Composite material and method for producing same, bipolar plate, flow battery

Abstract

The application relates to the technical field of liquid flow batteries, in particular to a composite material and a preparation method thereof, a bipolar plate and a liquid flow battery. The method comprises the following steps: extrusion molding of a slurry containing resin-I, resin-II, a conductive agent, a modifier and a dispersing agent to obtain a composite material; wherein the weight ratio of the resin-I, the resin-II, the conductive agent and the modifier in the slurry is 1-10:10-40:50-70:5-15; the ratio of the dispersing agent in mL to the total amount of the resin-I, the resin-II, the conductive agent and the modifier in g is 300-1000:100; the modifier contains a condensed ring aromatic hydrocarbon mixture, and the number of carbon atoms of the condensed ring aromatic hydrocarbon in the condensed ring aromatic hydrocarbon mixture is C 22 ‑C 24 . The method obtains the composite material with high bending strength and low hydrogen permeability; meanwhile, the liquid flow battery containing the composite material has high efficiency.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, specifically to a method for preparing a composite material, a composite material obtained by the method, a bipolar plate containing the composite material, and a flow battery containing the bipolar plate. 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 plate is a key component, connecting the positive and negative electrodes of different individual cells and conducting the internal circuitry. It should possess good conductivity, mechanical strength, and resistance to chemical oxidation and electrochemical corrosion. Based on the materials used, bipolar plates can be classified as metal bipolar plates, graphite bipolar plates, and composite material bipolar plates. However, in the actual operating environment of flow batteries, metal bipolar plates inevitably undergo electrochemical corrosion in strongly acidic or alkaline systems, thus failing to meet the battery's operational requirements. Graphite bipolar plates offer advantages such as high conductivity, low density, and good corrosion resistance; however, their mechanical strength is insufficient, making them prone to brittle fracture during processing. Composite bipolar plates combine the high conductivity of graphite with the high toughness of polymer materials and have gained widespread application. Furthermore, optimizing the bipolar plate structure is crucial for flow battery performance, but reports in this area are relatively limited, especially regarding the significant impact of the placement and number of inlet and outlet ports on battery performance.

[0004] How to efficiently optimize the bipolar plate structure design to ensure uniform electrolyte distribution in different parts of the flow channel and improve the performance of the flow battery is an urgent problem to be solved for the further commercialization of this technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of existing bipolar plates, such as the inability to simultaneously achieve high mechanical strength and high gas barrier properties, uneven electrolyte distribution within the flow channel, and low performance of flow batteries. This invention provides a method for preparing a composite material, a composite material prepared by this method, a bipolar plate containing the composite material, and a flow battery containing the bipolar plate. The composite material prepared by the method provided by this invention possesses both high mechanical strength and low hydrogen permeability. By using this composite material in a bipolar plate and combining it with a specific bipolar plate structure, a flow battery assembled from this bipolar plate exhibits excellent electrochemical performance. Furthermore, this method offers advantages such as simple process, low cost, and environmental friendliness.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a composite material, the method comprising: extruding a slurry containing resin-I, resin-II, a conductive agent, a modifier, and a dispersant to obtain a composite material;

[0007] In the slurry, the weight ratio of resin-I, resin-II, conductive agent and modifier is 1-10:10-40:50-70:5-15;

[0008] The ratio of the total amount of the dispersant (in mL) to the total amount of the resin-I, resin-II, conductive agent and modifier (in g) is 300-1000:100.

[0009] The modifier contains a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 .

[0010] Preferably, the method includes the following steps:

[0011] (1) The resin-I, resin-II, conductive agent, modifier and dispersant are mixed to obtain the slurry;

[0012] (2) The slurry is extruded in a twin-screw extruder to obtain the composite material.

[0013] Preferably, the polycyclic aromatic hydrocarbon has a structure of five benzene rings that are unsubstituted and / or alkyl-substituted, and more preferably has a structure of five benzene rings that are unsubstituted and / or C1-C2 alkyl-substituted;

[0014] Preferably, the polycyclic aromatic hydrocarbon mixture is prepared by the following method: mixing asphalt and toluene, extracting the resulting mixture, and then distilling the resulting extract to obtain the polycyclic aromatic hydrocarbon mixture.

[0015] A second aspect of the present invention provides a composite material prepared by the method provided in the first aspect.

[0016] The third aspect of the present invention provides a bipolar plate made of the composite material provided in the second aspect.

[0017] Preferably, the bipolar plate is provided with at least M electrolyte inlets and at least N electrolyte outlets, wherein M is a positive integer ≥ 2, N is a positive integer ≥ 1, and MN = 1; wherein the electrolyte inlets are provided along one side of the bipolar plate and the electrolyte outlets are provided along the other side of the bipolar plate.

[0018] The surface roughness Ra of the bipolar plate is 0.05-12.5μm, and no electrolyte flow channel is provided on the bipolar plate.

[0019] Preferably, 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.

[0020] A fourth aspect of the present invention provides a flow battery comprising the bipolar plate provided in the third aspect.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The method provided by the present invention obtains a composite material with both high flexural strength and low hydrogen permeability by limiting the slurry containing resin-I, resin-II, conductive agent, modifier and dispersant to extrusion molding, and then combining the content ratio of each component and a specific modifier. In particular, limiting the content ratio of each component, the mixing conditions and the extrusion molding conditions to within the preferred range is more conducive to improving the comprehensive performance of the composite material. At the same time, the method has the advantages of simple process flow, low cost and green environmental protection.

[0023] (2) The composite material provided by the present invention is used in bipolar plates, so that the bipolar plates have both high mechanical strength and low hydrogen permeability. In particular, when combined with a specific bipolar plate structure, namely, a specific number and specific structure of electrolyte inlet and electrolyte outlet, and a specific surface roughness, it is more conducive to improving the performance of the bipolar plates.

