Improved efficiency of redox flow batteries

Abstract

A method for a redox flow battery includes using a redox flow battery cell to store and release stored electrical energy. The using includes circulating a first electrolyte solution through a first circulation loop in fluid communication with a first electrode of the cell and a second electrolyte solution through a second circulation loop in fluid communication with a second electrode of the cell, where at least one first element from the first electrolyte solution of the first electrode permeates a separator layer and deposits in the second electrode as a first solid product, and a second element from the second electrolyte solution permeates the separator layer and deposits in the second electrode as a second solid product. The method also includes removing at least a portion of the first solid product or the second solid product from the first electrode and the second electrode, respectively.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority to U.S. Patent Application No. 17 / 119,427, filed December 11, 2020, the disclosure of which is incorporated herein by reference in its entirety.

[0002] (STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT) This invention was made with government support under Contract No. DE-AR000994 awarded by the Department of Energy. The government has certain rights in this invention. [Background technology]

[0003] Flow batteries, also known as redox flow batteries or redox flow cells, are designed to store electrical energy and convert it into chemical energy that can be later released back into electrical energy when there is demand. As an example, flow batteries may be used in conjunction with renewable energy systems, such as wind power systems, to store energy in excess of consumer demand and release that energy at a later time when there is greater demand.

[0004] A typical flow battery includes a redox flow cell with a negative electrode and a positive electrode separated by an electrolyte layer, which may include a separator such as an ion exchange membrane. A negative fluid electrolyte (sometimes called an anolyte or negolyte) is delivered to the negative electrode, and a positive fluid electrolyte (sometimes called a catholyte or phosphite) is delivered to the positive electrode, driving a reversible reduction reaction between a redox couple. During charging, supplied electrical energy causes a reduction reaction in one electrolyte and an oxidation reaction in the other. The separator prevents the electrolytes from freely and rapidly mixing, but selectively allows ions to pass through to complete the redox reaction. During discharge, chemical energy contained in the liquid electrolyte is released in a reverse reaction, and electrical energy is drawn from the electrodes. Summary of the Invention [Means for solving the problem]

[0005] A method for a redox flow battery according to an exemplary embodiment of the present disclosure includes, among other things, using a redox flow battery cell to store input electrical energy during charging and release the stored electrical energy during discharging. The cell has a separator layer disposed between a first electrode and a second electrode. The using includes circulating a first electrolyte solution through a first circulation loop in fluid communication with the first electrode of the cell and circulating a second electrolyte solution through a second circulation loop in fluid communication with the second electrode of the cell, wherein at least one of a first element from the first electrolyte solution in the first electrode permeates the separator layer and deposits as a first solid product in the second electrode, and a second element from the second electrolyte solution permeates the separator layer and deposits as a second solid product in the first electrode, and wherein at least one of the first electrolyte solution permeates the separator layer and deposits as a second solid product in the first electrode. At least a portion of the first solid product or the second solid product is removed from the first electrode and the second electrode, respectively, by circulating at least a portion of the second electrolyte solution from the first circulation loop through the second electrode to dissolve at least a portion of the first solid product and thereby remove it from the second electrode, or by circulating at least a portion of the second electrolyte solution from the second circulation loop through the first electrode to dissolve at least a portion of the second solid product and thereby remove it from the first electrode, or both. Use of the electrolyte solution reduces galvanic efficiency. Removal restores at least a portion of the reduced galvanic efficiency.

[0006] In a further example of the above, at least one of the first solid product and the second solid product is deposited on a separator layer.

[0007] In any further example described above, at least a portion of the first solid product is removed from the separator layer by circulating at least a portion of the first electrolyte solution from the first circulation loop through the second electrode.

[0008] In any further example of the above, at least a portion of the second solid product is removed from the separator layer by circulating at least a portion of the second electrolyte solution from the second circulation loop through the first electrode.

[0009] In any further example of the above, at least one of the first solid product and the second solid product packs into the separator layer.

[0010] In any further example described above, at least a portion of the first solid product is removed from the separator layer by circulating at least a portion of the first electrolyte solution from the first circulation loop through the second electrode.

[0011] In any further example of the above, at least a portion of the second solid product is removed from the separator layer by circulating at least a portion of the second electrolyte solution from the second circulation loop through the first electrode.

