Iron-chromium flow battery system and rebalancing method of electrolyte

Abstract

The invention provides an iron-chromium flow battery system and an electrolyte rebalancing method. The iron-chromium flow battery system comprises an iron-chromium flow battery main body and a rebalancing device, the rebalancing device comprises: a rebalancing agent storage tank for accommodating a rebalancing agent solution; the reducing agent storage tank is used for containing a reducing agent, and the reducing agent storage tank is communicated with the rebalancing agent storage tank; the rebalancing galvanic pile is respectively communicated with the electrolyte storage tank and the rebalancing agent storage tank which are subjected to state-of-charge shift in the iron-chromium flow battery main body through pipelines; and the pumps are respectively used for conveying the reducing agent, the electrolyte and the rebalancing agent. The iron-chromium flow battery system can realize rebalance of the electrolyte of the iron-chromium flow battery, has the advantages of low cost, no pollution and online continuous operation, and can effectively improve the long-term stability of the flow battery.

Description

Technical Field

[0001] This invention relates to redox flow battery technology, and more particularly to an iron-chromium flow battery system and a method for rebalancing the electrolyte. Background Technology

[0002] Iron-chromium flow batteries (ICFBs), as a low-cost flow battery technology, show promising potential for large-scale energy storage applications. ICFBs are one of the earliest flow battery technologies, first reported by Thaller of NASA in the 1970s. The reaction formula is as follows:

[0003] positive electrode:

[0004] negative electrode:

[0005] Because the redox potential of Cr ions at the negative electrode is more negative, the hydrogen evolution side reaction is more likely to occur, which leads to an increase in Fe in the electrolyte at both the positive and negative electrodes. 3+ and Cr 2+ An imbalance in the ratio of hydrogen ions to electrons leads to the loss of hydrogen ions and electrons in the system, resulting in an imbalance in the state of charge of the positive and negative electrolytes, thus causing capacity decay. Currently, there are various rebalancing methods to restore capacity. In patent CN108511779A, the inventors returned the hydrogen produced at the negative electrode to the system in the form of a fuel cell. The advantage of the hydrogen reduction method is that it does not produce toxic intermediate products during the reaction and does not require additional electrical energy consumption. However, this technology also faces certain challenges, especially the selection of hydrogen oxidation catalysts. Currently, commonly used catalysts are mostly precious metal materials such as Pt. These catalysts lack long-term stability under harsh conditions such as strong acids and strong oxidation, and are prone to corrosion and conversion into ionic states that enter the electrolyte, thus contaminating the electrolyte and affecting battery performance and lifespan. Furthermore, hydrogen molecules are extremely small and can easily escape from weak points in the system. Patents CN117039083B and CN119252978B both use hydrogen sulfide as a reducing agent to remove excess Fe from the positive electrode of the iron-chromium redox flow battery. 3+ Reduced to Fe 2+This method rebalances the charge state of the positive and negative electrodes. Its advantage is that it does not introduce additional metal ions; however, hydrogen sulfide is not only highly toxic but also flammable and explosive. Furthermore, the generated byproduct, elemental sulfur, needs to be collected periodically, which limits its application. Patents CN113314733A and CN118281259B employ a rebalancing stack where chlorine evolution occurs at the positive electrode; the negative electrode is the positive electrolyte of the iron-chromium redox flow battery, undergoing a reduction reaction. Concentrated hydrochloric acid is periodically added to the positive electrode of the rebalancing stack to achieve rebalancing of the iron-chromium redox flow battery system. However, the highly toxic chlorine gas produced by this method needs to be absorbed separately, and the continuously added concentrated hydrochloric acid dilutes the electrolyte of the iron-chromium redox flow battery. Therefore, this method is not perfect for long-term use. In patent CN111969234B, a rebalancing stack is also set up, in which vanadium ions are used as a medium to oxidize alcohols, acids, aldehydes and other reducing agents, so that the negative electrode of the rebalancing stack undergoes a reduction reaction. However, when a cation exchange membrane is used in the rebalancing stack, the cross-contamination problem between vanadium ions and iron and chromium ions is extremely serious. At the same time, the hydrochloric acid in the main system will also be reduced due to migration, resulting in a decrease in conductivity and ultimately affecting the voltage efficiency of the battery.

