Method for improving hydrophilicity and electrochemical activity of graphite felt through oxygen plasma treatment and application of graphite felt in flow battery

Abstract

The invention discloses a method for improving hydrophilicity and electrochemical activity of graphite felt through oxygen plasma treatment and application of the method in a flow battery, and belongs to the technical field of flow energy storage. The invention aims at solving the hydrophobicity of the graphite felt and improving the electrochemical performance of the negative electrode graphite felt. The hydrophobicity of the graphite felt is remarkably improved through simple plasma treatment, the capacity utilization rate and the energy efficiency of the electrolyte are improved, and the graphite felt can be used for a neutral aqueous organic flow battery with high capacity, high power and long service life and is very suitable for large-scale energy storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid flow energy storage, and particularly relates to a method for improving the hydrophilicity and electrochemical activity of graphite felt by oxygen plasma treatment and an application thereof in a liquid flow battery. Background Art

[0002] As the core of secondary energy, the efficient storage and stable supply of electricity are crucial to the transition to clean energy. Flow batteries, with their adjustable capacity, long cycle life, and high safety, have become an ideal technology for large-scale energy storage, playing an irreplaceable supporting role in the grid-connected application of intermittent renewable energy. However, traditional flow batteries, especially those represented by all-vanadium systems, are facing severe development bottlenecks. The high cost, strong corrosiveness, and cross-contamination of transition metal electrolytes not only increase the operating costs of battery systems, but also limit their long-term stability and safety, making the commercialization and large-scale application of traditional flow batteries difficult.

[0003] Compared to inorganic systems, neutral aqueous organic flow batteries utilize carbon-based organic molecules as redox-active materials. These materials are low-cost and sustainable, and the highly tunable organic molecular structures can enhance the electrode potential and solubility of the molecules, offering broader application prospects. In neutral aqueous organic flow batteries, electrode materials, as core components, play a crucial role in optimizing battery performance. Graphite felt is currently the typical electrode material for these batteries, as this carbon material offers advantages such as a three-dimensional structure and high stability. However, the pore structure of the original graphite felt electrode is complex, and it is difficult for the electrolyte to fully penetrate into it, resulting in a limited contact area between the electrode and the electrolyte, which in turn affects the battery's charge and discharge efficiency and energy density; the electrical conductivity of the graphite felt itself is relatively low, which limits the rapid transmission of electrons in the electrode material, increases the internal resistance of the battery, and reduces the battery's output power and cycle stability; there are fewer chemically active sites on the surface of the graphite felt, which makes it difficult to effectively promote the electrochemical reaction, resulting in a slow charge and discharge reaction rate of the battery and low energy conversion efficiency. Therefore, it needs to be modified to improve its hydrophilicity and electrochemical activity, thereby improving the capacity utilization of the electrolyte and the battery energy efficiency.

[0004] Therefore, modifying graphite felt electrode materials to improve their hydrophilicity and electrochemical activity is crucial for enhancing electrolyte capacity utilization and battery energy efficiency. Researchers have attempted to modify graphite felt using various methods. However, existing modification methods suffer from complex processes, high costs, and difficulty in large-scale production. Specifically, these methods are: First, insufficient surface wettability leads to low electrolyte contact efficiency. Traditional modification methods (such as acid treatment) degrade hydrophilicity, making it difficult to maintain a stable interface over the long term. Second, intrinsic catalytic activity is weak. While noble metal doping or nanoparticle loading can improve reaction kinetics, these methods suffer from uneven distribution of active sites, poor cycling stability, and high costs. Third, the electrode structure is susceptible to mechanical stress and chemical corrosion (such as fiber breakage) during long-term operation, resulting in reduced porosity and destruction of the conductive network. Fourth, existing modification processes (such as chemical deposition) are cumbersome and may involve toxic reagents, hindering large-scale production and green manufacturing. These methods are unable to meet the high demand for electrode materials in electrochemical energy storage systems such as flow batteries. It can be seen that the existing modification methods are often suitable for laboratory small-scale or pilot-scale stages, and are difficult to achieve industrial large-scale production, and cannot meet the large demand for electrode materials in electrochemical energy storage systems such as liquid flow batteries. Summary of the Invention

