Bipolar plates for flow batteries and flow batteries

Abstract

The application provides a bipolar plate of a flow battery and the flow battery, and relates to the technical field of batteries. The bipolar plate comprises a plate body and a cover plate. The plate body has a first surface. The plate body is provided with a first flow channel groove and a second flow channel groove. The first flow channel groove and the second flow channel groove are arranged at intervals in a first direction. Electrolyte in the first flow channel groove flows to the second flow channel groove. The first flow channel groove has a groove opening and a groove bottom wall opposite to each other in a second direction. The groove opening is located on the first surface. The first direction, the second direction and the extension direction of the first flow channel groove are perpendicular to each other. The cover plate is fixed to the plate body. At least part of the cover plate blocks the groove opening and is opposite to the groove bottom wall. A plurality of through holes are arranged at intervals on the cover plate. Each through hole is in communication with the first flow channel groove. By arranging the cover plate, the mass transfer between the electrolyte and the electrode in the flow battery can be enhanced on the basis of reducing the complexity of the flow field structure, and the energy efficiency of the flow battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to a bipolar plate and a flow battery. Background Technology

[0002] In flow batteries, the bipolar plates have a flow field structure, including an inflow channel and an outflow channel. The electrolyte flows from the inflow channel to the electrode, and after passing through the electrode, it flows to the outflow channel, enabling convective mass transfer between the electrolyte and the electrode. In related technologies, to ensure effective mass transfer between the electrolyte and the electrode, the flow rate of the electrolyte is optimized by changing the cross-sectional shape or size of the inflow and outflow channels. However, this results in a complex flow field structure and lacks versatility. Summary of the Invention

[0003] This application provides a bipolar plate and a flow battery, which can enhance mass transfer between the electrolyte and the electrodes in the flow battery while reducing the complexity of the flow field structure, thereby improving the energy efficiency of the flow battery.

[0004] To achieve the above objectives, the embodiments of this application adopt the following technical solutions: In a first aspect, a bipolar plate for a flow battery is provided. The bipolar plate includes a plate body and a cover plate. The plate body has a first surface and is provided with a first flow channel and a second flow channel, which are arranged at intervals in a first direction. Both the first and second flow channels are used to supply electrolyte flow, and the electrolyte flows from the first flow channel to the second flow channel.

[0005] The first flow channel has an opening and a bottom wall facing each other in a second direction, with the opening located on a first surface; wherein the first direction, the second direction, and the extension direction of the first flow channel are perpendicular to each other. A cover plate is fixed to the plate body, at least part of which blocks the opening and faces the bottom wall; the cover plate has multiple through holes spaced apart, each through hole communicating with the first flow channel.

[0006] By installing the aforementioned cover plate on the plate, the electrolyte in the first flow channel tank can flow to the electrode through the through-holes in the cover plate. Compared to the electrolyte flowing directly to the electrode through the tank opening, this reduces the flow area between the electrolyte in the first flow channel tank and the electrode. While ensuring the power of the driving pump remains constant, i.e., while ensuring the driving force on the electrolyte entering the first flow channel tank remains constant, the pressure of the electrolyte in the first flow channel tank can be increased. This increases the pressure difference between the first and second flow channel tanks, thereby increasing the flow velocity of the electrolyte in the first flow channel tank and promoting convective mass transfer between the electrolyte and the electrode.

[0007] Therefore, not only can the active substances in the electrolyte be quickly transported to the electrode surface, but the reaction products and by-reaction products can also be removed from the electrode surface, allowing the electrolyte to react fully on the electrode surface and effectively improving the energy efficiency of the flow battery.

[0008] Compared to the variable cross-section flow field structures in existing technologies, the first and second flow channel grooves in this embodiment have simpler structures, reducing the processing difficulty of the flow field structure and thus lowering the production cost and technical threshold of the bipolar plate. For different application scenarios, there is no need to redesign and optimize the flow field structure; simply setting different cover plates on the plate body can optimize the electrolyte flow rate to improve the performance of the flow battery. This makes the plate widely applicable, with good process compatibility and industrialization prospects, suitable for upgrading and retrofitting large-scale flow battery systems. Furthermore, the simpler structure of the first and second flow channel grooves makes cleaning and maintenance of them easier.

[0009] In one possible implementation of the first aspect, the cover plate includes a main body region, the outer contour of the main body region projected onto a reference plane is a first contour, and the outer contour of the slot projected onto the reference plane is a second contour, the first contour coinciding with the second contour; the reference plane is perpendicular to a second direction. The ratio of the sum of the cross-sectional areas of the plurality of through holes to the area of ​​the main body region is 45% to 55%.

[0010] It should be noted that when the ratio of the sum of the cross-sectional areas of multiple through-holes to the area of ​​the main body region is too large (greater than 55%), the porosity of the main body region is too high. This results in a lower electrolyte pressure within the first flow channel, leading to a smaller pressure difference between the first flow channel and its adjacent second flow channel. Consequently, the electrolyte flow velocity within the first flow channel is higher, resulting in poor convective mass transfer between the electrolyte and the electrode. Furthermore, an excessively high porosity weakens the effect of the cover plate on the uniform dispersion of the electrolyte, causing inconsistent electrolyte concentrations in different areas of the electrode surface. This may lead to insufficient reactants in certain areas of the electrode and easily cause concentration polarization.

[0011] When the ratio of the sum of the cross-sectional areas of multiple through holes to the area of ​​the main body region is too small (less than 45%), the opening ratio of the main body region is too small. Although it can increase the pressure difference between the first flow channel and its adjacent second flow channel, it will also significantly increase the flow resistance of the electrolyte, resulting in a large energy loss.

[0012] Therefore, by setting the porosity of the main region to 45%~55%, the pressure difference between the first flow channel and its adjacent second flow channel can be reduced while ensuring that the electrolyte has low flow resistance. This ensures the flow rate of the electrolyte in the first flow channel and improves the mass transfer effect between the electrolyte and the electrode. Furthermore, it can also avoid the situation of insufficient reactants in the local area of ​​the electrode, effectively reduce the degree of concentration polarization of the electrolyte on the electrode surface, and help improve the energy efficiency of the flow battery.

[0013] In one possible implementation of the first aspect, the cross-sectional area of ​​a single through-hole is 0.2 mm. 2 ~0.3mm 2 .

[0014] Given a fixed porosity in the main area, if the cross-sectional area of ​​a single through hole is too large, the number of through holes that can be opened in the main area will be small, and the through hole distribution will be sparse, which is not conducive to the uniform entry of electrolyte into the electrode. Furthermore, it will result in a smaller pressure of electrolyte flowing in the through hole, which will weaken the pressure difference of electrolyte convection mass transfer and affect the effect of electrolyte convection mass transfer.

[0015] Given a fixed opening ratio in the main area, if the cross-sectional area of ​​a single through-hole is too small, a large number of through-holes can be created in the main area, resulting in a dense distribution of through-holes. This reduces the structural strength of the cover plate, making it prone to being punctured by the electrolyte. Furthermore, an excessively small cross-sectional area of ​​the through-holes can easily lead to blockage, potentially causing low energy efficiency in the flow battery.

[0016] Therefore, the cross-sectional area of ​​a single through-hole is 0.2 mm. 2 ~0.3mm 2 While ensuring the structural strength of the cover plate, the electrolyte can be uniformly introduced into the electrode through multiple through holes. The pressure difference between the first flow channel and its adjacent second flow channel ensures the flow rate of the electrolyte in the first flow channel, thereby improving the energy efficiency of the flow battery.

[0017] In one possible implementation of the first aspect, at least a portion of the plurality of through holes are arranged along the extension direction of the first flow channel groove; the first flow channel groove has a flow channel inlet, and in two adjacent through holes, the cross-sectional area of ​​the through hole farther from the flow channel inlet is larger than the cross-sectional area of ​​the through hole closer to the flow channel inlet.