[0006] In summary, existing rebalancing technologies all have limitations to varying degrees and cannot meet the requirements for long-term stable operation of iron-chromium redox flow batteries. Therefore, there is an urgent need to develop a more advantageous rebalancing technology to ensure more stable operation of iron-chromium redox flow batteries. Summary of the Invention

[0007] The purpose of this invention is to address the limitations of existing iron-chromium redox flow battery rebalancing technology, which leads to poor long-term operational stability of iron-chromium redox flow batteries. This invention proposes an iron-chromium redox flow battery system that can achieve electrolyte rebalancing, has the advantages of low cost, no pollution, and continuous online operation, and can effectively improve the long-term stability of the flow battery.

[0008] It should be noted that, in this invention, unless otherwise specified, the specific meaning of "comprising" in relation to composition and description includes both open-ended meanings such as "comprising," "including," etc., and closed-ended meanings such as "composed of," "consisting of," etc., and similar meanings.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is: an iron-chromium redox flow battery system, comprising: an iron-chromium redox flow battery body and a rebalancing device;

[0010] The rebalancing device includes:

[0011] Rebalancing agent storage tank, used to contain rebalancing agent solution;

[0012] A reducing agent storage tank for containing a reducing agent, wherein the reducing agent storage tank is connected to a rebalancing agent storage tank;

[0013] The rebalancing stack is connected via pipelines to the electrolyte tank and the rebalancing agent tank in the main body of the iron-chromium redox flow battery, respectively, for electrochemical redox reactions.

[0014] And pumps used to transport reducing agents, electrolytes, and rebalancing agents.

[0015] Furthermore, the main body of the iron-chromium redox flow battery includes: a negative electrode storage tank, a positive electrode storage tank, a stack, and a pump; the negative electrode storage tank is used to contain an electrolyte containing chromium ions; the positive electrode storage tank is used to contain an electrolyte containing iron ions; the stack is used for charging and discharging; and the pump is used for circulating the electrolyte.

[0016] Furthermore, the fuel cell stack includes a separator, electrodes, bipolar plates, and a flow channel frame. The fuel cell stack is a multi-layered structure consisting of alternating layers of bipolar plates, electrodes, separators, electrodes, and bipolar plates, with the flow channel frame embedded within to form flow channels. Finally, the stack is assembled by compression, and the electrolyte undergoes a redox reaction in the electrodes.

[0017] Furthermore, the electrodes used in the fuel cell stack are carbon felt, DSA electrodes, platinum electrodes, or graphite electrodes. The preferred electrodes are carbon felt.

[0018] Furthermore, the rebalancing stack includes a separation diaphragm, electrodes, bipolar plates, and a flow channel frame. Similarly, the rebalancing stack is a multi-layered structure consisting of alternating layers of bipolar plates, electrodes, separation diaphragms, electrodes, and bipolar plates, with the flow channel frame embedded within to form flow channels, and finally assembled by compression. The rebalancing agent undergoes a redox reaction in the electrodes.

[0019] Furthermore, the separation membrane used in the rebalancing stack is a microporous membrane, anion exchange membrane, cation exchange membrane, or bipolar membrane. The separation membrane is preferably a bipolar membrane.

[0020] Furthermore, the electrodes used in the rebalancing stack are carbon felt, DSA electrodes, platinum electrodes, or graphite electrodes. The preferred electrodes are carbon felt.

[0021] Another object of the present invention discloses a method for rebalancing the electrolyte of an iron-chromium flow battery, comprising the following steps:

[0022] (1) When the positive and negative electrodes of the iron-chromium redox flow battery are out of balance, connect the rebalancing stack to the electrolyte storage tank on the side where the state of charge shifts.

[0023] (2) In the rebalancing stack, the rebalancing agent is oxidized and converted into a charged state, while the excess high-valence metal ions in the iron-chromium redox flow battery body are reduced.

[0024] (3) Add the reducing agent to the rebalancing agent storage tank, and react chemically with the rebalancing agent in the charged state to reduce the rebalancing agent in the charged state to the initial state;

[0025] Through the cycle of steps (2) and (3), electrons of the reducing agent are transferred to the iron-chromium redox flow battery body, thereby achieving electrolyte rebalancing.

[0026] Furthermore, the rebalancing agent includes a redox active substance and a solvent.

[0027] Furthermore, the redox active material is a redox active material (organic electrochemical active material) having a hindered amine hydroxylamine cyclic structure group. The redox active material having a hindered amine hydroxylamine cyclic structure group includes, but is not limited to, the redox active material described in patent CN120261648B, a low-cost flow battery and its application.

