Flow battery system and balancing method

Abstract

The invention belongs to the technical field of flow batteries, and provides a flow battery system and a balancing method, and the flow battery system comprises a charging and discharging unit which comprises a negative electrode electrolyte storage tank, a first electric pile and a positive electrode electrolyte storage tank. And the composite reactor floats at the waterline position of the positive electrode electrolyte storage tank and comprises a gas diffusion layer, a second ion exchange membrane, a capillary action layer and an electrolyte transport layer which are sequentially stacked, and the gas diffusion layer is higher than the waterline position of the positive electrode electrolyte storage tank. By adopting the flow battery system with the composite reactor, the charge balance of the electrolyte can be recovered through the oxidation-reduction reaction, the electrolyte chemical reduction efficiency and the electrolyte balance efficiency of the flow battery system are improved, the positive electrode electrolyte and the negative electrode electrolyte of the flow battery can be ensured to be completely recovered to the initial state, and the service life of the flow battery is prolonged. And the power consumption and the cost for recovering the performance and the capacity of the flow battery system are greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid flow batteries, and in particular relates to a liquid flow battery system and a balancing method. Background Art

[0002] Liquid flow batteries achieve the mutual conversion of electrical energy and chemical energy through reversible redox reactions (i.e. reversible changes in valence) of active substances in the positive and negative electrolyte solutions. During charging, an oxidation reaction occurs at the positive electrode to increase the valence of the active substance, and a reduction reaction occurs at the negative electrode to reduce the valence of the active substance. The discharge process is the opposite. Unlike general solid-state batteries, the positive and negative electrolyte solutions of liquid flow batteries are stored in the positive and negative electrode storage tanks outside the battery, respectively, and are transported to the inside of the battery for reaction through pumps and pipelines.

[0003] In a flow battery stack, electrons flow between the positive and negative electrodes in an external circuit, positive and negative ions flow inside the stack, and electrochemical redox reactions occur. The electrochemical reactions and energy storage of active materials in the positive half-cell or negative half-cell of any battery unit can only occur simultaneously. However, electrochemical side reactions will inevitably occur under normal operating conditions of flow batteries. Side reactions will irreversibly consume electrons, resulting in an imbalance in the charge state of the positive and negative electrolytes (charge imbalance for short), and ultimately leading to an imbalance in the capacity of the positive and negative electrodes and a reduction in capacity. Since flow batteries usually control the charging potential not to exceed the limit, and due to the extremely slow electrochemical kinetics of the oxygen evolution reaction and the extremely small oxygen evolution side reaction, the main side reaction of aqueous flow batteries is hydrogen evolution, which is also the main cause of charge imbalance and capacity imbalance in flow batteries. Summary of the invention

[0004] In view of the problems in the background technology, the present invention provides a liquid flow battery system and a balancing method.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A liquid flow battery system, comprising:

[0007] A charge-discharge unit, comprising a negative electrode electrolyte storage tank, a first battery stack and a positive electrode electrolyte storage tank; both ends of the negative electrode side of the first battery stack are connected to the negative electrode electrolyte storage tank through a pipeline, and both ends of the positive electrode side are connected to the positive electrode electrolyte storage tank through a pipeline;

[0008] A gas phase connecting tube is connected between the top of the negative electrode electrolyte storage tank and the top of the positive electrode electrolyte storage tank; a liquid phase connecting tube is connected between one side of the negative electrode electrolyte storage tank and the side of the positive electrode electrolyte storage tank; an electrolyte mixing tube is connected between the other side of the negative electrode electrolyte storage tank and the other side of the positive electrode electrolyte storage tank;

[0009] A composite reactor, floating at the waterline of the cathode electrolyte storage tank, comprising a gas diffusion layer, a second ion exchange membrane, a capillary action layer and an electrolyte transport layer stacked in sequence, wherein the gas diffusion layer is higher than the waterline of the cathode electrolyte storage tank;

[0010] A purification unit, connected to the charge and discharge unit, comprising a second battery stack and a cleaning agent storage tank; both ends of the negative electrode side of the second battery stack are connected to the electrolyte storage tank through a pipeline, and both ends of the positive electrode side are connected to the cleaning agent storage tank through a pipeline;

[0011] The gas absorption unit is connected to the purification unit and comprises an alkali liquid tank, wherein the alkali liquid tank is connected to the cleaning agent storage tank through a pipeline.

[0012] Preferably, the first battery stack comprises:

[0013] A first ion exchange membrane, with a first negative electrode and a first positive electrode respectively mounted on two sides;

[0014] A first negative electrode current collector plate is mounted on a surface of the first negative electrode away from the first ion exchange membrane;

[0015] The first positive current collecting plate is mounted on a surface of the first positive electrode away from the first ion exchange membrane.

[0016] Preferably, in the charge and discharge unit:

[0017] A first negative electrode liquid inlet pipe is connected between the bottom outlet of the negative electrode electrolyte storage tank and one end of the first negative electrode; the first negative electrode liquid inlet pipe is sequentially provided with a first electrolyte pump and a first heat exchanger along the electrolyte flow direction;

[0018] A first negative electrode liquid outlet pipe is connected between the other end of the first negative electrode and the top inlet of the negative electrode electrolyte storage tank.

[0019] Preferably, in the charge and discharge unit:

[0020] A first positive electrode liquid inlet pipe is connected between the bottom outlet of the positive electrode electrolyte storage tank and one end of the first positive electrode, and the first positive electrode liquid inlet pipe is sequentially provided with a second electrolyte pump and a second heat exchanger along the electrolyte flow direction;

[0021] The other end of the first positive electrode is connected to a first positive electrode liquid outlet pipe, one end of the first positive electrode liquid outlet pipe is connected to a side inlet of a positive electrode electrolyte storage tank, and a three-way valve is installed on the first positive electrode liquid outlet pipe.

[0022] Preferably, in the charge and discharge unit:

[0023] A first pressure gauge is installed on the top of the negative electrode electrolyte storage tank;

[0024] The side of the negative electrode electrolyte storage tank is also connected to a pressure relief pipe, the pressure relief pipe is higher than the waterline position and is installed with a first valve;

[0025] The side of the negative electrode electrolyte tank is also connected to a nitrogen bottle through a pipeline;

[0026] A second pressure gauge is installed on the top of the positive electrolyte storage tank;

[0027] An exhaust fan is installed on the inner wall of the positive electrode electrolyte storage tank, and the exhaust fan faces the gas diffusion layer.

[0028] Preferably, in the charge and discharge unit:

[0029] Along the flow direction of the electrolyte, the electrolyte mixing tube is sequentially installed with a first delivery pump and a second valve;

[0030] A third valve is installed on the gas phase connecting pipe;

[0031] A fourth valve is installed on the liquid phase communication pipe.

[0032] Preferably, a fixing member and a stacked upper floating plate and a lower floating plate are also provided in the composite reactor;

[0033] The upper floating plate is located on the periphery of the gas diffusion layer and is used to clamp the gas diffusion layer and float on the waterline position of the positive electrode electrolyte storage tank;

[0034] The lower floating plate is located on the peripheral side of the capillary action layer, and is used to clamp the capillary action layer and float at the waterline position of the positive electrode electrolyte storage tank;

[0035] The fixing member is used to connect the upper floating plate, the lower floating plate and the electrolyte transport layer.

[0036] Preferably, in the composite reactor:

[0037] The base of the gas diffusion layer is carbon felt or graphite felt, and is heat treated in air at 400-500° C. for 1-24 hours for activation;

[0038] The substrate is coated with a layer of catalyst, and the catalyst includes Pt, Ru, Ir, PtRu, and RuIr;

[0039] The substrate of the capillary action layer is carbon felt or graphite felt, and is heat-treated in air at 400-500° C. for 1-24 hours for activation;

[0040] The substrate of the electrolyte transport layer is carbon felt or graphite felt, and is activated by heat treatment in air at 400-500° C. for 1-24 hours.

[0041] Preferably, the second battery stack comprises:

[0042] The third ion exchange membrane has a second negative electrode and a second positive electrode mounted on two sides thereof;

[0043] A second negative electrode current collector plate is mounted on a surface of the second negative electrode away from the third ion exchange membrane;

[0044] The second positive electrode current collecting plate is mounted on a surface of the second positive electrode away from the third ion exchange membrane.

[0045] Preferably, in the purification unit:

[0046] One end of the second negative electrode is connected to a second negative electrode liquid inlet pipe, and the other end is connected to a second negative electrode liquid outlet pipe;

[0047] Along the electrolyte flow direction, the second negative electrode liquid inlet pipe starts from the three-way valve and is sequentially installed with a filter and a second delivery pump;

[0048] Along the electrolyte flow direction, one end of the second negative electrode liquid outlet pipe away from the second battery stack is connected to the bottom inlet of the positive electrode electrolyte storage tank;

[0049] Along the electrolyte flow direction, a second positive electrode liquid inlet pipe is connected between the bottom outlet of the cleaning agent storage tank and one end of the second positive electrode, and a third delivery pump is installed on the second positive electrode liquid inlet pipe;

[0050] Along the electrolyte flow direction, a second positive electrode liquid outlet pipe is connected between the other end of the second positive electrode and the top inlet of the cleaning agent storage tank;

[0051] A heater is installed at the lower section of the cleaning agent storage tank;

[0052] A cleaning agent feed port is arranged at the bottom of the cleaning agent storage tank, and a fifth valve is installed on the pipeline of the cleaning agent feed port.

