All-vanadium redox flow battery and bipolar plate, single cell and stack thereof

Abstract

The application provides a vanadium redox flow battery and a bipolar plate, a single cell and a stack thereof. The bipolar plate is provided with a vein type flow channel on one side surface. The vein type flow channel comprises two mirror-symmetrical single-side channels. Each single-side channel comprises an inlet flow channel, four branch flow channels and an outlet flow channel. The outlet of the inlet flow channel is communicated to the inlets of the four branch flow channels, and the outlets of the four branch flow channels are communicated to the inlet of the outlet flow channel. From the direction far away from the symmetry axis of the two single-side channels to the direction close to the symmetry axis, the four branch flow channels are respectively a first flow channel, a second flow channel, a third flow channel and a fourth flow channel. The bipolar plate of the vanadium redox flow battery provided by the application can significantly reduce the pressure drop loss of the electrolyte flow, realize the uniform flow distribution of the electrolyte on the electrode surface, and has the self-adaptive adjustment capacity for the dynamic flow change.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of liquid flow batteries, and relates to a bipolar plate of a full-vanadium liquid flow battery, in particular to a full-vanadium liquid flow battery, a bipolar plate thereof, a single cell and a stack. BACKGROUND

[0002] At present, the market of electrochemical energy storage all uses large-energy lithium iron phosphate batteries as carriers, but the lithium iron phosphate batteries have poor thermal stability, and as the volume capacity density is higher and higher, the ohmic heat, polarization heat and side reactions during charging and discharging cannot be dissipated in time due to the design of the cooling system, or the external temperature is too high and a series of reasons, which causes the service life of the battery to be reduced, the voltage to be unbalanced and other problems, and there is a risk of explosion. In actual use, when the charging and discharging reaches more than 3500 times, the service life of the lithium iron phosphate battery shows a significant downward trend, which cannot meet the increasing demand for long-life batteries in the market.

[0003] Therefore, a new type of full-vanadium liquid flow battery is developed to meet the demand for long-life batteries in the market. With the development of battery technology, full-vanadium liquid flow battery energy storage products have gradually begun to enter the industrial application stage.

[0004] The full-vanadium liquid flow battery realizes energy storage and release through the reversible oxidation-reduction reaction of different valence vanadium ions. The positive and negative electrolytes are sulfuric acid solutions containing V 4+ / V 5+ and V 2+ / V 3+ , respectively, and are separated by an ion exchange membrane. When charging, V 4+ at the positive electrode is oxidized to V 5+ , and V 3+ at the negative electrode is reduced to V 2+ ; when discharging, the process is reversed, and electrons transfer through the external circuit to complete energy conversion. In this process, hydrogen ions (H + ) migrate through the proton exchange membrane to maintain charge balance, and the electrolyte circulates through the external pump to ensure that the reaction continues.

[0005] The core structure of the full-vanadium liquid flow battery is composed of a stack, an electrolyte storage tank, a circulating pump, a pipeline system, a control system and an energy conversion device. The stack is the core unit of energy conversion and undertakes the key task of electrochemical reaction. The stack is composed of multiple single cells stacked in series through a bipolar plate. Each single cell includes a positive and negative electrode, an ion exchange membrane, a bipolar plate and a sealing assembly. The positive and negative electrodes usually use porous carbon materials (such as carbon felt or graphite felt), which have high specific surface area and electrical conductivity to provide active sites for the oxidation-reduction reaction of vanadium ions. The surface properties of the electrode material (such as hydrophilicity and electrochemical activity) directly affect the reaction kinetics and battery efficiency, so it is often modified by doping metal catalysts (such as bismuth and tin) or plasma treatment.

[0006] Bipolar plates, as the structural support and current collector of the stack, need to meet the requirements of high electrical conductivity, corrosion resistance and mechanical strength. The bipolar plate surface is usually designed with a flow channel structure to guide the uniform distribution of electrolyte and strengthen the mass transfer process. The contact resistance between the bipolar plate and the electrode is also a key factor affecting the ohmic polarization. A stack pressure of 0.5 MPa to 1.5 MPa is usually required to ensure tight contact between the interfaces, while avoiding excessive compression that leads to a decrease in the porosity of the porous electrode.

[0007] Ion exchange membranes, as the core functional material of the stack, bear the dual responsibilities of isolating the positive and negative electrolytes and selectively conducting protons. The electrolyte system consists of positive and negative electrolyte tanks, circulating pumps, pipelines and heat management units. Its function is to store active substances and ensure the continuous circulation of electrolyte in the stack. The positive electrolyte is a sulfuric acid solution containing V 4+ / V 5+ , and the negative electrolyte is a sulfuric acid solution containing V 2+ / V 3+ , and the volumes of the two are equal to achieve charge balance.

[0008] However, in the existing bipolar plate, the electrolyte in the flow channel will continue to react when it contacts the electrode; however, due to the excessive flow resistance caused by a single flow channel, the flow rate distribution is uneven, resulting in intense reaction at the inlet of the flow channel and reduced reaction at the outlet, which is not conducive to the uniform distribution of electrolyte and affects the normal discharge of the battery.