[0028] Furthermore, the redox-active substance with the hindered amine hydroxylamine cyclic structure group contains the structure in formula Y:

[0029] (Y)

[0030] In formula Y, the cyclic structure is a 3-membered ring, a 4-membered ring, a 5-membered ring, a 6-membered ring, a 7-membered ring, or an 8-membered ring; the cyclic structure contains one or more of carbon-carbon single bonds, carbon-carbon double bonds, and carbon-carbon triple bonds; R1, R2, R3, and R4 are independently selected from alkyl, cycloalkyl, aryl, and aralkyl groups, respectively.

[0031] Furthermore, the ring structure can be connected to the remaining molecular structure via introduced covalent bonds, and one or more of methyl, propyl, and phenyl groups can be attached to the ring, with no limit on the number of attached groups.

[0032] The hydroxylamine cyclic structure group of the hindered amine can undergo a highly reversible redox reaction of formula Ya. This reversible transformation between hydroxylamine, nitric oxide radical, and nitric oxide salt allows a single hindered amine hydroxylamine cyclic structure group to charge or release two electrons.

[0033] Furthermore, the hydroxylamine cyclic structure group of the hindered amine is one or more of the following: a 1-hydroxy-2,2,6,6-tetrasubstituted piperidine group, a 1-hydroxy-2,2,5,5-tetrasubstituted pyrrole group, a 1-hydroxy-2,2,5,5-tetrasubstituted pyrrolin group, a 1-oxy radical-2,2,6,6-tetrasubstituted piperidine group, and a 1-oxo-2,2,6,6-tetrasubstituted piperidinium group; these groups can all undergo reversible redox reactions as shown in Formula Ya, and have 2-electron charge / discharge characteristics.

[0034] (Ya)

[0035] Furthermore, the redox-active substance of the hindered amine hydroxylamine cyclic structure group is preferably (1-oxygen radical-2,2,6,6-tetramethylpiperidine-4-yl)trimethylammonium chloride.

[0036] Furthermore, the concentration of the redox active substance having hindered amine hydroxylamine cyclic structural groups in the rebalancing agent is greater than 0 and less than 4 mol / L, preferably 1 to 2 mol / L.

[0037] Furthermore, the solvent is one or more of hydrochloric acid aqueous solution, sulfuric acid aqueous solution, and phosphoric acid aqueous solution.

[0038] Furthermore, the concentration of acid in the solvent of the rebalancing agent is 0–12 mol / L, preferably 1–3 mol / L.

[0039] Furthermore, the reducing agent is one or more of the following: reducing gas, sugar, carboxylic acid, aldehyde, and alcohol.

[0040] Furthermore, the reducing agent is preferably one or more selected from hydrogen, hydrogen sulfide, fructose, glucose, sucrose, formic acid, acetic acid, oxalic acid, methanol, ethanol, ethylene glycol, acetone, propylene glycol, lactic acid, and glycerol.

[0041] Furthermore, the reducing agent is more preferably formic acid and / or glucose.

[0042] Furthermore, the amount of reducing agent added varies with the imbalance between the positive and negative electrodes of the flow battery, primarily varying with the hydrogen evolution rate at the negative electrode.

[0043] Furthermore, in step (2), an external voltage is applied to the rebalancing stack for driving, with a single-piece voltage ranging from 0.5V to 2.0V.

[0044] Another objective of this invention is to disclose the application of a rebalancing method for the electrolyte of an iron-chromium flow battery, which is used to restore the imbalance of the state of charge of the positive and negative electrode electrolytes of an iron-chromium flow battery caused by the hydrogen evolution side reaction in an online manner.

[0045] Furthermore, the method can also be applied to electrolyte rebalancing of other redox flow battery systems that generate hydrogen during operation; these other redox flow battery systems include: Zn-Br flow battery systems, Zn-Cl flow battery systems, vanadium-containing flow battery systems, Fe-V flow battery systems, other iron-based flow battery systems, or organic flow battery systems.

[0046] The iron-chromium redox flow battery system and electrolyte rebalancing method of the present invention have the following advantages compared with the prior art:

[0047] 1) The rebalancing agent used in this invention is an organic electrochemically active substance with a hindered amine hydroxylamine cyclic structure group. Its active component is, for example, (1-oxygen radical-2,2,6,6-tetramethylpiperidin-4-yl)trimethylammonium chloride, whose molecule is mainly composed of common elements such as carbon, hydrogen, oxygen, and nitrogen. These elements are widely available, the synthesis process is relatively mature, and the raw material cost is low. Compared with traditional rebalancing schemes that rely on noble metal catalysts (such as Pt) or rare metal ions, this invention has a significant advantage in material cost, which is conducive to the economical operation of large-scale energy storage systems.

