Preparation method of carbon fiber-tungsten sulfide-graphene compound for sodium ion battery

Abstract

The embodiment of the specification discloses a preparation method of a carbon fiber-tungsten sulfide-graphene compound for a sodium ion battery, which comprises the following steps: S1, dissolving sodium tungstate, hydroxylamine hydrochloride, thiourea and sodium hydroxide in deionized water, and uniformly stirring to prepare a reaction solution; s2, mixing the reaction liquid obtained in the step S1 with carbon fibers and graphene in a reaction kettle, and carrying out hydrothermal reaction at a constant temperature; s3, filtering, cleaning and drying a product obtained in the step S2 to obtain a composite material precursor; and S4, carrying out calcination treatment on the composite material precursor in an inert gas atmosphere at 800-950 DEG C to obtain the carbon fiber-tungsten sulfide-graphene composite material.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a method for preparing a carbon fiber-tungsten sulfide-graphene composite for sodium-ion batteries. Background Technology

[0002] In recent years, the demand for resource-rich and low-cost rechargeable batteries in the energy storage field has become increasingly urgent. Sodium-ion and potassium-ion batteries, which have similar energy storage mechanisms to lithium-ion batteries but have a wider range of raw material sources, have become research hotspots for next-generation electrochemical energy storage technologies.

[0003] Electrode materials, especially anode materials, are one of the key factors determining the performance of sodium / potassium ion batteries. Currently, researchers have explored a variety of anode material systems, mainly including carbon-based materials (such as graphite and hard carbon), alloy materials, metal oxides, phosphides, and organic compounds. Among them, metal sulfides have attracted much attention due to their unique physicochemical properties and are considered to be highly promising anode material candidates. This is mainly due to the following advantages: (1) Relatively good reaction kinetics: Compared with the corresponding metal oxides, the bond energy of metal-sulfur bonds (MS) in metal sulfides is usually lower than that of metal-oxygen bonds (MO), which makes it easier for them to break and recombine in electrochemical reactions, which is beneficial to alkali metal ions (Na+, Na ... + / K + (2) High theoretical capacity: Metal sulfides can store ions through a variety of mechanisms, including intercalation reactions, conversion reactions, and even alloying reactions, accompanied by significant pseudocapacitive behavior. These mechanisms contribute to their high theoretical specific capacity. (3) Suitable interlayer channels: Many layered metal sulfides have large interlayer spacing, which provides convenient channels for the reversible insertion and extraction of large sodium / potassium ions, and helps to achieve rapid ion transport.

[0004] Nevertheless, metal sulfide anodes still face significant challenges on their path to practical application. First, their intrinsic electronic conductivity is typically low, limiting rate performance improvements. Second, during charge and discharge, especially during conversion reactions, the material undergoes significant volume expansion / contraction, leading to electrode structure pulverization and separation of the active material from the current collector, resulting in rapid capacity decay. Summary of the Invention

[0005] This invention provides a method for preparing a carbon fiber-tungsten sulfide-graphene composite for sodium-ion batteries, in order to solve the problems of poor conductivity and ion diffusion, slow interface / surface reaction kinetics, and significant volume expansion during sodium ion storage in existing metal sulfide-based electrode materials.

[0006] To achieve the above objectives, the present invention provides the following solution: A method for preparing a carbon fiber-tungsten sulfide-graphene composite for sodium-ion batteries includes the following steps: S1. Dissolve sodium tungstate, hydroxylamine hydrochloride, thiourea, and sodium hydroxide in deionized water and stir until homogeneous to prepare a reaction solution; S2. The reaction solution obtained in step S1 is mixed with carbon fiber and graphene in a reaction vessel and subjected to a hydrothermal reaction at a constant temperature. S3. The product obtained in step S2 is filtered, washed and dried to obtain the composite material precursor. S4. The composite material precursor is calcined at 800-950 degrees Celsius in an inert gas atmosphere to obtain carbon fiber-tungsten sulfide-graphene composite material.

