Electrode frame performance test method based on current density distribution measurement

Abstract

The invention discloses an electrode frame performance test method based on current density distribution measurement, and the method comprises the following steps: S1, assembling a battery unit, a measurement unit and a display unit, and obtaining an electrode frame performance test system; s2, performing charge and discharge test on the flow battery in the battery unit, and acquiring and recording voltage signals at two ends of each resistor through a data acquisition card in the test unit; and S3, the display unit receives and analyzes the acquired voltage signal data in real time, and draws a real-time current density distribution cloud picture in the electrode frame. The method not only can monitor and record the current density distribution in the electrode frame in real time, but also can judge whether the design of the electrode frame is reasonable or not by evaluating the performance of the structure and the material of the electrode frame and analyzing the current distribution uniformity under different conditions through measurement results, and can identify weak areas possibly influencing the performance of the battery. And a specific guidance basis is provided for design and optimization of the electrode frame.

Description

Technical Field

[0001] The present invention relates to the technical field of battery detection, and specifically to a method for testing the performance of an electrode frame based on the measurement of current density distribution. Background Art

[0002] In the context of the dual-carbon goal, increasing the installed capacity ratio of renewable energy power generation such as solar energy and wind energy and developing long-duration energy storage technologies are the only way to achieve energy transformation. Due to its advantages such as intrinsic safety, long lifespan, and independent adjustability of power and capacity, the all-vanadium redox flow battery is one of the important technologies for realizing new energy consumption and long-duration energy storage.

[0003] When facing actual engineering applications, usually 6-8 stacks are assembled in series and parallel in a prefabricated cabin to form a megawatt-class battery system, and the power of a single stack is usually 10-32 kW. The high power of a single stack means that a single cell needs to have a relatively large electrode area. During the operation of the stack, the electrolyte is pumped into the electrode, and electrochemical reactions occur therein to achieve the storage and release of electrical energy. When the electrolyte enters the electrode, the electrode frame determines its overall distribution inside the electrode. When the electrolyte flows inside the electrode frame, electrochemical reactions are continuously carried out, and a concentration gradient from the inlet side to the outlet side is bound to be formed in the relatively large active area. Since the intensity of the electrochemical reaction is closely related to the concentration of the reactants, a large concentration gradient means a large current density gradient. Uneven local current density distribution will lead to increased local polarization, and even problems such as bubble generation and local overheating, thereby affecting the overall performance of the stack. Uneven current density distribution will significantly increase the overpotential of the stack and reduce the energy efficiency of the stack. Therefore, the design and structure of the electrode frame directly affect the current density distribution and polarization inside the electrode, and thus affect the output power and service life of the stack. Therefore, measuring the local current density distribution in a flow battery is of great significance for improving the battery performance and extending its service life.

[0004] Currently, the systems and methods for measuring local current density distribution mainly include:

[0005] (1) Slot-type current collection system. This system mainly consists of a current collection frame, multiple knife-shaped current collectors, and insulating sealing gaskets. Flow channels and through channels are engraved on the surface of the current collection frame, and the knife-shaped current collectors and these channels form the flow channel part of the flow battery. A Hall sensor is used to measure the current at the handle of the knife-shaped current collector to achieve the measurement of current density distribution. This method is limited by its own design and can only measure the current density of the flow channel rib part, and cannot measure the current density of the entire electrode plane. Therefore, its measurement resolution is not high. This system splits the traditional flow channel plate into three parts. Although the sealing structure is increased, there is still a relatively high risk of electrolyte leakage. At the same time, its processing is complex and the cost is high, making it difficult to be applicable to large-area flow channel measurement, which limits its development.

