Carbon fiber composite bipolar plate of flow battery and preparation method of carbon fiber composite bipolar plate

Abstract

The invention discloses a carbon fiber composite bipolar plate of a flow battery and a preparation method. The carbon fiber composite bipolar plate comprises a plurality of layers of carbon fiber needled web felt layers or carbon fiber surface felt layers which are laid in a laminated mode, and an adhesive is coated or a conductive hot melt adhesive film is laid between every two adjacent layers of carbon fiber needled web felt layers or carbon fiber surface felt layers to form an adhesive layer. The carbon fiber composite bipolar plate further comprises graphite paper layers, and the graphite paper layers are laid on the upper surface and the lower surface of a layered structure formed by the carbon fiber needled web felt layer or the carbon fiber surface felt layer and the bonding layer or are laid with the carbon fiber needled web felt layer or the carbon fiber surface felt layer in an alternating and laminated mode. The material is high in structural strength, low in internal resistance, thin in thickness, light in weight, resistant to strong acid and strong alkali, simple in mass production process, low in cost and high in practicability.

Description

Technical Field

[0001] This invention relates to the field of flow batteries, and in particular to a carbon fiber composite bipolar plate for flow batteries and its preparation method. Background Technology

[0002] Currently, there are three main types of bipolar plates used in flow batteries: graphite bipolar plates, conductive plastic bipolar plates, and flexible graphite bipolar plates. Graphite bipolar plates are made from high-strength, highly conductive graphite material (some are impregnated with resin to improve liquid resistance, sealing any voids in the graphite) through machining. The manufacturing process of conductive plastic bipolar plates involves selecting conductive carbon powder (expanded graphite powder, graphite powder, carbon nanotube powder, graphene powder, conductive carbon black powder, or carbon fiber powder, or a mixture of these), and mixing it with other additives (such as EBS, POE, etc.) and strong acid and alkali resistant resins (such as PE, PP, PTFE, and PVDF, etc.) at high temperatures using plastic mixing or twin-screw mixers to produce conductive plastic masterbatch. This masterbatch is then calendered into conductive plastic sheets, which are subsequently machined. The manufacturing process of flexible graphite bipolar plates is as follows: generally, a resin resistant to strong acids and alkalis (such as PVDF, PTEF, PVF, PP and PE) is selected and thoroughly mixed with expanded graphite powder. Then, the mixture is first rolled and shaped, and then hot-pressed to form a flexible graphite plate, which is then machined.

[0003] However, all of the aforementioned existing technologies and processes have certain problems:

[0004] Graphite bipolar plate: (1) Graphite plates are brittle and have poor strength, and are prone to breakage during transportation and installation; (2) In order to improve the strength of graphite bipolar plates, they are generally made thicker, which increases the battery volume, increases the battery weight, and reduces the energy density.

[0005] Conductive plastic bipolar plates: (1) Plastic electrode plates have slightly higher strength than graphite and can be made thinner. However, the main materials of conductive plastic electrode plates are PP, PE, PVDF or PTFE and other strong acid and alkali resistant plastic materials. After adding more carbon conductive powder, their brittleness increases and they are still easy to break during transportation and installation. (2) Plastic electrode plates are relatively thin and have a certain degree of brittleness, making them easy to crack during processing. (3) Conductive plastic electrode plates have a large internal resistance, which leads to the generation of resistive heat and energy loss. Especially under high current conditions, thermal runaway is easy to occur. In particular, PP and PE materials are plastic materials with poor temperature resistance. When thermal runaway is severe, the electrode plate may deform, causing safety accidents. (4) The manufacturing process of conductive plastic electrode plates is complicated and the production cost is still high.

[0006] Flexible graphite bipolar plates: (1) The mixing and pressing of expanded graphite and resin powder requires sufficient conductivity, so the resin content is relatively low. Therefore, flexible graphite bipolar plates still have the problem of low strength and easy delamination; (2) The strength of flexible graphite bipolar plates is the worst among all types of bipolar plates. They are prone to breakage under high pressure during stacking or during transportation; (3) They are prone to cracking during machining, and the cut ends are prone to delamination. Summary of the Invention

[0007] In order to solve the above-mentioned technical problems, the present invention provides a carbon fiber composite bipolar plate for flow batteries and a method for its preparation.

[0008] In a first aspect, the present invention provides a carbon fiber composite bipolar plate for a flow battery, which is achieved by the following technical solution.

[0009] A carbon fiber composite bipolar plate for a flow battery includes multiple layers of carbon fiber laid in layers. The carbon fiber layers are carbon fiber needle-punched mesh felt layers or carbon fiber surface felt layers. An adhesive is coated between adjacent carbon fiber layers or a conductive hot melt adhesive film is laid to form an adhesive layer.

[0010] Furthermore, the carbon fiber composite bipolar plate also includes a graphite paper layer, which is laid on the upper and lower surfaces of the layered structure formed by the carbon fiber layer and the adhesive layer.

[0011] Furthermore, the carbon fiber composite bipolar plate also includes a graphite paper layer, with the carbon fiber layer and the graphite paper layer being alternately stacked and laid, and the carbon fiber layer and the graphite paper layer being connected by an adhesive layer.

[0012] Secondly, the present invention provides a method for preparing a carbon fiber composite bipolar plate for a flow battery, which is achieved by the following technical solution.

