Rebalancing methods and systems for redox flow batteries

Abstract

Rebalancing methods and systems for redox flow battery systems are described. A reductant is selectively introduced from the reductant vessel into one or more of the rebalance tank, the negative electrolyte tank, or the positive electrolyte tank to reduce Fe < 3 + > ions to Fe < 2 + > ions. The rebalance system may be controlled by a controller in response to one or more measured characteristics of the iron flow battery.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 369,682 filed on July 28, 2022, the entire contents of which are incorporated herein by reference. Background Art

[0003] The large-scale integration of renewable energy from solar or wind sources into the power grid requires robust energy storage systems to improve its reliability, power quality and economy. Among the various energy storage technologies that have been considered and explored, redox flow batteries (RFBs) are unique because they can convert electrical energy into chemical potential energy by means of a reversible electrochemical reaction between two aqueous electrolyte solutions. In their simplest form, RFBs are electrochemical energy storage systems that directly and reversibly convert chemical energy into electricity. They are usually composed of two external storage tanks, two circulation pumps, and a flow battery with a porous diaphragm, which is filled with an active material containing ions, the metal ions can be in different valence states, and the porous diaphragm is located between the anode and the cathode and is used to separate the anolyte and the cathode electrolyte, and to utilize the current loop by allowing the transfer of balanced ions. The anolyte, the cathode electrolyte, the anode and the cathode are usually referred to as the negative electrode electrolyte, the positive electrode electrolyte, the negative electrode and the positive electrode, respectively. Thus, power and energy capacity can be independent, indicating that the storage capacity is determined by the amount of electrolyte used, and the power rating is determined by the active area of ​​the battery pack and the number of battery cells.

[0004] All-iron redox flow batteries (IFBs) are particularly attractive for grid-scale storage applications due to their advantages, such as low chemical toxicity and very low material costs due to the use of abundant iron, salt and water as electrolytes, compared to other redox flow battery technologies, such as all-vanadium redox flow batteries, zinc-bromine redox flow batteries or iron-chromium redox flow batteries.

[0005] By using different valence states of iron on the positive and negative sides of the IFB, contamination issues due to crossover are effectively eliminated. An iron-based cathode electrolyte solution and an iron-based cathode electrolyte solution stored in external storage tanks flow through the stack of cells. On the positive side, the half-cell reaction involves ferrous ions (Fe 2+ ) loses electrons during charging to form iron ions (Fe 3+ ), and Fe 3+ During discharge, electrons are gained to form Fe 2+ The positive reaction is given by Eq. 1. For the negative side, the half-cell reaction involves the plating and stripping of iron in the form of a solid plate. The negative reaction is represented by Eq. 2. The overall IFB reaction is shown in Eq. 3.

[0006]

[0007] One of the challenges of IFBs is that their lifetime depends on their capacity, which is prone to capacity decay. IFB capacity loss occurs mainly due to unavoidable unwanted side reactions such as H2 evolution on the negative side of the cell. The continuous generation of H2 eventually leads to an imbalance in the electrolyte and a change in the average oxidation state (AOS) of the electrolyte, as the Fe2+ from the negative side is generated during charging. 2+ Fe 0 The amount of plating is reduced, while Fe still exists on the positive side. 2+ To Fe 3+ oxidation, as shown in Equations 4 and 5.

[0008] Negative electrode: 2H + +2e - =H2↑ E 0 =0V (4)

[0009] Total: 2Fe 2+ +2H + =2Fe 3+ +H2↑ E 0 =0.77V (5)

[0010] Another reason for IFB efficiency decline and capacity loss may be due to the crossover of electrolyte and water through the membrane. For example, ferric ions in the positive side can be driven toward the negative side by the ferric ion concentration gradient and the electrophoretic force across the membrane, while ferrous ions in the negative side can migrate to the positive side. The absence of ferrous ions on the negative side accelerates the hydrogen evolution reaction (Eq. 4) and exacerbates the battery health status.

[0011] pH also plays a role in the optimal operation of iron redox flow batteries. If the pH of the negative electrode electrolyte is too low, i.e., high H + Concentration, the hydrogen evolution reaction is aggravated during the charging cycle, resulting in poor Coulombic efficiency and electrolyte pH imbalance. Similarly, if the pH of the negative electrode electrolyte becomes too high, iron tends to precipitate from the solution as iron oxides and hydroxides. For example, in the operation of some IFBs, the ideal pH values ​​of the positive electrode electrolyte and the negative electrode electrolyte are in the range of 0-1 and 4-5, respectively. Removing iron from the solution in the form of oxides and hydroxides leads to a decrease in the availability of iron ions in the solution, and thus reduces the available capacity on the anode side. Preferably, the IFB is operated using the negative electrode solution in a very narrow pH window, so that it is as high as possible to limit the possibility of generating H2 at the anode and as low as possible to avoid the formation of unwanted iron oxides and hydroxides.

[0012] In order to maintain the capacity of the battery, the excess Fe on the positive side of Eq. 3+ Should be reduced to Fe 2+, and the need to simultaneously recover the proton loss and subsequent pH increase caused by H2 evolution in the flow battery system. The answer in the prior art is to react the ferric ions with H2 by chemical or electrochemical methods to convert the H2 back into protons and reduce the ferric ions to ferrous ions, as shown in Equation 6. As a result, a relatively stable pH and state of charge (SOC) can be maintained in both the positive and negative electrolytes.

