CN114335427B - A three-dimensional V2O3@carbon nanofiber composite flexible electrode and its preparation method and application - Google Patents

Abstract

The invention discloses a three-dimensional V ₂ O ₃ Carbon nanofiber composite flexible electrode, preparation method and application thereof, wherein the electrode comprises carbon nanofibers and V distributed on the carbon nanofibers ₂ O ₃ ；V ₂ O ₃ Assembling the nano sheets to form a three-dimensional sea urchin shape, and embedding the three-dimensional sea urchin shape on the surface of the carbon nano fiber in a bead-hanging shape; three-dimensional sea urchin-like VO synthesized by solvothermal method ₂ And dissolving the vanadium source in a polyacrylonitrile solution to obtain a precursor solution, obtaining polymer fibers by an electrostatic spinning method from the precursor solution, and performing pre-oxidation and carbonization treatment on the polymer fibers in an inert atmosphere to obtain the composite flexible electrode. V of the invention ₂ O ₃ The surface of the carbon fiber is uniformly distributed in the form of beads, so that a complete conductive network is formed, the conductivity of the composite electrode is improved, and Li is reduced ⁺ The diffusion path of the material is used for relieving the volume expansion in the charge and discharge process, improving the stability of the material, and has the advantages of simple integral synthesis process, low cost and easy large-scale preparation and application.

Description

A three-dimensional V2O3@carbon nanofiber composite flexible electrode and its preparation method and application

technical field

The invention belongs to energy storage materials, in particular to a three-dimensional V2O3@carbon nanofiber composite flexible electrode, its preparation method and application.

Background technique

In recent years, lithium-ion batteries have been widely used in smart grids, high-power electric vehicles, and portable electronic products due to their high energy density, high safety, and environmental friendliness. However, the theoretical specific capacity (372mAh g ^-1 ) of graphite as an anode material for lithium-ion batteries (LIBs) is low, which cannot meet the needs of the next generation of lithium-based batteries, which greatly limits the further improvement of the energy density of lithium-ion batteries and affects the future. Wider application of energy storage technology. Vanadium oxides (such as V ₂ O ₃ , VO ₂ (B), V ₂ O ₅ , etc.) have become increasingly concerned layered crystal compounds due to their low cost, large specific capacity, and abundant resources. They have open structure and multiple valence states (+5, +4, +3), the reversible intercalation/deintercalation of lithium can be achieved. Among them, compared with other high-valent vanadium oxides, low-valent V ₂ O ₃ has lower toxicity and will also receive more attention.

However, the disadvantages of V ₂ O ₃ , such as poor electrical conductivity and large volume change during charging and discharging, limit its rate performance and cycle stability. In addition, traditional electrodes are easily separated from the current collector, and the metal current collector is deformed during repeated bending, which reduces the electrochemical performance of Li-ion batteries. Moreover, traditional electrodes cannot meet the functions of flexibility, bending and foldability, which is extremely unfavorable for the realization of industrialization and the development of flexible lithium batteries. Therefore, it is particularly important to explore a flexible electrode with simple process, time-saving and high-efficiency, and high electrochemical performance.

Contents of the invention

Purpose of the invention: the first purpose of the present invention is to provide a highly conductive three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode that reduces volume expansion during charging and discharging; the second purpose of the present invention is to provide the preparation of the above-mentioned composite flexible electrode Method; The third object of the present invention is to provide the application of the above-mentioned composite flexible electrode as a negative electrode material in a lithium-ion battery.

Technical solution: A three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode of the present invention, including carbon nanofibers and V ₂ O ₃ distributed on carbon nanofibers; the V ₂ O ₃ is assembled by nanosheets to form a three-dimensional Sea urchin-shaped, embedded in the surface of carbon nanofibers in the form of hanging beads.

Further, the diameter of the V ₂ O ₃ is 1-2 μm, and the diameter of the carbon nanofiber is 100-300 nm.

