Flow battery with sulfur-based fuel cell and operation method

Abstract

The invention belongs to the technical field of flow batteries, and provides a flow battery with a sulfur-based fuel cell and an operation method, and the flow battery comprises a main unit, a sulfur-based unit, a secondary loop unit, a battery control unit and a recycling unit. The flow cell of the sulfur-based fuel cell is generally suitable for a water-based iron-chromium flow cell and an air fuel cell, in addition, a secondary loop unit is arranged for combined hydrogen production, and due to the arrangement of the electrolyte storage tank and the gas storage tank, the conservation of reactants and electrochemical metering numbers between sulfur-based discharge and hydrogen production is constant, so that the hydrogen production efficiency is improved. The two loop units can operate at the same time or operate in a decoupling mode, the system is suitable for a large-scale iron-chromium flow battery energy storage system, and it is ensured that the iron-chromium flow battery operates at high electricity storage capacity, high discharge power, high discharge capacity, high battery performance, no pollution and low cost.

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 with a sulfur-based fuel cell and an operation method thereof. 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] The electrochemical side reactions of existing flow batteries will inevitably occur under normal operating conditions of the flow battery. The 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. Therefore, charge imbalance in flow batteries is an urgent problem to be solved, and how to effectively utilize the byproducts of the reaction when solving the charge imbalance is also a problem that needs attention. Summary of the invention

[0004] In order to solve the problems in the background technology, the present invention provides a liquid flow battery with a sulfur-based fuel cell and an operation method thereof.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A flow battery with a sulfur-based fuel cell, comprising: A main unit, comprising a main stack, a positive electrode electrolyte storage tank connected to the inlet and outlet of the positive electrode side of the main stack, and a negative electrode electrolyte storage tank connected to the inlet and outlet of the negative electrode side of the main stack; The sulfur-based unit comprises a first fuel cell and a sulfur-based storage tank connected to the inlet and outlet of the cathode side of the first fuel cell; the inlet and outlet of the cathode side of the first fuel cell are connected to the cathode electrolyte storage tank; The secondary circuit unit comprises a hydrogen reactor and a second fuel cell; the inlet and outlet of the hydrogen reactor are connected to the negative electrode electrolyte storage tank for producing hydrogen; the negative electrode side inlet of the second fuel cell is connected to the hydrogen reactor, and the negative electrode side outlet is connected to the negative electrode outlet pipe; the positive electrode side inlet of the second fuel cell is connected to an air source, and the positive electrode side outlet is connected to the positive electrode outlet pipe; A battery control unit, electrically connected to the main fuel cell stack, the first fuel cell and the second fuel cell, for controlling charging and discharging; The recycling unit is connected to the sulfur-based unit.

[0006] Preferably, the positive electrode side of the main stack includes a first positive electrode and a first positive current collecting plate located outside the first positive electrode; The negative electrode side of the main stack includes a first negative electrode and a first negative current collecting plate located outside the first negative electrode; A first ion exchange membrane is disposed between the first positive electrode and the first negative electrode.

[0007] Preferably, the positive electrode side of the first fuel cell includes a second positive electrode and a second positive current collecting plate located outside the second positive electrode; The cathode side of the first fuel cell includes a second cathode electrode and a second cathode current collecting plate located outside the second cathode electrode; A second ion exchange membrane is disposed between the second positive electrode and the second negative electrode.

[0008] Preferably, the recycling unit comprises: A cleaning agent tank connected to the positive electrode side inlet of the first fuel cell; An alkali liquid tank, wherein the alkali liquid tank is provided with a gas discharge pipeline; the alkali liquid tank is also provided with an alkali liquid pump, and the inlet and outlet of the alkali liquid pump are both connected to the alkali liquid tank; The positive electrode side outlet of the first fuel cell is connected to the positive electrode electrolyte storage tank via a second positive electrode liquid outlet pipe, and the second positive electrode liquid outlet pipe is connected to the alkaline solution tank via a branch.

[0009] Preferably, a reaction catalytic layer is provided inside the hydrogen reactor, and the reaction catalytic layer divides the inner cavity of the hydrogen reactor into an upper cavity and a lower cavity; The lower chamber is provided with an agitator and a heater located on one side of the agitator; The upper chamber is provided with a feed inlet and a gas outlet of the hydrogen reactor; A catalytic pipeline is connected between the upper chamber and the lower chamber, and a pump and a valve are arranged on the catalytic pipeline.

[0010] Preferably, the upper chamber of the hydrogen reactor is also connected to a gas storage tank, and the outlet of the gas storage tank is connected to the inlet of the positive electrode side of the second fuel cell.

[0011] Preferably, the positive electrode side of the second fuel cell is provided with a positive electrode catalyst layer, a third positive electrode and a third positive electrode current collecting plate in sequence from the inside to the outside; The negative electrode side of the second fuel cell is provided with a negative electrode catalyst layer, a third negative electrode and a third negative electrode current collecting plate in sequence from the inside to the outside; A third ion exchange membrane is installed between the positive electrode catalyst layer and the negative electrode catalyst layer.

[0012] Preferably, the battery control unit comprises: a first charging power source, electrically connected to the main battery stack, and used to charge the main battery stack; A first load, electrically connected to the main fuel cell stack and used for discharging the main fuel cell stack; a second charging power source, electrically connected to the first fuel cell, for charging the first fuel cell; a second load, electrically connected to the first fuel cell and used for discharging the first fuel cell; a third load, electrically connected to the second fuel cell and used for discharging the second fuel cell; a control console, electrically connected to the first charging power source, the first load, the second charging power source, the second load and the third load respectively; A fourth load is electrically connected to the console.

[0013] An operating method, applied to the above-mentioned liquid flow battery with a sulfur-based fuel cell, comprises the following steps: The main unit is charged and discharged several times until the storage capacity of the main unit drops to a target value; and / or, when the main unit is charged and discharged, the negative electrode electrolyte of the main unit is oxidized by the secondary circuit unit to produce hydrogen; Reducing the positive electrode electrolyte of the main unit through the sulfur-based unit, and / or, when the sulfur-based unit is working, oxidizing the negative electrode electrolyte of the main unit through the secondary circuit unit, and producing hydrogen; The elemental sulfur or sulfur ions produced by the sulfur-based unit are dissolved by the recycling unit, and / or, when the recycling unit is working, the negative electrode electrolyte of the main unit is oxidized by the secondary circuit unit to produce hydrogen.

[0014] Preferably, charging and discharging the main unit several times until the storage capacity of the main unit drops to a target value comprises the following steps: During each charge, 100% of the low-valent positive electrode cations are oxidized to high-valent positive electrode cations, and x% of the high-valent negative electrode cations are reduced to low-valent negative electrode cations. At the same time, hydrogen is released from the negative electrode, 1>x%>0. During each discharge, x% of the high-valent positive electrode cations are reduced to low-valent positive electrode cations, and x% of the low-valent negative electrode cations are oxidized to high-valent negative electrode cations. After several cycles of charge and discharge, the content of low-valent positive electrode cations drops to the target value.

[0015] Preferably, the negative electrode electrolyte of the main unit is oxidized by the secondary circuit unit to produce hydrogen, comprising the following steps: Oxidizing x% of low-valent negative electrode cations in the negative electrode electrolyte through a hydrogen reactor to produce hydrogen; The hydrogen gas is oxidized by the second fuel cell to produce H2O and discharge it.

[0016] Preferably, reducing the positive electrolyte of the main unit by the sulfur-based unit comprises the following steps: The first fuel cell reduces (1-x%) of the high-valent positive electrode cations in the positive electrode electrolyte to obtain (1-x%) of the low-valent positive electrode cations and elemental sulfur or sulfur ions.

