A multi-element composite bipolar plate for vanadium flow batteries and a method of manufacturing the same

Abstract

The application belongs to the field of vanadium flow battery, and particularly relates to a kind of multi-element composite bipolar plate for vanadium flow battery and its preparation method.The method comprises preparing coated metal microsphere conductive material I, preparing metal-coated conductive fiber II, and laying the coated metal microsphere conductive material I in two layers in the mold, embedding the metal-coated conductive fiber II in the middle, and obtaining a sandwich structure bipolar plate by hot pressing.The dense coated metal microsphere structure increases the conductive path in the bipolar plate, reduces the bulk resistance, the coating layer avoids direct contact between the metal and the vanadium electrolyte, reduces the corrosion effect of the electrolyte, the metal-coated conductive fiber structure increases the longitudinal conductivity of the bipolar plate, and the carbon fiber increases the mechanical strength and 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:

[0010] The present application discloses a preparation method of a multi-element composite bipolar plate for a vanadium flow battery, comprising the following steps:

[0011] 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 to form the coated metal microsphere conductive material I;

[0012] 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 benzene propyl emulsion is coated on the surface of the carbon fiber, and vacuum drying is carried out at 60-80℃ for standby use;

[0013] 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;

[0014] Step 4, test the sandwich structure bipolar plate;

[0015] The mass fraction of the bipolar plate is:

[0016] The copper powder content in the coated metal microsphere conductive material I is 10-15%, the coupling agent content is 2-3%, the antioxidant content is 1-2%, the toughening agent content is 4-5%, the graphene oxide content is 3-5%, the carbon black content is 20-30%, and the thermoplastic resin content is 40-60%.

[0017] The copper powder content in the metal-coated conductive fiber II is 26-40%, the styrene-acrylic emulsion content is 4-8%, and the carbon fiber cloth content is 52-70%.

[0018] The mass ratio of the coated metal microsphere conductive material I to the metal-coated conductive fiber II is 2:1.

[0019] Further, in the above method for preparing a multi-element composite bipolar plate for a vanadium flow battery, the thermoplastic resin in step 1 is PP, PE, or PVDF, all in powder form, and the particle size of the resin is 100-500 mesh; the graphene oxide is in powder form, and the particle size of the graphene oxide is 100-500 mesh; the carbon black is a multi-angled carbon black 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.

[0020] Further, in the above method for preparing a multi-element composite bipolar plate for a vanadium flow battery, the carbon fiber cloth in step 2 is degreased with acetone / ethanol / dimethylbenzene for 30-60 minutes, then placed in a mixed solution of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 1:1 to 2:1 for oxidation treatment for 60-120 minutes; 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 the intersection points.

[0021] Further, in the above method for preparing a multi-element composite bipolar plate for a vanadium flow battery, the coupling agent is one or both of a double-metal coupling agent and a phthalate coupling agent.

[0022] Further, in the above method for preparing a multi-element composite bipolar plate for a vanadium flow battery, 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 minutes.

[0023] Further, in the above method for preparing a multi-element composite bipolar plate for a vanadium flow battery, in the coated metal microsphere conductive material I, the multi-angled carbon black and the graphene oxide work together to increase the conductive path, the copper powder coating layer isolates the vanadium electrolyte corrosion, and at the same time, the longitudinal conductivity is improved.

[0024] Further, the preparation method of the multi-element composite bipolar plate for the vanadium flow battery, the metal-coated conductive fiber II significantly enhances the electrical conductivity and mechanical strength of the bipolar plate in the fiber direction by coating the surface of the carbon fiber with copper powder and combining the transverse conductivity of the carbon fiber itself.

[0025] Further, the preparation method of the multi-element composite bipolar plate for the vanadium flow battery, in the sandwich structure bipolar plate, the coated metal microsphere conductive material I provides high bulk electrical conductivity and corrosion-resistant coating, and the metal-coated conductive fiber II enhances the transverse conductivity and bending strength, and both of them cooperate to realize the balance of the longitudinal and transverse conductivity of the bipolar plate.

