Redox flow battery electrolytes with 2,5-dimercapto-1,3,4-thiadiazole ("DMTD") and derivatives thereof

Abstract

The disclosed technology relates to redox flow batteries (“RFB”), and more specifically to electrolytes based on 2,5-dimercapto-1,3,4-thiadiazole (“DMTD”) and its derivatives that can be used in RFB.

Description

Background Technology

[0001] The disclosed technology relates to redox flow batteries (“RFB”), and more specifically to electrolytes based on 2,5-dimercapto-1,3,4-thiadiazole (“DMTD”) and its derivatives that can be used in RFB.

[0002] Redox flow batteries (“RFBs”) are a promising new technology for utilizing renewable energy sources (e.g., solar and wind power) in future large-scale stationary energy storage applications. While current commercial RFBs use electrolytes based on vanadium metal dissolved in strong inorganic acids, major players in the industry will ultimately prefer electrolytes free of heavy metals, composed of non-corrosive and non-toxic organic compounds. Therefore, sustainable, low-cost organic-based RFB electrolytes with highly reversible redox properties and high specific energy retention after multiple cycles will be of great interest to this emerging and developing industry.

[0003] Examples of electrolyte organic chemistry in this field typically begin with some or all of relatively expensive starting materials and reagents, may require multiple steps to obtain the target end product, generate a large amount of undesirable process waste, and may also require cumbersome purification steps.

[0004] The use of organic redox compounds in RFB electrolytes is known. For example, G. Yu; *Chemical Society Reviews*. 47 Pages 69-103 (2018): Molecular engineering of organic electroactive materials for redox flow batteries provides general teachings on the prior art regarding organic RFB materials. US9,812,883B1, granted to Brushett on November 7, 2017, teaches RFB electrolytes containing a quinoxaline moiety; both US2016 / 0248114, published August 25, 2016, and US2016 / 0043423, published February 11, 2016, granted to Huskinson, teach RFB electrolytes containing a quinone or hydroquinone moiety; and US2018 / 0331363, published November 15, 2018, granted to Winsberg, teaches RFB electrolytes containing a 2,2,6,6-tetramethylpiperidinyloxy moiety.

[0005] DMTD derivatives have previously been used in electrochemical methods. For example, US Patent 6,340,539, granted to Yamaguchi on January 22, 2002, teaches the use of DMTD dilithium dihydrate salts as cathode materials in lithium-ion batteries. Similarly, T. Sotomura et al., *Nature*... 373 Page 598 (1995): Dimercaptan-Polyaniline Composite Electrodes for Lithium Batteries teaches the use of dimercaptan-polyaniline composite electrodes for lithium batteries. J. Lee: *Electrochimica Acta* 286 (2018) A Non-Absorbing Organic Redox Couple for Sensitization-Based Solar Cells with Metal-Free Counter Electrode teaches the use of 5-methylthio-1,3,4-thiadiazole-2-thiol and its oxidized dimer as a redox couple in sensitization-based solar cells, which may be a potential alternative to silicon-based photovoltaic devices.

[0006] However, the starting materials used in these compositions are either difficult to obtain, expensive, and do not provide the reversibility necessary for RFB applications, or their production processes are difficult and lead to undesirable waste. Similarly, the foregoing does not teach or suggest the use of DMTD or its derivatives as redox compounds for RFB electrolytes. Therefore, there is a need for inexpensive and readily produced organic compounds with reversible redox behavior to advance the RFB space. Summary of the Invention

[0007] Therefore, the disclosed technology solves the problems of difficult-to-produce and expensive but easily oxidized organic chemistry by providing an electrolyte containing DMTD or its derivatives for RFB batteries. Furthermore, the technology provides DMTD derivatives that can be conditioned to be soluble in a chosen medium, particularly an aqueous medium, where DMTD itself and some of its derivatives are inherently insoluble, while providing compounds with desired redox potentials.

[0008] In one embodiment, a redox flow battery electrolyte is provided, comprising: A) a polar solvent; and B) DMTD or a derivative thereof.

[0009] The polar solvent in the electrolyte described above can be, for example, water. The polar solvent can also be, for example, acetonitrile. In some embodiments, the polar solvent can be an organic solvent, such as a carbonate, ether, and / or glycol.

[0010] The DMTD derivative may comprise a monoalkylated DMTD compound. Such a monoalkylated DMTD compound may be prepared, for example, by a simple alkylation method using DMTD and an alkyl halide, and optionally an oxidizing agent such as hydrogen peroxide.

[0011] The DMTD derivative may also comprise an etherified DMTD compound. Such an etherified DMTD compound can be prepared, for example, by a simple alkylation method using DMTD and an ether halide, and optionally an oxidizing agent such as hydrogen peroxide.

[0012] The DMTD derivative may comprise a mono-alcohol DMTD compound. Such a mono-alkylated DMTD compound may be prepared, for example, by a simple alkylation method of DMTD and an alcohol halide, or by an epoxidation reaction of an epoxide and optionally an oxidizing agent such as hydrogen peroxide.

[0013] The DMTD derivatives also comprise DMTD-substituted esters or amides. Such DMTD-substituted esters and amides can be prepared, for example, by Michael-like conjugation addition with, for example, activated olefin-containing carboxylic acid esters or carboxamides, which can provide high conversion rates and generate virtually no process waste. These esters and amides can optionally be further reacted with a base and / or an oxidizing agent such as hydrogen peroxide.

[0014] The DMTD derivatives also comprise water-soluble esters or amides of DMTD. Such water-soluble esters or amides of DMTD can be obtained, for example, by adding DMTD to an activated reagent containing a quaternary nitrogen halide group and optionally a base and / or an oxidizing agent such as hydrogen peroxide.

[0015] DMTD derivatives also include zwitterionic DMTD esters or amides. Such zwitterionic DMTD esters or amides can be prepared, for example, by treating water-soluble DMTD esters or amides with a strong base.

[0016] The DMTD or its derivatives may be included in the electrolyte at a rate of about 1 wt.% to about 50 wt.%.

[0017] The electrolyte may also contain a supporting electrolyte to help make the electrolyte solution conductive, said supporting electrolyte being present in an amount from about 0.1 wt.% to about 20 wt.%. Currently envisioned supporting electrolytes may include, but are not limited to, lithium salts, sodium salts, potassium salts, and mixtures thereof.

[0018] A redox flow battery system is also provided, comprising the above-described electrolyte. In this battery system, during a state of charge, the electrolyte forms: A) an anolyte comprising DSSD and 2DS... - A) a polar solvent of the form or a mixture thereof; and B) a cathode electrolyte, said cathode electrolyte comprising DSSD or 2S - Polar solvents of or mixtures thereof.

[0019] The redox flow battery system may include an ion exchange membrane or a microporous membrane through which the electrolyte can readily flow. Current membranes envisioned for RFB systems include, but are not limited to, fluoropolymer-polymer copolymer membranes based on sulfonated tetrafluoroethylene, such as cellulose-based dialysis membranes, and functionalized polystyrene membranes blended with polyvinyl chloride. Detailed Implementation

[0020] The preferred features and embodiments will be described below in a non-limiting manner.

[0021] The present invention comprises an electrolyte that can be used in a redox flow battery (“RFB”). The electrolyte comprises: A) a polar solvent; and B) 2,5-dimercapto-1,3,4-thiadiazole (“DMTD”) or a derivative thereof.

[0022] The polar solvent can be any solvent in which DMTD or its derivatives are soluble in both their oxidized and reduced states. The solvent should also remain inert under the operating conditions of the RFB. It is anticipated that those skilled in the art can readily determine the solubility and inertness of a suitable solvent and thus select an appropriate solvent. The simplest solvent used for the techniques of this invention can be water. Polar solvents can also be, for example, alcohols, such as C1 to C2 alcohols. 10Alcohols or diols, including, for example, methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, and propylene glycol. Ethers can also be used as solvents, including, for example, dimethoxymethane, methoxybenzene (anisole), tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolane (DOL), 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane (DME), and bis(2-methoxyethyl) ether (diethylene glycol dimethyl ether). Polar solvents can also be ketones, such as acetone or acetylacetone. Nitriles, such as acetonitrile (CAN), methoxyacetonitrile, propionitrile, butyronitrile, isobutyronitrile, benzyl nitrile, and 3-methoxypropionitrile, can be used as solvents. Amines such as ethylenediamine and pyridine, or amines such as formamide, n-methylacetamide, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), and N-methyl-2-pyrrolidone (NMP) can also be used as solvents. Solvents can also be carbonates. Non-limiting examples of carbonates include propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone (γ-BL), γ-valerolactone (γ-VL), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and 1,2-butenyl carbonate. Other organic-based solvents, such as hexane, benzene, toluene, nitromethane, nitrobenzene, 1,2-dichloroethane, dimethyl sulfoxide (DMSO), ethyl acetate, and nitrobenzene, are also considered, to name just a few. The solvent can also be any combination of the aforementioned solvents.

[0023] Electrolytes may contain DMTD itself, DMTD derivatives themselves, or combinations thereof. DMTD derivatives may include, for example, monoalkylated DMTD compounds, DMTD ethers, DMTD esters, DMTD amides, DMTD alcohols, and zwitterionic DMTD esters, amides, and alcohols. Derivatives may be provided as pure compounds, but most commonly as mixtures of compounds.

[0024] DMTD derivatives comprise the reaction products of DMTD and other chemical reagents through a variety of different chemical reactions. These reactions include acid-based reactions, substitution with electron-deficient hydrocarbons, 1,4-addition to alkenes, disulfide formation, and ring-opening reactions of epoxides. These reactions can proceed in the presence of a wide range of functional groups that can provide the desired solubility and electrochemical performance. These functional groups include carbonyl-containing molecules, heteroatom-containing molecules (nitrogen, oxygen, sulfur), inorganic atoms, and unsaturation.

