Preparation method of V2O5-based / graphene composite fiber electrode material with skin-core structure

Abstract

The invention discloses a preparation method of a V2O5-based / graphene composite fiber electrode material with a skin-core structure, and relates to a preparation method of a composite fiber electrode material. The invention aims to solve the problem that a sodium ion battery assembled by a vanadium oxide-based composite fiber material is poor in cycling stability and rate capability. The method comprises the following steps: 1, preparing a V2O5-loaded carbon nanotube suspension; 2, preparing a spinning solution; 3, wet spinning; and 4, high-temperature treatment and heat treatment. The preparation method is used for preparing the V2O5-based / graphene composite fiber electrode material with the skin-core structure.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a composite fiber electrode material. BACKGROUND

[0002] V2O5 is an oxide of vanadium in the highest valence state, and has a theoretical specific capacity of 294.0 mA h g -1 for sodium storage. The oxide has the characteristics of high theoretical capacity, easy synthesis, good safety, etc., and can increase the diffusion capacity of Na + in the charging and discharging process when the oxide is used to form a sodium ion battery. The oxide is considered to be a good electrode material for a sodium ion battery, but the low conductivity, easy dissolution in the cycle process, and slow migration rate of Na + in the crystal seriously restrict the electrochemical sodium storage performance of the V2O5-based electrode material. Specifically, the cycle stability and rate performance of a sodium ion battery assembled from a vanadium oxide-based composite fiber material are poor. SUMMARY

[0003] The application aims to solve the problems of poor cycle stability and rate performance of a sodium ion battery assembled from a vanadium oxide-based composite fiber material, and further provides a preparation method of a V2O5-based / graphene composite fiber electrode material with a skin-core structure.

[0004] The preparation method of the V2O5-based / graphene composite fiber electrode material with the skin-core structure is performed according to the following steps:

[0005] I. Preparation of a carbon nanotube suspension loaded with V2O5:

[0006] ①Multi-walled carbon nanotubes are placed in a nitric acid solution and heated and stirred, and then the pH value is adjusted to 7, and then the multi-walled carbon nanotubes are sequentially subjected to standing and centrifugal drying of the upper suspension to obtain pre-functionalized carbon nanotubes;

[0007] ②The pre-functionalized carbon nanotubes are added to anhydrous ethanol and ultrasonically treated, and vanadium triisopropoxide is added in multiple portions, and after all the vanadium triisopropoxide is added, continuous stirring is performed, and distilled water is added in multiple portions in the continuous stirring process, to obtain a suspension, and the suspension is continuously stirred, and then subjected to sedimentation, washing and centrifugal separation, to obtain carbon nanotubes loaded with V2O5, and the carbon nanotubes loaded with V2O5 are added to deionized water to obtain a carbon nanotube suspension loaded with V2O5;

[0008] II. Preparation of a spinning solution:

[0009] ①The graphene oxide solution is stirred, and then quinoline is added and stirred, and then an imidazole compound is added and ultrasonically treated, to obtain a core layer spinning solution;

[0010] ②The carbon nanotube suspension loaded with V2O5 is stirred, and then the graphene oxide solution and quinoline are added and stirred, and then the imidazole compound is added and ultrasonically treated, to obtain a skin layer spinning solution;

[0011] III. Wet spinning:

[0012] The sheath-core structure base fiber electrode material is prepared by using the sheath spinning solution and the core spinning solution through a wet spinning machine provided with a coaxial spinneret;

[0013] IV. High temperature treatment and heat treatment:

[0014] The sheath-core structure base fiber electrode material is dried, then is subjected to high temperature treatment under an argon atmosphere, and then is subjected to heat treatment under an air atmosphere, so that the sheath-core structure V2O5 base / graphene composite fiber electrode material is obtained.

[0015] The present application has the following advantages:

[0016] In the sheath-core structure V2O5 base / graphene composite fiber electrode material, the inner layer of the fiber is a graphene fiber with stable electrical and mechanical properties, and the outer layer of the fiber is a graphene composite layer loaded with V2O5 carbon nanotube fiber. The fiber can be directly used as an electrode material after presodium, and is used for preparing a high-performance sodium ion battery positive electrode material.

