Flow battery electrode as well as application and treatment method thereof

Abstract

The invention discloses a flow battery electrode and application and a treatment method thereof, and the treatment method comprises the following steps: S100: clamping, fixing and drying a carbon felt under the condition of a compression ratio of 25-35% to form a preset stress structure; s200, placing the carbon felt subjected to stress presetting in a tubular furnace, and carrying out gradient heating heat treatment; meanwhile, the air velocity in the tubular furnace in the electrolyte flowing direction is controlled, so that the air velocity corresponding to the electrolyte inlet side area is 1.8-2.2 times of the air velocity corresponding to the electrolyte outlet side area; and S300, saturated steam is introduced, treatment is conducted for 2.0-2.5 h at the temperature of 135-145 DEG C, then gradient drying is conducted to the room temperature, and then cooling is conducted to the room temperature. According to the technical scheme, the energy efficiency and the cycling stability of the all-vanadium redox flow battery electrode are improved.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, and in particular to an electrode and its application and processing method. Background Technology

[0002] Flow batteries, with their long cycle life, high safety, and flexible power configuration, have shown broad application prospects in large-scale energy storage. As a core component of the battery, the performance of electrode materials directly determines the battery's energy conversion efficiency, power density, and long-term stability. Currently, commercial flow batteries generally use polyacrylonitrile-based carbon felt as the electrode substrate material. However, unmodified carbon felt has inherent defects such as insufficient surface catalytic activity, simple pore structure, and low mass transfer efficiency, making it difficult to meet the requirements of high current density operation.

[0003] To improve electrode performance, existing technologies mainly rely on strategies such as chemical oxidation treatment, catalytic material loading, or surface functionalization modification. These methods typically involve multiple strong oxidants, metal salts, or organic solvents, resulting in complex processes, high production costs, and the generation of large amounts of harmful waste liquid, posing significant environmental pressure. Furthermore, traditional treatment methods often lead to excessive oxidation or structural damage of the electrode surface, resulting in rapid performance degradation during long-term charge-discharge cycles. Simultaneously, the uniform pore structure cannot match the concentration gradient changes of the electrolyte during flow, making it difficult to synergistically optimize reactivity and mass transfer efficiency. Summary of the Invention

[0004] The main objective of this invention is to provide an electrode, its application, and a processing method thereof, which aims to improve the energy efficiency and cycle stability of flow battery electrodes.

[0005] To achieve the above objectives, the present invention proposes an electrode processing method, the processing method comprising the following steps:

[0006] S100: The carbon felt is clamped, fixed, and dried under a compression ratio of 25-35% to form a pre-stressed structure;

[0007] S200: The pre-stressed carbon felt is placed in a tube furnace for gradient heating heat treatment; at the same time, the air velocity along the electrolyte flow direction in the tube furnace is controlled so that the air velocity in the corresponding electrolyte inlet area is 1.8-2.2 times that in the corresponding electrolyte outlet area.

[0008] S300: Introduce saturated water vapor and treat at 135-145℃ for 2.0-2.5 hours, then gradually dry to room temperature, and then cool to room temperature.

[0009] In some embodiments of the present invention, in step S100, the drying temperature is 80±5℃ and the drying time is 2±0.3 hours.

[0010] In some embodiments of the present invention, in step S200, the gradient heating heat treatment is as follows: the temperature is increased to 150°C at a rate of 2.5 ± 0.3°C / min, then increased from 150°C to 250°C at a rate of 1.2 ± 0.2°C / min, then increased from 250°C to 300°C at a rate of 1.0 ± 0.1°C / min, and held at 300°C for 25 ± 2 minutes.

[0011] In some embodiments of the present invention, in step S200, the airflow velocity in the inlet side region is 90-110 ml / min, and the airflow velocity in the outlet side region is 45-55 ml / min.

[0012] In some embodiments of the present invention, in step S300, the heat preservation treatment is carried out in a closed pressure vessel at a pressure of 0.6-1.0 MPa; after the heat preservation is completed, the temperature is cooled to 120°C at a rate of 12-15°C / min, then cooled to 80°C at a rate of 8-10°C / min, and finally cooled to 60°C at a rate of 5-7°C / min, and then naturally cooled to room temperature.