[0017] Preferably, dissolving the elemental sulfur or sulfide ions produced by the sulfur-based unit by the recycling unit comprises the following steps: The supporting electrolyte is delivered to the first fuel cell through the recycling unit, and after the reaction, the elemental sulfur or sulfur ions generated in the first fuel cell are dissolved to obtain waste gas; The exhaust gases are absorbed by a re-recovery unit.

[0018] Beneficial effects of the present invention: 1. The sulfur-based fuel cell flow battery of the present invention is generally applicable to aqueous iron-chromium flow batteries and air fuel cells. In addition, a secondary circuit unit is provided for joint hydrogen production. Due to the provision of electrolyte storage tanks and gas storage tanks, the conservation of reactants and electrochemical stoichiometric numbers between sulfur-based discharge and hydrogen production, the secondary circuit unit can be operated simultaneously or decoupled, and is applicable to large-scale iron-chromium flow battery energy storage systems, and ensures high storage capacity, high discharge power and discharge capacity, high battery performance, pollution-free and low-cost (closed circuit, and the product is only nitrogen) operation of the iron-chromium flow battery; 2. The liquid flow battery and the first fuel cell (as a primary circuit), the secondary circuit hydrogen production and the fuel cell of the present invention can be operated jointly or decoupled and operated independently, which increases the flexibility of the energy storage system and expands the storage capacity / power, discharge capacity / power and use.

[0019] 3. The present invention is applicable to the field of large-scale liquid flow battery energy storage, and can be used for aqueous iron-chromium liquid flow batteries or other aqueous liquid flow batteries (neutral, acidic), hydrogen production, fuel cells, oil refining or sulfur-containing waste gas treatment in mines, ensuring the long-term stable operation of the energy storage system with high capacity, high performance, low auxiliary power consumption and low cost.

[0020] 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

[0021] 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.

[0022] Figure 1 A schematic structural diagram of a flow battery with a sulfur-based fuel cell of the present invention is shown; Figure 2 A flow chart showing the operating method of the present invention is shown.

[0023] In the figure: 1, positive electrode electrolyte storage tank; 2, first electrolyte pump; 3, first heat exchanger; 4, first positive electrode liquid inlet pipe; 5, main battery stack; 6, first positive electrode; 7, first ion exchange membrane; 8, first negative electrode; 9, first positive electrode collector plate; 10, first negative electrode collector plate; 11, first positive electrode liquid outlet pipe; 12, first three-way valve; 13, first charging power supply; 14, first load; 15, negative electrode electrolyte storage tank; 16, second electrolyte pump; 17, second heat exchanger ; 18, first negative electrode liquid inlet pipe; 19, first negative electrode liquid outlet pipe; 20, second three-way valve; 21, third three-way valve; 22, hydrogen reactor; 221, reaction catalyst layer; 23, feed inlet; 24, stirrer; 25, heater; 26, circulation valve; 27, circulation pump; 28, first pressure gauge; 29, gas outlet; 30, control valve; 31, air pump; 32, gas storage tank; 321, second pressure gauge; 33, gas pipeline; 34, sulfur-based storage tank; 341, nitrogen bottle; 342, third pressure gauge; 343, gas product outlet; 35, third electrolyte pump; 36, third heat exchanger; 37, first fuel cell; 38, second negative electrode; 39, second ion exchange membrane; 40, second positive electrode; 41, second negative current collector; 42, second positive current collector; 43, second load; 431, second charging power source; 44, air source; 45, first humidifier; 46, second humidifier; 47, second fuel cell; 48, first three negative electrodes; 49, negative catalyst layer; 50, third ion exchange membrane; 51, positive catalyst layer; 52, third positive electrode; 53, third negative current collecting plate; 54, third positive current collecting plate; 55, negative outlet pipe; 56, positive outlet pipe; 57, third load; 58, cleaning agent tank; 59, recovery pump; 60, fourth three-way valve; 61, recovery valve; 62, alkali liquid tank; 63, alkali liquid pump; 64, gas discharge pipeline; 65, control console; 66, fourth load. DETAILED DESCRIPTION

[0024] 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.

[0025] A flow battery with a sulfur-based fuel cell, such as Figure 1 As shown, it includes a main unit, a sulfur-based unit, a secondary circuit unit and a battery control unit.

[0026] The main unit includes a positive electrode electrolyte storage tank 1, a main stack 5 and a negative electrode electrolyte storage tank 15. According to the flow direction of the electrolyte, the positive electrode side outlet of the main stack 5 is connected to the first positive electrode outlet pipe 11, and the first positive electrode outlet pipe 11 is connected to one port of the first three-way valve 12, and then the other port of the first three-way valve 12 is connected to the inlet of the positive electrode electrolyte storage tank 1, and the last port of the first three-way valve 12 is connected to the sulfur-based unit through a pipeline. In addition, along the flow direction of the electrolyte, the outlet of the positive electrode side of the main stack 5 of the positive electrode electrolyte storage tank 1 is sequentially installed with a first electrolyte pump 2 and a three-way valve through a pipeline, and then connected to the first positive electrode inlet pipe 4 through the three-way valve, and the first positive electrode inlet pipe 4 is installed with a first heat exchanger 3 to heat the electrolyte. The outlet of the first positive electrode inlet pipe 4 is connected to the positive electrode side inlet of the main stack 5.

[0027] In addition, on the negative electrode side of the main stack 5, according to the flow path of the electrolyte, the outlet of the negative electrode electrolyte storage tank 15 is connected to the second electrolyte pump 16 and the third three-way valve 21 in sequence through pipelines, and then one port of the third three-way valve 21 is connected to the first negative electrode inlet pipe 18, the outlet of the first negative electrode inlet pipe 18 is connected to the negative electrode side inlet of the main stack 5, and a second heat exchanger 17 for heat exchange with the electrolyte is also provided on the first negative electrode inlet pipe 18. The negative electrode side outlet of the main stack 5 is connected to the first negative electrode outlet pipe 19, the outlet of the first negative electrode outlet pipe 19 is connected to the second three-way valve 20, and then connected to the inlet of the negative electrode electrolyte storage tank 15 through the second three-way valve 20.

[0028] Combination Figure 1 , the electrolyte flow path of the main unit is described below: During charging and discharging, the negative electrode electrolyte is discharged from the negative electrode electrolyte storage tank 15, driven by the second electrolyte pump 16, passes through the heat exchanger, and is adjusted to a temperature suitable for the operation of the liquid flow battery. If the ambient temperature is low, the heat exchanger will heat the electrolyte; on the contrary, if the battery temperature rises due to factors such as high current density circulation, the heat exchanger will cool the electrolyte. Finally, the negative electrode electrolyte smoothly enters the main battery stack 5. Similarly, the positive electrode electrolyte in the positive electrode electrolyte storage tank 1 enters the first positive electrode inlet pipe 4 through the first electrolyte pump 2, and the first heat exchanger 3 will exchange heat with the positive electrode electrolyte, and then the positive electrode electrolyte enters the positive electrode side of the main battery stack 5 for reaction, and returns to the positive electrode electrolyte storage tank 1 after the reaction.

[0029] Combination Figure 1 , the electrochemical reactions of the positive and negative electrodes of the main unit during the full charging process are described below: The electrochemical reactions and side reactions of the positive and negative electrodes during the charging process are: Positive electrode: A0-e-=A; Negative electrode: B0+e-= B; Hydrogen evolution side reaction: 2H+2e-=H2; The electrochemical reactions of the positive and negative electrodes during the discharge process are: Positive electrode: A+e-= A0; Negative electrode: Be-= B0.