[0053] Preferably, in the gas absorption unit:

[0054] A cleaning agent product discharge pipe is connected between a top inlet of the alkali liquid tank and a top outlet of the cleaning agent storage tank;

[0055] The top of the alkali liquid tank is also provided with an external exhaust pipe;

[0056] A circulation pipe is connected between the bottom outlet of the alkali liquid tank and another top inlet of the alkali liquid tank, and a fourth delivery pump is installed on the circulation pipe.

[0057] Preferably, it also includes a battery control unit;

[0058] The battery control unit comprises:

[0059] a first charging power source, the positive electrode of which is connected to the first positive current collecting plate, and the negative electrode of which is connected to the first negative current collecting plate;

[0060] a second charging power source, the positive electrode of which is connected to the second positive electrode current collecting plate, and the negative electrode of which is connected to the second negative electrode current collecting plate;

[0061] A load connected in parallel with the first charging power source;

[0062] The battery control unit is connected to the first charging power source and the second charging power source respectively, and is used to control the working states of the first charging power source and the second charging power source.

[0063] A balancing method, applied to the above-mentioned liquid flow battery system, comprises the following steps:

[0064] Charging and discharging step: performing several charging and discharging cycles through the charging and discharging unit until the storage capacity of the flow battery system is reduced to a target value, and then stopping the charging and discharging cycle of the charging and discharging unit;

[0065] Reduction step: After the charge and discharge step, the hydrogen released during the charge and discharge cycle is oxidized to balance the charge of the electrolyte until the storage capacity of the flow battery system is restored to 100%;

[0066] Purification step: After the reduction step, the catalyst in the electrolyte is removed by a purification unit;

[0067] Absorption step: when performing the purification step, the acid gas generated by the purification unit is absorbed by the gas absorption unit;

[0068] Mixing step: After the purification step is completed, the gas phase connecting tube and the electrolyte mixing tube are opened to mix the electrolytes in the negative electrode electrolyte storage tank and the positive electrode electrolyte storage tank, and to balance the liquid levels.

[0069] Preferably, performing several charge and discharge cycles by the charge and discharge unit until the storage capacity of the flow battery system decreases to a target value, and then stopping the charge and discharge cycle of the charge and discharge unit, comprises the following steps:

[0070] To perform a charge and discharge cycle:

[0071] During charging, the electrolyte in the negative electrode electrolyte storage tank enters the first battery stack to undergo a reduction reaction and a hydrogen evolution side reaction, obtaining a mixed electrolyte of i-valent negative electrode metal ions and j-valent negative electrode metal ions and hydrogen and returning to the negative electrode electrolyte storage tank, j>i; at the same time, the electrolyte in the positive electrode electrolyte storage tank enters the first battery stack to undergo an oxidation reaction, obtaining an electrolyte of m-valent positive electrode metal ions and returning to the positive electrode electrolyte storage tank, m>n;

[0072] During discharge, the electrolyte in the negative electrode electrolyte storage tank enters the first battery stack to undergo an oxidation reaction, obtaining an electrolyte of j-valent negative electrode metal ions and returning to the negative electrode electrolyte storage tank; at the same time, the electrolyte in the positive electrode electrolyte storage tank enters the first battery stack to undergo a reduction reaction, obtaining a mixed electrolyte of n-valent positive electrode metal ions and m-valent positive electrode metal ions and returning to the positive electrode electrolyte storage tank, and a charge and discharge cycle ends;

[0073] After a charge and discharge cycle is completed, it is determined whether the content of the n-valent positive metal ions in the positive electrolyte storage tank has dropped to a target value. If it has dropped to the target value, the charge and discharge cycle is stopped, otherwise the next charge and discharge cycle is executed.

[0074] Preferably, the hydrogen released during the oxidation charge and discharge cycle is used to balance the charge of the electrolyte until the storage capacity of the flow battery system is restored to 100%, comprising the following steps:

[0075] Charging the first battery stack at a constant voltage and connecting the gas phase connecting tube;

[0076] The hydrogen in the negative electrode electrolyte storage tank enters the positive electrode electrolyte storage tank through the gas phase connecting pipe; the hydrogen is oxidized through the gas diffusion layer to generate hydrogen ions, and at the same time, the electrolyte is adsorbed to the gas diffusion layer through the capillary action layer, so that the electrolyte dissolves the hydrogen ions, and the m-valent positive electrode metal ions in the electrolyte gain electrons to obtain n-valent positive electrode metal ions, until all the m-valent positive electrode metal ions in the electrolyte are reduced to n-valent positive electrode metal ions;

[0077] At the same time, the electrolyte in the positive electrode electrolyte storage tank enters the positive electrode side of the first stack and undergoes an oxidation reaction, so that all the n-valent positive electrode metal ions are oxidized to m-valent positive electrode metal ions, until the electrolyte state of the positive electrode electrolyte storage tank is 100% m-valent positive electrode metal ions;

[0078] At the same time, the electrolyte in the negative electrode electrolyte storage tank enters the negative electrode side of the first battery stack and undergoes a reduction reaction, so that all j-valent negative electrode metal ions are reduced to i-valent negative electrode metal ions, until the electrolyte state of the negative electrode electrolyte storage tank is 100% i-valent negative electrode metal ions.

[0079] Preferably, after the reduction step is completed, the catalyst in the electrolyte is removed by a purification unit, comprising the following steps:

[0080] charging the second battery stack with a constant current;

[0081] The electrolyte in the cathode electrolyte storage tank is transported to the cathode side of the second stack, the catalyst in the electrolyte is reduced and then deposited on the cathode side of the second stack, and then the electrolyte is returned to the cathode electrolyte storage tank;

[0082] At the same time, the cleaning agent in the cleaning agent storage tank is transported to the positive electrode side of the second fuel cell stack and undergoes an oxidation reaction to generate an acid cleaning gas;

[0083] The cleaning agent and pickling gas are recovered to the cleaning agent storage tank.

[0084] Preferably, the cleaning agent is a mixture of one or more of a neutral aqueous solution, a hydrochloric acid solution, a sulfuric acid solution, and a nitric acid solution.

[0085] Preferably, absorbing the acid gas generated by the purification unit by the gas absorption unit comprises the following steps:

[0086] Alkaline substances are used to absorb the acidic gases discharged from the upper space of the cleaning agent storage tank.

[0087] Beneficial effects of the present invention:

[0088] 1. The present invention adopts a liquid flow battery system with a composite reactor. When the battery capacity of the system decays to the target value during the charging and discharging process, the composite reactor can oxidize hydrogen into hydrogen ions, and then restore the charge balance of the electrolyte through the redox reaction, thereby restoring the capacity of the liquid flow battery to 100%, thereby improving the electrolyte chemical reduction efficiency and electrolyte balancing efficiency of the liquid flow battery system, ensuring that the positive and negative electrolytes of the liquid flow battery are completely restored to their initial states, greatly reducing the power consumption and cost of the liquid flow battery system performance and capacity recovery, and finally eliminating the main factors of battery performance and capacity decay caused by side reactions of the liquid flow battery, so that the battery performance and storage capacity remain stable for a long time, and improving the battery performance, system efficiency, capacity, cycle stability and cycle life of the liquid flow battery system;

[0089] 2. The system of the present invention combines a charge and discharge unit, a composite reactor, a purification unit, a gas absorption unit and a battery control unit. When the charge of the charge and discharge unit is unbalanced, the composite reactor is used to restore it. At the same time, the catalyst detached from the composite reactor can be purified by the purification unit. The gas generated by the purification unit can be absorbed by the gas absorption unit. The various devices in the entire system cooperate with each other and have the characteristics of automatic self-balancing, high reaction rate electrolyte capacity recovery, liquid flow battery performance / capacity recovery system and main system running simultaneously, catalyst degradation loss and power consumption are small, no need to add a complex capacity recovery system and consume extra time, avoid increasing the volume of the liquid flow battery, extremely low power consumption, low cost, high system efficiency, simple and easy to use, automatic quantitative control, and no introduction of toxic by-products (hydrogen evolution and iron ion reactants come from the main system, the product is free of impurities, and is not toxic to the liquid flow battery system or the environment), thereby ensuring the high storage capacity, high battery performance, high number of cycles and ultra-long life stable operation of the liquid flow battery.

[0090] 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

[0091] 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.

[0092] Figure 1 A schematic structural diagram of a liquid flow battery system of the present invention is shown;

[0093] Figure 2 The schematic diagram of the structure of the composite reactor of the present invention is shown;

[0094] Figure 3 A flow chart of a balancing method for a liquid flow battery system of the present invention is shown.

