Flow battery system

Abstract

The invention discloses a flow battery system, which belongs to the technical field of batteries and comprises a main battery system and a fuel battery system. The invention provides a flow battery system composed of a main battery system and a fuel battery system, and the flow battery system is based on the reduction effect of a reducing agent in a storage tank on high-valence metal ions in a positive electrode electrolyte and the reaction catalysis effect of a second catalyst layer in a reaction container on low-valence metal ions and hydrogen ions in a negative electrode electrolyte. And the hydrogen production operation can be realized while the capacity recovery of the main battery system is realized.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a liquid flow battery system. Background Art

[0002] Liquid flow batteries are generally composed of a stack unit, an electrolyte, an electrolyte storage and supply unit, a battery management and control unit, etc. Liquid flow batteries are high-performance storage batteries that use separate positive and negative electrolytes and independent circulation of the positive and negative electrodes. During operation, liquid flow batteries achieve mutual conversion of electrical energy and chemical energy through reversible redox reactions (i.e., reversible changes in valence states) of active substances in the positive and negative electrolyte solutions. During charging, an oxidation reaction occurs at the positive electrode to increase the valence state of the active substance, and a reduction reaction occurs at the negative electrode to reduce the valence state of the active substance, and the discharge process is the opposite. Unlike general solid-state batteries, the positive and negative electrolyte solutions of liquid flow batteries are respectively stored in the positive and negative electrode storage tanks outside the battery, and are transported to the inside of the battery for reaction through pumps and pipelines.

[0003] Since liquid flow batteries usually use aqueous electrolytes, liquid flow batteries are aqueous electrochemical energy storage systems. Compared with non-aqueous electrochemical energy storage systems (for example, compared with lithium batteries), aqueous liquid flow batteries have a significant disadvantage in that the thermodynamically stable voltage window of the electrolyte is narrow, which is limited by water electrolysis. Water electrolysis can lead to side reactions, namely, oxygen evolution at the positive electrode and hydrogen evolution at the negative electrode. In the liquid flow battery stack, electrons flow between the positive and negative electrodes in the external circuit, and the positive and negative electrode ions flow inside the stack, and electrochemical redox reactions occur. The electrochemical reactions and energy storage of the active substances of the positive half-cell or the negative half-cell of any battery unit can only occur simultaneously. However, electrochemical side reactions will inevitably occur under normal operating conditions of the liquid flow battery. The side reactions will irreversibly consume electrons, resulting in an imbalance in the charge state of the positive and negative electrolytes (referred to as charge imbalance), and ultimately leading to an imbalance in the capacity of the positive and negative electrodes and a reduction in capacity. Summary of the invention

[0004] The purpose of the present application is to provide a liquid flow battery system to solve the problem of capacity loss of existing liquid flow batteries mentioned in the above background technology.

[0005] To achieve the above objectives, the present application provides the following technical solutions: a liquid flow battery system, comprising a main battery system and a fuel cell system, wherein the main battery system comprises:

[0006] A first stack including a positive electrode and a negative electrode separated by an ion exchange membrane;

[0007] A positive electrode electrolyte storage tank is connected to the positive electrode of the first battery stack through a pipeline fluid, and a circulation loop is formed between the positive electrode electrolyte storage tank and the positive electrode;

[0008] A negative electrode electrolyte storage tank is connected to the negative electrode of the first battery stack through a pipeline fluid, and a circulation loop is formed between the negative electrode electrolyte storage tank and the negative electrode;

[0009] The fuel cell system comprises:

[0010] A second battery stack, comprising a positive electrode and a negative electrode separated by an ion exchange membrane, wherein the positive electrode of the second battery stack is connected to the positive electrolyte storage tank through a pipeline fluid, and a circulation loop is formed between the positive electrode of the second battery stack and the positive electrolyte storage tank;

[0011] A storage tank body, in which a reducing agent for reducing high-valent metal ions in the positive electrode electrolyte is stored, and the storage tank body is connected to the negative electrode of the second battery stack through a pipeline fluid, and a circulation loop is formed between the negative electrode and the storage tank body;

[0012] The liquid flow battery system further comprises:

[0013] The reaction container is connected to the negative electrode electrolyte storage tank through a pipeline fluid, and a circulation loop is formed between the reaction container and the negative electrode electrolyte storage tank. The reaction container is provided with a second catalytic layer for catalyzing the reaction between low-valent metal ions and hydrogen ions in the negative electrode electrolyte.