[0030] In the above reaction process, A represents a high-valent positive electrode cation, A0 represents a low-valent positive electrode cation, B represents a low-valent negative electrode cation, and B0 represents a high-valent negative electrode cation.

[0031] Combination Figure 1 , the capacity attenuation of the flow battery during the charging and discharging process is described below: During charging, the negative electrode produces a side reaction of hydrogen evolution, so the negative electrode cannot be fully charged at this time. In the subsequent discharge process, the negative electrode will limit the discharge of the positive electrode, resulting in the cathode liquid being unable to release 100% of the electricity. For example, if the electricity stored in the negative electrode is x%, then the positive electrode discharge is also x%. If the charging and discharging process is repeated multiple times, the hydrogen evolution reaction at the negative electrode will cause the storage capacity to become smaller and smaller, thereby reducing the storage capacity of the liquid flow battery. Therefore, in order to restore the capacity of the main unit, it is necessary to use a sulfur-based unit and a secondary circuit unit in conjunction.

[0032] In some optional embodiments, the core component of the flow battery is the main stack 5, which plays the role of a power unit and is the key to energy conversion. The main stack 5 can be constructed by connecting one or more battery cells (i.e., single cells) in series. Each battery cell contains positive and negative electrodes, an electrolyte, and an ion exchange membrane for separating the electrodes, and is equipped with a pair of positive and negative output terminals (i.e., bipolar plates or current collectors) to form a complete battery assembly. In this embodiment, the positive side of the main stack 5 includes a first positive electrode 6 and a first positive current collector 9 located outside the first positive electrode 6, and the negative side of the main stack 5 includes a first negative electrode 8 and a first negative current collector 10 located outside the first negative electrode 8; a first ion exchange membrane 7 is provided between the first positive electrode 6 and the first negative electrode 8. When the number of battery cells is ≥1, a plurality of groups of identical battery cells are connected in series through the first positive current collector 9 and the first negative current collector 10 to form a stack. The positive and negative electrolytes undergo electrochemical oxidation-reduction reactions in the stack.

[0033] It should be noted that in the standard charging process, the voltage is gradually increased from 0V to U1 in constant current or constant power mode. In this process, the reactant ions in the positive and negative electrolytes circulate inside the main battery stack 5, and electrochemical redox reactions occur on the surfaces of the positive and negative electrodes. The active substances in the positive and negative half-cells of the battery unit undergo electrochemical reactions simultaneously to achieve energy storage. Taking the iron-chromium flow battery as an example, during the charging process, the Fe 2+ The ions are oxidized to Fe 3+ Ion, Cr at the negative electrode 3+ The ions are reduced to Cr 2+ Ions. These ions then flow into the positive electrode electrolyte storage tank 1 and the negative electrode electrolyte storage tank 15 for storage. Through this series of reactions, the battery is effectively charged and ensures efficient storage and utilization of energy.

[0034] like Figure 1 As shown, the sulfur-based unit includes a first fuel cell 37 and a sulfur-based storage tank 34 connected to the inlet and outlet of the cathode side of the first fuel cell 37; the inlet and outlet of the cathode side of the first fuel cell 37 are connected to the cathode electrolyte storage tank 1. Specifically, in combination Figure 1 It can be seen that, along the flow direction of the electrolyte, the outlet of the sulfur-based storage tank 34 is connected to the third electrolyte pump 35 and the third heat exchanger 36 in sequence through the second negative electrode liquid inlet pipe until it is connected to the negative electrode side inlet of the first fuel cell 37, and the outlet of the first fuel cell 37 is connected to the inlet of the sulfur-based storage tank 34 through the second negative electrode liquid outlet pipe. In addition, along the flow direction of the electrolyte, the outlet of the positive electrode electrolyte storage tank 1 is connected to the second positive electrode liquid inlet pipe (sharing the three-way valve of the first electrolyte pump 2 with the first positive electrode liquid inlet pipe 7), and is connected to the positive electrode side inlet of the first fuel cell 37 through the pipeline, and the first heat exchanger 3 and the fourth three-way valve 60 are installed in sequence on the second positive electrode liquid outlet pipe. In addition, the positive electrode side outlet of the first fuel cell 37 is connected to the first three-way valve 12 through the second positive electrode liquid outlet pipe, and is connected to the inlet of the positive electrode electrolyte storage tank 1 through the first three-way valve 12.

[0035] Furthermore, the sulfur-based storage tank 34 is also equipped with a third pressure gauge 342 for monitoring the internal pressure of the sulfur-based storage tank 34. At the same time, a gas product outlet 343 is provided on the surface of the sulfur-based storage tank 34, and a nitrogen bottle 341 is connected through a pipeline.

[0036] Combination Figure 1 , the electrolyte flow of the sulfur-based unit is described below: In the working state, the sulfur-based electrolyte in the sulfur-based storage tank 34 is driven by the third electrolyte pump 35 and passes through the third heat exchanger 36 for temperature adjustment (for example, the operating temperature of the iron-chromium flow battery is 50-65°C), and then enters the negative electrode side of the first fuel cell 37. After the electrochemical reaction, the sulfur-based electrolyte returns to the sulfur-based storage tank 34. Similarly, the high-valent positive cations of the electrolyte in the positive electrode electrolyte storage tank 1 can enter the positive electrode side of the first fuel cell 37 for reaction, and the electrolyte with low-valent positive cations is obtained and then returns to the positive electrode electrolyte storage tank 1.

[0037] It should be noted that the positive electrode electrolyte of the sulfur-based fuel cell system contains active substances H2S or SO2 or their hydrates, and the supporting electrolyte can be neutral or slightly acidic.

[0038] Combination Figure 1 , the following is an example of the sulfur-based unit chemical reaction using an iron-chromium flow battery (the cathode electrolyte contains iron ions): The molar amount of the reducing agent stored in the sulfur-based storage tank 34 corresponds to 40% (set as the lower limit of the storage capacity of the iron-chromium flow battery) of the positive electrode electrolyte in the positive electrode electrolyte storage tank 1. 3+ Reduction to Fe 2+ The stoichiometric molar amount (for example, if hydrogen sulfide is used as the reducing agent, the molar ratio of hydrogen sulfide to the excess Fe3+ in the main system is x1=1:2). In the first fuel cell 37, under the action of the catalyst layer coated on the second negative electrode 38, the overall reaction of the fuel cell is: H2S+2Fe 3+ =S+2Fe 2+ +2H + , or SO2+2H2O+ 2Fe 3+ =2Fe 2+ + SO4 2- +4H + , reducing the excess Fe in the positive electrolyte of the main system 3+ (The first fuel cell 37 reacts to reduce 40% of the Fe 3+ ), and replenish the main system hydrogen ions. The first fuel cell 37 uses a second ion exchange membrane 39. During the discharge reaction of the first fuel cell 37, H + Diffusion across the second ion exchange membrane 39 toward the positive electrode, through the stoichiometric molar amounts of sulfur and Fe 3+ The reaction replenishes the H lost in the main unit during the charge and discharge operation phase. + .

[0039] Exemplarily, the positive side of the first fuel cell 37 includes a second positive electrode 40 and a second positive current collecting plate 42 located outside the second positive electrode 40; the negative side of the first fuel cell 37 includes a second negative electrode 38 and a second negative current collecting plate 41 located outside the second negative electrode 38; a second ion exchange membrane 39 is arranged between the second positive electrode 40 and the second negative electrode 38.

