A bipolar plate suitable for ladder flow battery and its application

Abstract

A bipolar plate suitable for a trapezoidal liquid flow battery or a battery stack, the bipolar plate is a trapezoidal flat plate structure, and an isosceles trapezoidal area for contacting an electrode is provided in the middle of one side surface or two side surfaces of the plate; the electrolyte flows into the electrode area from the lower bottom side of the trapezoidal electrode area and then flows out from the upper bottom side of the trapezoidal area, the lower bottom side of the trapezoidal area flowing in is called the inlet side side of the electrode area, and the upper bottom side of the trapezoidal area flowing out is called the outlet side side of the electrode area; two groups of groove groups consisting of one or more quadrilateral grooves are respectively provided on the left and right waists of the trapezoidal electrode area toward the middle of the electrode area, which are called guide grooves, one of the two groove groups is arranged near the inlet side, and the other is arranged near the outlet side. By causing the electrolyte to flow directly from the middle of the inlet cross section to the vicinity of the outlet wall, the concentration of active substances in the outlet attachment is increased, thereby effectively reducing the concentration gradient of reactive active substances in the inlet and outlet directions and reducing polarization.

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] Fossil energy is gradually depleting. The development and utilization of renewable energy is both a choice and a necessity. Countries around the world are paying more and more attention to the solutions to energy crises and environmental problems, which will determine the future direction of human society. However, to realize the utilization of renewable energy, the development of energy storage technology is an inevitable link. Electrochemical energy storage technology uses electrochemical redox active substances to respectively undergo electrolytic cell and primary battery processes to achieve the storage and release of electrical energy. Taking the discharge process as an example, a reduction reaction occurs at the positive electrode of the battery, and the positive electrode active substance obtains electrons. At the same time, an oxidation reaction occurs at the negative electrode of the battery, and the negative electrode active substance loses electrons, thereby forming a current from the positive electrode to the negative electrode in the external circuit to supply power to the power grid or electrical equipment. Liquid flow battery technology is one of the many point chemical energy storage technologies. Its characteristic is that the active material is no longer fixed to the positive and negative electrodes, but flows inside the electrodes through the action of pumps. Existing liquid flow battery technologies include all-vanadium liquid flow battery technology, zinc-iron liquid flow battery technology, zinc-bromine liquid flow battery technology, and new organic liquid flow battery technology. It is precisely because of this feature of flow batteries that they can increase the power and capacity of energy storage systems by increasing the electrode area and the volume or concentration of the electrolyte, respectively, thus becoming the preferred technology for large-scale energy storage applications. The Chinese patent (patent application number: 201410495737.5) proposes a new structure of a trapezoidal stack, which can effectively reduce the concentration polarization in the electrode and has high practicality. However, compared with traditional rectangular batteries, the four corners and walls of the trapezoidal battery are prone to excessive or insufficient electrolyte flow rates, resulting in uneven distribution of active materials and obvious local polarization, which in turn causes problems such as battery performance degradation and material corrosion. However, by rationally designing the bipolar plates of the flow battery or stack, the uniformity of the electrolyte distribution can be effectively improved, the battery efficiency can be improved, and the system cost can be reduced. Summary of the invention

[0003] In response to the problem of uneven electrolyte distribution in trapezoidal flow batteries, a new type of bipolar plate structure for flow batteries is proposed. The structure is simple and easy to process. By designing appropriately oriented trapezoidal flow guide grooves on the bipolar plates, the electrolyte can flow evenly into and out of the electrode reaction area, thereby achieving uniform distribution of active materials inside the trapezoidal battery, alleviating local effects, effectively reducing concentration gradients and overall polarization, improving battery performance, and reducing system costs.

[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 trapezoidal liquid flow battery or a battery stack, the bipolar plate being a trapezoidal flat plate structure, with an isosceles trapezoidal 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 lower bottom side of the trapezoidal electrode area and then flows out from the upper bottom side of the trapezoid, the lower bottom side of the inflowing trapezoid is referred to as the inlet side of the electrode area, and the upper bottom side of the outflowing trapezoid is referred to as the outlet side of the electrode area; two groups of groove groups consisting of one or more quadrilateral grooves are respectively provided on the left and right sides of the trapezoidal electrode area toward the middle of the electrode area, referred to as guide grooves, one of the two groove groups is arranged close to the inlet side, and the other is arranged close to the outlet side.