[0014] Furthermore, the main battery system is an iron-chromium liquid flow battery system, and the reducing agent in the storage tank is an amino reducing agent.

[0015] Furthermore, the ion exchange membrane of the second fuel cell stack is a cation exchange membrane.

[0016] Furthermore, the second catalytic layer is made of carbon felt, graphite felt, titanium mesh or SiO 2 The particle liner is the base layer and is covered with MoS 2 , Mo 2 The catalytic layer of C particles.

[0017] Furthermore, the liquid flow battery system also includes a gas storage tank body, and the gas storage tank body is fluidically connected to the reaction container through a gas recovery pipe.

[0018] Furthermore, the liquid flow battery system also includes a third battery stack, the third battery stack having a positive electrode and a negative electrode separated by an ion exchange membrane, the negative electrode of the third battery stack is led out with a first inlet tube and a first outlet tube, the end of the first inlet tube away from the third battery stack is connected to the fluid of the gas storage tank body, the positive electrode of the third battery stack is led out with a second inlet tube and a second outlet tube, the end of the second inlet tube away from the third battery stack is connected to an external gas source.

[0019] Furthermore, a third catalytic layer is disposed between the positive electrode and the ion exchange membrane and between the negative electrode and the ion exchange membrane of the third fuel cell stack.

[0020] Furthermore, both the first inlet pipe and the second inlet pipe are equipped with a humidifier.

[0021] Furthermore, the reaction container is provided with a self-circulation pipe, both ends of the self-circulation pipe are connected to the reaction container, and both ends of the self-circulation pipe are respectively arranged on both sides of the second catalytic layer.

[0022] Furthermore, the liquid flow battery system also includes a controller, which is configured to control the charging and discharging of the first battery stack and the discharging process of the second battery stack and the third battery stack.

[0023] Compared with the prior art, the beneficial effects of this application are:

[0024] The present application proposes a liquid flow battery system composed of a main battery system and a fuel cell system. Based on the reduction effect of the reducing agent in the storage tank on the high-valent metal ions in the positive electrode electrolyte and the catalytic effect of the second catalytic layer in the reaction container on the reaction of low-valent metal ions and hydrogen ions in the negative electrode electrolyte, it is possible to achieve hydrogen production operations while achieving capacity recovery of the main battery system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of an existing liquid flow battery system;

[0026] Figure 2 This is an overall schematic diagram of the liquid flow battery system of this application;

[0027] Figure 3 Schematic diagram of the main flow battery system;

[0028] Figure 4 Partial schematic diagram of the flow battery system for this application Figure 1 ;

[0029] Figure 5 Partial schematic diagram of the flow battery system for this application Figure 2 ;

[0030] Figure 6 Partial schematic diagram of the third battery stack. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] Reference Figure 1 , is a schematic diagram of the structure of an existing liquid flow battery system. The liquid flow battery is mainly composed of a battery stack 1, a positive electrolyte storage tank 2 and a negative electrolyte storage tank 3. The battery stack 1 and the positive electrolyte storage tank 2 and the negative electrolyte storage tank 3 are connected by pipelines, and pumps, valves, pipelines and heat exchangers are arranged on the pipelines to control the flow of electrolyte in the charge and discharge state of the liquid flow battery. The iron-chromium liquid flow battery is used as an example for explanation. At this time, the electrolyte flowing in the liquid flow system is FeCl 2 , CrCl 3 and HCl. During the operation of the flow battery, the electrolyte undergoes redox reactions at the positive and negative electrodes of the stack, and at the same time, electrons flow between the positive and negative electrodes in the first stack in the external circuit. Specifically, during the operation of the iron-chromium flow battery, the electrochemical reactions and side reactions of the positive and negative electrodes in the charging state are:

[0033] Positive electrode: Fe 2+ -e-=Fe 3+ , 0.77V vs SHE

[0034] Negative electrode: Cr 3+ +e-=Cr 2+ , -0.41V vs SHE

[0035] Hydrogen evolution side reaction: 2H + +2e-=H 2 , 0V vs SHE

[0036] The electrochemical reactions of the positive and negative electrodes in the discharge state are:

[0037] Positive electrode: Fe 3+ +e-=Fe 2+ , 0.77V vs SHE

[0038] Negative electrode: Cr 2+ -e-=Cr 3+ , -0.41V vs SHE

[0039] It can be seen that in a charge and discharge cycle of the flow battery, the negative electrode 1a of the stack 1 will undergo a hydrogen evolution side reaction in the charging state, and will cause an imbalance between the negative electrode and the positive electrode. Specifically, the mechanism of the capacity imbalance caused by the hydrogen evolution side reaction is as follows: in the charging state, since the negative electrode consumes part of the current (for example, 1%) for hydrogen evolution, the negative electrode where the hydrogen evolution side reaction occurs cannot be fully charged (for example, 99%, that is, 99% Cr is obtained by charging). 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 1a electrolyte will limit the subsequent discharge state and reduce the charge storage capacity of the flow battery energy storage system; in the discharge state, since the negative electrode 1a is not fully charged, the negative electrode 1a becomes the limiting side, so in the discharge state, 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 the discharge 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. In the charging state of the next cycle, the positive electrode 1b 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.

[0040] The mechanism of capacity loss accumulation of multiple cycles of iron-chromium flow battery is as follows: after 1000 cycles of charge and discharge, assuming that the capacity decays by 40% in total, 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 and discharge cycle will cause the capacity of the iron-chromium flow battery to decrease. In the charging state 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 the discharged state). 2 + , which can participate in charging), resulting in a 40% loss in the charge storage capacity of the iron-chromium 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. Based on the imbalance problem between the negative electrode and the positive electrode caused by the above-mentioned hydrogen evolution side reaction, the present application proposes a new flow battery system.

[0041] A liquid flow battery system, referring to Figure 2, including a main battery system and a fuel cell system, wherein the main battery system includes a first battery stack 10, the first battery stack 10 includes at least one group of battery cells, a single group of battery cells is composed of positive and negative electrodes / electrolyte and an ion exchange membrane separating the electrodes, and has a battery assembly with a pair of positive and negative output terminals (bipolar plates or current collectors). Exemplarily, the first battery stack 10 has a negative current collector 10e, a negative electrode 10d, an ion exchange membrane 10c, a positive electrode 20b and a positive current collector 20a. When the first battery stack 10 has When there are multiple groups of battery cells, the multiple groups of battery cells are connected in series through the negative current collector plate 10e and the positive current collector plate 10a to form a first battery stack 10. At this time, the negative current collector plate 10e and the positive current collector plate 10a are respectively a negative bipolar plate and a positive bipolar plate. When the first battery stack 10 is running (i.e., charging or discharging), the positive and negative electrolytes undergo electrochemical oxidation-reduction reactions in the first battery stack 10. At the same time, electrons flow between the positive electrode 10b and the negative electrode 10d in the first battery stack 10 in the external circuit. For details, refer to Figure 2 The first battery stack 10 is connected to a load 40 and a power supply 41. The first battery stack 10 is discharged and charged based on the load 40 and the power supply 41. In the normal charging state, a constant current or constant power is used to charge from 0V to U 1 , constant current density = j normal ; The reactant ions of the positive and negative electrolytes flow inside the first battery stack 10, and electrochemical redox reactions occur on the positive electrode 10b and the negative electrode 10d; For example, taking the main battery system as an iron-chromium flow battery system, in the charging state of the iron-chromium flow battery, the Fe in the electrolyte in the positive electrode 10b 2+ Oxidized to Fe 3+ , Cr in the electrolyte of the negative electrode 10d 3+ Reduction to Cr 2+ In the discharge state of the iron-chromium flow battery, the Fe 3+ Reduction to Fe 2+ , Cr in the electrolyte of the negative electrode 10d 2+ Oxidized to Cr 3+ , that is, the reactions occurring on the positive electrode 10b and the negative electrode 10d of the first battery stack 10 in the charge and discharge state are as follows:

[0042] The electrochemical reactions and side reactions of the positive and negative electrodes 10b in the charging state are:

[0043] Positive electrode: Fe 2+ -e-=Fe 3+ , 0.77V vs SHE

[0044] Negative electrode: Cr 3+ +e-=Cr 2+ , -0.41V vs SHE

[0045] Hydrogen evolution side reaction: 2H + +2e-=H 2 , 0V vs SHE

[0046] The electrochemical reactions of the positive and negative electrodes in the discharge state for 10 days are:

