Bipolar plate, flow battery and battery stack provided with interdigitated electrolyte flow channels

Abstract

This invention relates to the field of flow battery technology, specifically to a bipolar plate with interdigitated electrolyte channels, a flow battery, and a battery stack. The bipolar plate has interdigitated electrolyte channels, with a surface roughness Ra1 of 0.05-12.5 μm and a bottom surface roughness Ra2 of 0.05-12.5 μm for the interdigitated electrolyte channels. Each interdigitated electrolyte channel includes an inlet channel, at least one branch channel-I, at least one branch channel-II, and an outlet channel. Branch channels-I and-II are spaced apart, with branch channel-I connected to the outlet channel and branch channel-II connected to the inlet channel. The bipolar plate provided by this invention, when assembled into a flow battery, results in a flow battery with high energy efficiency and reduced voltage drop.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, specifically to a bipolar plate with interdigitated electrolyte channels, a flow battery, and a battery stack. Background Technology

[0002] Flow batteries are a type of electrochemical energy storage technology that typically utilizes the changes in the valence states of active materials in the liquid phases of the positive and negative electrodes during charging and discharging to store and release energy. Currently developed technologies include vanadium redox flow batteries, iron-chromium flow batteries, and zinc-bromine flow batteries. Flow batteries have independent energy units and power units. Energy units generally refer to the positive and negative electrolytes; the concentration and volume of active materials in the electrolyte determine the upper limit of the flow battery's energy. Power units generally refer to a single cell or a battery stack. The electrolyte flows through the electrodes within the battery stack, and the active materials react on the electrode surfaces, converting chemical energy into electrical energy, or vice versa.

[0003] The stack of a flow battery mainly consists of electrodes, a separator, bipolar plates, and current collectors. Among these, the bipolar plates are one of the key components, serving to connect the positive and negative electrodes of different individual cells and conduct electricity within the battery's internal circuitry. They should possess good conductivity, mechanical strength, and resistance to chemical oxidation and electrochemical corrosion. Optimization of the bipolar plate flow channel structure is of great significance to the performance of flow batteries, but reports in this area are relatively few.

[0004] CN108987763A discloses a bipolar plate for a flow battery with a graded interdigitated flow field. The bipolar plate has several branch channels in its electrolyte supply and drainage distribution channels, with the final-stage supply and drainage branch channels arranged in an interdigitated pattern and not interconnected. This forces the electrolyte to drain from the final-stage supply branch channel. This flow field allows for flexible and independent design of the geometry of each stage of the channel, increasing the cross-sectional area of ​​each stage before the final stage, further enhancing mass transfer and reducing pump power loss, thus improving battery voltage efficiency and battery system efficiency. However, the fabrication of this bipolar plate is difficult, complex, and costly, hindering its industrialization.

[0005] How to efficiently optimize the bipolar plate flow channel design to ensure uniform electrolyte distribution in all parts of the flow channel, thereby improving the energy efficiency of the flow battery and reducing voltage drop, is a problem that urgently needs to be solved for the further commercialization of this technology. Summary of the Invention

[0006] The purpose of this invention is to overcome the problem that the electrochemical performance of existing flow batteries needs further improvement, and to provide a bipolar plate with interdigitated electrolyte channels, a flow battery, and a battery stack. Assembling the bipolar plate provided by this invention into a flow battery results in a flow battery with high energy efficiency and reduced voltage drop. Furthermore, the bipolar plate provided by this invention has the advantages of simple manufacturing process, low cost, and environmental friendliness.

[0007] To achieve the above objectives, the first aspect of the present invention provides a bipolar plate having an interdigitated electrolyte flow channel, wherein the surface roughness Ra1 of the bipolar plate is 0.05-12.5 μm, and the surface roughness Ra2 of the bottom surface of the interdigitated electrolyte flow channel is 0.05-12.5 μm;

[0008] The interdigitated electrolyte flow channel includes an inlet flow channel, at least one branch flow channel-I, at least one branch flow channel-II, and an outlet flow channel;

[0009] The branch flow channel-I and the branch flow channel-II are arranged at intervals, and the branch flow channel-I is connected to the liquid outlet flow channel, while the branch flow channel-II is connected to the liquid inlet flow channel.

[0010] A second aspect of the present invention provides a flow battery, the flow battery comprising a positive electrode, a negative electrode, and a separator existing between the positive electrode and the negative electrode;

[0011] The flow battery further includes a first bipolar plate adjacent to the positive electrode and a second bipolar plate adjacent to the negative electrode;

[0012] The first bipolar plate and the second bipolar plate are each independently provided as bipolar plates for the first aspect.

[0013] A third aspect of the present invention provides a battery stack, the battery stack comprising the flow battery provided in the second aspect.

[0014] The bipolar plate provided by this invention has a specific structure of interdigitated electrolyte channels and a specific surface roughness. When the bipolar plate provided by this invention is assembled into a flow battery, the flow battery has high energy efficiency and can reduce voltage drop. Moreover, it has the advantages of excellent manufacturing performance, simple process, low cost and environmental friendliness. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a bipolar plate for a flow battery with interdigitated electrolyte channels provided by the present invention;

[0016] Figure 2 This is a specific embodiment provided by the present invention, showing a cross-sectional schematic diagram of the interdigitated electrolyte flow channel;

[0017] Figure 3 This is a specific embodiment of the present invention, a cross-sectional view of the electrolyte inlet along the flow direction of the electrolyte, wherein the arrow points to indicate the flow direction of the electrolyte;

[0018] Figure 4 This is a specific embodiment of the present invention, a cross-sectional view of the electrolyte outlet along the flow direction of the electrolyte, wherein the arrow points to indicate the flow direction of the electrolyte;

[0019] Figure 5 This is a schematic diagram of a flow battery provided by the present invention.