[0017] Loading the V2O5 nanosheet on the surface of the multi-walled carbon nanotube can enhance the Na + The diffusion capacity in the bulk phase of the composite material and the conductivity of the powder can be improved, and the dissolution of the vanadium oxide component can be effectively prevented. At the same time, the conductivity can be effectively improved, which is beneficial to the diffusion of ions and the inhibition of component dissolution.

[0018] The quinoline and imidazole compound assisted wet spinning can generate a large amount of graphitized carbon components in the fiber, which can improve the conductivity and enhance the mechanical properties of the fiber. The graphitized carbon and V2O5 can be in close contact, which can effectively inhibit the dissolution, improve the cycle stability and rate performance of the electrode electrochemical sodium storage, and has good application prospect in the fields of catalysis, electronic devices, electrochemical sensors and energy storage batteries. It is a new material with good application potential.

[0019] The present application relates to a preparation method of a sheath-core structure V2O5 base / graphene composite fiber electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The present application relates to a preparation method of a sheath-core structure V2O5 base / graphene composite fiber electrode material.

[0021] Figure 2The structure, morphology characterization map and mechanical property map of the core-sheath structure V2O5-based / graphene composite fiber electrode material prepared in Example 1 and the comparative experiment are shown in (a) and (b) are scanning electron micrographs of QVSCF, (c) is a scanning electron micrograph of PVSCF, (d) is a scanning electron micrograph of QVSCF and the element surface scanning photograph of O, C and V, (e) is an XRD pattern, (f) is a mechanical property map;

[0022] Figure 3 The sodium storage rate performance and bending stability characterization of the core-sheath structure V2O5-based / graphene composite fiber electrode material prepared in Example 1 and the comparative experiment are shown in (a) is the charge-discharge curve of QVSCF under different current densities, (b) is the rate performance under different current densities, (c) is the stability under different bending angles at 100 mA g -1 ;

[0023] Figure 4 The TEM photograph and impedance spectrum of graphitized carbon / amorphous carbon in the fiber of the core-sheath structure V2O5-based / graphene composite fiber electrode material prepared in Example 1 and the comparative experiment after 100 cycles are shown in (a) is the GRTEM photograph of graphitized carbon in QVSCF, (b) is the GRTEM photograph of amorphous carbon in PVSCF, (c) is the impedance spectrum of QVSCF, PVSCF and sodium sheet assembled into half-cell, (d) is the relationship curve between Z'-ω −1 / 2 in the low frequency region of the impedance spectrum of QVSCF and PVSCF. DETAILED DESCRIPTION

[0024] Specific embodiment one: a preparation method of a core-sheath structure V2O5-based / graphene composite fiber electrode material, which is carried out according to the following steps:

[0025] I. Preparation of V2O5-loaded carbon nanotube suspension:

[0026] ①The multi-walled carbon nanotubes are placed in a nitric acid solution and heated and stirred, then the pH value is adjusted to 7, and then the pre-functionalized carbon nanotubes are obtained by sequentially standing and centrifuging and drying the upper suspension;

[0027] ②The pre-functionalized carbon nanotubes are added to anhydrous ethanol and ultrasonicated, and the vanadium triisopropoxide is added in multiple portions, and the continuous stirring process is carried out, and distilled water is added in multiple portions during the continuous stirring process, to obtain a suspension, and the suspension is continuously stirred, and then settled, washed and centrifuged to obtain V2O5-loaded carbon nanotubes, and the V2O5-loaded carbon nanotubes are added to deionized water to obtain a V2O5-loaded carbon nanotube suspension;

[0028] II. Spinning solution preparation:

[0029] ①Stir the graphene oxide solution, then add quinoline and stir, then add the imidazole compound under ultrasonic, to obtain the core layer spinning solution;

[0030] ②Stir the carbon nanotube suspension loaded with V2O5, then add the graphene oxide solution and quinoline and stir, then add the imidazole compound under ultrasonic, to obtain the skin layer spinning solution;

[0031] III. Wet spinning:

[0032] The skin-core structure base fiber electrode material is prepared by using the skin layer spinning solution and the core layer spinning solution through a wet spinning machine provided with a coaxial spinneret;

[0033] IV. High temperature treatment and heat treatment:

[0034] The skin-core structure base fiber electrode material is dried, then high temperature treated under argon atmosphere, and then heat treated under air atmosphere, to obtain the skin-core structure V2O5 base / graphene composite fiber electrode material.

