Filtration applications in redox flow batteries

Abstract

A method for limiting the circulation of precipitates in a redox flow battery system is described. The methods include filtering the negative electrolyte, or the positive electrolyte, or both, in one or more filters. The filter may be located in the negative electrolyte circuit, the positive electrolyte circuit, or both. Filtering can be carried out in normal operation; it may also be performed during a refresh cycle.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. non-provisional patent application serial number 18 / 315,287 filed on May 10, 2023, which claims priority to U.S. patent application serial number 63 / 345,744 filed on May 25, 2022, the entire contents of which are incorporated herein by reference. Background Art

[0003] Energy storage systems play a key role in collecting and storing energy from a variety of sources for use in a variety of applications and industries, including buildings, transportation, utilities, and industry. A variety of energy storage systems are already in commercial use with new systems currently being developed to meet future storage needs. It is critical to develop cost-effective and eco-friendly energy storage systems to solve the energy crisis and overcome the mismatch between power generation and end-use. Current energy storage solutions explored include electrochemical and battery packs, thermal, thermochemical, flywheels, compressed air, pumped hydro, magnetic, biological, chemical, and hydrogen energy storage.

[0004] Renewable energy sources such as wind and solar are transient in nature in that they rely on environmental conditions and would benefit from associated energy storage to provide power when the wind is not blowing and the sun is not shining. Battery energy storage systems (BESS) such as redox flow batteries (RFBs) have attracted significant attention in large-scale stationary applications such as grid-scale energy storage. Some of the earliest published work detailing the use of redox flow batteries for storing electrical energy dates back to the 1950s, when German chemist Dr. Carl Walther Nicolai Kanero studied the use of Fe 3+ / Fe 2+ Cr 6 + / Cr 3+ 、Ti 4+ / Ti 3+ and Cl - / Cl2 redox pairs in liquids to store electrical energy. In the 1970s, NASA continued to work in this field, producing the first iron-chromium redox flow battery in 1973 to store energy in future lunar bases. Although the interest in building a base on the moon gradually faded, flow battery research continued to other chemicals, including zinc-bromine and all-iron flow batteries. In 1981, Hruska et al. demonstrated the ability of circulating all-iron redox flow batteries (IFBs), which is an attractive battery energy storage device for large-scale energy storage applications (such as load balancing and solar energy storage) due to the use of low-cost and large-scale available iron, salt and water as electrolytes and the chemical safety properties of the system. (Investigation of Factors Affecting Performance of the Iron-RedoxBattery (Research on the factors affecting the performance of iron-redox batteries), J.Electrochem.Soc., Vol. 28, No. 1, pp. 18-25, January 1981). In the late 1980s, Skyllas-Kazacos et al. from the University of New South Wales, Australia, used V 2+ / V 3+ and V 4+ / V 5+ Over the past 40 years, considerable effort has been put into developing all aspects of flow batteries.

[0005] In their simplest form, RFBs are electrochemical energy storage systems that convert chemical energy directly and reversibly into electricity. They usually consist of two external storage tanks filled with active materials containing ions, which metal ions can be in different valence states, two circulation pumps, and a flow battery with a porous diaphragm located between the anode and cathode and used to separate the anolyte and catholyte, and to utilize the current circuit by allowing the transfer of counter ions. The anolyte, catholyte, anode, and cathode are usually referred to as the negative electrolyte, positive electrolyte, negative electrode, and positive electrode, respectively.

[0006] All-vanadium redox flow batteries (VRFBs) have been the most widely studied system because they use the same active material in both half-cells, which prevents electrolyte contamination from one half-cell to the other through crossover at the membrane. However, VRBFs are inherently expensive due to the use of high-cost vanadium.

[0007] Similar to VRFB, the all-vanadium redox flow battery utilizes the same active material (Fe) in different valence states in both the positive and negative electrolytes for the positive and negative electrodes, respectively. The iron-based electrolyte solution is stored in an external storage tank and flows through the battery stack. The positive electrode side half-cell reaction involves Fe 2+ Loses electrons to form Fe 3 + And during discharge, Fe 3+ Gain electrons to form Fe 2+ ; This reaction is given by Equation 1. The negative electrode side half-cell reaction involves the deposition and dissolution of iron in the form of a solid plate; This reaction is given by Equation 2. The overall reaction is shown in Equation 3.

[0008] Redox Electrode:

[0009] Electroplating Electrode:

[0010] total:

[0011] During normal operation of the RFB, small inefficiencies can create big problems over the life of the battery pack. These problems can stem from many reasons, such as: active material crossover across the membrane, parasitic side reactions, or incomplete discharge of the battery pack. Even small inefficiencies can ultimately result in a poorly performing battery pack in a product designed to last more than 20,000 cycles. Engineering design is often required to suppress or correct these inefficiencies.

[0012] Mixing electrolytes together to rebalance and refresh the system is a way to rebalance a redox flow battery. Typically, this can involve mixing the electrolyte solutions (negative and positive electrolytes) completely. The electrolytes are then properly redistributed to the initial volume. This method generally corrects many problems in RFBs, including volume differences driven by osmotic pressure, redistribution of active materials and supporting electrolytes, and pH adjustments on both sides. Once the negative and positive electrolytes are mixed together, the resulting solution contains the average concentration of the components in the initial negative and positive electrolytes.

[0013] Maintaining optimal operating conditions within a redox flow battery stack often requires engineering controls to manage the health of the battery stack and the relative health of the electrolyte. 2+ / Fe 3+ In redox flow batteries that incorporate redox pairs, system inefficiencies associated with battery cycling can lead to accumulation of iron cations in the electrolyte, which if not managed can result in reduced battery capacity.

[0014] For more than 40 years, the parasitic evolution of H2(g) has been a technical challenge associated with redox flow battery technology. In 1979, Thaller reported the importance of rebalancing cells in iron-chromium RFBs to address the minor reactions (hydrogen evolution) at the chromium electrode. (US 4,159,366) 2 and directs it to the hydrogen (negative) electrode of the rebalance cell, and the positive electrode of the rebalance cell receives Fe from the rest of the system 2+ / Fe 3+ The electrochemical reactions that occur in the rebalance cell are opposite to the undesirable reactions that occur in the redox cell and are self-regulating (limited by total H2 availability). H2 / Fe 3+ The open circuit voltage of the rebalanced cell is about 0.7V, so energy is generated rather than consumed during the rebalance process, thereby demonstrating the electrochemical reorganization of H2. In 2005, Noah et al. reported the use of the same rebalance principle to improve the efficiency of conventional electrowinning copper processes, which use hydrolysis reactions as anode electron sources. (Hydrogen Reduction of Ferric Ions for Use in Copper Electrowinning, Idaho National Engineering and Environmental Laboratory, INEEL / EXT-05-02602, January 2005). In order to improve energy efficiency, an alternative anode reaction of ferrous ion oxidation is proposed, and H2 is used as an effective reducing agent for iron cations. In Thaller's work, iron cations and H2 gases in the electrolyte pass adjacent to each other in the electrochemical cell and are separated by a membrane, while Noah et al. are different, and they utilize a trickle bed column reactor to demonstrate the catalytic reduction of iron cations, and circulate the iron ion electrolyte by pumping the electrolyte solution from the reservoir to the top of the reactor. The electrolyte drains through the bed under gravity and into a reservoir just below the reactor. H2 is introduced into the bed through a small tube at the bottom and flows upward through the bed and out through an outlet tube.