[0013] However, for conventional chemical methods, such as trickle bed reactors and jelly roll reactors, and electrochemical methods for rebalancing AOS, catalysts including supported precious metals (e.g., carbon-supported Pt, Pd, Rh, Ru, Ir, Ta, or alloys thereof) are required to promote and accelerate the reaction between the iron ions in the IFB solution and the hydrogen. For chemical reactions at the three-phase boundary, mass transfer losses in these reactors have been a long-standing problem. A general approach to compensate for mass transfer limitations is to oversize the rebalancing reactor. However, oversizing the rebalancing reactor is costly and the rebalancing reactor also suffers from poor catalyst utilization. For electrochemical methods, expensive membranes such as Membranes, UOP redox membranes (URMs) or other proton exchange membranes are used to transfer protons between the positive and negative sides. An auxiliary electrical controller system may also be required. In addition, for chemical and electrochemical methods, customized electrolyte tanks may be required to maintain hydrogen pressure and return hydrogen to the hydrogen composite reactor, combined with an external H2 source to compensate for leaks. The use of customized high-pressure tanks increases the cost of the system.

[0014] 2Fe 3+ + H2=2Fe 2+ + 2H + (6)

[0015] Therefore, there is a need for an improved method and system for rebalancing an IFB. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a process flow diagram of one embodiment of a method for refreshing a redox flow battery having a rebalancing tank.

[0017] Figure 2 is a method flow diagram of another embodiment of a method for refreshing a redox flow battery having a rebalancing tank.

[0018] Figure 3 is a method flow diagram of another embodiment of a method for refreshing a redox flow battery having a rebalancing tank.

[0019] Figure 4 is a process flow diagram of another embodiment of a method for refreshing a redox flow battery.

[0020] Figure 5 is a process flow diagram of another embodiment of a method for refreshing a redox flow battery. DETAILED DESCRIPTION

[0021] The present invention discloses a rebalancing method and system for a redox flow battery system, the method and system are used to mitigate the Fe 3+ The benefits of the method and system include, but are not limited to, simplifying iron flow battery operation, improving system health, reducing the frequency of system maintenance, and significantly reducing the cost of iron flow battery systems.

[0022] Fe 3+ The solution has previously been used as a regulator to effectively control ppm-level hydrogen sulfide (H2S) in wastewater collection systems. Test results show that the reduction of dissolved H2S reaches nearly 100% in the neutral pH range, see, for example, TCPrathna and A.Srivastava, Ferric chloride for odour control: studies from wastewater treatment plants in India. Water Practice and Technology, (2021) 16(1):35-41; N.Aslanidouet et al., Regulatory agent for the reduction of hydrogen sulfide (H2S) in municipal wastewater. International Conference on the Protection and Restoration of the Environment IX, Kefalonia, June 2008; B. Wood, Sewer sulphide control with ferrous chloride - a case study. 10th Annual WIOANSW Water Industry Operations Conference and Exhibition thAnnual WIOA NSW Water Industry Operations Conference&Exhibition). Newcastle Jockey Club, April 2016: 131-136.

[0023] Hydrogen sulfide is used to reduce excess iron ions generated by unwanted side reactions in redox flow batteries. 3+ ionic solution, as shown in Equation 7, some Fe 3+ ions are reduced to Fe by sulfur ions from H2S 2 + , elemental sulfur is precipitated, and hydrogen ions from H2S are converted into protons. Unlike the prior art methods that require high-pressure hydrogen storage tanks and precious metal catalysts, the present invention does not require precious metal catalysts or proton exchange membranes. When hydrogen sulfide is used as a reducing agent in the IFB system, as shown in Equations 6 and 7, the harmful effects of inevitable hydrogen evolution can be restored, including Fe in the positive side 3+ Buildup and changes in electrolyte pH imbalance.

[0024] 2Fe 3+ + H2S = 2Fe 2+ + 2H + + S↓ (7)

[0025] When the rebalance tank or the positive electrolyte tank and / or the negative electrolyte tank are used as reduction reactors, their operating conditions are determined by a compromise between reaction rate, electrolyte thermal stability, capital cost, and operating cost. Elevated temperature and pressure favor the absorption of H2S and the reaction of H2S with Fe 3+The redox reaction between. Suitable electrolyte temperatures in the rebalance tank include, but are not limited to, ranges from -10°C to 100°C, or -10°C to 90°C, or -10°C to 80°C, or -10°C to 70°C, or -10°C to 60°C, or -10°C to 50°C, or 10°C to 100°C, or 10°C to 90°C, or 10°C to 80°C, or 10°C to 70°C, or 10°C to 60°C, or 10°C to 50°C, or 30°C to 100°C, or 30°C to 90°C, or 30°C to 80°C, or 30°C to 70°C, or 30°C to 60°C, or 30°C to 50°C. Suitable pressure ranges for rebalancing tanks include, but are not limited to, 0MPa to 6.9MPa, or 0MPa to 1.0MPa, or 0MPa to 5.0MPa, or 0MPa to 4.0MPa, or 0MPa to 3.0MPa, or 0MPa to 2.0MPa, or 0MPa to 1.0MPa, or 0MPa to 0.9MPa, or 0MPa to 0.8MPa, or 0MPa to 0.7MPa, or 0MPa to 0.6MPa, or 0MPa to 0.5MPa, or 0MPa to 0.4MPa, or 0MPa to 0.3MPa, or 0MPa to 0.2MPa. In order to avoid air entry and ferrous ion oxidation, the rebalancing tank can be purged with an inert gas. Suitable inert gases include, but are not limited to, nitrogen and / or argon.

