A method for constructing highly active gradient porous carbon nanofiber electrode materials based on PVP-PAN bicomponents and its application

Abstract

This invention relates to the field of battery materials and energy storage technology, specifically to a method for constructing a highly active gradient porous carbon nanofiber electrode material based on a PVP-PAN bicomponent and its application. Polyvinylpyrrolidone (PVP) and polyacrylonitrile (PAN) are mixed with N,N,-dimethylformamide to obtain an electrospinning precursor solution. Using electrospinning technology, the precursor solution is continuously electrospun in order of PVP content to obtain a raw composite fiber material. The obtained raw composite fiber material is flattened using a corundum plate and placed in a tube furnace for pre-oxidation and carbonization treatment to obtain a highly active porous carbon nanofiber electrode material with a gradient distribution of structure and composition. Applying this material to flow battery electrode materials can simultaneously address the mass transfer and charge transfer processes of the flow battery electrode reaction, improving battery efficiency and cycle stability. This invention is simple, easy to operate, and flexible in design, showing excellent application prospects.

Description

Technical Field

[0001] This invention relates to the field of battery materials and energy storage technology, specifically to a method for constructing highly active gradient porous carbon nanofiber electrode materials based on a PVP-PAN bicomponent and its application. Background Technology

[0002] The efficient use of clean and renewable energy sources and the reduction of traditional energy sources such as oil are key to ensuring long-term energy supply, improving the human living environment, and achieving green and sustainable development strategies. With the rapid development of renewable energy, large-scale energy storage technologies have also received widespread attention. Flow batteries, especially the rapidly developing vanadium redox flow battery technology, are among the most commercially viable large-scale energy storage technologies. They offer advantages such as easy scalability, long cycle life, high safety, fast response, and large capacity, making them one of the preferred technologies for large-scale energy storage.

[0003] Electrodes, as the site of electrochemical reactions in flow batteries, directly affect battery performance. Currently, the most widely used electrode material for flow batteries is polyacrylonitrile-based carbon fiber, which has advantages such as low cost, high conductivity, and stable properties, but its electrochemical reactivity is relatively poor. By adding catalysts and pore-forming agents to adjust the fiber surface activity and pore structure, electrode reactivity can be improved to some extent.

[0004] The main problems limiting the large-scale application of flow batteries are the performance degradation and low power density caused by concentration polarization at high current densities. Improving the pore structure of the electrodes to enhance mass transfer performance while maintaining good reactivity is an effective way to solve this problem. Electrospinning technology is used to continuously electrospin solutions of polyvinylpyrrolidone / polyacrylonitrile (PVP) precursors with different contents. Subsequent heat treatment pyrolyzes the PVP, providing richer active sites and larger pore structures for the electrospun carbon nanofiber electrodes. This structural and compositional change is a continuous gradient, resulting in highly active gradient porous carbon nanofiber electrode materials. This effectively improves the electrolyte transport rate within the porous electrode, increases the effective reaction area and electrolyte utilization, further enhancing battery performance and providing a new and simple approach for constructing high-performance flow batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a method for constructing highly active gradient porous carbon nanofiber electrode materials based on a PVP-PAN bicomponent, and to apply it to electrode materials for flow batteries. By mixing different masses of polyvinylpyrrolidone (PVP) with specific masses of polyacrylonitrile (PAN) and N,N,-dimethylformamide, electrospinning precursor solutions with different PVP contents are obtained. Using electrospinning technology, the electrospinning precursor solutions are continuously electrospun sequentially according to PVP content to obtain the original composite fiber material. After heat treatment to thermally decompose the PVP, a porous electrode material with a gradient structure is prepared. This method improves the electrode's electrochemical reactivity, enhances its pore structure, and promotes electrolyte mass transfer, thereby effectively improving battery performance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for constructing highly active gradient porous carbon nanofiber electrode materials based on a PVP-PAN bicomponent, comprising the following steps:

[0007] 1) Different masses of polyvinylpyrrolidone and a fixed mass of polyacrylonitrile were dissolved simultaneously in N,N,-dimethylformamide DMF to obtain PAN / DMF electrospinning precursor solutions with different PVP contents.