[0040] It should be noted that the first fuel cell 37 can also be composed of a group or more battery units (referred to as single cells) connected in series. During the normal discharge process of the first fuel cell 37, a constant current or constant power is used to discharge from U1 (0.3~0.6V) to 0, and the constant current density = jnormal (which can be set to 10~300mAcm -2 ). The reactant ions of the positive and negative electrolytes flow inside the first fuel cell 37 and undergo electrochemical redox reactions on the positive and negative electrodes. The electrochemical reactions of the active substances in the positive and negative half-cells of the battery unit and their energy storage occur simultaneously. During the discharge process, H2S at the negative electrode is oxidized to S (or SO2 is oxidized to SO4 2- ), the high-valent positive electrode cations are reduced to low-valent positive electrode cations, which flow into the positive electrode and negative electrode electrolyte storage tanks 15 for storage respectively.

[0041] It should be further explained that the second negative electrode 38 is coated with a catalyst, which is prepared by coating a metal catalyst or a metal oxide catalyst or a carbon-based catalyst on a carbon-based substrate (carbon felt, graphite felt, activated carbon, etc.) (metal catalysts include but are not limited to transition metal catalysts such as Fe, Zr, Co, Ni, Mn, MOF; metal oxide catalysts include but are not limited to TiO2, titanates, etc.; carbon-based catalysts include but are not limited to graphene, graphene oxide, carbon nanotubes, activated carbon, B / N element-doped nanocarbon materials, etc.), and different electrodes (carbon-based, graphite-based, titanium-based) and other options. By designing the catalytic layer, the hydrogen sulfide reducing agent and Fe can be accelerated. 3+ Reduction reaction, catalytic sulfur-based reducing agent to Fe 3+ The reduction reaction proceeds in the direction of the main reaction, improves the selectivity of the product S, and inhibits the side reactions, namely the oxidation reaction of H2S or SO2, Fe 3+ Reduction reaction, and replenishing the hydrogen ions H lost by hydrogen evolution in the main system electrolyte + The product H + From the second ion exchange membrane 39 to the second positive electrode 40, H + Enter the positive electrode electrolyte to replenish the H lost in the positive electrode electrolyte of the iron-chromium flow battery during the stage of hydrogen evolution leading to capacity loss + The product S after the oxidation of the reducing agent is deposited on the second negative electrode 38, or the product SO4 after the oxidation of the reducing agent 2-The reacted electrolyte is refluxed to the sulfur-based storage tank 34 together. The maximum value of the pressure gauge of the sulfur-based storage tank 34 is monitored to decrease and then no longer change, which is used to assist in indicating whether the oxidation process of the reducing agent is sufficient. The gas mixture (unreacted trace reducing agent H2S or SO2) in the gas phase space at the top of the sulfur-based storage tank 34 is discharged to the rear absorber through the gas product outlet 343.

[0042] like Figure 1 As shown, the sulfur-based unit is also connected to a recycling unit, which includes a cleaning agent tank 58 and an alkali liquid tank 62. The outlet of the cleaning agent tank 58 is connected to a fourth three-way valve 60 through a pipeline (a recovery pump 59 is provided on the pipeline), and one port of the fourth three-way valve 60 is connected to the positive electrode side inlet of the first fuel cell 37. A gas discharge pipeline 64 is provided on the top of the alkali liquid tank 62. In addition, an alkali liquid pump 63 is also configured outside the alkali liquid tank 62, and the inlet and outlet of the alkali liquid pump 63 are respectively connected to the top and bottom of the alkali liquid tank 62 through a pipeline. The positive electrode side outlet of the first fuel cell 37 is connected to the positive electrode electrolyte storage tank 1 through a pipeline, and the pipeline is connected to the alkali liquid tank 62 through a branch (a recovery valve 61 is installed), and the gas generated on the negative electrode side of the sulfur-based unit can be recovered through the alkali liquid tank 62.

[0043] like Figure 1 As shown, the secondary circuit unit includes a hydrogen reactor 22 and a second fuel cell 47; the inlet and outlet of the hydrogen reactor 22 are connected to the negative electrode electrolyte storage tank 15 for hydrogen production; the positive electrode side inlet of the second fuel cell 47 is connected to the hydrogen reactor 22. Specifically, a reaction catalyst layer 221 is provided inside the hydrogen reactor 22, and the reaction catalyst layer 221 divides the inner cavity of the hydrogen reactor 22 into an upper cavity and a lower cavity; wherein an agitator 24 and a heater 25 located on one side of the agitator 24 are installed in the lower cavity, and a feed port 23 (provided with a valve) and an air outlet 29 (provided with a valve) of the hydrogen reactor 22 are provided in the upper cavity; at the same time, the upper cavity is also connected to a first pressure gauge 28 for monitoring the internal pressure; and a catalytic pipeline is connected between the upper cavity and the lower cavity, and a circulation valve 26 and a circulation pump 27 are provided on the catalytic pipeline.

[0044] Furthermore, the upper chamber of the hydrogen reactor 22 is also connected to a gas storage tank 32 via a pipeline (a control valve 30 and an air pump 31 are installed on the pipeline in sequence), and the outlet of the gas storage tank 32 is connected to the inlet on the positive electrode side of the second fuel cell 47 via a gas pipeline 33, and a branch is provided on the gas pipeline 33, on which a second humidifier 46 is installed.

[0045] It should be noted that a second pressure gauge 321 for monitoring gas pressure is also installed on the gas storage pipe 32 .

[0046] The following is an explanation of the working process of the hydrogen reactor using the iron-chromium liquid flow battery as an example: During the charging / discharging of the iron-chromium flow battery and the discharging of the sulfur-based fuel cell, the secondary circuit unit consisting of hydrogen production and fuel cells can be started simultaneously, and the dual circuits can be decoupled, independent, or jointly operated. The secondary circuit hydrogen production and fuel cell discharge improve the storage capacity of the iron-chromium flow battery, improve the flexibility of hydrogen production / storage / discharge operation, and improve the discharge power and discharge capacity of the iron-chromium flow battery through the secondary circuit fuel cell.

[0047] The hydrogen production process can be carried out at any time during the charging or discharging of the iron-chromium flow battery. 2+ The electrolyte is discharged through the secondary circuit to produce hydrogen. The secondary circuit mainly consists of a hydrogen reactor 22 with a reaction catalyst layer 221 (such as MoS2, Mo2C particles, a base layer of carbon felt or graphite felt or titanium mesh or SiO2 particle lining), a built-in agitator 24, a heater 25 and a circulation pump 27. The hydrogen production reaction rate is increased by the catalyst, self-circulation and heating. The pressure is monitored by the first pressure gauge 28 and the accident overpressure is discharged through the outlet 29. In the hydrogen generator, the negative electrode electrolyte of the iron-chromium liquid flow battery produces hydrogen. Formula 2 Cr 2+ +2H + =H2+2Cr 3+ , hydrogen production reactant H + The H obtained from the discharge reaction of the first fuel cell 37 is + , diffuses across the membrane to the positive electrode side of the first fuel cell 37 during the discharge process of the first fuel cell 37, and then charges through the main stack 5 to make H + Diffusion across the membrane to the negative electrode side, and then through the hydrogen reactor 22 reduced to H2. The newly generated Cr 3+ The electrolyte returns to the negative electrode electrolyte storage tank 15 for continued charging of the iron-chromium liquid flow battery, thereby increasing the storage capacity of the iron-chromium liquid flow battery.

[0048] The hydrogen prepared by the hydrogen reactor 22 and the hydrogen produced from the hydrogen evolution side reaction are driven by the gas pump 31 and enter the gas storage tank 32 for storage, and then flow into the negative electrode side of the second fuel cell 47 for reaction after being humidified by the second humidifier 46.

