An integrated structure of an electrode frame and a bipolar plate and its application

Abstract

The present invention provides an integrated structure of an electrode frame and a bipolar plate, in which grooves for accommodating electrodes are provided in the middle of both side surfaces of a flat plate. On the upper and lower opposite sides of one side surface of the flat plate and on the left and right opposite sides of the other side surface of the flat plate, an anode or a cathode electrolyte distribution flow channel communicating with the groove is provided near the middle groove. Four electrolyte through holes are provided near the edge of the flat plate, two of which are communicated with the anode electrolyte distribution flow channel, and the other two electrolyte through holes are communicated with the cathode electrolyte distribution flow channel. By adopting this integrated structure of the electrode frame and the bipolar plate and using the misaligned arrangement of the flow channels on both sides of the flat plate, not only an integrated structure with electrode frames processed on both sides of the bipolar plate is realized, but also the problem of relatively thick thickness of the conventional integrated structure is solved. This structure can significantly reduce the volume of the stack. It is especially suitable for high-power density stack structures using ultra-thin electrodes.

Description

Technical Field

[0001] The present invention relates to a flow battery stack, and particularly to an integrated structure of an electrode frame and a bipolar plate of a flow battery stack. Background Art

[0002] The rapid development of countries has rapidly increased the huge demand for energy. Traditional fossil energy is increasingly difficult to meet the development needs, and many countries have gradually increased the proportion of renewable energy in the energy structure. A large number of renewable energies such as wind energy and solar energy are connected to the grid, which is extremely likely to cause an impact on the power grid and endanger the power grid safety in severe cases. Therefore, there is an urgent need for a buffer device to alleviate the problems brought by the discontinuity and uncontrollability of renewable energy. At the same time, the grid side also needs a buffer device to regulate the fluctuations of the grid and achieve the functions of frequency modulation and peak shaving. Energy storage technology has emerged based on this huge demand. Among many energy storage technologies, especially chemical energy storage has developed rapidly. Various types of energy storage batteries fully demonstrate the advantages of high efficiency and flexible design of chemical energy storage, and multiple energy storage demonstration application systems have been developed. Among them, flow batteries have made great progress in the past decade due to their high efficiency, independent design of power and capacity, deep charge and discharge, and high safety. Flow battery systems represented by all-vanadium flow batteries have been industrialized, and demonstration systems with a scale of up to one hundred megawatts have been carried out.

[0003] The stack is the core device of the flow battery and plays an important role as a power device. The stack is generally assembled by dozens or even hundreds of single cells in a filter press manner. A single cell is generally composed of a positive current collector plate, a positive electrode frame, a positive electrode, an ion conduction membrane, a negative electrode, a negative electrode frame, a negative current collector plate, and the sealing materials between them. Adjacent cells are connected by bipolar plates and are connected in series in the circuit. To improve the performance of the stack, it is necessary to increase the output power of the stack while maintaining the efficiency. The voltage of the stack is generally determined by the open circuit voltage of the reaction couple and cannot be set arbitrarily. Therefore, to increase the power of the stack, it is necessary to increase the working current of the stack. Through the polarization analysis of the battery, it can be known that ohmic polarization accounts for about 70% of the total polarization. Therefore, reducing the pole pitch and improving the conductivity of the material are important means to improve the performance of the flow battery. In the current flow batteries with high power density, the electrode thickness is often reduced to less than 1 mm. At this time, the design of the flow channel is very important. For the flow-through electrode structure, the electrolyte flows in from one side of the electrode, passes through the electrode in the direction perpendicular to the electrode thickness, and flows out from the other side of the electrode. The distribution flow channel of the electrolyte cannot be reduced to the same level as the electrode thickness, resulting in too large flow resistance and insufficient flow rate. At the same time, the volume of the stack should also be significantly reduced due to the reduction of the pole pitch and cannot be thickened due to the flow channel. In summary, high requirements are put forward for the design of the electrode frame in the ultra-thin electrode structure. Summary of the Invention

[0004] To solve the contradiction between the significant reduction in the volume of the stack due to the ultra-thin electrode and the requirement that the flow channel resistance should not be too large, which would otherwise increase the volume of the stack. The present invention proposes a flow battery stack structure, particularly relating to the integrated structure design of the electrode frame and bipolar plate of the flow battery stack.

[0005] An integrated structure of the electrode frame and bipolar plate is proposed, which includes a flat plate, and correspondingly arranged grooves for accommodating electrodes are respectively provided in the middle parts of the two side surfaces of the flat plate. Anodic electrolyte distribution flow channels communicating with the middle groove are provided at the upper and lower opposite sides of one side surface of the flat plate, close to the middle groove; correspondingly, cathodic electrolyte distribution flow channels communicating with the middle groove are provided at the left and right opposite sides of the other side surface of the flat plate, close to the middle groove.

