System and method for improving and maintaining high energy density of flow battery

Abstract

The invention discloses a system and a method for improving and maintaining high energy density of a flow battery, and belongs to the technical field of electrochemical energy storage. The system for improving and maintaining the high energy density of the flow battery comprises a main system used for providing power supply voltage and energy storage capacity, and the main system is connected with a lifting system used for improving the energy density of the flow battery. The system for improving and maintaining the high energy density of the flow battery further comprises an electrical control system connected with the main system and the lifting system. The invention also discloses a method for improving and maintaining the high energy density of the flow battery. According to the system and the method for improving and maintaining the high energy density of the flow battery, the energy density of the flow battery can be remarkably improved by optimizing the electrolyte composition and the overall design of the system, and the system and the method are suitable for commercial flow battery systems and are widely popularized and applied in the fields of electrochemical energy storage technology research, engineering application of energy storage technology and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and specifically relates to a system and method for improving and maintaining the high energy density of a flow battery. Background Art

[0002] A redox flow battery (RFB) is an energy storage technology that uses a flowing liquid electrolyte as an energy storage medium. It has advantages such as high safety performance, deep charge and discharge capabilities, and flexible design, and has received extensive attention in the field of large-scale energy storage. However, the low energy density limits the application prospects of flow batteries, so it is urgent to develop a flow battery system with high energy density.

[0003] The energy density of a flow battery is linearly related to the number of electrons transferred by the active material, the concentration of the active material, and the cell potential difference. Strategies for increasing the energy density can be classified into three categories: expanding the cell voltage, maximizing the actual concentration of the active material, and implementing a multi-electron transfer process. (1) Expanding the cell voltage: By adjusting the structure and properties of redox-active molecules (ROMs), the redox potential of the anolyte can be decreased or / and the redox potential of the catholyte can be increased, thereby achieving an expansion of the cell voltage. To make full use of the low-potential anolyte and high-potential catholyte, a non-aqueous electrolyte system with a wider electrochemical potential window is more preferred; (2) Increasing the actual concentration of the active material: Several effective strategies have been proposed to increase the actual concentration of ROMs, including ① adjusting the intermolecular interactions between ROMs and the interactions between ROMs and the electrolyte by molecular engineering to adjust the solubility of ROMs; ② using a redox-active eutectic system to remain liquid near the operating temperature, reducing or completely removing the inactive solvents used in traditional RFB electrolytes, thereby enhancing the actual concentration of the redox-active components; ③ semi-solid suspensions achieve a high actual concentration of ROMs by combining the high energy density of solid ROMs and the fluidity of liquid electrolytes; ④ the redox-targeting method achieves remote charge exchange through ROMs dissolved in the electrolyte, breaking the solubility limit between the solid active material deposited in the tank and the current collector of the electrochemical stack. While these methods increase the solubility of the active material, it should be noted that they will increase the viscosity of the electrolyte, thereby reducing the fluidity of the electrolyte; (3) Multi-electron transfer system: Increasing the number of electrons transferred during the reaction can multiply the energy density of the flow battery. Therefore, the development of a multi-electron transfer system is an important research direction in the field of high-energy-density flow battery research. Currently, there are many multi-electron transfer systems under research, such as halogens like bromine and iodine, and organic aromatic molecular systems such as bipyridine, diimide, and anthraquinone derivatives. In addition, the energy density of the flow battery also depends on the performance of the key materials of the battery. Currently, there is also research proposing the concept of soft colloidal electrode materials. These materials combine the structural stability of solid electrodes, the flexibility of liquid electrodes, and reduced lattice fatigue, thereby extending the service life of the electrode materials. This new type of material is expected to stimulate further research to develop soft electrode materials between solid and liquid states to achieve ultra-long-life and high-performance batteries.

[0004] Although some remarkable progress has been made in improving the energy density of flow batteries, there are still some challenges to be overcome. For example, the development of new electrolytes and electrode materials requires more experimental verification and performance optimization; the contradiction between the fluidity and energy density of the electrolyte in semi-solid flow batteries, the complexity of electrochemical reaction kinetics, and the characteristics of multiphase fluids; the application of advanced characterization techniques also needs to be further expanded and improved; in addition, the cost of flow batteries using these new technologies also needs to be further reduced and verified, and it still requires a long time of research before large-scale application.

[0005] In addition, the capacity decay problem during the long-term operation of flow batteries is also one of the reasons restricting their large-scale application. Therefore, it is urgently needed to research and design a system and method that can be quickly applied in engineering to improve and maintain the high energy density of flow batteries, so as to further reduce their cost and floor area and promote their wide application in the field of large-scale energy storage. Summary of the Invention

[0006] The object of the present invention is to provide a system and method for improving and maintaining the high energy density of flow batteries, which are used to solve the technical problem that the existing systems and methods for improving the energy density of flow batteries cannot be applied on a large scale.

[0007] To achieve the above object, in an embodiment of the present invention, a system for improving and maintaining the high energy density of flow batteries is provided, which includes a main system for providing a power supply voltage and energy storage capacity. The main system is connected to a boosting system for improving the energy density of flow batteries. The system for improving and maintaining the high energy density of flow batteries further includes an electrical control system connected to the main system and the boosting system.

[0008] The main system includes at least two subsystems. Each subsystem includes at least one subsystem stack. Both ends of the subsystem stack are respectively connected to a positive electrode storage tank and a negative electrode storage tank. The positive electrode storage tank and the negative electrode storage tank are both connected to an ion concentration average valence state detector. A positive electrode circulation pump is arranged between the positive electrode storage tank and the subsystem stack, and a negative electrode circulation pump is arranged between the negative electrode storage tank and the subsystem stack.