[0018] Understandably, within the first flow channel, as the electrolyte's flow path increases, the pressure drop loss increases, and the electrolyte flow rate decreases. In other words, the electrolyte velocity gradually decreases in the flow direction. Therefore, a flow dead zone easily forms at the end of the first flow channel furthest from the inlet (i.e., the end); or, the electrolyte flow rate at the end of the first flow channel is extremely low. This leads to insufficient supply of active material to the electrode surface, resulting in concentration polarization and reducing the energy efficiency of the flow battery.

[0019] Therefore, by making the cross-sectional area of ​​the through hole farther from the flow channel inlet larger than that of the through hole closer to the flow channel inlet in two adjacent through holes, the pressure drop loss caused by the excessive flow distance of the electrolyte can be balanced, and the flow rate of the electrolyte flowing at the end of the first flow channel can be increased. This ensures that the amount of electrolyte flowing per unit time on different cross-sections of the first flow channel is approximately the same, reducing the concentration polarization of the electrolyte on the electrode, thereby improving the energy efficiency of the flow battery.

[0020] In one possible implementation of the first aspect, a plurality of through holes arranged along the extension direction of the first flow channel include a first through hole and at least one second through hole. The through hole closest to the flow channel inlet is the first through hole, and the cross-sectional area of ​​the first through hole is a first area. The second through hole is located on the side of the first through hole away from the flow channel inlet, and the cross-sectional area of ​​the second through hole is a second area. In the extension direction of the first flow channel, the distance between the second through hole and the first through hole is a first spacing, and the ratio of the rate of change of the second area relative to the first area to the first spacing is 0.15% / mm to 0.35% / mm.

[0021] This can balance the pressure drop loss caused by the excessive flow distance of the electrolyte, increase the flow rate of the electrolyte flowing at the end of the first flow channel, so that the amount of electrolyte flowing per unit time on different cross sections of the first flow channel is roughly the same, making the active material more uniformly distributed on the electrode, reducing the concentration polarization of the electrolyte on the electrode, and thus improving the energy efficiency of the flow battery.

[0022] In one possible implementation of the first aspect, the cover plate has a first end face and a second end face facing away from each other, and the first end face and the second end face are arranged in the extension direction of the first flow channel groove; the plate body has a second surface connected to the first surface, the first flow channel groove penetrates the second surface, and the second end face faces away from the second surface.

[0023] The minimum distance between the hole wall and the first end face is 1.5mm~2mm, which can not only reduce the risk of concentration polarization and ensure the energy efficiency of the flow battery, but also ensure the structural strength of the cover plate and improve the overall reliability of the cover plate.

[0024] In one possible implementation of the first aspect, the first flow channel has a channel sidewall connected between the channel opening and the channel bottom wall, the channel sidewall including a first sidewall and a second sidewall opposite to each other in a first direction; at least a portion of the cover plate is accommodated within the first flow channel, and the cover plate is connected between the first sidewall and the second sidewall.

[0025] This avoids the cover plate covering the first surface, ensuring the effective connection area between the electrode and the plate, and ensuring the stability of current transmission between the electrode and the plate; in addition, it helps to reduce the superposition size of the plate and the cover plate in the second direction, thereby reducing the overall volume of the battery cell.

[0026] In one possible implementation of the first aspect, the cover plate is provided with multiple through-hole groups, which are spaced apart along a first direction. Each through-hole group includes multiple through holes, which are spaced apart along the extension direction of the first flow channel. This not only ensures that the electrolyte covers the electrode along the extension direction of the first flow channel, but also ensures that the electrolyte covers the electrode along the first direction, avoiding insufficient reactants in certain areas of the electrode. This effectively reduces the concentration polarization of the electrolyte on the electrode surface and helps improve the energy efficiency of the flow battery.

[0027] In one possible implementation of the first aspect, the cover plate is made of a composite material of graphite and thermoplastic resin. Graphite possesses electrical conductivity and heat resistance; thermoplastic resin softens easily when heated and hardens upon cooling, exhibiting adhesive properties. This allows for effective bonding of the graphite and thermoplastic resin, and also enables the cover plate to be integrally bonded and fixed to the plate body. This composite material combines the electrical conductivity of graphite with the toughness of thermoplastic resin, ensuring the structural reliability of the cover plate while also conducting electric current.

[0028] In a second aspect, embodiments of this application provide a flow battery, which includes a bipolar plate, electrodes, and an electrolyte. The bipolar plate is the same as the bipolar plate provided in the first aspect. The electrodes are fixed to a first surface of the bipolar plate. The electrolyte is adapted to flow along a first flow channel, and the electrolyte in the first flow channel is adapted to pass through the electrodes and flow along a second flow channel.

[0029] Understandably, the beneficial effects of the second aspect of the flow battery described above can be referenced to the beneficial effects of the first aspect and any of its possible implementations, which will not be repeated here. Attached Figure Description

[0030] Figure 1 A schematic diagram illustrating the working principle of a flow battery provided for some embodiments of this application; Figure 2 This is a partial structural schematic diagram of a bipolar plate provided in some embodiments of this application; Figure 3This is a schematic diagram of the diffusion path of the electrolyte between the bipolar plate and the electrode provided in some embodiments of this application; Figure 4 A perspective view of a bipolar plate provided for some embodiments of this application; Figure 5 According to Figure 4 A schematic diagram showing another angle of the bipolar plate; Figure 6 According to Figure 4 The diagram shows a cross-sectional structure of the bipolar plate at line AA. Figure 7 Schematic diagram of the fit between the plate and the frame provided in some embodiments of this application Figure 1 ; Figure 8 Schematic diagram of the fit between the plate and the frame provided in some embodiments of this application Figure 2 ; Figure 9 Perspective view of a bipolar plate provided for other embodiments of this application; Figure 10 This is a schematic diagram of the structure of a bipolar plate provided in other embodiments of this application; Figure 11 for Figure 10 Enlarged view of the circled area at point B.

[0031] 100, flow battery; e1, first direction; e2, second direction; S, reference plane; 1. Battery stack; 1a. Electrolyte; 1b. Electrode; 11. First electrode; 12. Second electrode; 13. First storage tank; 130. First electrolyte; 14. First drive pump; 15. Second storage tank; 150. Second electrolyte; 17. Ion exchange membrane; 2. Bipolar plate; 21. First bipolar plate; 22. Second bipolar plate; 3. Plate; 30. First surface; 3a. Flow field structure; 31. First flow channel groove; 310. Flow channel inlet; 311. Groove opening; 312. Groove bottom wall; 313. Groove side wall; 314. First side wall; 315. Second side wall; 32. Second flow channel groove; 33. Second surface; 34. Third surface; 4. Frame; 4a. First part; 4b. Second part; 41. Liquid inlet; 42. Liquid inlet channel; 43. Liquid outlet; 44. Liquid outlet channel; 5. Cover plate; 5a. Through hole group; 50. Through hole; 501. First through hole; 502. Second through hole; 503. First opening; 504. Second opening; 51. Main body area; 52. Fixed area; 521. Notch; 53. First end face; 54. Second end face. Detailed Implementation

[0032] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this embodiment, unless otherwise stated, "a plurality of" means two or more.

[0033] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0034] To facilitate understanding, before providing a detailed description of the bipolar plate and flow battery in the embodiments of this application, the relevant terms involved in the embodiments of this application will be explained first.

[0035] Energy efficiency (EE) is a key indicator that measures the energy utilization efficiency of a battery during charge-discharge cycles. Energy efficiency is equal to the ratio of discharge energy to charging energy. Higher energy efficiency indicates less energy loss during the charge-discharge process.