[0095] In the figure: 1, negative electrode electrolyte storage tank; 101, first pressure gauge; 102, first valve; 103, nitrogen bottle; 2, first electrolyte pump; 3, first heat exchanger; 4, first negative electrode liquid inlet pipe; 5, first battery stack; 6, first negative electrode; 7, first ion exchange membrane; 8, first positive electrode; 9, first negative electrode current collector; 10, first positive electrode current collector; 11, first negative electrode liquid outlet pipe; 12, first delivery pump; 121, first Second valve; 122, electrolyte mixing tube; 123, gas phase connecting tube; 124, third valve; 125, liquid phase connecting tube; 126, fourth valve; 13, first charging power source; 131, second charging power source; 14, load; 15, positive electrode electrolyte storage tank; 151, second pressure gauge; 16, second electrolyte pump; 17, second heat exchanger; 18, first positive electrode liquid inlet pipe; 19, first positive electrode liquid outlet pipe; 20, three-way valve; 21. Composite reactor; 22. Upper floating plate; 23. Lower floating plate; 24. Gas diffusion layer; 25. Capillary action layer; 26. Second ion exchange membrane; 27. Electrolyte transport layer; 28. Fixing member; 29. ​​Exhaust fan; 30. Filter; 31. Second delivery pump; 32. Second negative electrode liquid inlet pipe; 33. Second stack; 34. Second negative electrode; 35. Third ion exchange membrane; 36. Second positive electrode; 37. Second Negative electrode current collecting plate; 38, second positive electrode current collecting plate; 39, second negative electrode liquid outlet pipe; 40, cleaning agent storage tank; 401, second positive electrode liquid inlet pipe; 41, third delivery pump; 42, second positive electrode liquid outlet pipe; 43, heater; 44, cleaning agent feed port; 45, fifth valve; 46, alkali liquid tank; 461, circulation pipe; 47, cleaning agent product discharge pipe; 48, fourth delivery pump; 49, external exhaust pipe; 50, battery control unit. DETAILED DESCRIPTION

[0096] 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.

[0097] A flow battery system, such as Figure 1 As shown, it includes a charge and discharge unit, a composite reactor 21, a purification unit, a gas absorption unit and a battery control unit 50.

[0098] exist Figure 1In the embodiment, the charge and discharge unit includes a negative electrode electrolyte storage tank 1, a first battery stack 5 and a positive electrode electrolyte storage tank 15. The two ends of the negative electrode side of the first battery stack 5 are connected to the negative electrode electrolyte storage tank 1 through pipelines, and the two ends of the positive electrode side are connected to the positive electrode electrolyte storage tank 15 through pipelines. A gas phase connecting tube 123 is connected between the top of the negative electrode electrolyte storage tank 1 and the top of the positive electrode electrolyte storage tank 15; a liquid phase connecting tube 125 is connected between the side of the negative electrode electrolyte storage tank 1 and the side of the positive electrode electrolyte storage tank 15; and an electrolyte mixing tube 122 is connected between the bottom of the negative electrode electrolyte storage tank 1 and the bottom of the positive electrode electrolyte storage tank 15.

[0099] Further, in Figure 1 In the embodiment, the first stack 5 includes a first ion exchange membrane 7, a first negative current collector plate 9 and a first positive current collector plate 10. The first negative electrode 6 and the first positive electrode 8 are respectively installed on both sides of the first ion exchange membrane 7. The first negative current collector plate 9 is installed on a surface of the first negative electrode 6 away from the first ion exchange membrane 7. The first positive current collector plate 10 is installed on a surface of the first positive electrode 8 away from the first ion exchange membrane 7.

[0100] It should be noted that the first battery stack 5 is the power unit of the flow battery. As a place for energy exchange, it is the core component of the flow battery. The first battery stack 5 is composed of one or more battery cells (referred to as single cells) connected in series. The battery cell is composed of a positive and negative electrode / electrolyte and a first ion exchange membrane 7 that separates the electrodes, and a battery assembly having a pair of positive and negative output terminals (bipolar plates or current collectors). When the number of battery cells is ≥1, a plurality of groups of identical battery cells are connected in series through the first negative current collector 9 and the first positive current collector 10 to form a battery stack. At this time, the first negative current collector 9 and the first positive current collector 10 are respectively the negative bipolar plate and the positive bipolar plate. The positive and negative electrolytes undergo electrochemical oxidation-reduction reactions in the first battery stack 5. Electrons flow between the positive and negative electrodes in the first battery stack 5 in the external circuit. When the first battery stack 5 is charged, electrons flow from the positive electrode to the negative electrode in the external circuit. In the normal charging process, constant current or constant power is used to charge from 0V to U1, and the constant current density = jnormal. The reactant ions of the positive and negative electrolytes flow inside the first battery stack 5 and undergo electrochemical redox reactions on the positive and negative electrodes. The electrochemical reactions of the active materials in the positive and negative half-cells of the battery unit and their energy storage occur simultaneously. 2+ Oxidized to Fe 3+ ,Cr 3+ Reduction to Cr 2+ , and flow into the electrolyte storage tank for storage.

[0101] Furthermore, in the charge and discharge unit:

[0102] A first negative electrode liquid inlet pipe 4 is connected between the bottom outlet of the negative electrode electrolyte storage tank 1 and one end of the first negative electrode 6; the first negative electrode liquid inlet pipe 4 is sequentially provided with a first electrolyte pump 2 and a first heat exchanger 3 along the electrolyte flow direction; a first negative electrode liquid outlet pipe 11 is connected between the other end of the first negative electrode 6 and the top inlet of the negative electrode electrolyte storage tank 1.

[0103] At the same time, a first positive liquid inlet pipe 18 is connected between the bottom outlet of the positive electrolyte storage tank 15 and one end of the first positive electrode 8, and the first positive liquid inlet pipe 18 is sequentially provided with a second electrolyte pump 16 and a second heat exchanger 17 along the electrolyte flow direction; the other end of the first positive electrode 8 is connected to a first positive liquid outlet pipe 19, one end of the first positive liquid outlet pipe 19 is connected to the side inlet of the positive electrolyte storage tank 15, and a three-way valve 20 is installed on the first positive liquid outlet pipe 19.

[0104] It should be noted that during charging and discharging, the negative electrode electrolyte of the liquid flow battery flows out from the negative electrode electrolyte storage tank 1, is driven by the first electrolyte pump 2, and passes through the first heat exchanger 3 to form the temperature required by the liquid flow battery (for example, the liquid flow battery operating temperature is 50-65°C). When the ambient temperature is low, the first heat exchanger 3 heats the electrolyte; when the battery temperature rises (such as high current density circulation causes battery heating), the first heat exchanger 3 cools the electrolyte. After that, the electrolyte flows through the first negative electrode inlet pipe 4 to the first negative electrode 6 of the first battery stack 5 for reaction. After the reaction is completed, the electrolyte returns to the negative electrode electrolyte storage tank 1 through the first negative electrode outlet pipe 11. Similarly, the positive electrolyte of the liquid flow battery flows out from the positive electrolyte storage tank 15, is driven by the second electrolyte pump 16, and passes through the three-way valve 20 and the second heat exchanger 17 on the first positive liquid inlet pipe 18 to form the temperature required by the liquid flow battery (for example, the liquid flow battery operating temperature is 50-65°C). When the ambient temperature is low, the heat exchanger heats the electrolyte; when the battery temperature rises (such as high current density circulation causes the battery to heat up), the heat exchanger cools the electrolyte. After that, the electrolyte enters the first positive electrode 8 of the first battery stack 5, and finally returns to the positive electrolyte storage tank 15.

[0105] Furthermore, in the charge and discharge unit:

[0106] A first pressure gauge 101 is installed on the top of the negative electrolyte storage tank 1. A pressure relief pipe is also connected to the side of the negative electrolyte storage tank 1, which is higher than the waterline and is equipped with a first valve 102. A nitrogen bottle 103 (or a nitrogen generator) is also connected to the side of the negative electrolyte tank 1 through a pipeline; a second pressure gauge 151 is installed on the top of the positive electrolyte storage tank 15; an exhaust fan 29 is installed on the inner wall of the positive electrolyte storage tank 15, and the exhaust fan 29 faces the gas diffusion layer 24.

[0107] It should be noted that the first pressure gauge 101 can monitor the pressure in the negative electrode electrolyte storage tank 1 in real time, such as the pressure of hydrogen produced by the hydrogen evolution reaction. The second pressure gauge 151 can monitor the pressure in the positive electrode electrolyte storage tank 15.

[0108] Furthermore, in the charge and discharge unit:

[0109] Along the electrolyte flow direction, the first delivery pump 12 and the second valve 121 are installed in sequence on the electrolyte mixing tube 122; the third valve 124 is installed on the gas phase connecting tube 123; and the fourth valve 126 is installed on the liquid phase connecting tube 125.

[0110] It should be noted that the opening and closing of the gas phase interconnecting pipe 123 is controlled by the third valve 124. When the third valve 124 is opened, the hydrogen precipitated from the negative electrode during charging and discharging can enter the positive electrode electrolyte storage tank 15 through the gas phase interconnecting pipe 123, and then be oxidized into H by the composite reactor 21. + The liquid phase connecting tube 125 cooperates with the electrolyte mixing tube 122 to mix the electrolytes in the two electrolyte storage tanks and maintain the liquid level balance between the two.

