Nitrogen-doped vanadium dioxide nanofiber as well as preparation method and application thereof

Abstract

The invention discloses a nitrogen-doped vanadium dioxide nanofiber as well as a preparation method and application thereof, and belongs to the technical field of zinc ion batteries. The preparation method of the nitrogen-doped vanadium dioxide nanofiber comprises the following steps: a, adding a vanadium source and a reducing agent into water, and heating and stirring to react until the vanadium source is completely dissolved; b, polyvinylpyrrolidone is added and stirred to be dissolved, and a spinning solution is obtained; c, performing electrostatic spinning, and drying to obtain a nanofiber precursor; and d, putting the nanofiber precursor into a tubular furnace, and calcining in an inert gas atmosphere to obtain the nitrogen-doped vanadium dioxide nanofiber. By optimizing the preparation process, low-cost and high-efficiency vanadium dioxide nanofiber production is realized, the conductivity and cycling stability of VO2 are remarkably improved, and the problems that an existing vanadium dioxide nanofiber preparation method is high in cost and low in efficiency, and a prepared material is poor in electrochemical performance can be effectively solved.

Description

Technical Field

[0001] The invention belongs to the technical field of zinc ion batteries, and in particular relates to nitrogen-doped vanadium dioxide nanofibers and a preparation method and application thereof. Background Art

[0002] Vanadium dioxide (VO2) is formed by distorted [VO6] octahedrons, which form a tunnel-like skeleton by sharing corners and edges, with a length of 0.82 nm along the b-axis. 2 , the a-axis direction is 0.34nm 2 , c-axis direction is 0.5nm 2 This large tunnel structure is conducive to the rapid intercalation and extraction of zinc ions, and has good rate performance. Vanadium dioxide is considered to be one of the most promising cathode materials for aqueous zinc-ion batteries. However, the low conductivity of VO2 materials and the dissolution of VO2 during the charge and discharge cycle lead to poor rate performance and cycle stability of aqueous zinc-ion batteries, limiting the commercial application of Zn / VO2 aqueous batteries.

[0003] CN112233911B discloses a vanadium dioxide nano-carbon fiber composite material and its preparation method and use. The preparation method includes the following steps: a. Preparation of ethylene glycol vanadyl solution: mixing ammonium metavanadate and ethylene glycol, reacting to generate ethylene glycol vanadyl for standby use; b. Preparation of spinning solution: taking polyacrylonitrile solution and ethylene glycol vanadyl solution and mixing them evenly, and then diluting the mixed solution to a total content of polyacrylonitrile and ethylene glycol vanadyl of 5-20% v / v; c. electrostatic spinning with the spinning solution; d. Preparation of composite material. The method for preparing vanadium dioxide nano-carbon fiber composite material is relatively complex and costly.

[0004] Ultrafast Zn 2+ Intercalation and Deintercalation in Vanadium Dioxide. and Functional Fiber Mats with Tunable Diffuse Reflectance Composed of Electrospun VO2 / PVP Composite Fibers. disclose methods for preparing VO2 nanofibers. However, in the above prior art for preparing VO2 nanofibers, the process route is long, the preparation cost is high, the efficiency is low, and the electrochemical properties of the prepared materials are poor. Therefore, it is urgent to study a low-cost and high-efficiency method for preparing vanadium dioxide nanofibers that can improve the electrochemical properties of the materials. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the existing method for preparing vanadium dioxide nanofibers has high cost and low efficiency, and the electrochemical performance of the prepared material is poor.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] In a first aspect, the present invention provides a method for preparing nitrogen-doped vanadium dioxide nanofibers, comprising the following steps:

[0008] a. Add a vanadium source and a reducing agent to water, heat and stir the reaction until the vanadium source is completely dissolved to generate a blue solution;

[0009] b. Add polyvinyl pyrrolidone to the blue solution, stir and dissolve to obtain a spinning solution;

[0010] c. electrospinning the spinning solution, and drying the spinning solution to obtain a nanofiber precursor;

[0011] d. The nanofiber precursor is placed in a tubular furnace and calcined under an inert gas atmosphere, the heating rate is controlled to be 5 to 10°C / min, and the calcination temperature is 550 to 600°C to obtain nitrogen-doped vanadium dioxide nanofibers.

[0012] In the above step a, the vanadium source is at least one of vanadium pentoxide, ammonium metavanadate and ammonium polyvanadate; and the reducing agent is at least one of oxalic acid, citric acid and tartaric acid.