[0015] Current methods and systems for rebalancing all-iron RFB cells involve adding Fe 3+ Reduction to Fe 2+ Different engineering approaches (electrochemical or catalytic) have been demonstrated to rebalance the electrolyte within an all-iron redox flow battery; however, the basic principle of iron ion reduction remains largely the same as that taught by Thaller and Noah, where H2(g) is oxidized to produce protons (2H + ) and electron (2e- ), which enables Fe 3+ Catalytic reduction to Fe 2+ . Fe 3+ Reduction to Fe 2+ enables the charge state of the positive electrolyte to be changed; however, protons (H + ) migrates to the positive electrolyte. This process results in the removal of protons (H) from the negative electrolyte (during hydrogen evolution). + ) and (during rebalancing) released into the positive electrolyte. The result of the removal of protons from the negative electrolyte (H2 evolution) and insertion into the positive electrolyte (H2 recombination) is a deviation of the electrolyte pH from the optimal operating value (the positive electrolyte acidity increases, while the negative electrolyte acidity decreases). Increasing the pH of the negative electrolyte can result in an inability to completely oxidize the plated iron to ferrous cations, or oxidation or loss of Fe0 from the cell in the form of ferric hydroxide, ferric oxide, or iron flakes. This results in a reduction in the capacity of the negative electrolyte and causes precipitates / sediments to circulate in the electrolyte loop, which over time can lead to the formation of blockages. 3+ Direct introduction of cations into the higher pH negative electrolyte can result in precipitation of iron hydroxide or iron oxide byproducts, which can lead to electrolyte flow obstruction and battery failure.

[0016] Another failure mechanism experienced by RFBs is electrolyte crossover across the membrane (hydraulic crossover, crossover of active species, or a combination of both), which can be driven by changes in species concentrations, electrolyte flow rates, pressure, and osmotic pressure differences during charge and discharge. Electrolyte properties such as density, viscosity, and conductivity vary with the oxidation state of the active species. In the case of hybrid RFBs (such as all-iron RFBs), significant differences in iron ion concentrations in the electrolyte can lead to severe differences in osmotic pressure in the positive and negative electrolytes, which in turn can lead to electrolyte migration across the membrane, where Fe 3+ Moves from the positive electrolyte to the negative electrolyte and H2O moves from the negative electrolyte to the positive electrolyte.

[0017] There are strategies to reduce electrolyte crossover, such as using different and varying flow rates or backpressures for each electrolyte to compensate for any pressure difference across the membrane, or by enhancing the selectivity of the membrane to eliminate crossover of active species, which is very challenging to achieve in practice. In the case of an all-iron RFB where the active species in both electrolytes are the same, maximum system capacity can be restored by mixing and rebalancing the electrolytes so that each electrolyte tank has an equal number of active molecules.

[0018] As explained previously, IFBs operating with acidic electrolytes are known to have parasitic hydrogen evolution at the negative electrode. This becomes a problem because electrons are consumed by hydrogen evolution at the negative electrode instead of Fe 2+The electrolyte ends up with an unbalanced state of charge (SoC) due to the reduction of Fe2 to Fe0. In addition, protons are removed from the negative electrolyte, which significantly increases the pH, which can lead to the precipitation of iron hydroxide. Ideally, assuming a symmetrical charge and discharge regime, the charge balance and pH in the electrolyte would return to the original starting values ​​at the end of each cycle, with all redox activity occurring only at the active species. However, as previously mentioned, parasitic side reactions can occur, such as H2 evolution or precipitation of unwanted iron hydroxide species, which can lead to an imbalance in the electrolyte properties, including [Fe], [H + ] and electrolyte volume.

[0019] Ideally, an IFB operates with a negative electrolyte solution in a very narrow pH window, making it as high as possible to limit the possibility of H2 generation at the negative electrode and as low as possible to suppress the formation of unwanted iron oxides and hydroxides. However, the pH profile throughout a large IFB device is not uniform, and it is conceivable that the pH immediately after leaving the stack can be higher than the bulk electrolyte, resulting in localized areas in the system that are prone to precipitate formation.

[0020] The precipitate formed and retained in the battery stack is usually dissolved back into the electrolyte by continuous charge and discharge cycles. However, any material detached from the battery stack or system manifold may settle in the electrolyte storage tank and become difficult to dissolve back into the solution, and it is difficult to pump back into the solution via the electrolyte loop, thereby potentially causing damage to process equipment and instruments, or causing blockage in the electrolyte pipeline or battery stack. In addition, the formation of iron-based precipitates will reduce the concentration of active redox species in the RFB, thereby reducing the total capacity of the electrolyte. If the precipitate settles to the bottom of the tank and no longer dissolves in the solution, this effect will worsen over time. In this way, the precipitate suspended in the electrolyte and any other undesirable particles can be harmful to the system mechanical reliability, electrochemical performance and subsequent system efficiency.

[0021] Therefore, there is a need for a simple and effective method to remove unwanted particles from the electrolyte and / or allow precipitates containing active redox species to be dissolved back into solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a process flow diagram of one embodiment of normal operation of a redox flow battery with an optional rebalance system.

[0023] Figure 2 is a process flow diagram of one embodiment of a method for refreshing a redox flow battery.

[0024] Figure 3 It has a rebalancing system Figure 2A method flow chart of an implementation scheme of the refresh method.

[0025] Figure 4 is a process flow diagram of another embodiment of a method for refreshing a redox flow battery.

[0026] Figure 5 It has a rebalancing system Figure 4 A method flow chart of an implementation scheme of the refresh method.

[0027] Figure 6 is a process flow diagram of another embodiment of a method for refreshing a redox flow battery.

[0028] Figure 7 It has a rebalancing system Figure 6 A method flow chart of an implementation scheme of the refresh method.

[0029] Figure 8 is a process flow diagram of another embodiment of a method for refreshing a redox flow battery.

[0030] Fig. 9 It has a rebalancing system Figure 8 A method flow chart of an implementation scheme of the refresh method.

[0031] Fig.10 is a process flow diagram of another embodiment of a method for a normally operating redox flow battery.

[0032] Fig.11 is used for Fig.10 A method flow chart of a refreshing method according to an implementation scheme of the present invention. DETAILED DESCRIPTION

[0033] This utilizes a fluid filtration system to capture and / or redissolve any precipitates that may form or otherwise be present in the electrolyte loop in the redox flow battery system.