[0009] CN217214777U discloses a bipolar plate for a full vanadium redox flow battery, which is provided with: a liquid inlet connected to a main liquid inlet channel; a liquid inlet channel, which is a groove continuously extending along one side of the bipolar plate, the liquid inlet channel being connected to the liquid inlet; a liquid outlet channel, which is a groove continuously extending along the other side of the bipolar plate, the liquid outlet channel being arranged opposite the liquid inlet channel; a liquid outlet connected to a main liquid outlet channel, the liquid outlet being connected to the liquid outlet channel; a liquid distribution channel arranged between the liquid outlet channel and the liquid inlet channel, the liquid distribution channel being arranged perpendicular to the liquid inlet channel and being connected to the liquid inlet channel; and a partition plate arranged in the liquid distribution channel, the partition plate being arranged along the length direction of the liquid distribution channel.

[0010] CN119400890A discloses a new type of electrode frame-free all-vanadium redox flow battery, comprising two outer end plates, two insulating plates and two current collecting plates arranged between the two end plates in sequence, and at least one integrated bipolar plate arranged between the two current collecting plates, one pair of electrodes and a proton exchange membrane are arranged on the two sides of the integrated bipolar plate; the integrated bipolar plate comprises a bipolar plate body, an electrolyte flow channel region arranged in the middle of the two side surfaces of the bipolar plate body, electrode grooves for embedding electrodes are arranged on the two side surfaces of the integrated bipolar plate, and two electrodes are arranged on the outer sides of the positive electrolyte flow channel region and the negative electrolyte flow channel region respectively.

[0011] The bipolar plates of the all-vanadium redox flow battery disclosed in the prior art have certain defects, and there are problems of excessive flow resistance and uneven flow distribution caused by single flow channel design, which leads to intense reaction at the inlet of the flow channel and weakened reaction at the outlet, which is not conducive to the uniform distribution of electrolyte, and finally has an adverse effect on the normal discharge of the battery. SUMMARY

[0012] In view of the deficiencies in the prior art, the purpose of the present application is to provide an all-vanadium redox flow battery, a bipolar plate thereof, a single cell and a stack. The bipolar plate of the all-vanadium redox flow battery provided by the present application can significantly reduce the pressure drop loss of electrolyte flow by arranging vein type flow channels, realize uniform flow distribution of electrolyte on the surface of the electrode, and has self-adaptive adjustment capability for dynamic flow changes.

[0013] To achieve this purpose, the present application adopts the following technical solutions:

[0014] In a first aspect, the present application provides a bipolar plate of an all-vanadium redox flow battery, one side surface of the bipolar plate is provided with a vein type flow channel;

[0015] The vein type flow channel comprises two mirror-symmetrical single-sided channels, each single-sided channel comprises an inlet flow channel, four branch flow channels and an outlet flow channel; the outlet of the inlet flow channel is connected to the inlet of the four branch flow channels, and the outlet of the four branch flow channels is connected to the inlet of the outlet flow channel;

[0016] From the direction away from the symmetry axis of the two single-sided channels to the direction close to the symmetry axis, the four branch flow channels are respectively a first flow channel, a second flow channel, a third flow channel and a fourth flow channel;

[0017] The first flow channel comprises a flow channel which is turned from a horizontal direction to a vertical direction, and then to a horizontal direction, and finally connected to the outlet flow channel;

[0018] The second flow channel comprises a flow channel which is turned from a horizontal direction to a vertical direction, and then to a horizontal direction, and finally connected to the outlet flow channel;

[0019] The third flow channel comprises a flow channel which is gradually widened in cross-section width after extending downward in a vertical direction for a set length, then is branched into two flow channel branches, and finally is connected to an outlet flow channel;

[0020] The fourth flow channel comprises a flow channel which is extended downward in a vertical direction after being gradually narrowed in cross-section width and then being kept unchanged in a horizontal direction for a set length, and finally is connected to an outlet flow channel.

[0021] In the application, the two single-sided channels are mirror-symmetric, and the structure and size are completely the same.

[0022] In the application, the vein type flow channel on the surface of the bipolar plate is a fractal network structure, and the geometric characteristics include the following key elements: the vein type flow channel comprises two mirror-symmetric single-sided channels, each single-sided channel comprises an inlet flow channel (main vein), four branch flow channels (secondary veins) and an outlet flow channel (main vein), and the four branch flow channels have various flow channels (micro veins); the main vein, the secondary vein and the micro vein constitute a multi-level branch network, the main vein is responsible for long-distance transportation, the secondary vein and the micro vein realize uniform distribution of fluid in a larger area through dense bifurcation, and the micro vein end is gradually narrowed or expanded to adjust the local flow rate and pressure distribution.

[0023] In the application, the horizontal direction is a direction perpendicular to the symmetry axis of the two single-sided channels, the vertical direction is a direction parallel to the symmetry axis of the two single-sided channels, the horizontal direction and the vertical direction are perpendicular to each other, and a plane formed between the horizontal direction and the vertical direction is parallel to the surface of the bipolar plate.