[0047] Positive electrode: Fe 3+ +e-=Fe 2+ , 0.77V vs SHE

[0048] Negative electrode: Cr 2+ -e-=Cr 3+ , -0.41V vs SHE

[0049] Back to Figure 2 The above-mentioned liquid flow battery system further includes a positive electrode electrolyte storage tank 100 and a negative electrode electrolyte storage tank 200. The positive electrode electrolyte storage tank 100 and the negative electrode electrolyte storage tank 200 store electrolyte required for the operation of the liquid flow battery system. Taking the iron-chromium liquid flow battery system as an example, the electrolyte is composed of electrolyte active material Fe 2+ and Cr 3+ and acidic solutions such as HCl, H 2 SO 4 or mixed acid or other supporting electrolytes, and in the initial state, the positive and negative electrolytes in the first battery stack 10 have the same composition, wherein the positive electrolyte storage tank 100 is connected to the positive electrode 10b of the first battery stack 10 through a pipeline fluid, and a circulation loop is formed between the positive electrolyte storage tank 100 and the positive electrode 10b of the first battery stack 10, so that the positive electrolyte can circulate between the positive electrolyte storage tank 100 and the positive electrode 10b of the first battery stack 10, exemplarily, refer to Figure 3 The above-mentioned positive electrode electrolyte storage tank 100 is connected to the positive electrode 10b of the first battery stack 10 through the first distribution pipe 101 and the first reflux pipe 102, that is, the positive electrode electrolyte circulates between the positive electrode electrolyte storage tank 100 and the positive electrode 10b of the first battery stack 10 through the first distribution pipe 101 and the first reflux pipe 102, and at the same time, the above-mentioned first distribution pipe 101 and / or the first reflux pipe 102 are equipped with a pump 101b to control the circulation of the positive electrode electrolyte between the positive electrode electrolyte storage tank 100 and the positive electrode 10b of the first battery stack 10, and the first distribution pipe 101 is equipped with a heat exchanger 101c to make the electrolyte meet the required temperature for the reaction.

[0050] Correspondingly, the negative electrode electrolyte storage tank 200 is connected to the negative electrode 10d of the first battery stack 10 through a pipeline fluid, and a circulation loop is formed between the negative electrode electrolyte storage tank 200 and the negative electrode 10d of the first battery stack 10, so that the negative electrode electrolyte can circulate between the negative electrode electrolyte storage tank 200 and the negative electrode 10d of the first battery stack 10. Exemplarily, the negative electrode electrolyte storage tank 200 is connected to the negative electrode 10d of the first battery stack 10 through a second distribution pipe 201 and a second reflux pipe 202. 10d, that is, the negative electrode electrolyte circulates between the negative electrode electrolyte storage tank 200 and the negative electrode 10d of the first fuel cell stack 10 through the second distribution pipe 201 and the second reflux pipe 202, and at the same time, the second distribution pipe 201 and / or the second reflux pipe 202 are provided with a pump 201b for controlling the circulation of the negative electrode electrolyte between the negative electrode electrolyte storage tank 200 and the negative electrode 10d of the first fuel cell stack 10, and the second distribution pipe 201 is provided with a heat exchanger 201c for making the electrolyte meet the temperature required for the reaction.