[0035] The beneficial effects of the embodiment are:

[0036] In the skin-core structure V2O5 base / graphene composite fiber electrode material of the embodiment, the inner layer of the fiber is a graphene fiber with stable electrical and mechanical properties, and the outer layer of the fiber is a graphene composite layer of a carbon nanotube fiber loaded with V2O5. The fiber can be directly used as an electrode material after pre-sodium, and is used for preparing a high-performance sodium ion battery positive electrode material.

[0037] Loading the V2O5 nanosheet on the surface of the multi-walled carbon nanotube can enhance the Na + The diffusion ability in the bulk phase of the composite material and the conductivity of the powder can be improved, and the dissolution of the vanadium oxide component can be effectively prevented. At the same time, the conductivity can be effectively improved, which is beneficial to the diffusion of ions and the inhibition of component dissolution.

[0038] The quinoline and imidazole compound assisted wet spinning can generate a large amount of graphitized carbon component in the fiber, which can improve the conductivity and enhance the mechanical properties of the fiber. The graphitized carbon can be in close contact with V2O5, effectively inhibiting its dissolution, improving the cycle stability and rate performance of the electrode electrochemical sodium storage, and having good application prospects in the fields of catalysis, electronic devices, electrochemical sensors and energy storage batteries. It is a new material with good application potential.

[0039] Specific implementation two: the difference between this embodiment and specific implementation one is that: the concentration of the nitric acid solution in step one ① is 0.5mol / L~2mol / L; the heating and stirring in step one ① is specifically heating and stirring under the condition that the temperature is 90℃~120℃ and the stirring speed is 90r / min~120r / min for 6h~18h; the pH value is adjusted to 7 by using a NaOH solution with a concentration of 0.2mol / L~3.0mol / L in step one ①; the standing time in step one ① is 6h~48h, the bottom layer of insoluble powder is removed, and then the upper layer of the suspension is centrifuged and dried. The rest is the same as specific implementation one.

[0040] Specific implementation three: the difference between this embodiment and one of specific implementation one or two is that: the mass / volume ratio of the pre-functionalized carbon nanotubes to anhydrous ethanol in step one ② is 1g:(5~20)mL; the mass / volume ratio of the pre-functionalized carbon nanotubes to the total volume of vanadium triisopropoxide in step one ② is 1g:(0.2~3)mL; the total volume ratio of the total volume of vanadium triisopropoxide to the total volume of distilled water in step one ② is 1:(0.1~1); the concentration of the V2O5-loaded carbon nanotube suspension in step one ② is 20.0mg / mL~25.0mg / mL. The rest is the same as specific implementation one or two.

[0041] Specific implementation four: the difference between this embodiment and one of specific implementation one to three is that: in step one ②, the pre-functionalized carbon nanotubes are added to anhydrous ethanol, ultrasonic treatment is carried out under the condition that the ultrasonic power is 300W~700W for 15min~45min, vanadium triisopropoxide is added in 20~50 times under the condition that the stirring speed is 90r / min~120r / min, and the interval between each addition is 0.1h~1h, after the addition of vanadium triisopropoxide is completed, continuous stirring is carried out under the condition that the stirring speed is 90r / min~120r / min for 6h~18h, and distilled water is added in 50~100 times during the continuous stirring process, a suspension is obtained, the suspension is continuously stirred under the condition that the stirring speed is 90r / min~120r / min for 6h~18h, then it is settled for 0.5~3 days, washed with deionized water for 2~6 times, and finally centrifuged to obtain V2O5-loaded carbon nanotubes. The rest is the same as specific implementation one to three.

