CROSS REFERENCE TO RELATED APPLICATION

[0001] This PCT application claims the benefit of U.S. provisional application number 62/296,237, filed on February 17, 2016. This document is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] This invention relates to electrolytes that are useful in zinc halide rechargeable electrochemical cells (e.g., storage batteries). More specifically, this invention relates to aqueous electrolytes that reversibly electrolyze zinc halide in electrochemical storage cells or batteries.

BACKGROUND

[0003] Zinc-halide batteries were developed as devices for storing electrical energy.

Traditional zinc-halide batteries (e.g., zinc-bromine batteries) employed bipolar electrodes disposed in a static, i.e., non-flowing, zinc-bromide aqueous solution. The process of charging and discharging electrical current in a zinc-halide battery is generally achieved through a reaction of redox couples like Zn ²⁺ / Zn(s) and X ^" / X ₂ in zinc halide electrolyte, where X is a halogen (e.g., CI, Br, or I).

[0004] When the battery is charged with electrical current, the following chemical reactions occur:

Zn ²⁺ + 2e→ Zn

2X-→ X ₂ + 2e\

Conversely, when the battery discharges electrical current, the following chemical reactions occur:

Zn→ Zn ²⁺ + 2e

X ₂ + 2e-→2X ^" .

Additionally, in some batteries, polyhalide reactions may also occur. Some of these examples are described by the following:

XJ + 2e ^_ → 3X ^~ or

X„ + ne ^" → nX ^~ for n > 3.

[0005] The polyhalide reactions pictured above can include reactions between like halogens, e.g. Br ₃ , and reactions between non-like halogens, e.g., mixed halogens, such as Br ₂ Cl.

[0006] These zinc-halide storage batteries were typically configured in a bipolar

electrochemical cell stack, wherein each electrode is disposed in an aqueous zinc salt electrolyte. However, the performance of these storage batteries was highly inefficient due to secondary reactions of the dissolved species in the aqueous electrolyte. For example, in solution, elemental bromine exists in equilibrium with bromide ions to form polybromide ions, Br^, where m = 3, 5, or 7. Elemental bromine also possesses an increased vapor pressure that promotes hazardous pressure in the batteries. Furthermore, when aqueous zinc halide salts are ionized, zinc ions can exist as various complex ions and ion pairs, which promotes zinc dendrite formation and increased incidence of self-discharge in the batteries. To improve electrolyte durability in the batteries, halogen sequestration agents were added (e.g., quaternary ammonium salts); however, these sequestration agents possessed reduced solubility and reduce the stability of the electrolyte over numerous charge cycles.

SUMMARY OF THE INVENTION

[0007] One aspect of the disclosure provides an electrolyte including a zinc halide salt;

water; and carbon powder. Implementations of the disclosure may include one or more of the following optional features. In some implementations, the zinc halide salt is selected from ZnBr ₂ , ZnCb, Znl ₂ , or any combination thereof. The electrolyte may further include from about 25 wt% to about 50 wt% of the zinc halide salt. The electrolyte may include from about 25 wt% to about 50 wt% of the carbon powder.

[0008] In some examples, the zinc halide salt includes ZnBr ₂ . The electrolyte may include 28 wt% to about 37 wt% of ZnBr ₂ . The zinc halide salt may further include ZnCb and may include from about 1.5 wt% to about 7.5 wt% of ZnCl ₂ . The electrolyte may include from about 10 wt% to about 40 wt% of water, or may include from about 15 wt% to about 30 wt% of water.

[0009] In some implementations, the electrolyte includes a glyme. The glyme may include monoglyme, diglyme, triglyme, tetraglyme, pentaglyme, hexaglyme, or any combination thereof. The glyme may include tetraglyme. The electrolyte may further include an ether selected from DME-PEG, dimethyl ether, or any combination thereof. The DME-PEG may have an average molecular weight of from about 350 amu to about 3000 amu, or may have an average molecular weight of from about 1200 amu to about 3000 amu. The DME-PEG may be DME-PEG 2000, DME-PEG 1000, or a combination thereof.

[0010] In some implementations, the electrolyte includes a Ci-io glycol. The glycol may include ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, neopentyl glycol, hexalene glycol, or any combination thereof. The electrolyte may include from about 0.25 wt% to about 2.5 wt% of neopentyl glycol. [0011] In some examples, the electrolyte includes one or more quaternary ammonium agents. The one or more quaternary ammonium agents may include a quaternary ammonium agent selected from the group consisting of ammonium chloride, tetraethylammonium bromide, trimethylpropylammonium bromide, N-methyl-N-ethylmorpholinium bromide,

N-methyl-N-ethylmorpholinium bromide (MEMBr), 1 -ethyl- 1 -methylmorpholinium bromide, N-methyl-N-butylmorpholinium bromide, N-methyl-N-ethylpyrrolidinium bromide, N,N,N-triethyl-N-propylammonium bromide, N-ethyl-N-propylpyrrolidinium bromide, N-propyl-N-butylpyrrolidinium bromide, N-methyl-N-butylpyrrolidinium bromide,

1 -methyl- 1-butylpyrrolidinium bromide, N-ethyl-N-(2-chloroethyl)pyrrolidinium bromide, N-methyl-N-hexylpyrrolidinium bromide, N-methyl-N-pentylpyrrolidinium bromide, N-ethyl-N-pentylpyrrolidinium bromide, N-ethyl-N-butylpyrrolidinium bromide,

trimethylene-bis(N-methylpyrrolidinium) dibromide, N-butyl-N-pentylpyrrolidinium bromide, N-methyl-N-propylpyrrolidinium bromide, N-propyl-N-pentylpyrrolidinium bromide, l-ethyl-4-methylpyridinium bromide, l-ethyl-2-methylpyridinium bromide, l-butyl-3-methylpyridinium bromide, cetyltrimethylammonium bromide, and any

combination thereof. The one or more quaternary ammonium agents may also include a quaternary ammonium agent selected from the group consisting of ammonium chloride, tetraethylammonium bromide, trimethylpropylammonium bromide,

N-methyl-N-ethylmorpholinium bromide (MEMBr), 1 -ethyl- 1 -methylmorpholinium bromide, N-methyl-N-ethylpyrrolidinium bromide, 1 -methyl- 1-butylpyrrolidinium bromide, l-ethyl-4-methylpyridinium bromide, 1 -ethyl-2-methylpyridinium bromide,

l-butyl-3-methylpyridinium bromide, cetyltrimethylammonium bromide, and any

combination thereof.

[0012] In some examples, the one or more quaternary ammonium agents is

l-ethyl-4-methylpyridinium bromide. The one or more quaternary ammonium agents may also include 1 wt% to about 7 wt% 1 -ethyl-2-methylpyridinium bromide and may further include about 1.5 wt% to about 2.5 wt% 1 -methyl- 1-butylpyrrolidinium bromide. In some examples, the one or more quaternary ammonium agents include about 1.5 wt% to about 2.5 wt% l-butyl-3-methylpyridinium bromide, and may include about 1.5 wt% to about 5 wt% 1 -methyl- 1-ethylmorpholinium bromide, and may include about 0.5 wt% to about 1.5 wt% N-methyl-N-ethylmorpholinium bromide (MEMBr).

[0013] In some implementations, the one or more quaternary ammonium agents include about 14.5 wt% to about 16.5 wt% N-methyl-N-ethylpyrrolidinium bromide. The one or more quaternary ammonium agents may also include about 2 wt% to about 3 wt% trimethylpropylammonium bromide, and may include about 2 wt% to about 8 wt%

tetraethylammonium bromide, and may further include about 0.05 wt% to about 0.2 wt% cetyltrimethylammonium bromide.

[0014] In some examples, the electrolyte includes less than 1 wt% of one or more additives selected from Sn, In, Ga, Al, Tl, Bi, Pb, Sb, Ag, Mn, or Fe. The one or more additives may be selected from about .0008 wt% to about .0012 wt% of SnCl ₂ ^« H ₂ 0, from about .0008 wt% to about .0012 wt% of In, and combinations thereof.

[0015] The electrolyte may include an acid, or the conjugate base of an acid, selected from acetic acid, nitric acid, and citric acid. The electrolyte may include from about 0.3 wt% to about 0.6 wt% acetic acid, and may include from about 0.12 wt% to about 0.08 wt% nitric acid, and may further include from about 3.5 wt% to about 4.5 wt% citric acid. The electrolyte may also include from about 3.5 wt% to about 4.5 wt% potassium dihydrogen citrate, and may include from about 0.05 wt% to about 0.75 wt% of a crown ether, from about 0.15 wt% to about 0.5 wt% of 18-crown-6, and further include from about 0.05 wt% to about 0.2 wt% of 15-crown-5.

[0016] An additional aspect of the disclosure discloses an electrochemical cell including an anode, a cathode spaced apart from the anode, and an electrolyte disposed between the anode and the cathode. The electrolyte includes a zinc halide salt, water, a carbon powder material.

[0017] In some implementations, the zinc halide salt is selected from ZnBr ₂ , ZnCl ₂ , Znl ₂ , or any combination thereof. The electrolyte may further include from about 25 wt% to about 50 wt% of the zinc halide salt. The electrolyte may include from about 25 wt% to about 50 wt% of the carbon powder.