[0024] (3) Using the bipolar plate provided by the present invention in a flow battery can effectively improve the coulombic efficiency, voltage efficiency and energy efficiency of the flow battery. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a bipolar plate for a flow battery according to a specific embodiment of the present invention;

[0026] Figure 2This 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;

[0027] Figure 3 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.

[0028] Explanation of reference numerals in the attached figures

[0029] 6-1. Electrolyte inlet section; 6-11. First straight section; 6-12. Diameter expansion section

[0030] 6-2, Electrolyte outlet section; 6-21, Diameter reduction section; 6-22, Second straight section Detailed Implementation

[0031] 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.

[0032] 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.

[0033] In this invention, unless otherwise specified, "first" and "second" do not indicate a sequence or limit the various materials or steps; they are merely used to distinguish that these are not the same material or step. For example, in "first cylindrical section" and "second cylindrical section," "first" and "second" are only used to distinguish that these are not the same cylindrical section.

[0034] The first aspect of the present invention provides a method for preparing a composite material, the method comprising: extruding a slurry containing resin-I, resin-II, a conductive agent, a modifier, and a dispersant to obtain a composite material;

[0035] In the slurry, the weight ratio of resin-I, resin-II, conductive agent and modifier is 1-10:10-40:50-70:5-15;

[0036] The ratio of the total amount of the dispersant (in mL) to the total amount of the resin-I, resin-II, conductive agent and modifier (in g) is 300-1000:100.

[0037] The modifier contains a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 .

[0038] The inventors of this invention have discovered that, with a carbon atom number of C... 22 -C 24 A mixture of polycyclic aromatic hydrocarbons is used as a modifier, combined with resin-I, resin-II, a conductive agent, and a dispersant, resulting in a composite material prepared from this slurry that exhibits both high flexural strength and low hydrogen permeability. Specifically, the modifier in the slurry can mitigate the reduction in mechanical strength caused by the conductive agent. Combined with the synergistic effect of resin-I, resin-II, and the conductive agent, and their specific content ratios, the performance of the composite material can be further optimized. This results in a flow battery assembled with bipolar plates containing this composite material exhibiting excellent electrochemical performance, specifically high coulombic efficiency, voltage efficiency, and energy efficiency.

[0039] In some embodiments of the present invention, preferably, the method includes the following steps:

[0040] (1) The resin-I, resin-II, conductive agent, modifier and dispersant are mixed to obtain the slurry;

[0041] (2) The slurry is extruded in a twin-screw extruder to obtain the composite material.

[0042] In this invention, in step (1), the mixing aims to uniformly mix the resin-I, resin-II, conductive agent, modifier, and dispersant. Preferably, in step (1), the mixing conditions include: a temperature of 15-40°C, preferably 20-30°C; a rotation speed of 100-1000 rpm, preferably 300-800 rpm; and a time of 1-15 h, preferably 3-8 h.

[0043] In this invention, in step (2), the extrusion molding aims to obtain the composite material from the slurry. Preferably, in step (2), the extrusion molding conditions include: a temperature of 150-250°C, more preferably 180-230°C; a pressure of 10-25 MPa, more preferably 10-20 MPa; and a rotation speed of 150-240 rpm, more preferably 190-240 rpm.

[0044] In some embodiments of the present invention, preferably, the weight ratio of resin-I, resin-II, conductive agent, and modifier in the slurry is 3-10:10-35:55-70:7-15. Using this preferred weight ratio is more beneficial for improving the flexural strength and hydrogen permeability of the composite material.

[0045] In some embodiments of the present invention, preferably, the ratio of the total amount of the dispersant (in mL) to the total amount of the resin-I, resin-II, conductive agent, and modifier (in g) is 500-1000:100. These preferred conditions facilitate thorough mixing of the polymer branches in the solvent.

[0046] In some embodiments of the present invention, preferably, resin-I is ABS resin, and the content of butadiene-derived structural units in resin-I is 10-30 wt%. In the present invention, unless otherwise specified, ABS resin refers to acrylonitrile-butadiene-styrene copolymer.

[0047] In some embodiments of the present invention, preferably, the resin-II is selected from at least one of polyimide, polyethyleneimine, and polypropyleneimide, and the weight-average molecular weight of the resin-II is 1 × 10⁻⁶. 4 -5×10 4 g / mol.

[0048] In some embodiments of the present invention, preferably, the conductive agent is selected from at least one of Ketjen black, graphite, carbon nanotubes and carbon fibers.

[0049] In some embodiments of the present invention, preferably, the dispersant is selected from at least one of dimethyl sulfoxide, acetone, ethanol and propanol.

[0050] In a preferred embodiment of the present invention, preferably, the polycyclic aromatic hydrocarbon has a structure of five benzene rings that are unsubstituted and / or alkyl-substituted, and more preferably, has a structure of five benzene rings that are unsubstituted and / or C1-C2 alkyl-substituted.

[0051] In this invention, the source of the polycyclic aromatic hydrocarbon mixture has a wide range of choices. It can be obtained by purchase or by preparation. For details, please refer to "Pyrolysis Characteristics and Properties of Thermal Conversion Products of Toluene-Soluble Components in Medium-Temperature Asphalt", Zhu Yaming, Zhao Xuefei, Cheng Junxia, ​​Liu Wei, Lü Jun, Wang Ying; Materials Reports B: Research Article; June 2017 (B) Vol. 31 No. 6, pp. 109-125.

[0052] In one specific embodiment of the present invention, the polycyclic aromatic hydrocarbon mixture is prepared by the following method: mixing asphalt and toluene, extracting the resulting mixture, and then distilling the resulting extract to obtain the polycyclic aromatic hydrocarbon mixture.

[0053] In some embodiments of the present invention, preferably, the weight ratio of the asphalt to toluene is 1:1-15, for example, 1:1, 1:2, 1:5, 1:6, 1:8, 1:10, 1:15, and any value within the range of any two values, preferably 1:5-10.

