Flow battery stack with obliquely placed membrane

Abstract

The utility model belongs to the technical field of flow batteries, and particularly relates to a flow battery with an obliquely arranged membrane. The flow battery stack comprises a diaphragm, an electrode frame and a bipolar plate, wherein the electrode frame and the bipolar plate are arranged in parallel; the electrode frame is provided with a hollow area, the bipolar plate, the diaphragm and the hollow area define an electrode containing space, and the electrode is arranged in the electrode containing space; a certain angle is formed between the diaphragm and the bipolar plate, so that the height of the electrode accommodating space is gradually increased along the flowing direction of the electrolyte, and the electrode compression ratio of the electrode is gradually reduced along the flowing direction of the electrolyte; the height of the electrode accommodating space is the vertical distance between the diaphragm and the bipolar plate. In the application, the contact resistance can be reduced at a place with a high compression ratio. And at a place with a low compression ratio, the electrolyte is quickly updated, so that the phenomenon of electrolyte insufficiency is improved.

Description

Technical Field

[0001] The utility model belongs to the technical field of liquid flow batteries, and in particular relates to a liquid flow battery with an inclined membrane. Background Art

[0002] Liquid flow battery is a new type of energy storage technology. Due to its high safety, long life, large storage capacity, and adjustable power and capacity separation, it has received widespread attention in the field of energy storage in recent years. In the process of converting electrical energy to chemical energy in liquid flow batteries, energy loss is inevitable. During the charging and discharging process of the battery stack, in addition to the energy loss caused by side reactions, various polarization losses are the main source of energy loss in the battery stack. The polarization of liquid flow batteries is mainly divided into ohmic polarization, electrochemical polarization, and concentration polarization. Ohmic polarization is mainly determined by the internal resistance of each key material and the contact resistance; electrochemical polarization is mainly determined by the electron transfer rate of the electrochemical reaction; concentration polarization is mainly determined by whether the reactants are sufficient and the mass transfer rate.

[0003] In the design of liquid flow batteries, the degree of electrode compression not only determines the internal resistance of the electrode and the contact resistance between the electrode and the bipolar plate, but is also closely related to the mass transfer efficiency of the active material inside the battery stack. Current liquid flow battery technology generally reduces the ohmic internal resistance of the electrode by compressing the electrode while increasing the flow rate of the pump, accelerating the transfer of active materials and reducing concentration polarization; or using electrodes of different thicknesses for splicing in the active area to create an environment with different compression ratios in different areas to improve mass transfer efficiency. However, increasing the flow rate of the pump will increase pump consumption, and continuing to increase the flow rate after the flow rate exceeds the critical value will have limited effect on improving battery performance; although splicing electrodes of different thicknesses can reduce concentration polarization, the contact resistance between the spliced ​​electrodes will increase.

[0004] In order to solve the above problems, this application is proposed. Utility Model Content

[0005] In a first aspect, the present application provides a liquid flow battery stack with an inclined membrane, the liquid flow battery stack comprising: a diaphragm, an electrode frame and a bipolar plate arranged parallel to each other;

[0006] The electrode frame has a hollow area, the bipolar plate, the diaphragm and the hollow area are surrounded to form an electrode accommodation space, and the electrode is arranged in the electrode accommodation space;

[0007] The diaphragm and the bipolar plate are arranged at a certain angle so that the height of the electrode accommodating space gradually increases along the flow direction of the electrolyte, thereby gradually reducing the electrode compression ratio of the electrode along the flow direction of the electrolyte. The height of the electrode accommodating space is the vertical distance between the diaphragm and the bipolar plate.

[0008] Preferably, the bipolar plate has at least one surface for contacting an electrode, and the surface is arranged parallel to the flow direction of the electrolyte.

[0009] Preferably, the overall thickness of the bipolar plate remains unchanged.

[0010] Preferably, the overall porosity of the electrode before compression is consistent.

[0011] Preferably, the height of the electrode accommodating space gradually increases linearly along the flow direction of the electrolyte, so that the electrode compression ratio of the electrode gradually decreases linearly along the flow direction of the electrolyte.

[0012] Preferably, the electrode is a porous carbon material electrode.

[0013] Preferably, the compression ratio of the electrode at the electrolyte inlet and the compression ratio at the electrolyte outlet are 10% to 50%, for example, 10% to 30%.

[0014] A second aspect of the present application provides a method for reducing concentration polarization of a liquid flow battery, which uses a liquid flow battery stack with an inclined membrane as described in any one of the first aspects.

[0015] Specifically, the height of the electrode accommodating space is designed in combination with the characteristics of the electrode itself, so that the compression ratio of the electrode after assembly is not greater than a preset maximum compression ratio.

[0016] Preferably, the diaphragm can be fixed by physical compression molding, welding or hot melting.

[0017] Preferably, the diaphragm has a certain toughness strength.

