Carbon-based conductive double-sided adhesive tape for all-vanadium redox flow battery and preparation method thereof

Abstract

The application relates to a carbon-based conductive double-sided adhesive tape for a vanadium redox flow battery and a preparation method thereof, and belongs to the technical field of conductive adhesive, which comprises a support layer and adhesive layers attached to the upper and lower surfaces of the support layer, and the support layer is a polytetrafluoroethylene porous film; the raw materials of the adhesive layers comprise a matrix, conductive fillers, an additive and a solvent; the matrix comprises a PVDF-HFP copolymer and a bisphenol F type epoxy resin; the conductive fillers are a mixture of carbon nanotubes, graphene and flaky graphite; and the additive comprises a silane coupling agent and a fluorocarbon surfactant. The conductive double-sided adhesive tape prepared by the application has low contact resistance, high adhesive peeling strength, and can resist strong acid and strong oxidation environment of pentavalent vanadium ions, and can effectively adapt to the large-scale and rapid assembly requirements of the vanadium redox flow battery stack, and reduce the production cost.

Description

Technical Field

[0001] This application relates to the field of conductive adhesive technology, and in particular to a carbon-based conductive double-sided adhesive for vanadium redox flow batteries and its preparation method. Background Technology

[0002] Vanadium redox flow batteries (VRFBs) are one of the most promising large-scale, long-duration energy storage technologies for industrialization. They offer advantages such as scalability, high safety, and long cycle life, making them widely applicable to the energy storage needs of renewable energy sources such as wind and solar power. The electrodes and bipolar plates are the core components of the VRFB stack, and their connection method directly affects the battery's conductivity, sealing, mechanical stability, and assembly efficiency.

[0003] The existing method for preparing integrated electrodes for vanadium redox flow batteries typically involves the following steps: (1) coating conductive adhesive onto the surface of a bipolar plate; (2) hot-pressing the electrode (carbon felt / carbon cloth) with the bipolar plate; and (3) evaporating the solvent at high temperature and then curing. This method has the following technical problems: First, the process is cumbersome and difficult to control precisely on the assembly line, easily leading to uneven adhesive coating, insufficient hot-pressing curing, and residual organic solvents, thus hindering the large-scale rapid assembly of the fuel cell stack. Second, existing high-performance conductive adhesives often use metallic conductive fillers such as silver powder and copper powder (e.g., publication number CN121097113B), but these fillers are not suitable for the strong acid and V2O4 conditions of vanadium redox flow batteries. 5+ In strong oxidizing environments, metal fillers are easily oxidized and dissolved, leading to damage to the conductive network, and the dissolved metal ions can poison the vanadium electrolyte. Third, to simplify the assembly process, the industry has tried using pre-fabricated conductive adhesives or double-sided tapes, but conventional adhesives (such as polyurethane, acrylic, and ordinary bisphenol A epoxy resin) are problematic in strong acids and V... 5+ Under long-term corrosion, macromolecular chains will degrade and break, leading to electrode delamination. Furthermore, extremely corrosion-resistant materials (such as pure PTFE and pure PVDF) have almost no adhesiveness, making reliable mechanical anchoring impossible. Fourth, if pure carbon-based materials are used as conductive fillers, a very high proportion of carbon powder is often required to achieve ultra-low percolation thresholds and low contact resistance. This drastically reduces the volume of the resin matrix, causing the adhesive layer to become a dry, unbonded paste that is prone to delamination under slight external force or electrolyte erosion. Summary of the Invention

[0004] To address the problems existing in the prior art, the purpose of this application is to provide a carbon-based conductive double-sided adhesive for vanadium redox flow batteries and its preparation method, in order to solve the following technical problems: (1) simplifying the connection process between the electrode and the bipolar plate, realizing pre-formed, tear-and-stick rapid assembly; (2) using pure carbon-based conductive filler to avoid metal ion leaching and poisoning of the electrolyte; (3) balancing corrosion resistance and adhesion, and being effective in strong acids and V... 5+(4) Maintain high bonding strength under high conductive filler content and avoid powdering and delamination of adhesive layer.

[0005] In a first aspect, this application provides a carbon-based conductive double-sided adhesive for vanadium redox flow batteries, employing the following technical solution: the conductive double-sided adhesive includes a support layer and an adhesive layer adhered to the upper and lower surfaces of the support layer, and at least a portion of the adhesive layer penetrates into the pores of the support layer to form a through-type conductive channel; the support layer is a porous polytetrafluoroethylene film; the raw materials of the adhesive layer include a matrix, conductive filler, additives, and solvent; the matrix includes PVDF-HFP copolymer and bisphenol F type epoxy resin; the conductive filler is a mixture of carbon nanotubes, graphene, and flake graphite; and the additives include silane coupling agents and fluorocarbon surfactants.

