High-toughness and high-sealing flexible graphite bipolar plate with weldable edge and preparation method of high-toughness and high-sealing flexible graphite bipolar plate

Abstract

The invention discloses a high-toughness and high-sealing flexible graphite bipolar plate with weldable edges and a preparation method of the high-toughness and high-sealing flexible graphite bipolar plate. The bipolar plate is formed by pressing a carbon fiber skeleton layer, a sealing layer, a graphite conducting layer and a welding resin edge. The preparation method comprises the following steps: placing a lower mold on a hot press, laying the carbon fiber skeleton layer, the sealing layer, the graphite conductive layer and the welding resin edge on the lower mold, placing an upper mold, pressing at the pressure of 400-2000 tons per square meter, and keeping the temperature of a hot pressing flat plate at 150-350 DEG C; the materials are put into a pressing machine when the temperature is increased, the temperature is increased under the pressure maintaining condition, the temperature is increased at the speed of 2-20 DEG C / min, the pressure is maintained for 2-8 hours, and then the temperature is decreased at the speed of 5-30 DEG C / min; and after cooling to room temperature, taking down the pressed bipolar plate, and carrying out edging die cutting. The bipolar plate structure taking the carbon fibers as the framework has the characteristics of high strength, low internal resistance, small thickness, light weight, strong acid and strong alkali resistance, large-scale production and simple flow.

Description

Technical Field

[0001] The invention relates to the field of liquid flow batteries, and in particular to a flexible graphite bipolar plate with weldable edges, high toughness and high sealing properties, and a preparation method thereof. Background Art

[0002] There are three categories of liquid flow battery bipolar plates currently in use on the market, one is graphite bipolar plates, one is conductive plastic bipolar plates, and one is flexible graphite bipolar plates; the preparation process of graphite bipolar plates is: select high-strength and high-conductivity graphite materials (some of them will be impregnated with resin to seal the gaps in the graphite for better liquid resistance) and prepare them through machining. The preparation process of conductive plastic bipolar plates is: select conductive carbon powder (expanded graphite powder, graphite powder, carbon nanotube powder, graphene powder, conductive carbon black powder or carbon fiber powder or mixed powder of the above), and mix them with other additives such as EBS, POE, titanate, etc., and strong acid and alkali resistant resins such as PE, PP, PTFE and PVDF through plastic mixing or twin-screw mixing equipment at high temperature, and then make conductive plastic masterbatch, and then calender the conductive plastic masterbatch into conductive plastic sheet, and prepare them through machining. Flexible graphite bipolar plate preparation process: Generally, strong acid and alkali resistant resins such as PVDF, PTFE, PVF, PP and PE are selected and fully mixed with expanded graphite powder, then rolled and shaped, and then hot pressed into flexible graphite plates, which are then machined. At present, graphite bipolar plates and flexible graphite bipolar plates cannot be welded to the plate frame, and hot melt adhesive films need to be attached to assist welding. Conductive plastic bipolar plates can be directly welded to the plate frame.

[0003] The problems existing in the existing process are as follows:

[0004] Graphite bipolar plates: (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, graphite bipolar plates are generally made thicker, which increases the battery volume, increases the battery weight, and reduces the energy density; (3) The graphite plate processing flow channel needs to be machined, which has extremely low production efficiency and high processing costs; (4) The graphite plate itself cannot be welded. Welding with welding film has problems such as low weather resistance of welding hot melt adhesive and poor long-term acid and alkali resistance, and there are great risks in welding strength and reliability; (5) There are gaps in the graphite material, which need to be sealed with sealant, but the resin used for sealing is generally not resistant to strong acids and alkalis for a long time, and there is a risk of liquid leakage during long-term use.

