Iron-chromium flow battery rebalancing system utilizing oxygen evolution reaction

Abstract

The utility model discloses an iron-chromium flow battery rebalancing system utilizing oxygen evolution reaction, which belongs to the technical field of flow batteries and comprises a rebalancing battery, an external power supply, an anode liquid storage tank, an anode liquid inlet pipe, an anode circulating pump, an anode liquid outlet pipe, a cathode liquid storage tank, a cathode liquid inlet pipe, a cathode circulating pump and a cathode liquid outlet pipe. The rebalancing battery is a double-membrane three-chamber electrolytic tank, and the middle chamber is filled with hydrochloric acid, so that the concentration of active substances and hydrogen ions in the cathode electrolyte is basically not reduced. The rebalancing system for the iron-chromium flow battery provided by the utility model is simple in structure, low in cost and small in environmental harm, realizes the capacity recovery of the anode electrolyte of the iron-chromium flow battery, and greatly reduces the economic loss. The capacity of the iron-chromium flow battery is recovered by configuring the electrolyzed water rebalancing battery, the reduction reaction from iron ions to ferrous ions is realized by the cathode of the rebalancing battery, and the purpose of recovering the capacity of the flow battery is achieved.

Description

Technical Field

[0001] This invention belongs to the field of flow battery technology, and specifically relates to a rebalancing system for iron-chromium flow batteries that utilizes the oxygen evolution reaction. Background Technology

[0002] Flow battery energy storage technology boasts advantages such as high safety, long cycle life, and environmental friendliness, holding immense potential in large-scale energy storage technology. Iron-chromium redox flow batteries are lower in cost and more environmentally friendly, making them ideal for large-scale new energy storage. However, during charging, the negative electrode electrolyte of iron-chromium redox flow batteries experiences hydrogen evolution, leading to a relative excess of iron ions in the positive electrode electrolyte, i.e., an imbalance of state of charge (SOC) between the positive and negative electrodes. After multiple charge-discharge cycles, the electrolyte pH increases, and a large accumulation of iron ions in the positive electrode occurs, resulting in positive electrode electrolyte deactivation. This significantly impacts the charge-discharge performance of iron-chromium redox flow batteries, causing economic losses.

[0003] To address the capacity loss in iron-chromium redox flow batteries caused by positive electrode electrolyte deactivation, existing technologies include replacing the positive electrode electrolyte, electrochemical methods to restore positive electrode electrolyte activity, and chemical reduction methods. Replacing the positive electrode electrolyte is the most direct and simplest method, as it directly replaces the deactivated electrolyte with freshly prepared electrolyte, allowing the battery to continue operating; however, this results in significant economic losses. Chemical reduction methods utilize reducing agents to reduce iron ions in the deactivated electrolyte to ferrous ions, thereby restoring electrolyte activity and maintaining normal battery operation. However, this introduces new impurity ions, potentially affecting battery performance. The general approach to restoring positive electrode electrolyte activity using electrochemical methods involves configuring a rebalancing battery on the positive electrode side. The electrochemical reduction reaction reduces iron ions to ferrous ions, preventing other byproducts from entering the deactivated electrolyte and thus avoiding adverse effects on electrolyte performance.

[0004] Acidic iron-chromium redox flow batteries for capacity recovery currently include hydrogen fuel cells, electrolytic iron oxide batteries, and electrolytic hydrochloric acid recovery batteries. While hydrogen fuel cells produce water as a clean and pollution-free byproduct during the reduction of iron ions, hydrogen gas is highly dangerous during use and prone to explosion, thus requiring sophisticated equipment. Electrolytic hydrochloric acid recovery batteries use hydrochloric acid as a reducing agent; the reduction reaction on the hydrochloric acid side of the rebalancing battery produces chlorine gas, while hydrogen ions cross the membrane to the deactivated electrolyte side, replenishing it and achieving the desired effect. However, the chlorine gas produced is harmful to human health and causes significant environmental pollution, requiring additional exhaust gas treatment equipment, making them less advantageous in terms of environmental protection and cost.