[0009] The boosting system includes a boosting stack, which is connected to a control module and a boosting storage tank. A boosting circulation pump is arranged between the boosting storage tank and the boosting stack.

[0010] The control module includes at least four control components, and the control components are used to respectively control the liquid inlet and outlet between the boosting system and the subsystems.

[0011] The present invention also discloses a method for improving and maintaining a high energy density of a flow battery, which is implemented based on the above system and includes the following steps: The electrical control system obtains the average valence state value of the active ion concentration in each subsystem of the main system, and adjusts and improves the charging and discharging states of the flow battery of the system according to the obtained average valence state value of the active ion concentration, thereby realizing the improvement of the energy density of the flow battery.

[0012] One of the preferred embodiments of the present invention, the method includes:

[0013] Determine the composition of the main system in the system for improving and maintaining the high energy density of the flow battery;

[0014] The electrical control system obtains the average valence state value of the active ion concentration in each subsystem of the main system;

[0015] The electrical control system performs ratio analysis according to the obtained average valence state value of the active ion concentration;

[0016] The electrical control system adjusts and improves the charging and discharging states of the flow battery of the system according to the ratio size and the charging and discharging states of the main system.

[0017] One of the preferred embodiments of the present invention, determining the composition of the main system in the system for improving and maintaining the high energy density of the flow battery includes: determining the number of subsystems in the main system and the number of subsystem stacks in the subsystem according to requirements.

[0018] One of the preferred embodiments of the present invention, the electrical control system obtains the average valence state of the ion concentration in each subsystem of the main system, including: the electrical control system obtains the average valence state value of the active ion concentration in each subsystem through the ion concentration average valence state detector set in the subsystem.

[0019] One of the preferred embodiments of the present invention, the electrical control system performs ratio analysis according to the obtained average valence state value of the active ion concentration, including: the electrical control system calculates the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank to the average valence state value of the active ion concentration in the negative electrode storage tank in each subsystem according to the obtained average valence state value of the active ion concentration.

[0020] One of the preferred embodiments of the present invention, the electrical control system adjusts and improves the charging and discharging states of the flow battery of the system according to the ratio size and the charging and discharging states of the main system, including: the electrical control system analyzes the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank to the average valence state value of the active ion concentration in the negative electrode storage tank in each subsystem in the charging and discharging states of the main system and 1, and adjusts and improves the charging and discharging states of the flow battery of the system according to the comparison result.

[0021] In one of the preferred embodiments of the present invention, during the charging process of the main system, when the ratio of the average valence value of the active ion concentration in the positive electrode storage tank to the average valence value of the active ion concentration in the negative electrode storage tank in each subsystem is less than 1, the electrical control system controls the lifting system to form a flow battery with the positive electrode storage tanks in each subsystem for charging until the ratio of the average valence of the ion concentration in the electrolyte in the positive electrode storage tank to the average valence of the ion concentration in the electrolyte in the negative electrode storage tank in each subsystem is equal to 1.

[0022] In one of the preferred embodiments of the present invention, during the charging process of the main system, when the ratio of the average valence value of the active ion concentration in the positive electrode storage tank to the average valence value of the active ion concentration in the negative electrode storage tank in each subsystem is greater than 1, the electrical control system controls the lifting system to form a flow battery with the negative electrode storage tanks in each subsystem for charging until the ratio of the average valence value of the active ion concentration in the positive electrode storage tank to the average valence value of the active ion concentration in the negative electrode storage tank in each subsystem is equal to 1.

[0023] In one of the preferred embodiments of the present invention, during the discharging process of the main system, when the ratio of the average valence value of the active ion concentration in the positive electrode storage tank to the average valence value of the active ion concentration in the negative electrode storage tank in each subsystem is greater than 1, the electrical control system controls the lifting system to form a flow battery with the positive electrode storage tanks in each subsystem for discharging until the ratio of the average valence value of the active ion concentration in the positive electrode storage tank to the average valence value of the active ion concentration in the negative electrode storage tank in each subsystem is equal to 1.

[0024] In one of the preferred embodiments of the present invention, during the discharging process of the main system, when the ratio of the average valence value of the active ion concentration in the positive electrode storage tank to the average valence value of the active ion concentration in the negative electrode storage tank in each subsystem is less than 1, the electrical control system controls the lifting system to form a flow battery with the negative electrode storage tanks in each subsystem for discharging until the ratio of the average valence value of the active ion concentration in the positive electrode storage tank to the average valence value of the active ion concentration in the negative electrode storage tank in each subsystem is equal to 1.

[0025] In one of the preferred embodiments of the present invention, while the electrical control system performs ratio analysis based on the obtained average valence value of the active ion concentration, it also performs comparative analysis of the average valence value of the active ion concentration in the positive electrode storage tanks between each subsystem and comparative analysis of the average valence value of the active ion concentration in the negative electrode storage tanks between each subsystem, and adjusts the liquid inflow and outflow between the lifting system and the positive electrode storage tanks and negative electrode storage tanks in each subsystem according to the comparison results.

[0026] In one of the preferred embodiments of the present invention, when the average valence value of the active ion concentration in the positive electrode storage tank of one of the subsystems is greater than the average valence value of the active ion concentration in the positive electrode storage tanks of the other subsystems, the liquid inflow and return liquid volume between the positive electrode storage tank with a large average valence value of the active ion concentration and the lifting system are set to be less than the liquid inflow and return liquid volume between the positive electrode storage tanks of the other subsystems and the lifting system.