[0034] Redox flow batteries are particularly attractive energy storage solutions for very large scale energy projects due to their ability to deliver thousands of cycles with discharge durations greater than 4 hours. As RFB installations increase in size to facilitate MWh and GWh delivery, engineering solutions need to be employed to ensure that all aspects of the installation are protected from a variety of potential failure modes. Filtering debris and sediment in large scale redox flow battery installations helps protect critical components such as pumps, sensing equipment, cell stacks, and rebalancing auxiliary systems.

[0035] In a hybrid redox flow battery (e.g., IFB), it is desirable to take precautions to ensure that any plating material that is shed from the anode during cycling cannot circulate freely through the system. Otherwise, deposition of plating material in storage tanks or IFB piping may result in capacity loss and potentially the formation of blockages in the system, and ultimately system failure. It is also desirable to take precautions to ensure that any precipitates that may be formed by abnormal system conditions (e.g., an unexpected increase in the pH of one of the electrolytes caused by a mechanical failure or sensor failure) do not result in catastrophic system blockage.

[0036] Careful placement of filtration units in RFB systems, particularly hybrid systems, helps maintain the health of the entire system. Filters may be located directly before or after a single stack or string of stacks, and before, after, or inside the electrolyte storage tank to minimize the occurrence of blockage within the stack or the introduction of solids into the electrolyte tank. Filters may also be positioned before or after system rebalancing components, such as systems that recombine hydrogen or systems that achieve electrolyte tank rebalancing (if present). Due to the autonomous nature of the RFB device, the application of filters should not result in a reduction in electrolyte capacity. In systems such as iron flow batteries, iron precipitates (such as Fe0 or Fe2O3, Fe(OH)3, Fe(OH)2, etc.) captured in the filter are less stable at lower pH values ​​and may be redissolved back into the electrolyte during battery cycling. Alternatively, the accumulation of precipitates in an IFB system may require corrective measures to ensure that the system continues to operate at optimal efficiency.

[0037] Various types of RFBs may be used. Suitable RFBs include, but are not limited to, Fe / Sn, Fe / Ti, Fe / Cr, Fe / Fe, Fe / Zn, V / V, Zn / Br, and Zn / Ce.

[0038] The redox active species of RFBs depend on the type of RFB. The redox active species of Fe / Sn RFBs include Fe 2+ / Fe 3+ and Sn 0 / Sn 2+ The redox active species of Fe / Ti RFB include Fe 2+ / Fe 3+ and Ti 3+ / Ti 4+ The redox active species of Fe / Cr RFB include Fe 2+ / Fe 3+ and Cr 2+ / Cr 3+ The redox active species of Fe / Fe RFB include Fe 2+ / Fe 3+ and Fe 2+ / Fe0 The redox active species of Fe / Zn RFB include Fe 2+ / Fe 3+ and Zn 0 / Zn 2+ The redox active species of V / V RFB include VO2 + / VO 2+ and V 2+ / V 3+ The redox active species of Zn / Br RFB include Br2 / Br - and Zn 0 / Zn 2 + The redox active species of Zn / Ce RFB include Ce 3+ / Ce 4+ and Zn 2+ / Zn 0 .

[0039] In some embodiments, the redox active material in the negative electrolyte comprises Fe, or the redox active material in the positive electrolyte comprises Fe, or both.

[0040] In some embodiments, the redox active species in the negative electrolyte is plated on the negative electrode.

[0041] In some embodiments, the method further comprises a first rebalance system in fluid communication with the negative electrolyte, or a second rebalance system in fluid communication with the positive electrolyte, or both. Optionally, there is an additional filter upstream or downstream of the first rebalance system, or both; or there is an additional filter upstream or downstream of the second rebalance system, or both; or both.

[0042] In some embodiments, the method further comprises cleaning at least one filter after filtering the negative electrolyte, the positive electrolyte, or both in the at least one filter. Methods for cleaning the filter are well known to those skilled in the art. Suitable cleaning methods include, but are not limited to, backwashing, replacing the filter element, removing the screen filter, or a combination thereof for cleaning and replacement.

[0043] There are a variety of operating methods to ensure that the precipitate in the RFB is captured and / or redissolved back into solution to maintain electrolyte capacity.

[0044] Figure 1 Normal RFB operation during charge and discharge is depicted. Filters may be placed before or after the battery stack, or before, after or in the electrolyte tanks to prevent circulation of precipitates in the solution.

[0045] One aspect of the present invention is a method for limiting the circulation of precipitates in a redox flow battery system. In one embodiment, the method includes providing at least one rechargeable battery, the rechargeable battery including a negative electrode, a positive electrode, and a separator positioned between the negative electrode and the positive electrode, a negative electrolyte and a negative electrolyte tank (the negative electrolyte is in contact with the negative electrode), and a positive electrolyte and a positive electrolyte tank (the positive electrolyte is in contact with the positive electrode). The flow of the negative electrolyte circulating in the negative electrolyte loop includes a first negative electrolyte flow from the negative electrolyte tank to the negative electrode and a second negative electrolyte flow from the negative electrode to the negative electrolyte tank. The flow of the positive electrolyte circulating in the positive electrolyte loop includes a first positive electrolyte flow from the positive electrolyte tank to the positive electrode and a second positive electrolyte flow from the positive electrode to the positive electrolyte tank. The negative electrolyte or the positive electrolyte or both are filtered in at least one filter.

[0046] In some embodiments, at least one filter is present in the negative electrolyte loop.

[0047] There may be one or more filters in the negative electrolyte loop, one or more filters in the positive electrolyte loop, or one or more filters in both the negative electrolyte loop and the positive electrolyte loop. There may be one or more filters in the negative electrolyte tank, and / or there may be one or more filters on the first negative electrolyte stream, and / or there may be one or more filters on the second negative electrolyte stream. There may be one or more filters in the positive electrolyte tank, and / or there may be one or more filters on the first positive electrolyte stream, and / or there may be filters on the second positive electrolyte stream. There may be one or more filters at the positions described in the negative electrolyte loop, or there may be one or more filters at the positions described in the positive electrolyte loop, or there may be one or more filters at the positions described in both the negative electrolyte loop and the positive electrolyte loop.

[0048] Suitable filters include, but are not limited to, filters with candle or pleated filter elements, clean-in-place or backwash filters, bag filters, membrane filters, and / or fine mesh baskets or combinations thereof.

[0049] When the electrolytes (negative electrolyte and / or positive electrolyte) in the RFB system need to be refreshed, there are a number of ways to do this.

[0050] Figure 2Depicted is the operation of the RFB in a refresh procedure, where the positive electrolyte flows through the negative electrode and back to the positive electrolyte tank. In this configuration, the more acidic positive electrolyte can more effectively dissolve the precipitate in the filter downstream of the negative electrode and any precipitate that may be retained in the negative electrode cell. The negative electrolyte can be circulated from the negative electrolyte tank through the filter back to the tank to continue to capture any precipitate in the negative electrolyte stream.

[0051] In some embodiments, this is accomplished by redirecting the flow of the negative and positive electrolytes.