[0018] In some examples, the zinc halide salt includes ZnBr ₂ . The electrolyte may include 28 wt% to about 37 wt% of ZnBr ₂ . The zinc halide salt may further include ZnCl ₂ and may include from about 1.5 wt% to about 7.5 wt% of ZnCl ₂ . The electrolyte may include from about 10 wt% to about 40 wt% of water, or may include from about 15 wt% to about 30 wt% of water. In some implementations, there is not a separator or cathode cage within the electrochemical cell.

DETAILED DESCRIPTION

[0019] The present invention provides an electrolyte for use in secondary, i.e., rechargeable, zinc halide storage batteries (e.g., flow battery systems, or non flow battery systems). [0020] I. DEFINITIONS

[0021] As used herein, the term "electrochemical cell" or "cell" are used interchangeably to refer to a device capable of either generating electrical energy from chemical reactions or facilitating chemical reactions through the introduction of electrical energy.

[0022] As used herein, the term "battery" encompasses electrical storage devices comprising at least one electrochemical cell. A "secondary battery" is rechargeable, whereas a "primary battery" is not rechargeable. For secondary batteries of the present invention, a battery anode is designated as the positive electrode during discharge, and as the negative electrode during charge.

[0023] As used herein, an "electrolyte" refers to a substance that behaves as an electrically conductive medium. For example, the electrolyte facilitates the mobilization of electrons and cations in the cell. Electrolytes include mixtures of materials such as aqueous solutions of metal halide salts (e.g., ZnBr ₂ , ZnCl ₂ , or the like).

[0024] As used herein, the term "electrode" refers to an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g., a semiconductor, an electrolyte, or a vacuum). An electrode may also refer to either an anode or a cathode.

[0025] As used herein, the term "anode" refers to the negative electrode from which electrons flow during the discharging phase in the battery. The anode is also the electrode that undergoes chemical oxidation during the discharging phase. However, in secondary, or rechargeable cells, the anode is the electrode that undergoes chemical reduction during the cell's charging phase. Anodes are formed from electrically conductive or semiconductive materials, e.g., metals (e.g., titanium or TiC coated titanium), metal oxides, metal alloys, metal composites, semiconductors, or the like.

[0026] As used herein, the term "cathode" refers to the positive electrode into which electrons flow during the discharging phase in the battery. The cathode is also the electrode that undergoes chemical reduction during the discharging phase. However, in secondary or rechargeable cells, the cathode is the electrode that undergoes chemical oxidation during the cell's charging phase. Cathodes are formed from electrically conductive or semiconductive materials, e.g., metals, metal oxides, metal alloys, metal composites, semiconductors, or the like.

[0027] As used herein, the term "bipolar electrode" refers to an electrode that functions as the anode of one cell and the cathode of another cell. For example, in a battery stack, a bipolar electrode functions as an anode in one cell and functions as a cathode in an immediately adjacent cell. In some examples, a bipolar electrode comprises two surfaces, a cathode surface and an anode surface, wherein the two surfaces are connected by a conductive material. For instance, a bipolar electrode plate may have opposing surfaces wherein one surface is the anode surface, the other surface is the cathode surface, and the conductive material is the thickness of the plate between the opposing surfaces.

[0028] As used herein, the term "halide" refers to a halogen bearing a negative charge.

Examples of halides include fluoride (F ^" ), chloride (CI ^" ), bromide (Br ^" ), and iodide (Γ).

[0029] As used herein, the term "halogen" refers to any of the elements fluorine, chlorine, bromine, iodine, and astatine, occupying group VIIA (17) of the periodic table. Halogens are reactive nonmetallic elements that form strongly acidic compounds with hydrogen, from which simple salts can be made.

[0030] As used herein, the term "anion" refers to any chemical entity having one or more permanent negative charges. Examples of anions include, but are not limited to fluoride, chloride, bromide, iodide, arsenate, phosphate, arsenite, hydrogen phosphate, dihydrogen phosphate, sulfate, nitrate, hydrogen sulfate, nitrite, thiosulfate, sulfite, perchlorate, iodate, chlorate, bromate, chlorite, hypochlorite, hypobromite, carbonate, chromate, hydrogen carbonate (bicarbonate), dichromate, acetate, formate, cyanide, amide, cyanate, peroxide, thiocyanate, oxalate, hydroxide, and permanganate.

[0031] As used herein, "glyme" refers to an ether (e.g., a glycol ether). Examples include, but are not limited to, monoglyme (i.e., 1 ,2-dimethoxyethane), diglyme (i.e.,

bis(2-methoxyethyl) ether, tetraglyme (i.e., tetraethylene glycol dimethyl ether), pentaglyme, hexaglyme, heptaglyme, or any combination thereof.

[0032] As used herein, a "titanium material" may include, but is not limited to, titanium (in any oxidation state), TiC, alloys of TiC such as TiC _x M (where x is 0, 1, 2, 3, or 4 and M is a metal), titanium carbohyrides, non-stoichiometric titanium-carbon compounds, and combinations thereof.

[0033] As used herein, "titanium carbide" is used interchangeably with "titanium carbide material" and includes, but is not limited to TiC, alloys of TiC, such as TiC _x M (where x is 0, 1, 2, 3, or 4 and M is a metal), titanium carbohyrides, non-stoichiometric titanium-carbon compounds, and combinations thereof.

[0034] As used herein, the term "zinc metal" refers to elemental zinc, also commonly known as Zn(0) or Zn°.

[0035] As used herein, the term "dimethyl ether poly(ethylene glycol)" and its abbreviation "DME-PEG" are used interchangeably to refer to a polymer having the structure ;ocH ₃

, where n is an integer. DME-PEG 1000 refers to a DME-PEG polymer having a number average molecular weight (M _n ) about 1000, and DME-PEG 2000 refers to a DME-PEG polymer having a number average molecular weight (M _n ) of about 2000.

[0036] As used herein, the term "dimethyl ether" refers to an organic compound having the formula CH ₃ OCH ₃ .

[0037] As used herein, the term "alcohol" refers to any organic compound whose molecule contains one or more hydroxyl groups attached to a carbon atom. Examples of alcohols include methanol, ethanol, 1-propanol (i.e., n-propanol), 2-propanol (i.e., iso-propanol), 1-butanol (i.e., n-butanol), sec-butanol, iso-butanol, tert-butanol, 1-pentanol, or any combination thereof.

[0038] As used herein, the term "hydroxyl group" refers to an -OH group.

[0039] As used herein, the term "glycol" refers to any of a class of organic compounds belonging to the alcohol family. In the molecule of a glycol, two hydroxyl (-OH) groups are attached to different carbon atoms. Examples of glycols include Ci-io glycols including ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, neopentyl glycol, hexalene glycol, or any combination thereof. Other examples of glycols include substituted ethylene and substituted propylene clycols.

[0040] As used herein, the term "weight percent" and its abbreviation "wt%" are used interchangeably to refer to the product of 100 times the quotient of mass of one or more components divided by total mas nent: wt% = 100%

When referring to the concentration of components or ingredients for electrolytes, as described herein, wt% is based on the total weight of the electrolyte.

[0041] As used herein, the term "quaternary ammonium agent" refers to any compound, salt, or material comprising a quaternary nitrogen atom. For example, quaternary ammonium agents include ammonium halides (e.g., NH ₄ Br, NH ₄ C1, or any combination thereof), tetra-alkylammonium halides (e.g., tetramethylammonium bromide, tetramethylammonium chloride, tetraethylammonium bromide, tetraethylammonium chloride, combinations thereof or the like), heterocyclic ammonium halides (e.g., N-methyl-N-ethylpyrrolidinium halide, N-ethyl-N-methylpyrrolidinium halide, combinations thereof, or the like), or any combination thereof. Tetra-alkylammonium halides may be symmetrically substituted or asymmetrically substituted with respect to the substituents of the quaternary nitrogen atom. [0042] As used herein, the term "ammonium bromide complexing agent" refers to any compound, salt, or material comprising a quaternary nitrogen atom, wherein the quaternary nitrogen atom is not part of an imidazolium, pyridinium, pyrrolidinium, morpholinium, or phosphonium moiety. Examples of ammonium bromide complexing agents include:

tetraethylammonium bromide, trimethylpropylammonium bromide,

dodecyltrimethylammonium bromide, cetyltriethylammonium bromide, and

hexyltrimethylammonium bromide.

[0043] As used herein, the term "imidazolium bromide complexing agent" refers to any compound, salt, or material comprising a quaternary nitrogen atom, wherein the quaternary nitrogen atom is part of an imidazolium moiety. Examples of imidazolium bromide complexing agents include: l-ethyl-3-methylimidazolium bromide,

l-butyl-3-methylimidazoliium bromide, l-ethyl-2,3-dimethylimidazolium bromide, l-decyl-3-methylimidazolium bromide, l-butyl-2,3-dimethylimidazolium bromide, l-methyl-3-octylimidazollium bromide, and l-methyl-3-hexylimidazolium bromide.

[0044] As used herein, the term "pyridinium bromide complexing agent" refers to any compound, salt, or material comprising a quaternary nitrogen atom, wherein the quaternary nitrogen atom is part of a pyridinium moiety. Examples of pyridinium bromide complexing agents include: l-ethyl-3-methylpyridinium bromide, l-ethyl-2-methylpyridinium bromide, l-butyl-3-methylpyridinium bromide, l-butyl-3-methylpyridinium bromide,

l-butyl-4-methylpyridinium bromide, and 1-hexylpyridinium bromide.