[0027] One of the preferred embodiments of the present invention is that when the average valence value of the active ion concentration in the negative electrode storage tank of one subsystem is greater than that in the negative electrode storage tanks of the other subsystems, the inflow volume and the return volume between the negative electrode storage tank with a large average valence value of the active ion concentration and the lifting system are set to be greater than those between the negative electrode storage tanks of the other subsystems and the lifting system.

[0028] One of the preferred embodiments of the present invention is that the method further includes improving the energy density of the flow battery by adjusting the composition ratio of the electrolyte in the main system and the volume of the high-concentration electrolyte.

[0029] One of the preferred embodiments of the present invention is that adjusting the composition ratio of the electrolyte in the main system includes: setting the redox couple in the main system as M m+ / M (m+1)+ and N n+ / N (n+1)+ , the dissolution concentrations of the positive and negative redox active ions in the electrolyte at the initial specific temperature are both x mol / L, and the volumes of the electrolytes containing the redox couple are both X L; according to the physical and chemical properties of the active ions, when the concentration of N ions in the positive electrode electrolyte is (x - c) mol / L, the dissolution concentration of M is (x + a) mol / L; when the concentration of M ions in the negative electrode electrolyte is (x - d) mol / L, the dissolution concentration of N is (x + b) mol / L; adjusting the active ion concentrations in the positive and negative electrode electrolytes so that the concentration of the active ion M in the positive electrode electrolyte is (x + a) mol / L, the concentration of N ions is (x - c) mol / L, the concentration of the active ion N in the negative electrode electrolyte is (x + b) mol / L, and the concentration of M ions is (x - d) mol / L. At this time, the energy density of a single set of systems is:

[0030]

[0031] In the formula, ω is the energy density of the system, Wh / L; is the average voltage of the system, V; η1 is the utilization rate of the electrolyte in the system, %,; η2 is the utilization rate of the electrolyte in the system, %.

[0032] One of the preferred embodiments of the present invention is that adjusting the volume of the high-concentration electrolyte includes:

[0033] When a > b, set the volume of the positive electrode electrolyte to be (X - Z) L and the volume of the negative electrode electrolyte to be (X + Z) L. The energy density of a single set of systems is:

[0034]

[0035] In the formula, ω is the energy density of the system, Wh / L; is the system average voltage, V; η2 is the system electrolyte utilization rate, %; X is the volume of the electrolyte containing the redox couple;

[0036] When a < b, set the volume of the positive electrolyte as (X + Z) L and the volume of the negative electrolyte as (X - Z) L. The energy density of a single set of systems is:

[0037]

[0038] In the formula, ω is the system energy density, Wh / L; is the system average voltage, V; η1 is the system electrolyte utilization rate, %; X is the volume of the electrolyte containing the redox couple.

[0039] In summary, the beneficial effects of the present invention are as follows:

[0040] 1. The system for improving and maintaining the high energy density of the flow battery in the present invention adjusts the liquid inflow and return amounts between the boosting system and each subsystem in the main system through an external boosting system to improve and maintain the high energy density of the system.

[0041] 2. The system and method for improving and maintaining the high energy density of the flow battery in the present invention can significantly improve the energy density of the flow battery by optimizing the electrolyte composition and the overall design of the system. This system and method not only improve the energy storage efficiency of the flow battery, further reduce its cost and floor area, but also enhance its cycle stability and safety, providing strong support for the large-scale commercial application of the flow battery.

[0042] 3. The present invention proposes a process system for improving and maintaining the high energy density of the flow battery applicable to various scales that can be quickly engineered. This set of process systems consists of at least two subsystems and has the characteristics of improving the battery energy density, improving the system performance, thereby reducing costs, simplifying operations, and enabling quantitative control.

[0043] 4. The system for improving and maintaining the high energy density of the flow battery in the present invention also has the function of balancing the system differences between multiple sets of systems. The electrical control system compares and analyzes the average valence state values of the active ion concentrations in the positive electrode storage tanks between each subsystem and the average valence state values of the active ion concentrations in the negative electrode storage tanks between each subsystem based on the obtained average valence state values of the active ion concentrations, and adjusts the liquid inflow and outflow between the boosting system and the positive and negative electrode storage tanks in each subsystem according to the comparison results, thereby regulating the consistency between each subsystem.

[0044] 5. The system and method for improving and maintaining the high energy density of the flow battery in the present invention are applicable to commercial flow battery systems and are widely promoted and applied in the fields of electrochemical energy storage technology research, engineering application of energy storage technology, etc.

[0045] Other features and advantages of the present invention will be described in the following specification, and in part will be obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be expounded by the effects described in the specification and the accompanying drawings. Description of the Drawings

[0046] Figure 1 It is a schematic structural diagram of a system for improving and maintaining the high energy density of a flow battery in an embodiment of the present invention;

[0047] Figure 2 It is a schematic flowchart of a method for improving and maintaining the high energy density of a flow battery in an embodiment of the present invention;

[0048] Figure 3 It is a comparison result graph of the system energy density varying with cycles when the boosting system in Embodiment 1 of the present invention is not operating and operating according to different process parameters;

[0049] Figure 4 It is a comparison result graph of the voltage differences between two subsystems, namely the non-operating boosting system and the boosting system operating according to different process parameters, in Embodiment 1 of the present invention.

