Bipolar plate, preparation method and flow battery

Abstract

The invention relates to a bipolar plate, a preparation method and a flow battery, and relates to the technical field of flow batteries, and the preparation method comprises the following steps: (1) putting chopped graphite fibers and conductive particles into water, adding a dispersant for stirring and dispersing, then adding polyvinyl alcohol as a binder to prepare a mixed slurry, pouring the mixed slurry into wet forming equipment for suction filtration forming to obtain a mixed fiber net; (2) melting and mixing polypropylene and conductive particles in a mixing mill to obtain conductive plastic, and pressing the conductive plastic in a press to obtain a conductive film; and (3) alternately laminating the mixed fiber webs obtained in the step (1) and the step (2) and the conductive thin film, and then putting the laminated fiber webs and the conductive thin film into a press for compression molding to obtain the finished bipolar plate. The electrolyte has the advantage of relatively good conductivity when being applied to the flow battery.

Description

Technical Field

[0001] The present application relates to the technical field of flow batteries, and in particular to a bipolar plate, a preparation method and a flow battery. Background Art

[0002] With the increasing depletion of fossil energy and the continuous growth of energy demand, the development and application of new energy have become an inevitable trend. New energy sources such as photovoltaics and wind energy are highly intermittent and volatile, which will affect the stability of the traditional power grid when connected to the grid. Therefore, it is necessary to develop large-scale energy storage systems. Flow batteries have the advantages of high safety and high cycle life, and are an ideal large-scale energy storage technology. The main components of a flow battery include electrolyte, bipolar plate, electrode, ion membrane, etc. Among them, the bipolar plate plays roles such as separating and connecting batteries in series, conducting current, and providing structural support for the stack. Therefore, the bipolar plate needs to have high electrical conductivity, mechanical strength, airtightness, and corrosion resistance, etc.

[0003] Currently, bipolar plates are mainly divided into three categories: metal plates, graphite plates, and composite plates. Metal plates have good electrical conductivity and strength, but poor corrosion resistance. Graphite plates have excellent electrical conductivity and corrosion resistance, but are complex to process and have high material costs, unable to meet the requirements for large-scale application of flow batteries. Composite plates are a type of bipolar plate prepared with conductive carbon materials as the main body and resin as the binder. Their structure and properties are designable, and they are a type of bipolar plate that can meet the requirements for large-scale application of flow batteries. Currently, the electrical conductivity of composite plates is poor. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, one of the purposes of the present application is to provide a bipolar plate, a preparation method and a flow battery, which have the advantage of good electrical conductivity when applied to a flow battery.

[0005] The above object of the present application is achieved through the following technical solutions:

[0006] A preparation method of a bipolar plate includes the following steps:

[0007] (1) Put short-cut graphite fibers and conductive particles into water, add a dispersant and stir to disperse, then add polyvinyl alcohol as a binder to prepare a mixed slurry, and then pour the mixed slurry into a wet forming device for suction filtration forming to obtain a mixed fiber web;

[0008] (2) Put polypropylene and conductive particles into a mixer for melt mixing to obtain a conductive plastic, and then put it into a press to press into a conductive film;

[0009] (3) Alternately laminate the mixed fiber web and the conductive film obtained in step (1) and step (2), and then put it into a press for compression molding to obtain a finished bipolar plate.

[0010] In a preferred embodiment, the present application can be further configured as follows: the chopped graphite fibers are selected from one of polyacrylonitrile-based, pitch-based, and viscose-based fibers, with a length of 5-15 mm and a diameter of 5-7 μm; the dispersant is selected from one of polyethylene oxide, polyacrylamide, and sodium carboxymethyl cellulose; and the areal density of the mixed fiber web is 200-400 g / cm 3 .

[0011] In a preferred embodiment, the present application can be further configured as follows: the conductive particles include, but are not limited to, graphite powder, graphene powder, carbon nanotubes, and conductive carbon black.

[0012] In a preferred embodiment, the present application can be further configured as follows: the melt blending temperature is 180-220 °C.

[0013] In a preferred embodiment, the present application can be further configured as follows: in step (2), the pressing process includes two stages of hot pressing and cold pressing. The hot pressing temperature is 180-220 °C, the pressure is 6-10 MPa, the hot pressing time is 8-12 min, the cold pressing cooling method is water cooling, the pressure is 6-10 MPa, the cold pressing time is 6-15 min, and the thickness of the conductive film is 0.1-0.3 mm.

