Flow battery system and method of recovery thereof

Abstract

This application relates to a flow battery system and a recovery method thereof. The method is used to control the flow battery system to perform N recovery cycles. When the electrolyte needs to be recovered for the i-th cycle, the method includes: closing the valves between the working battery stack and the positive and negative electrolyte storage tanks; starting the recovery battery stack charging and opening the valves between the positive electrolyte storage tank, the positive storage tank, and the recovery battery stack, allowing the positive electrolyte to circulate in the positive electrolyte storage tank and the negative electrode of the recovery battery stack, and the negative electrolyte to circulate in the negative electrolyte storage tank and the positive electrode of the recovery battery stack; wherein, hydroxide ions in the negative electrolyte are converted into oxygen and water on the positive electrode side of the recovery battery stack, and cations are transported across the membrane to the negative electrode side of the recovery battery stack in the form of hydrated ions, converting ferricyanide ions in the positive electrolyte into ferrous cyanide ions; hydroxide ions and ferricyanide ions are accumulated products during the operation of the working battery stack.

Description

Technical Field

[0001] This application relates to the field of flow battery system technology, and in particular to a flow battery system and its recovery method. Background Technology

[0002] With the increasing severity of energy shortages and environmental pollution, the development and application of new energy technologies are attracting more and more attention. Renewable energy storage technologies, with their outstanding advantages such as low cost, excellent safety performance, and good environmental compatibility, are showing broad application prospects in the field of energy storage. Energy storage technologies for renewable energy can ensure the efficient and stable operation of renewable energy power generation connected to the grid. Energy storage technologies are mainly divided into two categories: physical energy storage and chemical energy storage.

[0003] Chemical energy storage systems, represented by flow batteries, have attracted widespread attention in the industry due to their abundant active material resources, high energy density, and low system cost. Unlike conventional batteries, each battery cell in a stack has a much larger capacity. In actual operation, ferricyanide accumulates in the positive electrode electrolyte, leading to increased battery polarization and capacity decay, as well as exacerbating water migration. Summary of the Invention

[0004] Therefore, it is necessary to provide a flow battery system and its recovery method to address the problems mentioned in the background technology, which can at least be free from the limitation of the number of recovery cycles, further improve the battery cycle stability and lifespan, and reduce the later operation and maintenance costs.

[0005] To address the aforementioned technical problems and other issues, according to some embodiments, one aspect of this application provides a recovery method for a flow battery system, the recovery method comprising:

[0006] The flow battery system includes a working stack and a recovery stack, which are respectively connected to the positive electrolyte storage tank and the negative electrolyte storage tank;

[0007] The method is used to control a flow battery system to perform N recovery cycles, wherein when the electrolyte needs to be recovered in the i-th cycle, the method includes:

[0008] Close the solenoid valves between the working stack and the positive and negative electrolyte storage tanks;

[0009] Start charging the recovery stack and open the solenoid valve between the positive electrolyte tank and the recovery stack, so that the positive electrolyte circulates in the positive electrolyte tank and the negative electrode of the recovery stack, and the negative electrolyte circulates in the negative electrolyte tank and the positive electrode of the recovery stack.

[0010] In this process, hydroxide ions in the negative electrode electrolyte are converted into oxygen and water on the positive electrode side of the recovery stack, and cations are transported across the membrane to the negative electrode side of the recovery stack in the form of hydrated ions, converting ferricyanide ions in the positive electrode electrolyte into ferricyanide ions; hydroxide ions and ferricyanide ions are accumulated products during the operation of the working stack.

[0011] In some embodiments, the flow battery system further includes: a first circulation pump and a second circulation pump;

[0012] The inlet of the first circulation pump is connected to the outlet of the negative electrolyte storage tank through a pipeline. A first solenoid valve is installed on the pipeline between the outlet of the first circulation pump and the inlet of the negative electrode of the working stack, and a second solenoid valve is installed on the pipeline between the outlet of the first circulation pump and the inlet of the positive electrode of the recovery stack.

[0013] The inlet of the second circulation pump is connected to the outlet of the positive electrolyte storage tank via a pipeline. A third solenoid valve is installed on the pipeline between the outlet of the second circulation pump and the inlet of the positive electrode of the working stack, and a fourth solenoid valve is installed on the pipeline between the outlet of the second circulation pump and the inlet of the negative electrode of the recovery stack.