[0020] Explanation of reference numerals in the attached figures

[0021] 1. Electrolyte outlet section; 2. Electrolyte inlet section; 3-1. Inlet channel

[0022] 3-2, Outlet Flow Channel; 4-1, Branch Flow Channel-I; 4-2, Branch Flow Channel-II

[0023] 11. Reduction section; 12. Second straight section; 21. First straight section

[0024] 22. Widened section

[0025] B1, diaphragm B2-1, positive electrode B2-2, negative electrode

[0026] B3, Seal B4-1, First bipolar plate B4-2, Second bipolar plate

[0027] B5, current collector; B6, end plate Detailed Implementation

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] In the description of this invention, it should be understood that the terms "center," "length," "width," "thickness," "upper," "lower," "left," "right," "vertical," "horizontal," "top," "bottom," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0030] The first aspect of the present invention provides a bipolar plate having an interdigitated electrolyte flow channel, wherein the surface roughness Ra1 of the bipolar plate is 0.05-12.5 μm, and the surface roughness Ra2 of the bottom surface of the interdigitated electrolyte flow channel is 0.05-12.5 μm;

[0031] The interdigitated electrolyte flow channel includes an inlet flow channel, at least one branch flow channel-I, at least one branch flow channel-II, and an outlet flow channel;

[0032] The branch flow channel-I and the branch flow channel-II are arranged at intervals, and the branch flow channel-I is connected to the liquid outlet flow channel, while the branch flow channel-II is connected to the liquid inlet flow channel.

[0033] In this invention, unless otherwise specified, the interdigitated electrolyte flow channel consists of an inlet flow channel, at least one branch flow channel-I, at least one branch flow channel-II, and an outlet flow channel. The branch flow channels-I and-II are spaced apart, and the branch flow channel-I is connected to the outlet flow channel, while the branch flow channel-II is connected to the inlet flow channel. That is, the flow direction of the electrolyte is sequentially the inlet flow channel, the sequentially spaced branch flow channels-I and-II, and the outlet flow channel.

[0034] In this invention, unless otherwise specified, the shape and size of the inlet channel and the outlet channel may be the same or different, preferably the same; the shape and size of the plurality of branch channels-I and branch channels-II may be the same or different, preferably the same.

[0035] In this invention, unless otherwise specified, the interdigitated electrolyte channel is a groove formed on the bipolar plate, comprising a bottom surface and two side surfaces. This invention achieves a bipolar plate roughness Ra1 of 0.05-12.5 μm and a bottom surface roughness Ra2 of 0.05-12.5 μm; this improves the energy efficiency of the flow battery assembled with this bipolar plate and reduces voltage drop.

[0036] In some embodiments of the present invention, preferably, the surface roughness Ra1 of the bipolar plate is 0.05-9 μm, for example, 0.05 μm, 0.1 μm, 1 μm, 3.2 μm, 5 μm, 6.3 μm, 9 μm, and any value within any range of any two values, and more preferably 0.063-7 μm. If the surface roughness Ra1 of the bipolar plate is too high, a gap exists between the electrode and the bipolar plate, which is not conducive to the diffusion of the electrolyte on the electrode; if the surface roughness Ra1 is too low, it may lead to misalignment between the electrode and the bipolar plate. Currently provided bipolar plates all have rough surfaces, with a surface roughness Ra1 generally greater than 12.5 μm.

[0037] In some embodiments of the present invention, preferably, the surface roughness Ra2 of the bottom surface of the interdigitated electrolyte flow channel is 0.05-9 μm, for example, 0.05 μm, 0.1 μm, 1 μm, 3.2 μm, 5 μm, 6.3 μm, 9 μm, and any value in the range of any two values, preferably 0.063-7 μm.

[0038] The present invention allows for a wide range of choices for the surface roughness Ra3 of the side surface of the interdigitated electrolyte flow channel. It can be a smooth surface or a rough surface. Preferably, the surface roughness Ra3 of the side surface of the interdigitated electrolyte flow channel is 0.05-4 μm.

[0039] In this invention, unless otherwise specified, the surface roughness Ra parameter is measured by a probe contact profilometer.

[0040] In some embodiments of the present invention, preferably, the interdigitated electrolyte channel has a regular shape or an irregular shape; more preferably, the inlet channel, the branch channel and the outlet channel are each independently a quadrangular prism, including but not limited to a cuboid.

[0041] In one specific embodiment of the present invention, for example, from a top view of the interdigitated electrode fluid flow channel (e.g.) Figure 1 From the perspective of the diagram, the interdigitated electrolyte flow channels (i.e., the inlet channel, five branch channels-I, five branch channels-II, and the outlet channel) can be conventional squares or rectangles, or other irregular structures (e.g., circles), preferably conventional squares or rectangles. In this invention, the cross-section of the interdigitated electrolyte flow channels can be a regular shape (e.g., a conventional square, rectangle, or trapezoid), or an irregular shape (e.g., a variable diameter shape); preferably a regular shape. This preferred embodiment not only helps reduce processing difficulty but also minimizes the dead zone of the electrolyte.

[0042] In some embodiments of the present invention, preferably, the thickness of the bipolar plate is 2-6 mm, for example, 2 mm, 2.5 mm, 3 mm, 5 mm, 6 mm, and any value within the range of any two values, preferably 2.5-5 mm.

[0043] In some embodiments of the present invention, preferably, the depths of the inlet channel, branch channel-I, branch channel-II, and outlet channel are the same or different, preferably the same.

[0044] In this invention, the depth of the interdigitated electrolyte channel is less than the thickness of the bipolar plate. Preferably, the depths of the inlet channel, branch channel-I, branch channel-II, and outlet channel are each independently 0.05-2.5 mm, for example, 0.05 mm, 0.1 mm, 1 mm, 2 mm, 2.5 mm, or any value within the range of any two values, preferably 0.1-2 mm.