[0014] In a preferred embodiment, the present application can be further configured as follows: in step (3), the stacking method is that the topmost and bottommost layers are conductive films, and the middle layers are alternating stacks of conductive films and fiber webs. The in-plane dimensions of the mixed fiber web and the conductive film are the same, that is, the length and width are the same.

[0015] In a preferred embodiment, the present application can be further configured as follows: the pressing process in step (3) includes two stages of hot pressing and cold pressing. First, hot pressing is performed to soften and flow the film, allowing it to fully penetrate the mixed fiber web, and then cold pressing is performed to harden and form the film, and bond the mixed fiber web and the conductive particles together. The hot pressing temperature is 180-220 °C, the pressure is 8-12 MPa, the hot pressing time is 8-12 min, the cold pressing cooling method is water cooling, the pressure is 8-12 MPa, and the cold pressing time is 6-15 min.

[0016] The present application also discloses a bipolar plate: which is prepared by the above-mentioned preparation method of a bipolar plate.

[0017] In a preferred embodiment, the present application can be further configured as follows: the thickness of the finished bipolar plate is 0.6-2 mm.

[0018] The present application also discloses a flow battery, which uses the above-mentioned bipolar plate.

[0019] The present application has the following advantages

[0020] (1) The bipolar plate has a regular graphite fiber network structure inside, with many electron transport channels, and the bipolar plate has good electrical conductivity.

[0021] (2) The overall structure of the bipolar plate is strengthened by the graphite fiber mesh, and the bipolar plate has high mechanical strength.

[0022] (3) The method for preparing a bipolar plate by wet forming of chopped graphite fibers in the present invention is simple in operation, convenient for industrial production, and is conducive to the batch preparation and application of high-performance and low-cost bipolar plates for flow batteries. Description of the Drawings

[0023] Figure 1 is the preparation flow chart of the bipolar plate of this application. Detailed Embodiments

[0024] The following further describes this application in detail with reference to the drawings. It should be noted that the order of steps in this application is only for convenience of description and can be changed according to needs.

[0025] Refer to Figure 1 , a method for preparing a bipolar plate disclosed in this application, includes the following steps

[0026] (1) Put chopped graphite fibers and conductive particles into water, add a dispersant and stir to disperse, then add polyvinyl alcohol as a binder to prepare a mixed slurry, and then pour the mixed slurry into a wet forming device for suction filtration forming to obtain a mixed fiber mesh;

[0027] (2) Put polypropylene and conductive particles into a mixer for melt mixing, and the melt mixing temperature is 180 - 220 °C to obtain a conductive plastic, and then put it into a press to press into a conductive film;

[0028] (3) Alternately stack the mixed fiber mesh and the conductive film obtained in step (1) and step (2), and then put them into a press for pressing and forming to obtain a finished bipolar plate.

[0029] The chopped graphite fibers are selected from one of polyacrylonitrile-based, pitch-based, and viscose-based fibers, with a length of 5 - 15 mm and a diameter of 5 - 7 μm. The dispersant is selected from one of polyethylene oxide, polyacrylamide, and sodium carboxymethyl cellulose. The areal density of the mixed fiber mesh is 200 - 400 g / cm 3 .

[0030] The conductive particles include but are not limited to graphite powder, graphene powder, carbon nanotubes, and conductive carbon black.

[0031] In step (2), the pressing process includes two stages: hot pressing and cold pressing. The hot pressing temperature is 180 - 220°C, the pressure is 6 - 10 MPa, the hot pressing time is 8 - 12 min. The cold pressing cooling method is water cooling, the pressure is 6 - 10 MPa, and the cold pressing time is 6 - 15 min. The thickness of the conductive film is 0.1 - 0.3 mm.

[0032] In step (3), the stacking method is that the topmost and bottommost layers are conductive films, and the middle layers are alternating laminations of conductive films and fiber meshes. The in-plane dimensions of the hybrid fiber mesh and the conductive film are the same, that is, the length and width are the same.

[0033] The pressing process in step (3) includes two stages: hot pressing and cold pressing. First, hot pressing is carried out to soften and flow the film, so that it fully penetrates into the hybrid fiber mesh, and then cold pressing is carried out to harden and form the film, and bond the hybrid fiber mesh and the conductive particles together; the hot pressing temperature is 180 - 220°C, the pressure is 8 - 12 MPa, the hot pressing time is 8 - 12 min, the cold pressing cooling method is water cooling, the pressure is 8 - 12 MPa, and the cold pressing time is 6 - 15 min.