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

[0007] The plane where the surface of the bipolar plate is located is plane A, the perpendicular bisector of the two bottom sides of the electrode area is line B, the median line of the electrode area is line C, the cross-section of the quadrilateral groove parallel to plane A is a convex quadrilateral D, one side E of quadrilateral D is located on any one of the two waists of the electrode area, and the other side F of quadrilateral D is located close to line B and parallel to line B or on line B.

[0008] In the two groups of grooves located on the same waist of the trapezoidal electrode area, the quadrilateral D corresponding to one group of grooves M is located on the side of line C close to the lower base of the trapezoidal electrode area, and the quadrilateral D corresponding to the other group of grooves N is located on the side of line C close to the upper base of the trapezoidal electrode area, and line B does not intersect with the sides E and F of any quadrilateral D at the same time; the two inner angles of the quadrilaterals where the side F of the quadrilateral D corresponding to the groove M are both greater than or equal to 90°, and the sum of the two inner angles of the quadrilaterals where the side F is located is greater than 180°; the two inner angles of the quadrilaterals where the side F of the quadrilateral D corresponding to the groove N are both less than or equal to 90°, and the sum of the two inner angles of the quadrilaterals where the side F is located is less than 180°.

[0009] Any two quadrilateral grooves in the four groove groups do not intersect or connect, the quadrilateral grooves on the two waists are arranged symmetrically on the left and right, the straight lines where the symmetrical groove sides F are located are parallel to each other, or the symmetrical groove sides F coincide with each other, so that the symmetrical grooves are connected to each other; or, any two quadrilateral grooves in the four groove groups do not intersect or connect, the quadrilateral grooves on the two waists are arranged alternately on the left and right from the inlet side to the outlet side, and the straight lines where the adjacent groove sides F are located are parallel to each other or coincide with each other.

[0010] 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.

[0011] Preferably, the difference between the interior angles of the two quadrilaterals where the side F is located is 0-20°.

[0012] Preferably, in the groove group M, the width of the side F is 2 to 60 mm, and the width of the side E is 5 to 100 mm; in the groove group N, the width of the side E is 2 to 60 mm, and the width of the side F is 5 to 100 mm.

[0013] Preferably, the depth of the quadrilateral groove is 0.1-100 mm.

[0014] Preferably, the quadrilateral grooves constituting the groove group have the same width and depth, or follow the principle that the guide grooves close to the lower bottom side of the trapezoidal electrode area are wider and / or deeper while the guide grooves close to the upper bottom side of the trapezoidal electrode area are narrower and / or deeper.

[0015] Preferably, the electrolyte inlet and outlet have a diameter of 1 to 120 mm.

[0016] The width of the plate body around the electrode area on the plate body is 1 to 400 mm; the thickness of the plate body is 0.5 to 100 mm.

[0017] Preferably, the intersections of the inner corners of the quadrilateral guide groove and the edges are all arc-shaped transitions.

[0018] 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.

[0019] Compared with the prior art, the bipolar plate structure adopted by the present invention is particularly suitable for trapezoidal 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.

[0020] Beneficial effects brought by the technical solution of the present invention

[0021] The bipolar plate has a simple structure and is easy to process. By designing trapezoidal flow guide grooves, the electrolyte flow rate and active material renewal rate near the wall of the trapezoidal flow battery are increased, thereby reducing battery polarization and improving battery performance. Specifically:

[0022] like Figure 1As shown in the figure, according to the basic principles of fluid mechanics, when the electrolyte enters the trapezoidal electrode area from the inlet section, it will flow in a direction perpendicular to the inlet section. At this time, the electrolyte on the left and right sides will be hindered by the two waists, making it difficult to flow. A stagnant flow area with a slow electrolyte renewal rate is formed near the wall near the electrolyte inlet, or even a flow dead zone. In this area, the electrolyte flow rate is low and the active material renewal rate is slow, causing the active material to decrease rapidly as the reaction proceeds, causing a large polarization. At the same time, as the electrolyte flows from the inlet to the outlet, the flow cross-sectional area continues to decrease, making the flow rate of the left and right walls near the outlet extremely large, and the active material renewal rate is extremely fast. This uneven active material renewal rate increases the internal polarization of the battery, thereby reducing the voltage efficiency and the electrolyte utilization rate.

