Method of forming gel flow channels in situ on bipolar plates, bipolar plates having gel flow channels, gel solutions, flow batteries

Abstract

This application provides a method for in-situ forming gel channels on a bipolar plate, a bipolar plate with gel channels, a gel solution, and a flow battery. The method includes using areas on a first and second bipolar plate not covered by an insulating mask layer as conductive areas; introducing a gel solution between the first and second bipolar plates; connecting the first bipolar plate to the negative terminal of a power supply as the cathode side, and connecting the second bipolar plate to the positive terminal of a power supply as the anode side; applying a constant voltage to cause the gel solution to grow in-situ into a gel layer in the conductive area of ​​the first bipolar plate, forming a gel channel in the first bipolar plate; switching the positive and negative terminals, and applying a constant voltage to cause the gel solution to grow in-situ into a gel layer in the conductive area of ​​the second bipolar plate, forming a gel channel in the second bipolar plate. The gel solution of this application directly grows in-situ on the surface of the bipolar plate to form channels, significantly reducing the contact resistance between the bipolar plate and the electrodes.

Description

Technical Field

[0001] This application relates to the field of flow batteries, and more particularly to a method for forming gel channels in situ on a bipolar plate, a bipolar plate having gel channels, a gel solution, and a flow battery. Background Technology

[0002] To meet the growing market demand, increasing battery stack power density and reducing costs are crucial. Flow channels, as one of the key components affecting battery performance, function to distribute the electrolyte onto the electrodes.

[0003] Currently, there are two main methods for implementing bipolar channels: 1. Assembling the channel plate and bipolar plate; 2. Integrating the bipolar plate and channel into a single unit. However, both methods have different problems: Method 1: When different materials come into contact, corresponding contact resistance will be generated. Since the bipolar plate contains resin, it will generate a certain contact resistance when in contact with the channel plate. This resistance will generate local charges, which will affect the conductivity, voltage efficiency, and energy efficiency between the plate and the channel. Method 2: Integrating the bipolar plate and channel into a single unit, the bipolar plate channel is formed by molding or extrusion. Because the bipolar plate is made of a mixture of natural graphite and resin, the molding process will lead to uneven distribution of material composition, resulting in uneven mechanical properties and conductivity, and even loss of liquid-resistant function in some areas. This can lead to breakage during assembly, resulting in material waste or leakage within the electrode stack.

[0004] Therefore, an improved method for fabricating the flow channel and a bipolar plate and flow battery having the flow channel are desired. Summary of the Invention

[0005] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of this application.

[0006] In one aspect, this application provides a method for forming gel channels in situ on a bipolar plate, comprising the following steps:

[0007] 1) At a temperature of 80-90℃, 500-1500 parts by weight of 8-12 wt% polyvinyl alcohol aqueous solution, 100-300 parts by weight of 20-50 wt% alkali metal chloride or alkaline earth metal chloride aqueous solution, 100-300 parts by weight of acrylamide, 0.05-0.08 parts by weight of crosslinking agent, 0.1-0.5 parts by weight of ammonium persulfate and 0.2-0.5 parts by weight of silver nanowires are mixed evenly and defoamed to obtain a gel solution;

[0008] 2) An insulating mask layer with a preset flow channel pattern is attached to one side of the first bipolar plate and one side of the second bipolar plate respectively, so that the areas of the first bipolar plate and the second bipolar plate not covered by the insulating mask layer are exposed as conductive areas.

[0009] 3) Position the side of the first bipolar plate with the insulating mask layer opposite to the side of the second bipolar plate with the insulating mask layer, and introduce the gel solution between the first bipolar plate and the second bipolar plate;

[0010] 4) Connect the first bipolar plate to the negative terminal of the power supply as the cathode side, and connect the second bipolar plate to the positive terminal of the power supply as the anode side. Apply a constant voltage to allow the gel solution to grow in situ into a gelled layer in the conductive region of the first bipolar plate, forming a gel channel in the first bipolar plate; and

[0011] 5) Connect the second bipolar plate to the negative terminal of the power supply as the cathode side, and connect the first bipolar plate to the positive terminal of the power supply as the anode side. Apply a constant voltage of the same amplitude as in step 4) to allow the gel solution to grow in situ into a gel layer in the conductive region of the second bipolar plate, forming the gel channel of the second bipolar plate.

