Multi-component composite bipolar plate for vanadium redox flow battery and preparation method of multi-component composite bipolar plate

Abstract

The invention belongs to the field of vanadium redox flow batteries, and particularly relates to a multi-element composite bipolar plate for a vanadium redox flow battery and a preparation method of the multi-element composite bipolar plate. The method comprises the following steps: preparing a coated metal microsphere conductive material I, preparing a metal coated conductive fiber II, flatly laying the coated metal microsphere conductive material I in a mold in an upper layer and a lower layer, embedding the metal coated conductive fiber II in the middle, and carrying out hot press molding to obtain the bipolar plate with the sandwich structure. The compact coated metal microsphere structure increases a conductive path in the bipolar plate and reduces the body resistance, the coating layer avoids direct contact between metal and a vanadium electrolyte and reduces the corrosion effect of the electrolyte, and the metal coated conductive fiber structure increases the longitudinal conductivity of the bipolar plate and improves the performance of the bipolar plate. The carbon fiber improves the mechanical strength and the transverse conductivity of the bipolar plate.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of vanadium flow batteries, and particularly relates to a multi-element composite bipolar plate for a vanadium flow battery and a preparation method thereof. BACKGROUND

[0002] The bipolar plate is an important component of the flow battery and mainly serves to collect current and transmit electrons. The main design idea of the bipolar plate is to increase the conductive path by adding different fillers to improve the conductivity of the bipolar plate and reduce the internal resistance of the bipolar plate.

[0003] At present, the bipolar plates on the market include pure graphite bipolar plates, graphite-based composite bipolar plates prepared by heating reaction or cross-linking of graphite and thermoplastic resin / thermosetting resin, pure graphite bipolar plates, and bipolar plates prepared from thermosetting resin. The bipolar plates prepared from pure graphite and thermosetting resin have good rigidity, but may be partially damaged during battery installation due to stress problems, affecting the overall charge and discharge of the battery. The carbon composite bipolar plates prepared from graphite and thermoplastic resin are prepared by extrusion or molding after blending of resin and conductive filler. The conductivity of such bipolar plates and the contact resistance after installation of the battery are relatively large, limiting the use of the bipolar plates.

[0004] Chinese patent CN117239167A, entitled "Preparation method of vanadium flow battery bipolar plate with long service life", filed on October 13, 2023, and published on December 15, 2023, discloses a preparation method of a vanadium flow battery bipolar plate. A metal oxide precursor material is compounded with graphite material to obtain a metal oxide graphite-based composite material. The metal oxide graphite-based composite material is pretreated before casting to obtain a homogeneous mixture with a uniform solid-liquid ratio. The obtained precast material is subjected to casting forming operation, and the casting sheet obtained by casting forming is subjected to sintering forming operation to obtain a composite bipolar plate. The bipolar plate prepared by the method may have poor mechanical properties and a risk of corrosion of the oxide by vanadium electrolyte.

[0005] Patent CN108023104A, entitled "Bipolar plate for vanadium battery and preparation method thereof", filed on November 3, 2016, and published on May 11, 2018, discloses a preparation method of a bipolar plate using carbon fiber cloth as a skeleton material. A resin layer is sprayed on both sides of the carbon fiber cloth, and a conductive layer is sprayed on the resin layer after curing. Then, hot pressing is performed. The bipolar plate prepared by the method has good conductivity in the direction of the carbon cloth, but the resin layer and the conductive layer fail to form a good path in the direction perpendicular to the carbon cloth, resulting in a large longitudinal resistance of the bipolar plate.

[0006] Patent CN109768296A, application name: a kind of vanadium redox flow battery bipolar plate and preparation process, application date: January 26, 2019, disclosure date: May 17, 2019, discloses a kind of vanadium redox flow battery bipolar plate, including silane coupling agent solution, grid carbon cloth treated with silane coupling agent solution, flexible graphite plate and conductive glue, according to the order of flexible graphite plate, graphite filling type conductive glue, grid carbon cloth, graphite filling type conductive glue, flexible graphite plate, it is prepared by using flat plate vulcanizing machine under vacuum moulding technology heating and pressurizing.The process of the bipolar plate is complex, and the phenomenon of multi-layer separation may occur.

[0007] The bipolar plate needs to have excellent electrical conductivity, certain rigidity, and certain toughness to ensure good wear resistance and durability during battery installation and testing. The testing and use of the flow battery is a long-term problem. Since the surface of the bipolar plate directly contacts vanadium electrolyte, some materials in the bipolar plate are easily reacted with acidic substances or are oxidized by vanadium due to long-term operation. Therefore, the corrosion resistance and oxidation resistance of the material are important technical indicators. SUMMARY

[0008] To solve the problems in the prior art, the present application provides a multi-element composite bipolar plate for a vanadium flow battery and a preparation method thereof. The bipolar plate prepared by the method can be used in a vanadium flow battery for a long time and has sufficient mechanical strength and electrical conductivity.