[0024] In the application, the vein type flow channel on the surface of the bipolar plate has precise regulation of fluid dynamics characteristics, so that the bipolar plate has significant performance advantages, specifically as follows: first, the fractal network of the vein type flow channel reduces the single-channel flow through multi-level branching, reduces the Reynolds number (Re), and makes the flow tend to be laminar, under the laminar condition, the fluid shear stress is greatly reduced, and compared with the traditional serpentine or parallel flow channel, the pressure drop loss is reduced by 20%~40%; second, uniform distribution of electrolyte is realized, that is, the bifurcation structure forces the fluid to be redistributed in each level of branch, which fundamentally eliminates the problem of uneven flow caused by length difference of flow channels, and ensures uniform distribution of electrolyte in a larger area; third, it has dynamic flow adaptation capability, that is, when the inlet flow increases, the laminar flow characteristics of the secondary vein can automatically limit the flow rate increase, avoiding local overload, and when the flow decreases, the micro vein can still maintain the basic flow to prevent the formation of dead zones, thereby stably coping with dynamic changes of flow.

[0025] In the application, the vertical flow channel of the fourth flow channel is designed to gradually narrow in cross-sectional width and then keep unchanged and extend downward for a certain length, so that the lower flow channel opening is narrowed to increase the flow rate, thereby ensuring the uniform flow rate of the flow channel.

[0026] In summary, the bipolar plate of the all-vanadium redox flow battery provided by the application can significantly reduce the pressure drop loss of the electrolyte flow, realize uniform flow distribution of the electrolyte on the electrode surface, and has self-adaptive adjustment capability for dynamic flow changes.

[0027] Preferably, two branch flow channels are arranged between the vertical flow channel in the second flow channel and the vertical flow channel of the third flow channel, for connecting the vertical flow channel in the second flow channel and the vertical flow channel of the third flow channel.

[0028] In the application, the vertical flow channel in the second flow channel is connected to the vertical flow channel of the third flow channel through two branch flow channels, realizing the series connection between the second flow channel and the third flow channel, for reducing the pressure difference between the second flow channel and the third flow channel.

[0029] Preferably, the two branch flow channels are a first branch flow channel and a second branch flow channel, respectively.

[0030] The first branch flow channel is connected to the starting point of the gradually widened cross-sectional width of the vertical flow channel of the third flow channel.

[0031] The second branch flow channel is connected to the flow channel branch close to the second flow channel among the two flow channel branches of the third flow channel.

[0032] Preferably, one flow channel branch of the third flow channel is directly connected to the outlet flow channel, and the other branch flow channel is connected to the outlet flow channel through the mouth-shaped return flow channel.

[0033] Preferably, the two flow channel branches in the third flow channel are a first flow channel branch and a second flow channel branch, respectively, the first flow channel branch is close to the second flow channel, and the second flow channel branch is away from the first flow channel.

[0034] The first flow channel branch is directly connected to the outlet flow channel, and the second flow channel branch is connected to the outlet flow channel through the mouth-shaped return flow channel.

[0035] The mouth-shaped return flow channel comprises a mouth-shaped flow channel formed by surrounding a circle of four-edge flow channels, one of the four-edge flow channels of the mouth-shaped return flow channel coincides with part of the first flow channel branch, and one coincides with part of the fourth flow channel.

[0036] In the application, the mouth-shaped return flow channel of the third flow channel is used to reduce the electrolyte flow rate and increase the contact time of the electrolyte with the electrode.

[0037] Preferably, two flow passage ways are arranged between the vertical flow passages of the fourth flow channels of the two single-sided channels, and the two flow passage ways communicate the fourth flow channels of the two single-sided channels.

[0038] Preferably, the two flow passage ways include a first flow passage way and a second flow passage way, the first flow passage way communicates the middle positions of the vertical flow passages of the two fourth flow channels where the cross-sectional width gradually narrows, and the second flow passage way communicates the positions of the vertical flow passages of the two fourth flow channels where the cross-sectional width gradually narrows and then remains unchanged.

[0039] Preferably, the lengths and cross-sectional dimensions of the inlet flow channel, the four branch flow channels and the outlet flow channel in the vein type flow channel are determined by the Navier-Stokes equation and the Poiseuille theorem.

[0040] In the present application, in order to uniformly distribute the flow of electrolyte on the entire electrode surface and also reduce the flow resistance of the entire flow channel, the relationship between the pressure and the flow rate of the main path and the branch path on the entire flow channel needs to be calculated.

[0041] The Navier-Stokes equation (abbreviated as NS equation) describes the motion law of viscous fluid, and its essence is the mathematical expression of Newton's second law (momentum conservation) and mass conservation law in continuous medium, which is derived in combination with the constitutive relation (such as Newton's viscosity law).

[0042] According to the NS equation, the relationship between the pressure and the flow rate in each flow channel of the main path and the branch path can be listed as follows:

[0043]

[0044]

[0045]

[0046]

[0047] where u, v, w are the velocities of the fluid in the x, y, z directions, is the fluid density, p is the fluid pressure, t is time, is the viscous force, f is the volume force in each direction. When the flow rate at each branch is determined, the flow resistance difference between the head and tail of the branch can be obtained by the Poiseuille theorem, that is:

[0048]

[0049] Wherein, ΔP is the pressure drop of the flow channel, which can be calculated by the NS equation, μ is the dynamic viscosity of the fluid, L is the length of the flow channel, Q is the volume flow rate, w and h are the length and width of the flow channel, according to the above formula, the length of each branch in the vein flow channel can be calculated when the minimum flow resistance is achieved, and the shape of the flow channel cross section can be determined, and through calculation, the length and width of the flow channel cross section can be obtained.