[0026] 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 electrical conductivity of ≥150 S / cm, and a bulk resistance of ≤15 mΩ·cm². In a test in a vanadium flow battery, after 100 cycles at a current density of 200 mA / cm², the battery has an energy efficiency of ≥81.2%, a coulomb efficiency of ≥98.1%, and a capacity retention rate of ≥80.1%.

[0027] The principle of the present application is:

[0028] 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 a coated metal microsphere conductive material I, which coats the metal core with conductive fillers and is carried out in an oxygen-free environment. The metal and the conductive filler are connected by a coupling agent. The metal particles in the middle increase the conductive path. The present application uses a multi-branched (branched) carbon black, so that the coated metal microsphere conductive material I has more conductive paths and the conductivity is increased. The carbon fiber has good conductivity and mechanical properties in the fiber transmission direction, 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 a metal-coated conductive fiber II. The carbon fiber surface is treated to have hydrophilic groups and defects. 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 vertical and horizontal directions by laminating. The carbon fiber cloth provides strong bending strength of the bipolar plate.

[0029] The present application has the following advantages and benefits:

[0030] 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:

[0031] 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 transport capacity between bipolar plates and reduce the bulk resistance of bipolar plates, the bulk resistance is ≤15mΩ·cm²; innovatively adopt the synergistic structure of coated metal microsphere conductive material I and metal coated conductive fiber II, and construct a three-dimensional conductive network penetrating through the thickness and lateral direction of the bipolar plate.

[0032] 2.Through the dense coating structure of coated metal microsphere conductive material I and the physical isolation effect of metal coated conductive fiber II, a double protection system is formed, which is crosslinked with thermoplastic resin to form a dense shell and is not easy to be eroded by vanadium sulfate electrolyte. The graphene oxide / carbon black composite coating layer on the outer layer of copper powder microspheres effectively blocks the direct contact between metal and vanadium electrolyte. After 100 cycles under a current density of 200mA / 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.

[0033] 3.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. Metal coated conductive fiber II has good mechanical strength and conductivity. The synergistic effect of the directional arrangement of carbon fiber cloth and the metal coating layer makes 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 pure resin matrix, while maintaining the high longitudinal conductivity of carbon fiber cloth, solving the industry problem of insufficient lateral conductivity of traditional carbon fiber cloth.

[0034] 4.The present application adopts continuous molding process of mixing and blending in internal mixer + flat hot pressing, the process window is wide, no complex equipment or high temperature sintering is needed, the process is simple and easy to operate, the raw material sources are wide, and it is suitable for large-scale industrial application.

[0035] 5.Compared with the prior art, the present application realizes the synchronous breakthrough of mechanical strength and corrosion resistance while maintaining high electrical conductivity (≥150S / cm), which provides key material support for long-life vanadium flow battery system. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is the surface morphology diagram of 5000 mesh copper powder coated with carbon black and graphene oxide;

[0037] Figure 2 It is the SEM diagram of 5000 mesh copper powder coated carbon fiber;

[0038] Figure 3 It is the SEM diagram of carbon fiber after removing glue and oxidation;

[0039] Figure 4 A schematic view of a bipolar plate of a sandwich structure;

[0040] 1-coated metal microsphere conductive material I; 2-metal coated conductive fiber II; 3-resin and carbon black mixture. DETAILED DESCRIPTION

[0041] The specific embodiments of the present application will be further described in conjunction 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.

[0042] Example 1

[0043] In this embodiment, the mass fraction of each component of the multi-element composite bipolar plate for vanadium flow battery is as follows:

[0044] Coated metal microsphere conductive material I:

[0045] 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%).

[0046] Metal coated conductive fiber II:

[0047] 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%).

[0048] The preparation method comprises the following steps:

[0049] Step 1, preparation of coated metal microsphere conductive material I: 40g copper powder is washed with 0.1mol / L dilute sulfuric acid 200ml for 10min, then washed with deionized water to neutral, and then weighed to get 38.6g copper powder. Take out 25g copper powder and mix with coupling agent 20g (containing 5g 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℃ under nitrogen protection, stir for 30min, then take out, put into the mixing machine with thermoplastic resin (polypropylene) 147.5g and toughening agent (POE) 10g, heat to 240℃, take out after 30min, get coated metal microsphere conductive material I.