[0009] The technical scheme of the present application is as follows: The present application discloses a preparation method of a multi-element composite bipolar plate for a vanadium flow battery, comprising the following steps: Step 1, preparation of coated metal microsphere conductive material I: copper powder is placed in 0.1 mol / L dilute sulfuric acid for acid washing and then washed with deionized water until neutral; the coupling agent is diluted with alcohol, then stirred with the copper powder, and carbon black, graphene oxide and antioxidant are added thereto, and the temperature is raised to 60-80℃, and stirred under nitrogen protection for 30-60 min; then thermoplastic resin and toughening agent are mixed and blended in an internal mixer to form a coated metal microsphere conductive material I; Step 2, preparation of metal-coated conductive fiber II: after surface oxidation treatment of carbon fiber cloth, the slurry prepared by mixing the dilute acid washed copper powder with the phenylpropyl emulsion is coated on the surface of the carbon fiber, and vacuum drying is carried out at 60-80℃ for standby use; Step 3, the coated metal microsphere conductive material I is laid in two layers on the mold, and the metal-coated conductive fiber II is embedded in the middle, and a sandwich structure bipolar plate is obtained by hot pressing; Step 4, test the sandwich structure bipolar plate; The mass fraction of the bipolar plate is: The coated metal microsphere conductive material I contains 10-15% of copper powder, 2-3% of coupling agent, 1-2% of antioxidant, 4-5% of toughening agent, 3-5% of graphene oxide, 20-30% of carbon black, and 40-60% of thermoplastic resin; The metal-coated conductive fiber II contains 26-40% of copper powder, 4-8% of styrene-acrylic emulsion, and 52-70% of carbon fiber cloth. The mass ratio of the coated metal microsphere conductive material I to the metal-coated conductive fiber II is 2:1.

[0010] Further, in the preparation method of the multi-element composite bipolar plate for vanadium flow batteries, the thermoplastic resin in step 1 is PP, PE or PVDF, all in the form of powder, and the particle size of the resin is 100-500 mesh; the graphene oxide is in the form of powder, and the particle size of the graphene oxide is 100-500 mesh; the carbon black is multi-angled, and the particle size is 1000-5000 mesh; the toughening agent is POE, EVA or SBS; and the antioxidant is one or more of antioxidant RY-512, antioxidant 145 and antioxidant SL398c.

[0011] Further, in the preparation method of the multi-element composite bipolar plate for vanadium flow batteries, the carbon fiber cloth is degreased by acetone / ethanol / dimethylbenzene for 30-60 min, and then placed in a mixed solution of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 1:1-2:1 for oxidation treatment for 60-120 min; the particle size of the copper powder in the coating slurry is 5000-10000 mesh; the solid content of the styrene-acrylic emulsion is 50%; and the carbon fiber cloth has horizontal and vertical orientation, and a hollow structure between intersections.

[0012] Further, in the preparation method of the multi-element composite bipolar plate for vanadium flow batteries, the coupling agent is one or both of a double-metal coupling agent and a phthalate coupling agent.

[0013] Further, in the preparation method of the multi-element composite bipolar plate for vanadium flow batteries, the temperature for hot pressing in step 3 is 200-240°C, the pressure is 10-20 MPa, and the pressure holding time is 10-20 min.

[0014] Further, in the preparation method of the multi-element composite bipolar plate for vanadium flow batteries, in the coated metal microsphere conductive material I, the multi-angled carbon black and the graphene oxide cooperatively increase the conductive path, the copper powder coating layer isolates the vanadium electrolyte corrosion, and at the same time, the longitudinal conductivity is improved.

[0015] Further, in the preparation method of the multi-element composite bipolar plate for vanadium flow batteries, the metal-coated conductive fiber II coats the surface of the carbon fiber with copper powder, combines the horizontal conductivity of the carbon fiber itself, and significantly enhances the electrical conductivity and mechanical strength of the bipolar plate along the fiber direction.

[0016] Further, the preparation method of the multi-element composite bipolar plate for vanadium flow batteries, in the sandwich structure bipolar plate, the coated metal microsphere conductive material I provides high bulk conductivity and corrosion-resistant coating, and the metal-coated conductive fiber II enhances the transverse conductivity and bending strength, and the two realize the balance of the longitudinal and transverse conductivity of the bipolar plate.

[0017] The bipolar plate prepared by the above method has a tensile strength of ≥46.6 MPa, a bending strength of ≥31.8 MPa, a surface conductivity of ≥150 S / cm, a bulk resistance of ≤15 mΩ·cm², and in a test in a vanadium flow battery, after 100 cycles at a current density of 200 mA / cm², the battery energy efficiency is ≥81.2%, the coulomb efficiency is ≥98.1%, and the capacity retention rate is ≥80.1%.