[0012] In one exemplary embodiment, forming the gel channels includes controlling the duration of applying a constant voltage based on the following formula (1) to obtain gel channels with different heights:

[0013] y=0.0332x+0.0411 (1)

[0014] Where y represents the height of the gel channel in mm, and x represents the time for applying constant voltage in min.

[0015] In one exemplary embodiment, the constant voltage is in the range of 2.5-3V.

[0016] In one exemplary embodiment, the weight-average molecular weight (Mw) of polyvinyl alcohol is in the range of 50,000-150,000 Da.

[0017] In one exemplary embodiment, the alkali metal chloride is lithium chloride.

[0018] In one exemplary embodiment, the alkaline earth metal chloride is calcium chloride.

[0019] In one exemplary embodiment, the crosslinking agent is selected from N,N-methylenebisacrylamide or polyethylene glycol diacrylate.

[0020] In one exemplary embodiment, the silver nanowires have a diameter of 20-100 nm and a length of 30-120 μm.

[0021] In an exemplary embodiment, the method may further include peeling the insulating mask layer from the first bipolar plate and the second bipolar plate, respectively.

[0022] On the other hand, this application provides a method for forming gel channels in situ on a bipolar plate, comprising the following steps:

[0023] 1) At a temperature of 80-90℃, 500-1500 parts by weight of 8-12 wt% polyvinyl alcohol aqueous solution, 100-300 parts by weight of 20-50 wt% alkali metal chloride or alkaline earth metal chloride aqueous solution, 100-300 parts by weight of acrylamide, 0.05-0.08 parts by weight of crosslinking agent, 0.1-0.5 parts by weight of ammonium persulfate and 0.2-0.5 parts by weight of silver nanowires are mixed evenly and defoamed to obtain a gel solution;

[0024] 2) An insulating mask layer with a preset flow channel pattern is attached to both sides of the first bipolar plate, so that the areas on both sides of the first bipolar plate not covered by the insulating mask layer are exposed as conductive areas; an insulating mask layer with a preset flow channel pattern is attached to one side of each of the two second bipolar plates, so that the areas on each second bipolar plate not covered by the insulating mask layer are exposed as conductive areas.

[0025] 3) The side of the first bipolar plate with the insulating mask layer is positioned opposite to the side of one of the two second bipolar plates with the insulating mask layer, and the other side of the first bipolar plate with the insulating mask layer is positioned opposite to the side of the other of the two second bipolar plates with the insulating mask layer, and the gel solution is introduced between the first bipolar plate and the two second bipolar plates respectively.

[0026] 4) Connect the first bipolar plate to the negative terminal of the power supply as the cathode side, and connect the two second bipolar plates to the positive terminal of the power supply as the anode side. Apply a constant voltage to allow the gel solution to grow in situ into a gelled layer in the conductive regions on both sides of the first bipolar plate, forming gel channels on both sides of the first bipolar plate; and

[0027] 5) Connect the two second bipolar plates to the negative terminal of the power supply as the cathode side, and connect the first bipolar plate to the positive terminal of the power supply as the anode side. Apply a constant voltage of the same amplitude as in step 4) to allow the gel solution to grow in situ into a gel layer in the conductive region of each of the two second bipolar plates, forming a single-sided gel flow channel of each of the second bipolar plates.

[0028] In an exemplary embodiment, the method may further include peeling the insulating mask layer from the first bipolar plate and the two second bipolar plates, respectively.

[0029] The in-situ gel channel formation method provided in this application can also be applied to the preparation of channels in a stack consisting of three or more single cells, and can be based on similar method steps as described above, which will not be repeated here.

[0030] On the other hand, this application provides a bipolar plate with gel channels, the bipolar plate having gel channels formed in situ by the above method.