[0050] The coated metal microsphere conductive material I is prepared by using copper powder as the core, coupling agent tightly adhering to the surface of the metal through reaction with the oxygen-containing functional groups on the surface, and the other end of the coupling agent being 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-angled carbon black can greatly increase the contact area of the microspheres and the resin, increase the conductive path of the material, and increase the conductivity.

[0051] Step 2, preparation of metal-coated conductive fiber II: take 300mm*300mm carbon fiber cloth 35g, soak the carbon fiber cloth in acetone solution for 60min, then put it in concentrated sulfuric acid / concentrated nitric acid 2.0L (concentrated sulfuric acid 1L, concentrated nitric acid 1L) solution and stir for 60min, then wash with water until neutral, take out and dry at 60℃ for 60min, take the treated copper powder 13g and phenylpropyl emulsion 4g, put them in a blender for 10min, apply the obtained slurry on the above-mentioned carbon fiber cloth, and put the coated carbon fiber cloth in a vacuum drying oven for drying, to obtain 50g of metal-coated carbon fiber cloth.

[0052] The metal-coated conductive fiber II is prepared by using a hollowed-out carbon fiber mesh as the substrate and coating copper powder on the surface, as shown in Figure 2 It can be seen from Figure 3 that the conductive carbon fiber is damaged after degumming and strong oxidizing agent oxidation, and the treated carbon fiber is more easily attached to the copper powder, which ensures the formation of a copper powder layer on the surface of the carbon fiber and facilitates the increase of the contact area of the carbon fiber and the resin and the conductive filler.

[0053] Step 3, 100g 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 temperature of the flat vulcanizing machine is raised to 240℃, the pressure is 10MPa, and the hot pressing time is 10min, to obtain a sandwich structure bipolar plate.

[0054] As shown in Figure 4 , the sandwich structure includes coated metal microsphere conductive material I 1, metal-coated conductive fiber II 2 and resin and carbon black mixture 3. The metal-coated conductive fiber II 2 is used as the supporting material, the horizontal and vertical grid structure of the carbon fiber provides strong mechanical strength, the resin and conductive particles are tightly bonded on the carbon fiber mesh coated with copper powder, providing super strong conductive capacity for the bipolar plate, the coated metal microsphere conductive material I 1 avoids the contact of copper powder with electrolyte, the carbon fiber coated with copper powder and the coated copper powder microspheres provide more conductive channels for the bipolar plate, and the resin and carbon black mixture 3 fills between the two conductive substances, which together improves the longitudinal conductivity of the bipolar plate.

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

[0056] Example 2

[0057] In this embodiment, the mass fraction of each component of the multi-element composite bipolar plate for vanadium flow battery is as follows:

[0058] Coated metal microsphere conductive material I:

[0059] 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%).

[0060] Metal-coated conductive fiber II:

[0061] 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%).

[0062] The preparation method comprises the following steps:

[0063] 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 weighed to obtain 58.6g of copper powder. Take out 30g of copper powder and mix with coupling agent 30g (containing 6g of phthalate coupling agent (TTs)) diluted with ethanol for 20min, then add antioxidant (antioxidant RY-512) 4g, graphene oxide 10g and carbon black 60g, and heat to 80℃ under nitrogen protection, stir for 60min, then take out, and put into a mixing machine with thermoplastic resin (polypropylene) 80g and toughening agent (POE) 10g, heat to 240℃, take out after 30min, obtain coated metal microsphere conductive material I.

