High-conductivity flexible graphite bipolar plate as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of flow batteries, and discloses a high-conductivity flexible graphite bipolar plate as well as a preparation method and application thereof. The preparation method of the flexible graphite bipolar plate comprises the following steps: firstly, soaking an expanded graphite plate in a mixed solution in a negative pressure environment, wherein the mixed solution comprises soluble indium salt and soluble tin salt; stirring, adding ammonia water, and carrying out hydrolysis reaction; after the reaction is finished, carrying out water washing, drying and heat treatment to obtain an indium tin oxide doped expanded graphite plate; then, thermosetting resin is infiltrated into micropores of the indium tin oxide doped expanded graphite plate through vacuum, and curing is carried out, so that the expanded graphite plate is prepared. A high-conductivity indium tin oxide doping phase is introduced into pores of the flexible graphite bipolar plate in situ, so that the conductivity of the graphite bipolar plate is improved, the pores of micropores are filled to a certain extent, the use amount of non-conductive resin is reduced, and the energy storage efficiency of the flow battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, specifically relating to a highly conductive flexible graphite bipolar plate, its preparation method, and its application. Background Technology

[0002] With the world actively promoting energy transition and vigorously developing renewable energy sources such as solar power, the intermittent and highly volatile nature of these energy sources poses a severe challenge to the stability and reliability of power supply, leading to frequent instances of wind and solar power curtailment. High-efficiency energy storage technology has become crucial for solving the grid connection problem. Flow batteries, with their advantages of independent energy storage and power output, excellent deep discharge capability, long cycle life, and high safety, have shown broad application prospects in multiple fields, including generation, grid, and user sides, becoming a highly promising electrochemical energy storage technology.

[0003] Flexible graphite bipolar plates are a core component of flow batteries, and their performance directly affects the energy conversion efficiency, power density, and lifespan of the battery. An ideal flow battery must simultaneously meet requirements such as high conductivity, strong liquid resistance, mechanical strength, and resistance to strong acid corrosion. However, traditional flexible graphite bipolar plates are typically manufactured by impregnating expanded graphite molded semi-finished products with a resin solution to fill pore volumes. But the poor conductivity of the resin solution results in a high resistance within the flexible graphite plate itself, affecting the flow battery's output performance. Some flexible graphite plates improve conductivity by adding a conductive layer to the surface; however, this method only improves the surface conductivity of the bipolar plate, i.e., improving contact resistance, and has little effect on improving the internal conductivity of the bipolar plate. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a highly conductive flexible graphite bipolar plate, its preparation method and application, wherein the flexible graphite bipolar plate can simultaneously improve its surface conductivity and internal conductivity while ensuring its airtightness and mechanical strength.

[0005] To address the aforementioned technical problems, a first aspect of the present invention provides a method for preparing a flexible graphite bipolar plate, comprising the following steps:

[0006] (1) Immerse the expanded graphite plate in a mixed solution under negative pressure, the mixed solution including soluble indium salt and soluble tin salt; stir, add ammonia water, and carry out hydrolysis reaction; after the reaction is completed, wash with water, dry and heat treat to obtain indium tin oxide doped expanded graphite plate;

[0007] (2) Thermosetting resin is impregnated into the micropores of the indium tin oxide-doped expanded graphite plate by vacuum impregnation, and then cured to obtain the flexible graphite bipolar plate.

[0008] Specifically, this invention involves immersing an expanded graphite plate in a mixed solution containing soluble indium and soluble tin salts. Under the influence of ammonia and negative pressure, and through heat treatment, a highly conductive indium tin oxide (ITO) doped phase is generated in situ within the pores of the expanded graphite plate. This process improves the conductivity of the flexible graphite bipolar plate, enhancing the energy conversion efficiency of the flow battery. Furthermore, it partially fills the pores of the expanded graphite plate, reducing the amount of non-conductive resin required for subsequent impregnation, further increasing the conductivity of the flexible graphite bipolar plate, and improving its airtightness and mechanical strength, thereby enhancing the energy storage efficiency of the flow battery. Simultaneously, by introducing highly conductive ITO into the pores of the expanded graphite plate, this invention not only improves the internal conductivity of the bipolar plate but also enhances its surface conductivity.

[0009] In some embodiments of the present invention, in step (1), the soluble indium salt is selected from at least one of indium trichloride, indium sulfate, indium acetate, and indium nitrate; preferably indium trichloride.