[0031] On the other hand, this application provides a gel solution for in-situ forming the above-mentioned bipolar plate with gel channels, the gel solution being prepared from the following components: 0.2-0.5 parts by weight of silver nanowires, 500-1500 parts by weight of 8-12 wt% of an aqueous solution of polyvinyl alcohol, 100-300 parts by weight of 20-50 wt% of an aqueous solution of an alkali metal chloride or alkaline earth metal chloride, 100-300 parts by weight of acrylamide, 0.05-0.08 parts by weight of a crosslinking agent, and 0.1-0.5 parts by weight of ammonium persulfate.

[0032] In another aspect, this application provides a flow battery that includes the aforementioned bipolar plate with gel channels.

[0033] In this application, flow batteries include, but are not limited to, all-vanadium redox flow batteries and iron-chromium redox flow batteries.

[0034] This application significantly reduces the contact resistance between the bipolar plate and the electrode by growing the flow channel directly in situ on the surface of the bipolar plate, and provides additional electrocatalytic sites due to the porous nature of the gel, and enables the growth of complex flow channel patterns.

[0035] This application adds silver nanowires and alkali metal chlorides or alkaline earth metal chlorides to give the gel channels good conductivity and mechanical properties. The introduction of alkali metal chlorides or alkaline earth metal chlorides also gives the gel channels good adhesion, preventing the gel from separating from the channels during use.

[0036] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application can be realized and obtained by means of the embodiments described in the description and the accompanying drawings. Attached Figure Description

[0037] The accompanying drawings are used to provide an understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0038] Figure 1 This is a schematic diagram of the tooling used for the monocell battery stack in Embodiment 1 of this application;

[0039] Figure 2 This is a schematic diagram of a bipolar plate with gel channels according to Embodiment 1 of this application;

[0040] Figure 3 This is a schematic diagram of the tooling used for the dual-cell battery stack in Embodiment 2 of this application;

[0041] Figure 4 The charge-discharge curves of a monolayer battery stack comprising a bipolar plate with gel channels, prepared according to Embodiment 1 of this application, and a prior art monolayer battery stack comprising a bipolar plate with flexible graphite channels are shown; and

[0042] Figure 5 The charge-discharge curves of a bipolar battery stack containing a bipolar plate with gel channels prepared according to Embodiment 2 of this application and a bipolar battery stack containing a bipolar plate with flexible graphite channels in the prior art are shown. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application are described in detail below. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be arbitrarily combined with each other.

[0044] The diameter of the silver nanowires can be 20-100 nm and the length can be 30-120 μm. Products from Beijing Deco Island Gold Technology Co., Ltd. or Xuzhou Jiechuang New Materials Technology Co., Ltd. can be used. Alternatively, other methods in this field can be used, such as the following steps: take 50 mL of silver nitrate aqueous solution with a silver ion concentration of 34 mg / mL and 50 mL of polyvinylpyrrolidone aqueous solution with a molecular weight of 40000 Da (concentration of 10 mg / mL) and stir thoroughly. Then add 650 mL of 0.5 mg / L nano copper aqueous solution as a reducing agent, and then centrifuge (conditions: 5000 rpm, 10 min) and wash to obtain silver nanowires.

[0045] Unless otherwise specified, all materials used in the following examples are commercially available.

[0046] Example 1:

[0047] This embodiment uses a single-cell battery stack including a first bipolar plate and a second bipolar plate.

[0048] Prepare 500g of a 10wt% polyvinyl alcohol (Mw=70000 Da) aqueous solution at 90℃, add 300g of a 30wt% calcium chloride aqueous solution, add 100g of acrylamide, 0.06g of crosslinking agent N,N'-methylenebisacrylamide, 0.1g of ammonium persulfate and 0.4g of silver nanowires, mix evenly, and defoam by ultrasonication to obtain a gel solution;

[0049] An insulating mask layer with a preset flow channel pattern is attached to one side of the first bipolar plate and one side of the second bipolar plate, respectively, so that the areas on the first bipolar plate and the second bipolar plate not covered by the insulating mask layer are exposed as conductive areas.