[0018] The principle of the present application is: The present application selects a thermoplastic resin with good fluidity, which is convenient for mechanical processing; the present application adopts two conductive structure modes, one is to prepare coated metal microsphere conductive material I, which is coated with metal core by conductive filler, and is carried out in the case of isolating oxygen, the metal and the conductive filler are connected by a coupling agent, the metal particles in the middle increase the conductive path, and the present application adopts multi-armed (branched) carbon black, so that the coated metal microsphere conductive material I has more conductive paths and increased conductivity; carbon fiber has good conductivity and mechanical properties in the direction of fiber transmission, but the conductivity in the direction perpendicular to the fiber is poor, the main reason is that there are very few conductive paths in the vertical direction, the second structure mode of the present application is to prepare metal-coated conductive fiber II, which is treated on the surface of carbon fiber to have hydrophilic groups and defects, and the copper powder coated microspheres are attached to the surface of the carbon fiber by the coupling agent, the sandwich formed by the coated metal microsphere conductive material I and the metal-coated conductive fiber II has good conductivity in the horizontal and vertical directions by laminating, and the carbon fiber cloth provides strong bending strength of the bipolar plate.

[0019] The present application has the following advantages and beneficial effects: The present application realizes multi-dimensional breakthrough of the performance of the bipolar plate of the vanadium flow battery through unique composite structure design and material modification technology, which is embodied in the following aspects: 1. The present application solves the problem of poor conductivity of low content conductive filler in thermoplastic resin, the addition of metal particles can increase the electron transmission capacity between the bipolar plates and reduce the bulk resistance of the bipolar plate, the bulk resistance is ≤15 mΩ·cm²; innovatively adopts the synergistic structure of coated metal microsphere conductive material I and metal-coated conductive fiber II, and constructs a three-dimensional conductive network penetrating through the thickness and transverse direction of the bipolar plate.

[0020] 2. Through the dense coating structure of the coated metal microsphere conductive material I and the physical isolation effect of the metal coated conductive fiber II, a double protection system is formed, which is cross-linked with the thermoplastic resin to form a dense shell, which is not easy to be eroded by vanadium sulfate electrolyte. The outer layer of copper powder microsphere graphene oxide / carbon black composite coating effectively blocks the direct contact of metal and vanadium electrolyte. After 100 cycles of test under a current density of 200 mA / cm², the coulombic efficiency is stable at ≥98.1%, and the capacity retention rate is ≥80.1%, which significantly prolongs the service life of the battery.

[0021] 3. The coated metal microsphere conductive material I reduces the bulk resistance of the material and increases the longitudinal (along the thickness direction) conductivity of the material. The addition of metal powder greatly increases the longitudinal conductive path. The metal coated conductive fiber II has good mechanical strength and conductivity. The directional arrangement of the carbon fiber cloth and the synergistic effect of the metal coating layer make the bipolar plate have high strength and high toughness. The tensile strength of the bipolar plate is 46.6-51.9 MPa, and the bending strength is 31.8-36.2 MPa, which is more than 60% higher than that of the pure resin matrix. At the same time, the longitudinal high conductivity of the carbon fiber cloth is maintained, and the industry problem of insufficient transverse conductivity of traditional carbon fiber cloth is solved.

[0022] 4. The present application adopts a continuous molding process of mixing and blending in an internal mixer + flat hot pressing, which has a wide process window, does not require complex equipment or high temperature sintering, and is simple and easy to operate. The raw material source is wide, and it is suitable for large-scale industrial application.

[0023] 5. Compared with the prior art, the present application realizes the synchronous breakthrough of mechanical strength and corrosion resistance while maintaining high electrical conductivity (≥150 S / cm), which provides key material support for long-life vanadium flow battery system. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is the surface morphology diagram of 5000 mesh copper powder coated with carbon black and graphene oxide; Figure 2 It is the SEM diagram of 5000 mesh copper powder coated carbon fiber; Figure 3 It is the SEM diagram of carbon fiber after removing glue and oxidation; Figure 4 It is a schematic diagram of the sandwich structure of the bipolar plate; 1. Coated metal microsphere conductive material I; 2. Metal coated conductive fiber II; 3. Resin and carbon black mixture. DETAILED DESCRIPTION

[0025] The specific embodiments of the present application will be further described in detail in combination with the drawings and examples of the specification. The following examples are used to illustrate the present application, but cannot be used to limit the scope of the present application.

