A bipolar plate suitable for rectangular liquid flow battery and its application

Abstract

A bipolar plate suitable for rectangular liquid flow batteries or battery stacks, the bipolar plate is a rectangular flat plate structure, a rectangular area for contacting an electrode is provided in the middle of one side surface or two side surfaces of the plate, which is called the electrode area; the electrolyte flows into the electrode area from the rectangular lower side of the electrode area and then flows out from the rectangular upper side, the rectangular lower side for inflow is called the electrode area inlet side, and the rectangular upper side for outflow is called the electrode area outlet side; a group of grooves consisting of more than two trapezoidal grooves are provided on the rectangular left side and right side of the electrode area toward the middle of the electrode area, which are called trapezoidal flow guide grooves. The bipolar plate has a simple structure and is easy to process. By promoting the electrolyte to flow toward the left and right walls of the electrode area, the uniformity of electrolyte distribution is effectively improved, thereby alleviating the local effect and improving battery performance.

Description

Technical Field

[0001] The present invention relates to the field of liquid flow batteries, and in particular to a liquid flow battery or a battery stack bipolar plate. Background Art

[0002] The development of industry is inseparable from energy, and as energy and environmental issues become increasingly prominent, carbon emission rights will become a stumbling block to national development. The development and utilization of renewable energy is one of the effective ways to solve the problem of carbon emissions. Clean energy such as wind energy and solar energy is inexhaustible and will occupy an increasingly important position in the future energy structure. In order to effectively utilize these renewable energy sources, it is extremely important to vigorously develop energy storage technology to ensure the smooth output of renewable energy. So far, a variety of energy storage technologies have been developed, including pumped storage, compressed air storage, flywheel storage, and electrochemical storage. Among them, electrochemical energy storage technology represented by flow batteries has the characteristics of low regional environmental restrictions and high flexibility, and is suitable for energy storage applications of various scales. Among them, flow batteries are suitable for static energy storage because of their advantages of independent design of power and capacity. When the flow battery is in operation, the electrolyte flows through the porous electrodes to produce an electrochemical redox reaction, thereby realizing the storage and release of energy. But generally speaking, the uneven flow of electrolyte in porous electrodes is very obvious, especially in the area where the electrode is attached to the liquid flow frame. The boundary layer effect is very significant, which is not conducive to the smooth progress of the electrochemical reaction, will cause large concentration polarization, and even lead to side reactions such as hydrogen and oxygen evolution, seriously reducing battery performance. Summary of the invention

[0003] Aiming at the performance degradation problem caused by the decrease of electrolyte flow velocity near the wall in liquid flow batteries, a new type of liquid flow battery bipolar plate structure is proposed. The structure is simple and easy to process. By designing appropriately oriented trapezoidal flow guide grooves on the bipolar plate, the electrolyte flow velocity near the wall is increased, thereby achieving uniform distribution of active materials inside the rectangular battery, alleviating local effects, reducing polarization, and ultimately improving battery efficiency.

[0004] To achieve the above purpose, the specific technical solution provided by the present invention is as follows:

[0005] A bipolar plate suitable for a rectangular liquid flow battery or a battery stack, the bipolar plate being a rectangular flat plate structure, with a rectangular area for contacting an electrode in the middle of one side surface or two side surfaces of the plate, referred to as the electrode area; the electrolyte flows into the electrode area from the rectangular lower side of the electrode area and then flows out from the rectangular upper side, the rectangular lower side for inflow is referred to as the electrode area inlet side, and the rectangular upper side for outflow is referred to as the electrode area outlet side; a group of grooves consisting of more than two trapezoidal grooves are respectively provided on the rectangular left side and right side of the electrode area toward the middle of the electrode area, referred to as the trapezoidal guide grooves.

[0006] The battery or battery stack design standards of the present invention are:

[0007] The plane where the surface of the bipolar plate body is located is plane A, the perpendicular bisector of the side of the entrance of the electrode area is line B, the cross section of the trapezoidal groove parallel to plane A is trapezoid C, the lower base D of trapezoid C coincides with the left side of the rectangular electrode area or the right side of the electrode area, and the upper base E of trapezoid C is located near line B and parallel to line B or on line B. Any two grooves in the two sets of trapezoidal groove groups do not intersect or penetrate, and more than two trapezoidal grooves in the two sets of trapezoidal groove groups are arranged symmetrically on the left and right, and the straight lines where the symmetrical groove sides E are located are parallel to each other; or, any two grooves in the two sets of trapezoidal groove groups do not intersect or penetrate, and more than two trapezoidal grooves in the two sets of trapezoidal groove groups are arranged alternately on the left and right, and the straight lines where the adjacent groove sides E are located are parallel to each other or coincide with each other; or more than two trapezoidal grooves in the two sets of trapezoidal groove groups are arranged symmetrically on the left and right, and the symmetrical grooves are connected to each other.