[0013] A method for preparing the above-mentioned carbon fiber composite bipolar plate for flow batteries includes the following steps:

[0014] Lay out the carbon fiber needled mesh felt or carbon fiber surface felt flat, and evenly coat or sprinkle adhesive or lay a conductive hot melt adhesive film on its top and bottom surfaces. Then, lay other carbon fiber needled mesh felts or carbon fiber surface felts in layers, with 1-6 layers laid. Evenly coat or sprinkle adhesive or lay a conductive hot melt adhesive film between the layers. Press the laid materials and cut them after pressing.

[0015] Alternatively, lay out carbon fiber needled mesh felt or carbon fiber surface felt flat, and evenly coat or apply adhesive or lay conductive hot melt adhesive film on its top and bottom surfaces. Then, lay 1-6 layers of carbon fiber needled mesh felt or carbon fiber surface felt, with adhesive or conductive hot melt adhesive film evenly applied between each layer. Next, coat or apply adhesive or lay conductive hot melt adhesive film on the top and bottom surfaces of the layered structure composed of carbon fiber needled mesh felt or carbon fiber surface felt, and lay graphite paper on top. Press the laid material, and then cut it after pressing.

[0016] Alternatively, lay out carbon fiber needled mesh felt or carbon fiber surface felt flat, and evenly coat or sprinkle adhesive or lay conductive hot melt adhesive film on its top and bottom surfaces. Then, alternately lay graphite paper and carbon fiber needled mesh felt or carbon fiber surface felt, laying 1-6 layers of carbon fiber needled mesh felt or carbon fiber surface felt, with adhesive or conductive hot melt adhesive film evenly coated or sprinkled between the layers. Press the laid material, and then cut it after pressing.

[0017] Furthermore, the preparation method of carbon fiber needle-punched mesh felt is as follows: select carbon fiber filaments, cut them into short carbon fiber fibers with a fiber length of 10-100mm, spread the cut carbon fibers into a mesh, and then needle-punch them to make carbon fiber needle-punched mesh felt; the preparation method of carbon fiber surface felt is as follows: select carbon fiber filaments, cut them into short carbon fiber fibers with a fiber length of 3-100mm, stably disperse the cut carbon fibers in a solvent, then add adhesive resin, stir and disperse evenly, filter and dry, and then hot-press and cure to make carbon fiber surface felt.

[0018] Furthermore, in the preparation method of carbon fiber surface mat, the solvent for dispersing the chopped carbon fibers is water.

[0019] Furthermore, in the preparation method of carbon fiber surface mat, the adhesive resin includes epoxy resin, acrylic resin, and polyurethane resin.

[0020] Furthermore, in the preparation method of carbon fiber surface mat, the amount of adhesive resin used is 1-20% of the total mass of the system.

[0021] Furthermore, the adhesive is a solid-phase adhesive, and the preparation method of the solid-phase adhesive is as follows: select one or more powders of strong acid and strong alkali resistant resin and expanded graphite to prepare a solid-phase adhesive.

[0022] Furthermore, the adhesive is a liquid-phase adhesive, and the preparation method of the liquid-phase adhesive is as follows: dissolving or partially dissolving one or more powders of expanded graphite with a strong acid and strong alkali resistant resin in an organic solvent to prepare a dispersion with a solid content of 20-70%; or preparing an emulsion with a solid content of 20-70% by dissolving one or more powders of expanded graphite with a strong acid and strong alkali resistant resin in water.

[0023] Furthermore, the preparation method of the conductive hot melt adhesive film is as follows: at a temperature of 160-400℃, a resin resistant to strong acids and alkalis, conductive carbon powder, and additives are mixed evenly, with the resin mass ratio being 30-70%, to form a conductive plastic masterbatch; then, the conductive plastic masterbatch is made into a conductive film with a thickness of 0.05-0.3mm and a sheet resistance of ≤150Ω; the conductive carbon powder includes expanded graphite powder, graphite powder, carbon nanotube powder, graphene powder, conductive carbon black powder, carbon fiber powder, or a combination of two or more of the above.

[0024] Furthermore, the strong acid and alkali resistant resin includes PVDF, PTFE, PVF, PP, PE, or a combination of two or more of the above.

[0025] Furthermore, the pressing method is high-temperature flat pressing or pre-pressing followed by high-temperature flat pressing; the pre-pressing conditions are: pressure ≥ 1 MPa, pre-pressing temperature ≥ 160℃, and pre-pressing time 10-300 seconds; the high-pressure flat pressing conditions are: pressure ≥ 2 MPa, hot pressing temperature ≥ 180℃, and hot pressing time 1-3 hours.

[0026] This application has the following beneficial effects.

[0027] 1. The carbon fiber composite bipolar plate of the present invention has relatively high strength and toughness due to the reinforcement and toughening of carbon fiber, and will not break during transportation and installation, which facilitates construction.

[0028] 2. The carbon fiber composite bipolar plate of the present invention has high strength and can be made thinner and lighter, which reduces the battery volume, reduces the battery weight, and increases the battery energy density.

[0029] 3. The carbon fiber composite bipolar plate of the present invention is mainly composed of carbon fiber, and the carbon fiber has formed a conductive network. It has low internal resistance, less internal resistive heat generation, and less energy loss. It will not cause thermal runaway under high current conditions. Even if the battery temperature is too high, the bipolar plate will not deform due to the high strength of the carbon fiber, which greatly reduces the occurrence of safety accidents.