The present invention also protects the preparation method of the three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode, which includes the following steps:

(1) Weigh V ₂ O ₅ and H ₂ C ₂ O ₄ ·2H ₂ O according to the reaction molar ratio, dissolve them in deionized water and stir until a dark blue solution is formed, then continue to add ethanol, water and hydrogen peroxide solution, and react. Cool to room temperature then, obtain _VO after suction filtration, washing, drying Powder;

(2) Weigh polyacrylonitrile and add it to N,N-dimethylformamide, stir until a uniform yellow solution is formed, add _VO2 powder to the yellow solution prepared in step (2), and continue stirring to obtain the precursor body solution, and the resulting precursor solution is subjected to defoaming treatment for use;

(3) Electrospinning the precursor solution prepared in step (2) to obtain V ₂ O ₃ @PAN polymer fibers;

(4) The prepared V ₂ O ₃ @PAN polymer fibers were pre-oxidized in air atmosphere, then carbonized in argon atmosphere, and finally cooled to room temperature to prepare three-dimensional V ₂ O ₃ @carbon nanofibers Composite flexible electrodes.

Further, in the step (2), the mass ratio of VO ₂ powder to polyacrylonitrile is 0.3-1.5:1. In step (2), VO ₂ powder must be added after forming a uniform yellow solution. If VO ₂ is added to the solution first, and then polyacrylonitrile is added, the fibers will cover V ₂ O ₃ , and it is impossible to obtain a beaded V ₂ O ₃ @carbon nanofibers. There is a specific relationship between the amount ratio of _VO2 powder and polyacrylonitrile. If the quality of _VO2 is too high, it will hinder the formation of interwoven carbon fibers and cause the carbon fibers to break; if the concentration of polyacrylonitrile in the spinning solution is too low, It will result in insufficient viscosity of the spinning solution and beading cannot appear on the fiber.

Further, in the step (3), the applied voltage of electrospinning is 10-15 kV, and the flow rate is 0.5-0.7 mL·h ^-1 . In actual operation, the distance between the metal needle and the aluminum foil collector is 15cm, the relative humidity is lower than 40%, and the temperature is not higher than 30°C. If the humidity of the spinning environment is too high, the spinning jet will absorb moisture in the air and solidify in advance, and the charge on the fiber will be neutralized, resulting in a decrease in the charge of the fiber, and the phenomenon of hanging and floating on the needle tip.

Further, in the step (4), the pre-oxidation temperature is 230-280° C., and the pre-oxidation time is 2-3 hours.

Further, in the step (4), the carbonization temperature is 600-700° C., and the carbonization time is 5-6 hours.

Further, in the step (1), the reaction molar ratio of V ₂ O ₅ and H ₂ C ₂ O ₄ ·2H ₂ O is 1:3; the volume ratio of ethanol, water and hydrogen peroxide solution is 40:5 : 2; the reaction temperature is 160～200°C, and the reaction time is 2～4h. The reaction molar ratio 1:3 is used _to form a uniform _VOC2O4 blue solution,

Further, in the step (2), the defoaming treatment specifically means that the electrospinning solution needs to be defoamed in a vacuum dryer for 1-2 hours. If there are bubbles in the solution, it will cause knots or breakage in the spun fibers.

The present invention further protects the application of the three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode as negative electrode material in lithium ion batteries.

The preparation principle of the present invention is as follows: referring to Fig. 1, with V ₂ O ₅ as vanadium source, oxalic acid as reducing agent, ethanol and water as solvent, urchin-like VO ₂ with three-dimensional structure is synthesized by solvothermal method; then VO ₂ was mixed with PAN solution to prepare electrospinning solution, and a three-dimensional VO ₂ @PAN film was prepared by electrospinning, which was then pre-oxidized in air and carbonized in argon. On the one hand, V ₂ O ₃ is obtained through the reduction reaction of VO ₂ , and the crystal structure of V ₂ O ₃ is a diamond-shaped corundum structure, in which vanadium atoms form three-dimensional VV chains, and the three-dimensional VV framework can form an open tunnel structure; on the other hand, polypropylene Nitrile is converted into carbon nanofibers. The prepared three-dimensional sea urchin-like V ₂ O ₃ has a large specific surface area and abundant active sites, which can promote the intercalation and deintercalation of lithium ions; at the same time, V ₂ O ₃ is evenly distributed on the surface of the carbon fiber in the form of hanging beads , forming a complete conductive network.