[0013] In the above step a, the vanadium concentration in the blue solution is controlled to be 0.1-0.5 mol / L, and the molar ratio of the reducing agent to the vanadium source is 2-4:1.

[0014] In the above step a, the mixture is heated to 90-100° C. and stirred for reaction for 2-4 hours.

[0015] In the above step b, the mass fraction of polyvinyl pyrrolidone in the spinning solution is 5-20%.

[0016] In the above step c, the voltage of the electrospinning machine is controlled to be 20-25 kV, the feed rate is 1-2 mL / h, the indoor temperature is 20-35° C., and the humidity is 30-50%.

[0017] In the above step c, drying is performed by placing the mixture in a vacuum drying oven at 60° C. for 12 to 24 hours.

[0018] In the above step d, the inert gas is N2 or Ar, and the calcination time is 1 to 4 hours.

[0019] In a second aspect, the present invention provides a nitrogen-doped vanadium dioxide nanofiber having a diameter of 50 to 400 nm, which is prepared by the above-mentioned preparation method.

[0020] In a third aspect, the present invention provides an application of the above-mentioned nitrogen-doped vanadium dioxide nanofibers in aqueous zinc ion batteries: nitrogen-doped vanadium dioxide nanofibers, acetylene black and polyvinylidene fluoride are mixed in a mass ratio of 8:1:1 as a positive electrode, 0.2 mm commercial zinc foil is used as a negative electrode, and 3M Zn(CF3SO3)2 is used as an electrolyte to assemble into a battery.

[0021] The beneficial effects of the present invention are as follows: the present invention provides an N-doped VO2 nanofiber electrode material and a preparation method thereof, and by optimizing the preparation process, realizes low-cost and high-efficiency production of vanadium dioxide nanofibers, significantly improves the conductivity and cycle stability of VO2, and greatly improves the rate performance and cycle stability of VO2-based aqueous zinc-ion batteries, and has good prospects for promotion and application.

[0022] The nitrogen-doped vanadium dioxide nanofibers of the present invention have a high specific surface area, excellent electrical conductivity and mechanical flexibility, and can effectively improve the rate performance and cycle stability of aqueous zinc ion batteries. At a current density of 5A / g, the specific capacity can reach 178mAh / g, and after 3000 cycles, the capacity retention rate is as high as 93.6%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 XRD pattern of nitrogen-doped vanadium dioxide nanofibers prepared in Example 1;

[0024] Figure 2 This is the SEM image of nitrogen-doped vanadium dioxide nanofibers prepared in Example 1;

[0025] Figure 3 is the rate performance curve of the assembled battery in Example 1;

[0026] Figure 4 The cycle performance of the battery assembled in Example 1. DETAILED DESCRIPTION

[0027] The technical solution of the present invention can be specifically implemented in the following manner.

[0028] The present invention uses vanadium pentoxide, ammonium metavanadate, and ammonium polyvanadate as raw materials, reduces them into a 4-valent vanadium solution by a reducing agent, then adds PVP to adjust the viscosity of the solution, prepares a nanofiber precursor by electrostatic spinning, and finally prepares VO2 nanofibers by a heat treatment process. This is achieved by the following technical solutions:

[0029] (1) Using one or more of vanadium pentoxide, ammonium metavanadate or ammonium polyvanadate as the vanadium source and one or more of oxalic acid, citric acid and tartaric acid as the reducing agent;

[0030] (2) dissolving a vanadium source and a reducing agent in an aqueous solution, controlling the vanadium concentration to be 0.1 to 0.5 mol / L, and the molar ratio of the reducing agent to the vanadium source to be 2 to 4:1, reacting at 90 to 100° C. with stirring for 2 to 4 hours, until the vanadium source is completely dissolved to generate a blue solution, which is marked as solution A;

[0031] (3) adding polyvinyl pyrrolidone (PVP) to solution A, stirring and dissolving to obtain solution B, wherein the mass fraction of PVP is controlled to be 5-20%, and the purpose of adding PVP is to adjust the viscosity of the solution;

[0032] (4) preparing a nanofiber precursor by electrospinning technology, controlling the voltage of the electrospinning machine to 20-25 kV, the feed rate to 1-2 mL / h, the room temperature to 20-35 ° C, the humidity to 30-50%, and then placing it in a vacuum drying oven at 60 ° C for 12-24 h to obtain a nanofiber precursor;

[0033] (5) The prepared nanofiber precursor is placed in a tubular furnace and calcined in a N2 or Ar inert gas atmosphere, with a heating rate of 5 to 10°C / min, a calcination temperature of 550 to 600°C, and a calcination time of 1 to 4 hours to obtain nitrogen-doped vanadium dioxide nanofibers with a diameter of 50 to 400 nm.