[0064] Step 2, preparation of metal-coated conductive fiber II:

[0065] Take 300mm*300mm carbon fiber cloth 35g, put it in dimethylbenzene solution and stir for 30min for degumming treatment, dry it, 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 it to neutral, take it out and put it in an oven at 80℃ for 30min, take the treated copper powder 28g and put it in a blender with phenylpropyl emulsion 11.2g and stir for 10min, apply the obtained slurry on the above-mentioned carbon fiber cloth, put the coated carbon fiber cloth in a vacuum drying oven and dry it, and get 70g metal-coated carbon fiber cloth.

[0066] Step 3, lay 140g coated metal microsphere conductive material I in 1.0mm thick mold in two layers, embed metal-coated conductive fiber II in the middle, heat the flat vulcanizing machine to 200℃, hot press for 20min, set the pressure to 20MPa, and get sandwich structure bipolar plate.

[0067] Step 4, test the performance 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.

[0068] Example 3

[0069] In this embodiment, the mass fraction of each component of the multi-element composite bipolar plate for vanadium flow battery is as follows:

[0070] Coated metal microsphere conductive material I:

[0071] 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%).

[0072] Metal-coated conductive fiber II:

[0073] Copper powder 20.4g (particle size 8000 mesh, mass fraction 34%), phenylpropyl emulsion 7.2g (mass fraction 50%, containing effective ingredient 3.6g, mass fraction 6%), carbon fiber cloth 36g (mass fraction 60%).

[0074] The preparation method comprises the following steps:

[0075] Step 1, preparation of coated metal microsphere conductive material I: 50 g of copper powder was washed with 200 ml of 0.1 mol / L dilute sulfuric acid for 2 min, then washed with water to neutral, and 47.9 g of copper powder was obtained. 24 g of copper powder was mixed with 25 g of coupling agent diluted with ethanol (containing 5 g of bimetallic coupling agent (TPM)) for 20 min, then 3 g of antioxidant (antioxidant RY-512), 8 g of graphene oxide and 50 g of carbon black were added, and the temperature was raised to 80°C under nitrogen protection. After stirring for 30 min, it was taken out and placed in an internal mixer with 100 g of thermoplastic resin (polypropylene) and 8 g of toughening agent (POE) to perform internal mixing. The temperature was raised to 230°C, and after 30 min, the coated metal microsphere conductive material I was obtained.

[0076] Step 2, preparation of metal-coated conductive fiber II:

[0077] Take 36 g of 300 mm * 300 mm carbon fiber cloth, soak in acetone solution for 30 min for degreasing treatment, dry, then place in concentrated sulfuric acid / concentrated nitric acid 2L (concentrated sulfuric acid 1.0L, concentrated nitric acid 1.0L) solution and stir for 120 min, then wash with water to neutral, take out and place in an oven at 70°C for 45 min. Dry, take 20.4 g of treated copper powder and 7.2 g of styrene-acrylic emulsion, place in a stirrer and stir for 10 min, apply the obtained slurry to the above carbon fiber cloth, and place the coated carbon fiber cloth in a vacuum drying oven to dry, obtaining 60 g of metal-coated carbon fiber cloth.

[0078] Step 3, 120 g of coated metal microsphere conductive material I was placed in a 1.0 mm thick mold in two layers, with metal-coated conductive fiber II embedded in the middle, and the temperature of the flat vulcanizing machine was raised to 230°C. Hot pressing for 15 min at a pressure of 15 MPa to obtain a sandwich structure bipolar plate.

[0079] Step 4, performance test 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.

[0080] Comparative Example 1

[0081] In this comparative example, the mass fraction of each component of the multi-element composite bipolar plate for vanadium flow battery is as follows:

[0082] Type I 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%).

[0083] Type II conductive fiber formula: styrene-acrylic emulsion 4g (containing 2g active ingredient, mass fraction 4%), carbon fiber cloth 35g.

[0084] The preparation method comprises the following steps:

[0085] Step 1, preparation of type I conductive polymer:

[0086] After washing 30g of copper powder with 200ml of 0.1mol / L dilute sulfuric acid for 10min, and then washing with water to neutral, 28.8g of copper powder was obtained. 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 temperature was raised to 60℃ under nitrogen protection. After stirring for 30min, it was taken out and placed in an internal mixer with 147.5g of polypropylene and 10g of toughening agent (POE) to perform internal mixing. The temperature was raised to 230℃, and after 30min, type I conductive polymer was obtained.

