Flexible graphite bipolar plate with self-repairing function and preparation method and application thereof

Abstract

The application belongs to the technical field of liquid flow batteries, and discloses a flexible graphite bipolar plate with a self-repairing function and a preparation method and application thereof. The flexible graphite bipolar plate comprises a flexible graphite-polymer composite matrix, microcapsules and a graphene conductive layer, wherein: the graphene conductive layer is arranged on the surface of the flexible graphite-polymer composite matrix; the microcapsules are dispersed in the flexible graphite-polymer composite matrix, and the core of the microcapsules is a liquid metal alloy containing Ga, and the shell of the microcapsules is polyurethane. By introducing the microcapsules containing the liquid metal alloy into the flexible graphite bipolar plate in situ, when microcracks are generated in the flexible graphite bipolar plate due to mechanical stress, thermal cycling and the like, the microcapsules will first break and release the liquid metal to fill the cracks, so that the graphite bipolar plate still maintains high mechanical strength and air tightness, thereby improving the conductive stability and use durability of the liquid flow battery.

Description

Technical Field

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

[0002] The randomness and undispatchability of clean energy sources such as wind and solar power are becoming increasingly prominent, putting immense pressure on power grid peak shaving and frequency regulation. Large-scale energy storage systems have become an indispensable "stabilizer" for new power systems. Flow batteries, with their unique structural design and performance advantages, offer an innovative solution to the challenge of renewable energy integration: their modular design allows for flexible configuration from kilowatts to megawatts, meeting diverse needs such as power generation smoothing, grid peak shaving and valley filling, and user demand management; their ultra-long cycle life of over 20 years significantly reduces total lifecycle costs, and their inherently safe liquid electrolyte system completely eliminates the risk of thermal runaway. These characteristics make flow batteries a key supporting technology for building high-proportion renewable energy power systems.

[0003] Traditional flexible graphite bipolar plates are prone to developing microcracks due to mechanical stress and thermal cycling during long-term operation of flow batteries, or under extreme low-temperature and high-pressure environments. This leads to increased contact resistance, electrolyte penetration, and ultimately reduced battery efficiency. Existing solutions typically involve carbon fiber reinforcement or polymer modification, but these methods only delay crack propagation and cannot achieve active repair.

[0004] Therefore, there is an urgent need to develop a flexible graphite bipolar plate with self-healing function to further improve the conductivity stability and service life of the bipolar plate. Summary of the Invention

[0005] 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 flexible graphite bipolar plate with self-healing function, its preparation method and application. The flexible graphite bipolar plate not only has self-healing function, but also reduces the loss of conductivity, airtightness and bending strength of the bipolar plate, thereby improving the conductivity stability and service life of the flow battery.

[0006] To address the aforementioned technical problems, a first aspect of the present invention provides a flexible graphite bipolar plate, comprising a flexible graphite-polymer composite matrix, microcapsules, and a graphene conductive layer. The graphene conductive layer is disposed on the surface of the flexible graphite-polymer composite matrix, and the microcapsules are dispersed in the flexible graphite-polymer composite matrix. The core of the microcapsules is a liquid metal alloy containing Ga, and the outer shell of the microcapsules is polyurethane.

[0007] Specifically, this invention introduces microcapsules containing liquid metal alloys in situ inside a flexible graphite bipolar plate. When microcracks appear in the flexible graphite bipolar plate due to mechanical stress, thermal cycling, etc., the microcapsules inside will rupture immediately, releasing the liquid metal alloy and filling the cracks. This not only plays a self-repairing role but also reduces the loss of conductivity, airtightness, and bending strength of the electrode plate, allowing the flexible graphite bipolar plate to maintain high mechanical strength and airtightness, thereby improving the conductivity stability and durability of the flow battery.

