A hierarchical tank design to improve the efficiency and capacity utilization of flow battery systems
By adopting a staged storage tank design in the flow battery system, the problem of uneven electrolyte mixing is solved, achieving efficient utilization of electrolyte and accurate SOC estimation, thereby improving the system efficiency and capacity utilization of the flow battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SUQIAN TIMES ENERGY STORAGE TECH CO LTD
- Filing Date
- 2023-02-03
- Publication Date
- 2026-05-19
AI Technical Summary
In existing flow battery systems, the single-tank design of the electrolyte leads to uneven electrolyte mixing, which reduces battery performance and the accuracy of SOC estimation, increases pump operating time, and reduces system efficiency.
The system adopts a tiered storage tank design, replacing a single storage tank with multiple small-volume tanks connected in series. The electrolyte flows in a "bottom-in, top-out" manner, achieving separation and tiered storage of high-SOC and low-SOC electrolytes. The system also utilizes a circulating pump to achieve efficient charging and discharging of the electrolyte.
It improves the utilization rate of electrolyte and the accuracy of SOC estimation, reduces pump power consumption, extends constant voltage charge and discharge time, and enhances the system efficiency and capacity utilization of flow batteries.
Smart Images
Figure CN116314937B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of flow battery technology, specifically relating to a graded storage tank design to improve the efficiency and capacity utilization of flow battery systems. Background Technology
[0002] In recent years, the global share of solar and wind power generation has gradually exceeded 10%, making them increasingly the lowest-cost sources of electricity. However, due to the instability of solar and wind power, direct grid connection can cause significant disruptions to the power grid. Energy storage technology is a crucial component for maximizing the utilization of renewable energy and maintaining the safe and stable operation of the power grid. Among numerous energy storage technologies, flow battery technology, with its long cycle life and high cycle efficiency, has demonstrated enormous potential for large-scale energy storage. In flow batteries, the positive and negative electrolytes are typically stored separately in positive and negative electrode tanks. These electrolytes are then transported to various components within the flow battery stack by a circulating pump, where the conversion of chemical energy into electrical energy occurs through the redox reaction of the positive and negative electrolytes.
[0003] The first difference between this invention and existing technologies lies in the graded electrolyte storage design. In this invention, the electrolyte flows in from the inlet at the bottom of the flow battery and flows out from the outlet at the top, with the same bottom-in, top-out pattern observed in each storage tank. This is because battery testing has shown that electrolyte flowing in from the top inlet disrupts the internal flow field, leading to a decrease in battery performance. Furthermore, the bottom-in, top-out flow path between storage tanks delays the mixing of charged and uncharged electrolytes, reducing the constant-voltage period. In contrast, existing electrolyte flow methods inevitably force mixing of electrolytes with different state of charge (SOC), thus reducing battery performance.
[0004] The second difference between this invention and existing technologies lies in the staged storage design. The purpose of the multi-stage tanks is to store electrolytes with different State of Charge (SOC). Charged electrolyte enters the first-stage tank, and each subsequent charge pushes electrolytes with similar SOCs into the first tank. Once the first-stage tank is full of electrolytes with similar SOCs, the continuously flowing electrolyte pushes the electrolyte from the previous stage into the next tank, thus achieving efficient charging and discharging of the electrolyte. Furthermore, unidirectional circulation avoids uneven mixing of the electrolyte; whereas existing electrolyte circulation pumps are bidirectional pumps, which can lead to mixing of electrolytes with different SOCs, reducing the accuracy of SOC estimation.
[0005] Currently, electrolyte storage tanks are typically independent, single tanks. While this reduces design and manufacturing costs, the single tank design leads to high-SOC electrolyte flowing directly back into the tank during each charge-discharge cycle, mixing with uncharged electrolyte. This results in repeatedly delivering charged electrolyte to the electrodes, increasing pump operating time and reducing battery system efficiency. Furthermore, uneven electrolyte mixing within the tank can cause significant deviations in the estimated SOC, negatively impacting charge-discharge performance. One solution is to dynamically adjust the pump speed based on the battery's SOC, increasing the demands on the battery management system. This invention, through a rationally designed electrolyte storage tank, achieves a proper distribution of high-SOC and low-SOC electrolytes, significantly reducing pump power consumption and improving battery system efficiency and electrolyte utilization. Summary of the Invention
[0006] This invention provides a graded tank design to improve the efficiency and capacity utilization of a flow battery system. By designing a single tank as multiple small-volume tanks connected in series, the electrolyte utilization and charging efficiency in each charging cycle are improved, the chance of mixed charged and uncharged electrolytes is reduced, the accuracy of SOC estimation is increased, and the performance of the flow battery is improved.