Beneficial effects: Compared with the prior art, the significant advantages of the present invention are: (1) The present invention prepares a three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode through a simple electrospinning method, V ₂ O ₃ The construction of the three-dimensional sea urchin structure can increase the contact area between the electrode material and the electrolyte, provide more active sites, and effectively avoid the agglomeration of the material during the cycle, maintain the integrity of the three-dimensional structure, and improve the conductivity of the electrode material. The stability and reaction kinetics of the material improve the high current long-term cycle performance and rate performance of the material. (2) The V ₂ O ₃ of the present invention is evenly distributed on the surface of the carbon fiber in the form of hanging beads, forming a complete conductive network, improving the conductivity of the composite electrode, reducing the diffusion path of Li ⁺ , and alleviating the charging problem. The volume expansion during discharge improves the stability of the material. (3) The present invention adopts the V ₂ O ₃ @carbon nanofiber composite flexible electrode synthesized by electrospinning method as the negative electrode material of lithium ion battery, which can not only improve the conductivity and structural stability of the material, but also solve the problem of rapid capacity decay in the cycle process problems, and exhibit good flexibility and bendability, providing a basis for the application of flexible lithium-ion batteries.

Description of drawings

Figure 1 is a block diagram of the preparation process of the three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode;

Fig. 2 is the photogram of the V ₂ O ₃ @ carbon nanofiber composite flexible electrode prepared in Example 1;

Fig. 3 is the SEM picture of the V ₂ O ₃ @ carbon nanofiber composite flexible electrode prepared in Example 1;

4 is a TEM image of the V ₂ O ₃ @carbon nanofiber composite flexible electrode prepared in Example 1;

Fig. 5 is the charge-discharge cycle performance diagram of V ₂ O ₃ @ carbon nanofibers in Example 6 as the negative electrode material of lithium ion battery under the current density of 5000mAg ^-1 ;

Fig. 6 is the SEM picture that comparative example 3 makes V ₂ O ₃ ;

FIG. 7 is a SEM image of the material prepared in Comparative Example 5.

Detailed ways

The technical solution of the present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

Example 1

A method for preparing a three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode, the preparation process is shown in Figure 1, and the specific steps are as follows:

Step 1) Dissolve V ₂ O ₅ and H ₂ C ₂ O ₄ ·2H ₂ O (1:3 molar ratio) in 40 mL of deionized water, and stir vigorously at 70°C for 2 h until a dark blue solution is formed Then, 5mL of the above solution was transferred to a 60ml stainless steel autoclave, followed by adding 40mL of ethanol, 5mL of water and 2mL of 30% hydrogen peroxide solution and kept stirring for 1h; then solvothermal reaction at 180°C for 3h; after cooling to room temperature, Filter and wash with distilled water and absolute ethanol three times, dry in vacuum at 80°C for 12 hours, and set aside;

Step 2) Weigh 0.4g PAN and add it to 4ml N,N-dimethylformamide, and magnetically stir at 60°C for 6h until a uniform yellow solution is formed;

Step 3) Weigh 0.15g of _VO2 powder prepared in step 1) and add it to the solution prepared in step 2), continue stirring for 24h to obtain a precursor solution, and pass the resulting solution through defoaming for 2h before use;

Step 4) Electrospinning the precursor solution prepared in step 3), the applied voltage is 12kV, the flow rate is 0.6ml·h ^-1 ; the distance between the metal needle and the aluminum foil collector is 15cm, and the relative humidity is lower than 40%, the temperature is not higher than 30°C, to obtain V ₂ O ₃ @PAN polymer fiber, ready for use;

Step 5) Raise the V ₂ O ₃ @PAN polymer fiber prepared in step 4 to the pre-oxidation temperature of 250°C at a heating rate of 3°C min ^-1 in an air atmosphere and keep it for 2h; then in an Ar atmosphere at a temperature of 3°C min The rate of ^-1 was raised to the carbonization temperature of 600°C for 6 hours, and finally cooled to room temperature to prepare a three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode.

As shown in Figure 2, the V ₂ O ₃ @carbon nanofiber composite flexible film prepared by electrospinning showed good flexibility and bendability.

Referring to Figure 3, it can be seen that the prepared electrode is composed of interwoven carbon nanofibers, three-dimensional sea urchin-like V ₂ O ₃ is evenly distributed on the surface of carbon nanofibers, the overall diameter is about 2 μm, and the diameter of carbon nanofibers is 200 nm. Referring to Figure 4, it can be seen that the three-dimensional sea urchin-like V ₂ O ₃ is assembled from nanosheets, and V ₂ O ₃ is embedded on the surface of carbon nanofibers.