[0054] In this invention, the first mixing is intended to uniformly mix the asphalt and toluene. Preferably, the conditions for the first mixing include: a temperature of 80-100°C, more preferably 85-95°C; and a rotation speed of 100-1000 rpm, more preferably 300-700 rpm.

[0055] In some embodiments of the present invention, preferably, the extraction conditions include: a temperature of 80-100°C, more preferably 85-95°C; and a time of 1-10 hours, more preferably 1-5 hours.

[0056] In this invention, the extract is filtered before distillation, the resulting extract is distilled, and the residue is recovered or discharged.

[0057] In this invention, the distillation aims to remove toluene from the extract to obtain the polycyclic aromatic hydrocarbon mixture. Preferably, the distillation conditions include: a temperature of 60-80°C, more preferably 65-75°C; and a pressure of 0.01-0.1 MPa, more preferably 0.05-0.1 MPa.

[0058] In this invention, unless otherwise specified, all pressures refer to gauge pressure.

[0059] In some embodiments of the present invention, preferably, the asphalt is selected from at least one of petroleum asphalt, coal tar pitch, direct coal liquefaction pitch, indirect coal liquefaction pitch, and mesophase pitch.

[0060] A second aspect of the present invention provides a composite material prepared by the method provided in the first aspect.

[0061] In some embodiments of the present invention, preferably, the composite material contains resin-I, resin-II, a conductive agent, and a modifier; more preferably, the composite material is composed of resin-I, resin-II, a conductive agent, and a modifier.

[0062] In some embodiments of the present invention, preferably, based on the total weight of the composite material, the content of resin-I is 1-10 wt%, preferably 3-10 wt%; the content of resin-II is 10-40 wt%, preferably 10-35 wt%; the content of the conductive agent is 50-70 wt%, preferably 55-70 wt%; and the content of the modifier is 5-15 wt%, preferably 7-15 wt%.

[0063] According to the present invention, preferably, the flexural strength of the composite material is ≥26MPa, more preferably 26-60MPa; the hydrogen permeability is ≤1.8×10⁻⁶. -6 cm 3 ·s -1 ·cm -2 Preferably 1×10 -7 -1.8×10 -6 cm 3 ·s -1 ·cm -2 .

[0064] In this invention, unless otherwise specified, the bending strength parameter is directly measured using an electronic universal testing machine; the hydrogen permeability parameter is measured using a permeation cell and a gas chromatograph.

[0065] The third aspect of the present invention provides a bipolar plate made of the composite material provided in the second aspect.

[0066] In this invention, by setting the number and structure of the electrolyte inlet and electrolyte outlet, the uniformity of electrolyte distribution can be effectively improved, thereby improving the electrochemical performance of the flow battery assembled from the bipolar plate.

[0067] In some embodiments of the present invention, preferably, the bipolar plate is provided with at least M electrolyte inlets and at least N electrolyte outlets, wherein M is a positive integer ≥ 2, N is a positive integer ≥ 1, and MN = 1; wherein the electrolyte inlets are provided along one side of the bipolar plate and the electrolyte outlets are provided along the other side of the bipolar plate.

[0068] The surface roughness Ra of the bipolar plate is 0.05-12.5μm, and no electrolyte flow channel is provided on the bipolar plate.

[0069] In this invention, unless otherwise specified, the electrolyte inlet is located along one side of the bipolar plate and the electrolyte outlet is located along the other side of the bipolar plate, meaning that if all of the electrolyte inlets 6-1 are located along one side of the bipolar plate (e.g., ...), Figure 1 In the length direction below the bipolar plate, then, a plurality of electrolyte outlets 6-2 are provided along the length direction on the other side of the bipolar plate (e.g., Figure 1 (Above the bipolar plate along its length).

[0070] In this invention, unless otherwise specified, the bipolar plate only has an electrolyte inlet and an electrolyte outlet. That is, the bipolar plate provided by this invention does not have an electrolyte flow channel, only an electrolyte inlet and an electrolyte outlet. In other words, the bipolar plate provided by this invention does not require a flow field structure, resulting in a simpler process, lower cost, and improved battery efficiency of the flow battery assembled from this bipolar plate. In contrast, existing bipolar plates without a flow field structure have rough surfaces, with a surface roughness Ra typically greater than 12.5 μm.

[0071] According to a preferred embodiment of the present invention, the surface roughness Ra of the bipolar plate is 0.05-9 μm, for example, 0.05 μm, 0.063 μm, 1 μm, 3.2 μm, 5 μm, 6.3 μm, 7 μm, 8 μm, 9 μm, and any value within the range of any two values, further selected as 0.063-7 μm. In the present invention, if the surface roughness Ra is too high, a gap exists between the electrode and the bipolar plate, which is not conducive to the diffusion of electrolyte on the electrode; if the surface roughness Ra is too low, it may lead to misalignment of the electrode and the bipolar plate.

[0072] In this invention, the surface roughness Ra parameter is measured using a probe contact profilometer. It should be noted that, in this invention, the surface of the bipolar plate refers to the effective surface in contact with the electrolyte.

[0073] In this invention, as long as the surface roughness Ra of the bipolar plate is maintained at 0.05-12.5 μm, there are no particular limitations on the specific implementation method for achieving this surface roughness Ra. Any method that achieves the aforementioned surface roughness Ra is within the protection scope of this invention. To further simplify the manufacturing process, preferably, the surface of the bipolar plate has a frosted structure; and / or, the surface of the bipolar plate is sprayed with carbon powder and / or an activated carbon layer; and / or, the surface of the bipolar plate is embossed with a patterned texture.

[0074] In this invention, there is no particular limitation on the method of obtaining the frosted structure; for example, it can be obtained by polishing.

[0075] 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 can achieve a surface roughness Ra of 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.

[0076] The present invention does not have a particular limitation on the amount of carbon powder and / or activated carbon layer sprayed on the surface of the bipolar plate; for example, the coating thickness can be 0.05-0.5 mm.

