Electrode based on multi-scale hole coating structure and preparation method and application thereof

Abstract

The invention belongs to the technical field of flow batteries, and discloses an electrode based on a multi-scale hole coating structure and a preparation method and application thereof, and the electrode is prepared by preparing carbon nanotube dispersion liquid with different length-diameter ratios into catalytic slurry, and uniformly coating two sides of the electrode with the catalytic slurry. According to the design, the unique advantages of the carbon nanotubes with different length-diameter ratios are fully exerted, and a continuous and uniform conductive channel is formed, so that the conductivity and catalytic activity of the electrode are remarkably improved. Besides, in the blending and coating process of the dispersion liquid, the carbon nanotubes with different length-diameter ratios are stacked and overlapped to generate a multi-scale pore channel structure: micron-scale large pore channels provide macroscopic channels for high-speed flow of electrolyte, and nano-scale pores provide more active sites for electrochemical reaction. When the electrode with the multi-scale hole coating structure is applied to the all-vanadium redox flow battery, the charge-discharge performance and the cycling stability of the battery are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid flow batteries, and in particular to an electrode based on a multi-scale pore coating structure and a preparation method and application thereof. Background Art

[0002] As a new large-scale energy storage technology, vanadium redox flow batteries (VRFBs) have demonstrated tremendous potential for renewable energy storage and power dispatch due to their excellent safety, long cycle life, and high energy density. However, high initial installation costs, particularly for the stack and vanadium salts, remain a key constraint to their widespread adoption.

[0003] Electrode materials play a crucial role in all-vanadium redox flow batteries, directly impacting their charge-discharge efficiency and long-term stability. Currently, graphite felt and carbon felt are the most commonly used electrode materials, offering excellent conductivity and chemical stability while also being relatively inexpensive to produce. However, at high current densities, conventional electrode materials, due to their small surface area and insufficient hydrophilicity, are prone to significant electrode polarization, leading to decreased battery efficiency.

[0004] In the existing technology, the specific surface area of ​​the electrode is mostly increased by improving the electrode preparation process (such as using low-diameter carbon fibers for preparation). However, due to the mutual constraints between the specific surface area and the electrode permeability, it is usually difficult to improve the performance of both at the same time. A significant decrease in the hydrophilicity of the electrode will lead to a significant increase in the electrolyte flow resistance and pump work, thereby affecting the battery performance. Therefore, the use of other processes to optimize the porous structure of the electrode, increase the specific surface area, and improve the interfacial affinity between the electrolyte and the electrode surface has become an effective way to reduce polarization and improve the battery charge and discharge efficiency. This optimization strategy will provide more competitive technical support for the commercial promotion of all-vanadium liquid flow batteries.

[0005] Carbon nanotubes, as one-dimensional nanomaterials with excellent electrical and mechanical properties, possess higher conductivity and a larger specific surface area, effectively improving the conductivity and reactivity of flow battery electrodes. Introducing carbon nanotubes onto electrode surfaces can effectively enhance the conductivity and reactivity of electrodes, promote rapid electron transfer within the electrodes, and reduce charge transfer resistance. Furthermore, the high specific surface area of ​​carbon nanotubes provides a larger contact area between reactants for electrochemical reactions, thereby increasing reactivity and significantly enhancing the overall performance of vanadium flow batteries.

[0006] However, existing methods for preparing multi-scale pore structure electrodes often suffer from complex processes and high costs, and the cycling stability and electrochemical performance of the prepared electrodes still need to be improved. Therefore, developing a multi-scale pore coating structure electrode with simple processes, low costs, and excellent performance and its preparation method are of great significance for promoting the commercial application of all-vanadium redox flow batteries. Summary of the Invention

[0007] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0008] A method for preparing an electrode based on a multi-scale pore-coated structure includes the following preparation steps:

[0009] S1: Dispersing large aspect ratio carbon nanotubes (L-CNTs) into a dispersion to obtain an L-CNT dispersion; dispersing small aspect ratio carbon nanotubes (S-CNTs) into a dispersion to obtain an S-CNTs dispersion;

[0010] S2: mixing the L-CNTs dispersion, the S-CNTs dispersion, and the binder to obtain a mixed catalyst slurry; the mass ratio of the total mass of the L-CNTs slurry and the S-CNTs slurry to the binder is 10:(5-1), wherein the mass ratio of the L-CNTs dispersion to the S-CNTs dispersion is 1:(1-5);

[0011] S3: After ultrasonic dispersion of the catalyst slurry, it is coated on both sides of the electrode. The catalyst loading is 0.1 mg / cm 2 -5.0mg / cm 2 .

[0012] In step S1 , the L-CNTs have a diameter of 1-50 nm and a length of 5-100 μm; the S-CNTs have a diameter of 1-50 nm and a length of 1-10 μm.