[0026] Example 1

[0027] In this embodiment, the mass fraction of each component of the multi-element composite bipolar plate for vanadium flow battery is as follows: Coated metal microsphere conductive material I: Copper powder 25g (particle size 5000 mesh, mass fraction 10%), coupling agent (bimetallic coupling agent (TPM)) 5g (mass fraction 2%), antioxidant (antioxidant RY-512) 5g (mass fraction 2%), toughening agent POE: 10g (mass fraction 4%), graphene oxide 7.5g (particle size 100 mesh, mass fraction 3%), carbon black 50g (particle size 1000 mesh, mass fraction 20%), thermoplastic resin (polypropylene) 147.5g (particle size 100 mesh, mass fraction 59%).

[0028] Metal-coated conductive fiber II: Copper powder 13g (particle size 5000 mesh, mass fraction 26%), benzene propyl emulsion 4g (solid content 50%, containing 2g active ingredient, mass fraction 4%), carbon fiber cloth 35g (mass fraction 70%).

[0029] The preparation method comprises the following steps: Step 1, preparation of coated metal microsphere conductive material I: 40g of copper powder is washed with 200ml of 0.1mol / L dilute sulfuric acid for 10min, then washed with deionized water to neutral, and then weighed to obtain 38.6g of copper powder. Take out 25g of copper powder and mix with coupling agent 20g (containing 5g of bimetallic coupling agent (TPM)) diluted with ethanol for 20min, then add antioxidant (antioxidant RY-512) 5g, graphene oxide 7.5g and carbon black 50g, heat to 60°C under nitrogen protection, stir for 30min, then take out, put into a banbury mixer with thermoplastic resin (polypropylene) 147.5g and toughening agent (POE) 10g, heat to 240°C, take out after 30min, obtain coated metal microsphere conductive material I.

[0030] The coated metal microsphere conductive material I takes copper powder as the core, one end of the coupling agent reacts with the oxygen-containing functional groups on the surface of the metal and tightly adheres to the surface, and the other end is entangled and bonded with carbon black and graphene oxide. Under the condition of stirring and heating, a coated structure is formed, as shown in Figure 1 The multi-armed carbon black can greatly increase the contact area of the microspheres with the resin, increase the conductive path of the material, and increase the conductivity.

[0031] Step 2: Preparation of metal-coated conductive fiber II: Take 35g of 300mm*300mm carbon fiber cloth, soak the carbon fiber cloth in acetone solution for 60min, then place it in 2.0L concentrated sulfuric acid / concentrated nitric acid solution (1L concentrated sulfuric acid, 1L concentrated nitric acid) and stir for 60min. Wash with water until neutral, take it out and dry at 60℃ for 60min. Take 13g of the treated copper powder and 4g of styrene-acrylic emulsion, place them in a mixer for 10min, and coat the resulting slurry onto the carbon fiber cloth. Place the coated carbon fiber cloth in a vacuum drying oven to dry, and obtain 50g of metal-coated carbon fiber cloth.

[0032] Metal-coated conductive fiber II uses a hollowed-out carbon fiber mesh as a matrix, coated with copper powder to achieve the desired effect. Figure 2 As shown. By Figure 3 It is evident that after degumming and oxidation by strong oxidizing agents such as acids, the surface of conductive carbon fibers is damaged. The treated carbon fibers are more likely to adhere to copper powder, ensuring the formation of a copper powder layer on the carbon fiber surface, which facilitates increasing the contact area between the carbon fibers, resin, and conductive fillers.

[0033] Step 3: Spread 100g of coated metal microsphere conductive material I in two layers in a 1.0mm thick mold, embed metal-coated conductive fiber II in the middle, heat the flat vulcanizing machine to 240℃, press at 10MPa for 10min to obtain a sandwich structure bipolar plate.

[0034] like Figure 4 As shown, the sandwich structure includes coated metal microsphere conductive material I1, metal-coated conductive fiber II2, and resin and carbon black mixture 3. The metal-coated conductive fiber II2 serves as the supporting material, and the transverse and longitudinal mesh structure of the carbon fiber provides it with strong mechanical strength. The resin and conductive particles are tightly bonded to the copper powder-coated carbon fiber mesh, providing the bipolar plate with super conductivity. The coated metal microsphere conductive material I1 prevents the copper powder from contacting the electrolyte. The copper powder-coated carbon fiber and the coated copper powder microspheres provide more conductive channels for the bipolar plate. The resin and carbon black mixture 3 fills the space between the two conductive materials, jointly improving the longitudinal conductivity of the bipolar plate.

[0035] Step 4: Conduct performance tests according to NB / T42007-2013 "Mechanical Performance Test Method for Bipolar Plates of Vanadium Redox Flow Batteries" and the battery test methods of the industry standard for vanadium redox flow batteries.