[0007] Further, in the reaction solution described in step S1, the concentration of sodium tungstate is 0.05~0.2 mol / L, the concentration of hydroxylamine hydrochloride is 0.1~0.6 mol / L, the concentration of sodium hydroxide is 0.01~0.2 mol / L, and the concentration of thiourea is 0.1~0.9 mol / L.

[0008] Furthermore, the hydrothermal reaction described in step S2 is carried out under a pressure of 1.5~4.0 MPa and a constant temperature of 180~240 degrees Celsius.

[0009] Furthermore, after step S3, a repeating reaction step is included: the composite material precursor is mixed and reacted with the reaction solution newly prepared in step S1, and then washed and dried; the repeating reaction step is performed 1 to 5 times.

[0010] The present invention also provides a carbon fiber-tungsten sulfide-graphene composite material, which is prepared by the aforementioned method for preparing carbon fiber-tungsten sulfide-graphene composite for sodium-ion batteries.

[0011] Furthermore, the tungsten sulfide in the composite material is a nanoparticle of 100~200 nm, and the tungsten sulfide and graphene are anchored on the surface of the carbon fiber.

[0012] Furthermore, the density of the carbon fiber is 1.7~1.9 g / L. .

[0013] The present invention also provides a negative electrode for sodium-ion batteries, comprising the above-mentioned carbon fiber-tungsten sulfide-graphene composite material.

[0014] The present invention also provides a sodium-ion battery, comprising a carbon fiber-tungsten sulfide-graphene composite material prepared by any of the preceding methods, or a negative electrode for a sodium-ion battery prepared from the carbon fiber-tungsten sulfide-graphene composite material prepared by any of the preceding methods.

[0015] One embodiment of this specification can achieve at least the following beneficial effects: This invention provides a method for preparing a carbon fiber-tungsten sulfide-graphene composite material, utilizing graphene as a nucleation site for tungsten sulfide. Because the nucleation process of tungsten sulfide crystals is difficult to control during growth, often resulting in particle agglomeration or uneven nucleation, graphene has numerous active sites on its surface, such as unsaturated bonds at the edges and functional groups on the surface. These sites facilitate the attachment of tungsten sulfide precursors, i.e., tungsten-ion-containing and sulfur-containing substances, thereby enabling uniform nucleation and growth of tungsten sulfide on the graphene surface, thus solving the problem of difficult tungsten sulfide nucleation.

[0016] In the composite material obtained by this preparation method, carbon fiber acts as a reinforcement. Carbon fiber itself has a stable structure and high strength, supporting the overall structure of the composite material like a skeleton. When the composite material is used as an electrode in a sodium-ion battery, tungsten sulfide undergoes volume changes during sodium ion insertion and extraction. Carbon fiber disperses the stress caused by this volume change, preventing the composite material from cracking or pulverizing, thus maintaining structural stability. Simultaneously, tungsten sulfide nanoparticles are uniformly anchored on the carbon fiber surface. This uniformly anchored structure, on the one hand, improves charge transport performance because both carbon fiber and graphene have good conductivity, making electron transport paths smoother. On the other hand, the uniformly distributed tungsten sulfide increases the contact area between the electrode and the electrolyte, forming more electric double layers at the interface, thus giving the material better capacitance performance. Furthermore, using carbon fiber as a carbon source during preparation allows the carbon elements provided by the carbon fiber to better combine with other components, forming a more stable structure. When sodium ions are inserted or extracted, this structure is not easily deformed, thus improving the structural stability during sodium ion insertion and extraction. At the same time, the carbon structure brought by carbon fibers can also increase electrochemical active sites, making it easier for sodium ions to undergo electrochemical reactions and enhancing electrochemical activity. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments or prior art of this specification, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of a method for preparing a carbon fiber-tungsten sulfide-graphene composite for sodium-ion batteries provided by the present invention; Figure 2 Here is a scanning electron microscope image of the composite material prepared in Example 1 of the present invention; Figure 3The specific capacity and coulombic efficiency values ​​of the electrode prepared using the carbon fiber-tungsten sulfide-graphene composite material obtained in Example 1 were measured at different current densities. Figure 4 Here is a scanning electron microscope image of the composite material prepared in Example 2 of this invention; Figure 5 The specific capacity and coulombic efficiency values ​​of the electrode prepared using the carbon fiber-tungsten sulfide-graphene composite material obtained in Example 2 were measured at different current densities. Figure 6 Here is a scanning electron microscope image of the composite material prepared in Example 3 of the present invention; Figure 7 The specific capacity and coulombic efficiency values ​​of the electrode prepared using the carbon fiber-tungsten sulfide-graphene composite material obtained in Example 3 were measured at different current densities. Detailed Implementation