[0010] In some embodiments of the present invention, in step (1), the soluble tin salt is selected from at least one of tin tetrachloride, tin ethoxide, tin propoxide, and tin butoxide; preferably tin tetrachloride.

[0011] In some embodiments of the present invention, in step (1), the concentration of the soluble indium salt in the mixed solution is 0.1-0.4 g / mL, the concentration of the soluble tin salt is 0.01-0.04 g / mL, and the solvent of the mixed solution is water.

[0012] In some embodiments of the present invention, in step (1), the concentration of the ammonia water is 1-4 mmol / L, and the volume ratio of the ammonia water to the mixed solution is (2-10):1; preferably (3-6):1.

[0013] In some embodiments of the present invention, in step (1), the temperature of the heat treatment is 300-600°C; preferably 400-600°C, and more preferably 500-550°C.

[0014] In some embodiments of the present invention, in step (1), the heat treatment time is 1-3 hours; preferably 1.5-2.5 hours.

[0015] In some embodiments of the present invention, in step (1), the drying temperature is 50-90°C; preferably 50-80°C; and more preferably 55-70°C.

[0016] In some embodiments of the present invention, in step (1), the preparation process of the expanded graphite plate is as follows: flake graphite is subjected to chemical treatment and thermal expansion treatment in sequence to obtain expanded graphite powder; then the expanded graphite powder is pressed into shape to obtain the expanded graphite plate.

[0017] In some embodiments of the present invention, the purity of the flake graphite is 97-99.8%.

[0018] In some embodiments of the present invention, the chemical reagents used in the chemical treatment are selected from at least one of nitric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, citric acid, hydrogen peroxide, and potassium permanganate.

[0019] In some embodiments of the present invention, the temperature of the chemical treatment is 30-90°C; preferably 40-80°C; more preferably 50-70°C.

[0020] In some embodiments of the present invention, the chemical treatment time is 1-3 hours; preferably 2-3 hours.

[0021] In some embodiments of the present invention, the temperature of the thermal expansion treatment is 500-800°C; preferably 600-800°C; and more preferably 600-750°C.

[0022] In some embodiments of the present invention, the thermal expansion treatment time is 1-10 min; preferably 2-5 min.

[0023] In some embodiments of the present invention, the pressure of the compression molding is 10-30 MPa; preferably 15-25 MPa.

[0024] In some embodiments of the present invention, the thickness of the expanded graphite plate is 0.6-3 mm; preferably 0.6-1.5 mm; and more preferably 0.6-0.8 mm.

[0025] In some embodiments of the present invention, the average density of the expanded graphite plate is 0.2-0.7 g / cm³. 3 The preferred value is 0.4-0.7 g / cm³. 3 .

[0026] In some embodiments of the present invention, in step (2), the thermosetting resin is selected from at least one of polyvinylidene fluoride, epoxy resin, and phenolic resin.

[0027] In some embodiments of the present invention, in step (2), the curing temperature is 50-95°C; preferably 60-80°C; and more preferably 60-70°C.

[0028] In some embodiments of the present invention, in step (2), the curing time is 60-180 minutes; preferably 70-120 minutes; more preferably 70-100°C.

[0029] A second aspect of the present invention provides a flexible graphite bipolar plate, which is prepared by the above-described method for preparing a flexible graphite bipolar plate; the flexible graphite bipolar plate includes an expanded graphite plate, wherein indium tin oxide is doped into the pores of the expanded graphite plate.

[0030] Specifically, the present invention improves the internal and surface conductivity of the flexible graphite bipolar plate by doping indium tin oxide into the pores of the expanded graphite plate, while also filling the micropores to a certain extent, thereby enhancing the airtightness and mechanical strength of the bipolar plate.

[0031] A third aspect of the present invention provides a flow battery comprising the aforementioned flexible graphite bipolar plate.

[0032] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages:

[0033] (1) The present invention generates a highly conductive indium tin oxide doped phase in situ inside the pores of the expanded graphite plate, which on the one hand significantly improves the conductivity of the flexible graphite bipolar plate and enhances the energy conversion efficiency of the flow battery; on the other hand, it fills the pores of the expanded graphite plate to a certain extent, further improving the conductivity of the flexible graphite bipolar plate and enhancing its airtightness and mechanical strength, thereby improving the energy storage efficiency of the flow battery.