[0051] Reference Figure 4 , and combined with Figure 1The fuel cell system includes a second stack 20, which is externally connected to a load 42, and the second stack 20 includes at least one group of battery cells, each battery cell is composed of positive and negative electrodes / electrolyte and an ion exchange membrane separating the electrodes, and has a battery assembly with a pair of positive and negative output terminals (bipolar plates or current collectors). Exemplarily, the second stack 20 has a negative current collector 20e, a negative electrode 20d, an ion exchange membrane 20c, a positive electrode 20b and a positive current collector 20a. When the second stack 20 is connected to a load 42, the load 42 is connected to the load 42, and the second stack 20 includes at least one group of battery cells, each group of battery cells is composed of positive and negative electrodes / electrolyte and an ion exchange membrane separating the electrodes, and has a pair of positive and negative output terminals (bipolar plates or current collectors). Exemplarily, the second stack 20 has a negative current collector 20e, a negative electrode 20d, an ion exchange membrane 20c, a positive electrode 20b and a positive current collector 20a. When the second battery stack 20 has multiple groups of battery cells, the multiple groups of battery cells are connected in series through the negative current collecting plate 20e and the positive current collecting plate 20a to form a second battery stack 20. At this time, the negative current collecting plate 20e and the positive current collecting plate 20a are respectively a negative bipolar plate and a positive bipolar plate. At the same time, the positive electrode 20b of the second battery stack 20 is connected to the positive electrolyte storage tank 100 through a pipeline fluid, and a circulation loop is formed between the positive electrode 20b of the second battery stack 20 and the positive electrolyte storage tank 100. For example, the first The positive electrode 20b of the second battery stack 20 is fluidly connected to the positive electrolyte storage tank 100 through the first recovery inlet pipe 301 and the first recovery return pipe 302 to realize the circulation of the positive electrolyte between the positive electrolyte storage tank 100 and the positive electrode of the second battery stack 20. In some embodiments, one end of the first recovery inlet pipe 301 is connected to the positive electrode 20b of the second battery stack 20, and the other end is connected to the first distribution pipe 101. For example, the first distribution pipe 101 is provided with a three-way valve 1 01a, for realizing the connection between the first distribution pipe 101 and the first recovery inlet pipe 301, correspondingly, one end of the above-mentioned first recovery return pipe 302 is connected to the positive electrode 20b of the second battery stack 20, and the other end is connected to the first reflux pipe 102. Exemplarily, the above-mentioned first reflux pipe 102 is provided with a three-way valve 102a for realizing the connection between the first reflux pipe 102 and the first recovery return pipe 302, and the first recovery inlet pipe 301 is provided with a heat exchanger 301c for making the electrolyte reach the reaction temperature.

[0052] Reference Figure 4The fuel cell system further comprises a storage tank 300, which is connected to the negative electrode 20d of the second stack 20 through a pipeline fluid to form a circulation loop between the storage tank 300 and the negative electrode 20d of the second stack 20. For example, the storage tank 300 is connected to the negative electrode 20d of the second stack 20 through a second recovery inlet pipe 303 and a second recovery return pipe 304, and a pump 303b is arranged on the second recovery inlet pipe 303 to drive the fluid (such as a reducing agent). A heat exchanger 303c is also arranged on the second recovery inlet pipe 303 to keep the fluid at a reaction temperature. At the same time, a reducing agent is stored in the storage tank 300, and the reducing agent is configured to react with the high-valent metal ions in the positive electrode electrolyte, that is, the excess high-valent metal ions in the positive electrode electrolyte are reduced by the reducing agent. Taking the main battery system as an iron-chromium liquid flow battery system as an example, the high-valent metal ions in the positive electrode electrolyte storage tank 100 are Fe 3+ Correspondingly, the storage tank 300 contains an amino reducing agent (such as hydrazine), and the negative electrode 20d of the second stack 20 is coated with a first catalytic layer. Exemplarily, the first catalytic layer is formed of a carbon-based coated metal or a metal oxide catalyst. The metal catalyst includes but is not limited to Pt, Pd, Cu, Co, Bi, Ni and their alloys; the metal oxide catalyst includes but is not limited to Al 2 O 3 , CuOx, etc.), under the action of the first catalytic layer, the excess Fe in the positive electrode electrolyte 3+ With N 2 H 4 A reaction occurs, namely 4Fe 3+ +N 2 H 4 =4Fe 2+ +N 2 +4H + , in order to convert the excess Fe generated in the cathode electrolyte into 3+ By reducing the capacity of the main battery system, the fuel cell system can be used to restore the capacity of the main battery system. At the same time, the H+ originally lost in the reaction product system and the active substance FeCl in the electrolyte reactant are 2 , easily separable nitrogen, 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 generated to the electrolyte of the main system of the liquid flow battery. The specific process of the above reduction is as follows:

[0053] The main battery system (for example, the iron-chromium flow battery system) runs a charge-discharge cycle, fully charges the main battery system, and then discharges it. The state after discharge is: the actual discharge capacity is 60% of the rated capacity (as a basis for judgment), and the positive electrode electrolyte state at the end of discharge is 60% Fe 2+ and 40% Fe3+ At this time, the main battery system is turned off, that is, the charging and discharging process of the main battery system is stopped. At this time, the electrolyte of the main system is in the state of discharge completion. At this time, according to the judgment basis, the positive electrode electrolyte state is 60% Fe 2+ and 40%Fe 3+ ; The negative electrode electrolyte state is 100% Cr 3+ .