[0005] Existing modification methods are complex and difficult to prepare on a large scale. The resulting graphite felt electrode materials suffer from bottlenecks such as uneven electrolyte distribution and insufficient reactive sites due to poor interfacial wettability. The present invention aims to provide a method for improving the hydrophilicity and electrochemical activity of graphite felt through oxygen plasma treatment, as well as its application in flow batteries. This innovative surface modification process significantly enhances the compatibility of the electrode-electrolyte interface, achieving simultaneous optimization of energy efficiency (by 5%) and capacity utilization (by over 20%) in flow battery applications. The modification process is simple and seamlessly integrates with existing electrode production lines, providing a low-cost, highly compatible electrode material solution for large-scale energy storage systems.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for improving the hydrophilicity and electrochemical activity of graphite felt by oxygen plasma treatment, comprising: Step 1, ultrasonically cleaning the cut graphite felt and then drying it to obtain pretreated graphite felt; Step 2: treating the pretreated graphite felt with oxygen plasma and allowing it to stand in air to obtain a graphite felt electrode material with high hydrophilicity and electrochemical activity; In step 2, the conditions for the oxygen plasma treatment are: a plasma generator power of 80-120 W, an oxygen flow rate of 70-90 mL / min, and an oxygen plasma treatment time of 5-7 min.

[0007] In step 1, the graphite felt is cut into squares with a thickness of 1 to 3 mm.

[0008] Preferably, the graphite felt is cut into squares with a thickness of 2 mm.

[0009] In step 1, the solvent used for ultrasonic cleaning is a mixed solution of water and ethanol with a volume ratio of 1:2, the ultrasonic frequency is 80 KHz, and the cleaning time is 15 min.

[0010] In step 1, the drying temperature is 50-60° C., and the drying time is 8-12 h.

[0011] Preferably, the drying temperature is 70° C. and the drying time is 10 hours.

[0012] Preferably, the plasma generator has a rated power of 100 W. After the graphite felt is placed in the plasma chamber, it is evacuated to a pressure below 0.2 mbar, and then filled with oxygen at a pressure of about 0.5 mbar, with an oxygen flow rate of 80 mL / min, and the treatment is carried out for 6 min.

[0013] In step 2, the mixture is allowed to stand in the air for 20 to 26 hours.

[0014] The graphite felt electrode material is obtained by the above-mentioned method of improving the hydrophilicity and electrochemical activity of graphite felt through oxygen plasma treatment.

[0015] Application of the above-mentioned graphite felt electrode material in the preparation of negative electrode material for neutral aqueous organic redox flow battery.

[0016] A neutral aqueous organic liquid flow battery uses the graphite felt electrode material as a negative electrode material.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for improving the hydrophilicity and electrochemical activity of graphite felt by oxygen plasma treatment. The graphite felt is treated with oxygen plasma, and high-energy plasma bombards the surface of the graphite felt, causing carbon atomic bonds to break, forming micro-nanoscale rough structures (such as nanopores and grooves), and increasing the specific surface area. The active oxygen in the oxygen plasma reacts with carbon atoms on the surface of the graphite felt, introducing oxygen-containing functional groups such as carboxyl (-COOH) and hydroxyl (-OH). The introduction of oxygen-containing functional groups and surface roughening work together to increase the contact angle of the treated graphite felt from 160.3° to almost zero contact angle, significantly improving electrolyte wettability and reducing battery internal resistance. At the same time, after the oxygen plasma treatment, EDS data of the graphite felt shows that its oxygen content increases from 1.96% to 2.25%, indicating that the number of oxygen-containing functional groups in the graphite felt has increased. The CV curve area of the treated graphite felt is significantly larger than that of the untreated graphite felt, further demonstrating that oxygen plasma treatment improves the electrochemical activity of the electrode. The surface energy of the treated graphite felt is reduced, making it easier for the electrolyte to spread and penetrate the surface, thereby increasing the contact area between the electrolyte and the graphite felt. The electrolyte can more fully penetrate the pore structure of the graphite felt, facilitating the electrochemical reaction. The method of the present invention has a short treatment time (<7 minutes), low energy consumption (<120W), and does not require the use of strong acids or bases, meeting green manufacturing requirements and being suitable for large-scale production.