[0049] like Figure 1As shown, the positive electrode side of the second fuel cell 47 is provided with a positive electrode catalyst layer 51, a third positive electrode 52 and a third positive current collector 54 in order from the inside to the outside; the negative electrode side of the second fuel cell 47 is provided with a negative electrode catalyst layer 49, a third negative electrode 48 and a third negative current collector 53 in order from the inside to the outside; a third ion exchange membrane 50 is installed between the positive electrode catalyst layer 51 and the negative electrode catalyst layer 49. The inlet of the positive electrode side of the second fuel cell 47 is connected to the air source 44, and the outlet is connected to the positive electrode outlet pipe 56, while the outlet of the negative electrode side of the second fuel cell 47 is connected to the negative electrode outlet pipe 55; and the air source 44 is also connected in parallel with the first humidifier 45, and the external air source or the air source 44 is humidified by the first humidifier 45 and flows into the positive electrode side of the second fuel cell 47 for reaction.

[0050] like Figure 1 As shown, the battery control unit is electrically connected to the main stack 5, the first fuel cell 37 and the second fuel cell 47 for controlling charging and discharging. Specifically, the battery control unit includes a first charging power supply 13, a first load 14, a second charging power supply 431, a second load 43, a third load 57 and a fourth load 66. The first charging power supply 13 is electrically connected to the main stack 5, and the first charging power supply 13 can charge the main stack 5; the first load 14 is electrically connected to the main stack 5 for discharging the main stack 5; the second charging power supply 431 is electrically connected to the first fuel cell 37 for charging the first fuel cell 37; the second load 43 is electrically connected to the first fuel cell 37 for discharging the first fuel cell 37; the third load 57 is electrically connected to the second fuel cell 47 for discharging the second fuel cell 47; the console 65 is electrically connected to the first charging power supply 13, the first load 14, the second charging power supply 431, the second load 43 and the third load 57 respectively; the fourth load 66 is electrically connected to the console, which can be used as a power load for the excess power of the entire liquid flow battery system.

[0051] Further, for the main stack 5, its corresponding charging and discharging module includes a first charging power supply 13 and a first load 14, which are arranged in parallel. For the first fuel cell 37, its corresponding charging and discharging module includes a second load 43 and a second charging power supply 431, which are arranged in parallel. For the second fuel cell 47, its corresponding charging and discharging module includes a third load 57, which is connected to the positive and negative electrodes of the second fuel cell 47.

[0052] It should be noted that the second fuel cell 47 is a hydrogen-oxygen fuel cell, which can allow hydrogen to react with oxygen absorbed from the air to generate H2O and discharge it.

[0053] like Figure 2 An operating method is shown, which is applied to a liquid flow battery with a sulfur-based fuel cell as described above, comprising the following steps: S1: performing several charge and discharge operations through the main unit until the storage capacity of the main unit drops to a target value; and / or, oxidizing the negative electrode electrolyte of the main unit through the secondary circuit unit when the main unit is charged and discharged, and producing hydrogen.

[0054] S2: reducing the positive electrode electrolyte of the main unit through the sulfur-based unit, and / or, when the sulfur-based unit is working, oxidizing the negative electrode electrolyte of the main unit through the secondary circuit unit, and producing hydrogen; S3: dissolving the elemental sulfur or sulfur ions produced by the sulfur-based unit through the recycling unit, and / or, when the recycling unit is working, oxidizing the negative electrode electrolyte of the main unit through the secondary circuit unit, and producing hydrogen.

[0055] It should be noted that in S1-S3, the secondary circuit unit can work continuously, and the continuous production of hydrogen increases the flexibility of the energy storage system, expands the storage capacity / power, discharge capacity / power and use (such as hydrogen filling and use after hydrogen production and external delivery).

[0056] Further, in S1, the main unit is charged and discharged several times until the storage capacity of the main unit drops to a target value, including the following steps: S101: During each charge, 100% of the low-valent positive electrode cations are oxidized to high-valent positive electrode cations, and x% of the high-valent negative electrode cations are reduced to low-valent negative electrode cations, and hydrogen is released at the negative electrode, 1>x%>0. S102: During each discharge, x% of the high-valent positive electrode cations are reduced to low-valent positive electrode cations, and x% of the low-valent negative electrode cations are oxidized to high-valent negative electrode cations. S103: After several times of charge and discharge, the content of low-valent positive electrode cations drops to the target value.

[0057] Furthermore, in S1-S3, the negative electrode electrolyte of the main unit is oxidized by the secondary circuit unit to produce hydrogen, which includes the following steps: A: x% of the low-valent negative electrode cations in the negative electrode electrolyte are oxidized by the hydrogen reactor 22 to produce hydrogen. B: The hydrogen is oxidized by the second fuel cell 47 to produce H2O and discharge it.

[0058] Further, S2 reduces the positive electrolyte of the main unit through the sulfur-based unit, comprising the following steps: S201: reducing (1-x%) of high-valent positive electrode cations in the positive electrode electrolyte through the first fuel cell 37 to obtain (1-x%) of low-valent positive electrode cations and elemental sulfur or sulfur ions.

[0059] Further, in S3, the elemental sulfur or sulfur ions produced by the sulfur-based unit are dissolved by the recycling unit, comprising the following steps: S301: The supporting electrolyte is delivered to the first fuel cell 37 through the recycling unit, and after the reaction, the elemental sulfur or sulfur ions generated in the first fuel cell 37 are dissolved to obtain waste gas. S302: The waste gas is absorbed by the recycling unit.

[0060] It should be noted that whether elemental sulfur or sulfur ions are generated in the first fuel cell 37 after the reaction is dissolved depends on the reactants. If the reactant is H2S, elemental sulfur will be generated; if the reactant is SO2, S 6+ .

[0061] The following describes the operation method by combining S1-S3 and taking the iron-chromium flow battery as an example, wherein the reaction formula of the iron-chromium flow battery is as follows: In a charge and discharge cycle, the electrochemical reactions and side reactions of the positive and negative electrodes during the charging process are: Positive electrode: Fe 2+ -e - = Fe 3+ ; Negative electrode: Cr 3+ +e - = Cr 2+ ; Hydrogen evolution side reaction: 2H + +2e - =H2; The electrochemical reactions of the positive and negative electrodes during the discharge process are: Positive electrode: Fe 3+ +e - = Fe 2+ ; Negative electrode: Cr 2+ -e - = Cr 3+ Combining the above reaction process, the iron-chromium liquid flow battery can be divided into the charging and discharging stage, the sulfur-based reduction stage, the recycling stage and the hydrogen production stage.

[0062] 1. Charging and discharging stage, which requires multiple charging and discharging cycles During the charging process, the positive electrode electrolyte of the iron-chromium flow battery flows out from the positive 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 iron-chromium flow battery (for example, the operating temperature of the iron-chromium flow battery 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. Finally, the positive electrode electrolyte (containing 100% F 2+ ) flows into the main stack 5 through the heat exchanger. After the reaction, the positive electrode electrolyte (100% F at this time) 3+), flows into the positive electrode electrolyte storage tank 1 for storage. At the same time, the electrolyte of the negative electrode electrolyte storage tank 15 enters the main stack 5 to undergo reduction reaction and hydrogen evolution side reaction to obtain Cr 2+ and Cr 3+ The mixed electrolyte and hydrogen are then returned to the negative electrode electrolyte storage tank 15.