[0007] To achieve the above objectives, the present invention adopts the following technical solution:
[0008] A staged storage tank design for improving the efficiency and capacity utilization of a flow battery system is characterized by comprising a flow battery section and an electrolyte storage tank section. The flow battery section includes individual flow battery cells. The electrolyte storage tank section includes a positive electrolyte inlet, a positive electrolyte outlet, a negative electrolyte inlet, a negative electrolyte outlet, a positive electrolyte circulation pump, a negative electrolyte circulation pump, a positive electrolyte storage tank, and a negative electrolyte storage tank. The positive electrolyte storage tank includes a fifth-stage positive electrolyte storage tank, a fourth-stage positive electrolyte storage tank, and a third-stage positive electrolyte storage tank. The system comprises a positive electrode electrolyte storage tank, a second-stage positive electrode electrolyte storage tank, and a first-stage positive electrode electrolyte storage tank. The negative electrode electrolyte storage tanks include a fifth-stage negative electrode electrolyte storage tank, a fourth-stage negative electrode electrolyte storage tank, a third-stage negative electrode electrolyte storage tank, a second-stage negative electrode electrolyte storage tank, and a first-stage negative electrode electrolyte storage tank. The inlets and outlets of the positive and negative electrode electrolyte storage tanks are arranged diagonally, including an electrolyte circulation inlet and an electrolyte circulation outlet. Each staged storage tank is arranged sequentially and connected in sequence via electrolyte pipelines in a "bottom-in, top-out" manner.
[0009] Furthermore, the single cell of the flow battery has a sandwich structure, in which the battery end plate, current collector, bipolar plate, electrode frame and electrode are assembled in sequence with the ion exchange membrane as the center of symmetry and fastened together with screws; wherein the battery end plate is made of stainless steel, the current collector is made of brass sheet, the bipolar plate is made of flexible graphite plate, the electrode frame is made of polypropylene and the electrode is carbon felt electrode.
[0010] Furthermore, the positive electrode electrolyte storage tank and the negative electrode electrolyte storage tank are connected in sequence and form an electrolyte circulation loop with the positive and negative electrodes of the battery, respectively. By splitting a single electrolyte storage tank into multiple electrolyte storage tanks connected in series, the graded storage of electrolyte can be achieved.
[0011] Furthermore, the number of positive electrolyte inlets, positive electrolyte outlets, negative electrolyte inlets, and negative electrolyte outlets are the same, and there are at least two electrolyte storage tanks on each side.
[0012] Furthermore, the graded storage tanks are all the same size, the inlet of the graded storage tank is at the bottom of the side wall of the tank body, and the outlet of the graded storage tank is at the top of the side wall of the tank body; the inlet and the outlet are diagonally distributed; the flow direction of the electrolyte in each storage tank is "bottom in, top out".
[0013] Furthermore, the total liquid storage capacity of the graded storage tanks is consistent with the liquid storage capacity of a single independent storage tank.
[0014] Furthermore, the length of the connecting pipeline between the graded storage tanks only needs to meet the connection requirements of the storage tanks.
[0015] Furthermore, the flow battery testing system includes either an aqueous organic system or a vanadium-based system.