[0005] Conductive plastic bipolar plates: (1) Plastic electrode plates are slightly stronger than graphite and can be made thinner. However, the main materials of conductive plastic electrode plates are strong acid and alkali resistant plastic materials such as PP, PE, PVDF or PTFE. After adding more carbon conductive powder, the brittleness increases and it is still easy to break during transportation and installation; (2) Plastic electrode plates are thin and have a certain degree of brittleness, which is easy to crack during processing; (3) Conductive plastic electrode plates have a large internal resistance, which leads to the generation of resistance heat and energy loss. Especially under high current conditions, thermal runaway is easy to occur, especially PP and PE materials are plastic materials with poor temperature resistance. When thermal runaway is severe, the electrode plate may deform and cause 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 mixed pressing of expanded graphite and resin powder needs to ensure sufficient conductivity, so the resin content is relatively low. Therefore, the flexible graphite bipolar plate still has the problem of low strength and easy delamination; (2) The strength of flexible graphite bipolar plates is the weakest among all types of bipolar plates. Under high pressure during stacking or during transportation, they are prone to breakage; (3) During machining, they are prone to cracking and the cut ends are prone to delamination; (4) Flexible graphite bipolar plates themselves cannot be welded. Welding with welding film has problems such as low weathering life of welding hot melt adhesive and poor long-term acid and alkali resistance, and there are great risks in welding fastness and reliability; and flexible graphite bipolar plates are laminated structures, and welding film can only be welded on its surface, which has the risk of delamination; (5) Flexible graphite bipolar plate materials are relatively brittle, and some microcracks and micropores may exist during the production process. In some usage scenarios, sealant impregnation and sealing are also required, but the resin used for sealing is generally not resistant to strong acids and alkalis for a long time, and there is a risk of liquid leakage in long-term use. Summary of the invention

[0007] In order to solve the above-mentioned technical problems, the present invention provides a flexible graphite bipolar plate with high toughness and high sealing properties and a preparation method for weldable edges. The present invention uses carbon fiber fabric as the skeleton material. The carbon fiber can be compounded with weldable plastic on its extended edges through the extension of four sides to form a weldable edge, which can then be directly welded to the plate frame. During the pressing process, the materials can be laid according to different resin content ratios, so that the resin content of the middle layer of the bipolar plate is high, which increases the sealing and liquid resistance. The bipolar plate structure using carbon fiber as the skeleton in this application has the characteristics of high strength, low internal resistance, thin thickness, light weight, strong acid and alkali resistance, and simple mass production process. It is a composite bipolar plate with low cost and can be mass-produced.

[0008] In a first aspect, the present invention provides a flexible graphite bipolar plate with weldable edges, high toughness and high sealing properties, which is achieved through the following technical solutions.

[0009] A high-toughness and high-sealability flexible graphite bipolar plate with weldable edges is formed by pressing together a carbon fiber skeleton layer, a sealing layer, a graphite conductive layer and a welding resin edge.

[0010] Furthermore, a weldable edge high-toughness and high-sealing flexible graphite bipolar plate includes a carbon fiber skeleton layer, a sealing layer is provided on both sides of the carbon fiber skeleton layer, a graphite conductive layer is provided in the center of the outer side of the sealing layer, and a welding resin edge is provided around the graphite conductive layer.

[0011] In a second aspect, the present invention provides a method for preparing a flexible graphite bipolar plate with weldable edges, high toughness and high sealing properties, which is achieved through the following technical solutions.

[0012] A method for preparing the above-mentioned weldable edge high-toughness and high-seal flexible graphite bipolar plate comprises the following steps:

[0013] Place the lower mold on the hot press, and lay the carbon fiber skeleton layer, sealing layer, graphite conductive layer, and welding resin edge on the lower mold. After placing the upper mold, press it at a pressure of 400-2000 tons per square meter, and keep the temperature of the hot pressing plate at 150-350℃; put the material into the press at the beginning of heating, and heat it under pressure at 2-20℃ / min, keep the pressure for 2-8 hours, and then cool it at 5-30℃ / min; after cooling to room temperature, remove the pressed bipolar plate and perform edge-cutting.

[0014] Furthermore, the carbon fiber skeleton layer is selected from one or more of carbon fiber mesh, carbon fiber felt, and carbon fiber cloth.

