An iron-chromium liquid flow battery system including a rebalancing device and a capacity recovery method

Abstract

This invention discloses an iron-chromium redox flow battery system and a capacity recovery method including a rebalancing device, belonging to the field of flow battery technology. It includes an iron-chromium redox flow battery module, a rebalancing device, and an electrolyte readjustment module. The rebalancing device is used to electrolyze and reduce the ferric ions in the positive electrode electrolyte of the iron-chromium redox flow battery module to ferrous ions. The electrolyte readjustment module is used to correct the concentration of the reduced positive electrode electrolyte in the rebalancing device. The rebalancing device of this invention uses water electrolysis to reduce the Fe in the positive electrode electrolyte of the iron-chromium redox flow battery. 3+ Reduced to Fe 2+ This avoids the emission of electrolysis byproducts and cross-contamination of impurity ions across the membrane, making the entire rebalancing process clean and simple to operate. The electrolyte readjustment module optimizes the concentration and volume of the electrolyte after activity recovery, making it closer to the initial electrolyte composition and avoiding the problem of deteriorated flow battery performance caused by differences in electrolyte volume and concentration after capacity recovery.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid flow batteries, and in particular relates to an iron-chromium liquid flow battery system including a rebalancing device and a capacity recovery method. Background Art

[0002] Liquid flow battery is a new type of large-scale electrochemical energy storage device. It stores electrical energy in electrolyte solution during charging and converts the stored energy into electrical energy during discharge. The output power of the battery depends on the size and number of battery stacks, and the storage capacity depends on the concentration and volume of the electrolyte. During the battery charging and discharging process, only the ion valence state in the positive and negative electrolytes changes. The electrolyte can be recycled and reused, and the operation is safe.

[0003] Among all flow batteries, iron-chromium flow batteries have great application prospects due to the low cost of iron and chromium. However, during the long-term operation of iron-chromium flow batteries, the occurrence of hydrogen evolution side reactions will lead to an imbalance of iron ions in the positive electrode, making Fe 2+ Lack of Fe 3+ Excess will eventually lead to a decrease in battery capacity. Currently, catalyst deposition is usually used to inhibit hydrogen evolution. However, due to reasons such as catalytic efficiency, a small amount of hydrogen is still released.

[0004] Therefore, one of the key R&D technologies for iron-chromium flow batteries is to restore the active ion concentration of the positive and negative electrolytes to their initial state by some methods so that the battery system capacity can be restored. For example, in NASA's early research on iron-chromium flow battery systems, hydrogen and iron ions were used to rebalance the battery, and H2 was used to convert the Fe in the positive electrolyte into 3+ Reduction to Fe 2+ The rebalanced electrolyte is returned to the main system to restore capacity, but the hydrogen electrode needs to use Pt or W catalyst. However, during the rebalancing process, Pt will penetrate into the negative electrode electrolyte through the ion membrane, thereby contaminating the negative electrode electrolyte and causing the battery safety performance to deteriorate. In addition, Pt is relatively expensive and not suitable for industrial applications. The W catalyst has poor stability and will deactivate after a period of use, resulting in Fe 3+ The reduction efficiency is poor. For example, the Fe-Cr liquid flow battery rebalancing system disclosed in patent number CN105702997A reduces Fe by electrolytic reduction of the rebalancing battery. 3+ , where the positive electrode solution of the rebalancing battery contains active cations (Fe 2+) of the positive electrode electrolyte, and the negative electrode solution of the rebalanced battery is the positive electrode storage tank of the main system flow battery. Although this method can achieve capacity recovery to a certain extent, it has the following problems: 1. The cost of the rebalancing solution used in this method is high; 2. Each rebalancing of the system requires a series of subsequent processing operations such as draining waste liquid, filling new liquid, and treating waste liquid, which is cumbersome and has high operating costs; 3. The active cation concentration of the positive electrode electrolyte after reduction is unknown. During continuous operation, the active ion concentration and volume deviation of the positive electrode liquid are likely to cause the performance of the flow battery to deteriorate.

[0005] In summary, researching and designing a safe, efficient, convenient, easy-to-operate and low-cost system and method for recovering the capacity of flow batteries is an urgent problem to be solved in this research field. Summary of the invention

[0006] In view of the shortcomings of the prior art, the main purpose of the present invention is to provide an iron-chromium liquid flow battery system including a rebalancing device and a capacity recovery method. The iron-chromium liquid flow battery system including a rebalancing device of the present invention comprises an iron-chromium liquid flow battery module, a rebalancing device and an electrolyte readjustment module, and the three modules are operated step by step. When the capacity of the iron-chromium liquid flow battery module decays to a certain amount during operation, the iron-chromium liquid flow battery module is turned off, and the rebalancing battery module is turned on to electrolyze the Fe in the positive electrode electrolyte of the iron-chromium liquid flow battery. 3+ Reduction to Fe 2+ , thereby restoring the activity of the electrolyte, and then turning on the electrolyte readjustment module to achieve electrolyte concentration correction. The operation of the three modules forms a closed-loop system of the iron-chromium flow battery, realizing the long-term operation of the iron-chromium flow battery, with zero pollution and zero emission of electrolysis byproducts, and low electrolyte rebalancing cost, which greatly reduces economic losses and reduces operating costs.