[0050] Preferably, the calculation aims to achieve the minimum flow resistance of the electrolyte in the flow channel, and the length and cross-sectional size obtained through the calculation make the flow channel meet the condition of the minimum flow resistance.

[0051] Preferably, the top of the vein flow channel is provided with a liquid inlet, and the liquid inlet is communicated to the inlet of the inlet flow channel.

[0052] The bottom of the vein flow channel is provided with a liquid outlet, and the liquid outlet is communicated to the outlet of the outlet flow channel.

[0053] In the present application, the vein flow channel is left-right symmetrical, and the electrolyte flows into the vein flow channel from a liquid inlet at the top, and the flowing electrolyte is divided into two left-right mirror-symmetrical single channels through the left-right two inlet flow channels.

[0054] In the second aspect, the present application provides a single cell, which comprises the bipolar plate of the first aspect.

[0055] In the present application, the single cell comprises a positive electrode, a negative electrode, a separator, two bipolar plates, a sealing strip and an electrode frame; wherein the bipolar plate, the positive electrode, the separator and the negative electrode are stacked to form a stacked structure, and the side surface of the bipolar plate provided with the vein flow channel faces the positive electrode and the negative electrode respectively, and the outside of the stacked structure is fixed by the electrode frame; the sealing strip is arranged between the bipolar plate and the electrode frame; wherein the bipolar plate needs to be closely combined with the positive electrode and the negative electrode, so that the electrolyte on the bipolar plate fully contacts the positive electrode and the negative electrode, and the electrolyte does not flow out, thereby realizing more uniform charging and discharging.

[0056] In the third aspect, the present application provides an electric pile, which comprises the single cell of the second aspect.

[0057] In the fourth aspect, the present application provides a full vanadium redox flow battery, which comprises the electric pile of the third aspect.

[0058] Compared with the prior art, the present application has the following beneficial effects:

[0059] (1) In the application, the vein type flow channel on the surface of the bipolar plate is a fractal network structure, and the geometric characteristics include the following key elements: the vein type flow channel includes two mirror-symmetrical single channels, each single channel includes an inlet flow channel (main vein), four branch flow channels (secondary veins) and an outlet flow channel (main vein), and various flow channels (micro veins) are arranged in the four branch flow channels; the main vein, the secondary vein and the micro vein form a multi-level branch network, the main vein is responsible for long-distance transportation, and the secondary vein and the micro vein realize uniform distribution of fluid in a larger area through dense bifurcation, and the end of the micro vein is in a gradually narrowing or expanding shape to adjust the local flow rate and pressure distribution.

[0060] (2) In the application, the vein type flow channel on the surface of the bipolar plate can precisely control the fluid dynamics characteristics, so that the bipolar plate has significant performance advantages, as follows: first, the fractal network of the vein type flow channel reduces the single channel flow through multi-level flow splitting, reduces the Reynolds number (Re), and makes the flow tend to be in a laminar state; under the laminar condition, the fluid shear stress is greatly reduced, and compared with the traditional serpentine or parallel flow channel, the pressure drop loss is reduced by 20%-40%; second, uniform distribution of electrolyte is realized, that is, the bifurcation structure forces the fluid to be redistributed in each level of branch, which fundamentally eliminates the problem of uneven flow caused by length difference of the flow channel, and ensures that the electrolyte is uniformly distributed in a larger area; third, the dynamic flow adaptation capability is achieved, that is, when the inlet flow increases, the laminar flow characteristics of the secondary vein can automatically limit the flow rate increase, avoiding local overload, and when the flow decreases, the micro channel of the micro vein can still maintain the basic flow to prevent the formation of dead zones, thereby stably coping with the dynamic change of the flow.

[0061] (3) In the application, the flow channel in the vertical direction of the fourth flow channel is arranged to have a gradually narrowing cross-sectional width first and then remain unchanged and extend downward for a certain length, so that the lower flow channel opening is narrowed to increase the flow rate, thereby ensuring the uniformity of the flow rate of the flow channel. BRIEF DESCRIPTION OF DRAWINGS

[0062] Figure 1 It is a structure diagram of one side surface of a bipolar plate of a full vanadium flow battery provided in an embodiment.

[0063] Figure 2 It is an exploded view of a single cell provided in another embodiment.

[0064] Figure 3 It is a structure diagram of the assembled single cell provided in another embodiment.

[0065] Wherein, 1-bipolar plate; 2-inlet flow channel; 3-outlet flow channel; 4-first flow channel; 5-second flow channel; 6-third flow channel; 7-fourth flow channel; 8-first branch flow channel; 9-second branch flow channel; 10-first flow channel branch; 11-second flow channel branch; 12-first flow channel passage; 13-second flow channel passage; 14-liquid inlet; 15-liquid outlet; 16-negative electrode; 17-separator; 18-sealing strip; 19-electrode frame. DETAILED DESCRIPTION

[0066] It should be understood that, in the description of the present application, the terms "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only for the purpose of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0067] It should be noted that, in the description of the present application, unless otherwise specified and limited, the terms "provided", "communicated", "connected" should be understood broadly. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0068] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as a specific limitation on the present application.