[0019] Preferred embodiments of the present invention will now be described in more detail. While preferred embodiments of the present invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products. In the following embodiments, unless otherwise explicitly stated, "%" refers to weight percentage.

[0020] like Figure 1 As shown, the present invention provides a method for preparing the above-mentioned carbon fiber-tungsten sulfide-graphene, comprising the following steps: Step S1: Dissolve sodium tungstate, hydroxylamine hydrochloride, thiourea and sodium hydroxide in deionized water, stir well, and prepare a reaction solution.

[0021] In this step, sodium tungstate, hydroxylamine hydrochloride, thiourea, and sodium hydroxide are dissolved in deionized water and stirred until homogeneous to prepare the reaction solution. The concentrations of each substance in the reaction solution must be controlled within specific ranges: sodium tungstate 0.05–0.2 mol / L, hydroxylamine hydrochloride 0.1–0.6 mol / L, sodium hydroxide 0.01–0.2 mol / L, and thiourea 0.1–0.9 mol / L. To ensure sufficient sulfur source, the molar ratio of hydroxylamine hydrochloride to thiourea can be controlled within the range of 1:1–1.5. The dissolution and stirring process can refer to the following conditions: dissolving in deionized water at 30°C, and stirring for approximately 30 minutes using magnetic stirring to ensure homogeneity. This reaction solution will serve as the raw material for the subsequent hydrothermal reaction, providing the necessary tungsten and sulfur sources for the formation of tungsten sulfide on the carbon fiber surface using graphene as nucleation sites.

[0022] Step S2: The reaction solution obtained in step S1 is mixed with carbon fiber and graphene in a reaction vessel and subjected to a hydrothermal reaction at a constant temperature.

[0023] In this step, the reaction solution obtained in step S1 is mixed with carbon fibers and graphene in a reactor. This mixing method aims to ensure that the graphene is fully dispersed in the reaction solution and adheres to the surface or between the carbon fibers, providing a site for the preferential selective nucleation of tungsten sulfide in the subsequent process. The carbon fibers can be polyacrylonitrile-based carbon fibers or graphite carbon fibers, with a preferred density of 1.7~1.9 g / L. The concentration of graphene in the reaction solution is 5-10 mg / ml. After mixing, the carbon fibers need to be immersed in the reaction solution and subjected to a hydrothermal reaction at a constant temperature ("constant temperature" means the difference from a specific temperature does not exceed 0.5 degrees Celsius) under a pressure of 1.5-4.0 MPa for a reaction time of 8-48 hours (the reaction time can be adjusted according to the reaction temperature). This step provides a large number of nucleation sites for tungsten sulfide through graphene. Combined with the above reaction conditions, tungsten sulfide nanoparticles with a size of 100-200 nm can be generated, and tungsten sulfide and graphene can be uniformly distributed on the surface of the carbon fibers.

[0024] The aforementioned "constant temperature" can be, for example, a temperature within the range of 180 to 240 degrees Celsius. That is, the reaction temperature can be kept constant at a specific temperature between 180 and 240 degrees Celsius. For example, it could be a specific temperature selected from 180 to 240 degrees Celsius, such as 180 degrees Celsius, 185 degrees Celsius, 190 degrees Celsius, 195 degrees Celsius, 200 degrees Celsius, or 205 degrees Celsius. For instance, with a constant temperature of 190 degrees Celsius, the temperature fluctuation of the reaction system is controlled within ±0.5 degrees Celsius, meaning the reaction temperature is between 189.5 degrees Celsius and 190.5 degrees Celsius.