[0025] DMTD derivatives can therefore be, for example, reaction products of DMTD with a haloalkyl or aryl "group" and optionally a base and / or an oxidizing agent. DMTD derivatives can also be reaction products of DMTD with a haloether ("halo-ether") group (which includes simple ethers and polyethers) and optionally a base and / or an oxidizing agent. DMTD derivatives can also be reaction products of DMTD with a carboxylic acid ester group and optionally a base and / or an oxidizing agent. DMTD derivatives can also be reaction products of DMTD with a carboxamide group and optionally a base and / or an oxidizing agent. DMTD derivatives can also be reaction products of DMTD with a haloalcohol ("halo-alcohol") group or an epoxy group and optionally a base and / or an oxidizing agent.

[0026] As used herein, depending on the context, the term "group" in, for example, alkyl or aryl, haloether, haloalcohol, (meth)acrylate, and (meth)acrylamide groups, refers to the structure of the group itself or the structure that the group will form upon reaction with another compound. For example, methyl can be CH4 as in its lone state or -CH3 as in its bonded form, or as another example, methyl acrylate can refer to CH2=CHC(O)OCH3 as in its lone state or -CH2CHC(O)OCH3 as in its bonded form.

[0027] As used herein, the parentheses “()” surrounding the term “methyl” indicate that the term “methyl” may or may not be present. Therefore, (meth)acrylate can refer to both acrylate and methacrylate, and (meth)acrylamide includes both acrylamide and methacrylamide.

[0028] Typically, DMTD derivatives can be represented by formula I:

[0029] Formula I

[0030]

[0031] in

[0032] Each “X” is individually an alkali metal or alkaline earth metal, such as Li, Na, K, Mg, or Ca; a trialkylamine or quaternary ammonium (containing ammonia for the purposes of this disclosure); or H;

[0033] "m" is 1, 2, or 3, and "n" is 1 or 2; and

[0034] Where “Y” is:

[0035] “R”, straight chain, branched chain, saturated or unsaturated or cyclic C1 to C2 12 Or from C1 to C 10Or C1 to C8 or even C1 to C6 alkyl or aryl; or H;

[0036] [RO] o R", where "o" is an integer from 1 to 100;

[0037] “R[OH] p "A", where "p" is an integer from 1 to 6 and "A" is H or an amine, such as a trialkylamine or a quaternary ammonium salt; or

[0038] A carboxylic acid ester group or a carboxamide group, such as itaconic acid ester, maleic acid ester, or (meth)acrylate or (meth)acrylamide that will form "CH2CH[CH3 or H]C(O)[O or NH]Z", wherein "Z" can be H, X, "R", or RN. + (R)3SO3 - RN + (R)3SO3 - K + "RSO3" - Na + ", RSO3 - NH4 + "RSO3H" or "RN" + (R)3Cl - ".

[0039] A base can be used in the preparation of DMTD derivatives. This base can be, for example, an alkali metal or alkaline earth metal hydroxide or carbonate, or an amine, such as a trialkylamine or quaternary ammonium. Alternatively, a strong base can be used after the preparation of the derivative to induce deprotonation of the unsubstituted sulfur atom. In either case, if a base is used, then “X” in Formula I can be an alkali metal or alkaline earth metal, such as Li, Na, K, Mg, or Ca, or a trialkylamine or quaternary ammonium. If no base is used, then “X” will be H, and the associated positive and negative charges will be absent.

[0040] Formula I can be achieved through unsubstituted sulfur atoms, i.e., "S" - m “”, coupled or uncoupled. In the case that the DMTD derivative is not sulfur-coupled, “n” in Equation 1 will be 1 and “m” will be 1, as shown in Equation II below.

[0041] Formula II

[0042]

[0043] In the case of a sulfur-coupled DMTD derivative, "n" in Formula I will be 2, "m" can be 1, 2, or 3, and "X" and its associated positive and negative charges will be absent. Such coupled DMTD derivatives can be prepared by preparing an uncoupled compound and then introducing an oxidizing agent such as hydrogen peroxide or other agents known to those skilled in the art. Examples of coupled DMTD derivatives are shown in Formulas III, IV, and V below.

[0044] Formula III

[0045]

[0046] Formula IV

[0047]

[0048] Formula V

[0049]

[0050] The substituent Y in the aforementioned DMTD derivative can be derived from a straight-chain, branched, saturated or unsaturated, or cyclic alkyl or aryl group (unsaturated alkyl is synonymous with olefin). In such embodiments, DMTD can be alkylated or arylated with an alkyl or aryl halide to obtain a monoalkylated DMTD derivative, and then optionally salted with an equivalent amount of a base (i.e., the base or alkaline earth metal or amine that will provide "X"). Although the substituent can be a saturated alkyl or aryl group, the derivative is collectively referred to herein and in the claims as a "monoalkylated" DMTD derivative. Such a monoalkylated DMTD derivative can be a mixture of sulfide-coupled and uncoupled species as described above. A monoalkylated DMTD derivative can be represented by formula VI:

[0051] Style VI

[0052]

[0053] Where X, m, and n are as described in Equation I, and R is a straight-chain, branched, saturated or unsaturated, cyclic C1 to C2 chain. 12 Or from C1 to C 10 Or C1 to C8 or even C1 to C6 alkyl or aryl; or H.

[0054] Examples of R groups may include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl, including their branched forms such as isobutyl, ethylhexyl, isopentyl, etc., as well as aromatic groups (e.g., benzyl) or cyclic groups (e.g., cyclohexyl).

[0055] In some embodiments, DMTD may be reacted with a benzyl halide and optionally a base and / or an oxidizing agent to provide a monoarylated DMTD derivative of one or more of formula VI (1), (2), (3) or (4).

[0056]

[0057] The substituent Y in the DMTD derivative of Formula I can be derived from an ether group. In such embodiments, DMTD can be etherified with a haloether to obtain a monoether DMTD derivative, and then optionally salted with an equivalent amount of a base (i.e., the base or alkaline earth metal or amine that will provide "X"). This monoether DMTD derivative can be a mixture of sulfide-coupled and uncoupled species as described above. The monoether DMTD derivative can be represented by Formula VII:

[0058] Equation VII

[0059]

[0060] Where X, R, m and n are as described in Equation I, and “o” is an integer from 1 to 100 or 1 to 75 or 1 to 50 or 1 to 25 or 1 to 20 or 1 to 15 or 1 to 10 or 2 to 10 or 4 to 10 or 6 to 10.

[0061] Examples of usable simple ethers (i.e., [RO]) o The R group (where o is 1) includes dimethyl ether (both Rs are methyl, o is 1), diethyl ether (both Rs are ethyl, o is 1), dipropyl ether (both Rs are propyl, o is 1), methyl ethyl ether (one R is methyl, one R is ethyl, o is 1), and methyl phenyl ether (one R is methyl, one R is n-phenyl, o is 1).

[0062] Example polyethers that can be used (i.e., [RO]) o The R group (where o is 2 to 100) contains paraformaldehyde (i.e., [RO)). o R groups, where repeating R is methyl and non-repeating R is H, o is 8 to 100), polyethylene glycol (i.e., [RO)). o R groups, where repeating R is ethyl and non-repeating R is H, and o is 2 to 100), polypropylene glycol (i.e., [RO)). o R groups, where repeating R is isopropyl and non-repeating R is H, and o is 2 to 100), polytetrahydrofuran (i.e., [RO)). o R group, wherein repeating R is butyl and non-repeating R is H, and o is 2 to 100).

[0063] In some embodiments, DMTD can be reacted with a halomethyl ether and optionally with a base and / or an oxidizing agent to provide a monoether DMTD derivative of one or more of formula VII(1), (2), (3) or (4).

[0064]

[0065] In some embodiments, DMTD can be reacted with a polyethylene glycol halide and optionally a base and / or an oxidizing agent to provide a monoether DMTD derivative of one or more of formula VII(5), (6), (7) or (8):

[0066]

[0067] The substituent Y of the DMTD derivative of Formula I can also be derived from a haloalcohol or an epoxy group. In such embodiments, DMTD can be reacted with a haloalcohol or an epoxide to give a monool DMTD derivative, and then optionally salted with an equivalent base (i.e., an alkali metal or alkaline earth metal or amine that will provide "X"). This monool DMTD derivative can be a mixture of sulfide-coupled and uncoupled species as described above. The monool DMTD derivative can be represented by Formula VIII:

[0068] Formula VIII

[0069]

[0070] Where X, R, m, and n are as described in Formula I, and “p” is an integer from 1 to 6 and “A” is H or an amine, such as a trialkylamine or a quaternary ammonium salt.

[0071] Example monools (i.e., R[OH]) p Group A, where p is 1 and A is H, comprises propanol (i.e., R is straight-chain or branched propyl), which is obtained from, for example, a halopropanol, such as chloropropanol or propylene oxide; hexanol (i.e., R is straight-chain or branched hexyl), which is obtained from, for example, a halohexanol, such as chlorohexanol; butanol (i.e., R is straight-chain or branched butyl), which is obtained from, for example, a halobutanol, such as chlorobutanol or propylene oxide; and phenylpropanol (i.e., R is propyl or ethylbenzene), which is obtained from, for example, a halophenylpropanol group, such as chlorophenylethanol or styrene oxide.

[0072] Examples of polyols that can be used (i.e., R[OH]) p Group A, where p is 2 to 6 and A is H, includes sugar alcohols, polyvinyl alcohol, ethylene glycol (i.e., R is ethyl and p is 2), propylene glycol (i.e., R is linear or branched propyl and p is 2), butylene glycol (i.e., R is linear or branched butyl and p is 2), and glycerol (i.e., R is butyl and p is 3).