[0045] In this invention, unless otherwise specified, the lengths of the inlet and outlet channels are the same and are equal to the length of the effective area of ​​the bipolar plate.

[0046] In this invention, unless otherwise specified, the number of branch channels-I and branch channels-II is the same.

[0047] In some embodiments of the present invention, preferably, within every 50 mm along the length of the bipolar plate, the number of branch channels-I and branch channels-II are each 2-6, preferably 4-6. In the present invention, too few branch channels are detrimental to the uniform distribution of the electrolyte, while too many are detrimental to electrolyte diffusion.

[0048] In some embodiments of the present invention, preferably, each of the branch channels-I and branch channels-II is independently and uniformly distributed along the length direction of the bipolar plate.

[0049] In some embodiments of the present invention, preferably, the cross-section of the interdigitated electrolyte channel is a regular shape or an irregular shape, preferably a regular shape. This preferred embodiment not only reduces processing difficulty but also minimizes dead zones in the electrolyte. The regular shape includes, but is not limited to, rectangles, squares, and trapezoids. When the regular shape is a square, it indicates that the depth and width of the interdigitated electrolyte channel are the same.

[0050] In some embodiments of the present invention, preferably, the width of the interdigitated electrolyte channel gradually decreases (wider at the top and narrower at the bottom) along the direction from the surface to the bottom. More preferably, the cross-section of the interdigitated electrolyte channel is trapezoidal (e.g., ...). Figure 2(As shown). This configuration is more conducive to enhancing electrolyte mass transfer and reducing battery concentration polarization resistance.

[0051] In some embodiments of the present invention, preferably, such as Figure 2 As shown, the included angle δ between the bottom and side surfaces of the interdigitated electrolyte flow channel is ≥90°, for example, 90°, 100°, 120°, 130°, 150°, and any value within the range of any two values, and is more preferably 100-150°.

[0052] In some embodiments of the present invention, preferably, the widths of the inlet channel, branch channel-I, branch channel-II, and outlet channel are the same or different, preferably the same.

[0053] In some embodiments of the present invention, preferably, the width of the inlet channel, branch channel-I, branch channel-II and outlet channel is each independently 1-5mm, for example, 1mm, 1.5mm, 3.5mm, 4mm, 5mm, and any value in the range of any two values, preferably 1.5-4.5mm.

[0054] In some embodiments of the present invention, preferably, the interdigitated electrolyte flow channel is a single-channel structure or a parallel multi-channel structure. This arrangement is more conducive to electrolyte diffusion and mass transfer.

[0055] According to a specific embodiment of the present invention, such as Figure 1 As shown, the bipolar plate is provided with an electrolyte inlet 2 (e.g., Figure 1 (as shown in the lower left corner) and electrolyte outlet 1 (e.g.) Figure 1 (As shown in the upper right corner). The present invention does not have a particular limitation on the location of the electrolyte inlet and electrolyte outlet. In order to reduce electrolyte dead zones, preferably, the electrolyte inlet and electrolyte outlet are arranged diagonally on the bipolar plate.

[0056] In some embodiments of the present invention, such as Figure 3-4 As shown, along the flow direction of the electrolyte, the electrolyte inlet 2 is sequentially divided into a first straight section 21 and an expanding section 22; the electrolyte outlet 1 is sequentially divided into a narrowing section 11 and a second straight section 12.

[0057] In this invention, unless otherwise specified, the electrolyte inlet 2 is composed of a first straight cylindrical section 21 and an expanding section 22; the electrolyte outlet 1 is composed of a narrowing section 11 and a second straight cylindrical section 12.

[0058] In some embodiments of the present invention, such as Figure 3-4As shown, along the flow direction of the electrolyte, the cross-sections of the first straight cylindrical section 21 and the second straight cylindrical section 12 are each independently a regular shape, preferably a rectangle or a square; the cross-sections of the expanding section 22 and the contracting section 11 are each independently a regular or irregular shape, preferably a regular shape, and more preferably a rectangle, a square, or a trapezoid. This preferred method not only helps reduce processing difficulty but can also reduce the dead zone of the electrolyte.

[0059] In this invention, unless otherwise specified, the cross-sections of the first straight cylindrical section 21, the second straight cylindrical section 12, the expanded diameter section 22, and the reduced diameter section 11 refer to planes parallel to the thickness of the bipolar plate.

[0060] In this invention, unless otherwise specified, the regular shapes include, but are not limited to, rectangles, squares, and trapezoids.

[0061] In some embodiments of the present invention, such as Figure 3-4 As shown, along the flow direction of the electrolyte, the included angle α of the expanding section 22 is ≥90°, preferably 100-150°. For example, α includes but is not limited to 90°, 100°, 120°, 135°, and 150°; the included angle β of the narrowing section 11 is ≤90°, preferably 30-80°. For example, β includes but is not limited to 30°, 45°, 60°, 80°, and 90°.

[0062] In some embodiments of the present invention, such as Figure 3-4 As shown, the ratio of the inner diameter m of the expanding section 22 to the inner diameter n of the first straight section 21 is 1.1-15:1, preferably 2-10:1; preferably, the ratio of the inner diameter p of the reducing section 11 to the inner diameter q of the second straight section 12 is 1.1-15:1, preferably 2-10:1.

[0063] In one specific embodiment of the present invention, the inner diameter m of the expanding section 22 and the inner diameter p of the narrowing section 11 are each independently 0.5-5mm, preferably 1-4.5mm, more preferably 1.5-4.5mm; preferably, the inner diameter n of the first straight section 21 and the inner diameter q of the second straight section 12 are each independently 0.5-2.5mm, more preferably 0.5-1.5mm.

