Redox flow batteries

Abstract

A redox flow battery includes a catholyte including a first organic compound having a redox potential; an anolyte including a second organic compound having a redox potential; and a solvent; wherein the redox potential of the first organic compound is the same or higher than the redox potential of the second compound.

Description

Atty. Dkt. No.: 118537-0601REDOX FLOW BATTERIESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional Application No. 63 / 679,928, filed August 6, 2024, which is incorporated herein by reference in its entirety.FIELD

[0002] This technology relates to redox flow batteries. More particularly, this technology relates to organic redox flow batteries utilizing a solvent comprising sulfolane, y- valerolactone, or any of one of these solvents in a mixture of acetonitrile or propylene carbonate.BACKGROUND

[0003] After many years of intensive use of coal and oil combustion as main energy sources, humanity is increasingly oriented towards the use of electricity. Efficient storage of electricity-compatible with various applications-remains a challenge. Lithium ion-based battery, long dedicated to smartphones and small devices, has been a potential short-term solution. Their use in bigger applications, such as in the car industry, could lead to a scarcity of their raw materials (Li, Co, rare-earth), and result in a very significant increase of cost.

[0004] To overcome this problem and prepare for the future, several sustainable approaches have been considered in the Energy Storage Systems (ESSs) field. One of them is the development of redox flow batteries (RFBs). The energy is stored in liquid electrolyte solutions which flow through a battery of electrochemical cells during charge and discharge. The “redox” term refers to chemical reduction and oxidation reactions involved.Atty. Dkt. No.: 118537-0601

[0005] These redox flow batteries have several advantages over previously presented systems. Power conversion is separated from energy storage, thus allowing for independent power and energy sizing. This separation from energy storage allows for virtually unlimited ESS capacity and are only limited by the tanker size and the electrolyte concentration. In redox flow battery systems, the redox reactions are totally reversible, meaning that the same cell is used to operate as converter of electricity into chemical energy and vice-versa. From an infrastructure point of view, the redox flow battery system is relatively easy to develop. The setup requires only two tanks each provided with a pump and a cell provided with an ion exchange membrane between two electrodes. Therefore, redox flow battery systems have very few wear parts, and the equipment maintenance costs are extremely reduced. Lastly, there is a clear separation between the two electrolyte storage, which prevents selfdischarge and the battery lifetime is mainly chemically dependent.

[0006] However, there are several points concerning redox flow battery systems that remain to be improved. Currently the energy density provided by the RFBs is insufficient for mobile applications. Parameters such as solubility and temperature of electrolytes remain crucial. Also, the cost of these EESs remains high due to their poor presence in the energy market.

[0007] Historically, the RFB systems were first used in France in 1933 with a vanadium- based electrolyte. Today, vanadium RFBs still are the most marketed flow batteries, due to a number of advantages they present on other chemistries (V at both electrodes, no crosscontamination issues, and water-based solution). However, vanadium is costly, and these vanadium-based RFBs have a relatively low energy density. Furthermore, the capital cost of a vanadium-based RFB is attributed to the cost of the membrane materials, which are used to prepare the exchange membrane that separates the two poles of the battery. Such membranes are developed to be permeable only to anions, and are based on cationic functionalized polymers. This type of material is subjected to significant electrical charge stress over time, which impacts the longevity of the RFB. While metal coordination complexes appeared to be the most stable electrolyte, the critical technical and economic limitations associated with these complexes, such as low solubility, inferior electrochemicalAtty. Dkt. No.: 118537-0601 activity, and high costs, have motivated researchers to explore cheaper and easier to synthesize compounds.

[0008] Redox-active organic materials (ROMs) are a promising alternative option for improving current RFB systems as ROMs have: I) the molecular diversity, II) structural tailorability, and III) natural abundance that make them electrolytes of choice. Thus, there have been several RFB systems developed with redox-active organic materials. An important feature of these RFB systems is a one nitrogen-containing aromatic scaffold that is very soluble and highly tunable. However, the most known redox-active organic based RFB system still lacks high efficiency, robustness, and a large open circuit potential (OCV). This disclosure addresses the need for improved redox-active organic material based RFB systems.SUMMARY

[0009] In an aspect, a redox flow battery includes a catholyte comprising a first organic compound having a redox potential; an anolyte comprising a second organic compound having a redox potential; and a solvent comprising sulfolane or y-valerolactone; wherein the redox potential of the first organic compound is the same or higher than the redox potential of the second compound.

[0010] In some embodiments, the solvent further comprises acetonitrile or propylene carbonate. In some embodiments, the redox potential of the first organic compound may be higher than the redox potential of the second compound. In some embodiments, the first compound and the second compound may be different compounds.

[0011] In some embodiments, the first compound and the second compound may be the same compounds. In some embodiments, the first compound and the second compound each comprise a conjugated heterocyclic compound. In some embodiments, the first compound comprises the conjugated heterocyclic compound in a first oxidation state, the second compound comprises the conjugated heterocyclic compound in a second oxidation state, and the first oxidation state is a higher oxidation state than the second oxidation state.Atty. Dkt. No.: 118537-0601

[0012] On another aspect, a redox flow battery includes a catholyte comprising a conjugated heterocyclic compound in a first oxidation state; an anolyte comprising a conjugated heterocyclic compound in a second oxidation state; and a solvent comprising sulfolane or y-valerolactone; wherein the first oxidation state is a higher oxidation state than the second oxidation state. In some embodiments, the conjugated heterocyclic compound in the first oxidation state may be a conjugated heterocyclic cationic compound, and / or wherein the conjugated heterocyclic compound in the second oxidation state may be a conjugated heterocyclic cationic compound. In some embodiments, the solvent further comprises acetonitrile or propylene carbonate.

[0013] In a further aspect, a redox flow battery includes a catholyte that includes a compound of Formula I; and an anolyte comprising the compound of Formula I. In such embodiments, the compound of Formula (I) is represented by the following structure:wherein: X is -4, -3, -2, -1, 0, +1, +2, +3, or +4; each Rla, Rlb, Rlc, R2a, R2b, R2c, R2d, R3a, R3b, R3C, and R3dis independently H, halide, CF3, CBn, CI3, NH2, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, CO2R, or Ar1; each Y is independently -L-Z; each L is independently C1-C12 alkylene; each Z is independently - N(R4a)sW; each R4ais independently C1-C12 alkyl; each W is independently tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis- trifluoromethanesulfonimide, halide, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, or sulfite; each Ar1is independently unsubstituted or substituted phenyl or unsubstituted or substituted heteroaryl; each Ar1is independently substituted with 0 to 5 substituents; the substituents are each independently selected from the group consisting of halide, CF3, NH2, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2,Atty. Dkt. No.: 118537-0601CN, or aryl. In some embodiments, the compound of Formula I in the catholyte comprises a radical dication and / or wherein the compound of Formula I in the anolyte comprises a neutral radical. In some embodiments, where each Y is -CH2-CH2-CH2-N(Me)3W; each W is hexafluorophosphate or trifluoromethanesulfonate, each Rla, Rlb, Rlc, R2b, R2c, R2d, R3a, R3b, and R3cis independently H; and R2aand R3deach methoxy. In some embodiments, the compound of Formula I may be:

[0014] In some embodiments, any one of the redox flow batteries described herein further includes a separator disposed between the anolyte and the catholyte.