[0008] Meanwhile, Ga-containing liquid metal alloys not only have repair properties, but also, after the microcapsules rupture, the liquid metal alloys can form Ga-C bonds with graphite while repairing the cracks. In addition to providing mechanical strength repair, the high electrical conductivity of the liquid metal alloys themselves can also greatly maintain the electrical conductivity of the flexible graphite bipolar plate before the cracks occurred.

[0009] In some embodiments of the invention, the liquid metal alloy further includes In and / or Sn. For example, Ga, In, and Sn; Ga and In; Ga and Sn.

[0010] In some embodiments of the present invention, the liquid metal alloy comprises, by weight percentage, 60-95% Ga, 0-30% In, and 0-20% Sn. For example, 60-70% Ga, 20-25% In, and 10-15% Sn; 75-95% Ga and 5-25% In; 85-95% Ga and 5-15% Sn. The specific composition of the liquid metal alloy mainly affects the melting point of the metal alloy. Increasing the In content can slightly increase the melting point, while selecting appropriate ratios of Ga, In, and Sn can maintain the liquid fluidity of the metal over a wider temperature range, thereby ensuring the stability of the microcapsule's self-healing function.

[0011] In some embodiments of the present invention, the diameter of the microcapsules is 10-100 μm.

[0012] In some embodiments of the present invention, the raw material components for preparing the flexible graphite-polymer composite matrix include, by weight: 60-80 parts of flexible graphite and 15-20 parts of polymer; the flexible graphite includes expanded graphite, and the polymer includes polyvinylidene fluoride.

[0013] In some embodiments of the present invention, the components of the microcapsules in the flexible graphite-polymer composite matrix are distributed in a gradient, wherein the distribution density in the edge flow channel region is 4000-6000 capsules / cm². 3 The distribution density in the central plane region is 1000-2500 individuals / cm². 3 .

[0014] Specifically, introducing microcapsules into a flexible graphite-polymer composite matrix will, to some extent, reduce the bending resistance and electrical conductivity of the flexible graphite bipolar plate itself, and the more microcapsules added, the more significant the performance impact. Meanwhile, cracks in flexible graphite bipolar plates tend to concentrate in the edge flow channel region, while cracks are generally less likely to form in the central planar region. Therefore, this invention creates a component gradient distribution of microcapsules, with more at the edges and less in the center. This balances the contradiction between repair performance and the intrinsic properties of the bipolar plate, and also allows the self-healing function of the microcapsules to be better utilized.

[0015] In some embodiments of the present invention, the thickness of the graphene conductive layer is 3-5 layers.

[0016] A second aspect of the present invention provides a method for preparing the above-mentioned flexible graphite bipolar plate, comprising the following steps: (1) Atomize liquid metal alloy into microdroplets, then mix the microdroplets with isocyanate, organic solvent, emulsifier and polyol to form an emulsion; heat to form a polyurethane shell on the surface of the microdroplets; centrifuge and dry to obtain microcapsules; (2) The microcapsules are prepared into a slurry with flexible graphite and polymer, and then the slurry is injected into a mold and pressed to obtain a flexible graphite-polymer composite matrix; (3) A graphene conductive layer is deposited on the surface of the flexible graphite-polymer composite matrix to obtain the flexible graphite bipolar plate.

[0017] In some embodiments of the present invention, in step (1), the preparation process of the microdroplets is as follows: first, Ga and other metals (In and / or Sn) are melted and then atomized into microdroplets of 10-100 μm.

[0018] In some embodiments of the present invention, in step (1), the isocyanate includes hexamethylene diisocyanate, the organic solvent includes xylene solution, the emulsifier includes sodium dodecyl sulfate, and the polyol includes polyether triol.

[0019] In some embodiments of the present invention, in step (1), the heating temperature is 45-55°C and the time is 1-3 hours, and an interfacial polymerization method is used to form a 2-3 μm thick polyurethane shell on the surface of the microdroplets.