[0006] In the above integrated structure, four electrolyte through holes are respectively provided at the four peripheral edges of the flat plate close to the electrolyte distribution flow channels, wherein two electrolyte through holes communicate with the anodic electrolyte distribution flow channels, and the other two electrolyte through holes communicate with the cathodic electrolyte distribution flow channels.

[0007] The above integrated structure includes a rectangular flat plate, and correspondingly arranged grooves for accommodating electrodes are respectively provided in the middle parts of the two side surfaces of the flat plate. Anodic electrolyte distribution flow channels communicating with the middle groove are provided at the two opposite long sides of one side surface of the flat plate, close to the middle groove; correspondingly, cathodic electrolyte distribution flow channels communicating with the middle groove are provided at the two opposite wide sides of the other side surface of the flat plate, close to the middle groove.

[0008] In the above integrated structure, electrolyte through holes are respectively provided at the positions of the rectangular flat plate close to the four corners, wherein two electrolyte through holes communicate with the anodic electrolyte distribution flow channels, and the other two electrolyte through holes communicate with the cathodic electrolyte distribution flow channels.

[0009] In the above integrated structure, the thickness of the flat plate is 1 - 8 mm.

[0010] The above integrated structure is used as both the electrode frame and the bipolar plate in the flow battery stack.

[0011] The present invention has the following advantages:

[0012] 1. The integrated structure of the electrode frame and bipolar plate proposed by the present invention, by arranging misaligned flow channels on both sides of the bipolar plate, not only realizes the integrated structure with electrode frames processed on both sides of the bipolar plate, but also solves the problem of the relatively thick thickness of the conventional integrated structure, significantly reducing the volume of the stack. It is particularly suitable for the high-power density stack structure using ultra-thin electrodes.

[0013] 2. The misaligned flow channels on both sides of the bipolar plate change both the flow path and direction of the electrolyte, resulting in a change in the concentration distribution of the electrolyte when it flows out of the electrode. The concentration polarization distribution of the battery thus changes, and the polarization decreases.

[0014] 3. The integrated structure of the electrode frame and the bipolar plate in the present invention eliminates the seal between the bipolar plate and the electrode frame, improving the reliability of the stack. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is the layout of the electrode frame and the bipolar plate in the conventional flow battery stack structure (the positive electrode frame is in the front);

[0016] where 1. positive electrode frame; 2. bipolar plate; 3. negative electrode frame; 4. positive electrolyte inlet distribution channel; 5. positive electrolyte outlet distribution channel;

[0017] Figure 2 is the layout of the electrode frame and the bipolar plate in the conventional flow battery stack structure (the negative electrode frame is in the front);

[0018] where 6. negative electrolyte inlet distribution channel; 7. positive electrolyte outlet distribution channel;

[0019] Figure 3 is the integrated structure of the electrode frame and the bipolar plate proposed by the present invention (positive isometric view);

[0020] Figure 4 is the integrated structure of the electrode frame and the bipolar plate proposed by the present invention (negative isometric view). DETAILED DESCRIPTION OF THE INVENTION

[0021] Comparative Example:

[0022] Figure 1 and Figure 2 are the layout methods of the electrode frame and the bipolar plate in the conventional flow battery stack structure, where the two sides of the bipolar plate are sealed and assembled by pressing against the positive and negative electrode frames through sealing gaskets. The positive and negative electrode frames are 3 mm, the bipolar plate is 1 mm, and the sealing gasket is 1 mm thick. Therefore, the total thickness after assembly is 8.6 mm (the sealing gasket is compressed by 20%).

[0023] Example

[0024] Figure 3 and Figure 4The integrated structure of the electrode frame and bipolar plate proposed by the present invention has a thickness of 3.5 mm. On the front side, there are 4 inlet distribution channels and 5 outlet distribution channels for the positive electrode electrolyte, and on the back side, there are 6 inlet distribution channels and 7 outlet distribution channels for the negative electrode electrolyte. The flow direction of the positive electrode electrolyte in the electrode is orthogonal to that of the negative electrode electrolyte in the electrode. This structure makes full use of the part of the bipolar plate where no flow channels are provided, and flow channels are arranged on the other side. Through the staggered arrangement of the flow channels, the space occupied by the thickness of the flow channels is saved. While achieving the same function, the thickness is reduced by about 60%. With this structure, the electrode thickness can be reduced to the order of hundreds of micrometers.