[0005] In summary, it is imperative to develop a rebalancing battery system that is highly safe, environmentally friendly, and low-cost for restoring the capacity of iron-chromium flow batteries. Utility Model Content

[0006] The main objective of this invention is to provide a rebalancing system for iron-chromium redox flow batteries that utilizes the oxygen evolution reaction. The provided iron-chromium redox flow battery rebalancing system has a simple structure, low cost, and minimal environmental impact. It achieves capacity recovery of the positive electrode electrolyte in iron-chromium redox flow batteries, significantly reducing economic losses.

[0007] To achieve the above objectives, this utility model provides a rebalancing system for an iron-chromium redox flow battery that utilizes the oxygen evolution reaction, comprising a rebalancing battery, an external power supply, an anode storage tank, an anode inlet pipe, an anode circulation pump, an anode outlet pipe, a cathode storage tank, a cathode inlet pipe, a cathode circulation pump, and a cathode outlet pipe.

[0008] The positive and negative terminals of the external power supply are respectively connected to the two ends of the rebalancing battery;

[0009] The anode storage tank is connected to the anode terminal of the rebalancing battery via the anode inlet pipe and the anode outlet pipe to form a closed anode loop; the anode circulation pump is installed on the anode inlet pipe or the anode outlet pipe; the anode storage tank is configured to store pure water or an aqueous solution; the electrolysis reaction in the closed anode loop is the electrolytic oxidation of water into oxygen;

[0010] The cathode storage tank is connected to the cathode terminal of the rebalancing battery through the cathode inlet pipe and the cathode outlet pipe to form a closed cathode loop; the cathode circulation pump is installed on the cathode inlet pipe or the cathode outlet pipe; the cathode storage tank is configured to store deactivated iron-chromium flow battery positive electrode electrolyte; the electrolysis reaction in the closed cathode loop is the electrolytic reduction of ferric ions in the positive electrode electrolyte to ferrous ions.

[0011] In some specific embodiments of this invention, the rebalancing battery is a dual-membrane three-chamber electrolytic cell, comprising a cathode chamber, an intermediate chamber, and an anode chamber. The cathode chamber and the intermediate chamber are separated by a cathode-side ion exchange membrane, and the anode chamber and the intermediate chamber are separated by an anode-side ion exchange membrane. Compared to a single-membrane dual-chamber electrolytic cell, the dual-membrane three-chamber electrolytic cell avoids electrolyte cross-contamination caused by contact between the cathode and anode electrolytes, and prevents a significant decrease in the concentration of the positive electrode electrolyte.

[0012] In some specific embodiments of this utility model, the cathode chamber includes a cathode end plate, a cathode current collector, a cathode electrode, and a cathode-side ion exchange membrane connected in sequence; the intermediate chamber includes an intermediate chamber sealing device; and the anode chamber includes an anode-side ion exchange membrane, an anode electrode, an anode current collector, and an anode end plate connected in sequence.

[0013] In some specific embodiments of this utility model, the intermediate chamber sealing device is filled with hydrochloric acid. In this application, the anode chamber is water, the cathode chamber is deactivated positive electrolyte, and the intermediate chamber is filled with hydrochloric acid. The hydrochloric acid in the intermediate chamber can provide hydrogen ions to the deactivated positive electrolyte, while the intermediate chamber sealing device can prevent cross-contamination between the anode and cathode electrolytes. This application uses the above-mentioned double-membrane three-chamber electrolytic cell to ensure that the concentration of active materials and hydrogen ions in the cathode electrolyte does not decrease significantly, thus guaranteeing the recovery of effective components of the positive electrolyte in the iron-chromium redox flow battery.

[0014] In some specific embodiments of this utility model, the molar concentration of hydrochloric acid in the intermediate chamber sealing device is 3.0M to 8.0M. For example, it can be selected from 3.0M, 3.5M, 4.0M, 4.5M, 5.0M, 5.5M, 6.0M, 6.5M, 7.0M, 7.5M, and 8.0M.