[0007] In order to achieve the above-mentioned purpose, the present invention provides an iron-chromium liquid flow battery system including a rebalancing device, including an iron-chromium liquid flow battery module, a rebalancing device and an electrolyte readjustment module, wherein the rebalancing device is used to electrolytically reduce the trivalent iron ions in the positive electrode electrolyte in the iron-chromium liquid flow battery module to divalent iron ions, and the electrolyte readjustment module is used to correct the concentration of the reduced positive electrode electrolyte in the rebalancing device.

[0008] In some specific embodiments of the present invention, the rebalancing device includes a cathode liquid storage tank, a cathode pump, an electrolytic cell stack, an anode liquid storage tank and an anode pump;

[0009] The cathode liquid storage tank is used to store positive electrode electrolyte, and the anode liquid storage tank is used to store anode electrolyte, and the anode electrolyte is pure water or an aqueous solution;

[0010] The anode liquid storage tank is connected to the anode side of the electrolytic cell stack through an anode circulation pipeline to form a closed anode loop. The anode pump is arranged on the anode circulation pipeline to realize the circulation of the anode electrolyte in the closed anode loop. The electrolysis reaction in the closed anode loop is a process in which water is electrolytically oxidized into oxygen.

[0011] The cathode liquid storage tank is connected to the cathode side of the electrolytic cell stack through a cathode circulation pipeline to form a closed cathode loop. The cathode pump is arranged on the cathode circulation pipeline to realize the circulation of the positive electrode electrolyte in the closed cathode loop. The electrolysis reaction in the closed cathode loop is a process of electrolytic reduction of trivalent iron ions in the positive electrode electrolyte to divalent iron ions.

[0012] In some specific embodiments of the present invention, the rebalancing device further comprises a gas-liquid separator, which is disposed on the anode circulation pipeline and is used to separate the anode gas product during the electrolysis process.

[0013] In some specific embodiments of the present invention, the rebalancing device also includes an anode electrolyte volume measurement and control device, which is connected to the anode liquid storage tank and is used to measure the volume of the anode electrolyte in the anode liquid storage tank and replenish materials.

[0014] In some specific embodiments of the present invention, the electrolyte readjustment module includes a transfer liquid storage tank and a concentration correction device connected to each other, and the transfer liquid storage tank is connected to the cathode chamber outlet of the electrolytic cell stack through a transfer pipeline, and is used to store the positive electrode electrolyte after electrolytic reduction;

[0015] The concentration correction device is used to monitor the volume and ion concentration of the positive electrode electrolyte after electrolytic reduction stored in the transfer liquid storage tank, and to replenish materials according to the monitoring results to achieve concentration correction of the positive electrode electrolyte after electrolytic reduction;

[0016] The transfer liquid storage tank is also connected to the cathode liquid storage tank via a delivery pipeline, and the delivery pipeline is used to deliver the concentration-corrected electrolytically reduced positive electrode liquid to the cathode liquid storage tank.

[0017] In some specific embodiments of the present invention, the concentration correction device includes a volume measurement and control unit, a concentration monitoring unit and a material replenishment unit, wherein the volume measurement and control unit is used to measure the volume of the electrolyte in the transfer storage tank and to control the volume of the electrolyte discharged from the transfer storage tank to the cathode storage tank; the concentration monitoring unit is used to monitor the Fe content of the electrolyte. 2+ , Fe 3+ Cr 3+ and H +concentration; the material replenishment unit replenishes the material according to the monitoring results of the concentration monitoring unit.

[0018] In some specific embodiments of the present invention, an evaporator is provided in the transfer liquid storage tank for evaporating the water content of the electrolyte in the transfer liquid storage tank.

[0019] In some specific embodiments of the present invention, the iron-chromium flow battery module includes a negative electrode storage tank, a negative electrode pump, a flow battery stack, a positive electrode storage tank and a positive electrode pump;

[0020] The negative electrode liquid storage tank is used to store negative electrode electrolyte, and the positive electrode liquid storage tank is used to store positive electrode electrolyte; the positive electrode liquid storage tank also serves as the cathode liquid storage tank in the rebalancing device;

[0021] The negative electrode liquid storage tank is connected to the negative electrode side of the liquid flow battery stack through a negative electrode circulation pipeline to form a closed negative electrode loop, and the negative electrode pump is arranged on the negative electrode circulation pipeline to circulate and transport the negative electrode electrolyte between the negative electrode liquid storage tank and the negative electrode of the liquid flow battery stack;

[0022] The positive electrode liquid storage tank is connected to the positive electrode side of the liquid flow battery stack through a positive electrode circulation pipeline to form a closed positive electrode loop. The positive electrode pump is arranged on the positive electrode circulation pipeline to circulate and transport the positive electrode electrolyte between the positive electrode storage tank and the positive electrode of the liquid flow battery stack.

[0023] In some specific embodiments of the present invention, a test control system is provided between the flow battery stack and the electrolytic cell stack for monitoring and setting operating parameters of the iron-chromium flow battery module and the rebalancing device.