[0006] (2) Mother - daughter bipolar plate structure: By opening embedding grooves on the upper and lower surfaces of the mother bipolar plate, the daughter bipolar plate is embedded into the embedding grooves of the mother bipolar plate. There is a graphite electrode on the daughter bipolar plate, and one end of it is provided with a terminal extending outside the plate frame. The current density distribution is obtained by measuring the magnitude of the current flowing out of the terminal with a multimeter. This design cannot achieve the measurement of the current density within the electrode plane. At the same time, the influence of the lateral current is not eliminated, and its application is restricted by a low spatial resolution.

[0007] (3) Hollow - coated battery current - collecting structure: This structure includes a flow - channel frame and a hollow - coated printed circuit board. Alternately arranged flow - channel grooves are engraved on the surface of the flow - channel frame. A conductive copper strip is arranged on one side of the hollow - coated printed circuit board, and a wiring hole is arranged on the other side. By combining the flow - channel frame with the hollow - coated printed circuit board and measuring the current at the wiring hole, the current density distribution can be calculated. This design can only achieve the measurement of the current density on the flow - channel ribs, and the spatial accuracy of the measurement is low. In addition, its conductive copper strip is in direct contact with the electrolyte. Although a corrosion - resistant coating is designed, corrosion still cannot be avoided, which restricts the service life and measurement accuracy. At the same time, this structure has a high risk of electrolyte leakage.

[0008] (4) Total internal reflection optical system: This system includes an incident light unit, a prism, an imaging detection unit, and a battery device unit. By modifying the traditional battery structure to cooperate with the prism. During the reaction process, the concentration of the active substance changes, causing the light intensity of the outgoing light to change. The imaging detection unit can inversely calculate the current density distribution on the electrode surface by capturing the change in light intensity. Although this method has the characteristics of high precision, its complex optical path and sophisticated optical equipment increase the cost complexity of this method and limit its popularization and application. Summary of the Invention

[0009] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a method for testing the performance of an electrode frame based on the measurement of current density distribution. This method solves the following technical problems existing in the prior art: (1) It is impossible to completely monitor the current density distribution in the entire active area, and only the current density measurement at the flow - channel ribs can be achieved, with a low spatial resolution; (2) It is impossible to detect the current density distribution in a large active area. The optical system measurement method is difficult to achieve large - area current density measurement, and it has high cost and great difficulty; (4) The performance of the flow - battery electrode frame is not analyzed from the perspective of current density distribution.

[0010] To achieve the above - mentioned purpose, the present invention provides the following technical solutions:

[0011] In the first aspect of the present invention, a system for testing the performance of an electrode frame based on the measurement of current density distribution is provided, including a battery unit, a measurement unit, and a display unit; wherein,

[0012] The battery cell includes a flow battery, which is composed of a printed circuit board, a first bipolar plate, a second bipolar plate, a first electrode frame, a second electrode frame, a negative electrode, a positive electrode, a first current collector plate, a second current collector plate, a first end plate, a second end plate, and a separator;

[0013] The measurement unit includes a data acquisition card, which is connected to the display unit through a data line and is used to collect the voltage signals at both ends of each resistor and transmit them to the display unit;

[0014] The display unit is responsible for analyzing the collected data in real time and drawing a cloud map of the real-time current density distribution within the electrode frame.

[0015] Preferably, the electrochemically reactive regions on the first bipolar plate are processed in blocks. In order to better reflect the transport and distribution of the active substances inside the electrode frame, the number of blocks should be as large as possible to improve the measurement spatial resolution. The size of the divided grid is determined by the area of the active region and can be flexibly designed. According to the number of blocks, the size of each block and the interval between blocks are designed, but it is necessary to ensure that the interval between blocks is not greater than 2 mm and not less than 0.5 mm to ensure that the measured area is closest to the total active region area.

[0016] Preferably, the process of dividing the first bipolar plate into blocks includes the following steps: First, grooves between the grids are processed on the surface of the first bipolar plate, noting that it cannot penetrate completely; then, epoxy resin is filled in the grooves of the grids. After it solidifies, the back of the first bipolar plate is cut until the solidified resin is exposed, and a bipolar plate with a completely divided design can be processed, which also ensures the electrical insulation between the grids.