[0016] This invention also provides a method for designing a tiered storage tank to improve the efficiency and capacity utilization of a flow battery system. The specific steps of the method are as follows: First, electrolyte is added to the last-stage storage tank. This tank uses a circulation pump and a delivery pipeline to allow the electrolyte to flow from the inlet at the bottom of the flow battery into the electrodes. The partially charged electrolyte in the flow battery flows out from the outlet at the top of the battery and is delivered to the first-stage storage tank through the delivery pipeline. The charged high-SOC electrolyte gradually fills each stage of the storage tank and pushes the uncharged electrolyte into the next stage of the storage tank, delaying the mixing of high-SOC and low-SOC electrolytes and improving the utilization rate of the electrolyte in each charge-discharge cycle.
[0017] Furthermore, the circulating pump includes either a peristaltic pump or a magnetic pump.
[0018] Furthermore, the rotational speed of the circulating pump is 10-400 rpm.
[0019] Furthermore, the electrolyte circulation pump is connected to the inlet of the flow battery and the outlet of the last-stage storage tank.
[0020] Furthermore, the inlet and outlet of the graded storage tank are arranged diagonally to delay the mixing of electrolyte in the storage tank.
[0021] The beneficial effects of this invention are as follows:
[0022] (1) This invention can separate high SOC electrolyte and low SOC electrolyte by simply updating the independent single storage tank to a graded storage tank, thereby achieving consistency of SOC of electrolyte in each storage tank, making the SOC estimate more accurate and improving the utilization rate of electrolyte.
[0023] (2) Compared with adding additives to the electrolyte to improve the electrolyte utilization rate, the present invention can improve the electrolyte utilization rate through physical methods only. The method has lower cost and better stability.
[0024] (3) The graded storage tank involved in this invention extends the holding time of high current during constant pressure charging and discharging, reduces constant pressure charging time and reduces pump work time, thereby indirectly improving system efficiency. Attached Figure Description
[0025] Figure 1 This is a schematic diagram of a graded storage tank for improving electrolyte utilization and the efficiency of a flow battery stack system, as described in this invention.
[0026] Figure 2 This is a schematic diagram of a single flow battery involved in this invention;
[0027] Figure 3 This is a schematic diagram of the electrolyte storage tank involved in this invention;
[0028] Figure 4 This is a graph showing the relationship between the discharge current and discharge capacity of the five-stage storage tank battery in an aqueous organic system under different rotation speeds in Embodiment 1 of the present invention.
[0029] Figure 5 This is a graph showing the relationship between the discharge current and discharge capacity of the battery in the non-graded storage tank in Comparative Example 1 of the present invention and time under different rotation speeds in an aqueous organic system.
[0030] Figure 6 This is a comparison chart of the energy efficiency and capacity utilization of the pilot-scale fuel cell stack in Embodiment 2 of the present invention, under a full vanadium system, with and without a tiered storage tank design.
[0031] List of identifiers in attached diagrams:
[0032] 1. Single-cell stack; 2. Positive electrolyte inlet; 3. Positive electrolyte outlet; 4. Negative electrolyte inlet; 5. Negative electrolyte outlet; 6. Positive electrolyte circulation pump; 7. Negative electrolyte circulation pump; 8. Fifth-stage positive electrolyte storage tank; 9. Fourth-stage positive electrolyte storage tank; 10. Third-stage positive electrolyte storage tank; 11. Second-stage positive electrolyte storage tank; 12. First-stage positive electrolyte storage tank; 13. Fifth-stage negative electrolyte storage tank; 14. Fourth-stage negative electrolyte storage tank; 15. Third-stage negative electrolyte storage tank; 16. Second-stage negative electrolyte storage tank; 17. First-stage negative electrolyte storage tank; 18. Battery end plate; 19. Current collector; 20. Bipolar plate; 21. Electrode frame; 22. Carbon felt; 23. Electrolyte circulation inlet; 24. Electrolyte circulation outlet. Implementation
[0033] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Example
[0034] like Figure 1 As shown, the flow battery staged storage tank design involved in this invention includes a flow battery section and an electrolyte storage tank section. Its main components are a single-cell stack 1, a positive electrolyte inlet 2, a positive electrolyte outlet 3, a negative electrolyte inlet 4, a negative electrolyte outlet 5, a positive electrolyte circulation pump 6, a negative electrolyte circulation pump 7, a fifth-stage positive electrolyte storage tank 8, a fourth-stage positive electrolyte storage tank 9, a third-stage positive electrolyte storage tank 10, a second-stage positive electrolyte storage tank 11, a first-stage positive electrolyte storage tank 12, a fifth-stage negative electrolyte storage tank 13, a fourth-stage negative electrolyte storage tank 14, a third-stage negative electrolyte storage tank 15, a second-stage negative electrolyte storage tank 16, and a first-stage negative electrolyte storage tank 17.