[0025] Step S3: The product obtained in step S2 is filtered, washed and dried to obtain the composite material precursor.

[0026] In this step, when filtering the product obtained in step S2, conventional filtration methods such as atmospheric pressure filtration, vacuum filtration, and hot filtration can be used. After filtration, the product is washed with deionized water or ethanol as the washing solution. The washing can be performed once or repeatedly (e.g., 2-5 times). After washing, the product is dried using atmospheric pressure drying or vacuum drying at a temperature of 30-80 degrees Celsius. After the above filtration, washing, and drying processes, the composite material precursor can be obtained.

[0027] Step S4: The composite material precursor is calcined at 800~950 degrees Celsius in an inert gas atmosphere to obtain carbon fiber-tungsten sulfide-graphene composite material.

[0028] In this step, the prepared composite precursor is calcined at 800-950 degrees Celsius in an inert gas atmosphere, which can be nitrogen or argon. This calcination process yields a carbon fiber-tungsten sulfide-graphene composite material. This calcination step further strengthens the bonding between tungsten sulfide and graphene on the carbon fiber surface, improving the structural stability of the composite material and thus enhancing its electrochemical performance when used as a negative electrode material in sodium-ion batteries. The high-temperature calcination process promotes the formation of a stable interfacial bond between carbon fiber, graphene, and tungsten sulfide through possible carbon-oxygen-tungsten (COW) chemical bonds and strong physical entanglement. This strong interaction ensures that the active material does not detach from the conductive framework during repeated sodium ion insertion / extraction, thereby guaranteeing the structural integrity and long-cycle stability of the electrode.

[0029] In the above steps, after step S3, there is also a repeated reaction step, that is, the composite material precursor obtained in step S3 is mixed with the reaction solution newly prepared in step S1 and reacted (the reaction conditions can refer to the hydrothermal reaction conditions in step S2). After the reaction is completed, it is washed. The washing solution can be deionized water or ethanol. The washing can be performed once or repeatedly (e.g., 1 to 5 times, preferably 2 to 5 times). After washing, it is dried. The drying can be performed by normal pressure drying or reduced pressure drying, and the drying temperature is 30 to 80 degrees Celsius. The repeated reaction step is performed 1 to 5 times. Through this repeated reaction step, the loading of carbon fiber surface active material (such as tungsten sulfide) can be increased. The higher the tungsten sulfide content in the composite material, the higher its sodium storage capacity.

[0030] Example 1 Example 1 of the present invention: A carbon fiber-tungsten sulfide-graphene composite material was prepared according to the following steps: (1) Preparation of reaction solution First, 0.05 mol / L sodium tungstate, 0.1 mol / L hydroxylamine hydrochloride, 0.01 mol / L sodium hydroxide, and 0.15 mol / L thiourea (the molar ratio of hydroxylamine hydrochloride to thiourea is 1:1.5) were dissolved in deionized water at 30°C. The solution was stirred at 300 rpm for 30 minutes using a magnetic stirrer to ensure complete dissolution and homogeneity of all substances, thus preparing the reaction solution. This reaction solution provides the tungsten source (sodium tungstate), the sulfur source (thiourea), and the necessary conditioning substances for the subsequent hydrothermal reaction.

[0031] (2) Hydrothermal reaction A density of 1.7 g / L was selected. Polyacrylonitrile-based carbon fibers were cut into small pieces of 10mm × 10mm × 5mm. To remove surface organic colloids and activate the surface, they were calcined at 850°C for 2 hours under a nitrogen atmosphere at a heating rate of 5°C / min. This process helps introduce more active sites on the carbon fiber surface. After cleaning with deionized water and drying at 80°C for 10 hours, the carbon fibers were transferred together with the above reaction solution and 5 mg / mL graphene into a polytetrafluoroethylene-lined reactor, ensuring complete immersion of the carbon fibers in the reaction solution. After sealing the reactor, the internal pressure was adjusted to 1.55 MPa, and the reaction temperature was set at 200°C (a constant temperature with fluctuations controlled within ±0.5°C, i.e., 199.5°C to 200.5°C), maintaining these conditions for 24 hours. During this process, graphene provides nucleation sites for tungsten sulfide, and under the above conditions, tungsten sulfide nanoparticles with a size of approximately 100 nm can be generated.