[0034] The technical solution and effects of the present invention are further illustrated below through practical examples.

[0035] Example

[0036] Example 1

[0037] (1) A certain amount of vanadium pentoxide powder is dispersed in a certain amount of deionized water, and the molar mass is controlled at 0.2M; then a certain amount of citric acid is added as a reducing agent, and the molar ratio of the reducing agent to the vanadium pentoxide is 2:1; then the solution is heated to 90°C and stirred for 2 hours to form a blue solution A; polyvinyl pyrrolidone is added during the stirring process, and the mass fraction of the polyvinyl pyrrolidone is controlled to be 5%, thereby obtaining a solution B.

[0038] (2) Take a certain amount of solution B (10 mL) for electrospinning, control the voltage of the electrospinning machine to 20 kV, the feed rate to 1 mL / h, the room temperature to 20 ° C, the humidity to 30%, and put it into a vacuum drying oven after spinning, and dry it at 60 ° C for 12 hours. The vanadium dioxide nanofiber precursor can be obtained. Subsequently, the vanadium dioxide nanofiber precursor is placed in a tubular furnace and calcined in a N2 gas atmosphere, controlling the heating rate to 5 ° C / min, the calcination temperature to 550 ° C, and the calcination time to 2 hours to obtain nitrogen-doped vanadium dioxide nanofibers.

[0039] (3) VO2 nanofibers, acetylene black and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 8:1:1 as the positive electrode, 0.2 mm commercial zinc foil was used as the negative electrode, and 3 M Zn(CF3SO3)2 was used as the electrolyte. The assembled battery was left to stand for 12 h and then electrochemically tested on a difficult test system with a voltage window of 0.2-1.6 V.

[0040] Figure 1 This is the XRD diagram of the prepared nitrogen-doped VO2 nanofibers. It can be seen from the figure that the position of the strongest peak 2θ is 29.1°. Compared with the JCPDF standard card, it is the characteristic peak position of vanadium dioxide. No characteristic peaks of other vanadium oxides are seen, and the content of other products is relatively small. The product synthesized by the method of the present invention is nitrogen-doped VO2.

[0041] Figure 2 The scanning electron microscope image of the prepared nitrogen-doped VO2 nanofibers is shown in FIG. 1 . As can be seen from the image, the product prepared by the method of the present invention is a nanofiber with a diameter of 50 nm.

[0042] Figure 3 This is the rate performance curve of the assembled battery. It can be seen from the figure that the battery assembled with the nitrogen-doped vanadium dioxide nanofibers of the present invention has a specific capacity of 394, 365, 343, 326, 303, 248 and 178 mAh / g at currents of 0.2, 0.4, 0.6, 0.8, 1, 2 and 5 A / g, respectively.

[0043] Figure 4 The figure is a cycle performance diagram of the assembled battery. It can be seen from the figure that the nitrogen-doped vanadium dioxide nanofibers of the present invention are used as the positive electrode material of the zinc ion battery. At a current density of 5A / g, after 3000 cycles, the capacity retention rate reaches 93.6%.

[0044] Example 2

[0045] (1) A certain amount of ammonium metavanadate powder is dispersed in a certain amount of deionized water, and the molar mass is controlled at 0.4 M; then a certain amount of oxalic acid is added as a reducing agent, and the molar ratio of the reducing agent to vanadium pentoxide is 3:1; then the solution is heated to 95° C. and stirred for 2 h to form a blue solution A; polyvinyl pyrrolidone is added during the stirring process, and the mass fraction of the polyvinyl pyrrolidone is controlled to be 10% to obtain a solution B.

[0046] (2) Take a certain amount of solution B (10 mL) for electrospinning, control the voltage of the electrospinning machine to 25 kV, the feed rate to 2 mL / h, the room temperature to 30 ° C, the humidity to 50%, and after the spinning is completed, put the substrate into a vacuum drying oven and dry it at 60 ° C for 12 hours. The vanadium dioxide nanofiber precursor can be obtained. Subsequently, the vanadium dioxide nanofiber precursor is placed in a tubular furnace and calcined in a N2 gas atmosphere, the heating rate is controlled to be 5 ° C / min, the calcination temperature is 600 ° C, and the calcination time is 4 hours to obtain nitrogen-doped vanadium dioxide nanofibers with a diameter of 100 nm.