[0035] like Figure 2 As shown, the single cell of the flow battery involved in this invention has a sandwich structure. The battery components are assembled sequentially with the ion exchange membrane as the center of symmetry and fastened together with screws. The battery end plate 18 is made of stainless steel, the current collector 19 is made of brass sheet, the bipolar plate 20 is made of flexible graphite plate, the electrode frame 21 is made of polypropylene, and the electrode 22 is a carbon felt electrode.
[0036] like Figure 3 As shown, the inlet and outlet of the graded storage tank involved in this invention are arranged diagonally, including an electrolyte circulation inlet 23 and an electrolyte circulation outlet 24; each graded storage tank is arranged sequentially and connected sequentially through an electrolyte pipeline in the manner of electrolyte "bottom in, top out". Example
[0037] The following is a detailed implementation method for the design of graded storage tanks.
[0038] The positive electrode storage tank is divided into five stages. The stage directly connected to the battery outlet is the fifth stage, and the tank directly connected to the circulation pump is the first stage. The arrangement of the negative electrode storage tank is the same as that of the positive electrode side. First, equal volumes of positive and negative electrolytes are added to the positive electrode storage tank 12 and the negative electrode storage tank 17, respectively. The positive electrode circulation pump 6 and the negative electrode circulation pump 7 are then turned on to deliver the electrolyte to the single battery for cyclic charging and discharging. During charging, the SOC of the electrolyte entering the single battery increases. The electrolyte that completes a single charge cycle is delivered from the electrolyte outlet to the fifth stage storage tank. As the charging process continues, when the fifth stage storage tank gradually fills with high SOC electrolyte, the electrolyte that completes subsequent charging will push the electrolyte in the fifth stage storage tank to flow into each stage storage tank in sequence, realizing the graded storage of electrolytes with different SOCs.
[0039] The total volume of each storage tank is similar to that of a single storage tank, but each tank contains electrolyte, and there is no interruption in the electrolyte circulation process. Furthermore, the viscosity of the positive and negative electrode electrolytes may change significantly during charging and discharging, requiring adjustment of the pump speed of the positive and negative electrode circulation pumps to ensure the uniformity of the electrolyte flow rate. Example
[0040] The design principle of the fuel cell stack tiered storage tank is the same as that of the single-cell tiered storage tank. The stack tiered storage tank constructs tiered spaces by adding vertical or horizontal partitions to a single large storage tank, with the number of partitions ranging from 1 to 10. The stack storage tank is a cuboid. The vertical partition tank consists of equally spaced vertical partitions connected to the bottom and side walls of the tank. Except for the inlet of the first-stage tank, which is located at the bottom, the top space of the other tiered tanks is used to ensure continuous electrolyte flow. In this type of tank, the electrolyte that rises during charging first fills the first-stage tank. Subsequently, as charging continues, the electrolyte being charged in each stage pushes the electrolyte in the first-stage tank into the next stage tank, achieving tiered storage of electrolytes with different SOCs.
[0041] Since the vertical partition needs to overcome gravity to propel the electrolyte flow during the electrolyte circulation process, it is essential to ensure that each space in the vertical partition tank stores a certain amount of electrolyte to guarantee that there is no interruption in the flow during battery charging and discharging.
[0042] Another type of staged electrolyte storage tank is the horizontal baffle tank. The inlet and outlet are arranged diagonally, and the electrolyte flows in a serpentine pattern from top to bottom. The baffles maintain an angle of 0-15° with the horizontal line. The outlet of this type of tank is located at the bottom and is directly connected to a circulation pump, which transports the electrolyte to the fuel cell stack. The charged electrolyte flows back into the tank through the return outlet at the top.