[0008] The area occupied by the groove on the plane of the plate body is 10% to 90% of the area of ​​the electrode region on the plane of the plate body.

[0009] Preferably, the lower base angle of the trapezoid C is 45-89°.

[0010] Preferably, the width of the upper base E of the trapezoid C is 2 to 60 mm, and the width of the lower base F is 5 to 100 mm.

[0011] Preferably, the depth of the trapezoidal groove is 0.1-100 mm.

[0012] Preferably, the trapezoidal grooves constituting the groove group have the same width and depth, or follow the principle that the guide grooves near the inlet side of the electrode area are narrower in width and / or smaller in depth while the guide grooves near the outlet side of the electrode area are wider in width and / or deeper.

[0013] Preferably, the electrolyte inlet and outlet have a diameter of 2 to 100 mm.

[0014] The width of the plate body around the electrode area on the plate body is 3 to 500 mm; the thickness of the plate body is 1 to 100 mm.

[0015] Preferably, the inner corners of the trapezoidal guide grooves and the intersections with the edges are all arc-shaped transitions.

[0016] The bipolar plate provided by the present invention can be made of materials such as graphite, but is not limited thereto. The groove structure on the plate body can be formed by mechanical processing, engraving, hot pressing, etc., but is not limited thereto.

[0017] Compared with the prior art, the bipolar plate structure adopted by the present invention is particularly suitable for rectangular liquid flow batteries, which can greatly improve the uniformity of active material distribution, thereby ensuring uniform reactions within the battery and the battery stack, reducing local effects, and improving battery efficiency. Especially for high-power battery stacks, it can effectively reduce costs and save materials.

[0018] Beneficial effects brought by the technical solution of the present invention

[0019] The bipolar plate has a simple structure and is easy to process. It effectively improves the uniformity of electrolyte distribution by causing the electrolyte to flow toward the left and right walls of the electrode area, thereby alleviating local effects and improving battery performance. Specifically:

[0020] During the operation of a flow battery, the electrolyte undergoes an electrochemical reaction while flowing in the electrode. Affected by the viscosity of the fluid itself, according to the fully developed flow theory, the fluid velocity is low in the area near the wall, and within a certain range, the closer to the wall, the smaller the fluid velocity, until the velocity at the wall drops to 0. In this low velocity area, the active material is updated slowly, and as the reaction continues, there is a shortage of active material supply (such as Figure 1 As shown in the figure, polarization increases, voltage efficiency decreases, electrolyte utilization decreases, and ultimately the overall performance of the battery decreases.

[0021] By adding trapezoidal guide grooves in the electrolyte flow area, the electrolyte is forced to flow from the middle of the flow section (higher flow velocity) to near the wall (lower flow velocity), thereby accelerating the renewal rate of active substances in the area near the wall, making the spatial distribution of active substances more uniform, reducing the concentration gradient on the flow section, reducing polarization, and improving battery efficiency and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the active material concentration distribution in a rectangular flow battery.

[0023] Figure 2 Example 1.

[0024] Figure 3 Example 2.

[0025] Figure 4 Example 3.

[0026] Figure 5 Comparative example 4.

[0027] Explanation of symbols:

[0028] 1-negative electrode electrolyte inlet, 2-plate body, 3-electrode area inlet side, 4-electrode area, 5-trapezoidal guide groove, 6-positive electrode electrolyte inlet, 7-left and right sides of the electrode area, 8-negative electrode electrolyte outlet, 9-electrode area outlet side, 10-positive electrode electrolyte outlet. DETAILED DESCRIPTION

[0029] Example 1

[0030] like Figure 2 As shown, a bipolar plate for a liquid flow battery. It is made of graphite pressing, including a bipolar plate body 2, on which a negative electrolyte inlet 1, a negative electrolyte outlet 8, a positive electrolyte inlet 6, and a positive electrolyte outlet 10 are provided. Among them, the negative electrolyte inlet 1 and the positive electrolyte inlet 7 are located on the lower bottom side of the plate body, and the negative electrolyte outlet 8 and the positive electrolyte outlet 10 are located on the upper bottom side of the plate body. An electrode area 4 is provided in the middle of the plate body, and the area is rectangular. A trapezoidal guide groove is provided in the electrode area, and the trapezoidal guide groove is symmetrically distributed one by one about the perpendicular midline of the side of the inlet of the electrode area.