[0050] Wherein, 1 - boosting storage tank, 2 - boosting circulation pump, 3 - boosting stack, 4 - positive electrode storage tank, 5 - first average valence state detector of active ion concentration, 6 - subsystem stack, 7 - second average valence state detector of active ion concentration, 8 - negative electrode storage tank, 9 - electrical control system, 10 - positive electrode circulation pump, 11 - negative electrode circulation pump, 12 - second control valve, 13 - sixth control valve, 14 - first control valve, 15 - fifth control valve, 16 - third control valve, 17 - eighth control valve, 18 - third average valence state detector of active ion concentration, 19 - fourth average valence state detector of active ion concentration, 20 - fourth control valve, 21 - seventh control valve. Detailed Embodiments

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0052] The present invention provides a system for improving and maintaining the high energy density of a flow battery, as Figure 1As shown, it includes a main system for providing a power supply voltage and energy storage capacity. The main system is connected to a boosting system for increasing the energy density of the flow battery. The system for increasing and maintaining the high energy density of the flow battery further includes an electrical control system 9 connected to the main system and the boosting system. The electrical control system 9 controls the operation of the entire system for increasing and maintaining the high energy density of the flow battery.

[0053] The main system includes at least two subsystems. The number of subsystems depends on the demand, and the subsystems are connected in series. Each subsystem includes at least one subsystem stack 6. The number of subsystem stacks 6 depends on the demand. When the number of subsystem stacks 61 is greater than or equal to 2, the subsystem stacks 6 within the subsystem are connected in series or in parallel. Both ends of the subsystem stack 6 are respectively connected to a positive electrode storage tank 4 and a negative electrode storage tank 8. Both the positive electrode storage tank 4 and the negative electrode storage tank 8 are connected to an average valence state detector for active ion concentration to detect the average valence state value of the active ion concentration. A positive electrode circulation pump 10 is provided between the positive electrode storage tank 4 and the subsystem stack 6, and a negative electrode circulation pump 11 is provided between the negative electrode storage tank 8 and the subsystem stack 6. The electrolyte in the positive electrode storage tank 4 is pumped into the subsystem stack 6 through the positive electrode circulation pump 10, and the electrolyte in the negative electrode storage tank 8 is pumped into the subsystem stack 6 through the negative electrode circulation pump 11. Among them, the average valence state detector for active ion concentration includes a first average valence state detector for active ion concentration 5, a second average valence state detector for active ion concentration 7, a third average valence state detector for active ion concentration 18, and a fourth average valence state detector for active ion concentration 19.

[0054] The boosting system includes a boosting stack 3. The boosting stack 3 is connected to a control module and a boosting storage tank 1 through pipelines. The solution in the boosting storage tank 1 of the boosting system is a solution containing substances that can be oxidized and / or reduced. A boosting circulation pump 2 is provided between the boosting storage tank 1 and the boosting stack 3. The solution in the boosting storage tank 1 is pumped into the boosting stack 3 through the boosting circulation pump 2.

[0055] The control module includes at least four control components, and the control components are used to respectively control the liquid inlet and outlet between the boosting system and the subsystem. Preferably, the control components include a first control component, a second control component, a third control component, and a fourth control component. Among them, the first control component includes a first control valve 14 and a fifth control valve 15, the second control component includes a second control valve 12 and a sixth control valve 13, the third control component includes a third control valve 16 and a seventh control valve 21, and the fourth control component includes a fourth control valve 20 and an eighth control valve 17.

[0056] Working process: The positive storage tanks 4 or negative storage tanks 8 in each subsystem in the main system are combined to form the negative storage tank of the lifting system. The lifting storage tank 1 in the lifting system is the positive storage tank of the lifting system, which forms a redox flow battery system together with the lifting stack 3 and the lifting circulation pump 2. The electrical control system 9 obtains the values displayed by the average valence state detectors of the active ion concentrations in each subsystem in the main system, and adjusts the control valves in the control module according to the obtained values, thereby regulating the charging and discharging states of the redox flow battery, and thus achieving an increase in the energy density of the redox flow battery.

[0057] A method for increasing and maintaining a high energy density of a redox flow battery, which is realized based on the above-mentioned system for increasing and maintaining a high energy density of a redox flow battery, includes the following steps: The electrical control system 9 obtains the average valence state values of the active ion concentrations in each subsystem in the main system, and adjusts the charging and discharging states of the redox flow battery in the lifting system according to the obtained average valence state values of the active ion concentrations, thereby achieving an increase in the energy density of the redox flow battery.

[0058] Specifically, as Figure 2 shown, the method includes:

[0059] Step (1): Determine the composition of the main system in the system for increasing and maintaining a high energy density of a redox flow battery; specifically, determine the number of subsystems in the main system and the number of subsystem stacks 6 in the subsystems according to requirements. At the same time, it is also necessary to determine whether the combination of positive storage tanks 4 in each subsystem is used as the negative storage tank of the lifting system or the combination of negative storage tanks 8 is used as the negative storage tank of the lifting system;

[0060] Step (2): The electrical control system 9 obtains the average valence state values of the active ion concentrations in each subsystem in the main system; specifically, the electrical control system 9 obtains the values displayed by the average valence state detectors of the active ion concentrations in each subsystem in the main system;

[0061] Step (3): The electrical control system 9 performs ratio analysis according to the obtained average valence state values of the active ion concentrations; specifically, the electrical control system 9 calculates the ratio of the average valence state value of the active ion concentration in the positive storage tank 4 to the average valence state value of the active ion concentration in the negative storage tank 8 in each subsystem according to the average valence state values of the active ion concentrations obtained in step (2);

[0062] Step (4): The electrical control system 9 adjusts the charging and discharging states of the redox flow battery in the lifting system according to the ratio size and the charging and discharging states of the main system; specifically, the electrical control system 9 analyzes the ratio of the average valence state value of the active ion concentration in the positive storage tank 4 to the average valence state value of the active ion concentration in the negative storage tank 8 in each subsystem under the charging and discharging states of the main system and the size compared with 1, and adjusts the charging and discharging states of the redox flow battery in the lifting system according to the comparison result, including the following four situations:

[0063] ① During the charging process of the main system, when the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank 4 to the average valence state value of the active ion concentration in the negative electrode storage tank 8 in each subsystem is less than 1, the electrical control system 9 controls the lifting system to form a flow battery with the positive electrode storage tank 4 in each subsystem for charging until the ratio of the average valence state of the active ion concentration in the electrolyte of the positive electrode storage tank 4 to the average valence state of the active ion concentration in the electrolyte of the negative electrode storage tank 8 in each subsystem is equal to 1;

[0064] ② During the charging process of the main system, when the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank 4 to the average valence state value of the active ion concentration in the negative electrode storage tank 8 in each subsystem is greater than 1, the electrical control system 9 controls the lifting system to form a flow battery with the negative electrode storage tank 8 in each subsystem for charging until the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank 4 to the average valence state value of the active ion concentration in the negative electrode storage tank 8 in each subsystem is equal to 1;

[0065] ③ During the discharging process of the main system, when the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank 4 to the average valence state value of the active ion concentration in the negative electrode storage tank 8 in each subsystem is greater than 1, the electrical control system 9 controls the lifting system to form a flow battery with the positive electrode storage tank 4 in each subsystem for discharging until the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank 4 to the average valence state value of the active ion concentration in the negative electrode storage tank 8 in each subsystem is equal to 1;

[0066] ④ During the discharging process of the main system, when the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank 4 to the average valence state value of the active ion concentration in the negative electrode storage tank 8 in each subsystem is less than 1, the electrical control system 9 controls the lifting system to form a flow battery with the negative electrode storage tank 8 in each subsystem for discharging until the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank 4 to the average valence state value of the active ion concentration in the negative electrode storage tank 8 in each subsystem is equal to 1;

[0067] Preferably, while the electrical control system 9 performs ratio analysis based on the obtained average valence state value of the active ion concentration, it also performs comparative analysis of the average valence state value of the active ion concentration in the positive electrode storage tank 4 between each subsystem and comparative analysis of the average valence state value of the active ion concentration in the negative electrode storage tank 8 between each subsystem, and adjusts the liquid inlet and outlet between the lifting system and the positive electrode storage tank 4 and the negative electrode storage tank 8 in each subsystem according to the comparison results, specifically including the following situations:

[0068] ① When the average valence state value of the active ion concentration in the positive electrode storage tank 4 of one subsystem is greater than the average valence state value of the active ion concentration in the positive electrode storage tanks 4 of the other subsystems, the liquid inlet volume and the return liquid volume between the positive electrode storage tank 4 with a large average valence state value of the active ion concentration and the lifting system are set to be less than the liquid inlet volume and the return liquid volume between the positive electrode storage tanks 4 of the other subsystems and the lifting system.

[0069] ② When the average valence value of the active ion concentration in the negative electrode storage tank 8 of one of the subsystems is greater than that in the negative electrode storage tanks 8 of the other subsystems, set the inflow and return flow volumes between the negative electrode storage tank 8 with a large average valence value of the active ion concentration and the lifting system to be greater than the inflow and return flow volumes between the negative electrode storage tanks 8 of the other subsystems and the lifting system;

[0070] Preferably, a method for improving and maintaining the high energy density of a flow battery further includes improving the energy density of the flow battery by adjusting the composition ratio of the electrolyte in the main system and adjusting the volume of the high-concentration electrolyte;

[0071] Set the redox couple in the main system to M m+ / M (m+1)+ and N n+ / N (n+1)+ (M and N are redox couples in flow batteries such as iron-chromium, all-vanadium, all-iron, zinc-bromine, zinc-iron, etc.), and their concentrations in the electrolyte are both x mol / L, and the volume of the electrolyte containing the redox couple is both X L. At this time, the energy density of a single set of systems is:

[0072]

[0073] In the formula, ω is the system energy density, Wh / L; is the system average voltage (system characteristic value), V; η0 is the system electrolyte utilization rate (under this condition, system characteristic value), %;

[0074] Improving the energy density of the battery by adjusting the composition ratio of the electrolyte includes: setting that when the concentration of N ions in the positive electrode electrolyte is (x - c) mol / L under the limitations of the dissolution concentration and electrolyte viscosity, the dissolution concentration of M is (x + a) mol / L; when the concentration of M ions in the negative electrode electrolyte is (x - d) mol / L, the dissolution concentration of N is (x + b) mol / L; accordingly, adjust the active ion concentrations in the positive and negative electrode electrolytes so that the concentration of active ion M in the positive electrode electrolyte is (x + a) mol / L, the concentration of N ions is (x - c) mol / L, the concentration of active ion N in the negative electrode electrolyte is (x + b) mol / L, and the concentration of M ions is (x - d) mol / L. Among them, a, b, c, and d are related to the physical and chemical properties of the redox active ions, and their values are related to the common ion effect and salt effect of the ions. At this time, the energy density of a single set of systems is:

[0075]

[0076] In the formula, ω is the system energy density, Wh / L; is the system average voltage, V; η1 is the system electrolyte utilization rate, %,; η2 is the system electrolyte utilization rate, %;

[0077] Furthermore, on the premise of adjusting the concentration as described above, the total amount of active ions can also be adjusted by adjusting the volume of the high-concentration electrolyte, so as to achieve the purpose of improving the energy density of the system:

[0078] When a > b, set the volume of the positive electrolyte as (X - Z) L and the volume of the negative electrolyte as (X + Z) L. The energy density of a single set of the system is:

[0079]

[0080] In the formula, ω is the energy density of the system, Wh / L; is the average voltage of the system, V; η2 is the utilization rate of the electrolyte of the system, %; X is the volume of the electrolyte containing the redox couple;

[0081] When a < b, set the volume of the positive electrolyte as (X + Z) L and the volume of the negative electrolyte as (X - Z) L. The energy density of a single set of the system is:

[0082]

[0083] In the formula, ω is the energy density of the system, Wh / L; is the average voltage of the system, V; η1 is the utilization rate of the electrolyte of the system, %; X is the volume of the electrolyte containing the redox couple.