[0111] exist Figure 2 In the embodiment, the composite reactor 21 floats at the waterline position of the positive electrode electrolyte storage tank 15, and includes an upper floating plate 22, a lower floating plate 23, a fixing member 28, and a gas diffusion layer 24, a second ion exchange membrane 26, a capillary action layer 25, and an electrolyte transport layer 27 stacked in sequence, and the gas diffusion layer 24 is higher than the waterline position of the positive electrode electrolyte storage tank 15. The upper floating plate 22 is located on the periphery of the gas diffusion layer 24, and is used to clamp the gas diffusion layer 24 and float at the waterline position of the positive electrode electrolyte storage tank 15; the lower floating plate 23 is located on the periphery of the capillary action layer 25, and is used to clamp the capillary action layer 25 and float at the waterline position of the positive electrode electrolyte storage tank 15; the fixing member 28 is used to connect the upper floating plate 22, the lower floating plate 23, and the electrolyte transport layer 27, for example, in the form of bolt fixing.

[0112] It should be noted that the upper floating plate 22 and the lower floating plate 23 are hollow corrosion-resistant plates, and the plate materials include but are not limited to PP, PPH, PVDF, etc. The floating plate adopts a hollow design, and the size of its internal space can make the gas diffusion layer 24, the capillary action layer 25, the second ion exchange membrane 26 and the electrolyte transport layer 27 float on the liquid surface of the positive electrode electrolyte storage tank 15 as a whole after absorbing the electrolyte.

[0113] It should be further explained that the area at the waterline position of the positive electrolyte storage tank 15 is limited by the diameter of the storage tank. Due to the hollow design of the floating plate, the second ion exchange membrane 26 is located exactly at the waterline position of the positive electrolyte storage tank 15, thereby maximizing the cross-sectional area at the waterline position as the ion exchange channel area. For the positive electrolyte storage tank 15, the composite reactor 21 in the tank can have a sufficiently high reaction rate relative to the waterline area.

[0114] Furthermore, the gas diffusion layer 24 uses carbon felt or graphite felt as a substrate, heat-treated in air at 400-500°C for 1-24 hours for activation, and coated with a metal catalyst or a metal composite catalyst on one side of the substrate, the metal catalyst includes but is not limited to: Pt, Ru, Ir, etc.; the metal composite catalyst includes but is not limited to PtRu, RuIr, etc. For example, Pt / C (30% to 60% Pt mixed with a carbon substrate) is used, and PVDF is used as an adhesive to be coated on the carbon felt or graphite felt substrate, and finally the gas diffusion layer 24 is dried in an oven.

[0115] In addition, the capillary action layer 25 uses carbon felt or graphite felt as a substrate, and is activated by heat treatment in air at 400-500°C for 1-24 hours. The capillary action layer 25 is clamped by the upper floating plate 22 and the lower floating plate 23 below the water line of the positive electrode electrolyte storage tank 15, and contacts the second ion exchange membrane 26 above.

[0116] In addition, the electrolyte transport layer 27 uses carbon felt or graphite felt with higher hardness as a substrate, and is activated by heat treatment in air at 400-500° C. for 1-24 hours, so as to absorb and transport the electrolyte and support the capillary action layer 25. Moreover, the capillary action layer 25 and the electrolyte transport layer 27 can ensure sufficient electrolyte wettability.

[0117] It should be noted that during the charging process, hydrogen from the negative electrode electrolyte storage tank 1 enters the upper space of the positive electrode electrolyte storage tank 15 and contacts the gas diffusion layer 24 of the composite reactor 21. The gas diffusion layer 24 is located in the gas phase space of the positive electrode electrolyte storage tank 15, and the hydrogen is oxidized to H + The second ion exchange membrane 26 is located at the waterline position so that H + The capillary action layer 25 and the electrolyte transport layer 27 are automatically located below the waterline of the positive electrode electrolyte storage tank 15. The electrolyte below the waterline undergoes diffusion and reduction reactions. Taking the liquid flow battery as an example, the Fe 3+ Reduced to Fe 2+ , and H passing through the second ion exchange membrane 26 +Together, they enter the electrolyte below the waterline of the cathode electrolyte storage tank 15. At the same time, as hydrogen is consumed in the composite reactor 21, the pressure in the upper space of the cathode electrolyte storage tank 15 begins to decrease, and then more hydrogen is automatically drawn from the cathode electrolyte storage tank 1 through the pressure difference to enter the upper space of the cathode electrolyte storage tank 15, maintaining the continuous reaction of sodium hydroxide in the composite reactor 21. The above design maximizes the composite reactor 21's resistance to the degradation loss of metal or composite metal catalysts caused by flooding, or the reduction in the rate of hydrogen oxidation reaction caused by insufficient electrolyte.

[0118] exist Figure 1 In the embodiment, the purification unit is connected to the charge and discharge unit, including a second battery stack 33 and a cleaning agent tank 40. The two ends of the negative electrode side of the second battery stack 33 are connected to the electrolyte tank 15 through a pipeline, and the two ends of the positive electrode side are connected to the cleaning agent tank 40 through a pipeline.

[0119] It should be noted that after the positive electrode electrolyte reacts through the composite reactor 21, trace amounts of catalyst degrade and fall off into the electrolyte in the positive electrode electrolyte storage tank 15. Catalyst degradation and shedding are common phenomena in chemical reactions and electrochemical reactions of acidic systems. In the subsequent operation process, these detached catalysts flow into the liquid flow battery system, and the catalyst in the positive electrode electrolyte of the liquid flow battery diffuses across the membrane in the first ion exchange membrane 7 of the first stack 5, thereby being deposited on the first negative electrode 6 of the liquid flow battery energy storage system, and more hydrogen evolution reactions are catalyzed at the negative electrode during the charging process, resulting in accelerated capacity decay of the liquid flow battery energy storage system.

[0120] Further, in the purification unit, the structure of the second stack 33 is the same as that of the first stack 5, including a third ion exchange membrane 35, a second negative electrode current collector plate 37 and a second positive electrode current collector plate 38. The second negative electrode 34 and the second positive electrode 36 are respectively installed on both sides of the third ion exchange membrane 35; the second negative electrode current collector plate 37 is installed on a surface of the second negative electrode 34 away from the third ion exchange membrane 35; and the second positive electrode current collector plate 38 is installed on a surface of the second positive electrode 36 away from the third ion exchange membrane 35.

[0121] In addition, in the purification unit, one end of the second negative electrode 34 is connected to the second negative electrode liquid inlet pipe 32, and the other end is connected to the second negative electrode liquid outlet pipe 39. Along the flow direction of the electrolyte, the second negative electrode liquid inlet pipe 32 takes the three-way valve 20 as the starting point, and is sequentially installed with a filter 30 and a second delivery pump 31; at the same time, along the flow direction of the electrolyte, the end of the second negative electrode liquid outlet pipe 39 away from the second battery stack 33 is connected to the bottom inlet of the positive electrode electrolyte storage tank 15; in addition, a second positive electrode liquid inlet pipe 401 is connected between the bottom outlet of the cleaning agent storage tank 40 and one end of the second positive electrode 36, and a third delivery pump 41 is installed on the second positive electrode liquid inlet pipe 401; a second positive electrode liquid outlet pipe 42 is connected between the other end of the second positive electrode 36 and the top inlet of the cleaning agent storage tank 40.

[0122] In addition, a heater 43 is installed at the lower section of the cleaning agent storage tank 40 , a cleaning agent feed port 44 is provided at the bottom of the cleaning agent storage tank 40 , and a fifth valve 45 is installed on the pipeline of the cleaning agent feed port 44 .

[0123] It should be noted that the purification unit can remove the catalyst that has fallen off in the composite reactor 21. When it is working, it charges the second battery stack 33. When the constant current charging is performed until the charging voltage of the second battery stack 33 rises sharply by about 0.5V, it means that the electrolyte purification is completed and the charging is stopped. In addition, since the amount of catalyst falling off is very small, the power consumption of the purification unit is very small, which greatly improves the efficiency of the liquid flow battery system.

[0124] exist Figure 1 In the embodiment, the gas absorption unit is connected to the purification unit, and includes an alkali liquid tank 46, which is connected to the cleaning agent storage tank 40 through a pipeline. In addition, a cleaning agent product discharge pipe 47 is connected between a top inlet of the alkali liquid tank 46 and a top outlet of the cleaning agent storage tank 40; an external exhaust pipe 49 is also opened on the top of the alkali liquid tank 46; a circulation pipe 461 is connected between the bottom outlet of the alkali liquid tank 46 and another top inlet of the alkali liquid tank 46, and a fourth delivery pump 48 is installed on the circulation pipe 461.

[0125] It should be noted that the alkali liquid tank 46 uses alkaline substances such as sodium hydroxide to absorb acidic gas products (mainly absorbing gas products Cl2 and water vapor, etc.) discharged from the upper space of the cleaning agent storage tank 40.

[0126] Further, the battery control unit 50 includes a first charging power source 13, a second charging power source 131, a load 14 and a battery control unit 50. The first charging power source 13 has a positive electrode connected to the first positive current collector 10, and a negative electrode connected to the first negative current collector 9. The second charging power source 131 has a positive electrode connected to the second positive current collector 38, and a negative electrode connected to the second negative current collector 37. The load 14 is connected in parallel with the first charging power source 13; the battery control unit 50 is connected to the first charging power source 13 and the second charging power source 131, respectively, for controlling the working states of the first charging power source 13 and the second charging power source 131.