[0026] One aspect of the invention is a method of rebalancing an iron flow battery. In one embodiment, the method includes operating an iron flow battery. The iron flow battery includes a negative electrode, a positive electrode, a separator between the negative electrode and the positive electrode, a negative electrolyte tank, a negative electrolyte flow between the negative electrolyte tank and the negative electrode, and a positive electrolyte tank, a positive electrolyte flow between the positive electrolyte tank and the positive electrode. A reductant is selectively introduced from a reductant container into one or more of the rebalancing tank, the negative electrolyte tank, or the positive electrolyte tank to rebalance the Fe 3+ ions are reduced to Fe 2+ ion.

[0027] In some embodiments, there is a separate rebalance tank. In other embodiments, the reductant is introduced into the catholyte tank and / or the anolyte tank. The location of introduction of the reductant depends on the specific method used.

[0028] In some embodiments, the reducing agent is H2S.

[0029] In some embodiments, the method further comprises: measuring a characteristic of the iron flow battery; and controlling the reductant flow to one or more of the rebalance tank, or the negative electrolyte tank, or the positive electrolyte tank based on the measured characteristic of the iron flow battery. The characteristic may be one or more physical, chemical or electrochemical characteristics of the positive electrolyte, the negative electrolyte and / or the battery pack. These characteristics include, but are not limited to, tank level, pressure drop (dP), electrolyte pH, concentration, turbidity, state of charge (SOC), stack voltage, current, resistance, pump motor maximum current, electrolyte color, viscosity, density, conductivity, electrolyte flow rate, etc. The characteristic may be measured using one or more sensors suitable for the characteristic being measured.

[0030] In some embodiments, the method further comprises filtering the negative electrode electrolyte, the positive electrode electrolyte, or both in a filtration unit comprising a filter. In some embodiments, the filtration unit is located between the positive electrode electrolyte tank and the positive electrode, or between the negative electrode electrolyte tank and the negative electrode, or between the positive electrode electrolyte tank and the rebalance tank, or between the negative electrode electrolyte tank and the rebalance tank, or a combination thereof.

[0031] In some embodiments, the method further comprises collecting precipitate from the filtration unit in a precipitate collection tank. In some embodiments, depending on the method, the precipitate collection tank may also be connected to one or more of the positive electrolyte tank, the negative electrolyte tank, and / or the rebalance tank.

[0032] In some embodiments, the rebalance tank is selectively bidirectionally connected to the positive electrolyte tank, and the reductant tank is selectively connected to the rebalance tank. The method may also include introducing a portion of the positive electrolyte into the rebalance tank. The reductant is introduced into the rebalance tank to reduce at least a portion of the Fe in the positive electrolyte in the rebalance tank. 3+ ions to increase the Fe in the positive electrolyte in the rebalance tank 2+ ions. The rebalance tank with an increased amount of Fe 2+ A portion of the positive electrode electrolyte of the ions is introduced into the positive electrode electrolyte tank.

[0033] In some embodiments, the rebalance tank is selectively connected to the positive electrolyte tank in one direction downstream, the negative electrolyte tank is selectively connected to the rebalance tank in one direction downstream, and the reductant tank is selectively connected to the rebalance tank. The method may also include introducing a portion of the positive electrolyte into the rebalance tank. The reductant is introduced into the rebalance tank to reduce at least a portion of the Fe in the positive electrolyte in the rebalance tank. 3+ ions to increase the Fe in the positive electrolyte in the rebalance tank 2+ ions. The rebalance tank with an increased amount of Fe 2+ A portion of the positive electrode electrolyte ions are introduced into the negative electrode electrolyte tank.

[0034] In some embodiments, the rebalance tank is selectively bidirectionally connected to the positive electrolyte tank, the negative electrolyte tank is selectively bidirectionally connected to the rebalance tank, and the reductant tank is selectively connected to the rebalance tank. The method may also include introducing a portion of the positive electrolyte and a portion of the negative electrolyte into the rebalance tank to form a mixed electrolyte. The reductant is introduced into the rebalance tank to reduce at least a portion of the Fe in the mixed electrolyte in the rebalance tank. 3+ ions to increase Fe in the positive electrolyte in the rebalance tank 2+ ions. The rebalance tank with an increased amount of Fe 2+ The first part of the mixed electrolyte with an increased amount of Fe ions is introduced into the positive electrolyte tank and the electrolyte with an increased amount of Fe 2+ The second portion of the ionic mixed electrolyte is introduced into the negative electrode electrolyte tank.

[0035] In some embodiments, the reducing agent tank is selectively connected to the positive electrolyte tank. The method may further include introducing a reducing agent into the positive electrolyte tank to reduce at least a portion of the Fe 3+ ions to increase the Fe content of the positive electrolyte in the positive electrolyte tank 2+ The amount of ions.

[0036] In some embodiments, the reducing agent tank is selectively connected to the positive electrolyte tank and the negative electrolyte tank. The method may also include introducing a reducing agent into the positive electrolyte tank to reduce at least a portion of the Fe 3+ ions to increase the Fe content of the positive electrolyte in the positive electrolyte tank 2+ ions; or introducing a reducing agent into the negative electrode electrolyte tank to reduce at least a portion of Fe in the negative electrode electrolyte in the negative electrode electrolyte tank 3+ ions to increase the Fe content of the negative electrolyte in the negative electrolyte tank 2+ the amount of ions; or both.

[0037] In some embodiments, the rebalance tank comprises a multiphase chemical reactor. The reactor can be a single-stage reactor or a multistage reactor. Suitable single-stage reactors include, but are not limited to, continuous stirred tank reactors, fluidized bed reactors, plug flow reactors, and bubble column reactors. The multistage reactor comprises at least two of these reactors, which can be of the same type or of different types.