[0034] (2) By introducing a highly conductive indium tin oxide doped phase into the pores of the expanded graphite plate, the present invention not only significantly improves the internal conductivity of the flexible graphite bipolar plate, but also improves its surface conductivity, thereby greatly enhancing the overall conductivity of the bipolar plate.

[0035] (3) The flexible graphite bipolar plate prepared by this invention simultaneously possesses good mechanical strength, airtightness, and overall conductivity, achieving a bending strength of 45.2-45.7 MPa, an airtightness of 0.0277-0.0283 sccm, an in-plane conductivity of 461-512 S / cm, and a contact resistance of 2.36-2.47 mΩ·cm. 2 ). Detailed Implementation

[0036] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0037] Example 1

[0038] A method for preparing a flexible graphite bipolar plate includes the following steps:

[0039] (1) Add 99% pure flake graphite to sulfuric acid and chemically treat it at 50°C for 3 hours; then wash it with pure water until neutral, and then heat treat it at 600°C for 2 minutes to obtain expanded graphite sheets.

[0040] (2) Expanded graphite sheets are pressed in a mold at a pressure of 15 MPa to obtain a thickness of 0.8 mm and an average density of 0.4 g / cm³. 3 Expanded graphite plates.

[0041] (3) Dissolve indium trichloride (InCl3) and tin tetrachloride (SnCl4) in deionized water to prepare a mixed solution (the concentration of InCl3 is 0.2 g / mL and the concentration of SnCl4 is 0.02 g / mL), and stir in a water bath; then add ammonia water with a concentration of 2 mmol / L (the volume ratio of the mixed solution to ammonia water is 3:1) to make InCl3 and SnCl4 undergo hydrolysis reaction; after washing with water, drying at 60℃ and heat treatment at 550℃ for 1.5 hours, indium tin oxide (ITO) doped expanded graphite plate is obtained.

[0042] (4) The epoxy resin solution is impregnated into the micropores of the indium tin oxide-doped expanded graphite plate by vacuum impregnation. After washing, it is cured in a water bath at 70°C for 70 minutes and then dried to obtain the flexible graphite bipolar plate of this embodiment.

[0043] Example 2

[0044] A method for preparing a flexible graphite bipolar plate includes the following steps:

[0045] (1) Add 99.2% pure flake graphite to sulfuric acid and chemically treat it at 60°C for 2 hours; then wash it with pure water until neutral, and then heat treat it at 650°C for 2 minutes to obtain expanded graphite sheets.

[0046] (2) Expanded graphite sheets are pressed in a mold at a pressure of 20 MPa to obtain a thickness of 0.7 mm and an average density of 0.6 g / cm³. 3 Expanded graphite plates.

[0047] (3) Dissolve indium trichloride (InCl3) and tin tetrachloride (SnCl4) in deionized water to prepare a mixed solution (the concentration of InCl3 is 0.3 g / mL and the concentration of SnCl4 is 0.03 g / mL), and stir in a water bath; then add ammonia water with a concentration of 1 mmol / L (the volume ratio of the mixed solution to ammonia water is 5:1) to make InCl3 and SnCl4 undergo hydrolysis reaction; after washing with water, drying at 70℃ and heat treatment at 500℃ for 2 hours, indium tin oxide (ITO) doped expanded graphite plate is obtained.

[0048] (4) The polyvinylidene fluoride resin solution was impregnated into the micropores of the indium tin oxide-doped expanded graphite plate under vacuum. After washing, it was cured in a water bath at 60°C for 90 minutes and then dried to obtain the flexible graphite bipolar plate of this embodiment.

[0049] Example 3

[0050] A method for preparing a flexible graphite bipolar plate includes the following steps:

[0051] (1) Add 99.5% pure flake graphite to sulfuric acid and chemically treat it at 70°C for 2 hours; then wash it with pure water until neutral, and then heat treat it at 750°C for 5 minutes to obtain expanded graphite sheets.

[0052] (2) Expanded graphite sheets are pressed in a mold at a pressure of 25 MPa to obtain a thickness of 0.6 mm and an average density of 0.7 g / cm³. 3 Expanded graphite plates.