[0013] In some embodiments of the present invention, in step S100, the clamping and fixing adopts a gradient pressure distribution method, with the pressure distribution along the length of the carbon felt as follows: the pressure in the inlet area is 0.25-0.35 MPa, the pressure in the middle area is 0.30-0.40 MPa, and the pressure in the outlet area is 0.35-0.45 MPa, forming a pre-set stress gradient field that works synergistically with subsequent thermal oxidation.

[0014] In some embodiments of the present invention, in step S200, a gas flow monitoring and regulation device is set at both ends of the tubular furnace to monitor the gas flow on the inlet side and the outlet side in real time. When the flow rate ratio is detected to deviate from the range of 1.8-2.2:1, the output of the two mass flow controllers is automatically adjusted to maintain the flow rate ratio stable.

[0015] In some embodiments of the present invention, the carbon felt is a polyacrylonitrile-based carbon felt with a thickness of 5±0.5 mm and a density of 0.12±0.02 g / cm³.

[0016] This invention also discloses the application of the electrode processing method in flow battery packs.

[0017] The present invention also discloses a flow battery electrode, which is made by the aforementioned processing method.

[0018] The technical solution of this invention improves the electrochemical performance of the electrode at high current density by constructing a pre-set stress gradient field that matches the electrolyte flow direction, while optimizing the electrolyte flow and active material transport efficiency, thereby achieving a systematic improvement in energy efficiency across the entire current density range and significantly improving the internal uniformity of the stack. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1 This is a flowchart of the electrode processing method of the present invention;

[0021] Figure 2 This is an electron microscope image of the electrode of the present invention;

[0022] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0025] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, the user should consider such a combination of technical solutions to be non-existent and not within the scope of protection claimed by this invention.

[0026] See appendix Figure 1-2

[0027] Example 1

[0028] This embodiment provides a method for preparing a composite electrode structure, specifically including the following steps:

[0029] S100: A 5mm thick, 0.12g / cm³ polyacrylonitrile-based carbon felt is clamped and fixed under a 30% compression ratio, with a pressure of 0.35MPa in the inlet area, 0.40MPa in the middle area, and 0.45MPa in the outlet area. It is then dried at 85℃ for 2.2 hours to form a pre-stressed structure.

[0030] S200: Place the pre-stressed carbon felt in a tube furnace and raise the temperature to 150℃ at a rate of 2.5℃ / min, to 250℃ at a rate of 1.2℃ / min, and to 300℃ at a rate of 1.0℃ / min, and hold at 300℃ for 25 minutes; at the same time, control the air flow rate in the tube furnace along the direction of electrolyte flow so that the air flow rate in the inlet area is 100ml / min and the air flow rate in the outlet area is 50ml / min.

[0031] S300: Introduce saturated water vapor, treat at 140℃ for 2.2 hours, then cool to 120℃ at a rate of 12℃ / min, to 80℃ at a rate of 8℃ / min, to 60℃ at a rate of 5℃ / min, and finally cool naturally to room temperature.

[0032] Example 2

[0033] In this embodiment, a compression ratio of 35% is used in S100, and the air flow rate on the inlet side is 110 ml / min and the air flow rate on the outlet side is 45 ml / min in S200 (flow rate ratio 2.44:1). Other steps are the same as in Embodiment 1.

[0034] Example 3

[0035] In this embodiment, the components are uniformly clamped and fixed in S100 with a compression ratio of 30%, and the other steps are the same as in Embodiment 1.

[0036] Example 4

[0037] In this embodiment, the steam treatment time in S300 is extended to 2.5 hours, and the other steps are the same as in Embodiment 1.

[0038] Comparative Example 1

[0039] In this comparative example, the air flow rate on both the inlet and outlet sides was 75 ml / min (flow rate ratio 1:1) in S200, and the other steps were the same as in Example 1.

[0040] Comparative Example 2

[0041] In this comparative example, the compression and fixation step is omitted in S100, and the product is directly dried. The other steps are the same as in Example 1.

[0042] Comparative Example 3

[0043] In this comparative example, the carbon felt was directly heated to 300°C in a tubular furnace in an S200, and the other steps were the same as in Example 1.

[0044] Comparative Example 4

[0045] In this comparative example, the steam treatment step is omitted in S300, and only drying is performed. The other steps are the same as in Example 1.

[0046] Comparative Example 5

[0047] This comparative example uses commercially available raw polyacrylonitrile-based carbon felt (without any treatment).

