A cobalt vanadium sulfide / graphene three-dimensional composite aerogel and a preparation method thereof

Abstract

This invention relates to the field of sodium-ion battery anode material technology, and discloses a cobalt vanadium sulfide / graphene three-dimensional composite aerogel and its preparation method, comprising: mixing cobalt salt, vanadium salt, urea, thioacetamide and water and reacting at high temperature to obtain cobalt vanadium sulfide; mixing cobalt vanadium sulfide, graphene oxide (GO) dispersion, multi-walled carbon nanotubes and polyvinyl alcohol solution for pre-crosslinking; then adding ascorbic acid and high-temperature hydrothermal molding to obtain composite hydrogel; solvent displacement and freeze-drying of composite hydrogel to obtain composite aerogel; and finally calcining under an inert atmosphere to obtain the product. The three-dimensional aerogel framework of this invention can uniformly and confinedly disperse cobalt vanadium sulfide, inhibiting the agglomeration of nanoparticles; the interconnected three-dimensional pore structure can provide rapid diffusion channels for electrolytes / reactants, shortening the ion and molecule transport distance, significantly improving the material mass transfer efficiency, and exhibiting superior reaction kinetics in energy storage, catalysis, adsorption and other applications.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, and more specifically, to a cobalt vanadium sulfide / graphene three-dimensional composite aerogel and its preparation method. Background Technology

[0002] With the escalating global energy crisis and the rapid development of energy storage technologies, sodium-ion batteries, due to their abundant and widely distributed sodium resources, low cost, and electrochemical performance similar to lithium-ion batteries, have become one of the most promising new energy storage devices for large-scale energy storage and portable electronic devices. The negative electrode, as a core component of sodium-ion batteries, directly determines the battery's energy density, cycle life, rate performance, and safety. Its performance is one of the key bottlenecks restricting the industrialization of sodium-ion batteries. Therefore, developing high-performance, low-cost, and directly applicable sodium-ion battery negative electrode materials has become a research hotspot and urgent need in the current energy storage field.

[0003] Currently, sodium-ion battery anode materials are mainly classified into several categories, including carbon-based materials, alloy-based materials, and conversion-type sulfide materials. However, each type of material has insurmountable defects in practical applications. Carbon-based materials (such as hard carbon, soft carbon, and graphene) possess good conductivity and structural stability, but their theoretical specific capacity is low, typically only 200-350 mAh / g, which is insufficient to meet the application requirements of high-energy-density sodium-ion batteries. Furthermore, graphene, as a novel carbon material, is prone to self-stacking of its sheets, leading to a decrease in ion transport efficiency. Additionally, the fragile mechanical properties of pure graphene aerogel limit its practical application. Alloy-based materials (such as Sn, Sb, and P-based materials) have high theoretical specific capacities, but the sodium-ion insertion / extraction process causes severe volume expansion (up to 300%-500%), leading to electrode pulverization and detachment, which in turn causes rapid degradation of battery cycle performance, severely affecting the long-term service stability of the battery.

[0004] Conversion-type sulfide materials (such as cobalt sulfide and vanadium sulfide) have become an important research direction for sodium-ion battery anode materials due to their high theoretical specific capacity, excellent ionic conductivity, and good sodium storage activity. Among them, cobalt-vanadium sulfide combines the synergistic advantages of cobalt sulfide and vanadium sulfide, has abundant sodium storage mechanisms, a theoretical capacity significantly higher than that of traditional carbon-based materials, and excellent electrochemical kinetic performance, and is considered a highly promising high-performance sodium-ion battery anode material. However, the conductivity of these materials still needs to be improved, and they also suffer from significant volume expansion and structural collapse during charge-discharge cycles, which makes it difficult to fully realize their electrochemical performance and limits their large-scale application.

[0005] To address the shortcomings of single materials, researchers have attempted to synthesize aerogels by combining cobalt sulfide, vanadium sulfide, and other materials with graphene, hoping to achieve a synergistic improvement in electrochemical performance and structural stability.

[0006] However, existing composite aerogel materials still suffer from many key problems, severely restricting their direct application as negative electrode sheets for sodium-ion batteries. The primary problem is their fragile mechanical properties: the three-dimensional network structure of existing composite aerogels mainly relies on van der Waals forces or weak chemical bonds between graphene sheets, lacking effective stress transfer paths. This results in low compressive strength and poor toughness, making them susceptible to collapse, cracking, or even pulverization under external forces during electrode preparation, battery assembly, transportation, and charge-discharge cycles. They cannot withstand the mechanical stress during battery assembly and service, making them unsuitable for direct use as negative electrode sheets for sodium-ion batteries. Additional binders and conductive agents must be added, and molding must rely on current collectors. This not only increases the complexity and cost of electrode preparation but may also affect the conductivity and ion transport efficiency of the electrode due to the insulating properties of the binder, thereby impairing the overall electrochemical performance of the battery.