[0050] The first bipolar plate with its insulating mask layer is positioned opposite the second bipolar plate with its insulating mask layer. A gel solution is introduced between the first and second bipolar plates to form a tooling for a single-cell battery stack. Figure 1 The schematic structure of the tooling shown;

[0051] The first bipolar plate is connected to the negative terminal of the power supply as the cathode side, and the second bipolar plate is connected to the positive terminal of the power supply as the anode side. A constant voltage of 3V is applied for 60 minutes (based on formula (1)) so that the gel solution grows in situ into a gel layer in the conductive area of ​​the first bipolar plate, forming a single-sided gel channel with a protrusion height of about 1.8mm on the first bipolar plate.

[0052] The second bipolar plate is connected to the negative terminal of the power supply as the cathode side, and the first bipolar plate is connected to the positive terminal of the power supply as the anode side. The same 3V constant voltage is applied for 60 minutes (based on formula (1)) so that the gel solution grows in situ into a gel layer in the conductive area of ​​the second bipolar plate, forming a single-sided gel flow channel with a protrusion height of about 1.8 mm on the second bipolar plate.

[0053] Finally, the two bipolar plates were removed from the fixture, the insulating mask layer was peeled off, and they were washed with deionized water to obtain two bipolar plates with single-sided gel channels.

[0054] Figure 2 This is a schematic diagram of the bipolar plate with gel flow channels in this embodiment. Figure 2 It can be seen that a meandering (snake-like) gel channel 2 is formed on the bipolar plate 1.

[0055] Example 2:

[0056] This embodiment uses a dual-cell battery stack including a shared first bipolar plate and two second bipolar plates.

[0057] The preparation of the gel solution is the same as in Example 1;

[0058] An insulating mask layer with a preset flow channel pattern is attached to both sides of the first bipolar plate, so that the areas on both sides of the first bipolar plate not covered by the insulating mask layer are exposed as conductive areas; an insulating mask layer with a preset flow channel pattern is attached to one side of each of the two second bipolar plates, so that the area on that side of each second bipolar plate not covered by the insulating mask layer is exposed as a conductive area.

[0059] A first bipolar plate and two second bipolar plates are respectively located on one side of the first bipolar plate. The side of the first bipolar plate with the insulating mask layer is positioned opposite the side of one of the second bipolar plates with the insulating mask layer, and the other side of the first bipolar plate with the insulating mask layer is positioned opposite the side of the other second bipolar plate with the insulating mask layer. A gel solution is introduced between the first bipolar plate and each of the second bipolar plates to form a tooling for a dual-cell battery stack. Figure 3 The schematic structure of the tooling shown;

[0060] The first bipolar plate is connected to the negative terminal of the power supply as the cathode side, and the two second bipolar plates are connected to the positive terminal of the power supply as the anode side. A constant voltage of 3V is applied for 60 minutes (based on formula (1)) so that the gel solution grows in situ into a gel layer in the conductive area on both sides of the first bipolar plate, forming a double-sided gel flow channel with a 1.8mm protrusion height on the first bipolar plate.

[0061] Two second bipolar plates are connected to the negative terminal of the power supply as the cathode side, and the first bipolar plate is connected to the positive terminal of the power supply as the anode side. The same 3V constant voltage is applied for 60 minutes (based on formula (1)) so that the gel solution grows in situ into a gel layer in the conductive area of ​​each of the two second bipolar plates, forming a single-sided gel flow channel with a 1.8mm protrusion height on each of the second bipolar plates.

[0062] Finally, the three bipolar plates were removed from the fixture, their respective insulating mask layers were peeled off, and they were cleaned with deionized water to obtain a first bipolar plate with a double-sided gel channel and two second bipolar plates with a single-sided gel channel.