[0073] Examples of usable alkanolamines (i.e., R[OH]) p The A group (where A is an amine) includes ethanolamine (i.e., R is ethyl, p is 1, A is NH2), propanolamine (i.e., R is propyl, p is 1, A is NH2), propanol dimethylamine (i.e., R is propyl, p is 1, A is N(CH3)2), and propanol quaternary ammonium halide salt (i.e., R is propyl, p is 1, A is N). + (CH3)3·Cl - ).

[0074] In some embodiments, DMTD may be reacted with glycidyl and optionally with a base and / or an oxidizing agent to provide a monool derivative of one or more of formula VIII(1), (2), (3) or (4).

[0075]

[0076] In some embodiments, DMTD may be reacted with glycidyl methacrylate and optionally with a base and / or an oxidizing agent to provide a monool derivative of one or more of formula VIII (5), (6), (7) or (8).

[0077]

[0078] In some embodiments, DMTD may be reacted with a 2-epoxy quaternary ethylamine halide and optionally with a base and / or an oxidizing agent to provide a monool derivative of one or more of formula VIII (9), (10), (11) or (12).

[0079]

[0080]

[0081] In some embodiments, DMTD can be reacted with an activated olefin-containing carboxylic acid ester or carboxamide in a Michael-like conjugate addition reaction to yield a substituted ester DMTD derivative, and optionally salted with an equivalent base (i.e., a base or alkaline earth metal or amine that will provide "X"). Such a monocarboxylic acid ester / carboxamide DMTD derivative can be a mixture of sulfide-coupled and uncoupled species as described above.

[0082] Those skilled in the art will readily conceive of carboxylic acid ester groups capable of 1,4-addition, including monocarboxylic acid esters, dicarboxylic acid esters, and higher carboxylic acid esters, such as tricarboxylic acid esters, tetracarboxylic acid esters, etc. Example carboxylic acid esters may include, but are not limited to, itaconic acid esters, citrate esters, maleate esters, fumarate esters, mesocarboxylic acid esters, and (meth)acrylates. Carboxylic acid esters may be in the form of salts having an alkali metal or alkaline earth metal amino group or esters having an "R" group. Where a salt is required, the carboxylic acid ester can be obtained by 1,4-addition to a salt-forming monomer or by adding an ester followed by saponification with an alkali metal or alkaline earth metal hydroxide or ammonium hydroxide.

[0083] Typically, carboxylic acid esters containing DMTD derivatives can be generated by a 1,4-addition reaction between DMTD and a carboxylic acid or a carboxylic acid ester. When the 1,4-addition is with a carboxylic acid, the reaction is followed by a reaction with a desired base to form a salt. For example, DMTD can react with aconitic acid to form a DMTD derivative, wherein the aconitic acid is attached to a substituent sulfur, and subsequently reacts with an alkali metal hydroxide, an alkaline earth metal hydroxide, or ammonium hydroxide. This reaction can be represented, for example, by the following reaction mechanism:

[0084]

[0085] Another example can be a carboxylic acid ester containing a DMTD derivative, generated by a 1,4-addition reaction between DMTD and a dialkyl itaconic acid ester such as dimethyl itaconic acid, wherein the substituent Y of the DMTD derivative of formula I is dimethyl itaconic acid, for example, as represented by the following formula:

[0086]

[0087] In the foregoing examples, the carboxylic acid ester can also be, for example, a dialkali metal salt or alkaline earth metal salt of itaconic acid, such as disodium itaconic acid, represented by, for example, the following formula:

[0088]

[0089] Another example of a carboxylic ester containing a DMTD derivative can be produced by a 1,4-addition reaction between DMTD and a dialkyl maleate, such as dimethyl maleate, wherein the substituent Y of the DMTD derivative of formula I will be dimethyl maleate, as represented by the following formula:

[0090]

[0091] In the foregoing examples, the carboxylic acid ester can also be, for example, a dialkali metal salt or an alkaline earth metal salt of maleate, such as disodium maleate, represented by, for example, the following formula:

[0092]

[0093] Other examples may involve reactions of, for example, methyl acrylate with DMTD or dimethyl maleate with DMTD. Where a salt is required, these examples may also involve reactions of, for example, sodium acrylate or disodium maleate, or the aforementioned esters may be saponified in the presence of sodium hydroxide to obtain a salt.

[0094] Those skilled in the art will readily conceive of carboxamide groups capable of 1,4-addition, and including monocarboxamides and dicarboxamides. Examples of carboxamides may include, but are not limited to, itacamide, citrileamide, maleamide, fumaramide, mesocarboxamide, and (meth)acrylamide. Carboxamides can be primary amides, or can be substituted with one or more "R" groups to form secondary or tertiary amide groups.

[0095] One aspect of this technology comprises (meth)acrylates and (meth)acrylamide derivatives of DMTD. In one embodiment, the (meth)acrylate or (meth)acrylamide may contain a quaternary ammonium group or a sulfate group. In either case (acrylate or amide), the ester or amide derivative may be represented by the following formula:

[0096] Formula IX

[0097]

[0098] Where X, m, and n are as described in Equation I, and “Z” is H, X, “R”, RSO3 - Na + , RSO3H, RN + (R)3SO3 - RN + (R)3SO3 - K + , RSO3 - NH4 + or RN + (R)3Cl - .

[0099] In some embodiments, DMTD can be reacted with methyl acrylate to provide a monoacrylate DMTD derivative of formula IX in a coupled or uncoupled form, wherein Z is CH3, m is 1, 2 or 3, n is 1 or 2, and X is optionally an alkali metal or alkaline earth metal or an amine.

[0100] In some embodiments, DMTD can be reacted with 2-ethylhexyl acrylate to provide a monoacrylate DMTD derivative of formula IX in a coupled or uncoupled form, wherein Z is 2-ethylhexyl, m is 1, 2 or 3, n is 1 or 2, and X is optionally an alkali metal or alkaline earth metal or an amine.

[0101] In some embodiments, DMTD can be reacted with methacryloyloxyethyltrimethylammonium chloride to provide a monomethacrylate DMTD derivative of formula IX in a coupled or uncoupled form, wherein Z is (CH2)2N. + (CH3)3Cl - m is 1, 2 or 3 and n is 1 or 2, and X is an optional alkali metal or alkaline earth metal or amine.

[0102] In some embodiments, DMTD can be reacted with methacryloylaminopropyltrimethylammonium chloride to provide a monomethacrylamide DMTD derivative of formula IX in a coupled or uncoupled form, wherein Z is (CH2)3N + (CH3)3Cl - m is 1, 2 or 3 and n is 1 or 2, and X is an optional alkali metal or alkaline earth metal or amine.

[0103] In some embodiments, DMTD can be reacted with 2-acryloylamino-2-methylpropanesulfonic acid to provide a DMTD derivative of formula IX in a coupled or uncoupled form, wherein Z is C(CH3)2CH2SO3H, m is 1, 2 or 3 and n is 1 or 2, and X is optionally an alkali metal or alkaline earth metal or an amine.

[0104] In some embodiments, DMTD can be reacted with sodium 2-acryloylamino-2-methylpropanesulfonate to provide a DMTD derivative of formula IX in a coupled or uncoupled form, wherein Z is C(CH3)2CH2SO3. - Na + m is 1, 2 or 3 and n is 1 or 2, and X is an optional alkali metal or alkaline earth metal or amine.

[0105] In some embodiments, DMTD esters or amide derivatives (such as those discussed above) can be treated with strong bases such as LiOH, NaOH, KOH, Ca(OH)2, or quaternary ammonium compounds such as R4NOH to produce zwitterionic species as shown in Formula X:

[0106] Formula X

[0107]

[0108] For example, DMTD can be reacted with methacryloylaminopropyltrimethylammonium chloride to provide a monomethacrylamide DMTD derivative of formula IX, wherein Z is (CH2)3N + (CH3)3Cl - m is 1, 2, or 3 and n is 1 or 2, then treated with NaOH to obtain a zwitterion of formula X':

[0109] Formula X'

[0110]

[0111] DMTD or its derivatives may be included in the electrolyte in amounts from about 1 wt.% to about 50 wt.%, or in some cases, from about 2.5 wt.% to about 30 wt.%, or even from about 5 wt.% to about 25 wt.%, or from about 10 wt.% to about 20 wt.%.

[0112] The electrolyte may also include a supporting electrolyte, which may be present in an amount from about 0.1 wt.% to about 20 wt.%, or from about 0.25 wt.% to about 15 wt.%, or even from about 0.5 wt.% to about 10 wt.% of the electrolyte. Such a supporting electrolyte may be present to make the solution more conductive. Currently envisioned supporting electrolytes may include, but are not limited to, lithium salts, sodium salts, potassium salts, and mixtures thereof. Examples of supporting electrolytes include, but are not limited to, sodium phosphate, sodium chloride, potassium phosphate, potassium chloride, potassium hexafluorophosphate, lithium hexafluorophosphate, tetrabutylammonium fluorophosphate, tetrabutylammonium chloride, lithium perchlorate, lithium nitrate, etc.

[0113] A redox flow battery system is also provided, comprising the electrolyte described above. In the battery system, during a state of charge, the electrolyte forms: A) an anolyte comprising a coupling compound (which may be referred to as DSSD) and two charged compounds (which may be referred to as 2DS). - A) a polar solvent of or a mixture thereof; and B) a cathodic electrolyte comprising DSSD or 2S. - or a polar solvent of a mixture thereof, wherein D is the main DMTD body, for example:

[0114]

[0115] And S originates from the salt-forming sulfur of the main DMTD host, for example:

[0116]

[0117] DSSD means, for example:

[0118]

[0119] And DS - This refers to, for example:

[0120]

[0121] Where Y is as described above.