[0036] Example 2

[0037] In this embodiment, the mass fractions of each component in a multi-element composite bipolar plate for a vanadium redox flow battery are as follows: Coated metal microsphere conductive material I: Copper powder 30g (particle size 10000 mesh, mass fraction 15%), coupling agent (phthalate coupling agent (TTs)) 6g (mass fraction 3%), antioxidant (antioxidant RY-512, antioxidant 145) 4g (mass fraction 2%), toughening agent POE: 10g (mass fraction 5%), graphene oxide 10g (particle size 500 mesh, mass fraction 5%), carbon black 60g (particle size 5000 mesh, mass fraction 30%), thermoplastic resin (polypropylene) 80g (particle size 500 mesh, mass fraction 40%).

[0038] Metal-coated conductive fiber II: Copper powder 28g (particle size 10000 mesh, mass fraction 40%), benzene propyl emulsion 11.2g (solid content 50%, containing 5.6g active ingredient, mass fraction 8%), carbon fiber cloth 36.4g (mass fraction 52%).

[0039] The preparation method comprises the following steps: Step 1, preparation of coated metal microsphere conductive material I: 60g of copper powder is washed with 200ml of 0.1mol / L dilute sulfuric acid for 10min, then washed with deionized water to neutral, and then taken out and weighed to obtain 58.6g of copper powder. 30g of copper powder is mixed with 30g of coupling agent diluted with ethanol (containing 6g of phthalate coupling agent (TTs)) for 20min, then antioxidant (antioxidant RY-512) 4g, graphene oxide 10g and carbon black 60g are added, and the temperature is raised to 80℃ under nitrogen protection, and stirred for 60min, then taken out, and placed in a banbury mixer with thermoplastic resin (polypropylene) 80g and toughening agent (POE) 10g, heated to 240℃, and taken out after 30min, to obtain coated metal microsphere conductive material I.

[0040] Step 2, preparation of metal-coated conductive fiber II: Take 300mm*300mm carbon fiber cloth 35g, put it in dimethylbenzene solution and stir for 30min for degumming treatment, dry, and then put it in concentrated sulfuric acid / concentrated nitric acid solution 2.1L (concentrated sulfuric acid 1.4L, concentrated nitric acid 0.7L) and stir for 120min, then wash with water to neutral, take out and put in an oven at 80℃ and dry for 30min, take the treated copper powder 28g and benzene propyl emulsion 11.2g and put them in a stirrer and stir for 10min, then apply the obtained slurry on the above-mentioned carbon fiber cloth, and put the coated carbon fiber cloth in a vacuum drying oven and dry, to obtain 70g of metal-coated carbon fiber cloth.

[0041] Step 3, 140g of coated metal microsphere conductive material I is laid in two layers on a 1.0mm thick mold, and metal coated conductive fiber II is embedded in the middle. The hot press is heated to 200℃, and hot pressing is performed for 20min with a pressure of 20MPa. A sandwich structure bipolar plate is obtained.

[0042] Step 4, performance testing is performed according to the mechanical property test method of vanadium flow battery bipolar plate in NB / T42007-2013 and the battery test method of vanadium flow battery industry standard.

[0043] Example 3

[0044] In this embodiment, the mass fraction of each component of the multi-element composite bipolar plate for vanadium flow battery is as follows: Coated metal microsphere conductive material I: Copper powder 24g (particle size 8000 mesh, mass fraction 12%), coupling agent (bimetallic coupling agent (TPM)) 5g (mass fraction 2.5%), antioxidant (antioxidant 145) 3g (mass fraction 1.5%), toughening agent POE 10g (mass fraction 5%), graphene oxide 8g (particle size 200 mesh, mass fraction 4%), carbon black 50g (particle size 2000 mesh, mass fraction 25%), thermoplastic resin (polypropylene) 100g (particle size 200 mesh, mass fraction 50%).

[0045] Metal coated conductive fiber II: Copper powder 20.4g (particle size 8000 mesh, mass fraction 34%), benzene propyl emulsion 7.2g (mass fraction 50%, containing effective component 3.6g, mass fraction 6%), carbon fiber cloth 36g (mass fraction 60%).

[0046] The preparation method comprises the following steps: Step 1, preparation of coated metal microsphere conductive material I: 50g of copper powder is washed with 200ml of 0.1mol / L dilute sulfuric acid for 2min, then washed with water to neutralize, and 47.9g of copper powder is obtained. 24g of copper powder is mixed with coupling agent diluted with ethanol 25g (containing 5g of bimetallic coupling agent (TPM)) for 20min, then 3g of antioxidant (antioxidant RY-512), 8g of graphene oxide and 50g of carbon black are added, and the temperature is raised to 80℃ under nitrogen protection. After stirring for 30min, it is taken out and placed in an internal mixer with thermoplastic resin (polypropylene) 100g and toughening agent (POE) 8g for mixing. The temperature is raised to 230℃, and after 30min, the coated metal microsphere conductive material I is obtained.

