Method and system for rebalancing capacity of iron-chromium flow battery

Abstract

The invention belongs to the technical field of flow batteries, and discloses an iron-chromium flow battery capacity rebalancing method and system, and the method comprises the following steps: a rebalancing solution storage tank, a rebalancing galvanic pile and one of main system electrolyte storage tanks form a set of flow battery system, and the rebalancing solution storage tank is filled with an ammonium chloride solution; the ammonia reaction dissolving tank is filled with a mixed solution of ammonia water and ammonium chloride; and controlling the flow battery system to charge according to requirements, and reducing Fe < 3 + > in the positive electrode electrolyte of the main system or Cr < 3 + > in the negative electrode electrolyte of the main system. The rebalancing method provided by the invention is suitable for engineering application, is simple and convenient to operate, can recover an iron-chromium flow battery capacity system on line, and can realize long-term operation of the battery and efficient utilization of the electrolyte. Waste gas generated by rebalancing is nitrogen which is green, safe and pollution-free and can be directly discharged; no other'three wastes' are generated in the process.

Description

Technical Field

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

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

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

[0004] Therefore, one of the key research and development technologies for iron-chromium flow batteries is to restore the active ion concentrations of the positive and negative electrode electrolytes to their initial states through some methods so that the capacity of the battery system can be restored.

[0005] In the prior art, in the early research of NASA's iron-chromium flow battery system, Fe 3+ -H 2 Rebalance the battery to achieve capacity recovery, but its hydrogen electrode requires the use of Pt or W catalysts, and Pt will penetrate into the negative electrode electrolyte through the ion membrane, thereby contaminating the negative electrode electrolyte. In addition, Pt is relatively expensive and is not suitable for industrial applications; W catalysts have poor stability and will become deactivated after a period of use.

[0006] For example, in the invention patent application with publication number CN105702997A, Fe is reduced by electrolytic reduction through a rebalanced cell. 3+ The positive electrode solution of the rebalanced battery is a positive electrode electrolyte containing active cations, and the negative electrode solution is a positive electrode storage tank of the main system flow battery. However, the cost of the rebalanced solution in this method is high, and each rebalancing requires draining the waste liquid, filling with new liquid, and treating the waste liquid. The labor cost and waste liquid treatment cost are also high.

[0007] For example, the utility model patent with publication number CN217485504U uses a method of reducing Fe by electrolytic reduction through a rebalanced battery. 3+The positive electrode solution of the rebalancing battery is hydrochloric acid, and the negative electrode solution is the positive electrode storage tank of the main system flow battery. However, the rebalancing solution in this method is a controlled drug, which is not easy to purchase and requires corresponding qualifications. It will produce toxic gases such as chlorine. The subsequent amount of waste acid and alkali is large, and the cost of treating the waste liquid is high.

[0008] In summary, the existing methods and devices for rebalancing the capacity of flow batteries have problems such as complex processes and high costs. Therefore, there is an urgent need for a method and system for achieving capacity rebalancing in an efficient, convenient and easy-to-operate manner. Summary of the invention

[0009] In view of the above problems, the present invention provides a capacity rebalancing method and system for an iron-chromium liquid flow battery, which adopts the following technical solutions:

[0010] A method for rebalancing the capacity of an iron-chromium liquid flow battery comprises the following steps: forming a liquid flow battery system through a rebalancing solution storage tank, a rebalancing stack and one of the main system electrolyte storage tanks, wherein the rebalancing solution storage tank is filled with an ammonium chloride solution of a set concentration; the ammonia reaction dissolution tank is filled with a mixed solution of ammonia water and ammonium chloride; controlling the liquid flow battery system to charge according to demand, reducing the Fe in the positive electrode electrolyte of the main system 3+ Or Cr in the negative electrode electrolyte of the main system 3+ During the rebalancing process, the nitrogen and chlorine generated in the rebalancing solution storage tank are discharged into the ammonia reaction dissolution tank; when it is detected that the pH value of the solution in the ammonia reaction dissolution tank is less than the set value, the ammonia in the ammonia cylinder 7 is adjusted to enter the ammonia reaction dissolution tank according to the set flow rate, and the ammonia entering the ammonia reaction dissolution tank reacts with the chlorine generated during the charging process in the rebalancing solution storage tank to generate nitrogen and ammonium chloride; when it is detected that the pH value of the solution in the rebalancing solution storage tank is greater than the set value, the ammonium chloride precipitated in the ammonia reaction dissolution tank is transferred to the rebalancing solution storage tank.