[0008] 2) The electrospinning precursor solution prepared in step 1) is sequentially drawn into a syringe with a stainless steel needle. Using electrospinning technology, the electrospinning precursor solution is continuously electrospinned according to the order of PVP content to obtain the original nanofiber material with a gradient distribution of PVP content.

[0009] 3) The original nanofiber material with a gradient distribution of PVP content obtained in step 2) is flattened with a corundum plate, placed in a tube furnace for pre-oxidation and carbonization treatment, and then cooled to room temperature to obtain a highly active porous carbon nanofiber electrode material with a gradient distribution of composition and structure.

[0010] Furthermore, in the above-mentioned method for constructing a highly active gradient porous carbon nanofiber electrode material based on a PVP-PAN bicomponent, in step 1), the molecular weight of the polyacrylonitrile is 150,000 and the molecular weight of the polyvinylpyrrolidone is 80,000.

[0011] Furthermore, in the above-mentioned method for constructing a highly active gradient porous carbon nanofiber electrode material based on a PVP-PAN bicomponent, in step 1), the mass ratio of polyacrylonitrile to polyvinylpyrrolidone in the mixed solution of polyacrylonitrile, polyvinylpyrrolidone, and N,N-dimethylformamide is 1:0, 5:1, or 3:1.

[0012] Furthermore, in the above-mentioned method for constructing a highly active gradient porous carbon nanofiber electrode material based on a PVP-PAN two-component system, in step 1), the total mass percentage concentration of polyacrylonitrile and polyvinylpyrrolidone is 10wt% to 20wt%.

[0013] Furthermore, in the above-mentioned method for constructing highly active gradient porous carbon nanofiber electrode materials based on PVP-PAN bicomponents, in step 2), the process conditions of the electrospinning technology are as follows: the stainless steel nozzle is of model G15 to G22; the take-up device is a stainless steel roller with a rotation speed of 50 to 150 r / min; the voltage between the nozzle and the roller is 18 to 22 kV; the distance between the nozzle and the roller is 10 to 15 cm; the spinning temperature is 25°C to 35°C; the spinning humidity is 30% RH to 50% RH; and the pushing speed is 20 to 40 μL / min.

[0014] Furthermore, in the above-mentioned method for constructing a highly active gradient porous carbon nanofiber electrode material based on PVP-PAN bicomponents, the pre-oxidation treatment conditions in step 3) are: heating to 290°C at a heating rate of 1°C / min in an air atmosphere and holding at that temperature for 60min.

[0015] Furthermore, in the above-mentioned method for constructing a highly active gradient porous carbon nanofiber electrode material based on PVP-PAN bicomponents, the carbonization treatment conditions in step 3) are: heating at a rate of 4℃ / min under a nitrogen or argon atmosphere, and holding at 1000℃ for 120min.

[0016] Application of highly active gradient porous carbon nanofiber electrode materials based on PVP-PAN bicomponents prepared according to any of the above methods in flow batteries.

[0017] Furthermore, in the above applications, the flow battery includes vanadium redox flow batteries, iron redox flow batteries, iron-chromium redox flow batteries, and organic flow batteries.

[0018] The advantages and beneficial effects of this invention are:

[0019] 1. This invention utilizes a simple and controllable electrospinning technique, combined with subsequent pre-oxidation and carbonization processes, to easily obtain an integrated composite multilayer carbon nanofiber electrode with different porosities and pore size distributions. It can easily construct porous carbon fiber electrode materials with gradient structures. The method is simple, flexible, and universal.

[0020] 2. The present invention allows for adjustment of fiber composition and structural characteristics based on requirements and electrochemical reaction characteristics, facilitating adjustment of preparation conditions according to application characteristics, and is simple to operate and easy to control.

[0021] 3. This invention applies the gradient-structured carbon nanofiber material to the electrode of a flow battery, taking into account both the material's activity and mass transfer performance. While improving the reaction kinetics of the vanadium battery electrode, it also enhances the transport performance of active materials, effectively reduces concentration polarization, and enables the battery to be charged and discharged at higher current densities, thereby more effectively improving the electrolyte utilization rate and power density of the battery. Attached Figure Description

[0022] Figure 1 (a1-a3) are scanning electron microscope (SEM) images of the blank carbon nanofiber electrode material ECNFs prepared in Example 1 at different magnifications; (b1-b3) are SEM images of the front side (the side with high PVP content) of the gradient structure porous carbon nanofiber electrode material PG-ECNFs at different magnifications.