[0036] Pressure drop: refers to the decrease in pressure caused by energy loss during the flow of a fluid.

[0037] Concentration polarization refers to the phenomenon in which, during an electrode reaction, the diffusion rate of reactants or products is lower than the electrochemical reaction rate, resulting in a concentration gradient between the solution near the electrode surface and the bulk solution, which in turn causes the electrode potential to deviate from the equilibrium value.

[0038] Due to its advantages such as independent design of power and capacity, high safety, long cycle life, and ease of scaling, flow batteries are widely used in large-scale energy storage scenarios, such as grid-connected peak shaving of renewable energy sources such as wind power and photovoltaics, grid-side energy storage, microgrid systems, and backup power sources.

[0039] See Figure 1 , Figure 1 This is a schematic diagram illustrating the working principle of a flow battery 100 provided in some embodiments of this application. The flow battery 100 typically includes an electrolyte 1a and a battery stack 1. The battery stack 1 can convert electrical energy into chemical energy and store it in the electrolyte 1a. When needed, the chemical energy in the electrolyte 1a can be converted back into electrical energy and released to a power source or external load. The battery stack 1 can be assembled from multiple battery cells by stacking.

[0040] The battery cell may include an electrode 1b and an ion exchange membrane 17. The electrode 1b is a porous electrode, which can serve as a site for redox reactions of active substances (such as iron ions, chromium ions, vanadium ions, etc.) in the electrolyte 1a. For example, the electrode 1b includes an electrode material containing a catalyst, which can promote the redox reactions of active substances on the electrode 1b.

[0041] In some embodiments, see Figure 1 Electrode 1b may include a first electrode 11 and a second electrode 12, with an ion exchange membrane 17 disposed between the first electrode 11 and the second electrode 12. One of the first electrode 11 and the second electrode 12 is a positive electrode, and the other is a negative electrode. Electrolyte 1a includes a first electrolyte 130 and a second electrolyte 150, with the first electrode 11 in contact with the first electrolyte 130 and the second electrode 12 in contact with the second electrolyte 150.

[0042] For example, when the first electrode 11 is the positive electrode and the second electrode 12 is the negative electrode, the first electrolyte 130 is the positive electrolyte and the second electrolyte 150 is the negative electrolyte; or, when the first electrode 11 is the negative electrode and the second electrode 12 is the positive electrode, the first electrolyte 130 is the negative electrolyte and the second electrolyte 150 is the positive electrolyte. The first electrolyte 130 can be stored in the first storage tank 13, and the second electrolyte 150 can be stored in the second storage tank 15.

[0043] Continue reading Figure 1 When the flow battery 100 is operating, the first electrolyte 130 in the first storage tank 13 is transported to the battery stack 1 by the first drive pump 14, so that the first electrode 11 comes into contact with the first electrolyte 130. The active substances in the first electrolyte 130 will undergo a redox reaction on the surface of the first electrode 11, thereby realizing the interconversion of chemical energy and electrical energy. The electrical energy is stored and released through the charging and discharging of the flow battery 100. Hydrogen ions are conducted from one side of the ion exchange membrane 17 to the other side under the drive of the potential difference. At the same time, the ion exchange membrane 17 can block other ions in the first electrolyte 130 from passing through.

[0044] It should be understood that when the flow battery 100 is working, the process of converting chemical energy into electrical energy between the second electrode 12 and the second electrolyte 150 can be referred to the process of converting chemical energy into electrical energy between the first electrolyte 130 and the first electrode 11, which will not be repeated here.

[0045] For example, the flow battery 100 can be an iron-chromium flow battery, a vanadium redox flow battery, a lithium-ion flow battery, or a lead-acid flow battery. For ease of explanation, the following description uses an iron-chromium flow battery as an example, but this should not be construed as a limitation of this application.

[0046] The positive electrode electrolyte of an iron-chromium flow battery may include divalent iron ions (Fe2+). 2+ ) and ferric ions (Fe 3+ The negative electrode electrolyte may include divalent chromium ions (Cr). 2+ ) and trivalent chromium ions (Cr 3+ When an iron-chromium flow battery is charged, the Fe in the positive electrode electrolyte... 2+ An oxidation reaction occurs at the positive electrode, Fe 2+ It loses electrons at the positive electrode surface and transforms into Fe. 3+ Cr in the negative electrode electrolyte 3+ A reduction reaction occurs, Cr 3+ Electrons are gained at the negative electrode surface to transform into Cr. 2+ When the iron-chromium redox flow cell discharges, the Fe in the positive electrode electrolyte... 3+ A reduction reaction occurs, Fe 3+ Electrons are gained at the positive electrode surface and the metal is converted into Fe. 2+ Cr in the negative electrode electrolyte 2+ An oxidation reaction occurs, Cr 2+ The porous electrode surface loses electrons and transforms into Cr. 3+ .

[0047] See Figure 1 In some embodiments, the battery cell of the flow battery 100 may further include a bipolar plate 2, which is typically bonded tightly to the electrode 1b via a hot-pressing process. The bipolar plate 2, as a key component of the flow battery 100, primarily serves to conduct current. Electrons generated by the redox reaction of the active material on the electrode 1b need to pass through a low-resistance path. During discharge, electrons are conducted out through this path, and during charging, electrons are introduced through the same path.

[0048] Therefore, efficient current collection and conduction are crucial for reducing the internal resistance of the flow battery 100 and improving its energy efficiency. The bipolar plate 2 provides a large-area, highly conductive surface that effectively collects and conducts the current generated at each active point on the electrode 1b. For example, the bipolar plate 2 can conduct the current to adjacent battery cells or ultimately to the end plates at both ends of the battery stack 1.

[0049] The bipolar plate 2 may include a first bipolar plate 21 and a second bipolar plate 22. The first bipolar plate 21 is connected to the side surface of the first electrode 11 facing away from the ion exchange membrane 17, and the second bipolar plate 22 is connected to the side surface of the second electrode 12 facing away from the ion exchange membrane 17.

[0050] See Figure 2 and Figure 3 , Figure 2This is a partial structural schematic diagram of the bipolar plate 2 provided in some embodiments of this application; Figure 3 This is a schematic diagram of the diffusion path of electrolyte 1a between bipolar plate 2 and electrode 1b provided in some embodiments of this application; the bipolar plate 2 usually has a flow field structure 3a, which not only guides the flow path of electrolyte 1a in electrode 1b, but also directly affects the uniformity of electrolyte 1a distribution on electrode 1b, mass transfer efficiency, voltage drop loss and concentration polarization, thereby affecting the energy efficiency of flow battery 100 and the overall performance of the battery.

[0051] The flow field structure 3a on the bipolar plate 2 can be an interdigitated flow field. The flow field structure 3a includes a first flow channel 31 and a second flow channel 32. The first flow channel 31 and the second flow channel 32 are arranged at intervals in a first direction e1, which is perpendicular to the extension direction of the first flow channel 31 and the extension direction of the second flow channel 32. Both the first flow channel 31 and the second flow channel 32 are used for the flow of electrolyte 1a. The first flow channel 31 can serve as an inflow channel, and the second flow channel 32 can serve as an outflow channel. Electrolyte 1a can flow from the first flow channel 31 to the electrode 1b, and after passing through the electrode 1b, electrolyte 1a can flow to the second flow channel 32. This allows bipolar plate 2 to conduct electrolyte 1a in addition to conducting current. Convection mass transfer can occur between electrolyte 1a and electrode 1b. This mass transfer between electrolyte 1a and electrode 1b allows the active substances (i.e., reactants, such as Fe in the positive electrode electrolyte) in electrolyte 1a to be transferred. 2+ ) is transported to the surface of electrode 1b and carries away reaction products (e.g., Fe) from the surface of electrode 1b. 2+ Fe obtained from oxidation reaction 3+ ).

