obtained. (3) The CoSe2 / C material obtained in step (2) and ammonium fluoride are placed in the downstream and upstream of the ceramic boat at a mass ratio of 2~4:1, respectively, and fluorinated under an argon atmosphere to obtain F-CoSe2 nanoflower material.

[0011] Preferably, the polyimide powder is prepared as follows: 30 g / L of each polyimide powder is used... -1 benzidine and 60 gL -1 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride was dissolved in dimethylformamide solution, stirred evenly at room temperature, and then transferred to a high-pressure reactor and reacted at 180–200℃ for 6–8 h. After drying, polyimide powder was obtained.

[0012] Preferably, in step (1), the mass ratio of polyimide powder, cobalt nitrate and polyvinylpyrrolidone is 10:1:1.

[0013] Preferably, the concentration of the argon-hydrogen mixture in step (2) is 10%.

[0014] Preferably, in step (3), the mass ratio of CoSe2 / C material to ammonium fluoride is 3:1.

[0015] Preferably, the fluorination reaction in step (3) specifically involves heating the CoSe2 / C composite material, which was placed downstream and upstream of the tube furnace in step (2) respectively, with ammonium fluoride in an argon atmosphere to 180-200°C at a heating rate of 2°C / min, for a heat treatment time of 2 hours, and holding at that temperature for 1-3 hours. After natural cooling, the F-CoSe2 nanoflower material is obtained.

[0016] This invention also provides a high specific surface area F-CoSe2 nanoflower material, which is prepared by any of the above preparation methods.

[0017] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0018] 1. This invention employs a multi-step preparation process combining high-temperature sintering and gas-phase selenization / fluorination with polyimide as the carbon source and template, successfully synthesizing a fluorine-doped CoSe2 nanoflower material. The F-CoSe2 nanoflower material effectively solves the problems of low specific surface area and insufficient active sites in traditional CoSe2 materials, thereby significantly improving physicochemical adsorption capacity and providing abundant interfaces for the anchoring and conversion of polysulfides.

[0019] 2. In this embodiment of the invention, the introduction of fluorine atoms for doping effectively solves the problems of weak surface polarity and limited catalytic conversion ability of CoSe2 materials for polysulfides. The introduction of F atoms optimizes the electronic structure of CoSe2, increases the positive charge of Co sites, and thus achieves stronger chemisorption and faster catalytic conversion kinetics for polysulfides, effectively suppressing the shuttle effect. Attached Figure Description

[0021] Figure 1 The image shows scanning electron microscope (SEM) images of F-CoSe2 nanoflower material, CoSe2 nanoflower material, and intermediate products of Example 1.

[0022] Figure 2 The X-ray photoelectron spectroscopy of the F-CoSe2 nanoflower material in Example 1 is shown.

[0023] Figure 3 The images show the X-ray diffraction (XRD) patterns of the F-CoSe2 nanoflower material and the CoSe2 nanoflower material from Example 1.

[0024] Figure 4 (a) is a SEM cross-sectional view of the F-CoSe2@PP membrane of Example 2; Figure 4 (b) Optical images of the F-CoSe2@PP diaphragm and the CoSe2@PP diaphragm of Example 2; Figure 4 (c) is a test diagram of the contact angle between the F-CoSe2@PP diaphragm and the CoSe2@PP diaphragm in Example 2 and the electrolyte.

[0025] Figure 5 (ab) are potentiostatic intermittent titration (GITT) diagrams of lithium-sulfur batteries using the F-CoSe2@PP separator of Example 2 and lithium-sulfur batteries using the CoSe2@PP separator for batteries with different modified separators. Figure 5 (c) The potential difference at the Li2S nucleation and activation points of different lithium-sulfur batteries using the F-CoSe2@PP separator of Example 2 and the lithium-sulfur battery using the CoSe2@PP separator. Detailed Implementation

[0027] This application provides a high specific surface area F-CoSe2 nanoflower material and its preparation method. By leveraging the high specific surface area of ​​the nanoflower material to enhance physicochemical adsorption capacity and increase reaction activation sites to improve catalytic activity, it addresses the technical problems of limited specific surface area and insufficient exposure of active sites in traditional CoSe2 materials.

[0028] The technical solution in this application is to solve the above problems, and the overall approach is as follows:

[0029] By designing a C / Co / CoO precursor derived from polyimide, a structural template and carbon source are provided for the subsequent selenization reaction. This precursor is then converted into a CoSe2 / C composite material with a high specific surface area nanoflower structure via gas-phase selenization. Finally, a low-temperature gas-phase fluorination strategy is employed to introduce F atoms into the CoSe2 lattice, thereby regulating its electronic structure and creating more active sites. The F-CoSe2 nanoflower material of this invention combines the advantages of high specific surface area physical adsorption with fluorine-doped enhanced chemical adsorption / catalytic function. When used to modify lithium-sulfur battery separators, it can simultaneously achieve efficient anchoring and rapid conversion of polysulfides, as well as a significant improvement in overall battery performance.