[0023] By adding a trapezoidal flow guide structure with an appropriate structure in the electrolyte flow area, the flow velocity distribution of the electrolyte on the electrolyte flow cross section is made more uniform and the concentration gradient is smaller, thereby reducing battery polarization and improving the overall performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of flow velocity distribution and flow direction in a trapezoidal flow battery

[0025] Figure 2 Example 1

[0026] Figure 3 Example 2

[0027] Figure 4 Example 3

[0028] Figure 5 Comparative Example 4

[0029] Explanation of symbols:

[0030] 1-negative electrolyte inlet, 2-plate, 3-side of electrode area inlet, 4-electrode area, 5-flow guide groove, 6-positive electrolyte inlet, 7-left and right sides of electrode area, 8-negative electrolyte outlet, 9-side of electrode area outlet, 10-positive electrolyte outlet DETAILED DESCRIPTION

[0031] Example 1

[0032] like Figure 2As 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 trapezoidal. Four quadrilateral guide grooves are provided in the electrode area, and the quadrilateral guide grooves are symmetrically distributed one by one about the perpendicular midline of the lower bottom side of the trapezoidal electrode area and are not connected.

[0033] The plate body is 10mm 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 13mm; in the trapezoid where the electrode area is located, the side length of the lower bottom side is 500mm, the side length of the upper bottom side is 280mm, and the height is 300mm. The depth of the quadrilateral grooves is 2mm. There are 4 quadrilateral grooves in the electrode area. The two quadrilateral grooves close to the lower bottom are located on the waist with a side length of 200mm, and the side length parallel to the perpendicular midline of the lower bottom of the trapezoid is 150mm. The two quadrilateral internal angles where the sides parallel to the perpendicular midline of the lower bottom of the trapezoid are located are both 110°; the two quadrilateral grooves close to the upper bottom are located on the waist with a side length of 160mm, and the side length parallel to the perpendicular midline of the lower bottom of the trapezoid is 180mm. The two quadrilateral internal angles where the sides parallel to the perpendicular midline of the lower bottom of the trapezoid are located are both 75°.

[0034] The same quadrilateral 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.

[0035] Example 2

[0036] 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 trapezoidal. Four quadrilateral guide grooves are provided in the electrode area, and the quadrilateral guide grooves are symmetrically distributed and connected with each other about the perpendicular midline of the lower bottom side of the trapezoidal electrode area.

[0037] The plate body is 12.5mm 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 12mm; in the trapezoid where the electrode area is located, the lower bottom side is 550mm long, the upper bottom side is 300mm long, and the height is 300mm. The depth of the quadrilateral grooves is 4mm. There are 4 quadrilateral grooves in the electrode area. The two quadrilateral grooves close to the lower base have a side length of 140mm on the waist, and a side length of 110mm parallel to the perpendicular midline of the lower base of the trapezoid. The two quadrilateral internal angles of the sides parallel to the perpendicular midline of the lower base of the trapezoid are both 100°; the two quadrilateral grooves close to the upper base have a side length of 130mm on the waist, and a side length of 120mm parallel to the perpendicular midline of the lower base of the trapezoid. The two quadrilateral internal angles of the sides parallel to the perpendicular midline of the lower base of the trapezoid are both 70°; the sides of the two symmetrical quadrilateral grooves parallel to the perpendicular midline of the lower base of the trapezoid coincide.

[0038] The same quadrilateral 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.

[0039] Example 3

[0040] 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 trapezoidal. Eight quadrilateral guide grooves are provided in the electrode area, of which four are located on the side of the middle line of the trapezoid where the electrode area is located close to the upper bottom of the trapezoid, and the other four are located on the side of the middle line of the trapezoid where the electrode area is located close to the lower bottom of the trapezoid. The quadrilateral guide grooves are staggered left and right about the perpendicular midline of the lower bottom side of the trapezoidal electrode area and are not connected.

[0041] 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 14mm; in the trapezoid where the electrode area is located, the lower bottom side is 480mm long, the upper bottom side is 220mm long, and the height is 290mm. The depth of the quadrilateral grooves is 2.5mm. There are 8 quadrilateral grooves in the electrode area. The sides of the 4 quadrilateral grooves close to the lower base are 38mm, 42mm, 46mm and 50mm respectively on the waist, and the side parallel to the perpendicular midline of the lower base of the trapezoid is 30mm. The two quadrilateral internal angles of the sides parallel to the perpendicular midline of the lower base of the trapezoid are both 115°; the sides of the two quadrilateral grooves close to the upper base are 20mm, 24mm, 28mm and 32mm respectively on the waist, and the side parallel to the perpendicular midline of the lower base of the trapezoid is 40mm. The two quadrilateral internal angles of the sides parallel to the perpendicular midline of the lower base of the trapezoid are both 80°.