[0018] The graphite felt obtained by the method of the present invention can significantly improve its hydrophilicity. Furthermore, oxygen plasma treatment increases the number of oxygen-containing functional groups in the graphite felt. This solution significantly improves the hydrophilicity and electrochemical activity of the electrode, and enhances the capacity utilization of the electrolyte and the energy efficiency of the battery. This modified electrode is used as the negative electrode in neutral aqueous organic flow batteries. When combined with viologen derivatives and TEMPO derivatives, its application in neutral aqueous flow batteries demonstrates high energy efficiency and capacity utilization.

[0019] The application provided by the present invention is that the flow battery using the treated graphite felt as the electrode material is significantly improved in terms of charge and discharge efficiency, energy density, power density, etc. compared with the original electrode flow battery: the current density is increased from 60 mA / cm 2 Measured 140 mA / cm 2 , 60 mA / cm 2 Capacity utilization rate is 18.2% higher, 80 mA / cm 2 20.0% higher capacity utilization, 100 mA / cm 2 Capacity utilization rate is 22.2% higher, 120 mA / cm 2 High capacity utilization rate of 33.3%, 140 mA / cm 2The capacity utilization rate is as high as 50.0%; the graphite felt electrode material treated by this method also has good chemical stability and thermal stability, and can maintain stable performance in a wide temperature range and chemical environment. It is suitable for high-capacity, high-power, and long-life neutral aqueous organic liquid flow batteries, providing an effective way for large-scale energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 : This is a measured contact angle diagram of the original graphite felt (GF) and the graphite felt after oxygen plasma treatment (OGF) in an embodiment of the present invention, wherein A is the original graphite felt and B is the graphite felt after oxygen plasma treatment; Figure 2 This is a scanning electron microscope energy spectrum test diagram of the original graphite felt (GF) and the graphite felt after oxygen plasma treatment (OGF) of the present invention; Figure 3 CV test graphs of the original graphite felt (GF) and the graphite felt after oxygen plasma treatment (OGF) of the present invention; Figure 4 This is a test diagram of a 0.5 M diol-Vi / 0.4 M MiAcNH-TEMPO battery in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0022] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0023] The present invention is described in further detail below with reference to the embodiments and accompanying drawings: Example 1 A method for improving the hydrophilicity and electrochemical activity of graphite felt by oxygen plasma treatment, the specific steps are as follows: Step 1: Cut the 2 mm graphite felt into 2 × 2 cm pieces and prepare another piece of the same graphite felt for later use. Step 2: Ultrasonic clean the graphite felt with ethanol and deionized water respectively, and bake it in a 70℃ oven for 10 hours to ensure that the graphite felt is completely dry; Step 3: Set the plasma generator rated power to 100 W, place the graphite felt in the plasma chamber, evacuate to a pressure below 0.2 mbar, and then fill with oxygen at approximately 0.5 mbar for 6 minutes; Step 4: The treated plasma is placed in room temperature air for 24 hours to obtain highly hydrophilic and electrochemically active graphite felt.