[0030] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0031] Example 1

[0032] Preparation of F-CoSe2 nanoflower materials

[0033] (1) Preparation of polyimide precursor: First, prepare 1.8 g benzidine, 3.6 g 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride and 60 mL dimethylformamide (DMF). Dissolve benzidine in 30 mL of DMF and stir magnetically until completely dissolved to obtain solution A. Then, dissolve 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride in another 30 mL of DMF to obtain solution B. Under continuous stirring, slowly add solution B to solution A and react at room temperature for 4-6 h to obtain a viscous polyimide acid solution. Subsequently, transfer the polyimide acid solution to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and heat-treat at 180 °C for 10 h to complete the imidization reaction. After the reaction, cool naturally to room temperature and wash the obtained solid product three times with anhydrous ethanol and deionized water to thoroughly remove residual solvent and byproducts. Finally, the product was dried in a vacuum drying oven at 80°C for 12 hours, and then ground to obtain a brownish-yellow polyimide powder.

[0034] (2) Preparation and selenization of C / Co / CoO composite material: Weigh 100 mg of polyimide powder from step (1), 10 mg of cobalt nitrate, and 10 mg of polyvinylpyrrolidone, mix them, add the mixture to 100 mL of ultrapure water, and sonicate at room temperature for 1 hour to form a uniform suspension, so that cobalt ions and polyvinylpyrrolidone are uniformly dispersed on the surface of nanospheres. Then, heat the suspension at 80 °C and stir magnetically for 6 hours to completely evaporate the solvent and obtain a solid mixture. Grind the solid mixture thoroughly in an agate mortar, and then transfer it to a quartz boat in a tube furnace. Heat to 600 °C at a heating rate of 5 °C / min under a nitrogen atmosphere, and sinter at this temperature for 6 hours. After natural cooling, the C / Co / CoO composite material is obtained.

[0035] 100 mg of the C / Co / CoO composite material and 500 mg of selenium powder were respectively loaded into two ceramic boats. The ceramic boat containing the selenium powder was placed in the upstream zone of a tube furnace, and the ceramic boat containing the C / Co / CoO composite material was placed in the downstream zone. Argon gas was first introduced to purge air, and then switched to an argon-hydrogen mixture (V(H2) / V(Ar) = 10 / 90, total gas flow rate 100 sccm). The temperature was increased to 400℃ at a heating rate of 5℃ / min, and calcined at this temperature for 6 hours for selenization. After the reaction was completed, the mixture was cooled to room temperature under argon protection to obtain the CoSe2 / C nanoflower material.

[0036] (3) Fluoride doping: Weigh 100 mg of the CoSe2 / C nanoflower material obtained in step (2) and 500 mg of ammonium fluoride, and place them in two ceramic boats respectively. Place the ceramic boat containing ammonium fluoride in the upstream zone of the tube furnace and the ceramic boat containing the CoSe2 / C nanoflower material in the downstream zone. In an argon atmosphere, heat the material to 180°C at a heating rate of 2°C / min, heat-treat for 2 h, and hold at this temperature for 2 h to perform fluoride doping. After the reaction is complete, allow it to cool naturally to room temperature, wash the product three times with anhydrous ethanol to remove residual fluoride salts, and finally vacuum dry at 60°C for 6 h to obtain F-CoSe2 nanoflower material.

[0037] Please refer to Figure 1 , Figure 1 Scanning electron microscope images of F-CoSe2 nanoflower materials show that the F-CoSe2 nanoflowers maintain a high specific surface area structure throughout multiple preparation and reaction processes. This structure, assembled from many nanosheet units, exhibits excellent structural stability. From the start of the reaction to the formation of the final product, this unique nanostructure consistently maintains its high specific surface area and multiple active sites, thus providing continuous and efficient catalysis for the electrochemical reaction.

[0038] Please refer to Figure 2 , Figure 2 XPS analysis revealed the surface chemical composition of the F-CoSe2 nanoflower material. The full spectrum showed characteristic peaks for Co 2p, O 1s, F 1s, C 1s, and Se 3d, indicating the presence of these elements. In the partial spectra, the C 1s peak provided information about carbon; the splitting and shifting of the Co 2p peak showed different valence states of Co; and the Se 3d peak reflected the chemical state of Se. Compared with CoSe2 / C, the presence of the F 1s peak in F-CoSe2 / C further confirms the successful introduction of F.

[0039] Please refer to Figure 3 , Figure 3 The XRD patterns of F-CoSe2 nanoflower materials and CoSe2 / C nanoflower materials were compared. F atom doping caused the XRD peaks of F-CoSe2 nanoflower materials to shift to a larger angle overall. This is mainly because the radius of F atoms is small, and doping leads to a reduction in lattice spacing.

[0040] The present invention has the following technical effects:

[0041] 1. In Embodiment 1 of the present invention, a fluorine-doped CoSe2 / C nanoflower composite material is designed and synthesized as a commercial PP membrane modification material. The nanoflower structure design can increase the specific surface area of ​​the material and enrich the pore structure, thereby enhancing the adsorption efficiency of polysulfides and lithium-ion transport from a physical perspective.