[0045] As used herein, the term "pyrrolidinium bromide complexing agent" refers to any compound, salt, or material comprising a quaternary nitrogen atom, wherein the quaternary nitrogen atom is part of a pyrrolidinium moiety. An example of a pyrrolidinium bromide complexing agent is 1 -butyl- 1-methylpyrrolidinium bromide.

[0046] As used herein, the term "morpholinium bromide complexing agent" refers to any compound, salt, or material comprising a quaternary nitrogen atom, wherein the quaternary nitrogen atom is part of a morpholinium moiety. An example of a morpholinium bromide complexing agent is N-ethyl-N-methylmorpholinium bromide.

[0047] As used herein, the term "phosphonium bromide complexing agent" refers to any compound, salt, or material comprising a quaternary phosphonium atom. An example of a phosphonium bromide complexing agent is tetraethylphosphonium bromide.

[0048] As used herein, the term "crown ether" refers to a cyclic chemical compound consisting of a ring containing at least three ether groups. Examples of crown ethers include 12-crown-4, 15-crown-5, 18-crown-6, dibenzo-18-crown-6, and diaza-18-crown-6. [0049] As used herein, an "alkyl" group refers to a saturated aliphatic hydrocarbon group containing 1-20 (e.g., 1-16, 1-12, 1-8, 1-6, or 1-4) carbon atoms. An alkyl group can be straight or branched. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl, decyl, dodecyl, and cetyl.

[0050] As used herein, an "aryl" group used alone or as part of a larger moiety as in

"aralkyl", "aralkoxy", or "aryloxyalkyl" refers to monocyclic (e.g., phenyl); bicyclic (e.g., indenyl, naphthalenyl, tetrahydronaphthyl, tetrahydroindenyl); tricyclic (e.g., fluorenyl, tetrahydrofluorenyl, anthracenyl, or tetrahydroanthracenyl); or a benzofused group having 3 rings. For example, a benzofused group includes phenyl fused with two or more C _4-8 carbocyclic moieties. An aryl is optionally substituted with one or more substituents including aliphatic (e.g., alkyl, alkenyl, or alkynyl); cycloalkyl; (cycloalkyl)alkyl;

heterocycloalkyl; (heterocycloalkyl)alkyl; aryl; heteroaryl; alkoxy; cycloalkyloxy;

heterocycloalkyloxy; aryloxy; heteroaryloxy; aralkyloxy; heteroaralkyloxy; aroyl;

heteroaroyl; amino; aminoalkyl; nitro; carboxy; carbonyl (e.g., alkoxycarbonyl,

alkylcarbonyl, aminocarbonyl, (alkylamino)alkylaminocarbonyl, arylaminocarbonyl, heteroarylaminocarbonyl; or sulfonylcarbonyl); aryalkylcarbonyloxy; sulfonyl (e.g., alkylsulfonyl or aminosulfonyl); sulfinyl (e.g., alkylsulfinyl); sulfanyl (e.g., alkylsulfanyl); cyano; halo; hydroxyl; acyl; mercapto; sulfoxy; urea; thiourea; sulfamoyl; sulfamide; oxo; or carbamoyl. Alternatively, an aryl may be unsubstituted.

[0051] Examples of substituted aryls include haloaryl, alkoxycarbonylaryl,

alkylaminoalkylaminocarbonylaryl, p, w-dihaloaryl, -amino-p-alkoxycarbonylaryl, m-amino-ffi-cyanoaryl, aminoaryl, alkylcarbonylaminoaryl, cyanoalkylaryl, alkoxyaryl, aminosulfonylaryl, alkylsulfonylaryl, aminoaryl, >-halo-m-aminoaryl, cyanoaryl,

hydroxyalkylaryl, alkoxyalkylaryl, hydroxyaryl, carboxyalkylaryl, dialkylaminoalkylaryl, m-heterocycloaliphatic-o-alkylaryl, heteroarylaminocarbonylaryl, nitroalkylaryl,

alkylsulfonylaminoalkylaryl, heterocycloaliphaticcarbonylaryl, alkylsulfonylalkylaryl, cyanoalkylaryl, heterocycloaliphaticcarbonylaryl, alkylcarbonylaminoaryl, hydroxyalkylaryl, alkylcarbonylaryl, aminocarbonylaryl, alkylsulfonylaminoaryl, dialkylaminoaryl, alkylaryl, and trihaloalkylaryl.

[0052] As used herein, an "aralkyl" group refers to an alkyl group (e.g., a Ci^ alkyl group) that is substituted with an aryl group. Both "alkyl" and "aryl" are defined herein. An example of an aralkyl group is benzyl. A "heteroaralkyl" group refers to an alkyl group that is substituted with a heteroaryl. [0053] As used herein, a "cycloalkyl" group refers to a saturated carbocyclic mono-, bi-, or tri-, or multicyclic (fused or bridged) ring of 3-10 (e.g., 5-10) carbon atoms. Without limitation, examples of monocyclic cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, or the like. Without limitation, examples of bicyclic cycloalkyl groups include octahydro-indenyl, decahydro-naphthyl, bicyclo[3.2.1]octyl, bicyclo[2.2.2]octyl, bicyclo[3.3.1]nonyl, bicyclo[3.3.2.]decyl, bicyclo[2.2.2]octyl, bicycle[2.2.1]heptanyl, bicycle[3.1.1]heptanyl, or the like. Without limitation, multicyclic groups include adamantyl, cubyl, norbornyl, or the like. Cycloalkyl rings can be optionally substituted at any chemically viable ring position.

[0054] As used herein, a "heterocycloalkyl" group refers to a 3-10 membered mono or bicyclic (fused or bridged) (e.g., 5 to 10 membered mono or bicyclic) saturated ring structure, in which one or more of the ring atoms is a heteroatom (e.g., N, O, S, or combinations thereof). Examples of a heterocycloalkyl group include optionally substituted piperidyl, piperazyl, tetrahydropyranyl, tetrahydrofuryl, 1 ,4-dioxolanyl, 1 ,4-dithianyl, 1,3-dioxolanyl, oxazolidyl, isoxazolidyl, morpholinyl, thiomorpholyl, octahydro-benzofuryl,

octahydro-chromenyl, octahydro-thiochromenyl, octahydro-indolyl, octahydro-pyrindinyl, decahydro-quinolinyl, octahydro-benzo[6]thiopheneyl, 2-oxa-bicyclo[2.2.2]octyl, l-aza-bicyclo[2.2.2]octyl, 3-aza-bicyclo[3.2.1]octanyl, 2,6-dioxa-tricyclo[3.3.1.0 ³ ' ⁷ ]nonyl, tropane, or the like. A monocyclic heterocycloalkyl group may be fused with a phenyl moiety such as tetrahydroisoquinoline. Heterocycloalkyl ring structures can be optionally substituted at any chemically viable position on the ring or rings.

[0055] A "heteroaryl" group, as used herein, refers to a monocyclic, bicyclic, or tricyclic ring structure having 4 to 15 ring atoms wherein one or more of the ring atoms is a heteroatom (e.g., N, O, S, or combinations thereof) and wherein one or more rings of the bicyclic or tricyclic ring structure is aromatic. A heteroaryl group includes a benzofused ring system having 2 to 3 rings. For example, a benzofused group includes benzo fused with one or two C ₄ -8 heterocyclic moieties (e.g., indolizyl, indolyl, isoindolyl, 3H-indolyl, indolinyl, benzo[b]furyl, benzo [6]thiophenyl, quinolinyl, or isoquinolinyl). Some examples of heteroaryl are azetidinyl, pyridyl, lH-indazolyl, furyl, pyrrolyl, thienyl, thiazolyl, oxazolyl, imidazolyl, tetrazolyl, benzofuryl, isoquinolinyl, benzthiazolyl, xanthene, thioxanthene, phenothiazine, dihydroindole, benzo[l,3]dioxole, benzo[6]furyl, benzo[6]thiophenyl, indazolyl, benzimidazolyl, benzthiazolyl, puryl, cinnolyl, quinolyl, quinazolyl, cinnolyl, phthalazyl, quinazolyl, quinoxalyl, isoquinolyl, 4H-quinolizyl, benzo- 1,2,5-thiadiazolyl, or 1,8-naphthyridyl. [0056] As used herein, the term "carbon powder " refers to any powder material comprising at least 90 wt% of carbon by weight of the carbon material (e.g., greater than 95 wt% of carbon by weight of the carbon material or greater than 99 wt% of carbon by weight of the carbon material). Carbon powders include without limitation powders comprising of or consisting essentially of activated carbon, amorphous carbon, carbon blacks, soots, fullerenes, nanotubes, bucky balls, single wall nanotube, multiwall nanotubes, graphite, graphene, glassy carbon, diamond, and the like. Carbon powder may also refer to a powder comprising or consisting essentially of a carbon material formed from pyrolysis of both natural and synthetic materials such as coconut shell or plastic resins. Carbon powder may also refer to carbon material that may be obtained from carbon sources which are not initially in powdered form, but are reduced in size by any suitable size reduction method (such as milling, attrition, screening, or the like) to create the desired particle size. In some instances carbon powder comprises a plurality of particles of a size to be suspended in the electrolyte.

[0057] II. ZINC HALIDE ELECTROLYTE

[0058] In one aspect, the present invention provides a zinc halide electrolyte that comprises a zinc halide salt, water, and a carbon powder. Electrolytes of the present invention are useful in flow cell battery systems, such as those described in U.S. Pat. Nos. 5,851,694; 5,702,842; and 5,607,788. In some examples, electrolytes of the present invention are useful in non-flow cell battery systems, such as those described in U.S. Pat. No. 5,591,538; U.S. Pat. Pub. No. US20150010792A1 ; and US20150010833A1.