[0077] The present invention does not have any particular limitation on the pattern on the surface of the bipolar plate. It can be a regular pattern or an irregular pattern, as long as the surface roughness Ra of the bipolar plate meets the requirements.

[0078] According to the present invention, preferably, the thickness of the bipolar plate is 2-6 mm, for example, 2 mm, 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, and any value within the range of any two values, and more preferably 2.5-5 mm.

[0079] In some embodiments of the present invention, preferably, the number M of electrolyte inlets is 2-6, for example, 2, 3, 4, 5, or 6; and the number N of electrolyte outlets is 1-5, for example, 1, 2, 3, 4, or 5.

[0080] In some embodiments of the present invention, preferably, the electrolyte inlet is uniformly disposed along one side of the bipolar plate, and the electrolyte outlet is uniformly disposed along the other side of the bipolar plate.

[0081] According to a specific embodiment of the present invention, such as Figure 1 As shown, the bipolar plate is provided with 3 electrolyte inlets and 2 electrolyte outlets, and the 3 electrolyte inlets 6-1 are evenly arranged along the length of the other side of the bipolar plate (e.g., Figure 1 (As shown in the lower length direction) and two electrolyte outlets 6-2 are evenly arranged along one side of the bipolar plate in the length direction (e.g., Figure 1 (As shown in the upper length direction). This setting improves the uniformity of electrolyte distribution while reducing dead zones in the electrolyte.

[0082] In some embodiments of the present invention, preferably, along the flow direction of the electrolyte, the electrolyte inlet is sequentially divided into a first straight section and an expanding section; the electrolyte outlet is sequentially divided into a narrowing section and a second straight section.

[0083] In this invention, unless otherwise specified, the electrolyte inlet consists of a first cylindrical section and an expanding section; the electrolyte outlet consists of a narrowing section and a second cylindrical section.

[0084] In some embodiments of the present invention, preferably, the cross-sections of the first straight cylindrical section and the second straight cylindrical section are each independently regular in shape along the flow direction of the electrolyte, preferably rectangular or square.

[0085] In some embodiments of the present invention, preferably, the cross-sections of the expanding section and the contracting section along the flow direction of the electrolyte are each independently a regular shape or an irregular shape, preferably a regular shape, and more preferably a rectangle, square, or trapezoid. This preferred approach not only helps reduce processing difficulty but can also reduce the dead zone of the electrolyte.

[0086] In this invention, unless otherwise specified, the cross-sections of the first straight section, the second straight section, the expanded section, and the reduced section refer to planes parallel to the thickness of the bipolar plate.

[0087] In this invention, unless otherwise specified, the regular shapes include, but are not limited to, rectangles, squares, and trapezoids.

[0088] In some embodiments of the present invention, preferably, along the flow direction of the electrolyte, the included angle α of the expanding section is ≥90°, preferably 100-150°, for example, α includes but is not limited to 90°, 100°, 120°, 135°, 150°; the included angle β of the narrowing section is ≤90°, preferably 30-80°, for example, β includes but is not limited to 30°, 45°, 60°, 80°, 90°.

[0089] In some embodiments of the present invention, preferably, 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, more preferably 2-10:1; preferably, the ratio of the inner diameter p of the reduced section to the inner diameter q of the second straight section is 1.1-15:1, more preferably 2-10:1.

[0090] In one specific embodiment of the present invention, the inner diameter m of the expanding section and the inner diameter p of the contracting section are each independently 0.5-5 mm, preferably 1-4.5 mm, more preferably 1.5-4.5 mm; further preferably, the inner diameter n of the first straight section and the inner diameter q of the second straight section are each independently 0.5-2.5 mm, preferably 0.5-1.5 mm.

[0091] In some embodiments of the present invention, preferably, the lengths of the electrolyte inlet and the electrolyte outlet are each independently the same as the thickness of the bipolar plate.

[0092] In one specific embodiment of the present invention, the lengths of the electrolyte inlet and the electrolyte outlet are each independently 2-6 mm, preferably 2.5-5 mm.

[0093] In some embodiments of the present invention, preferably, in the electrolyte inlet section, 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 section, the ratio of the length c of the narrowing section to the length d of the second straight section is 3-1:1.

[0094] In this invention, unless otherwise specified, the inner diameter and length of the first straight section, the second straight section, the expanding section, and the contracting section refer to the width perpendicular to the electrolyte flow direction and the depth parallel to the electrolyte flow direction, respectively.

[0095] In some embodiments of the present invention, such as Figure 2-3 As shown, along the flow direction of the electrolyte, the electrolyte inlet 6-1 is sequentially divided into a first cylindrical section 6-11 and an expanding section 6-12, and the electrolyte outlet 6-2 is sequentially divided into a constricting section 6-21 and a second cylindrical section 6-22. The cross-sections of the first cylindrical section 6-11 and the second cylindrical section 6-22 are both rectangular or square, while the cross-sections of the expanding section 6-12 and the constricting section 6-21 are both trapezoidal, rectangular, or square. The included angle α of the expanding section 6-12 is ≥90°, and the included angle β of the constricting section 6-21 is ≤90°. The lengths of the electrolyte inlet 6-1 and the electrolyte outlet 6-2 are each independently the same as the thickness of the bipolar plate; the ratio of the inner diameter m of the expanding section 6-12 to the inner diameter n of the first cylindrical section 6-11 is 1.1-15:1; the ratio of the inner diameter p of the narrowing section 6-21 to the inner diameter q of the second cylindrical section 6-22 is 1.1-15:1; in the electrolyte inlet 6-1, the ratio of the length a of the expanding section 6-12 to the length b of the first cylindrical section 6-11 is 3-1:1; in the electrolyte outlet 6-2, the ratio of the length c of the narrowing section 6-21 to the length d of the second cylindrical section 6-22 is 3-1:1. This preferred embodiment is more conducive to enhancing mass transfer, reducing the concentration polarization resistance of the battery, and preventing the bipolar plate from shifting during battery assembly, thereby suppressing electrolyte leakage.