[0012] In any further example described above, the steps of circulating at least a portion of the first electrolyte solution from the first circulation loop through the second electrode and circulating at least a portion of the second electrolyte solution from the second circulation loop through the first electrode are performed sequentially.

[0013] In a further example of any of the above, the method includes draining the first electrolyte solution into a first tank and draining the second electrolyte solution into a second tank before circulating at least a portion of the first electrolyte solution from the first circulation loop through the second electrode and circulating at least a portion of the second electrolyte solution from the second circulation loop through the first electrode.

[0014] A method for a redox flow battery according to an exemplary embodiment of the present disclosure includes, among other things, using a redox flow battery cell to store input electrical energy during charging and release the stored electrical energy during discharging. The cell has a separator layer between a first electrode and a second electrode. The using includes circulating a polysulfide electrolyte solution through a first circulation loop in fluid communication with the first electrode of the cell and circulating a manganese electrolyte solution through a second circulation loop in fluid communication with the second electrode of the cell, wherein at least one of sulfur from the polysulfide electrolyte solution of the first electrode permeates the separator layer and precipitates as a solid sulfur-containing product, and manganese from the manganese electrolyte solution permeates the separator layer and precipitates as a solid manganese-containing product. and removing at least a portion of the solid sulfur product or solid manganese product from the separator layer or the opposing electrode by circulating at least a portion of the polysulfide electrolyte solution from the first circulation loop through the second electrode to dissolve at least a portion of the solid sulfide product and thereby remove it from the separator layer, circulating at least a portion of the manganese electrolyte solution from the second circulation loop through the first electrode to dissolve at least a portion of the solid manganese product from the separator layer and thereby remove it from the separator layer, or both.

[0015] In a further example of the above, the method includes passing a polysulfide electrolyte solution containing dissolved solid sulfide products in a first direction through a bi-directional filter and passing a manganese electrolyte solution containing dissolved solid manganese products in a second, opposite direction through the bi-directional filter.

[0016] In any further example above, at least one of the solid sulfur product and the solid manganese product is deposited on the separator layer.

[0017] In any further example above, at least one of the solid sulfur product and the solid manganese product reduces the porosity of the separator layer.

[0018] In a further example of any of the above, the method includes draining the polysulfide electrolyte into a first tank and draining the manganese electrolyte solution into a second tank before circulating at least a portion of the polysulfide electrolyte solution from the first circulation loop through the second electrode and circulating at least a portion of the manganese electrolyte solution from the second circulation loop through the first electrode.

[0019] In a further example of any of the above, the method includes, after circulating at least a portion of the polysulfide electrolyte solution from the first circulation loop through the second electrode and before circulating at least a portion of the manganese electrolyte solution from the second circulation loop through the first electrode, draining the polysulfide electrolyte solution into the first tank.

[0020] In any further example described above, at least a portion of the solid sulfur product is removed from the second electrode by circulating at least a portion of the polysulfide electrolyte solution from the first circulation loop through the second electrode.

[0021] In any further example above, at least a portion of the solid manganese product is removed from the first electrode by circulating at least a portion of the manganese electrolyte solution from the second circulation loop through the first electrode.

[0022] In any further example described above, the steps of circulating at least a portion of the polysulfide electrolyte solution from the first circulation loop through the second electrode and circulating at least a portion of the manganese electrolyte solution from the second circulation loop through the first electrode are performed sequentially.

[0023] In any further example of the foregoing, after circulating at least a portion of the polysulfide electrolyte solution from the first circulation loop through the second electrode and circulating at least a portion of the manganese electrolyte solution from the second circulation loop through the first electrode, a decrease in galvanic efficiency of at least 25% results from the operation.

[0024] A redox flow battery according to an exemplary embodiment of the present disclosure includes, among other things, a cell having first and second electrodes and an ion exchange layer disposed between the first and second electrodes, a first circulation loop fluidly connected to the first electrode, a polysulfide electrolyte contained in the first circulation loop, a second circulation loop fluidly connected to the second electrode, a manganese electrolyte contained in the second circulation loop, a bi-directional filter, and a first auxiliary loop connecting the first circulation loop to the second electrode through the bi-directional filter, the first auxiliary loop configured to receive the polysulfide electrolyte flow. The flow of polysulfide electrolyte through the first auxiliary loop removes solid sulfur products from at least one of the ion exchange layer and the second electrode. The redox flow battery also includes a second auxiliary loop connecting the second circulation loop to the first electrode through the bi-directional filter, the second auxiliary loop configured to receive the manganese electrolyte flow. Solid manganese product is removed from at least one of the ion exchange layer and the first electrode by flow of manganese electrolyte through the second auxiliary loop.