[0047] Step 2, preparation of metal coated conductive fiber II: Take 36g of 300mm*300mm carbon fiber cloth, put it in an acetone solution for 30min for degumming treatment, dry it, then put it in a concentrated sulfuric acid / concentrated nitric acid 2L (concentrated sulfuric acid 1.0L, concentrated nitric acid 1.0L) solution and stir for 120min, then wash it with water until it is neutral, take it out and put it in an oven at 70°C for 45min, take 20.4g of treated copper powder and 7.2g of phenylpropyl emulsion, put them in a blender and stir for 10min, apply the obtained slurry to the above carbon fiber cloth, dry the coated carbon fiber cloth in a vacuum drying oven, and obtain 60g of metal-coated carbon fiber cloth.

[0048] Step 3, place 120g of coated metal microspheres conductive material I in a 1.0mm thick mold in two layers, embed metal-coated conductive fiber II in the middle, heat the flat vulcanizing machine to 230°C, hot press for 15min, and set the pressure to 15MPa to obtain a sandwich structure bipolar plate.

[0049] Step 4, according to the "Mechanical property test method of vanadium redox flow battery bipolar plate" of NB / T42007-2013 and the battery test method of vanadium redox flow battery industry standard, the performance test is carried out.

[0050] Comparative Example 1 In this comparative example, the mass fraction of each component of a multi-element composite bipolar plate for a vanadium flow battery is as follows: I type conductive polymer formula: copper powder 25g (particle size 8000 mesh, mass fraction 10%), coupling agent (bimetallic coupling agent (TPM)) 5g (mass fraction 2%), antioxidant (antioxidant RY-512) 5.0g (mass fraction 2%), toughening agent POE: 10g (mass fraction 4%), graphene oxide 7.5g (particle size 200 mesh, mass fraction 3%), carbon black 50g (mass fraction 20%), polypropylene 147.5g (particle size 200 mesh, mass fraction 59%).

[0051] II type conductive fiber formula: phenylpropyl emulsion 4g (containing 2g of active ingredient, mass fraction 4%), carbon fiber cloth 35g.

[0052] The preparation method comprises the following steps: Step 1, preparation of I type conductive polymer: 30g copper powder was washed with 200ml of 0.1mol / L dilute sulfuric acid for 10min, then washed with water to neutral, and weighed to obtain 28.8g of copper powder. 25g of copper powder was mixed with 20g of coupling agent diluted with ethanol (containing 5g of coupling agent) for 20min, then 2.5g of antioxidant (antioxidant RY-512), 7.5g of graphene oxide and 60g of carbon black were added, and the mixture was heated to 60℃ under nitrogen protection, stirred for 30min, then taken out, and placed in a mixer with 147.5g of polypropylene and 10g of toughening agent (POE) to be mixed, heated to 230℃, and taken out after 30min to obtain a type I conductive polymer.

[0053] Step 2, preparation of type II conductive fiber: 300mm*300mm carbon fiber cloth 35.1g was soaked in acetone solution for 60min, then stirred in a concentrated sulfuric acid / concentrated nitric acid 2.0L (concentrated sulfuric acid 1L, concentrated nitric acid 1L) solution for 60min, then washed with water to neutral, dried, and 4g of styrene-acrylic emulsion was placed in a blender for 10min, and the obtained slurry was coated on the above-mentioned carbon fiber cloth, and the coated carbon fiber cloth was placed in a vacuum drying oven to dry, obtaining 37g of type II conductive fiber.

[0054] Step 3, 140g of conductive composite material was laid on the upper and lower layers of a 1.0mm thick mold, and carbon fiber cloth was placed in the middle, and the flat vulcanizing machine was heated to 230℃, hot pressed for 10min, and the pressure was set to 15MPa, and after cooling, a bipolar plate product was obtained.

[0055] Step 4, performance test according to the mechanical property test method of vanadium redox flow battery bipolar plate in NB / T42007-2013 and the battery test method of vanadium redox flow battery industry standard.

[0056] Comparative Example 2 In this comparative example, the mass fraction of each component of a bipolar plate for a vanadium redox flow battery is as follows: Copper powder 30g (particle size 8000 mesh, mass fraction 15%), coupling agent (phthalate coupling agent (TTs)) 6g (mass fraction 3%), antioxidant (antioxidant RY-512, antioxidant 145) 4g (mass fraction 2%), toughening agent POE: 10g (mass fraction 5%), graphene oxide 10g (particle size 200 mesh, mass fraction 5%), carbon black 60g (mass fraction 30%), polypropylene 80g (particle size 200 mesh, mass fraction 40%).