[0064] In some embodiments of the present invention, such as Figure 3-4 As shown, the lengths of the electrolyte inlet 2 and the electrolyte outlet 1 are each independently the same as the thickness of the bipolar plate.

[0065] In one specific embodiment of the present invention, preferably, the lengths of the electrolyte inlet 2 and the electrolyte outlet 1 are each independently 2-6 mm, preferably 2.5-5 mm.

[0066] In some embodiments of the present invention, such as Figure 3-4 As shown, in the electrolyte inlet 2, the ratio of the length a of the expanding section 22 to the length b of the first straight section 21 is 3-1:1; in the electrolyte outlet 1, the ratio of the length c of the narrowing section 11 to the length d of the second straight section 12 is 3-1:1.

[0067] In this invention, unless otherwise specified, the inner diameter and length of the first straight section 21, the second straight section 12, the expanding section 22, and the contracting section 11 refer to the width perpendicular to the electrolyte flow direction and the depth parallel to the electrolyte flow direction, respectively.

[0068] In this invention, the following is adopted: Figure 3-4 The electrolyte inlet 2 and electrolyte outlet 1 shown are more conducive to enhancing mass transfer, reducing the concentration polarization resistance of the battery, and preventing the bipolar plates from shifting during battery assembly, thereby suppressing electrolyte leakage.

[0069] In this invention, as long as the surface roughness Ra1 of the bipolar plate is 0.05-12.5 μm and the surface roughness Ra2 of the bottom surface of the interdigitated electrolyte channel is 0.05-12.5 μm, there are no particular limitations on the specific implementation method for achieving this surface roughness Ra. Any method that can achieve the above-mentioned surface roughness Ra is within the protection scope of this invention. To further simplify the manufacturing process, preferably, the surface of the bipolar plate and the bottom surface of the interdigitated electrolyte channel are each independently frosted; and / or, the surface of the bipolar plate and the bottom surface of the interdigitated electrolyte channel are each independently sprayed with carbon powder and / or activated carbon layer; and / or, the surface of the bipolar plate and the bottom surface of the interdigitated electrolyte channel are each independently embossed with a patterned texture.

[0070] In this invention, there is no particular limitation on the method of obtaining the frosted structure; for example, it can be obtained by polishing. Specific implementation methods of polishing are well known to those skilled in the art, and will not be described in detail here.

[0071] The present invention does not particularly limit the specific operation of spraying the carbon powder and / or activated carbon layer; for example, it can be carried out by thermal spraying or vapor deposition. Spraying the carbon powder and / or activated carbon layer on the surface of the bipolar plate and the bottom surface of the interdigitated electrolyte channel can make the surface roughness Ra1 and Ra2 each independently 0.05-12.5 μm, and the carbon powder and / or activated carbon layer sprayed on the surface of the bipolar plate can increase its electronic conductivity.

[0072] The present invention does not impose any particular limitation on the amount of carbon powder and / or activated carbon layer sprayed on the surface of the bipolar plate and the bottom surface of the interdigitated electrolyte channel. For example, the coating thickness can be 0.05-0.5 mm independently.

[0073] This invention does not impose any particular limitation on the pattern of the bipolar plate surface and the bottom surface of the interdigitated electrolyte flow channel. They can each be an independent regular pattern or an independent irregular pattern, as long as the surface roughness Ra1 of the bipolar plate and the surface roughness Ra2 of the bottom surface of the interdigitated electrolyte flow channel each meet the requirements. It should be noted that, in this invention, the surface of the bipolar plate refers to the effective surface in contact with the electrolyte, that is, it includes both the surface roughness Ra1 of the bipolar plate and the surface roughness Ra2 of the bottom surface of the interdigitated electrolyte flow channel.

[0074] This invention allows for a wide range of material selection for the bipolar plate, as long as it can achieve the function of conducting the internal circuitry of the battery. Preferably, the material of the bipolar plate is selected from at least one of graphite / polymer composite materials, metal / polymer composite materials, and graphite / metal composite materials. This preferred embodiment is more conducive to improving the conductivity and mechanical properties of the bipolar plate. This invention does not limit the use of graphite / polymer composite materials, metal / polymer composite materials, and graphite / metal composite materials; these can be commercially available or prepared by existing methods, and all can be used in this invention; for example, the graphite bipolar plate material disclosed in CN101308924B.

[0075] According to a particularly preferred embodiment of the present invention, the bipolar plate is provided with an interdigitated electrolyte flow channel, the surface roughness Ra1 of the bipolar plate is 0.063-7 μm, and the surface roughness Ra2 of the bottom surface of the interdigitated electrolyte flow channel is 0.063-7 μm;

[0076] The interdigitated electrolyte flow channel includes an inlet flow channel, at least one branch flow channel-I, at least one branch flow channel-II, and an outlet flow channel;

[0077] The branch flow channel-I and the branch flow channel-II are arranged at intervals, and the branch flow channel-I is connected to the liquid outlet flow channel, while the branch flow channel-II is connected to the liquid inlet flow channel.

[0078] The included angle δ between the bottom and side surfaces of the interdigitated electrolyte flow channel is 100-150°.

[0079] The bipolar plate is provided with an electrolyte inlet and an electrolyte outlet; along the electrolyte flow direction, the electrolyte inlet is divided into a first cylindrical section and an expanding section; the electrolyte outlet is divided into a constricting section and a second cylindrical section.

[0080] Wherein, along the flow direction of the electrolyte, the included angle α of the expanding section is 100-150°; and the included angle β of the narrowing section is 30-80°.

[0081] The ratio of the inner diameter m of the expanding section to the inner diameter n of the first straight section is 2-10:1; the ratio of the inner diameter p of the narrowing section to the inner diameter q of the second straight section is 2-10:1.