[0048] Experimental methods

[0049] The electrodes treated in Examples 1-5 and Comparative Examples 1-5 were used as electrodes for vanadium redox flow batteries and assembled into single cells. The positive electrode electrolyte was 20 mL of 1 M VOSO4 + 3 M H2SO4 solution, and the negative electrode electrolyte was 20 mL of 1 M V3⁺ + 3 M H2SO4 solution. The operating electrolyte densities were 100 mA / cm², 200 mA / cm², 300 mA / cm², and 400 mA / cm², respectively. The charge / discharge efficiencies are shown in Tables 1-4.

[0050] Table 1: Charge and discharge efficiency data at a current density of 100 mA / cm²

[0051] Electrode type Capacity efficiency (%) Energy efficiency (%) Voltage efficiency (%) Example 1 95.5 84.3 88.3 Example 2 94.8 83.8 88.4 Example 3 94.5 83.5 88.4 Example 4 94.0 83.0 88.3 Comparative Example 1 91.0 79.5 87.4 Comparative Example 2 88.5 76.8 86.7 Comparative Example 3 90.5 78.2 86.4 Comparative Example 4 86.0 74.5 86.6 Comparative Example 5 85.2 69.1 81.2

[0052] As shown in Table 1, the energy efficiency of Example 1 (84.3%) is significantly better than that of Example 3 and Comparative Example 1, demonstrating that the synergistic effect of steps S100 and S200 is key to improving performance. In Example 3, due to the lack of gradient pressure, although the compression ratio was the same, the uneven stress distribution inside the electrode resulted in slightly lower capacity and voltage efficiencies than in Example 1.

[0053] Table 2: Charge and discharge efficiency data at a current density of 200 mA / cm²

[0054] Electrode type Capacity efficiency (%) Energy efficiency (%) Voltage efficiency (%) Example 1 94.2 78.5 83.3 Example 2 93.5 77.8 83.2 Example 3 93.0 77.5 83.3 Example 4 92.5 77.0 83.2 Comparative Example 1 89.5 72.3 80.7 Comparative Example 2 86.8 69.5 80.0 Comparative Example 3 88.5 71.2 80.4 Comparative Example 4 84.2 66.5 79.0 Comparative Example 5 83.5 62.5 74.8

[0055] As shown in Table 2, the energy efficiency of Example 1 is better than that of Examples 2 and 3, indicating that gradient pressure and gradient flow velocity need to be matched in a coordinated manner. The capacity efficiency of Example 2 decreased due to the excessively high compression ratio; the voltage efficiency of Example 3 was not optimized because the uniform pressure could not form a stress gradient field.

[0056] Table 3: Charge and discharge efficiency data at a current density of 300 mA / cm²

[0057] Electrode type Capacity efficiency (%) Energy efficiency (%) Voltage efficiency (%) Example 1 92.0 65.0 70.7 Example 2 91.3 64.5 70.6 Example 3 90.5 70.0 77.3 Example 4 89.8 63.5 70.7 Comparative Example 1 87.2 65.8 75.4 Comparative Example 2 84.5 63.2 74.8 Comparative Example 3 85.8 64.5 75.2 Comparative Example 4 82.0 60.5 73.8 Comparative Example 5 81.5 55.5 68.1

[0058] As shown in Table 3, at a current density of 300 mA / cm², the energy efficiency of Example 1 (65.0%) is significantly higher than that of Example 3 and Comparative Example 3, mainly due to the stress gradient field pre-set with gradient pressure. In Example 3, under high current density, the uniform pressure leads to stress concentration at the electrode edges, resulting in lower capacity and voltage efficiencies than Example 1. Comparative Example 3, by omitting the gradient pressure pre-set, suffers from uneven stress distribution after heat treatment, resulting in an energy efficiency of only 64.5%.