Example 2

Step 1) Dissolve V ₂ O ₅ and H ₂ C ₂ O ₄ ·2H ₂ O (1:3 molar ratio) in 40 mL of deionized water, and stir vigorously at 70°C for 2 h until a dark blue solution is formed Then, 5mL of the above solution was transferred to a 60ml stainless steel autoclave, followed by adding 40mL of ethanol, 5mL of water and 2ml of 30% hydrogen peroxide solution and kept stirring for 1; then solvothermal reaction at 180°C for 3h; after cooling to room temperature, Filter and wash with distilled water and absolute ethanol three times, dry in vacuum at 80°C for 12 hours, and set aside;

Step 2) Weigh 0.4g PAN and add it to 4ml N,N-dimethylformamide, and magnetically stir at 60°C for 6h until a uniform yellow solution is formed;

Step 3) Weigh 0.15g of _VO2 powder prepared in step 1) and add it to the solution prepared in step 2), continue stirring for 24h to obtain a precursor solution, and pass the resulting solution through defoaming for 2h before use;

Step 4) Electrospinning the precursor solution prepared in step 3), the applied voltage is 12kV, the flow rate is 0.6ml·h ^-1 ; the distance between the metal needle and the aluminum foil collector is 15cm, and the relative humidity is lower than 40%, the temperature is not higher than 30°C, to obtain V ₂ O ₃ @PAN polymer fiber, ready for use;

Step 5) Raise the V ₂ O ₃ @PAN polymer fiber prepared in step 4) to a pre-oxidation temperature of 280°C at a heating rate of 3°C min ^-1 in an air atmosphere and keep it warm for 3h; then in an Ar atmosphere at a temperature of 3°C The rate of min ^-1 was raised to the carbonization temperature of 700°C for 6 hours, and finally cooled to room temperature to prepare a three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode.

Example 3

A method for preparing a three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode, the specific steps are as follows:

Step 1) Dissolve V ₂ O ₅ and H ₂ C ₂ O ₄ ·2H ₂ O (1:3 molar ratio) in 40 mL of deionized water, and stir vigorously at 70°C for 2 h until a dark blue solution is formed Then, 5mL of the above solution was transferred to a 60ml stainless steel autoclave, followed by adding 40mL of ethanol, 5mL of water and 2mL of 30% hydrogen peroxide solution and kept stirring for 1h; then solvothermal reaction at 180°C for 3h; after cooling to room temperature, Filter and wash with distilled water and absolute ethanol three times, dry in vacuum at 80°C for 12 hours, and set aside;

Step 2) Weigh 0.4g PAN into 4mL N,N-dimethylformamide, and magnetically stir at 60°C for 6h until a uniform yellow solution is formed;

Step 3) Weigh 0.15g of _VO2 powder prepared in step 1) and add it to the solution prepared in step 2), continue stirring for 24h to obtain a precursor solution, and pass the resulting solution through defoaming for 2h before use;

Step 4) Electrospinning the precursor solution prepared in step 3), the applied voltage is 12kV, the flow rate is 0.6ml·h ^-1 ; the distance between the metal needle and the aluminum foil collector is 15cm, and the relative humidity is lower than 40%, the temperature is not higher than 30°C, to obtain V ₂ O ₃ @PAN polymer fiber, ready for use;

Step 5) Raise the V ₂ O ₃ @PAN polymer fiber prepared in step 4 to the pre-oxidation temperature of 230°C at a heating rate of 3°C min ^-1 in an air atmosphere and keep it for 2h; then in an Ar atmosphere at a temperature of 3°C min The rate of ^-1 was increased to the carbonization temperature of 600°C for 5 hours, and finally cooled to room temperature to prepare a three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode.

Example 4

A method for preparing a three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode, the specific steps are as follows:

Step 1) Dissolve V ₂ O ₅ and H ₂ C ₂ O ₄ ·2H ₂ O (1:3 molar ratio) in 40 mL of deionized water, and stir vigorously at 70°C for 2 h until a dark blue solution is formed Then, 5mL of the above solution was transferred to a 60ml stainless steel autoclave, followed by adding 40mL of ethanol, 5mL of water and 2mL of 30% hydrogen peroxide solution and kept stirring for 1h; then solvothermal reaction at 180°C for 3h; after cooling to room temperature, Filter and wash with distilled water and absolute ethanol three times, dry in vacuum at 80°C for 12 hours, and set aside;

Step 2) Weigh 0.5g PAN and add to 4ml N,N-dimethylformamide, and magnetically stir at 60°C for 6h until a uniform yellow solution is formed;