[0052] In one embodiment, the flow of the negative electrolyte in the negative electrolyte loop is interrupted by redirecting the first negative electrolyte flow to form a second negative electrolyte loop. The second negative electrolyte loop includes a third negative electrolyte flow from the negative electrolyte tank, directly returning to the negative electrolyte tank. The flow of the positive electrolyte in the positive electrolyte loop is interrupted by redirecting the first positive electrolyte flow to form a second positive electrolyte loop. The second positive electrolyte loop includes a third positive electrolyte flow from the positive electrolyte tank to the negative electrode and from the negative electrode to the positive electrolyte tank. After the refresh is completed, the third positive electrolyte flow is redirected to the positive electrode, and the positive electrolyte loop is reformed. The third negative electrolyte flow is redirected to the negative electrode, and the first negative electrolyte loop is reformed.

[0053] Figure 3 1 depicts the operation of the RFB in a refresh procedure, wherein the positive electrolyte flows through the negative electrode and back to the positive electrolyte tank, and the positive electrolyte also flows through the electrolyte rebalance system and back to the positive electrolyte tank, as shown in FIG. Figure 2 As shown. The rebalance system further acidifies the positive electrolyte, for example by putting hydrogen back into solution as H+ protons. In one embodiment, a portion of the third positive electrolyte stream and hydrogen are passed into the rebalance system to form a treated stream, and the treated stream is passed into the positive electrolyte tank.

[0054] Figure 4 Depicts the operation of the RFB in a refresh procedure where the negative and positive electrolytes are thoroughly mixed together. This function enables the negative electrolyte, which has a higher pH and is more prone to precipitate formation, to mix with the more acidic positive electrolyte, which is able to dissolve the precipitate into solution. This also allows more acidic electrolyte to flow through the filter in the negative electrolyte loop and dissolve the precipitate that has been captured.

[0055] In one embodiment, the negative electrolyte loop is interrupted by redirecting the second negative electrolyte flow to the positive electrolyte tank, and the positive electrolyte loop is interrupted by redirecting the second positive electrolyte flow to the negative electrolyte tank. After refreshing, the second negative electrolyte flow is redirected to the negative electrolyte tank, and the negative electrolyte loop is reformed. The second positive electrolyte flow is redirected to the positive electrolyte tank, and the positive electrolyte loop is reformed.

[0056] Figure 5 depicts the RFB operation during the refresh procedure, where the negative and positive electrolytes are thoroughly mixed together, as shown in Figure 4 As shown, the mixed electrolyte also flows through the electrolyte rebalance system and returns to the positive electrolyte tank. In one embodiment, a portion of the first electrolyte stream and hydrogen are passed into the rebalance system to form a treated stream; and the treated stream is passed into the negative electrolyte tank.

[0057] Figure 6 Depicted is the RFB operation in a refresh procedure where the negative and positive electrolytes bypass all of the cell stacks and mix thoroughly together.

[0058] In one embodiment, the negative electrolyte loop is interrupted by redirecting the first negative electrolyte flow to the positive electrolyte tank, and the positive electrolyte loop is interrupted by redirecting the first positive electrolyte flow to the negative electrolyte tank. After refreshing, the first negative electrolyte flow is redirected to the negative electrolyte tank, and the negative electrolyte loop is reformed. The first positive electrolyte flow is redirected to the positive electrolyte tank, and the positive electrolyte loop is reformed.

[0059] Figure 7 Depicted is the RFB operation in a refresh procedure, where the negative electrolyte and positive electrolyte bypass all cell stacks and are thoroughly mixed together, and the mixed electrolyte also flows through the electrolyte rebalance system and back to the positive electrolyte tank. In one embodiment, a portion of the first positive electrolyte stream and hydrogen are passed into the rebalance system to form a treated stream, and the treated stream is passed into the positive electrolyte tank.

[0060] Figure 8 Depicted is the operation of an RFB during an unconventional refresh procedure, where each electrolyte is circulated through a filter and returned to its respective tank. The goal is to capture precipitates in either solution and prevent their circulation through the battery stack.

[0061] In one embodiment, the negative electrolyte loop is interrupted by redirecting the first negative electrolyte flow to form a second negative electrolyte loop, the second negative electrolyte loop comprising a third negative electrolyte flow from the negative electrolyte tank directly back to the negative electrolyte tank. The positive electrolyte loop is interrupted by redirecting the first positive electrolyte flow to form a second positive electrolyte loop, the second positive electrolyte loop comprising a third positive electrolyte flow from the positive electrolyte tank directly back to the positive electrolyte tank. After refreshing, the first negative electrolyte flow is redirected to the negative electrolyte tank, and the negative electrolyte loop is reformed. The first positive electrolyte flow is redirected to the positive electrolyte tank, and the positive electrolyte loop is reformed.

[0062] Fig. 9 Depicts the operation of the RFB in an unconventional refresh procedure, where each electrolyte circulates through a filter and returns to its respective tank. The positive electrolyte is also sent to a rebalance system to further acidify the stream. The purpose is to capture precipitates in either solution and prevent their circulation through the battery stack. In one embodiment, a portion of the third positive electrolyte stream and hydrogen are passed through the rebalance system to form a treated stream, and the treated stream is passed into the positive electrolyte tank.

[0063] Fig.10 The RFB operation in normal operation is shown, where negative and positive electrolytes are circulated through negative and positive filters positioned before the battery cells, through the battery cells, and back to the negative and positive electrolyte tanks.

[0064] Fig.11 The RFB operation during an unconventional refresh procedure is shown, where the negative electrolyte flows through the positive filter and negative electrode and back to the negative electrolyte tank, and the positive electrolyte flows through the negative filter and positive electrode and back to the positive electrolyte tank. This allows the filter to change back and forth between the negative electrolyte, which is more likely to contain precipitates, and the positive electrolyte, which is more likely to dissolve precipitates, because of the pH difference between the two.

[0065] Another aspect of the present invention is a method for limiting the circulation of precipitates in a redox flow battery system. In one embodiment, the method includes: providing at least one rechargeable battery, the rechargeable battery comprising a negative electrode, a positive electrode, and a separator positioned between the negative electrode and the positive electrode, a negative electrolyte and a negative electrolyte tank (the negative electrolyte is in contact with the negative electrode), and a positive electrolyte and a positive electrolyte tank (the positive electrolyte is in contact with the positive electrode), wherein the redox active material in the negative electrolyte comprises Fe, or wherein the redox active material in the positive electrolyte comprises Fe, or both. The flow of the negative electrolyte circulating in the negative electrolyte loop, the negative electrolyte loop comprising a first negative electrolyte flow from the negative electrolyte tank to the negative electrode and a second negative electrolyte flow from the negative electrode to the negative electrolyte tank. The flow of the positive electrolyte circulating in the positive electrolyte loop, the positive electrolyte loop comprising a first positive electrolyte flow from the positive electrolyte tank to the positive electrode and a second positive electrolyte flow from the positive electrode to the positive electrolyte tank. The negative electrolyte or the positive electrolyte or both are filtered in at least one filter. The at least one filter comprises a filter in the negative electrolyte loop, a filter in the positive electrolyte loop, or both.