[0122] The redox flow battery system may also include an ion exchange membrane or a microporous membrane through which the electrolyte can readily flow. Current membranes envisioned for RFB systems include, but are not limited to, fluoropolymer-polymer copolymer membranes based on sulfonated tetrafluoroethylene, such as cellulose-based dialysis membranes, and functionalized polystyrene membranes blended with polyvinyl chloride. However, any membrane that can prevent redox species cross-linking in both charge states and allow positive or negative ions to diffuse as charge carriers to maintain charge neutrality can be used.

[0123] Unless otherwise indicated, the amounts of each chemical component described are presented to exclude any solvents or diluents that are commonly found in commercial materials, i.e., based on the active chemicals. However, unless otherwise indicated, each chemical or composition mentioned herein should be interpreted as a commercial-grade material that may contain isomers, byproducts, derivatives, and other such materials as commonly understood to be present in commercial-grade materials.

[0124] Example

[0125] Sample 1: Synthesis of 2-(methylcarboxyethyl)thio-5-thiol-1,3,4-thiadiazole. 225 g of DMTD and 600 mL of toluene solvent were added to a 2 L flask, followed by the addition of 138.8 g of methyl acrylate over 30 minutes. An exothermic reaction occurred from 23 °C to 29 °C. The mixture was heated at 85 °C for six hours, after which the reaction became clear and all starting materials were dissolved. Toluene was vacuum stripped on a rotary evaporator to provide a solid upon cooling. This solid was recrystallized overnight in a refrigerator by final cooling from reagent-grade toluene:methanol 6:1 volume:volume. The product was dried in a vacuum oven at 90 °C for 16 hours to remove all recrystallization solvent.

[0126] Sample 2: Synthesis of 2-(ethylcarboxyethyl)thio-5-thiol-1,3,4-thiadiazole. 150.2 g of DMTD and 400 mL of toluene solvent were added to a 2 L flask, followed by the addition of 100.1 g of ethyl acrylate over 30 minutes. The mixture was heated at 85 °C for six hours, after which the reaction became clear and all starting materials dissolved. Toluene was vacuum stripped on a rotary evaporator under a 4 mmHg vacuum at 80 °C to provide the desired product as a solid upon cooling.

[0127] Sample 3: Synthesis of 2-(2-ethylhexylcarboxyethyl)thio-5-thiol-1,3,4-thiadiazole. 150.2 g of DMTD, 150 g of toluene solvent, and 184.3 g of 2-ethylhexyl acrylate were added to a 1 L flask, and the mixture was heated at 85 °C for 7 h. The toluene solvent was then stripped under vacuum at 2 mm Hg and 80 °C for 5 h on a rotary evaporator to provide the desired product as a yellow liquid.

[0128] Sample 4: Synthesis of 2-(n-butylcarboxyethyl)thio-5-thiol-1,3,4-thiadiazole. 150.2 g of DMTD and 450 mL of toluene solvent were added to a 2 L flask, followed by the addition of 128.2 g of n-butyl acrylate over 30 minutes. An exothermic reaction occurred from 23 °C to 28 °C. The mixture was heated at 80 °C for six hours, after which the reaction became clear and all starting materials dissolved. Toluene was vacuum stripped on a rotary evaporator under a 2 mm Hg vacuum at 80 °C to provide the desired product as a solid upon cooling.

[0129] Sample 5: Synthesis of 2-(2-hydroxyethylcarboxyethyl)thio-5-thiol-1,3,4-thiadiazole. 150.2 g of DMTD, 150 g of toluene solvent, and 120 g of 97% pure 2-hydroxyethyl acrylate were added to a 1 L flask, and the mixture was heated at 85 °C for five hours. The toluene solvent was then vacuum stripped at 3 mm Hg and 80 °C for four hours on a rotary evaporator. After filtration through a silica filter aid, a viscous yellow liquid product was obtained.

[0130] Sample 6: Synthesis of 2-(2-ethoxyethoxycarboxyethyl)thio-5-thiol-1,3,4-thiadiazole. 150.2 g of DMTD, 150 g of toluene solvent, and 188.2 g of 2-ethoxyethoxy acrylate were added to a 1 L flask, and the mixture was heated at 85 °C for two hours. The toluene solvent was then stripped under vacuum at 3 mm Hg and 80 °C for four hours on a rotary evaporator. The product was a viscous yellow liquid.

[0131] Sample 7: Synthesis of 2-(laurylcarboxy-2-methylethyl)thio-5-thiol-1,3,4-thiadiazole. 129 g of DMTD, 216.2 g of lauryl methacrylate, and 0.2 g of sodium hydroxide catalyst were added to a 1-liter flask and heated at 105 °C for 14 hours. After this time, the reaction became clear, and all starting materials were dissolved. The mixture was vacuum stripped for six hours in a rotary evaporator under a 2 mm Hg vacuum and at 80 °C to provide the desired product as a low-melting-point solid.

[0132] Sample 8: Synthesis of 2-(methylcarboxy-2-methylethyl)thio-5-thiol-1,3,4-thiadiazole. 182.1 g DMTD, 121.3 g methyl methacrylate, 0.3 g potassium tert-butoxide catalyst, and 400 mL toluene solvent were added to a two-liter flask and heated at 100 °C for 12 hours. After this time, a small amount of yellow solid was removed by filtration. The mixture was then vacuum stripped for six hours on a rotary evaporator under a 2 mm Hg vacuum and at 80 °C to provide the desired product as a yellow solid upon cooling.

[0133] Sample 9: Synthesis of 2-(n-hexyl)thio-5-thiol-1,3,4-thiadiazole. 150.2 g of DMTD and 900 mL of ethanol were added to a 3-L flask, followed by the addition of 56.1 g of potassium hydroxide in portions over a 30-minute period. The reaction was heated at 75 °C for 2 hours under nitrogen and then cooled to 24 °C. 165.1 g of n-hexyl bromide was added over 20 minutes, and the mixture was heated under reflux (77 °C) for 6 hours. Ethanol was distilled off from the reaction mixture, and the residue was dissolved in 400 g of water / 600 mL of toluene and transferred to a separatory funnel. The organic phase was washed with additional water, collected, and dried over anhydrous sodium sulfate. After removing toluene on a rotary evaporator, the resulting low-melting-point solid was recrystallized from reagent-grade toluene:n-hexane (80:20 wt: wt) and dried in a vacuum oven to give the pure product.

[0134] Samples 10 to 13: The following DMTD monoalkylates were prepared using a similar procedure from the corresponding alkyl bromides:

[0135] Sample 10: 2-(2-ethylhexyl)thio-5-thiol-1,3,4-thiadiazole

[0136] Sample 11: 2-Cyclohexylthio-5-thiol-1,3,4-thiadiazole

[0137] Sample 12: 2-Isopentylthio-5-thiol-1,3,4-thiadiazole

[0138] Sample 13: 2-(ethylcarboxymethyl)thio-5-thiol-1,3,4-thiadiazole

[0139] Sample 14: Synthesis of 2-(methacryloylaminopropyltrimethylammonium chloride)thio-5-thiol-1,3,4-thiadiazole. 84.1 g DMTD, 247 g 50% aqueous solution of methacryloylaminopropyltrimethylammonium chloride, 0.42 g sodium hydroxide, and 300 g water were added to a 1-liter flask and heated at 90 °C for 8 hours under nitrogen. The mixture was transferred to an open beaker and allowed to stand in a 65 °C oven to evaporate most of the aqueous solvent, followed by vacuum drying at 95 °C and 2 mm Hg for 20 hours. The final product was a crystalline solid.

[0140] Sample 15: Synthesis of 2-(methacryloylaminopropyltrimethylammonium)thio-5-thioanion-1,3,4-thiadiazole. 122.7 g of 2-(methacryloylaminopropyltrimethylammonium chloride)thio-5-thiol-1,3,4-thiadiazole, 13.2 g of sodium hydroxide, and 200 g of deionized water were added to a 1-liter flask and heated at 70 °C for three hours under nitrogen. The mixture was transferred to an open beaker and allowed to stand in a 65 °C oven to evaporate most of the aqueous solvent, followed by vacuum drying at 95 °C and 5 mm Hg for 18 hours. The obtained crystalline solid was dissolved in 250 mL of ethanol and cooled to precipitate sodium chloride, which was removed by filtration. Ethanol was removed at 95 °C in both a 65 °C oven and a vacuum oven until constant weight was achieved.

[0141] Sample 16: Synthesis of 2-(acrylamido-2-methylpropanesulfonic acid)thio-5-thiol-1,3,4-thiadiazole. 98.15 g DMTD, 135.4 g 2-acrylamido-2-methylpropanesulfonic acid, 0.2 g sodium hydroxide, and 200 g isopropanol solvent were added to a 1-liter flask and heated at 80 °C for 8 hours under nitrogen. The mixture was transferred to an open beaker and allowed to stand in a 65 °C oven to evaporate most of the aqueous solvent, followed by vacuum drying at 95 °C and 4 mm Hg for 22 hours. The final product was a crystalline solid.

[0142] Sample 17: Synthesis of sodium 2-(acrylamido-2-methylpropanesulfonate anion)thio-5-thiol-1,3,4-thiadiazole. 150.2 g of DMTD, 320.9 g of a 50% aqueous solution of sodium 2-acrylamido-2-methylpropanesulfonate, and 80 g of deionized water solvent were added to a 1-liter flask, and the mixture was heated at 80 °C for 6 hours under nitrogen. The mixture was transferred to an open beaker and allowed to stand in a 65 °C oven to evaporate most of the water solvent, followed by vacuum drying at 100 °C and 3 mm Hg for 16 hours. The final product was a crystalline solid.