[0082] A second aspect of the present invention provides a flow battery, such as Figure 5 As shown, the flow battery includes a positive electrode B2-1, a negative electrode B2-2, and a separator B1 located between the positive electrode B2-1 and the negative electrode B2-2.

[0083] The flow battery further includes a first bipolar plate B4-1 adjacent to the positive electrode B2-1 and a second bipolar plate B4-2 adjacent to the negative electrode B2-2;

[0084] The first bipolar plate B4-1 and the second bipolar plate B4-2 are each independently the bipolar plates described in the first aspect above.

[0085] The positive electrode B2-1 and negative electrode B2-2 described in this invention can be various electrode materials conventionally used in the art. Preferably, the positive electrode and negative electrode are each independently selected from at least one of porous carbon fiber materials, powdered carbon materials, and porous metal materials, and more preferably porous carbon fiber materials.

[0086] In one specific embodiment of the present invention, preferably, the positive electrode B2-1 and the negative electrode B2-2 are each independently selected from at least one of carbon paper, carbon felt, graphite paper, and graphite felt. Both the positive electrode B2-1 and the negative electrode B2-2 are commercially available.

[0087] In this invention, the separator B1 can be any separator conventionally used in the art, and the invention does not particularly limit it, as long as it allows the passage of connecting ions between the positive and negative electrodes of the battery (preventing the passage of other ions and solvents). The connecting ions include, but are not limited to, H+. + Na + K + Li + OH- ions. Preferably, the membrane B1 is selected from at least one of cation exchange membranes, anion exchange membranes, and sieving membranes; more preferably, it can be at least one of sulfonic acid type membrane materials, polymer porous membrane materials, organic / inorganic composite materials, and inorganic membrane materials. The membrane is commercially available.

[0088] According to the present invention, it is understood that, as Figure 5As shown, the positive electrode B2-1 is adjacent to the diaphragm B1 and the first bipolar plate B4-1, with the diaphragm B1 on one side and the first bipolar plate B4-1 on the other side. The negative electrode B2-2 is adjacent to the diaphragm B1 and the second bipolar plate B4-2, with the diaphragm B1 on one side and the second bipolar plate B4-2 on the other side. The surface roughness Ra1 of the first bipolar plate B4-1 and the second bipolar plate B4-2 adjacent to the electrodes (positive electrode and negative electrode) satisfies the above-mentioned requirements.

[0089] According to the present invention, preferably, the flow battery further includes a positive electrode electrolyte and a negative electrode electrolyte. The present invention offers a wide range of choices for the positive and negative electrode electrolytes, allowing for appropriate selection based on the specific type of flow battery. In the present invention, it is understood that the positive electrode includes a positive electrode, a first bipolar plate, and a positive electrode electrolyte, and the negative electrode includes a negative electrode, a second bipolar plate, and a negative electrode electrolyte. Preferably, the flow battery is a vanadium redox flow battery. Preferably, the positive electrode electrolyte causes a reaction at the positive electrode involving the interconversion of pentavalent and tetravalent vanadium ions; preferably, the negative electrode electrolyte causes a reaction at the negative electrode involving the interconversion of trivalent and divalent vanadium ions. For example, the positive electrode electrolyte can be a solution of V(IV) + V(V) + H₂SO₄, wherein the total concentration of V(IV+V) is 1.4-1.6 mol / L and the concentration of H₂SO₄ is 1.8-5 mol / L; the negative electrode electrolyte can be a solution of V(II) + V(III) + H₂SO₄, wherein the total concentration of V(II+III) can be 1.4-1.6 mol / L and the concentration of H₂SO₄ can be 1.8-5 mol / L. The positive or negative electrode electrolyte may also contain anions corresponding to the corresponding valence state of the V ions. This invention does not limit the type of anion, as long as the above-mentioned corresponding V ions and their concentrations, along with a solution of sulfuric acid of a specific concentration, are satisfied.

[0090] According to the present invention, preferably, the flow battery further includes an end plate B6 disposed on the outer side of the first bipolar plate B4-1 and the second bipolar plate B4-2. In the present invention, the side closer to the separator is the inner side, and the side farther from the separator is the outer side. The end plate is used to fix the flow battery, and the material of the end plate includes, but is not limited to, metal materials, metal / polymer composite materials, and glass fiber / polymer composite materials.

[0091] According to the present invention, preferably, a sealing element B3 is independently provided between the first bipolar plate B4-1 and the positive electrode B2-1, and between the second bipolar plate B4-2 and the negative electrode B2-2. The sealing element is used to prevent electrolyte leakage. The present invention does not particularly limit the arrangement and material of the sealing element; those skilled in the art can make appropriate selections according to actual conditions.

[0092] According to a preferred embodiment of the present invention, current collectors B5 are respectively disposed on the outer sides of the first bipolar plate B4-1 and the second bipolar plate B4-2. The present invention does not particularly limit the arrangement and material of the current collectors, and those skilled in the art can make appropriate selections according to actual conditions.

[0093] According to the present invention, the all-vanadium redox flow battery uses an acid solution of vanadium ions in mixed valence states of V(IV+V) and V(II+III) as the positive and negative electrolytes, respectively. During the charging / discharging process, the electrolyte circulates between the battery and the storage tank by a peristaltic pump. The electrolyte is delivered into the battery from the inlet and undergoes an electrochemical reaction on the electrodes as it flows through the battery. After the reaction is completed, the electrolyte flows out from the outlet. The battery separates the positive and negative electrolytes by a separator material.

[0094] A third aspect of the present invention provides a battery stack, the battery stack including the flow battery provided in the second aspect. Those skilled in the art can make corresponding configurations according to actual conditions, and the battery stack may include two or more flow batteries connected in series.