[0059] Table 4: Charge and discharge efficiency data at a current density of 400 mA / cm²

[0060] Electrode type Capacity efficiency (%) Energy efficiency (%) Voltage efficiency (%) Example 1 90.5 62.5 69.0 Example 2 89.8 61.8 68.8 Example 3 89.2 61.2 68.7 Example 4 88.5 60.5 68.4 Comparative Example 1 86.5 58.5 67.6 Comparative Example 2 83.2 55.8 67.1 Comparative Example 3 84.8 57.0 67.2 Comparative Example 4 80.5 53.0 65.8 Comparative Example 5 79.0 48.9 61.9

[0061] As shown in Table 4, at a current density of 400 mA / cm², Example 1 exhibits the most significant energy efficiency of 62.5%, which is superior to Examples 2 and 4. This solution, through the precise synergy of S100 and S200, enables the electrode to achieve an energy efficiency far exceeding that of Comparative Example 5 at 400 mA / cm².

[0062] In summary, this invention optimizes the internal pore structure and active site distribution of the electrode by constructing a gradient pressure distribution on the carbon felt to form a directional pre-set stress gradient field. Simultaneously, a gradient airflow is set along the electrolyte flow direction, allowing the stress gradient field and airflow gradient to work synergistically, significantly improving the electrolyte flow uniformity and active material transport efficiency. This effectively suppresses electrochemical polarization under high current density, simultaneously improving voltage efficiency and capacity efficiency, thereby achieving systematic optimization of energy efficiency. This technical solution demonstrates performance advantages across the entire current density range (100-400 mA / cm²), and these advantages continue to expand under high current density conditions.

[0063] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for processing an electrode, characterized in that, The processing method includes the following steps: S100: The carbon felt is clamped, fixed, and dried under a compression ratio of 25-35% to form a pre-stressed structure; S200: Place the carbon felt, which was kept in a clamped and compressed state in step S100, into a tube furnace for gradient heating heat treatment; at the same time, control the air flow rate in the tube furnace along the direction of electrolyte flow so that the air flow rate in the corresponding electrolyte inlet area is 1.8-2.2 times that in the corresponding electrolyte outlet area. S300: Saturated water vapor is introduced under continuous clamping and compression, and the mixture is treated at 135-145℃ for 2.0-2.5 hours, then gradually dried to room temperature, and then cooled to room temperature.

2. The electrode processing method as described in claim 1, characterized in that, In step S100, the drying temperature is 80±5℃ and the drying time is 2±0.3 hours.

3. The electrode processing method as described in claim 1, characterized in that, In step S200, the gradient heating heat treatment is as follows: the temperature is increased to 150°C at a rate of 2.5 ± 0.3°C / min, then increased from 150°C to 250°C at a rate of 1.2 ± 0.2°C / min, then increased from 250°C to 300°C at a rate of 1.0 ± 0.1°C / min, and held at 300°C for 25 ± 2 minutes.

4. The electrode processing method as described in claim 1, characterized in that, In step S200, the airflow velocity in the inlet side region is 90-110 ml / min, and the airflow velocity in the outlet side region is 45-55 ml / min.

5. The electrode processing method as described in claim 1, characterized in that, In step S300, the heat preservation treatment is carried out in a closed pressure vessel at a pressure of 0.6-1.0 MPa. After the heat preservation is completed, the temperature is cooled to 120°C at a rate of 12-15°C / min, then cooled to 80°C at a rate of 8-10°C / min, and finally cooled to 60°C at a rate of 5-7°C / min, and then allowed to cool naturally to room temperature.

6. The electrode processing method as described in claim 1, characterized in that, In step S100, the clamping and fixing adopts a gradient pressure distribution method. The pressure distribution along the length of the carbon felt is as follows: the pressure in the inlet area is 0.25-0.35MPa, the pressure in the middle area is 0.30-0.40MPa, and the pressure in the outlet area is 0.35-0.45MPa, forming a pre-set stress gradient field that works in conjunction with subsequent thermal oxidation.

7. The electrode processing method as described in claim 1, characterized in that, In step S200, gas flow monitoring and regulation devices are installed at both ends of the tubular furnace to monitor the gas flow on the inlet and outlet sides in real time. When the flow rate ratio is detected to deviate from the range of 1.8-2.2:1, the output of the two mass flow controllers is automatically adjusted to maintain the flow rate ratio stable.

8. The electrode processing method as described in claim 1, characterized in that, The carbon felt is a polyacrylonitrile-based carbon felt with a thickness of 5±0.5 mm and a density of 0.12±0.02 g / cm³.

9. A flow battery electrode, characterized in that, The electrode is made by the processing method according to any one of claims 1-8.

10. The application of a method for processing the electrode according to any one of claims 1 to 5 in a flow battery pack.

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