[0015] In some embodiments, any one of the redox flow batteries described herein further includes an electrolyte salt. In some embodiments, the electrolyte salt is a lithium, sodium, potassium, ammonium, or alkylammonium salt of tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatoborate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof.

[0016] In some embodiments, any one of the redox flow batteries described herein further includes a solvent. In some embodiments, the solvent comprises a nitrile solvent, an ether solvent, dimethylformamide, water, a halogenated solvent, an ionic liquid, sulfolane, y- valerolactone, acetonitrile, or propylene carbonate or a mixture of any two or more thereof.

[0017] In a yet further aspect, a method of operating any one of the redox flow batteries described herein includes flowing the catholyte through a catholyte compartment and flowing the anolyte through an anolyte compartment, wherein the catholyte and anolyte compartments are separated by a separator and electron transfer from the anolyte to the catholyte is supported.Atty. Dkt. No.: 118537-0601

[0018] In some embodiments of the methods, after electron transfer, the method includes regenerating the catholyte and / or the anolyte by an external power source. In some embodiments, the redox flow battery is an open redox flow battery cell including one or more current collectors, one or more graphite bipolar plates, one or more teflon gaskets, carbon felt electrodes, and a porous separator comprising an exchange membrane. In some embodiments, the one or more teflon gaskets comprise expanded polytetrafluoroethylene (ePTFE).BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 shows the D and k° measured depending on the nature of the solvent and supporting electrolyte concentration, according to the examples.

[0020] FIG. 2 shows the D and k° oftcC+with BAPFe or TBATFSI depending on the solvent and temperature in °C, according to the examples. The structure oftcC+is shown in Example 1.

[0021] FIG. 3 A is a cyclic voltammogram of the carbocation electrolytetcC+ in acetonitrile, according to the examples.

[0022] FIG. 3B illustrates the monitoring of a cycling experiment of a complete redox flow battery cell assembled with 2 x 4 mL of 1 mMtcC+ in a 0.1 M solution of TBAPFe in acetonitrile with a flow rate of 2 x 8 mL / min, according to the examples.

[0023] FIG. 4A is a cyclic voltammogram of the carbocation electrolytetcC+ in sulfolane, according to the examples.

[0024] FIG. 4B illustrates the monitoring of a cycling experiment of a complete redox flow battery cell assembled with 2 x 4 mL of 1 mMtcC+ in a 0.1 M solution of TBAPFe in sulfolane with a flow rate of 2 x 8 mL / min, according to the examples.

[0025] FIG. 5 A is a cyclic voltammogram of the carbocation electrolytetcC+ in y- valerolactone, according to the examples.

[0026] FIG. 5B illustrates the monitoring of a cycling experiment of a complete redoxAtty. Dkt. No.: 118537-0601 flow battery cell assembled with 2 x 4 mL of 1 mMtcC+ in a 0.1 M solution of TBAPFe in y- valerolactone with a flow rate of 2 x 8 mL / min, according to the examples.

[0027] FIG. 6 illustrates the concentration and energy density of several redox-active organic materials obtained versus vanadium RFBs, according to the examples.

[0028] FIG. 7A illustrates the monitoring of a cycling experiment of a complete redox flow battery cell assembled with 2 x 4 mL of 1 mMtcC+ in a 0.1 M solution of TBAPFe in sulfolane at 45°C with a flow rate of 2 x 8 mL / min, according to the examples.

[0029] FIG. 7B is a cyclic voltammogram (CV) of the initial electrolyte solution, and of the reservoirs at the working (Ew) and counter (Ec) electrode after more than 400 charge and discharge cycles, where the arrow indicates the formation of a new compound during a side reaction at Ew, according to the examples.

[0030] FIG. 8 is a scheme of the open RFB cell used with the gold plate current collector (CC), graphite bipolar plate (BPP), teflon gasket (TG), the carbon felt electrodes (electrodes) and the exchange membrane (EM) (left), while the right side is a picture of the actual cell assembled.DETAILED DESCRIPTION

[0031] Various embodiments are described hereinafter. It should be noted that the specific embodiments are not intended as an exhaustive description or as a limitation to the broader aspects discussed herein. One aspect described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced with any other embodiment s).

[0032] As used herein, “about” will be understood by persons of ordinary skill in the art and will vary to some extent depending upon the context in which it is used. If there are uses of the term which are not clear to persons of ordinary skill in the art, given the context in which it is used, “about” will mean up to plus or minus 10% of the particular term.Atty. Dkt. No.: 118537-0601

[0033] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the embodiments and does not pose a limitation on the scope of the claims unless otherwise stated. No language in the specification should be construed as indicating any non-claimed element as essential.

[0034] In general, “substituted” refers to an alkyl, alkenyl, alkynyl, aryl, or ether group, as defined below (e.g., an alkyl group) in which one or more bonds to a hydrogen atom contained therein are replaced by a bond to non-hydrogen or non-carbon atoms. Substituted groups also include groups in which one or more bonds to a carbon(s) or hydrogen(s) atom are replaced by one or more bonds, including double or triple bonds, to a heteroatom. Thus, a substituted group will be substituted with one or more substituents, unless otherwise specified. In some embodiments, a substituted group is substituted with 1, 2, 3, 4, 5, or 6 substituents. Examples of substituent groups include: halogens (i.e., F, Cl, Br, and I); hydroxyls; alkoxy, alkenoxy, alkynoxy, aryloxy, aralkyloxy, heterocyclyloxy, and heterocyclylalkoxy groups; carbonyls (oxo); carboxyls; esters; urethanes; oximes; hydroxylamines; alkoxyamines; aralkoxyamines; thiols; sulfides; sulfoxides; sulfones; sulfonyls; sulfonamides; amines; N-oxides; hydrazines; hydrazides; hydrazones; azides; amides; ureas; amidines; guanidines; enamines; imides; isocyanates; isothiocyanates; cyanates; thiocyanates; imines; nitro groups; nitriles (i.e., CN); and the like.