[0020] In some embodiments of the present invention, in step (2), the flexible graphite includes expanded graphite, and the preparation process of the expanded graphite is as follows: natural flake graphite is intercalated with concentrated sulfuric acid / nitric acid at a volume ratio of (2-4):1 for 20-25 hours, and then rapidly thermally expanded at 1000-1100℃ for 20-40 seconds to obtain a specific surface area ≥50 m². 2 / g of expanded graphite.

[0021] In some embodiments of the present invention, in step (2), the slurry includes slurry A and slurry B, wherein the content of microcapsules in slurry A is higher than the content of microcapsules in slurry B; slurry A and slurry B are injected into the edge flow channel area and the center plane area of ​​the mold respectively by casting molding method to form a flexible graphite-polymer composite matrix with a gradient distribution of microcapsules.

[0022] In some embodiments of the present invention, the mass ratio of microcapsules to flexible graphite in slurry A is 1:(2-3), and the mass ratio of microcapsules to flexible graphite in slurry B is 1:(15-18). Both slurry A and slurry B are obtained by ball milling and mixing in N-methylpyrrolidone solution.

[0023] In some embodiments of the present invention, in step (2), the pressing process conditions are: pressure 8-12MPa, temperature 170-190℃, and time 25-35 minutes.

[0024] In some embodiments of the present invention, before depositing a graphene conductive layer on the surface of the flexible graphite-polymer composite matrix, a step is further included in which a resin solution is impregnated into the micropores of the flexible graphite-polymer composite matrix by vacuum, and then cured.

[0025] In some embodiments of the present invention, the resin solution comprises a phenolic resin ethanol solution.

[0026] In some embodiments of the present invention, the curing is performed using a water bath at 75-85°C.

[0027] In some embodiments of the present invention, in step (3), a chemical vapor deposition method is used to introduce methane gas at 750-850°C and to deposit a graphene conductive layer on the surface of the flexible graphite-polymer composite matrix using a power of 280-32W. The deposition time is 25-35 minutes.

[0028] A third aspect of the present invention provides a flow battery comprising the aforementioned flexible graphite bipolar plate.

[0029] In some embodiments of the present invention, the flow battery is a vanadium redox flow battery or a zinc-bromine flow battery.

[0030] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages: (1) The present invention introduces microcapsules containing liquid metal alloy in situ inside the flexible graphite bipolar plate. When the flexible graphite bipolar plate develops microcracks due to mechanical stress, thermal cycling, etc., the microcapsules inside will rupture and release the liquid metal alloy to fill the cracks, so that the graphite bipolar plate still maintains high mechanical strength and airtightness, thereby improving the conductivity stability and durability of the flow battery.

[0031] (2) The microcapsules of the present invention contain liquid metal Ga. After the microcapsules rupture, the liquid metal alloy can repair the cracks and form Ga-C bonds with graphite. This not only provides mechanical strength repair, but also maintains the conductivity of the graphite bipolar plate before cracks are generated by the high conductivity of the liquid metal alloy itself, thereby improving the energy conversion efficiency of the flow battery. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the fabrication process of the self-healing flexible graphite bipolar plate of the present invention. Detailed Implementation

[0033] 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.

[0034] The following is a schematic diagram of the fabrication process of the self-healing flexible graphite bipolar plate in the embodiments. Figure 1 As shown.

[0035] Example 1 A method for preparing a self-healing flexible graphite bipolar plate includes the following steps: (1) Natural flake graphite was intercalated with concentrated sulfuric acid / nitric acid at a volume ratio of 3:1 for 24 hours, and then rapidly thermally expanded at 1050℃ for 30 seconds to obtain expanded graphite powder with a specific surface area of ​​55m² / g.

[0036] (2) A molten alloy of Ga (62wt%), In (25wt%), and Sn (13wt%) was atomized into 50μm microdroplets. Then, the microdroplets (69wt%) were mixed with hexamethylene diisocyanate (1.29wt%), xylene solution (8.42wt%), sodium dodecyl sulfate (0.43wt%), polyether triol (0.65wt%), and deionized water (20.21wt%) to form an emulsion. The mixture was reacted at 50℃ for 2 hours to form a 2.5μm thick cross-linked polyurethane shell on the surface of the microdroplets, thus obtaining microcapsules.