[0063] The discharge process is similar to the charging process. During the discharge process of the iron-chromium flow battery, the positive electrode Fe 3+ Reduction to Fe 2+ ,Cr 2+ Oxidized to Cr 3+ , respectively refluxed to the positive electrode electrolyte storage tank 1 and the negative electrode electrolyte storage tank 15, but at this time, due to the influence of the negative electrode hydrogen evolution reaction, the positive electrode Fe 3+ Cannot be completely restored to F 2+ At this point, a charge and discharge cycle ends.

[0064] During the charge and discharge cycle of the iron-chromium flow battery, the capacity will be unbalanced due to the side reaction of hydrogen evolution. Specifically, during the charging stage, the negative electrode consumes a small amount of current (for example, 1%) due to hydrogen evolution, causing its charging state to fail to reach full charge (i.e. 99% of the Cr 2+ is charged), while the positive electrode is fully charged (100% Fe 3+ At this point, the electrolyte in the negative electrode will restrict subsequent discharge and weaken the charge storage capacity of the iron-chromium flow battery energy storage system. In the discharge stage, because the negative electrode is not fully charged, it becomes a limiting factor. Therefore, the discharge capacity of the iron-chromium flow battery is limited to 99% of its total capacity, and the positive electrode electrolyte cannot be fully discharged (the remaining 1% of high-valent Fe 3+ , that is, 99% of the active material is in the discharge state Fe 2+ This charge imbalance during the charge and discharge cycle causes the capacity of the iron-chromium flow battery to gradually decrease. During the next charge cycle, the positive electrode does not start from a fully discharged state (because only 99% of the active material is in the discharged state). 2+ ), resulting in a 1% loss in the charge storage capacity of the iron-chromium flow battery. As the number of cycles increases, the capacity loss will continue to accumulate (i.e., cumulative capacity decay), eventually leading to an irreversible decrease in the storage capacity of the iron-chromium flow battery system.

[0065] After multiple charge and discharge cycles, the capacity loss of the iron-chromium flow battery gradually accumulates as follows: Assume that after 1000 cycles, the battery capacity has decreased by 40% in total. This means that at the end of a charge and discharge cycle, the positive electrode electrolyte is not completely discharged, and 40% of the active substances are still in a high-valent state (i.e., Fe 3+ ), while only 60% of the active substances (Fe 2+) is in the discharge state; at the same time, the negative electrode has been fully discharged and all converted into Cr 3+ This charge imbalance in the charge and discharge cycle is the main reason for the decrease in the capacity of the iron-chromium flow battery. In the subsequent charging process, since only 60% of the active material in the positive electrode can participate in the charging, the battery's charge storage capacity will lose 40%. This loss is irreversible and directly leads to a 40% reduction in the storage capacity of the iron-chromium flow battery system, thereby shortening the battery's cycle life.

[0066] 2. Preparation Procedures before Sulfide Reduction When the charge storage capacity of the main unit drops to the target value, the charge and discharge cycle ends, and then the main unit of the iron-chromium flow battery is charged again (normal charging, constant current or constant power charging from 0V to U1, constant current density = jnormal). After full charge, the state is: the actual charging capacity is 60% of the rated capacity (based on the above judgment basis), then the positive electrode electrolyte state at the end of charging is 100% Fe 3+ (Actually 60% Fe 2+ Participated in this charging and became Fe 3+ , there is 40% excess Fe in the positive electrolyte 3+ , at this time the actual SOC of the positive electrode = 100%); the electrolyte state of the negative electrode is 60% Cr 2+ +40% Cr 3+ (Actually only 60% Cr 3+ Participated in this charge, and there is still 40% Cr 3+ In the uncharged state. At this time, the actual SOC of the negative electrode is 60%). At this time, the charging process of the main system of the iron-chromium liquid flow battery is stopped, and the positive electrode electrolyte state is 100% Fe 3+ (Actual SOC of positive electrode = 100%); the electrolyte state of negative electrode is 60% Cr 2+ +40% Cr 3+ (Actual SOC of negative electrode = 60%).

[0067] 2. Sulfide reduction stage 1. Preparation Procedure The main battery stack 5 is charged from 0V to U1 at a constant current or constant power, and the constant current density = jnormal. The state after full charge is: the actual charging capacity is 60% of the rated capacity, and the state of the positive electrode electrolyte after full charge is 100% Fe 3+ (Actually 60% Fe 2+ Participated in this charging and became Fe 3+ , there is 40% excess Fe in the positive electrolyte 3+ , at this time the actual SOC of the positive electrode = 100%); the electrolyte state of the negative electrode is 60% Cr 2+ +40% Cr3+ (Actually only 60% Cr 3+ Participated in this charge, and there is still 40% Cr 3+ In the uncharged state. At this time, the actual SOC of the negative electrode = 60%).

[0068] 2. After the preparation procedure is completed, the first fuel cell 37 performs discharge and simultaneously reduces the excess Fe 3+ , supplement the main unit's H + The first fuel cell 37 supplies a constant current density (10-100 mA cm) to the second load 43. -2 ) discharges to the inflection point U2 (0-0.5v) where the voltage drops sharply.

[0069] When the iron-chromium flow battery uses hydrochloric acid as the supporting electrolyte, the reducing agent hydrogen sulfide and Fe 3+ Overall reaction H2S+2Fe 3+ =S+2Fe 2+ +2H + Since H2S is oxidized to S at a potential of 0.142V, Fe 3+ Reduction to Fe 2+ The potential is 0.77 V, and the catalytic layer enhances the kinetics of sulfur-based hydrothermal reactions, so H2S and Fe 3+ The polarization overpotential of the reaction is extremely low and close to 0V, which improves the efficiency of the fuel cell and increases the power generation. When the iron-chromium flow battery uses sulfuric acid / sulfuric acid mixed acid / other mixed acid containing sulfuric acid as the supporting electrolyte, the reductant SO2 oxidation reaction SO2+2H2O-2e - = SO4 2- +4H + , the iron ion reacts to form Fe 3+ +e - = Fe2+, total reaction SO2+2H2O+ 2Fe 3+ =2Fe 2+ + SO4 2- +4H + The oxidation potential of SO2 is 0.158V, so under catalytic conditions, SO2 and Fe 3+ The polarization overpotential of the reaction is low, which improves the efficiency of the fuel cell and increases the power generation. Depending on the different fuel cell structure designs, electrolytes (different iron-chromium concentrations), different reducing agents (sulfur-based reducing agents such as hydrogen sulfide and sulfur dioxide), different catalysts, and different electrodes, the constant voltage charging voltage U2 and current density j2 setting values ​​are different.

[0070] During reduction, the negative electrode side of the first fuel cell 37 operates as follows: The positive electrolyte in the positive electrolyte storage tank 1 passes through the second negative electrode 38 of the first fuel cell 37. At this time, 100% of Fe 3+ Reduction to 100% Fe 2+ After the reduction is completed, it flows back to the positive electrode electrolyte storage tank 1 for storage.

[0071] During the reduction, the operation procedure of the positive electrode side of the first fuel cell 37 is as follows: The sulfur-based electrolyte (reducing agent) in the sulfur-based storage tank 34 flows into the second negative electrode 38 and contacts the catalyst layer coated on the electrode to perform an electrochemical reaction. The design of the catalyst layer can accelerate the reaction of the hydrogen sulfide reducing agent and Fe 3+ Reduction reaction, catalytic sulfur-based reducing agent to Fe 3+ The reduction reaction proceeds in the direction of the main reaction, improves the selectivity of the product S, and inhibits the side reactions, namely the oxidation reaction of H2S or SO2, Fe 3+ Reduction reaction, and replenishing the hydrogen ions H lost by hydrogen evolution in the main system electrolyte + The product H + Conducted from the second cation exchange membrane 39 to the second positive electrode 40. Positive electrode, H + Enter the main system positive electrode electrolyte to replenish the H lost in the iron-chromium flow battery positive electrode electrolyte during the hydrogen evolution-induced capacity loss stage + .