[0007] In addition to the above, existing cobalt vanadium sulfide / graphene-related composite aerogels and other types of negative electrode sheets also have the following problems: First, cobalt vanadium sulfide has poor dispersion in the graphene matrix and is prone to agglomeration, making it difficult to fully expose its sodium storage active sites and obstructing ion transport pathways, thus failing to fully utilize its high capacity advantage; Second, the pore structure of composite aerogels is difficult to control. If the pores are too large, the structural stability will further decrease, and if the pores are too small, it will hinder the rapid diffusion of sodium ions, resulting in poor battery rate performance; Third, the preparation process of some composite aerogels is complex and the reaction conditions are harsh (such as high temperature, high pressure, and long-term reaction), resulting in high production costs. Moreover, toxic and harmful reagents may be used in the preparation process, which does not meet the requirements of green and environmentally friendly industrialization; Fourth, existing negative electrode sheets generally have problems with low initial coulombic efficiency and insufficient cycle stability. Either the side reaction is aggravated due to the instability of the SEI film, or the active material is lost due to the destruction of the material structure, making it difficult to meet the requirements of long-term battery service in practical applications.

[0008] In summary, current sodium-ion battery anode sheets suffer from numerous defects, including low capacity, severe volume expansion, insufficient conductivity, and poor cycle stability. Existing composite aerogels, due to their fragile mechanical properties, cannot be directly used as anode sheets, and they also have issues related to dispersibility, pore structure, and fabrication processes. Therefore, developing a cobalt-vanadium sulfide / graphene three-dimensional composite aerogel with a simple fabrication process, low cost, excellent mechanical properties, and direct usability as a sodium-ion battery anode sheet, to address the aforementioned technical pain points of existing anode sheets, is of significant practical importance and application value for promoting the industrial application of sodium-ion batteries. Summary of the Invention

[0009] In view of this, the present invention proposes a cobalt vanadium sulfide / graphene three-dimensional composite aerogel and its preparation method, aiming to solve the problems of low capacity, severe volume expansion, insufficient conductivity and poor cycle stability of sodium-ion battery negative electrode sheets in the current technology.

[0010] This invention proposes a method for preparing a cobalt vanadium sulfide / graphene three-dimensional composite aerogel, comprising the following steps: 1) Cobalt salt, vanadium salt, urea, thioacetamide and water are mixed to obtain a mixed reaction solution, and the mixed reaction solution is reacted at high temperature to obtain cobalt vanadium sulfide; 2) Mix and stir the cobalt vanadium sulfide, graphene oxide (GO) dispersion, multi-walled carbon nanotubes, and polyvinyl alcohol solution obtained in step 1) to carry out a pre-crosslinking reaction; 3) Add ascorbic acid to the pre-crosslinked system and perform high-temperature hydrothermal molding to obtain a composite hydrogel; 4) The composite hydrogel was solvent-displaced with anhydrous ethanol and then freeze-dried to obtain the composite aerogel; 5) The composite aerogel was calcined under an inert atmosphere to obtain a cobalt vanadium sulfide / graphene three-dimensional composite aerogel.

[0011] Preferably, the molar ratio of cobalt, urea, thioacetamide and vanadium in the mixed reaction solution in step 1) is 1:10~50:1~10:0.2~1; The reaction in step 1) is carried out at a temperature of 80~160℃ for 8~24h.

[0012] Preferably, the concentration of the graphene oxide (GO) dispersion in step 2) is 5-8 g / L; The concentration of the polyvinyl alcohol solution is 3~8 g / L; The multi-walled carbon nanotubes have a length of 0.5~2μm and an outer diameter of 20~30nm.

[0013] Preferably, the mixing ratio of cobalt vanadium sulfide, graphene oxide (GO) dispersion, multi-walled carbon nanotubes, and polyvinyl alcohol solution in step 2) is 0.5~1g: 8~12mL: 0.5~1g: 4~6mL; The temperature of the pre-crosslinking reaction is 0~5℃ and the time is 30~40min.

[0014] Preferably, the amount of ascorbic acid added in step 3) is 30-40% of the mass of graphene oxide (GO).

[0015] Preferably, the high-temperature hydrothermal forming in step 3) is performed at a temperature of 160~180℃ for 10~15h.

[0016] Preferably, the number of solvent replacements in step 4) is 3 to 5 times; The freeze-drying temperature is -30~-45℃, and the time is 24h.

[0017] Preferably, the calcination treatment in step 5) is performed at a temperature of 200~220℃ for 120~180 min.

[0018] This invention provides a cobalt vanadium sulfide / graphene three-dimensional composite aerogel prepared by the above preparation method.