[0059] In some embodiments, the zinc halide salt is ZnBr ₂ , ZnCb, Znl ₂ , or any combination thereof. As mentioned above, the zinc halide salt in the electrolyte is reversibly electrolyzed when the flow system is electrical charged and discharged. Accordingly, when the flow battery system is electrically charged, the zinc from the zinc salt is converted to neutral zinc metal, and the halide forms a di-halide or polyhalide species (e.g. Br ₂ , Cl ₂ , or the like). In some embodiments, the zinc halide electrolyte comprises from about 20 wt% to about 60 wt% of zinc halide salt. For example, the zinc halide electrolyte comprises from about 25 wt% to about 50 wt% (e.g., from about 25 wt% to about 45 wt%, from about 27 wt% to about 35 wt%) of zinc halide salt.

[0060] In some embodiments, the zinc halide electrolyte comprises ZnBr ₂ . For instance, the zinc halide electrolyte comprises from about 28 wt% to about 37 wt% of ZnBr ₂ . In some embodiments, the zinc halide electrolyte comprises ZnCl ₂ . For instance, the zinc halide electrolyte comprises from about 1.5 wt% to about 7.5 wt% of ZnCb. And, in some embodiments, the zinc halide electrolyte comprises ZnBr ₂ and ZnCl ₂ . For instance, the zinc halide electrolyte comprises from about 28 wt% to about 37 wt% of ZnBr ₂ and from about 1.5 wt% to about 7.5 wt% of ZnCl ₂ .

[0061] Zinc halide electrolytes of the present invention further comprise a carbon powder. The carbon powder functions to reversibly sequester (e.g., absorb and desorb) the halogen species in the electrolyte. For example, carbon powder adsorbs and desorbs bromine, i.e., Br ₂ , based on a concentration gradient as the flow battery system electrically charges and discharges. As the battery system charges and Br ₂ concentration increases in the electrolyte, Br ₂ absorbs into the carbon powder. As the battery system discharges and Br ₂ is reduced to bromide, i.e., Br ^" , the reduction in the concentration gradient of Br ₂ in the discharging cell drives bromine out of the carbon powder.

[0062] Carbon powders suitable for use in electrolytes of the present invention include activated carbon, amorphous carbon, carbon blacks, soots, fullerenes, nanotubes, bucky balls, single wall nanotubes, multiwall nanotubes, graphite, graphene, glassy carbon, diamond, and the like, or any combination thereof. In some embodiments, the carbon powder comprises activated carbon, amorphous carbon, carbon blacks, or any combination thereof.

[0063] In some embodiments, the zinc halide electrolyte comprises a ratio of wt% of carbon powder to wt% of zinc halide salt of from about 1 :2 to about 1 :1. For instance, the zinc halide electrolyte comprises a ratio of wt% of carbon blacks powder to wt% of zinc halide salt (e.g., ZnBr ₂ , ZnCb, or any combination thereof) of from about 1 :2 to about 1 :1 (e.g., from about 1 :2 to 1 : 1.75, from about 1 :2 to 1 :1.50, or from about 1 :2 to 1 :1.5). In other examples, the zinc halide electrolyte comprises from about 10 wt% to about 30 wt% of carbon powder. In other instances, the zinc halide electrolyte comprises from about

12.5 wt% to about 25 wt% of carbon powder.

[0064] In some examples, including flowing and non-flowing cell batteries, a solid carbon electrode may be included as part of the cathode or near the cathode in addition to the powdered carbon contained in the electrolyte. The solid carbon electrode may be contained within a cathode cage or other means of containment, or may be integrated with the cathode. In some examples, when a solid carbon electrode is included, the total halide (e.g. bromine) absorption of the carbon powder and carbon electrode should be sufficient for the capacity of the battery. For example, using activated carbon for the electrolyte and graphine for the solid carbon electrode provides for flexibility in battery construction and may allow for advantages in conduction and halide absorption. The graphine of the solid carbon may be a better conductor with higher conductivity than activated carbon but the graphine does not absorb halides (e.g. bromine) as well. The activated carbon in powder form may be better at absorbing halides (e.g. bromine) but may not be as good of a conductor as the solid carbon graphine. The ratio or amounts of solid carbon in the electrode and powdered carbon in the electrolyte may be adjusted to alter the absorption of halides and the electrical conductivity of the cathode depending on the application.

[0065] In some embodiments, zinc halide electrolyte comprises 21 moles of ZnBr ₂ and 3.8 kg ± 100 g of carbon powder.

[0066] The carbon powders suited for use in the present invention can be mixed with the liquid (e.g., liquid at room temperature) components of the zinc-halide electrolyte to form a pumpable mixture. For example, the carbon powder has a mean particle diameter of less than 0.75 mm (e.g., from about 250 nm to about 700 μπι, from about 500 nm to about 500 μπι, or from about 250 nm to about 250 μπι). In other examples, the carbon powder is substantially suspended (e.g., at least 50 wt% of the carbon powder (by weight of the carbon powder) remains suspended in the electrolyte for at least 30 minutes after vigorous mixing) in the zinc halide electrolyte. In some examples, the electrolyte is not required to be pumped and may allow for a greater range of particle sizes. When the electrolyte is not pumped, faster settling rates may be acceptable, (e.g. faster than 30 minutes) allowing for a larger particle size.

[0067] In other examples, the carbon powders suited for use in the present invention can also be mixed with the liquid (e.g., liquid at room temperature) components of the zinc-halide electrolyte to form a mixture that may not be pumped. For example, the carbon powder has a mean particle diameter of less than 1.5 mm (e.g., from about 250 nm to about 1400 μπι, from about 500 nm to about 500 μηι, or from about 250 nm to about 250 μηι). In examples where the electrolyte is not required to be pumped a greater range of particle sizes may be allowable. When the electrolyte does not have to be pumped faster settling rates may be acceptable, (e.g. faster than 30 minutes) allowing for the larger particle size. In electrolytes that are not pumped the settling of the larger particle size may create a packed powder that provides improved bromine absorption.

[0068] In some embodiments, the zinc halide electrolyte comprises from about 10 wt% to about 40 wt% of water. For instance, the zinc halide electrolyte comprises from about 15 wt% to about 30 wt% of water. In some embodiments, the electrolyte comprises from about 30 wt% to about 50 wt% of water. In some embodiments, the electrolyte further comprises from about 35 wt% to about 45 wt% of water. In some examples, the water is de- mineralized until its resistance is greater than about 8 ΜΩ-cm (e.g., about 10 ΜΩ-cm or greater or greater than about 10 ΜΩ-cm). [0069] The zinc halide electrolyte comprising carbon powder may be used in static or flow battery systems. In a flow battery system, the electrolyte is stored in tanks or reservoirs and pumped to an electrochemically active site where it replenishes spent electrolyte. In a static cell or cell stack, the electrolyte is suited for use in those cells or stacks that include an internal mixer to ensure that the carbon particles remain substantially suspended in the zinc halide electrolyte.

[0070] Zinc halide electrolytes of the present invention may optionally comprise additional additives that enhance the performance of the battery system in which the electrolyte is used. For example, the zinc halide electrolyte may optionally comprise one or more alkali metal salts (e.g., KBr, KCl, or the like), a glyme, an ether, an alcohol, an inorganic acid, one or more quaternary ammonium agents, a stabilizing agent, or any combination thereof.

[0071] In some embodiments, the electrolyte comprises from about 4 wt% to about 12 wt% (e.g., from about 3 wt% to about 5 wt%) of potassium bromide (KBr). In some

embodiments, the electrolyte comprises from about 4 wt% to about 6 wt% of potassium bromide (KBr).

[0072] In some embodiments, the electrolyte comprises from about 2 wt% to about 6 wt% (e.g., from about 3 wt% to about 5 wt%) of potassium chloride (KCl). In some embodiments, the electrolyte comprises from about 4 wt% to about 7 wt% of potassium chloride (KCl). In some embodiments, the electrolyte comprises from about 5.5 wt% to about 7 wt% of potassium chloride (KCl).

[0073] In some embodiments, the electrolyte further comprises from about 0.25 wt% to about 5 wt% (e.g., from about 0.5 wt% to about 3.75 wt%) of a glyme. In some examples, the glyme comprises monoglyme, diglyme, triglyme, tetraglyme, pentaglyme, hexaglyme, or any combination thereof. For instance, the glyme comprises tetraglyme. In other examples, the electrolyte comprises from about 0.5 wt% to about 2.5 wt% of tetraglyme.

[0074] In some embodiments, the electrolyte further comprises from about 0.025 wt% to about 2.0 wt% (e.g., from about 0.05 wt% to about 0.5 wt%) of an ether. In some

embodiments, the ether is a crown ether, DME-PEG, dimethyl ether, or any combination thereof. In a further embodiment, the ether is a crown ether. And, in some embodiments, the electrolyte further comprises from about 0.25 wt% to about 1.25 wt% (e.g., from about 0.5 wt% to about 1 1.5 wt%) of DME-PEG or dimethyl ether. In some examples, the DME- PEG has an average molecular weight (e.g., a number average molecular weight M _n ) of from about 350 amu to about 3000 amu. In other examples, the DME-PEG has an average molecular weight of from about 1200 amu to about 3000 amu. And, in some examples, the electrolyte further comprises from about 2.5 wt% to about 5 wt% of DME-PEG, wherein the DME-PEG has an average molecular weight (e.g., a number average molecular weight M _n ) of from about 1500 amu to about 2500 amu (e.g., about 2000 amu). In some embodiments, the ether is a crown ether. For example, the crown ether is 18-crown-6. For example, the crown ether is 15-crown-5. For example, the crown ether is 12-crown-4.