[0017] Preferably, the surface of the printed circuit board in contact with the first bipolar plate is designed with the same divided size and layout, and the divided size of this surface is controlled to be slightly smaller than or equal to the divided size of the first bipolar plate.

[0018] Preferably, the divided blocks of the printed circuit board need to be gold-plated; each divided block on the printed circuit board is connected to a resistor with an accurate resistance value, and a pair of pin headers are used to connect to both ends of the resistor respectively to lead out the electric potential at both ends of the resistor and arrange them on both sides of the printed circuit board; on the back of the printed circuit board, a current collection area is designed and gold-plated to ensure that all the currents flowing in / out of the divided blocks converge here and then flow in / out of the current collector plate; in order to measure the current density of each grid, it is ensured that the circuit inside the printed circuit board is: the divided blocks on the front of the printed circuit board - the resistors connected to the divided blocks - the current collection area on the back of the printed circuit board.

[0019] The second aspect of the present invention provides a method for testing the performance of an electrode frame based on current density distribution measurement using the above system, comprising the following steps:

[0020] S1. Assemble the battery unit, the measurement unit and the display unit to obtain a performance testing system for the electrode frame based on current density distribution measurement;

[0021] S2. Perform charge and discharge tests on the flow battery in the battery unit, and simultaneously collect and record the voltage signals at both ends of each resistor through the data acquisition card in the test unit and save them;

[0022] S3. The display unit receives and analyzes the collected voltage signal data in real time, and draws a real-time current density distribution contour map within the electrode frame.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) High spatial resolution of current density measurement:

[0025] Through the printed circuit board design, the present invention realizes the high spatial resolution measurement of current density. By means of the grids with the same number and a large number in the bipolar plate and the printed circuit board design, each grid can independently collect the local current density at its location, so as to accurately capture the current distribution changes in the electrode frame area. The large number of grids ensures the high-resolution measurement characteristics. This high-spatial-resolution measurement method can identify the current density differences in each area within the electrode frame, providing more detailed data support for studying the current distribution under different flow rates and different working conditions. Compared with the existing patents for current density measurement that can only measure the distribution at the flow channel ribs, the measurement resolution is greatly improved.

[0026] (2) This method is easy to scale up the size:

[0027] In actual scientific research and production, the size of the electrode frame is not unique, and its design is constantly adjusted for different application scenarios. The present invention can be flexibly adjusted in combination with the bipolar plate design through the segmented bipolar plate design and the printed circuit board design. At the same time, based on the mature printed circuit board manufacturing process and the segmented bipolar plate processing process, both can be processed and manufactured at any size, with the characteristics of being easy to scale up and universality.

[0028] (3) Provide optimization guidance for evaluating the performance of the electrode frame:

[0029] The present invention can not only monitor and record the current density distribution within the electrode frame in real time, but also evaluate the performance of the electrode frame structure and materials based on these data. By analyzing the current distribution uniformity under different conditions through the measurement results, it is possible to determine whether the electrode frame design is reasonable and identify weak areas that may affect the battery performance. This comprehensive performance evaluation provides a specific guiding basis for the design and optimization of the electrode frame, enabling developers to improve the material selection, structure design, and fluid flow rate distribution of the electrode frame according to the measurement results, thereby further enhancing the overall performance of the flow battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of the electrode frame performance test system based on the measurement of current density distribution provided by the present invention;

[0031] Figure 2 is a schematic diagram of the first bipolar plate design;

[0032] Figure 3 : (a) is a schematic diagram of the design of the side of the printed circuit board in contact with the first bipolar plate; (b) is a schematic diagram of the design of the current collection area on the back of the printed circuit board;

[0033] Figure 4 : is the charging current density distribution diagram at a current density of 100 mA / cm² when SOC = 0.1 2

[0034] Reference signs in the figures:

[0035] 1, printed circuit board; 2, first bipolar plate; 2', second bipolar plate; 3, first electrode frame; 3', second electrode frame; 4, negative electrode; 4' positive electrode; 5, first current collection plate; 5', second current collection plate, 6, first end plate; 6', second end plate; 7, diaphragm. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0037] Refer to Figure 1 ​, the present invention provides a performance test system for an electrode frame based on current density distribution measurement. The system consists of three units, namely a battery unit, a measurement unit, and a display unit. Among them, the battery unit includes a flow battery, which is composed of a printed circuit board 1, a first bipolar plate 2, a second bipolar plate 2', a first electrode frame 3, a second electrode frame 3', a negative electrode 4, a positive electrode 4', a first current collector plate 5, a second current collector plate 5', a first end plate 6, a second end plate 6', and a diaphragm 7; the measurement unit includes a printed circuit board 1 and a data acquisition card; the display unit is mainly composed of a computer; the battery unit is connected to the measurement unit through a data cable; it should be noted here that the printed circuit board 1 belongs to both the battery unit and the measurement unit, and the display unit realizes data processing analysis and result display by installing relevant software on the computer.

[0038] Assemble the battery unit: Stack them in the order of the first end plate 6 - the first current collector plate 5 - the printed circuit board 1 - the first bipolar plate 2 - the first electrode frame 3 - the negative electrode 4 - the diaphragm 7 - the positive electrode 4' - the second electrode frame 3' - the second bipolar plate 2' - the second current collector plate 5' - the second end plate 6', and then fasten the four corners with bolts, spring washers, and hex nuts. Design corresponding battery fixtures according to the sizes of the first electrode frame 3 and the second electrode frame 3'. The first end plate 6 and the second end plate 6' are made of aluminum, plastic, acrylic, etc., and their sizes are the same as those of the first electrode frame 3 and the second electrode frame 3'; both the first bipolar plate 2 and the second bipolar plate 2' are made of graphite, and liquid inlet and outlet ports a are reserved on the sides (see Figure 1 ). During the assembly process, attention should be paid to sealing. Add black fluororubber sheets between the two electrode frames, namely the first electrode frame 3 and the second electrode frame 3', and the two bipolar plates, namely the first bipolar plate 2 and the second bipolar plate 2', to ensure sealing. The liquid inlet and outlet methods, electrodes, and diaphragms need to be selected according to requirements.

[0039] Design the first bipolar plate 2. As Figure 2 shown, the electrochemically reactive area on the first bipolar plate 2, which is equivalent to the area of the first electrode frame 3, is processed in blocks. In order to better reflect the transport and distribution of active substances inside the electrode frame, the number of blocks should be as many as possible to improve the measurement spatial resolution. The size of the obtained block grid is determined by the area of the active area and can be flexibly designed. According to the number of blocks, design the size of each block and the interval between blocks, but it is necessary to ensure that the interval between blocks cannot be greater than 2 mm and cannot be less than 0.5 mm to ensure that the measured area is closest to the total active area.

[0040] Specifically, first, grooves are machined on the surface of the first bipolar plate 2 between the grids, and it should be noted that they cannot penetrate completely; then, epoxy resin is filled in the grooves of the grids. After it solidifies, the back surface of the first bipolar plate 2 is machined until the solidified resin is exposed, and a bipolar plate with a completely segmented design can be machined, which also ensures electrical insulation between the grids.