[0063] Performance testing:

[0064] Two bipolar plates with gel channels prepared in Example 1 and two commercially available bipolar plates with flexible graphite channels were assembled into monolithic battery stacks using commercially available proton exchange membranes and carbon felt electrodes, respectively. All-vanadium redox flow battery charge-discharge tests were then conducted, including constant current charge-discharge at 40 A using the monolithic battery stack. The effective area of ​​the battery reaction was 250 cm². 2The initial vanadium electrolyte for both the positive and negative electrodes had a valence state of 3.5, with 1.5 L of electrolyte used for both electrodes. A single-cell battery stack, including a bipolar plate with flexible graphite channels, was first subjected to 50 charge-discharge cycles. The battery charge-discharge voltage curves are shown below. Figure 4 The dashed line in the figure shows the process; then, the monolithic battery stack of Example 1, including an integrated bipolar plate with gel channels, was subjected to 50 charge-discharge cycles, and the charge-discharge voltage curve is shown in the figure. Figure 4 As shown by the solid line in the image. Figure 4 The comparison results show that the initial charging voltage of the monolithic battery stack with integrated bipolar plate and gel flow channel in Example 2 is lower than that of the monolithic battery stack with flexible graphite flow channel, while the initial discharge voltage is higher than that of the monolithic battery stack with flexible graphite flow channel, which effectively reduces the polarization voltage during charging and discharging. In addition, the constant voltage section of the monolithic battery stack with integrated bipolar plate and gel flow channel in Example 1 is placed later, and the discharge time is longer than that of the monolithic battery stack with flexible graphite flow channel, which further improves the energy conversion efficiency of the stack.

[0065] The three bipolar plates with gel channels prepared in Example 2 and multiple commercially available bipolar plates with flexible graphite channels were assembled into dual-cell battery stacks with commercially available proton exchange membranes and carbon felt electrodes, respectively. All-vanadium redox flow battery charge-discharge tests were conducted, including constant current charge-discharge at 40 A using the dual-cell battery stack. The effective reaction area of ​​the battery was 250 cm². 2 The initial vanadium electrolyte for both the positive and negative electrodes had a valence state of 3.5, with 1.5 L of electrolyte used for both electrodes. The bipolar battery stack, including bipolar plates with flexible graphite channels, was first subjected to 50 charge-discharge cycles. The battery charge-discharge voltage curves are shown below. Figure 5 The dashed line in the figure shows the process; next, the dual-cell battery stack of Example 2, including an integrated bipolar plate with gel channels, was subjected to 50 charge-discharge cycles, and the charge-discharge voltage curves are shown in the figure. Figure 5 As shown by the solid line in the image. From... Figure 5 The comparison results showed that the initial charging voltage of the dual-cell battery stack with integrated bipolar plates and gel channels prepared in Example 2 was lower than that of the dual-cell battery stack with bipolar plates containing conventional channels, while the initial discharge voltage was higher than that of the dual-cell battery stack with bipolar plates containing conventional channels. This effectively reduced the polarization voltage during charging and discharging. Furthermore, the constant voltage section of the gel-channel integrated bipolar plate battery stack was placed later, resulting in a longer discharge time than that of the dual-cell battery stack with bipolar plates containing conventional channels, which further improved the energy conversion efficiency of the battery stack.

[0066] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for in-situ forming gel channels on a bipolar plate, characterized in that, Includes the following steps: 1) At a temperature of 80-90℃, 500-1500 parts by weight of 8-12 wt% polyvinyl alcohol aqueous solution, 100-300 parts by weight of 20-50 wt% alkali metal chloride or alkaline earth metal chloride aqueous solution, 100-300 parts by weight of acrylamide, 0.05-0.08 parts by weight of crosslinking agent, 0.1-0.5 parts by weight of ammonium persulfate and 0.2-0.5 parts by weight of silver nanowires are mixed evenly and defoamed to obtain a gel solution; 2) An insulating mask layer with a preset flow channel pattern is attached to one side of the first bipolar plate and one side of the second bipolar plate respectively, so that the areas of the first bipolar plate and the second bipolar plate not covered by the insulating mask layer are exposed as conductive areas. 3) Position the side of the first bipolar plate with the insulating mask layer opposite to the side of the second bipolar plate with the insulating mask layer, and introduce the gel solution between the first bipolar plate and the second bipolar plate; 4) Connect the first bipolar plate to the negative terminal of the power supply as the cathode side, and connect the second bipolar plate to the positive terminal of the power supply as the anode side. Apply a constant voltage to allow the gel solution to grow in situ into a gelled layer in the conductive region of the first bipolar plate, forming a gel channel in the first bipolar plate; and 5) Connect the second bipolar plate to the negative terminal of the power supply as the cathode side, and connect the first bipolar plate to the positive terminal of the power supply as the anode side. Apply a constant voltage of the same amplitude as in step 4) to allow the gel solution to grow in situ into a gel layer in the conductive region of the second bipolar plate, forming the gel channel of the second bipolar plate.