[0075] In some embodiments, the electrolyte further comprises from about 0.05 wt% to about 0.5 wt% of an alcohol, wherein the alcohol is substantially miscible in water. For example, the alcohol comprises a C alcohol. In other examples, the alcohol comprises methanol, ethanol, 1-propanol (i.e., n-propanol), 2-propanol (i.e., iso-propanol), 1-butanol (i.e., n-butanol), sec-butanol, iso-butanol, tert-butanol, 1-pentanol, or any combination thereof. And in some examples, the electrolyte further comprises from about 0.125 wt% to about 0.375 wt% of tert-butanol.

[0076] In some embodiments, the electrolyte further comprises from about 0.175 wt% to about 2.5 wt% (e.g., from about 0.25 wt% to about 2 wt%) of a Ci-io glycol. In some examples, the electrolyte further comprises from about 0.175 wt% to about 2.5 wt% (e.g., from about 0.25 wt% to about 2 wt%) of a substituted ethylene glycol or a substituted propylene glycol. In some examples, the glycol comprises ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, neopentyl glycol, hexalene glycol, or any combination thereof. And, in some examples, the electrolyte further comprises from about 0.125 wt% to about 1.75 wt% of neopentyl glycol.

[0077] In some embodiments, the electrolyte further comprises one or more quaternary ammonium agents. And, in some examples, the one or more quaternary ammonium agents is a salt of Formula I

Formula I

wherein is saturated, partially unsaturated, or fully unsaturated; Xi, X ₂ , X ₃ , X ₄ , and X ₅ are each independently selected from carbon, oxygen, and nitrogen, provided that at least one of Xi, X ₂ , X ₃ , X ₄ , and X ₅ is nitrogen;

each R is independently hydrogen, alkyl, cycloalkyl, aryl, arylalkyl, heterocycloalkyl, or heteroaryl, wherein each R is independently and optionally substituted with halo, -CN, -N0 ₂ , -OQ ₂ , -S(0) _z Q ₂ , -S(0) _z N(Q ₂ ) ₂ , -N(Q ₂ ) ₂ , -C(0)OQ ₂ , -C(0)Q ₂ , -C(0)N(Q ₂ ) ₂ , -C(0)N(Q ₂ )(OQ ₂ ), -N(Q ₂ )C(0)Q ₂ , -N(Q ₂ )C(0)N(Q ₂ ) ₂ , -N(Q ₂ )C(0)OQ ₂ , -N(Q ₂ )S(0) _z Q ₂ , or heterocycloalkyl or alkyl optionally substituted with 1-3 Q ₃ substituents;

each Q ₂ is independently hydrogen, alkyl, cycloalkyl, aryl, arylalkyl, heterocycloalkyl, or heteroaryl, each optionally substituted with 1-3 Q ₃ substituents; each Q ₃ is independently halo, oxo, CN, N0 ₂ , CF ₃ , OCF ₃ , OH, -S(0) _z (Ci _-6 alkyl), -N(Ci _-6 alkyl) ₂ , -COO(Ci- ₆ alkyl), -C(O) (Ci _-6 alkyl), -0(Ci _-6 alkyl), or a C _1-6 alkyl optionally substituted with 1 -3 substituents selected from halo, oxo, -CN, -N0 ₂ , -CF ₃ , -OCF3, -OH, -SH, -S(0) _z H, -NH ₂ , or -COOH;

m is 0, 1, 2, 3, 4, or 5;

n is 0, 1, or 2; and

Y is an anion (e.g., a halide (e.g., bromide)).

[0078] In one embodiment, one or two of Xi, X ₂ , X ₃ , X ₄ , and X ₅ are nitrogen, and the rest are carbon. In a further embodiment, one of Xi, X ₂ , X ₃ , X ₄ , and X ₅ is nitrogen, and the rest are carbon. In another further embodiment, two of Xi, X ₂ , X ₃ , X4, and X ₅ are nitrogen, and the

rest are carbon. In still a further embodiment,

pyrimidine, pyrazine, piperazine, piperidine, morpholine, 1,3-oxazinane, 1 ,2-oxazinane, pyrrolidine, pyrrole, pyrazole, imidazole, oxazole, isoxazole, 1,2,3-oxadiazole,

1,3,4-oxadiazole, 1,2,3-triazole, 1 ,2,4-triazole, 1,2,3,4-oxatriazole, 1,2,3,5-oxatriazole, 1 ,2,4,5-oxatriazole, and t

[0079] In one embodime

piperazine, piperidine, morpholine, 1,3-oxazinane, and 1,2-oxazinane. In one embodiment, xr ^x ,

^A s is selected from pyridine, pyrimidine, and pyrazine. In a further embodiment, is pyridine.

[0080] In one embodiment, is selected from piperidine, morpholine, x ₃ x.

1,3-oxazinane, and 1,2-oxazinane. In a further embodiment, ^A 5 is selected from

piperidine and morpholine. In one embodiment, is piperidine. In one

embodiment, is morpholine.

X ₃ X _|

[0081] In one embodiment, ^A _X 5A is selected from pyrrolidine, pyrrole, pyrazole, imidazole, oxazole, isoxazole, 1,2,3-oxadiazole, 1,3,4-oxadiazole, 1,2,3-triazole,

1 ,2,4-triazole, 1,2,3,4-oxatriazole, 1,2,3,5-oxatriazole, 1,2,4,5 -oxatriazole, and tetrazole. In

another embodiment, is selected from pyrrole, pyrazole, and imidazole. In one

embodiment, pyrazole. In one

embodiment, is pyrrolidine.

[0082] In one embodiment, n is 1. In another embodiment, n is 0. [0083] In one embodiment, each R is independently alkyl or cycloalkyl, wherein each R is independently and optionally substituted with halo, -CN, -N0 ₂ , -OQ2, -S(0) _z Q ₂ ,

-S(0)zN(Q ₂ ) ₂ , -N(Q ₂ ) ₂ , -C(0)OQ ₂ , -C(0)Q ₂ , -C(0)N(Q ₂ ) ₂ , -C(0)N(Q ₂ )(OQ ₂ ),

-N(Q ₂ )C(0)Q ₂ , -N(Q ₂ )C(0)N(Q ₂ ) ₂ , -N(Q ₂ )C(0)OQ ₂ , -N(Q ₂ )S(0) _z Q ₂ , or heterocycloalkyl or alkyl optionally substituted with 1-3 Q ₃ substituents. In another embodiment, each R is independently alkyl or cycloalkyl, wherein each R is independently and optionally substituted with halo, heterocycloalkyl, -CN, -N0 ₂ , -OQ ₂ , -N(Q ₂ ) ₂ , -C(0)OQ ₂ , -C(0)Q ₂ , or -C(0)N(Q ₂ ) ₂ . In a further embodiment, each R is alkyl, which is independently and optionally substituted with halo, heterocycloalkyl, -CN, -N0 ₂ , -OQ ₂ , -N(Q ₂ ) ₂ , -C(0)OQ ₂ , -C(0)Q ₂ , or -C(0)N(Q ₂ ) ₂ . In still a further embodiment, each R is alkyl, which is independently and optionally substituted with halo, heterocycloalkyl, -CN, -N0 ₂ , -N(Q ₂ ) ₂ , or -C(0)N(Q ₂ ) ₂ . In yet a further embodiment, each R is alkyl, which is independently and optionally substituted with halo or heterocycloalkyl.

[0084] In another embodiment, each R is alkyl, which is substituted with heterocycloalkyl. In a further embodiment, R is alkyl, which is substituted with pyrrolidine. In a further embodiment, R is propyl, which is substituted with heterocycloalkyl. In a further

embodiment, R is propyl, which is substituted with pyrrolidine.

[0085] In one embodiment, each R is an unsubstituted alkyl. In another embodiment, R is selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl, decyl, dodecyl, and cetyl. In one embodiment, R is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, and cetyl. In one embodiment, R is methyl. In one embodiment, R is ethyl. In one embodiment, R is propyl. In one embodiment, R is butyl. In one embodiment, R is pentyl. In one embodiment, R is hexyl. In one embodiment, R is heptyl. In one embodiment, R is octyl. In one embodiment, R is dodecyl. In one embodiment, R is nonyl. In one

embodiment, R is decyl. In one embodiment, R is dodecyl. In one embodiment, R is cetyl.

[0086] In one embodiment, Y is an anion selected from fluoride, chloride, bromide, iodide, arsenate, phosphate, arsenite, hydrogen phosphate, dihydrogen phosphate, sulfate, nitrate, hydrogen sulfate, nitrite, thiosulfate, sulfite, perchlorate, iodate, chlorate, bromate, chlorite, hypochlorite, hypobromite, carbonate, chromate, hydrogen carbonate (bicarbonate), dichromate, acetate, formate, cyanide, amide, cyanate, peroxide, thiocyanate, oxalate, hydroxide, and permanganate. In a further embodiment, Y is a monovalent anion selected from fluoride, chloride, bromide, iodide, dihydrogen phosphate, nitrate, perchlorate, hypochlorite, hydrogen carbonate (bicarbonate), acetate, formate, cyanide, and hydroxide. In another further embodiment, Y is a bivalent anion selected from hydrogen phosphate, sulfate, and carbonate. In still a further embodiment, Y is selected from fluoride, chloride, bromide and iodide. In one embodiment, Y is chloride. In one embodiment, Y is bromide. In one embodiment, Y is iodide.