[0054] Based on the above judgment and discharge end status, charge the main battery system again (normal charging, constant current or constant power charging from 0V to U 1 , constant current density = jnormal), the state after full charge is: the actual charging capacity is 60% of the rated capacity, then the positive electrode electrolyte state at the end of charging is 100% Fe 3+ ; The negative electrode electrolyte state is 60% Cr 2+ +40%Cr 3+ , at this time, the actual SOC of the negative electrode is 60%), at this time, the main battery system is turned off, that is, the charging process of the main battery system is stopped. At this time, the electrolyte of the main system is in the state of charging completion. At this time, according to the judgment basis, the state of the positive electrode electrolyte is 100% Fe 3 + ; The negative electrode electrolyte state is 60% Cr 2+ +40% Cr 3+ .

[0055] The fuel cell system starts, that is, the fuel cell system performs discharge, that is, the electrical load is discharged at a constant current density j 2 (e.g. 10~100mAcm -2 ) discharge to the inflection point U where the voltage drops sharply 2 (close to 0, for example, 0-0.5V), during the discharge process of the fuel cell system, the positive electrode electrolyte in the main battery system flows from the positive electrode electrolyte storage tank 100 to the positive electrode 20b of the second stack 20, and the excess Fe 3 An electrochemical reaction occurs at the positive electrode 20b of the second stack 20, and the excess Fe 3+ Ions are reduced to Fe 2+ After the reduction is completed, it flows back to the positive electrode electrolyte storage tank for storage. On the negative electrode side of the second stack 20, the reductant is oxidized to produce nitrogen N 2 The reacted electrolyte flows back into the storage tank 300 together.

[0056] During the discharge process of the fuel cell, the main battery system starts the charging process at the same time, and the Fe 2+ During the charging process, it turns back into Fe 3+ , on the negative electrode side of the first stack 10, the remaining 40% Cr in the negative electrolyte3+ Continue the reduction reaction, that is, Cr 3+ Cr 2+ Then it flows back to the negative electrode electrolyte storage tank 200, and finally 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 main battery system is fully charged, and the capacity of the iron-chromium flow battery is fully restored (both the positive and negative electrodes are SOC = 100%). At this time, the reduction process of the flow battery system can be judged based on the change of the current density in the first battery stack 10, that is, the first battery stack 10 is charged with a voltage U 1 During charging, the charging current first increases and then decreases until the charging current battery no longer changes, then it can be determined that the capacity recovery process of the liquid flow battery has been completed. Correspondingly, the above-mentioned liquid flow battery system is also configured with a controller 44, which controls the actions of the first battery stack 10, the second battery stack 20 and the subsequent third battery stack 30 through the controller 44 to achieve automatic control of the charging and discharging operations of the liquid flow battery system.

[0057] In some embodiments, the ion exchange membrane 20c of the second stack 20 is a cation exchange membrane to allow H generated on the second negative electrode side to + It can pass through and flow back to the main battery system to compensate for the H lost due to the hydrogen evolution side reaction during the operation of the main battery system. + To supplement.

[0058] Continue to refer to Figure 4 The above-mentioned fuel cell system also includes a pressure gauge 300a, an exhaust valve 300b and a nitrogen bottle 300c arranged on the storage tank body 300. The operation process of the fuel cell system can be monitored based on the pressure gauge 300a, and the pressure of the storage tank body 300 can be released through the exhaust valve 300b to ensure the safe operation of the fuel cell system.

