Pretreatment process of PAN-based carbon fiber and application of PAN-based carbon fiber in preparation of high-activity flow battery electrode material

Abstract

The invention belongs to the technical field of battery materials, and particularly discloses a pretreatment process of PAN-based carbon fibers and application of the PAN-based carbon fibers in preparation of a high-activity flow battery electrode material. The method comprises the following steps: soaking a polyacrylonitrile (PAN) precursor in an aqueous solution containing a pretreating agent such as potassium dichromate, and carrying out chemical pretreatment, so that the surface of the PAN fiber is subjected to primary structural transformation; and respectively carrying out pre-oxidation and carbonization treatment on the obtained material to obtain the PAN-based carbon fiber electrode material with the catalyst on the surface. When the obtained carbon fiber material is used as an electrode material of the all-vanadium redox flow battery, the electrode reaction kinetics of the positive electrode and the negative electrode of the battery can be effectively improved, and the energy conversion efficiency and the rate capability of the battery are improved. The method is easy to operate, compared with a traditional electrode preparation technology, energy consumption is low, the process is simple, large-scale production is easy to achieve, and the method has good application prospects in the field of vanadium battery electrode materials.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a pretreatment process for PAN-based carbon fibers and its application in the preparation of highly active flow battery electrode materials. Background Technology

[0002] The excessive consumption of fossil fuels has led to irreversible environmental pollution and an energy depletion crisis. Developing renewable energy sources such as solar and wind power is a key way to overcome the energy predicament. However, these renewable energy sources suffer from intermittency and instability. The introduction of large-scale energy storage technologies can effectively address the volatility and intermittency of renewable energy. Vanadium redox flow batteries, due to their advantages such as long cycle life, large storage capacity, high safety, and environmental friendliness, have become one of the important technologies for large-scale, long-term energy storage.

[0003] Electrodes, as a crucial component of vanadium redox batteries, have a vital impact on battery performance and cycle life. Currently, commercially available PAN-based carbon felt (CF) is the most widely used electrode material in flow batteries, primarily due to its low cost, good conductivity, and stability. However, this material exhibits poor electrochemical reactivity, and it is difficult to simultaneously achieve high conductivity and electrocatalytic activity. Post-activation treatment of finished graphite felt can effectively enhance the activity of electrode materials, and this is currently the most widely used electrode activation process. However, the multi-step heat treatment process is time-consuming and energy-intensive. Shortening the process flow and reducing manufacturing costs are fundamental to achieving cost reduction and efficiency improvement in flow battery energy storage. Therefore, developing a simple and efficient novel activation process for porous carbon fiber electrodes for flow batteries is of great significance. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a pretreatment process for PAN-based carbon fibers and its application in the preparation of highly active flow battery electrode materials. The pretreatment process regulates the surface properties of PAN-based fibers, simultaneously considering the surface activity and conductivity of the carbon fiber electrode, reducing battery polarization during charge and discharge, thereby improving the battery's charge and discharge performance. Furthermore, the pretreatment process simplifies the electrode preparation process, is simple to implement, highly designable, and has broad applicability.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a pretreatment process for PAN-based carbon fibers, characterized by comprising the following steps: Step 1: Dissolve an appropriate amount of pretreatment agent in deionized water and mix well to obtain a pretreatment agent aqueous solution with a concentration of 0.1~2wt%; Step 2: Immerse the PAN fibers in the above pretreatment agent aqueous solution to perform preliminary chemical oxidation treatment on their surface; wherein, the temperature of the pretreatment agent aqueous solution is 20℃~80℃, and the immersion time is 1~5min; Step 3: The pretreated fibers are washed and dried, followed by pre-oxidation and carbonization to obtain highly active PAN-based carbon fiber electrode materials; The pre-oxidation process conditions are: heat treatment at 200–300°C for 0.5–2 hours in air atmosphere; the carbonization process conditions are: heat treatment at 800–1300°C for 1–3 hours in vacuum or inert atmosphere.

[0006] Furthermore, in step 1), the pretreatment agent is potassium dichromate or potassium permanganate.

[0007] This invention also discloses the application of PAN-based carbon fiber materials prepared by the above-mentioned PAN-based carbon fiber pretreatment process in the preparation of highly active flow battery electrode materials, that is, the application of them as highly active electrode materials in all-vanadium redox flow batteries.