[0006] The above technical solution utilizes a porous polytetrafluoroethylene (PTFE) film as a support layer, endowing the double-sided adhesive with excellent resistance to acids, alkalis, and pentavalent vanadium ion attack. On the matrix side, the PVDF-HFP copolymer provides flexibility and chemical corrosion resistance, while bisphenol F epoxy resin provides rigidity and high adhesion. Together, they construct a weather-resistant adhesive network that is both flexible and rigid. Simultaneously, the bisphenol F epoxy resin plays an excellent "lubricating and dragging" role, carrying the large molecular segments of the PVDF-HFP copolymer and nanoscale conductive fillers deep into the micron-sized pores of the PTFE, forming a through-type mechanical anchoring and conductive channel. This effectively solves the problem of insufficient adhesion in conventional corrosion-resistant materials. Furthermore, the pure carbon-based filler, composed of carbon nanotubes, graphene, and flake graphite, not only completely avoids the leaching of metal ions to poison the vanadium electrolyte, but also constructs a dense three-dimensional conductive network through the multi-dimensional synergistic effect of points (carbon nanotubes), surfaces (graphene), and volumes (flake graphite). Combined with the interface optimization effect of silane coupling agents and fluorocarbon surfactants, it greatly reduces the contact resistance of the all-vanadium redox flow battery.

[0007] Optionally, based on the total mass of the matrix, conductive filler, and additives (100%), the content of the PVDF-HFP copolymer is 28-37%, the content of the bisphenol F epoxy resin is 2-10%, the content of the carbon nanotubes is 10-20%, the content of the graphene is 12-18%, the content of the flake graphite is 24-35%, the content of the silane coupling agent is 1-4%, and the content of the fluorocarbon surfactant is 0.5-3%.

[0008] Through the above technical solution, at this specific ratio, the content ratio of PVDF-HFP to bisphenol F epoxy resin can achieve an excellent balance between flexible film formation and rigid adhesion. At the same time, the total amount of carbon-based filler exceeding 50% can achieve an extremely low percolation threshold in the resin matrix. Furthermore, due to the dispersing effect of specific additives, the adhesive layer is prevented from becoming a dry powder paste without adhesion due to an excessively high proportion of conductive filler. Thus, on a macroscopic level, both the high adhesive peel strength and ultra-low contact resistance of the conductive adhesive are taken into account.

[0009] Optionally, the carbon nanotubes are multi-walled carbon nanotubes, the graphene has a sheet diameter of 0.5~15 μm, and the flake graphite has a particle size of 60~120 mesh.

[0010] The above technical solutions further refine the microstructure of the three pure carbon-based conductive fillers. When multi-walled carbon nanotubes with specific diameters and lengths, graphene with specific sheet diameters, and flake graphite with specific mesh sizes are mixed, the large-particle-size flake graphite constructs the macroscopic main conductive framework, the sheet graphene fills the gaps in the framework and provides good surface contact, while the multi-walled carbon nanotubes with a suitable aspect ratio act as flexible "conductive bridges" that interweave and connect the fillers and polymer segments. This precise matching of different dimensions further reduces the contact resistance between the carbon fillers, giving the double-sided adhesive superior all-dimensional electron transport performance.

[0011] Optionally, the silane coupling agent is 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, and the fluorocarbon surfactant is perfluorohexyl ethyl phosphate.

[0012] Through the above technical solutions, silane coupling agents with epoxy groups can chemically bond with the surface of bisphenol F epoxy resin and modified carbon fillers, enhancing the interfacial compatibility between inorganic fillers and organic matrices. Perfluorohexyl ethyl phosphate not only exhibits excellent low surface tension wetting properties in the system, but its fluorine-containing long chains can also generate strong "fluorine-fluorine" affinity interactions with fluorine atoms in the support layer PTFE and the matrix PVDF-HFP, thereby further enhancing the interfacial bonding force between the adhesive layer and the porous film support layer and preventing delamination of the battery under long-term immersion in strong acid.

[0013] Optionally, the mass ratio of the carbon nanotubes, graphene, and flake graphite is 1:0.8~1.2:1.8~2.2.