[0038] In some embodiments, the multiphase reactor comprises a trickle bed reactor, a fluidized bed reactor, a bubble column reactor, or a combination thereof.

[0039] Another aspect of the present invention is a rebalancing system for an iron flow battery. In one embodiment, the iron flow battery includes a negative electrode, a positive electrode, a separator between the negative electrode and the positive electrode, a negative electrolyte tank, a negative electrolyte flow between the negative electrolyte tank and the negative electrode, and a positive electrolyte tank, a positive electrolyte flow between the positive electrolyte tank and the positive electrode. The rebalancing system may include a reductant container selectively connected to one or more of the rebalancing tank, the positive electrolyte tank, or the negative electrolyte tank, the reductant container containing Fe 3+ ions are reduced to Fe 2+ Ion reducing agent.

[0040] In some embodiments, the rebalance system further includes a controller responsive to the measured characteristic of the redox flow battery to selectively allow reductant flow to the positive electrolyte tank.

[0041] In some embodiments, the rebalance system further comprises a filtration unit, the filtration unit comprising a filter, the filter being located between the positive electrolyte tank and the positive electrode, or between the negative electrolyte tank and the negative electrode, or between the positive electrolyte tank and the rebalance tank, or between the negative electrolyte tank and the rebalance tank, or a combination thereof. In some embodiments, the filtration unit further comprises a sediment collection tank connected to the filter.

[0042] The SOC or Fe in the cathode electrolyte can be adjusted by connecting the cathode electrolyte tank to a separate rebalancing tank. 3+ Concentration, such as Figure 1 As shown. During operation of the IFB system, the physical, chemical or electrochemical characteristics of the positive and negative electrolytes and the battery pack are monitored and controlled. These characteristics include, but are not limited to, tank level, electrolyte pH, concentration, turbidity, SOC, stack voltage, etc. For example, when the state of charge, pH or conductivity of the positive electrolyte is outside a predetermined operating range, a certain amount of the positive electrolyte is pumped into the rebalance tank. Sufficient hydrogen sulfide is then introduced into the rebalance tank to convert Fe 3+ Reduction to Fe 2+ . After the positive electrolyte in the rebalance tank is restored, the rebalanced positive electrolyte is returned to the IFB positive electrolyte tank. The SOC of the positive side is reduced as needed without any noticeable effect on the total iron concentration or electrolyte volume in the positive side. Proton losses and electrolyte pH increases attributed to hydrogen evolution can also be compensated and restored. Byproduct sulfur can be collected from the rebalance tank and a filter unit that can be connected to the battery positive electrolyte tank.

[0043] Figure 1The illustrated rebalancing method 100 includes an IFB stack 105 including a positive electrode 110, a negative electrode 115, and a separator 120. In operation, a positive electrolyte flows from a positive electrolyte tank 125 to the positive electrode 110 and back to the positive electrolyte tank 125, and a negative electrolyte flows from a negative electrolyte tank 130 to the negative electrode 115 and back to the negative electrolyte tank 130.

[0044] The positive electrolyte tank 125 is selectively bidirectionally connected to the rebalance tank 135. One or more physical, chemical or electrochemical characteristics of the system are monitored and controlled by the controller 140, and these characteristics are measured by sensors (not shown). When one or more characteristics are outside a predetermined operating range, the controller 140 allows the positive electrolyte to flow from the positive electrolyte tank 125 to the rebalance tank 135. The reductant from the reductant container 145 is introduced into the rebalance tank 135, where the reductant converts Fe 3+ Reduction to Fe 2+ When sufficient amount of Fe 3+ Has been reduced to Fe 2+ When , the reductant flow stops, and the refreshed positive electrolyte returns to the positive electrolyte tank 125. In some cases, a bidirectional pump 150 may be used to enable the positive electrolyte to flow into and out of the positive electrolyte tank.

[0045] In some methods, there is a filtration unit 155 including a filter 160 to remove precipitates from the positive electrolyte flowing between the positive electrolyte tank 125 and the rebalance tank 135. There may be a precipitate collection tank 165 connected to the filtration unit 155. If desired, the precipitate collection tank 165 may also be connected to the rebalance tank 135 to remove precipitates from the rebalance tank 135.

[0046] Figure 2 The rebalancing design in the IFB system can be used to solve the ion crossover and pH imbalance problems during long-term operation. During the operation of the IFB system, the characteristics of the positive and negative electrolytes and the battery pack are monitored and controlled as described above. For example, when the level gauge, ion concentration, or electrolyte pH in the positive or negative electrolyte tank is triggered and the electrolyte becomes unbalanced between the positive and negative sides, a certain amount of positive electrolyte is pumped into the rebalancing tank. Sufficient hydrogen sulfide is then introduced into the rebalancing tank to reduce the Fe in the electrolyte. 3+ . Refresh the acidic Fe in the rebalance tank 2+ The electrolyte is discharged into the negative electrolyte tank without worrying about the formation of Fe(OH)3 precipitates. Ion accumulation on the positive side and pH increase on the negative side can be corrected simultaneously. Byproduct sulfur can be collected from the rebalance tank and filter unit connected to the negative electrolyte tank.

[0047] Figure 2The illustrated rebalancing method 200 includes an IFB stack 205 including a positive electrode 210, a negative electrode 215, and a separator 220. In operation, a positive electrolyte flows from a positive electrolyte tank 225 to the positive electrode 210 and back to the positive electrolyte tank 225, and a negative electrolyte flows from a negative electrolyte tank 230 to the negative electrode 215 and back to the negative electrolyte tank 230.