[0052] Figure 2 The direction indicated by the middle arrow is the flow direction of electrolyte 1a. Figure 3 The direction indicated by the middle arrow is the diffusion direction of electrolyte 1a.

[0053] During the flow of electrolyte 1a from the first flow channel 31 to the second flow channel 32, when the flow rate of electrolyte 1a is low, the convective mass transfer effect between electrolyte 1a and electrode 1b is poor, which easily leads to mass transfer polarization. Reactants on the surface of electrode 1b (e.g., Fe) 2+ The concentration of ) decreases, and the reaction products (e.g., Fe) 3+ The concentration gradient of the electrolyte accumulates on the surface of electrode 1b, generating an additional overpotential and affecting the energy efficiency of the flow battery 100.

[0054] It should be understood that by increasing the flow rate of electrolyte 1a within the first flow channel 31, the convective mass transfer of electrolyte 1a can be increased. However, increasing the flow rate of electrolyte 1a within the first flow channel 31 by increasing the driving force of the drive pump (e.g., the first drive pump 14 described above) will result in higher power consumption of the drive pump.

[0055] In related technologies, the flow rate of electrolyte 1a is adjusted by changing the flow field structure 3a. For example, by changing the shape or size of the cross-section of the flow channel (first flow channel 31 or second flow channel 32), the cross-sectional size of the flow channel varies along the flow direction of electrolyte 1a (including uniform or stepped changes). This adjusts the flow rate of electrolyte 1a, improving the convective mass transfer effect between electrolyte 1a and electrode 1b while ensuring the power consumption of the driving pump. However, this leads to the following problems: Question 1: The design and manufacturing of bipolar plate 2 is quite difficult. When setting the flow field structure 3a on bipolar plate 2 or when producing bipolar plate 2, it is necessary to precisely control the mold and processing technology, which increases the processing difficulty of flow field structure 3a, thereby increasing the production cost of bipolar plate 2 and raising the technical threshold for producing bipolar plate 2.

[0056] Question 2: The flow field structure needs to be redesigned and optimized for different application scenarios, lacking versatility.

[0057] Question 3: The complex structure of the first flow channel 31 and the second flow channel 32 may make cleaning and maintenance more difficult.

[0058] Therefore, how to improve the mass transfer between the electrolyte 1a and the electrode 1b in the flow battery 100 and improve the energy efficiency of the flow battery 100 while ensuring the power consumption of the driving pump and reducing the complexity of the flow field structure 3a has become a technical problem that urgently needs to be solved in this field.

[0059] To solve the above-mentioned technical problems, this application provides a bipolar plate 2 for a flow battery 100, see reference. Figure 4 , Figure 5 and Figure 6 , Figure 4 A perspective view of the bipolar plate 2 provided for some embodiments of this application; Figure 5 According to Figure 4 A schematic diagram of another angle of the bipolar plate 2 shown; Figure 6 According to Figure 4 The diagram shows a cross-sectional view of the bipolar plate at line AA. The bipolar plate 2 includes a plate body 3 with a first surface 30. A first flow channel 31 and a second flow channel 32 are formed on the plate body 3. The electrode 1b can be fixed to the first surface 30. The flow path of the electrolyte 1a within the first flow channel 31, the electrode 1b, and the second flow channel 32 is shown in the reference diagram. Figure 2 and Figure 3 The flow path of electrolyte 1a shown is roughly the same, so it will not be described again.

[0060] The bipolar plate 2 can be either a first bipolar plate 21 or a second bipolar plate 22. It is understood that when the bipolar plate 2 is the first bipolar plate 21, the electrode 1b corresponding to the first bipolar plate 21 is the first electrode 11, and the structure of the second bipolar plate 22 can be designed with reference to the structure of the first bipolar plate 21.

[0061] In some embodiments, the first flow channel 31 can be a plurality of channels spaced apart along the first direction e1, and the second flow channel 32 can be a plurality of channels spaced apart along the first direction e1. The plurality of first flow channel channels 31 and the plurality of second flow channel channels 32 are arranged sequentially and alternately along the first direction e1. The first flow channel channel 31 has a slot opening 311 and a bottom wall 312 opposite each other in the second direction e2, the slot opening 311 penetrating the first surface 30; wherein the first direction e1, the second direction e2, and the extension direction of the first flow channel channel 31 are perpendicular to each other. The first flow channel channel 31 also has a sidewall 313, which connects the slot opening 311 and the bottom wall 312, and includes a first sidewall 314 and a second sidewall 315 opposite each other in the first direction e1.

[0062] See Figure 7 and Figure 8 , Figure 7 This application provides schematic diagrams illustrating the cooperation between the plate 3 and the frame 4 in some embodiments. Figure 1 ; Figure 8 This application provides schematic diagrams illustrating the cooperation between the plate 3 and the frame 4 in some embodiments. Figure 2 In some embodiments, the flow battery 100 further includes a frame 4, which can be connected to the plate 3. The frame 4 includes a first portion 4a and a second portion 4b, and the first portion 4a and the second portion 4b are respectively located on opposite sides of the plate 3 in the extending direction of the first flow channel 31.

[0063] The first part 4a has an inlet channel 42 and an inlet 41, with the inlet channel 42 connecting the inlet 41 and the first channel groove 31; the second part 4b has an outlet channel 44 and an outlet 43, with the outlet channel 44 connecting the outlet 43 and the second channel groove 32.

[0064] Driven by the pump, electrolyte 1a flows into inlet channel 42 through inlet 41 and is then distributed into multiple first channel tanks 31. Electrolyte 1a in the first channel tank 31 passes through electrode 1b into second channel tank 32, and electrolyte 1a in the second channel tank 32 flows out through outlet channel 44 and outlet 43.

[0065] in, Figure 7 In the illustrated embodiment, the distance between the liquid inlet 41 and the plurality of first flow channel grooves 31 is different, and the distance between the liquid outlet 43 and the plurality of second flow channel grooves 32 is different. Figure 8 In the embodiment shown, the distance between the liquid inlet 41 and the multiple first flow channel 31 is the same, and the distance between the liquid outlet 43 and the multiple second flow channel 32 is the same. This can improve the uniformity of the flow velocity of electrolyte 1a in different first flow channel 31 and also improve the uniformity of the flow velocity of electrolyte 1a in different second flow channel 32. The concentration distribution of active substances in electrolyte 1a is more uniform, which can effectively reduce concentration polarization.

[0066] It should be noted that the flow battery 100 may include an electrode plate frame, and the frame 4 may be part of the electrode plate frame; or, in some other embodiments, the bipolar plate 2 includes a frame 4 and a plate 3, that is, the frame 4 may be part of the bipolar plate 2.

[0067] See Figures 4-6 In some embodiments, the plate 3 has a second surface 33 and a third surface 34, which are arranged in the extending direction of the first flow channel 31. A first surface 30 is connected between the second surface 33 and the third surface 34. The first flow channel 31 extends through the second surface 33 along its extending direction to form a flow channel inlet 310 of the first flow channel 31. The flow channel inlet 310 is connected to the outlet of the liquid inlet channel 42, and the electrolyte 1a in the liquid inlet channel 42 can enter the first flow channel 31 through the flow channel inlet 310.

[0068] In some embodiments, the bipolar plate 2 may further include a cover plate 5, which is fixed to the plate body 3. At least a portion of the cover plate 5 blocks the groove 311 and is opposite to the bottom wall 312 of the groove. The cover plate 5 has a plurality of through holes 50, which are spaced apart. At least a portion of the plurality of through holes 50 are arranged along the extension direction of the first flow channel groove 31, and each through hole 50 communicates with the first flow channel groove 31. For example, a portion of the plurality of through holes 50 is arranged along the extension direction of the first flow channel groove 31; or, all of the plurality of through holes 50 are arranged along the extension direction of the first flow channel groove 31.