[0011] Furthermore, the method also includes the following steps: the nitrogen in the ammonia reaction and dissolution tank is absorbed by the aqueous solution to filter out the unreacted ammonia and then discharged.

[0012] Furthermore, the rebalancing solution storage tank is a positive electrode electrolyte storage tank for the rebalancing stack, and one of the main system electrolyte storage tanks is a negative electrode electrolyte storage tank for the rebalancing stack.

[0013] Furthermore, the method also includes the following steps: determining the supply rate of ammonia to the ammonia reaction dissolution tank and the generation rate of ammonium chloride in the ammonia reaction dissolution tank according to the capacity of the main system electrolyte storage tank that needs to be replenished and the rate at which chlorine is produced in the rebalancing solution storage tank during the rebalancing process.

[0014] Further, the method further includes the following steps: determining the total amount of ammonia gas required and the total amount of ammonium chloride generated in the ammonia gas reaction dissolution tank according to the capacity of the main system electrolyte storage tank that needs to be supplemented;

[0015] Determine the final concentration of the ammonium chloride generated in the ammonia reaction dissolution tank according to the total amount of ammonium chloride generated in the ammonia reaction dissolution tank and the liquid filling volume in the ammonia reaction dissolution tank;

[0016] The initial concentration of ammonium chloride in the rebalance solution storage tank is determined based on the liquid filling volume in the rebalance solution storage tank and the total amount of ammonia gas required.

[0017] Furthermore, the following steps are included: based on the solubility of ammonium chloride at 20°C, determining the ratio of the capacity of the main system electrolyte storage tank that needs to be replenished to the liquid filling volume in the rebalancing solution storage tank, and the ratio of the capacity of the main system electrolyte storage tank that needs to be replenished to the liquid filling volume in the ammonia reaction dissolution tank.

[0018] The present invention also provides an iron-chromium liquid flow battery capacity rebalancing system, which is used for the iron-chromium liquid flow battery capacity rebalancing method, and comprises a rebalancing solution storage tank, a rebalancing stack, an ammonia reaction dissolution tank, an ammonia gas cylinder, a control unit, a first pH meter, a second pH meter and an ammonium chloride crystal transfer pipeline;

[0019] Wherein, the rebalancing solution storage tank, the rebalancing stack and one of the main system electrolyte storage tanks constitute a set of liquid flow battery system, and the main system electrolyte storage tank includes a main positive electrode electrolyte storage tank and a main negative electrode electrolyte storage tank;

[0020] The gas outlet of the rebalance solution storage tank is connected to the ammonia reaction and dissolution tank through a first gas phase pipeline, and the ammonia reaction and dissolution tank is connected to the ammonia gas cylinder through a second gas phase pipeline. The first pH meter is arranged on the ammonia reaction and dissolution tank and is communicatively connected to the control unit; the second pH meter is arranged on the rebalance solution storage tank and is communicatively connected to the control unit; and both ends of the ammonium chloride crystal transfer pipeline are respectively connected to the ammonia reaction and dissolution tank and the rebalance solution storage tank.

[0021] Furthermore, a valve is provided on the ammonium chloride crystal transfer pipeline, and the valve is communicatively connected with the control unit.

[0022] Furthermore, a flow control device is also provided on the second gas phase pipeline, and the flow control device is communicatively connected with the control unit.