[0030] 4. The carbon fiber composite bipolar plate of the present invention has a large contact area with the electrode graphite felt because of the fiber texture of carbon fiber on its surface. The resistance between the two is low and the loss caused by the contact resistance is small.

[0031] 5. The manufacturing process of the carbon fiber composite bipolar plate of the present invention is simple, the production cost is low, the price advantage is obvious, and the overall cost performance is strong. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the carbon fiber composite bipolar plate of the flow battery according to the first structure of the present invention;

[0033] Figure 2 This is a schematic diagram of the carbon fiber composite bipolar plate of the flow battery according to the second structure of the present invention;

[0034] Figure 3 This is a schematic diagram of the carbon fiber composite bipolar plate of the flow battery according to the third structure of the present invention.

[0035] The structure consists of: 1. Carbon fiber layer; 2. Adhesive layer; 3. Graphite paper layer. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise specified, the experimental methods used in the present invention are conventional methods, and the experimental equipment, materials, reagents, etc. used can all be purchased from relevant material sales companies.

[0037] This invention provides three structures for carbon fiber composite bipolar plates used in flow batteries, as detailed below:

[0038] like Figure 1 As shown, the carbon fiber composite bipolar plate includes multiple layers of carbon fiber 1 laid in layers. The carbon fiber layer 1 is a carbon fiber needle-punched mesh felt layer or a carbon fiber surface felt layer. An adhesive is coated between two adjacent carbon fiber layers 1 or a conductive hot melt adhesive film is laid to form an adhesive layer 2.

[0039] like Figure 2 As shown, the carbon fiber composite bipolar plate is made by laying a layer of graphite paper 3 on the upper and lower surfaces of the first type of carbon fiber composite bipolar plate.

[0040] like Figure 3 As shown, the carbon fiber composite bipolar plate includes a carbon fiber layer 1 and a graphite paper layer 3. The carbon fiber layer 1 and the graphite paper layer 3 are alternately stacked and laid, and the carbon fiber layer 1 and the graphite paper layer 3 are connected by an adhesive layer 2.

[0041] The fabrication processes for the above three types of carbon fiber composite bipolar plates are as follows:

[0042] 1. Preparation of carbon fiber needle-punched mesh felt: Select carbon fiber filaments and cut them into short carbon fiber fibers with a length of 10-100mm. Spread the cut carbon fibers into a mesh, and then needle-punch them using a needle-punching device (needle-punching density 10-40 needles / cm). 2The carbon fiber needle-punched mesh felt is made by selecting carbon fiber filaments and cutting them into short carbon fiber fibers with a fiber length of 3-100mm. The short-cut carbon fibers are then stably dispersed in a solvent (mainly water), and then an adhesive resin (such as epoxy resin, acrylic resin, and polyurethane resin) is added. After stirring and dispersing evenly, the fibers are filtered, dried, and then hot-pressed and cured to make carbon fiber surface felt with a weight of 8-100g per square meter.

[0043] 2. Preparation of graphite paper: Graphite paper is made by rolling expanded graphite powder from flake graphite. Alternatively, expanded graphite from flake graphite is mixed with high-temperature and acid / alkali-resistant resin powder (such as PVDF, PTFE, PVF, PP, PE, etc., some of which are themselves powders; if the resin is in particle form, it needs to be ground into powder. Before grinding, it is cooled with liquid nitrogen and ground to a size within 50μm in a cold state). The resin accounts for 10-30% of the mass, and the remainder is expanded graphite. Then, the mixture is rolled to form graphite paper.

[0044] 3. Preparation of adhesive / conductive hot melt adhesive film:

[0045] Option 1:

[0046] Select resins resistant to strong acids and alkalis, such as PVDF, PTFE, PVF, PP, and PE. Some of these resins are already in powder form; if they are in particle state, they need to be ground into powder. Before grinding, they should be cooled with liquid nitrogen and ground in a cold state to a size within 50 μm. Then, select expanded graphite pulverized by an air jet mill, with a size within 150 μm. Mix one, two, or more of the above-mentioned resins resistant to strong acids and alkalis and expanded graphite uniformly with high-speed stirring or air jet mixing to prepare a solid-phase adhesive for bonding.

[0047] Option 2:

[0048] Select resins resistant to strong acids and alkalis, such as PVDF, PTFE, PVF, PP, and PE. Some of these resins are already in powder form; if they are in particle state, they need to be ground into powder. Before grinding, they should be cooled with liquid nitrogen and ground in a cold state to a size within 50 μm. Then, select expanded graphite pulverized using an air jet mill, with a size within 150 μm. Dissolve or partially dissolve one, two, or more of the above-mentioned resins resistant to strong acids and alkalis and expanded graphite in one of the organic solvents such as NMP, DMA, DMF, and DEF to prepare a dispersion with a solid content of 20-70%; or directly prepare an emulsion in water with a solid content of 20-70%. This produces a liquid-phase adhesive for bonding.