[0069] In one specific embodiment, as shown in Figure 1 The present application provides a bipolar plate 1 of a vanadium redox flow battery, one side surface of the bipolar plate 1 is provided with a vein type flow channel;

[0070] The vein type flow channel includes two mirror-symmetrical single-sided channels, each single-sided channel includes an inlet flow channel 2, four branch flow channels and an outlet flow channel 3; the outlet of the inlet flow channel 2 is communicated to the inlet of the four branch flow channels, and the outlet of the four branch flow channels is communicated to the inlet of the outlet flow channel 3;

[0071] From the direction away from the symmetry axis of the two single-sided channels to the direction close to the symmetry axis, the four branch flow channels are respectively a first flow channel 4, a second flow channel 5, a third flow channel 6 and a fourth flow channel 7;

[0072] The first flow channel 4 includes a flow channel which is converted from horizontal direction to vertical direction, and then to horizontal direction, and finally connected to the outlet flow channel 3;

[0073] The second flow channel 5 includes a flow channel which is converted from horizontal direction to vertical direction, and then to horizontal direction, and finally connected to the outlet flow channel 3;

[0074] The third flow channel 6 includes a flow channel which is extended downward in vertical direction for a certain length, and then the cross-sectional width is gradually widened, and then divided into two flow channel branches, and finally connected to the outlet flow channel 3;

[0075] The fourth flow channel 7 includes a flow channel which is converted from horizontal direction to vertical direction, and then the cross-sectional width is gradually narrowed and then kept unchanged and extended downward for a certain length, and then converted to horizontal direction, and finally connected to the outlet flow channel 3.

[0076] In the application, the two single-sided channels are mirror-symmetric, and the structure and size are completely the same.

[0077] In the application, the surface vein type flow channel of the bipolar plate 1 is a fractal network structure, and the geometric characteristics include the following key elements. The vein type flow channel includes two mirror-symmetric single-sided channels. Each single-sided channel includes an inlet flow channel 2 (main vein), four branch flow channels (secondary veins), and an outlet flow channel 3 (main vein). The four branch flow channels have various flow channels (micro veins). The main vein, secondary vein, and micro vein constitute a multi-level branch network. The main vein is responsible for long-distance transportation. The secondary vein and the micro vein realize uniform distribution of fluid in a larger area through dense bifurcation. The micro vein ends gradually narrow or expand to adjust local flow rate and pressure distribution.

[0078] In the application, the horizontal direction is perpendicular to the symmetry axis of the two single-sided channels, and the vertical direction is parallel to the symmetry axis of the two single-sided channels. The horizontal direction and the vertical direction are perpendicular to each other, and the plane formed between the horizontal direction and the vertical direction is parallel to the surface of the bipolar plate 1.

[0079] In the application, the vein type flow channel on the surface of the bipolar plate 1 can significantly improve the performance of the bipolar plate 1 by precisely regulating the fluid dynamics, as follows: first, the fractal network of the vein type flow channel reduces the flow of a single channel through multi-stage shunting, reduces the Reynolds number (Re), and makes the flow tend to be laminar, under the laminar condition, the fluid shear stress is greatly reduced, and the pressure drop loss is reduced by 20% to 40% compared with the traditional serpentine or parallel flow channel; second, the uniform distribution of electrolyte is realized, that is, the bifurcation structure forces the fluid to be redistributed in each level of branch, which fundamentally eliminates the problem of uneven flow caused by the length difference of the flow channel, and ensures the uniform distribution of electrolyte in a larger area; third, the dynamic flow adaptation capability is achieved, that is, when the inlet flow increases, the laminar characteristics of the secondary vein can automatically limit the flow rate increase, avoiding local overload, and when the flow decreases, the micro vein can still maintain the basic flow to prevent the formation of dead zones, thereby stably coping with the dynamic change of flow.

[0080] In the application, the vertical flow channel of the fourth flow channel 7 is designed to have a gradually narrowing cross-sectional width, then remain unchanged and extend downward for a certain length, so that the lower flow channel opening is narrowed to increase the flow rate, thereby ensuring the uniform flow rate of the flow channel.

[0081] In summary, the bipolar plate 1 of the all-vanadium redox flow battery provided by the application can significantly reduce the pressure drop loss of electrolyte flow, realize the uniform flow distribution of electrolyte on the surface of the electrode, and has the self-adaptive adjustment capability to the dynamic flow change.

[0082] In some embodiments, two branch flow channels are arranged between the vertical flow channel of the second flow channel 5 and the vertical flow channel of the third flow channel 6, for connecting the vertical flow channel of the second flow channel 5 and the vertical flow channel of the third flow channel 6.

[0083] In the application, the vertical flow channel of the second flow channel 5 is connected to the vertical flow channel of the third flow channel 6 through two branch flow channels, realizing the series connection between the second flow channel 5 and the third flow channel 6, for reducing the pressure difference between the second flow channel 5 and the third flow channel 6.

[0084] In some embodiments, the two branch flow channels are a first branch flow channel 8 and a second branch flow channel 9, respectively.

[0085] The first branch flow channel 8 is connected to the starting point of the gradually widened cross-sectional width of the vertical flow channel of the third flow channel 6.

[0086] The second branch flow channel 9 is connected to the flow channel branch close to the second flow channel 5 among the two flow channel branches of the third flow channel 6.