[0024] In some specific embodiments of the present invention, a first liquid stop valve is provided on the positive electrode circulation pipeline connected to the inlet of the positive electrode chamber of the liquid flow battery stack.

[0025] In some specific embodiments of the present invention, a second liquid stop valve is provided on the positive electrode circulation pipeline connected to the cathode chamber inlet of the electrolytic cell stack; a third liquid stop valve is provided on the positive electrode circulation pipeline connected to the cathode chamber outlet of the electrolytic cell stack.

[0026] In some specific embodiments of the present invention, a fourth liquid-stop valve is provided on the transfer pipeline; and a fifth liquid-stop valve is provided on the delivery pipeline.

[0027] In the iron-chromium liquid flow battery system including the rebalancing device of the present invention, the iron-chromium liquid flow battery module, the rebalancing device and the electrolyte readjustment module are operated step by step. When each module is operated step by step, the switch states between each liquid stop valve are in different combination states, so that the positive electrode electrolyte can be circulated normally in different modules.

[0028] Another aspect of the present invention further provides a method for recovering the capacity of the aforementioned iron-chromium liquid flow battery system including a rebalancing device, comprising:

[0029] When the battery capacity attenuation of the iron-chromium liquid flow battery module is detected, the operation of the iron-chromium liquid flow battery module is stopped, and the rebalancing device is started to perform a charging process, so that the positive electrode electrolyte in the cathode storage tank and the anode electrolyte in the anode storage tank undergo an electrochemical reaction, the trivalent iron ions in the positive electrode electrolyte are electrolytically reduced to divalent iron ions, and the anode electrolyte undergoes a water electrolysis and oxidation reaction to produce oxygen;

[0030] After completing the electrolytic reduction of the positive electrode electrolyte in the rebalancing device, stop the operation of the rebalancing device, start the electrolyte readjustment module, and pump all the positive electrode electrolyte after electrolytic reduction in the rebalancing device into the electrolyte readjustment module. The electrolyte readjustment module corrects the concentration of the positive electrode electrolyte after electrolytic reduction to restore the concentration to the initial electrolyte level, and then pumps the reduced positive electrode electrolyte after concentration correction into the positive electrode storage tank as needed, stops the electrolyte readjustment module, and operates the iron-chromium liquid flow battery module.

[0031] In some specific embodiments of the present invention, when it is monitored that the battery capacity of the iron-chromium flow battery module decays to 10-90% of the original battery capacity, the operation of the iron-chromium flow battery module is stopped and the rebalancing device is started to perform the charging process.

[0032] In some specific embodiments of the present invention, the electrolyte readjustment module performs concentration correction on the positive electrode electrolyte after electrolytic reduction, including:

[0033] First, the volume of the positive electrode electrolyte after electrolysis reduction stored in the transfer liquid storage tank is measured by using a volume measurement and control unit. When the measured volume increases with the initial positive electrode electrolyte volume by more than a preset value, the evaporator in the transfer liquid storage tank heats and concentrates the electrolyte until the volume returns to the initial level. If the volume is less than the preset value, the heating and concentration step is omitted.

[0034] The concentration monitoring unit is then used to determine the Fe content in the positive electrode electrolyte after electrolytic reduction. 2+ , Fe 3+ Cr 3+ and H + The concentration of the positive electrode electrolyte is corrected by calculating the difference between the concentration level of the positive electrode electrolyte and the initial concentration level of the positive electrode electrolyte according to the measurement result of the concentration monitoring unit, and then using the material replenishment unit to replenish materials according to the calculation result to complete the concentration correction of the positive electrode electrolyte after the electrolyte is reduced.

[0035] In some specific embodiments of the present invention, the charging process of the rebalancing device is a constant current charging process, and the current in the constant current charging process is 40-80 mA / cm 2, the charging cut-off voltage is 1.8~2.2V.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The iron-chromium liquid flow battery system including a rebalancing device of the present invention includes an iron-chromium liquid flow battery module, a rebalancing battery device and an electrolyte readjustment module. The three modules operate step by step to realize the integration of iron-chromium liquid flow battery operation and capacity recovery. Compared with each independent module, the system has been combined and optimized in structure, saving space and reducing device costs.

[0038] The rebalancing device of the present invention electrolyzes water to remove Fe in the positive electrode electrolyte of the iron-chromium liquid flow battery. 3+ Reduction to Fe 2+ , eliminating the cost of using other chemicals for electrolysis, and avoiding the emission of electrolysis byproducts and cross-contamination of impurity ions across the membrane. The entire rebalancing process is clean and easy to operate. The anode realizes the oxygen evolution reaction from water to oxygen, as well as the enrichment of hydrogen ions. The hydrogen ions can cross the membrane to the cathode side, which serves the purpose of regulating the hydrogen ion concentration in the deactivated positive electrode electrolyte.