[0049] Option 3:

[0050] Select a strong acid and alkali resistant resin, such as PVDF, PTFE, PVF, PP, PE, etc., and melt it at a temperature of 160-400℃ using a mixing mill or twin-screw mixer. Select a conductive carbon powder, such as expanded graphite powder, graphite powder, carbon nanotube powder, graphene powder, conductive carbon black powder, carbon fiber powder, or a mixture of two or more of the above powders. Mix the strong acid and alkali resistant resin and conductive carbon powder uniformly at high temperature using a plastic mixing mill or twin-screw mixer, with the resin accounting for 30-70% of the total mass. Additives, such as dispersant EBS, toughening agent POE, coupling agent carbonate, etc., are added during high-temperature mixing, with the additives accounting for 5-20% of the total mass of the system. Finally, a conductive plastic masterbatch is prepared. The conductive plastic masterbatch is then used to form a conductive film with a thickness of 0.05-0.3mm using a blown film machine or casting machine, with a sheet resistance of less than 150Ω. The resulting conductive film is a hot-melt film material and can be used as a conductive hot-melt adhesive film for bonding layers.

[0051] 4. Construction:

[0052] The carbon fiber needle-punched mesh felt or carbon fiber surface felt prepared above is laid flat. An adhesive or conductive hot melt adhesive film is then evenly coated or applied to its top and bottom surfaces. Then, layers of carbon fiber needle-punched mesh felt or carbon fiber surface felt are laid, with adhesive (solid or liquid phase) or conductive hot melt adhesive film applied evenly between layers. Graphite paper can also be laid on the top and bottom surfaces (graphite paper, 0.05-0.2mm thick, can be added between the layers of carbon fiber needle-punched mesh felt or carbon fiber surface felt). 1-6 layers of carbon fiber needle-punched mesh felt or carbon fiber surface felt are laid. The laid material is then pre-pressed to set its shape. Pre-pressing is performed using a roller or flatbed press with a pressure ≥1 MPa, a pre-pressing temperature ≥160℃, and a pre-pressing time of 10-300 seconds. The pre-pressed part is then subjected to high-pressure flat pressing with a pressure ≥2 MPa, a hot pressing temperature ≥180℃, and a hot pressing time of 1-3 hours (depending on the equipment, pre-pressing can be omitted, and high-temperature flat pressing can be performed directly). After pressing, remove and cut.

[0053] 5. Testing:

[0054] Density test: Compressed density 1.0-2.2 g / cm³ 3 Sheet resistance test: Sheet resistance value ≤ 0.5Ω; Vertical resistance test: Resistance ≤ 0.5Ω; Thickness test: Thickness 0.6-1.2mm; Bending strength ≥ 50Mpa.

[0055] The thickness of the bipolar plate prepared in this application was tested using a digital rotary thickness tester; the bending resistance test standard of the bipolar plate was based on GB / T 40398.2-2021 Test Method for Carbon-Carbon Composite Materials; the sheet resistance of the bipolar plate was tested using a four-probe sheet resistance tester, and the vertical resistance was tested using a multi-variable transformer.

[0056] Example 1

[0057] Using Zhongfu Shenying 49s grade carbon fiber filaments, short-cut carbon fiber staples of 70mm were prepared, then laid and needle-punched to produce a carbon fiber needle-punched mesh felt with a basis weight of 80g / m². Solvay 5130 grade PVDF powder was used as a solid-phase binder at a dosage of 160g / m². 0.1mm thick graphite paper was used as an interlayer reinforcing liquid-resistant layer. The manufacturing steps are as follows:

[0058] (1) First, a sheet of graphite paper is laid under the carbon fiber needled mesh felt. PVDF powder is evenly spread between the graphite paper and the carbon fiber needled mesh felt. Then, a layer of graphite paper is laid on the carbon fiber needled mesh felt. PVDF powder is evenly spread on the graphite paper. Then, a second layer of carbon fiber mesh felt is laid on top of it. This process is repeated until three layers of carbon fiber mesh felt are laid (this structure includes four layers of graphite paper and three layers of PVDF powder) to form the initial structure.

[0059] (2) The initial structure is pre-pressed and shaped by upper and lower steel rollers at a temperature of 160℃ and a pressure of 1MPa at a linear speed of 1s / cm.

[0060] (3) Press the pre-pressed shaping part through a flat press. The flat press is a stainless steel plate heated from top and bottom. The flat pressing temperature is 180℃ and the flat press pressure is 2MPa. The flat press starts to heat up from the pressing and holds at 180℃ for 1 hour. Then it cools down naturally to below 50℃. Open the flat press and take out the pressed carbon fiber composite bipolar plate. At this time, the carbon fiber composite bipolar plate is fully bonded by PVDF between the layers and the graphite paper between the layers has been penetrated by PVDF.

[0061] Tested parameters of the carbon fiber composite bipolar plate are as follows: bending strength ≥70 MPa, tensile strength ≥60 MPa, carbon fiber composite bipolar plate thickness 0.92 mm, surface sheet resistance 50 mΩ, vertical resistance 300 mΩ, and no leakage or delamination under 600 kPa pressure in concentrated sulfuric acid solution for 6 hours.

[0062] Example 2

[0063] Using Zhongfu Shenying 49s grade carbon fiber filaments, short-cut carbon fiber staples of 70mm were prepared, then laid and needle-punched to produce a carbon fiber needle-punched mesh felt with a basis weight of 80g / m². A PVDF NMP dispersion (50% solids content) was used as the liquid binder, at a dosage of 320g / m². 0.1mm thick graphite paper was used as the interlayer reinforcement liquid-resistant layer. The manufacturing steps are as follows:

[0064] (1) First, a piece of graphite paper is laid under the carbon fiber needled mesh felt. PVDF dispersion is evenly brushed between the graphite paper and the carbon fiber needled mesh felt. Then, a layer of graphite paper is laid on the carbon fiber needled mesh felt. PVDF dispersion is evenly brushed on the graphite paper. Then, a second layer of carbon fiber mesh felt is laid on top of it. This process is repeated until three layers of carbon fiber mesh felt are laid (this structure includes four layers of graphite paper and three layers of PVDF dispersion brushing layer) to form the initial structure.