[0087] In some embodiments, the one or more quaternary ammonium agents is a salt of Formula la, Formula lb, Formula Ic, Formula Id, or Formula Ie.

wherein

each R, R', and R" is independently hydrogen, alkyl, cycloalkyl, aryl, arylalkyl, heterocycloalkyl, or heteroaryl, wherein each R, R', and R" is independently and optionally substituted with halo, -CN, -N0 ₂ , -OQ ₂ , -S(0) _z Q ₂ , -S(0) _z N(Q ₂ ) ₂ , -N(Q ₂ ) ₂ , -C(0)OQ ₂ , -C(0)Q ₂ , -C(0)N(Q ₂ ) ₂ , -C(0)N(Q ₂ )(OQ ₂ ), -N(Q ₂ )C(0)Q ₂ , -N(Q ₂ )C(0)N(Q ₂ ) ₂ ,

-N(Q ₂ )C(0)OQ ₂ , -N(Q ₂ )S(0)zQ2, or heterocycloalkyl or alkyl optionally substituted with 1-3 Q ₃ substituents;

each Q ₂ is independently hydrogen, alkyl, cycloalkyl, aryl, arylalkyl, heterocycloalkyl, or heteroaryl, each optionally substituted with 1 -3 Q ₃ substituents;

each Q ₃ is independently halo, oxo, CN, N0 ₂ , CF ₃ , OCF ₃ , OH, -S(0) _z (Ci- ₆ alkyl),-N(Ci _-6 alkyl) ₂ , -COO(C _)-6 alkyl), -C(O) (Ci _-6 alkyl), -0(C. _-6 alkyl), or a Ci- ₆ alkyl optionally substituted with 1-3 substituents selected from halo, oxo, -CN, -N0 ₂ , -CF ₃ , -OCF ₃ , -OH, -SH, -S(0)zH, -NH ₂ , or -COOH;

k is 0, 1, or 2; and

Y is an anion.

[0088] In some embodiments of Formulas Ia-Ie, each R, R', and R" is independently alkyl or cycloalkyl, wherein each R, R', and R" is independently and optionally substituted with halo, -CN, -N0 ₂ , -OQ ₂ , -S(0) _z Q ₂ , -S(0) _z N(Q ₂ ) ₂ , -N(Q ₂ ) ₂ , -C(0)OQ ₂ , -C(0)Q ₂ , -C(0)N(Q ₂ ) ₂ , -C(0)N(Q )(OQ ₂ ), -N(Q ₂ )C(0)Q ₂ , -N(Q ₂ )C(0)N(Q ₂ ) ₂ , -N(Q ₂ )C(0)OQ ₂ , -N(Q ₂ )S(0) _z Q ₂ , or heterocycloalkyl or alkyl optionally substituted with 1-3 Q ₃ substituents. In another embodiment, each R, R', and R" is independently alkyl or cycloalkyl, wherein each R, R', and R" is independently and optionally substituted with halo, heterocycloalkyl, -CN, -NO2, -OQ2, -N(Q ₂ ) 2, -C(0)OQ ₂ , -C(0)Q ₂ , or -C(0)N(Q ₂ ) ₂ . In a further embodiment, each R, R', and R" is independently alkyl, which is independently and optionally substituted with halo, heterocycloalkyl, -CN, -N0 ₂ , -OQ2, -N(Q ₂ ) ₂ , -C(0)OQ ₂ , -C(0)Q ₂ , or -C(0)N(Q ₂ ) ₂ . In still a further embodiment, each R, R', and R" is independently alkyl, which is independently and optionally substituted with halo, heterocycloalkyl, -CN, -NO2, -N(Q ₂ ) 2, or -C(0)N(Q ₂ ) ₂ .

[0089] In one embodiment, each R, R', and R" is independently an unsubstituted alkyl. In another embodiment, each R, R', and R" is independently selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl, decyl, dodecyl, and cetyl. In one embodiment, each R, R', and R" is independently selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, and cetyl.

[0090] In some embodiments of Formulas Ia-Ie, Y is selected from fluoride, chloride, bromide, iodide, arsenate, phosphate, arsenite, hydrogen phosphate, dihydrogen phosphate, sulfate, nitrate, hydrogen sulfate, nitrite, thiosulfate, sulfite, perchlorate, iodate, chlorate, bromate, chlorite, hypochlorite, hypobromite, carbonate, chromate, hydrogen carbonate (bicarbonate), dichromate, acetate, formate, cyanide, amide, cyanate, peroxide, thiocyanate, oxalate, hydroxide, and permanganate. In a further embodiment, Y is a monovalent anion selected from fluoride, chloride, bromide, iodide, dihydrogen phosphate, nitrate, perchlorate, hypochlorite, hydrogen carbonate (bicarbonate), acetate, formate, cyanide, and hydroxide. In another further embodiment, Y is selected from a bivalent anion selected from hydrogen phosphate, sulfate, and carbonate. In still a further embodiment, Y is selected from fluoride, chloride, bromide and iodide. In one embodiment, Y is chloride. In one embodiment, Y is bromide. In one embodiment, Y is iodide.

[0091] In some embodiments of Formulas Ia-Ie, k is 0 or 1. In a further embodiment, k is 0. In another further embodiment, k is 1.

[0092] In some embodiments of Formula la, each R and R' is independently selected from methyl, ethyl, butyl, and hexyl. In a further embodiment, k is 1 ; R' is selected from ethyl, butyl, and hexyl; and R is methyl. In another further embodiment, k is 0 and R' is selected from ethyl, butyl, and hexyl.

[0093] In one embodiment, the salt of Formula la is selected from

l-ethyl-3-methylpyridinium bromide, l-ethyl-2-methylpyridinium bromide, l-butyl-3-methylpyridinium bromide, l-butyl-4-methylpyridinium bromide, and 1- hexylpyridinium bromide.

[0094] In some embodiments of Formula lb, each R, R', and R" is independently selected from methyl and propyl.

[0095] In one embodiment, the salt of Formula lb is 1 -methyl- 1-propylpiperidinium bromide.

[0096] In some embodiments of Formula Ic, each R, R', and R" is independently selected from methyl, ethyl, and butyl. In a further embodiment, k is 0.

[0097] In one embodiment, the salt of Formula Ic is selected from

N-methyl-N-ethylmorpholinium bromide and N-methyl-N-butylmorpholinium bromide.

[0098] In some embodiments of Formula Id, each R, R', and R" is independently selected from methyl, ethyl, butyl, hexyl, octyl, arid decyl. In a further embodiment, k is 1 and R is methyl.

[0099] In one embodiment, the salt of Formula Id is selected from

l-ethyl-3-methylimidazolium bromide, l-butyl-3-methylimidazolium bromide,

l-ethyl-2,3-dimethylimidazolium bromide, l-decyl-3-methylimidazolium bromide, l-butyl-2,3-dimethylimidazolium bromide, l-methyl-3-octylimidazolium bromide, and 1 -methyl-3-hexylimidazolium bromide.

[0100] In some embodiments of Formula Ie, each R, R', and R" is independently selected from methyl, ethyl, propyl, butyl, pentyl, and hexyl. In another embodiment, k is 0 and each R' and R" is independently an alkyl, which is optionally substituted by heterocycloalkyl or halo. In a further embodiment, k is 0 and each R' and R" is independently selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, 2-choroethyl, or 3-(N-methylpyrrolidinium)propyl.

[0101] In one embodiment, the salt of Formula Ie is selected from

N-methyl-N-ethylpyrrolidinium bromide, N-ethyl-N-propylpyrrolidinium bromide, N-propyl- N-butylpyrrolidinium bromide, N-methyl-N-butylpyrolidinium bromide,

N-ethyl-N-(2-chloroethyl)pyrrolidinium bromide, N-methyl-N-hexylpyrrolidinium bromide, N-methyl-N-pentylpyrrolidinium bromide, N-ethyl-N-pentylpyrrolidinium bromide,

N-ethyl-N-butylpyrrolidinium bromide, N-butyl-N-pentylpyrrolidinium bromide,

N-methyl-N-propylpyrrolidinium bromide, trimethylene-bis(N-methylpyrrolidinium) dibromide, and N-propyl-N-pentylpyrrolidinium bromide.