[0057] The preparation method comprises the following steps: Step 1, 32g copper powder is washed with 200ml of 0.1mol / L dilute sulfuric acid for 2min, then washed with water to neutral, and 30.8g of copper powder is obtained. 30g of copper powder is mixed with 30g of coupling agent diluted with ethanol (containing 6g of coupling agent) for 20min, then 10g of graphene oxide, 4g of antioxidant and 80g of carbon black are added, and the temperature is raised to 80℃ under nitrogen protection. After stirring for 30min, 80g of polypropylene and 10g of toughening agent are put into the internal mixer for mixing, and the temperature is raised to 240℃. After 60min, the conductive composite material is obtained.

[0058] Step 2, 140g of conductive composite material is laid on the upper and lower layers of a 1.0mm thick mold, and carbon fiber cloth is placed in the middle. The flat plate vulcanizing machine is heated to 230℃, and hot pressing is performed for 20min at a pressure of 15MPa. After cooling, the bipolar plate product is obtained.

[0059] Step 3, the performance test is carried out according to the "Mechanical property test method of bipolar plate for all-vanadium redox flow battery" of NB / T42007-2013 and the battery test method of all-vanadium redox flow battery industry standard.

[0060] Comparative Example 3 In this comparative example, the mass fraction of each component of the bipolar plate for vanadium flow battery is as follows: Graphene oxide 8g (mass fraction 4%), carbon black 70g (mass fraction 35%), coupling agent (bimetallic coupling agent (TPM)) 5g (mass fraction 2.5%), antioxidant (antioxidant RY-512) 3g (mass fraction 1.5%), toughening agent POE: 8g (mass fraction 4%), polypropylene 106g (mass fraction 53%).

[0061] The preparation method comprises the following steps: Step 1, 25g of coupling agent (containing 5g of coupling agent) is mixed with 3g of antioxidant (antioxidant RY-512), 8g of graphene oxide and 70g of carbon black, and the temperature is raised to 80℃ under nitrogen protection. After stirring for 30min, 106g of polypropylene and 8g of toughening agent POE are put into the internal mixer for mixing, and the temperature is raised to 240℃. After 30min, the conductive composite material is obtained.

[0062] Step 2, 140g of conductive composite material is laid on the upper and lower layers of a 1.0mm thick mold, and carbon fiber cloth is placed in the middle. The flat plate vulcanizing machine is heated to 240℃, and hot pressing is performed for 20min at a pressure of 15MPa. After cooling, the bipolar plate product is obtained; Step 3, the performance test is carried out according to the "Mechanical property test method of bipolar plate for all-vanadium redox flow battery" of NB / T42007-2013 and the battery test method of all-vanadium redox flow battery industry standard.

[0063] According to the test standard stipulated by the flow battery industry, the bipolar plates prepared in the above examples and comparative examples were made into 110mm*70mm samples and punched, and Nafion 212 film produced by DuPont Company was used for battery test, and the results are shown in Table 1 below: Table 1 Test results of examples and comparative examples Test item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Thickness (mm) 1.01 0.99 0.99 1.01 0.99 1.00 Tensile strength (MPa) 51.9 46.6 49.6 43.8 27.8 25.6 Flexural strength (MPa) 36.2 31.8 34.6 31.0 26.5 23.6 Electrical conductivity (S / cm) 150 250 200 180 100 90 Bulk resistance (mΩ*cm 2 ) 15 8 10 18 14 30 <![CDATA[200mA / cm 2 After 100 cycles, the battery energy efficiency EE (%) 81.2 82.5 82.3 80.5 78.1 73.2 <![CDATA[200mA / cm 2 After 100 cycles, the battery coulombic efficiency CE (%) 98.2 98.5 98.1 97.6 97.1 97.8 Battery capacity retention rate (%) after 100 cycles at 200 mA / cm2 80.1 83.5 81.6 76.5 72.2 63.5 By comparing example 1 with example 2, the addition amount of copper powder directly affects the conductivity of the bipolar plate, and the addition amount of copper powder in example 2 is larger, and the bulk resistance of the bipolar plate is smaller; comparing example 1 with comparative example 1, the experimental results show that the bulk resistance of the bipolar plate without coating copper powder slurry is obviously larger than that of the bipolar plate with metal ion attached, which shows that the transverse arrangement of carbon fibers hinders the transmission of electrons, and the addition of metal powder can obviously increase the electron transmission path and increase the transmission efficiency; the results of example 2 and comparative example 2 show that the addition of carbon fiber cloth coating makes the tensile strength of the bipolar plate decrease obviously, and the copper powder coated conductive particles can increase the conductive path; the test results of comparative example 3 are that the traditional conductive filler is added to the plastic, and the mechanical properties and conductivity do not reach the standard.

[0064] According to the description and examples of the present application, the above-mentioned embodiments can be changed and modified by the relevant skilled person, and the technical scope of the present application is not limited to the above-mentioned description, and the modifications and changes of the present application also belong to the scope of the present application, and the technical scope must be determined according to the scope of claims.