[0042] Specific implementation five: the difference between this embodiment and one of specific implementation one to four is that: the imidazole compound in steps two ① and ② is 1-methylimidazole, 1-methyl-3-octyl imidazolium chloride, 1-ethyl-3-methyl imidazole bromide, 1-ethyl-3-methyl imidazolium dicyanamide or 1-butyl-3-methyl imidazole chloride. The rest is the same as specific implementation one to four.

[0043] Embodiment six: different from one of embodiments one to five is that: the concentration of graphene oxide in the core layer spinning solution in step two 1 is 20.0 mg / mL to 25.0 mg / mL, and the mass ratio of graphene oxide to quinoline in the core layer spinning solution is 1:(0.1 to 5), and the mass ratio of graphene oxide to imidazole compounds is 1:(0.1 to 5); the concentration of V2O5-loaded carbon nanotubes in the skin layer spinning solution in step two 2 is 10 mg / mL to 12.5 mg / mL, and the mass ratio of V2O5-loaded carbon nanotubes to graphene oxide in the skin layer spinning solution is 1:(0.1 to 5), the mass ratio of V2O5-loaded carbon nanotubes to quinoline is 1:(0.1 to 5), and the mass ratio of V2O5-loaded carbon nanotubes to imidazole compounds is 1:(0.1 to 5). The others are the same as embodiments one to five.

[0044] Embodiment seven: different from one of embodiments one to six is that: in step two 1, the graphene oxide solution is stirred at a stirring speed of 90 r / min to 120 r / min for 6 h to 18 h, then quinoline is added, and stirred at a stirring speed of 90 r / min to 120 r / min for 6 h to 18 h, then imidazole compounds are added, and ultrasonic is performed at a power of 300 W to 700 W for 15 min to 45 min to obtain the core layer spinning solution; in step two 2, the V2O5-loaded carbon nanotube suspension is stirred at a stirring speed of 90 r / min to 120 r / min for 6 h to 18 h, then the graphene oxide solution and quinoline are added, and stirred at a stirring speed of 90 r / min to 120 r / min for 6 h to 18 h, then imidazole compounds are added, and ultrasonic is performed at a power of 300 W to 700 W for 15 min to 45 min to obtain the skin layer spinning solution. The others are the same as embodiments one to six.

[0045] Embodiment eight: different from one of embodiments one to seven is that: the inner jet diameter of the coaxial spinneret in step three is 100 μm to 1500 μm, and the outer jet diameter is 200 μm to 2750 μm; in step three, the skin layer spinning solution and the core layer spinning solution are used to prepare the skin-core structure base fiber electrode material by the wet spinning machine equipped with the coaxial spinneret at a core layer advancing rate of 0.01 mL / min to 1 mL / min and a shell layer advancing rate of 0.01 mL / min to 1 mL / min, and the coagulation bath used in the wet spinning is 2 mg / mL to 30 mg / mL of anhydrous calcium chloride ethanol solution. The others are the same as embodiments one to seven.

[0046] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that the high-temperature treatment in step four is specifically high-temperature treatment for 1h~8h under the condition of argon atmosphere and temperature of 550℃~900℃, and then natural cooling to room temperature under argon atmosphere. The others are the same as specific embodiments one to eight.

[0047] Specific embodiment ten: the difference between this embodiment and one of the specific embodiments one to nine is that the heat treatment in step four is specifically heat treatment for 1h~3h under the condition of air atmosphere and temperature of 260℃~300℃. The others are the same as specific embodiments one to nine.