[0039] The electrolyte readjustment module of the present invention optimizes the concentration and volume of the electrolyte after activity recovery, making it closer to the initial electrolyte composition, avoiding the problem of poor performance of the flow battery caused by differences in electrolyte volume and concentration after capacity recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. The drawings in the following description are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0041] Figure 1 A schematic structural diagram of an iron-chromium liquid flow battery system including a rebalancing device according to Embodiment 1 of the present invention is shown;

[0042] Figure 2 A schematic diagram showing the working principle of an electrolyte readjustment module of an iron-chromium liquid flow battery system including a rebalancing device according to Embodiment 1 of the present invention is shown;

[0043] Figure 3 The capacity change results of the iron-chromium liquid flow battery system including the rebalancing device according to the second embodiment of the present invention after two capacity recovery operations are performed are shown;

[0044] Figure 4A voltage-time curve diagram of constant current charging of a rebalancing device during the first capacity recovery operation of an iron-chromium liquid flow battery system including a rebalancing device according to Example 2 of the present invention is shown;

[0045] Figure 5 A voltage-time curve of the constant current charging of the rebalancing device during the second capacity recovery operation of the iron-chromium liquid flow battery system including the rebalancing device according to Example 2 of the present invention is shown.

[0046] Among them, the above-mentioned drawings include the following figure marks: 1. negative electrode liquid storage tank, 2. negative electrode pump, 2. liquid flow battery stack, 4. positive electrode pump, 5. positive electrode liquid storage tank, 6. cathode pump, 7. electrolytic cell stack, 8. anode pump, 9. anode liquid storage tank, 10. gas-liquid separator, 11. transfer liquid storage tank, 12. first stop liquid valve 1, 13. second stop liquid valve, 14. third stop liquid valve, 15. fourth stop liquid valve, 16. fifth stop liquid valve. DETAILED DESCRIPTION

[0047] It should be noted that, in the absence of conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper limit and the lower limit of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or the intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope. The application is further described in detail below in conjunction with specific embodiments, and these embodiments cannot be construed as limiting the scope of protection claimed in the present application.

[0048] Example 1

[0049] This embodiment provides an iron-chromium liquid flow battery system including a rebalancing device, and its structure is as shown in FIG. Figure 1 , including an iron-chromium liquid flow battery module, a rebalancing device and an electrolyte readjustment module. The rebalancing device is used to electrolytically reduce the trivalent iron ions in the positive electrode electrolyte in the iron-chromium liquid flow battery module to divalent iron ions, and the electrolyte readjustment module is used to correct the concentration of the reduced positive electrode electrolyte in the rebalancing device.

[0050] Among them, the iron-chromium liquid flow battery module includes a negative electrode storage tank 1, a negative electrode pump 2, a liquid flow battery stack 3, a positive electrode pump 4 and a positive electrode storage tank 5; the negative electrode pump 2 is a centrifugal pump, the positive electrode pump 4 is a peristaltic pump, and the flow rates of the negative electrode pump 2 and the positive electrode pump 4 are set to be the same; the negative electrode storage tank 1 is used to store the negative electrode electrolyte, and the bottom of the negative electrode storage tank 1 is connected to the inlet of the negative electrode chamber of the liquid flow battery stack 3 through the first negative electrode circulation pipeline. The negative electrode pump 2 is arranged on the first negative electrode circulation pipeline, and the top of the negative electrode storage tank 1 is connected to the outlet of the negative electrode chamber of the liquid flow battery stack 3 through the second negative electrode circulation pipeline, thereby forming a closed negative electrode loop, and the negative electrode pump 2 realizes the circulation of the negative electrode electrolyte in the loop.

[0051] The positive electrode storage tank 5 is used to store positive electrode electrolyte. The bottom of the positive electrode storage tank 5 is connected to the inlet of the positive electrode chamber of the liquid flow battery stack 3 through the first positive electrode circulation pipeline. A positive electrode pump 4 is arranged on the first positive electrode circulation pipeline. The top of the positive electrode storage tank 5 is connected to the outlet of the positive electrode chamber of the liquid flow battery stack 3 through the second positive electrode circulation pipeline, thereby forming a closed positive electrode loop. The positive electrode pump 4 realizes the circulation of the positive electrode electrolyte in the loop. At the same time, the positive electrode pump 4 can adjust the direction of the liquid, and all the positive electrode electrolyte can be pumped into the positive electrode storage tank 5 when the iron-chromium liquid flow battery module finishes running.

[0052] Among them, the rebalancing device includes a cathode liquid storage tank, a cathode pump 6, an electrolytic cell stack 7, an anode pump 8, an anode liquid storage tank 9, a gas-liquid separator 10 and an anode electrolyte volume measurement and control device. The cathode pump 6 and the anode pump 8 are both centrifugal pumps with the same flow rate. The cathode liquid storage tank is the positive electrode storage tank 5, which stores cathode electrolyte (i.e., positive electrode electrolyte). The bottom of the cathode liquid storage tank is connected to the cathode chamber inlet of the electrolytic cell stack 7 through the first cathode circulation pipeline. A cathode pump 6 is provided on the first cathode circulation pipeline, and the top of the cathode liquid storage tank is connected to the cathode chamber outlet of the electrolytic cell stack 7 through the second cathode circulation pipeline, thereby forming a closed cathode loop, and the cathode pump 6 realizes the circulation of the cathode electrolyte in the loop.