[0014] Through the above technical solution, within this ratio range, flake graphite, serving as the macroscopic conductive framework, dominates, while one-dimensional carbon nanotubes and two-dimensional graphene, in a near 1:1 ratio, act as microscopic interstitial fillers and bridging agents. This precise ratio effectively balances the steric hindrance and van der Waals forces between nanomaterials, avoiding the self-aggregation of single carbon nanomaterials (such as the disordered entanglement of carbon nanotubes or the π-π stacking of graphene), and achieving the densest "point-line-surface-volume" packing within the resin matrix. This not only minimizes the obstruction of electronic pathways by the insulating resin but also forms a mechanically stable reinforcing network, ensuring that the conductive network remains intact even under harsh conditions such as high negative pressure assembly or electrolyte scouring in vanadium redox flow batteries.

[0015] Secondly, this application provides a method for preparing the above-mentioned conductive double-sided adhesive, the method comprising the following steps: S1. The carbon nanotubes and graphene are dispersed in an oxidant for oxidation reaction, and the product after oxidation reaction is mixed with the silane coupling agent for modification treatment to obtain a modified filler. S2. The modified filler, flake graphite, PVDF-HFP copolymer, bisphenol F epoxy resin, fluorocarbon surfactant and solvent are mixed to obtain a conductive adhesive solution; S3. The conductive adhesive liquid is uniformly coated on the upper and lower surfaces of the plasma-treated polytetrafluoroethylene porous film to obtain a pre-sample. The pre-sample is then treated with a stepped negative pressure wetting process and dried to obtain a carbon-based conductive double-sided adhesive for vanadium redox flow batteries.

[0016] The above technical solution effectively solves the problem of easy agglomeration of nano-carbon materials through pre-oxidation and silanization modification. Combined with plasma treatment to activate the PTFE surface and the crucial "stepped negative pressure wetting process," a dynamic pressure difference is used to infuse and penetrate the conductive adhesive containing fillers into the micropores of the PTFE. This preparation process ingeniously constructs a physically penetrating mechanical interlocking and conductive through-structure, transforming the cumbersome traditional "on-site adhesive application-hot pressing" process into a "tear-and-stick" pre-made double-sided adhesive, greatly improving the assembly efficiency and yield of vanadium redox flow battery stacks.

[0017] Optionally, the carbon nanotubes and graphene are dispersed in an oxidant for oxidation reaction, and the product after oxidation reaction is mixed with the silane coupling agent for modification treatment. The specific method for obtaining the modified filler includes the following steps: (1) Disperse the carbon nanotubes and graphene in an oxidant, sonicate them in a water bath at 50-80 °C for 1-2 h, wash the product after sonication until the pH is 6.5-8, and then dry it at 70-90 °C; (2) Mix the silane coupling agent with an aqueous ethanol solution and add the product obtained by drying in step (1). Modify the product at 60~80℃, then wash and filter it in sequence, and dry the solid product obtained by filtration to obtain the modified filler.

[0018] The purpose of oxidative modification of carbon nanotubes and graphene using the above technical solutions is to: (1) introduce oxygen-containing functional groups such as hydroxyl and carboxyl groups onto the surface of carbon materials to improve their reactivity with silane coupling agents; and (2) destroy the hydrophobicity of the carbon material surface to improve its dispersibility in organic solvents and prevent aggregation. Subsequent water bath silanization treatment promotes the coupling agent to be firmly anchored to the carbon material surface through chemical bonds. This step operates under mild conditions and has uniform reaction sites, laying a material foundation for the long-term storage stability and coating uniformity of the subsequent high-concentration conductive adhesive.

[0019] Optionally, in step S3, the specific method for treating the presample using a stepped negative pressure impregnation process is as follows: the presample is placed in a sealed vacuum environment, firstly evacuated to -0.03~-0.06 MPa and held for 200~400 s, then evacuated to -0.08~-0.12 MPa and held for 200~400 s, and this constitutes one cycle, for a total of 3~5 cycles.

[0020] Through the above technical solution, this stepped, circulating "breathing" permeation mechanism can effectively extract residual air from the micron-level deep pores of PTFE during the low negative pressure stage, while forcing the high-viscosity conductive adhesive to penetrate deeper into the pores during the high negative pressure stage. After 3 to 5 dynamic pressure differential cycles, microscopic bubbles at the support layer interface can be effectively eliminated, maximizing the "riveting" interlocking depth between the adhesive layer and the porous film, achieving ultra-low contact resistance and high peel strength.