[0034] The following is a further description in combination with embodiments.

[0035] Embodiment 1

[0036] (1) Weigh 10 g of chopped graphite fibers and 10 g of conductive particles, and add them to 10 L of water in sequence. Then add 0.5 g of polyethylene oxide for stirring and dispersion, and then add 5 g of polyvinyl alcohol as a binder. After stirring for a period of time, a mixed slurry is prepared for standby.

[0037] (2) Pour the prepared mixed slurry into a wet forming device, then open the drainage switch and carry out suction filtration forming to obtain a hybrid fiber mesh with in-plane dimensions of 30 cm × 30 cm.

[0038] (3) Weigh polypropylene plastic and conductive particles in a weight ratio of 4:1, and then put them into a mixer for high-temperature melting and mixing. After the polypropylene and the conductive particles are mixed evenly, polypropylene conductive plastic is obtained.

[0039] (4) Put the uniformly mixed polypropylene conductive plastic into a square mold with in-plane dimensions of 30 cm × 30 cm and a thickness of 0.15 mm. Then put the mold into a press, first hot press at 200°C and 8 MPa for 8 min, and then cold press at 8 MPa for 6 min to obtain a conductive film.

[0040] (5) Prepare two sheets of the hybrid fiber mesh prepared in step (2) and three sheets of the conductive film prepared in step (4), and then put them into a square mold with in-plane dimensions of 30 cm × 30 cm and a thickness of 0.6 mm for alternating stacking.

[0041] (6)Finally, place the mold into a press. First, hot press at 200 °C and 8 MPa for 10 min, then cold press at 8 MPa for 10 min. Finally, a finished bipolar plate with a thickness of 0.6 mm is obtained.

[0042] Example 2

[0043] (1) Weigh 15 g of chopped graphite fibers and 15 g of conductive particles and add them to 10 L of water in sequence. Then add 0.5 g of polyethylene oxide for stirring and dispersion, and further add 5 g of polyvinyl alcohol as a binder. After stirring for a period of time, prepare a mixed slurry for standby.

[0044] (2) Pour the prepared mixed slurry into a wet forming device, then open the drain switch for suction filtration forming to obtain a mixed fiber web with an in-plane size of 30 cm × 30 cm.

[0045] (3) Weigh polypropylene plastic and conductive particles in a weight ratio of 4:1, then put them into a mixer for high-temperature melting and mixing. After the polypropylene and conductive particles are mixed evenly, polypropylene conductive plastic is obtained.

[0046] (4) Put the evenly mixed polypropylene conductive plastic into a square mold with an in-plane size of 30 cm × 30 cm and a thickness of 0.3 mm. Then place the mold into a press. First, hot press at 200 °C for 8 min, then cold press at 10 MPa for 8 min to obtain a conductive film.

[0047] (5) Prepare two pieces of the mixed fiber web prepared in step (2) and three pieces of the conductive film prepared in step (4), then place them into a square mold with an in-plane size of 30 cm × 30 cm and a thickness of 1 mm for alternating stacking.

[0048] (6) Finally, place the mold into a press. First, hot press at 200 °C and 10 MPa for 10 min, then cold press at 10 MPa for 10 min. Finally, a finished bipolar plate with a thickness of 1 mm is obtained.

[0049] Example 3

[0050] (1) Weigh 15 g of chopped graphite fibers and 15 g of conductive particles and add them to 10 L of water in sequence. Then add 0.5 g of polyethylene oxide for stirring and dispersion, and further add 5 g of polyvinyl alcohol as a binder. After stirring for a period of time, prepare a mixed slurry for standby.

[0051] (2) Pour the prepared mixed slurry into a wet forming device, then open the drain switch for suction filtration forming to obtain a mixed fiber web with an in-plane size of 30 cm × 30 cm.

[0052] (3) Weigh polypropylene plastic and conductive particles in a weight ratio of 4:1, and then put them into a mixer for high-temperature melting and mixing. After the polypropylene and conductive particles are mixed evenly, polypropylene conductive plastic is obtained.