[0042] 2. In the F-CoSe2 nanoflower material of Embodiment 1 of the present invention, the transition metal selenide enhances the catalytic conversion of polysulfides. F atom doping can adjust the electronic structure, increase the positive charge density of metal sites, provide more catalytic conversion active sites, and improve the catalytic efficiency of intermediate polysulfide conversion in lithium-sulfur batteries in practical applications.

[0043] Example 2

[0044] The F-CoSe2 nanoflower material obtained in Example 1 was mixed with a conductive agent (Super P) and a binder (PVDF) in a ratio of 8:1:1 and ground for 30 min. Then, an N-methylpyrrolidone (NMP) solution was added and the mixture was ground again to form a uniform slurry. The slurry was then coated onto a commercial PP membrane and dried in an oven at 60 °C for 10 hours to obtain the modified F-CoSe2@PP membrane.

[0045] The CoSe2 / C nanoflower material obtained in step (2) of Example 1 was mixed with conductive agent (Super P) and binder (PVDF) in a ratio of 8:1:1 and ground for 30 min. Then, N-methylpyrrolidone (NMP) solution was added and grinding was continued to form a uniform slurry. The slurry was then coated onto a commercial PP membrane and dried in an oven at 60 °C for 10 hours to obtain the modified CoSe2@PP membrane.

[0046] For performance evaluation of F-CoSe2@PP membrane and CoSe2@PP membrane, please refer to [reference needed]. Figure 4 , Figure 4 (a) shows that the thickness of the F-CoSe2@PP membrane is approximately 17 micrometers. Figure 4 (b) Shows the morphology of F-CoSe2@PP separator in three states: folded, folded, and unfolded. As can be seen from the figure, after folding and unfolding, the modified PP separator can recover to its initial state well, which indicates that it has good flexibility and recoverability, which helps to relieve mechanical stress and extend the battery's service life. Figure 4 (c) shows that after the electrolyte was added, the contact angle of CoSe2@PP was 19.3°, while that of F-CoSe2@PP was close to 0°, indicating that F-CoSe2@PP has superior wettability. This characteristic means that F-CoSe2@PP can more effectively promote the uniform distribution of electrolyte inside the battery and the rapid transport of lithium ions during charging and discharging, thereby improving the battery's charge-discharge efficiency and cycle stability.

[0047] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0048] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a high specific surface area F-CoSe2 nanoflower material, characterized in that, The method comprises the following steps: (1) mixing polyimide powder, cobalt nitrate and polyvinylpyrrolidone in a mass ratio of 8-10:1:1 in ultrapure water, dispersing by ultrasonic, stirring at 70-90 DEG C until the solvent is completely evaporated, to obtain a solid mixture; grinding the solid mixture and sintering under nitrogen atmosphere at high temperature to obtain a C / Co / CoO composite material; (2) loading selenium powder and the C / Co / CoO composite material in a mass ratio of 4-6:1 into porcelain boats and placing them in the downstream and upstream of a tube furnace respectively, calcining at high temperature in argon-hydrogen mixed gas for 5-7h to obtain a CoSe2 / C material; (3) placing the CoSe2 / C material prepared in step (2) and ammonium fluoride in a mass ratio of 2-4:1 in the downstream and upstream of porcelain boats respectively, and fluorinating in an argon atmosphere to obtain a F-CoSe2 nanoflower material.

2. The method for preparing a high specific surface area F-CoSe2 nanoflower material as described in claim 1, characterized in that, The polyimide powder preparation method is as follows: dissolving diphenylamine with a concentration of 30 g / L -1 and 3,3',4,4'-benzophenone tetracarboxylic dianhydride with a concentration of 60 g / L -1 in a dimethylformamide solution, stirring uniformly at room temperature, then transferring to a high-pressure reaction kettle at 180-200°C for continuous reaction for 6-8 h, and drying to obtain a polyimide powder.

3. The method according to claim 1, wherein the method comprises the steps of: (a) preparing a F-CoSe2 nanoflower material; (b) preparing a F-CoSe2 nanoflower material with a high specific surface area. In step (1), the mass ratio of polyimide powder, cobalt nitrate and polyvinylpyrrolidone is 10:1:

1.

4. The method according to claim 1, wherein the method is characterized by, In step (2), the concentration of argon-hydrogen mixed gas is 10%.

5. The method for preparing a high specific surface area F-CoSe2 nanoflower material as described in claim 1, characterized in that, In step (3), the mass ratio of CoSe2 / C material to ammonium fluoride is 3:

1.

6. The method according to claim 1, wherein the method is characterized by, In step (3), the fluorination reaction is specifically heating the CoSe2 / C composite material and ammonium fluoride in the downstream and upstream of the tube furnace in step (2) to 180-200 DEG C at a heating rate of 2 DEG C / min in an argon atmosphere, heat treatment time is 2h, and the temperature is kept for 1-3h, and then naturally cooled to obtain the F-CoSe2 nanoflower material.

7. A high specific surface area F-CoSe2 nanoflower material, characterized in that, The F-CoSe2 nanoflower material is prepared by the method of any one of claims 1-6.

Images