[0048] The beneficial effects of the present application are verified by the following examples:

[0049] Example one:

[0050] A preparation method of a skin-core structure V2O5-based / graphene composite fiber electrode material, which is carried out according to the following steps:

[0051] I. Preparation of V2O5-loaded carbon nanotube suspension:

[0052] ①Put the multi-walled carbon nanotubes into a nitric acid solution, heat and stir under the condition of temperature of 98℃ and stirring speed of 120r / min for 12h, then adjust the pH value to 7 by using a NaOH solution with a concentration of 0.5mol / L, stand for 8h, remove the insoluble powder at the bottom, then centrifuge and dry the upper suspension to obtain pre-functionalized carbon nanotubes;

[0053] The concentration of the nitric acid solution is 1.5mol / L;

[0054] ②Put the pre-functionalized carbon nanotubes into anhydrous ethanol, ultrasonic for 30min under the condition of ultrasonic power of 500W, add triisopropoxy vanadium oxide in 20 times under the condition of stirring speed of 90r / min, and the interval between each addition is 0.5h, after all the triisopropoxy vanadium oxide is added, continuously stir for 12h under the condition of stirring speed of 90r / min, and add distilled water in 50 times during the continuous stirring process, obtain a suspension, continue to stir the suspension under the condition of stirring speed of 120r / min for 12h, then stand for 2 days, wash with deionized water for 3 times, finally centrifuge to obtain V2O5-loaded carbon nanotubes, put the V2O5-loaded carbon nanotubes into deionized water to obtain a V2O5-loaded carbon nanotube suspension;

[0055] The mass of the pre-functionalized carbon nanotube to the volume of anhydrous ethanol is 1g:6mL; the mass of the pre-functionalized carbon nanotube to the total volume of vanadium triisopropoxide is 1g:1mL; the total volume of the vanadium triisopropoxide to the total volume of distilled water is 1:0.5; the concentration of the V2O5-loaded carbon nanotube suspension is 25.0mg / mL;

[0056] II. Spinning solution preparation:

[0057] ①Under the condition that the stirring speed is 120r / min, the graphene oxide solution is stirred for 12h, then quinoline is added, under the condition that the stirring speed is 120r / min, stirring for 12h, then imidazole compound is added, under the condition that the power is 500W, ultrasonic treatment for 30min, to obtain the core layer spinning solution;

[0058] The imidazole compound is 1-methyl imidazole;

[0059] The concentration of graphene oxide in the core layer spinning solution is 20mg / mL, and the mass ratio of graphene oxide to quinoline in the core layer spinning solution is 1:0.2, and the mass ratio of graphene oxide to imidazole compound is 1:0.2;

[0060] ②Under the condition that the stirring speed is 120r / min, the V2O5-loaded carbon nanotube suspension is stirred for 10h, then graphene oxide solution and quinoline are added, under the condition that the stirring speed is 120r / min, stirring for 12h, then imidazole compound is added, under the condition that the power is 500W, ultrasonic treatment for 20min, to obtain the skin layer spinning solution;

[0061] The imidazole compound is 1-methyl imidazole;

[0062] The concentration of the V2O5-loaded carbon nanotube in the skin layer spinning solution is 10mg / mL, and the mass ratio of the V2O5-loaded carbon nanotube to graphene oxide in the skin layer spinning solution is 1:1, the mass ratio of the V2O5-loaded carbon nanotube to quinoline is 1:0.4, and the mass ratio of the V2O5-loaded carbon nanotube to imidazole compound is 1:1;

[0063] III. Wet spinning:

[0064] Under the condition that the core layer advancing rate is 0.1mL / min and the shell layer advancing rate is 0.1mL / min, the skin layer spinning solution and the core layer spinning solution are used to prepare the skin-core structure base fiber electrode material through the wet spinning machine equipped with a coaxial spinneret, and the coagulation bath used in the wet spinning is anhydrous calcium chloride ethanol solution with a concentration of 20mg / mL;

[0065] The inner nozzle diameter of the coaxial spinneret is 400 μm, and the outer nozzle diameter is 1100 μm.

[0066] Four, high-temperature treatment and heat treatment:

[0067] The core-sheath structure fiber electrode material is dried, and then high-temperature treated under the condition of argon atmosphere and temperature of 850℃ for 1.5h, and then naturally cooled to room temperature under the argon atmosphere, and then heat treated under the condition of air atmosphere and temperature of 290℃ for 2h, to obtain the core-sheath structure V2O5-based / graphene composite fiber electrode material (QVSCF).