[0023] Furthermore, it also includes a positive electrode solution circulation pump and a negative electrode solution circulation pump;

[0024] Wherein, the circulation of the negative electrode electrolyte is realized between the negative electrode of the rebalanced stack and the main positive electrode electrolyte storage tank or the main negative electrode electrolyte storage tank through the negative electrode solution circulation pump;

[0025] The positive electrode electrolyte is circulated between the positive electrode of the rebalanced stack and the rebalanced solution storage tank through the positive electrode solution circulation pump.

[0026] Furthermore, it also includes an exhaust gas absorption filter tank;

[0027] The gas outlet of the ammonia reaction dissolution tank is connected to the tail gas absorption filter tank through a third gas phase pipeline.

[0028] Furthermore, the tail gas absorption filter tank is filled with an aqueous solution.

[0029] Beneficial effects of the present invention:

[0030] 1. The rebalancing method of the present invention is suitable for engineering applications, is easy to operate, can restore the capacity system of the iron-chromium liquid flow battery online, and can achieve long-term operation of the battery and efficient use of the electrolyte.

[0031] 2. The rebalancing chemical in the present invention is liquid ammonia, and the waste gas generated by the rebalancing process is nitrogen, which is green, safe, pollution-free and can be directly discharged; the process does not produce other "three wastes".

[0032] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 A structural schematic diagram of a capacity rebalancing system for an iron-chromium liquid flow battery according to an embodiment of the present invention is shown.

[0035] In the figure: 1. Main system electrolyte storage tank; 2. Rebalancing solution storage tank; 3. Rebalancing stack; 4. Positive electrode solution circulation pump; 5. Negative electrode solution circulation pump; 6. Ammonia reaction dissolution tank; 7. Ammonia gas cylinder; 8. Tail gas absorption filter tank; 9. First gas phase pipeline; 10. Second gas phase pipeline; 11. Third gas phase pipeline; 12. Control unit; 13. First PH meter; 14. Second PH meter; 15. Ammonium chloride crystal transfer pipeline; 16. Valve; 17. Flow control device. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] It should be noted that the terms "first", "second", etc. in this application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable under appropriate circumstances, so as to describe the embodiments of the present application described here.

[0038] The present invention provides a capacity rebalancing method and system for an iron-chromium liquid flow battery, which is suitable for engineering applications, is easy to operate, and can restore the capacity of the iron-chromium liquid flow battery online without generating waste gas.

[0039] like Figure 1 As shown, a capacity rebalancing system for an iron-chromium liquid flow battery includes a rebalancing solution storage tank 2, a rebalancing stack 3, a cathode solution circulation pump 4, a cathode solution circulation pump 5, an ammonia reaction dissolution tank 6 and an ammonia gas cylinder 7.

[0040] Among them, the rebalancing solution storage tank 2, the rebalancing stack 3 and one of the main system electrolyte storage tanks 1 form a set of liquid flow battery system, and the main system electrolyte storage tank 1 includes a main positive electrode electrolyte storage tank and a main negative electrode electrolyte storage tank. The rebalancing solution storage tank 2 is the positive electrode electrolyte storage tank of the rebalancing stack 3, and one of the main system electrolyte storage tanks 1 is the negative electrode electrolyte storage tank of the rebalancing stack 3.

[0041] For example, the rebalance solution storage tank 2 is filled with an ammonium chloride solution of a set concentration, and the solvent thereof may be hydrochloric acid, and / or a compound / mixture containing iron ions and chromium ions.

[0042] The negative electrode electrolyte is circulated between the negative electrode of the rebalancing stack 3 and the main positive electrode electrolyte storage tank or the main negative electrode electrolyte storage tank through the negative electrode solution circulation pump 5. For example, the negative electrode inlet of the rebalancing stack 3 is connected to the outlet of the negative electrode solution circulation pump 5, the inlet of the negative electrode solution circulation pump 5 is connected to the electrolyte outlet of the main positive electrode electrolyte storage tank or the main negative electrode electrolyte storage tank, and the negative electrode outlet of the rebalancing stack 3 is connected to the electrolyte inlet of the main positive electrode electrolyte storage tank or the main negative electrode electrolyte storage tank.