[0043] Horizontal baffle tanks can reduce pump consumption caused by gravity during electrolyte flow. During charging, electrolyte with rising SOC will flow in a serpentine pattern into the next stage space. The arrangement of the serpentine space reduces the direct injection of high SOC electrolyte and its mixing with low SOC electrolyte. As charging continues, the electrolyte being charged in each stage will push the electrolyte of the previous stage to flow downwards step by step. This process allows electrolytes with similar SOC to continuously flow in a serpentine pattern in the tank, achieving graded storage of electrolytes with different SOCs in the tank.
[0044] The battery system layout for the non-graded storage tank experiment is similar to that in Example 1, except that the graded storage tank is replaced with a large non-graded storage tank, and the electrolyte volume in the non-graded storage tank is the same as that in the graded storage tank. The inlet and outlet of the non-graded storage tank are also arranged diagonally, with the outlet located at the bottom of the tank.
[0045] Although the inlet and outlet of the non-graded storage tank are arranged diagonally, it was observed that the high SOC electrolyte after charging does not flow slowly back to the top layer of electrolyte. Instead, it is sprayed into the storage tank at a high pressure under the action of the circulation pump. This causes the high SOC electrolyte to mix directly with the low SOC electrolyte, resulting in inaccurate SOC estimation and limiting the system efficiency of the battery.
[0046] like Figure 4 As shown, Figure 4 The graph shows the relationship between discharge current, discharge capacity, and time for a five-stage tank battery in an aqueous organic system. Discharge current and capacity are directly proportional to rotational speed. Under five-stage tank conditions, the charge-discharge process is relatively stable, the curves are smooth, and the peak charging capacity is similar at different rotational speeds. This indicates that batteries using five-stage tanks have superior SOC estimates and better battery stability.
[0047] like Figure 5 As shown, Figure 5 The graph shows the relationship between discharge current, discharge capacity, and time for a non-graded tank battery in an aqueous organic system. Unlike graded tank batteries, due to the mixing of high-SOC and low-SOC electrolytes, the discharge capacity of the non-graded tank battery is lower than that of the graded tank battery under the same conditions. Therefore, its discharge time is shorter than that of the graded tank battery when it is above 50 rpm. This indicates that the efficiency of the non-graded tank battery is significantly worse than that of the graded tank battery.
[0048] like Figure 6 As shown, Figure 6This chart compares the energy efficiency and capacity utilization of a pilot-scale battery stack using different types of storage tanks within a vanadium-based all-system configuration. The energy efficiency comparison reveals that horizontally separated batteries achieve an average efficiency increase of 2.5% compared to batteries with non-graded storage tanks, while vertically separated batteries achieve an average efficiency increase of 1.5%. The pilot-scale battery stack's validation of graded storage tanks further demonstrates that limiting the mixing of electrolytes with different State of Charge (SOC) levels helps in accurately estimating SOC and improves battery performance.
[0049] Figure 6 In the capacity utilization comparison, the capacity utilization rate of the graded storage tank battery is significantly higher than that of the non-graded storage tank battery. Specifically, the capacity utilization rate of the vertically partitioned storage tank battery is 15% higher than that of the non-graded storage tank battery, and the capacity utilization rate of the horizontally partitioned storage tank battery is 10% higher. The graded storage tank design of this invention not only improves the overall energy efficiency of the battery, but also significantly improves the capacity utilization rate of the electrolyte, which is of great significance for the development of high-energy-density, low-cost flow batteries.
[0050] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.