[0015] Furthermore, the preparation method of the carbon fiber mesh tire is: select carbon fiber filaments, cut them into carbon fiber staple fibers with a fiber length of 50-100 mm, air-form the chopped carbon fibers into a web, and then needle-punch them to make a carbon fiber needle-punched mesh tire; the preparation method of the carbon fiber thin mat is: select carbon fiber filaments, cut them into carbon fiber staple fibers with a fiber length of 5-100 mm, stably disperse the chopped carbon fibers in a solvent (the solvent is preferably water), and then add an adhesive resin (the adhesive resin includes acrylic resin, polyurethane resin, epoxy resin, resin The mass ratio of carbon fiber is 1-3%), after being stirred and dispersed evenly, it is filtered and dried, and then hot-pressed and solidified to make a carbon fiber felt; the preparation method of the carbon fiber cloth is: select pre-oxidized filaments, curl them, and the curl degree is 3-9 / cm, and then cut them into 38-150mm pre-oxidized short filaments, and then spin them, use ring spinning, Siro or airflow process to make 10-30 double-strand yarns, and then weave them into cloth, and then carbonize them at 1000-1500℃ and graphitize them at 1600-2200℃ to make graphitized carbon fiber cloth.

[0016] Furthermore, the sealing layer uses powder or film as a sealing material; using powder as a sealing material: evenly mix the strong acid and alkali resistant resin and the expanded graphite with a size of 100-300 meshes, with the resin mass accounting for 15-80%, to make a sealing powder material; using a film as a sealing material: the strong acid and alkali resistant resin is mixed with the conductive carbon powder through a mixer or a twin-screw internal mixer at a temperature of 160-400°C, with the resin mass accounting for 15-80%, and then add additives during high-temperature mixing, with the additive mass accounting for 2-10%, and finally make a conductive resin masterbatch, and the conductive resin masterbatch is made into a sealing film material with a thickness of 0.05-0.4mm through a film blowing machine or a cast film machine.

[0017] Furthermore, the graphite conductive layer is made of mixed graphite powder or composite graphite film; the mixed graphite powder is used as the graphite conductive layer: worm graphite made from expandable graphite is crushed into 100-300 mesh, and then the worm graphite powder is mixed with acid- and alkali-resistant resin powder, with the resin mass accounting for 2-20%, to obtain mixed graphite powder; the composite graphite film is used as the graphite conductive layer: worm graphite powder made of expandable graphite is mixed with acid- and alkali-resistant resin powder at a certain temperature, with the acid-resistant resin mass accounting for 2-20%, and then rolled into a graphite film.

[0018] Furthermore, resin powder or resin film is used as the resin material for the welding edge; using resin powder as the resin material for the welding edge: selecting 300-1500 mesh acid- and alkali-resistant resin material for welding with the plate frame, adding inorganic fillers and additives, and preparing welding powder material, wherein the resin content is 60-90%, the additive mass accounts for 0.5-5%, and the remainder is inorganic fillers; using resin film as the resin material for the welding edge: selecting acid- and alkali-resistant resin material for welding with the plate frame, adding inorganic fillers, the resin content is 60-90%, and adding additives during high-temperature mixing, the additive mass accounts for 2-10%, and finally making plastic masterbatch, and the plastic masterbatch is made into a welding film material with a thickness of 0.05-0.4mm through a film blowing machine or a cast film machine.

[0019] This application has the following beneficial effects.

[0020] (1) The bipolar plate of the present application has relatively high strength and toughness due to the reinforcement and toughening of carbon fiber, and will not break during transportation and installation, which is convenient for construction;

[0021] (2) Due to its high strength, the bipolar plate of the present application can be made thinner and lighter, which reduces the volume and weight of the battery and improves the battery energy density;

[0022] (3) Since the bipolar plate of the present application is mainly composed of carbon fiber, and the carbon fiber has formed a conductive network, its internal resistance is low, the internal resistance heat is less, the energy loss is less, and thermal runaway will not be caused 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;

[0023] (4) The bipolar plate of the present application can be welded on all sides, which solves the problem that the flexible graphite bipolar plate itself cannot be welded. With its high conductivity, it can completely replace the weldable conductive plastic bipolar plate;

[0024] (5) Due to the presence of the sealing layer, the bipolar plate of the present application has extremely high gas and liquid sealing properties, which solves the risk of reduced sealing properties of the flexible graphite bipolar plate during long-term use;

[0025] (6) The manufacturing process of the bipolar plate of the present application can be fully operated by a robot arm, and the mold pressing controls the dimensional accuracy, so the production efficiency is high, the price advantage is obvious, and the overall cost performance is high.