Step 3) Weigh 0.15g of _VO2 powder prepared in step 1) and add it to the solution prepared in step 2), continue to stir for 24 hours to obtain a precursor solution, and pass the resulting solution through defoaming for 1 hour before use;

Step 4) Electrospinning the precursor solution prepared in step 3), the applied voltage is 15kV, the flow rate is 0.7ml·h ^-1 ; the distance between the metal needle and the aluminum foil collector is 15cm, and the relative humidity is lower than 40%, the temperature is not higher than 30°C, to obtain V ₂ O ₃ @PAN polymer fiber, ready for use;

Step 5) Raise the V ₂ O ₃ @PAN polymer fiber prepared in step 4 to the pre-oxidation temperature of 250°C at a heating rate of 3°C min ^-1 in an air atmosphere and keep it for 2h; then in an Ar atmosphere at a temperature of 3°C min The rate of ^-1 was raised to the carbonization temperature of 600°C for 6 hours, and finally cooled to room temperature to prepare a three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode.

Example 5

A method for preparing a three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode, the specific steps are as follows:

Step 1) Dissolve V ₂ O ₅ and H ₂ C ₂ O ₄ ·2H ₂ O (1:3 molar ratio) in 40 mL of deionized water, and stir vigorously at 70°C for 2 h until a dark blue solution is formed . Then, 5mL of the above solution was transferred to a 60ml stainless steel autoclave, followed by adding 40mL of ethanol, 5mL of water and 2mL of 30% hydrogen peroxide solution and kept stirring for 1h; then solvothermal reaction at 180°C for 3h; after cooling to room temperature, use Wash with distilled water and absolute ethanol for three times, vacuum-dry at 80°C for 12 hours, and set aside;

Step 2) Weigh 0.3g PAN and add it to 4ml N,N-dimethylformamide, and magnetically stir at 60°C for 6h until a uniform yellow solution is formed;

Step 3) Weigh 0.45g of _VO powder prepared in step 1) and add it to the solution prepared in step 2, continue to stir for 24 hours to obtain a precursor solution, and pass the resulting solution through defoaming for 2 hours before use;

Step 4) Electrospinning the precursor solution prepared in Step 3 with an applied voltage of 10kV and a flow rate of 0.5ml·h ^-1 ; the distance between the metal needle and the aluminum foil collector is 15cm, and the relative humidity is lower than 40 %, the temperature is not higher than 30°C to obtain V ₂ O ₃ @PAN polymer fiber, which is ready for use;

Step 5) Raise the V ₂ O ₃ @PAN polymer fiber prepared in step 4 to the pre-oxidation temperature of 250°C at a heating rate of 3°C min ^-1 in an air atmosphere and keep it for 2h; then in an Ar atmosphere at a temperature of 3°C min The rate of ^-1 was raised to the carbonization temperature of 600°C for 6 hours, and finally cooled to room temperature to prepare a three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode.

Comparative example 1

The specific preparation process is the same as in Example 1, except that the pre-oxidation temperature in step 5) is 220° C., and the pre-oxidation time is 1 h.

Comparative example 2

The specific preparation process is the same as in Example 1, except that the carbonization temperature in step 5) is 500° C., and the carbonization time is 5 hours.

Comparative example 3

The specific preparation process is the same as in Example 1, except that the molar ratio of V ₂ O ₅ to H ₂ C ₂ O ₄ ·2H ₂ O in step 1) is 1:2. See Figure 6. Since the reaction molar ratio does not reach 1:3, the prepared morphology is lumpy, indicating that a small amount of oxalic acid cannot completely convert V ₂ O ₅ into VOC ₂ O ₄ . Self-assembled into a flower-like morphology, no hanging bead structure can be obtained.

Comparative example 4

The specific preparation process is the same as in Example 1, except that the mass ratio of VO ₂ to PAN added is 0.2:1.

Comparative example 5

The specific preparation process is the same as that in Example 1, the difference is that _VO powder is first added to the solution, and then PAN is added. Referring to Figure 7, it can be clearly seen that the fibers are wrapped outside the V ₂ O ₃ , and the morphology of hanging beads cannot be formed.

The results of characterizing the products prepared in Examples 1-5 and Comparative Examples 1-5 are shown in Table 1 below.