[0037] (3) Preparation of slurry A: Expanded graphite powder (60wt%), polyvinylidene fluoride (15wt%), and microcapsules (25wt%) are ball-milled and mixed in N-methylpyrrolidone solution for 2 hours; Preparation of slurry B: Expanded graphite powder (80wt%), polyvinylidene fluoride (15wt%), and microcapsules (5wt%) are ball-milled and mixed in N-methylpyrrolidone solution for 2 hours.

[0038] (4) Using the casting molding method, first inject slurry A into the edge flow channel area of ​​the mold, and then inject slurry B into the center plane area; mold at 10MPa pressure and 180℃ for 30 minutes to obtain a prefabricated flexible graphite-polymer composite matrix with a thickness of 0.8mm; then vacuum impregnate the prefabricated flexible graphite-polymer composite matrix with 30% phenolic resin ethanol solution for 2 hours, and then cure it in a water bath at 80℃ for 6 hours to obtain a flexible graphite-polymer composite matrix.

[0039] (5) At 800℃ and 300W power, methane was introduced and graphene was deposited on the surface of the flexible graphite-polymer composite substrate for 30 minutes using plasma-enhanced chemical vapor deposition to form a graphene conductive layer, thus obtaining the self-healing flexible graphite bipolar plate of this embodiment.

[0040] Example 2 A method for preparing a self-healing flexible graphite bipolar plate includes the following steps: (1) Natural flake graphite was intercalated with concentrated sulfuric acid / nitric acid at a volume ratio of 3:1 for 24 hours, and then rapidly thermally expanded at 1050℃ for 30 seconds to obtain expanded graphite powder with a specific surface area of ​​55m² / g.

[0041] (2) Microdroplets (69 wt%) were mixed with hexamethylene diisocyanate (1.29 wt%), xylene solution (8.42 wt%), sodium dodecyl sulfate (0.43 wt%), polyether triol (0.65 wt%) and deionized water (20.21 wt%) to form an emulsion. The mixture was reacted at 50 °C for 2 hours to form a 3 μm thick cross-linked polyurethane shell on the surface of the microdroplets, thus obtaining microcapsules.

[0042] (3) Preparation of slurry A: Expanded graphite powder (60wt%), polyvinylidene fluoride (15wt%), and microcapsules (25wt%) are ball-milled and mixed in N-methylpyrrolidone solution for 2 hours; Preparation of slurry B: Expanded graphite powder (80wt%), polyvinylidene fluoride (15wt%), and microcapsules (5wt%) are ball-milled and mixed in N-methylpyrrolidone solution for 2 hours.

[0043] (4) Using the casting molding method, first inject slurry A into the edge flow channel area of ​​the mold, and then inject slurry B into the center plane area; mold at 12MPa pressure and 190℃ for 25 minutes to obtain a prefabricated flexible graphite-polymer composite matrix with a thickness of 0.7mm; then vacuum impregnate the prefabricated flexible graphite-polymer composite matrix with 30% phenolic resin ethanol solution for 1.5 hours, and then cure it in a water bath at 80℃ for 7 hours to obtain a flexible graphite-polymer composite matrix.

[0044] (5) At 850°C and 300W power, methane was introduced and graphene was deposited on the surface of the flexible graphite-polymer composite substrate for 35 minutes using plasma-enhanced chemical vapor deposition to form a graphene conductive layer, thus obtaining the self-healing flexible graphite bipolar plate of this embodiment.

[0045] Example 3 A method for preparing a self-healing flexible graphite bipolar plate includes the following steps: (1) Natural flake graphite was intercalated with concentrated sulfuric acid / nitric acid at a volume ratio of 3:1 for 24 hours, and then rapidly thermally expanded at 1050℃ for 30 seconds to obtain expanded graphite powder with a specific surface area of ​​55m² / g.