[0095] The present invention will be described in detail below through embodiments.

[0096] Example 1

[0097] (1) As Figure 1-4 As shown, the dimensions of the bipolar plate are: length 80mm, width 60mm, and thickness 3mm. For the central structure, the overall flow channel shape of its interdigitated electrolyte channel is a cuboid (length 48mm, width 40mm). The interdigitated electrolyte channel includes an inlet channel, 5 branch channels-I, 5 branch channels-II, and an outlet channel. Branch channels-I and branch channels-II are arranged alternately, and branch channels-I are connected to the outlet channel, while branch channels-II are connected to the inlet channel.

[0098] The inlet channel, branch channel-I, branch channel-II, and outlet channel all have a depth of 0.5 mm and a width of 3 mm; the inlet channel and outlet channel are both 48 mm long; and the branch channel-I and branch channel-II are both 32 mm long.

[0099] Along the length of the bipolar plate, there are 5 branch channels-I and 5 branch channels-II within every 50 mm.

[0100] The cross-section of the interdigitated electrolyte channel is a regular shape, and the included angle δ between the bottom and side surfaces of the interdigitated electrolyte channel is 90°.

[0101] The surface of the bipolar plate adjacent to the electrode has a frosted structure with a surface roughness Ra1 of 6.3 μm; the bottom surface of the interdigitated electrolyte flow channel also has a frosted structure with a surface roughness Ra2 of 5 μm. The bipolar plate is made of graphite / epoxy resin composite material (prepared according to the method in Example 5 of CN101308924B, specifically using epoxy resin purchased from Hebei Yueteng Anticorrosion Materials Co., Ltd. instead of the phenolic resin powder). An electrolyte inlet 2 is also provided on the bipolar plate. Figure 1 (bottom left corner) and electrolyte outlet 1 ( Figure 1 (Top right corner) The lengths of the electrolyte inlet 2 and the electrolyte outlet 1 are both 3mm. The ratio of the length a of the expansion section 22 to the length b of the first straight section 21 is 2:1; the ratio of the length c of the reduction section 11 to the length d of the second straight section 12 is 2:1.

[0102] Along the flow direction of the electrolyte, the electrolyte inlet 2 is divided into a first cylindrical section 21 and an expanding section 22, and the electrolyte outlet 1 is divided into a constricting section 11 and a second cylindrical section 12. Along the flow direction of the electrolyte, the cross-sections of the first cylindrical section 21 and the second cylindrical section 12 are both rectangular; the cross-sections of the expanding section 22 and the constricting section 11 are both trapezoidal.

[0103] Along the flow direction of the electrolyte, the included angle α of the expanding section 22 is 135°, and the included angle β of the narrowing section 11 is 45°. Along the flow direction of the electrolyte, the inner diameter m of the expanding section 22 increases from 0.5 mm to 4.5 mm; the inner diameter p of the narrowing section 11 decreases from 4.5 mm to 0.5 mm; the inner diameter n of the first straight section 21 and the inner diameter q of the second straight section 12 are both 0.5 mm. That is, the ratio of the inner diameter m of the expanding section 22 to the inner diameter n of the first straight section 21 is 9:1; the ratio of the inner diameter p of the narrowing section 11 to the inner diameter q of the second straight section 12 is 9:1.

[0104] Example 2

[0105] According to Example 1, the only difference is that the surface roughness Ra1 of the bipolar plate adjacent to the electrode is 12.5 μm, and the surface roughness Ra2 of the bottom surface of the interdigitated electrolyte channel is 10 μm, while the other conditions are the same.

[0106] Example 3

[0107] According to Example 1, the difference is that, along the direction from the surface to the bottom of the interdigitated electrolyte channel, the cross-section of the interdigitated electrolyte channel is trapezoidal (wider at the top and narrower at the bottom), and the included angle δ between the bottom and side surfaces of the interdigitated electrolyte channel is 100°, with the other conditions being the same.

[0108] Example 4

[0109] According to Example 1, the difference is that, along the direction from the surface to the bottom of the interdigitated electrolyte channel, the cross-section of the interdigitated electrolyte channel is trapezoidal (wider at the top and narrower at the bottom), and the included angle δ between the bottom and side surfaces of the interdigitated electrolyte channel is 150°, with the other conditions being the same.

[0110] Example 5

[0111] According to Example 1, the difference is that, along the flow direction of the electrolyte, the electrolyte inlet and the electrolyte outlet are respectively the first straight section and the second straight section, and the cross-section of the first straight section and the second straight section are both rectangular.

[0112] The inner diameter of both the first and second straight sections is 2mm, and all other conditions are the same.

[0113] Example 6

[0114] According to Example 1, the difference is that, along the flow direction of the electrolyte, the inner diameter m of the expanding section is increased from 0.5 mm to 6 mm; the inner diameter p of the narrowing section is decreased from 6 mm to 0.5 mm; the inner diameter n of the first straight section and the inner diameter q of the second straight section are both 0.5 mm; that is, the ratio of the inner diameter m of the expanding section to the inner diameter n of the first straight section is 12:1; the ratio of the inner diameter p of the narrowing section to the inner diameter q of the second straight section is 12:1, and the other conditions are the same.

[0115] Example 7

[0116] According to Example 1, the difference is that the depth of the inlet channel, branch channel-I, branch channel-II and outlet channel are replaced with 2.5 mm and the width is replaced with 1 mm, while the other conditions are the same.

[0117] Example 8

[0118] According to Example 1, the difference is that a 0.2 mm thick activated carbon layer is sprayed on the surface of the bipolar plate adjacent to the electrode, with a surface roughness Ra1 of 3.2 μm, and a 0.1 mm thick activated carbon layer is sprayed on the bottom surface of the interdigitated electrolyte channel, with a surface roughness Ra2 of 6.3 μm, and the other conditions are the same.