[0026] (7) The bipolar plate density prepared in this application is 1.0-1.9 g / cm 3 , square resistance ≤40mΩ, conductivity ≥320S / cm, thickness tolerance ±5%, bending strength ≥50Mpa, tensile strength ≥60Mpa, hydrogen permeability test under 1.5Mpa pressure, hydrogen permeability ≤5×10 -6 cm 3 / cm 2 ·min. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of the weldable edge high-toughness high-sealability flexible graphite bipolar plate of the present invention.

[0028] Among them, 1. carbon fiber skeleton layer; 2. sealing layer; 3. graphite conductive layer; 4. welding resin edge. DETAILED DESCRIPTION

[0029] The invention is further described below with reference to the accompanying drawings and embodiments. Unless otherwise specified, the experimental method used in the present invention is a conventional method, and the experimental equipment, materials, reagents, etc. used can be purchased from relevant material sales companies.

[0030] 1. Preparation of materials and auxiliary materials

[0031] 1. Preparation of carbon fiber skeleton:

[0032] With carbon fiber mesh as the skeleton:

[0033] Select carbon fiber filaments, cut them into carbon fiber staple fibers with a fiber length of 50-100 mm, air-lay the chopped carbon fibers, and then needle-punch them through a needle-punch device to make a carbon fiber needle-punched net tire with a square meter weight of 20-150 g;

[0034] With carbon fiber felt as the skeleton:

[0035] Select carbon fiber filaments, cut them into short carbon fiber staples with a fiber length of 5-100mm, stably disperse the short carbon fiber in water, and then add adhesive resin, generally acrylic, polyurethane, epoxy and other resins, and the resin mass accounts for 1-3% of the carbon fiber. After stirring and dispersing evenly, filter and dry, and then heat press and solidify to make a carbon fiber felt, the carbon fiber felt has a square meter weight of 20-150g;

[0036] With carbon fiber cloth as the skeleton:

[0037] Pre-oxidized filaments are selected, curled with a curl of 3-9 / cm, chopped into 38-150mm pre-oxidized short filaments, and then spun using ring spinning, siro or airflow processes to make 10-30 double-strand yarns, which are then woven into cloth using a rapier loom with a square meter weight of 100-300g. The cloth is then carbonized at 1000-1500℃ and graphitized at 1600-2200℃ to make graphitized carbon fiber cloth with a square meter weight of 20-100g.

[0038] 2. Preparation of graphite conductive layer materials:

[0039] Using mixed graphite powder as the graphite conductive layer: using expandable graphite, expandable graphite 60-100 mesh, 160-300 times expansion ratio, made of worm graphite, crushed into 100-300 mesh worm graphite powder, then the worm graphite powder is mixed with acid and alkali resistant resin powder (such as one or more of PVDF, PTFE, PVF, PP, PE, etc., the resin powder fineness is 1000-1500 mesh), the mixing method is mechanical stirring or air flow mixing, and the resin mass accounts for 2-20%.

[0040] Using composite graphite film as graphite conductive layer: worm graphite powder is made of expandable graphite, and is mixed with acid- and alkali-resistant resin powder (such as one or more of PVDF, PTFE, PVF, PP, PE, etc., with a resin powder fineness of 1000-1500 mesh) through a powder airflow mixing device at a temperature of 130-200°C, wherein the acid-resistant resin accounts for 2-20% by mass, and the rest is worm graphite, and then it is rolled into graphite film.

[0041] 3. Preparation of sealing layer:

[0042] Use powder as sealing material: select strong acid and alkali resistant resins, such as PVDF, PTFE, PVF, PP, PE, etc. Some of these resins are powders themselves. If they are in particle state, they need to be ground into powders. Cool with liquid nitrogen before grinding, and grind to a fineness of 1000-1500 mesh in a cold state. Then select expanded graphite crushed by an air flow mill, the size of which is 100-300 mesh. Mix the strong acid and alkali resistant resins and expanded graphite evenly through high-speed stirring or air flow mixing, with the resin mass accounting for 15-80%. Make sealing powder material;

[0043] Using the membrane as the sealing material: you can choose strong acid and alkali resistant resins, such as PVDF, PTFE, PVF, PP, PE, etc., through a mixer or a twin-screw internal mixer, at a temperature of 160-400°C, select conductive carbon powders, such as expanded graphite powder, graphite powder, carbon nanotube powder, graphene powder, conductive carbon black powder, and carbon fiber powder. Mix one or more of these powders with resin powder through an internal mixer, where the resin mass accounts for 15-80%. Add additives during high-temperature mixing, such as dispersant EBS, toughening agent POE, coupling agent carbonate, etc., and the additive mass accounts for 2-10%. Finally, a conductive resin masterbatch is made, and the conductive resin masterbatch is made into a sealing film material with a thickness of 0.05-0.4mm through a film blowing machine or a cast film machine.