[0043] The positive electrode electrolyte is circulated between the positive electrode of the rebalancing stack 3 and the rebalancing solution storage tank 2 through the positive electrode solution circulation pump 4. For example, the positive electrode inlet of the rebalancing stack 3 is connected to the outlet of the positive electrode solution circulation pump 4, the inlet of the positive electrode solution circulation pump 4 is connected to the electrolyte outlet of the rebalancing solution storage tank 2, and the positive electrode outlet of the rebalancing stack 3 is connected to the electrolyte inlet of the rebalancing solution storage tank 2.

[0044] The gas outlet of the rebalance solution storage tank 2 is connected to the ammonia reaction and dissolution tank 6 through the first gas phase pipeline 9, and the ammonia reaction and dissolution tank 6 is connected to the ammonia gas cylinder 7 through the second gas phase pipeline 10, wherein the ammonia reaction and dissolution tank 6 is filled with a mixed solution of ammonia water and ammonium chloride.

[0045] For example, the iron-chromium liquid flow battery capacity rebalancing system further includes a control unit 12 , a first pH meter 13 , a second pH meter 14 and an ammonium chloride crystal transfer pipeline 15 .

[0046] Among them, the first pH meter 13 is arranged on the ammonia reaction and dissolution tank 6, and is connected to the control unit 12 for communication, and the first pH meter 13 is used to send the measured pH value of the solution in the ammonia reaction and dissolution tank 6 to the control unit 12. The second pH meter 14 is arranged on the rebalance solution storage tank 2, and is connected to the control unit 12 for communication, and the second pH meter 14 is used to send the measured pH value of the solution in the rebalance solution storage tank 2 to the control unit 12. Both ends of the ammonium chloride crystal transfer pipeline 15 are connected to the ammonia reaction and dissolution tank 6 and the rebalance solution storage tank 2, respectively.

[0047] For example, a valve 16 is also provided on the ammonium chloride crystal transfer pipeline 15 , and the valve 16 is communicatively connected with the control unit 12 , and the control unit 12 is used to control the opening and closing of the valve 16 .

[0048] A flow control device 17 is also provided on the second gas phase pipeline 10 . The flow control device 17 is in communication connection with the control unit 12 . The control unit 12 is used for controlling the flow of ammonia entering the ammonia reaction and dissolution tank 6 through the flow control device 17 .

[0049] For example, the iron-chromium liquid flow battery capacity rebalancing system also includes a tail gas absorption filter tank 8, which is filled with an aqueous solution. The gas outlet of the ammonia reaction and dissolution tank 6 is connected to the tail gas absorption filter tank 8 through a third gas phase pipeline 11. The tail gas absorption filter tank 8 is used to absorb the unreacted ammonia in the ammonia reaction and dissolution tank 6.

[0050] Based on the above-mentioned iron-chromium liquid flow battery capacity rebalancing system, the present invention also provides an iron-chromium liquid flow battery capacity rebalancing method, comprising the following steps: forming a liquid flow battery system through a rebalancing solution storage tank 2, a rebalancing stack 3 and one of the main system electrolyte storage tanks 1; controlling the liquid flow battery system to charge according to demand, reducing the Fe in the positive electrode electrolyte of the main system 3+ Or Cr in the negative electrode electrolyte of the main system 3+ , as follows:

[0051] S1. When the rebalancing solution storage tank 2, the main cathode electrolyte storage tank, and the rebalancing stack 3 form a liquid flow battery, the battery is automatically charged continuously or intermittently according to the demand setting to restore the Fe 3+ , thereby realizing the recovery of the electrolyte capacity of the main system, extending the battery life and ensuring the battery performance.