[0008] The advantages of this invention are: The process of this invention is simple, efficient, and universally applicable; The chemical pretreatment process proposed in this invention has advantages over the post-activation process, such as simple process, low cost and energy saving. The novel pretreatment process can simultaneously optimize the surface activity and conductivity of electrodes, thereby improving electrode performance to a greater extent. The pretreatment process proposed in this invention only requires simple pretreatment based on existing mature processes, without affecting subsequent processes, and is suitable for large-scale production. Attached Figure Description

[0009] Figure 1 Scanning electron microscope images of commercial carbon felt CF (a) and PAN-based carbon fiber electrode material K2Cr2O7-CF (b) prepared in Example 1.

[0010] Figure 2 Cyclic voltammetry curves of commercial carbon felt CF and PAN-based carbon fiber electrode material K2Cr2O7-CF prepared in Example 1 in 0.1MVOSO4+2MH2SO4.

[0011] Figure 3 A single cell assembled from commercial carbon felt CF and the PAN-based carbon fiber electrode material K2Cr2O7-CF prepared in Example 1 showed an efficiency of 200 mA·cm⁻¹. -2 The charge / discharge curves (a) and energy efficiency EE (b) are shown below. Detailed Implementation

[0012] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0013] Comparative example: Commercial carbon felt CF electrode material.

[0014] Commercially available finished PAN (polyacrylonitrile) based carbon felt (CF) has a thickness of 2.4 mm, a porosity of 75%~95%, and a fiber diameter of 5~20 μm. Surface morphology is as follows: Figure 1 As shown in (a).

[0015] Example 1: PAN-based carbon fiber electrode material prepared by pretreatment process: 1. Pretreatment of PAN precursor fibers The PAN precursor fiber was immersed in a 0.2wt% potassium dichromate aqueous solution at 60℃ for 2 minutes, washed with deionized water, and then dried in a vacuum drying oven at 60℃.

[0016] 2. Heat treatment The chemically pretreated PAN fibers were heat-treated at 250°C for 60 min in air, and then heat-treated at 1000°C for 120 min in nitrogen atmosphere to obtain PAN-based carbon fiber (K2Cr2O7-CF) electrode material.

[0017] Figure 1 (b) A scanning electron microscope image of PAN-based carbon fiber material prepared by the pretreatment process, showing that the fiber diameter is about 10 μm.

[0018] Example 2: PAN-based carbon fiber electrode material prepared by pretreatment process: 1. Pretreatment of PAN precursor fibers The PAN precursor fiber was immersed in a 2wt% potassium dichromate aqueous solution at 20℃ for 3 minutes, washed with deionized water, and then dried in a vacuum drying oven at 60℃.

[0019] 2. Heat treatment The chemically pretreated PAN fibers were heat-treated at 220°C for 60 min in air, and then heat-treated at 1000°C for 120 min in nitrogen atmosphere to obtain PAN-based carbon fiber (K2Cr2O7-CF) electrode material.

[0020] The PAN-based carbon fiber material prepared by the pretreatment process has a fiber diameter of about 10 μm and a surface loaded with catalyst particles of tens to hundreds of nanometers, which helps to improve the active area, surface capacitance and electrochemical activity of the material.

[0021] Example 3: PAN-based carbon fiber electrode material prepared by pretreatment process: 1. Pretreatment of PAN precursor fibers The PAN precursor fiber was immersed in a 0.1wt% potassium dichromate aqueous solution at 80℃ for 1 minute, washed with deionized water, and then dried in a vacuum drying oven at 60℃.

[0022] 2. Heat treatment The chemically pretreated PAN fibers were heat-treated at 230°C for 60 min in air, and then heat-treated at 1000°C for 120 min in nitrogen atmosphere to obtain PAN-based carbon fiber (K2Cr2O7-CF) electrode material.

[0023] The PAN-based carbon fiber material prepared by the pretreatment process has a fiber diameter of about 10 μm and is loaded with catalyst particles of tens of nanometers on its surface, which helps to improve the active area, surface capacitance and electrochemical activity of the material.