[0021] Optionally, in step S3, the drying temperature is 50~60 ℃; after drying, a curing treatment is also included, specifically: the dried sample is first cured at 70~90 ℃ and vacuum degree 0.05~0.1 MPa for 5~6 h, and then cured at 110~130 ℃ for 1~2 h.

[0022] The above technical solution establishes a gradient temperature combined with vacuum drying and curing process. The initial medium-temperature stage slowly and gently removes organic solvents from the system, preventing solvent boiling that could lead to pinholes or microbubbles within the adhesive layer. The later vacuum and high-temperature curing stages promote a complete cross-linking reaction of the bisphenol F epoxy resin. This gradient curing process helps release the internal stress generated during coating and impregnation, giving the final double-sided adhesive an extremely dense microstructure and effectively resisting micro-leakage of the adhesive layer by strong acid electrolytes.

[0023] Optionally, the oxidant is hydrogen peroxide with a mass concentration of 20-30%.

[0024] Through the above technical solution, hydrogen peroxide with a concentration of 20-30% has a "mild oxidation" effect under an ultrasonic environment of 50-80 ℃: if the concentration is too low, it will not be able to introduce sufficient active sites such as hydroxyl groups on the surface of carbon materials, resulting in the failure of subsequent silane coupling modification; if the concentration is too high or traditional strong mixed acid is used, it will seriously destroy the intrinsic conjugated lattice structure of carbon nanotubes and graphene, resulting in an irreversible decrease in conductivity.

[0025] In summary, this application includes at least one of the following beneficial technical effects: 1. This application uses a PTFE porous film as a support layer, combined with a "flexible and rigid" matrix of PVDF-HFP copolymer and bisphenol F type epoxy resin, and utilizes the resin to drag and carry pure carbon fillers composed of carbon nanotubes, graphene and flake graphite deep into the PTFE channels. This successfully prepares a conductive double-sided adhesive with low contact resistance, high adhesion peel strength and resistance to strong acid and strong oxidation environment of pentavalent vanadium ions. At the same time, it can effectively adapt to the large-scale and rapid assembly requirements of vanadium redox flow battery stacks and reduce production costs. 2. The preparation process of this application utilizes stepped negative pressure wetting treatment and plasma activation to enable the high-viscosity conductive adhesive to physically penetrate the porous network of polytetrafluoroethylene, thereby constructing a deep mechanical riveting and a through-type three-dimensional electronic pathway without bubble defects, which solves the defect of conventional strong corrosion resistant materials that are "conductive but not adhesive". 3. In the preferred case, by precisely matching the microscopic size of pure carbon materials of different dimensions and by specific mild hydrogen peroxide ultrasonic oxidation / epoxy silanization modification, carbon-based fillers with extremely high solid content are uniformly dispersed in the resin network without agglomeration, without damaging the carbon lattice structure or introducing toxic metal ions, thus achieving extremely excellent full-interface conductivity and long-term electrochemical service stability. Detailed Implementation

[0026] The present application will be further described in detail below with reference to specific embodiments.

[0027] The following examples further illustrate the carbon-based conductive double-sided adhesive for vanadium redox flow batteries and its preparation method as described in this application. The examples are implemented based on the technical solution of this application, providing detailed implementation methods and specific operating procedures; however, the scope of protection of this application is not limited to the following examples.

[0028] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0029] Polytetrafluoroethylene porous film: Purchased from Wuxi Xiangjian PTFE Products Co., Ltd.; PVDF-HFP copolymer: Purchased from Beijing Aipusilon Technology Co., Ltd.; VDF:HFP = 90:10; Bisphenol F type epoxy resin: purchased from Guangzhou Taiji New Materials Co., Ltd.; Carbon nanotubes-1: Purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., part number XFM04, with a length of 0.5~2 μm and a diameter of 5~15 nm; Carbon nanotubes-2: Purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., serial number XFM19, length 10~30 μm, diameter 20~30 nm; Graphene-1: Purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., product number XF021, sheet diameter 5~10 μm, thickness 3~10 nm; Graphene-2: Purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., product number XF002-2, sheet diameter 0.5~5 μm, thickness 0.8~1.2 nm; Flake graphite-1: Purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., item number XF050, 80 mesh; Flake graphite-2: Purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., item number XF051, 100 mesh.