[0023] Figure 2 The images show the cyclic voltammetry curves of the front (high PVP content side: PGH-ECNFs) and back (PVP-free side: PGO-ECNFs) of the blank carbon nanofiber electrode material ECNFs and the gradient structure porous carbon nanofiber electrode material PG-ECNFs prepared in Example 1 in vanadium electrolyte.

[0024] Figure 3 The figures show a comparison of charge-discharge curves (a), capacity (b), voltage efficiency and coulombic efficiency (c), energy efficiency (d) of two groups of batteries prepared in Example 2 with blank ECNFs or PG-ECNFs as electrodes, and a cycle stability curve (e) of the battery with PG-ECNFs as electrodes. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] Example 1

[0027] (I) Comparative Example – Blank Carbon Nanofiber Electrode Material

[0028] The preparation method includes the following steps:

[0029] 1) Preparation of blank electrospinning precursor solution

[0030] The dried polyacrylonitrile (PAN) powder with a molecular weight of 150,000 was dissolved in N,N,-dimethylformamide (DMF) and magnetically stirred at 80°C for 6 hours until completely dissolved, to obtain a blank PAN / DMF electrospinning precursor solution with a mass percentage concentration of 14 wt% polyacrylonitrile (PAN).

[0031] 2) Preparation of original blank polyacrylonitrile nanofiber materials by electrospinning

[0032] A blank PAN / DMF electrospinning precursor solution was drawn into the syringe of an electrospinning device. Electrospinning was then performed to obtain raw blank polyacrylonitrile nanofibers. Electrospinning conditions: G20 stainless steel nozzle, stainless steel roller take-up unit, roller speed 100 r / min; voltage between nozzle and roller 20 kV; distance between nozzle and roller 12 cm; spinning temperature 25℃; spinning humidity 30% RH; feed rate 30 μL / min; 6 mL precursor solution spun.

[0033] 3) Pre-oxidation and carbonization

[0034] The obtained blank polyacrylonitrile nanofiber material was flattened with a corundum plate and placed in a tube furnace for pre-oxidation treatment, i.e., heated to 290℃ at a heating rate of 1℃ / min in air atmosphere and held for 60min; then carbonization treatment was performed, i.e., heated to 1000℃ for 120min in N2 atmosphere at a heating rate of 5℃ / min and then cooled to room temperature to obtain blank carbon nanofiber electrode material ECNFs.

[0035] like Figure 1 As shown in a1-a3, the diameter of the obtained blank carbon nanofiber electrode material is about 100-150 nm, and the fiber surface is relatively smooth.

[0036] (II) Highly Active Porous Carbon Nanofiber Electrode Materials

[0037] The preparation method includes the following steps:

[0038] 1) Preparation of electrospinning precursor solution

[0039] Dry polyacrylonitrile (PAN) powder with a molecular weight of 150,000 and polyvinylpyrrolidone (PVP) with a molecular weight of 85,000 were dissolved in N,N,-dimethylformamide (DMF) in different proportions. The mixture was magnetically stirred at 80°C for 6 hours until completely dissolved, resulting in three (PAN+PVP) / DMF electrospinning precursor solutions with a PAN mass percentage concentration of 14 wt% and PAN:PVP mass ratios of 1:0, 5:1, and 3:1.

[0040] 2) Preparation of original composite fiber materials by electrospinning

[0041] Three (PAN+PVP) / DMF electrospinning precursor solutions were separately drawn into the syringe of an electrospinning device. Using electrospinning technology, the precursor solutions were continuously electrospun according to their PVP content, i.e., the mass ratios of polyacrylonitrile (PAT):polyvinylpyrrolidone (PVP) in the precursor solutions were 1:0, 5:1, and 3:1, respectively, to obtain raw fiber materials with a gradient PVP content distribution. Electrospinning conditions: G20 stainless steel nozzle, stainless steel roller take-up unit, roller speed 100 r / min; voltage between nozzle and roller 20 kV; distance between nozzle and roller 12 cm; spinning temperature 25℃; spinning humidity 30% RH; push speed 30 μL / min; 2 mL of each of the three (PAN+PVP) / DMF electrospinning precursor solutions was continuously spun.