[0052] Among them, the rebalancing solution storage tank 2 is filled with an ammonium chloride solution of a set concentration, the solvent of which can be hydrochloric acid, and / or a compound / mixture containing iron ions and chromium ions. The reaction occurring during the charging process of the rebalancing stack 3 is as follows:

[0053] Positive electrode: 2NH 4 Cl-8e - =N 2 +Cl 2 +8H +

[0054] Negative electrode: Fe 3+ +e - =Fe 2+

[0055] S11, during the rebalancing process, the nitrogen and chlorine generated in the rebalancing solution storage tank 2 are discharged into the ammonia reaction dissolution tank 6 through the first gas phase pipeline 9.

[0056] S12, when the control unit 12 detects through the first pH measuring instrument 13 that the pH value of the solution in the ammonia reaction and dissolution tank 6 is less than the set value, the flow control device 17 is controlled to adjust the ammonia in the ammonia cylinder 7 to automatically enter the ammonia reaction and dissolution tank 6 continuously or intermittently according to the set flow rate, and the ammonia entering the ammonia reaction and dissolution tank 6 reacts with the chlorine generated during the charging process in the rebalance solution storage tank 2 to generate nitrogen and ammonium chloride, and the reaction equation is as follows:

[0057] 8NH 3 +3Cl 2 =N 2 +6NH 4 cl.

[0058] S13, the nitrogen in the ammonia reaction dissolution tank 6 is discharged into the tail gas absorption filter tank 8 through the third gas phase pipeline 11, and is filtered and absorbed by the aqueous solution to remove the ammonia that may not react completely, and then discharged.

[0059] S14. As the reaction proceeds, the concentration of ammonium chloride in the rebalancing solution storage tank 2 gradually decreases, and the concentration of ammonium chloride in the ammonia reaction and dissolution tank 6 gradually increases to supersaturation and precipitation; when the control unit 12 detects through the second pH measuring instrument 14 that the pH value of the solution in the rebalancing solution storage tank 2 is greater than the set value, the valve 16 on the ammonium chloride crystal transfer pipeline 15 is controlled to open, and the ammonium chloride crystal transfer pipeline 15 transfers the ammonium chloride precipitated in the ammonia reaction and dissolution tank 6 to the rebalancing solution storage tank 2, thereby realizing the recycling of ammonium chloride.

[0060] S2, when the rebalancing solution storage tank 2, the main negative electrode electrolyte storage tank, and the rebalancing stack 3 form a liquid flow battery, the battery is automatically charged continuously or intermittently according to the demand setting to restore the Cr in the negative electrode electrolyte of the main system. 3+ , thereby restoring the electrolyte capacity of the main system, extending the battery life and ensuring battery performance.

[0061] The rebalancing solution storage tank 2 is filled with an ammonium chloride solution of a set concentration, the solvent of which may be hydrochloric acid, and / or a compound / mixture containing iron ions and chromium ions. The reactions occurring during the charging process of the rebalancing stack 3 are as follows:

[0062] Positive electrode: 2NH 4 Cl-8e - =N 2 +cl 2 +8Cr +

[0063] Negative electrode: Cr 3+ +e - =Cr 2+

[0064] S21, during the rebalancing process, the nitrogen and chlorine generated in the rebalancing solution storage tank 2 are discharged into the ammonia reaction dissolution tank 6 through the first gas phase pipeline 9.

[0065] S22, when the control unit 12 detects through the first pH measuring instrument 13 that the pH value of the solution in the ammonia reaction and dissolution tank 6 is less than the set value, the flow control device 17 is controlled to adjust the ammonia in the ammonia cylinder 7 to automatically enter the ammonia reaction and dissolution tank 6 continuously or intermittently according to the set flow rate, and the ammonia entering the ammonia reaction and dissolution tank 6 reacts with the chlorine generated during the charging process in the rebalance solution storage tank 2 to generate nitrogen and ammonium chloride, and the reaction equation is as follows:

[0066] 8NH 3 +3Cl 2 =N 2 +6NH 4 Cl.