[0053] (4) Put the evenly mixed polypropylene conductive plastic into a square mold with an inner size of 30 cm × 30 cm and a thickness of 0.3 mm. Then put the mold into a press, first hot press at 200 °C for 8 min, and then cold press at 12 MPa for 10 min to obtain a conductive film.

[0054] (5) Prepare 3 sheets of the mixed fiber web prepared in step (2) and 4 sheets of the conductive film prepared in step (4), and then alternately stack them in a square mold with an inner size of 30 cm × 30 cm and a thickness of 1.5 mm.

[0055] (6) Finally, put the mold into a press, first hot press at 200 °C and 10 MPa for 10 min, and then cold press at 10 MPa for 10 min to finally obtain a finished bipolar plate with a thickness of 1.5 mm.

[0056] The following are the performance parameters of the finished bipolar plates prepared in three embodiments.

[0057] Table 1 Performance parameters of bipolar plates

[0058]

[0059] This application also discloses a bipolar plate: prepared by the above-mentioned preparation method of a bipolar plate, and the thickness of the finished bipolar plate is 0.6 - 2 mm.

[0060] This application also discloses a flow battery that uses the above-mentioned bipolar plate.

[0061] The implementation principle of this embodiment is: The bipolar plate has a regular graphite fiber network structure inside, with many electron transport channels and good conductivity of the bipolar plate.

[0062] The embodiments of this specific implementation manner are all preferred embodiments of this application, and do not limit the protection scope of this application accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.

Claims

1. A method for preparing a bipolar plate, characterized in that: The following steps are included: (1) putting short-cut graphite fibers and conductive particles into water, adding a dispersant to stir and disperse, adding polyvinyl alcohol as a binder to prepare a mixed slurry, and then pouring the mixed slurry into a wet molding device for suction filtration molding to obtain a mixed fiber web; (2) placing polypropylene and conductive particles in a mixer for melt mixing to obtain a conductive plastic, which is then placed in a press to form a conductive film; (3) alternately laminating the mixed fiber web and the conductive film obtained in step (1) and step (2); Then put it into a press and press it into shape to obtain a finished bipolar plate.

2. The method for preparing a bipolar plate according to claim 1, characterized in that: The short-cut graphite fiber is selected from one of polyacrylonitrile-based, asphalt-based and viscose-based fibers, with a length of 5-15 mm and a diameter of 5-7 μm. The dispersant is selected from one of polyethylene oxide, polyacrylamide and sodium carboxymethyl cellulose. The surface density of the mixed fiber web is 200-400 g / cm 3 .

3. The method for preparing a bipolar plate according to claim 1, characterized in that: The conductive particles include, but are not limited to, graphite powder, graphene powder, carbon nanotubes, and conductive carbon black.

4. The method for preparing a bipolar plate according to claim 1, characterized in that: The melt mixing temperature is 180-220°C.

5. The method for preparing a bipolar plate according to claim 1, characterized in that: In step (2), the pressing process includes two stages: hot pressing and cold pressing. The hot pressing temperature is 180-220°C, the pressure is 6-10MPa, the hot pressing time is 8-12min, the cold pressing cooling method is water cooling, the pressure is 6-10MPa, the cold pressing time is 6-15min, and the thickness of the conductive film is 0.1-0.3mm.

6. The method for preparing a bipolar plate according to claim 5, characterized in that: In step (3), the stacking method is that the top and bottom layers are conductive films, and the middle layers are alternately stacked with conductive films and fiber mesh, and the in-plane dimensions of the mixed fiber mesh and the conductive film are the same.

7. The method for preparing a bipolar plate according to claim 5, characterized in that: The pressing process in step (3) includes two stages: hot pressing and cold pressing. Hot pressing is first performed to soften and flow the film and fully penetrate the mixed fiber web. Cold pressing is then performed to harden and form the film and bond the mixed fiber web and the conductive particles together. The hot pressing temperature is 180-220°C, the pressure is 8-12MPa, and the hot pressing time is 8-12min. The cold pressing cooling method is water cooling, the pressure is 8-12MPa, and the cold pressing time is 6-15min.

8. A bipolar plate, characterized in that: The bipolar plate is prepared by the method for preparing a bipolar plate as described in any one of claims 1 to 7.

9. A bipolar plate according to claim 8, characterized in that: The thickness of the finished bipolar plate is 0.6-2mm.

10. A liquid flow battery, characterized in that: A bipolar plate as described in any one of claims 8 to 9 is used.

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