[0014] Secondly, this application provides a recovery method for a flow battery system, the flow battery system including a working stack and a recovery stack sharing the same positive electrode electrolyte storage tank, and a positive electrode storage tank connected to the recovery stack; the positive electrode storage tank contains an alkaline liquid;

[0015] The method is used to control a flow battery system to perform N recovery cycles, wherein when the electrolyte needs to be recovered in the i-th cycle, the method includes:

[0016] Shut down the circulation pump connected to the working fuel cell stack, as well as the solenoid valve between them;

[0017] Start charging the recovery stack, and simultaneously turn on the circulation pump, as well as the positive electrolyte storage tank and the solenoid valve between the positive storage tank and the recovery stack, so that the positive electrolyte circulates in the positive electrolyte storage tank and the negative electrode of the recovery stack, and the alkaline liquid circulates in the positive storage tank and the positive electrode of the recovery stack.

[0018] In this process, hydroxide ions in the alkaline liquid are converted into oxygen and water on the positive electrode side of the recovery stack, and cations are transported across the membrane to the negative electrode side of the recovery stack in the form of hydrated ions, converting ferricyanide ions in the positive electrode electrolyte into ferricyanide ions; ferricyanide ions are the accumulated products during the operation of the working stack.

[0019] In some embodiments, the flow battery system includes a first circulation pump and a second circulation pump;

[0020] The inlet of the first circulation pump is connected to the outlet of the negative electrolyte storage tank and the outlet of the positive electrolyte storage tank through a pipeline. The outlet of the first circulation pump is connected to the inlet of the negative electrode of the working stack and the inlet of the positive electrode of the recovery stack through a pipeline.

[0021] The inlet of the second circulation pump is connected to the outlet of the positive electrolyte storage tank via a pipeline, and the outlet of the second circulation pump is connected to the inlet of the negative electrode of the working stack and the inlet of the positive electrode of the recovery stack via a pipeline.

[0022] In some embodiments, the alkaline solution is an aqueous solution of alkali with a hydroxide concentration of 1M-8M.

[0023] In some embodiments, the working stack and the recovery stack include one single cell or two or more single cells connected in series, and the stacking structure of the single cells is the same.

[0024] Thirdly, this application provides a flow battery system, including electrolyte recovery using the recovery method described in any of the above embodiments.

[0025] In some embodiments, when the charging capacity of the working stack is lower than 80% to 95% of the initial capacity, electrolyte recovery is performed after the working stack discharges.

[0026] In some embodiments, the working stack and the recovery stack include one single cell or two or more single cells connected in series, and the stacking structure of the single cells is the same.

[0027] In some embodiments, the stack operation is restored by stepped constant current charging; wherein the current density is 10 mA / cm². 2 -100mA / cm 2 The single-cell charging cutoff voltage is 0.5V-1.0V.

[0028] In some embodiments, the positive and negative electrodes of the working stack and the recovery stack include at least one of graphite bipolar plates, stainless steel bipolar plates, or titanium bipolar plates.

[0029] The diaphragm of the working stack and the recovery stack is at least one of perfluorosulfonic acid membrane, sulfonated polyether ether ketone membrane or polybenzimidazole membrane.

[0030] The flow battery system and recovery method provided in this application have the following unexpected technical effects:

[0031] The flow battery system provided in this application has two methods for connecting the recovery stack. In both methods, the recovery stack shares the positive electrolyte storage tank and circulation pump with the working stack. Only some additional pipelines are needed. When the recovery stack is working, the positive electrolyte of the original working stack can be used as the negative electrolyte of the recovery stack. Through the charging process of the recovery stack, the positive electrolyte gains electrons on its negative electrode side and is reduced to ferrocyanide. At the same time, the negative electrolyte or alkaline solution converts hydroxide ions into oxygen and water on the positive electrode side of the recovery stack.