[0119] Example 9

[0120] According to Example 1, the difference is that a patterned (wavy) design is pressed onto the surface of the bipolar plate adjacent to the electrode, and its surface roughness Ra1 is 4 μm. A patterned (wavy) design is pressed onto the bottom surface of the interdigitated electrolyte channel, and its surface roughness Ra2 is 0.063 μm. All other conditions are the same.

[0121] Comparative Example 1

[0122] According to Example 1, the difference is that the surface of the bipolar plate adjacent to the electrode is a rough surface, that is, the surface roughness Ra1 is 25 μm, and the other conditions are the same.

[0123] Comparative Example 2

[0124] According to Example 1, the difference is that the bottom surface of the interdigitated electrolyte channel is a rough surface, that is, the surface roughness Ra2 is 25μm, and the other conditions are the same.

[0125] Comparative Example 3

[0126] According to Example 1, the difference is that branch channel-I is connected to the inlet channel and branch channel-II is connected to the outlet channel, while the other conditions are the same.

[0127] Test case

[0128] Electrochemical performance tests were conducted on the flow batteries assembled from the bipolar plates of Examples 1-9 and Comparative Examples 1-3.

[0129] like Figure 5 As shown, the flow battery includes a separator B1 (perfluorosulfonic acid separator, commercially available from Chemours Chemical Company, product name Nafion115), a positive electrode B2-1 disposed on one side of the separator and a negative electrode B2-2 disposed on the other side. Both the positive and negative electrodes are porous carbon fiber felts, commercially available from SGL Chemical Company, product name GFD2.5EA, with dimensions of 48mm×40mm×2.5mm.

[0130] The flow battery also includes a first bipolar plate B4-1 adjacent to the positive electrode and a second bipolar plate B4-2 adjacent to the negative electrode, wherein the first bipolar plate B4-1 and the second bipolar plate B4-2 are the same and are independently the bipolar plates of Examples 1-9 and Comparative Examples 1-3, respectively.

[0131] Both the first bipolar plate B4-1 and the second bipolar plate B4-2 are equipped with a current collector B5 (made of copper plate) and an end plate B6 (made of aluminum alloy) on their outer sides, and these components are fastened with bolts through pre-set holes; a sealing element B3 is provided between the first bipolar plate B4-1 and the positive electrode B2-1, and between the second bipolar plate B4-2 and the negative electrode B2-2, to prevent electrolyte leakage; the positive electrode electrolyte is 0.8 mol·L⁻¹. -1 V(IV) + 0.8 mol·L -1 V(V) + 3mol·L -1 The H2SO4 solution, with a negative electrode electrolyte of 0.8 mol·L⁻¹ -1 V(III) + 0.8 mol·L -1 V(II) + 3 mol·L -1A solution of H2SO4 is used. A peristaltic pump is used to deliver the electrolyte into the battery to obtain a vanadium redox flow battery. The electrolyte inlet 2 and the electrolyte outlet 1 allow the electrolyte to circulate.

[0132] The battery's output performance was measured using a potentiostat, and the energy efficiency was measured and calculated using charge-discharge tests. The test results are listed in Table 1.

[0133] Table 1

[0134] Energy efficiency, % Flow resistance pressure drop, kPa Example 1 83.1 43 Example 2 79.4 48 Example 3 85.2 40 Example 4 86.7 38 Example 5 77.4 50 Example 6 80.9 44 Example 7 76.6 53 Example 8 82.2 44 Example 9 81.5 45 Comparative Example 1 70.1 64 Comparative Example 2 68.7 65 Comparative Example 3 74.8 55

[0135] As can be seen from the results in Table 1, the flow batteries obtained by using the bipolar plates provided by the present invention in Examples 1-9 have significantly higher energy efficiency than those in Comparative Examples 1-3 and significantly lower voltage drop than those in Comparative Examples 1-3, exhibiting excellent electrochemical performance.

[0136] Comparing Examples 1 and 2, 8-9, it can be seen that the technical solution of adjusting the surface roughness Ra1 of the bipolar plate and the surface roughness Ra2 of the bottom surface of the interdigitated electrolyte flow channel within the preferred protection range is more conducive to improving the electrochemical performance of the flow battery.

[0137] Comparing Examples 1 and 3-4, it can be seen that the technical solution of adjusting the included angle δ between the bottom and side surfaces of the interdigitated electrolyte flow channel in the bipolar plate within the preferred protection range is more conducive to improving the electrochemical performance of the flow battery.

[0138] Comparing Examples 1 and 5-6, it can be seen that the technical solution of adjusting the electrolyte inlet and electrolyte outlet in the bipolar plate within the preferred protection range is more conducive to improving the electrochemical performance of the flow battery.

[0139] Comparing Examples 1 and 7, it can be seen that the technical solution of adjusting the depth and width of the inlet channel, branch channel-I, branch channel-II and outlet channel in the bipolar plate independently within the preferred protection range is more conducive to improving the electrochemical performance of the flow battery.

[0140] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A bipolar plate, characterized in that, The bipolar plate is provided with interdigitated electrolyte channels. The surface roughness Ra1 of the bipolar plate is 0.05-9 μm, and the surface roughness Ra2 of the bottom surface of the interdigitated electrolyte channels is 0.05-9 μm. The interdigitated electrolyte flow channel includes an inlet flow channel, at least one branch flow channel-I, at least one branch flow channel-II, and an outlet flow channel; The branch flow channel-I and the branch flow channel-II are arranged at intervals, and the branch flow channel-I is connected to the liquid outlet flow channel, while the branch flow channel-II is connected to the liquid inlet flow channel. The bipolar plate is provided with an electrolyte inlet and an electrolyte outlet. Along the flow direction of the electrolyte, the electrolyte inlet is divided into a first straight section and an expanding section; the electrolyte outlet is divided into a narrowing section and a second straight section. The ratio of the inner diameter m of the expanded section to the inner diameter n of the first straight section is 1.1-15:1; The ratio of the inner diameter p of the reduced diameter section to the inner diameter q of the second straight section is 1.1-15:1; The cross-section of the interdigitated electrolyte channel is trapezoidal; the included angle δ between the bottom and side surfaces of the interdigitated electrolyte channel is 100-150°.