[0065] (2) The initial structure is pre-pressed and shaped by upper and lower steel rollers at a temperature of 160℃ and a pressure of 1MPa at a linear speed of 1s / cm.

[0066] (3) Press the pre-pressed shaping parts through a flat press. The flat press is a stainless steel plate heated from top and bottom. The flat press temperature is 180℃ and the flat press pressure is 2MPa. The flat press starts to heat up from the pressing and holds at 180℃ for 2 hours (longer time to facilitate full evaporation of solvent). Then it cools down naturally to below 50℃. Open the flat press and take out the pressed carbon fiber composite bipolar plate. At this time, the carbon fiber composite bipolar plate is fully bonded by PVDF between the layers, and the graphite paper between the layers has been penetrated by PVDF.

[0067] Tested parameters of the carbon fiber composite bipolar plate are as follows: bending strength ≥65Mpa, tensile strength ≥60Mpa, carbon fiber composite bipolar plate thickness 0.8mm, surface sheet resistance 50mΩ, vertical resistance 350mΩ, and no leakage or delamination under 600Kpa pressure in concentrated sulfuric acid solution for 6 hours.

[0068] Example 3

[0069] Using Zhongfu Shenying 49s grade carbon fiber filaments, short-cut carbon fiber staples of 70mm were prepared, then laid and needle-punched to produce a carbon fiber needle-punched mesh felt with a basis weight of 80g / m². Solvay 5130 grade PVDF powder was used as the solid-phase binder, at a dosage of 160g / m². The manufacturing steps are as follows:

[0070] (1) First, PVDF powder is evenly spread on the carbon fiber needle-punched mesh felt, and then a second layer of carbon fiber mesh felt is laid. This process is repeated until four layers of carbon fiber mesh felt (the structure includes three layers of PVDF powder) are laid to form the initial structure.

[0071] (2) The initial structure is pre-pressed and shaped by upper and lower steel rollers at a temperature of 160℃ and a pressure of 1MPa at a linear speed of 1s / cm.

[0072] (3) Press the pre-pressed shaping part through a flat press. The flat press is a stainless steel plate heated from top and bottom. The flat pressing temperature is 180℃ and the flat press pressure is 2MPa. The flat press starts to heat up from the pressing and holds at 180℃ for 1 hour. Then it cools down naturally to below 50℃. Open the flat press and take out the pressed carbon fiber composite bipolar plate. At this time, the carbon fiber composite bipolar plate is fully bonded by PVDF between the layers.

[0073] Tested parameters of the carbon fiber composite bipolar plate are as follows: bending strength ≥60 MPa, tensile strength ≥60 MPa, carbon fiber composite bipolar plate thickness 0.65 mm, surface sheet resistance 200 mΩ, vertical resistance 300 mΩ, and no leakage or delamination under 300 kPa pressure in concentrated sulfuric acid solution for 6 hours.

[0074] Example 4

[0075] Using Zhongfu Shenying 49s grade carbon fiber filaments, short-cut carbon fiber staples of 70mm were prepared, then laid and needle-punched to produce a carbon fiber needle-punched mesh felt with a basis weight of 80g / m². A PVDF NMP dispersion (50% solids content) was used as the liquid binder, at a dosage of 160g / m². The manufacturing steps are as follows:

[0076] (1) First, PVDF dispersion is evenly brushed onto the carbon fiber needle-punched mesh felt, then a second layer of carbon fiber mesh felt is laid, and so on until four layers of carbon fiber mesh felt are laid (this structure includes three layers of PVDF dispersion brushing layer) to form the initial structure.

[0077] (2) The initial structure is pre-pressed and shaped by upper and lower steel rollers at a temperature of 160℃ and a pressure of 1MPa at a linear speed of 1s / cm.

[0078] (3) Press the pre-pressed shaping parts through a flat press. The flat press is a stainless steel plate with upper and lower heating. The flat pressing temperature is 180℃ and the flat press pressure is 2MPa. The flat press starts to heat up from the pressing and holds at 180℃ for 2 hours (the time is longer to facilitate the full evaporation of solvent). Then it cools down naturally to below 50℃. Open the flat press and take out the pressed carbon fiber composite bipolar plate. At this time, the carbon fiber composite bipolar plate is fully bonded by PVDF between the layers.

[0079] Tested parameters of the carbon fiber composite bipolar plate are as follows: bending strength ≥60Mpa, tensile strength ≥60Mpa, carbon fiber composite bipolar plate thickness 0.65mm, surface sheet resistance 230mΩ, vertical resistance 400mΩ, and no leakage or delamination under 300Kpa pressure in concentrated sulfuric acid solution for 6 hours.