[0031] The thickness of the plate is 9mm; the negative electrolyte inlet 1, the negative electrolyte outlet 8, the positive electrolyte inlet 6 and the positive electrolyte outlet 10 are all circular with a diameter of 10.5mm; in the rectangle where the electrode area is located, the side length of the inlet and outlet is 320mm, and the other two sides are 220mm. The depth of the trapezoidal grooves is 1mm. There are 6 identical trapezoidal grooves in the electrode area. The cross-section of the trapezoidal groove on the plane parallel to the plate body is an isosceles trapezoid, with a lower base length of 42mm, an upper base length of 26mm, and a lower base angle of 80°. The lower base of the isosceles trapezoidal cross-section coincides with the left or right side of the electrode area.

[0032] The same trapezoidal flow guide grooves are machined on both sides of the plate; all intersections with corners are transitioned in arcs. The grooves on the bipolar plate are machined and carved.

[0033] Example 2

[0034] like Figure 3 As shown, a bipolar plate for a liquid flow battery. It is made of graphite pressing, including a bipolar plate body 2, on which a negative electrolyte inlet 1, a negative electrolyte outlet 8, a positive electrolyte inlet 6, and a positive electrolyte outlet 10 are provided. Among them, the negative electrolyte inlet 1 and the positive electrolyte inlet 7 are located on the lower bottom side of the plate body, and the negative electrolyte outlet 8 and the positive electrolyte outlet 10 are located on the upper bottom side of the plate body. An electrode area 4 is provided in the middle of the plate body, and the area is rectangular. A trapezoidal guide groove is provided in the electrode area. The trapezoidal guide groove is symmetrically distributed left and right about the perpendicular midline of the side of the electrode area inlet and is connected.

[0035] The thickness of the plate is 12mm; the negative electrolyte inlet 1, the negative electrolyte outlet 8, the positive electrolyte inlet 6 and the positive electrolyte outlet 10 are all circular with a diameter of 13mm; in the rectangle where the electrode area is located, the side length of the inlet and outlet is 400mm, and the other two sides are 330mm long. The depth of the trapezoidal grooves is 2.5mm. There are 6 identical trapezoidal grooves in the electrode area. The cross-section of the trapezoidal groove on the plane parallel to the plate body is a trapezoid, with a lower bottom side length of 60mm, an upper bottom side length of 45mm, and a height of 200mm. The lower bottom angle close to the inlet side of the electrode area is 75°, and the lower bottom of the trapezoidal cross-section coincides with the left or right side of the electrode area.

[0036] The same trapezoidal flow guide grooves are machined on both sides of the plate; all intersections with corners are transitioned in arcs. The grooves on the bipolar plate are machined and carved.

[0037] Example 3

[0038] like Figure 4 As shown, a bipolar plate for a liquid flow battery. It is made of graphite pressing, including a bipolar plate body 2, on which a negative electrolyte inlet 1, a negative electrolyte outlet 8, a positive electrolyte inlet 6, and a positive electrolyte outlet 10 are provided. Among them, the negative electrolyte inlet 1 and the positive electrolyte inlet 7 are located on the lower bottom side of the plate body, and the negative electrolyte outlet 8 and the positive electrolyte outlet 10 are located on the upper bottom side of the plate body. An electrode area 4 is provided in the middle of the plate body, and the area is rectangular. A trapezoidal guide groove is provided in the electrode area, and the trapezoidal guide groove is staggered left and right about the perpendicular midline of the side edge of the electrode area inlet.

[0039] The plate body is 15mm thick; the negative electrolyte inlet 1, the negative electrolyte outlet 8, the positive electrolyte inlet 6 and the positive electrolyte outlet 10 are all circular with a diameter of 9mm; in the rectangle where the electrode area is located, the side length of the inlet and outlet is 360mm, and the other two sides are 280mm long. The depth of the trapezoidal grooves is 1.5mm. There are 12 identical trapezoidal grooves in the electrode area. The cross-section of the trapezoidal groove on the plane parallel to the plate body is an isosceles trapezoid, with a lower base length of 22mm, an upper base length of 11mm, and a height of 210mm. The lower base of the isosceles trapezoidal cross-section coincides with the left or right side of the electrode area.

[0040] The same trapezoidal flow guide grooves are machined on both sides of the plate; all intersections with corners are transitioned in arcs. The grooves on the bipolar plate are machined and carved.