[0025] The various features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description. The drawings accompanying the detailed description can be briefly described as follows. [Brief explanation of the drawings]

[0026] [Figure 1] 1 illustrates an exemplary redox flow battery. [Figure 2] 2 illustrates a method for cleaning the redox flow battery of FIG. 1. [Figure 3] 1 a-b show images of the electrodes of the exemplary redox flow battery of FIG. 1 before and after performing the method of FIG. 2, respectively. [Figure 4] 1 a-b show images of a cross section of an exemplary separator layer of the exemplary redox flow battery of FIG. 1 before and after performing the method of FIG. 2, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0027] Redox flow batteries ("RFBs") utilize electrochemically active species that include ions of elements that have multiple reversible oxidation states in a selected liquid solution. Exemplary species can include transition metals such as vanadium, iron, manganese, chromium, zinc, or molybdenum, or other elements such as sulfur, cerium, lead, tin, titanium, germanium, bromine, or chlorine. While these species have been used, not all of them are compatible with each other for use together. For example, over time, there is mixing of species due to species crossover through the separator. If incompatible, the crossover species may react and collect within the RFB, precipitating as an insoluble solid that would negatively impact the performance of the RFB.

[0028] FIG. 1 shows a schematic diagram of an exemplary RFB 20. The RFB 20 in this example includes a single common cell 22 or a stack of common cells. However, in other examples, multiple cells would be used. The cell 22 includes a first electrode 22a, a second electrode 22b, and an ion-selective separator layer 22c between the electrodes 22a and 22b. For example, the electrodes 22a and 22b may be porous carbon structures such as carbon paper or carbon felt. The separator layer may be an ion-selective separator layer 22c that electrically insulates the electrodes while allowing selected ions to pass through to complete the redox reaction.

[0029] A first circulation loop 26 is fluidly connected to the first electrode 22a of the cell 22, and a second circulation loop 28 is fluidly connected to the second electrode 22b of the cell 22. As used herein, "loop" refers to a continuous, closed-circuit fluid path. The first circulation loop 26 and the second circulation loop 28 may include respective electrolyte storage tanks 30 and 32. A negative electrolyte solution 34 is contained in the first circulation loop 26 (i.e., fluidly connected to tank 30), and a positive electrolyte solution 36 is contained in the second circulation loop 28 (i.e., fluidly connected to tank 32).

[0030] RFB20 has at least one electrochemical activity SeedsSecond electrolysis with Quality At least one electroactive compound that functions in a redox couple Seeds First electrolysis Quality As will be understood, the terms "first" and "second" are used to distinguish between two different electrolytes / electrodes. It should be further understood that the terms "first" and "second" are interchangeable in that the first electrolyte / electrode may be alternately referred to as the second electrolyte / electrode, and vice versa.

[0031] As discussed above, a variety of electrochemically active species can be used in the RFB 20. One example of a set of species that can be used in the RFB as the first and second electrolytes 34 / 36 is sulfur and manganese, respectively. In this example, the polysulfide electrolyte solution 34 is contained in the first recirculation loop 26 (i.e., fluidly connected to tank 30), and the manganese electrolyte solution 36 is contained in the second circulation loop 28 (i.e., fluidly connected to tank 32). The polysulfide electrolyte solution 34 has a pH greater than 12, and the manganese electrolyte solution has a pH greater than 14. The electrolytes shown in the figures and described herein are for illustrative purposes only, and this description is not limited to any particular electrolyte chemistry.

[0032] The polysulfide in the polysulfide electrolyte solution 34 generally refers to a salt of sulfur in a basic pH solution. For example, the salt may be of the formula NaS in sodium hydroxide. x where x is 1 to 8. In one example, the polysulfide electrolyte solution 34 is 1 M Na2S in 7.5 M sodium hydroxide. x Manganese in electrolyte solution 36 generally refers to permanganate or manganate in alkaline or basic solution. In one example, manganese electrolyte solution 36 may be 1 M sodium permanganate (NaMnO4) in 7.5 M sodium hydroxide (NaOH), or in another example, 2 M NaMnO4 in 3 M NaOH.

[0033] A polysulfide electrolyte solution 34 is circulated through the first electrode 22a and a manganese electrolyte solution 36 is circulated through the second electrode 22b.