[0035] As used herein, “alkyl” groups include straight chain and branched alkyl groups having from 1 to about 20 carbon atoms, and typically from 1 to 12 carbons or, in some embodiments, from 1 to 8 carbon atoms. As employed herein, “alkyl groups” include cycloalkyl groups as defined below. Alkyl groups may be substituted or unsubstituted.Atty. Dkt. No.: 118537-0601Examples of straight chain alkyl groups include methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl groups. Examples of branched alkyl groups include, but are not limited to, isopropyl, sec-butyl, t-butyl, neopentyl, and isopentyl groups. Representative substituted alkyl groups may be substituted one or more times with, for example, amino, thio, hydroxy, cyano, alkoxy, and / or halo groups such as F, Cl, Br, and I groups. As used herein the term haloalkyl is an alkyl group having one or more halo groups. In some embodiments, haloalkyl refers to a per-haloalkyl group.

[0036] The term “alkylene” refers to a saturated linear divalent hydrocarbon moiety or a branched saturated divalent hydrocarbon moiety. Exemplary alkylene groups include, but are not limited to, methylene, ethylene, propylene, butylene, pentylene, 2-methylpropylene, and the like.

[0037] The term “heteroalkylene” refers to an alkylene group as defined herein in which one or more chain atoms or hydrogen atoms are replaced with a heteroatom such as O, N, P, or S. Exemplary heteroalkylenes include, but are not limited to, polyethylene glycol derived heteroalkylenes such as PEG2 (i.e, 2 molecules of ethylene glycols are linked), PEG3, 2-m ethoxy ethylene, 2 -hydroxy ethyl, 2,3 -dihydroxypropyl, etc.

[0038] Cycloalkyl groups are cyclic alkyl groups such as, but not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl groups. In some embodiments, the cycloalkyl group has 3 to 8 ring members, whereas in other embodiments the number of ring carbon atoms range from 3 to 5, 6, or 7. Cycloalkyl groups may be substituted or unsubstituted. Cycloalkyl groups further include polycyclic cycloalkyl groups such as, but not limited to, norbornyl, adamantyl, bornyl, camphenyl, isocamphenyl, and carenyl groups, and fused rings such as, but not limited to, decalinyl, and the like. Cycloalkyl groups also include rings that are substituted with straight or branched chain alkyl groups as defined above. Representative substituted cycloalkyl groups may be monosubstituted or substituted more than once, such as, but not limited to: 2,2-; 2,3-; 2,4-; 2,5-; or 2,6-disubstituted cyclohexyl groups or mono-, di-, or tri -substituted norbornyl or cycloheptyl groups, which may be substituted with, for example, alkyl, alkoxy, amino, thio, hydroxy, cyano, and / or halo groups.Atty. Dkt. No.: 118537-0601

[0039] Alkenyl groups are straight chain, branched or cyclic alkyl groups having 2 to about 20 carbon atoms, and further including at least one double bond. In some embodiments alkenyl groups have from 1 to 12 carbons, or, typically, from 1 to 8 carbon atoms. Alkenyl groups may be substituted or unsubstituted. Alkenyl groups include, for instance, vinyl, propenyl, 2-butenyl, 3-butenyl, isobutenyl, cyclohexenyl, cyclopentenyl, cyclohexadienyl, butadienyl, pentadienyl, and hexadienyl groups among others. Alkenyl groups may be substituted similarly to alkyl groups. Divalent alkenyl groups, i.e., alkenyl groups with two points of attachment, include, but are not limited to, CH-CH=CH2, C=CH2, or C=CHCH3.

[0040] As used herein, “aryl” or “aromatic,” groups are cyclic aromatic hydrocarbons that do not contain heteroatoms. Aryl groups include monocyclic, bicyclic and polycyclic ring systems. Thus, aryl groups include, but are not limited to, phenyl, azulenyl, heptalenyl, biphenylenyl, indacenyl, fluorenyl, phenanthrenyl, triphenylenyl, pyrenyl, naphthacenyl, chrysenyl, biphenyl, anthracenyl, indenyl, indanyl, pentalenyl, and naphthyl groups. In some embodiments, aryl groups contain 6-14 carbons, and in others from 6 to 12 or even 6- 10 carbon atoms in the ring portions of the groups. The phrase “aryl groups” includes groups containing fused rings, such as fused aromatic-aliphatic ring systems (e.g., indanyl, tetrahydronaphthyl, and the like). Aryl groups may be substituted or unsubstituted.

[0041] As used herein, “arylene” refers to a bivalent group derived from an arene where a hydrogen atom has been removed from two ring carbon atoms.

[0042] Heteroalkyl group include straight and branched chain alkyl groups as defined above and further include 1, 2, 3, 4, 5, or 6 heteroatoms independently selected from oxygen, sulfur, and nitrogen. Thus, heteroalkyl groups include 1 to 12 carbon atoms, 1 to 10 carbons or, in some embodiments, from 1 to 8, or 1, 2, 3, 4, 5, or 6 carbon atoms, or any range therein (e.g., 1-4). Examples of heteroalkyl groups include, but are not limited to, -(CH2CH2O)I-5CH3, -(CH2)I-6O(CH2)I-6 CH3, -(CH2)i-6NRa(CH2)i-6 CH3, -(CH2)I-6S(CH2)l-6 CH3, -(CH2)l-6O(CH2)l-6O(CH2)l-6 CH3, -(CH2)l-6 NRa(CH2)l-6 NRa(CH2)l-6CH3, -(CH2)1-6O(CH2)1-6O(CH2)1-6O(CH2)1-6CH3, -(CH2)i-6NRa(CH2)i-6NRa(CH2)i-6NRa(CH2)i-6CH3, with the total number of carbon atoms in the heteroalkyl group being 1 to 12 and Rais a hydrogen or a substituted or unsubstituted alkyl, alkenyl, aryl or aralkyl group. OtherAtty. Dkt. No.: 118537-0601 examples of heteroalkyl groups include, but are not limited to, groups having different heteroatoms in a single group. Such examples of heteroalkyl groups include, but are not limited to, -(CH2)I-6S(CH2)I-6O(CH2)I-6, -(CH2)I-6 NRa(CH2)i-6)O(CH2)i-6, -(CH2)I-6O(CH2)I-6 NRa(CH2)i-6S(CH2)i-6, -(CH2)i-6NRa(CH2)i-6O(CH2)i-6S(CH2)i-6, with the total number of carbon atoms in the heteroalkyl group being 1 to 12. In some embodiments, heteroalkyl groups include, but are not limited to, polyoxyethylene groups, such as - (OCH2CH2-)I-5CH3, for example, -O(CH2)2O(CH2)2OCH3, -O(CH2)2O(CH2)2O(CH2)2OCH3, - O(CH2)2O(CH2)2O(CH2)2O(CH2)2OCH3.