[0096] According to a particularly preferred embodiment of the present invention, a bipolar plate is provided, wherein the material of the bipolar plate contains a composite material, wherein the composite material is prepared by extruding a slurry containing resin-I, resin-II, a conductive agent, a modifier, and a dispersant to obtain the composite material;

[0097] In the slurry, the weight ratio of resin-I, resin-II, conductive agent and modifier is 3-10:10-35:55-70:7-15;

[0098] The ratio of the total amount of the dispersant (in mL) to the total amount of the resin-I, resin-II, conductive agent and modifier (in g) is 500-1000:100.

[0099] The modifier contains a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 The polycyclic aromatic hydrocarbon has a structure of five benzene rings that are unsubstituted and / or C1-C2 alkyl-substituted;

[0100] Wherein, resin-I is ABS resin, and the content of butadiene-derived structural units in resin-I is 10-30 wt%; resin-II is selected from at least one of polyimide, polyethyleneimine, and polypropyleneimide;

[0101] The bipolar plate is provided with at least M electrolyte inlets and at least N electrolyte outlets, wherein M is a positive integer ≥ 2, N is a positive integer ≥ 1, and MN = 1; wherein the electrolyte inlets are provided along one side of the bipolar plate and the electrolyte outlets are provided along the other side of the bipolar plate.

[0102] The surface roughness Ra of the bipolar plate is 0.05-12.5μm, and no electrolyte flow channel is provided on the bipolar plate;

[0103] 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.

[0104] A fourth aspect of the present invention provides a flow battery comprising the bipolar plate provided in the third aspect.

[0105] The present invention will be described in detail below through embodiments.

[0106] Bending strength parameters were obtained directly using an electronic universal testing machine;

[0107] The hydrogen permeability parameter was obtained by using a permeation cell and a gas chromatograph.

[0108] Preparation Example

[0109] 500g of asphalt and 2500g of toluene were mixed evenly and extracted in a constant temperature water bath at 90℃ and 500rpm for 5 hours. The resulting extract was filtered, and the liquid mixture was distilled at 0.09MPa and 70℃ to obtain a mixture of polycyclic aromatic hydrocarbons (PAHs). The total carbon number of the PAHs in the mixture was C. 22 -C 24 Furthermore, fused-ring aromatic hydrocarbons have a structure of five benzene rings that are unsubstituted and / or C1-C2 alkyl-substituted.

[0110] Example I-1

[0111] (1) Resin-I (ABS resin, butadiene structural unit content of 16wt%) and Resin-II (polyimide, weight average molecular weight of 3×10) were mixed. 4 The following ingredients (g / mol), conductive agent (graphite), modifier (mixture of polycyclic aromatic hydrocarbons), and dispersant (dimethyl sulfoxide) were mixed (at 25°C, at 500 rpm, for 8 hours) to obtain a slurry;

[0112] In the slurry, the weight ratio of resin-I, resin-II, conductive agent and modifier is 8:20:60:12; the ratio of the dispersant in mL to the total amount of resin-I, resin-II, conductive agent and modifier in g is 800:100.

[0113] (2) The above slurry was extruded in a twin-screw extruder (temperature 200℃, pressure 15MPa, speed 220rpm) to obtain composite material S1;

[0114] The physical properties of composite material S1 are listed in Table 1.

[0115] Example I-2

[0116] (1) Resin-I (ABS resin, butadiene structural unit content of 16wt%) and Resin-II (polyethyleneimine, weight average molecular weight of 1.5×10⁻⁶) were mixed. 4 The following ingredients were mixed (g / mol), conductive agent (carbon nanotubes), modifier (mixture of polycyclic aromatic hydrocarbons) and dispersant (acetone) (at 30℃, at 600 rpm, for 5 h) to obtain a slurry;

[0117] In the slurry, the weight ratio of resin-I, resin-II, conductive agent and modifier is 10:22:56:12; the ratio of the dispersant in mL to the total amount of resin-I, resin-II, conductive agent and modifier in g is 500:100.

[0118] (2) The above slurry was extruded in a twin-screw extruder (temperature 180℃, pressure 20MPa, speed 190rpm) to obtain composite material S2;

[0119] The physical properties of composite material S2 are listed in Table 1.

[0120] Example I-3

[0121] (1) Resin-I (ABS resin, butadiene structural unit content of 16wt%) and Resin-II (polypropyleneimide, weight average molecular weight of 2×10) were mixed. 4 The following ingredients were mixed (g / mol), conductive agent (carbon nanotubes), modifier (mixture of polycyclic aromatic hydrocarbons) and dispersant (ethanol) (at 20℃, at 300 rpm, for 8 h) to obtain a slurry;

[0122] In the slurry, the weight ratio of resin-I, resin-II, conductive agent and modifier is 10:28:55:7; the ratio of the dispersant in mL to the total amount of resin-I, resin-II, conductive agent and modifier in g is 1000:100.

[0123] (2) The above slurry was extruded in a twin-screw extruder (temperature 230℃, pressure 10MPa, speed 240rpm) to obtain composite material S3;

[0124] The physical properties of composite material S3 are listed in Table 1.

[0125] Example I-4

[0126] The method of Example I-1 is different except that in step (1), the weight ratio of resin-I, resin-II, conductive agent and modifier is replaced with 2:39:53:6, and the other conditions are the same, to obtain composite material S4.

[0127] The physical properties of composite material S4 are listed in Table 1.

[0128] Example I-5

[0129] The method of Example I-1 is different except that in step (1), the ratio of the total amount of dispersant in mL to the total amount of resin-I, resin-II, conductive agent and modifier in g is 300:100, and the other conditions are the same, to obtain composite material S5.

[0130] The physical properties of composite material S5 are listed in Table 1.

[0131] Example I-6

[0132] The method of Example I-1 is different except that in step (1), the mixing conditions are replaced with a temperature of 15°C, a rotation speed of 100 rpm, and a time of 10 h, while the other conditions are the same, and the composite material S6 is obtained.