[0067] S23, the nitrogen in the ammonia reaction dissolution tank 6 is discharged into the tail gas absorption filter tank 8 through the third gas phase pipeline 11, and the ammonia that may not react completely is absorbed by the aqueous solution and then discharged.

[0068] S24. As the reaction proceeds, the concentration of ammonium chloride in the rebalancing solution storage tank 2 gradually decreases, and the concentration of ammonium chloride in the ammonia reaction and dissolution tank 6 gradually increases to supersaturation and precipitation; when the control unit 12 detects through the second pH measuring instrument 14 that the pH value of the solution in the rebalancing solution storage tank 2 is greater than the set value, the valve 16 on the ammonium chloride crystal transfer pipeline 15 is controlled to open, and the ammonium chloride crystal transfer pipeline 15 transfers the ammonium chloride precipitated in the ammonia reaction and dissolution tank 6 to the rebalancing solution storage tank 2, thereby realizing the recycling of ammonium chloride.

[0069] S3. Determine the supply rate of ammonia to the ammonia reaction and dissolution tank 6 and the generation rate of ammonium chloride in the ammonia reaction and dissolution tank 6 according to the capacity of the main system electrolyte storage tank 1 that needs to be replenished and the rate at which the rebalancing solution storage tank 2 produces chlorine during the rebalancing process.

[0070] For example, (1) the capacity of the main system electrolyte storage tank 1 that needs to be replenished after running for a period of time is 1000aAh; the rebalancing solution storage tank 2 is a mixed solution of ammonium chloride and hydrochloric acid with a set concentration, and the rate of chlorine generation during the rebalancing process is bmol / h.

[0071] It is necessary to control the supply rate of ammonia from the liquid ammonia cylinder to the ammonia reaction and dissolution tank 6 to be at least 8 / 3b mol / h through the flow control device 17.

[0072] Then the generation rate of ammonium chloride in the ammonia reaction dissolution tank 6 is 2b mol / h.

[0073] S4. Determine the generation rate of ammonium chloride per unit volume of the ammonia reaction and dissolution tank 6 according to the liquid filling volume in the ammonia reaction and dissolution tank 6 and the generation rate of ammonium chloride in the ammonia reaction and dissolution tank 6.

[0074] If the liquid filling volume in the ammonia reaction and dissolution tank 6 is c L, the generation rate of ammonium chloride per unit volume of the ammonia reaction and dissolution tank 6 is 2b / c mol / L / h.

[0075] S5. Determine the consumption rate of ammonium chloride in the rebalancing solution storage tank 2 according to the liquid filling volume in the rebalancing solution storage tank 2 and the generation rate of ammonium chloride in the ammonia reaction dissolution tank 6.

[0076] For example, if the liquid filling volume in the rebalancing solution storage tank 2 is d L, the consumption rate of ammonium chloride in the rebalancing solution storage tank 2 is 2b / d mol / L / h.

[0077] S6. Determine the total amount of ammonia substance required and the total amount of ammonium chloride generated in the ammonia reaction and dissolution tank 6 according to the capacity that needs to be replenished in the main system electrolyte storage tank 1, and determine the final concentration of the ammonium chloride generated in the ammonia reaction and dissolution tank 6 according to the total amount of ammonium chloride generated in the ammonia reaction and dissolution tank 6 and the liquid filling volume in the ammonia reaction and dissolution tank 6; determine the initial concentration of ammonium chloride in the rebalancing solution storage tank 2 according to the liquid filling volume in the rebalancing solution storage tank 2 and the total amount of ammonia substance required.

[0078] For example, the total amount of ammonia required to supplement the main system with a capacity of 1000aAh is 12.44a mol, the total amount of ammonium chloride generated in the ammonia reaction dissolution tank 6 is 9.33a mol, and the final concentration of the generated ammonium chloride is 9.33a / c mol / L; the total amount of ammonium chloride consumed in the rebalance solution storage tank 2 is 9.33a mol, and the required initial concentration of ammonium chloride is at least 9.33a / d mol / L.