[0053] The anode liquid storage tank 9 is used to store the anode electrolyte (pure water). The bottom of the anode liquid storage tank 9 is connected to the inlet of the anode chamber of the electrolytic cell stack 7 through the first anode circulation pipeline. An anode pump 6 is provided on the first anode circulation pipeline. The top of the anode liquid storage tank 9 is connected to the outlet of the anode chamber of the electrolytic cell stack 7 through the second anode circulation pipeline, thereby forming a closed anode loop. The anode pump 8 realizes the circulation of the anode electrolyte in the loop.

[0054] The gas-liquid separator 10 is arranged on the second anode circulation pipeline, and is used to separate the anode gas product in the electrolysis process, discharge the gas out of the battery structure, and the electrolyte continues to circulate in the pipeline. The anode electrolyte volume measurement and control device is connected to the anode liquid storage tank 9, and is used to realize the volume measurement of the anode electrolyte in the anode liquid storage tank 9 and the material replenishment.

[0055] A test control system is provided between the flow battery stack 3 and the electrolytic cell stack 7 for monitoring and setting the operating parameters of the iron-chromium flow battery module and the rebalancing device, so as to understand the battery performance status and control the operation of the battery.

[0056] Among them, the electrolyte readjustment module includes a connected transfer liquid storage tank 11 and a concentration correction device. The transfer liquid storage tank 11 is used to store the positive electrode electrolyte after electrolytic reduction. An evaporator is provided in the transfer liquid storage tank 11 for evaporating the water content of the electrolyte in the transfer liquid storage tank 11; a transfer pipeline is connected in parallel to the second cathode circulation pipeline, and the top of the transfer liquid storage tank 11 is connected to the cathode chamber outlet of the electrolytic cell stack 7 through the transfer pipeline, and the bottom of the transfer liquid storage tank 11 is connected to the cathode liquid storage tank through the delivery pipeline to deliver the positive electrode liquid after electrolytic reduction after concentration correction to the cathode liquid storage tank; the concentration correction device is used to monitor the volume and ion concentration of the positive electrode electrolyte after electrolytic reduction stored in the transfer liquid storage tank, and to replenish materials according to the monitoring results to achieve concentration correction of the positive electrode electrolyte after electrolytic reduction.

[0057] Specifically, Figure 2 As shown, the concentration correction device includes a volume measurement and control unit, a concentration monitoring unit and a material replenishment unit. The volume measurement and control unit is used to measure the volume of the electrolyte in the transfer liquid storage tank 11 and to control the volume of the electrolyte discharged from the transfer liquid storage tank 11 to the cathode liquid storage tank. The concentration monitoring unit is used to monitor the Fe 2+ , Fe 3+ Cr 3+ and H + The material replenishment unit replenishes materials according to the monitoring results of the concentration monitoring unit to achieve concentration adjustment.

[0058] Among them, the first positive electrode circulation pipeline connected to the positive electrode chamber inlet of the flow battery stack 3 is provided with a first liquid stop valve 12; the first positive electrode circulation pipeline connected to the cathode chamber inlet of the electrolytic cell stack 7 is provided with a second liquid stop valve 13; the second positive electrode circulation pipeline connected to the cathode chamber outlet of the electrolytic cell stack 7 is provided with a third liquid stop valve 14; the transfer pipeline is provided with a fourth liquid stop valve 15, and the delivery pipeline is provided with a fifth stop valve 16. When each module is operated step by step, the switch states between the liquid stop valves are in different combination states to realize the normal circulation of the electrolyte of different modules.

[0059] The operation process of the iron-chromium liquid flow battery system including the rebalancing device designed in this embodiment is as follows: the iron-chromium liquid flow battery module, the rebalancing device and the electrolyte readjustment module are operated step by step. When the iron-chromium liquid flow battery module is in operation, the first liquid stop valve 12 is in an open state, the negative electrode electrolyte circulates in a closed negative electrode loop, and the positive electrode electrolyte circulates in a closed positive electrode loop. The test control system is used to monitor the performance state of the liquid flow battery and control the operation of the iron-chromium liquid flow battery module. When the capacity of the liquid flow battery decays to a certain amount (10% to 90% of the initial battery capacity), the operation of the iron-chromium liquid flow battery module is stopped, the liquid flow direction of the positive electrode pump 4 is changed so that all the positive electrode electrolyte flows into the positive electrode storage tank 5, and the first liquid stop valve 12 is closed;

[0060] After the operation of the iron-chromium liquid flow battery module is finished, the rebalancing device is started to operate to realize the electrolytic reduction of the inactivated iron ions in the positive electrolyte to achieve the purpose of capacity recovery. At this time, the first stop valve 12, the fourth stop valve 15 and the fifth stop valve 16 are in a closed state, and the second stop valve 13 and the third stop valve 14 are in an open state; the cathode electrolyte circulates in a closed cathode loop, and the anode electrolyte circulates in a closed anode loop. The Fe ions to be reduced are calculated according to the loss capacity of the liquid flow battery. 3+ The amount of the electrolytic cell stack is set by the test control system, and the anode undergoes a water electrolysis oxidation reaction to form oxygen, and the cathode undergoes a trivalent iron ion electrolysis reduction reaction to form divalent iron ions, and the gas-liquid separator 10 separates the anode gas product during the electrolysis process; when the electrolysis is completed, the anode electrolyte volume measurement and control device is used to supplement the anode electrolyte in the anode liquid storage tank 9 after the electrolysis for the next electrolysis;