[0127] It should be noted that the liquid flow battery system of the present invention is controlled and operated as a whole by the battery control unit 50. The battery control unit 50 has built-in operation control strategies and codes, which can control the charging, discharging and operation of the first charging power source 13, the second charging power source 131 and the power load 14. The battery control unit 50 can also start and stop and operate the pumps, valves, heat exchangers and heaters 43 and other equipment related to the charging and discharging unit, the purification unit and the gas absorption unit.

[0128] It should be further explained that when the battery control unit 50 and the system battery performance are reduced (such as voltage efficiency VE, stack efficiency EE, system efficiency, etc.) and the storage capacity is attenuated (for example, reduced by 40%), the positive electrode electrolyte self-balancing reduction system and its operating program (including the composite reactor 21), the unit, the electrolyte equalization system and its operating program (liquid level balance is achieved through pipelines) are started, and the battery performance and charge and discharge capacity of the liquid flow battery can be automatically self-balanced to achieve recovery, which significantly improves the cycle life of the main system of the liquid flow battery and can achieve long-term operation with basically no attenuation of battery performance and capacity.

[0129] like Figure 3 As shown, this is a balancing method applied to Figure 1 A liquid flow battery system comprising the following steps:

[0130] S1: Charge and discharge step, several charge and discharge cycles are performed through the charge and discharge unit until the storage capacity of the liquid flow battery system is reduced to the target value, and then the charge and discharge cycle of the charge and discharge unit is stopped. S2: Reduction step, after the charge and discharge step is completed, the hydrogen released during the oxidative charge and discharge cycle is balanced to balance the charge of the electrolyte until the storage capacity of the liquid flow battery system is restored to 100%. S3a: Purification step, after the reduction step is completed, the catalyst in the electrolyte is removed by the purification unit. S3b: Absorption step, when executing the purification step, the acid gas generated by the purification unit is absorbed by the gas absorption unit, which mainly uses alkaline substances to absorb the acid gas discharged from the upper space of the cleaning agent storage tank 40. S4: Mixing step, after the purification step is completed, the gas phase connecting tube 123 and the electrolyte mixing tube 122 are opened to mix the electrolytes in the negative electrode electrolyte storage tank 1 and the positive electrode electrolyte storage tank 15, and the liquid level is balanced.

[0131] Furthermore, in S1, the following steps are included:

[0132] S101: Execute a charge and discharge cycle:

[0133] During charging, the electrolyte in the negative electrode electrolyte storage tank 1 enters the first battery stack 5 to undergo a reduction reaction and a hydrogen evolution side reaction, and a mixed electrolyte of i-valent negative electrode metal ions and j-valent negative electrode metal ions and hydrogen are obtained and returned to the negative electrode electrolyte storage tank 1, j>i; at the same time, the electrolyte in the positive electrode electrolyte storage tank 15 enters the first battery stack 5 to undergo an oxidation reaction, and an electrolyte of m-valent positive electrode metal ions is obtained and returned to the positive electrode electrolyte storage tank 15, m>n;

[0134] During discharge, the electrolyte in the negative electrode electrolyte storage tank 1 enters the first battery stack 5 to undergo an oxidation reaction, obtaining an electrolyte of j-valent negative electrode metal ions and returning to the negative electrode electrolyte storage tank 1; at the same time, the electrolyte in the positive electrode electrolyte storage tank 15 enters the first battery stack 5 to undergo a reduction reaction, obtaining a mixed electrolyte of n-valent positive electrode metal ions and m-valent positive electrode metal ions and returning to the positive electrode electrolyte storage tank 15, and a charge and discharge cycle ends;

[0135] S102: After a charge-discharge cycle is completed, it is determined whether the content of the n-valent positive metal ions in the positive electrolyte storage tank 15 has dropped to a target value. If it has dropped to the target value, the charge-discharge cycle is stopped, otherwise the next charge-discharge cycle is executed.

[0136] Furthermore, in S2, the following steps are included:

[0137] S201 : charging the first battery stack 5 at a constant voltage and connecting the gas phase connecting tube 123 .

[0138] S202: The hydrogen in the negative electrode electrolyte storage tank 1 enters the positive electrode electrolyte storage tank 15 through the gas phase connecting tube 123; the hydrogen is oxidized through the gas diffusion layer 24 to generate hydrogen ions, and at the same time, the electrolyte is adsorbed to the gas diffusion layer 24 through the capillary action layer 25, so that the electrolyte dissolves the hydrogen ions, and the m-valent positive electrode metal ions in the electrolyte gain electrons to obtain n-valent positive electrode metal ions, until all the m-valent positive electrode metal ions in the electrolyte are reduced to n-valent positive electrode metal ions.

[0139] At the same time, the electrolyte in the positive electrode electrolyte storage tank 15 enters the positive electrode side of the first battery stack 5 and undergoes an oxidation reaction, so that all the n-valent positive electrode metal ions are oxidized to m-valent positive electrode metal ions, until the electrolyte state of the positive electrode electrolyte storage tank 15 is 100% m-valent positive electrode metal ions.

[0140] At the same time, the electrolyte in the negative electrode electrolyte storage tank 1 enters the negative electrode side of the first battery stack 5 and undergoes a reduction reaction, so that all the j-valent negative electrode metal ions are reduced to i-valent negative electrode metal ions, until the electrolyte state of the negative electrode electrolyte storage tank 1 is 100i-valent negative electrode metal ions.

[0141] Furthermore, in S3a, the following steps are included:

[0142] S301a: charging the second battery stack 33 with a constant current.

[0143] S302a: The electrolyte in the positive electrode electrolyte storage tank 15 is transported to the negative electrode side of the second battery stack 33 , the catalyst in the electrolyte is reduced and deposited on the negative electrode side of the second battery stack 33 , and then the electrolyte returns to the positive electrode electrolyte storage tank 15 .

[0144] S303a: The cleaning agent in the cleaning agent storage tank 40 is transported to the positive electrode side of the second fuel cell stack 33 and undergoes an oxidation reaction to generate an acid cleaning gas.

[0145] S304a: Recover the cleaning agent and pickling gas to the cleaning agent storage tank 40, wherein the cleaning agent is a mixture of one or more of a neutral aqueous solution, a hydrochloric acid solution, a sulfuric acid solution, and a nitric acid solution.

[0146] It should be noted that, for a liquid flow battery system, the electrolyte may be neutral or acidic, such as sulfuric acid, hydrochloric acid, or a mixed acid system.

[0147] The electrochemical reactions and side reactions of the positive and negative electrodes during the charging process are:

[0148] Positive electrode: A0-e-=A;

[0149] Negative electrode: B0+e-=B;

[0150] Hydrogen evolution side reaction: 2H++2e-=H 2 ;

[0151] The electrochemical reactions of the positive and negative electrodes during the discharge process are:

[0152] Positive electrode: A+e-=A0;

[0153] Negative electrode: Be-=B0.

[0154] The mechanism by which the hydrogen evolution side reaction causes capacity imbalance in a flow battery during a charge and discharge cycle is as follows. During the charging process, since hydrogen evolution at the negative electrode consumes part of the current (for example, x%), the negative electrode where the hydrogen evolution side reaction occurs cannot be fully charged (for example, 1-x%, that is, charging to obtain 1-x% B), while the positive electrode reaches a fully charged state (100%, that is, charging to obtain 100% A). In this case, the negative electrode electrolyte will limit the subsequent discharge process and reduce the charge storage capacity of the flow battery energy storage system. During the discharge process, since the negative electrode is not fully charged, the negative electrode becomes the limiting side. Therefore, during the discharge process, the discharge capacity of the flow battery will be limited to 1-x% of its capacity, and the positive electrode electrolyte will not be fully discharged (the remaining x% is in a high-valence state, that is, 1-x% of the active material is in the discharge state A0, and the remaining x% A). The charge imbalance of the charge and discharge cycle will cause the capacity of the flow battery to decrease. During the charging process of the next cycle, the positive electrode will not start from a fully discharged state (because only 1-x% of the active material in the positive electrode is in the discharge state A0), resulting in a loss of x% of the charge storage capacity of the flow battery. The accumulation of capacity loss over multiple cycles (cumulative capacity decay) causes an irreversible reduction in the storage capacity of the flow battery system.

[0155] The mechanism of capacity loss accumulation of flow battery after multiple cycles is as follows. After 1000 cycles of charge and discharge, assuming that the capacity has decayed by x% in total, after the discharge of this charge and discharge cycle, the positive electrode electrolyte is not fully discharged (the remaining x% is in a high-valent state, that is, 1-x% of the active material is in the discharge state A0, and the remaining x% is A); while the negative electrode is fully discharged (100% is B0). The charge imbalance of the charge and discharge cycle will cause the capacity of the flow battery to decrease. During the charging process of the next cycle, the positive electrode will not start from a fully discharged state (because only 1-x% of the active material in the positive electrode is in the discharge state A0 and participates in charging), resulting in a loss of x% in the charge storage capacity of the flow battery, which irreversibly reduces the storage capacity of the flow battery system by x%, resulting in a reduction in the cycle life of the flow battery.