[0024] Example 2 Application of the modified graphite felt prepared above as negative electrode material: The graphite felt prepared by treating the oxygen plasma in the embodiment is used to prepare the electrode material of the neutral aqueous organic liquid flow battery, which can be prepared by the following steps: Step 1: Assemble the battery stack The neutral aqueous organic redox flow battery used in the test is a single-cell structure. The positive terminal plate, positive insulating plate, positive conductive plate, positive flow frame, positive graphite felt, positive gasket, anion exchange membrane, negative gasket, modified negative graphite felt, negative flow frame, negative conductive plate, negative insulating plate, and negative terminal plate are bolted together in this order. External piping is connected and bolts are checked for looseness. If loose, they can be tightened. Before testing, a leak and pressure test should be performed. Two liquid storage bottles and a peristaltic pump are connected to the aforementioned fixture. After 2 hours of circulation, if there is no leakage or change in liquid volume, the fixture can be retained for future use.

[0025] Step 2: Electrolyte preparation The anolyte used was a dihydroxyviologen derivative solution with the chemical formula C 16 H 18 N2O4Cl2, referred to as diol-Vi; the cathode electrolyte uses a methylimidazole-functionalized (2,2,6,6-tetramethylpiperidin-1-yl)oxy solution with the chemical formula C 15 H 26N4O2, referred to as MiAcNH-TEMPO; 943 mg of diol-Vi and 1.15 g of MiAcNH-TEMPO were weighed and dissolved in 5 mL and 8.75 mL of 1 M NaCl solution, respectively. Stir or sonicate until completely dissolved, with the concentrations of the two in the NaCl solution being 0.5 M and 0.4 M. Argon was bubbled through for 10 minutes. The diol-Vi derivative and MiAcNH-TEMPO served as the battery's anolyte and catholyte, respectively, referred to as 0.5 M diol-Vi / 0.4 M MiAcNH-TEMPO.

[0026] Step 3: Assemble the neutral aqueous organic redox flow battery and perform performance testing Place the battery stack prepared in step 1 and the solution from step 2 in a glove box, using the resulting modified graphite felt (OGF) as the negative electrode. Connect the external power supply, peristaltic pump, and Newway tester, set the program, and conduct the charge and discharge test.

[0027] After the above steps, the basic test data of the prepared 0.5 M diol-Vi / 0.4 M MiAcNH-TEMPO system are as follows: voltage range 0.3~1.5 V (single electron test), current density from 60 mA / cm 2 Measured 140 mA / cm 2 60 mA / cm 2 Charge capacity of 12.56 Ah L -1 , the capacity utilization rate is 93.73% and the energy efficiency is 71.35%. 140 mA / cm 2 Charge capacity of 2.82 Ah L -1 , the capacity utilization rate was 21.04%, and the energy efficiency was 37.88%. Therefore, the above battery tests show that the modified graphite felt has good electrochemical activity, its actual capacity utilization rate is higher, and it can be used to test batteries with higher concentrations, using this OGF as the negative electrode of neutral aqueous organic flow batteries.

[0028] The present invention conducts relevant tests on the OGF prepared in the above embodiment, and the test results are shown in FIG. Figure 1-Figure 4 : from Figure 1 It can be seen from the above that the OGF in the embodiment has excellent hydrophilicity, and the GF hydrophilic contact angle is 160.3°. Figure 2 It can be seen from the scanning electron microscope energy spectrum test of OGF in the embodiment that the oxygen content is 2.25%, which is a certain improvement over the 1.19% of GF. Figure 3 It can be seen that the scanning area of OGF is larger than that of GF, and the electrochemical activity of OGF is better than that of GF. Figure 4It can be seen that the battery current density of 0.5 M R-diol-Vi / 0.4 M MiAcNH-TEMPO is increased from 60 mA / cm 2 Measured 140 mA / cm 2 , the capacity utilization of OGF is higher than that of GF.