[0044] 4. Preparation of welding edge resin material:

[0045] Use resin powder as welding edge resin material: select acid and alkali resistant resin materials for welding with plate frame, such as PE, PP, PVDF, PTFE, PVF, LDPE, etc., select 300-1500 mesh powder, if there is no powder, grind it into powder. In order to adjust the difference in thermal expansion coefficient with the conductive area, inorganic fillers such as one or more of carbon black, white carbon black, titanium dioxide, talcum powder and glass fiber can be added to the powder, and the resin content is 60-90%. During the preparation process, additives such as dispersant EBS, toughening agent POE, coupling agent carbonate, etc. can also be added, and the mass proportion of additives is 0.5-5%.

[0046] Use resin film as welding edge resin material: select acid and alkali resistant resin materials for welding with plate frame, such as PE, PP, PVDF, PTFE, PVF, LDPE, etc., and add inorganic fillers such as carbon black, white carbon black, titanium dioxide, talcum powder and glass fiber to the resin powder to adjust the difference in thermal expansion coefficient with the conductive area, with a resin content of 60-90%. Add additives such as dispersant EBS, toughening agent POE, coupling agent carbonate, etc. during high temperature mixing, with the additive mass accounting for 2-10%, and finally make plastic masterbatch, which is made into welding film material with a thickness of 0.05-0.4mm through a film blowing machine or a cast film machine.

[0047] 5. Preparation of hot pressing mold:

[0048] According to the product size, a stainless steel mold is made. A set of molds consists of two steel plates. The lower steel plate is generally 1.5-4mm thick, and the upper mold is 1-3mm thick. The lower mold generally needs to be milled with a groove. The groove depth is determined according to the thickness of the bipolar plate. The groove depth is consistent with the thickness of the bipolar plate. The welding edge position around the lower mold can be milled to a shallower or deeper depth. The upper mold can be made into a plane, groove or convex according to the product situation and the corresponding welding edge position around the product requirements. The other positions are in a plane mirror state.

[0049] 2. Paving materials:

[0050] 1. Laying the base material:

[0051] Place the hot pressing mold on the hot press, first place the lower mold. Spray the release agent or lay the release film on the lower mold, and then lay the materials. First, lay the welding edge powder or film material around the welding edge of the lower mold; then lay the powder or film material of the middle graphite conductive layer;

[0052] 2. Laying the sealing layer material:

[0053] Lay sealing powder or film material on the base material;

[0054] 3. Laying carbon fiber skeleton:

[0055] Laying a carbon fiber skeleton on the closed layer material;

[0056] 4. Laying the sealing layer material:

[0057] Laying closed powder or film material on the carbon fiber skeleton;

[0058] 5. Laying and loading

[0059] The materials are laid on the sealing layer. First, the welding edge powder or film material is laid around the welding edge positions; then the powder or film material of the middle graphite conductive layer is laid.

[0060] The order and number of layers of material laying can be adjusted according to specific needs and are not limited to the above structure.

[0061] 6. Place the upper mold

[0062] After accurate alignment, place the upper mold on top. Spray a release agent on the upper mold or lay a release film underneath it.

[0063] 3. Pressing

[0064] The press is a multi-layer press. A mold loaded with materials is placed on each layer, and then pressed at a pressure of 400-2000 tons per square meter. The temperature of each layer of the hot pressing plate of the press is maintained at 150-350℃. The material is placed in the press at the beginning of the heating, and the temperature is raised under pressure at 2-20℃ / min. The pressure is maintained for 2-8 hours, and then the temperature is lowered at 5-30℃ / min.

[0065] 4. Cutting

[0066] After the laminating machine cools down to room temperature, remove the mold, then remove the pressed bipolar plate, and use a die-cutting machine to cut the edges (see Figure 1 ).