[0032] The recovery method for this flow battery system not only solves the problems of increased stack polarization and capacity decay caused by the accumulation of ferricyanide in the positive electrode during operation, but also balances the ion concentration and ion strength of the positive and negative electrodes, suppressing water migration. Furthermore, compared to related technologies that restore the positive electrode electrolyte by adding a zinc plate to the recovery stack and using a discharge method, the flow battery system provided in this application can continuously achieve electrolyte recovery without consuming zinc plates, and its recovery capability is not limited by the number of uses. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained from these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the flow battery system provided in Embodiment 1 of this application;

[0035] Figure 2 This is a schematic diagram of the stacked structure of the fuel cell stack;

[0036] Figure 3 This is a schematic diagram illustrating the specific process of the recovery method provided in Embodiment 2 of this application;

[0037] Figure 4 The efficiency curve of the flow battery system obtained using the recovery method provided in Example 2;

[0038] Figure 5 The charging capacity change curve of the flow battery system obtained by using the recovery method provided in Example 2;

[0039] Figure 6 The charge-discharge curves of the flow battery system obtained using the recovery method provided in Example 2 are shown below.

[0040] Figure 7 This is a schematic diagram of the flow battery system provided in Embodiment 3 of this application;

[0041] Figure 8 This is a schematic diagram illustrating the specific process of the recovery method provided in Embodiment 4 of this application;

[0042] Figure 9 The efficiency curve of the flow battery system obtained using the recovery method provided in Example 4;

[0043] Figure 10 The charging capacity change curve of the flow battery system obtained by using the recovery method provided in Example 4;

[0044] Figure 11 The charge-discharge curves of the flow battery system obtained using the recovery method provided in Example 4 are shown below.

[0045] Figure 12 The efficiency curves of the flow battery system provided in the comparative example;

[0046] Figure 13 The charging capacity variation curve of the flow battery system provided in the comparative example;

[0047] Figure 14 The charge-discharge curves of the flow battery system provided in the comparative example are shown.

[0048] Explanation of reference numerals in the attached figures:

[0049] 1. Working electrode stack; 2. Restoration electrode stack; 3. Positive electrode electrolyte storage tank; 4. Negative electrode electrolyte storage tank; 51. First circulation pump; 52. Second circulation pump; 61. First solenoid valve; 62. Second solenoid valve; 63. Third solenoid valve; 64. Fourth solenoid valve; 65. Fifth solenoid valve; 66. Sixth solenoid valve; 7. Positive electrode storage tank. Detailed Implementation

[0050] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0052] When using the terms “including,” “having,” and “comprising” as described herein, another component may be added unless explicitly qualifying terms such as “only,” “consisting of,” etc. are used. Unless otherwise stated, singular terms may include plural forms and should not be construed as having a quantity of one.

[0053] It should be understood that although the terms “first,” “second,” etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, without departing from the scope of this application, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

[0054] In this application, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a direct connection or an indirect connection through an intermediate medium, or they can refer to the internal connection of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0055] The positive and negative electrolytes of an alkaline zinc-iron flow battery have different compositions. The positive electrolyte contains ferrocyanide ions (Fe(CN)6). 4- The electrolyte consists of an alkaline solution containing zinc ions at the cathode and an alkaline solution containing zinc ions at the anode. During charging and discharging, cations are transported across the membrane as hydrated ions. Due to the zinc corrosion side reaction at the anode, the ferricyanide ion conversion at the cathode is incomplete, leading to the accumulation of oxidized ferricyanide ions (Fe(CN)6). 3- Meanwhile, the number of hydrated cations and hydroxides on the negative electrode side gradually increases, eventually leading to an imbalance in the ion concentration and ion strength of the positive and negative electrode electrolytes, which exacerbates water migration and stack polarization.

[0056] Common electrolyte recovery methods are mainly divided into two categories: chemical recovery and electrochemical in-situ recovery. Chemical recovery requires the addition of chemical reducing agents such as ascorbic acid, glucose, and hydrogen peroxide to the electrolyte. These reducing agents consume the alkali in the system, exacerbate water migration, and induce oxygen evolution side reactions. Electrochemical in-situ recovery, on the other hand, is costly and difficult to meet the needs of large-scale and commercial applications. Therefore, developing novel electrolyte recovery methods suitable for alkaline zinc-iron flow battery systems to improve battery operational stability and cycle life is of great significance for promoting their commercial application.

[0057] The following is combined Figures 1 to 14 This application provides a detailed description of the flow battery system and its recovery method.