[0133] The physical properties of composite material S6 are listed in Table 1.

[0134] Example I-7

[0135] The method of Example I-1 is different except that in step (2), the extrusion molding conditions are replaced with a temperature of 160°C, a pressure of 22MPa, and a rotation speed of 160rpm, while the other conditions are the same, and the composite material S7 is obtained.

[0136] The physical properties of composite material S7 are listed in Table 1.

[0137] Example I-8

[0138] The method of Example I-1 is different except that in step (2), the extrusion molding conditions are replaced with a temperature of 100°C, a pressure of 5MPa, and a rotation speed of 100rpm, while the other conditions are the same, and the composite material S8 is obtained.

[0139] The physical properties of composite material S8 are listed in Table 1.

[0140] Example I-9

[0141] The method of Example I-1 is followed, except that in step (1), resin-I is replaced with polyethylene, while the other conditions are the same, to obtain composite material S9.

[0142] The physical properties of composite material S9 are listed in Table 1.

[0143] Comparative Example I-1

[0144] The method of Example I-1 is different except that in step (1), the weight ratio of resin-I, resin-II, conductive agent and modifier is replaced with 12:44:42:2, and the other conditions are the same, to obtain composite material DS1.

[0145] The physical properties of the composite material DS1 are listed in Table 1.

[0146] Comparative Example I-2

[0147] The method of Example I-1 is followed, except that in step (1), no modifier (mixture of polycyclic aromatic hydrocarbons) is added, and the other conditions are the same, to obtain composite material DS2.

[0148] The physical properties of the composite material DS2 are listed in Table 1.

[0149] Comparative Example I-3

[0150] The method of Example I-1 is followed, except that in step (1), resin-I (ABS resin, polybutadiene content of 16wt%) is not added, and the other conditions are the same, to obtain composite material DS3.

[0151] The physical properties of the composite material DS3 are listed in Table 1.

[0152] Comparative Example I-4

[0153] The method of Example I-1 is followed, except that in step (1), the modifier (mixture of polycyclic aromatic hydrocarbons) is replaced with a modifier (naphthalene), and the other conditions are the same, to obtain the composite material DS4.

[0154] The physical properties of the composite material DS4 are listed in Table 1.

[0155] Comparative Example I-5

[0156] The method of Example 1 is followed, except that in step (1), the modifier (mixture of polycyclic aromatic hydrocarbons) is replaced with the modifier (anthracene), and the other conditions are the same, to obtain the composite material DS5.

[0157] The physical properties of the composite material DS5 are listed in Table 1.

[0158] Table 1

[0159]

[0160] Note: * refers to the weight ratio of resin-I, resin-II, conductive agent, and modifier in the slurry.

[0161] As can be seen from the results in Table 1, compared with Comparative Examples I-1 to I-5, the composite materials prepared in Examples I-1 to I-9 have higher flexural strength parameters and lower hydrogen permeability parameters. That is, the composite materials provided by the present invention have higher mechanical strength and higher gas barrier properties.

[0162] Comparing Examples I-1 and I-4, it can be seen that by limiting the weight ratio of resin-I, resin-II, conductive agent and modifier in the slurry to a preferred range, the resulting composite material has a higher flexural strength parameter and a lower hydrogen permeability parameter.

[0163] Comparing Examples I-1 and I-5, it can be seen that by limiting the ratio of the total amount of dispersant (in mL) to the total amount of resin-I, resin-II, conductive agent and modifier (in g) within a preferred range, the resulting composite material has a higher flexural strength parameter and a lower hydrogen permeability parameter.

[0164] Comparing Examples I-1 and I-6, it can be seen that by limiting the mixing conditions within the preferred range, the resulting composite material has a higher flexural strength parameter and a lower hydrogen permeability parameter.

[0165] Comparing Examples I-1 and I-7, or comparing Examples I-1 and I-8, it can be seen that by limiting the conditions of slurry extrusion molding within the preferred range, the resulting composite material has a higher flexural strength parameter and a lower hydrogen permeability parameter.

[0166] Comparing Examples I-1 and I-9, it can be seen that by limiting the type of resin-I in the slurry to a preferred range, the resulting composite material has a higher flexural strength parameter and a lower hydrogen permeability parameter.

[0167] Example II-1

[0168] like Figure 1-3 As shown, the bipolar plate P1 is a flat plate structure with dimensions of 80 mm in length, 60 mm in width, and 3 mm in thickness. Its surface roughness Ra is 5 μm. The material of the bipolar plate is the composite material S1 obtained in Example I-1.

[0169] The bipolar plate has three electrolyte inlets and two electrolyte outlets, with the three electrolyte inlets evenly distributed along one side of the bipolar plate. Figure 1 As shown below along the length direction, two electrolyte outlets are evenly arranged along the length direction of the other side of the bipolar plate. Figure 1 (as shown in the upper length direction);

[0170] The lengths of the electrolyte inlet and outlet are both 3 mm; the ratio of the length a of the expansion section to the length b of the first straight section is 2:1; the ratio of the length c of the reduction section to the length d of the second straight section is 2:1.

[0171] Along the flow direction of the electrolyte, the electrolyte inlet is divided into a first straight section and an expanding section, and the electrolyte outlet is divided into a narrowing section and a second straight section. Along the flow direction of the electrolyte, the cross-sections of the first and second straight sections are both rectangular, while the cross-sections of the expanding and narrowing sections are both trapezoidal.

[0172] Along the flow direction of the electrolyte, the included angle α of the expanding section is 135°, and the included angle β of the narrowing section is 45°.

[0173] Along the flow direction of the electrolyte, the inner diameter m of the expanding section increases from 0.5 mm to 4.5 mm; the inner diameter p of the narrowing section decreases from 4.5 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 9:1; the ratio of the inner diameter p of the narrowing section to the inner diameter q of the second straight section is 9:1.