[0067] The thickness of the bipolar plates prepared in the following embodiments of the present application is tested by a laser thickness tester; the bending resistance test detection standard refers to GB / T 40398.2-2021 Carbon-Carbon Composite Carbon Material Test Method; the square resistance and conductivity can be tested by using a four-probe square resistance tester and an RTS-9 dual-electric 4-probe resistance tester; the airtightness is tested by using a homemade hydrogen permeation tester to detect the hydrogen permeation amount.

[0068] Example 1

[0069] 1. Preparation of carbon fiber skeleton:

[0070] Zhongfu Shenying 49s brand carbon fiber filaments are used, which are chopped into 70mm carbon fiber staple fibers, and then laid and needle-punched to make a carbon fiber needle-punched mesh with a square meter weight of 80g.

[0071] 2. Preparation of conductive graphite material:

[0072] Select expandable graphite with 100 mesh and 160 expansion ratio to make worm graphite at 900℃, and then crush it into 200 mesh powder. Select Solvay 5130PVDF powder, add it to 200 mesh worm graphite powder, the addition amount is 10%, and then use a mixer to stir and mix the powder at 200 rpm.

[0073] 3. Preparation of sealing material:

[0074] Select expandable graphite with 100 mesh and 160 expansion ratio to make worm graphite at 900℃, and then crush it into 200 mesh powder. Select Solvay 5130PVDF powder, add it to 200 mesh worm graphite powder, the addition amount is 25%, and then use a mixer to stir and mix the powder at 200 rpm.

[0075] 4. Preparation of welding edge material:

[0076] Select 400-mesh Yangzi Petrochemical 2650-grade LDPE powder, add 15% by mass of 1000-mesh pigment carbon black, 10% by mass of 1000-mesh white carbon black, and then add additives, which are 1% EBS and 1% titanate, and mix them mechanically and stir them evenly.

[0077] 5. Open the mold:

[0078] Use 4mm stainless steel as the bottom template, the template size is 1200mm*700mm; 100mm away from the four sides, fine mill out the edges with a width of 20mm and a depth of 0.6mm; the middle size is 1080mm*580mm, and all the grooves with a depth of 0.8mm are fine milled.

[0079] Use 2.2mm stainless steel plate as the upper template, the template size is 1200mm*700mm; leave 20mm width of four sides at 100mm away, and mill off the rest, with a milling depth of 0.2mm.

[0080] 6. Paving materials:

[0081] Spray the release agent evenly on the bottom mold loading surface, and spread the welding edge material at 330g / ㎡ in the 0.6mm deep groove; spread the conductive graphite material at 490g / ㎡ in the middle 0.8mm deep groove; spread 100g / ㎡ of sealing material on it; then put 80g / ㎡ of carbon fiber mesh tire; spread 100g / ㎡ of sealing material on the mesh tire, and spread the welding edge material and graphite conductive material on the sealing material in line with the bottom layer, with the same amount as the bottom layer. Align the upper template and spray the release agent evenly on the upper template contacting the material surface. The material is laid on each layer of the hot press according to the above laying method.

[0082] 7. Hot pressing:

[0083] After putting the materials into the hot press, the pressurization starts, the pressure is 900 tons / ㎡; the hot press temperature is 190℃, and the temperature is kept for 2 hours; the temperature is increased at 5℃ / min and the temperature is decreased at 15℃ / min.

[0084] 8. Die cutting:

[0085] Use stamping die-cutting to cut the pressed bipolar plates flush with the edges to complete the production of finished products.

[0086] 9. Detection:

[0087] Density test, welding edge density: 1.2g / cm3, conductive area 1.6g / cm3; square resistance test: conductive area square resistance 32mΩ; conductivity test: conductivity 320-360S / cm; thickness uniformity test, welding edge thickness 0.39-0.42mm, conductive area thickness 0.77-0.82mm; bending strength 62Mpa, tensile strength ≥80Mpa; air tightness test, hydrogen permeation test under 1.5Mpa pressure, hydrogen permeability 3×10 -6 cm 3 / cm 2 ·min.