[0041] Comparative Example 4

[0042] The comparative example is a flat bipolar plate without trapezoidal flow guide grooves, and the structure is as follows Figure 5Taking the all-vanadium liquid flow battery as an example, the commercial software package COMSOL Multiphysics @ Carry out simulation calculations. The mathematical models used in the simulation mainly include:

[0043] Conservation of momentum and continuity equation:

[0044]

[0045]

[0046] in, and P represent the velocity vector and pressure respectively, μ and μ * They represent the intrinsic viscosity and effective viscosity of the electrolyte respectively, and K represents the permeability of the porous medium (porous electrode), which is obtained by the Carman-Kozeny equation.

[0047] Material conservation equation:

[0048]

[0049] where c i is the concentration of material i, S i is the source term in the conservation equation for material i, is the effective diffusion coefficient in the porous electrode region.

[0050] Boundary conditions and initial conditions:

[0051]

[0052] The inlet pressure is set to 25000Pa and the outlet pressure is set to 0Pa.

[0053] In the model, the concentration of vanadium ions at the inlet is related to the charge and discharge state (SoC) to eliminate the influence of reaction time. Based on the assumption of fully developed flow, the diffusion flux of all materials at the outlet is set to 0. The wall boundary is set to 0 flux. The specific expression is:

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060] and are the initial concentrations of vanadium ions at the positive and negative electrodes, respectively, which are set to 1600 mol m -3 The relative error factor of the model convergence is 1×10 -6 For details of the relevant mathematical model, see Yue,M.,et al.(2018)."Flow Field Design and optimization of high power density vanadium flow batteries:A novel trapezoid flow battery."Aiche Journal 64.

[0061] Using 3 mm thick carbon felt as electrode, at 180 mA cm -2 When the battery is charged at a current density of , and the SoC is 50%, the results of simulation calculations for the embodiment and the comparative example are shown in the following table:

[0062]

[0063] It can be seen that the bipolar plate structure of the present invention can effectively improve the uniformity of electrolyte distribution, thereby reducing polarization, improving electrolyte utilization, and increasing power density.

Claims

1. A bipolar plate suitable for a rectangular flow battery or a battery stack, characterized in that: The bipolar plate is a rectangular flat plate structure, and a rectangular area for contacting the electrode is provided in the middle of one side surface or two side surfaces of the flat plate, which is called the electrode area; the electrolyte flows into the electrode area from the lower side of the rectangle and then flows out from the upper side of the rectangle, the lower side of the rectangle for inflow is called the inlet side of the electrode area, and the upper side of the rectangle for outflow is called the outlet side of the electrode area; a group of grooves consisting of more than two trapezoidal grooves are respectively provided on the left side and the right side of the rectangle of the electrode area toward the middle of the electrode area, which are called trapezoidal flow guide grooves; The plane where the surface of the bipolar plate is located is plane A, the perpendicular bisector of the side of the entrance of the electrode area is line B, the cross section of the trapezoidal groove parallel to plane A is trapezoid C, the lower base D of trapezoid C coincides with the left side of the rectangular electrode area or the right side of the electrode area, and the upper base E of trapezoid C is located near line B and parallel to line B or on line B; Any two grooves in the two groups of trapezoidal grooves do not intersect or penetrate each other, and more than two trapezoidal grooves in the two groups of trapezoidal grooves are symmetrically arranged one by one, and the straight lines where the symmetrical groove edges E are located are parallel to each other; Or, any two grooves in the two sets of trapezoidal grooves do not intersect or penetrate, and more than two trapezoidal grooves in the two sets of trapezoidal grooves are staggered left and right, and the straight lines where the edges E of adjacent grooves are located are parallel to or coincide with each other; Or two or more trapezoidal grooves in two sets of trapezoidal grooves are arranged symmetrically one by one, and the symmetrical grooves are connected to each other; The width and depth of the trapezoidal grooves of the groove group follow the principle that the guide grooves close to the inlet side of the electrode area are narrower and / or smaller in depth, while the guide grooves close to the outlet side of the electrode area are wider and / or deeper; the bottom angle of the trapezoid C is 45~89.9°.

2. The bipolar plate according to claim 1, characterized in that: Four through holes are provided on the bipolar plate as inlet and outlet for the positive and negative electrolytes.

3. The bipolar plate according to claim 1, characterized in that: The area occupied by the groove on the plane of the plate body is 10% to 90% of the area of ​​the electrode region on the plane of the plate body.

4. Use of the bipolar plate according to any one of claims 1 to 3 in a rectangular liquid flow battery.

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