[0069] The cover plate 5 is made of a composite material of graphite and thermoplastic resin. Graphite has electrical conductivity and heat resistance, while thermoplastic resin softens easily when heated and hardens when cooled, and has adhesive properties. The thermoplastic resin can not only effectively bond with graphite, but also bond and fix the cover plate 5 to the plate body 3 as a whole. This composite material combines the electrical conductivity of graphite with the toughness of thermoplastic resin, ensuring the structural reliability of the cover plate 5 while also conducting current.

[0070] When manufacturing the cover plate 5, graphite powder can be mixed with thermoplastic resin particles and melted at high temperature, and then formed by hot pressing or injection molding.

[0071] For example, the graphite mentioned above can be flexible graphite, and the thermoplastic resin can be thermoplastic epoxy resin. The material of the plate 3 is also a composite material of flexible graphite and thermoplastic resin. Flexible graphite has flexible physical properties such as compressibility and stretchability, and can quickly return to its original shape after being compressed. The cover plate 5 made of this material has strong impact resistance and is not easily damaged under the impact of electrolyte 1a.

[0072] The cover plate 5 and the plate body 3 can be integrated through a hot pressing process to ensure the overall structural stability of the bipolar plate 2 and its long-term sealing performance.

[0073] By providing the cover plate 5 on the plate 3, the electrolyte 1a in the first flow channel 31 can flow to the electrode 1b through the through hole 50 on the cover plate 5. Compared to the electrolyte 1a flowing directly to the electrode 1b through the slot 311, this reduces the flow area of ​​the electrolyte 1a between the first flow channel 31 and the electrode 1b. While ensuring the power of the driving pump remains constant, i.e., while ensuring the driving force on the electrolyte 1a entering the first flow channel 31 remains constant, the pressure of the electrolyte 1a in the first flow channel 31 can be increased, thus increasing the pressure difference between the first flow channel 31 and the second flow channel 32. This, in turn, increases the flow rate of the electrolyte 1a in the first flow channel 31, promoting convective mass transfer between the electrolyte 1a and the electrode 1b. Therefore, not only can the active substances in the electrolyte 1a be rapidly transported to the surface of the electrode 1b, but reaction products and by-reaction products can also be removed from the surface of the electrode 1b, allowing the electrolyte 1a to react fully on the surface of the electrode 1b, effectively improving the energy efficiency of the flow battery 100.

[0074] Compared to the variable cross-section flow field structure 3a in the prior art, the structures of the first flow channel 31 and the second flow channel 32 in this embodiment are simpler, reducing the processing difficulty of the flow field structure 3a and thus lowering the production cost and technical threshold of the bipolar plate 2. For different application scenarios, there is no need to redesign and optimize the flow field structure 3a; simply setting different cover plates 5 on the plate body 3 can optimize the flow rate of the electrolyte 1a to improve the performance of the flow battery 100. This makes the plate body 3 more widely applicable, with good process compatibility and industrialization prospects, suitable for upgrading and retrofitting large-scale flow battery 100 systems. Furthermore, the simpler structure of the first flow channel 31 and the second flow channel 32 makes cleaning and maintenance of the first flow channel 31 and the second flow channel 32 more convenient.

[0075] Continue reading Figures 4-6In some embodiments, the cover plate 5 includes a main body region 51, which is opposite to the bottom wall 312 of the groove in the second direction e2 and is used to block the groove opening 311. The outer contour of the orthographic projection of the main body region 51 onto the reference plane S is a first contour, and the outer contour of the orthographic projection of the groove opening 311 onto the reference plane S is a second contour. The first contour and the second contour coincide. The reference plane S is perpendicular to the second direction e2.

[0076] For example, the cover plate 5 only includes the main body region 51, and the surface of the cover plate 5 facing away from the bottom wall 312 of the groove has the same shape and size as the groove opening 311. At least a portion of the cover plate 5 can be accommodated in the first flow channel groove 31, that is, at least a portion of the main body region 51 is accommodated in the first flow channel groove 31. The surface of the cover plate 5 facing away from the bottom wall 312 of the groove can be flush with the first surface 30 of the plate body 3; or, the surface of the cover plate 5 facing away from the bottom wall 312 of the groove can also protrude from the first surface 30; or, the surface of the cover plate 5 facing away from the bottom wall 312 of the groove can also be located between the groove opening 311 and the bottom wall 312 of the groove. The opposite ends of the cover plate 5 in the first direction e1 are respectively fixed to the first side wall 314 and the second side wall 315.

[0077] In this way, the cover plate 5 can be prevented from covering the first surface 30, ensuring the effective connection area between the electrode 1b and the plate 3, and ensuring the stability of current transmission between the electrode 1b and the plate 3; in addition, it is beneficial to reduce the superposition size of the plate 3 and the cover plate 5 in the second direction e2, thereby reducing the overall volume of the battery cell.

[0078] In some other embodiments, see Figure 9 , Figure 9 This is a perspective view of the bipolar plate 2 provided in some other embodiments of this application; the cover plate 5 may also be disposed on the first surface 30. The cover plate 5 includes a main body region 51 and a fixing region 52. At least a portion of the fixing region 52 is connected to opposite ends of the main body region 51 in the first direction e1. The fixing region 52 is fixed to the first surface 30, which facilitates the connection of the cover plate 5 to the plate body 3 (e.g., by hot pressing). Figure 9 The main area 51 and the fixed area 52 are schematically divided by a dashed line, which does not exist in the cover plate 5. For example, a notch 521 may be provided on the fixed area 52. The notch 521 is opposite to and communicates with the slot 311 of the second flow channel 32. The shape and size of the notch 521 are the same as the shape and size of the slot 311 of the second flow channel 32.

[0079] See Figure 4 and Figure 9In some embodiments, the cover plate 5 is provided with a plurality of through hole groups 5a, which are arranged at intervals along the first direction e1. Each through hole group 5a includes a plurality of through holes 50, which are arranged at intervals along the extension direction of the first flow channel groove 31. For example, the number of through hole groups 5a on the main body region 51 can be two, three, or four; the number of through holes 50 in each through hole group 5a can be 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40.

[0080] In this way, not only can the electrolyte 1a cover the electrode 1b along the extension direction of the first flow channel 31, but the electrolyte 1a can also cover the electrode 1b along the first direction e1, avoiding the situation of insufficient reactants in the local area of ​​the electrode 1b, effectively reducing the degree of concentration polarization of the electrolyte 1a on the surface of the electrode 1b, and helping to improve the energy efficiency of the flow battery 100.

[0081] In some embodiments, the ratio of the sum of the cross-sectional areas of the plurality of through holes 50 to the area of ​​the main body region 51 is 45% to 55%, that is, the opening ratio of the main body region 51 is 45% to 55%. For example, the ratio of the sum of the cross-sectional areas of the plurality of through holes 50 to the area of ​​the main body region 51 can be 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, or 55%.

[0082] It should be noted that the cross-section of the through hole 50 refers to the plane intersected by the plane perpendicular to the second direction e2 on the through hole 50. The shape of the cross-section of the through hole 50 can be circular, elliptical, rectangular, triangular, other regular or irregular shapes. This application does not limit the shape of the cross-section of the through hole 50.

[0083] See Figure 6 The through-hole 50 has a first opening 503 and a second opening 504 opposite each other in the second direction e2, with the second opening 504 located on the side of the first opening 503 away from the bottom wall 312 of the groove. The dimensions of different cross-sections of the through-hole 50 can be the same or different. When the dimensions of different cross-sections of the through-hole 50 are all the same, that is, the dimensions of the first opening 503 and the second opening 504 are the same, the sum of the cross-sectional areas of the multiple through-holes 50 is equal to the sum of the areas of the second openings 504 of all the through-holes 50. When the dimensions of different cross-sections of the through-hole 50 are different, the sum of the cross-sectional areas of the multiple through-holes 50 is the sum of the areas of any cross-section of the multiple through-holes 50, including the sum of the areas of the second openings 504 of all the through-holes 50.