[0043] Aralkyl groups are substituted aryl groups in which an alkyl group as defined above has a hydrogen or carbon bond of the alkyl group replaced with a bond to an aryl group as defined above. In some embodiments, aralkyl groups contain 7 to 14 carbon atoms, 7 to 10 carbon atoms, e.g., 7, 8, 9, or 10 carbon atoms or any range therein (e.g., 7- 8). Aralkyl groups may be substituted or unsubstituted. Substituted aralkyl groups may be substituted at the alkyl, the aryl or both the alkyl and aryl portions of the group. Representative substituted and unsubstituted alkaryl groups include but are not limited to alkylphenyl such as methylphenyl, (chloromethyl)phenyl, chloro(chloromethyl)phenyl, or fused alkaryl groups such as 5-ethylnaphthalenyl.

[0044] Heterocyclyl groups are non-aromatic ring compounds containing 3 or more ring members, of which one or more is a heteroatom such as, but not limited to, N, O, and S. In some embodiments, the heterocyclyl group contains 1, 2, 3 or 4 heteroatoms. In some embodiments, heterocyclyl groups include mono-, bi- and tricyclic rings having 3 to 16 ring members, whereas other such groups have 3 to 6, 3 to 10, 3 to 12, or 3 to 14 ring members. Heterocyclyl groups encompass partially unsaturated and saturated ring systems, such as, for example, imidazolinyl and imidazolidinyl groups. The phrase also includes bridged polycyclic ring systems containing a heteroatom such as, but not limited to, quinuclidyl. The phrase also includes heterocyclyl groups that have other groups, such as alkyl, oxo or halo groups, bonded to one of the ring members, referred to as “substituted heterocyclyl groups”. Heterocyclyl groups include, but are not limited to, aziridinyl, azetidinyl, pyrrolidinyl, imidazolidinyl, pyrazolidinyl, thiazolidinyl, tetrahydrothiophenyl,Atty. Dkt. No.: 118537-0601 tetrahydrofuranyl, dioxolyl, pyrrolinyl, piperidyl, piperazinyl, morpholinyl, thiomorpholinyl, tetrahydropyranyl, and tetrahydrothiopyranyl groups. Representative substituted heterocyclyl groups may be mono-substituted or substituted more than once, such as, but not limited to, morpholinyl groups, which are 2-, 3-, 4-, 5-, or 6-substituted, or disubstituted with various substituents such as those listed above. The heteroatom(s) may also be in oxidized form, if chemically possible.

[0045] Heteroaryl groups are aromatic ring compounds containing 5 or more ring members, of which, one or more is a heteroatom such as, but not limited to, N, O, and S. Heteroaryl groups include, but are not limited to, groups such as pyrrolyl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, thiophenyl, benzothiophenyl, furanyl, imidazolyl, benzofuranyl, indolyl, azaindolyl (pyrrolopyridinyl), indazolyl, benzimidazolyl, imidazopyridinyl (azabenzimidazolyl), pyrazolopyridinyl, triazolopyridinyl, benzotriazolyl, benzoxazolyl, benzothiazolyl, benzothiadiazolyl, imidazopyridinyl, isoxazolopyridinyl, thianaphthyl, purinyl, xanthinyl, adeninyl, guaninyl, quinolinyl, isoquinolinyl, tetrahydroquinolinyl, quinoxalinyl, and quinazolinyl groups. Heteroaryl groups include fused ring compounds in which all rings are aromatic such as indolyl groups and include fused ring compounds in which only one of the rings is aromatic, such as 2,3-dihydro indolyl groups. The phrase “heteroaryl groups” includes fused ring compounds and also includes heteroaryl groups that have other groups bonded to one of the ring members, such as alkyl groups, referred to as “substituted heteroaryl groups.” Representative substituted heteroaryl groups may be substituted one or more times with various substituents such as those listed above. The heteroatom(s) may also be in oxidized form, if chemically possible.

[0046] The term “halogen” or “halo” as used herein refers to bromine, chlorine, fluorine, or iodine. In some embodiments, the halogen is fluorine. In other embodiments, the halogen is chlorine or bromine. The term “halide” as used herein refers to the anion of a halogen, such as bromide, chloride, fluoride, and iodide. In some embodiments, the halide is chloride or iodide.

[0047] The terms “alkoxy” refers to a substituted or unsubstituted alkyl group bonded to an oxygen atom, such as a moiety of the formula -ORa, wherein Rais alkyl as definedAtty. Dkt. No.: 118537-0601 herein. Examples include but are not limited to methoxy and ethoxy. Representative substituted alkoxy groups may be substituted one or more times with substituents such as those listed above, such as methoxymethyl and fluoromethoxy.

[0048] The term “alkylamino” refers to a moiety of the formula -NHRa, where Rais alkyl as defined herein.

[0049] The term “dialkyl amino” refers to a moiety of the formula -NRaRb, wherein Raand Rbare independently alkyl as defined herein.

[0050] Disclosed herein are redox flow battery systems comprising conjugated heterocyclic carbenium compounds as both the anolyte and catholyte and carbon particles, wherein the conjugated heterocyclic carbenium compounds are redox active compounds that can reversibly be reduced and oxidized. The heterocyclic carbocations disclosed herein have one positive charge carried by the aromatic central carbon C+ and two positive charges carried by the two quaternary ammonium groups -NMe3+. Also disclosed herein is the use of y-valerolactone and sulfolane as compatible solvents for the organic redox flow batteries (RFBs) described herein and are favorable over acetonitrile, which is moderately toxic.

[0051] As shown in the Examples, sulfolane and y-valerolactone are suitable solvents for RFB. Also shown in the Examples, the compounds of Formula I, which are heterocyclic carbocations with one positive charge carried by the aromatic central carbon C+ and two positive charges carried by the two quaternary ammonium groups -NMe3+. Such tri cationic comopunds are highly soluble and provide an astonishing energy density value of 65 Wh / L, which is almost three times of that of a commerical VRFBs.

[0052] Redox flow batteries contemplated for use include organic redox flow batteries comprising organic compounds that are redox active. Such redox flow batteries may be symmetrical, where the anolyte and catholyte are composed of the same organic compound, and non-symmetrical.