[0048] The rebalance tank 235 is selectively in one-way downstream communication with the positive electrolyte tank 225 (i.e., flows from the positive electrolyte tank 225 to the rebalance tank 235). The negative electrolyte tank 230 is selectively in one-way downstream communication with the rebalance tank 235 (i.e., flows from the rebalance tank 235 to the negative electrolyte tank 230). One or more physical, chemical, or electrochemical characteristics of the system are monitored and controlled by the controller 240, which are measured by sensors (not shown). When one or more characteristics are outside of a predetermined operating range, the controller 240 allows the positive electrolyte to flow from the positive electrolyte tank 225 to the rebalance tank 235. The reductant from the reductant container 245 is introduced into the rebalance tank 235, where the reductant converts the Fe 3+ Reduction to Fe 2+ When sufficient amount of Fe 3+ Has been reduced to Fe 2+ When , the reductant flow stops, and refreshed positive electrolyte is sent to negative electrolyte tank 230. If necessary, a rebalance pump 250 can be between positive electrolyte tank 225 and rebalance tank 235, and another rebalance pump 250 can be between rebalance tank 235 and negative electrolyte tank 230.

[0049] In some methods, there is a filtration unit 255 including a filter 260 to remove precipitates from the positive electrolyte flowing between the rebalance tank 235 and the negative electrolyte tank 230. There may be a precipitate collection tank 265 connected to the filtration unit 255. If desired, the precipitate collection tank 265 may also be connected to the rebalance tank 235 to remove precipitates from the rebalance tank 235.

[0050] Iron ions that cross from the low pH positive side to the high pH negative side can lead to the precipitation of Fe(OH)3 during IFB operation. The precipitation of Fe(OH)3 not only contaminates the membrane and causes severe cell capacity loss, but also blocks the flow channels, increases the flow resistance and IFB area specific resistance (ASR), and ultimately leads to permanent damage to the IFB stack. Figure 3As shown, both the positive electrolyte tank and the negative electrolyte tank are connected to a separate rebalance tank via a bidirectional pump. The positive electrolyte and the negative electrolyte can be loaded into or discharged from the rebalance tank separately or simultaneously. During operation of the IFB system, the characteristics of the positive and negative electrolytes and the battery pack are monitored and controlled as described above. For example, an increase in turbidity or pressure drop of the negative electrolyte may indicate Fe 3+ From the positive side to the negative side, a certain amount of negative electrolyte is pumped into the rebalance tank, and then sufficient hydrogen sulfide is introduced into the rebalance tank. After the loaded negative electrolyte is refreshed with hydrogen sulfide, the acidic Fe 2+ The electrolyte is discharged back into the negative electrolyte tank. This process can be repeated until the turbidity of the negative electrolyte drops below a threshold. Sulfur will be captured in the rebalance tank and in the two filter units connected to the IFB electrolyte tank.

[0051] Figure 3 The illustrated rebalancing method 300 includes an IFB stack 305 including a positive electrode 310, a negative electrode 315, and a separator 320. In operation, a positive electrolyte flows from a positive electrolyte tank 325 to the positive electrode 310 and back to the positive electrolyte tank 325, and a negative electrolyte flows from a negative electrolyte tank 330 to the negative electrode 315 and back to the negative electrolyte tank 330.

[0052] The rebalance tank 335 is selectively in bidirectional communication with the positive electrolyte tank 325. The negative electrolyte tank 330 is selectively in bidirectional communication with the rebalance tank 335. One or more physical, chemical or electrochemical characteristics of the system are monitored and controlled by the controller 340, and these characteristics are measured by sensors (not shown). When one or more characteristics are outside a predetermined operating range, the controller 340 allows the positive electrolyte to flow from the positive electrolyte tank 325 to the rebalance tank 335, or the negative electrolyte to flow from the negative electrolyte tank 330 to the rebalance tank 335. The reductant from the reductant container 345 is introduced into the rebalance tank 335, where the reductant converts Fe 3+ Reduction to Fe 2+ When sufficient amount of Fe 3+ Reduced to Fe 2+ When the reductant flow is stopped, the reductant flow is stopped. The refreshed electrolyte is sent to the positive electrolyte tank 325 and the negative electrolyte tank 330. If necessary, a rebalance pump 350 can be between the positive electrolyte tank 325 and the rebalance tank 335, and another pump 350 can be between the rebalance tank 335 and the negative electrolyte tank 330.

[0053] In some methods, there is a filtration unit 355 including a filter 360 to remove precipitates from the refreshed electrolyte flowing between the rebalance tank 335 and the positive electrolyte tank 325 and / or between the rebalance tank 335 and the negative electrolyte tank 330. There may be a precipitate collection tank 365 connected to the filtration unit 355. If desired, the precipitate collection tank 365 may also be connected to the rebalance tank 335 to remove precipitates from the rebalance tank 335.

[0054] In addition to being independent of each other, the rebalancing system and the battery system can be integrated and utilize at least one common component. During IFB operation, the SOC, pH, conductivity, or pressure of the positive and negative sides are monitored and acquired. Figure 4 As shown, when any of these parameter thresholds are triggered, a certain amount of hydrogen sulfide is introduced directly into the positive electrolyte tank 425. The iron ion concentration and pH of the positive electrolyte will be adjusted accordingly. The sulfur precipitate is collected from the positive electrolyte tank and filtration unit before the battery stack.