[0047] Example 3

[0048] A certain amount of ammonium polyvanadate powder is dispersed in a certain amount of deionized water, and the molar mass is controlled at 0.5M; then a certain amount of citric acid is added as a reducing agent, and the molar ratio of the reducing agent to vanadium pentoxide is 4:1, and then heated to 100°C and stirred for 2 hours to form a blue solution A. Polyvinyl pyrrolidone is added during the stirring process, and the mass fraction of polyvinyl pyrrolidone is controlled to be 20%, thereby obtaining a solution B.

[0049] Take a certain amount of solution B (10mL) for electrospinning, control the voltage of the electrospinning machine to 25kV, the feed rate to 1mL / h, the indoor temperature to 30℃, the humidity to 50%, and after spinning, put the substrate into a vacuum drying oven and dry it at 60℃ for 12h. The vanadium dioxide nanofiber precursor can be obtained. Subsequently, the vanadium dioxide nanofiber precursor is placed in a tubular furnace and calcined in a N2 gas atmosphere, controlling the heating rate to 10℃ / min, the calcination temperature to 600℃, and the calcination time to 4h to obtain nitrogen-doped vanadium dioxide nanofibers with a diameter of 200nm.

Claims

1. A method for preparing nitrogen-doped vanadium dioxide nanofibers, characterized in that: The steps include: a. Add a vanadium source and a reducing agent to water, heat and stir the reaction until the vanadium source is completely dissolved to generate a blue solution; b. Add polyvinyl pyrrolidone to the blue solution, stir and dissolve to obtain a spinning solution; c. electrospinning the spinning solution, and drying the spinning solution to obtain a nanofiber precursor; d. The nanofiber precursor is placed in a tubular furnace and calcined under an inert gas atmosphere, the heating rate is controlled to be 5 to 10°C / min, and the calcination temperature is 550 to 600°C to obtain nitrogen-doped vanadium dioxide nanofibers.

2. The method for preparing nitrogen-doped vanadium dioxide nanofibers according to claim 1, characterized in that: In step a, the vanadium source is at least one of vanadium pentoxide, ammonium metavanadate and ammonium polyvanadate; and the reducing agent is at least one of oxalic acid, citric acid and tartaric acid.

3. The method for preparing nitrogen-doped vanadium dioxide nanofibers according to claim 1, characterized in that: In step a, the vanadium concentration in the blue solution is controlled to be 0.1-0.5 mol / L, and the molar ratio of the reducing agent to the vanadium source is 2-4:

1.

4. The method for preparing nitrogen-doped vanadium dioxide nanofibers according to claim 1, characterized in that: In step a, heat to 90-100° C. and stir to react for 2-4 hours.

5. The method for preparing nitrogen-doped vanadium dioxide nanofibers according to claim 1, characterized in that: In step b, the mass fraction of polyvinyl pyrrolidone in the spinning solution is 5-20%.

6. The method for preparing nitrogen-doped vanadium dioxide nanofibers according to claim 1, characterized in that: In step c, the voltage of the electrospinning machine is controlled to be 20-25 kV, the feed rate is 1-2 mL / h, the indoor temperature is 20-35° C., and the humidity is 30-50%.

7. The method for preparing nitrogen-doped vanadium dioxide nanofibers according to claim 1, characterized in that: In step c, drying is performed by placing the product in a vacuum drying oven at 60° C. for 12 to 24 hours.

8. The method for preparing nitrogen-doped vanadium dioxide nanofibers according to claim 1, characterized in that: In step d, the inert gas is N2 or Ar, and the calcination time is 1 to 4 hours.

9. Nitrogen-doped vanadium dioxide nanofibers, characterized in that: The diameter is 50 to 400 nm and is prepared by the preparation method according to any one of claims 1 to 8.

10. Application of nitrogen-doped vanadium dioxide nanofibers in aqueous zinc ion batteries, characterized in that: The nitrogen-doped vanadium dioxide nanofibers described in claim 9, acetylene black and polyvinylidene fluoride are mixed in a mass ratio of 8:1:1 as the positive electrode, 0.2 mm commercial zinc foil is used as the negative electrode, and 3M Zn(CF3SO3)2 is used as the electrolyte to assemble into a battery.

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