[0087] In some embodiments, one of the third flow channels 6 is directly connected to the outlet flow channel 3, and the other is connected to the outlet flow channel 3 through the H-shaped backflow channel.

[0088] In some embodiments, the two flow channel branches of the third flow channel 6 are the first flow channel branch 10 and the second flow channel branch 11, respectively, the first flow channel branch 10 is close to the second flow channel 5, and the second flow channel branch 11 is away from the first flow channel 4.

[0089] The first flow channel branch 10 is directly connected to the outlet flow channel 3, and the second flow channel branch 11 is connected to the outlet flow channel 3 through the H-shaped backflow channel.

[0090] The H-shaped backflow channel comprises a H-shaped flow channel formed by surrounding a circle with four side flow channels, one of the four side flow channels of the H-shaped backflow channel coincides with part of the first flow channel branch 10, and one coincides with part of the fourth flow channel 7.

[0091] In the present application, the H-shaped backflow channel of the third flow channel 6 is used to reduce the flow rate of the electrolyte and increase the contact time of the electrolyte with the electrode.

[0092] In some embodiments, two flow channel passages are provided between the vertical flow channels of the fourth flow channel 7 of the two single-sided channels, and the two flow channel passages connect the fourth flow channels 7 of the two single-sided channels.

[0093] In some embodiments, the two flow channel passages comprise a first flow channel passage 12 and a second flow channel passage 13, the first flow channel passage 12 connects the middle position of the vertical flow channels of the two fourth flow channels 7 where the cross-sectional width gradually narrows, and the second flow channel passage 13 connects the position where the cross-sectional width of the vertical flow channels of the two fourth flow channels 7 gradually narrows and then remains unchanged.

[0094] In some embodiments, the length and cross-sectional size of the inlet flow channel 2, the four branch flow channels and the outlet flow channel 3 in the vein type flow channel are determined by the Navier-Stokes equation and the Poiseuille theorem.

[0095] In the present application, in order to uniformly distribute the flow rate of the electrolyte on the entire electrode surface and also reduce the flow resistance of the entire flow channel, it is necessary to calculate the relationship between the pressure and the flow rate of the main road and the branch road on the entire flow channel:

[0096] The Navier-Stokes equation (abbreviated as NS equation) describes the motion law of viscous fluid, which is essentially the mathematical expression of Newton's second law (momentum conservation) and mass conservation law in continuous medium, which is derived by combining the constitutive relation (such as Newton's viscosity law);

[0097] According to the NS equation, the relationship between the pressure and the flow rate in each flow channel of the main road and the branch road can be listed as follows:

[0098]

[0099]

[0100]

[0101]

[0102] wherein u, v, w are the velocities of the fluid in the x, y, z directions, is the fluid density, p is the fluid pressure, t is the time, is the viscous force, f is the volume force in each direction. When the flow rate at each branch is determined, the flow resistance difference between the head and tail of the branch can be obtained by using the Poiseuille theorem, that is:

[0103]

[0104] wherein ΔP is the pressure drop of the flow channel, μ is the dynamic viscosity of the fluid, L is the length of the flow channel, Q is the volume flow rate, w, h are the length and width of the flow channel. According to the above formula, the length of each branch in the vein flow channel at the minimum flow resistance can be calculated, and the shape of the flow channel cross section can be determined. Through calculation, the length and width of the flow channel cross section can be obtained.

[0105] In some embodiments, the calculation aims to achieve the minimum flow resistance of the electrolyte in the flow channel, and the length and cross-sectional size obtained through the calculation make the flow channel meet the condition of the minimum flow resistance.

[0106] In some embodiments, the top of the vein flow channel is provided with a liquid inlet 14 which is communicated to the inlet of the inlet flow channel 2.

[0107] The bottom of the vein flow channel is provided with a liquid outlet 15 which is communicated to the outlet of the outlet flow channel 3.

[0108] In the present application, the vein flow channel is left-right symmetrical, and the electrolyte flows into the vein flow channel from the top liquid inlet 14. The flowing electrolyte is divided into two left-right mirror symmetrical single channels through the left-right two inlet flow channels 2.

[0109] In another specific embodiment, as shown in Figure 2 and Figure 3 The present application provides a single cell, which comprises the above-mentioned bipolar plate 1.

[0110] In the present application, the single cell comprises a positive electrode (not shown in the figure), a negative electrode 16, a diaphragm 17, two bipolar plates 1, a sealing strip 18 and an electrode frame 19; wherein the bipolar plate 1, the positive electrode, the diaphragm 17, the negative electrode 16 and the bipolar plate 1 are stacked to form a stacked structure, and the side surface of the bipolar plate 1 provided with the vein type flow channel faces the positive electrode and the negative electrode 16 respectively, and the outside of the stacked structure is fixed by the electrode frame 19; the sealing strip 18 is arranged between the bipolar plate 1 and the electrode frame 19; wherein the bipolar plate 1 needs to be closely combined with the positive electrode and the negative electrode 16, so that the electrolyte on the bipolar plate 1 fully contacts the positive electrode and the negative electrode 16, and the electrolyte does not flow out, thereby realizing more uniform charging and discharging.

[0111] In another specific embodiment, the present application provides a stack comprising the single cell described above.