[0046] (2) Microdroplets (69 wt%) were mixed with hexamethylene diisocyanate (1.29 wt%), xylene solution (8.42 wt%), sodium dodecyl sulfate (0.43 wt%), polyether triol (0.65 wt%) and deionized water (20.21 wt%) to form an emulsion. The mixture was reacted at 50 °C for 1.5 hours to form a 2 μm thick cross-linked polyurethane shell on the surface of the microdroplets, thus obtaining microcapsules.

[0047] (3) Preparation of slurry A: Expanded graphite powder (60wt%), polyvinylidene fluoride (15wt%), and microcapsules (25wt%) are ball-milled and mixed in N-methylpyrrolidone solution for 2 hours; Preparation of slurry B: Expanded graphite powder (80wt%), polyvinylidene fluoride (15wt%), and microcapsules (5wt%) are ball-milled and mixed in N-methylpyrrolidone solution for 2 hours.

[0048] (4) Using the casting molding method, first inject slurry A into the edge flow channel area of ​​the mold, and then inject slurry B into the center plane area; mold at 8MPa pressure and 170℃ for 35 minutes to obtain a prefabricated flexible graphite-polymer composite matrix with a thickness of 0.9mm; then vacuum impregnate the prefabricated flexible graphite-polymer composite matrix with 30% phenolic resin ethanol solution for 2 hours, and then cure it in a water bath at 80℃ for 5 hours to obtain a flexible graphite-polymer composite matrix.

[0049] (5) At 750°C and 300W power, methane was introduced and graphene was deposited on the surface of the flexible graphite-polymer composite substrate for 25 minutes using plasma-enhanced chemical vapor deposition to form a graphene conductive layer, thus obtaining the self-healing flexible graphite bipolar plate of this embodiment.

[0050] Comparative Example 1 A method for preparing a flexible graphite bipolar plate includes the following steps: (1) Natural flake graphite was intercalated with concentrated sulfuric acid / nitric acid at a volume ratio of 3:1 for 24 hours, and then rapidly thermally expanded at 1050℃ for 30 seconds to obtain expanded graphite powder with a specific surface area of ​​55m² / g.

[0051] (2) Expanded graphite powder (80wt%) and polyvinylidene fluoride (20wt%) were ball-milled and mixed in N-methylpyrrolidone solution for 2 hours; then the resulting slurry was injected into a mold and molded at 10MPa pressure and 180℃ for 30 minutes to obtain a prefabricated composite plate with a thickness of 0.7mm; then the prefabricated composite plate was vacuum impregnated with 30% phenolic resin ethanol solution for 2 hours and cured in a water bath at 80℃ for 6 hours to obtain a flexible graphite-polymer composite matrix.

[0052] (4) Methane was introduced at 800℃ and 300W power, and graphene was deposited on the surface of the flexible graphite-polymer composite matrix for 30 minutes by plasma-enhanced chemical vapor deposition to form a graphene conductive layer, thus obtaining the flexible graphite bipolar plate of this comparative example.

[0053] Comparative Example 2 A method for preparing a self-healing flexible graphite bipolar plate includes the following steps: (1) Natural flake graphite was intercalated with concentrated sulfuric acid / nitric acid at a volume ratio of 3:1 for 24 hours, and then rapidly thermally expanded at 1050℃ for 30 seconds to obtain expanded graphite powder with a specific surface area of ​​55m² / g.

[0054] (2) A molten alloy of Ga (62wt%), In (25wt%), and Sn (13wt%) was atomized into 50μm microdroplets. Then, the microdroplets (69wt%) were mixed with hexamethylene diisocyanate (1.29wt%), xylene solution (8.42wt%), sodium dodecyl sulfate (0.43wt%), polyether triol (0.65wt%), and deionized water (20.21wt%) to form an emulsion. The mixture was reacted at 50℃ for 2 hours to form a 2.5μm thick cross-linked polyurethane shell on the surface of the microdroplets, thus obtaining microcapsules.