[0053] (3) Dissolve indium trichloride (InCl3) and tin tetrachloride (SnCl4) in deionized water to prepare a mixed solution (the concentration of InCl3 is 0.15 g / mL and the concentration of SnCl4 is 0.015 g / mL), and stir in a water bath; then add ammonia water with a concentration of 3 mmol / L (the volume ratio of the mixed solution to ammonia water is 6:1) to make InCl3 and SnCl4 undergo hydrolysis reaction; after washing with water, drying at 55℃ and heat treatment at 500℃ for 2.5 hours, indium tin oxide (ITO) doped expanded graphite plate is obtained.

[0054] (4) The phenolic resin solution was impregnated into the micropores of the indium tin oxide-doped expanded graphite plate by vacuum impregnation. After washing, it was cured in a water bath at 70°C for 100 minutes and dried to obtain the flexible graphite bipolar plate of this embodiment.

[0055] Comparative Example 1

[0056] A method for preparing a flexible graphite bipolar plate includes the following steps:

[0057] (1) Add 99.5% pure flake graphite to sulfuric acid and chemically treat it at 70°C for 2 hours; then wash it with pure water until neutral, and then heat treat it at 750°C for 5 minutes to obtain expanded graphite sheets.

[0058] (2) Expanded graphite sheets are pressed in a mold at a pressure of 25 MPa to obtain a thickness of 0.6 mm and an average density of 0.7 g / cm³. 3 Expanded graphite plates.

[0059] (3) The phenolic resin solution was impregnated into the micropores of the expanded graphite plate by vacuum. After washing, it was cured in a water bath at 70°C for 100 minutes and dried to obtain the flexible graphite bipolar plate of this comparative example.

[0060] The difference between Comparative Example 1 and Example 3 is that the expanded graphite plate was not doped with indium tin oxide.

[0061] Comparative Example 2

[0062] A method for preparing a flexible graphite bipolar plate includes the following steps:

[0063] (1) Add 99.5% pure flake graphite to sulfuric acid and chemically treat it at 70°C for 2 hours; then wash it with pure water until neutral, and then heat treat it at 750°C for 5 minutes to obtain expanded graphite sheets.

[0064] (2) Expanded graphite sheets are pressed in a mold at a pressure of 25 MPa to obtain a thickness of 0.6 mm and an average density of 0.7 g / cm³. 3 Expanded graphite plates.

[0065] (3) Antimony trichloride (SbCl3) and tin tetrachloride (SnCl4) were dissolved in deionized water to prepare a mixed solution (the concentration of SbCl3 was 0.15 g / mL and the concentration of SnCl4 was 0.015 g / mL), and stirred in a water bath; then 3 mmol / L ammonia water was added (the volume ratio of the mixed solution to ammonia water was 6:1) to cause SbCl3 and SnCl4 to undergo a hydrolysis reaction; after washing with water, drying at 55℃ and heat treatment at 500℃ for 2.5 hours, antimony tin oxide (ATO) doped expanded graphite plate was obtained.

[0066] (4) The phenolic resin solution was impregnated into the micropores of the antimony tin oxide-doped expanded graphite plate under vacuum. After washing, it was cured in a water bath at 70°C for 100 minutes and dried to obtain the flexible graphite bipolar plate of this comparative example.

[0067] The difference between Comparative Example 2 and Example 3 is that antimony trichloride was used instead of indium trichloride in Example 1.

[0068] Comparative Example 3

[0069] A method for preparing a flexible graphite bipolar plate includes the following steps:

[0070] (1) Add 99.5% pure flake graphite to sulfuric acid and chemically treat it at 70°C for 2 hours; then wash it with pure water until neutral, and then heat treat it at 750°C for 5 minutes to obtain expanded graphite sheets.

[0071] (2) Expanded graphite sheets are pressed in a mold at a pressure of 25 MPa to obtain a thickness of 0.6 mm and an average density of 0.7 g / cm³. 3 Expanded graphite plates.

[0072] (3) The phenolic resin solution is impregnated into the micropores of the expanded graphite plate through vacuum. After washing, it is cured in a water bath at 70°C for 100 minutes and then dried to obtain the expanded graphite plate matrix.

[0073] (4) A layer of indium tin oxide film was deposited on the surface of the expanded graphite substrate by magnetron sputtering to obtain the flexible graphite bipolar plate of this comparative example.

[0074] The difference between Comparative Example 3 and Example 3 is that indium tin oxide is coated on the surface of the flexible graphite bipolar plate.