[0053] A redox flow battery includes a catholyte including a first organic compound having a redox potential, an anolyte including a second organic compound having a redoxAtty. Dkt. No.: 118537-0601 potential; and a solvent comprising sulfolane or y-valerolactone. In some embodiments, the solvent further comprises acetonitrile or propylene carbonate. In the battery, the redox potential of the first organic compound is the same or higher than the redox potential of the second compound. The first compound and the second compound may be the same or different compounds.

[0054] The first compound and the second compound may be conjugated heterocyclic compounds. For example, the first compound may be a conjugated heterocyclic compound in a first oxidation state, and the second compound may be a conjugated heterocyclic compound in a second oxidation state, where the first oxidation state is a higher oxidation state than the second oxidation state. In this context, “higher oxidation state’ refers to a state that is both positive and larger.

[0055] Provided in one aspect is a redox flow battery including: a catholyte including a conjugated heterocyclic compound in a first oxidation state; an anolyte including a conjugated heterocyclic compound in a second oxidation state; and a solvent comprising sulfolane or y-valerolactone; wherein the first oxidation state is a higher oxidation state than the second oxidation state. In some embodiments, the solvent further comprises acetonitrile or propylene carbonate. The conjugated heterocyclic compound in the first oxidation state may be a conjugated heterocyclic cationic compound, and / or wherein the conjugated heterocyclic compound in the second oxidation state is a conjugated heterocyclic cationic compound.

[0056] A redox flow battery may include a catholyte that includes a radical dication of a conjugated heterocyclic carbenium compound; and an anolyte includes a neutral radical of the conjugated heterocyclic carbenium compound. Accordingly, the catholyte is in a higher oxidation state than the anolyte. The battery may also contain a solvent such as sulfolane or y-valerolactone. In some embodiments, the solvent further comprises acetonitrile or propylene carbonate. The radical dication and neutral radical of the conjugated heterocyclic carbenium compound, while having different oxidation states / charges, may have the same atomic components and structure of the cathodic and anodic species (i.e. they are the same compound in a different oxidation state).Atty. Dkt. No.: 118537-0601

[0057] Provided in another aspect is a redox flow battery includes a catholyte having a compound of Formula I; and an anolyte including the compound of Formula I; wherein the compound of Formula I is represented by the structures disclosed herein. In some embodiments, the compound of Formula I in the catholyte comprises a radical dication and / or wherein the compound of Formula I in the anolyte comprises a neutral radical.Heterocyclic Carbenium Compounds

[0058] Conjugated heterocyclic carbenium ions (salts) may be prepared from successive double S\Ar reactions between tris(2,6-dimethoxyphenyl)carbenium ion and primary amines at moderate-to-high temperatures with methanol elimination. The stable carbenium salts are of particular interest because: 1) they are stable under mild acidic or basic aqueous conditions; 2) the stepwise and temperature dependence of the synthesis allows versatility by using aliphatic or aromatic amines, and forming unsymmetrical ions; 3) they can be functionalized via C-H borylation, and / or metal-catalyzed cross-coupling; and 4) the negative counterions can be exchanged to affect the physical and chemical properties of the salts. Not only are these conjugated heterocyclic carbenium compounds fluorescent with large extinction coefficients and long fluorescence life times, these conjugated heterocyclic carbenium compounds are redox active species with three stable redox states: carbodi cation, carbocation, and neutral carboradical.

[0059] The redox states of the heterocyclic carbenium compounds are illustrated in the below Scheme. Neutral radical (C") and radical dication (C++') can lose and gain an electron respectively to form the carbocation (C+), resulting in the battery discharge and generation of electricity (Scheme 1; steps with red dashed arrows). Alternately, the carbocation (C+) can gain or lose an electron to convert to the neutral radical (C") or radical dication (C++') respectively, resulting in battery charge (Scheme A; steps with blue solid arrows).Scheme AAtty. Dkt. No.: 118537-0601

[0060] Their stability, reduction and oxidation potential, solubility in organic solvent, and tunability via simple organic transformation make these compounds ideal candidates to be tested as the anolyte and catholyte for RFBs.

[0061] The conjugated heterocyclic carbenium compounds disclosed herein are compounds of Formula I. The compound of Formula (I) is represented by the following structure:wherein:X is -4, -3, -2, -1, 0, +1, +2, +3, or +4; each Rla, Rlb, Rlc, R2a, R2b, R2c, R2d, R3a, R3b, R3c, and R3dis independently H, halide, CF3, CBn, CI3, NH2, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, CO2R, or Ar1; each Y is independently -L-Z; each L is independently C1-C12 alkylene; each Z is independently -N(R4a)3W; each R4ais independently C1-C12 alkyl; each W is independently tetrafluoroborate, hexafluorophosphate, perchlorate, tetrary lb orate, trifluoromethanesulfonate, oxalatoborate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, or sulfite; each Ar1is independently unsubstituted or substituted phenyl or unsubstituted or substituted heteroaryl; each Ar1is independently substituted with 0 to 5 substituents; the substituents are each independently selected from the group consisting of halide, CF3, NH2, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, or aryl.Atty. Dkt. No.: 118537-0601

[0062] In some embodiments, in the compound of Formula I each Y is -CH2-CH2-CH2- N(Me)sW; each W is hexafluorophosphate or trifluoromethanesulfonate, each Rla, Rlb, Rlc, R2b, R2C, R2d, R3a, R3b, and R3cis independently H; and R2aand R3dare methoxy.

[0063] In some embodiments, the compound of Formula I is:

[0064] The compounds of Formula I described herein further include a counter anion (i.e. where they are the carbocation or dicarbocation they are salts). Illustrates counterions (i.e. anions) of carbocations of Formula I include, but are not limited to, halides (e.g., Cl, F, I, and Br), an anion derived from organic compounds such as carboxylates, phosphates, sulfates, tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis- trifluoromethanesulfonimide, an anion of an ionic liquid, hydroxide, carbonate, bicarbonate, hydrogen sulfate, sulfite, or a mixture of any two or more thereof. In some embodiments, the compound of formula I also includes an anion that is tetrafluoroborate, hexafluorophosphate, or a mixture of any two or more thereof.Additional Components

[0065] The redox flow battery, such as any one of the redox flow batteries described herein, may also include a separator disposed between the anolyte and the catholyte.