[0174] Examples II-2 to II-9

[0175] Assemble bipolar plates according to Example II-1, except that the material of the bipolar plates is replaced with the composite materials (S1-S9) of Examples I-2 to I-9 respectively, while the other conditions are the same, to obtain bipolar plates P2-P9.

[0176] Example II-10

[0177] Assemble the bipolar plate according to Example II-1, except that the number of electrolyte outlets is replaced with 1, while the other conditions are the same, to obtain bipolar plate P10.

[0178] Example II-11

[0179] The bipolar plate was assembled according to Example II-1, except that the number of electrolyte outlets was 4, while the other conditions were the same, resulting in bipolar plate P11.

[0180] Example II-12

[0181] Assemble the bipolar plate according to Example II-1, except that the surface roughness of the bipolar plate is replaced with 12.5 μm, while the other conditions are the same, to obtain bipolar plate P12.

[0182] Example II-13

[0183] Assemble the bipolar plate according to Example II-1, except 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.

[0184] The inner diameter of both the electrolyte inlet and the electrolyte outlet is 1.5 mm, and all other conditions are the same, resulting in bipolar plate P13.

[0185] Example II-14

[0186] Assemble the bipolar plate according to Example 1, except that, along the electrolyte flow direction, 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, to obtain bipolar plate P14.

[0187] Comparative Examples II-1 to II-5

[0188] Assemble bipolar plates according to Example II-1, except that the material of the bipolar plates is replaced with the composite materials (DS1-DS5) of Comparative Examples I-1 to I-5 respectively, while the other conditions are the same, to obtain bipolar plates DP1-DP5.

[0189] Test case

[0190] Assemble a flow battery:

[0191] The flow battery includes a separator (perfluorosulfonic acid separator, commercially available from Chemours Chemical Company, product name Nafion115), a positive electrode disposed on one side of the separator and a negative electrode disposed on the other side, wherein the positive electrode and the negative electrode are both porous carbon fiber felt, commercially available from SGL Chemical Company, product name GFD4.6EA, with dimensions of 60mm×40mm×4.6mm.

[0192] 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 and second bipolar plates are respectively the aforementioned bipolar plates (P1-P14 and DP1-DP5); both the first and second bipolar plates are provided with current collectors (made of copper plates) and end plates (made of aluminum alloy) on their outer sides, and the above components are fastened with bolts through pre-set holes; sealing elements are provided between the first bipolar plate and the positive electrode, and between the second bipolar plate and the negative electrode, to prevent electrolyte leakage; wherein, the positive electrode electrolyte is 0.8 mol / L. -1 V(IV) + 0.8 mol L -1 V(V) + 3molL -1 The H2SO4 solution, with a negative electrode electrolyte of 0.8 mol / L... -1 V(II) + 0.8 mol L -1 V(III) + 3mol L -1 A solution of H2SO4 was prepared; the electrolyte was delivered to the fuel cell stack using a peristaltic pump, resulting in vanadium redox flow batteries (Q1-Q14 and DQ1-DQ5).

[0193] The output performance of the vanadium redox flow batteries (Q1-Q14 and DQ1-DQ5) was measured using a potentiostat. The coulombic efficiency, voltage efficiency, and energy efficiency were calculated using the charge-discharge curves. The test results are listed in Table 2.

[0194] Table 2

[0195] Coulomb efficiency, % Voltage efficiency, % Energy efficiency, % Example II-1 91.9 92.8 85.3 Example II-2 92.7 93.0 86.2 Example II-3 91.5 92.0 84.2 Example II-4 90.2 91.7 82.7 Example II-5 89.1 90.4 80.5 Example II-6 88.7 89.3 79.2 Example II-7 86.5 87.9 76.0 Example II-8 85.2 87.0 74.1 Example II-9 84.3 86.3 72.8 Example II-10 86.9 87.3 75.9 Example II-11 88.3 89.4 78.9 Example II-12 85.6 86.8 74.3 Example II-13 84.8 85.8 72.8 Example II-14 84.9 86.0 73.0 Comparative Example II-1 83.9 84.2 70.6 Comparative Example II-2 83.1 83.8 69.6 Comparative Example II-3 80.0 79.9 63.9 Comparative Example II-4 82.9 82.4 68.3 Comparative Example II-5 82.4 81.6 67.2

[0196] As can be seen from the results in Table 2, compared with Comparative Examples II-1 to II-5, the flow batteries assembled from bipolar plates prepared in Examples II-1 to II-14 have higher coulombic efficiency, voltage efficiency and energy efficiency. That is, the flow batteries provided by the present invention have higher efficiency and excellent electrochemical performance.

[0197] Comparing Examples II-1 and Examples II-2 to II-9, it can be seen that the present invention controls the efficiency parameters of the flow battery by adjusting the performance of the composite material (flexural strength parameter and hydrogen permeability parameter).

[0198] Comparing Examples II-1 and II-10, or comparing Examples II-1 and II-11, it can be seen that the present invention obtains a flow battery with high efficiency parameters by limiting the number of electrolyte inlets M and the number of electrolyte outlets N to satisfy MN=1.

[0199] Comparing Examples II-1 and II-12, it can be seen that the present invention, by limiting the surface roughness of the bipolar plate to meet the preferred protection range, results in a flow battery with high efficiency parameters.

[0200] Comparing Examples II-1 and II-13, or comparing Examples II-1 and II-14, it can be seen that the present invention, by limiting the structural configuration of the electrolyte inlet and electrolyte outlet to meet the preferred protection range, results in a flow battery with high efficiency parameters.