[0059] In some embodiments, reference Figure 5 , and combined with Figure 1The liquid flow battery system further comprises a reaction vessel 400, which is fluidically connected to the negative electrode electrolyte storage tank 200 through a pipeline to form a circulation loop between the reaction vessel 400 and the negative electrode electrolyte storage tank 200. In some embodiments, the reaction vessel 400 is fluidically connected to the negative electrode electrolyte storage tank 200 through a hydrogen production inlet pipe 401 and a hydrogen production return pipe 402. Specifically, one end of the hydrogen production inlet pipe 401 is connected to the reaction vessel 400, and the other end is connected to the second distribution pipe 201. One end of the hydrogen production return pipe 402 is connected to the reaction vessel 400, and the other end is connected to the second return pipe 202. Exemplarily, the second distribution pipe 201 and the second return pipe 202 are respectively provided with a three-way valve 201a and a three-way valve 202a to realize the connection between the second distribution pipe 201 and the hydrogen production inlet pipe 401 and the second return pipe 202 and the hydrogen production return pipe 402. Continue to refer to Figure 5 The reaction vessel 400 is provided with a second catalyst layer 404, and the second catalyst layer 404 is configured to enable the low-valent metal ions in the negative electrode electrolyte to react with the hydrogen ions. For example, taking the main battery system as an iron-chromium liquid flow battery, the low-valent metal ions in the negative electrode electrolyte are Cr 2+ Correspondingly, the second catalyst layer 404 is made of carbon felt, graphite felt, titanium mesh or SiO 2 The particle liner is the base layer and is covered with MoS 2 , Mo 2 The catalytic layer of C particles, at this time, the reaction equation in the reaction container 400 is 2Cr 2+ +2H + =H 2 +2Cr 3+ In some embodiments, the liquid flow battery system also includes a self-circulation pipe 403 configured on the reaction container 400, both ends of the self-circulation pipe 403 are connected to the reaction container 400, and the two ends of the self-circulation pipe 403 are respectively configured on both sides of the second catalytic layer. Taking the second catalytic layer along the horizontal cross-section of the reaction container 400 as an example, at this time, the two ends of the self-circulation pipe 403 are respectively configured on the upper and lower sides of the second catalytic layer, and at the same time, a pump 403b and a valve 403a are configured on the self-circulation pipe 403. Through the action of the pump 403b on the self-circulation pipe 403, the negative electrode electrolyte in the reaction container 400 can circulate and contact with the second catalytic layer 404 to accelerate the reaction process.

[0060] Continue to refer to Figure 5 The reaction vessel 400 is provided with a pressure gauge and a safety valve (not shown). The pressure is monitored by the pressure gauge and the safety valve discharges overpressure in case of accidents to ensure the safe operation of the system.

[0061] Reference Figure 5The liquid flow battery system further includes a gas storage tank 500, which is fluidically connected to the reaction vessel 400 through a gas recovery pipe 501. The gas recovery pipe 501 is provided with a pump 501b and a valve 501a. The hydrogen generated in the reaction vessel 400 or the hydrogen flowing into the reaction vessel 400 (for example, the hydrogen generated by the hydrogen evolution side reaction on the negative electrode side during the operation of the main battery system) flows to the gas storage tank 500 for storage via the action of the pump 501b. In some examples, the gas storage tank 500 is provided with a pressure gauge (not shown).

[0062] Reference Figure 6 The liquid flow battery system further includes a third battery stack 30, which is externally connected to a load, and the third battery stack 30 includes at least one group of battery cells, each battery cell is composed of positive and negative electrodes / electrolyte and an ion exchange membrane separating the electrodes, and has a battery assembly with a pair of positive and negative output terminals (bipolar plates or current collectors). Exemplarily, the third battery stack 30 includes a negative current collector 30e, a negative electrode 30d, an ion exchange membrane 30c, a positive electrode 30b and a positive electrode When the third battery stack 30 has multiple battery cells, the multiple battery cells are connected in series through the negative current collector plate 30d and the positive current collector plate 30a to form the third battery stack 30. At this time, the negative current collector plate 30d and the positive current collector plate 30a are respectively negative bipolar plates and positive bipolar plates. At the same time, the third catalyst layer 30f is configured between the positive electrode 30b and the ion exchange membrane 30c of the third battery stack 30 and between the negative electrode 30d and the ion exchange membrane 30c. Figure 6 The negative electrode of the third battery stack 30 is led out with a first inlet tube 600 and a first outlet tube 601, wherein the end of the first inlet tube 600 away from the third battery stack 30 is connected to the fluid of the gas tank body 500, and a humidifier 600a is arranged on the first inlet tube 600. Correspondingly, the positive electrode 30b of the third battery stack 30 is led out with a second inlet tube 602 and a second outlet tube 603, and the end of the second inlet tube 602 away from the third battery stack 30 is externally connected to an air source or a gas source (such as an oxygen source), and a humidifier 602a is arranged on the second inlet tube 602. During the operation of the third battery stack 30 (i.e., during the discharge process), the hydrogen from the gas tank body 500 is oxidized at the negative electrode to form hydrogen ions, and the oxygen in the air source is reduced.