[0084] It should be noted that when the ratio of the sum of the cross-sectional areas of the multiple through holes 50 to the area of ​​the main body region 51 is too large (greater than 55%), the porosity of the main body region 51 is too high. This results in a lower pressure of the electrolyte 1a within the first flow channel 31, leading to a smaller pressure difference between the first flow channel 31 and its adjacent second flow channel 32. Consequently, the flow velocity of the electrolyte 1a within the first flow channel 31 is lower, and the convective mass transfer effect between the electrolyte 1a and the electrode 1b is poor. Furthermore, an excessively high porosity weakens the effect of the cover plate 5 on the uniform dispersion of the electrolyte 1a, causing inconsistent electrolyte 1a concentrations in different areas of the electrode 1b surface. This may result in insufficient reactants in certain areas of the electrode 1b, easily leading to concentration polarization.

[0085] When the ratio of the sum of the cross-sectional areas of the multiple through holes 50 to the area of ​​the main body region 51 is too small (less than 45%), the opening ratio of the main body region 51 is too small. Although it can increase the pressure difference between the first flow channel 31 and its adjacent second flow channel 32, it will also significantly increase the flow resistance of the electrolyte 1a, resulting in a large energy loss.

[0086] Therefore, by setting the porosity of the main body region 51 to 45%~55%, the pressure difference between the first flow channel 31 and its adjacent second flow channel 32 can be reduced while ensuring that the electrolyte 1a has a small flow resistance. This ensures the flow rate of the electrolyte 1a in the first flow channel 31 and improves the mass transfer effect between the electrolyte and the electrode. Furthermore, it can also avoid the situation of insufficient reactants in the local area of ​​the electrode 1b, effectively reduce the degree of concentration polarization of the electrolyte 1a on the surface of the electrode 1b, and help improve the energy efficiency of the flow battery 100.

[0087] In some embodiments, the cross-sectional area of ​​a single through-hole 50 is 0.2 mm. 2 ~0.3mm 2 For example, the cross-sectional area of ​​a single through-hole 50 is 0.2 mm. 2 0.22mm 2 0.24mm 2 0.26mm 2 0.28mm 2 Or 0.3mm 2 It is understandable that the cross-sectional area of ​​the first opening 503 and the second opening 504 of the through hole 50 is 0.2 mm. 2 ~0.3mm 2 .

[0088] Given a fixed opening ratio in the main body region 51, if the cross-sectional area of ​​a single through hole 50 is too large, the number of through holes 50 that can be opened in the main body region 51 will be small, and the distribution of through holes 50 will be sparse, which is not conducive to the uniform entry of electrolyte 1a into electrode 1b; and it will also result in a smaller pressure of electrolyte 1a flowing in the through hole 50, which will weaken the pressure difference of electrolyte 1a convective mass transfer and affect the effect of electrolyte 1a convective mass transfer.

[0089] Given a fixed opening ratio in the main body region 51, if the cross-sectional area of ​​a single through-hole 50 is too small, the number of through-holes 50 that can be opened in the main body region 51 will be large, resulting in a dense distribution of through-holes 50. This reduces the structural strength of the cover plate 5, making it easier for the electrolyte 1a to break through the cover plate 5. In addition, if the cross-sectional area of ​​the through-hole 50 is too small, it is also easy for the through-hole 50 to become blocked, which may lead to excessively low energy efficiency of the flow battery 100.

[0090] Therefore, by setting the cross-sectional area of ​​a single through-hole 50 to 0.2mm... 2 ~0.3mm 2 While ensuring the structural strength of the cover plate 5, the electrolyte 1a can be uniformly introduced into the electrode 1b through multiple through holes 50. The pressure difference between the first flow channel 31 and its adjacent second flow channel 32 ensures the flow rate of the electrolyte 1a in the first flow channel 31 and improves the energy efficiency of the flow battery 100.

[0091] To verify the effects of the porosity of the main body region 51 and the cross-sectional area of ​​a single through hole 50 on the energy efficiency of the flow battery 100, an electrochemical test experiment can be conducted on the flow battery 100.

[0092] For example, the flow battery 100 used in the test is an iron-chromium flow battery, and it is a single cell with a capacity of 2.6 Ah, an electrolyte flow rate of 40 ml / min, and an electrode area of ​​50 cm². 2 The test parameters include: test temperature 65±2℃; charging current 3.5A (current density 70mA / cm²). 2 Charge to 1.3V; discharge current is 3.5A (current density is 70mA / cm²). 2 Discharge to 0.8V.

[0093] Electrochemical testing experiment one can set up multiple embodiments, in which the porosity of the main region 51 in multiple embodiments is in the range of 45%~55%, and the cross-sectional area of ​​a single through hole 50 is set at 0.2mm. 2 ~0.3mm 2 Within the range. Electrochemical testing experiment one can also set up multiple comparative examples, in which the porosity of the main region 51 and / or the cross-sectional area of ​​a single through hole 50 are not within the above range.

[0094] In the various embodiments and comparative examples, the bipolar plate 2 has eight first flow channel grooves 31 and eight second flow channel grooves 32. The lengths of the first and second flow channel grooves 31 and 32 are the same, and their cross-sections are both rectangular. Along the extension direction of the first flow channel groove 31, its cross-sectional shape and cross-sectional area remain unchanged; similarly, along the extension direction of the second flow channel groove 32, its cross-sectional shape and cross-sectional area remain unchanged. Furthermore, the through-hole 50 has a circular cross-section, and the shape and size of any cross-section of the through-hole 50 are identical.

[0095] The parameters of cover plate 5 and the energy efficiency test results of the battery in multiple embodiments and comparative examples are shown in Table 1: Table 1. Parameters of cover plate 5 and battery test results

[0096] As shown in Table 1, the energy efficiency of the flow battery 100 in Examples 1, 2, and 3 all exceeds 81.5%. Among them, in Example 2, the porosity of the main body region 51 is 50%, and the cross-sectional area of ​​the through hole 50 is 0.25 mm. 2 The flow battery 100 achieved an energy efficiency of 81.89%. This indicates that when the porosity of the main body region 51 is within the range of 45% to 55%, the cross-sectional area of ​​a single through-hole 50 is set at 0.2 mm. 2 ~0.3mm 2 Within the acceptable flow resistance range, a large pressure difference exists between the first flow channel 31 and the adjacent second flow channel 32, and the electrolyte 1a can flow uniformly into the electrode 1b through the through hole 50 on the cover plate 5; therefore, it helps to improve the energy efficiency of the flow battery 100.

[0097] Although the aperture ratio of the main body region 51 in Comparative Example 1 is in the range of 45% to 55%, the cross-sectional area of ​​the through hole 50 is too small (less than 0.2 mm). 2 The through-hole 50 is prone to blockage, which may lead to low energy efficiency of the flow battery 100. In addition, although the small cross-sectional area of ​​the through-hole 50 can increase the pressure difference between the first flow channel 31 and the adjacent second flow channel 32, it will also significantly increase the flow resistance of the electrolyte 1a, resulting in large energy loss and causing the energy efficiency of the flow battery 100 to be lower than that of the flow batteries 100 in Examples 1-3.