[0066] Any of the redox flow batteries described herein may also include an electrolyte salt. In some embodiments, the electrolyte salt is a lithium, sodium, potassium, ammonium, or alkylammonium salt of tetrafluoroborate, hexafluorophosphate, perchlorate, tetrary lb orate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis- trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof. In some embodiments, the electrolyte is an alkylammonium salt of tetrafluoroborate,Atty. Dkt. No.: 118537-0601 hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof. In some embodiments, the alkylammonium salt is a tetrabutylammonium salt, tetraethylammonium salt, or a mixture thereof. In some embodiments, the electrolyte salt is tetrabutylammonium hexafluorophosphate, tetrabutyl ammonium tetrafluoroborate, tetraethylammonium tetrafluoroborate, or a mixture of any two or more thereof.

[0067] Any one of the redox flow batteries described herein may further include a solvent. In some embodiments, the solvent is a nitrile solvent, such as acetonitrile; an ether solvent, such as tetrahydrofuran; dimethylformamide; water; a halogenated solvent, such as dichloromethane; an ionic liquid; sulfolane, y- valerolactone, acetonitrile or propylene carbonate, or a mixture of any two or more thereof. In some embodiments, the solvent comprises sulfolane, y-valerolactone, or any of one of these solvents in a mixture of acetonitrile or propylene carbonate or any mixture thereofMethods of Use

[0068] Provided in another aspect is a method of operating the redox flow battery and includes flowing the catholyte through a catholyte compartment and flowing the anolyte through an anolyte compartment, wherein the catholyte and anolyte compartments are separated by a separator and electron transfer from the anolyte to the catholyte is supported.

[0069] The redox flow batteries described herein are suitable for use with the heterocyclic carbocation compounds disclosed herein. An illustrative example is shown in Figure 9 and overcomes the previous issues associated with using commercially available electrochemical cells as described in Example 3 and shown in Figures 8a, 8b, 8c, and 8d. In some embodiments, the redox flow batter is an open redox flow battery cell comprising one or more current collectors, one or more graphite bipolar plates, one or more teflon gaskets, carbon felt electrodes, and a porous separator comprising an exchange membrane. In some embodiments, the one or more teflon gaskets comprise expanded polytetrafluoroethylene (ePTFE).Atty. Dkt. No.: 118537-0601

[0070] The present invention, thus generally described, will be understood more readily by reference to the following examples, which are provided by way of illustration and are not intended to be limiting of the present invention.EXAMPLES

[0071] Example 1. Redox Flow Battery Solvents with Decreased Toxicity. The choice of solvent in Symmetrical Organic Redox Flow Batteries (SORFBs) may be based upon factors such as large volumes, costs, and potential toxicity. To achieve higher energy densities than those of Vanadium Redox Flow Batteries (VRFBs), organic solvents as,cC support media where used, wherein,CC represents a compound with the following structure:Acetonitrile (CEECN) was selected as a model solvent due to its wide electrochemical window (~6.0 V), positive impact on energy density, and established status in electrochemistry. Sulfolane may also be used due to its electrochemical stability window (7.5V), high boiling point (287°C), low flammability, and low toxicity. Furthermore, its derivation from the capture of SO2 in industrial processes endows this solvent with significant potential for the revalorization of toxic waste. Another solvent is y- valerolactone (yVL), which is sourced from wood lignin, and offers ecological and economic advantages. yVL also has a high boiling point, low flammability, and is nontoxic (LD50 = 8800 g / kg rat oral).Electrochemical kinetic parametersAtty. Dkt. No.: 118537-0601

[0072] The electronic processes (Ei / 2Redand EI / 2OX, difference equals Egap) via CV (cyclic voltammetry) acquisition were determined at different scan rates (FIG. 1). Electrochemical kinetic parameters of the model compound in the presence of different supporting electrolytes were determined at different concentrations and also different solvents. The diffusion coefficient D reflects the ability of the species, in their different oxidation states, to move in the supporting solvent, while the electron transfer rate value k° corresponds to the speed at which an electron can move from one chemical species to another depending on the conditions (the higher the value, the more efficient the exchange and movement).

[0073] During the preliminary study oftcC+under the basic C+conditions, both the diffusion (D > 4.10'6cm2 / s) and transfer rate (k° > 9.10'3cm / s) parameters remain very good. Thus, these parameters were evaluated in sulfolane at 60°C, 45°C and 30°C in the presence of 0. IM or 0.3M TBAPFe (TB A is tetrabuylammonium) (FIG. 2). A difference of one order of magnitude in the values of D for all the concentrations used (-1.10-7 cm2 / s) was observed, linked to the high viscosity of sulfolane. The values of k° are greatly affected with a drop of about 2 orders of magnitude (-1.10'4cm / s). Despite these lower values, the reversibility of the electronic processes and the robustness of this is preserved under all conditions. The recent use of TBATFSI (tetrabutyl ammonium fluorosulfonyl imide), led to a slightly better value, but especially a better reversibility than TBAPFe.RFB test

[0074] Flow cyclic testing using the RFB prototype as described in Example 3, illustrates that both sulfolane and y-valerolactone are suitable solvents for RFB. The results are summarized in FIGS. 4A and 4B for sulfolane and FIGS. 5A and 5B for y-valerolactone. The results for acetonitrile are shown in FIGS. 3A and 3B.

[0075] Example 2. High Energy Density Tris Cationic Electrolyte Containing Ammonium Arms.

[0076] Commercial vanadium RFBs (VRFBs) are available with reported energy densities (Ed) of 15-25 Wh / L at concentrations up to 1600 mM in water. The first generation of carbenium C+was poorly soluble and did not reach 2 Wh / L of Ed. Nitro modificationNO2C+of the core allowed to increase this value by 5 times, while substitution of the alkyl arms byAtty. Dkt. No.: 118537-0601PEGs led to values above 10 Wh / L. However, the second generation of DMQA+, even optimized in the formofNO2 / PEGc+, does not reach 20Wh / L of Ed. The compounds for carbeniums C+,NO2C+,PEGC+andNO2 / PEGC+have the following structures:

[0077] Due to its high solubility (>1000mM in CH3CN), the tri-cationictcC compound reaches a value of 65 Wh / L in energy density, which is almost three times that of commercial VRFBs (FIG. 6).

[0078] Example 3. Redox Flow Battery Prototype For Heterocyclic Carbocation Electrolyte.

[0079] A commercially available electrochemical cell was used for studies as described in Examples 1 and 2, but it led to several hardware difficulties and chemical compatibilities: compatibility of pump tubing the solvent CH3CN used (leading to cracked tubing in the peristatic pump), nature of the BPP (leading to BPP absorbing the solvent), leakage at the interface, as well as the membrane compatibility due to pressure or radical formation(leading to carbon felt “leaks” or “toasted” membranes).