Table 1 Test results

It can be seen from Table 1 that when the molar ratio of V ₂ O ₅ to H ₂ C ₂ O ₄ ·H ₂ O is 1:3, the three-dimensional sea urchin-like V ₂ O ₃ can be finally obtained. When the mass ratio of _VO2 to PAN is 0.3-1.5, the pre-oxidation temperature is 230-280°C, the pre-oxidation time is 2-3h, the carbonization temperature is 600-700°C, and the carbonization time is 5-6h, flexible and crystalline Good V ₂ O ₃ @carbon nanofibers.

Example 6

The three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode prepared in Example 1 is used as the negative electrode material of lithium ion battery, and the specific steps are as follows:

(1) Punch out the V ₂ O ₃ @carbon nanofiber flexible film with a manual punching machine into a disc with a diameter of 12mm, and use it as a working electrode;

(2) The disc electrode of 12mm obtained in (1) is used as the working electrode, the lithium metal sheet is used as the reference electrode, and the Celgard disc is used as the separator, and the organic electrolyte (EC:DEC:DMC= ₁ :1) containing 1M LiPF : 1) As battery electrolyte; adopt 2032 type battery case, assemble and complete button cell in the glove box that is filled with argon gas, carry out electrochemical performance test after placing 24h.

After the electrochemical performance cycle test, as shown in Figure 5, when the current density is 5000mA g ^-1 , the initial capacity is 336mAh g ^-1 , after 8000 cycles, the capacity increases to 305mAh g ^-1 , and the capacity retention rate is 90%. , indicating that the V ₂ O ₃ @carbon nanofiber flexible electrode prepared by electrospinning has a stable structure and a good conductive network, which improves the conductivity of the electrode and makes it difficult to agglomerate during Li ⁺ transport, providing a good Specific capacity and excellent long-term cycle stability, it is a very potential electrode material for lithium-ion batteries.

Claims (6)

1. A three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode, characterized in that: it includes carbon nanofibers and V ₂ O ₃ distributed on the carbon nanofibers; the V ₂ O ₃ is assembled by nanosheets to form a three-dimensional Sea urchin-shaped, embedded in the surface of carbon nanofibers in the form of hanging beads; The preparation method of the three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode includes the following steps: (1) Weigh V ₂ O ₅ and H ₂ C ₂ O ₄ 2H ₂ O according to the reaction molar ratio, dissolve them in deionized water and stir until a dark blue solution is formed, then continue to add ethanol, water and hydrogen peroxide solution, and react. Cool to room temperature then, obtain _VO after suction filtration, washing, drying Powder; (2) Weigh polyacrylonitrile and add it to N,N-dimethylformamide, stir until a uniform yellow solution is formed, add VO ₂ powder into the yellow solution prepared in step (2), and continue stirring to obtain the precursor body solution, and the resulting precursor solution is subjected to defoaming treatment for use; (3) Electrospinning the precursor solution prepared in step (2) to obtain VO ₂ @PAN polymer fibers; (4) The prepared VO ₂ @PAN polymer fibers were pre-oxidized in air atmosphere, then carbonized in argon atmosphere, and finally cooled to room temperature to prepare three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode; In the step (1), the reaction molar ratio of V ₂ O ₅ and H ₂ C ₂ O ₄ ·2H ₂ O is 1:3; in the step (4), the pre-oxidation temperature is 230~280°C, the pre-oxidation The oxidation time is 2~3 h, the carbonization temperature is 600~700°C, and the carbonization time is 5~6 h. 2. The three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode according to claim 1, characterized in that: the diameter of the V ₂ O ₃ is 1~2 μm, and the diameter of the carbon nanofiber is 100~ 300 nm. 3. The three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode according to claim 1, characterized in that: in the step (2), the mass ratio of VO ₂ powder to polyacrylonitrile is 0.3~1.5: 1. 4. The three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode according to claim 1, characterized in that: in the step (3), the applied voltage of electrospinning is 10~15 kV, and the flow rate is 0.5~ 0.7 mL·h ^-1 . 5. The three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode according to claim 1, characterized in that: in the step (1), the volume ratio of ethanol, water and hydrogen peroxide solution is 40:5: 2; The reaction temperature is 160~200℃, and the reaction time is 2~4h. 6. The three-dimensional V ₂ O ₃ @carbon nanofiber composite flexible electrode according to claim 1, characterized in that: in the step (2), the defoaming treatment specifically refers to defoaming the solution in a vacuum desiccator for 1 ~2 h.

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