[0080] Example 5

[0081] Using Zhongfu Shenying 49s grade carbon fiber filaments, short-cut carbon fiber staples of 70mm were prepared, then needle-punched to produce a carbon fiber needle-punched mesh felt with a basis weight of 80g per square meter. A conductive PE film with a thickness of 0.1mm and a sheet resistance of 100Ω was prepared using SP conductive carbon black (25% by mass), flake graphite powder (20% by mass), additives (5% by mass), and PE particles (50% by mass). This conductive PE film was then used as a conductive hot melt adhesive film. The manufacturing steps are as follows:

[0082] (1) First, a layer of conductive PE film is laid under the carbon fiber needle-punched mesh felt, then a second layer of conductive PE film is laid on top of it, then a second layer of carbon fiber mesh felt is laid on top of it, then a layer of conductive PE film is laid on the second layer of mesh felt, and finally a layer of PE film is laid on the outermost layer to form the initial structure; (this structure includes two layers of carbon fiber mesh felt and five layers of conductive PE film) to form the initial structure;

[0083] (2) The initial structure is pre-pressed and shaped by upper and lower steel rollers at a temperature of 160℃ and a pressure of 1MPa at a linear speed of 1s / cm.

[0084] (3) Press the pre-pressed shaping part through a flat press. The flat press is a stainless steel plate heated from top and bottom. The flat pressing temperature is 180℃ and the flat press pressure is 2MPa. The flat press starts to heat up from the pressing and holds at 180℃ for 1 hour. Then it cools down naturally to below 50℃. Open the flat press and take out the pressed carbon fiber composite bipolar plate. At this time, the carbon fiber composite bipolar plate is fully bonded between layers by conductive PE film.

[0085] Tested parameters of the carbon fiber composite bipolar plate are as follows: bending strength ≥70 MPa, tensile strength ≥60 MPa, carbon fiber composite bipolar plate thickness 0.65 mm, surface sheet resistance 450 mΩ, vertical resistance 600 mΩ, and no leakage or delamination under 600 kPa pressure in concentrated sulfuric acid solution for 6 hours.

[0086] Example 6

[0087] Using Zhongfu Shenying 49s grade carbon fiber filaments, short-cut carbon fiber staples of 70mm were prepared, then needle-punched to form a carbon fiber needle-punched mesh felt with a basis weight of 80g per square meter. A conductive PE film with a thickness of 0.1mm and a sheet resistance of 100Ω was prepared using SP conductive carbon black (20% by mass), flake graphite powder (20% by mass), additives (5% by mass), and PE particles (50% by mass). This conductive PE film was used as a conductive hot melt adhesive film. A 0.2mm thick graphite paper was used as the surface covering layer. The manufacturing steps are as follows:

[0088] (1) First, a layer of conductive PE film is laid under the carbon fiber needle-punched mesh felt, then a second layer of conductive PE film is laid on it, then a second layer of carbon fiber mesh felt is laid on it, then a third layer of conductive PE film is laid on it, and finally graphite paper is laid on the outermost layer (this structure includes two layers of carbon fiber mesh felt, three layers of conductive PE film and two layers of graphite paper) to make the initial structure.

[0089] (2) The initial structure is pressed by a flat press. The flat press is a stainless steel plate heated from top to bottom. The flat press temperature is 180℃ and the flat press pressure is 2MPa. The flat press starts to heat up from the pressing and holds at 180℃ for 2 hours. Then it is allowed to cool down naturally to below 50℃. The flat press is opened and the pressed carbon fiber composite bipolar plate is taken out. At this time, the layers of the carbon fiber composite bipolar plate are fully bonded by the conductive PE film.

[0090] Tested parameters of the carbon fiber composite bipolar plate are as follows: bending strength ≥50 MPa, tensile strength ≥50 MPa, carbon fiber composite bipolar plate thickness 0.9 mm, surface sheet resistance 45 mΩ, vertical resistance 300 mΩ, and no leakage or delamination under 600 kPa pressure in concentrated sulfuric acid solution for 6 hours.

[0091] Example 7

[0092] Using Zhongfu Shenying 49s grade carbon fiber filaments, short-cut carbon fiber staples of 70mm were prepared, then needle-punched to produce a carbon fiber needle-punched mesh felt with a basis weight of 80g per square meter. A conductive PE film with a thickness of 0.1mm and a sheet resistance of 100Ω was prepared using SP conductive carbon black (20% by mass), flake graphite powder (20% by mass), additives (5% by mass), and PE particles (50% by mass). This conductive PE film was used as a conductive hot melt adhesive film. Shandong Dongyue 202 PVDF powder was also used as an adhesive. A 0.2mm thick graphite paper was used as the surface covering layer. The manufacturing steps are as follows:

[0093] (1) First, a layer of conductive PE film is laid under the carbon fiber needle-punched mesh felt, and PVDF powder is evenly spread on it. The amount of powder spread is 160g. Then, a second layer of carbon fiber mesh felt is laid on it, and then a second layer of conductive PE film is laid on it. Then, graphite paper is laid on the outermost layer (this structure includes two layers of carbon fiber mesh felt, layers of conductive PE film, one layer of PVDF powder and two layers of graphite paper) to form the initial structure.

[0094] (2) The initial structure is pressed by a flat press. The flat press is a stainless steel plate heated from top to bottom. The flat press temperature is 180℃ and the flat press pressure is 2MPa. The flat press starts to heat up from the pressing and holds at 180℃ for 2 hours. Then it is allowed to cool down naturally to below 50℃. The flat press is opened and the pressed carbon fiber composite bipolar plate is taken out. At this time, the layers of the carbon fiber composite bipolar plate are fully bonded by conductive PE film and PVDF powder.