[0019] This invention also provides an application of the aforementioned cobalt vanadium sulfide / graphene three-dimensional composite aerogel as a negative electrode sheet for sodium-ion batteries.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention uses graphene oxide as a substrate and ascorbic acid as a reducing crosslinking agent to construct a three-dimensional graphene network framework. At the same time, polyvinyl alcohol, multi-walled carbon nanotubes and cobalt vanadium sulfide are composited, and the multi-component crosslinking forms a stable three-dimensional composite aerogel network. Compared with the defects of existing powdered cobalt vanadium sulfide which is prone to agglomeration and stacking, the three-dimensional aerogel framework can uniformly confine and disperse cobalt vanadium sulfide, and completely suppress the agglomeration and clumping of nanoparticles. The preparation method of solvent replacement + freeze drying retains rich micropores, mesopores and macropores, which is different from the problem of pore collapse and low porosity caused by traditional high temperature direct drying. The interconnected three-dimensional pore structure can provide rapid diffusion channels for electrolytes / reactants, shorten the ion and molecule transport distance, significantly improve the mass transfer efficiency of materials, and have better reaction kinetics in energy storage, catalysis, adsorption and other application scenarios.

[0021] (2) Graphene sheets provide a large-area conductive substrate, and carbon nanotubes interpenetrate to build conductive bridges, which synergistically reduce the overall internal resistance of the material and make up for the lack of conductivity of cobalt vanadium sulfide semiconductors, and significantly improve the electron conduction rate; cobalt vanadium bimetallic sulfide provides abundant active sites: cobalt and vanadium bimetallic synergistic effect, compared with single metal sulfides, has better redox reversibility, more defect sites and electrochemical active centers, which greatly improves energy storage capacity and electrocatalytic / photocatalytic reaction efficiency; polyvinyl alcohol, as a flexible adhesive, enhances the interfacial bonding force between inorganic sulfides and carbon-based materials, and solves the industry pain point of large interfacial contact resistance and easy peeling and detachment of heterogeneous materials.

[0022] (3) The present invention adds an inert atmosphere high-temperature calcination activation process after aerogel molding. High-temperature calcination can further reduce graphene oxide and carbonize organic additives, strengthen the graphitization degree of carbon-based skeleton, and improve the mechanical strength and resistance to compression and deformation of the material itself. High-temperature activation can optimize the crystal structure of cobalt vanadium sulfide, remove residual functional groups and impurities inside the material, and enhance the integrity and chemical stability of sulfide crystals. The carbon-sulfide heterostructure forms a strong chemical bond, which effectively alleviates the volume expansion and structural pulverization of active materials during charging and discharging and continuous catalytic reaction. Compared with conventional composite materials, the long-term cycle stability and reusability are greatly improved. Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0024] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0025] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0026] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0027] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0028] This invention proposes a method for preparing a cobalt vanadium sulfide / graphene three-dimensional composite aerogel, comprising the following steps: 1) Cobalt salt, vanadium salt, urea, thioacetamide and water are mixed to obtain a mixed reaction solution, and the mixed reaction solution is reacted at high temperature to obtain cobalt vanadium sulfide; 2) Mix and stir the cobalt vanadium sulfide, graphene oxide (GO) dispersion, multi-walled carbon nanotubes, and polyvinyl alcohol solution obtained in step 1) to carry out a pre-crosslinking reaction; 3) Add ascorbic acid to the pre-crosslinked system and perform high-temperature hydrothermal molding to obtain a composite hydrogel; 4) The composite hydrogel was solvent-displaced with anhydrous ethanol and then freeze-dried to obtain the composite aerogel; 5) The composite aerogel was calcined under an inert atmosphere to obtain a cobalt vanadium sulfide / graphene three-dimensional composite aerogel.

[0029] In this invention, the molar ratio of cobalt, urea, thioacetamide and vanadium in the mixed reaction solution in step 1) is 1:10~50:1~10:0.2~1, preferably 1:20~40:3~8:0.4~0.8, more preferably 1:25~35:4~6:0.5~0.7, and even more preferably 1:30:5:0.6.

[0030] In this invention, the temperature of the reaction in step 1) is 80~160℃, preferably 100~140℃, more preferably 110~130℃, and even more preferably 120℃; the time is 8~24h, preferably 12~20h, more preferably 14~18h, and even more preferably 16h.

[0031] In this invention, step 1) further includes a step of separating and purifying cobalt vanadium sulfide, specifically by filtering, washing and drying the reactants; the filtration is performed using a microporous membrane with a cutoff size of 0.45 μm; the microporous membrane is one of polyethersulfone membrane, polyvinylidene fluoride membrane, and regenerated cellulose membrane.

[0032] In this invention, the concentration of the graphene oxide (GO) dispersion in step 2) is 5-8 g / L, preferably 5.5-7.5 g / L, more preferably 6-7 g / L, and even more preferably 6.5 g / L.