[0034] The following equations describe exemplary reactions within cell 22 and the resulting standard electrode potential (E), which is defined herein as the difference between the standard electrode potentials of two electrode reactions: o ) versus the standard hydrogen electrode (SHE) and open cell voltage (OCV) are specified.

[0035] Negative: 2Na2S2←→ Na2S4+ 2Na + + 2e - E o = -0.492 vs. SHE If positive: 2NaMnO4 + 2Na + + 2e - ←→ 2Na2MnO4 E o = + 0.564 vs. SHE Net cell: 2Na2S2+ 2NaMnO4←→ Na2S4+ 2Na2MnO4 OCV = 1.06V During operation of the RFB 20, sulfur may migrate from the first electrode 22a through the ion-selective separator layer 22c to the second electrode 22b. The sulfur precipitates as solid sulfur species or manganese sulfur species. Additionally, the migrated sulfur species may convert permanganate and manganate species into solid manganese oxide species (Mn y O z The permanganate and manganate species similarly migrate from the second electrode 22b to the low potential sulfur electrolyte 34 in the first electrode 22a and are reduced to insoluble manganate hydroxides Mn(OH), Mn y O z The polysulfide electrolyte solution may form sulfur species, or manganate sulfur species. Over time, loss of sulfur and manganese species and clogging with insoluble sulfur and manganese species will reduce the shuttling efficiency to a level that is not feasible for use as an RFB. Therefore, polysulfide electrolyte solutions and manganese electrolyte solutions will generally be incompatible with each other in an RFB.

[0036] However, to clean / maintain the RFB 20, e.g., to reduce / minimize the presence of solid deposits within the electrodes 22a / 22b and ion-selective separator layer 22c, an electrolyte take-off method (ETM) 50, shown in FIG. 2, can be used. With continued reference to FIGS. 1 and 2, the method 50 generally involves draining the electrolyte 34 / 36 from the cell 22 to its respective tank 30 / 32, in step 52. In step 54, a negative (e.g., polysulfide) electrolyte solution 34 is pumped through the second electrode 22b via connector 84a, thereby discharging the S 0 Any solids that have a tendency to dissolve when exposed to the reducing (e.g., poly-fed) solution, such as Zn, are reduced, dissolved, and recaptured. The negative (e.g., polysulfide) electrolyte solution 34 passes in direction 80b through bi-directional filter 80 (to capture any remaining solids, such as precipitated Mn) and connector 86b, and returns to the polysulfide solution tank via first auxiliary loop 82a.

[0037] In step 56, the negative (e.g., polysulfide) electrolyte solution 34 is drained back to tank 30. Next, in step 58, the positive (e.g., manganese) electrolyte solution 36 is pumped through first electrode 22a (after draining) via connector 84a, which oxidizes and dissolves any solids, such as Mn(OH)2 or manganese oxide precipitates. The manganese electrolyte solution 36 is then routed through connector 86a to the same bi-directional filter 80, passing in a second direction 80a (to capture any remaining solids, such as precipitated S), but as part of a second auxiliary loop 82b. The bi-directional filter 80 allows for the recapture of filtered-out precipitate species to be recaptured within the negative (e.g., polysulfide) electrolyte solution 34 and the positive (e.g., manganese) electrolyte solution 36. In step 60, the positive (e.g., manganese) electrolyte solution 36 is drained back to tank 52. The electrolyte 34 / 36 can then be reintroduced into the cell for normal RFB 20 operation.

[0038] It should be understood that in some instances steps 58-60 and 54-56 may be switched or only one of the two may be performed.

[0039] Once the solid products, such as sulfur and / or manganese products, have been removed to a desired level, the negative electrolyte solution 34 is then passed back to the first loop 26 and the positive electrolyte solution 36 is passed back to the second loop 28.

[0040] Imaging performed on electrodes 22a / 22b and ion-selective separator layer 22c after ETM method 50 was performed revealed that ETM method 50 reduced the amount of solid deposits on electrodes 22a / 22b and ion-selective separator layer 22c. Figures 3a-3b show images of electrodes 22a / 22b before and after performing the ETM method described above. As shown, the ETM method reduced the amount of solid deposit buildup within electrodes 22a / 22b. Figures 4a-4b show images of a cross section of an exemplary ion-selective separator layer 22c, which in this example is a PFSA membrane (perfluorosulfonic acid membrane), before and after performing the ETM method described above, respectively. In Figures 4a-4b, the brightest bands indicate manganese-rich regions. As shown in Figure 4b, the brightest bands have a reduced thickness compared to the corresponding bands in Figure 4a, indicating that the ETM method reduced the amount of manganese within ion-selective separator layer 22c.