[0072] (2) Iron-chromium flow battery recharging procedure The negative electrode side operation procedure of the main battery stack 5 is as follows: The negative electrode electrolyte of the iron-chromium flow battery flows out of the negative electrode electrolyte storage tank 15 and enters the main stack 5. The main stack 5 is charged by the first charging power supply 13 at a constant voltage U1. At this time, the electrolyte state on the negative electrode side of the main stack 5 is 60% Cr 2+ +40% Cr 3+ Therefore, during discharge, 40% Cr 3+ Reduced to 40% Cr 3+ , and finally get 100 Cr 2+ And return to the negative electrode electrolyte storage tank 15, and the remaining reaction is the hydrogen evolution side reaction.

[0073] The operating procedure of the positive electrode side of the main battery stack 5 is as follows: When the main battery stack 5 is charged, 100% of the Fe in the positive electrode electrolyte 2+ 40% corresponds to 40% Cr on the negative electrode side 3+ Reduction reaction, 60% Fe 2+ Corresponding to the hydrogen evolution reaction on the negative electrode side. 2+ Reduced to 100% Fe 2+ Reflux to the positive electrode electrolyte storage tank 1.

[0074] During the recharging stage, the first fuel cell 37 discharges and reduces the generated Fe 2+ After being transported to the main stack 5, the positive electrode of the main stack 5 continues to generate Fe 2+ Oxidized to Fe 3+ When the first fuel cell 37 converts all the excess Fe 3+ (40% in total) are all converted into Fe 2+ , this part of Fe 2+ The main battery stack 5 is precharged, and then the electrolyte in the positive electrode electrolyte storage tank 1 is completely oxidized to Fe 3+ At this time, the negative electrode of the main stack 5 pre-charges the remaining 40% Cr in the negative electrode electrolyte storage tank 15 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 iron-chromium flow battery is fully charged, and the capacity of the iron-chromium flow battery is fully recovered (both the positive and negative electrodes are SOC=100%).

[0075] During the sulfur-based reduction stage, the main system recharging operation procedure, charging stop procedure and parameter settings are as follows: The first charging power source 13 charges the main battery stack 5 at a constant voltage U1 until the cut-off current density limit j is reached. min The main system storage capacity is restored to the rated capacity. The main battery stack 5 is charged at constant voltage U1, and the charging current first increases and then decreases until the current density ≤ j min And it no longer changes, and the main system storage capacity is restored to the rated capacity. Based on the current and capacity criteria, it is judged that the recharging joint operation of the sulfur-based fuel cell and the iron-chromium flow battery (sulfur-based reduction stage) has been completed.

[0076] Depending on the stack design, electrolyte / catalyst / electrode selection, etc. of the iron-chromium flow battery system, the charging voltage U1 and current density limit j min As an example, U1 can be set to 1.2~1.3V, j min Can be set to 1~10mAcm -2 The positive electrode electrolyte reduction system operation phase, that is, the first charging power source 13 maintains the main battery stack 5 at a constant voltage U1 charging operation phase until the main battery stack 5 current density ≤ j min At the same time, when the main system storage capacity is restored to the rated capacity, it means that the main system has excess Fe 3+ When the reduction process is completed, the first charging power source 13 stops charging, and the entire sulfur-based reduction phase ends. The above stop procedure indicates that the iron-chromium positive electrode electrolyte reduction operation has been completed, the iron-chromium main system recharge and the battery capacity / performance recovery have been completed.

[0077] It should be noted that the sulfur-based reduction stage issues program run and stop instructions according to the above program, parameter settings and criteria, can automatically continue the reaction and terminate according to the criteria, can quantitatively determine that the capacity recovery of the iron-chromium liquid flow battery is complete, and complete the complete recovery of the state of charge, capacity and performance of the iron-chromium liquid flow battery electrolyte. Through the design of the above system and program method, the complexity, power consumption and cost of the iron-chromium liquid flow battery capacity and performance recovery subsystem are effectively reduced, and the overall system efficiency of the iron-chromium liquid flow battery is improved. The sulfur-based fuel cell and the iron-chromium liquid flow battery positive electrode electrolyte undergo a discharge reaction, and the only product is the H originally lost by the system. + , the active substance FeCl2 of the electrolyte, the sulfur deposited on the negative electrode side of the first fuel cell 37 or the supporting electrolyte component SO4 2- , a small amount of water vapor, the reactants and liquid products are all substances in the main system of the iron-chromium liquid flow battery, and no additional pollution or toxic substances are produced to the electrolyte of the main system of the liquid flow battery. Therefore, the sulfur-based unit has the advantages of simplicity, low cost, automatic continuous reaction and stop, quantifiable capacity recovery endpoint, automatic termination of the charge and discharge program according to the judgment criteria, and low power consumption. This subsystem is mainly designed for a closed-loop iron-chromium liquid flow battery, and it has a wide range of application prospects and can be applied to other aqueous liquid flow batteries.

[0078] 3. Recycling Stage During the discharge phase of the first fuel cell 37, a trace amount of sulfur solids are deposited on the second negative electrode 38 with catalyst, resulting in electrode passivation. After the discharge of the first fuel cell 37 is completed, the second charging power supply 431 is started to charge the first fuel cell 37. The electrolyte in the cleaning agent tank 58 is a supporting electrolyte (the supporting electrolyte of the iron-chromium liquid flow battery, such as hydrochloric acid, sulfuric acid, etc.), and the electrolyte flows into the second positive electrode 40 of the first fuel cell 37. The hydrochloric acid (under the condition that the supporting electrolyte of the iron-chromium liquid flow battery is hydrochloric acid) at the second positive electrode 40 decomposes into chlorine gas, enters the electrolyte, and flows into the alkali liquid tank 62 to be absorbed. The electrolyte in the sulfur-based storage tank 34 is driven by the third electrolyte pump 35, and the sulfur solids on the second negative electrode 38 with catalyst react and dissolve into polysulfide ions Sx-, enter the electrolyte, and flow back into the sulfur-based storage tank 34.

[0079] It should be noted that the first fuel cell 37 is charged with a constant current until the charging voltage U3 rises sharply to an inflection point U 3cr , it means that the trace sulfur solids deposited on the electrolytic cell have been purified, the passivation problem of the electrolytic cell electrodes has been avoided, and the introduction of impurities has been avoided due to the use of the supporting electrolyte of the iron-chromium liquid flow battery as a cleaning agent. At this time, charging is stopped.

[0080] 4. Hydrogen production stage During the charging / discharging of the main stack 5 of the iron-chromium flow battery and the discharging of the first fuel cell 37, the secondary circuit unit consisting of hydrogen production and fuel cell can be started simultaneously, and the dual circuits can realize decoupled independent or joint operation. Through the hydrogen production and fuel cell discharge of the secondary circuit, the storage capacity of the iron-chromium flow battery is improved, the flexibility of hydrogen production / storage / discharge operation is improved, and the discharge power and discharge capacity of the iron-chromium flow battery are improved through the fuel cell of the secondary circuit.

[0081] The process of the hydrogen production stage has been described in the process flow of the hydrogen reactor 22 and will not be repeated here.