[0033] In this invention, the preparation method of the graphene oxide GO dispersion in step 2) includes the following steps: after mixing graphene oxide GO with water, ultrasonic treatment is carried out in an ice-water bath for 30-60 minutes, followed by magnetic stirring for 12-24 hours to ensure that the GO sheets are completely peeled off and evenly dispersed, and a brownish-yellow stable suspension is obtained, which is the graphene oxide GO dispersion.

[0034] In this invention, the concentration of the polyvinyl alcohol solution is 3~8 g / L, preferably 4~7 g / L, more preferably 5~6.5 g / L, and even more preferably 5.8 g / L.

[0035] In this invention, the length of the multi-walled carbon nanotube is 0.5~2μm, preferably 0.8~1.8μm, more preferably 1.0~1.6μm, and even more preferably 1.3μm; the outer diameter is 20~30nm, preferably 22~28nm, more preferably 24~26nm, and even more preferably 25nm.

[0036] In this invention, the mixing ratio of cobalt vanadium sulfide, graphene oxide (GO) dispersion, multi-walled carbon nanotubes, and polyvinyl alcohol solution in step 2) is 0.5~1g:8~12mL:0.5~1g:4~6mL, preferably 0.6~0.9g:9~11mL:0.6~0.9g:4.5~5.5mL, further preferably 0.7~0.8g:9.5~10.5mL:0.7~0.8g:4.8~5.2mL, and even more preferably 0.75g:10mL:0.75g:5mL.

[0037] In this invention, the mixing order of cobalt vanadium sulfide, graphene oxide GO dispersion, multi-walled carbon nanotubes and polyvinyl alcohol solution in step 2) is as follows: first mix cobalt vanadium sulfide, graphene oxide GO dispersion and multi-walled carbon nanotubes, and then add polyvinyl alcohol solution.

[0038] In this invention, the temperature of the pre-crosslinking reaction is 0~5℃, preferably 1~4℃, more preferably 2~3℃; the time is 30~40min, preferably 32~38min, more preferably 34~36min, and more preferably 35min.

[0039] In this invention, the amount of ascorbic acid added in step 3) is 30-40% of the mass of graphene oxide (GO), preferably 32-38%, more preferably 34-36%, and even more preferably 35%.

[0040] In this invention, the temperature of the high-temperature hydrothermal forming in step 3) is 160~180℃, preferably 165~175℃, more preferably 168~172℃, and even more preferably 170℃; the time is 10~15h, preferably 11~14h, more preferably 12~13h, and even more preferably 12.5h.

[0041] In this invention, the solvent replacement in step 4) is performed 3 to 5 times.

[0042] In this invention, the freeze-drying temperature is -45~-30℃, preferably -42~-33℃, and more preferably -40~-35℃; the time is 24h.

[0043] In this invention, the calcination temperature in step 5) is 200~220℃, preferably 205~215℃, more preferably 208~212℃, and even more preferably 210℃; the time is 120~180min, preferably 130~170min, more preferably 140~160min, and even more preferably 150min.

[0044] This invention provides a cobalt vanadium sulfide / graphene three-dimensional composite aerogel prepared by the above preparation method.

[0045] This invention also provides an application of the aforementioned cobalt vanadium sulfide / graphene three-dimensional composite aerogel as a negative electrode sheet for sodium-ion batteries.

[0046] Example 1 (1) 0.5 mmol CoCl2·6H2O, 0.5 mmol VCl3, 15 mmol urea, and 2.5 mmol thioacetamide were added to deionized water and magnetically stirred until homogeneous. The mixture was then transferred to a reaction vessel with a polytetrafluoroethylene substrate and reacted at 120°C for 24 h. After the reaction, the slurry was filtered through a microporous membrane (polyethersulfone membrane) with a cutoff size of 0.45 μm. Impurities were removed by repeated washing with water and ethanol. Finally, the product was dried overnight in an oven at 120°C and then ground to obtain cobalt vanadium sulfide.

[0047] (2) Mix 1g of cobalt vanadium sulfide prepared in step (1), 10mL of graphene oxide GO dispersion with a concentration of 5g / L, and 1g of multi-walled carbon nanotubes with a length of 0.5~2μm and an outer diameter of 20~30nm (purchased from Aladdin Reagent, CAS No.: 308068-56-6) and ultrasonically disperse for 10min. Then add 5mL of polyvinyl alcohol solution with a concentration of 5g / L and mix. Perform a pre-crosslinking reaction in an ice-water bath (0℃) for 30min.

[0048] (3) Add ascorbic acid to the pre-crosslinked system. The amount added is 40% of the mass of graphene oxide (GO) (0.025g). Heat the mixture to 180°C in a reaction vessel with polytetrafluoroethylene substrate and perform high-temperature hydrothermal molding for 12h to obtain composite hydrogel.

[0049] (4) The composite hydrogel was subjected to solvent replacement three times with anhydrous ethanol, then frozen at -25°C for 8 hours, and then transferred to a freeze dryer and freeze-dried at -40°C for 14 hours to obtain the composite aerogel.