[0055] Figure 4 The illustrated rebalancing method 400 includes an IFB stack 405 including a positive electrode 410, a negative electrode 415, and a separator 420. In operation, a positive electrolyte flows from a positive electrolyte tank 425 to the positive electrode 410 and back to the positive electrolyte tank 425, and a negative electrolyte flows from a negative electrolyte tank 430 to the negative electrode 415 and back to the negative electrolyte tank 430.

[0056] In this embodiment, there is no rebalance tank. The reductant from the reductant container 445 is introduced into the positive electrolyte tank 425 where it converts Fe 3+ Reduction to Fe 2+ When sufficient amount of Fe 3+ Reduced to Fe 2+ When , stop the reducing agent flow.

[0057] One or more physical, chemical or electrochemical characteristics of the system, which are measured by sensors (not shown), are monitored and controlled by controller 440. When one or more characteristics are outside of a predetermined operating range, controller 340 allows reductant to flow from reductant container 445 to positive electrolyte tank 425.

[0058] In some methods, there is a filtration unit 455 including a filter 460 to remove precipitates from the positive electrolyte flowing out of the positive electrolyte tank 425. There may be a precipitate collection tank 465 connected to the filtration unit 455. If desired, the precipitate collection tank 465 may also be connected to the positive electrolyte tank 425 to remove precipitates from the positive electrolyte tank 425.

[0059] like Figure 5 As shown, when parameters such as turbidity, pH or pressure on the negative side are outside the predetermined operating range, a certain amount of hydrogen sulfide can be directly introduced into the negative electrolyte tank. The ferric ions crossing over from the positive side can be reduced to ferrous ions, which reduces the possibility of Fe(OH)3 precipitation on the high pH negative side. The sulfur precipitate is collected from the positive and negative electrolyte tanks and the filtration unit before the battery stack.

[0060] Figure 5 The illustrated rebalancing method 500 includes an IFB stack 505 including a positive electrode 510, a negative electrode 515, and a separator 520. In operation, a positive electrolyte flows from a positive electrolyte tank 525 to the positive electrode 510 and back to the positive electrolyte tank 525, and a negative electrolyte flows from a negative electrolyte tank 530 to the negative electrode 515 and back to the negative electrolyte tank 530.

[0061] In this embodiment, there is no rebalance tank. The reductant from the reductant container 545 is introduced into the positive electrolyte tank 525 and the negative electrolyte tank 530 where the reductant converts Fe 3+ Reduction to Fe 2+ When sufficient amount of Fe 3+ Reduced to Fe 2+ When , stop the reducing agent flow.

[0062] One or more physical, chemical or electrochemical characteristics of the system, which are measured by sensors (not shown), are monitored and controlled by controller 540. When one or more characteristics are outside of a predetermined operating range, controller 540 allows reductant to flow from reductant container 545 to positive electrolyte tank 525 and negative electrolyte tank 530.

[0063] In some methods, there is a filtration unit 555 including a filter 560 to remove precipitates from the positive electrolyte flowing between the positive electrolyte tank 525 and the positive electrode 510 and / or between the negative electrolyte tank 530 and the negative electrode 515. There may be a precipitate collection tank 565 connected to the filtration unit 555. If necessary, the precipitate collection tank 565 may also be connected to the rebalance tank 335 to remove precipitates from the rebalance tank 335.

[0064] like Figure 4 and Figure 5 The integration of the rebalancing system and the battery system shown can simplify the system design, reduce the physical footprint of the system, and reduce the system cost. However, it has higher requirements for the electrolyte tank and system sealing.

[0065] The hydrogen generated on the anode side of the IFB can be released into the environment after the acid is removed. The proton loss and the subsequent increase in electrolyte pH due to hydrogen evolution can be compensated by adopting a rebalancing system. The hydrogen sulfide in the rebalancing system can be stored in a high-pressure gas cylinder. A hydrogen sulfide generator is an alternative to rebalancing the IFB system when needed. It can generate hydrogen sulfide by the reaction between ferrous sulfide and hydrochloride, the reaction between inorganic materials and water (including thioacetamide), or the reaction between metal or non-metal sulfide and water (such as aluminum sulfide, phosphorus pentasulfide or silicon disulfide). The sulfur trapped in the electrolyte tank and the filter unit is a byproduct. Alternatively, hydrogen and sulfur can be combined to prepare hydrogen sulfide for recycling.

[0066] Specific implementation plan

[0067] While the following is described in conjunction with specific embodiments, it should be understood that this description is intended to illustrate and not to limit the scope of the foregoing description and the appended claims.