[0066] In some embodiments, there is one or more of the following: a filter in the negative electrolyte tank, a filter on the first negative electrolyte stream, or a filter on the second negative electrolyte stream; or one or more of a filter in the positive electrolyte tank, a filter on the first positive electrolyte stream, or a filter on the second positive electrolyte stream; or both.

[0067] In some embodiments, the method further comprises: a first rebalance system in communication with the negative electrolyte fluid, or a second rebalance system in communication with the positive electrolyte fluid, or both; and optionally, an additional filter upstream or downstream of the first rebalance system, or both; or an additional filter upstream or downstream of the second rebalance system, or both; or both.

[0068] In some embodiments, the method further comprises cleaning the at least one filter after filtering the negative electrolyte, the positive electrolyte, or both in the at least one filter.

[0069] The RFB system may include a control system for controlling the operation of the RFB and the refreshing of the electrolyte. The control system is known to those skilled in the art. Any suitable control system may be used. In some embodiments, the control system may include a sensor that communicates electronically with the controller. One or more characteristics may be used to control the flow of the electrolyte, including but not limited to dP, pH, flow rate, pump current draw, turbidity, color, viscosity, impedance, voltage, current, or a combination thereof. As known in the art, a suitable sensor (e.g., a sensor for measuring a characteristic, including but not limited to dP, pH, flow rate, turbidity, color, viscosity, or a combination thereof) will be selected based on the characteristics used in controlling the electrolyte flow. Each characteristic (or characteristic combination) will have a predetermined operating range, and the controller will respond to the operating range by opening or closing the appropriate valve to allow the redirection and / or subsequent reversal of the flow through the filter device. For example, the sensor may be a dP meter to measure the dP of the electrolyte flow passing through the filter in normal operation. The measured dP may be sent to the controller, which will formulate an appropriate system response based on the measured dP and the predetermined filter dP upper and lower limits to start a backwash or refresh procedure.

[0070] In some embodiments, the system employs a control feedback loop based on multiple system inputs (including but not limited to pressure drop (dP), SoC, pH, pump motor current draw, turbidity, electrolyte color, impedance, voltage, current, viscosity, density, conductivity and / or electrolyte flow rate) to trigger backwashing with a more acidic electrolyte (catholyte or reset anolyte) or changing the electrolyte supply to the filter to regain any lost electrolyte capacity and clear the filter of particulate matter.

[0071] In some embodiments, the apparatus further comprises a rebalancing system, such as a hydrogen recombination unit in fluid communication with either electrolyte loop for generating hydrogen ions.

[0072] In some embodiments, the positive electrolyte flows continuously to the positive chamber.

[0073] In some embodiments, the controller is a control valve.

[0074] In some embodiments, the device further includes a sensor in electronic communication with the controller, the sensor being located in the negative electrolyte primary loop.

[0075] In some embodiments, the measured property includes pH, gas pressure, flow rate, turbidity, viscosity, impedance, voltage, current, or a combination thereof.

[0076] In some embodiments, the measured property is pH, wherein the controller is a control valve, and further comprising a sensor in electronic communication with the controller, wherein the sensor is a pH meter, and wherein the sensor is located in the negative electrolyte main loop.

[0077] The method can be operated under any suitable operating conditions. Standard operating conditions include, but are not limited to, operating within a temperature window of -25°C to 60°C. The power output from the redox flow battery stack can be in the range of from 250W to 100kW, typically from 1kW to 75kW, and more typically from 5kW to 50kW, wherein the system is typically capable of delivering the target power typically, but not exclusively, between 2 hours and 24 hours. The concentration of the redox active species in the electrolyte can be from 0.1M to 7M, typically from 0.5M to 5M, and more typically from 1M to 3.5M. The electrolyte is typically passed through the stack at a flow rate of 0.05 to 50ml min-1cm-2, typically from 0.1 to 25ml min-1cm-2, and more typically from 0.25 to 5ml min-1cm-2.

[0078] Figure 1 One embodiment of an RFB process flow diagram of the RFB system 100 is illustrated.

[0079] The RFB system 100 includes a rechargeable battery 105, which includes a negative electrode 110, a positive electrode 115, and a separator 120. There are a negative electrolyte tank 125 and a positive electrolyte tank 130.

[0080] The negative electrolyte circulates in a negative electrolyte loop from the negative electrolyte tank 125 to the negative electrode 110 in the cell 105 and back to the negative electrolyte tank 125. Valves 200 and 230 are open, and valves 215, 220, 235, and 255 are closed. A first negative electrolyte stream 135 flows from the negative electrolyte tank 125 to the negative electrode 110 in the cell 105, where the negative electrolyte contacts the negative electrode 110. A second negative electrolyte stream 140 flows from the negative electrode 110 in the cell 105 back to the negative electrode tank 125.

[0081] The positive electrolyte circulates in the positive electrolyte loop from the positive electrolyte tank 130 to the cell 105 and back to the positive electrolyte tank 130. Valve 275 and valve 215 are open, and valve 280 is closed. A first positive electrolyte stream 145 flows from the positive electrolyte tank 130 to the positive electrode 115 in the cell 105, where the positive electrolyte contacts the positive electrode 115. Valve 147 and valve 149 are open, and valves 250 and 265 are closed, allowing a second positive electrolyte stream 150 to flow from the positive electrode 115 in the cell 105 back to the positive electrolyte tank 130.

[0082] There is at least one filter 155 in the negative electrolyte loop or the positive electrolyte loop or both. There can be one or more filters in the negative electrolyte loop, or one or more filters in the positive electrolyte loop, or one or more filters in both loops. The filter 155 can be in the negative electrolyte tank 125, on the first negative electrolyte flow 135 between the negative electrolyte tank 125 and the negative electrode 110 in the battery 105, or on the second negative electrolyte flow 140 between the negative electrode 110 in the battery 105 and the negative electrolyte tank 125. The filter 155 can be in the positive electrolyte tank 130, on the first positive electrolyte flow 145 between the positive electrolyte tank 130 and the positive electrode 115 in the battery 105, or on the second positive electrolyte flow 150 between the positive electrode 115 in the battery 105 and the positive electrolyte tank 130.

[0083] In some embodiments, the RFB system 100 includes a hydrogen recombination system 160. Valve 163 is opened to allow a portion 165 of the first positive electrolyte stream 145 to flow to the cathode side 170 of the hydrogen recombination system 160. A hydrogen gas stream 175 from the negative electrolyte tank 125 is sent to the negative side 180. The hydrogen reduces the redox active species in the positive electrolyte. Valve 187 is opened to allow the treated stream 185 to be combined with the second positive stream 150 from the positive electrode 115 of the cell 105 and returned to the positive electrolyte tank 130.

[0084] Unused hydrogen stream 190 from hydrogen recombination system 160 is sent to positive electrolyte tank 130. Stream 195 extends between positive electrolyte tank 130 and negative electrolyte tank 125 to connect the tank headspaces and equalize their pressures.

[0085] Figure 2 One embodiment of a refresh method flow chart of the RFB system 100 is illustrated.