[0068] The difference between the present comparative experiment and Example 1 is that: the quinoline and imidazole compounds in steps 2① and 2② are replaced by PVP, and the mass of PVP is equal to the total mass of quinoline and imidazole compounds; the core-sheath structure V2O5-based / graphene composite fiber electrode material prepared in step 4 is abbreviated as PVSCF. The others are the same as Example 1.

[0069] Figure 1 The preparation flow chart of the core-sheath structure V2O5-based / graphene composite fiber of Example 1, the scanning electron microscope image, the high-resolution transmission electron microscope image and the Raman spectrum image of the V2O5-loaded carbon nanotube prepared in step 1②, (a) is the preparation flow chart, (b) is the scanning electron microscope image, (c) is the high-resolution transmission electron microscope image, and (d) is the Raman spectrum image. As shown in the figures, V2O5 has been successfully loaded on the surface of the multi-walled carbon nanotube, and V2O5 presents a mixed structure of nanocrystal and amorphous crystal phase. The characteristic peaks of V2O5 and multi-walled carbon nanotube are clearly visible from the Raman spectrum of the composite material, and the existence of the V2O5 component can be determined.

[0070] Figure 2The structure, morphology characterization map and mechanical property map of the core-sheath structure V2O5-based / graphene composite fiber electrode material prepared in Example 1 and the comparative experiment are shown in (a) and (b) are scanning electron micrographs of QVSCF, (c) is a scanning electron micrograph of PVSCF, (d) is a scanning electron micrograph of QVSCF and an element surface scanning photograph of O, C and V, (e) is an XRD spectrum, (f) is a mechanical property map; as can be seen from the figure, the prepared composite fiber is a core-sheath structure, V element exists in the outer layer, and V element does not exist in the inner layer, which shows that the outer layer is a composite of V2O5-multi-walled carbon nanotube and graphene layer, and the inner layer is a graphene fiber structure. V2O5-multi-walled carbon nanotubes synthesized with the assistance of quinoline and imidazole compounds are uniformly attached to the surface of the graphene sheet layer; V2O5-multi-walled carbon nanotubes synthesized with the assistance of PVP do not closely contact with graphene. It can be seen from the XRD spectrum that the core-sheath structure fiber synthesized with the assistance of quinoline and imidazole compounds has a large amount of graphitized carbon inside, while the core-sheath structure fiber synthesized with the assistance of PVP has a large amount of amorphous carbon inside. It can be known from the mechanical property test that the mechanical property (227 MPa) of the composite fiber synthesized with the assistance of quinoline and imidazole compounds is much better than that (178 MPa) of the composite fiber synthesized with the assistance of PVP.

[0071] Figure 3 The sodium storage rate performance and bending stability characterization of the core-sheath structure V2O5-based / graphene composite fiber electrode material prepared in Example 1 and the comparative experiment are shown in (a) is the charge-discharge curve of QVSCF under different current densities, (b) is the rate performance under different current densities, (c) is the stability under different bending angles at 100 mA g -1 It can be seen from figure (a) that the core-sheath structure fiber electrode of QVSCF can be stably functional between 2.4 V and 1.0 V. It can be known from figure (b) that the rate performance of QVSCF is obviously better than that of PVSCF; it can be observed from figure (c) that the electrical stability of QVSCF is obviously better than that of PVSCF when the electrode is bent at an angle of 0°-180°.

[0072] Figure 4 The TEM photos and impedance spectrum of graphitized carbon / amorphous carbon in the fiber of the core-sheath structure V2O5-based / graphene composite fiber electrode material prepared in Example 1 and the comparative experiment after 100 cycles are shown in (a) is a GRTEM photo of graphitized carbon in QVSCF, (b) is a GRTEM photo of amorphous carbon in PVSCF, (c) is an impedance spectrum of QVSCF, PVSCF and sodium sheet assembled into a half-cell, (d) is an impedance spectrum of QVSCF and PVSCF in the low-frequency region of Z'-ω −1 / 2The relationship curve between the volume of the carbon and the resistance of the fiber is shown in Figure 6. It can be seen from the figure that a large amount of graphitized carbon can be observed in the QVSCF, while a large amount of amorphous carbon exists in the PVSCF fiber. The graphitized carbon helps to enhance the electrical conductivity and mechanical properties of the composite fiber. After being assembled into a fiber battery, it can be seen from Figure 6(c) that the resistance of the QVSCF is smaller than that of the PVSCF composite fiber; and it can be seen from Figure 6(d) that the Na + diffusion rate of the QVSCF is greater than that of the PVSCF composite fiber.