[0079] S7. According to the solubility of ammonium chloride at room temperature (20°C), determine the ratio of the capacity of the main system electrolyte storage tank 1 that needs to be replenished to the liquid filling volume in the rebalancing solution storage tank 2, and the ratio of the capacity of the main system electrolyte storage tank 1 that needs to be replenished to the liquid filling volume in the ammonia reaction dissolution tank 6.

[0080] For example, the solubility of ammonium chloride at room temperature (20°C) is 37.2 g / 100 g water, i.e. 6.95 mol / L, so it is determined that 9.33a / d<6.95 and 9.33a / c>6.95.

[0081] After the rebalancing is completed, the ammonium chloride crystals in the ammonia reaction dissolution tank 6 are transferred to the rebalancing solution storage tank 2 for use in the next rebalancing.

[0082] Based on the above parameters, the specific results of the rebalancing test are shown in Table 1:

[0083] Table 1

[0084] Working conditions Capacity recovery rate / % Before rebalancing 100 Rebalance - 1 94.30 Rebalance - 2 93.74 Rebalance - 3 95.35

[0085] The battery capacity rebalancing method and system provided by the present invention are suitable for commercial liquid flow battery systems, can be widely promoted and applied in the fields of electrochemical energy storage technology research, engineering application of energy storage technology, etc., and can automatically restore the capacity system of iron-chromium liquid flow battery online. The rebalancing solution in the present invention is liquid ammonia, and the waste gas generated by the rebalancing process is nitrogen, which is green, safe, pollution-free and can be directly discharged; the process does not generate other "three wastes".

[0086] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for rebalancing the capacity of an iron-chromium flow battery, characterized in that: The following steps are involved: A liquid flow battery system is formed by a rebalancing solution storage tank, a rebalancing stack and one of the main system electrolyte storage tanks. The rebalancing solution storage tank is filled with an ammonium chloride solution of a set concentration; the ammonia reaction dissolution tank is filled with a mixed solution of ammonia water and ammonium chloride; Control the flow battery system to charge according to demand and restore the Fe in the positive electrode electrolyte of the main system 3+ Or Cr in the negative electrode electrolyte of the main system 3+ ; During the rebalancing process, the nitrogen and chlorine generated in the rebalancing solution storage tank are discharged into the ammonia reaction dissolution tank; When it is detected that the pH value of the solution in the ammonia reaction and dissolution tank is less than the set value, the ammonia in the ammonia gas cylinder 7 is adjusted to enter the ammonia reaction and dissolution tank according to the set flow rate, and the ammonia entering the ammonia reaction and dissolution tank reacts with the chlorine generated during the charging process in the rebalance solution storage tank to generate nitrogen and ammonium chloride; When it is detected that the pH value of the solution in the rebalance solution storage tank is greater than the set value, the ammonium chloride precipitated in the ammonia reaction dissolution tank is transferred to the rebalance solution storage tank.

2. The method for rebalancing the capacity of an iron-chromium flow battery according to claim 1, characterized in that: The following steps are also included: The nitrogen in the ammonia reaction dissolution tank is absorbed by the aqueous solution to filter out the unreacted ammonia and then discharged.

3. The method for rebalancing the capacity of an iron-chromium flow battery according to claim 1, characterized in that: The rebalancing solution storage tank is the positive electrode electrolyte storage tank of the rebalancing stack, and one of the main system electrolyte storage tanks is the negative electrode electrolyte storage tank of the rebalancing stack.

4. The method for rebalancing the capacity of an iron-chromium flow battery according to any one of claims 1 to 3, characterized in that: The following steps are also included: The supply rate of ammonia to the ammonia reaction dissolution tank and the generation rate of ammonium chloride in the ammonia reaction dissolution tank are determined based on the capacity of the main system electrolyte storage tank that needs to be replenished and the rate at which chlorine is produced in the rebalancing solution storage tank during the rebalancing process.