[0048] 2) The organic rebalancing agent molecules of the present invention have a large spatial structure, which makes it difficult for them to pass through the ion membrane into the iron-chromium main system electrolyte during the internal circulation of the fuel cell stack, thereby avoiding the common problem of ion cross-contamination in traditional methods (such as the mutual migration between vanadium ions and iron and chromium ions).

[0049] 3) The reducing agents selected in this invention include common organic compounds such as sugars (such as fructose and glucose), carboxylic acids (such as formic acid and acetic acid), and alcohols (such as methanol and ethanol). They are inexpensive and readily available, can be used on a large scale, and will not significantly increase operating costs.

[0050] 4) The rebalancing system of this invention can regulate the state of charge of the electrolyte while the iron-chromium redox flow battery is operating normally, without requiring downtime for maintenance, thus improving the system's availability and operational efficiency. Furthermore, it does not introduce any additional metal ions or other impurities, maintaining the chemical stability and electrochemical performance of the electrolyte system.

[0051] 5) The rebalancing stack of this invention is structurally basically the same as the main stack of an iron-chromium redox flow battery, and can use the same carbon felt electrodes, bipolar plates, flow channel frames, and other components, with only the separator being different (preferably a bipolar membrane). This reduces the complexity of manufacturing and maintenance, and also avoids dependence on precious metal electrodes.

[0052] 6) The rebalancing method of the iron-chromium redox flow battery electrolyte of the present invention uses the rebalancing agent in a cycle between the oxidized and reduced states, without generating waste salt or wastewater. Only the consumed reducing agent needs to be replenished periodically, which greatly improves the ease of system operation and maintenance and is in line with the development direction of green energy storage technology.

[0053] 7) This method is not only applicable to iron-chromium flow batteries, but can also be extended to other hydrogen-generating redox flow battery systems such as Zn-Br, Zn-Cl, vanadium-containing flow batteries, Fe-V systems, all-iron flow batteries, and organic flow batteries.

[0054] The iron-chromium redox flow battery system and electrolyte rebalancing method of this invention have the advantages of improving system cycle life, reducing operating costs, and simplifying maintenance procedures. They have good application prospects and large-scale promotion potential in the field of redox flow batteries. Attached Figure Description

[0055] Figure 1 A schematic diagram showing the rebalancing of the fuel cell stack placed on the positive electrode reservoir side of the flow battery.

[0056] Figure 2 A schematic diagram showing the rebalancing of the battery stack placed on the negative electrode reservoir side of the flow battery.

[0057] Figure 3 Discharge cycle data graph from Example 1. Detailed Implementation

[0058] The present invention will be further described below with reference to embodiments. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0059] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0060] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0061] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0062] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0063] In this specification, the terms "optional" or "optional" are used to indicate the use or omission of certain substances, components, procedures, application conditions, etc.

[0064] In this instruction manual, when "room temperature" or "room temperature" is used, the temperature can be 15-25℃.

[0065] Unless otherwise specified, all reagents or instruments used in this instruction manual are commercially available products.

[0066] Example 1

[0067] This embodiment discloses an iron-chromium redox flow battery system, such as Figure 1 and Figure 2 As shown, it includes: the main body of the iron-chromium redox flow battery and a rebalancing device;

[0068] The main body of the iron-chromium redox flow battery adopts a conventional configuration, including a negative electrode storage tank, a positive electrode storage tank, a stack, and a pump and related auxiliary equipment. The negative electrode storage tank is used to contain chromium-containing electrolyte; the positive electrode storage tank is used to contain iron-containing electrolyte; the stack is used for charging and discharging; and the pump and related auxiliary equipment are used to circulate the electrolyte. The stack includes a separator, carbon felt, bipolar plates, and a flow channel frame. The positive electrode electrolyte is 70L, and the negative electrode electrolyte is 70L. The iron ion concentration in both the positive and negative electrode electrolytes is 1mol / L, the chromium ion concentration is 1mol / L, and the hydrochloric acid concentration is 3mol / L. The charge / discharge stack power is 4.36kW, with 56 cells in series, and the operating power density is 100mW / cm³. 2 The ion exchange membrane is a perfluorosulfonic acid membrane.