2. The method according to claim 1, characterized in that, The constant voltage is in the range of 2.5-3V.

3. The method according to claim 1 or 2, characterized in that, The weight-average molecular weight (Mw) of polyvinyl alcohol is in the range of 50,000-150,000 Da; and / or, The alkali metal chloride is lithium chloride; and / or, The alkaline earth metal chloride is calcium chloride; and / or... The crosslinking agent is selected from N,N-methylenebisacrylamide or polyethylene glycol diacrylate; and / or The silver nanowires have a diameter of 20-100 nm and a length of 30-120 μm.

4. A method for forming gel channels in situ on a bipolar plate, characterized in that, Includes the following steps: 1) At a temperature of 80-90℃, 500-1500 parts by weight of 8-12 wt% polyvinyl alcohol aqueous solution, 100-300 parts by weight of 20-50 wt% alkali metal chloride or alkaline earth metal chloride aqueous solution, 100-300 parts by weight of acrylamide, 0.05-0.08 parts by weight of crosslinking agent, 0.1-0.5 parts by weight of ammonium persulfate and 0.2-0.5 parts by weight of silver nanowires are mixed evenly and defoamed to obtain a gel solution; 2) An insulating mask layer with a preset flow channel pattern is attached to both sides of the first bipolar plate, so that the areas on both sides of the first bipolar plate not covered by the insulating mask layer are exposed as conductive areas. An insulating mask layer with a preset flow channel pattern is attached to one side of each of the two second bipolar plates, so that the area on one side of the second bipolar plate not covered by the insulating mask layer is exposed as a conductive area. 3) The first bipolar plate with an insulating mask layer is positioned opposite to one of the two second bipolar plates with an insulating mask layer, and the other side of the first bipolar plate with an insulating mask layer is positioned opposite to one side of the other of the two second bipolar plates with an insulating mask layer, and the gel solution is introduced between the first bipolar plate and the two second bipolar plates respectively. 4) Connect the first bipolar plate to the negative terminal of the power supply as the cathode side, and connect the two second bipolar plates to the positive terminal of the power supply as the anode side. Apply a constant voltage to allow the gel solution to grow in situ into a gel layer in the conductive areas on both sides of the first bipolar plate, forming the gel channels on both sides of the first bipolar plate. as well as 5) Connect the two second bipolar plates to the negative terminal of the power supply as the cathode side, and connect the first bipolar plate to the positive terminal of the power supply as the anode side. Apply a constant voltage of the same amplitude as in step 4) to allow the gel solution to grow in situ into a gel layer in the conductive region of each of the two second bipolar plates, forming a single-sided gel flow channel of each of the second bipolar plates.

5. The method according to claim 4, characterized in that, The constant voltage is in the range of 2.5-3V.

6. The method according to claim 4 or 5, characterized in that, The weight-average molecular weight (Mw) of polyvinyl alcohol is in the range of 50,000-150,000 Da; and / or, The alkali metal chloride is lithium chloride; and / or, The alkaline earth metal chloride is calcium chloride; and / or... The crosslinking agent is selected from N,N-methylenebisacrylamide or polyethylene glycol diacrylate; and / or The silver nanowires have a diameter of 20-100 nm and a length of 30-120 μm.

7. A bipolar plate with gel flow channels, characterized in that, The bipolar plate has a gel channel formed in situ by any one of claims 1-3 or by any one of claims 4-6.

8. A flow battery, characterized in that, The flow battery includes the bipolar plate with gel channels as described in claim 7.

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