[0015] In some specific embodiments of this utility model, the cathode electrode and the anode electrode are each independently selected from any one of carbon felt, carbon paper, or carbon cloth.

[0016] In some specific embodiments of this utility model, the anode-side ion exchange membrane and the cathode-side ion exchange membrane are each independently either a cation exchange membrane or an anion exchange membrane.

[0017] In some optional embodiments of this utility model, the connection between the anode storage tank and the anode inlet pipe and the anode outlet pipe is detachable; the connection between the cathode storage tank and the cathode inlet pipe and the cathode outlet pipe is detachable.

[0018] In some specific embodiments of this utility model, the iron-chromium redox flow battery rebalancing system further includes an electrolyte composition monitoring unit, which is disposed within the cathode storage tank. The electrolyte composition monitoring unit is used to regulate the concentration of the reduced cathode electrolyte after the rebalancing battery electrolysis is completed.

[0019] In some specific embodiments of this utility model, the electrolyte component monitoring unit includes an electrolyte concentration monitoring device and a concentration recovery device. The electrolyte concentration monitoring device is used to measure the concentration of active substance ions in the reduced cathode electrolyte. The concentration recovery device replenishes materials based on the measurement results of the electrolyte concentration monitoring device.

[0020] Specifically, the active ions include ferrous ions, trivalent chromium ions, and hydrogen ions in the electrolyte. By setting up an electrolyte component monitoring unit, the concentration of active substances in the electrolyte can be fine-tuned after electrolysis, compensating for any losses or deficiencies that may occur during electrolysis, and restoring the concentration of active substances in the deactivated electrolyte to the required value.

[0021] In some specific embodiments of this invention, the iron-chromium redox flow battery rebalancing system further includes a gas control device, which is disposed on the anode storage tank. The gas control device is used to discharge oxygen, a reaction product, from the anode storage tank, thereby stabilizing the pressure in the anode storage tank.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The iron-chromium redox flow battery rebalancing system provided by this utility model has a simple structure, low cost, and minimal environmental impact. It achieves capacity recovery of the positive electrode electrolyte in iron-chromium redox flow batteries, significantly reducing economic losses. By configuring an electrolytic water rebalancing battery, the capacity of the iron-chromium redox flow battery is restored. The cathode of the rebalancing battery achieves the reduction reaction from iron ions to ferrous ions, thus achieving the purpose of restoring the flow battery capacity.

[0024] 2. The anode reactant in the rebalancing battery is water, which is clean, easy to produce, and has a simple composition. This avoids the problem of introducing impurity ions into the deactivated electrolyte, thus affecting the performance of the flow battery, which is caused by using other chemical substances in the reaction. The anode product oxygen is environmentally friendly and harmless, eliminating the need for exhaust gas treatment equipment and allowing for further utilization of the product oxygen, thus achieving economic benefits.

[0025] 3. The rebalancing battery adopts a dual-membrane, three-chamber electrolytic cell. The middle chamber contains a high concentration of hydrochloric acid, which can ensure that the active material and hydrogen ion concentration in the cathode electrolyte do not decrease significantly, thus ensuring the recovery of the effective components of the positive electrode electrolyte in the iron-chromium redox flow battery.

[0026] 4. The electrolyte component monitoring unit installed in the cathode storage tank of the electrolytic cell is used to monitor the concentration of active substance ions in the electrolyte. It can make fine adjustments to the concentration of active substances in the electrolyte after electrolysis, make up for possible losses and deficiencies caused by electrolysis, and restore the concentration of active substances in the deactivated electrolyte to the required value. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an undue limitation of the present invention. In the drawings:

[0028] Figure 1A schematic diagram of the rebalancing system of an iron-chromium redox flow battery utilizing the oxygen evolution reaction in an embodiment of this invention is shown.

[0029] Figure 2 This invention illustrates a schematic diagram of the rebalancing cell in an iron-chromium flow battery utilizing the oxygen evolution reaction, according to an embodiment of the present invention.