2. The bipolar plate according to claim 1, wherein, The thickness of the bipolar plate is 2-6 mm.

3. The bipolar plate according to claim 2, wherein, The thickness of the bipolar plate is 2.5-5 mm.

4. The bipolar plate according to claim 1, wherein, The inlet channel, branch channel-I, branch channel-II, and outlet channel may have the same or different depths.

5. The bipolar plate according to claim 1, wherein, The depths of the inlet channel, branch channel-I, branch channel-II, and outlet channel are each independently 0.05-2.5 mm.

6. The bipolar plate according to claim 5, wherein, The depths of the inlet channel, branch channel-I, branch channel-II, and outlet channel are each independently 0.1-2 mm.

7. The bipolar plate according to claim 1, wherein, Along the length of the bipolar plate, the number of branch channels-I and branch channels-II is independently 2-6 per 50mm.

8. The bipolar plate according to claim 7, wherein, Along the length of the bipolar plate, the number of branch channels-I and branch channels-II is independently 4-6 per 50mm.

9. The bipolar plate according to claim 1, wherein, Each of the branch channels-I and branch channels-II is independently and uniformly distributed along the length of the bipolar plate.

10. The bipolar plate according to claim 1, wherein, The widths of the inlet channel, branch channel-I, branch channel-II, and outlet channel may be the same or different.

11. The bipolar plate according to claim 1, wherein, The widths of the inlet channel, branch channel-I, branch channel-II, and outlet channel are each 1-5 mm.

12. The bipolar plate according to claim 11, wherein, The widths of the inlet channel, branch channel-I, branch channel-II, and outlet channel are each independently 1.5-4.5 mm.

13. The bipolar plate according to claim 1, wherein, The interdigitated electrolyte flow channel is either a single-channel structure or a parallel multi-channel structure.

14. The bipolar plate according to claim 1, wherein, Along the flow direction of the electrolyte, the cross-sections of the first and second straight cylindrical sections are each independently a regular shape; the cross-sections of the expanding and contracting sections are each independently a regular or irregular shape.

15. The bipolar plate according to claim 14, wherein, Along the flow direction of the electrolyte, the cross-sections of the first and second straight cylindrical sections are independently rectangular and square, respectively; the cross-sections of the expanding and contracting sections are independently regular shapes.

16. The bipolar plate according to claim 15, wherein, The cross-sections of the expanded and reduced diameter sections are independently rectangular, square, or trapezoidal.

17. The bipolar plate according to claim 1, wherein, Along the flow direction of the electrolyte, the included angle α of the expanding section is ≥90°; the included angle β of the narrowing section is ≤90°.

18. The bipolar plate according to claim 17, wherein, Along the flow direction of the electrolyte, the included angle α of the expanding section is 100-150°; the included angle of the narrowing section is 30-80°.

19. The bipolar plate according to claim 1, wherein, The ratio of the inner diameter m of the expanded section to the inner diameter n of the first straight section is 2-10:

1.

20. The bipolar plate according to claim 1, wherein, The ratio of the inner diameter p of the reduced diameter section to the inner diameter q of the second straight section is 2-10:

1.

21. The bipolar plate according to claim 1, wherein, The lengths of the electrolyte inlet and electrolyte outlet are each independently the same as the thickness of the bipolar plate.

22. The bipolar plate according to claim 1, wherein, In the electrolyte inlet, the ratio of the length a of the expanding section to the length b of the first straight section is 3-1:1; in the electrolyte outlet, the ratio of the length c of the narrowing section to the length d of the second straight section is 3-1:

1.

23. The bipolar plate according to claim 1, wherein, The surface of the bipolar plate and the bottom surface of the interdigitated electrolyte flow channel are each independently frosted; and / or The surface of the bipolar plate and the bottom surface of the interdigitated electrolyte channel are each independently coated with carbon powder and / or activated carbon layers.

24. The bipolar plate according to claim 1, wherein, The material of the bipolar plate is selected from at least one of graphite / polymer composite material, metal / polymer composite material and graphite / metal composite material.

25. A flow battery, comprising a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode; The flow battery further includes a first bipolar plate adjacent to the positive electrode and a second bipolar plate adjacent to the negative electrode; The first bipolar plate and the second bipolar plate are each independently the bipolar plate described in any one of claims 1-24.

26. The flow battery according to claim 25, wherein, The flow battery also includes a positive electrolyte and a negative electrolyte.

27. The flow battery according to claim 26, wherein, The positive electrode electrolyte causes a reaction at the positive electrode involving the interconversion of pentavalent and tetravalent vanadium ions.

28. The flow battery according to claim 26, wherein, The negative electrode electrolyte causes a reaction at the negative electrode involving the interconversion of trivalent and divalent vanadium ions.

29. The flow battery according to claim 25, wherein, The flow battery also includes an end plate disposed on the outer side of the first bipolar plate and the second bipolar plate.

30. The flow battery according to claim 25, wherein, Each of the first bipolar plate and the positive electrode, and the second bipolar plate and the negative electrode, is independently provided with a sealing element.

31. The flow battery according to claim 25, wherein, Current collectors are respectively provided on the outer sides of the first bipolar plate and the second bipolar plate.

32. A battery stack comprising the flow battery of claim 25.

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