[0058] Example 1

[0059] Figure 1 This embodiment illustrates a flow battery system. A recovery stack is internally connected to the flow battery system, which includes one working stack, one recovery stack, two storage tanks (a positive electrolyte tank 3 and a negative electrolyte tank 4), two circulation pumps, and four solenoid valves connected by pipelines.

[0060] Specific connection methods are as follows: Figure 1 As shown, the inlet end of the first circulating pump 51 is connected to the outlet end of the negative electrode electrolyte storage tank 4 through a pipe. A first solenoid valve 61 is installed on the pipe between the outlet end and the inlet end of the negative electrode of the working stack 1, and a second solenoid valve 62 is installed on the pipe between the outlet end and the inlet end of the positive electrode of the recovery stack 2.

[0061] The inlet of the second circulation pump 52 is connected to the outlet of the positive electrolyte storage tank 3 via a pipe. A third solenoid valve 63 is installed on the pipe between the outlet and the inlet of the positive electrode of the working stack 1, and a fourth solenoid valve 64 is installed on the pipe between the outlet and the inlet of the negative electrode of the recovery stack 2.

[0062] For example, the working stack 1 and the recovery stack 2 each comprise a single cell or two or more single cells connected in series, with an active area of ​​800 cm². 2 -4000cm 2 Furthermore, the stacking structure of individual cells is identical, and the stacking structure is as follows: Figure 2 As shown, the stack includes a current collector, bipolar plate, electrode frame, electrodes, and diaphragm that are stacked repeatedly n times. Positive and negative end plates and positive and negative insulating plates are respectively provided at both ends of the stack.

[0063] Furthermore, the positive and negative electrodes are at least one of graphite bipolar plates, stainless steel bipolar plates, or titanium bipolar plates; the electrodes are at least one of carbon felt, graphite felt, nickel foam, or titanium foam; and the diaphragm is at least one of perfluorosulfonic acid membrane, sulfonated polyether ether ketone membrane, or polybenzimidazole membrane.

[0064] In the above embodiments, the use of conductive and corrosion-resistant bipolar plates can reduce internal resistance and improve stack stability; high specific surface area electrodes can accelerate the reaction and improve efficiency; selective separators can inhibit the penetration of active materials, reduce self-discharge, and improve battery efficiency and cycle life.

[0065] In this embodiment, both the positive and negative electrodes of the single cell are carbon felt, with an active area of ​​1000 cm². 2 A stack of 10 alkaline zinc-iron flow batteries was assembled using a perfluorosulfonic acid proton exchange membrane as the ion-conducting membrane. The positive electrode electrolyte storage tank 3 contained 60 L of 0.4 mol / L K₄Fe(CN)₆. 4- The positive electrode electrolyte is +2 mol / L NaOH, and the negative electrode electrolyte storage tank 4 contains 60 L of 0.2 mol / L Na2Zn(OH) solution. 4 The negative electrode electrolyte is composed of 1.6 mol / L NaOH and 0.8 mol / L KOH.

[0066] The working stack 1 operates during the normal charging and discharging process of the battery. The charging and discharging strategy is constant power charging and discharging. The charging and discharging power of a single cell is 50-300W, and the charging and discharging power of a multi-cell stack is the range of charging and discharging power of a single cell multiplied by the number of cells in the stack. Charging is subject to both time and voltage cutoffs. Upon reaching any cutoff condition, the stack will switch to the discharging state. The charging cutoff voltage for a single cell is 2.15V. Discharging is subject to voltage cutoff, with a single cell cutoff voltage of 0.8V. A small-power discharge is performed once every 10 charge-discharge cycles, with a single cell discharge power of 10-80W. In this embodiment, the working stack 1 undergoes constant power charging for 2 hours, with a charging power of 625W and a charging cutoff voltage of 21.5V. The discharging power is 625W, and the cutoff voltage is 8V. A small-power discharge is performed once every 10 charge-discharge cycles, with a discharge power of 150W and a cutoff voltage of 8V.

[0067] It should be understood that, in addition to the structure described above, flow battery systems may also include other conventional electrical or mechanical units, such as control units, signal receiving units, and sensor units. Since these units are not the focus of this application, they will not be described in detail here.

[0068] Example 2

[0069] Based on the flow battery system provided in Example 1, this example provides a recovery method with the following specific process: Figure 3 As shown, the method is used to control the flow battery system to perform N recovery cycles, wherein steps S1-S2 are performed when the electrolyte needs to be recovered for the i-th time.