[0069] The rebalancing device includes:

[0070] Rebalancing agent storage tank, used to contain rebalancing agent solution;

[0071] A reducing agent storage tank is used to contain reducing agent. The reducing agent storage tank is connected to a rebalancing agent storage tank for replenishing reducing agent. A delivery pump is installed on the pipeline between the reducing agent storage tank and the rebalancing agent storage tank.

[0072] The rebalancing stack is connected via pipelines to both the electrolyte tank where the state of charge shift occurs and the rebalancing agent tank within the main body of the iron-chromium redox flow battery. Specifically, the rebalancing stack is connected to the electrolyte tank in the main body of the iron-chromium redox flow battery via one pipeline, forming a circulation loop; simultaneously, the rebalancing stack is connected to the rebalancing agent tank via another pipeline, forming a circulation loop. Internally, the rebalancing stack is divided into two half-cells by a separating membrane; one half-cell is in contact with the electrolyte where the state of charge shift occurs, and the other half is in contact with the rebalancing agent solution.

[0073] And pumps and related auxiliary equipment used to transport reducing agents, electrolytes, and rebalancing agents.

[0074] The rebalancing stack includes a separation diaphragm, electrodes, bipolar plates, and a flow channel frame. The electrodes are carbon felt. The separation diaphragm is a bipolar membrane, and the applied charging voltage per diaphragm during rebalancing charging is 1V. The active component of the rebalancing agent is (1-oxyradical-2,2,6,6-tetramethylpiperidin-4-yl)trimethylammonium chloride at a concentration of 1.5 mol / L, along with 3 mol / L hydrochloric acid. The rebalancing agent volume is 20 L, and the reducing agent is formic acid.

[0075] Figure 1This diagram illustrates the rebalancing stack placed on the positive electrode reservoir side of a flow battery for rebalancing. When the positive and negative electrodes of the iron-chromium flow battery are out of balance, the rebalancing stack is connected to the positive electrode reservoir to form a loop. The concentration of ferric ions in the positive electrode reservoir increases, and the rebalancing stack electrochemically reduces these ferric ions to ferrous ions (Fe2+) in the positive electrode reservoir. Simultaneously, the rebalancing agent in the rebalancing agent reservoir is electrochemically oxidized from its initial state to a charged state. Then, the reducing agent in the reducing agent reservoir is slowly added to the rebalancing agent reservoir, restoring the rebalancing agent from its charged state to its initial state. In this way, the rebalancing agent acts as a catalyst, transferring electrons provided by the reducing agent to the ferric ions in the positive electrode reservoir through the rebalancing stack, thereby restoring and rebalancing the electrolyte's state of charge.

[0076] Figure 2 This diagram illustrates the rebalancing stack placed on the negative electrode reservoir side of a flow battery for rebalancing. When the positive and negative electrode charges of the iron-chromium flow battery are unbalanced, the rebalancing stack is connected to the negative electrode reservoir to form a loop. The concentration of trivalent chromium ions in the negative electrode reservoir increases, and the rebalancing stack electrochemically reduces these ions to divalent chromium ions. Simultaneously, the rebalancing agent in the rebalancing agent reservoir is electrochemically oxidized from its initial state to a charged state. Then, the reducing agent in the reducing agent reservoir is slowly added to the rebalancing agent reservoir, restoring the rebalancing agent from its charged state to its initial state. In this way, the rebalancing agent acts as a catalyst, transferring electrons provided by the reducing agent to the trivalent chromium ions in the negative electrode reservoir through the rebalancing stack, thereby restoring and rebalancing the electrolyte's state of charge. Figure 3 To demonstrate the effectiveness of the rebalancing device, it was shown that after capacity decay, the capacity can be significantly restored after using the rebalancing device. The reactions that occur during rebalancing are as follows:

[0077] Electrochemical oxidation occurs on the rebalancing agent side of the rebalancing stack:

[0078]

[0079] An electrochemical reduction reaction occurs on the electrolyte side of the rebalancing stack's flow battery:

[0080]

[0081] The chemical reaction of the reducing agent being slowly added to the rebalancing agent storage tank:

[0082]