[0063] Although the embodiments of the present application have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A liquid flow battery system, characterized in that: The invention comprises a main battery system and a fuel cell system, wherein the main battery system comprises: A first battery stack (10) comprising a positive electrode (10b) and a negative electrode (10d) separated by an ion exchange membrane (10c); A positive electrode electrolyte storage tank (100) is connected to the positive electrode (10b) of the first battery stack (10) via a pipeline fluid, and a circulation loop is formed between the positive electrode electrolyte storage tank (100) and the positive electrode (10b); A negative electrode electrolyte storage tank (200) is connected to the negative electrode (10d) of the first battery stack (10) through a pipeline fluid, and a circulation loop is formed between the negative electrode electrolyte storage tank (200) and the negative electrode (10d); The fuel cell system comprises: A second battery stack (20), comprising a positive electrode (20b) and a negative electrode (20d) separated by an ion exchange membrane (20c), the positive electrode (20b) of the second battery stack (20) being connected to the positive electrolyte storage tank (100) via a pipeline fluid, and a circulation loop is formed between the positive electrode (20b) of the second battery stack (20) and the positive electrolyte storage tank (100); A storage tank (300) stores a reducing agent for reducing high-valent metal ions in a positive electrode electrolyte, and the storage tank (300) is connected to the negative electrode (20d) of the second battery stack (20) through a pipeline fluid, and a circulation loop is formed between the negative electrode (20d) and the storage tank (300); The liquid flow battery system further comprises: The reaction container (400) is connected to the negative electrode electrolyte storage tank (200) through a pipeline fluid, and a circulation loop is formed between the reaction container (400) and the negative electrode electrolyte storage tank (200). The reaction container (400) is provided with a second catalytic layer (404) for catalyzing the reaction between low-valent metal ions and hydrogen ions in the negative electrode electrolyte.

2. A liquid flow battery system according to claim 1, characterized in that: The main battery system is an iron-chromium liquid flow battery system, and the reducing agent in the storage tank (300) is an amino reducing agent.

3. A liquid flow battery system according to claim 1, characterized in that: The ion exchange membrane (20c) of the second battery stack (20) is a cation exchange membrane.

4. A liquid flow battery system according to claim 1, characterized in that: The second catalytic layer (404) is a catalytic layer having carbon felt, graphite felt, titanium mesh or SiO2 particle lining as a base layer and covered with MoS2, Mo2C particles.

5. A liquid flow battery system according to claim 1, characterized in that: The liquid flow battery system further comprises a gas storage tank (500), and the gas storage tank (500) is fluidically connected to the reaction container (400) via a gas recovery pipe (501).

6. A liquid flow battery system according to claim 5, characterized in that: The liquid flow battery system also includes a third battery stack (30), the third battery stack (30) having a positive electrode (30b) and a negative electrode (30d) separated by an ion exchange membrane (30c), a first inlet pipe (600) and a first outlet pipe (601) leading out of the negative electrode (30d) of the third battery stack (30), an end of the first inlet pipe (600) away from the third battery stack (30) being connected to the fluid of the gas storage tank body (500), a second inlet pipe (602) and a second outlet pipe (603) leading out of the positive electrode (30b) of the third battery stack (30), an end of the second inlet pipe (602) away from the third battery stack (30) being connected to an external gas source.

7. A liquid flow battery system according to claim 6, characterized in that: A third catalytic layer (30f) is disposed between the positive electrode (30b) and the ion exchange membrane (30c) and between the negative electrode (30d) and the ion exchange membrane (30c) of the third battery stack (30).

8. A liquid flow battery system according to claim 6, characterized in that: The first inlet pipe (600) and the second inlet pipe (602) are both provided with a humidifier.

9. A liquid flow battery system according to claim 1, characterized in that: The reaction container (400) is provided with a self-circulation pipe (403), both ends of which are connected to the reaction container (400), and both ends of the self-circulation pipe (403) are respectively arranged on both sides of the second catalytic layer (404).

10. A liquid flow battery system according to claim 6, characterized in that: The liquid flow battery system further comprises a controller (44), wherein the controller (44) is configured to control the charging and discharging of the first battery stack (10) and the discharging process of the second battery stack (20) and the third battery stack (30).

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