[0061] After the operation of the rebalancing device is finished, the electrolyte readjustment module is started. At this time, the third liquid stop valve 14 is closed, the fourth liquid stop valve 15 is opened, and all the reduced positive electrode electrolyte is pumped into the transfer liquid storage tank 11. The concentration correction device adjusts the concentration of the reduced positive electrode electrolyte. The volume of the electrolyte in the transfer liquid storage tank is first measured by the volume measurement and control unit. When the volume increases with the initial positive electrode electrolyte volume by more than a preset value (the preset value is greater than 0), the evaporator heats and concentrates the electrolyte until the volume returns to the initial level, and then the concentration monitoring unit is used to measure the Fe content in the electrolyte. 2+ , Fe 3+ Cr 3+ and H + When the concentration values ​​are all less than the initial positive electrode electrolyte level, calculation is performed and the material replenishment unit is used to replenish the electrolyte, and FeCl2, FeCl3, CrCl3 and HCl are added until the concentration values ​​are restored to the initial electrolyte level; when the volume growth of the electrolyte flowing into the transfer storage tank 11 is less than the preset value, the heating and concentration step is omitted, and the concentration measurement and material replenishment are directly performed;

[0062] Finally, close the second stop valve 13 and the fourth stop valve 15, open the fifth stop valve 16, and use the volume measurement and control unit to discharge the same volume of electrolyte as the initial electrolyte into the positive electrode storage tank 5. At this time, close the fifth stop valve 16 again, open the first stop valve 12, and operate the iron-chromium liquid flow battery module again.

[0063] When the iron-chromium flow battery unit is running, the test control system is used to test the iron-chromium flow battery module at 60-160 mA / cm 2 The constant current charge and discharge test is performed, wherein the charge and discharge cut-off voltage is 0.6V to 1.2V. When the rebalancing device is running, the test control system is used to conduct 40 to 80 mA / cm 2 Constant current charging is performed to achieve capacity recovery of the iron-chromium liquid flow battery unit, where the charging cut-off voltage is 1.8~2.2V.

[0064] Example 2

[0065] This embodiment provides a method for recovering capacity of the iron-chromium liquid flow battery system including the rebalancing device of embodiment 1, comprising the following steps:

[0066] When the battery capacity of the iron-chromium flow battery module is monitored to decay, the operation of the iron-chromium flow battery module is stopped, and the rebalancing device is started to perform a constant current charging process, so that the positive electrode electrolyte in the cathode storage tank and the anode electrolyte in the anode storage tank undergo an electrochemical reaction, the trivalent iron ions in the positive electrode electrolyte are electrolytically reduced to divalent iron ions, and the anode electrolyte undergoes a water electrolytic oxidation reaction to produce oxygen;

[0067] The electrochemical reaction formula is:

[0068] Anode: 2H2O→2O2↑+4H + +4e - ;

[0069] Cathode: Fe 3+ +e - →Fe 2+ ;

[0070] After the electrolytic reduction of the positive electrode electrolyte in the rebalancing device is completed, the operation of the rebalancing device is stopped, and the electrolyte readjustment module is started to pump all the electrolytically reduced positive electrode electrolyte in the rebalancing device into the electrolyte readjustment module. The electrolyte readjustment module performs concentration correction on the electrolytically reduced positive electrode electrolyte. The volume measurement and control unit is first used to measure the volume of the electrolytically reduced positive electrode electrolyte stored in the transfer liquid storage tank. When the measured volume increases with the initial positive electrode electrolyte volume by more than a preset value, the evaporator in the transfer liquid storage tank heats and concentrates the electrolyte until the volume returns to the initial level. If it is less than the preset value, the heating and concentration step is omitted.

[0071] The concentration monitoring unit is then used to determine the Fe content in the positive electrode electrolyte after electrolytic reduction. 2+ , Fe 3+ Cr 3+ and H + The concentration of the positive electrode electrolyte is calculated based on the measurement result of the concentration monitoring unit, and then the material replenishment unit is used to replenish the material according to the calculation result to restore the concentration to the initial electrolyte level. The reduced positive electrode electrolyte after concentration correction is discharged into the positive electrode storage tank using the volume measurement and control unit, the electrolyte readjustment module is stopped, and the iron-chromium liquid flow battery module is operated.

[0072] In this embodiment, the constant current charging current of the rebalancing device is 50mA / cm 2 , the charging cut-off voltage is 2.0 V. The cathode reservoir tank stores 40 mL of the positive electrolyte of the iron-chromium flow battery, and the anode reservoir tank stores 50 ml of deionized water.