[0042] 3) Pre-oxidation and carbonization

[0043] The obtained raw carbon nanofiber material was flattened using a corundum plate and placed in a tube furnace for pre-oxidation treatment, i.e., heated to 290℃ at a heating rate of 1℃ / min and held for 60 min in air. Then, carbonization treatment was performed, i.e., heated to 1000℃ for 120 min at a heating rate of 5℃ / min in N2 atmosphere, and then cooled to room temperature to obtain PVP-doped highly active gradient porous carbon nanofiber electrode material PG-ECNFs. The side with high PVP content was designated as the front side of the fiber electrode, denoted as PGH-ECNFs; the side with zero PVP content was designated as the back side of the fiber electrode, denoted as PG0-ECNFs.

[0044] like Figure 1 As shown in Figure b(1-3), the front side of the obtained highly active porous carbon nanofiber electrode material PG-ECNFs, i.e. the side with a higher PVP content in the precursor solution, has a fiber diameter of approximately 200-300 nm, which is significantly increased compared to the original ECNFs. Furthermore, the overlap between the fibers is looser. This is because PVP, as a sacrificial polymer, undergoes thermal decomposition under high temperature conditions, resulting in greater space between the PAN-based fibers. In addition, the surface of the obtained carbon fibers remains relatively smooth, indicating that PVP does not form mixed fibers with PAN, but rather forms independent filaments. Therefore, carbon fiber electrodes with larger pores can be obtained after its decomposition.

[0045] Example 2: Electrochemical performance of PVP-doped highly active gradient porous carbon nanofiber electrode material

[0046] 1) Cyclic Voltmeter-Ammeter Test

[0047] Methods: A three-electrode system was used, with 1 cm prepared in Example 1 as an example. 2Blank carbon nanofiber electrode material ECNFs and highly active porous carbon nanofiber electrode material PG-ECNFs were used as working electrodes, saturated calomel electrode as reference electrode, platinum sheet as counter electrode, and 0.1M VOSO4+2.0M H2SO4 as electrolyte. The electrochemical performance of the electrodes was investigated by cyclic voltammetry at a scan rate of 5mV / s.

[0048] like Figure 2 As shown, the CV curves measured on both the front and back sides of ECNFs and PG-ECNFs both show V 2+ / V 3+ The redox peaks of the redox couple were observed. However, compared to ECNFs, the CV curves measured on the PG-ECNFs electrode showed larger peak currents and smaller peak potential differences. This may be attributed to the more complete contact between the PG-ECNFs electrode material and the electrolyte, and the easier mass transfer, which contributes to a larger electroactive area and reaction kinetics. Furthermore, the side with higher PVP content, i.e., PGH-ECNFs, achieved optimal electrochemical activity in contact with the electrolyte, indicating that the gradient structure design is more conducive to electrolyte penetration and mass transfer within the electrode, thereby improving electrochemical performance.

[0049] 2) Single-cell charge / discharge test

[0050] Method: The 1cm samples prepared in Example 1 were respectively... 2 Blank carbon nanofiber electrode materials and highly active porous carbon nanofiber electrode materials were used as positive and negative electrodes, respectively, with one side of PGH-ECNFs in contact with the membrane; Nafion 212 was used as the ion exchange membrane, 1.65 MV. 3+ / V 4+ Using 3.0M H₂SO₄ as the electrolyte, a single cell was assembled and charge-discharge tests were conducted. The charge and discharge cutoff voltages were 1.75V and 1V, respectively, and the current density was 100mA / cm². 2 ~400mA / cm 2 Five charge-discharge cycles were performed at each current density. The corresponding charge-discharge curves for different current densities and their capacity comparisons are shown below. Figure 3 As shown in a and 3b, the battery efficiency is as follows: Figure 3 Figures c and 3d are shown. Furthermore, a vanadium battery assembled with PG-ECNFs as positive and negative electrodes was subjected to 500 cycle stability tests, and the corresponding battery efficiency degradation is shown below. Figure 3 e.