[0088] Embodiment 2:

[0089] 1. Preparation of carbon fiber skeleton:

[0090] Select Zhongfu Shenying 49s carbon fiber filaments, cut them into carbon fiber staple fibers with a fiber length of 50 mm, stably disperse the chopped carbon fiber in deionized water, then add acrylic resin accounting for 3% of the mass of the carbon fiber, stir and disperse evenly, filter and dry, and then heat press and solidify to make a carbon fiber felt with a square meter weight of 80g;

[0091] 2. Preparation of conductive graphite material:

[0092] Select expandable graphite with 100 mesh and 160 expansion ratio to make worm graphite at 900℃, and then crush it into 200 mesh powder. Select Solvay 5130PVDF powder, add it to 200 mesh worm graphite powder, the addition amount is 10%, and then use a mixer to stir and mix the powder at 200 rpm.

[0093] 3. Preparation of sealing material:

[0094] Select expandable graphite with 100 mesh and 160 expansion ratio to make worm graphite at 900℃, and then crush it into 200 mesh powder. Select 1000 mesh PE material of Yanshan Petrochemical 1158, with 60% PE and 40% worm graphite powder, use a mixer to stir and mix the powder at 200 rpm.

[0095] 4. Preparation of welding edge material:

[0096] Select 1000 mesh LDPE powder of Yanshan Petrochemical 1158 brand, add 20% 1000 mesh carbon black pigment into the resin powder, and then add an additive, the additive is 1% titanate, and mix mechanically and stir evenly.

[0097] 5. Open the mold:

[0098] Use 4mm stainless steel as the bottom template, the template size is 1200mm*700mm; 100mm away from the four sides, the middle size is 110mm*600mm, and all grooves with a depth of 0.8mm are milled out.

[0099] Use 2mm stainless steel plate as the upper template, the template size is 1200mm*700mm; the surface is mirror polished.

[0100] 6. Paving materials:

[0101] Spray the release agent evenly on the bottom mold loading surface, and spread the welding edge material at 500g / ㎡ within the 0.8mm deep groove position and 20mm width; spread the graphite conductive material at 490g / ㎡ within the remaining 0.8mm deep groove range; spread 100g / ㎡ of sealing material on it; then put 80g / ㎡ of carbon fiber mesh tire; spread 100g / ㎡ of sealing material on the mesh tire, and spread the welding edge material and graphite conductive material on the sealing material in the same amount as the bottom layer. Align and place the upper template, and spray the release agent evenly on the upper template contacting the material surface. The material is laid on each layer of the hot press according to the above laying method.

[0102] 7. Hot pressing:

[0103] After putting the materials into the hot press, the pressurization starts, the pressure is 1000 tons / ㎡; the hot press temperature is 180℃, and the temperature is kept for 2 hours; the temperature is increased at 10℃ / min and the temperature is decreased at 20℃ / min.

[0104] 8. Die cutting:

[0105] Use stamping die-cutting to cut the pressed bipolar plates flush with the edges to complete the production of finished products.

[0106] 9. Detection:

[0107] Density test, welding edge density: 1.35g / cm3, conductive area 1.6g / cm3; square resistance test: conductive area square resistance 30mΩ; conductivity test: conductivity 350-400S / cm; thickness uniformity test, welding edge thickness 0.38-0.40mm, conductive area thickness 0.79-0.82mm; bending strength 58Mpa, tensile strength ≥82Mpa; air tightness test, hydrogen permeation test under 1.5Mpa pressure, hydrogen permeability 2.85×10 -6 cm 3 / cm 2 ·min.

[0108] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A weldable edge high toughness high sealing flexible graphite bipolar plate, characterized by: It is formed by pressing together a carbon fiber skeleton layer (1), a sealing layer (2), a graphite conductive layer (3) and a welding resin edge (4).

2. The weldable edge high toughness high sealing flexible graphite bipolar plate according to claim 1, characterized in that: The invention comprises a carbon fiber skeleton layer (1), a sealing layer (2) is arranged on both sides of the carbon fiber skeleton layer (1), a graphite conductive layer (3) is arranged in the center of the outer side of the sealing layer (2), and a welding resin edge (4) is arranged around the graphite conductive layer (3).

3. A method for preparing the weldable edge high toughness and high sealing flexible graphite bipolar plate according to claim 1 or 2, characterized in that: The following steps are involved: A lower mold is placed on a hot press, and a carbon fiber skeleton layer (1), a sealing layer (2), a graphite conductive layer (3), and a welding resin edge (4) are laid on the lower mold. After placing an upper mold, the materials are pressed at a pressure of 400-2000 tons per square meter, and the temperature of the hot pressing plate is maintained at 150-350°C; the materials are placed in the press at the beginning of heating, and heated under pressure at a rate of 2-20°C / min, and the pressure is maintained for 2-8 hours, and then cooled at a rate of 5-30°C / min; after cooling to room temperature, the pressed bipolar plates are removed and die-cut to flush the edges.