[0143] Sample 18: Synthesis of disodium 2-(acrylamido-2-methylpropanesulfonic acid anion)thio-5-thioanion-1,3,4-thiadiazole. Under nitrogen atmosphere, 72.7 g of 2-(acrylamido-2-methylpropanesulfonic acid)-5-thiol-1,3,4-thiadiazole prepared in Sample 16, 16.25 g of sodium hydroxide, and 200 g of deionized water solvent were added to a 1-liter flask, and the mixture was heated at 85 °C for 3 hours. The mixture was transferred to an open beaker and allowed to stand in a 65 °C oven to evaporate most of the water solvent, followed by vacuum drying at 3 mm Hg and 105 °C for 16 hours. The final product was a crystalline solid.

[0144] Sample 19: Synthesis of 2-(methacryloyloxyethyltrimethylammonium chloride)thio-5-thiol-1,3,4-thiadiazole. 65.9 g of DMTD, 126.5 g of 72% aqueous solution of methacryloyloxyethyltrimethylammonium chloride, 0.2 g of sodium hydroxide, and 125 g of water were added to a 1-liter flask and heated at 90 °C for 8 hours under nitrogen. The mixture was transferred to an open beaker and allowed to stand in a 65 °C oven to evaporate most of the aqueous solvent, followed by vacuum drying at 2.5 mm Hg and 95 °C for 23 hours. The final product was a crystalline solid.

[0145] Sample 20: Synthesis of 2-(2-hydroxypropyltrimethylammonium chloride)thio-5-thiol-1,3,4-thiadiazole. 45.07 g DMTD, 45.9 g industrial-grade glycidyltrimethylammonium chloride, and 200 g reagent-grade acetonitrile were added to a 1-liter flask, and the mixture was heated at 80 °C for 8 hours under nitrogen. The mixture was transferred to an open beaker, and most of the solvent was evaporated by standing in a 65 °C oven, followed by vacuum drying at 3.5 mm Hg and 90 °C for 22 hours. The final product was a yellow crystalline solid.

[0146] Sample 21: Synthesis of bis-2-(n-hexyl-5-disulfide)-1,3,4-thiadiazole. Under nitrogen atmosphere, 229 g of 2-(n-hexyl)thio-5-thiol-1,3,4-thiadiazole prepared in Sample 9 was added to a 1-liter flask, followed by the addition of 55.4 g of a 35% aqueous hydrogen peroxide solution over 45 minutes, while maintaining the temperature between 75°C and 80°C. The reaction was heated at 85°C for four hours, cooled, and dissolved in 300 mL of reagent-grade toluene. This solution was washed with additional deionized water using a separatory funnel, collected, and dried over anhydrous sodium sulfate. The toluene solvent was removed using a rotary evaporator to obtain a disulfide as a low-melting-point wax.

[0147] Sample 22: Synthesis of sodium 2-(n-hexyl)thio-5-thioanion-1,3,4-thiadiazole. 42.5 g of 2-(n-hexyl)thio-5-thiool-1,3,4-thiadiazole prepared in Sample 9, 7.25 g of sodium hydroxide, and 200 mL of toluene solvent were added to a 1 L flask, and the mixture was heated under reflux for 6 h. The aqueous distillate was collected using a Dean Stark separator. The reaction mixture was transferred to an open beaker, and most of the solvent was evaporated by standing in a 65 °C oven, followed by vacuum drying at 2 mm Hg and 90 °C for 18 h. The final product was a pale yellow solid.

[0148] Sample 23: Synthesis of 2-[(methacryloyloxy)ethyl-dimethyl-(3-sulfopropyl)ammonium]thio-5-thiol-1,3,4-thiadiazole. 86.6 g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 46.6 g of DMTD, 0.3 g of sodium hydroxide, and 250 g of deionized water were added to a one-liter flask, and the mixture was heated at 85°C for six hours under nitrogen. The mixture was transferred to an open beaker and allowed to stand in a 65°C oven to evaporate most of the aqueous solvent, followed by vacuum drying at 85°C and 3 mm Hg for 18 hours. The product was obtained as a glassy solid.

[0149] Sample 24: Synthesis of potassium 2-[(methacryloyloxy)ethyl-dimethyl-(3-sulfopropyl)ammonium]thio-5-thioanion-1,3,4-thiadiazole. 59.3 g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 40 g of DMTD monopotassium salt, 0.3 g of potassium hydroxide, and 200 g of deionized water were added to a 1-liter flask, and the mixture was heated at 85°C for six hours under nitrogen. The mixture was transferred to an open beaker and allowed to stand in a 65°C oven to evaporate most of the aqueous solvent, followed by vacuum drying at 85°C and 5 mm Hg for 20 hours. A product as a yellow solid was obtained.

[0150] Sample 25: Synthesis of potassium 2-[(methacryloyloxy-3-sulfopropyl)thio-5-thiol-1,3,4-thiadiazole]. 73.9 g of potassium 3-sulfopropyl methacrylate, 45.07 g of DMTD, 0.2 g of sodium hydroxide, and 250 g of deionized water were added to a 1-liter flask and heated at 85-90°C for 12 hours under nitrogen. The mixture was transferred to an open beaker and allowed to stand in a 65°C oven to evaporate most of the aqueous solvent, followed by vacuum drying at 3 mm Hg and 90°C for 28 hours. A product as a yellow solid was obtained.

[0151] Sample 26: Synthesis of 2-[(methacryloyloxy-3-sulfopropyl)thio-5-thioanion-1,3,4-thiadiazole dipotassium]. 49.7 g of potassium 3-sulfopropyl methacrylate, 38 g of DMTD monopotassium salt, 0.3 g of potassium hydroxide, and 225 g of deionized water were added to a 1-liter flask, and the mixture was heated at 85 °C for six hours under nitrogen. The clarified mixture was transferred to an open beaker and allowed to stand in a 65 °C oven to evaporate most of the aqueous solvent, followed by vacuum drying at 3.5 mm Hg and 95 °C for 24 hours. A product in the form of an amber solid was obtained.

[0152] Sample 27: Synthesis of 2-(2-methylethyl-2-carboxylate anion)thio-5-thioanion-1,3,4-thiadiazole dipotassium. 100 g of the ester prepared in Example 8, 44.8 g of potassium hydroxide, and 300 g of deionized water were added to a one-liter flask and heated under reflux (90 °C) for 14 hours, while collecting the distillate in a Dean Stark separator. The clarified mixture was transferred to an open beaker and allowed to stand in a 65 °C oven to evaporate most of the aqueous solvent, followed by vacuum drying at 4.5 mm Hg and 95 °C for 26 hours. A product as a pale yellow crystalline solid was obtained.

[0153] Sample 28: Synthesis of disodium 2-(propyl-2,3-dicarboxylate anion)thio-5-thiol-1,3,4-thiadiazole. 65.25 g itaconic acid, 75.1 g DMTD, 0.3 g sodium hydroxide, and 200 g deionized water were added to a 1-liter flask, and the mixture was heated at 90 °C for six hours under nitrogen. The clarified mixture was cooled to room temperature, and 40 g of sodium hydroxide was added, followed by heating at 70 °C for four hours. The mixture was transferred to an open beaker and allowed to stand in a 65 °C oven to evaporate most of the aqueous solvent, followed by vacuum drying at 95 °C and 4 mm Hg for 26 hours. The product was obtained as a yellow solid powder.

[0154] Sample 29: Synthesis of 2-(propyl-2,3-dicarboxylate anion)thio-5-thioanion-1,3,4-thiadiazole trisodium salt. 40 g of monosodium DMTD, 30.2 g of itaconic acid, and 250 g of deionized water were added to a 1-liter flask. Then, 18.6 g of sodium hydroxide was added, and the mixture was heated at 90 °C for 12 hours under nitrogen. The mixture was cooled to room temperature, and a small amount of insoluble solids were removed through filter paper. The clarified mixture was transferred to an open beaker and allowed to stand in a 65 °C oven to evaporate most of the aqueous solvent, followed by vacuum drying at 100 °C and 2 mm Hg for 28 hours. The product was obtained as a yellow solid powder.

[0155] Sample 30: Synthesis of disodium 2-(ethyl-2,3-dicarboxylate anion)thio-5-thiol-1,3,4-thiadiazole. 46.45 g of maleic acid, 60.1 g of DMTD, 0.25 g of sodium hydroxide, and 175 g of deionized water were added to a 1-liter flask, and the mixture was heated at 90 °C for six hours under nitrogen. The clarified mixture was cooled to room temperature, and 32 g of sodium hydroxide was added, followed by heating at 70 °C for four hours. The mixture was transferred to an open beaker and allowed to stand in a 65 °C oven to evaporate most of the aqueous solvent, then dried under vacuum at 95 °C and 2 mm Hg for 24 hours. A product as a yellow solid was obtained.

[0156] Sample 31: Synthesis of disodium 2-(2-methylethyl-2-carboxylate anion)thio-5-thioanion-1,3,4-thiadiazole. 35 g of monosodium DMTD salt, 22 g of sodium methacrylate, 0.3 g of sodium hydroxide catalyst, and 200 g of deionized water solvent were added to a 1-liter flask, and the mixture was heated at 90 °C for 8 hours and then cooled. A small amount of insoluble solid was removed by filtration through filter paper. The clarified mixture was transferred to an open beaker and allowed to stand in a 65 °C oven to evaporate most of the water solvent, followed by vacuum drying at 2.5 mmHg and 95 °C for 24 hours. A product in the form of a pale yellow solid was obtained.

[0157] Sample 32: Synthesis of 2-(2,3-dicarboxypropyl)thio-5-thiol-1,3,4-thiadiazole. 105.16 g of 2,5-dimercapto-1,3,4-thiadiazole, 300 g of deionized water, 91.1 g of itaconic acid, and 0.3 g of sodium hydroxide catalyst were added to a 1 L flask, and the mixture was heated at 88 °C for 10 hours under nitrogen and then cooled. Most of the water was evaporated in an open beaker in a steam oven at 65 °C. The product was then dried in a vacuum oven at 95 °C until constant weight. The product yield was 194 g.