[0030] Figure 3 This diagram illustrates the operation of the electrolyte component monitoring unit in the iron-chromium redox flow battery rebalancing system utilizing the oxygen evolution reaction in an embodiment of this invention.

[0031] Figure 4 The diagram shows the charging curve of the rebalanced battery during the capacity recovery process of the iron-chromium redox flow battery using the oxygen evolution reaction rebalance system according to an embodiment of the present invention.

[0032] Figure 5 The diagram shows the capacity change curve of the iron-chromium redox flow battery after capacity recovery using the iron-chromium redox flow battery rebalancing system utilizing the oxygen evolution reaction in the embodiment of this utility model.

[0033] The above-mentioned figures include the following reference numerals: 1. Cathode storage tank; 2. Cathode inlet pipe; 3. Cathode circulation pump; 4. Cathode outlet pipe; 5. Electrolyte component monitoring unit; 6. DC power supply; 7. Rebalancing battery; 8. Anode circulation pump; 9. Anode inlet pipe; 10. Anode storage tank; 11. Gas control device; 12. Anode outlet pipe; 13. Cathode end plate; 14. Cathode current collector; 15. Cathode electrode; 16. Cathode-side ion exchange membrane; 17. Intermediate chamber sealing device; 18. Anode-side ion exchange membrane; 19. Anode electrode; 20. Anode current collector; 21. Anode end plate. Detailed Implementation

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0035] Example

[0036] like Figure 1 As shown, the iron-chromium redox flow battery rebalancing system designed in this utility model using oxygen evolution reaction includes a cathode storage tank 1, a cathode inlet pipe 2, a cathode circulation pump 3, a cathode outlet pipe 4, an electrolyte component monitoring unit 5, a DC power supply 6, a rebalancing battery 7, an anode circulation pump 8, an anode inlet pipe 9, an anode storage tank 10, a gas control device 11, and an anode outlet pipe 12.

[0037] like Figure 2As shown, the rebalancing battery 7 in the rebalancing system designed in this utility model is essentially a double-membrane three-chamber electrolytic cell, consisting of a cathode chamber, an intermediate chamber, and an anode chamber. The structure of the rebalancing battery 7 includes, in sequence, a cathode end plate 13, a cathode current collector 14, a cathode electrode 15, a cathode-side ion exchange membrane 16, an intermediate chamber sealing device 17, an anode-side ion exchange membrane 18, an anode electrode 19, an anode current collector 20, and an anode end plate 21. The cathode electrode 15 and anode electrode 19 are made of carbon felt and placed in a plate frame. The cathode-side ion exchange membrane 16 and the anode-side ion exchange membrane 18 are both proton exchange membranes. Gaskets are added between the components, and nuts and bolts are used to compress and fix the battery structure, forming a sealed space to prevent electrolyte leakage during internal liquid flow. The intermediate chamber in the three chambers stores hydrochloric acid with a molar concentration of 3.0M to 8.0M, which replenishes hydrogen ions to the deactivated positive electrode electrolyte of the iron-chromium redox flow battery, ensuring a constant electrolyte composition.

[0038] The iron-chromium redox flow battery rebalancing system utilizing the oxygen evolution reaction of this invention is connected to the working system of the iron-chromium redox flow battery. The positive electrode storage tank in the working system of the iron-chromium redox flow battery serves as the cathode storage tank 1 of the rebalancing system. The cathode storage tank 1 stores the deactivated positive electrode electrolyte of the iron-chromium redox flow battery. When the iron-chromium redox flow battery system is running, the positive electrode electrolyte circulates between the positive electrode of the battery stack and the positive electrode storage tank. The inlet and outlet of the positive electrode storage tank (i.e., cathode storage tank 1) connected to the rebalancing battery 7 are closed. When the iron-chromium redox flow battery experiences capacity loss, the operation of the iron-chromium redox flow battery system is stopped, and the positive electrode electrolyte is returned to the positive electrode storage tank (i.e., cathode storage tank 1). The rebalancing battery 7 (i.e., the electrolytic cell) then starts operating. The deactivated positive electrode electrolyte circulates between the cathode of the electrolytic cell and the cathode storage tank 1. The deactivated electrolyte acts as the cathode reactant in the electrolytic cell, realizing the conversion of iron ions to ferrous ions during electrolysis. The inlet and outlet of the cathode storage tank 1 connected to the battery stack of the iron-chromium redox flow battery system are closed.