Claims

1. A method for preparing a multi-element composite bipolar plate for a vanadium redox flow battery, characterized in that, Includes the following steps: Step 1: Preparation of coated metal microsphere conductive material I: Copper powder is acid-washed in 0.1 mol / L very dilute sulfuric acid and then washed with deionized water until neutral; the coupling agent is diluted with alcohol and stirred with copper powder, and carbon black, graphene oxide and antioxidant are added. The mixture is heated to 60-80℃ and stirred for 30-60 min under nitrogen protection; then it is mixed with thermoplastic resin and toughening agent to form coated metal microsphere conductive material I. Step 2: Preparation of metal-coated conductive fiber II: After surface oxidation treatment of carbon fiber cloth, a slurry prepared by dilute acid-washed copper powder and styrene-acrylic emulsion is coated on the surface of carbon fiber and vacuum dried at 60-80℃ for later use. Step 3: The coated metal microsphere conductive material I is laid flat in two layers in the mold, with the metal-coated conductive fiber II embedded in the middle, and the sandwich structure bipolar plate is obtained by hot pressing. Step 4: Test the sandwich structure bipolar plate; The mass fraction of the bipolar plate is: The coated metal microsphere conductive material I contains 10-15% copper powder, 2-3% coupling agent, 1-2% antioxidant, 4-5% toughening agent, 3-5% graphene oxide, 20-30% carbon black, and 40-59% thermoplastic resin; Metal-coated conductive fiber II contains 26-40% copper powder, 4-8% styrene-acrylic emulsion, and 52-70% carbon fiber cloth; Furthermore, the mass ratio of coated metal microsphere conductive material I to metal-coated conductive fiber II is 2:

1.

2. The method for preparing a multi-element composite bipolar plate for a vanadium redox flow battery according to claim 1, characterized in that, The thermoplastic resin mentioned in step 1 is PP, PE, or PVDF, all of which are powder resins with a particle size of 100-500 mesh; the graphene oxide is powdered graphene oxide with a particle size of 100-500 mesh; the carbon black is carbon black with multiple tentacles with a particle size of 1000-5000 mesh; the toughening agent is POE, EVA, or SBS; and the antioxidant is one or more of antioxidant RY-512, antioxidant 145, and antioxidant SL398c.

3. The method for preparing a multi-element composite bipolar plate for a vanadium redox flow battery according to claim 1, characterized in that, Step 2: After degumming the carbon fiber cloth with acetone / ethanol / xylene for 30-60 minutes, it is placed in a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 1:1-2:1 for 60-120 minutes for oxidation treatment; the copper powder in the coating slurry has a particle size of 5000-10000 mesh; the solid content of the styrene-acrylic emulsion is 50%; the carbon fiber cloth has a transverse and longitudinal orientation, and the intersections are hollow structures.

4. The method for preparing a multi-element composite bipolar plate for a vanadium redox flow battery according to claim 1, characterized in that, The coupling agent is one or both of bimetallic coupling agents and phthalate coupling agents.

5. The method for preparing a multi-element composite bipolar plate for a vanadium redox flow battery according to claim 1, characterized in that, The hot pressing temperature in step 3 is 200-240℃, the pressure is 10-20MPa, and the holding time is 10-20 minutes.

6. The method for preparing a multi-element composite bipolar plate for a vanadium redox flow battery according to claim 1, characterized in that, In the coated metal microsphere conductive material I, multi-tentacle carbon black and graphene oxide work together to increase the conductive pathway, while the copper powder coating layer isolates the vanadium electrolyte corrosion and improves the longitudinal conductivity.

7. The method for preparing a multi-element composite bipolar plate for a vanadium redox flow battery according to claim 1, characterized in that, The metal-coated conductive fiber II significantly enhances the conductivity and mechanical strength of the bipolar plate along the fiber direction by coating the surface of the carbon fiber with copper powder and combining it with the lateral conductivity of the carbon fiber itself.

8. The method for preparing a multi-element composite bipolar plate for a vanadium redox flow battery according to claim 1, characterized in that, In the sandwich structure bipolar plate, coated metal microsphere conductive material I provides high bulk conductivity and corrosion-resistant coating, while metal-coated conductive fiber II enhances lateral conductivity and bending strength. The two work together to achieve a balance between longitudinal and lateral conductivity of the bipolar plate.

9. The bipolar plate prepared by the method according to any one of claims 1-8, characterized in that, In tests conducted on vanadium redox flow batteries, after 100 cycles at a current density of 200 mA / cm², the tensile strength was ≥46.6 MPa, the flexural strength was ≥31.8 MPa, the surface conductivity was ≥150 S / cm, the bulk resistance was ≤15 mΩ·cm², the battery energy efficiency was ≥81.2%, the coulombic efficiency was ≥98.1%, and the capacity retention was ≥80.1%.

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