[0156] In some embodiments, the electrolyte may include FeCl 2 , CrCl 3 and HCL, where A is Fe and B is Cr. In a charge and discharge cycle, the electrochemical reactions and side reactions of the positive and negative electrodes during the charging process are:

[0157] Positive electrode: Fe 2+ -e - =Fe 3+ ;

[0158] Negative electrode: Cr 3+ +e - =Cr 2+ ;

[0159] Hydrogen evolution side reaction: 2H + +2e - =H 2 ;

[0160] The electrochemical reactions of the positive and negative electrodes during the discharge process are:

[0161] Positive electrode: Fe 3+ +e - =Fe 2+ ;

[0162] Negative electrode: Cr 2+ -e - =Cr 3+ .

[0163] It should be further explained that the present invention is applicable to the field of large-scale liquid flow battery energy storage, and can be used for capacity and battery performance monitoring, judgment and recovery of aqueous liquid flow batteries or other aqueous liquid flow batteries (neutral, acidic), and automatically and self-balancingly maintain the high capacity, high performance, low auxiliary power consumption and low cost long-term stable operation of iron-chromium and other aqueous liquid flow battery energy storage systems.

[0164] Combine the following Figure 1-Figure 3 content, the electrolyte includes FeCl 2 , CrCl 3 The operation of HCL's flow battery is described as follows:

[0165] 1. Charging and discharging stage

[0166] During charging, the electrolyte in the negative electrode electrolyte storage tank 1 enters the first battery stack 5 through the first negative electrode liquid inlet pipe 4 to undergo reduction reaction and hydrogen evolution side reaction, thereby obtaining Cr 2+ and Cr 3+ The mixed electrolyte and hydrogen are then returned to the negative electrode electrolyte storage tank 1 through the first negative electrode liquid outlet pipe 11; at the same time, the electrolyte in the positive electrode electrolyte storage tank 15 enters the first battery 5 for oxidation reaction to obtain F 3+ The electrolyte is then returned to the positive electrode electrolyte storage tank 15.

[0167] During discharge, the electrolyte in the negative electrode electrolyte storage tank 1 enters the first battery stack 5 and undergoes oxidation reaction to obtain Cr 3+ The electrolyte of the positive electrode electrolyte storage tank 15 enters the first battery stack 5 for reduction reaction to obtain F 2+ and F 3+The mixed electrolyte is returned to the positive electrode electrolyte storage tank 15, and a charge and discharge cycle is completed.

[0168] After a cycle, the side reaction will irreversibly consume electrons, resulting in an imbalance in the charge state of the positive and negative electrolytes (charge imbalance for short), and ultimately leading to an imbalance in the capacity of the positive and negative electrodes and a reduction in capacity. In a charge and discharge cycle of a flow battery, the mechanism by which the hydrogen evolution side reaction causes capacity imbalance is as follows. During the charging process, since hydrogen evolution at the negative electrode consumes part of the current (for example, x%, x=1), the negative electrode where the hydrogen evolution side reaction occurs cannot be fully charged (for example, 1-x%=99%, that is, charging to obtain 99% Cr 2+ ), while the positive electrode reaches a fully charged state (100%, i.e., charging to obtain 100% Fe 3 + ). In this case, the negative electrode electrolyte will limit the subsequent discharge process and reduce the charge storage capacity of the flow battery energy storage system. During the discharge process, since the negative electrode is not fully charged, the negative electrode becomes the limiting side. Therefore, during the discharge process, the discharge capacity of the flow battery will be limited to 99% of its capacity, and the positive electrode electrolyte will not be fully discharged (the remaining 1% is in a high-valent state, that is, 99% of the active material is in a discharged state Fe 2+ , remaining 1% Fe 3+ The charge imbalance of the charge-discharge cycle will cause the capacity of the flow battery to decrease. During the charging process of the next cycle, the positive electrode will not start from a fully discharged state (because only 99% of the active material in the positive electrode is in a discharged state). 2+ ), resulting in a 1% loss in the charge storage capacity of the flow battery. The capacity loss accumulates over multiple cycles (cumulative capacity decay), which irreversibly reduces the storage capacity of the flow battery system.

[0169] The mechanism of capacity loss accumulation of flow battery after multiple cycles is as follows. After 1000 cycles of charge and discharge, assuming that the capacity decays by y%, for example, y% = 40%, then after the discharge of this charge and discharge cycle, the positive electrode electrolyte is not completely discharged (the remaining 40% is in a high-valent state, that is, 60% of the active material is in a discharged state Fe 2+ , the remaining 40% is Fe 3+ ); while the negative electrode is fully discharged (100% Cr 3+ The charge imbalance of the charge-discharge cycle will cause the capacity of the flow battery to decrease. During the charging process of the next cycle, the positive electrode will not start from a fully discharged state (because only 60% of the active material in the positive electrode is in a discharged state). 2+ , which can participate in charging), resulting in a 40% loss in the charge storage capacity of the flow battery, thereby irreversibly reducing the storage capacity of the flow battery system by 40%, resulting in a reduction in the cycle life of the flow battery.

[0170] Take a certain flow battery as an example. For example, after 1,000 cycles of charge and discharge, when it is found that the storage capacity of the flow battery system has irreversibly decreased by 40% (that is, when the storage capacity remains at 60%, for example, the designed storage capacity of the flow battery system is 100MWh, then the actual storage capacity is 60MWh). When it is determined that the storage capacity has decayed by 40% as above, the charge and discharge cycle is stopped.

[0171] 2. Restoration Phase

[0172] After the charge and discharge phase, the positive electrode electrolyte is 60% Fe2+ and 40% Fe3+; the negative electrode electrolyte is 100% Cr3+. Therefore, in the reduction phase, the positive electrode electrolyte needs to be restored to 100% F3+ and the negative electrode electrolyte to 100% Cr2+.

[0173] First, the second charging power supply 131 is used to charge the first battery stack 5 at a constant voltage, and at the same time, the third valve 124 is opened to conduct the gas phase connecting pipe 123, so that the hydrogen in the upper part of the negative electrode electrolyte storage tank 1 enters the upper space of the positive electrode electrolyte storage tank 1.

[0174] The hydrogen in the negative electrode electrolyte storage tank 1 enters the upper space of the positive electrode electrolyte storage tank 15 through the gas phase connecting pipe 123. After the hydrogen contacts the gas diffusion layer 24 of the composite reactor 21, the hydrogen is oxidized to H + The metal catalyst (e.g., Pt / C, Ru / C, Ir / C, or PtRu / C, RuIr / C) accelerates the reduction of hydrogen, and the electrolyte is drawn into the gas diffusion layer 24 by the capillary action layer 25 to dissolve H + Then this part is oxidized to produce H + The electrolyte in the positive electrode electrolyte storage tank 15 below the water line undergoes diffusion and reduction reaction in the capillary action layer 25 and the electrolyte transport layer 27 through the second ion exchange membrane 26. 3+ Reduced to 40% Fe 2+ , and H passing through the second ion exchange membrane 26 + Together they enter the electrolyte below the water line of the positive electrode electrolyte storage tank 15 .

[0175] At the same time, the electrolyte in the positive electrode electrolyte storage tank 15 enters the positive electrode side of the first stack 5 and undergoes an oxidation reaction, causing the newly generated 40% F 2+ All oxidized to F 3+ , until the electrolyte state of the positive electrolyte tank 15 is 100% F 3+ Finally, the positive electrode electrolyte returns to the positive electrode electrolyte storage tank 15 through the first positive electrode liquid outlet pipe 19 and the three-way valve 20.

[0176] At the same time, the electrolyte in the negative electrode electrolyte storage tank 1 enters the negative electrode side of the first stack 5 and undergoes a reduction reaction, making 40% Cr 3+ (corresponding to the 40% F2+ newly generated on the positive electrode side) is all reduced to Cr 2+ , until the electrolyte state of the negative electrode electrolyte tank 1 is 100Cr 2+ .

[0177] It should be noted that during the entire reduction stage, the composite reactor 21 continuously generates new Fe 2+ The first stack 5 is transported to the positive electrode side, and Fe 2+ Oxidized to Fe 3+ When all the excess Fe in the composite reactor 21 3+ (40% in total) are all converted into Fe 2+ This part of Fe2+ is completely oxidized to Fe through the positive electrode of the first stack 5 3+ ; At this time, the remaining 40% Cr 3+ All reduced to Cr 2+ The final cathode electrolyte state is 100% Fe 3+ , the negative electrode electrolyte state is 100% Cr 2+ , that is, the state in which the main system of the liquid flow battery is fully charged, and the capacity of the liquid flow battery is fully recovered (both the positive and negative electrodes are SOC = 100%).

[0178] It should be noted that the progress of the restoration phase can be judged by the following indicators:

[0179] 1) Charging stop procedure. After the charging and discharging unit is fully charged, the first charging power supply 13 starts charging the first battery stack 5, maintaining the constant voltage charging at U1, and the charging current first increases and then decreases until the current density is ≤jmin and no longer changes. At this time, it can be judged that the electrolysis process in the reduction stage has been completed.