[0082] 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 flow battery with a sulfur-based fuel cell, characterized in that: include: A main unit comprises a main battery stack (5), a positive electrode electrolyte storage tank (1) connected to the inlet and outlet of the positive electrode side of the main battery stack (5), and a negative electrode electrolyte storage tank (15) connected to the inlet and outlet of the negative electrode side of the main battery stack (5); A sulfur-based unit comprises a first fuel cell (37) and a sulfur-based storage tank (34) connected to the inlet and outlet of the cathode side of the first fuel cell (37); the inlet and outlet of the cathode side of the first fuel cell (37) are connected to the cathode electrolyte storage tank (1); The secondary circuit unit comprises a hydrogen reactor (22) and a second fuel cell (47); the inlet and outlet of the hydrogen reactor (22) are connected to the negative electrode electrolyte storage tank (15) for producing hydrogen; the negative electrode side inlet of the second fuel cell (47) is connected to the hydrogen reactor (22), and the negative electrode side outlet is connected to the negative electrode outlet pipe (55); the positive electrode side inlet of the second fuel cell (47) is connected to the air source (44), and the positive electrode side outlet is connected to the positive electrode outlet pipe (56); A battery control unit, electrically connected to the main battery stack (5), the first fuel cell (37) and the second fuel cell (47), and used for controlling charging and discharging; The recycling unit is connected to the sulfur-based unit.

2. A liquid flow battery with a sulfur-based fuel cell according to claim 1, characterized in that: The positive electrode side of the main battery stack (5) comprises a first positive electrode (6) and a first positive current collecting plate (9) located outside the first positive electrode (6); The negative electrode side of the main battery stack (5) comprises a first negative electrode (8) and a first negative current collecting plate (10) located outside the first negative electrode (8); A first ion exchange membrane (7) is provided between the first positive electrode (6) and the first negative electrode (8).

3. A liquid flow battery with a sulfur-based fuel cell according to claim 1, characterized in that: The positive electrode side of the first fuel cell (37) comprises a second positive electrode (40) and a second positive current collecting plate (42) located outside the second positive electrode (40); The negative electrode side of the first fuel cell (37) comprises a second negative electrode (38) and a second negative current collecting plate (41) located outside the second negative electrode (38); A second ion exchange membrane (39) is provided between the second positive electrode (40) and the second negative electrode (38).

4. A liquid flow battery with a sulfur-based fuel cell according to claim 3, characterized in that: The recycling unit comprises: A cleaning agent tank (58) connected to the positive electrode side inlet of the first fuel cell (37); An alkali liquid tank (62), wherein the alkali liquid tank (62) is provided with a gas discharge pipeline (64); the alkali liquid tank (62) is also provided with an alkali liquid pump (63), wherein the inlet and the outlet of the alkali liquid pump (63) are both connected to the alkali liquid tank (62); The positive electrode side outlet of the first fuel cell (37) is connected to the positive electrode electrolyte storage tank (1) via a second positive electrode liquid outlet pipe, and the second positive electrode liquid outlet pipe is connected to the alkaline solution tank (62) via a branch.

5. A liquid flow battery with a sulfur-based fuel cell according to claim 1, characterized in that: A reaction catalytic layer (221) is arranged inside the hydrogen reactor (22), and the reaction catalytic layer (221) divides the inner cavity of the hydrogen reactor (22) into an upper cavity and a lower cavity; The lower chamber is provided with an agitator (24) and a heater (25) located on one side of the agitator (24); The upper chamber is provided with a feed inlet (23) and a gas outlet (29) of a hydrogen reactor (22); A catalytic pipeline is connected between the upper chamber and the lower chamber, and a pump and a valve are arranged on the catalytic pipeline.

6. A liquid flow battery with a sulfur-based fuel cell according to claim 5, characterized in that: The upper chamber of the hydrogen reactor (22) is also connected to a gas storage tank (32), and the outlet of the gas storage tank (32) is connected to the inlet of the positive electrode side of the second fuel cell (47).

7. A flow battery with a sulfur-based fuel cell according to claim 1, characterized in that: The positive electrode side of the second fuel cell (47) is provided with a positive electrode catalyst layer (51), a third positive electrode (52) and a third positive electrode current collecting plate (54) in sequence from the inside to the outside; The negative electrode side of the second fuel cell (47) is provided with a negative electrode catalyst layer (49), a third negative electrode (48) and a third negative electrode current collecting plate (53) in sequence from the inside to the outside; A third ion exchange membrane (50) is installed between the positive electrode catalyst layer (51) and the negative electrode catalyst layer (49).

8. A liquid flow battery with a sulfur-based fuel cell according to any one of claims 1 to 7, characterized in that: The battery control unit comprises: A first charging power source (13), electrically connected to the main battery stack (5), and used for charging the main battery stack (5); A first load (14) is electrically connected to the main fuel cell stack (5) and is used for discharging the main fuel cell stack (5); a second charging power source (431), electrically connected to the first fuel cell (37), and used to charge the first fuel cell (37); a second load (43), electrically connected to the first fuel cell (37), and used for discharging the first fuel cell (37); a third load (57), electrically connected to the second fuel cell (47) and used for discharging the second fuel cell (47); A control console (65) electrically connected to the first charging power source (13), the first load (14), the second charging power source (431), the second load (43) and the third load (57) respectively; A fourth load (66) is electrically connected to the console.

9. An operating method, applied to a liquid flow battery with a sulfur-based fuel cell according to any one of claims 1 to 8, characterized in that: The following steps are involved: The main unit is charged and discharged several times until the storage capacity of the main unit drops to a target value; and / or, when the main unit is charged and discharged, the negative electrode electrolyte of the main unit is oxidized by the secondary circuit unit to produce hydrogen; Reducing the positive electrode electrolyte of the main unit through the sulfur-based unit, and / or, when the sulfur-based unit is working, oxidizing the negative electrode electrolyte of the main unit through the secondary circuit unit, and producing hydrogen; The elemental sulfur or sulfur ions produced by the sulfur-based unit are dissolved by the recycling unit, and / or, when the recycling unit is working, the negative electrode electrolyte of the main unit is oxidized by the secondary circuit unit to produce hydrogen.

10. An operating method according to claim 9, characterized in that: The main unit is charged and discharged several times until the storage capacity of the main unit drops to the target value, including the following steps: During each charge, 100% of the low-valent positive electrode cations are oxidized to high-valent positive electrode cations, and x% of the high-valent negative electrode cations are reduced to low-valent negative electrode cations. At the same time, hydrogen is released from the negative electrode, 1>x%>0. During each discharge, x% of the high-valent positive electrode cations are reduced to low-valent positive electrode cations, and x% of the low-valent negative electrode cations are oxidized to high-valent negative electrode cations. After several cycles of charge and discharge, the content of low-valent positive electrode cations drops to the target value.

11. An operating method according to claim 10, characterized in that: The negative electrode electrolyte of the main unit is oxidized by the secondary circuit unit to produce hydrogen, including the following steps: Oxidizing x% of low-valent negative electrode cations in the negative electrode electrolyte through a hydrogen reactor (22) to produce hydrogen; The hydrogen gas is oxidized by the second fuel cell (47) to produce H2O and discharge it.

12. An operating method according to claim 10, characterized in that: Reducing the positive electrolyte of the main unit through the sulfur-based unit includes the following steps: The first fuel cell (37) reduces (1-x%) of the high-valent positive electrode cations in the positive electrode electrolyte to obtain (1-x%) of the low-valent positive electrode cations and elemental sulfur or sulfur ions.

13. An operating method according to claim 10, characterized in that: The elemental sulfur or sulfur ions produced by the sulfur-based unit are dissolved by a recycling unit, comprising the following steps: The supporting electrolyte is delivered to the first fuel cell (37) through the recycling unit, and after the reaction, the elemental sulfur or sulfur ions generated in the first fuel cell (37) are dissolved to obtain waste gas; The exhaust gases are absorbed by a re-recovery unit.

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