5. The method for rebalancing the capacity of an iron-chromium flow battery according to claim 4, characterized in that: The following steps are also included: According to the capacity of the main system electrolyte storage tank that needs to be replenished, determine the total amount of ammonia substance required and the total amount of ammonium chloride generated in the ammonia reaction dissolution tank; Determine the final concentration of the ammonium chloride generated in the ammonia reaction dissolution tank according to the total amount of ammonium chloride generated in the ammonia reaction dissolution tank and the liquid filling volume in the ammonia reaction dissolution tank; The initial concentration of ammonium chloride in the rebalance solution storage tank is determined based on the liquid filling volume in the rebalance solution storage tank and the total amount of ammonia gas required.

6. The method for rebalancing the capacity of an iron-chromium flow battery according to claim 5, characterized in that: The following steps are also included: Based on the solubility of ammonium chloride at 20°C, determine the ratio of the capacity of the main system electrolyte storage tank that needs to be replenished to the liquid filling volume in the rebalancing solution storage tank, as well as the ratio of the capacity of the main system electrolyte storage tank that needs to be replenished to the liquid filling volume in the ammonia reaction dissolution tank.

7. An iron-chromium liquid flow battery capacity rebalancing system, characterized in that: The method for rebalancing the capacity of an iron-chromium flow battery according to any one of claims 1 to 6 comprises a rebalancing solution storage tank, a rebalancing stack, an ammonia reaction dissolution tank, an ammonia gas cylinder, a control unit, a first pH meter, a second pH meter and an ammonium chloride crystal transfer pipeline; Wherein, the rebalancing solution storage tank, the rebalancing stack and one of the main system electrolyte storage tanks constitute a set of liquid flow battery system, and the main system electrolyte storage tank includes a main positive electrode electrolyte storage tank and a main negative electrode electrolyte storage tank; The gas outlet of the rebalance solution storage tank is connected to the ammonia reaction and dissolution tank through a first gas phase pipeline, and the ammonia reaction and dissolution tank is connected to the ammonia gas cylinder through a second gas phase pipeline. The first pH meter is arranged on the ammonia reaction and dissolution tank and is communicatively connected to the control unit; the second pH meter is arranged on the rebalance solution storage tank and is communicatively connected to the control unit; and both ends of the ammonium chloride crystal transfer pipeline are respectively connected to the ammonia reaction and dissolution tank and the rebalance solution storage tank.

8. The iron-chromium liquid flow battery capacity rebalancing system according to claim 7, characterized in that: The ammonium chloride crystal transfer pipeline is also provided with a valve, and the valve is communicatively connected with the control unit.

9. The iron-chromium liquid flow battery capacity rebalancing system according to claim 7, characterized in that: The second gas phase pipeline is also provided with a flow control device, and the flow control device is communicatively connected with the control unit.

10. The iron-chromium liquid flow battery capacity rebalancing system according to any one of claims 7 to 9, characterized in that: Also includes a positive electrode solution circulation pump and a negative electrode solution circulation pump; Wherein, the circulation of the negative electrode electrolyte is realized between the negative electrode of the rebalanced stack and the main positive electrode electrolyte storage tank or the main negative electrode electrolyte storage tank through the negative electrode solution circulation pump; The positive electrode electrolyte is circulated between the positive electrode of the rebalanced stack and the rebalanced solution storage tank through the positive electrode solution circulation pump.

11. The iron-chromium liquid flow battery capacity rebalancing system according to any one of claims 7 to 9, characterized in that: It also includes an exhaust gas absorption filter tank; The gas outlet of the ammonia reaction dissolution tank is connected to the tail gas absorption filter tank through a third gas phase pipeline.

12. The iron-chromium liquid flow battery capacity rebalancing system according to claim 11, characterized in that: The tail gas absorption filter tank is filled with an aqueous solution.

Images