[0032] (3) Filtering, drying and repeating the reaction After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The product was then separated by vacuum filtration. The product was washed twice each with deionized water and anhydrous ethanol (soaking for 10 minutes each time before filtration) to remove residual impurities. After washing, the product was dried in an 80°C, atmospheric pressure drying oven for 10 hours to obtain the composite material precursor. The precursor was mixed with the newly prepared reaction solution from step (1) in the same proportion and transferred back into the reactor. The reaction was carried out under the hydrothermal reaction conditions (200°C, 1.55 MPa, 24 hours) as described in step (2). After the reaction was completed, the washing (washing twice each with deionized water and ethanol) and drying (drying at 80°C, atmospheric pressure for 10 hours) steps were repeated. This repeated reaction was carried out three times to obtain a four-stage precursor.

[0033] (4) Calcination The four precursors were placed in a quartz boat and transferred to a tube furnace. Nitrogen gas was introduced as a protective gas (nitrogen flow rate of 200 mL / min). After the air in the furnace was completely replaced, the heating rate was set to 5 degrees Celsius / min, and the temperature was raised to 850 degrees Celsius. The mixture was then calcined at this temperature for 2 hours. After calcination, it was allowed to cool naturally to room temperature to obtain carbon fiber-tungsten sulfide-graphene composite material 1. The scanning electron microscope image of the obtained composite material is shown below. Figure 2 As shown, from Figure 2 It can be seen that tungsten sulfide nanoparticles and graphene are uniformly anchored on the carbon fiber surface, exhibiting a stable structure. Figure 2From the image characteristics, the material exhibits a loose, porous network structure, composed of numerous interwoven and aggregated nanoscale fibers or sheets, forming unevenly sized clusters. Significant voids exist between these aggregates, resulting in a high overall porosity. Functionally, this high porosity provides ample transport channels for sodium ion insertion / extraction, mitigating the volume expansion stress caused by the conversion reaction in tungsten sulfide during charging and discharging, and improving structural stability. Simultaneously, the nanoscale interwoven network structure increases the contact area between the material and the electrolyte, thereby increasing the number of active sites for electrochemical reactions and ultimately contributing to improved capacity and rate performance of sodium-ion batteries.

[0034] (5) Electrochemical performance test of half cell The composite material 1 was ground for 24 hours and mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 8:1:1 (first, 1 part by mass of polyvinylidene fluoride was dissolved in 19 parts by mass of methylpyrrolidone, then 8 parts by mass of the composite material and 1 part by mass of conductive carbon black were added, and the mixture was stirred for 3 hours to form a uniform slurry). The slurry was coated on aluminum foil (approximately 20 μm thick), dried at 110 degrees Celsius for 24 hours, and cut into electrode sheets with a diameter of 12 mm. Using lithium metal as the reference and counter electrodes, and a CR2032 coin cell as the casing, the battery was assembled in an argon glove box (oxygen and moisture <0.01 ppm). The separator was Celgard 2400, and the electrolyte was 0.8 mol / L lithium hexafluorophosphate (solvent: ethylene carbonate: diethyl carbonate = 1:1, volume ratio). Figure 3 As shown, Figure 3 The specific capacity and coulombic efficiency values ​​of the electrode prepared using the carbon fiber-tungsten sulfide-graphene composite material obtained in Example 1 were measured at different current densities.

[0035] Example 2

[0036] Example 2 of the present invention prepares a carbon fiber-tungsten sulfide-graphene composite material according to the following steps: (1) Preparation of reaction solution First, 0.12 mol / L sodium tungstate, 0.35 mol / L hydroxylamine hydrochloride, 0.1 mol / L sodium hydroxide, and 0.5 mol / L thiourea (the molar ratio of hydroxylamine hydrochloride to thiourea is 1:1.4) were dissolved in deionized water at 30 degrees Celsius. The mixture was stirred at 350 r / min for 30 minutes using a magnetic stirrer to ensure that all substances were completely dissolved and mixed evenly, thus preparing the reaction solution.