[0050] (5) After the composite aerogel is heated to room temperature, it is transferred to a tube furnace, and inert gas nitrogen is introduced to remove air. Then, the temperature is raised to 200℃ at a rate of 5℃ / min and calcined for 150min to obtain cobalt vanadium sulfide / graphene three-dimensional composite aerogel.

[0051] Example 2 (1) 0.5 mmol CoCl2·6H2O, 0.5 mmol VCl3, 15 mmol urea, and 2.5 mmol thioacetamide were added to deionized water and magnetically stirred until homogeneous. The mixture was then transferred to a reaction vessel with a polytetrafluoroethylene substrate and reacted at 120°C for 24 h. After the reaction, the slurry was filtered through a microporous membrane (polyethersulfone membrane) with a cutoff size of 0.45 μm. Impurities were removed by repeated washing with water and ethanol. Finally, the product was dried overnight in an oven at 120°C and then ground to obtain cobalt vanadium sulfide.

[0052] (2) Mix 0.6g of cobalt vanadium sulfide prepared in step (1), 9mL of graphene oxide GO dispersion with a concentration of 6.5g / L, and 0.9g of multi-walled carbon nanotubes with a length of 0.5~2μm and an outer diameter of 20~30nm, and then ultrasonically disperse for 10min. Then add 4.5mL of polyvinyl alcohol solution with a concentration of 5.8g / L and mix. Perform a pre-crosslinking reaction at 0℃ for 35min.

[0053] (3) Add ascorbic acid to the pre-crosslinked system. The amount added is 30% of the mass of graphene oxide (GO). Heat the mixture to 160°C in a reaction vessel with a polytetrafluoroethylene substrate and perform high-temperature hydrothermal molding for 10 hours to obtain a composite hydrogel.

[0054] (4) The composite hydrogel was subjected to solvent replacement four times with anhydrous ethanol, then frozen at -25°C for 8 hours, and then transferred to a freeze dryer and freeze-dried at -30°C for 24 hours to obtain the composite aerogel.

[0055] (5) After the composite aerogel is heated to room temperature, it is transferred to a tube furnace, and inert gas nitrogen is introduced to remove air. Then, the temperature is raised to 210℃ at a rate of 5℃ / min and calcined for 180min to obtain cobalt vanadium sulfide / graphene three-dimensional composite aerogel.

[0056] Example 3 (1) 0.5 mmol CoCl2·6H2O, 0.5 mmol VCl3, 15 mmol urea, and 2.5 mmol thioacetamide were added to deionized water and magnetically stirred until homogeneous. The mixture was then transferred to a reaction vessel with a polytetrafluoroethylene substrate and reacted at 120°C for 24 h. After the reaction, the slurry was filtered through a microporous membrane (polyethersulfone membrane) with a cutoff size of 0.45 μm. Impurities were removed by repeated washing with water and ethanol. Finally, the product was dried overnight in an oven at 120°C and then ground to obtain cobalt vanadium sulfide.

[0057] (2) Mix 0.5g of cobalt vanadium sulfide prepared in step (1), 8mL of graphene oxide GO dispersion with a concentration of 7.5g / L, and 0.8g of multi-walled carbon nanotubes with a length of 0.5~2μm and an outer diameter of 20~30nm, and then ultrasonically disperse for 10min. Then add 6mL of polyvinyl alcohol solution with a concentration of 8g / L and mix. Perform a pre-crosslinking reaction at 0℃ for 38min.

[0058] (3) Add ascorbic acid to the pre-crosslinked system. The amount added is 35% of the mass of graphene oxide (GO). The mixture is heated to 165°C in a reaction vessel with a polytetrafluoroethylene substrate and hydrothermally molded for 13 hours to obtain a composite hydrogel.

[0059] (4) The composite hydrogel was subjected to solvent replacement three times with anhydrous ethanol, then frozen at -25°C for 8 hours, and then transferred to a freeze dryer and freeze-dried at -35°C for 24 hours to obtain the composite aerogel.

[0060] (5) After the composite aerogel is heated to room temperature, it is transferred to a tube furnace, and inert gas nitrogen is introduced to remove air. Then, the temperature is raised to 210℃ at a rate of 5℃ / min and calcined for 140min to obtain cobalt vanadium sulfide / graphene three-dimensional composite aerogel.

[0061] Example 4 (1) 0.5 mmol CoCl2·6H2O, 0.5 mmol VCl3, 15 mmol urea, and 2.5 mmol thioacetamide were added to deionized water and magnetically stirred until homogeneous. The mixture was then transferred to a reaction vessel with a polytetrafluoroethylene substrate and reacted at 120°C for 24 h. After the reaction, the slurry was filtered through a microporous membrane (polyethersulfone membrane) with a cutoff size of 0.45 μm. Impurities were removed by repeated washing with water and ethanol. Finally, the product was dried overnight in an oven at 120°C and then ground to obtain cobalt vanadium sulfide.