[0030] Example 1 A carbon-based conductive double-sided adhesive for vanadium redox flow batteries, the conductive double-sided adhesive comprising a support layer and an adhesive layer adhered to the upper and lower surfaces of the support layer, wherein the support layer is a porous polytetrafluoroethylene film. The raw materials of the adhesive layer include a matrix, conductive filler, additives, and solvent. The matrix is ​​a PVDF-HFP copolymer and bisphenol F epoxy resin. The conductive filler is carbon nanotube-1, graphene-1, and flake graphite-1. The additives are 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane (silane coupling agent) and perfluorohexyl ethyl phosphate (fluorocarbon surfactant). Based on the total mass of the matrix, conductive filler, and additives as 100%, the content of PVDF-HFP copolymer is 32%, the content of bisphenol F epoxy resin is 5%, the content of carbon nanotube-1 is 15%, the content of graphene-1 is 15%, the content of flake graphite-1 is 30% (the mass ratio of carbon nanotube, graphene, and flake graphite is 1:1:2), the content of 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane is 2%, and the content of perfluorohexyl ethyl phosphate is 1%.

[0031] A method for preparing carbon-based conductive double-sided adhesive for vanadium redox flow batteries, the method comprising the following steps: S1. Weigh the raw materials for the adhesive layer according to the above content. The preparation of the modified filler includes the following steps: (1) Weigh the raw materials of matrix, conductive filler and additive according to the above content, and disperse carbon nanotube-1 and graphene-1 in hydrogen peroxide with a mass concentration of 25%. The amount of carbon nanotube-1, graphene-1 and hydrogen peroxide is 15 g: 15 g: 1000 mL. Sonicate in a water bath at 60 ℃ for 1 h, and wash the ultrasonically treated product with deionized water multiple times and filter until the pH is 7.5. Then dry at 80 ℃ for 10 h. (2) Prepare a mixed solvent of ethanol and deionized water (volume ratio of ethanol to deionized water is 9:1), and add 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane. The volume ratio of 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane to the mixed solvent is 1:50. Stir at room temperature for 30 min to allow it to fully hydrolyze. Then add the product obtained by drying in step (1), and reflux and stir at 70 °C for 4 h. After the reaction is completed, wash with anhydrous ethanol, filter, and dry in a vacuum drying oven at 80 °C for 10 h to obtain the modified filler. S2. The modified filler, flake graphite-1, PVDF-HFP copolymer, bisphenol F epoxy resin, perfluorohexyl ethyl phosphate and N-methylpyrrolidone are mixed, with the amount of N-methylpyrrolidone being 120% of the total mass of the matrix, conductive filler and additives, to obtain a conductive adhesive solution. S3. The conductive adhesive liquid is uniformly coated on the upper and lower surfaces of the polytetrafluoroethylene porous film that has been surface activated by argon plasma (processing power 200W, time 2 min), and the wet film thickness is 60 μm to obtain a pre-sample. The sample was then subjected to a stepped negative pressure impregnation process: the sample was placed in a sealed vacuum chamber, and first the vacuum was evacuated to -0.05 MPa (low negative pressure treatment) and held for 300 s. Then the vacuum was evacuated to -0.1 MPa (high negative pressure treatment) and held for 300 s. This was one cycle, and a total of 4 cycles were performed. Finally, the processed sample was transferred to an oven and pre-dried at 50 °C for 2 h, then cured at 80 °C and 0.08 MPa for 5 h, and finally cured at 120 °C for 1 h to form adhesive layers on the upper and lower surfaces of the polytetrafluoroethylene porous film. A PET release film was then placed on the surface of the adhesive layer and gently rolled flat to achieve double-sided release film protection, resulting in carbon-based conductive double-sided adhesive for vanadium redox flow batteries.

[0032] Example 2 The procedure was carried out as described in Example 1, except that 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane (silane coupling agent) was replaced by an equal mass of silane coupling agent KH-550.

[0033] Example 3 The procedure was carried out as described in Example 1, except that perfluorohexyl ethyl phosphate (a fluorocarbon surfactant) was replaced by sodium perfluorooctane sulfonate (another conventional fluorocarbon surfactant) at the same mass.

[0034] Example 4 The method was implemented as in Example 1, except that carbon nanotube-1 was replaced with carbon nanotube-2 of equal mass.

[0035] Example 5 The method was implemented as in Example 1, except that graphene-1 was replaced by graphene-2 ​​in equal mass.

[0036] Example 6 The method is implemented in accordance with Example 1, except that flake graphite-1 is replaced with flake graphite-2.