[0018] In the process of realizing the present application, the inventors also found that the prior art also reduces concentration polarization and improves performance by designing bipolar plates of different thicknesses, but bipolar plates of different thicknesses are difficult to manufacture.

[0019] Compared with the prior art, this application has the following beneficial effects:

[0020] 1. The membrane is placed at an angle so that the compression ratio of the electrode gradually decreases with the flow direction, thereby reducing the polarization of the flow battery and improving the performance of the flow battery.

[0021] 2. The solution of the present application is easy to implement. It only requires the diaphragm to be installed in an offset manner and the thickness of the electrode frame of the compression molded film to be slightly offset. Normal bipolar plates and electrodes of the same thickness can be used to achieve different compression ratios.

[0022] 3. In this application, the contact resistance can be reduced where the electrode compression ratio is high, and the electrolyte is quickly renewed where the electrode compression ratio is low, so that the electrolyte shortage phenomenon is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of a single cell in a flow battery stack.

[0024] List of reference numerals:

[0025] 1. Bipolar plate, 2. Electrode, 3. Diaphragm, 4. Electrode frame position. DETAILED DESCRIPTION

[0026] The present application is further described in detail below in conjunction with embodiments.

[0027] Those skilled in the art will appreciate that the following examples are only used to illustrate the present application and should not be considered to limit the scope of the present application. If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the art or the product specifications are used. If the manufacturer of the materials or equipment used is not specified, they are all conventional products that can be purchased.

[0028] Those skilled in the art will appreciate that, unless expressly stated otherwise, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present application refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" to another element, it may be directly connected to the other element, or there may be intermediate elements. In addition, the "connection" used herein may include wireless connections.

[0029] In the description of this application, unless otherwise specified, "plurality" means two or more. The terms "inside", "upper", "lower", etc. indicate positions or state relationships based on the positions or state relationships shown in the drawings, which are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operate in a specific position, and therefore cannot be understood as limiting this application.

[0030] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "provided with" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this application are understood according to specific circumstances.

[0031] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as those generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0032] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. If not otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution. If not otherwise specified, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0034] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0035] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B".

[0036] Example 1

[0037] A liquid flow battery stack with an inclined membrane, the liquid flow battery stack comprising: a diaphragm, an electrode frame and a bipolar plate arranged parallel to each other;

[0038] The electrode frame has a hollow area, the bipolar plate, the diaphragm and the hollow area are surrounded to form an electrode accommodation space, and the electrode is arranged in the electrode accommodation space;

[0039] The diaphragm and the bipolar plate are arranged at a certain angle so that the height of the electrode accommodating space gradually increases linearly along the flow direction of the electrolyte, so that the electrode compression ratio of the electrode gradually decreases linearly along the flow direction of the electrolyte. The height of the electrode accommodating space is the vertical distance between the diaphragm and the bipolar plate.

[0040] like Figure 1 The height of the electrode accommodation space gradually increases linearly along the electrolyte flow direction, with a height of H1 at the electrolyte inlet and a height of H2 at the electrolyte outlet. H1 is smaller than H2.

[0041] Since the height of the electrode accommodation space is not uniformly set, when the electrode 2 is assembled into the electrode frame and squeezed by the diaphragm 3, the electrode part at the minimum height H1 is subjected to the greatest compression, and the electrode part at the maximum height H2 is subjected to the least compression. During the operation of the battery stack, at the entrance where the electrolyte enters the battery stack, that is, at the minimum height H1, the active substances participating in the reaction of the electrolyte are the most sufficient, and then the active substances gradually decrease along the flow direction of the electrolyte, and at the electrolyte outlet, that is, at the maximum height H2, the active substances are the least. According to the battery stack of the present application, the electrode compression rate at the electrolyte inlet is the largest, and a smaller ohmic internal resistance can be obtained. Since the active substances here are sufficient, the concentration difference caused by the larger electrode compression rate is less affected; near the electrolyte outlet, there are fewer active substances, and the electrode compression rate is small, so the active substances in the electrolyte can be transferred and replaced faster. Therefore, according to the battery stack of the present application, the polarization loss of the liquid flow battery can be effectively reduced, and the optimal solution between the ohmic internal resistance and concentration polarization of the electrode can be achieved, thereby improving the battery conversion efficiency, and at the same time, there is no need to increase additional pump consumption.

[0042] In this embodiment, the compression ratio of the electrode at the electrolyte inlet is 70%, and the compression ratio of the electrode at the electrolyte outlet is 10%.

[0043] The compression ratio refers to the ratio of the amount of compression of the electrode in the compressive direction to the free size of the electrode before compression.

[0044] The bipolar plate has at least one surface for contacting the electrode, and the surface is arranged parallel to the flow direction of the electrolyte. The overall thickness of the bipolar plate remains unchanged.