[0070] Specifically, when the working stack 1 is working, the first solenoid valve 61, the third solenoid valve 63, the first circulation pump 51 and the second circulation pump 52 are opened. When the charging capacity drops to 80%-95% of the initial capacity (preferably 90%-95%), after the working stack 1 has finished discharging, the second solenoid valve 62 and the fourth solenoid valve 64 are opened, and the first solenoid valve 61 and the third solenoid valve 63 are closed. At this time, the positive electrolyte of the original working stack 1 is transformed into the negative electrolyte of the recovery stack 2, and the negative electrolyte of the original working stack 1 is transformed into the positive electrolyte of the recovery stack 2.

[0071] Recovery stack 2 employs stepped constant current charging; the current density is 10 mA / cm². 2 -100mA / cm 2 The single-cell charging cutoff voltage is 0.5V-1.0V. In this embodiment, the step current density of the recovery stack 2 is 80mA / cm². 2 40mA / cm 2 20mA / cm 2The cutoff voltages are 1.0V, 0.6V, and 0.6V, respectively. During operation, the oxygen generated at the positive electrode of recovery stack 2 is discharged into the air through a pipeline. Figure 1 As shown, by restoring the charge of fuel cell stack 2, the accumulated Fe(CN)6 is removed. 3- Transformed into Fe(CN)6 4- The positive and negative electrode reactions are as follows:

[0072] Positive electrode: 4OH - -4e - =2H₂O + O₂↑

[0073] Negative electrode: Fe(CN)6 3- +e - =Fe(CN)6 4-

[0074] Figures 4 to 6 The efficiency curve, charging capacity evolution curve, and long-cycle charge-discharge voltage curve of the flow battery system shown in Example 1 are presented respectively after adopting the electrolyte recovery method provided in Example 2. In this example, the working stack 1 operated for 1035 cycles and underwent 10 recovery cycles. The charging capacity decreased from the initial 18.01 Ah to 17.62 Ah, a capacity decay of 2.16%. At the same time, the coulombic efficiency of the working stack 1 remained at 98.26%, the energy efficiency remained at 85.79%, and the water mobility was only 0.7%.

[0075] Example 3

[0076] Compared to Example 1, the main difference in Example 2 lies in the connection method of the restored fuel cell stack 2. The following is a detailed explanation... Figure 7 Example 3 will be further explained.

[0077] Figure 7 Another flow battery system according to this application is shown. In this system, the recovery stack 2 is externally connected to the flow battery system, which includes three storage tanks (a positive electrolyte tank, a negative electrolyte tank, and a positive electrode tank) and six solenoid valves.

[0078] Specific connection methods are as follows: Figure 7 As shown, the inlet of the first circulation pump 51 is connected to the outlet of the negative electrolyte storage tank 4 and the outlet of the positive electrolyte storage tank 7 through a pipeline, and is equipped with a first solenoid valve 61 and a fifth solenoid valve 65 respectively; the outlet of the first circulation pump 51 is connected to the inlet of the negative electrode of the working stack 1 and the inlet of the positive electrode of the recovery stack 2 through a pipeline, and is equipped with a second solenoid valve 62 and a sixth solenoid valve 66 respectively.

[0079] The inlet of the second circulation pump 52 is connected to the outlet of the positive electrolyte storage tank 3 through a pipe. The outlet is connected to the inlet of the negative electrode of the working stack 1 and the inlet of the positive electrode of the recovery stack 2 through a pipe. A third solenoid valve 63 and a fourth solenoid valve 64 are respectively provided.

[0080] The positive electrode storage tank 7 contains an aqueous solution of alkali for restoring the positive electrode electrolyte of the fuel cell stack 2. The alkali used is one or more of sodium hydroxide, potassium hydroxide, or lithium hydroxide, and the hydroxide concentration is 1M-8M, preferably 2M-5M.

[0081] Example 4

[0082] This embodiment provides a recovery method based on the flow battery system provided in Embodiment 4. The specific process is as follows: Figure 8 As shown. The method is used to control the flow battery system to perform N recovery cycles, wherein steps S1-S2 are executed when the electrolyte needs to be recovered for the i-th time.