[0037] (2) Hydrothermal reaction A density of 1.8 g / L was selected. Graphite carbon fibers were cut into small pieces of 10mm × 10mm × 5mm and transferred together with the above reaction solution and 7mg / mL graphene into a polytetrafluoroethylene-lined reactor, ensuring that the carbon fibers were completely immersed in the reaction solution. After sealing the reactor, the pressure inside the reactor was adjusted to 1.90MPa, and the reaction temperature was set to 210 degrees Celsius (a constant temperature, with temperature fluctuations controlled within ±0.5 degrees Celsius, i.e., 209.5 degrees Celsius to 210.5 degrees Celsius). The reaction was maintained under these conditions for 24 hours. During this process, graphene promoted the nucleation of tungsten sulfide, generating tungsten sulfide nanoparticles with a size of approximately 150nm.

[0038] (3) Filtering, drying and repeating the reaction After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The product was then separated by atmospheric pressure filtration. The product was washed four times with alternating deionized water and anhydrous ethanol (soaking for 15 minutes each time before filtration). After washing, the product was placed in a vacuum drying oven at 60 degrees Celsius (vacuum degree < 5 Pa) and dried for 8 hours to obtain the composite material precursor. The precursor was mixed with the newly prepared reaction solution from step (1) in the same proportion and transferred back into the reactor. The reaction was carried out under the hydrothermal reaction conditions (210 degrees Celsius, 1.90 MPa, 24 hours) as described in step (2). After the reaction was completed, the washing (washing with alternating deionized water and ethanol four times) and drying (drying under vacuum at 60 degrees Celsius for 8 hours) steps were repeated. This repeated reaction step was carried out three times to obtain a four-stage precursor.

[0039] (4) Calcination The four precursors were placed in a quartz boat and transferred to a tube furnace. Argon gas was introduced as a protective gas (argon flow rate of 250 mL / min). After the air in the furnace was completely replaced, the heating rate was set to 6 degrees Celsius / min, raising the temperature to 875 degrees Celsius, and calcining at this temperature for 2.5 hours. After calcination, the mixture was allowed to cool naturally to room temperature to obtain carbon fiber-tungsten sulfide-graphene composite material 2. The scanning electron microscope image of the obtained composite material is shown below. Figure 4 As shown, from Figure 4 It can be seen that tungsten sulfide nanoparticles with a size of about 150 nm are uniformly distributed and tightly bonded to the carbon fiber surface.

[0040] (5) Electrochemical performance test of half cell The composite material 2 was ground for 24 hours, then mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 8:1:1 (mixing method as in Example 1), coated onto aluminum foil (approximately 20 μm thick), dried at 110 degrees Celsius for 24 hours, and cut into electrode sheets with a diameter of 12 mm. Battery assembly and testing conditions were the same as in Example 1. Figure 5The figure shows the specific capacity and coulombic efficiency values ​​of the electrode prepared using the carbon fiber-tungsten sulfide-graphene composite material obtained in Example 2, measured at different current densities.

[0041] Example 3 Example 3 of the present invention prepares a carbon fiber-tungsten sulfide-graphene composite material according to the following steps: (1) Preparation of reaction solution First, 0.15 mol / L sodium tungstate, 0.6 mol / L hydroxylamine hydrochloride, 0.2 mol / L sodium hydroxide, and 0.9 mol / L thiourea (the molar ratio of hydroxylamine hydrochloride to thiourea is 1:1.2) are dissolved in deionized water at 30 degrees Celsius. The mixture is stirred at 400 r / min for 30 minutes using a magnetic stirrer to ensure that all substances are completely dissolved and mixed evenly, thus preparing the reaction solution.