[0112] In another specific embodiment, the present application provides a full vanadium redox flow battery comprising the stack described above.

[0113] Embodiment

[0114] The present embodiment provides a bipolar plate 1 of a full vanadium redox flow battery, one side surface of the bipolar plate 1 is provided with a vein type flow channel;

[0115] The vein type flow channel comprises two single-sided channels which are mirror-symmetric and have the same structure and size, each single-sided channel comprises an inlet flow channel 2, four branch flow channels and an outlet flow channel 3; the outlet of the inlet flow channel 2 is connected to the inlet of the four branch flow channels, and the outlet of the four branch flow channels is connected to the inlet of the outlet flow channel 3; the top of the vein type flow channel is provided with a liquid inlet 14 which is connected to the inlet of the inlet flow channel 2; the bottom of the vein type flow channel is provided with a liquid outlet 15 which is connected to the outlet of the outlet flow channel 3;

[0116] From the direction far away from the symmetry axis of the two single-sided channels to the direction close to the symmetry axis, the four branch flow channels are respectively a first flow channel 4, a second flow channel 5, a third flow channel 6 and a fourth flow channel 7;

[0117] The first flow channel 4 comprises a flow channel which is converted from the horizontal direction to the vertical direction, and then to the horizontal direction, and finally connected to the outlet flow channel 3;

[0118] The second flow channel 5 comprises a flow channel which is converted from the horizontal direction to the vertical direction, and then to the horizontal direction, and finally connected to the outlet flow channel 3;

[0119] The third flow channel 6 comprises a flow channel which is extended downward by a certain length from the vertical direction, and then the cross-sectional width is gradually widened, and then the flow channel is branched into two flow channel branches, and finally connected to the outlet flow channel 3.

[0120] The two flow channel branches in the third flow channel 6 are a first flow channel branch 10 and a second flow channel branch 11, the first flow channel branch 10 is close to the second flow channel 5, and the second flow channel branch 11 is away from the first flow channel 4;

[0121] The first flow channel branch 10 is directly communicated to the outlet flow channel 3, and the second flow channel branch 11 is communicated to the outlet flow channel 3 through a mouth-shaped backflow channel;

[0122] The mouth-shaped backflow channel includes a mouth-shaped flow channel formed by surrounding a circle by four edge flow channels, one of the four edge flow channels of the mouth-shaped backflow channel coincides with part of the first flow channel branch 10, and one coincides with part of the fourth flow channel 7;

[0123] Two branch flow channels are arranged between the vertical flow channel of the second flow channel 5 and the vertical flow channel of the third flow channel 6 for communicating the vertical flow channel of the second flow channel 5 and the vertical flow channel of the third flow channel 6, realizing the series connection between the second flow channel 5 and the third flow channel 6;

[0124] The two branch flow channels are a first branch flow channel 8 and a second branch flow channel 9; the first branch flow channel 8 is communicated to the starting position of the gradually widened cross-sectional width of the vertical flow channel of the third flow channel 6; and the second branch flow channel 9 is communicated to the flow channel branch of the two flow channel branches of the third flow channel 6 close to the second flow channel 5;

[0125] The fourth flow channel 7 includes a flow channel formed by a horizontal direction, a vertical direction with a cross-sectional width gradually narrowing first and then remaining unchanged and extending downward for a set length, and a horizontal direction again, and finally communicated to the outlet flow channel 3;

[0126] Two flow channel passages are arranged between the vertical flow channels of the fourth flow channels 7 of the two single-sided passages, and the two flow channel passages communicate the fourth flow channels 7 of the two single-sided passages;

[0127] The two flow channel passages include a first flow channel passage 12 and a second flow channel passage 13; the first flow channel passage 12 communicates to the middle position of the gradually narrowed cross-sectional width of the vertical flow channels of the two fourth flow channels 7; and the second flow channel passage 13 communicates to the position where the cross-sectional width of the vertical flow channels of the two fourth flow channels 7 is gradually narrowed to remain unchanged;

[0128] The length and cross-sectional size of the inlet flow channel 2, the four branch flow channels, and the outlet flow channel 3 in the vein type flow channel are determined by Navier-Stokes equation (NS equation) and Poiseuille theorem; the calculation is targeted to achieve the minimum flow resistance of the electrolyte in the flow channel, and the length and cross-sectional size obtained by the calculation make the flow channel meet the condition of the minimum flow resistance;

[0129] According to the NS equation, the relationship between the pressure and the flow rate in each section of the main road and the branch road can be listed as follows:

[0130]

[0131]

[0132]

[0133]

[0134] wherein u, v, w are the velocities of the fluid in the x, y, z directions, is the fluid density, p is the fluid pressure, t is the time, is the viscous force, f is the volume force in each direction. When the flow rate at each branch is determined, the flow resistance difference between the head and tail of the branch can be obtained by using the Poiseuille theorem, that is:

[0135]

[0136] wherein ΔP is the pressure drop of the flow channel, μ is the dynamic viscosity of the fluid, L is the length of the flow channel, Q is the volume flow rate, w, h are the length and width of the flow channel. According to the above formula, the length of each branch in the vein type flow channel at the minimum flow resistance can be calculated, and the shape of the flow channel cross section can be determined. Through calculation, the length and width of the flow channel cross section can be obtained.