[0087] Step 2, preparation of type II conductive fiber:

[0088] Take 300mm*300mm carbon fiber cloth 35.1g, soak in acetone solution for 60min, then place in concentrated sulfuric acid / concentrated nitric acid 2.0L (concentrated sulfuric acid 1L, concentrated nitric acid 1L) solution and stir for 60min, then wash with water to neutral, take out and dry. Put the styrene-acrylic emulsion 4g in a blender for 10min, apply the obtained slurry on the above carbon fiber cloth, and place the coated carbon fiber cloth in a vacuum drying oven to dry, obtaining 37g of type II conductive fiber.

[0089] Step 3, take 140g of conductive composite and lay it on the upper and lower layers of a 1.0mm thick mold, and place the carbon fiber cloth in the middle. The temperature of the flat vulcanizing machine is raised to 230℃, and hot pressing is carried out for 10min with a pressure of 15MPa. After cooling, the bipolar plate product is obtained.

[0090] Step 4, performance test 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.

[0091] Comparative Example 2

[0092] In the present comparative example, the mass fraction of each component of the bipolar plate for a vanadium flow battery is as follows:

[0093] Copper powder 30 g (particle size 8000 mesh, mass fraction 15%), coupling agent (phthalate coupling agent (TTs)) 6 g (mass fraction 3%), antioxidant (antioxidant RY-512, antioxidant 145) 4 g (mass fraction 2%), toughening agent POE: 10 g (mass fraction 5%), graphene oxide 10 g (particle size 200 mesh, mass fraction 5%), carbon black 60 g (mass fraction 30%), polypropylene 80 g (particle size 200 mesh, mass fraction 40%).

[0094] The preparation method comprises the following steps:

[0095] Step 1, 32 g of copper powder is washed with 200 ml of 0.1 mol / L dilute sulfuric acid for 2 min, then washed with water to neutralize, and 30.8 g of copper powder is obtained. 30 g of copper powder is mixed with 30 g of coupling agent diluted with ethanol (containing 6 g of coupling agent) for 20 min, then 10 g of graphene oxide, 4 g of antioxidant and 80 g of carbon black are added, and the temperature is raised to 80°C under nitrogen protection. Stir for 30 min, then take out, put into the mixing mill with 80 g of polypropylene and 10 g of toughening agent, heat to 240°C, and take out after 60 min to obtain the conductive composite material.

[0096] Step 2, 140 g of conductive composite material is laid on the upper and lower layers of a 1.0 mm thick mold, and carbon fiber cloth is placed in the middle. The flat vulcanizing machine is heated to 230°C, and hot pressing is performed for 20 min with a pressure setting of 15 MPa. After cooling, the bipolar plate product is obtained.

[0097] Step 3, performance testing 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 the all-vanadium redox flow battery industry standard.

[0098] Comparative Example 3

[0099] In the present comparative example, the mass fraction of each component of the bipolar plate for a vanadium flow battery is as follows:

[0100] Graphene oxide 8 g (mass fraction 4%), carbon black 70 g (mass fraction 35%), coupling agent (bimetallic coupling agent (TPM)) 5 g (mass fraction 2.5%), antioxidant (antioxidant RY-512) 3 g (mass fraction 1.5%), toughening agent POE: 8 g (mass fraction 4%), polypropylene 106 g (mass fraction 53%).

[0101] The preparation method comprises the following steps:

[0102] Step 1, coupling agent 25g (containing 5g coupling agent) and antioxidant (antioxidant RY-512) 3g, graphene oxide 8g, carbon black 70g, nitrogen protection, heated to 80℃, stirred for 30min, then put into the internal mixer with polypropylene 106g and toughening agent POE 8g, heated to 240℃, 30min, then take out, get conductive composite material.