[0024] Performance testing: 1) Cyclic Voltammetry (CV) Test Methods: The electrochemical performance of the materials was tested using a three-electrode system. The PAN-based carbon fiber (K2Cr2O7-CF) electrode material prepared by the pretreatment process in Example 1 and commercial CF were used as working electrodes, with an electrode area of ​​0.5 × 0.5 cm. 2 A 232-type saturated calomel electrode was used as the reference electrode; a 0.5 × 0.5 cm electrode was used. 2 A platinum sheet was used as the auxiliary electrode, and 0.1M VOSO4 + 2.0M H2SO4 was used as the electrolyte.

[0025] like Figure 2 As shown, the electrode material obtained through pretreatment exhibits significantly higher surface redox reaction currents than the blank CF, and a smaller redox peak position difference, indicating that it possesses excellent electrochemical activity and reversibility.

[0026] 2) Battery charge and discharge test Methods: PAN-based carbon fiber (K2Cr2O7-CF) prepared in Example 1 and commercial CF were used as electrode materials, with an area of ​​3×3cm. 2 Nafion 212 is an ion exchange membrane with a 1.65 MV capacity. 3.5+ A single cell was assembled using 3.0 M H₂SO₄ as the electrolyte. The charge / discharge cutoff voltages were 1.65 V and 1.0 V, respectively. The charge / discharge curves and battery efficiency are shown below. Figure 3 As shown.

[0027] Figure 3 (a) shows the reaction of CF and K2Cr2O7-CF at 200 mA·cm⁻¹ -2 A comparison of the charge-discharge performance of the assembled batteries showed that the battery assembled with K2Cr2O7-CF exhibited a lower charging voltage, a higher discharging voltage, and less battery polarization. The results indicate that K2Cr2O7-CF possesses superior charge-discharge performance.

[0028] Figure 3(b) Energy efficiency (EE) of the battery assembled from CF and K2Cr2O7-CF at different current densities. The battery operates stably even at high current densities; and at 200 mA·cm⁻¹... -2 Under these conditions, the energy efficiency of the K2Cr2O7-CF battery is 79.16%, which is higher than the 72.13% of the commercial CF battery.

[0029] In summary, the electrode material manufactured using this method has the following advantages compared to existing products: 1. Using a substance with strong oxidizing properties that can form a metal-based catalyst after calcination as a pretreatment agent to pretreat PAN-based fibers can pre-oxidize the fibers, thereby reducing the pre-oxidation temperature of subsequent heat treatment. Furthermore, the surface of the prepared electrode material is loaded with a metal-based catalyst, which accelerates the redox reaction of electroactive ions. 2. Compared with the post-activation process, the catalyst loading and anchoring can be achieved during the pretreatment process, which can simplify the preparation process, reduce costs and save energy. 3. The prepared highly active electrode material has a metal-based catalyst loaded on its surface, which can effectively improve the electrode activity and conductivity without affecting the stability of the matrix, thereby improving the battery performance; 4. The pretreatment process is for the treatment of the raw filament and does not affect the subsequent preparation of carbon fiber electrodes. It is universal and suitable for large-scale production. 5. The prepared electrode material has excellent electrochemical activity and reversibility, superior charge-discharge performance, and good energy efficiency.

Claims

1. A pretreatment process for PAN-based carbon fibers, characterized in that: Includes the following steps: Step 1: Dissolve an appropriate amount of pretreatment agent in deionized water and mix well to obtain a pretreatment agent aqueous solution with a concentration of 0.1~2wt%; Step 2: Immerse the PAN fibers in the above pretreatment agent aqueous solution to perform preliminary chemical oxidation treatment on their surface; wherein, the temperature of the pretreatment agent aqueous solution is 20℃~80℃, and the immersion time is 1~5min; Step 3: The pretreated fibers are washed and dried, followed by pre-oxidation and carbonization to obtain highly active PAN-based carbon fiber electrode materials; The pre-oxidation process conditions are: heat treatment at 200-300℃ for 0.5-2 hours in air atmosphere; the carbonization process conditions are: heat treatment at 800-1300℃ for 1-3 hours in vacuum or inert atmosphere.

2. The pretreatment process for PAN-based carbon fiber according to claim 1, characterized in that: In step 1), the pretreatment agent is potassium dichromate or potassium permanganate.

3. The pretreatment process for PAN-based carbon fibers according to claim 1 or 2, characterized in that: The prepared PAN-based carbon fiber material is used as a highly active electrode material in flow batteries.

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