[0180] 2) Process stop procedure. While executing 1) the charging procedure, the top gas phase connecting pipe 123 and the third valve 124 of the negative electrode electrolyte storage tank 1 and the positive electrode electrolyte storage tank 15 are opened. It is observed that the pressure shown on the first pressure gauge 101 first increases and then decreases, and decreases to the pressure value P1 of the negative electrode electrolyte storage tank 1 at the start of charging and does not change. Through this pressure criterion, it can be judged that the electrolysis process in the reduction stage has been completed and the hydrogen evolution in the main system has been completely eliminated.

[0181] The above stop procedure indicates that the operation of the positive electrode electrolyte self-balancing reduction system has been completed.

[0182] It should be further explained that the U1 and jmin settings are different for different stack designs, electrolyte / catalyst / electrode selections of the flow battery system. As an example, U1 can be set to 1.2-1.3V, and jmin can be set to 2-10mAcm-2. Similarly, the P1 setting value is also different. As an example, the pressure P1 setting value of the negative electrode electrolyte storage tank 1 can be 50-200pa.

[0183] 3. Purification stage

[0184] The operating procedure of the negative electrode side of the second stack 33 is as follows:

[0185] The positive electrode electrolyte flows out of the positive electrode electrolyte storage tank 15, driven by the second delivery pump 31, and flows into the second negative electrode 34 of the second battery stack 33 through the three-way valve 20 and the second negative electrode inlet pipe 32. During the negative electrode charging process, the trace catalyst carried in the positive electrode electrolyte is reduced and deposited on the second negative electrode 34, and the purified positive electrode electrolyte flows back to the positive electrode electrolyte storage tank 15 through the second negative electrode outlet pipe 39.

[0186] The operation procedure of the positive electrode side of the second stack 33 is as follows:

[0187] The cleaning agent flows out of the cleaning agent storage tank 40, is driven by the third delivery pump 41, and is charged to the second battery stack 33. After an electrochemical reaction (oxidation reaction) occurs at the second positive electrode 36, it flows back to the cleaning agent storage tank 40, and the cleaning agent is consumed after electrolytic oxidation. According to the type of liquid flow battery (all-vanadium liquid flow battery, liquid flow battery, all-iron liquid flow battery, etc.), the cleaning agent is designed as a supporting electrolyte for the liquid flow battery, including but not limited to: neutral aqueous solution, hydrochloric acid solution, sulfuric acid solution, nitric acid solution, mixed acid solution. Therefore, the cleaning agent will not cause ion diffusion across the membrane, avoiding contamination of the negative electrode of the second battery stack 33 (i.e., the positive electrolyte of the liquid flow battery system). The products after the electrolysis of the cleaning agent include easily separated gases (for example, if the cleaning agent is hydrochloric acid, then the gas product Cl2).

[0188] 4. Absorption Stage

[0189] When purifying the electrolyte, the gaseous product flows out from the top of the cleaning agent storage tank 40 and flows into the alkali liquid tank 46 for absorption, and the unabsorbed part (part of the water vapor, etc.) is discharged through the external exhaust pipe 49.

[0190] 5. Mixing stage

[0191] During the charge and discharge phase, some ions and water molecules migrate from the negative electrode side to the positive electrode side through the first ion exchange membrane 7, resulting in an unbalanced liquid level in the negative electrode electrolyte storage tank 1 and the positive electrode electrolyte storage tank 15, resulting in a loss of charge and discharge capacity of the flow battery system. After the reduction phase and the purification phase are completed, the positive electrode electrolyte is purified and has been restored to its initial state and rated storage capacity, and the mixing phase can be started.

[0192] In the mixing stage, the positive electrolyte of the flow battery flows out from the positive electrolyte storage tank 15, is driven by the first delivery pump 12, passes through the second valve 121 and the electrolyte mixing pipe 122, and flows into the negative electrolyte storage tank 1. The third valve 124 and the gas phase connecting pipe 123 are opened, and the electrolyte circulates and mixes between the positive electrolyte storage tank 15 and the negative electrolyte storage tank 1. After multiple cycles, the positive and negative electrolytes are evenly mixed.

[0193] 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 liquid flow battery system, characterized in that: include: A charge-discharge unit comprises a negative electrode electrolyte storage tank (1), a first battery stack (5) and a positive electrode electrolyte storage tank (15); the two ends of the negative electrode side of the first battery stack (5) are connected to the negative electrode electrolyte storage tank (1) through a pipeline, and the two ends of the positive electrode side are connected to the positive electrode electrolyte storage tank (15) through a pipeline; A gas phase communication tube (123) is connected between the top of the negative electrode electrolyte storage tank (1) and the top of the positive electrode electrolyte storage tank (15); a liquid phase communication tube (125) is connected between one side of the negative electrode electrolyte storage tank (1) and the side of the positive electrode electrolyte storage tank (15); and an electrolyte mixing tube (122) is connected between the other side of the negative electrode electrolyte storage tank (1) and the other side of the positive electrode electrolyte storage tank (15); A composite reactor (21) floats at the waterline of the positive electrode electrolyte storage tank (15), comprising a gas diffusion layer (24), a second ion exchange membrane (26), a capillary action layer (25) and an electrolyte transport layer (27) stacked in sequence, wherein the gas diffusion layer (24) is higher than the waterline of the positive electrode electrolyte storage tank (15); A purification unit connected to the charge and discharge unit, comprising a second battery stack (33) and a cleaning agent storage tank (40); the two ends of the negative electrode side of the second battery stack (33) are connected to the electrolyte storage tank (15) through a pipeline, and the two ends of the positive electrode side are connected to the cleaning agent storage tank (40) through a pipeline; The gas absorption unit is connected to the purification unit and comprises an alkali liquid tank (46), wherein the alkali liquid tank (46) is connected to the cleaning agent storage tank (40) via a pipeline.

2. A liquid flow battery system according to claim 1, characterized in that: The first battery stack (5) comprises: A first ion exchange membrane (7) having a first negative electrode (6) and a first positive electrode (8) mounted on two side surfaces thereof; A first negative electrode current collector (9) is mounted on a surface of the first negative electrode (6) away from the first ion exchange membrane (7); The first positive current collecting plate (10) is mounted on a surface of the first positive electrode (8) away from the first ion exchange membrane (7).

3. A liquid flow battery system according to claim 2, characterized in that: In the charge and discharge unit: A first negative electrode liquid inlet pipe (4) is connected between the bottom outlet of the negative electrode electrolyte storage tank (1) and one end of the first negative electrode (6); the first negative electrode liquid inlet pipe (4) is provided with a first electrolyte pump (2) and a first heat exchanger (3) in sequence along the electrolyte flow direction; A first negative electrode liquid outlet pipe (11) is connected between the other end of the first negative electrode (6) and the top inlet of the negative electrode electrolyte storage tank (1).

4. A liquid flow battery system according to claim 2, characterized in that: In the charge and discharge unit: A first positive electrode liquid inlet pipe (18) is connected between the bottom outlet of the positive electrode electrolyte storage tank (15) and one end of the first positive electrode (8), and a second electrolyte pump (16) and a second heat exchanger (17) are sequentially arranged on the first positive electrode liquid inlet pipe (18) along the electrolyte flow direction; The other end of the first positive electrode (8) is connected to a first positive electrode liquid outlet pipe (19), one end of the first positive electrode liquid outlet pipe (19) is connected to a side inlet of a positive electrode electrolyte storage tank (15), and a three-way valve (20) is installed on the first positive electrode liquid outlet pipe (19).

5. A liquid flow battery system according to claim 2, characterized in that: In the charge and discharge unit: A first pressure gauge (101) is installed on the top of the negative electrode electrolyte storage tank (1); The side of the negative electrode electrolyte storage tank (1) is also connected to a pressure relief pipe, the pressure relief pipe is higher than the waterline and is equipped with a first valve (102); The side of the negative electrode electrolyte storage tank (1) is also connected to a nitrogen bottle (103) via a pipeline; A second pressure gauge (151) is installed on the top of the positive electrolyte storage tank (15); An exhaust fan (29) is installed on the inner wall of the positive electrode electrolyte storage tank (15), and the exhaust fan (29) faces the gas diffusion layer (24).

6. A liquid flow battery system according to claim 1, characterized in that: In the charge and discharge unit: Along the electrolyte flow direction, the electrolyte mixing pipe (122) is sequentially installed with a first delivery pump (12) and a second valve (121); A third valve (124) is installed on the gas phase communication pipe (123); A fourth valve (126) is installed on the liquid phase communication pipe (125).

7. A liquid flow battery system according to claim 2, characterized in that: A fixing member (28) and a stacked upper floating plate (22) and a lower floating plate (23) are also provided in the composite reactor (21); The upper floating plate (22) is located on the periphery of the gas diffusion layer (24) and is used to clamp the gas diffusion layer (24) and float at the waterline position of the positive electrode electrolyte storage tank (15); The lower floating plate (23) is located on the peripheral side of the capillary action layer (25) and is used to clamp the capillary action layer (25) and float at the waterline position of the positive electrode electrolyte storage tank (15); The fixing member (28) is used to connect the upper floating plate (22), the lower floating plate (23) and the electrolyte transport layer (27).