[0041] According to the design of the first bipolar plate 2 above, the printed circuit board 1 is designed. As Figure 3 shown, the same segmented size and layout design are carried out on the side of the printed circuit board 1 that contacts the first bipolar plate 2 (see Figure 3 (a)). In order to reduce the fitting requirements of the device, the segmented size of this surface can be slightly smaller than or equal to the segmented size of the first bipolar plate 2. In order to reduce the contact resistance between the printed circuit board 1 and the first bipolar plate 2, the segments of the printed circuit board 1 are gold-plated; each segment on the printed circuit board 1 is connected to a resistor with an accurate resistance value, and a pair of pin headers are used to connect to both ends of the resistor respectively to lead out the electric potential at both ends of the resistor and arrange them on both sides of the printed circuit board 1. On the back surface of the printed circuit board 1, a current collecting area with a larger area is designed (see Figure 3 (b)), and this current collecting area is gold-plated to ensure that all the currents flowing in / out of the segments converge here and then flow in / out of the current collecting plate. In order to measure the current density of each grid, it is necessary to ensure that the circuit inside the printed circuit board 1 is: the segments on the front surface of the printed circuit board 1 - the resistors connected to the segments - the current collecting area on the back surface of the printed circuit board 1.

[0042] In the measuring unit, the pin headers distributed on the printed circuit board 1 are connected to the data acquisition card through wires, and the data acquisition card is connected to the computer (display unit) through data lines. During the operation of the battery, under the condition that the acquisition frequency is 10, the data acquisition card records the voltage signals at both ends of each resistor and saves them.

[0043] The display unit is responsible for analyzing the collected data in real time and drawing a real-time current density distribution nephogram within the electrode frame. At the same time, the measuring unit can also record the battery voltage, current, and voltage of each segment in real time to assist in the performance analysis of the electrode frame.

[0044] Working principle: When the battery discharges, the current flows from the positive electrode to the negative electrode. The charging process is the opposite. Since the bipolar plates are completely segmented, the current can only flow into or out of each grid, thus forming a complete current loop. In the design of the printed circuit board, each grid is connected to a resistor with an accurate resistance value. Therefore, the current will also flow through each resistor. By using a data acquisition card, the voltage across each resistor is collected. According to Ohm's law I = U / R, the current passing through each grid can be obtained. Combining the area of each grid, dividing the current by the grid area can calculate the current density of each grid. Finally, according to the position of each grid, arranging the calculated data can obtain the current density distribution inside the electrode frame area.

[0045] Example 1

[0046] S1. Refer to Figure 1 , stack and fasten in the order of the first end plate 6 - the first current collector plate 5 - the printed circuit board 1 - the first bipolar plate 2 - the first electrode frame 3 - the negative electrode 4 - the diaphragm 7 - the positive electrode 4 - the second electrode frame 3' - the second bipolar plate 2' - the second current collector plate 5' - the second end plate 6' to assemble the battery cell; then assemble the battery cell, the measurement unit (charge and discharge tester) and the display unit to obtain an electrode frame performance test system based on current density distribution measurement;

[0047] S2. Conduct charge and discharge tests on the flow battery in the battery cell, and at the same time collect and record the voltage signals across each resistor through the data acquisition card in the test unit and save them;

[0048] Specifically, conduct a full - cell test on the flow battery: Ambient temperature: room temperature, keep constant temperature and humidity during the test; Electrolyte: all - vanadium electrolyte, the main components are 1.7M V 3.5+ and sulfuric acid; During the experiment, measure at a current density of 100 mA / cm 2 , and perform constant - current charge and discharge for 5 cycles at cut - off voltages of 0.8V and 1.65V to complete the activation of the electrolyte.

[0049] After completing the activation of the electrolyte, conduct the electrode frame performance test. Specifically, select 100 mA / cm 2 as the test condition. At the beginning of the charge and discharge test cycle, turn on the measurement unit, set the acquisition frequency to 10, and keep the charge and discharge cut - off voltages unchanged.

[0050] S3. The display unit receives and analyzes the collected voltage signal data in real time, and draws a real - time current density distribution cloud map inside the electrode frame.

[0051] Specifically, perform electrode frame performance analysis on the received acquisition data, select the charging data when the electrolyte state is 0.1 (SOC = 0.1), select a total of 3 seconds of up and down time at this moment, and take the average value as the data of the current density distribution at this moment; arrange the data according to the grid division design for plotting, and the charging current density distribution at SOC = 0.1 can be obtained; calculate the average value of the current density under all grids, and calculate the percentage deviation of each grid from the average current density. Finally, plot the graph to obtain the charging current density distribution graph at 100 mA / cm 2 under the current density (see Figure 4 ).