[0013] The L-CNTs dispersion is prepared by uniformly mixing a predetermined amount of L-CNTs in deionized water, an ethanol solution, an isopropanol solution, or a mixture thereof to form an L-CNTs dispersion having a mass fraction of 2-5%, and ultrasonically treating the dispersion in a water bath at a temperature of 10-50° C., with an ultrasonic power of 100 W to 800 W and an ultrasonic time of 30-80 min.

[0014] The s-CNTs dispersion is prepared by uniformly mixing a predetermined amount of s-CNTs in deionized water, an ethanol solution, an isopropanol solution, or a mixture thereof to form a 5-20% L-CNTs dispersion, and ultrasonically treating the dispersion in a water bath at a temperature of 10-50° C., with an ultrasonic power of 100 W to 800 W and a ultrasonic time of 30-80 minutes.

[0015] In step S2, the binder is a membrane solution having a mass percentage of 3% to 20%. The membrane solution type includes any one of a perfluorosulfonic acid polyelectrolyte (Nafion) membrane solution, a sulfonated polyetheretherketone polyelectrolyte membrane solution, a sulfonated polysulfone polyelectrolyte membrane solution, a phosphated polybenzimidazole membrane solution, a quaternized polysulfone polyelectrolyte membrane solution, and a polybenzimidazole polyelectrolyte membrane solution, or one or more combinations thereof.

[0016] The blending step is: mixing the two dispersions and the binder at 10-50° C. and ultrasonically at 100-800W for 20-90 minutes.

[0017] In step S3, the catalyst slurry is coated on both sides of the electrode, and the coating method includes but is not limited to one of brushing, spraying, transfer printing, etc.

[0018] An electrode based on a multi-scale pore-coated structure is prepared by the above-mentioned preparation method.

[0019] An application based on a multi-scale pore-coated structure electrode is particularly suitable for use in vanadium flow batteries.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) This invention breaks through the limitations of conventional porous electrode structures in all-vanadium redox flow batteries. By stacking and overlapping carbon nanotubes with different aspect ratios, a multi-scale pore-coating structure is constructed. The micron-scale macroporous structure provides macroscopic channels for the high-speed flow of electrolytes, while the nanoscale pores provide more active sites for electrochemical reactions.

[0022] (2) The unique advantages of carbon nanotubes with different aspect ratios are fully utilized to form a continuous and uniform conductive channel, thereby significantly improving the conductivity and catalytic activity of the electrode.

[0023] (3) The preparation method of the present invention is simple in process and suitable for large-scale promotion and application.

[0024] The results of repeated tests show that at a current density of 200mA / cm 2 Under the working conditions, the coulombic efficiency of the battery is 98.3%±0.1%, and the energy efficiency is 85.6%±0.1%; after 2000 cycles, the energy efficiency retention rate of the battery still reaches 98.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the preparation process of the multi-scale pore-coated electrode structure;

[0026] Figure 2In the figure, a is a schematic diagram of the surface structure of the multi-scale pore-coated electrode, and b is a local magnified view of the surface structure;

[0027] Figure 3 This is a graph showing the performance results of the battery after 2000 cycles in Example 1. DETAILED DESCRIPTION

[0028] The examples described below are implemented based on the technical solutions of the present invention, and provide detailed implementation methods and specific operating procedures, but do not limit the scope of protection of the patent of the present invention. Any technical solutions obtained in the form of equivalent replacement or equivalent transformation should fall within the scope of protection of the present invention.

[0029] Example 1

[0030] like Figure 1 As shown in FIG, the detailed steps for preparing the multi-scale pore-coated electrode structure are as follows:

[0031] Step 1: Disperse 10 mg of high aspect ratio carbon nanotubes (L-CNTs) in 50 mL of ethanol solution to obtain L-CNT dispersion; disperse 10 mg of low aspect ratio carbon nanotubes (S-CNTs) in 50 mL of ethanol solution to obtain S-CNTs dispersion; wherein the length of L-CNTs is 10-20 nm, the tube diameter is 10-20 μm, and the length of S-CNTs is 10-20 nm, the tube diameter is 0.5-2 μm.

[0032] Step 2: Mix 50 mL of the L-CNTs dispersion, 50 mL of the S-CNTs dispersion and 1 mL of Nafion binder in step 1 to obtain a mixed catalyst slurry.

[0033] Step 3: Ultrasonic dispersion of the mixed catalyst slurry obtained in step 2 was performed at a temperature of 30°C for 120 min. The obtained ultrasonic dispersion was injected into the ultrasonic sprayer, and the spraying speed and spraying path of the ultrasonic sprayer were controlled. The catalyst dispersion was evenly sprayed onto the untreated carbon felt. Finally, the spraying load was obtained by weighing to be 0.5 mg / cm 2 , 1.0mg / cm 2 , 1.5mg / cm 2 and 2.0 mg / cm 2 Multi-scale pore-coated structure electrodes (such as Figure 2 shown).