8. A liquid flow battery system according to claim 1, characterized in that: In the composite reactor (21): The base of the gas diffusion layer (24) is carbon felt or graphite felt, and is heat-treated in air at 400-500° C. for 1-24 hours for activation; The substrate is coated with a layer of catalyst, and the catalyst includes Pt, Ru, Ir, PtRu, and RuIr; The substrate of the capillary action layer (25) is carbon felt or graphite felt, and is heat-treated in air at 400-500° C. for 1-24 hours for activation; The substrate of the electrolyte transport layer (27) is carbon felt or graphite felt, and is heat-treated in air at 400-500° C. for 1-24 hours for activation.

9. A liquid flow battery system according to claim 4, characterized in that: The second battery stack (33) comprises: A third ion exchange membrane (35) having a second negative electrode (34) and a second positive electrode (36) mounted on two side surfaces thereof; A second negative electrode current collector (37) is mounted on a surface of the second negative electrode (34) away from the third ion exchange membrane (35); The second positive current collecting plate (38) is mounted on a surface of the second positive electrode (36) away from the third ion exchange membrane (35).

10. A liquid flow battery system according to claim 9, characterized in that: In the purification unit: One end of the second negative electrode (34) is connected to a second negative electrode liquid inlet pipe (32), and the other end is connected to a second negative electrode liquid outlet pipe (39); Along the electrolyte flow direction, the second negative electrode liquid inlet pipe (32) starts from the three-way valve (20) and is sequentially installed with a filter (30) and a second delivery pump (31); Along the electrolyte flow direction, one end of the second negative electrode liquid outlet pipe (39) away from the second battery stack (33) is connected to the bottom inlet of the positive electrode electrolyte storage tank (15); Along the electrolyte flow direction, a second positive electrode liquid inlet pipe (401) is connected between the bottom outlet of the cleaning agent storage tank (40) and one end of the second positive electrode (36), and a third delivery pump (41) is installed on the second positive electrode liquid inlet pipe (401); Along the electrolyte flow direction, a second positive electrode liquid outlet pipe (42) is connected between the other end of the second positive electrode (36) and the top inlet of the cleaning agent storage tank (40); A heater (43) is installed at the lower section of the cleaning agent storage tank (40); The cleaning agent storage tank (40) is provided with a cleaning agent feed port (44) at the bottom, and a fifth valve (45) is installed on the pipeline of the cleaning agent feed port (44).

11. A liquid flow battery system according to claim 1, characterized in that: In the gas absorption unit: A cleaning agent product discharge pipe (47) is connected between a top inlet of the alkali liquid tank (46) and a top outlet of the cleaning agent storage tank (40); The top of the alkali liquid tank (46) is also provided with an external exhaust pipe (49); A circulation pipe (461) is connected between the bottom outlet of the alkali liquid tank (46) and another top inlet of the alkali liquid tank (46), and a fourth delivery pump (48) is installed on the circulation pipe (461).

12. A liquid flow battery system according to claim 9 or 10, characterized in that: Also included is a battery control unit (50); The battery control unit (50) comprises: A first charging power source (13), the positive electrode of which is connected to the first positive electrode current collecting plate (10), and the negative electrode of which is connected to the first negative electrode current collecting plate (9); A second charging power source (131), the positive electrode of which is connected to the second positive electrode current collecting plate (38), and the negative electrode of which is connected to the second negative electrode current collecting plate (37); A load (14) connected in parallel with the first charging power source (13); The battery control unit (50) is connected to the first charging power source (13) and the second charging power source (131) respectively, and is used to control the working states of the first charging power source (13) and the second charging power source (131).

13. A balancing method, applied to a liquid flow battery system according to any one of claims 1 to 12, characterized in that: The following steps are involved: Charging and discharging step: performing several charging and discharging cycles through the charging and discharging unit until the storage capacity of the flow battery system is reduced to a target value, and then stopping the charging and discharging cycle of the charging and discharging unit; Reduction step: After the charge and discharge step, the hydrogen released during the charge and discharge cycle is oxidized to balance the charge of the electrolyte until the storage capacity of the flow battery system is restored to 100%; Purification step: After the reduction step, the catalyst in the electrolyte is removed by a purification unit; Absorption step: when performing the purification step, the acid gas generated by the purification unit is absorbed by the gas absorption unit; Mixing step: After the purification step is completed, the gas phase connecting tube (123) and the electrolyte mixing tube (122) are opened to mix the electrolytes in the negative electrode electrolyte storage tank (1) and the positive electrode electrolyte storage tank (15), and to balance the liquid levels.

14. A balancing method according to claim 13, characterized in that: Performing several charge and discharge cycles through the charge and discharge unit until the storage capacity of the flow battery system is reduced to a target value, and then stopping the charge and discharge cycle of the charge and discharge unit, including the following steps: To perform a charge and discharge cycle: During charging, the electrolyte in the negative electrode electrolyte storage tank (1) enters the first battery stack (5) to undergo a reduction reaction and a hydrogen evolution side reaction, thereby obtaining a mixed electrolyte of i-valent negative electrode metal ions and j-valent negative electrode metal ions and hydrogen, which is then returned to the negative electrode electrolyte storage tank (1), where j>i; at the same time, the electrolyte in the positive electrode electrolyte storage tank (15) enters the first battery stack (5) to undergo an oxidation reaction, thereby obtaining an electrolyte of m-valent positive electrode metal ions, which is then returned to the positive electrode electrolyte storage tank (15), where m>n; During discharge, the electrolyte in the negative electrode electrolyte storage tank (1) enters the first battery stack (5) to undergo an oxidation reaction, thereby obtaining an electrolyte containing j-valent negative electrode metal ions and returning to the negative electrode electrolyte storage tank (1); at the same time, the electrolyte in the positive electrode electrolyte storage tank (15) enters the first battery stack (5) to undergo a reduction reaction, thereby obtaining a mixed electrolyte containing n-valent positive electrode metal ions and m-valent positive electrode metal ions and returning to the positive electrode electrolyte storage tank (15), thereby completing a charge and discharge cycle; After a charge and discharge cycle is completed, it is determined whether the content of the n-valent positive electrode metal ions in the positive electrode electrolyte storage tank (15) has dropped to a target value. If it has dropped to the target value, the charge and discharge cycle is stopped, otherwise the next charge and discharge cycle is executed.

15. A balancing method according to claim 14, characterized in that: The hydrogen released during the oxidation charge and discharge cycle balances the charge of the electrolyte until the storage capacity of the flow battery system is restored to 100%, including the following steps: Charging the first battery stack (5) at a constant voltage and conducting the gas phase connecting tube (123); The hydrogen gas in the negative electrode electrolyte storage tank (1) enters the positive electrode electrolyte storage tank (15) through the gas phase connecting pipe (123); the hydrogen gas is oxidized through the gas diffusion layer (24) to generate hydrogen ions, and at the same time, the electrolyte is adsorbed to the gas diffusion layer (24) through the capillary action layer (25), so that the electrolyte dissolves the hydrogen ions and the m-valent positive electrode metal ions in the electrolyte gain electrons to obtain n-valent positive electrode metal ions, until all the m-valent positive electrode metal ions in the electrolyte are reduced to n-valent positive electrode metal ions; At the same time, the electrolyte in the positive electrode electrolyte storage tank (15) enters the positive electrode side of the first battery stack (5) and undergoes an oxidation reaction, so that all n-valent positive electrode metal ions are oxidized to m-valent positive electrode metal ions, until the electrolyte state of the positive electrode electrolyte storage tank (15) is 100% m-valent positive electrode metal ions; At the same time, the electrolyte in the negative electrode electrolyte storage tank (1) enters the negative electrode side of the first battery stack (5) and undergoes a reduction reaction, so that all the j-valent negative electrode metal ions are reduced to i-valent negative electrode metal ions, until the electrolyte state of the negative electrode electrolyte storage tank (1) is 100% i-valent negative electrode metal ions.

16. A balancing method according to claim 15, characterized in that: After the reduction step is completed, the catalyst in the electrolyte is removed by a purification unit, including the following steps: Charging the second battery stack (33) with a constant current; The electrolyte in the positive electrode electrolyte storage tank (15) is transported to the negative electrode side of the second battery stack (33), the catalyst in the electrolyte is reduced and then deposited on the negative electrode side of the second battery stack (33), and then the electrolyte is returned to the positive electrode electrolyte storage tank (15); At the same time, the cleaning agent in the cleaning agent storage tank (40) is transported to the positive electrode side of the second battery stack (33) and undergoes an oxidation reaction to generate an acid cleaning gas; The cleaning agent and pickling gas are recovered to the cleaning agent storage tank (40).

17. A balancing method according to claim 16, characterized in that: The cleaning agent is a mixture of one or more of a neutral aqueous solution, a hydrochloric acid solution, a sulfuric acid solution, and a nitric acid solution.

18. A balancing method according to any one of claims 13 to 17, characterized in that: The acid gas generated by the purification unit is absorbed by the gas absorption unit, comprising the following steps: Alkaline substances are used to absorb acidic gas discharged from the upper space of the cleaning agent storage tank (40).

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