[0062] (2) Mix 0.8g of cobalt vanadium sulfide prepared in step (1), 11mL of graphene oxide GO dispersion with a concentration of 5.5g / L, and 0.6g of multi-walled carbon nanotubes with a length of 0.5~2μm and an outer diameter of 20~30nm, and then ultrasonically disperse for 10min. Then add 5.2mL of polyvinyl alcohol solution with a concentration of 4g / L and mix. Perform a pre-crosslinking reaction at 0℃ for 35min.

[0063] (3) Add ascorbic acid to the pre-crosslinked system. The amount added is 38% of the mass of graphene oxide (GO). The mixture is heated to 170°C in a reaction vessel with a polytetrafluoroethylene substrate and hydrothermally molded for 15 hours to obtain a composite hydrogel.

[0064] (4) The composite hydrogel was subjected to solvent replacement three times with anhydrous ethanol, then frozen at -25°C for 8 hours, and then transferred to a freeze dryer and freeze-dried at -40°C for 24 hours to obtain the composite aerogel.

[0065] (5) After the composite aerogel is heated to room temperature, it is transferred to a tube furnace, and inert gas nitrogen is introduced to remove air. Then, the temperature is raised to 212℃ at a rate of 5℃ / min and calcined for 170min to obtain cobalt vanadium sulfide / graphene three-dimensional composite aerogel.

[0066] Example 5 (1) 0.5 mmol CoCl2·6H2O, 0.5 mmol VCl3, 15 mmol urea, and 2.5 mmol thioacetamide were added to deionized water and magnetically stirred until homogeneous. The mixture was then transferred to a reaction vessel with a polytetrafluoroethylene substrate and reacted at 120°C for 24 h. After the reaction, the slurry was filtered through a microporous membrane (polyethersulfone membrane) with a cutoff size of 0.45 μm. Impurities were removed by repeated washing with water and ethanol. Finally, the product was dried overnight in an oven at 120°C and then ground to obtain cobalt vanadium sulfide.

[0067] (2) Mix 0.7g of cobalt vanadium sulfide prepared in step (1), 11mL of graphene oxide GO dispersion with a concentration of 8g / L, and 0.75g of multi-walled carbon nanotubes with a length of 0.5~2μm and an outer diameter of 20~30nm, and then ultrasonically disperse for 10min. Then add 4.8mL of polyvinyl alcohol solution with a concentration of 8g / L and mix. Perform a pre-crosslinking reaction at 0℃ for 34min.

[0068] (3) Add ascorbic acid to the pre-crosslinked system. The amount added is 34% of the mass of graphene oxide (GO). The mixture is heated to 168°C in a reaction vessel with a polytetrafluoroethylene substrate and hydrothermally molded for 14 hours to obtain a composite hydrogel.

[0069] (4) The composite hydrogel was subjected to solvent replacement three times with anhydrous ethanol, then frozen at -25°C for 8 hours, and then transferred to a freeze dryer and freeze-dried at -45°C for 24 hours to obtain the composite aerogel.

[0070] (5) After the composite aerogel is heated to room temperature, it is transferred to a tube furnace, and inert gas nitrogen is introduced to remove air. Then, the temperature is raised to 210℃ at a rate of 5℃ / min and calcined for 150min to obtain cobalt vanadium sulfide / graphene three-dimensional composite aerogel.

[0071] Comparative Example 1 Example 1: The cobalt vanadium sulfide prepared in step (1).

[0072] Comparative Example 2 (1) 0.5 mmol CoCl2·6H2O, 0.5 mmol VCl3, 15 mmol urea, and 2.5 mmol thioacetamide were added to deionized water and magnetically stirred until homogeneous. The mixture was then transferred to a reaction vessel with a polytetrafluoroethylene substrate and reacted at 120°C for 24 h. After the reaction, the slurry was filtered through a microporous membrane (polyethersulfone membrane) with a cutoff size of 0.45 μm. Impurities were removed by repeated washing with water and ethanol. Finally, the product was dried overnight in an oven at 120°C and then ground to obtain cobalt vanadium sulfide.

[0073] (2) Mix 1g of cobalt vanadium sulfide prepared in step (1), 10mL of graphene oxide GO dispersion with a concentration of 5g / L, and 1g of multi-walled carbon nanotubes with a length of 0.5~2μm and an outer diameter of 20~30nm (purchased from Aladdin Reagent, CAS No.: 308068-56-6) and ultrasonically disperse for 10min. Then add 5mL of polyvinyl alcohol solution with a concentration of 5g / L and mix. Perform a pre-crosslinking reaction in an ice-water bath (0℃) for 30min.

[0074] (3) Add ascorbic acid to the pre-crosslinked system. The amount added is 40% of the mass of graphene oxide (GO) (0.025g). Heat the mixture to 180°C in a reaction vessel with polytetrafluoroethylene substrate and perform high-temperature hydrothermal molding for 12h to obtain composite hydrogel.