[0158] Samples 33-36: Prepared from acrylic acid, methacrylic acid, maleic acid, or aconitic acid using a procedure similar to that of Example 32:

[0159] Sample 33: 2-(2-Carboxyethyl)thio-5-thiol-1,3,4-thiadiazole

[0160] Sample 34: 2-(2-methylethyl-2-carboxy)thio-5-thiol-1,3,4-thiadiazole

[0161] Sample 35: 2-(1,2-dimethoxyethyl)thio-5-thiol-1,3,4-thiadiazole

[0162] Sample 36: 2-(1,2,3-tricarboxypropyl)thio-5-thiol-1,3,4-thiadiazole

[0163] Sample 37: Synthesis of 2-(propyl-2,3-dicarboxylate anion)thio-5-thioanion-1,3,4-thiadiazole trisodium. Sample 29 was prepared using an alternative procedure. 32 g of the diacid product prepared in Example 32, 250 g of deionized water, and 13.7 g of sodium hydroxide were added to a 1 L flask and heated at 85 °C for 6 h under nitrogen. The mixture was transferred to an open beaker and most of the water was evaporated in a steam oven at 65 °C. The product was dried to constant weight in a vacuum oven at 95 °C to obtain 38.8 g of a pale yellow solid.

[0164] Samples 38-44: The procedure of Sample 37 was used to prepare the following products from the carboxylic acids prepared from Samples 33-36:

[0165] Sample 38: 2-(ethyl-2-carboxylate anion)thio-5-thioanion-1,3,4-thiadiazole dipotassium

[0166] Sample 39: 2-(ethyl-1,2-dicarboxylate anion)thio-5-thioanion-1,3,4-thiadiazole tripotassium

[0167] Sample 40: 2-(propyl-2,3-dicarboxylate anion)thio-5-thioanion-1,3,4-thiadiazole tripotassium

[0168] Sample 41: 2-(propyl-1,2,3-tricarboxylate anion)thio-5-thioanion-1,3,4-thiadiazole tetrapotassium

[0169] Sample 42: 2-(2-methylethyl-2-carboxylate anion)thio-5-thioanion-1,3,4-thiadiazole dipotassium

[0170] Sample 43: 2-(propyl-1,2,3-tricarboxylate anion)thio-5-thioanion-1,3,4-thiadiazole tetrasodium

[0171] Sample 44: 2-(2-methylethyl-2-dicarboxylate anion)thio-5-thioanion-1,3,4-thiadiazole disodium

[0172] Sample 45: Synthesis of 2-(propyl-2,3-dicarboxylate anion)thio-5-thiol-1,3,4-thiadiazole diammonium. 40 g of the diacid product prepared in Sample 32, 19 g of ammonia solution, and 212.8 g of deionized water were added to a 1 L flask, and the mixture was stirred at 25 °C for three hours under nitrogen. The reaction mixture was clear and free of solids. 271 g of a 20 wt% aqueous solution of the product was obtained.

[0173] Sample 46: Synthesis of 2-(propyl-1,2,3-tricarboxylate anion)thio-5-thiol-1,3,4-thiadiazole triammonium. This product was prepared in 20.3 wt% deionized water using a procedure similar to that of Sample 45, starting with the tricarboxylic acid prepared in Sample 36.

[0174] Sample 47: Preparation of 1M potassium chloride in a phosphate buffer solution at pH 7. Add 74.55 g potassium chloride, 6.309 g potassium dihydrogen phosphate, and 9.343 g dipotassium hydrogen phosphate to a 1 L volumetric flask. Dilute the mixture with deionized water to 1.0 L and mix until homogeneous.

[0175] Sample 48: Preparation of 1M sodium chloride in a phosphate buffer solution at pH 7. Add 58.5 g sodium chloride, 5.56 g sodium dihydrogen phosphate, and 7.62 g disodium hydrogen phosphate to a 1 L volumetric flask. Dilute the mixture with deionized water to 1.0 L and mix until homogeneous.

[0176] When indicated, CV and H-cell assessments were performed in a pH 7 buffer solution prepared in sample 47 or 48. Electrochemical tests to confirm the function of the formulated DMTD derivative as an RFB electrolyte consisted of cyclic voltammetry (CV) millivolt peak gap measurements and H-cell cycle testing / specific energy retention measurements.

[0177] CV millivolt peak gap measurements involve scanning the electrolyte with a cyclic voltammogram at a specified temperature and scan rate. The electrolytes in Table 1 were scanned at a temperature of 22 °C and a scan rate of 100 mV / s. In RFB applications, a CV cathode / anode peak gap of 600 mV or less is considered a feasible result for electrolyte redox reversibility. The results of the CV millivolt tests are shown in Table 1.

[0178] Table 1: CV electrochemical tests of DMTD derivatives

[0179]

[0180]

[0181]

[0182] H-cell cycle testing / specific energy retention measurements involved galvanostatic discharge-charge of a symmetric cell, where a monoalkylated DMDT anion / disulfide was used as both the cathode and anode in the H-cell under galvanostatic control. The two compartments of the H-cell were separated by G5 glass paste. Voltage cutoff values ​​were determined based on CV data (Table 1). This simple H-cell setup allows for direct evaluation of the stability of the monoalkylated DMDT during electrochemical cycling (J. Am. Chem. Soc. 2016, 138, 13230; J. Am. Chem. Soc. 2017, 139, 2924). Charge-discharge cycling (one hour charge and one hour discharge) was performed at a rate of 1C from 100% charge. For H-cell testing, an efficiency class of 70% to 85% was considered very good performance. The results of the H-cell testing are shown in Table 2.

[0183] Table 2: Electrochemical tests of H-cell cells containing DMTD derivatives

[0184]

[0185]

[0186]

[0187] Every document mentioned above is incorporated herein by reference, including any prior application for which priority is claimed, whether or not specifically listed above. Reference to any document in any jurisdiction is not an admission that such document is qualified as prior art or constitutes general knowledge to a person skilled in the art. Unless expressly indicated in the examples or otherwise herein, all numerical values ​​specifying amounts of materials, reaction conditions, molecular weights, carbon numbers, etc., in this specification should be understood to be modified by the word “about.” It should be understood that the upper and lower limits, ranges, and ratios set forth herein can be combined independently. Similarly, the ranges and amounts of each element of the invention can be used in combination with the ranges or amounts of any other element.

[0188] As used herein, the transitional term "comprising," synonymous with "including," "containing," or "characterized by," is inclusive or open-ended and does not exclude additional unlisted elements or method steps. However, in each statement of "comprising" herein, it is intended that the term also cover the phrases "consistently composed of" and "composed of" as alternative embodiments, wherein "consisting of" excludes any unspecified elements or steps and "consistently composed of" allows the inclusion of additional unlisted elements or steps that do not materially affect the substantial or essential and novel characteristics of the composition or method under consideration.

[0189] While certain representative embodiments and details have been shown for illustrative purposes, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention. In this respect, the scope of the invention will be limited only by the following claims.

[0190] A redox flow battery electrolyte comprising, substantially composed of: A) a polar solvent; and B) DMTD or a derivative thereof.

[0191] According to the redox flow battery electrolyte described in the previous paragraph, the polar solvent includes water, is substantially composed of water, and is composed of water.

[0192] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, or comprises organic solvents such as carbonates, ethers, ketones, nitriles, alcohols, glycols, amines, amides, organic solvents, and combinations thereof.

[0193] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises C1 to C2. 10 Alcohols are basically composed of alcohols.

[0194] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises C1 to C2. 10 Diol, which is basically composed of, is composed of.

[0195] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises methanol, is substantially composed of, or is composed of.

[0196] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises ethanol, is substantially composed of ethanol, or is composed of ethanol.

[0197] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises 1-propanol, is substantially composed of, or is composed of.

[0198] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises 2-propanol, is substantially composed of therein, or is composed of therein.

[0199] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises ethylene glycol, is substantially composed of, or is composed of.

[0200] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises propylene glycol, is substantially composed of, or is composed of.

[0201] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises dimethoxymethane, substantially composed of, or is composed of.

[0202] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises methoxybenzene (anisole), substantially composed of, or composed of.

[0203] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises tetrahydrofuran (THF), is substantially composed of, or is composed of.

[0204] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises 2-methyltetrahydrofuran, is substantially composed of, or is composed of.

[0205] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, or comprises 1,4-dioxane.

[0206] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, 1,3-dioxolane (DOL), or is composed of, 1,3-dioxolane.

[0207] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, or comprises 4-methyl-1,3-dioxolane.

[0208] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, 1,2-dimethoxyethane (DME), or is composed of, or is composed of, 1,2-dimethoxyethane.

[0209] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, or comprises bis(2-methoxyethyl) ether (diethylene glycol dimethyl ether).

[0210] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises acetone, is substantially composed of, or is composed of.

[0211] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises acetylacetone, is substantially composed of, or is composed of.

[0212] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises acetonitrile (CAN), is substantially composed of, or is composed of.

[0213] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises methoxyacetonitrile, is substantially composed of, or is composed of.

[0214] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises propionitrile, is substantially composed of, or is composed of.

[0215] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises nitrile, substantially comprises, or comprises the same.

[0216] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises isobutyronitrile, is substantially composed of, or is composed of.

[0217] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises benzyl nitrile, is substantially composed of, or is composed of.

[0218] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises 3-methoxypropionitrile, is substantially composed of, or is composed of.

[0219] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, or comprises ethylenediamine.

[0220] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises pyridine, is substantially composed of, or is composed of.

[0221] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises formamide, is substantially composed of formamide, or is composed of formamide.

[0222] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, or comprises n-methylacetamide.