[0083] Specifically, when the working stack 1 is running, the first solenoid valve 61, the second solenoid valve 62 and the third solenoid valve 63 are opened, and the first circulation pump 51 and the second circulation pump 52 are started. When the charging capacity drops to the threshold (i.e. 90%-95%), the first circulation pump 51 and the second circulation pump 52 are closed first, the first solenoid valve 61, the second solenoid valve 62 and the third solenoid valve 63 are closed, the fourth solenoid valve 64, the fifth solenoid valve 65 and the sixth solenoid valve 66 are opened, and then the first circulation pump 51 and the second circulation pump 52 are started again. At this time, the positive electrolyte of the original working stack 1 is transformed into the negative electrolyte of the recovery stack 2.

[0084] It should be understood that the positive and negative electrode reactions during the restoration of the fuel cell stack operation are the same as in Example 1, and will not be elaborated further here. Figures 9-11 The efficiency curve, charging capacity evolution curve, and long-cycle charge-discharge voltage curve of the flow battery system shown in Example 3 are presented respectively after adopting the recovery method provided in Example 4. In this example, the working stack 1 operated for 1025 cycles and underwent 10 recovery cycles. The charging capacity decreased from the initial 18.06 Ah to 17.94 Ah, a capacity decay of approximately 0.67%. The coulombic efficiency of the working stack 1 was 98.03%, the energy efficiency was 87.42%, and the water mobility was 2.74%.

[0085] Comparative Example 1

[0086] Compared with Examples 1 and 3, Comparative Example 1 did not connect a recovery stack, but the rest of the stack structure, electrolyte composition, and charge / discharge test conditions were the same as in Examples 1 and 3. The efficiency curve, charging capacity evolution curve, and long-cycle charge / discharge voltage curve of the flow battery system in the comparative example are shown below. Figures 12-14As shown in Table 1, the specific performance parameters of the comparative examples, Examples 1 and 3 are compared.

[0087] Table 1. Efficiency, capacity, and water migration rate of the flow battery systems provided in Examples 1, 3, and the comparative examples at different recovery cycles.

[0088]

[0089] As shown in Table 1, the comparative example did not undergo electrolyte recovery and ran for 184 cycles. The charging capacity decreased from the initial 18.1 Ah to 7.85 Ah, a capacity decay of approximately 56.6%. The coulombic efficiency of the battery was 98.32%, the energy efficiency was 86.58%, and the water mobility was 6.2%.

[0090] In the above embodiments, the flow battery system and its recovery method provided in this application, through an internal recovery system and an external recovery system, compared with the control group without electrolyte recovery, after 1035 and 1025 cycles (10 recovery cycles) through electrolyte recovery operation, the capacity decay is only 2.16% and 0.67%, and the water mobility is reduced to 0.7% and 2.74%, respectively. At the same time, the coulombic efficiency and energy efficiency remain stable, demonstrating excellent long-cycle operation performance.

[0091] It effectively solves the problem of increased stack polarization and capacity decay caused by the accumulation of ferricyanide in the positive electrode during the operation of the working stack, balances the concentration and intensity of positive and negative electrode ions, and inhibits water migration; at the same time, the recovery system is not limited by the number of recovery cycles, further improving the battery cycle stability and lifespan, and reducing the later operation and maintenance costs.

[0092] Please note that the above embodiments are for illustrative purposes only and do not imply any limitation on the present invention.

[0093] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0094] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for restoring a flow battery system, characterized in that, The flow battery system includes a working stack and a recovery stack that are respectively connected to the positive electrode electrolyte storage tank and the negative electrode electrolyte storage tank; The method is used to control the flow battery system to perform N recovery cycles, wherein when the electrolyte needs to be recovered during the i-th cycle, the method includes: Close the valves between the working fuel cell stack and the positive electrolyte storage tank and the negative electrolyte storage tank; Start charging the recovery stack and open the valve between the positive electrode electrolyte tank and the positive electrode tank and the recovery stack, so that the positive electrode electrolyte circulates in the positive electrode electrolyte tank and the negative electrode of the recovery stack, and the negative electrode electrolyte circulates in the negative electrode electrolyte tank and the positive electrode of the recovery stack. In this process, hydroxide ions in the negative electrode electrolyte are converted into oxygen and water on the positive electrode side of the recovery stack, and cations are transported across the membrane to the negative electrode side of the recovery stack in the form of hydrated ions, converting ferricyanide ions in the positive electrode electrolyte into ferricyanide ions; the hydroxide ions and ferricyanide ions are accumulated products during the operation of the working stack.