Claims

1. A method for preparing a core-shell structured V2O5-based / graphene composite fiber electrode material, characterized in that... It is done in the following steps: I. Preparation of carbon nanotube suspension loaded with V2O5: ① Place multi-walled carbon nanotubes in a nitric acid solution, heat and stir, then adjust the pH to 7, and then let stand and centrifuge and dry the upper suspension to obtain prefunctionalized carbon nanotubes. ② Add prefunctionalized carbon nanotubes to anhydrous ethanol and sonicate. Add triisopropoxyvanadium oxide in multiple portions. After all the triisopropoxyvanadium oxide is added, stir continuously and add distilled water in multiple portions during the continuous stirring process to obtain a suspension. Continue stirring the suspension, then let it settle, wash and centrifuge to obtain carbon nanotubes loaded with V2O5. Add the carbon nanotubes loaded with V2O5 to deionized water to obtain a carbon nanotube suspension loaded with V2O5. II. Preparation of spinning solution: ① Stir the graphene oxide solution, then add quinoline and stir, then add imidazole compounds and sonicate to obtain the core spinning solution; ② Stir the carbon nanotube suspension loaded with V2O5, then add graphene oxide solution and quinoline and stir, then add imidazole compound and sonicate to obtain skin spinning solution; III. Wet spinning: Sheath-core structured fiber electrode materials were prepared by using a wet spinning machine equipped with a coaxial spinneret and a sheath spinning solution and a core spinning solution. IV. High-Temperature Treatment and Heat Treatment: The core-shell structured fiber electrode material is dried, then subjected to high-temperature treatment in an argon atmosphere, and finally heat-treated in an air atmosphere to obtain the core-shell structured V2O5-based / graphene composite fiber electrode material.

2. The method for preparing a core-shell structured V2O5-based / graphene composite fiber electrode material according to claim 1, characterized in that... The concentration of the nitric acid solution mentioned in step 1① is 0.5 mol / L to 2 mol / L; the heating and stirring mentioned in step 1① is specifically carried out at a temperature of 90℃ to 120℃ and a stirring speed of 90 r / min to 120 r / min for 6 h to 18 h; the pH value is adjusted to 7 using a NaOH solution with a concentration of 0.2 mol / L to 3.0 mol / L in step 1①; the suspension is allowed to stand for 6 h to 48 h to remove the bottom layer of insoluble powder, and then the upper suspension is centrifuged and dried.

3. The method for preparing a core-shell structured V2O5-based / graphene composite fiber electrode material according to claim 1, characterized in that... The mass ratio of the prefunctionalized carbon nanotubes to the volume of anhydrous ethanol in step 1② is 1 g:(5~20) mL; the mass ratio of the prefunctionalized carbon nanotubes to the total volume of triisopropoxyvanadium oxide in step 1② is 1 g:(0.2~3) mL; the total volume ratio of the triisopropoxyvanadium oxide to the total volume of distilled water in step 1② is 1:(0.1~1); and the concentration of the carbon nanotube suspension loaded with V2O5 in step 1② is 20.0 mg / mL~25.0 mg / mL.