[0137] Application Example

[0138] The single cell of the all-vanadium redox flow battery provided in the embodiment comprises a positive electrode, a negative electrode 16, a diaphragm 17, two bipolar plates 1, a sealing strip 18 and an electrode frame 19. The bipolar plate 1, the positive electrode, the diaphragm 17, the negative electrode 16 and the bipolar plate 1 are stacked to form a stacked structure, and the side surface of the bipolar plate 1 provided with the vein type flow channel faces the positive electrode and the negative electrode 16, respectively. The outside of the stacked structure is fixed by the electrode frame 19. The sealing strip 18 is arranged between the bipolar plate 1 and the electrode frame 19. The bipolar plate 1 needs to be closely combined with the positive electrode and the negative electrode 16, so that the electrolyte on the bipolar plate 1 fully contacts the positive electrode and the negative electrode 16, and the electrolyte does not flow out, thereby realizing more uniform charging and discharging.

[0139] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed in the present application can be easily thought of by those skilled in the art, and all of them fall within the protection scope and disclosure scope of the present application.

Claims

1. A bipolar plate for a vanadium redox flow battery, characterised in that, The one side surface of the bipolar plate is provided with a vein type flow channel; The vein type flow channel comprises two mirror-symmetrical single-side channels, each single-side channel comprising an inlet flow channel, four branch flow channels and an outlet flow channel; the outlet of the inlet flow channel is communicated to the inlet of the four branch flow channels, and the outlet of the four branch flow channels is communicated to the inlet of the outlet flow channel; The four branch flow channels are respectively a first flow channel, a second flow channel, a third flow channel and a fourth flow channel from the direction far away from the symmetry axis of the two single-side channels to the direction close to the symmetry axis; The first flow channel comprises a flow channel which is converted from horizontal direction to vertical direction, then to horizontal direction, and finally communicated to the outlet flow channel; The second flow channel comprises a flow channel which is converted from horizontal direction to vertical direction, then to horizontal direction, and finally communicated to the outlet flow channel; The third flow channel comprises a flow channel which is extended downward for a certain length from vertical direction, then the cross-sectional width is gradually widened, and then the flow channel is branched into two flow channel branches, and finally communicated to the outlet flow channel; The fourth flow channel comprises a flow channel which is converted from horizontal direction to vertical direction, then the cross-sectional width is gradually narrowed, and then kept unchanged and extended downward for a certain length, and then converted to horizontal direction, and finally communicated to the outlet flow channel.

2. The bipolar plate of claim 1, wherein Two branch flow channels are arranged between the vertical flow channel of the second flow channel and the vertical flow channel of the third flow channel, for communicating the vertical flow channel of the second flow channel and the vertical flow channel of the third flow channel.

3. The bipolar plate of claim 2, wherein The two branch flow channels are respectively a first branch flow channel and a second branch flow channel; The first branch flow channel is communicated to the starting position of the gradually widened cross-sectional width of the vertical flow channel of the third flow channel; The second branch flow channel is communicated to the flow channel branch of the third flow channel close to the flow channel branch of the second flow channel.

4. The bipolar plate of claim 1, wherein One of the two flow channel branches of the third flow channel is directly communicated to the outlet flow channel, and the other flow channel branch is communicated to the outlet flow channel through a mouth-shaped return flow channel; The two flow channel branches of the third flow channel are respectively a first flow channel branch and a second flow channel branch, the first flow channel branch is close to the second flow channel, and the second flow channel branch is far away from the first flow channel; The first flow channel branch is directly communicated to the outlet flow channel, and the second flow channel branch is communicated to the outlet flow channel through a mouth-shaped return flow channel; The mouth-shaped return flow channel comprises a mouth-shaped flow channel formed by surrounding a circle with four edge flow channels, one of the four edge flow channels of the mouth-shaped return flow channel coincides with part of the first flow channel branch, and one of the four edge flow channels coincides with part of the fourth flow channel.

5. The bipolar plate of claim 1, wherein Two flow channel passages are arranged between the vertical flow channels of the fourth flow channels of the two single-side channels, and the two flow channel passages communicate the fourth flow channels of the two single-side channels; The two flow channel passages comprise a first flow channel passage and a second flow channel passage, the first flow channel passage communicates the middle positions of the gradually narrowed cross-sectional widths of the vertical flow channels of the two fourth flow channels, and the second flow channel passage communicates the positions where the cross-sectional widths of the vertical flow channels of the two fourth flow channels are gradually narrowed and then kept unchanged.

6. The bipolar plate of claim 1, wherein The length and cross-sectional size of the inlet flow channel, the four branch flow channels and the outlet flow channel in the vein type flow channel are determined by Navier-Stokes equation and Poiseuille theorem.

7. The bipolar plate of claim 1, wherein The top of the vein flow channel is provided with a liquid inlet, which is communicated to the inlet of the inlet flow channel; The bottom of the vein flow channel is provided with a liquid outlet, which is communicated to the outlet of the outlet flow channel.

8. A single cell characterized by The single cell comprises the bipolar plate according to any one of claims 1-7.

9. A stack, characterized by The stack comprises the single cell according to claim 8.

10. An all-vanadium redox flow battery characterised in that, The all-vanadium redox flow battery comprises the stack according to claim 9.

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