[0073] In this embodiment, two capacity recovery operations are performed. During the operation of the rebalancing device, two constant current charging processes with the same parameters are performed. The first capacity recovery is performed when the battery capacity of the iron-chromium liquid flow battery module decays to 57.46%, and the second capacity recovery is performed when the battery capacity of the iron-chromium liquid flow battery module decays to 61.45%. The capacity change results of the capacity recovery of the iron-chromium liquid flow battery system are shown as follows: Figure 3 As shown in the figure, after each capacity recovery, the discharge capacity of the battery reaches more than 95% of the original discharge capacity, indicating that it has a significant capacity recovery effect. The charging curves of the rebalancing device for two rebalancings are shown in the figure. Figure 4 , Figure 5 As shown in the figure, it can be seen that during the two rebalancing processes, the charging median voltage of the rebalancing device is 1.70V and 1.72V respectively, the voltage value changes little, and it can be reused. The entire rebalancing process is clean and easy to operate. The anode realizes the oxygen evolution reaction from water to oxygen and the enrichment of hydrogen ions. The hydrogen ions can cross the membrane to the cathode side, thereby regulating the hydrogen ion concentration in the deactivated positive electrode electrolyte.

[0074] The above-described embodiments only represent the embodiments of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. The present invention can also be implemented in other specific ways or other specific forms without departing from the gist or essential features of the present invention. Therefore, the described embodiments should be regarded as illustrative rather than restrictive in any respect. The scope of the present invention should be described by the attached claims, and any changes equivalent to the intention and scope of the claims should also be included in the scope of the present invention.

Claims

1. An iron-chromium liquid flow battery system comprising a rebalancing device, characterized in that: It includes an iron-chromium liquid flow battery module, a rebalancing device and an electrolyte readjustment module. The rebalancing device is used to electrolytically reduce the trivalent iron ions in the positive electrode electrolyte in the iron-chromium liquid flow battery module to divalent iron ions, and the electrolyte readjustment module is used to correct the concentration of the reduced positive electrode electrolyte in the rebalancing device.

2. The iron-chromium liquid flow battery system comprising a rebalancing device according to claim 1, characterized in that: The rebalancing device comprises a cathode liquid storage tank, a cathode pump, an electrolytic cell stack, an anode liquid storage tank and an anode pump; The cathode liquid storage tank is used to store positive electrode electrolyte, and the anode liquid storage tank is used to store anode electrolyte, and the anode electrolyte is pure water or an aqueous solution; The anode liquid storage tank is connected to the anode side of the electrolytic cell stack through an anode circulation pipeline to form a closed anode loop. The anode pump is arranged on the anode circulation pipeline to realize the circulation of the anode electrolyte in the closed anode loop. The electrolysis reaction in the closed anode loop is a process in which water is electrolytically oxidized into oxygen. The cathode liquid storage tank is connected to the cathode side of the electrolytic cell stack through a cathode circulation pipeline to form a closed cathode loop. The cathode pump is arranged on the cathode circulation pipeline to realize the circulation of the positive electrode electrolyte in the closed cathode loop. The electrolysis reaction in the closed cathode loop is a process of electrolytic reduction of trivalent iron ions in the positive electrode electrolyte to divalent iron ions.

3. The iron-chromium liquid flow battery system comprising a rebalancing device according to claim 2, characterized in that: The rebalancing device further comprises a gas-liquid separator, which is arranged on the anode circulation pipeline and is used for separating anode gas products in the electrolysis process.

4. The iron-chromium liquid flow battery system comprising a rebalancing device according to claim 2, characterized in that: The rebalancing device also includes an anode electrolyte volume measurement and control device, which is connected to the anode liquid storage tank and is used to measure the volume of the anode electrolyte in the anode liquid storage tank and replenish materials.

5. The iron-chromium liquid flow battery system comprising a rebalancing device according to claim 2, characterized in that: The electrolyte readjustment module includes a transfer liquid storage tank and a concentration correction device connected to each other, wherein the transfer liquid storage tank is connected to the cathode chamber outlet of the electrolytic cell stack through a transfer pipeline and is used to store the positive electrode electrolyte after electrolytic reduction; The concentration correction device is used to monitor the volume and ion concentration of the positive electrode electrolyte after electrolytic reduction stored in the transfer liquid storage tank, and to replenish materials according to the monitoring results to achieve concentration correction of the positive electrode electrolyte after electrolytic reduction; The transfer liquid storage tank is also connected to the cathode liquid storage tank via a delivery pipeline, and the delivery pipeline is used to deliver the concentration-corrected electrolytically reduced positive electrode liquid to the cathode liquid storage tank.

6. The iron-chromium liquid flow battery system comprising a rebalancing device according to claim 5, characterized in that: The concentration correction device includes a volume measurement and control unit, a concentration monitoring unit and a material replenishment unit, wherein the volume measurement and control unit is used to measure the volume of the electrolyte in the transfer liquid storage tank and to control the volume of the electrolyte discharged from the transfer liquid storage tank to the cathode liquid storage tank; The concentration monitoring unit is used to monitor the Fe 2+ , Fe 3+ Cr 3+ and H + concentration; The material replenishment unit replenishes materials according to the monitoring result of the concentration monitoring unit.