[0102] In some embodiments, the one or more quaternary ammonium agent comprises an

agent having the chemical formula , wherein Ri, R ₂ , R ₃ , and R4 are each independently hydrogen or an alkyl group, and Y is an anion as defined herein. In some embodiments, the one or more quaternary ammonium agents comprises ammonium halides (e.g., NH ₄ Br, NH ₄ C1, or any combination thereof); tetra-alkylammonium halides (e.g., tetramethylammonium bromide, tetramethylammonium chloride, tetraethylammonium bromide, tetraethylammonium chloride, combinations thereof, or the like); heterocyclic ammonium halides (e.g., N-methyl-N-ethylpyrrolidinium halide,

N-ethyl-N-methylpyrrolidinium halide, combinations thereof, or the like); or any

combination thereof. In some embodiments, the one or more quaternary ammonium agents comprises a quaternary ammonium agent selected from the group consisting of ammonium chloride, ammonium bromide, tetraethylammonium bromide, trimethylpropylammonium bromide, N-methyl-N-ethylmorpholinium bromide, N-ethyl-N-methylmorpholinium bromide, N-methyl-N-butylmorpholinium bromide, N-methyl-N-ethylpyrrolidinium bromide, N,N,N-triethyl-N-propylammonium bromide, N-ethyl-N-propylpyrrolidinium bromide, N-propyl-N-butylpyrrolidinium bromide, N-methyl-N-butylpyrolidinium bromide,

N-ethyl-N-(2-chloroethyl)pyrrolidinium bromide, N-methyl-N-hexylpyrrolidinium bromide, N-methyl-N-pentylpyrrolidinium bromide, N-ethyl-N-pentylpyrrolidinium bromide,

N-ethyl-N-butylpyrrolidinium bromide, trimethylene-bis(N-methylpyrrolidinium) dibromide, N-butyl-N-pentylpyrrolidinium bromide, N-methyl-N-propylpyrrolidinium bromide,

N-propyl-N-pentylpyrrolidinium bromide, and any combination thereof. In some examples, the electrolyte comprises from about 1 wt% to about 5 wt % of one or more quaternary ammonium agents. In some examples, the electrolyte comprises from about 3 wt% to about 7 wt% of one or more quaternary ammonium agents. And, in some embodiments, the one or more quaternary ammonium agents comprises N-methyl-N-ethylmorpholinium bromide. In other examples, the electrolyte comprises from about 0.25 wt% to about 1.25 wt% of

N-methyl-N-ethylmorpholinium bromide. And, in some examples, the one or more quaternary ammonium agents comprises tetraethylammonium bromide,

trimethylpropylammonium bromide, or any combination thereof. For instance, the electrolyte comprises from about 1 wt% to about 5 wt% of tetraethylammonium bromide.

[0103] In some embodiments, the one or more quaternary ammonium agents comprises a quaternary ammonium agent selected from the group consisting of an ammonium bromine complexing agent, an imidazolium bromine complexing agent, a pyrrolidinium bromine complexing agent, a pyridinium bromine complexing agent, a phosphonium bromine complexing agent, and a morpholinium bromine complexing agent. [0104] In some embodiments, the one or more quaternary ammonium agents comprises a quaternary ammonium agent selected from the group consisting of (TEA)

tetraethylammonium bromide, (MEM)N-Ethyl-N-methylmorpholiniumbromide,

trimethylpropylammonium bromide, l-ethyl-3-methylimidazolium bromide,

l-butyl-3 -methylimidazolium bromide, 1 -butyl- 1 -methylpyrrolidinium bromide,

l-ethyl-3-methylpyridinium bromide, l-ethyl-3-methylpyridinium bromide,

l-ethyl-2-methylpyridinium bromide, 1 -methyl- 1 -propylpiperidinium bromide,

dodecyltrimethylammonium bromide, l-ethyl-2,3-dimethylimidazolium bromide, l-decyl-3 -methylimidazolium bromide, l-butyl-2,3-dimethylimidazolium bromide, l-methyl-3-octylimidazolium bromide, l-methyl-3-hexylimidazolium bromide,

l-butyl-3 -methylpyridinium bromide, l-butyl-4-methylpyridinium bromide,

1-hexylpyridinium bromide, tetraethylphosphonium bromide,

1 -methyl- 1 -propylpyrrolidinium bromide, hexyltrimethylammonium bromide, and cetyltriethylammonium bromide.

[0105] In some embodiments, the one or more quaternary ammonium agents comprises l-ethyl-3-methylpyridinium bromide, l-ethyl-2-methylpyridinium bromide, l-butyl-3 -methyl pyridinium bromide, or 1 -butyl- 1 -methyl pyrrolidinium bromide. For example, the electrolyte comprises from about 1 wt% to about 5 wt% (e.g., from about 1.5 wt% to about 4 wt%) of l-ethyl-3-methylpyridinium bromide, 1 -ethyl-2 -methylpyridinium bromide, l-butyl-3 -methyl pyridinium bromide, 1 -ethyl- 1 -methylmorpholinium bromide, or

1 -butyl- 1 -methyl pyrrolidinium bromide.

[0106] In some embodiments, the one or more quaternary ammonium agents comprises cetyltriethylammonium bromide (CTAB). For example, the electrolyte comprises from about 0.01 wt% to about 1 wt% (e.g., from about 0.05 wt% to about 0.5 wt%) of

cetyltriethylammonium bromide (CTAB).

[0107] In some embodiments, the one or more quaternary ammonium agents comprises tetraethylammonium bromide, trimethylpropylammonium bromide, or any combination thereof. For example, the electrolyte comprises from about 1 wt% to about 6 wt% (e.g., from about 1.5 wt% to about 5 wt%) of tetraethylammonium bromide. For example, the electrolyte comprises from about 1 wt% to about 5 wt% (e.g., from about 1.5 wt% to about 3.5 wt%) of trimethylpropylammonium bromide.

[0108] Without being bound by theory, it is thought that the quaternary ammonium agents enhance electrochemistry by creating a buoyancy effect with the bromine complexes formed with the quaternary ammonium agents. As bromide ions in the electrolyte pseudo- polymerize, they become heavier and sink to the bottom of the electrolyte volume, reducing kinetics in the cell. Quaternary ammonium agents that create a buoyancy effect help mitigate this issue, bringing the pseudo-polymerized bromide ions off the bottom of the electrolyte volume, and increasing kinetics in the cell.

[0109] In some embodiments, the electrolyte further comprises less than 1 wt% of one or more additives selected from Sn, In, Ga, Al, Tl, Bi, Pb, Sb, Ag, Mn, Fe, or any combination thereof. For example, the electrolyte comprises less than 1 wt% of Sn and In.

[0110] In some embodiments, the electrolyte further comprises sufficient HBr to impart the electrolyte with a pH of from about 2 to about 4 (from about 2.5 to about 3.5).

[0111] In some embodiments, the electrolyte further comprises from about 0.1 wt% to about

2 wt% (e.g., from about 0.3 wt% to about 1 wt%) of acetic acid. In alternative embodiments, the electrolyte comprises from about 0.1 wt% to about 2 wt% of acetic acid, sodium acetate, potassium acetate, or any combination thereof.

[0112] In some embodiments, the electrolyte further comprises from about 2 wt% to about 8 wt% (e.g., from about 3 wt% to about 5 wt%) citric acid monohydrate. In some

embodiments, the electrolyte further comprises from about 2 wt% to about 8 wt% (e.g., from about 3 wt% to about 5 wt%) of potassium dihydrogen citrate monohydrate.

[0113] In some embodiments, the electrolyte further comprises from about 2 wt% to about 8 wt% (e.g., from about 3 wt% to about 5 wt%) oxalic acid. In some embodiments, the electrolyte further comprises from about 2 wt% to about 8 wt% (e.g., from about 3 wt% to about 5 wt%) of oxalic acid.

[0114] In some embodiments the electrolyte further comprises a stable additive. For example, the stable additive is acetic acid, sodium acetate, oxalic acid, sodium oxalate, citric acid, potassium citrate, 18-crown-6, dicyandiamide, succinic acid, sodium methane sulfonate, sodium proprionate, sodium malonate, sodium hexanoate, sodium hexafluoroaluminate, sebacic acid, potassium trifluoromethanesulfonate, acetonitrile, propionitrile, acquivion ionomer, sodium butyrate, melamine, sebaic acid, 2,2 bipyridine, dodecanedioic acid, sodium trichloroacetate, dodecanoic acid, sodium dodecanoate, 15-crown-5, or trichloroacetic acid. In some embodiments the additives enhance electrochemistry. In other embodiments the additives do not change the electrochemistry.

[0115] Another aspect of the present invention provides an electrolyte for use in a secondary zinc halide electrochemical cell comprising from about 30 wt% to about 40 wt% of ZnBr ₂ , ZnCl ₂ , or any combination thereof; from about 4 wt% to about 12 wt% of KBr; from about 4 wt% to about 12 wt% of KCl; from about 0.5 wt% to about 10 wt% of a glyme; and from about 1 wt% to about 5 wt % of one or more quaternary ammonium agents.

[0116] Another aspect of the present invention provides an electrolyte for use in a secondary zinc halide electrochemical cell comprising from about 30 wt% to about 40 wt% of ZnBr ₂ ; from about 4 wt% to about 12 wt% of KBr; from about 4 wt% to about 12 wt% of KCl; from about 0.5 wt% to about 10 wt% of a glyme; and from about 1 wt% to about 5 wt % of one or more quaternary ammonium agents.

[0117] Another aspect of the present invention provides an electrolyte for use in a secondary zinc halide electrochemical cell comprising from about 30 wt% to about 40 wt% of ZnBr ₂ and from about 0.01 wt% to about 0.9 wt% of one or more additives selected from Sn, In, Ga, Al, Tl, Bi, Pb, Sb, Ag, Mn, Fe, or any combination thereof.

[0118] In some embodiments, the electrolyte comprises from about 30 wt% to about 40 wt% of ZnBr2; from about 5 wt% to about 15 wt% of KBr; from about 5 wt% to about 15 wt% of KCl; from about 0.5 wt% to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt% to about 2 wt% of acetic acid; and from about 0.05 wt% to about 4 wt% of a crown ether.