[0034] Comparative Example 1

[0035] Compared with Example 1, the only difference is that L-CNTs slurry is not added, and other conditions are the same. The specific operation steps are:

[0036] Step 1: Disperse 10 mg of small aspect ratio carbon nanotubes (S-CNTs) into 50 mL of ethanol solution to obtain an S-CNTs dispersion; wherein the S-CNTs have a length of 10-20 nm and a diameter of 0.5-2 μm.

[0037] Step 2: Mix 50 mL of the S-CNTs dispersion prepared in step 1 with 0.5 mL of Nafion binder to obtain a mixed catalyst slurry.

[0038] Step 3: Ultrasonic dispersion of the mixed catalyst slurry obtained in step 2 was performed at a temperature of 30°C for 120 min. The obtained ultrasonic dispersion was injected into the ultrasonic sprayer, and the spraying speed and spraying path of the ultrasonic sprayer were controlled. The catalyst dispersion was evenly sprayed onto the untreated carbon felt. The spraying load was obtained by weighing and was 0.5 mg / cm 2 , 1.0mg / cm 2 , 1.5mg / cm 2 and 2.0 mg / cm 2 Pore-coated structure electrode.

[0039] Comparative Example 2

[0040] Compared to Example 1, the only difference is that no S-CNT slurry was added, and other conditions were the same. The specific operation steps are as follows: Step 1: Disperse 10 mg of high aspect ratio carbon nanotubes (L-CNTs) in 50 mL of ethanol solution to obtain an L-CNT dispersion; wherein the L-CNTs have a length of 10-20 nm and a diameter of 10-20 μm.

[0041] Step 2: Mix 50 mL of the L-CNTs dispersion prepared in step 1 with 0.5 mL of Nafion binder to obtain a mixed catalyst slurry.

[0042] Step 3: Ultrasonic dispersion of the mixed catalyst slurry obtained in step 2 was performed at a temperature of 30°C for 120 min. The obtained ultrasonic dispersion was injected into the ultrasonic sprayer, and the spraying speed and spraying path of the ultrasonic sprayer were controlled. The catalyst dispersion was evenly sprayed onto the untreated carbon felt. The spraying load was obtained by weighing and was 0.5 mg / cm 2 , 1.0mg / cm 2 , 1.5mg / cm 2 and 2.0 mg / cm 2 Pore-coated structure electrode.

[0043] Comparative Example 3

[0044] Compared with Example 1, the only difference is that the aspect ratios of the added L-CNTs and S-CNTs are different, and other conditions are the same. The specific operation steps are:

[0045] Step 1: Disperse 10 mg of high aspect ratio carbon nanotubes (L-CNTs) in 50 mL of ethanol solution to obtain L-CNT dispersion; disperse 10 mg of low aspect ratio carbon nanotubes (S-CNTs) in 50 mL of ethanol solution to obtain S-CNTs dispersion; wherein the length of L-CNTs is 30-80 nm, the tube diameter is 10-30 μm, and the length of S-CNTs is 10-20 nm, and the tube diameter is 0.5-2 μm.

[0046] Step 2: Mix 50 mL of the L-CNTs dispersion, 50 mL of the S-CNTs dispersion and 1 mL of Nafion binder in step 1 to obtain a mixed catalyst slurry.

[0047] Step 3: Ultrasonic dispersion of the mixed catalyst slurry obtained in step 2 was carried out at a temperature of 30°C for 120 min. The obtained ultrasonic dispersion was injected into the ultrasonic sprayer, and the spraying speed and spraying path of the ultrasonic sprayer were controlled. The catalyst dispersion was evenly sprayed onto the untreated carbon felt. The spraying load was obtained by weighing and was 0.5 mg / cm 2 , 1.0mg / cm 2 , 1.5mg / cm 2 and 2.0 mg / cm 2 Multi-scale pore-coated structure electrode.

[0048] In order to characterize the actual performance of the multi-scale pore-coated structure electrodes prepared in Example 1 and Comparative Examples 1 and 4, the treated carbon felt, the carbon felt in Example 1, and the carbon felt in the comparative example were used as the positive and negative electrodes of the battery to form an all-vanadium redox flow battery, and constant current charge and discharge tests were carried out. The positive electrode electrolyte was 30 mL of 1.7 mol / L VO 2+ , 3mol / L H2SO4 solution, the negative electrode electrolyte is 30mL of 1.7mol / LV 3+ , 3mol / L H2SO4 solution.