[0037] Example 7 The method of Example 1 was followed, except that, based on the total mass of the matrix, conductive filler and additives as 100%, the content of PVDF-HFP copolymer was 30%, the content of bisphenol F epoxy resin was 3%, the content of carbon nanotube-1 was 18%, the content of graphene-1 was 14%, the content of flake graphite-1 was 32% (the mass ratio of carbon nanotube, graphene and flake graphite was 1:0.8:1.8), the content of 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane was 2%, and the content of perfluorohexyl ethyl phosphate was 1%.

[0038] The preparation of modified fillers includes the following steps: (1) Weigh the raw materials of matrix, conductive filler and additive according to the above content, and disperse carbon nanotube-1 and graphene-1 in hydrogen peroxide with a mass concentration of 25%. The amount of carbon nanotube-1, graphene-1 and hydrogen peroxide is 15 g: 15 g: 1000 mL. Sonicate in a water bath at 50 ℃ for 2 h, and wash the ultrasonically treated product with deionized water multiple times and filter until the pH is 7. Then dry at 70 ℃ for 12 h. (2) Prepare a mixed solvent of ethanol and deionized water (volume ratio of ethanol to deionized water is 9:1), and add 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane. The volume ratio of 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane to the mixed solvent is 1:50. Stir at room temperature for 30 min to allow it to fully hydrolyze. Then add the product obtained from drying in step (1), and reflux and stir at 60 °C for 6 h. After the reaction is completed, wash with anhydrous ethanol, filter, and dry in a vacuum drying oven at 70 °C for 8 h to obtain the modified filler.

[0039] Example 8 The method described in Example 1 was followed, except that, based on the total mass of the matrix, conductive filler, and additives as 100%, the content of PVDF-HFP copolymer was 35%, the content of bisphenol F epoxy resin was 8%, the content of carbon nanotube-1 was 12%, the content of graphene-1 was 14%, the content of flake graphite-1 was 26% (the mass ratio of carbon nanotubes, graphene, and flake graphite was 1:1.2:2.2), the content of 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane was 3%, and the content of perfluorohexyl ethyl phosphate was 2%.

[0040] The preparation of modified fillers includes the following steps: (1) Weigh the raw materials of matrix, conductive filler and additive according to the above content, and disperse carbon nanotube-1 and graphene-1 in hydrogen peroxide with a mass concentration of 25%. The amount of carbon nanotube-1, graphene-1 and hydrogen peroxide is 15 g: 15 g: 1000 mL. Sonicate in an 80 ℃ water bath for 0.5 h, and wash the ultrasonically treated product with deionized water multiple times and filter until the pH is 8. Then dry at 90 ℃ for 6 h. (2) Prepare a mixed solvent of ethanol and deionized water (volume ratio of ethanol to deionized water is 9:1), and add 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane. The volume ratio of 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane to the mixed solvent is 1:50. Stir at room temperature for 30 min to allow it to fully hydrolyze. Then add the product obtained by drying in step (1), and reflux and stir at 80 °C for 2 h. After the reaction is completed, wash with anhydrous ethanol, filter, and dry in a vacuum drying oven at 60 °C for 8 h to obtain the modified filler.

[0041] Example 9 The procedure was carried out as described in Example 1, except that the treated sample was finally transferred to an oven and pre-dried at 60°C for 1.5 h, then cured at 90°C and 0.05 MPa for 6 h, and finally cured at 110°C for 2 h to obtain carbon-based conductive double-sided adhesive for vanadium redox flow batteries.

[0042] Comparative Example 1 The procedure was carried out as in Example 1, except that the PVDF-HFP copolymer was replaced by an equal mass of bisphenol F epoxy resin.

[0043] Comparative Example 2 The procedure was carried out as in Example 1, except that the bisphenol F epoxy resin was replaced by an equal mass of PVDF-HFP copolymer.

[0044] Comparative Example 3 The method was implemented as in Example 1, except that the same mass of flake graphite-1 was replaced with graphene-1.

[0045] Comparative Example 4 The method was implemented as in Example 1, except that graphene-1 was replaced by flake graphite-1 by mass.

[0046] Comparative Example 5 The method described in Example 1 is followed, except that no modified filler is prepared. Instead, the raw materials of the adhesive layer are directly mixed to obtain a conductive adhesive liquid, and the conductive adhesive liquid is used to prepare a conductive double-sided adhesive according to the method described in the Example.