[0083] As can be seen from the three reaction equations above, (1-oxyradical-2,2,6,6-tetramethylpiperidin-4-yl)trimethylammonium chloride acts as a catalyst throughout the rebalancing process. Its active material remains unchanged before and after the rebalancing reaction, enabling it to transfer reduction electrons provided by formic acid to ferric ions, reducing ferric ions to ferrous ions, thereby achieving rebalancing of the charge state of the positive and negative electrodes of the iron-chromium flow battery. Furthermore, because (1-oxyradical-2,2,6,6-tetramethylpiperidin-4-yl)trimethylammonium chloride has a large volume, it does not easily permeate through the ion-exchange membrane into the electrolyte of the iron-chromium flow battery, effectively avoiding cross-contamination. Simultaneously, the entire rebalancing process does not generate wastewater or waste salts and has no impact on the electrolyte concentration or volume, greatly reducing the maintenance burden and ensuring the long-term stable operation of the iron-chromium flow battery.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An iron-chromium flow battery system, characterized by, include: Iron-chromium redox flow battery main body and rebalancing device; The rebalancing device includes: Rebalancing agent storage tank, used to contain rebalancing agent solution; A reducing agent storage tank for containing a reducing agent, wherein the reducing agent storage tank is connected to a rebalancing agent storage tank; The rebalancing stack is connected via pipelines to the electrolyte tank and the rebalancing agent tank in the main body of the iron-chromium redox flow battery, respectively, where the state of charge shift occurs. And pumps for conveying reducing agent, electrolyte and rebalancing agent respectively.

2. The iron-chromium liquid flow battery system of claim 1, wherein, The main body of the iron-chromium redox flow battery includes: a negative electrode storage tank, a positive electrode storage tank, a stack, and a pump; the negative electrode storage tank is used to contain chromium ion-containing electrolyte; the positive electrode storage tank is used to contain iron ion-containing electrolyte; the stack is used for charging and discharging, and the pump is used for circulating the electrolyte.

3. The iron-chromium liquid flow battery system of claim 1, wherein, The rebalancing stack includes a separation diaphragm, electrodes, bipolar plates, and a flow channel frame.

4. The iron-chromium liquid flow battery system of claim 3, wherein, The separation membrane used in the rebalancing stack is a microporous membrane, anion exchange membrane, cation exchange membrane, or bipolar membrane. And / or, the electrodes used in the rebalancing stack are carbon felt, DSA electrodes, platinum electrodes, or graphite electrodes.

5. A method for rebalancing the electrolyte in an iron-chromium flow battery, characterized in that, The iron-chromium redox flow battery system according to any one of claims 1-4 includes the following steps: (1) When the positive and negative electrodes of the iron-chromium redox flow battery are out of balance, connect the rebalancing stack to the electrolyte storage tank on the side where the state of charge shifts. (2) In the rebalancing stack, the rebalancing agent is oxidized and converted into a charged state, while the excess high-valence metal ions in the iron-chromium redox flow battery body are reduced. (3) Add the reducing agent to the rebalancing agent storage tank, and react chemically with the rebalancing agent in the charged state to reduce the rebalancing agent in the charged state to the initial state; Through the cycle of steps (2) and (3), electrons of the reducing agent are transferred to the iron-chromium redox flow battery body, thereby achieving electrolyte rebalancing.

6. The rebalancing method for the electrolyte of an iron-chromium flow battery according to claim 5, characterized in that, The rebalancing agent includes redox-active substances and solvents; And / or, the reducing agent is one or more of sugars, carboxylic acids, aldehydes and alcohols.

7. The rebalancing method for the electrolyte of an iron-chromium flow battery according to claim 6, characterized in that, The redox active substance is a redox active substance having hindered amine hydroxylamine cyclic structure groups; And / or, the solvent is one or more of hydrochloric acid aqueous solution, sulfuric acid aqueous solution, and phosphoric acid aqueous solution.

8. The method for rebalancing the electrolyte in an iron-chromium flow battery according to claim 7, characterized in that, The redox-active substance containing the hindered amine hydroxylamine cyclic structure group has the structure in formula Y: ； （Y）； In formula Y, the cyclic structure is a 3-membered ring, a 4-membered ring, a 5-membered ring, a 6-membered ring, a 7-membered ring, or an 8-membered ring; the cyclic structure contains one or more of carbon-carbon single bonds, carbon-carbon double bonds, and carbon-carbon triple bonds; R1, R2, R3, and R4 are independently selected from alkyl, cycloalkyl, aryl, and aralkyl groups, respectively.

9. The rebalancing method for the electrolyte of an iron-chromium flow battery according to claim 7, characterized in that, In step (2), an external voltage is applied to the rebalancing stack for driving.

10. An application of the rebalancing method for the electrolyte of an iron-chromium flow battery according to any one of claims 5-9, characterized in that, The method is used to restore online the state of charge imbalance of the positive and negative electrolytes in an iron-chromium flow battery caused by the hydrogen evolution side reaction.

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