[0041] Without being bound by any theory, removing solid sulfur and manganese species according to the ETM method 50 described above improves the efficiency and lifespan of the RFB 20 in one or both of the following ways: The solid species trapped on the electrodes 22a / 22b prevent active species in the electrolyte 34 / 36 from reaching sites on the electrodes 22a / 22b, which promotes the reactions described above in the RFB 20. Therefore, reducing the amount of solid deposits that accumulate on the electrodes 22a / 22b promotes more reactions to occur on the electrodes 22a / 22b. Furthermore, solids that clog the ion-selective separator layer 22c can reduce the porosity of the membrane 22c, thereby inhibiting the ion exchange that balances the reactions described above. Solids may clog the ion-selective separator layer 22c by depositing directly on the ion-selective separator layer 22c or by encountering the ion-selective separator layer 22c from the electrodes 22a / 22b. Similarly, reducing the buildup of solid deposits in or on ion-selective separator layer 22c in turn promotes ion exchange, thereby limiting the cell's resistance to RFB 20.

[0042] The efficiency of the RFB 20 can be expressed as the galvanic efficiency, which is the ratio of the average discharge voltage to the average charge voltage of the RFB 20. Operation of the RFB 20 leads to a decrease in galvanic efficiency over time. In one example, a single pass of the ETM method 50 recovers at least 25% of the decrease in galvanic efficiency over the preceding cycle since the start of the RFB or the last ETM. The improvement in the galvanic efficiency of the RFB 20 is due to a reduction in the amount of solid deposits on the electrodes 22a / 22b and / or the ion-selective separator layer 22c, as described above.

[0043] If solids resulting from electrolyte crossover collect in tank 30 or 32, these solids would then be periodically removed from the lower reservoir of tank 30 or 32 (solids sink because they have a significantly higher density than the liquid). It is anticipated that this process would not need to be performed frequently, if at all, and would not need to be fully automated (i.e., it would be part of an annual maintenance procedure). Solids recovered from filter 80 and / or tank 30 / 32 could be recycled, e.g., provided back to the respective electrolyte 34 / 36, which in some instances allows the RFB to replenish the capacity of electrode 34 / 36. However, in other instances, the solids are not recycled.

[0044] Since Mn has multiple oxidation states, disproportionation is one possibility. Manganate is Mn(V)O4 3- When disproportionated to MnO2, the compound rapidly decomposes and precipitates to MnO2, but under strongly alkaline conditions this disproportionation reaction is not a major concern (i.e., pH ≥ 14). However, at high concentrations of NaOH, the following reaction can occur slowly:

[0045] 4NaMnO4+ 4NaOH → 4Na2MnO4+ 2H2O + O2 No further reduction of manganese(VI) occurs. The reaction is slow. 7.5M OH - MnO4 in - Measurements using a 4 M solution of ZnO show 80% capacity retention after one month of storage of the fully charged solution. Nevertheless, this reaction results in a permanent loss of capacity unless mitigation strategies, such as those described below, are employed. The reversible potential of the manganese couple is 0.401 V vs. SHE for O evolution at pH = 14. o Oxygen evolution is also a concern, as the reversible potential of the polysulfide is 157 mV higher than that of the E for H evolution. Therefore, the cathode material must be selected to minimize catalysis of O evolution. o H2 generation is not a concern as it exceeds

[0046] Small amounts of O2 generated from the disproportionation reaction or by the oxygen evolution reaction at the cathode can lead to electrolyte imbalance and cause a decay of the energy capacity in the RFB. In this case, O2 can be consumed by allowing it to react with negolite by connecting the gas space above the posolite and negolite tanks (this gas space is maintained as an N2 blanket to prevent anolyte release).

[0047] O2+ 2H2O + 4Na2S2←→ 2Na2S4+ 4NaOH The net result of this and the reactions described above is the discharge of both electrolytes, so that they remain at constant composition. Another result of these reactions is that the pH of the polysulfide electrolyte solution 34 increases and that of the manganese electrolyte solution 36 decreases, while the water concentration and [OH - The change in [( ...