[0047] Comparative Example 6 The procedure was carried out as described in Example 1, except that perfluorohexyl ethyl phosphate (a fluorocarbon surfactant) was replaced by sodium dodecylbenzene sulfonate (another type of surfactant).

[0048] Comparative Example 7 The procedure was carried out as described in Example 1, except that perfluorohexyl ethyl phosphate (fluorocarbon surfactant) was replaced by an equal mass of 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane (silane coupling agent).

[0049] Comparative Example 8 The procedure was carried out in accordance with Example 1, except that the stepped negative pressure impregnation process was changed to atmospheric pressure (0.1 MPa) impregnation process.

[0050] Comparative Example 9 The procedure was carried out in accordance with Example 1, except that a single-stage negative pressure immersion was used: only -0.1 MPa treatment was applied, without step-by-step circulation.

[0051] Application Examples 1-9 and Comparative Examples 1-9 are integrated electrodes for all-vanadium redox flow batteries. Peel off the PET release film from both sides of the conductive double-sided adhesive, attach one side of the conductive double-sided adhesive to the surface of the bipolar plate (graphite), and then attach the electrode (carbon felt) to the other side of the conductive double-sided adhesive. Press and bond at 25°C and 0.2 MPa for 8 minutes to complete the preparation of the integrated electrode.

[0052] Test case Contact resistance: Place the sample between the upper and lower gold-plated electrodes of the contact resistance tester, and apply pressure in increments of 0.1 MPa to 1.0 MPa, holding each pressure for 30 seconds until the resistance stabilizes (change rate <5%). Current terminal: Apply DC current I (10~100 mA). Voltage terminal: Measure the stack voltage drop V. Total resistance: R. total =V / I, contact resistance ρ c =(Rtotal -R blank )×A,R blank This is a blank resistor, where A is the contact area (cm²). 2 ), R blank The test method is as follows: a graphite bipolar plate (3 mm thick) and a carbon paper electrode (0.3 mm thick) are directly stacked together, and R is measured under a pressure of 1.0 MPa. blank = 85±5 mΩ·cm 2 ; Vertical resistivity: Place the sample between the upper and lower parallel electrodes of the four-wire low-resistivity tester, apply pressure to 0.5 MPa, hold the pressure for 60 s to stabilize the contact, set the tester to constant current output I = 50 mA, read the stable voltage value V, and calculate the volume resistivity Rᵥ according to the formula: Rᵥ = 0.5 MPa. v =IV, measure and record the actual thickness t of the sample, and calculate the vertical volume resistivity ρ. v =R v ×tA, where A is the effective test area of ​​the sample; Adhesive strength: The 180° peel strength was determined according to GB / T 2792-2014; the sample size was 25 mm × 150 mm, the peel speed was 300 mm / min, the peel angle was 180°, and the average peel force of the middle stable section was taken to calculate the peel strength (unit: N / 25 mm). The criteria for determining the "stable section" are: the continuous section in the peel curve where the peel force fluctuation amplitude is <10%, which is usually the peel length range of 20~100 mm. The average peel force of this section is taken as the adhesive strength value. Corrosion resistance: The positive electrode electrolyte composition for 100% SOC is: 1.6 M VOSO4 + 3.0 M H2SO4, where V 5+ The concentration was 1.6 M. The integrated electrode (50 mm × 50 mm) was completely immersed in 200 mL of electrolyte and placed in a 50 ℃ constant temperature water bath. Samples were removed every 7 days, rinsed with deionized water, and dried. The adhesion between the electrode and the bipolar plate was observed, and the peel strength retention rate was tested. Evaluation criteria: "Good": After 30 days of immersion, no visible delamination, cracking, bubbles, or other defects were observed between the electrode and the bipolar plate, and the peel strength retention rate was ≥80%; "Poor": Obvious delamination, cracking, or bubbles appeared within 30 days of immersion, or the peel strength retention rate was <60%.

[0053] The contact resistance, bonding strength, corrosion resistance and vertical resistivity of the integrated electrodes of the all-vanadium redox flow batteries prepared in Application Examples 1-9 and Comparative Examples 1-9 were tested respectively. The test results are shown in Table 1. Table 1