[0075] (4) The composite hydrogel was subjected to solvent replacement three times with anhydrous ethanol, then frozen at -25°C for 8 hours, and then transferred to a freeze dryer and freeze-dried at -40°C for 14 hours to obtain the composite aerogel.

[0076] Compared with Example 1, the composite aerogel in this comparative example was not calcined to enhance its strength.

[0077] Comparative Example 3 Preparation of reduced graphene oxide aerogel: Ascorbic acid was added to 10 mL of graphene oxide (GO) dispersion with a concentration of 5 g / L. The amount added was 40% (0.025 g) of the mass of graphene oxide (GO). The mixture was then heated to 95 °C in a polytetrafluoroethylene (PTFE) substrate and hydrothermally molded for 3 h to obtain a three-dimensional network hydrogel.

[0078] The hydrogel was soaked and washed in water for 2 days, with the water changed every 8 hours to remove impurities. Then, the hydrogel was subjected to solvent replacement three times with anhydrous ethanol, and then frozen at -25°C for 8 hours. Finally, it was transferred to a freeze-drying device and freeze-dried at -40°C for 14 hours to obtain reduced graphene oxide aerogel.

[0079] The physical properties of the aerogel materials prepared in Examples 1-5, Comparative Examples 2 and 3 were tested using the following specific methods: 1. The apparent density of the aerogel was tested according to standard GB / T 6343-2009; 2. The specific surface area of ​​the aerogel was tested using the BET / N2 adsorption method; 3. The thermal conductivity of the aerogel was tested according to standard GB-T 10294-2008; 4. The mechanical properties of the aerogel, including tensile strength and flexural strength, were determined using a universal testing machine.

[0080] The test results are shown in Table 1.

[0081] Table 1. Test results of physical properties of aerogel materials prepared in Examples 1-5, Comparative Examples 2 and 3

[0082] The electrochemical performance of the materials prepared in Examples 1-5 and Comparative Example 1 was tested using the following methods: The aerogels prepared in Examples 1-5 can be directly used as the negative electrode of sodium-ion batteries; The cobalt vanadium sulfide prepared in Comparative Example 1 was used as a sodium-ion battery anode using conventional methods. The preparation method is as follows: The cobalt vanadium sulfide prepared in Comparative Example 1 was mixed uniformly with a conductive agent (conductive carbon black) and a binder (PVDF polyvinylidene fluoride) at a mass ratio of 5:2:1, and then coated onto the surface of the current collector (aluminum foil with a thickness of 80 μm) at a coating amount of 0.03 mg / cm². 2 Then it is placed in a roller press (pressure of 10MPa) and pressed for 30 minutes, and finally dried in an oven at 100℃ for 24 hours to obtain the negative electrode sheet of sodium ion battery.

[0083] Assemble a sodium-ion battery as follows: Prussian blue, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1. An equal volume of 1-methylpyrrolidone was added, and the mixture was ground and coated onto the surface of aluminum foil. After drying and rolling, the positive electrode of a sodium-ion battery was obtained. The cells are stacked in the following order: negative electrode → separator → positive electrode → separator → negative electrode... to form a battery cell (the number of negative electrodes is 10). The area of ​​the negative electrode is 1.3 times that of the positive electrode, and the outermost layer is all negative electrodes. The separator is made of polypropylene membrane. Place the stacked battery cells into an aluminum-plastic film bag, heat seal it, and leave the liquid injection port open; A 1 mol / L NaPF6 solution was used as the electrolyte, and the solvent was a mixed solvent of EC (ethylene carbonate): EMC (ethyl methyl carbonate): DMC (dimethyl carbonate) = 1:1:1, with 5 wt% fluoroethylene carbonate added as a film-forming aid. The electrolyte is injected into the aluminum-plastic film bag, with the injection volume being 5 times the total mass of the electrode. The bag is left to stand for 12 hours to age, and then the aluminum-plastic film bag is sealed. The initially assembled battery is charged with a small current (0.02C) until the upper limit voltage is reached to complete the formation. After formation, the air inside the bag is removed, it is sealed again, and then placed inside a hard outer shell to obtain the battery to be tested.

[0084] The following tests were performed on the battery under test: 1. Place it at room temperature and perform constant current charge and discharge at a current density of 500 mAg-1. Calculate its initial discharge specific capacity and discharge specific capacity after 100 constant current charge and discharge cycles.

[0085] 2. Test the battery at 2A·g -1 The discharge capacity after 500 cycles at a high current density.

[0086] The test results are shown in Table 2.

[0087] Table 2. Electrochemical performance test results of the composite materials prepared in Examples 1-5 and Comparative Example 1.