[0086] In this case, normal operation of the RFB system 100 is interrupted by redirecting the first negative electrolyte flow 135. Valve 200 is closed, preventing the negative electrolyte from flowing to the negative electrode 110 of the cell 105. Valve 205 is opened, allowing the third negative electrolyte flow 210 to flow back to the negative electrolyte tank 125.

[0087] Valve 215 is closed, preventing the first positive electrolyte stream 145 from flowing to the positive electrode 115. Valve 220 is opened, and a third positive electrolyte stream 225 is sent to contact the negative electrode 110 in the cell 105. Valve 230 is closed, and valves 235 and 237 are opened, allowing a fourth positive electrolyte stream 240 to flow back to the positive electrolyte tank 130.

[0088] exist Figure 3In the illustrated embodiment, the RFB system 100 includes a hydrogen recombination system 160. Valve 163 is opened to allow a portion 165 of the first positive electrolyte stream 145 to flow to the cathode side 170 of the hydrogen recombination system 160. A hydrogen stream 175 from the negative electrolyte tank 125 is sent to the negative side 180. The hydrogen reduces the redox active species in the positive electrolyte. Valve 147 is closed and valve 187 is opened to allow the treated stream 185 to return to the positive electrolyte tank 130.

[0089] Unused hydrogen gas stream 190 is sent to positive electrolyte tank 130. Stream 195 extends between positive electrolyte tank 130 and negative electrolyte tank 125 to connect the tank headspaces and equalize their pressures.

[0090] Figure 4 Another embodiment of a refresh method for RFB system 100 is illustrated. In this case, valve 200 is open, and valves 205 and 220 are closed. A first negative electrolyte stream 135 flows from negative electrolyte tank 125 to negative electrode 110 of battery 105. Valve 245 is closed, and valves 235 and 237 are opened, allowing a second negative electrolyte stream 140 to be sent to positive electrolyte tank 130.

[0091] Valve 275 and valve 215 are open, and valve 265 and valve 280 are closed. The first positive electrolyte stream 145 is sent to the positive electrode 115. Valve 149 is closed, preventing the second positive electrolyte stream 150 from returning to the positive electrolyte tank 130. Valve 147, valve 250, and valve 230 are open, allowing the second positive electrolyte stream 150 to flow to the negative electrolyte tank 125.

[0092] Figure 5 The embodiment includes a hydrogen recombination system 160. Valve 163 is opened to allow a portion 165 of the first positive electrolyte stream 145 to flow to the cathode side 170 of the hydrogen recombination system 160. A hydrogen gas stream 175 from the negative electrolyte tank 125 is sent to the negative side 180. The hydrogen reduces the redox active species in the positive electrolyte. Valve 147 and valve 187 are opened to allow the treated stream 185 to be combined with the second positive electrolyte stream 150 from the positive electrode 115 of the cell 105 and returned to the positive electrolyte tank 130.

[0093] Figure 6 Another embodiment of a refreshing method for the RFB system 100 is shown. Valve 200 and valve 205 are closed, and valve 255 and valve 260 are opened, allowing the first negative electrolyte stream 135 to flow to the positive electrolyte tank 130. Valve 215 and valve 280 are closed, and valve 275, valve 265, and valve 270 are opened, allowing the first positive electrolyte stream 145 to flow to the negative electrolyte tank 125.

[0094] exist Figure 7In an embodiment of the present invention, the RFB system 100 includes a hydrogen recombination system 160. Valve 163 is opened to allow a portion 165 of the first positive electrolyte stream 145 to flow to the cathode side 170 of the hydrogen recombination system 160. A hydrogen gas stream 175 from the negative electrolyte tank 125 is sent to the negative side 180. The hydrogen reduces the redox active species in the positive electrolyte. Valve 147 and valve 250 are closed, and valve 187 and valve 149 are opened to allow the treated stream 185 to return to the positive electrolyte tank 130.

[0095] Figure 8 Another embodiment of a refresh method flow chart for the RFB system 100 is illustrated. In this case, normal operation of the RFB system 100 is interrupted by redirecting the first negative electrolyte flow 135. Valve 200 and valve 255 are closed, preventing the negative electrolyte from flowing to the negative electrode 110 of the battery 105. Valve 205 is opened, allowing the third negative electrolyte flow 210 to flow back to the negative electrolyte tank 125.

[0096] Valve 215 and valve 275 are closed, preventing first positive electrolyte flow 145 from flowing to positive electrode 115. Valve 280 is opened, and first positive electrolyte flow 145 is returned to positive electrolyte tank 130.

[0097] exist Fig. 9 In an embodiment of the present invention, the RFB system 100 includes a hydrogen recombination system 160. Valve 163 is opened to allow a portion 165 of the first positive electrolyte stream 145 to flow to the cathode side 170 of the hydrogen recombination system 160. A hydrogen gas stream 175 from the negative electrolyte tank 125 is sent to the negative side 180. The hydrogen reduces the redox active species in the positive electrolyte. Valve 147 and valve 250 are closed, and valve 187 and valve 149 are opened to allow the treated stream 185 to return to the positive electrolyte tank 130.

[0098] exist Fig.10 In the embodiment of the present invention, there are two pairs of three-way valves 305, 310, 315, 320 that control the flow of negative electrolyte and positive electrolyte to the negative electrode 110 and the positive electrode 115 of the battery 105. In normal operation, valves 305 and 310 are set to allow negative electrolyte to flow through filter 155A to the negative electrode 110, while preventing negative electrolyte from flowing to filter 155B and positive electrode 115. Valves 315 and 320 are set to allow positive electrolyte to flow through filter 155B to the positive electrode 115, and prevent positive electrolyte from flowing to filter 155A and negative electrode 110.

[0099] exist Fig.11, during the refresh method, valve 305 is set to send negative electrolyte through filter 155B while preventing negative electrolyte from flowing to filter 155A. Valve 320 is set to send negative electrolyte to negative electrode 110 while preventing negative electrolyte from flowing to positive electrode 115. Valve 315 is set to send positive electrolyte through filter 155A while preventing positive electrolyte from flowing to filter 155B. Valve 310 is set to send positive electrolyte to positive electrode 115 while preventing positive electrolyte from flowing to the negative electrode.

[0100] Figure 10 to Figure 11 The method shown in can be combined with Figures 1 to 9 In any of the methods shown in .

[0101] Specific implementation plan

[0102] 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.