[0098] In Comparative Example 2, the open area ratio of the main body region 51 is in the range of 45% to 55%, but the cross-sectional area of ​​the through hole 50 is too large (greater than 0.3 mm). 2When the size of the main area 51 and the spacing between adjacent through holes 50 are fixed, if the cross-sectional area of ​​a single through hole 50 is too large, the number of through holes 50 will be small, resulting in an excessive flow of electrolyte 1a in a local area of ​​electrode 1b and insufficient supply of electrolyte 1a in other areas, that is, insufficient supply of active material. This leads to uneven distribution of active material on the surface of electrode 1b, resulting in the energy efficiency of the flow battery 100 being lower than that of the flow battery 100 in Examples 1-3.

[0099] In Comparative Example 3, the cross-sectional area of ​​the through hole 50 is 0.2 mm. 2 ~0.3mm 2 Within the range, however, the opening ratio of the main body region 51 is too low (below 45%), and the cover plate 5 has a large obstruction effect on the electrolyte 1a. The electrolyte 1a is difficult to flow into the electrode 1b evenly, which directly affects the flow and distribution of the active material. Therefore, the discharge performance of this battery is low, and the energy efficiency of the flow battery 100 in Comparative Example 3 is lower than that of the flow battery 100 in Examples 1-3.

[0100] In Comparative Example 4, the cross-sectional area of ​​the through hole 50 is 0.2 mm. 2 ~0.3mm 2 Within the specified range, however, the opening ratio of the main body region 51 is too high (above 55%), which significantly weakens the effect of the cover plate 5 in increasing the pressure difference between the first flow channel 31 and the adjacent second flow channel 32, and also significantly weakens the effect of uniform distribution of the electrolyte 1a. Therefore, the energy efficiency of the flow battery 100 in Comparative Example 4 is lower than that of the flow batteries 100 in Examples 1-3.

[0101] In Comparative Example 5, the bipolar plate 2 does not include the cover plate 5, and the flow battery 100 has a lower energy efficiency, below 80%.

[0102] Please see Figure 10 and Figure 11 , Figure 10 Schematic diagrams of the structure of the bipolar plate 2 provided in other embodiments of this application; Figure 11 for Figure 10 Enlarged view of the circled portion at point B; in other embodiments, this application also provides a bipolar plate 2, the structure of which can refer to the above description. Figures 4-6 The structure of plate 3 shown is designed accordingly, and will not be described in detail in this application. The structure of cover plate 5 is similar to... Figures 4-6 The cover plate 5 shown has a generally similar structure, with the following differences: at least some of the multiple through holes 50 are arranged along the extension direction of the first flow channel groove 31, and in two adjacent through holes 50, the cross-sectional area of ​​the through hole 50 farther from the flow channel inlet 310 is larger than the cross-sectional area of ​​the through hole 50 closer to the flow channel inlet 310.

[0103] Understandably, within the first flow channel 31, as the flow path of the electrolyte 1a increases, the pressure drop loss of the electrolyte 1a increases, and the flow velocity of the electrolyte 1a decreases. In other words, the velocity of the electrolyte 1a gradually decreases in the flow direction. Therefore, a flow dead zone easily forms at the end of the first flow channel 31 furthest from the inlet 310 (i.e., the end point); or, the flow rate of the electrolyte 1a at the end of the first flow channel 31 furthest from the inlet 310 is extremely low. This leads to insufficient supply of active material to the surface of the electrode 1b, resulting in concentration polarization and reducing the energy efficiency of the flow battery 100.

[0104] Therefore, by having a larger cross-sectional area for the through-hole 50 farther from the flow channel inlet 310 than the through-hole 50 closer to the flow channel inlet 310, the pressure drop loss caused by the excessive flow distance of the electrolyte 1a can be balanced, thereby increasing the flow rate of the electrolyte 1a flowing at the end of the first flow channel 31 away from the flow channel inlet 310. This ensures that the amount of electrolyte 1a flowing per unit time on different cross-sections of the first flow channel 31 is approximately the same, reducing the concentration polarization of the electrolyte 1a on the electrode 1b, and thus improving the energy efficiency of the flow battery 100.

[0105] It should be understood that, for ease of display, Figure 11 The difference in aperture (i.e., the difference in cross-sectional area) between two adjacent through holes 50 has been magnified. In actual implementation, the difference in aperture between two adjacent through holes 50 should be much smaller than shown in the figure.

[0106] See Figure 9 , Figure 10 and Figure 11 In some embodiments, a plurality of through holes 50 arranged along the extending direction of the first flow channel 31 include a first through hole 501 and at least one second through hole 502. The through hole 50 closest to the flow channel inlet 310 is the first through hole 501, and the cross-sectional area of ​​the first through hole 501 is a first area. The second through hole 502 is located on the side of the first through hole 501 away from the flow channel inlet 310, and the cross-sectional area of ​​the second through hole 502 is a second area. The second area is larger than the first area, and the rate of change of the second area relative to the first area is as follows: C i =(S i -S1) / S1; Among them, C i S1 is the rate of change of the second area relative to the first area, and S is the first area. i This is the second area.

[0107] In the extending direction of the first flow channel 31, the distance between the second through hole 502 and the first through hole 501 is the first spacing, and the ratio of the rate of change of the second area relative to the first area to the first spacing is 0.15% / mm to 0.35% / mm. For example, the ratio of the rate of change of the second area relative to the first area to the first spacing is 0.15% / mm, 0.17% / mm, 0.2% / mm, 0.22% / mm, 0.25% / mm, 0.28% / mm, 0.3% / mm, 0.32% / mm, or 0.35% / mm.

[0108] It should be noted that the distance between the first through hole 501 and the second through hole 502 can refer to the distance between the centroid of the first through hole 501 and the centroid of the second through hole 502. When the shapes and sizes of different cross-sections of the first through hole 501 are the same, and when the shapes and sizes of different cross-sections of the second through hole 502 are the same, the distance between the centroid of the first through hole 501 and the centroid of the second through hole 502 is equal to the distance between the geometric centroid of the outline shape of the first opening 503 and the geometric centroid of the outline shape of the second opening 504.

[0109] When the outline shape of the first opening 503 is a regular shape, its geometric centroid is its geometric center; when the outline shape of the second opening 504 is a regular shape, its geometric centroid is its geometric center. For example, when the outline shape of the first opening 503 is rectangular, and the outline shape of the second opening 504 is also rectangular, the distance between the first opening 503 and the second opening 504 is the distance between the geometric centers of the two rectangles. When the outline shapes of the first opening 503 and the second opening 504 are both circular, the distance between the first through hole 501 and the second through hole 502 is equal to the distance between the centers of the two circles.

[0110] To verify the rate of change of the second area relative to the first area and the first spacing L i The effect of the ratio on the energy efficiency of the flow battery 100 can be investigated by conducting an electrochemical test experiment two on the flow battery 100. The test method and parameters for the electrochemical test experiment two can be designed with reference to the electrochemical test experiment one for the flow battery 100 in the above embodiments.

[0111] The test experiment can set up multiple embodiments and multiple comparative examples. In the multiple embodiments and multiple comparative examples, the rate of change of the second area relative to the first area of ​​the bipolar plate 2 is related to the first spacing L. i The ratios are different, and other parameters of bipolar plate 2 can be designed with reference to bipolar plate 2 in Example 2; the test results of energy efficiency of batteries in multiple examples and multiple comparative examples are shown in Table 2: Table 2. Ratio of the rate of change of the second area relative to the first area to the first spacing (C) i / Li ) and battery test results

[0112] As can be seen from Table 2, in Examples 4, 5 and 6, C i / L i The value is in the range of 0.15% / mm to 0.35% / mm. The energy efficiency of the flow battery 100 in Examples 4, 5, and 6 is greater than 82.4%, which is greater than the energy efficiency of the flow battery 100 in Examples 1-3. In Example 5, C... i / L i The value is 0.25% / mm, and this flow battery has the best performance, with an energy efficiency of 82.71%. Compared with the flow battery in the prior art (i.e., Comparative Example 5), the energy efficiency of the flow battery in Example 5 is improved by nearly 3 percentage points.