[0080] Flow cell measurements were carried out on a BioLogic SP-200 (galvanostatic mode) and the EC -Lab® software (vl 1.33) (BioLogic Science Instruments) in an argon- filled glovebox. A 5 cm2single-cell flow battery (Fuel Cell Technologies Inc., see figureAtty. Dkt. No.: 118537-0601 below) was utilized with the acid cell configuration, allowing the tubing to feed directly into the flow plate with no contact with the metallic frame. The cell was from a supplier with aluminium end plates, electrically insulated from the gold plate current collector (CC), which was in contact with a graphite bipolar plate (BPP) with an engraved serpentine flow path that guided the liquid electrolyte. A PTFE gasket (TG) with a cutout corresponding to the exchange surface of 5 cm2hosted the carbon felt electrodes (2x electrode), which were in direct contact with the exchange membrane (EM). This succession of 5 elements was repeated in reverse order on the other side of the EM to complete the assembly of the cell. Daramic-175 porous separators were purchased from Daramic LLC (Owensboro, KY) and used as exchange membrane between the anolyte and catholyte. ePTFE gaskets (Compressible ePTFE Plastic Sheet - 1 / 64" Thick, USA Sealing Inc.) were used in the flow cell to avoid leakage of liquid. Commercial carbon felt electrodes (Sigracet® 29AA, from SGL Carbon) and commercial separator were ultra-sonically cleaned with isopropanol and dried under vacuum prior to use (FIG. 8).

[0081] All components of the flow cell were dried in an oven overnight, assembled outside of the glovebox, and immediately brought into the glovebox through an antechamber via a 5-hour evacuation / argon backfill process. The assembled flow cell was allowed to equilibrate in the glovebox for 12 hours prior to use. If required, even more detailed assembly is available in the Supporting Information of the work of Marshak and coworkers (Dalton Trans. 2020, 49, 16047-16053).

[0082] Para. 1. A redox flow battery comprising: a catholyte comprising a first organic compound having a redox potential; an anolyte comprising a second organic compound having a redox potential; and a solvent comprising sulfolane or y-valerolactone; wherein the redox potential of the first organic compound is the same or higher than the redox potential of the second compound.

[0083] Para. 2. The redox flow battery of Para. 1, wherein the solvent further comprises acetonitrile or propylene carbonate.

[0084] Para. 3. The redox flow battery of Paras. 1 or 2, wherein the redox potential of theAtty. Dkt. No.: 118537-0601 first organic compound is higher than the redox potential of the second compound.

[0085] Para. 4. The redox flow battery of Para. 3, wherein the first compound and the second compound are different compounds.

[0086] Para. 5. The redox flow battery of Para. 3, wherein the first compound and the second compound are the same compounds.

[0087] Para. 6. The redox flow battery of Para. 5, wherein the first compound and the second compound each comprise a conjugated heterocyclic compound.

[0088] Para. 7. The redox flow battery of Para. 6, wherein the first compound comprises the conjugated heterocyclic compound in a first oxidation state, the second compound comprises the conjugated heterocyclic compound in a second oxidation state, and the first oxidation state is a higher oxidation state than the second oxidation state.

[0089] Para. 8. A redox flow battery comprising: a catholyte comprising a conjugated heterocyclic compound in a first oxidation state; an anolyte comprising a conjugated heterocyclic compound in a second oxidation state; and a solvent comprising sulfolane or y-valerolactone; wherein the first oxidation state is a higher oxidation state than the second oxidation state.

[0090] Para. 9. The redox flow battery of Para. 8, wherein the conjugated heterocyclic compound in the first oxidation state is a conjugated heterocyclic cationic compound, and / or wherein the conjugated heterocyclic compound in the second oxidation state is a conjugated heterocyclic cationic compound.

[0091] Para. 10. The redox flow battery of Paras. 8 or 9, wherein the solvent further comprises acetonitrile or propylene carbonate.

[0092] Para. 11. A redox flow battery comprising: a catholyte comprising a compound of Formula I; andAtty. Dkt. No.: 118537-0601 an anolyte comprising the compound of Formula I; wherein the compound of Formula (I) is represented by the following structure:wherein:X is -4, -3, -2, -1, 0, +1, +2, +3, or +4; each Rla, Rlb, Rlc, R2a, R2b, R2c, R2d, R3a, R3b, R3c, and R3dis independently H, halide, CF3, CBr3, CI3, NH2, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, CO2R, or Ar1; each Y is independently -L-Z; each L is independently C1-C12 alkylene; each Z is independently -N(R4a)3W; each R4ais independently C1-C12 alkyl; each W is independently tetrafluoroborate, hexafluorophosphate, perchlorate, tetrary lb orate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, or sulfite; each Ar1is independently unsubstituted or substituted phenyl or unsubstituted or substituted heteroaryl; each Ar1is independently substituted with 0 to 5 substituents; the substituents are each independently selected from the group consisting of halide, CF3, NH2, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, or aryl.

[0093] Para. 12. The redox flow battery of Para. 11, wherein the compound of Formula I in the catholyte comprises a radical dication and / or wherein the compound of Formula I in the anolyte comprises a neutral radical.Atty. Dkt. No.: 118537-0601

[0094] Para. 13. The redox flow battery of claim 10, wherein: each Y is -CH2-CH2-CH2-N(Me)3W; each W is hexafluorophosphate or trifluoromethanesulfonate, each Rla, Rlb, Rlc, R2b, R2c, R2d, R3a, R3b, and R3cis independently H; and R2aand R3dare methoxy.

[0095] Para. 14. The redox flow battery of any one of Paras. 11-13, wherein the compound of Formula I is:

[0096] Para. 15. The redox flow battery of any one of Paras. 1-14 further comprising a separator disposed between the anolyte and the catholyte.

[0097] Para. 16. The redox flow battery of any one of Paras. 1-15 further comprising an electrolyte salt.

[0098] Para. 17. The redox flow battery of Para. 16, wherein the electrolyte salt is a lithium, sodium, potassium, ammonium, or alkylammonium salt of tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof.

[0099] Para. 18. The redox flow battery of any one of Paras. 11-17 further comprising a solvent.

[0100] Para. 19. The redox flow battery of Para. 18, wherein the solvent comprises a nitrile solvent, an ether solvent, dimethylformamide, water, a halogenated solvent, an ionic liquid, sulfolane, y- valerolactone, acetonitrile, or propylene carbonate, or a mixture of anyAtty. Dkt. No.: 118537-0601 two or more thereof.

[0101] Para. 20. A method of operating the redox flow battery of any one of Paras. 1-19 the method comprising: flowing the catholyte through a catholyte compartment and flowing the anolyte through an anolyte compartment, wherein the catholyte and anolyte compartments are separated by a separator and electron transfer from the anolyte to the catholyte is supported.