[0039] The cathode inlet pipe 2 connects the bottom of the cathode storage tank 1 and the cathode chamber inlet of the rebalancing battery 7. A cathode circulation pump 3 is installed on it. The cathode outlet pipe 4 connects the cathode chamber outlet of the rebalancing battery 7 and the top of the cathode storage tank 1, forming a cathode circulation route for the cathode electrolyte. The cathode circulation pump 3 is used to pump the electrolyte in the cathode storage tank into the cathode of the electrolytic cell, realizing the circulation of the cathode electrolyte in the cathode circulation route, and causing the electrolytic reduction of ferric ions to ferrous ions.

[0040] Electrolyte composition monitoring unit 5 is located inside cathode storage tank 1, and includes an electrolyte concentration monitoring device and a concentration recovery device, as shown in the schematic diagram below. Figure 3As shown, this device is used to monitor the concentration of active substance ions in the electrolyte and to sample and measure the electrolyte after electrolysis. If the concentration of active substance in the electrolyte differs from the required value, material can be added to fine-tune the concentration of active substance in the electrolyte after electrolysis, making up for any losses or deficiencies that may occur during electrolysis and restoring the concentration of active substance in the deactivated electrolyte to the required value.

[0041] The anode storage tank 8 is used to store the anode electrolyte and provide reactant water to the anode of the rebalancing cell 7.

[0042] The anode inlet pipe 9 connects the bottom of the anode storage tank 10 and the anode chamber inlet of the rebalancing battery 7. An anode circulation pump 8 is installed on it. The anode outlet pipe 12 connects the anode chamber outlet of the rebalancing battery 7 and the top of the anode storage tank 10, forming an anode circulation route for the anode electrolyte. The anode circulation pump pumps the electrolyte in the anode storage tank into the anode of the electrolytic cell, realizing the circulation of the anode electrolyte in the anode circulation route, and the reaction of water being electrolyzed and oxidized into oxygen occurs.

[0043] The gas control device 11 is a pressure-dividing valve type gas control device, which is installed on the anode storage tank 8 to separate oxygen from the anode product of the electrolytic cell and discharge it to ensure stable pressure in the storage tank.

[0044] A constant current charging test was performed on the rebalancing battery 7 using a DC power supply 6 to achieve capacity recovery of the iron-chromium flow battery, wherein the charging current density was 30–80 mA / cm². 2 The charging cutoff voltage is 1.8V to 2.4V, and the resulting charging curve is shown in [reference needed]. Figure 4 As shown in the diagram, the electrolysis reaction voltage is approximately 1.5V, a relatively low value sufficient to restore the charging capacity. At the cathode of the electrolytic cell, a reduction reaction occurs where iron ions gain electrons and are reduced to ferrous ions, thus restoring the activity of the positive electrode electrolyte in the iron-chromium redox flow battery. At the anode, an oxidation reaction occurs where water loses electrons, resulting in oxygen evolution and hydrogen ion accumulation. The capacity change of the iron-chromium redox flow battery electrolyte after capacity recovery is shown in the diagram. Figure 5 As shown in the figure, the electrolysis reaction of the rebalancing system can restore the decayed electrolyte capacity to its initial state, and the electrolyte capacity retention rate is approximately the same before and after restoration.

[0045] The embodiments described above are merely illustrative of implementation methods of this utility model, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this utility model. This utility model can also be implemented in other specific ways or forms without departing from its spirit or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of this utility model should be defined by the appended claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of this utility model.