[0113] Comparative Example 7, C i / L i If the value is too large, it means that the cross-sectional area of ​​the first through hole 501 is increased too much compared to the first through hole 501. This causes the flow rate of electrolyte 1a at the end of the first flow channel 31 to be higher than that at the inlet end per unit time. This results in the cover plate 5 over-regulating the flow rate of electrolyte 1a, and the active material is unevenly distributed on the electrode 1b. As a result, the energy efficiency of the flow battery 100 in Comparative Example 7 is 81.99%, which is lower than the energy efficiency of the flow battery 100 in Examples 4, 5 and 6.

[0114] Comparative Example 6, C i / L i If the value is too small, it means that the cross-sectional area of ​​the first through hole 501 has increased too little compared to the first through hole 501. This results in the flow rate of electrolyte 1a at the inlet end of the first flow channel 31 being higher than that at the end of the flow channel 31 per unit time. As a result, the active material is unevenly distributed on the electrode 1b. The energy efficiency of the flow battery 100 in Comparative Example 6 is 82.09%, which is lower than the energy efficiency of the flow battery 100 in Examples 4, 5 and 6.

[0115] Therefore, by using the ratio of the rate of change of the second area relative to the first area to the first spacing of 0.15% / mm to 0.35% / mm, the pressure drop loss caused by the excessive flow distance of the electrolyte 1a can be balanced, and the flow rate of the electrolyte 1a flowing at the end of the first flow channel 31 away from the flow channel inlet 310 can be increased. This can solve the problem of excessive flow rate and insufficient liquid supply at the end in the traditional design, so that the amount of electrolyte 1a flowing per unit time on different cross sections of the first flow channel 31 is approximately the same, making the active material more uniformly distributed on the electrode 1b, reducing the concentration polarization of the electrolyte 1a on the electrode 1b, and thus improving the energy efficiency of the flow battery 100.

[0116] See Figure 10 and Figure 11 and combined Figure 4 In some embodiments, the cover plate 5 has a first end face 53 and a second end face 54 facing away from each other, and the first end face 53 and the second end face 54 are arranged in the extension direction of the first flow channel groove 31; the second end face 54 faces away from the second surface 33 of the plate body 3, and the first end face 53 may be flush with the second surface 33.

[0117] The minimum distance D between the wall of the through hole 50 and the first end face 53 is 1.5mm to 2mm, that is, the minimum distance D between the wall of the through hole 50 closest to the first end face 53 and the first end face 53 is 1.5mm to 2mm. For example, the minimum distance between the wall of the through hole 50 and the first end face 53 is 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm or 2mm.

[0118] Understandably, when the distance D between the wall of the through hole 50 and the first end face 53 is too large, there is a risk of insufficient supply of active material to the electrode 1b surface corresponding to the area between the through hole 50 and the first end face 53, leading to concentration polarization and affecting the energy efficiency of the flow battery 100. Conversely, when the distance between the wall of the through hole 50 and the first end face 53 is too small, the structural strength of the area between the through hole 50 and the first end face 53 is insufficient, resulting in poor overall structural reliability of the cover plate 5.

[0119] Therefore, by setting the minimum distance D between the hole wall of the through hole 50 and the first end face 53 to 1.5mm~2mm, not only can the risk of concentration polarization be reduced and the energy efficiency of the flow battery 100 be guaranteed, but the structural strength of the cover plate 5 can also be guaranteed and the overall reliability of the cover plate 5 can be improved.

[0120] It should be noted that the feature that the minimum distance D between the wall of the through hole 50 and the first end face 53 is 1.5mm to 2mm can be applied to any embodiment of this application.

[0121] This application also provides a flow battery 100, which includes a bipolar plate 2, an electrode 1b, and an electrolyte 1a. The configuration of the electrode 1b and the electrolyte 1a with the bipolar plate 2 can be referred to... Figure 1 The flow battery 100 in the illustrated embodiment is designed with bipolar plate 2 as described in any of the above embodiments. It is understood that the beneficial effects achieved by the flow battery 100 in this application embodiment can be referenced to the beneficial effects brought by the bipolar plate 2 in any of the above embodiments, and will not be repeated here.

[0122] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A bipolar plate for a flow battery, characterized in that, include: The plate has a first surface and a first flow channel and a second flow channel are provided on the plate. The first flow channel and the second flow channel are arranged at intervals in a first direction. Both the first flow channel and the second flow channel are used for electrolyte flow, and the electrolyte flows from the first flow channel to the second flow channel. The first flow channel has an opening and a bottom wall opposite each other in a second direction, the opening being located on the first surface; wherein the first direction, the second direction, and the extension direction of the first flow channel are perpendicular to each other; the first flow channel has a flow channel inlet; A cover plate is fixed to the plate body. At least a portion of the cover plate blocks the groove and is opposite to the bottom wall of the groove. The cover plate has multiple through holes, which are spaced apart. Each through hole communicates with the first flow channel groove, and at least a portion of the multiple through holes are arranged along the extension direction of the first flow channel groove. The plurality of through holes arranged along the extension direction of the first flow channel groove include a first through hole and at least one second through hole. The through hole closest to the flow channel inlet is the first through hole, and the cross-sectional area of ​​the first through hole is a first area. The second through hole is located on the side of the first through hole away from the flow channel inlet, and the cross-sectional area of ​​the second through hole is a second area. In the extending direction of the first flow channel groove, the distance between the second through hole and the first through hole is the first spacing, and the ratio of the rate of change of the second area relative to the first area to the first spacing is 0.15% / mm~0.35% / mm.

2. The bipolar plate according to claim 1, characterized in that, The cover plate includes a main body area, the outer contour of the main body area projected onto the reference plane is a first contour, the outer contour of the slot projected onto the reference plane is a second contour, and the first contour and the second contour coincide. The reference plane is perpendicular to the second direction; The ratio of the sum of the cross-sectional areas of the plurality of through holes to the area of ​​the main body region is 45% to 55%.

3. The bipolar plate according to claim 1 or 2, characterized in that, The cross-sectional area of ​​a single through hole is 0.2 mm. 2 ~0.3mm 2 .

4. The bipolar plate according to claim 1 or 2, characterized in that, In two adjacent through holes, the cross-sectional area of ​​the through hole farther from the flow channel inlet is larger than that of the through hole closer to the flow channel inlet.

5. The bipolar plate according to claim 1 or 2, characterized in that, The cover plate has a first end face and a second end face facing away from each other, and the first end face and the second end face are arranged in the extending direction of the first flow channel groove; the plate body has a second surface, the second surface is connected to the first surface, the first flow channel groove penetrates the second surface, and the second end face faces away from the second surface; The minimum distance between the wall of the through hole and the first end face is 1.5mm to 2mm.

6. The bipolar plate according to claim 1 or 2, characterized in that, The first flow channel has a channel sidewall connected between the channel opening and the channel bottom wall, and the channel sidewall includes a first sidewall and a second sidewall opposite to each other in the first direction; at least a portion of the cover plate is accommodated in the first flow channel, and the cover plate is connected between the first sidewall and the second sidewall.

7. The bipolar plate according to claim 1 or 2, characterized in that, The cover plate is provided with a plurality of through hole groups, which are arranged at intervals along the first direction. Each through hole group includes a plurality of through holes, which are arranged at intervals along the extension direction of the first flow channel groove.

8. The bipolar plate according to claim 1 or 2, characterized in that, The cover plate is made of a composite material of graphite and thermoplastic resin.

9. A flow battery, characterized in that, include: A bipolar plate, as described in any one of claims 1-8; Electrodes are fixed to the first surface; An electrolyte adapted to flow along the first flow channel, wherein the electrolyte in the first flow channel is adapted to pass through the electrode and flow along the second flow channel.

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