[0103] Step 2, take 140g conductive composite material and lay it on the 1.0mm thick mold, put carbon fiber cloth in the middle, heat the flat vulcanizing machine to 240℃, hot press for 20min, the pressure is set at 15MPa, after cooling, the bipolar plate product is obtained;

[0104] Step 3, according to the mechanical property test method of bipolar plate of all-vanadium redox flow battery in NB / T42007-2013 and the battery test method of all-vanadium redox flow battery industry standard, the performance test is carried out.

[0105] According to the test standard stipulated by the flow battery industry, the bipolar plates prepared in the above examples and comparative examples are made into 110mm*70mm samples, and are punched, and the Nafion212 film produced by Dupont Company is used for battery test, and the results are shown in the following table 1:

[0106] Table 1 detection results of examples and comparative examples

[0107] 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

[0108] 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, it can be seen that the transverse arrangement of carbon fiber 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 tensile strength of the bipolar plate without adding carbon fiber cloth coating is obviously reduced, 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.

[0109] According to the description and examples of the present application, the above-mentioned embodiments can be changed and modified by the related technical personnel, and the technical scope of the present application is not limited to the above-mentioned description, and the modification and change of the present application also belongs 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 flow battery, characterized by, It comprises the following steps: Step 1, preparation of coated metal microsphere conductive material I: copper powder is placed in 0.1 mol / L extremely 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 hot plastic 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 acid-washed copper powder with the styrene-acrylic emulsion is coated on the surface of the carbon fiber, and vacuum drying is carried out at 60-80℃, ready for 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; The temperature of the hot pressing is 200-240℃, the pressure is 10-20 MPa, and the pressure holding time is 10-20 minutes; In the coated metal microsphere conductive material I, the multi-armed carbon black and the graphene oxide synergistically increase the conductive path, and the copper powder coating layer isolates the vanadium electrolyte corrosion, while improving the longitudinal conductivity; The metal-coated conductive fiber II coats the surface of the carbon fiber with copper powder, and significantly enhances the electrical conductivity and mechanical strength of the bipolar plate along the fiber direction by combining the transverse conductivity of the carbon fiber itself; In the sandwich structure bipolar plate, the coated metal microsphere conductive material I provides high bulk conductivity and corrosion-resistant coating, the metal-coated conductive fiber II enhances the transverse conductivity and bending strength, and the two synergistically achieve balanced longitudinal and transverse conductivity of the bipolar plate; Step 4, test the sandwich structure bipolar plate; In the test in the vanadium flow battery, after 100 cycles at a current density of 200 mA / cm², the tensile strength is ≥46.6 MPa, the bending strength is ≥31.8 MPa, the surface conductivity is ≥150 S / cm, the bulk resistance is ≤15 mΩ·cm², the battery energy efficiency is ≥81.2%, the coulomb efficiency is ≥98.1%, and the capacity retention rate is ≥80.1%; The mass fraction of the bipolar plate is: In the coated metal microsphere conductive material I, the copper powder is 10-15%, the coupling agent is 2-3%, the antioxidant is 1-2%, the toughening agent is 4-5%, the graphene oxide is 3-5%, the carbon black is 20-30%, and the thermoplastic resin is 40-59%; In the metal-coated conductive fiber II, the copper powder is 26-40%, the styrene-acrylic emulsion is 4-8%, and the carbon fiber cloth is 52-70%; And the mass ratio of the coated metal microsphere conductive material I to the metal-coated conductive fiber II is 2:

1.

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

3. The method of claim 1, wherein the method further comprises: In step 2, the carbon fiber cloth is degummed by acetone / ethanol / xylene for 30-60 min, and then is placed in a mixed solution of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 1:1-2:1 for oxidation treatment for 60-120 min; the particle size of the copper powder coated with the slurry is 5000-10000 mesh; the solid content of the styrene-acrylic emulsion is 50%; the carbon fiber cloth has horizontal and vertical orientation, and a hollow structure between the intersection points.

4. The method of claim 1, wherein the method further comprises: The coupling agent is one or both of a double metal coupling agent and a phthalate coupling agent.

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