Claims

1. A rebalancing system for an iron-chromium flow cell utilizing the oxygen evolution reaction, characterized in that, It includes a rebalancing battery, an external power supply, an anode storage tank, an anode inlet pipe, an anode circulation pump, an anode outlet pipe, a cathode storage tank, a cathode inlet pipe, a cathode circulation pump, and a cathode outlet pipe; The positive and negative terminals of the external power supply are respectively connected to the two ends of the rebalancing battery; The anode storage tank is connected to the anode terminal of the rebalancing battery via the anode inlet pipe and the anode outlet pipe to form a closed anode loop; the anode circulation pump is installed on the anode inlet pipe or the anode outlet pipe; the anode storage tank is configured to store pure water or an aqueous solution; the electrolysis reaction in the closed anode loop is the electrolytic oxidation of water into oxygen; The cathode storage tank is connected to the cathode terminal of the rebalancing battery through the cathode inlet pipe and the cathode outlet pipe to form a closed cathode loop; the cathode circulation pump is installed on the cathode inlet pipe or the cathode outlet pipe; the cathode storage tank is configured to store deactivated iron-chromium flow battery positive electrode electrolyte; the electrolysis reaction in the closed cathode loop is the electrolytic reduction of ferric ions in the positive electrode electrolyte to ferrous ions.

2. The iron-chromium redox flow cell rebalancing system utilizing the oxygen evolution reaction according to claim 1, characterized in that, The rebalancing battery is a dual-membrane three-chamber electrolyzer, comprising a cathode chamber, an intermediate chamber, and an anode chamber. The cathode chamber and the intermediate chamber are separated by a cathode-side ion exchange membrane, and the anode chamber and the intermediate chamber are separated by an anode-side ion exchange membrane.

3. The iron-chromium redox flow cell rebalancing system utilizing the oxygen evolution reaction according to claim 2, characterized in that, The cathode chamber includes a cathode end plate, a cathode current collector, a cathode electrode, and a cathode-side ion exchange membrane connected in sequence; the intermediate chamber includes an intermediate chamber sealing device; the anode chamber includes an anode-side ion exchange membrane, an anode electrode, an anode current collector, and an anode end plate connected in sequence.

4. The iron-chromium redox flow cell rebalancing system utilizing the oxygen evolution reaction according to claim 3, characterized in that, The intermediate chamber sealing device is filled with hydrochloric acid.

5. The iron-chromium redox flow cell rebalancing system utilizing the oxygen evolution reaction according to claim 4, characterized in that, The molar concentration of hydrochloric acid in the intermediate chamber sealing device is 3.0M~8.0M.

6. The iron-chromium redox flow cell rebalancing system utilizing the oxygen evolution reaction according to claim 3, characterized in that, The cathode electrode and the anode electrode are each independently selected from any one of carbon felt, carbon paper, or carbon cloth.

7. The iron-chromium redox flow cell rebalancing system utilizing the oxygen evolution reaction according to claim 2, characterized in that, The anode-side ion exchange membrane and the cathode-side ion exchange membrane are each independently either a cation exchange membrane or an anion exchange membrane; And / or, the connection between the anode storage tank and the anode inlet pipe and the anode outlet pipe is a detachable connection; And / or, the connection between the cathode storage tank and the cathode inlet pipe and the cathode outlet pipe is a detachable connection.

8. The iron-chromium redox flow cell rebalancing system utilizing the oxygen evolution reaction according to claim 1, characterized in that, The iron-chromium redox flow battery rebalancing system also includes an electrolyte composition monitoring unit, which is located inside the cathode storage tank.

9. The iron-chromium redox flow cell rebalancing system utilizing the oxygen evolution reaction according to claim 8, characterized in that, The electrolyte component monitoring unit includes an electrolyte concentration monitoring device and a concentration recovery device. The electrolyte concentration monitoring device is used to measure the concentration of active substance ions in the reduced cathode electrolyte. The concentration recovery device replenishes materials based on the measurement results of the electrolyte concentration monitoring device.

10. The iron-chromium redox flow cell rebalancing system utilizing the oxygen evolution reaction according to claim 1, characterized in that, The iron-chromium redox flow battery rebalancing system also includes a gas control device, which is installed on the anode storage tank.

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