[0042] The same quadrilateral 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.

[0043] Comparative Example 4

[0044] The comparative example is a flat bipolar plate without trapezoidal flow guide grooves, and the structure is as follows Figure 5 Taking 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:

[0045] Conservation of momentum and continuity equation:

[0046]

[0047]

[0048] in, and P represent the velocity vector and pressure, respectively. μ and μ* represent the intrinsic viscosity and effective viscosity of the electrolyte, respectively. K represents the permeability of the porous medium (porous electrode), which is obtained by the Carman-Kozeny equation.

[0049] Material conservation equation:

[0050]

[0051] 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.

[0052] Boundary conditions and initial conditions:

[0053]

[0054] The inlet pressure is set to 24000Pa and the outlet pressure is set to 0Pa.

[0055] 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:

[0056]

[0057] (Negative electrode inlet)

[0058]

[0059] (Positive inlet)

[0060] (exit)

[0061] (Other borders)

[0062] 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.

[0063] Using 4.5 mm thick carbon felt as electrode, at 150 mA cm -2 When the battery is charged at a current density of , and the SoC is 75%, the results of simulation calculations for the embodiment and the comparative example are shown in the following table:

[0064]

[0065] It can be seen that the bipolar plate structure of the present invention can effectively improve the uniformity of the concentration distribution of the electrolyte and active material in the trapezoidal liquid flow battery stack, thereby reducing polarization, improving the utilization rate of the electrolyte, increasing the power density, and ultimately reducing the cost.

Claims

1. A bipolar plate suitable for a ladder-shaped liquid flow battery or a battery stack, characterized in that: The bipolar plate is a trapezoidal flat plate structure, and an isosceles trapezoidal area for contacting the 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 lower bottom side of the trapezoidal electrode area and then flows out from the upper bottom side of the trapezoidal area, the lower bottom side of the trapezoidal area for inflow is called the inlet side of the electrode area, and the upper bottom side of the trapezoidal area for outflow is called the outlet side of the electrode area; two groups of groove groups consisting of one or more quadrilateral grooves are respectively provided on the left and right sides of the trapezoidal electrode area toward the middle of the electrode area, which are called guide grooves, and one of the two groove groups is arranged close to the inlet side, and the other is arranged close to the outlet side; The width and depth of the quadrilateral grooves of the groove group follow the principle that the guide grooves close to the lower bottom side of the trapezoidal electrode area are wider and / or deeper, while the guide grooves close to the upper bottom side of the trapezoidal electrode area are narrower and / or deeper; The plane where the surface of the bipolar plate is located is plane A, the perpendicular bisector of the two bottom sides of the electrode area is line B, the median line of the electrode area is line C, the cross section of the quadrilateral groove parallel to plane A is a convex quadrilateral D, one side E of the quadrilateral D is located on any one of the two waists of the electrode area, and the other side F of the quadrilateral D is located near line B and parallel to line B or on line B; In the two groups of grooves located on the same waist of the trapezoidal electrode region, the quadrilateral D corresponding to one group of grooves M is located on the side of line C close to the lower bottom edge of the trapezoidal electrode region, and the quadrilateral D corresponding to the other group of grooves N is located on the side of line C close to the upper bottom edge of the trapezoidal electrode region, and the line B does not intersect with the side E and the side F of any quadrilateral D at the same time; The two quadrilateral interior angles of the side F of the quadrilateral D corresponding to the groove M are both greater than or equal to 90°, and the sum of the two quadrilateral interior angles of the side F is greater than 180°; the two quadrilateral interior angles of the side F of the quadrilateral D corresponding to the groove N are both less than or equal to 90°, and the sum of the two quadrilateral interior angles of the side F is less than 180°; Any two quadrilateral grooves in the four groove groups do not intersect or connect, the quadrilateral grooves on the two waists are arranged symmetrically on the left and right, the straight lines where the symmetrical groove sides F are located are parallel to each other, or the symmetrical groove sides F coincide with each other, so that the symmetrical grooves are connected to each other; or, any two quadrilateral grooves in the four groove groups do not intersect or connect, the quadrilateral grooves on the two waists are arranged alternately on the left and right from the inlet side to the outlet side, and the straight lines where the adjacent groove sides F are located are parallel to each other or coincide with each other.

2. The bipolar plate according to claim 1, characterized in that: The difference between the interior angles of the two quadrilaterals on which side F lies is 0~20°.

3. 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.

4. 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.

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

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