[0103] A first embodiment of the present invention is a method for limiting the circulation of precipitates in a redox flow battery system, the method comprising providing at least one rechargeable battery comprising a negative electrode, a positive electrode, and a separator positioned between the negative electrode and the positive electrode, a negative electrolyte and a negative electrolyte tank (the negative electrolyte is in contact with the negative electrode), and a positive electrolyte and a positive electrolyte tank (the positive electrolyte is in contact with the positive electrode); circulating the flow of the negative electrolyte in a negative electrolyte loop, the negative loop comprising a first negative electrolyte flow from the negative electrolyte tank to the negative electrode and a second negative electrolyte flow from the negative electrode to the negative electrolyte tank, and circulating the flow of the positive electrolyte in a positive electrolyte loop, the positive electrolyte loop comprising a first positive electrolyte flow from the positive electrolyte tank to the positive electrode and a second positive electrolyte flow from the positive electrode to the positive electrolyte tank; and filtering the negative electrolyte, or the positive electrolyte, or both in at least one filter. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, wherein at least one filter includes a filter in the negative electrolyte circuit, or a filter in the positive electrolyte circuit, or both. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, wherein the filter in the negative electrolyte circuit includes one or more of the filter in the negative electrolyte tank, the filter on the first negative electrolyte stream, or the filter on the second negative electrolyte stream; or wherein the filter in the positive electrolyte circuit includes one or more of the filter in the positive electrolyte tank, the filter on the first positive electrolyte stream, or the filter on the second positive electrolyte stream; or both of the above. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, wherein at least one filter includes a filter in the negative electrolyte circuit. One embodiment of the present invention is one, any or all of the embodiments from the previous embodiment of this paragraph to the first embodiment of this paragraph, which also includes interrupting the flow of negative electrolyte in the negative electrolyte loop by redirecting the first negative electrolyte flow to form a second negative electrolyte loop, the second negative electrolyte loop includes a third negative electrolyte flow from the negative electrolyte tank and directly returns to the negative electrolyte tank; interrupting the flow of positive electrolyte in the positive electrolyte loop by redirecting the first positive electrolyte flow to form a second positive electrolyte loop, the second positive electrolyte loop includes a third positive electrolyte flow from the positive electrolyte tank to the negative electrode and from the negative electrode to the positive electrolyte tank; redirecting the third positive electrolyte flow to the positive electrode and reforming the positive electrolyte loop; and redirecting the third negative electrolyte flow to the negative electrode and reforming the first negative electrolyte loop.One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, which also includes passing a portion of the third positive electrolyte stream and hydrogen into the rebalance system to form a treated stream; and passing the treated stream into the positive electrolyte tank. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, which also includes interrupting the negative electrolyte loop by redirecting the second negative electrolyte stream to the positive electrolyte tank, and interrupting the positive electrolyte loop by redirecting the second positive electrolyte stream to the negative electrolyte tank; and redirecting the second negative electrolyte stream to the negative electrolyte tank and reforming the negative electrolyte loop, and redirecting the second positive electrolyte stream to the positive electrolyte tank and reforming the positive electrolyte loop. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, and further includes: passing a portion of the first positive electrolyte flow and hydrogen from the negative electrolyte tank into the rebalance system to form a treated flow; and passing the treated flow into the negative electrolyte tank. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, and further includes interrupting the negative electrolyte loop by redirecting the first negative electrolyte flow to the positive electrolyte tank, and interrupting the positive electrolyte loop by redirecting the first positive electrolyte flow to the negative electrolyte tank; and redirecting the first negative electrolyte flow to the negative electrolyte tank and reforming the negative electrolyte loop, and redirecting the first positive electrolyte flow to the positive electrolyte tank and reforming the positive electrolyte loop. One embodiment of the present invention is one, any or all of the embodiments from the previous embodiment of this paragraph to the first embodiment of this paragraph, and also includes: passing a portion of the first positive electrolyte flow and hydrogen into a rebalance system to form a treated flow; and passing the treated flow into the positive electrolyte tank. One embodiment of the present invention is one, any or all of the embodiments from the previous embodiment of this paragraph to the first embodiment of this paragraph, which also includes interrupting the negative electrolyte loop by redirecting the first negative electrolyte flow to form a second negative electrolyte loop, the second negative electrolyte loop includes a third negative electrolyte flow from the negative electrolyte tank and directly returns to the negative electrolyte tank, and interrupting the positive electrolyte loop by redirecting the first positive electrolyte flow to form a second positive electrolyte loop, the second positive electrolyte loop includes a third positive electrolyte flow from the positive electrolyte tank and directly returns to the positive electrolyte tank; and redirecting the first negative electrolyte flow to the negative electrolyte tank and reforming the negative electrolyte loop, and redirecting the first positive electrolyte flow to the positive electrolyte tank and reforming the positive electrolyte loop.One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, further comprising: passing a portion of the third positive electrolyte stream and hydrogen into a rebalance system to form a treated stream; and passing the treated stream into the positive electrolyte tank. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, wherein the redox active material in the negative electrolyte includes Fe, or wherein the redox active material in the positive electrolyte includes Fe, or both. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, wherein the redox active material in the negative electrolyte is plated on the negative electrode. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, further comprising a first rebalance system in fluid communication with the negative electrolyte, or a second rebalance system in fluid communication with the positive electrolyte, or both; and optionally, an additional filter upstream or downstream of the first rebalance system, or both; or an additional filter upstream or downstream of the second rebalance system, or both; or both of the above. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, which also includes cleaning at least one filter after filtering the negative electrolyte, the positive electrolyte, or both in at least one filter. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the first embodiment of this paragraph, wherein there is a first filter between the negative electrolyte tank and the negative electrode, and there is a second filter between the positive electrolyte tank and the positive electrode, and also includes interrupting the flow of the negative electrolyte in the negative electrolyte loop by redirecting the first negative electrolyte flow through the second filter and to the negative electrode to form a second negative electrolyte loop; interrupting the flow of the positive electrolyte in the positive electrolyte loop by redirecting the first positive electrolyte flow through the first filter and to the positive electrode forming the second positive electrolyte loop to form a second positive electrolyte loop; redirecting the first negative electrolyte flow to the first filter and reforming the negative electrolyte loop; and redirecting the first positive electrolyte flow to the second filter and reforming the positive electrolyte loop.

[0104] A second embodiment of the present invention is a method for limiting the circulation of precipitates in a redox flow battery system, the method comprising providing at least one rechargeable battery comprising a negative electrode, a positive electrode, and a separator positioned between the negative electrode and the positive electrode, a negative electrolyte and a negative electrolyte tank (the negative electrolyte is in contact with the negative electrode), and a positive electrolyte and a positive electrolyte tank (the positive electrolyte is in contact with the positive electrode), wherein the redox active material in the negative electrolyte comprises Fe, or wherein the redox active material in the positive electrolyte comprises Fe, or both; circulating the negative electrolyte Flow in a negative electrolyte loop, the negative loop includes a first negative electrolyte flow from a negative electrolyte tank to a negative electrode and a second negative electrolyte flow from the negative electrode to the negative electrolyte tank, and circulates a flow of a positive electrolyte in a positive electrolyte loop, the positive electrolyte loop includes a first positive electrolyte flow from a positive electrolyte tank to a positive electrode and a second positive electrolyte flow from the positive electrode to the positive electrolyte tank; and filtering the negative electrolyte, or the positive electrolyte, or both in at least one filter, wherein at least one filter includes a filter in the negative electrolyte loop, or a filter in the positive electrolyte loop, or both. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the second embodiment of this paragraph, wherein the filter in the negative electrolyte circuit includes one or more of the filter in the negative electrolyte tank, the filter on the first negative electrolyte flow, or the filter on the second negative electrolyte flow; or wherein the filter in the positive electrolyte circuit includes one or more of the filter in the positive electrolyte tank, the filter on the first positive electrolyte flow, or the filter on the second positive electrolyte flow; or both of the above. One embodiment of the present invention is one, any or all of the previous embodiments of this paragraph to the second embodiment of this paragraph, which also includes a first rebalancing system connected to the negative electrolyte fluid, or a second rebalancing system connected to the positive electrolyte fluid, or both; and optionally, additional filters upstream or downstream of the first rebalancing system, or both; or additional filters upstream or downstream of the second rebalancing system, or both; or both of the above.