2. The recovery method according to claim 1, characterized in that, The flow battery system also includes: a first circulation pump and a second circulation pump; The inlet of the first circulating pump is connected to the outlet of the negative electrode electrolyte storage tank through a pipe. A first valve is installed on the pipe between the outlet of the first circulating pump and the inlet of the negative electrode of the working stack, and a second valve is installed on the pipe between the outlet of the first circulating pump and the inlet of the positive electrode of the recovery stack. The inlet of the second circulation pump is connected to the outlet of the positive electrolyte storage tank via a pipe. A third valve is installed on the pipe between the outlet of the second circulation pump and the inlet of the positive electrode of the working stack, and a fourth valve is installed on the pipe between the outlet of the second circulation pump and the inlet of the negative electrode of the recovery stack.

3. A method for restoring a flow battery system, characterized in that, The flow battery system includes a working stack and a recovery stack sharing the same positive electrode electrolyte storage tank, as well as a positive electrode storage tank connected to the recovery stack; the positive electrode storage tank contains an alkaline liquid. The method is used to control the flow battery system to perform N recovery cycles, wherein when the electrolyte needs to be recovered during the i-th cycle, the method includes: Close the circulation pump connected to the working fuel cell stack, as well as the valve between them; Start the charging of the recovery stack, and simultaneously turn on the circulation pump, the positive electrolyte storage tank, and the valve between the positive storage tank and the recovery stack, so that the positive electrolyte circulates in the positive electrolyte storage tank and the negative electrode of the recovery stack, and the alkaline liquid circulates in the positive storage tank and the positive electrode of the recovery stack. In this process, hydroxide ions in the alkaline liquid are converted into oxygen and water on the positive electrode side of the recovery stack, and cations are transported across the membrane to the negative electrode side of the recovery stack in the form of hydrated ions, converting ferricyanide ions in the positive electrode electrolyte into ferricyanide ions; the ferricyanide ions are accumulated products during the operation of the working stack.

4. The recovery method according to claim 3, characterized in that, The flow battery system includes a first circulation pump and a second circulation pump; The inlet of the first circulating pump is connected to the outlet of the negative electrolyte storage tank and the outlet of the positive storage tank via a pipeline. The outlet of the first circulating pump is connected to the inlet of the negative electrode of the working stack and the inlet of the positive electrode of the recovery stack via a pipeline. The inlet of the second circulation pump is connected to the outlet of the positive electrolyte storage tank via a pipe, and the outlet of the second circulation pump is connected to the inlet of the negative electrode of the working stack and the inlet of the positive electrode of the recovery stack via a pipe.

5. The recovery method according to claim 4, characterized in that, The alkaline solution is an aqueous solution of alkali with a hydroxide concentration of 1M-8M.

6. A flow battery system, characterized in that, include: The electrolyte is restored using the recovery method described in claim 1 or 2. Alternatively, the electrolyte can be restored using the restoration method described in claim 3 or 4.

7. The flow battery system according to claim 6, characterized in that, When the charging capacity of the working stack is lower than 80% to 95% of the initial capacity, the electrolyte is restored after the working stack has finished discharging.

8. The flow battery system according to claim 6, characterized in that, The working stack and the recovery stack each comprise a single cell or two or more single cells connected in series, and the stacking structure of the single cells is identical.

9. The flow battery system according to claim 6, characterized in that, The recovery of the stack operation is a stepwise constant current charging; wherein the current density is 10 mA / cm 2 - 100 mA / cm 2 , and the single-section charging cutoff voltage is 0.5 V-1.0 V.

10. The flow battery system according to claim 6, characterized in that, The working stack and the recovery stack's positive and negative electrodes include at least one of graphite bipolar plates, stainless steel bipolar plates, or titanium bipolar plates. The diaphragm of the working stack and the recovery stack is at least one of a perfluorosulfonic acid membrane, a sulfonated polyether ether ketone membrane, or a polybenzimidazole membrane.

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