[0042] (2) Hydrothermal reaction A density of 1.9 g / L was selected. Polyacrylonitrile-based carbon fibers were cut into small pieces of 10mm × 10mm × 5mm and transferred together with the above-mentioned reaction solution and 10mg / mL graphene into a polytetrafluoroethylene-lined reactor, ensuring that the carbon fibers were completely immersed in the reaction solution. After sealing the reactor, the internal pressure was adjusted to 3.35MPa, and the reaction temperature was set at 240 degrees Celsius (a constant temperature, with temperature fluctuations controlled within ±0.5 degrees Celsius, i.e., 239.5 degrees Celsius to 240.5 degrees Celsius), maintaining these conditions for 36 hours. During this process, graphene provides sufficient nucleation sites for tungsten sulfide, generating tungsten sulfide nanoparticles with a size of approximately 200nm.

[0043] (3) Filtering, drying and repeating the reaction After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The product was then separated by hot filtration (keeping the filtrate temperature at 60 degrees Celsius). The product was washed five times alternately with deionized water and anhydrous ethanol (soaking for 20 minutes each time before filtration). After washing, the product was dried in an 80-degree Celsius atmospheric pressure drying oven for 6 hours to obtain the composite material precursor. The precursor was mixed with the newly prepared reaction solution from step (1) in the same proportion and transferred back into the reactor. The reaction was carried out under the hydrothermal reaction conditions (240 degrees Celsius, 3.35 MPa, 36 hours) as described in step (2). After the reaction was completed, the washing (washing with deionized water and ethanol alternately five times) and drying (drying at 80 degrees Celsius atmospheric pressure for 6 hours) steps were repeated. This repeated reaction step was performed five times to obtain the six-times precursor.

[0044] (4) Calcination The six precursors were placed in a quartz boat and transferred to a tube furnace. Nitrogen gas was introduced as a protective gas (nitrogen flow rate of 300 mL / min). After the air in the furnace was completely replaced, the heating rate was set to 8 degrees Celsius / min, and the temperature was raised to 950 degrees Celsius. The mixture was then calcined at this temperature for 3 hours. After calcination, it was allowed to cool naturally to room temperature to obtain the carbon fiber-tungsten sulfide-graphene composite material. The scanning electron microscope image of the obtained composite material is shown below. Figure 6 As shown, from Figure 6 It can be seen that tungsten sulfide nanoparticles with a size of about 200 nm are uniformly attached to the carbon fiber surface with good structural integrity.

[0045] (5) Electrochemical performance test of half cell The composite material 3 was ground for 24 hours, then mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 8:1:1 (mixing method as in Example 1), coated onto aluminum foil (approximately 20 μm thick), dried at 110 degrees Celsius for 24 hours, and cut into electrode sheets with a diameter of 12 mm. Battery assembly and testing conditions were the same as in Example 1. Figure 7 The specific capacity and coulombic efficiency values ​​of the electrode prepared using the carbon fiber-tungsten sulfide-graphene composite material obtained in Example 3 were measured at different current densities.

[0046] In the preparation method of the carbon fiber-tungsten sulfide-graphene composite for sodium-ion batteries of the present invention, the problem of difficult nucleation of tungsten sulfide is solved by using graphene as the nucleation active site for tungsten sulfide. The principle is that, compared with carbon fiber and the reaction liquid bulk, graphene has higher surface energy and abundant structural defects (such as edges, vacancies, functional groups, etc.). Under hydrothermal reaction conditions, tungsten-containing precursor ions preferentially adsorb onto these high-energy active sites, leading to an increase in local concentration, thereby significantly reducing the nucleation barrier of tungsten sulfide and promoting preferential heterogeneous nucleation and growth of tungsten sulfide on the graphene surface. In contrast, the relatively inert surface of carbon fiber and nucleation in homogeneous solutions require higher supersaturation and are therefore inhibited under the aforementioned reaction conditions. This effectively ensures that tungsten sulfide nanoparticles grow with graphene as the main carrier and subsequently achieve stable composite formation through close interweaving with carbon fiber. In the composite material prepared in this way, carbon fibers act as a reinforcement, making the composite structure stable. Tungsten sulfide nanoparticles are uniformly anchored on the surface of the carbon fibers, thus exhibiting good capacitance and charge transport properties. This makes it suitable as an electrode material for sodium-ion batteries with high capacity, high rate performance, and long cycle life. In addition, by using carbon fibers as a carbon source, the structural stability and electrochemical activity during sodium ion insertion (extraction) are improved, which is beneficial for achieving high rate performance and cycle stability.