[0045] The electrode 2 is a porous carbon material electrode, including but not limited to a carbon felt electrode, a carbon fiber cloth electrode, and a carbon paper electrode. In this embodiment, the electrode is a carbon felt electrode.

[0046] Figure 1 Schematic diagram of a single cell in a flow battery stack. Figure 1 The two arrows in the middle indicate the flow direction of the electrolyte.

[0047] The positions of the electrode frames at both ends of the compression molded diaphragm are slightly misaligned in the axial direction, so that the diaphragm is at a certain tilt angle after compression molding. Specifically, the positions of the electrode frames at both ends of the compression molded diaphragm are slightly misaligned in the axial direction by designing the electrode frames, for example, to have different thicknesses.

[0048] Figure 1 It can be seen that during the operation of the battery stack, the inlet direction of the positive electrode electrolyte is different from that of the negative electrode electrolyte, but both enter from the position with a high electrode compression ratio and exit from the position with a low electrode compression ratio.

[0049] The battery stack of this embodiment includes a plurality of stacked cells. Specifically, when one of the cells is decomposed, each cell 120 includes a diaphragm 3 disposed in the middle, and electrodes 2, bipolar plates 1, and electrode frames disposed on both sides of the diaphragm 3 in sequence. The electrodes 2 are one of the positive electrodes and the negative electrodes. End plates are used to fix the two ends of the plurality of stacked cells to form a battery stack.

[0050] The surfaces of the bipolar plate 1, the electrode frame and the end plate are all rectangular.

[0051] In this embodiment, 170 cells are stacked to form a battery stack. Each electrode has an area of ​​approximately 2200 cm 2 , where the electrolyte inlet compression ratio is about 10%, the outlet compression ratio is about 30%, and the average compression ratio is about 20%.

[0052] Comparative Example 1

[0053] The only difference from Example 1 is that the diaphragm is normally arranged, not tilted, that is, the diaphragm is arranged parallel to the bipolar plate. At this time, the compression ratio of the electrode at the electrolyte inlet and the electrolyte outlet is 20%.

[0054] The performance tests were performed on the battery stacks of Example 1 and Comparative Example 1:

[0055] The performance of the stacks of Example 1 and Comparative Example 1 was tested at 80, 130, 170, 200, and 240 mA / cm 2 The constant current charge and discharge were carried out with a current density of , and the average data from the 4th to the 6th cycle were selected as the reliable performance data. The voltage efficiency of the two stacks was compared, as shown in Table 2.

[0056] Table 2 shows that at 200 mA / cm 2 At a current density of , the voltage efficiency of the battery stack in Example 1 is higher than that of the battery stack in Comparative Example 1, and the voltage efficiency can be increased by about 1.3%.

[0057] Table 2 Voltage efficiency comparison

[0058] <![CDATA[Current density (mA / cm 2 )]]> Example 1 Comparative Example 1 (non-tilted) 80 90.5％ 89.5％ 130 88.6％ 87.5％ 170 87.1％ 85.9％ 200 86.4％ 85.1％ 240 84.6％ 83.2％

Claims

1. A flow battery stack with an inclined membrane, characterized in that: The flow battery stack comprises: a diaphragm, an electrode frame and a bipolar plate arranged in parallel with each other; The electrode frame has a hollow area, the bipolar plate, the diaphragm and the hollow area are surrounded to form an electrode accommodation space, and the electrode is arranged in the electrode accommodation space; The diaphragm and the bipolar plate are arranged at a certain angle so that the height of the electrode accommodating space gradually increases along the flow direction of the electrolyte, thereby gradually reducing the electrode compression ratio of the electrode along the flow direction of the electrolyte. The height of the electrode accommodating space is the vertical distance between the diaphragm and the bipolar plate.

2. The liquid flow battery stack with inclined membrane placement according to claim 1, characterized in that: The bipolar plate has at least one surface for contacting an electrode, and the surface is arranged parallel to the flow direction of the electrolyte.

3. The liquid flow battery stack with tilted membrane placement according to claim 1, characterized in that: The overall thickness of the bipolar plate remains unchanged.

4. The liquid flow battery stack with tilted membrane placement according to claim 1, characterized in that: The overall porosity of the electrode before compression is consistent.

5. The liquid flow battery stack with tilted membrane placement according to claim 1, characterized in that: The height of the electrode accommodating space gradually increases linearly along the flow direction of the electrolyte, so that the electrode compression ratio of the electrode gradually decreases linearly along the flow direction of the electrolyte.

6. The liquid flow battery stack with tilted membrane placement according to claim 1, characterized in that: The electrode is a porous carbon material electrode.

7. The liquid flow battery stack with inclined membrane placement according to claim 1, characterized in that: The compression ratio of the electrode at the electrolyte inlet and the compression ratio at the outlet are 10% to 50%.

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