4. The method for preparing a core-shell structured V2O5-based / graphene composite fiber electrode material according to claim 1, characterized in that... In step 1②, prefunctionalized carbon nanotubes are added to anhydrous ethanol and sonicated for 15 to 45 minutes at an ultrasonic power of 300 W to 700 W. Vanadium triisopropoxy is added in 20 to 50 portions at a stirring speed of 90 to 120 r / min, with an interval of 0.1 to 1 hour between each addition. After all the vanadium triisopropoxy has been added, the mixture is stirred continuously for 6 to 18 hours at a stirring speed of 90 to 120 r / min, with distilled water added in 50 to 100 portions during this continuous stirring process to obtain a suspension. The suspension is then stirred for another 6 to 18 hours at a stirring speed of 90 to 120 r / min, followed by sedimentation for 0.5 to 3 days. The suspension is then washed 2 to 6 times with deionized water and finally centrifuged to obtain carbon nanotubes loaded with V₂O₅.

5. The method for preparing a core-shell structured V2O5-based / graphene composite fiber electrode material according to claim 1, characterized in that... The imidazole compounds mentioned in steps ① and ② are 1-methylimidazolium, 1-methyl-3-octyl imidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium dicyandiamide, or 1-butyl-3-methylimidazolium chloride.

6. The method for preparing a core-shell structured V2O5-based / graphene composite fiber electrode material according to claim 1, characterized in that... In step 2①, the concentration of graphene oxide in the core spinning solution is 20.0 mg / mL to 25.0 mg / mL, and the mass ratio of graphene oxide to quinoline in the core spinning solution is 1:(0.1~5), and the mass ratio of graphene oxide to imidazole compounds is 1:(0.1~5); in step 2②, the concentration of V2O5-loaded carbon nanotubes in the skin spinning solution is 10 mg / mL to 12.5 mg / mL, and the mass ratio of V2O5-loaded carbon nanotubes to graphene oxide in the skin spinning solution is 1:(0.1~5), the mass ratio of V2O5-loaded carbon nanotubes to quinoline is 1:(0.1~5), and the mass ratio of V2O5-loaded carbon nanotubes to imidazole compounds is 1:(0.1~5).

7. The method for preparing a core-shell structured V2O5-based / graphene composite fiber electrode material according to claim 1, characterized in that... In step 2①, the graphene oxide solution is stirred for 6 to 18 hours at a stirring speed of 90 to 120 r / min. Then, quinoline is added, and the mixture is stirred for 6 to 18 hours at a stirring speed of 90 to 120 r / min. Next, an imidazole compound is added, and the mixture is sonicated for 15 to 45 minutes at a power of 300 to 700 W to obtain the core spinning solution. In step 2②, the carbon nanotube suspension loaded with V2O5 is stirred for 6 to 18 hours at a stirring speed of 90 to 120 r / min. Then, the graphene oxide solution and quinoline are added, and the mixture is stirred for 6 to 18 hours at a stirring speed of 90 to 120 r / min. Next, an imidazole compound is added, and the mixture is sonicated for 15 to 45 minutes at a power of 300 to 700 W to obtain the skin spinning solution.

8. The method for preparing a core-shell structured V2O5-based / graphene composite fiber electrode material according to claim 1, characterized in that... In step three, the inner nozzle diameter of the coaxial spinneret is 100μm~1500μm, and the outer nozzle diameter is 200μm~2750μm. In step three, under the conditions of a core layer advance rate of 0.01mL / min~1mL / min and a shell layer advance rate of 0.01mL / min~1mL / min, the core-shell structure fiber electrode material is prepared by using the skin layer spinning solution and the core layer spinning solution through a wet spinning machine equipped with a coaxial spinneret. The coagulation bath used in the wet spinning is an ethanol solution of anhydrous calcium chloride with a concentration of 2mg / mL~30mg / mL.

9. The method for preparing a core-shell structured V2O5-based / graphene composite fiber electrode material according to claim 1, characterized in that... The high-temperature treatment described in step four is specifically carried out in an argon atmosphere at a temperature of 550℃~900℃ for 1h~8h, followed by natural cooling to room temperature in an argon atmosphere.

10. The method for preparing a core-shell structured V2O5-based / graphene composite fiber electrode material according to claim 1, characterized in that... The heat treatment described in step four is specifically carried out in an air atmosphere at a temperature of 260℃~300℃ for 1h~3h.

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