[0084] The following solution takes two subsystems connected in series and one stack for each subsystem as an example. Set the concentration of active ion M in the positive electrolyte of this system as (x + a) mol / L and the concentration of active ion N in the negative solution as (x + b) mol / L. The process of boosting and maintaining the high energy density of the battery is as follows:

[0085] (1) The lifting storage tank 1, the lifting circulation pump 2, the lifting stack 3 and the positive storage tanks 4 in the two subsystems form a set of flow battery system, where the lifting storage tank 1 is the positive storage tank of the lifting system, and the positive storage tanks 4 in the two subsystems form the negative storage tank of the lifting system;

[0086] (2) The solution in the lifting storage tank 1 is a solution containing substances that can be oxidized and / or reduced;

[0087] (3) During the charging process of the main system (including at the end of charging) and during the discharging process (including at the end of discharging), the electrical control system 9 reads and records the values of the first active ion concentration average valence detector 5, the second active ion concentration average valence detector 7, the third active ion concentration average valence detector 18, and the fourth active ion concentration average valence detector 19 in the active ion concentration average valence detector as A - p, A - q, B - p, and B - q respectively;

[0088] (4) T - 1 analysis and comparison Magnitude compared with 1:

[0089] ① During the charging process, when is less than 1, the electrical control system 9 controls the start of the lifting circulation pump 2, the lifting stack 3, the inlet / outlet liquid system (the first control valve 14, the second control valve 12, the third control valve 16, the fourth control valve 20), and the positive electrode storage tank 4 in the two subsystems to form a flow battery system for charging, so that equals 1;

[0090] ② During the charging process, when is greater than 1, the electrical control system 9 controls the start of the lifting circulation pump 2, the lifting stack 3, the inlet / outlet liquid system (the fifth control valve 15, the sixth control valve 13, the seventh control valve 21, the eighth control valve 17), and the negative electrode storage tank 8 in the two subsystems to form a flow battery system for charging, so that equals 1;

[0091] ③ During the discharging process, when is greater than 1, the electrical control system 9 controls the start of the lifting circulation pump 2, the lifting stack 3, the inlet / outlet liquid system (the first control valve 14, the second control valve 12, the third control valve 16, the fourth control valve 20), and the positive electrode storage tank 4 in the two subsystems to form a flow battery system for discharging, so that equals 1;

[0092] ④ During the discharging process, when is less than 1, the electrical control system 9 controls the start of the lifting circulation pump 2, the lifting stack 3, the inlet / outlet liquid system ((the fifth control valve 15, the sixth control valve 13, the seventh control valve 21, the eighth control valve 17), and the negative electrode storage tank 8 in the two subsystems to form a flow battery system for discharging, so that equals 1;

[0093] (5) In the above (4) situation, the system energy density is:

[0094]

[0095] Or:

[0096]

[0097] In the formula, ω is the system energy density, Wh / L; is the system average voltage, V; η2 is the system electrolyte utilization rate, %; X is the ionic solution volume, x + a is the concentration of the active ion M in the positive electrode electrolyte in the system, and x + b is the concentration of the active ion N in the negative electrode solution;

[0098] (6) Further, during the process of (4), the electrical control system 9 simultaneously analyzes the magnitudes of A-p and B-p, and A-q and B-q. If A-p is greater than B-p, the fourth control valve 20 and the third control valve 16 are adjusted to a larger opening; otherwise, the first control valve 14 and the second control valve 12 are adjusted to a larger opening. If A-q is greater than B-q, the fifth control valve 15 and the sixth control valve 13 are adjusted to a larger opening; otherwise, the seventh control valve 21 and the eighth control valve 17 are adjusted to a larger opening, synchronously achieving the purpose of balancing the differences between different process systems.

[0099] (7) ① When the lifting storage tank 1, the positive electrode storage tank 4 in two subsystems of the main system, and the lifting stack 3 form a flow battery, taking the iron-chromium flow battery and the all-vanadium flow battery as examples, the reactions occurring in the lifting stack of the lifting system during the lifting process are as follows:

[0100] Positive electrode:

[0101] Negative electrode:

[0102] ② When the lifting storage tank 1, the negative electrode storage tank 8 in two subsystems of the main system, and the lifting stack 3 form a flow battery, taking the iron-chromium flow battery and the all-vanadium flow battery as examples, the reactions occurring in the lifting stack of the lifting system during the lifting process are as follows:

[0103] Positive electrode: aR - ne - =bO

[0104] Negative electrode:

[0105] Example 1

[0106] As follows, a battery system with two sets of sub-process systems (one stack for each process system), a supporting lifting system, and a total control system built according to the above process was tested and verified. During the test, parameters such as the flow rate and power of the lifting system were analyzed and adjusted according to the actual operating conditions of the supporting main system. The specific test results are as Figures 3 - 4 shown:

[0107] Figure 3 It is a comparison result graph of the system energy density versus the cycle for the case where the lifting system does not operate (blank group) and the cases where it operates according to different process parameters (experimental group 1, experimental group 2, experimental group 3, experimental group 4), where Figure 3 in: (1) The system energy density is normalized with the discharge energy density of the first cycle of the blank group (i.e., the lifting system not operating) as 100%; (2) Experimental group 1, experimental group 2, experimental group 3, and experimental group 4 operate the lifting system according to different process parameters.