[0075] Performance testing

[0076] The mechanical strength, airtightness, and electrical conductivity of the flexible graphite bipolar plate samples prepared in Examples 1-3 and Comparative Examples 1-3 were tested. Specifically: electrical conductivity was tested using a four-probe resistance meter (KDY-4) to measure the in-plane conductivity and contact resistance; airtightness was tested using a flowmeter method with an airtightness tester (BTY-G3); and bending strength was tested using a three-point bending method with a mechanical testing machine (WDW-10D). The results are shown in Table 1.

[0077] Table 1:

[0078]

[0079] As shown in Table 1, the flexible graphite bipolar plates prepared in Examples 1-3 all exhibit good bending strength, airtightness, and overall conductivity. Specifically, the bending strength reaches 45.2-45.7 MPa, the airtightness reaches 0.0277-0.0283 sccm, the in-plane conductivity reaches 461-512 S / cm, and the contact resistance reaches 2.36-2.47 mΩ·cm. 2 ).

[0080] Compared to Example 3, Comparative Examples 1-3 show a certain degree of decrease in both in-plane conductivity and surface contact resistance compared to Example 3, due to the absence of indium tin oxide doping in the flexible graphite bipolar plate, the doping with other metal oxides, and the indium tin oxide covering the surface of the flexible graphite bipolar plate, respectively. The airtightness is also reduced.

[0081] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A method for preparing a flexible graphite bipolar plate, characterized in that, Includes the following steps: (1) Immerse the expanded graphite plate in a mixed solution under negative pressure, the mixed solution including soluble indium salt and soluble tin salt; stir, add ammonia water, and carry out hydrolysis reaction; after the reaction is completed, wash with water, dry and heat treat to obtain indium tin oxide doped expanded graphite plate; (2) Thermosetting resin is impregnated into the micropores of the indium tin oxide-doped expanded graphite plate by vacuum impregnation, and then cured to obtain the flexible graphite bipolar plate.

2. The method for preparing a flexible graphite bipolar plate according to claim 1, characterized in that, In step (1), the soluble indium salt is selected from at least one of indium trichloride, indium sulfate, indium acetate, and indium nitrate; and / or, the soluble tin salt is selected from at least one of tin tetrachloride, tin ethoxide, tin propoxide, and tin butoxide.

3. The method for preparing a flexible graphite bipolar plate according to claim 1 or 2, characterized in that, In step (1), the concentration of the soluble indium salt in the mixed solution is 0.1-0.4 g / mL, the concentration of the soluble tin salt is 0.01-0.04 g / mL; and / or, the concentration of the ammonia water is 1-4 mmol / L, and the volume ratio of the ammonia water to the mixed solution is (2-10):

1.

4. The method for preparing a flexible graphite bipolar plate according to claim 1, characterized in that, In step (1), the temperature of the heat treatment is 300-600℃; and / or the heat treatment time is 1-3 hours.

5. The method for preparing a flexible graphite bipolar plate according to claim 1, characterized in that, In step (2), the thermosetting resin is selected from at least one of polyvinylidene fluoride, epoxy resin, and phenolic resin.

6. The method for preparing a flexible graphite bipolar plate according to claim 1 or 5, characterized in that, In step (2), the curing temperature is 50-95℃; and / or the curing time is 60-180 minutes.

7. The method for preparing a flexible graphite bipolar plate according to claim 1, characterized in that, In step (1), the preparation process of the expanded graphite plate is as follows: flake graphite is subjected to chemical treatment and thermal expansion treatment in sequence to obtain expanded graphite powder; then the expanded graphite powder is pressed into shape to obtain the expanded graphite plate.

8. The method for preparing a flexible graphite bipolar plate according to claim 7, characterized in that, The chemical reagents used in the chemical treatment are selected from at least one of nitric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, citric acid, hydrogen peroxide, and potassium permanganate; and / or, the chemical treatment time is 1-3 hours; and / or, the temperature of the thermal expansion treatment is 500-800℃.

9. A flexible graphite bipolar plate, characterized in that, The flexible graphite bipolar plate is prepared by any one of claims 1-8; the flexible graphite bipolar plate includes an expanded graphite plate, wherein indium tin oxide is doped into the pores of the expanded graphite plate.

10. A flow battery, characterized in that, Including the flexible graphite bipolar plate as described in claim 9.

Images