[0054] As can be seen from Table 1, the integrated vanadium redox flow battery electrodes prepared in Examples 1-9 of this application all have contact resistances below 510 mΩ·cm. 2 The bonding strength is higher than 1.24 N / 25 mm, the vertical resistivity is lower than 380 mΩ·cm, and the bonding remains good after being immersed in 100% SOC positive electrode electrolyte at 50℃ for 30 days. This proves that the technical solution of this application has successfully solved the technical problem of balancing high conductivity, high bonding strength and corrosion resistance.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A carbon-based conductive double-sided adhesive for vanadium redox flow batteries, characterized in that, The conductive double-sided adhesive includes a support layer and an adhesive layer adhered to the upper and lower surfaces of the support layer, with at least a portion of the adhesive layer penetrating into the pores of the support layer to form a through-type conductive channel. The support layer is a porous polytetrafluoroethylene film. The raw materials of the adhesive layer include a matrix, conductive filler, additives, and solvent. The matrix includes a PVDF-HFP copolymer and a bisphenol F epoxy resin. The conductive filler is a mixture of carbon nanotubes, graphene, and flake graphite. The additives include silane coupling agents and fluorocarbon surfactants.

2. The conductive double-sided adhesive according to claim 1, characterized in that, Based on the total mass of the matrix, conductive filler, and additives as 100%, the content of the PVDF-HFP copolymer is 28-37%, the content of the bisphenol F epoxy resin is 2-10%, the content of the carbon nanotubes is 10-20%, the content of the graphene is 12-18%, the content of the flake graphite is 24-35%, the content of the silane coupling agent is 1-4%, and the content of the fluorocarbon surfactant is 0.5-3%.

3. The conductive double-sided adhesive according to claim 1, characterized in that, The carbon nanotubes are multi-walled carbon nanotubes, the graphene has a sheet diameter of 0.5~15 μm, and the flake graphite has a particle size of 60~120 mesh.

4. The conductive double-sided adhesive according to claim 1, characterized in that, The silane coupling agent is 2-(3,4-epoxycyclohexane)ethyltrimethoxysilane, and the fluorocarbon surfactant is perfluorohexyl ethyl phosphate.

5. The conductive double-sided adhesive according to claim 3, characterized in that, The mass ratio of carbon nanotubes, graphene, and flake graphite is 1:0.8~1.2:1.8~2.

2.

6. A method for preparing the conductive double-sided adhesive according to any one of claims 1 to 5, characterized in that, The preparation method includes the following steps: S1. The carbon nanotubes and graphene are dispersed in an oxidant for oxidation reaction, and the product after oxidation reaction is mixed with the silane coupling agent for modification treatment to obtain a modified filler. S2. The modified filler, flake graphite, PVDF-HFP copolymer, bisphenol F epoxy resin, fluorocarbon surfactant and solvent are mixed to obtain a conductive adhesive solution; S3. The conductive adhesive liquid is uniformly coated on the upper and lower surfaces of the plasma-treated polytetrafluoroethylene porous film to obtain a pre-sample. The pre-sample is then treated with a stepped negative pressure wetting process and dried to obtain a carbon-based conductive double-sided adhesive for vanadium redox flow batteries.

7. The method for preparing conductive double-sided adhesive according to claim 6, characterized in that, The method for dispersing the carbon nanotubes and graphene in an oxidant for oxidation reaction, and then mixing the product after oxidation reaction with the silane coupling agent for modification treatment to obtain the modified filler includes the following steps: (1) Disperse the carbon nanotubes and graphene in an oxidant, sonicate them in a water bath at 50-80 °C for 1-2 h, wash the product after sonication until the pH is 6.5-8, and then dry it at 70-90 °C; (2) Mix the silane coupling agent with an aqueous ethanol solution and add the product obtained by drying in step (1). Modify the product at 60~80 °C, then wash and filter it in sequence, and dry the solid product obtained by filtration to obtain the modified filler.

8. The method for preparing conductive double-sided adhesive according to claim 6, characterized in that, In step S3, the specific method for treating the presample using a stepped negative pressure impregnation process is as follows: the presample is placed in a sealed vacuum environment, firstly evacuated to -0.03~-0.06 MPa and held for 200~400 s, then evacuated to -0.08~-0.12 MPa and held for 200~400 s, and this constitutes one cycle, and a total of 3~5 cycles are performed.

9. The method for preparing conductive double-sided adhesive according to claim 6, characterized in that, In step S3, the drying temperature is 50~60 ℃; after drying, a curing treatment is also included, specifically: the dried sample is first cured at 70~90 ℃ and a vacuum degree of 0.05~0.1 MPa for 5~6 h, and then cured at 110~130 ℃ for 1~2 h.

10. The method for preparing conductive double-sided adhesive according to claim 7, characterized in that, The oxidant is hydrogen peroxide with a mass concentration of 20-30%.

Images