[0223] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises N,N-dimethylformamide (DMF), is substantially composed of, or is composed of.

[0224] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises N,N-dimethylacetamide (DMA), is substantially composed of, or is composed of.

[0225] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises N-methyl-2-pyrrolidone (NMP), is substantially composed of, or is composed of.

[0226] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises propylene carbonate (PC), is substantially composed of, or is composed of.

[0227] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises ethylene carbonate (EC), is substantially composed of, or is composed of.

[0228] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, or consists of γ-butyrolactone (γ-BL).

[0229] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, or is composed of γ-valerol (γ-VL).

[0230] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises dimethyl carbonate (DMC), is substantially composed of, or is composed of.

[0231] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises diethyl carbonate (DEC), is substantially composed of, or is composed of.

[0232] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, ethyl methyl carbonate (EMC), or is composed of, ethyl methyl carbonate.

[0233] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, or comprises 1,2-butenyl carbonate.

[0234] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises hexane, is substantially composed of hexane, or is composed of hexane.

[0235] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises benzene, is substantially composed of, or is composed of.

[0236] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises toluene, is substantially composed of, or is composed of.

[0237] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises nitromethane, is substantially composed of, or is composed of.

[0238] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises nitrobenzene, is substantially composed of, or is composed of.

[0239] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, or comprises 1,2-dichloroethane.

[0240] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises dimethyl sulfoxide (DMSO), is substantially composed of, or is composed of.

[0241] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises ethyl acetate, substantially of, or is composed of ethyl acetate.

[0242] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the polar solvent comprises, substantially comprises, or comprises nitroethane.

[0243] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the electrolyte comprises, is substantially composed of, or is composed of DMTD derivatives.

[0244] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD derivative comprises a compound of formula I, substantially composed thereof, or composed of:

[0245] Formula I

[0246]

[0247] in

[0248] Each "X" individually represents an alkali metal or alkaline earth metal, such as Li, Na, K, Mg, or Ca; a trialkylamine or quaternary ammonium (containing ammonia); or H;

[0249] "m" is 1, 2, or 3, and "n" is 1 or 2; and

[0250] Where “Y” is:

[0251] “R”, straight chain, branched chain, saturated or unsaturated or cyclic C1 to C2 12 Or from C1 to C 10 Or C1 to C8 or even C1 to C6 alkyl or aryl; or H;

[0252] [RO] o R", where "o" is an integer from 1 to 100;

[0253] “R[OH] p "A", where "p" is an integer from 1 to 6 and "A" is H or an amine, such as a trialkylamine or a quaternary ammonium salt; or

[0254] A carboxylic acid ester group or a carboxamide group, such as itaconic acid ester, maleic acid ester, or (meth)acrylate or (meth)acrylamide that will form "CH2CH[CH3 or H]C(O)[O or NH]Z", wherein "Z" can be H, X, "R", or RN. + (R)3SO3 - RN + (R)3SO3 - K + "RSO3"- Na + ", RSO3 - NH4 + "RSO3H" or "RN" + (R)3Cl - ".

[0255] According to any one of the preceding paragraphs, the redox flow battery electrolyte, wherein n in Formula I is 1 and m in Formula I is 1, provides the uncoupled compound of Formula II:

[0256] Formula II

[0257]

[0258] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD derivative comprises, substantially comprises, or comprises: monoalkylated derivatives, etherified derivatives, alcohol derivatives, carboxylic acid ester derivatives, carboxamide derivatives, and combinations thereof.

[0259] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD derivative comprises, substantially comprises, or comprises the reaction product of DMTD with a halogenated alkyl or aryl group.

[0260] According to any one of the preceding paragraphs, the redox flow battery electrolyte, wherein the substituent Y of the DMTD derivative of Formula I is "R", and is straight-chain, branched, saturated or unsaturated or cyclic C1 to C2. 12 Or from C1 to C 10 Or C1 to C8 or even C1 to C6 alkyl or aryl; or H;

[0261] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD derivative comprises a compound of formula VI, substantially composed thereof, or composed of:

[0262] Style VI

[0263]

[0264] Where X, m, and n are as described in Equation I, and R is a straight-chain, branched, saturated or unsaturated, cyclic C1 to C2 chain. 12 Or from C1 to C 10 Or C1 to C8 or even C1 to C6 alkyl or aryl; or H.

[0265] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes methyl, substantially composed of, or composed of.

[0266] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes ethyl, substantially composed of, or composed of.

[0267] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes propyl, is substantially composed of, or is composed of.

[0268] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes butyl, is substantially composed of, or is composed of.

[0269] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes pentyl, is substantially composed of, or is composed of.

[0270] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes hexyl, is substantially composed of, or is composed of.

[0271] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes a heptyl group, is substantially composed of a heptyl group, or is composed of a heptyl group.

[0272] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes octyl, is substantially composed of, or is composed of.

[0273] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes nonyl, is substantially composed of, or is composed of.

[0274] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes decyl, is substantially composed of, or is composed of.

[0275] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group comprises undecyl, is substantially composed of, or is composed of.

[0276] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group comprises, is substantially composed of, or is composed of dodecyl groups.

[0277] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes isobutyl, is substantially composed of, or is composed of.

[0278] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes ethylhexyl, is substantially composed of, or is composed of.

[0279] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes isopentyl, is substantially composed of, or is composed of.

[0280] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes benzyl, is substantially composed of, or is composed of.

[0281] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the “R” group includes cyclohexyl, is substantially composed of, or is composed of.

[0282] According to any one of the preceding paragraphs, the redox flow battery electrolyte, wherein the DMTD derivative comprises, substantially comprises, the reaction product of DMTD with a haloether (halogenated ether) group.

[0283] According to any one of the preceding paragraphs, the redox flow battery electrolyte wherein the substituent Y of the DMTD derivative of Formula I is "[RO"]. o R", where "o" is an integer from 1 to 100.

[0284] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD derivative comprises, substantially comprises, and comprises: a compound of formula VII, or is composed of:

[0285] Equation VII

[0286]

[0287] Where X, R, m and n are as described in Equation I, and “o” is an integer from 1 to 100 or 1 to 75 or 1 to 50 or 1 to 25 or 1 to 20 or 1 to 15 or 1 to 10 or 2 to 10 or 4 to 10 or 6 to 10.

[0288] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the ether of the halide ether includes dimethyl ether, is substantially composed of, or is composed of.

[0289] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the ether of the halide ether includes diethyl ether, is substantially composed of, or is composed of.

[0290] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the ether of the halide ether includes dipropyl ether, is substantially composed of, or is composed of.

[0291] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the ether of the halide ether includes methyl ethyl ether, is substantially composed of, or is composed of.

[0292] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the ether of the halide ether includes methyl phenyl ether, is substantially composed of, or is composed of.

[0293] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the ether of the halide ether includes paraformaldehyde, is substantially composed of, or is composed of.

[0294] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the ether of the halide ether comprises polyethylene glycol, is substantially composed of, or is composed of.

[0295] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the ether of the halide ether comprises, is substantially composed of, or is composed of polypropylene glycol.

[0296] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the ether of the halide ether comprises polytetrahydrofuran, is substantially composed of, or is composed of.

[0297] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD derivative comprises, substantially comprises, the reaction product of DMTD and a carboxylic acid ester group.

[0298] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I comprises a carboxylic acid ester group, is substantially composed of therewith, or is composed of therewith.

[0299] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I comprises a monocarboxylic acid ester group, is substantially composed of therewith, or is composed of therewith.

[0300] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes a dicarboxylic acid ester group, is substantially composed of therewith, or is composed of therewith.

[0301] According to any one of the preceding paragraphs, the DMTD derivative, wherein the carboxylic acid ester includes a tricarboxylic acid ester, is substantially composed of, or is composed of.

[0302] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes an itaconic acid ester group, is substantially composed of it, or is composed of it.

[0303] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes a maleate group, is substantially composed of it, or is composed of it.

[0304] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes a citrate group, is substantially composed of therewith, or is composed of therewith.

[0305] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes a fumarate group, is substantially composed of therefrom, or is composed of therefrom.

[0306] According to any one of the preceding paragraphs, the redox flow battery electrolyte, wherein the substituent Y of the DMTD derivative of Formula I includes a methyl ester group, is substantially composed of therewith, or is composed of therewith.

[0307] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes (meth)acrylate groups, is substantially composed of, or is composed of.

[0308] According to any one of the preceding paragraphs, the redox flow battery electrolyte, wherein the substituent Y of the DMTD derivative of Formula I includes "CH2CH[CH3 or H]C(O)OZ", substantially composed of, or composed of, wherein "Z" can be H, X, "R", or RN. + (R)3SO3 - RN + (R)3SO3 - K + "RSO3" - Na + ", RSO3 - NH4 + "RSO3H" or "RN" + (R)3Cl - ".

[0309] According to any one of the preceding paragraphs, the redox flow battery electrolyte, wherein the DMTD derivative comprises, substantially comprises, the reaction product of DMTD and a carboxamide group.

[0310] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes a carboxamide group, is substantially composed of therewith, or is composed of therewith.

[0311] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes a monocarboxamide group, is substantially composed of therewith, or is composed of therewith.

[0312] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes a dicarboxamide group, is substantially composed of therewith, or is composed of therewith.

[0313] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes a primary carboxamide group, is substantially composed of therewith, or is composed of therewith.

[0314] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes a secondary carboxamide group, is substantially composed of therewith, or is composed of therewith.

[0315] According to any one of the preceding paragraphs, the redox flow battery electrolyte, wherein the substituent Y of the DMTD derivative of Formula I includes a tertiary carboxamide group, is substantially composed of therewith, or is composed of therewith.

[0316] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes an itaconamide group, is substantially composed of it, or is composed of it.