[0055] (3) Preparation of slurry: Expanded graphite powder (60wt%), polyvinylidene fluoride (15wt%), and microcapsules (25wt%) are ball-milled and mixed in N-methylpyrrolidone solution for 2 hours.

[0056] (4) Using the casting molding method, a prefabricated flexible graphite-polymer composite matrix with a thickness of 0.8 mm is obtained by injecting slurry into the mold; then the prefabricated flexible graphite-polymer composite matrix is ​​vacuum impregnated with 30% phenolic resin ethanol solution for 2 hours, and then cured in a water bath at 80℃ for 6 hours to obtain a flexible graphite-polymer composite matrix.

[0057] (5) Methane was introduced at 800℃ and 300W power, and graphene was deposited on the surface of the flexible graphite-polymer composite matrix for 30 minutes using plasma-enhanced chemical vapor deposition to form a graphene conductive layer, thus obtaining the self-healing flexible graphite bipolar plate of this comparative example.

[0058] The difference between Comparative Example 2 and Example 1 is that the components of the microcapsules in the flexible graphite-polymer composite matrix are uniform and do not exhibit a gradient distribution.

[0059] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is the composition of the droplets in step (2). In Comparative Example 3, In (87wt%) and Sn (13wt%) molten alloy was atomized into 50μm droplets.

[0060] Performance testing The conductivity, flexural strength, and airtightness of the flexible graphite bipolar plate samples prepared in Examples 1-3 and Comparative Examples 1-3 were tested before and after crack induction. Specifically: conductivity was tested using a four-probe resistance meter; flexural strength was tested using a mechanical testing machine via a three-point bending test; and airtightness was tested using a flowmeter-based airtightness tester. Crack induction was achieved by subjecting each flexible graphite bipolar plate to 50 cycles of low-temperature-room-temperature cycling at -40℃ (liquid nitrogen bath) / 25℃ (room temperature).

[0061] The test results for electrical conductivity, flexural strength, and airtightness are shown in Tables 1-3, respectively.

[0062] Table 1:

[0063] As shown in Table 1, the initial conductivity of Examples 1-3 was slightly lower than that of Comparative Example 1. However, after the low temperature-room temperature cycle induced the formation of cracks, the conductivity of Comparative Example 1 decreased by 20%, while the conductivity of Examples 1-3 decreased by <5%. This proves that when cracks are formed, the liquid metal alloy released by the rupture of microcapsules has a certain degree of repair effect on the cracks and basically maintains the conductivity.

[0064] Table 2:

[0065] As shown in Table 2, the initial air tightness of Examples 1-3 was similar to that of Comparative Example 1. However, after the low temperature-room temperature cycle induced the formation of cracks, the air tightness of Comparative Example 1 dropped significantly to 3.451 sccm, while the air tightness of Examples 1-3 only dropped by <6%. This proves that when cracks are formed, the release of liquid metal alloy from the rupture of microcapsules has a certain degree of repair effect on the cracks.

[0066] Table 3:

[0067] As shown in Table 3, the initial bending strength of Examples 1-3 was slightly lower than that of Comparative Example 1. However, after the low temperature-room temperature cycle induced the formation of cracks, the bending strength of Comparative Example 1 decreased by 27%, while the bending strength of Examples 1-3 recovered to more than 95% of the original strength. This proves that when cracks are formed, the release of liquid metal alloy from the rupture of microcapsules has a certain degree of repair effect on the cracks.