[0047] This invention also provides a carbon fiber-tungsten sulfide-graphene composite material, prepared by the method described above for preparing carbon fiber-tungsten sulfide-graphene composites for sodium-ion batteries. In this composite material, the tungsten sulfide consists of 100-200 nm nanoparticles, and the tungsten sulfide and graphene are anchored on the surface of the carbon fiber. The density of the carbon fiber is 1.7-1.9 g / L. .

[0048] The present invention also provides a negative electrode for sodium-ion batteries, comprising the above-mentioned carbon fiber-tungsten sulfide-graphene composite material.

[0049] The present invention also provides a sodium-ion battery, comprising a carbon fiber-tungsten sulfide-graphene composite material prepared by any of the preceding methods, or a negative electrode for a sodium-ion battery prepared from the carbon fiber-tungsten sulfide-graphene composite material prepared by any of the preceding methods.

[0050] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0051] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0052] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a carbon fiber-tungsten sulfide-graphene composite for sodium-ion batteries, characterized in that, Includes the following steps: S1. Dissolve sodium tungstate, hydroxylamine hydrochloride, thiourea, and sodium hydroxide in deionized water and stir until homogeneous to prepare a reaction solution; S2. The reaction solution obtained in step S1 is mixed with carbon fiber and graphene in a reaction vessel and subjected to a hydrothermal reaction at a constant temperature. S3. The product obtained in step S2 is filtered, washed and dried to obtain the composite material precursor. S4. The composite material precursor is calcined at 800-950 degrees Celsius in an inert gas atmosphere to obtain carbon fiber-tungsten sulfide-graphene composite material.

2. The method for preparing the carbon fiber-tungsten sulfide-graphene composite for sodium-ion batteries according to claim 1, characterized in that, In the reaction solution described in step S1, the concentration of sodium tungstate is 0.05~0.2 mol / L, the concentration of hydroxylamine hydrochloride is 0.1~0.6 mol / L, the concentration of sodium hydroxide is 0.01~0.2 mol / L, and the concentration of thiourea is 0.1~0.9 mol / L.

3. The method for preparing the carbon fiber-tungsten sulfide-graphene composite for sodium-ion batteries according to claim 1, characterized in that, The hydrothermal reaction described in step S2 is carried out at a pressure of 1.5~4.0 MPa and a constant temperature of 180~240 degrees Celsius.

4. The method for preparing the carbon fiber-tungsten sulfide-graphene composite for sodium-ion batteries according to any one of claims 1 to 3, characterized in that, The process after step S3 includes a repeating reaction step: the composite material precursor is mixed and reacted with the reaction solution prepared in step S1, and then washed and dried; the repeating reaction step is performed 1 to 5 times.

5. A carbon fiber-tungsten sulfide-graphene composite material, characterized in that, It is prepared by the method for preparing carbon fiber-tungsten sulfide-graphene composite for sodium-ion batteries according to any one of claims 1 to 4.

6. The carbon fiber-tungsten sulfide-graphene composite material according to claim 5, characterized in that, In the composite material, tungsten sulfide consists of nanoparticles of 100-200 nm, and the tungsten sulfide and graphene are anchored on the surface of carbon fibers.

7. The carbon fiber-tungsten sulfide-graphene composite material according to claim 5 or 6, characterized in that, The density of the carbon fiber is 1.7~1.9 g / g.

8. A negative electrode for a sodium-ion battery, characterized in that, It includes the carbon fiber-tungsten sulfide-graphene composite material according to any one of claims 5 to 7.

9. A sodium-ion battery, comprising: A carbon fiber-tungsten sulfide-graphene composite material prepared by any one of claims 1 to 4, or a negative electrode for a sodium-ion battery prepared by any one of claims 5 to 7.

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