[0052] Figure 4 It shows the distribution of the flow battery inside the negative electrode. The overall distribution law is large at the inlet and small at the outlet. However, the current density near the outlet side is significantly lower than the average value, indicating that the mass transfer in this area is weak under this condition and needs to be strengthened.

[0053] Parts not involved in the present invention are the same as or can be implemented by the prior art. Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An electrode frame performance test system based on current density distribution measurement, characterized in that: It includes a battery unit, a measuring unit and a display unit; wherein, The battery unit comprises a liquid flow battery, which is composed of a printed circuit board (1), a first bipolar plate (2), a second bipolar plate (2'), a first electrode frame (3), a second electrode frame (3'), a negative electrode (4), a positive electrode (4'), a first current collecting plate (5), a second current collecting plate (5'), a first end plate (6), a second end plate (6') and a diaphragm (7); The measuring unit includes a data acquisition card, which is connected to the display unit via a data line and is used to collect the voltage signal across each resistor and transmit it to the display unit; The display unit is responsible for real-time analysis of the collected data and drawing a real-time current density distribution cloud diagram in the electrode frame.

2. The electrode frame performance testing system based on current density distribution measurement according to claim 1, characterized in that: The electrochemical reaction active area on the first bipolar plate (2) is processed into blocks, and the size of the obtained block grid is determined by the area size of the active area; The size of each block and the interval between blocks are designed according to the number of blocks. The interval between the blocks cannot be greater than 2 mm and cannot be less than 0.5 mm to ensure that the measured area is as close to the total active area as possible.

3. The electrode frame performance testing system based on current density distribution measurement according to claim 2, characterized in that: The first bipolar plate (2) is processed in blocks, comprising the steps of: firstly, processing grooves between grids on the surface of the first bipolar plate (2); then filling the grooves of the grids with epoxy resin, and after the epoxy resin solidifies, cutting the back side of the first bipolar plate (2) until the solidified resin is exposed, thereby processing a bipolar plate with a completely block design, and ensuring electrical insulation between the grids.

4. The electrode frame performance testing system based on current density distribution measurement according to claim 3, characterized in that: The same block size and arrangement design is performed on the side of the printed circuit board (1) in contact with the first bipolar plate (2), and the block size of this side is controlled to be slightly smaller than or equal to the block size of the first bipolar plate (2).

5. The electrode frame performance testing system based on current density distribution measurement according to claim 4, characterized in that: The blocks of the printed circuit board (1) need to be gold-plated; each block on the printed circuit board (1) is connected to a resistor with a precise resistance value, and a pair of pins are used to connect the two ends of the resistor respectively, so as to lead out the electric potential at the two ends of the resistor, and arrange it on both sides of the printed circuit board (1); a current collecting area is designed on the back of the printed circuit board (1), and the current collecting area is gold-plated to ensure that all currents flowing out of / into the blocks converge here and then flow out of / into the current collecting plate; in order to achieve the measurement of the current density of each grid, it is ensured that the circuit inside the printed circuit board (1) is: the block on the front of the printed circuit board (1) - the resistor connected to the block - the current collecting area on the back of the printed circuit board (1).

6. A method for testing electrode frame performance based on current density distribution measurement using the system according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, assembling a battery unit, a measuring unit and a display unit to obtain an electrode frame performance test system based on current density distribution measurement; S2, performing a charge and discharge test on the flow battery in the battery unit, and at the same time collecting and recording the voltage signal at both ends of each resistor through the data acquisition card in the test unit and saving it; S3. The display unit receives and analyzes the collected voltage signal data in real time, and draws a real-time current density distribution cloud diagram in the electrode frame.

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