[0095] Tested parameters of the carbon fiber composite bipolar plate are as follows: bending strength ≥50 MPa, tensile strength ≥50 MPa, carbon fiber composite bipolar plate thickness 0.85 mm, surface sheet resistance 50 mΩ, vertical resistance 300 mΩ, and no leakage or delamination under 600 kPa pressure in concentrated sulfuric acid solution for 6 hours.

[0096] Example 8

[0097] Using Zhongfu Shenying 49s grade carbon fiber filaments, short-cut carbon fiber staples of 6mm were prepared, dispersed in water, and then 12% acrylic resin was added. After filtration, the mixture was hot-pressed and cured to form a carbon fiber surface mat with a basis weight of 40g per square meter. A conductive PE film with a thickness of 0.1mm and a sheet resistance of 100Ω was prepared by mixing SP conductive carbon black (25% by mass), flake graphite powder (20% by mass), additives (5% by mass), and PE particles (50% by mass). This conductive PE film was used as a conductive hot melt adhesive film. A 0.2mm thick graphite paper was used as a surface covering layer. The manufacturing steps are as follows:

[0098] (1) First, a layer of conductive PE film is laid under the carbon fiber surface felt, then a second layer of conductive PE film is laid on it, then a second layer of carbon fiber surface felt is laid on it, then a third layer of conductive PE film is laid on it, and finally graphite paper is laid on the outermost layer (this structure includes two layers of carbon fiber surface felt, three layers of conductive PE film and two layers of graphite paper) to make the initial structure.

[0099] (2) The initial structure is pressed by a flat press. The flat press is a stainless steel plate heated from top to bottom. The flat press temperature is 180℃ and the flat press pressure is 5MPa. The flat press starts to heat up from the pressing and holds at 180℃ for 2 hours. Then it is allowed to cool down naturally to below 50℃. The flat press is opened and the pressed carbon fiber composite bipolar plate is taken out. At this time, the layers of the carbon fiber composite bipolar plate are fully bonded by the conductive PE film.

[0100] Tested parameters of the carbon fiber composite bipolar plate are as follows: bending strength ≥50 MPa, tensile strength ≥50 MPa, carbon fiber composite bipolar plate thickness 0.8 mm, surface sheet resistance 45 mΩ, vertical resistance 300 mΩ, and no leakage or delamination under 600 kPa pressure in concentrated sulfuric acid solution for 6 hours.

[0101] Example 9

[0102] Using Zhongfu Shenying 49s grade carbon fiber filaments, short-cut carbon fiber staples of 6mm were prepared, dispersed in water, and then 12% acrylic resin was added. After filtration, the mixture was hot-pressed and cured to form a carbon fiber surface mat with a basis weight of 40g per square meter. A conductive PE film with a thickness of 0.1mm and a sheet resistance of 100Ω was prepared by mixing SP conductive carbon black (25% by mass), flake graphite powder (20% by mass), additives (5% by mass), and PE particles (50% by mass). This conductive PE film was used as a conductive hot melt adhesive film. A 0.2mm thick graphite paper was used as a surface covering layer. The manufacturing steps are as follows:

[0103] (1) First, a layer of conductive PE film is laid under the carbon fiber surface felt, then a layer of conductive PE film is laid on top of it, then a second layer of carbon fiber surface felt is laid on top of it, then a layer of conductive PE film is laid on top of it, and finally a layer of PE film is laid on the outermost layer to form the initial structure.

[0104] (2) The initial structure is pressed by a flat press. The flat press is a stainless steel plate heated from top to bottom. The flat press temperature is 180℃ and the flat press pressure is 5MPa. The flat press starts to heat up from the pressing and holds at 180℃ for 2 hours. Then it is allowed to cool down naturally to below 50℃. The flat press is opened and the pressed carbon fiber composite bipolar plate is taken out. At this time, the layers of the carbon fiber composite bipolar plate are fully bonded by the conductive PE film.

[0105] Tested parameters of the carbon fiber composite bipolar plate are as follows: bending strength ≥50 MPa, tensile strength ≥50 MPa, carbon fiber composite bipolar plate thickness 0.7 mm, surface sheet resistance 450 mΩ, vertical resistance 700 mΩ, and no leakage or delamination under 600 kPa pressure in concentrated sulfuric acid solution for 6 hours.

[0106] The data comparison for Examples 1-9 is shown in the table below:

[0107]

[0108]

[0109] The experimental results above show that Examples 1-9 have higher conductivity and mechanical strength than existing bipolar plate materials. Example 1 has the best overall performance. Examples 6, 7, 8, and 9 are improvements on Example 1, with lower material and process costs, making them more suitable for mass production. Examples 2 and 4 have issues with organic solvent evaporation, which may limit production environments in some cases. Examples 3 and 4 have relatively weak resistance to liquid seepage. Although the conductivity of Examples 3, 5, and 9 is lower than other examples, they have the lowest cost, simple production processes, and can be thermofused. Therefore, appropriate construction methods can be selected based on actual conditions.

[0110] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A carbon fiber composite bipolar plate for a flow battery, characterized in that: It includes multiple layers of carbon fiber (1) laid in layers, wherein the carbon fiber layer is a carbon fiber needle-punched mesh felt layer or a carbon fiber surface felt layer, and an adhesive is coated or a conductive hot melt adhesive film is laid between two adjacent carbon fiber layers (1) to form an adhesive layer (2).