[0049] As shown in Table 1, the multi-scale pore-coated structure electrodes at different loadings in Example 1 have significantly different performances. Compared with the carbon felt that has not been treated in any way, the performance of the electrodes sprayed with carbon nanotube dispersions with different loadings is significantly improved. And with the increase in the sprayed CNT loading, the voltage efficiency and energy efficiency of the battery are significantly improved. It can be clearly seen that carbon nanotubes with different aspect ratios are overlapped and stacked with each other during the spraying process, constructing pore structures of various scales. The micron-scale pore structure promotes the rapid flow of electrolytes, while the nano-scale pores provide more active sites for electrochemical reactions (such as Figure 2 b). When the CNT loading is 2.0 mg / cm 2When the battery is charged, the voltage efficiency reaches 88.11% and the energy efficiency reaches 85.60%. After 2000 cycles, the energy efficiency retention rate of the battery reaches 98.5% (as shown in Figure 2). Figure 3 shown).

[0050] As shown in Table 2, further comparisons of battery performance using different dispersion configurations reveal that the electrode structures obtained by blending L-CNTs and S-CNTs in Examples 1 and 3 exhibit superior performance compared to the single CNT loading structures in Comparative Examples 1 and 2. It is clear that single CNT loading alone cannot construct a multi-scale pore structure on the electrode surface.

[0051] Table 1 Comparison of properties of different carbon felts in Example 1

[0052]

[0053] Table 2 Comparison of the performance of different carbon felts in Example 1 and the comparative example

[0054]

Claims

1. A method for preparing an electrode based on a multi-scale pore-coated structure, characterized in that: The preparation process includes the following: S1: Dispersing large aspect ratio carbon nanotubes (L-CNTs) into a dispersion to obtain an L-CNT dispersion; dispersing small aspect ratio carbon nanotubes (S-CNTs) into a dispersion to obtain an S-CNTs dispersion; S2: mixing the L-CNTs dispersion, the S-CNTs dispersion, and the binder to obtain a mixed catalyst slurry; the mass ratio of the total mass of the L-CNTs slurry and the S-CNTs slurry to the binder is 10:(5-1), wherein the mass ratio of the L-CNTs dispersion to the S-CNTs dispersion is 1:(1-5); S3: After ultrasonic dispersion of the catalyst slurry, it is coated on both sides of the electrode. The catalyst loading is 0.1 mg / cm 2 -5.0mg / cm 2 .

2. The method for preparing an electrode based on a multi-scale pore coating structure according to claim 1, characterized in that: In step S1 , the L-CNTs have a diameter of 1-50 nm and a length of 5-100 μm; the S-CNTs have a diameter of 1-50 nm and a length of 1-10 μm.

3. The method for preparing an electrode based on a multi-scale pore coating structure according to claim 1, characterized in that: The L-CNTs dispersion is prepared by uniformly mixing a predetermined amount of L-CNTs in deionized water, an ethanol solution, an isopropanol solution, or a mixture thereof to form an L-CNTs dispersion having a mass fraction of 2-5%, and ultrasonically treating the dispersion in a water bath at a temperature of 10-50° C., with an ultrasonic power of 100 W to 800 W and an ultrasonic time of 30-80 min.

4. The method for preparing an electrode based on a multi-scale pore coating structure according to claim 1, characterized in that: The s-CNTs dispersion is prepared by uniformly mixing a predetermined amount of s-CNTs in deionized water, an ethanol solution, an isopropanol solution, or a mixture thereof to form a 5-20% L-CNTs dispersion, and ultrasonically treating the dispersion in a water bath at a temperature of 10-50° C., with an ultrasonic power of 100 W to 800 W and a ultrasonic time of 30-80 minutes.

5. The method for preparing an electrode based on a multi-scale pore coating structure according to claim 1, characterized in that: In step S2, the binder is a membrane solution with a mass percentage of 3%-20%.

6. The method for preparing an electrode based on a multi-scale pore coating structure according to claim 5, characterized in that: The membrane solution types include any one of perfluorosulfonic acid polyelectrolyte membrane solution, sulfonated polyetheretherketone polyelectrolyte membrane solution, sulfonated polysulfone polyelectrolyte membrane solution, phosphated polybenzimidazole membrane solution, quaternized polysulfone polyelectrolyte membrane solution, and polybenzimidazole polyelectrolyte membrane solution, or a mixture of two or more thereof.

7. The method for preparing an electrode based on a multi-scale pore coating structure according to claim 1, characterized in that: In step S2, the mixing step is: ultrasonically mixing the two dispersions and the binder at 100-800W for 20-90 minutes at 10-50°C.

8. The method for preparing an electrode based on a multi-scale pore coating structure according to claim 1, characterized in that: In step S3, the catalyst slurry is coated on both sides of the electrode, and the coating method includes but is not limited to one of brushing, spraying, and transfer printing.

9. An electrode based on a multi-scale pore coating structure, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. An application of an electrode based on a multi-scale pore coating structure, characterized in that: Electrodes for vanadium flow batteries.

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