Claims
1. A graded storage tank system for improving the efficiency and capacity utilization of a flow battery system, characterized in that, The system includes a flow battery section and an electrolyte storage tank section. The flow battery section comprises individual flow battery cells. The electrolyte storage tank section includes a positive electrolyte inlet, a positive electrolyte outlet, a negative electrolyte inlet, a negative electrolyte outlet, a positive electrolyte circulation pump, a negative electrolyte circulation pump, a positive electrolyte storage tank, and a negative electrolyte storage tank. The positive electrolyte storage tank includes a fifth-stage positive electrolyte storage tank, a fourth-stage positive electrolyte storage tank, and a positive electrode storage tank. The system includes a third-stage electrolyte storage tank, a second-stage positive electrolyte storage tank, and a first-stage positive electrolyte storage tank. The negative electrolyte storage tank comprises a fifth-stage negative electrolyte storage tank, a fourth-stage negative electrolyte storage tank, a third-stage negative electrolyte storage tank, a second-stage negative electrolyte storage tank, and a first-stage negative electrolyte storage tank. The inlets and outlets of both the positive and negative electrolyte storage tanks are diagonally arranged, including an electrolyte circulation inlet and an electrolyte circulation outlet. Each of the graded storage tanks is arranged sequentially and connected in sequence through electrolyte pipelines in the manner of "bottom in, top out" electrolyte. The specific steps of using the graded storage tank system are as follows: First, the electrolyte is added to the last-stage storage tank. The electrolyte flows into the electrode from the inlet at the bottom of the flow battery through the circulation pump and the delivery pipeline. The partially charged electrolyte in the flow battery flows out from the outlet at the top of the battery and is delivered to the first-stage storage tank through the delivery pipeline. The charged high-SOC electrolyte will gradually fill each stage of the storage tank and push the uncharged electrolyte into the next stage of the storage tank, delaying the mixing of high-SOC electrolyte and low-SOC electrolyte and improving the utilization rate of electrolyte in each charge-discharge cycle. The electrolyte circulation pump is connected to the inlet of the flow battery and the outlet of the last stage storage tank; the inlet and outlet of the stage storage tank are arranged diagonally to delay the mixing of electrolyte in the storage tank.
2. The graded storage tank system for improving the efficiency and capacity utilization of a flow battery system as described in claim 1, characterized in that, The single cell of the flow battery has a sandwich structure, in which the battery end plate, current collector, bipolar plate, electrode frame and electrode are assembled in sequence with the ion exchange membrane as the center of symmetry and fastened together with screws; wherein the battery end plate is made of stainless steel, the current collector is made of brass sheet, the bipolar plate is made of flexible graphite plate, the electrode frame is made of polypropylene and the electrode is carbon felt electrode.
3. The graded storage tank system for improving the efficiency and capacity utilization of a flow battery system as described in claim 1, characterized in that, The positive electrode electrolyte storage tank and the negative electrode electrolyte storage tank are connected in sequence and form an electrolyte circulation loop with the positive and negative electrodes of the battery, respectively. The single electrolyte storage tank is divided into multiple electrolyte storage tanks connected in series, thereby realizing the graded storage of electrolyte.
4. The graded storage tank system for improving the efficiency and capacity utilization of a flow battery system as described in claim 1, characterized in that, The number of positive electrolyte inlets, positive electrolyte outlets, negative electrolyte inlets, and negative electrolyte outlets are the same, and there are at least two electrolyte storage tanks on each side.
5. A graded storage tank system for improving the efficiency and capacity utilization of a flow battery system as described in claim 1, characterized in that, The graded storage tanks are all the same size. The inlet of the graded storage tank is at the bottom of the side wall of the tank body, and the outlet of the graded storage tank is at the top of the side wall of the tank body. The inlet and outlet are diagonally distributed. The flow direction of the electrolyte in each storage tank is "bottom in, top out".
6. A graded storage tank system for improving the efficiency and capacity utilization of a flow battery system as described in claim 1, characterized in that, The total liquid storage capacity of the graded storage tanks is the same as that of a single independent storage tank.
7. A graded storage tank system for improving the efficiency and capacity utilization of a flow battery system as described in claim 1, characterized in that, The length of the connecting pipeline between the graded storage tanks only needs to meet the connection requirements of the storage tanks.
8. A graded storage tank system for improving the efficiency and capacity utilization of a flow battery system as described in claim 1, characterized in that, The aforementioned flow battery testing system includes either an aqueous organic system or a vanadium-based system.
9. A graded storage tank system for improving the efficiency and capacity utilization of a flow battery system as described in claim 1, characterized in that, The circulating pump includes either a peristaltic pump or a magnetic pump, and the rotational speed of the circulating pump is 10-400 rpm.