[0108] Figure 4Figure showing the comparison results of the voltage differences between two subsystems when the lifting system is not operating and when the lifting system operates according to different process parameters. Among them, Figure 4 Among them: (1) The voltage difference between systems is normalized with the voltage difference between systems at the end of the first cycle of charging in the blank group (i.e., the lifting system does not operate the balancing control program) being 100%; (2) Experimental group 1, experimental group 2, experimental group 3, and experimental group 4 are the lifting systems operating according to different process parameters.

[0109] From the above Figure 3 and Figure 4 it can be seen that when the lifting system is not operating, the energy density of the system is relatively low and gradually decays as the cycle progresses; along with the attenuation of the system capacity, the voltage difference between systems shows a gradually increasing trend, and the increase in the voltage difference between systems further leads to a decrease in the energy density of the system, forming a negative feedback; when the lifting system is operating, the energy density of the system is increased, and when the process parameters of the lifting system are appropriate, the high energy density of the system can be maintained, and further the voltage difference between systems is reduced, and the reduction of the system voltage difference further positively feedbacks on the energy density of the system.

[0110] In summary, the system and method for improving and maintaining the high energy density of the flow battery according to the present invention can not only significantly improve the energy density of the flow battery, but also reduce costs and floor space, enhance cycle stability and safety, and provide strong support for the large-scale commercial application of the flow battery by optimizing the electrolyte composition and the overall design of the system.

[0111] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A system for increasing and maintaining a high energy density of a flow battery, characterized in that: It includes a main system for providing a power supply voltage and energy storage capacity. The main system is connected to a boosting system for increasing the energy density of the flow battery. The system for increasing and maintaining the high energy density of the flow battery further includes an electrical control system connected to the main system and the boosting system.

2. The system for improving and maintaining the high energy density of a flow battery according to claim 1, wherein: The main system includes at least two subsystems. Each subsystem includes at least one subsystem stack. Both ends of the subsystem stack are respectively connected to a positive electrode storage tank and a negative electrode storage tank. Ion concentration average valence detectors are connected to both the positive electrode storage tank and the negative electrode storage tank. A positive electrode circulation pump is provided between the positive electrode storage tank and the subsystem stack. A negative electrode circulation pump is provided between the negative electrode storage tank and the subsystem stack.

3. A system for improving and maintaining a high energy density of a flow battery according to claim 2, characterized in that: The boosting system includes a boosting stack. The boosting stack is connected to a control module and a boosting storage tank. A boosting circulation pump is provided between the boosting storage tank and the boosting stack.

4. A system for increasing and maintaining a high energy density of a flow battery, as claimed in claim 3, wherein: The control module includes at least four control components, and the control components are used to respectively control the liquid inflow and outflow between the boosting system and the subsystems.

5. A method for improving and maintaining a high energy density of a flow battery, implemented based on the system for improving and maintaining a high energy density of a flow battery according to any one of claims 1-4, characterized in that, It includes the following steps: The electrical control system obtains the average valence state values of the active ions in each subsystem of the main system, and adjusts the charging and discharging states of the flow battery in the boosting system according to the obtained average valence state values of the active ions, so as to achieve an increase in the energy density of the flow battery.

6. A method for improving and maintaining a high energy density of a flow battery, as described in claim 5, characterized in that The method includes: Determining the composition of the main system in the system for increasing and maintaining the high energy density of the flow battery; The electrical control system obtains the average valence state values of the active ions in each subsystem of the main system; The electrical control system performs ratio analysis according to the obtained average valence state values of the active ions; The electrical control system adjusts the charging and discharging states of the flow battery in the boosting system according to the ratio size and the charging and discharging states of the main system.

7. A method for increasing and maintaining the high energy density of a flow battery, characterized in that: Determining the composition of the main system in the system for increasing and maintaining the high energy density of the flow battery includes: determining the number of subsystems in the main system and the number of subsystem stacks in the subsystems according to requirements.

8. A method for increasing and maintaining a high energy density of a flow battery, as described in claim 6, characterized in that: The electrical control system obtains the average valence state of the ions in each subsystem of the main system, including: the electrical control system obtains the average valence state values of the active ions in each subsystem through the ion concentration average valence detectors provided in the subsystems.

9. A method for improving and maintaining a high energy density of a flow battery according to claim 6, characterized in that: The electrical control system performs ratio analysis according to the obtained average valence state values of the active ions, including: the electrical control system calculates the ratio of the average valence state value of the active ions in the positive electrode storage tank to the average valence state value of the active ions in the negative electrode storage tank in each subsystem according to the obtained average valence state values of the active ions.

10. A method for improving and maintaining a high energy density of a flow battery, characterized in that: The electrical control system adjusts the charging and discharging states of the flow battery in the boosting system according to the ratio size and the charging and discharging states of the main system, including: the electrical control system analyzes the ratio of the average valence state value of the active ions in the positive electrode storage tank to the average valence state value of the active ions in the negative electrode storage tank in each subsystem in the charging and discharging states of the main system and the size compared with 1, and adjusts the charging and discharging states of the flow battery in the boosting system according to the comparison result.