7. The iron-chromium liquid flow battery system comprising a rebalancing device according to claim 6, characterized in that: An evaporator is arranged in the transfer liquid storage tank, which is used to evaporate the water content of the electrolyte in the transfer liquid storage tank.

8. The iron-chromium liquid flow battery system comprising a rebalancing device according to claim 2, characterized in that: The iron-chromium liquid flow battery module includes a negative electrode storage tank, a negative electrode pump, a liquid flow battery stack, a positive electrode storage tank and a positive electrode pump; The negative electrode liquid storage tank is used to store negative electrode electrolyte, and the positive electrode liquid storage tank is used to store positive electrode electrolyte; the positive electrode liquid storage tank also serves as the cathode liquid storage tank in the rebalancing device; The negative electrode liquid storage tank is connected to the negative electrode side of the liquid flow battery stack through a negative electrode circulation pipeline to form a closed negative electrode loop, and the negative electrode pump is arranged on the negative electrode circulation pipeline to circulate and transport the negative electrode electrolyte between the negative electrode liquid storage tank and the negative electrode of the liquid flow battery stack; The positive electrode liquid storage tank is connected to the positive electrode side of the liquid flow battery stack through a positive electrode circulation pipeline to form a closed positive electrode loop. The positive electrode pump is arranged on the positive electrode circulation pipeline to circulate and transport the positive electrode electrolyte between the positive electrode storage tank and the positive electrode of the liquid flow battery stack.

9. The iron-chromium liquid flow battery system comprising a rebalancing device according to claim 8, characterized in that: A test control system is provided between the flow battery stack and the electrolytic cell stack, for monitoring and setting operating parameters of the iron-chromium flow battery module and the rebalancing device.

10. The iron-chromium liquid flow battery system comprising a rebalancing device according to claim 8, characterized in that: A first liquid stop valve is provided on the positive electrode circulation pipeline connected to the positive electrode chamber inlet of the liquid flow battery stack.

11. The iron-chromium liquid flow battery system comprising a rebalancing device according to claim 2 or 5, characterized in that: A second liquid-stop valve is provided on the positive electrode circulation pipeline connected to the cathode chamber inlet of the electrolytic cell stack; a third liquid-stop valve is provided on the positive electrode circulation pipeline connected to the cathode chamber outlet of the electrolytic cell stack.

12. The iron-chromium liquid flow battery system comprising a rebalancing device according to claim 5, characterized in that: The transfer pipeline is provided with a fourth liquid stop valve; the delivery pipeline is provided with a fifth liquid stop valve.

13. A method for capacity recovery using an iron-chromium liquid flow battery system comprising a rebalancing device as claimed in any one of claims 1 to 12, characterized in that: include: When the battery capacity attenuation of the iron-chromium liquid flow battery module is detected, the operation of the iron-chromium liquid flow battery module is stopped, and the rebalancing device is started to perform a charging process, so that the positive electrode electrolyte in the cathode storage tank and the anode electrolyte in the anode storage tank undergo an electrochemical reaction, the trivalent iron ions in the positive electrode electrolyte are electrolytically reduced to divalent iron ions, and the anode electrolyte undergoes a water electrolysis and oxidation reaction to produce oxygen; After completing the electrolytic reduction of the positive electrode electrolyte in the rebalancing device, stop the operation of the rebalancing device, start the electrolyte readjustment module, and pump all the positive electrode electrolyte after electrolytic reduction in the rebalancing device into the electrolyte readjustment module. The electrolyte readjustment module corrects the concentration of the positive electrode electrolyte after electrolytic reduction to restore the concentration to the initial electrolyte level, and then pumps the reduced positive electrode electrolyte after concentration correction into the positive electrode storage tank as needed, stops the electrolyte readjustment module, and operates the iron-chromium liquid flow battery module.

14. The method for recovering capacity of an iron-chromium liquid flow battery system comprising a rebalancing device according to claim 13, characterized in that: The electrolyte readjustment module performs concentration correction on the positive electrode electrolyte after electrolytic reduction, including: First, the volume of the positive electrode electrolyte after electrolysis reduction stored in the transfer liquid storage tank is measured by using a volume measurement and control unit. When the measured volume increases with the initial positive electrode electrolyte volume by more than a preset value, the evaporator in the transfer liquid storage tank heats and concentrates the electrolyte until the volume returns to the initial level. If the volume is less than the preset value, the heating and concentration step is omitted. The concentration monitoring unit is then used to determine the Fe content in the positive electrode electrolyte after electrolytic reduction. 2+ , Fe 3+ Cr 3+ and H + The concentration of the positive electrode electrolyte is corrected by calculating the difference between the concentration level of the positive electrode electrolyte and the initial concentration level of the positive electrode electrolyte according to the measurement result of the concentration monitoring unit, and then using the material replenishment unit to replenish materials according to the calculation result to complete the concentration correction of the positive electrode electrolyte after the electrolyte is reduced.

15. The method for capacity recovery of an iron-chromium liquid flow battery system comprising a rebalancing device according to claim 13, characterized in that: The charging process of the rebalancing device is a constant current charging process, and the current in the constant current charging process is 40-80 mA / cm 2 , the charging cut-off voltage is 1.8~2.2V.

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