[0088] As shown in Table 1, the cobalt vanadium sulfide / graphene three-dimensional composite aerogel prepared in this invention has a moderate apparent density and a high specific surface area, thanks to the three-dimensional cross-linked network constructed by graphene, multi-walled carbon nanotubes and polyvinyl alcohol, as well as the hierarchical porous structure retained by freeze-drying. Compared with the uncalcined Comparative Example 2 and the pure graphene aerogel Comparative Example 3, the tensile strength, flexural strength and electrical conductivity of the sample after calcination in an inert atmosphere are significantly improved. Calcination not only strengthens the graphitization degree and mechanical stability of the carbon-based skeleton, but also optimizes the crystal structure of cobalt vanadium sulfide and enhances the interfacial bonding force, enabling the material to possess the excellent mechanical strength and electrical conductivity required for self-supporting negative electrode sheets. As shown in Table 2, the three-dimensional composite aerogel, when used as the negative electrode of a sodium-ion battery, exhibits an initial discharge specific capacity of 970.25~984.13 mAh / g, significantly higher than that of the comparative example 1 using pure cobalt vanadium sulfide powder electrode. After 100 cycles, the capacity retention rate is approximately 77%, and even after 500 cycles at a high current of 2 A / g, it still maintains a high capacity of 473.96~490.81 mAh / g. This is because the three-dimensional interconnected channels accelerate sodium ion transport, the uniformly dispersed cobalt vanadium sulfide fully exposes active sites, and the stable composite framework effectively alleviates volume expansion and structural pulverization during charge and discharge, ultimately achieving a synergistic improvement in high specific capacity, excellent cycle stability, and high rate performance.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a cobalt vanadium sulfide / graphene three-dimensional composite aerogel, characterized in that, Includes the following steps: 1) Cobalt salt, vanadium salt, urea, thioacetamide and water are mixed to obtain a mixed reaction solution, and the mixed reaction solution is reacted at high temperature to obtain cobalt vanadium sulfide; 2) Mix and stir the cobalt vanadium sulfide, graphene oxide (GO) dispersion, multi-walled carbon nanotubes, and polyvinyl alcohol solution obtained in step 1) to carry out a pre-crosslinking reaction; 3) Add ascorbic acid to the pre-crosslinked system and perform high-temperature hydrothermal molding to obtain a composite hydrogel; 4) The composite hydrogel was solvent-displaced with anhydrous ethanol and then freeze-dried to obtain the composite aerogel; 5) The composite aerogel was calcined under an inert atmosphere to obtain a cobalt vanadium sulfide / graphene three-dimensional composite aerogel.

2. The method for preparing a cobalt vanadium sulfide / graphene three-dimensional composite aerogel according to claim 1, characterized in that, In step 1), the molar ratio of cobalt, urea, thioacetamide and vanadium in the mixed reaction solution is 1:10~50:1~10:0.2~1; The reaction in step 1) is carried out at a temperature of 80~160℃ for 8~24h.

3. The method for preparing a cobalt vanadium sulfide / graphene three-dimensional composite aerogel according to claim 1, characterized in that, The concentration of the graphene oxide (GO) dispersion in step 2) is 5-8 g / L; The concentration of the polyvinyl alcohol solution is 3~8 g / L; The multi-walled carbon nanotubes have a length of 0.5~2μm and an outer diameter of 20~30nm.

4. The method for preparing a cobalt vanadium sulfide / graphene three-dimensional composite aerogel according to claim 1, characterized in that, The mixing ratio of cobalt vanadium sulfide, graphene oxide (GO) dispersion, multi-walled carbon nanotubes, and polyvinyl alcohol solution in step 2) is 0.5~1g: 8~12mL: 0.5~1g: 4~6mL; The temperature of the pre-crosslinking reaction is 0~5℃ and the time is 30~40min.

5. The method for preparing a cobalt vanadium sulfide / graphene three-dimensional composite aerogel according to claim 1, characterized in that, The amount of ascorbic acid added in step 3) is 30-40% of the mass of graphene oxide (GO).

6. The method for preparing a cobalt vanadium sulfide / graphene three-dimensional composite aerogel according to claim 1, characterized in that, The high-temperature hydrothermal forming in step 3) is performed at a temperature of 160~180℃ for 10~15h.

7. The method for preparing a cobalt vanadium sulfide / graphene three-dimensional composite aerogel according to claim 1, characterized in that, The solvent replacement in step 4) is performed 3 to 5 times; The freeze-drying temperature is -30~-45℃, and the time is 24h.

8. The method for preparing a cobalt vanadium sulfide / graphene three-dimensional composite aerogel according to claim 1, characterized in that, The calcination treatment in step 5) is carried out at a temperature of 200~220℃ for 120~180 min.

9. The cobalt vanadium sulfide / graphene three-dimensional composite aerogel prepared by the preparation method of any one of claims 1 to 8.

10. The application of the cobalt vanadium sulfide / graphene three-dimensional composite aerogel as described in claim 9 as a negative electrode sheet for sodium-ion batteries.

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