[0025] The staggered flow of the positive and negative electrode electrolytes results in a staggered concentration distribution of the positive and negative electrode electrolytes. The concentrations at the corresponding positions on both sides of the bipolar plate change accordingly. In the conventional flow battery stack structure, the positive and negative electrodes are arranged corresponding to each other on both sides of the bipolar plate, and the electrolytes flow in the same direction. The concentrations of the positive and negative electrodes reach the minimum value simultaneously when flowing out of the electrodes, resulting in increased polarization. In the structure proposed by the present invention, the positive and negative electrodes are also arranged corresponding to each other on both sides of the bipolar plate, but the electrolytes flow in a staggered and orthogonal manner. The minimum values of the concentrations of the positive and negative electrodes when flowing out of the electrodes are also staggered, so the battery polarization is reduced.

[0026] A full vanadium flow battery stack with 5 cells is assembled using the above integrated structure with a thickness of 3.5 mm. The electrode thickness is 0.5 mm, and the depths of the 4 inlet distribution channels for the positive electrode electrolyte, 5 outlet distribution channels for the positive electrode electrolyte, 6 inlet distribution channels for the negative electrode electrolyte, and 7 outlet distribution channels for the positive electrode electrolyte are 1.5 mm. At the same time, a conventional flow battery stack structure is assembled. To ensure the same flow conditions, the depths of the 4 inlet distribution channels for the positive electrode electrolyte, 5 outlet distribution channels for the positive electrode electrolyte on the 1 positive electrode frame, and the 6 inlet distribution channels for the negative electrode electrolyte, 7 outlet distribution channels for the positive electrode electrolyte on the 3 negative electrode frames are 1.5 mm. The thicknesses of both the 1 positive electrode frame and the 3 negative electrode frames are 3.5 mm. To ensure that the electrode thickness is the same at 0.5 mm, graphite plates with a thickness of 3.7 mm are arranged between the electrodes and the bipolar plates. Performance tests are carried out on the two stacks. The test current densities are 80, 120, and 160 mA / cm2 respectively, and the stack flow rate is 0.8 m3 / h for both. The charging cut-off voltage of the stack is 7.75 V, and the discharging cut-off voltage is 5 V. The ion conduction membrane is Nafion115. The performance test results of the stacks are shown in Table 1.

[0027]

[0028] It can be seen from the performance comparison that, under the same conditions of electrode thickness and electrode, the ohmic internal resistance and electrochemical resistance of the stack are basically the same, and the main factor affecting the voltage efficiency of the stack is concentration polarization. For the all-vanadium redox flow battery stack adopting the structure proposed by the present invention, the flow directions of the positive and negative electrode electrolytes are orthogonal, and the concentration distribution is in an orthogonal form. Therefore, the positions with the lowest concentration are misaligned, the concentration polarization of the entire stack is reduced, which is manifested as an increase in the voltage efficiency of the stack.

Claims

1. An integrated structure of an electrode frame and a bipolar plate, comprising a flat plate, and correspondingly arranged grooves for accommodating electrodes are respectively provided in the middle parts of the two side surfaces of the flat plate; On the upper and lower opposite sides of one side surface of the flat plate, near the middle groove, an anodic electrolyte distribution flow channel communicating with the middle groove is provided; On the left and right opposite sides of the other side surface of the flat plate, near the middle groove, a cathodic electrolyte distribution flow channel communicating with the middle groove is provided; The thickness of the integrated structure of the electrode frame and the bipolar plate is 3.5 mm.

2. The integrated structure according to claim 1, wherein: Four electrolyte through holes are respectively provided near the peripheral edges of the flat plate close to the electrolyte distribution flow channels, wherein two electrolyte through holes communicate with the anodic electrolyte distribution flow channel, and the other two electrolyte through holes communicate with the cathodic electrolyte distribution flow channel.

3. The integrated structure according to claim 1, characterized in that: It comprises a rectangular flat plate, and correspondingly arranged grooves for accommodating electrodes are respectively provided in the middle parts of the two side surfaces of the flat plate; On the two opposite long sides of one side surface of the flat plate, near the middle groove, an anodic electrolyte distribution flow channel communicating with the middle groove is provided; On the two opposite wide sides of the other side surface of the flat plate, near the middle groove, a cathodic electrolyte distribution flow channel communicating with the middle groove is provided.

4. The integrated structure according to claim 3, wherein: Electrolyte through holes are respectively provided at the positions of the rectangular flat plate close to the four corners, wherein two electrolyte through holes communicate with the anodic electrolyte distribution flow channel, and the other two electrolyte through holes communicate with the cathodic electrolyte distribution flow channel.

5. Application of the integrated structure according to any one of claims 1-4 as both an electrode frame and a bipolar plate in a flow battery stack.

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