2. The carbon fiber composite bipolar plate for a flow battery according to claim 1, characterized in that: The carbon fiber composite bipolar plate also includes a graphite paper layer (3), which is laid on the upper and lower surfaces of the layered structure formed by the carbon fiber layer (1) and the adhesive layer (2).

3. The carbon fiber composite bipolar plate for a flow battery according to claim 1, characterized in that: The carbon fiber composite bipolar plate also includes a graphite paper layer (3), and the carbon fiber layer (1) and the graphite paper layer (3) are alternately stacked and laid, and the carbon fiber layer (1) and the graphite paper layer (3) are connected by an adhesive layer (2).

4. A method for preparing a carbon fiber composite bipolar plate for a flow battery according to any one of claims 1-3, characterized in that: Includes the following steps: Lay out the carbon fiber needled mesh felt or carbon fiber surface felt flat, and evenly coat or sprinkle adhesive or lay a conductive hot melt adhesive film on its top and bottom surfaces. Then, lay other carbon fiber needled mesh felts or carbon fiber surface felts in layers, with 1-6 layers laid. Evenly coat or sprinkle adhesive or lay a conductive hot melt adhesive film between the layers. Press the laid materials and cut them after pressing. Alternatively, carbon fiber needled mesh felt or carbon fiber surface felt can be laid flat, and adhesive can be evenly coated or spread on its top and bottom surfaces or a conductive hot melt adhesive film can be laid. Then, other carbon fiber needled mesh felt or carbon fiber surface felt can be laid in layers, with 1-6 layers of carbon fiber needled mesh felt or carbon fiber surface felt laid. Adhesive can be evenly coated or spread between the layers or a conductive hot melt adhesive film can be laid. Then, apply or sprinkle adhesive or lay conductive hot melt adhesive film on the upper and lower surfaces of the layered structure composed of carbon fiber needle-punched mesh felt or carbon fiber surface felt, and lay graphite paper; press the laid material, and cut it after pressing. Alternatively, lay out carbon fiber needled mesh felt or carbon fiber surface felt flat, and evenly coat or sprinkle adhesive or lay conductive hot melt adhesive film on its top and bottom surfaces. Then, alternately lay graphite paper and carbon fiber needled mesh felt or carbon fiber surface felt, laying 1-6 layers of carbon fiber needled mesh felt or carbon fiber surface felt, with adhesive or conductive hot melt adhesive film evenly coated or sprinkled between the layers. Press the laid material, and then cut it after pressing.

5. The method for preparing a carbon fiber composite bipolar plate for a flow battery according to claim 4, characterized in that: The preparation method of carbon fiber needle-punched mesh felt is as follows: Select carbon fiber filaments, cut them into short carbon fiber fibers with a fiber length of 10-100mm, spread the cut carbon fibers into a mesh, and then needle-punch them to make carbon fiber needle-punched mesh felt; The preparation method of carbon fiber surface felt is as follows: Select carbon fiber filaments, cut them into short carbon fiber fibers with a fiber length of 3-100mm, stably disperse the cut carbon fibers in a solvent, then add adhesive resin, stir and disperse evenly, filter and dry, and then hot-press and cure to make carbon fiber surface felt.

6. The method for preparing a carbon fiber composite bipolar plate for a flow battery according to claim 4, characterized in that: The adhesive is a solid-phase adhesive, and the preparation method of the solid-phase adhesive is as follows: select one or more powders of strong acid and strong alkali resistant resin and expanded graphite to make a solid-phase adhesive.

7. The method for preparing a carbon fiber composite bipolar plate for a flow battery according to claim 4, characterized in that: The adhesive is a liquid-phase adhesive, and the preparation method of the liquid-phase adhesive is as follows: dissolving or partially dissolving one or more powders of expanded graphite with a strong acid and strong alkali resistant resin in an organic solvent to prepare a dispersion with a solid content of 20-70%; or dissolving one or more powders of expanded graphite with a strong acid and strong alkali resistant resin in water to prepare an emulsion with a solid content of 20-70%.

8. The method for preparing a carbon fiber composite bipolar plate for a flow battery according to claim 4, characterized in that: The conductive hot melt adhesive film is prepared by mixing strong acid and alkali resistant resin, conductive carbon powder and additives at a temperature of 160-400℃, with the resin mass ratio being 30-70%, to form conductive plastic masterbatch. The conductive plastic masterbatch is then made into a conductive film with a thickness of 0.05-0.3 mm; the conductive carbon powder includes expanded graphite powder, graphite powder, carbon nanotube powder, graphene powder, conductive carbon black powder, carbon fiber powder, or a combination of two or more of the above.

9. A method for preparing a carbon fiber composite bipolar plate for a flow battery according to any one of claims 6-8, characterized in that: The strong acid and alkali resistant resin includes PVDF, PTFE, PVF, PP, PE, or a combination of two or more of the above.

10. The method for preparing a carbon fiber composite bipolar plate for a flow battery according to claim 4, characterized in that: The pressing method is either high-temperature flat pressing or pre-pressing followed by high-temperature flat pressing; the pre-pressing conditions are: pressure ≥ 1 MPa, pre-pressing temperature ≥ 160℃, and pre-pressing time 10-300 seconds; the high-pressure flat pressing conditions are: pressure ≥ 2 MPa, hot pressing temperature ≥ 180℃, and hot pressing time 1-3 hours.

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