[0068] Meanwhile, as shown in Tables 1-3, in Comparative Example 2 compared to Example 1, the microcapsules in the flexible graphite-polymer composite matrix did not exhibit a gradient distribution, resulting in a higher microcapsule content in the central planar region. This led to a 6% decrease in the initial conductivity of the flexible graphite bipolar plate and a 1.2% decrease in initial bending resistance, although the initial airtightness remained similar to that of Example 1. After induced cracking, the smaller number of cracks in the central planar region meant that more microcapsules could not effectively participate in self-healing. Therefore, the decrease in conductivity, airtightness, and bending strength after cycling was similar to that of Example 1, demonstrating that more microcapsules in the central planar region had a negative impact on conductivity and bending strength, and that more microcapsules in the central planar region did not provide an effective performance improvement.

[0069] Compared to Example 1, Comparative Example 3 does not contain Ga in the metal alloy microdroplets, and the metal melting point is >100℃. It is solid at room temperature. Therefore, the flexible graphite bipolar plate cannot self-repair cracks after inducing cracks at lower temperatures. The conductivity, airtightness, and bending strength before cycling are similar to those of Example 1, while after cycling they are similar to those of Comparative Example 1.

[0070] 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 flexible graphite bipolar plate, characterized in that, The invention comprises a flexible graphite-polymer composite matrix, microcapsules, and a graphene conductive layer. The graphene conductive layer is disposed on the surface of the flexible graphite-polymer composite matrix, and the microcapsules are dispersed within the flexible graphite-polymer composite matrix. The core of each microcapsule is a liquid metal alloy containing Ga, and the outer shell of the microcapsule is polyurethane. The diameter of each microcapsule is 10-100 μm, and the composition of the microcapsules in the flexible graphite-polymer composite matrix is ​​gradient-distributed, wherein the distribution density in the edge flow channel region is 4000-6000 capsules / cm². 3 The distribution density in the central plane region is 1000-2500 individuals / cm². 3 .

2. The flexible graphite bipolar plate according to claim 1, characterized in that, The liquid metal alloy also includes In and / or Sn.

3. The flexible graphite bipolar plate according to claim 1, characterized in that, The raw material components for preparing the flexible graphite-polymer composite matrix include, by weight, 60-80 parts of flexible graphite and 15-20 parts of polymer; the flexible graphite includes expanded graphite, and the polymer includes polyvinylidene fluoride.

4. A method for preparing a flexible graphite bipolar plate as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Atomize the liquid metal alloy into microdroplets, and then mix the microdroplets with isocyanate, organic solvent, emulsifier and polyol to form an emulsion; Heating forms a polyurethane shell on the surface of the microdroplets; after centrifugation and drying, microcapsules are obtained. (2) The microcapsules are prepared into a slurry with flexible graphite and polymer, and then the slurry is injected into a mold and pressed to obtain a flexible graphite-polymer composite matrix; (3) A graphene conductive layer is deposited on the surface of the flexible graphite-polymer composite matrix to obtain the flexible graphite bipolar plate.

5. The method for preparing a flexible graphite bipolar plate according to claim 4, characterized in that, In step (2), the slurry includes slurry A and slurry B, wherein the content of microcapsules in slurry A is higher than that in slurry B; slurry A and slurry B are injected into the edge flow channel area and the center plane area of ​​the mold respectively by casting molding method to form a flexible graphite-polymer composite matrix with a gradient distribution of microcapsules.

6. The method for preparing a flexible graphite bipolar plate according to claim 4, characterized in that, Before depositing a graphene conductive layer on the surface of the flexible graphite-polymer composite matrix, the method further includes a step of impregnating a resin solution into the micropores of the flexible graphite-polymer composite matrix through vacuum, followed by curing.

7. The method for preparing a flexible graphite bipolar plate according to claim 4, characterized in that, In step (3), a chemical vapor deposition method is used to introduce methane gas at 750-850°C to deposit a graphene conductive layer on the surface of the flexible graphite-polymer composite matrix. The deposition time is 25-35 minutes.

8. A flow battery, characterized in that, Includes the flexible graphite bipolar plate as described in any one of claims 1-4.

Images