[0317] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes a maleamide group, is substantially composed of it, or is composed of it.

[0318] According to any one of the preceding paragraphs, the redox flow battery electrolyte, wherein the substituent Y of the DMTD derivative of Formula I includes a citrile group, is substantially composed of therein, or is composed of therein.

[0319] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes a fumarate group, is substantially composed of therewith, or is composed of therewith.

[0320] According to any one of the preceding paragraphs, the redox flow battery electrolyte, wherein the substituent Y of the DMTD derivative of Formula I includes a methyl amide group, is substantially composed of therewith, or is composed of therewith.

[0321] According to any one of the preceding paragraphs, the redox flow battery electrolyte, wherein the substituent Y of the DMTD derivative of Formula I includes a (meth)acrylamide group, is substantially composed of therewith, or is composed of therewith.

[0322] According to any one of the preceding paragraphs, the redox flow battery electrolyte, wherein the substituent Y of the DMTD derivative of Formula I includes "CH2CH[CH3 or H]C(O)NHZ", substantially composed of, or composed of, wherein "Z" can be H, "R", or "RSO3". - Na + “RSO3H” or “RN” + (R)3Cl - ".

[0323] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD derivative comprises a compound of formula IX, is substantially composed thereof, or is composed of:

[0324] Formula IX

[0325]

[0326] Where X, m, and n are as described in Equation I, and “Z” is H, X, “R”, RSO3 - Na + , RSO3H, RN + (R)3SO3 - RN + (R)3SO3 - K + , RSO3 - NH4 + or RN + (R)3Cl - .

[0327] According to any one of the preceding paragraphs, the redox flow battery electrolyte, wherein the DMTD derivative comprises, substantially comprises, the reaction product of DMTD with a haloalcohol group.

[0328] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD derivative comprises, substantially comprises, the reaction product of DMTD and epoxy groups.

[0329] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the substituent Y of the DMTD derivative of Formula I includes "R[OH]". p "A", which is basically composed of, and is composed of, where "p" is an integer from 1 to 6 and "A" is H or an amine, such as a trialkylamine or a quaternary ammonium salt.

[0330] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD derivative comprises, substantially comprises, and comprises: a compound of formula VIII, or comprises:

[0331] Formula VIII

[0332]

[0333] Where X, R, m, and n are as described in Formula I, and “p” is an integer from 1 to 6 and “A” is H or an amine, such as a trialkylamine or a quaternary ammonium salt.

[0334] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p Group A includes propanol, is essentially composed of it, and is composed of it.

[0335] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p Group A includes hexanol, which is essentially composed of it, and is composed of it.

[0336] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p Group A includes butanol, which is essentially composed of it, and is composed of it.

[0337] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p Group A includes phenylpropanol, is essentially composed of it, and is composed of it.

[0338] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p Group A includes sugar alcohols, which are essentially composed of sugar alcohols, which are composed of sugar alcohols.

[0339] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p Group A includes polyvinyl alcohol, which is essentially composed of it, and is composed of it.

[0340] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p Group A includes ethylene glycol, is essentially composed of it, and is composed of it.

[0341] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p Group A includes propylene glycol, is essentially composed of it, and is composed of it.

[0342] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p Group A includes butanediol, which is essentially composed of it, and is composed of it.

[0343] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p The A group includes glycerol, which is essentially composed of glycerol, which is composed of glycerol.

[0344] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p The A group includes ethanolamine, which is essentially composed of it, and is composed of it.

[0345] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p Group A includes propanolamine, which is essentially composed of, and is composed of.

[0346] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p Group A includes propanol dimethylamine, which is essentially composed of it, and is composed of it.

[0347] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alcohol group (i.e., R[OH]) p Group A includes propanol quaternary ammonium halide salts, which are essentially composed of, and are composed of.

[0348] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD derivative is further reacted with an alkali.

[0349] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alkali comprises, is substantially composed of, or is composed of: alkali metals or alkaline earth metals, trialkylamines, quaternary ammoniums, or combinations thereof.

[0350] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the base comprises Li, is substantially composed of, is substantially composed of, or is composed of.

[0351] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the base comprises Na, is substantially composed of, is substantially composed of, or is composed of.

[0352] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the base includes K, is substantially composed of K, is composed of K, is substantially composed of K, or is composed of K.

[0353] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the base comprises Mg, is substantially composed of, is substantially composed of, or is composed of.

[0354] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the alkali comprises Ca, is substantially composed of, is substantially composed of, or is composed of.

[0355] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD derivative is further reacted with an oxidizing agent.

[0356] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD derivative is further reacted with hydrogen peroxide.

[0357] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein n in Formula I is 2 and m in Formula I is 1, 2 or 3, provides a coupling compound of any one of Formulas III, IV and V:

[0358] Formula III

[0359]

[0360] Formula IV

[0361]

[0362] Formula V

[0363]

[0364] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD or its derivative is present in an amount of about 1 wt.% to about 50 wt.%.

[0365] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD or its derivative is present in an amount of about 2.5 wt.% to about 30 wt.%.

[0366] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD or its derivative is present in an amount of about 5 wt.% to about 25 wt.%.

[0367] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the DMTD or its derivative is present in an amount of about 10 wt.% to about 20 wt.%.

[0368] The redox flow battery electrolyte according to any one of the preceding paragraphs further includes a support electrolyte, is substantially composed of therein, or is composed of therein.

[0369] The redox flow battery according to any one of the preceding paragraphs, wherein the supporting electrolyte is present in an amount of about 0.1 wt.% to about 20 wt.%.

[0370] The redox flow battery according to any one of the preceding paragraphs, wherein the supporting electrolyte is present in an amount of about 0.25 wt.% to about 15 wt.%.

[0371] The redox flow battery according to any one of the preceding paragraphs, wherein the supporting electrolyte is present in an amount of about 0.5 wt.% to about 10 wt.%.

[0372] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the supporting electrolyte comprises, substantially comprises, or comprises at least one of lithium, sodium, potassium, or mixtures thereof.

[0373] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the supporting electrolyte comprises sodium phosphate, is substantially composed of, or is composed of.

[0374] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the supporting electrolyte comprises sodium chloride, is substantially composed of sodium chloride, or is composed of sodium chloride.

[0375] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the supporting electrolyte comprises potassium phosphate, is substantially composed of potassium phosphate, or is composed of potassium phosphate.

[0376] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the supporting electrolyte comprises potassium chloride, is substantially composed of potassium chloride, or is composed of potassium chloride.

[0377] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the supporting electrolyte comprises potassium hexafluorophosphate, is substantially composed of, or is composed of.

[0378] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the supporting electrolyte comprises lithium hexafluorophosphate, is substantially composed of, or is composed of.

[0379] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the supporting electrolyte comprises tetrabutylammonium fluorophosphate, is substantially composed of, or is composed of.

[0380] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the supporting electrolyte comprises tetrabutylammonium chloride, is substantially composed of, or is composed of.

[0381] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the supporting electrolyte comprises lithium perchlorate, is substantially composed of, or is composed of.

[0382] The redox flow battery electrolyte according to any one of the preceding paragraphs, wherein the supporting electrolyte comprises lithium nitrate, is substantially composed of lithium nitrate, or is composed of lithium nitrate.

[0383] A redox flow battery system comprising, substantially comprising, and wherein, during a state of charge, the electrolyte forms: A) an anolyte comprising DSSD and 2DSSD. - A polar solvent of or a mixture thereof, substantially composed of, or composed of; and B) a cathode electrolyte, said cathode electrolyte comprising DSSD or 2S - or a polar solvent of its mixture, which is essentially composed of it.

[0384] The redox flow battery system according to any one of the preceding paragraphs further includes, is substantially composed of, or is composed of an ion exchange membrane or a microporous membrane.

[0385] The redox flow battery system according to any one of the preceding paragraphs further comprises, substantially comprises, and consists of, wherein the membrane comprises, substantially comprises, and consists of a fluoropolymer-polymer copolymer based on sulfonated tetrafluoroethylene.

[0386] According to any one of the preceding paragraphs, the redox flow battery system wherein the membrane comprises, is substantially composed of, or is composed of cellulose-based dialysis membranes.

[0387] According to any one of the preceding paragraphs, the redox flow battery system wherein the membrane comprises, is substantially composed of, or is composed of a functionalized polystyrene blended with polyvinyl chloride.

Claims

1. A redox flow battery electrolyte comprising: A) a polar solvent; and B) 1 wt.% to 50 wt.% of 2-(methylcarboxyethyl)thio-5-thiol-1,3,4-thiadiazole, wherein the polar solvent comprises acetonitrile.

2. The redox flow battery electrolyte of claim 1, further comprising a supporting electrolyte.

3. The redox flow battery electrolyte of claim 2, wherein the supporting electrolyte is present in an amount of 0.1 wt.% to 20 wt.%.

4. The redox flow battery electrolyte of claim 2, wherein the supporting electrolyte is at least one of lithium, sodium, potassium, or mixtures thereof.

5. The redox flow battery electrolyte of claim 3, wherein the supporting electrolyte is at least one of lithium, sodium, potassium, or mixtures thereof.

6. A redox flow battery system comprising an electrolyte according to any one of the preceding claims, wherein during a charging state, the electrolyte forms: A) an anolyte comprising a polar solvent comprising DSSD, 2DS- or a mixture thereof; and B) a catholyte comprising a polar solvent comprising DSSD or 2S - or a mixture thereof.

7. The redox flow battery system of claim 6, further comprising an ion exchange membrane or a microporous membrane.

8. The redox flow battery system of claim 7, further comprising wherein the membrane is a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer.

9. The redox flow battery system of claim 7, wherein the membrane is a cellulose-based dialysis membrane.

10. The redox flow battery system of claim 7, wherein the membrane comprises a functionalized polystyrene blended with polyvinyl chloride.

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