[0102] Para. 21. The method of Para. 20, wherein after electron transfer, the method comprises regenerating the catholyte and / or the anolyte by an external power source.

[0103] Para. 22. The redox flow battery of any one of Paras. 1-19, wherein the redox flow battery is an open redox flow battery cell comprising one or more current collectors, one or more graphite bipolar plates, one or more teflon gaskets, carbon felt electrodes, and a porous separator comprising an exchange membrane.

[0104] While certain embodiments have been illustrated and described, it should be understood that changes and modifications can be made therein in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the following claims.

[0105] The embodiments, illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms “comprising,” “including,” “containing,” etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claimed technology. Additionally, the phrase “consisting essentially of’ will be understood to include those elements specifically recited and those additional elements that do not materially affect the basic and novel characteristics of the claimed technology. The phrase “consisting of’ excludes any element not specified.Atty. Dkt. No.: 118537-0601

[0106] The present disclosure is not to be limited in terms of the particular embodiments described in this application. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and compositions within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds, compositions, or biological systems, which can of course vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0107] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0108] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a nonlimiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like, include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.

[0109] All publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individuallyAtty. Dkt. No.: 118537-0601 indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.

[0110] Other embodiments are set forth in the following claims.

Claims

Atty. Dkt. No.: 118537-0601WHAT IS CLAIMED IS:

1. A redox flow battery comprising: a catholyte comprising a first organic compound having a redox potential; an anolyte comprising a second organic compound having a redox potential; and a solvent comprising sulfolane or y-valerolactone; wherein the redox potential of the first organic compound is the same or higher than the redox potential of the second compound.

2. The redox flow battery of claim 1, wherein the solvent further comprises acetonitrile or propylene carbonate.

3. The redox flow battery of claim 1 or 2, wherein the redox potential of the first organic compound is higher than the redox potential of the second compound.

4. The redox flow battery of claim 3, wherein the first compound and the second compound are different compounds.

5. The redox flow battery of claim 3, wherein the first compound and the second compound are the same compounds.

6. The redox flow battery of claim 5, wherein the first compound and the second compound each comprise a conjugated heterocyclic compound.

7. The redox flow battery of claim 6, wherein the first compound comprises the conjugated heterocyclic compound in a first oxidation state, the second compound comprises the conjugated heterocyclic compound in a second oxidation state, and the first oxidation state is a higher oxidation state than the second oxidation state.

8. A redox flow battery comprising: a catholyte comprising a conjugated heterocyclic compound in a first oxidation state; an anolyte comprising a conjugated heterocyclic compound in a second oxidation state;Atty. Dkt. No.: 118537-0601 and a solvent comprising sulfolane or y-valerolactone; wherein the first oxidation state is a higher oxidation state than the second oxidation state.

9. The redox flow battery of claim 8, wherein the conjugated heterocyclic compound in the first oxidation state is a conjugated heterocyclic cationic compound, and / or wherein the conjugated heterocyclic compound in the second oxidation state is a conjugated heterocyclic cationic compound.

10. The redox flow battery of claim 8 or 9, wherein the solvent further comprises acetonitrile or propylene carbonate.

11. A redox flow battery comprising: a catholyte comprising a compound of Formula I; and an anolyte comprising the compound of Formula I; wherein the compound of Formula (I) is represented by the following structure:wherein:X is -4, -3, -2, -1, 0, +1, +2, +3, or +4; each Rla, Rlb, Rlc, R2a, R2b, R2c, R2d, R3a, R3b, R3c, and R3dis independently H, halide, CF3, CBr3, CI3, NH2, C1-C12 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, CO2R, or Ar1; each Y is independently -L-Z;Atty. Dkt. No.: 118537-0601 each L is independently C1-C12 alkylene; each Z is independently -N(R4a)sW; each R4ais independently C1-C12 alkyl; each W is independently tetrafluoroborate, hexafluorophosphate, perchlorate, tetrary lb orate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide, hydroxide, carbonate, bicarbonate, sulfate, hydrogen sulfate, or sulfite; each Ar1is independently unsubstituted or substituted phenyl or unsubstituted or substituted heteroaryl; each Ar1is independently substituted with 0 to 5 substituents; the substituents are each independently selected from the group consisting of halide, CF3, NH2, C1-C4 alkyl, C1-C4 alkoxy, C1-C4 alkylamino, C1-C4 dialkyl amino, NO2, CN, or aryl.

12. The redox flow battery of claim 11, wherein the compound of Formula I in the catholyte comprises a radical dication and / or wherein the compound of Formula I in the anolyte comprises a neutral radical.

13. The redox flow battery of claim 11 or 12, wherein: each Y is -CH2-CH2-CH2-N(Me)3W; each W is hexafluorophosphate or trifluoromethanesulfonate, each Rla, Rlb, Rlc, R2b, R2c, R2d, R3a, R3b, and R3cis independently H; and R2aand R3dare methoxy.

14. The redox flow battery of claim 11, wherein the compound of Formula I is:Atty. Dkt. No.: 118537-060115. The redox flow battery of claim 1 further comprising a separator disposed between the anolyte and the catholyte.

16. The redox flow battery of claim 1 further comprising an electrolyte salt.

17. The redox flow battery of claim 16, wherein the electrolyte salt is a lithium, sodium, potassium, ammonium, or alkylammonium salt of tetrafluoroborate, hexafluorophosphate, perchlorate, tetrarylborate, trifluoromethanesulfonate, oxalatob orate, oxalate, phosphate, bis-trifluoromethanesulfonimide, halide; or a mixture of any two or more thereof.

18. The redox flow battery of claim 11 further comprising a solvent.

19. The redox flow battery of claim 18, wherein the solvent comprises a nitrile solvent, an ether solvent, dimethylformamide, water, a halogenated solvent, an ionic liquid, sulfolane, y- valerolactone, acetonitrile, propylene carbonate, or a mixture of any two or more thereof.

20. A method of operating the redox flow battery of claim 1, the method comprising: flowing the catholyte through a catholyte compartment and flowing the anolyte through an anolyte compartment, wherein the catholyte and anolyte compartments are separated by a separator and electron transfer from the anolyte to the catholyte is supported.

21. The method of claim 20, wherein after electron transfer, the method comprises regenerating the catholyte and / or the anolyte by an external power source.

22. The redox flow battery of claim 1, wherein the redox flow battery is an open redox flow battery cell comprising one or more current collectors, one or more graphite bipolar plates, one or more teflon gaskets, carbon felt electrodes, and a porous separator comprising an exchange membrane.

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