[0068] A first embodiment of the present invention is a method of rebalancing an iron flow battery, the method comprising operating an iron flow battery comprising a negative electrode, a positive electrode, a separator between the negative electrode and the positive electrode, a negative electrolyte tank, a negative electrolyte flow between the negative electrolyte tank and the negative electrode, and a positive electrolyte tank, a positive electrolyte flow between the positive electrolyte tank and the positive electrode; selectively introducing a reductant from a reductant container into one or more of a rebalancing tank, a negative electrolyte tank, or a positive electrolyte tank to rebalance the Fe 3+ ions are reduced to Fe 2+ions. An embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, wherein the reducing agent is H2S. An embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, and the embodiment further includes measuring the characteristics of the iron liquid flow battery; and controlling the reducing agent flow to one or more of the rebalance tank, or the negative electrolyte tank, or the positive electrolyte tank based on the measured characteristics of the iron liquid flow battery. An embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, and the embodiment further includes filtering the negative electrolyte, the positive electrolyte, or both in a filtration unit including a filter. An embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiments of this paragraph, wherein the filtration unit is located between the positive electrolyte tank and the positive electrode, or between the negative electrolyte tank and the negative electrode, or between the positive electrolyte tank and the rebalance tank, or between the negative electrolyte tank and the rebalance tank, or a combination thereof. The embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, and the embodiment further includes collecting the precipitate from the filtration unit in the precipitate collection tank. The embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the rebalance tank is selectively bidirectionally connected to the positive electrolyte tank, and wherein the reductant tank is selectively connected to the rebalance tank, and the method further includes introducing a portion of the positive electrolyte into the rebalance tank; introducing the reductant into the rebalance tank to reduce at least a portion of the Fe in the positive electrolyte in the rebalance tank. 3+ ions to increase the Fe in the positive electrolyte in the rebalance tank 2+ ions; and the increased amount of Fe 2+ An embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the rebalance tank is selectively connected to the positive electrolyte tank in one direction downstream, and the negative electrolyte tank is selectively connected to the rebalance tank in one direction downstream, and the reductant tank is selectively connected to the rebalance tank, and the embodiment further includes introducing a portion of the positive electrolyte into the rebalance tank; introducing the reductant into the rebalance tank to reduce at least a portion of the Fe in the positive electrolyte in the rebalance tank. 3+ ions to increase the Fe in the positive electrolyte in the rebalance tank 2+ ions; the rebalance tank with an increased amount of Fe 2+ions into the negative electrolyte tank. An embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the rebalance tank is selectively bidirectionally connected to the positive electrolyte tank, and wherein the negative electrolyte tank is selectively bidirectionally connected to the rebalance tank, and wherein the reductant tank is selectively connected to the rebalance tank, and the embodiment further includes introducing a portion of the positive electrolyte and a portion of the negative electrolyte into the rebalance tank to form a mixed electrolyte; introducing the reductant into the rebalance tank to reduce at least a portion of the Fe in the mixed electrolyte in the rebalance tank. 3+ ions to increase the Fe in the positive electrolyte in the rebalance tank 2+ ions; the rebalance tank with an increased amount of Fe 2+ The first part of the mixed electrolyte with an increased amount of Fe ions is introduced into the positive electrolyte tank and the electrolyte with an increased amount of Fe 2+ The second part of the mixed electrolyte of ions is introduced into the negative electrolyte tank. An embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the reducing agent tank is selectively connected to the positive electrolyte tank, and the embodiment further includes introducing the reducing agent into the positive electrolyte tank to reduce at least a portion of Fe in the positive electrolyte in the positive electrolyte tank. 3+ ions to increase the Fe content of the positive electrolyte in the positive electrolyte tank 2+ ions. An embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the reducing agent tank is selectively connected to the positive electrolyte tank and the negative electrolyte tank, and the embodiment further includes introducing the reducing agent into the positive electrolyte tank to reduce at least a portion of the Fe in the positive electrolyte in the positive electrolyte tank. 3+ ions to increase the Fe content of the positive electrolyte in the positive electrolyte tank 2+ ions; or introducing a reducing agent into the negative electrode electrolyte tank to reduce at least a portion of Fe in the negative electrode electrolyte in the negative electrode electrolyte tank 3+ ions to increase the Fe content of the negative electrolyte in the negative electrolyte tank 2+ ion amount; or both. An embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the rebalance tank comprises a multiphase reactor. An embodiment of the present invention is one, any one or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the multiphase reactor comprises a trickle bed reactor, a fluidized bed reactor, a bubble column reactor or a combination thereof.

[0069] A second embodiment of the present invention is a rebalancing system for an iron flow battery, the iron flow battery comprising a negative electrode, a positive electrode, a separator between the negative electrode and the positive electrode, a negative electrode electrolyte tank, a negative electrode electrolyte flow between the negative electrode electrolyte tank and the negative electrode, and a positive electrode electrolyte tank, a positive electrode electrolyte flow between the positive electrode electrolyte tank and the positive electrode, the rebalancing system comprising a reductant container selectively connected to one or more of the rebalancing tank, the positive electrode electrolyte tank or the negative electrode electrolyte tank, the reductant container containing Fe 3+ ions are reduced to Fe 2+ ion reducing agent. An embodiment of the present invention is one, any or all of the second embodiment of this paragraph to the previous embodiment of this paragraph, and the embodiment further includes a controller that responds to the measured characteristics of the redox flow battery to selectively allow the reductant flow to the positive electrolyte tank. An embodiment of the present invention is one, any or all of the second embodiment of this paragraph to the previous embodiment of this paragraph, and the embodiment further includes a filtration unit that includes a filter located between the positive electrolyte tank and the positive electrode, or between the negative electrolyte tank and the negative electrode, or between the positive electrolyte tank and the rebalancing tank, or between the negative electrolyte tank and the rebalancing tank, or a combination thereof. An embodiment of the present invention is one, any or all of the second embodiment of this paragraph to the previous embodiment of this paragraph, wherein the filtration unit further includes a precipitate collection tank connected to the filter.

[0070] Although there is no further detailed description, it is believed that those skilled in the art can utilize the present invention to the greatest extent by using the foregoing description and can easily determine the essential characteristics of the present invention without departing from the spirit and scope of the present invention to make various changes and modifications of the present invention and adapt it to various usages and conditions. Therefore, the aforementioned preferred specific embodiments should be understood as merely illustrative and not to limit the rest of the present disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0071] In the foregoing, all temperatures are set forth in degrees Celsius and all parts and percentages are by weight unless otherwise indicated.