11. A method for improving and maintaining a high energy density of a flow battery, as described in claim 10, characterized in that: During the charging process of the main system, when the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank to the average valence state value of the active ion concentration in the negative electrode storage tank in each subsystem is less than 1, the electrical control system controls the lifting system and the positive electrode storage tanks in each subsystem to form a flow battery for charging until the ratio of the average valence state of the ion concentration in the electrolyte of the positive electrode storage tank to the average valence state of the ion concentration in the electrolyte of the negative electrode storage tank in each subsystem is equal to 1.

12. A method for improving and maintaining a high energy density of a flow battery according to claim 10, characterized in that: During the charging process of the main system, when the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank to the average valence state value of the active ion concentration in the negative electrode storage tank in each subsystem is greater than 1, the electrical control system controls the lifting system and the negative electrode storage tanks in each subsystem to form a flow battery for charging until the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank to the average valence state value of the active ion concentration in the negative electrode storage tank in each subsystem is equal to 1.

13. A method for improving and maintaining a high energy density of a flow battery according to claim 10, characterized in that: During the discharging process of the main system, when the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank to the average valence state value of the active ion concentration in the negative electrode storage tank in each subsystem is greater than 1, the electrical control system controls the lifting system and the positive electrode storage tanks in each subsystem to form a flow battery for discharging until the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank to the average valence state value of the active ion concentration in the negative electrode storage tank in each subsystem is equal to 1.

14. A method for increasing and maintaining a high energy density of a flow battery according to claim 10, characterized in that: During the discharging process of the main system, when the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank to the average valence state value of the active ion concentration in the negative electrode storage tank in each subsystem is less than 1, the electrical control system controls the lifting system and the negative electrode storage tanks in each subsystem to form a flow battery for discharging until the ratio of the average valence state value of the active ion concentration in the positive electrode storage tank to the average valence state value of the active ion concentration in the negative electrode storage tank in each subsystem is equal to 1.

15. A method for increasing and maintaining a high energy density of a flow battery, as claimed in claim 10, characterized in that: While the electrical control system performs ratio analysis based on the obtained average valence state value of the active ion concentration, it also conducts comparative analysis of the average valence state value of the active ion concentration in the positive electrode storage tanks among the subsystems and comparative analysis of the average valence state value of the active ion concentration in the negative electrode storage tanks among the subsystems, and adjusts the liquid inflow and outflow between the lifting system and the positive electrode storage tanks and negative electrode storage tanks in each subsystem according to the comparison results.

16. A method for increasing and maintaining a high energy density of a flow battery, characterized in that: When the average valence state value of the active ion concentration in the positive electrode storage tank of one subsystem is greater than the average valence state value of the active ion concentration in the positive electrode storage tanks of the other subsystems, the liquid inflow and return liquid volume between the positive electrode storage tank with a large average valence state value of the active ion concentration and the lifting system are set to be less than the liquid inflow and return liquid volume between the positive electrode storage tanks of the other subsystems and the lifting system.

17. A method for improving and maintaining a high energy density of a flow battery according to claim 15, characterized in that: When the average valence state value of the active ion concentration in the negative electrode storage tank of one subsystem is greater than the average valence state value of the active ion concentration in the negative electrode storage tanks of the other subsystems, the liquid inflow and return liquid volume between the negative electrode storage tank with a large average valence state value of the active ion concentration and the lifting system are set to be greater than the liquid inflow and return liquid volume between the negative electrode storage tanks of the other subsystems and the lifting system.

18. A method for improving and maintaining a high energy density of a flow battery, characterized in that: The method further includes improving the energy density of the flow battery by adjusting the composition ratio of the electrolyte in the main system and adjusting the volume of the high-concentration electrolyte.

19. A method for improving and maintaining a high energy density of a flow battery, characterized in that: The composition ratio of the electrolyte in the said formulation main system includes: setting the redox couple in the main system as M m+ / M (m+1)+ and N n+ / N (n +1)+ , at the initial specific temperature, the dissolution concentrations of the positive and negative redox active ions in the electrolyte are both x mol / L, and the volume of the electrolyte containing the redox couple is X L; according to the physical and chemical properties of the active ions, when in the positive electrolyte, the concentration of N ions is (x - c) mol / L, the dissolution concentration of M is (x + a) mol / L; when in the negative electrolyte, the concentration of M ions is (x - d) mol / L, the dissolution concentration of N is (x + b) mol / L; adjust the concentrations of the active ions in the positive and negative electrolytes so that the concentration of the active ion M in the positive electrolyte is (x + a) mol / L, the concentration of N ions is (x - c) mol / L, the concentration of the active ion N in the negative electrolyte is (x + b) mol / L, and the concentration of M ions is (x - d) mol / L. At this time, the energy density of a single set of the system is: where ω is the system energy density, Wh / L; is the average system voltage, V; η1 is the system electrolyte utilization rate, %,; η2 is the system electrolyte utilization rate, %.

20. A method for improving and maintaining a high energy density of a flow battery, characterized in that: The adjustment of the volume of the high-concentration electrolyte includes: When a > b, set the volume of the positive electrolyte to (X - Z) L, the volume of the negative electrolyte to (X + Z) L, and the energy density of a single set of the system is: where ω is the system energy density, Wh / L; is the average system voltage, V; η2 is the system electrolyte utilization rate, %; X is the volume of the electrolyte containing the redox couple; When a < b, set the volume of the positive electrolyte to (X + Z) L, the volume of the negative electrolyte to (X - Z) L, and the energy density of a single set of the system is: Where ω is the system energy density, Wh / L; is the system average voltage, V; η1 is the system electrolyte utilization rate, %; X is the volume of the electrolyte containing the redox couple.

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