4. The method for preparing a weldable edge high-toughness high-seal flexible graphite bipolar plate according to claim 3, characterized in that: The carbon fiber skeleton layer (1) is selected from one or more of carbon fiber mesh, carbon fiber felt, and carbon fiber cloth.

5. The method for preparing a weldable edge high-toughness high-sealability flexible graphite bipolar plate according to claim 4, characterized in that: The preparation method of the carbon fiber mesh tire is as follows: selecting carbon fiber filaments, chopping them into carbon fiber staple fibers with a fiber length of 50-100 mm, air-forming the chopped carbon fibers into a web, and then needle-punching them to form a carbon fiber needle-punched mesh tire; The preparation method of the carbon fiber felt is as follows: selecting carbon fiber filaments, chopping them into carbon fiber staple fibers with a fiber length of 5-100 mm, stably dispersing the chopped carbon fibers in a solvent, then adding an adhesive resin, stirring and dispersing them evenly, filtering and drying them, and then hot pressing and curing them to make a carbon fiber felt; the preparation method of the carbon fiber cloth is as follows: selecting pre-oxidized filaments, curling them with a curl of 3-9 / cm, chopping them into pre-oxidized staple fibers with a length of 38-150 mm, spinning them, using a ring spindle, siro or airflow process to make 10-30 English count double-strand yarns, then weaving them into cloth, and then carbonizing them at 1000-1500° C. and graphitizing them at 1600-2200° C. to make graphitized carbon fiber cloth.

6. The method for preparing a weldable edge high-toughness high-sealability flexible graphite bipolar plate according to claim 3, characterized in that: The sealing layer (2) uses powder or film as the sealing material; using powder as the sealing material: evenly mix strong acid and alkali resistant resin and expanded graphite with a size of 100-300 meshes, with the resin accounting for 15-80% by weight, to prepare a sealing powder material; using film as the sealing material: mixing the strong acid and alkali resistant resin with conductive carbon powder through a mixer or a twin-screw internal mixer at a temperature of 160-400° C., with the resin accounting for 15-80% by weight, adding an auxiliary agent during high-temperature mixing, with the auxiliary agent accounting for 2-10% by weight, and finally preparing a conductive resin masterbatch, and the conductive resin masterbatch is formed into a sealing film material with a thickness of 0.05-0.4 mm through a film blowing machine or a casting machine.

7. The method for preparing a weldable edge high-toughness high-sealability flexible graphite bipolar plate according to claim 3, characterized in that: The graphite conductive layer (3) is made of mixed graphite powder or composite graphite film; the mixed graphite powder is used as the graphite conductive layer: worm graphite made of expandable graphite is crushed into 100-300 meshes, and then the worm graphite powder is mixed with acid- and alkali-resistant resin powder, with the resin accounting for 2-20% by weight, to obtain the mixed graphite powder; the composite graphite film is used as the graphite conductive layer: worm graphite powder made of expandable graphite is mixed with acid- and alkali-resistant resin powder at a certain temperature, with the acid-resistant resin accounting for 2-20% by weight, and then rolled to form a graphite film.

8. The method for preparing a weldable edge high-toughness high-sealability flexible graphite bipolar plate according to claim 3, characterized in that: The welding resin edge (4) uses resin powder or resin film as the welding edge resin material; using resin powder as the welding edge resin material: selecting 300-1500 mesh acid-alkali resistant resin material for welding with the plate frame, adding inorganic filler and auxiliary agent, and preparing welding powder material, wherein the resin content is 60-90%, the auxiliary agent accounts for 0.5-5% by weight, and the remainder is inorganic filler; using resin film as the welding edge resin material: selecting acid-alkali resistant resin material for welding with the plate frame, adding inorganic filler, the resin content is 60-90%, and adding auxiliary agent during high temperature mixing, the auxiliary agent accounts for 2-10% by weight, and finally preparing plastic masterbatch, and the plastic masterbatch is made into welding film material with a thickness of 0.05-0.4mm through a film blowing machine or a casting machine.

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