[0048] While the above description is provided with respect to an RFB 20 using sulfur / manganese chemistry, it should be understood that the above-described ETM method 50 would also be applicable to RFBs using different chemistries, even if solids form for reasons other than those described above. For example, aqueous vanadium chemistries known in the art may form precipitates at high ambient temperatures (typically in a positive electrolyte) or low ambient temperatures (typically in a negative electrolyte), which can be redissolved using ETM method 50. Other exemplary chemistries that could utilize ETM method 50 are Fe / Cr or Ti / Mn chemistries, both of which are known in the art. In these examples, metal plating on the negative electrode is a particular concern and can be mitigated by exposing the material to an oxidizing positive electrolyte using ETM method 50. The oxidizing electrolyte can also eliminate film formation caused by ligands in metal-ligand chemistries.

[0049] Although the illustrated examples show combinations of features, not all of them need to be combined to realize the benefits of various embodiments of the present disclosure. In other words, a system designed in accordance with an embodiment of the present disclosure need not necessarily include all of the features shown in any one of the figures or in all of the portions generally shown in the figures. Furthermore, selected features of one exemplary embodiment may be combined with selected features of other exemplary embodiments.

[0050] The foregoing description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.

Claims

1. 1. A method for a redox flow battery, comprising:

1. Using a redox flow battery cell to store input electrical energy during charging and release the stored electrical energy during discharging, the cell having a separator layer disposed between a first electrode and a second electrode; The use, circulating a first electrolyte solution through a first circulation loop in fluid communication with the first electrode of the cell; circulating a second electrolyte solution through a second circulation loop in fluid communication with the second electrode of the cell; Including, At least one of a first element from the first electrolyte solution in the first electrode permeates the separator layer and deposits as a first solid product in the second electrode, a second element from the second electrolyte solution in the second electrode permeates the separator layer and deposits as a second solid product in the first electrode, and at least one of the first solid product and the second solid product packs into the separator layer. said using; circulating at least a portion of the first electrolyte solution from the first circulation loop through the second electrode to dissolve and remove at least a portion of the first solid product from the separator layer and the second electrode; circulating at least a portion of the second electrolyte solution from the second circulation loop through the first electrode to dissolve and remove at least a portion of the second solid product from the separator layer and the first electrode, thereby removing at least a portion of the first solid product or a portion of the second solid product from the first electrode and the second electrode, respectively; Including, A method wherein said using reduces galvanic efficiency and said removing restores at least a portion of the reduced galvanic efficiency.

2. 2. The method of claim 1, wherein the steps of circulating at least a portion of the first electrolyte solution from the first circulation loop through the second electrode and circulating at least a portion of the second electrolyte solution from the second circulation loop through the first electrode are performed sequentially.

3. 10. The method of claim 1, further comprising the steps of: draining the first electrolyte solution into a first tank; and draining the second electrolyte solution into a second tank before circulating at least a portion of the first electrolyte solution from the first circulation loop through the second electrode and circulating at least a portion of the second electrolyte solution from the second circulation loop through the first electrode.

4. A redox flow battery, a cell having first and second electrodes and an ion exchange layer disposed between the first and second electrodes; a first circulation loop in fluid communication with the first electrode; a polysulfide electrolyte contained in the first circulation loop; a second circulation loop in fluid communication with the second electrode; a manganese electrolyte contained in the second circulation loop; Equipped with 1. A redox flow battery wherein, in use, at least one of a first element from the polysulfide electrolyte in the first electrode permeates the ion exchange layer and deposits as a solid sulfur product in the second electrode, a second element from the manganese electrolyte permeates the ion exchange layer and deposits a solid manganese product in the first electrode, and at least one of the solid sulfur product and the solid manganese product packs into the ion exchange layer; a bidirectional filter; a first auxiliary loop connecting the first circulation loop with the second electrode through the bi-directional filter, the first auxiliary loop configured to receive the polysulfide electrolyte flow, the flow of the polysulfide electrolyte through the first auxiliary loop removing the solid sulfur product from at least one of the ion exchange layer and the second electrode; a second auxiliary loop connecting the second circulation loop with the first electrode through the bi-directional filter, the second auxiliary loop configured to receive the manganese electrolyte flow, the flow of the manganese electrolyte through the second auxiliary loop removing the solid manganese product from at least one of the ion exchange layer and the first electrode; A redox flow battery comprising:

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