[0029] The present invention discloses a method for improving the hydrophilicity and electrochemical activity of graphite felt. After oxygen plasma treatment, the hydrophilicity and electrochemical activity of the graphite felt are improved. As the negative electrode, the viologen derivative diol-Vi is used as the anolyte, and the TEMPO derivative or ferrocene is used as the catholyte. The electrolyte materials are all dissolved in 1 M NaCl to increase the conductivity of the solution. AMVN / DSVN membrane is used as the anion exchange membrane to form a neutral aqueous organic flow battery with single or double electron storage. Taking OGF as an example, the current density is increased from 60 mA / cm 2 Measured 140 mA / cm 2 When the concentration is 0.5 M, the neutral aqueous organic flow battery based on diol-Vi / MiAcNH-TEMPO shows that the capacity utilization of OGF far exceeds that of GF.

[0030] The present invention discloses a method for improving the hydrophilicity and electrochemical activity of graphite felt and its application in liquid flow batteries. The prior art reports that the hydrophilicity and electrochemical activity of graphite felt are poor, which seriously limits the large-scale development of aqueous organic liquid flow batteries. The present invention can significantly improve the hydrophilicity of graphite felt by treating graphite felt with oxygen plasma. At the same time, oxygen plasma treatment increases the number of oxygen-containing functional groups in the graphite felt. This solution significantly improves the hydrophilicity and electrochemical activity of the electrode, and improves the capacity utilization of the electrolyte and the energy efficiency of the battery. This modified electrode is used as the negative electrode of a neutral aqueous organic liquid flow battery, and is matched with a viologen derivative and a TEMPO derivative and applied to a neutral aqueous liquid flow battery to exhibit high energy efficiency and capacity utilization.

[0031] The above content is only for explaining the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for improving the hydrophilicity and electrochemical activity of graphite felt by oxygen plasma treatment, characterized in that: include: Step 1, ultrasonically cleaning the cut graphite felt and then drying it to obtain pretreated graphite felt; Step 2: treating the pretreated graphite felt with oxygen plasma and allowing it to stand in air to obtain a graphite felt electrode material with high hydrophilicity and electrochemical activity; The conditions for the oxygen plasma treatment are: a plasma generator power of 80-120 W, an oxygen flow rate of 70-90 mL / min, and an oxygen plasma treatment time of 5-7 min.

2. The method for improving the hydrophilicity and electrochemical activity of graphite felt by oxygen plasma treatment according to claim 1, characterized in that: In step 1, the graphite felt is cut into squares with a thickness of 1 to 3 mm.

3. The method for improving the hydrophilicity and electrochemical activity of graphite felt by oxygen plasma treatment according to claim 1, characterized in that: In step 1, the solvent used for ultrasonic cleaning is a mixed solution of water and ethanol with a volume ratio of 1:2, the ultrasonic frequency is 80 KHz, and the cleaning time is 15 min.

4. The method for improving the hydrophilicity and electrochemical activity of graphite felt by oxygen plasma treatment according to claim 1, characterized in that: In step 1, the drying temperature is 50-60° C., and the drying time is 8-12 h.

5. The method for improving the hydrophilicity and electrochemical activity of graphite felt by oxygen plasma treatment according to claim 1, characterized in that: In step 2, the conditions for the oxygen plasma treatment are: plasma generator power is 100 W, oxygen flow rate is 80 mL / min, and oxygen plasma treatment time is 6 min.

6. The method for improving the hydrophilicity and electrochemical activity of graphite felt by oxygen plasma treatment according to claim 1, characterized in that: In step 2, the mixture is allowed to stand in the air for 20 to 26 hours.

7. A graphite felt electrode material obtained by the method for improving the hydrophilicity and electrochemical activity of graphite felt by oxygen plasma treatment according to any one of claims 1 to 6.

8. Use of the graphite felt electrode material according to claim 7 in the preparation of electrode materials for neutral aqueous organic liquid flow batteries.

9. A neutral aqueous organic flow battery, characterized in that: The neutral aqueous organic liquid flow battery uses the graphite felt electrode material according to claim 7 as the negative electrode material.

10. The neutral aqueous organic flow battery according to claim 9, characterized in that The battery also includes a positive electrode material, an electrolyte, a separator and a current collector.

Images