[0105] 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.

[0106] 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 limiting the circulation of precipitates in a redox flow battery system, the method comprising: Providing at least one rechargeable battery (105), the rechargeable battery comprising a negative electrode (110), a positive electrode (115), and a separator (120) positioned between the negative electrode (110) and the positive electrode (115), a negative electrolyte and a negative electrolyte tank (125), the negative electrolyte being in contact with the negative electrode (110), and a positive electrolyte and a positive electrolyte tank (130), the positive electrolyte being in contact with the positive electrode (115); Circulating the flow of the negative electrolyte in a negative electrolyte loop, the negative loop comprising a first negative electrolyte flow (135) from the negative electrolyte tank (125) to the negative electrode (110) and a second negative electrolyte flow (140) from the negative electrode (110) to the negative electrolyte tank (125), and circulating the flow of the positive electrolyte in a positive electrolyte loop, the positive electrolyte loop comprising a first positive electrolyte flow (145) from the positive electrolyte tank (130) to the positive electrode (115) and a second positive electrolyte flow (150) from the positive electrode (115) to the positive electrolyte tank (130); as well as The negative electrolyte, or the positive electrolyte, or both are filtered in at least one filter (155).

2. The method of claim 1, wherein the at least one filter (155) comprises a filter (155) in the negative electrolyte loop, or a filter (155) in the positive electrolyte loop, or both; wherein the filter (155) in the negative electrolyte circuit comprises one or more of a filter (155) in the negative electrolyte tank (125), a filter (155) on the first negative electrolyte flow (135), or a filter (155) on the second negative electrolyte flow (140); or wherein the filter (155) in the positive electrolyte circuit comprises one or more of a filter (155) in the positive electrolyte tank (130), a filter (155) on the first positive electrolyte flow (145), or a filter (155) on the second positive electrolyte flow (150); or Both.

3. The method according to any one of claims 1 to 2, further comprising: interrupting the flow of the negative electrolyte in the negative electrolyte loop by redirecting the first negative electrolyte flow (135) to form a second negative electrolyte loop, the second negative electrolyte loop comprising a third negative electrolyte flow (210) from the negative electrolyte tank (125) directly back to the negative electrolyte tank (125); interrupting the flow of the positive electrolyte in the positive electrolyte loop by redirecting the first positive electrolyte flow (145) to form a second positive electrolyte loop, the second positive electrolyte loop comprising a third positive electrolyte flow (225) from the positive electrolyte tank (130) to the negative electrode (110) and from the negative electrode (110) to the positive electrolyte tank (130); redirecting the third positive electrolyte flow (225) to the positive electrode (115) and reforming the positive electrolyte loop; as well as The third negative electrolyte flow (210) is redirected to the negative electrode (110) and the first negative electrolyte loop is reformed.

4. The method according to any one of claims 1 to 2, further comprising: interrupting the negative electrolyte loop by redirecting the second negative electrolyte flow (140) to the positive electrolyte tank (130), and interrupting the positive electrolyte loop by redirecting the second positive electrolyte flow (150) to the negative electrolyte tank (125); as well as The second negative electrolyte flow (140) is redirected to the negative electrolyte tank (125) and the negative electrolyte loop is reformed, and the second positive electrolyte flow (150) is redirected to the positive electrolyte tank (130) and the positive electrolyte loop is reformed.

5. The method according to any one of claims 1 to 2, further comprising: interrupting the negative electrolyte loop by redirecting the first negative electrolyte flow (135) to the positive electrolyte tank (130), and interrupting the positive electrolyte loop by redirecting the first positive electrolyte flow (145) to the negative electrolyte tank (125); as well as The first negative electrolyte flow (135) is redirected to the negative electrolyte tank (215) and the negative electrolyte loop is reformed, and the first positive electrolyte flow (145) is redirected to the positive electrolyte tank (130) and the positive electrolyte loop is reformed.

6. The method according to any one of claims 1 to 2, further comprising: interrupting the negative electrolyte loop by redirecting the first negative electrolyte flow (135) to form a second negative electrolyte loop, the second negative electrolyte loop comprising a third negative electrolyte flow (210) from the negative electrolyte tank (125) directly returning to the negative electrolyte tank (125), and interrupting the positive electrolyte loop by redirecting the first positive electrolyte flow (145) to form a second positive electrolyte loop, the second positive electrolyte loop comprising a third positive electrolyte flow from the positive electrolyte tank directly returning to the positive electrolyte tank (130); as well as The first negative electrolyte flow (135) is redirected to the negative electrolyte tank (125) and the negative electrolyte loop is reformed, and the first positive electrolyte flow (145) is redirected to the positive electrolyte tank (130) and the positive electrolyte loop is reformed.

7. The method according to any one of claims 1 to 2, wherein there is a first filter (155A) between the negative electrolyte tank (125) and the negative electrode (110), and there is a second filter (155B) between the positive electrolyte tank (130) and the positive electrode (115), and the method further comprises: interrupting the flow of the negative electrolyte in the negative electrolyte loop by redirecting the first negative electrolyte flow (135) through the second filter (155B) and to the negative electrode (110) to form a second negative electrolyte loop; interrupting the flow of the positive electrolyte in the positive electrolyte loop by redirecting the first positive electrolyte flow (145) through the first filter (155A) and to the positive electrode (115) to form a second positive electrolyte loop; redirecting the first negative electrolyte flow (135) to the first filter (155A) and reforming the negative electrolyte loop; as well as The first positive electrolyte flow (145) is redirected to the second filter (155B) and the positive electrolyte loop is reformed.

8. The method of any one of claims 1 to 2, wherein the redox active material in the negative electrolyte comprises Fe, or wherein the redox active material in the positive electrolyte comprises Fe, or both.

9. The method according to any one of claims 1 to 2, further comprising: Passing at least a portion of the negative electrolyte or the positive electrolyte, or both, into a first rebalance system (160) in fluid communication with the negative electrolyte or a second rebalance system (160) in fluid communication with the positive electrolyte, or both; and Optionally, there is an additional filter (155) upstream or downstream of the first rebalancing system (160) or both; or there is an additional filter (155) upstream or downstream of the second rebalancing system (160) or both; or both of the above.

10. The method according to any one of claims 1 to 2, further comprising: The at least one filter (155) is cleaned after filtering the negative electrolyte or the positive electrolyte or both in the at least one filter (155).

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