[0201] 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 method for preparing a composite material, characterized in that, The method includes: extruding a slurry containing resin-I, resin-II, a conductive agent, a modifier, and a dispersant to obtain a composite material; In the slurry, the weight ratio of resin-I, resin-II, conductive agent and modifier is 1-10:10-40:50-70:5-15; The ratio of the total amount of the dispersant (in mL) to the total amount of the resin-I, resin-II, conductive agent and modifier (in g) is 300-1000:

100. The modifier contains a mixture of polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbons in the mixture have a carbon number of C. 22 -C 24 Furthermore, the polycyclic aromatic hydrocarbon has a structure of five benzene rings that are unsubstituted and / or alkyl-substituted; Wherein, resin-I is ABS resin, and the content of butadiene-derived structural units in resin-I is 10-30 wt%; resin-II is selected from at least one of polyimide, polyethyleneimine, and polypropyleneimide, and the weight-average molecular weight of resin-II is 1 × 10⁻⁶. 4 -5×10 4 g / mol.

2. The method according to claim 1, wherein, The method includes the following steps: (1) The resin-I, resin-II, conductive agent, modifier and dispersant are mixed to obtain the slurry; (2) The slurry is extruded in a twin-screw extruder to obtain the composite material.

3. The method according to claim 2, wherein, In the slurry, the weight ratio of resin-I, resin-II, conductive agent and modifier is 3-10:10-35:55-70:7-15.

4. The method according to claim 2, wherein, The ratio of the total amount of the dispersant (in mL) to the total amount of the resin-I, resin-II, conductive agent, and modifier (in g) is 500-1000:

100.

5. The method according to claim 2, wherein, In step (1), the mixing conditions include: temperature of 15-40℃; rotation speed of 100-1000rpm; and time of 1-15h. In step (2), the extrusion molding conditions include: temperature of 150-250℃; pressure of 10-25MPa; and rotation speed of 150-240rpm.

6. The method according to claim 5, wherein, In step (1), the mixing conditions include: temperature of 20-30℃; rotation speed of 300-800rpm; and time of 3-8h. In step (2), the extrusion molding conditions include: temperature of 180-230℃; pressure of 10-20MPa; and rotation speed of 190-240 rpm.

7. The method according to claim 1, wherein, The conductive agent is selected from at least one of Ketjen black, graphite, carbon nanotubes and carbon fibers; The dispersant is selected from at least one of dimethyl sulfoxide, acetone, ethanol and propanol.

8. The method according to any one of claims 1-7, wherein, The fused-ring aromatic hydrocarbon has a structure of five benzene rings that are unsubstituted and / or C1-C2 alkyl-substituted.

9. The method according to claim 8, wherein, The polycyclic aromatic hydrocarbon mixture is prepared by the following method: mixing asphalt and toluene, extracting the resulting mixture, and then distilling the resulting extract to obtain the polycyclic aromatic hydrocarbon mixture; The asphalt is selected from at least one of petroleum asphalt, coal tar pitch, direct coal liquefaction pitch, indirect coal liquefaction pitch, and mesophase pitch.

10. A composite material prepared by the method of any one of claims 1-9.

11. The composite material according to claim 10, wherein, The composite material contains resin-I, resin-II, a conductive agent, and a modifier; Wherein, based on the total weight of the composite material, the content of resin-I is 1-10 wt%; the content of resin-II is 10-40 wt%; the content of the conductive agent is 50-70 wt%; and the content of the modifier is 5-15 wt%.

12. The composite material according to claim 11, wherein, Based on the total weight of the composite material, the content of resin-I is 3-10 wt%; the content of resin-II is 10-35 wt%; the content of the conductive agent is 55-70 wt%; and the content of the modifier is 7-15 wt%.

13. The composite material according to claim 10, wherein, The composite material has a flexural strength ≥26MPa and a hydrogen permeability ≤1.8×10⁻⁶. -6 cm 3 ·s -1 ·cm -2 .

14. The composite material according to claim 13, wherein, The composite material has a flexural strength of 26-60 MPa and a hydrogen permeability of 1×10⁻⁶ MPa. -7 -1.8×10 -6 cm 3 ·s -1 ·cm -2 .

15. A bipolar plate, characterized in that, The bipolar plate is made of the composite material described in any one of claims 10-14.

16. The bipolar plate according to claim 15, wherein, The bipolar plate is provided with at least M electrolyte inlets and at least N electrolyte outlets, wherein M is a positive integer ≥ 2, N is a positive integer ≥ 1, and MN = 1; wherein the electrolyte inlets are provided along one side of the bipolar plate and the electrolyte outlets are provided along the other side of the bipolar plate. The surface roughness Ra of the bipolar plate is 0.05-12.5 μm, and no electrolyte flow channel is provided on the bipolar plate.

17. The bipolar plate according to claim 16, wherein, 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.

18. The bipolar plate according to claim 16, wherein, The number of electrolyte inlets M is 2-6, and the number of electrolyte outlets N is 1-5; The electrolyte inlet is uniformly arranged along one side of the bipolar plate, and the electrolyte outlet is uniformly arranged along the other side of the bipolar plate.

19. The bipolar plate according to claim 17, 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; Along the flow direction of the electrolyte, the cross-sections of the expanding section and the contracting section are each independently a regular shape or an irregular shape.

20. The bipolar plate according to claim 19, 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. Along the flow direction of the electrolyte, the cross-sections of the expanding section and the contracting section are each independently a regular shape.

21. The bipolar plate according to claim 20, wherein, Along the flow direction of the electrolyte, the cross-sections of the expanding section and the contracting section are independently rectangular, square, or trapezoidal.

22. The bipolar plate according to claim 17, 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°. 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.

23. The bipolar plate according to claim 22, wherein, Along the flow direction of the electrolyte, the included angle α of the expanding section is 100-150°; the included angle β of the narrowing section is 30-80°. 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. 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.

24. The bipolar plate according to claim 17, wherein, The lengths of the electrolyte inlet and electrolyte outlet are each independently the same as the thickness of the bipolar plate; In the electrolyte inlet section, 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 section, the ratio of the length c of the narrowing section to the length d of the second straight section is 3-1:

1.

25. A flow battery, characterized in that, The flow battery contains the bipolar plate as described in any one of claims 15-24.

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