Claims

1. A method for rebalancing an iron flow battery, the method comprising: operating the iron flow battery, the iron flow battery comprising a negative electrode (115), a positive electrode (110), a separator (120) between the negative electrode (115) and the positive electrode (110), a negative electrolyte tank (130), a negative electrolyte flow between the negative electrolyte tank (130) and the negative electrode (115), and a positive electrolyte tank (125), a positive electrolyte flow between the positive electrolyte tank (125) and the positive electrode (110); and A reductant is selectively introduced from a reductant tank (145) into one or more of a rebalance tank (135), the negative electrolyte tank, or the positive electrolyte tank to convert Fe 3+ ions are reduced to Fe 2+ ion.

2. The method of claim 1, wherein the reducing agent is H2S.

3. The method according to any one of claims 1 to 2, further comprising: measuring characteristics of the iron flow battery; as well as The reductant flow to one or more of the rebalance tank (135), or the negative electrolyte tank, or the positive electrolyte tank is controlled based on the measured characteristics of the iron flow battery.

4. The method according to any one of claims 1 to 2, further comprising: filtering the negative electrolyte, the positive electrolyte, or both in a filtration unit (155) comprising a filter (160); as well as The precipitate is optionally collected from the filtration unit (155) in a precipitate collection tank (165).

5. The method according to any one of claims 1 to 2, wherein the rebalance tank (135) is selectively bidirectionally connected to the positive electrolyte tank (125), and wherein the reductant tank (145) is selectively connected to the rebalance tank (135), the method further comprising: introducing a portion of the cathode electrolyte into the rebalance tank (135); The reducing agent is introduced into the rebalance tank (135) to reduce at least a portion of the Fe 3+ ions to increase the Fe in the positive electrolyte in the rebalance tank (135). 2+ The amount of ions; as well as The rebalance tank (135) is supplied with an increased amount of Fe 2+ A portion of the positive electrode electrolyte ions is introduced into the positive electrode electrolyte tank (125).

6. The method according to any one of claims 1 to 2, wherein the rebalance tank (235) is selectively connected to the positive electrolyte tank (225) downstream in one direction, and wherein the negative electrolyte tank (230) is selectively connected to the rebalance tank (235) downstream in one direction, and wherein the reductant tank (245) is selectively connected to the rebalance tank (135), the method further comprising: introducing a portion of the cathode electrolyte into the rebalance tank (235); The reducing agent is introduced into the rebalance tank (235) to reduce at least a portion of the Fe 3+ ions to increase the Fe in the positive electrolyte in the rebalance tank (235). 2+ The amount of ions; as well as The rebalance tank (235) is provided with an increased amount of Fe 2+ A portion of the ions of the positive electrode electrolyte is introduced into the negative electrode electrolyte tank (230).

7. The method according to any one of claims 1 to 2, wherein the rebalance tank (335) is selectively bidirectionally connected to the positive electrolyte tank (325), and wherein the negative electrolyte tank (330) is selectively bidirectionally connected to the rebalance tank (335), and wherein the reductant tank (345) is selectively in communication with the rebalance tank (335), the method further comprising: Introducing a portion of the positive electrode electrolyte and a portion of the negative electrode electrolyte into the rebalance tank (335) to form a mixed electrolyte; The reducing agent is introduced into the rebalance tank (335) to reduce at least a portion of the Fe 3+ ions to increase the Fe in the positive electrolyte in the rebalance tank (335). 2+ The amount of ions; as well as The rebalance tank (335) is supplied with an increased amount of Fe 2+ The first portion of the mixed electrolyte containing ions is introduced into the positive electrolyte tank (325), and the electrolyte with an increased amount of Fe 2+ A second portion of the mixed electrolyte ions is introduced into the negative electrode electrolyte tank (330).

8. The method according to any one of claims 1 to 2, wherein the reductant tank (445) is selectively connected to the positive electrolyte tank (425), the method further comprising: The reducing agent is introduced into the positive electrolyte tank (425) to reduce at least a portion of the Fe 3+ ions to increase the Fe in the positive electrolyte in the positive electrolyte tank (425). 2+ The amount of ions.

9. The method according to any one of claims 1 to 2, wherein the reductant tank (545) is selectively connected to the positive electrolyte tank (525) and the negative electrolyte tank (530), the method further comprising: The reducing agent is introduced into the positive electrolyte tank (525) to reduce at least a portion of the Fe 3+ ions to increase the Fe in the positive electrolyte in the positive electrolyte tank (525). 2+ The amount of ions; or The reducing agent is introduced into the negative electrode electrolyte tank (530) to reduce at least a portion of the Fe 3+ ions to increase the Fe in the negative electrolyte in the negative electrolyte tank (530). 2+ The amount of ions; or Both.

10. A rebalancing system for an iron flow battery, the iron flow battery comprising a negative electrode (115), a positive electrode (110), a separator (120) between the negative electrode (115) and the positive electrode (110), a negative electrolyte tank (130), a negative electrolyte flow between the negative electrolyte tank (130) and the negative electrode (115), and a positive electrolyte tank (125), a positive electrolyte flow between the positive electrolyte tank (125) and the positive electrode (110), the rebalancing system comprising: A reductant container (145) is selectively connected to one or more of the rebalance tank (135), the positive electrolyte tank, or the negative electrolyte tank, the reductant container containing Fe 3+ ions are reduced to Fe 2+ Ion reducing agent.

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