[0051] like Figure 3 As shown in figures a to 3d, single cells using PVP-doped highly active gradient porous carbon nanofiber electrode materials as both positive and negative electrodes exhibit higher charge-discharge capacity and battery efficiency at all current densities. At a current density of 200 mA / cm²... 2Under these conditions, the battery's energy efficiency reaches over 80%. As the current density increases, the difference in energy efficiency between the two methods widens, indicating that the highly active gradient porous carbon nanofiber electrode material obtained after PVP doping can achieve higher rate performance. This is attributed to the gradient pore structure and larger electroactive area of ​​this electrode material. Furthermore, after 500 consecutive charge-discharge cycles, the battery efficiency did not show significant degradation. Figure 3 e) further demonstrates that the battery assembled with gradient functional electrode materials has excellent cycle stability.

Claims

1. A method for constructing highly active gradient porous carbon nanofiber electrode materials based on a PVP-PAN bicomponent, characterized in that, Includes the following steps: 1) Different masses of polyvinylpyrrolidone and a fixed mass of polyacrylonitrile were dissolved simultaneously in N,N,-dimethylformamide DMF to obtain PAN / DMF electrospinning precursor solutions with different PVP contents. 2) The electrospinning precursor solution prepared in step 1) is sequentially drawn into a syringe with a stainless steel needle. Using electrospinning technology, the electrospinning precursor solution is continuously electrospinned according to the order of PVP content to obtain the original nanofiber material with a gradient distribution of PVP content. 3) The original nanofiber material with a gradient distribution of PVP content obtained in step 2) is flattened with a corundum plate, placed in a tube furnace for pre-oxidation and carbonization treatment, and then cooled to room temperature to obtain a highly active porous carbon nanofiber electrode material with a gradient distribution of composition and structure.

2. The method for constructing a highly active gradient porous carbon nanofiber electrode material based on a PVP-PAN bicomponent according to claim 1, characterized in that, In step 1), the molecular weight of the polyacrylonitrile is 150,000 and the molecular weight of the polyvinylpyrrolidone is 80,000.

3. The method for constructing a highly active gradient porous carbon nanofiber electrode material based on a PVP-PAN bicomponent according to claim 1, characterized in that, In step 1), the mass ratio of polyacrylonitrile to polyvinylpyrrolidone in the mixed solution of polyacrylonitrile, polyvinylpyrrolidone and N,N-dimethylformamide is 1:0, 5:1 and 3:1, respectively.

4. The method for constructing a highly active gradient porous carbon nanofiber electrode material based on a PVP-PAN bicomponent according to claim 1, characterized in that, In step 1), the total mass percentage concentration of polyacrylonitrile and polyvinylpyrrolidone is 10 wt% to 20 wt%.

5. A method for constructing a highly active gradient porous carbon nanofiber electrode material based on a PVP-PAN bicomponent according to claim 1, characterized in that, In step 2), the process conditions for the electrospinning technology are as follows: the stainless steel nozzle is model G15~G22; the take-up device is a stainless steel roller with a rotation speed of 50~150 r / min; the voltage between the nozzle and the roller is 18~22 kV; the distance between the nozzle and the roller is 10~15 cm; the spinning temperature is 25 ℃~35 ℃; the spinning humidity is 30%RH~50%RH; and the pushing speed is 20~40µL / min.

6. The method for constructing a highly active gradient porous carbon nanofiber electrode material based on a PVP-PAN bicomponent according to claim 1, characterized in that, In step 3), the pre-oxidation treatment conditions are: heating to 290 °C at a heating rate of 1 °C / min in an air atmosphere and holding at that temperature for 60 min.

7. A method for constructing a highly active gradient porous carbon nanofiber electrode material based on a PVP-PAN bicomponent according to claim 1, characterized in that, In step 3), the carbonization conditions are: under a nitrogen or argon atmosphere, the heating rate is 4 °C / min, and the temperature is held at 1000 °C for 120 min.

8. The application of the highly active gradient porous carbon nanofiber electrode material based on the PVP-PAN bicomponent constructed according to any one of claims 1-7 in flow batteries.

9. The application according to claim 8, characterized in that, The flow batteries include vanadium redox flow batteries, iron redox flow batteries, iron-chromium redox flow batteries, and organic flow batteries.

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