[0119] In some embodiments, the electrolyte comprises from about 30 wt% to about 40 wt% of ZnBr2; from about 5 wt% to about 15 wt% of KBr; from about 5 wt% to about 15 wt% of KCl; from about 0.5 wt% to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt% to about 2 wt% of acetic acid; from about 0.05 wt% to about 4 wt% of a crown ether; and wherein the one or more quaternary ammonium agents comprises tetraethylammonium bromide.

[0120] In some embodiments, the electrolyte comprises from about 30 wt% to about 40 wt% of ZnBr ₂ ; from about 5 wt% to about 15 wt% of KBr; from about 5 wt% to about 15 wt% of KCl; from about 0.5 wt% to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt% to about 2 wt% of acetic acid; from about 0.05 wt% to about 4 wt% of a crown ether; and wherein the one or more quaternary ammonium agents comprises trimethylpropylammonium bromide.

[0121] In some embodiments, the electrolyte comprises from about 30 wt% to about 40 wt% of ZnBr ₂ ; from about 5 wt% to about 15 wt% of KBr; from about 5 wt% to about 15 wt% of KCl; from about 0.5 wt% to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt% to about 2 wt% of acetic acid; from about 0.05 wt% to about 4 wt% of a crown ether; and wherein the one or more quaternary ammonium agents comprises tetraethylammonium bromide, methylethylpyridinium bromide, and cetyltriethylammonium bromide. In a further embodiment, the methylethylpyridinium bromide is

l-ethyl-2-methylpyridinium bromide. In a further embodiment, the methylethylpyridinium bromide is l-ethyl-3-methylpyridinium bromide.

[0122] In some embodiments, the electrolyte comprises from about 30 wt% to about 40 wt% of ZnBr2; from about 5 wt% to about 15 wt% of KBr; from about 5 wt% to about 15 wt% of KC1; from about 0.5 wt% to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt% to about 2 wt% of acetic acid; from about 0.05 wt% to about 4 wt% of a crown ether; and wherein the one or more quaternary ammonium agents comprises triethylpropylammonium bromide, methylethylpyridinium bromide, and

cetyltriethylammonium bromide. In a further embodiment, the methylethylpyridinium bromide is l-ethyl-2-methylpyridinium bromide.

[0123] In some embodiments, the electrolyte comprises from about 30 wt% to about 40 wt% of ZnBr ₂ ; from about 5 wt% to about 15 wt% of KBr; from about 5 wt% to about 15 wt% of KC1; from about 0.5 wt% to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt% to about 2 wt% of acetic acid; from about 0.05 wt% to about 4 wt% of a crown ether; and wherein the one or more quaternary ammonium agents comprises triethylpropylammonium bromide, l-butyl-3-methylpyridinium bromide, and

cetyltriethylammonium bromide.

[0124] In some embodiments, the electrolyte comprises from about 30 wt% to about 40 wt% of ZnBr ₂ ; from about 5 wt% to about 15 wt% of KBr; from about 5 wt% to about 15 wt% of KC1; from about 0.5 wt% to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt% to about 2 wt% of acetic acid; from about 0.05 wt% to about 4 wt% of a crown ether; and wherein the one or more quaternary ammonium agents comprises tetraethylammonium bromide, l-butyl-3-methylpyridinium bromide, and

cetyltriethylammonium bromide.

[0125] In some embodiments, the electrolyte comprises from about 30 wt% to about 40 wt% of ZnBr ₂ ; from about 5 wt% to about 15 wt% of KBr; from about 5 wt% to about 15 wt% of KC1; from about 0.5 wt% to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt% to about 2 wt% of acetic acid; from about 0.05 wt% to about 4 wt% of a crown ether; and wherein the one or more quaternary ammonium agents comprises tetraethylammonium bromide, 1 -ethyl- 1 bromide, and

cetyltriethylammonium bromide.

[0126] In some embodiments, the electrolyte comprises from about 30 wt% to about 40 wt% of ZnBr ₂ ; from about 5 wt% to about 15 wt% of KBr; from about 5 wt% to about 15 wt% of KC1; from about 0.5 wt% to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt% to about 2 wt% of acetic acid; from about 0.05 wt% to about 4 wt% of a crown ether; and wherein the one or more quaternary ammonium agents comprises trimethylpropylammonium bromide, 1 -butyl- 1 -methylpyrrolidinium bromide, and cetyltriethylammonium bromide.

[0127] In some embodiments, the electrolyte comprises from about 30 wt% to about 40 wt% of ZnBr ₂ ; from about 5 wt% to about 15 wt% of KBr; from about 5 wt% to about 15 wt% of KC1; from about 0.5 wt% to about 10 wt% of one or more quaternary ammonium agents; wherein the one or more quaternary ammonium agents comprises tetraethylammonium bromide, methylethylpyridinium bromide, and cetyltriethylammonium bromide.

[0128] In some embodiments, the electrolyte comprises from about 30 wt% to about 40 wt% of ZnBr ₂ ; from about 5 wt% to about 15 wt% of KBr; from about 5 wt% to about 15 wt% of KC1; from about 0.5 wt% to about 10 wt% of one or more quaternary ammonium agents; wherein the one or more quaternary ammonium agents comprises trimethylpropylammonium bromide, 1 -butyl- 1 -methylpyrrolidinium bromide, and cetyltriethylammonium bromide.

[0129] III. METHODS OF PREPARING A ZINC HALIDE ELECTROLYTE

[0130] Another aspect of the present invention provides a method of preparing an electrolyte for use in a secondary zinc halide electrochemical cell comprising mixing ZnBr ₂ , KBr, KC1, water, and carbon powder to generate a mixture, wherein the mixture comprises from about 15 wt% to about 20 wt% of ZnBr ₂ ; and from about 7.5 wt% to about 20 wt% of carbon powder, and from about 25 wt% to about 45 wt% of water.

[0131] Mixing may be accomplished using any suitable means (e.g., vortexing, high speed mixing, shaking, agitating, or the like).

[0132] IV. EXAMPLES

[0133] A typical electrolyte composition of 2 mol/liter of ZnBr ₂ (approximately 50% ZnBr ₂ by weight) is considered. Bromine will be used for this example, but any halogen, such as chlorine may be substituted for bromine. In the fully discharged state the electrolyte is all ZnBr ₂ and the carbon powder is substantially free of any bromine. As the battery is charged, zinc plates out on the anode or an anodic surface and bromine or polybromine species are formed at the cathode or cathodic surface, and bromine is absorbed by the carbon powder. This results in the following charging equation:

[0134] ZnBr ₂ + X e- ==> Zn(anode) + Br ₂ (cathode)

[0135] In this case, the electrolyte having 1 liter of 2 mol/liter ZnBr ₂ will produce 2 mol/liter of Br ₂ which weighs -358 grams. The carbon powder (e.g., powdered activated carbon) can absorb bromine ~1 : 1 by weight. In this instance, 358 grams of carbon powder is required. The 358 grams of carbon powder (~170mls) may be added to the liter of electrolyte. Some of the 358 grams of carbon material may be in solid form or be part of an electrode assembly. In some examples, a high concentration of carbon powder may be used to effectively "gel" the electrolyte into a less mobile liquid.

[0136] In at least one example, each mole of bromine contained within the electrolyte and carbon powder may provide approximately 26.8 amp-hours of capacity. As such, a 2 /liter system may provide 53.6 Ah of capacity from the electrochemical cell. The electrochemical cell with bromide will provide 1.8 V of voltage across the electrochemical cell resulting in approximately 96.5 wh/liter for a 2 mol/liter ZnBr ₂ electrolyte having carbon powder.

Approximately 10.5 Liters of 2 mol/liter ZnBr ₂ of electrolyte and carbon powder is required per kWh. In 10.5 liters of ZnBr ₂ of electrolyte and carbon powder, 21 mol of ZnBr ₂ is required and about 3.8 kg of carbon powder.

[0137] This may result in an economically superior electrolyte. For example, current costs for the electrolyte, using commodity pricing include: zinc costs about $2 per kg; Br ₂ costs about $2 per kg; and activated carbon powder cost about $1 per kg. As a result, per Kwh of electrolyte there is approximately $4 of carbon, $3 of Zn and $4 of Br ₂ for a total of only $11/kWh for the electrolyte, which includes the active electrochemical components of the electrochemical cell. This compares very favorably for instance with the compounds required for lithium based batteries which cost well over $100/kWh. This significant reduction in electrolyte costs is advantageous when large amounts of kWh are required such as grid scale applications.

[0138] Example 1 A - Electrolyte Formulations

[0139] Ingredients used in the electrolyte formulations described below were reagent grade.

[0140] An example of one electrolyte of the present invention was formulated as follows:

[0141] Table 1 : Electrolyte no. 1 formulation

Ingredient Amount (g) Wt %

1 -ethyl-2-methylpyridinium bromide 4.96 1.55

tetraethylammonium bromide 6.1 1.91

18-crown-6 0.55 0.17

cetyltrimethylammonium bromide 0.4 0.13

Total: 234.12 100.00

[0142] In the example electrolyte, a typical activated carbon of 85 grams may absorb 50 grams of bromine. The absorption ratio of bromine absorbed by carbon to carbon by weight may be 1 : 1.7. The 85 grams of ZnBr ₂ has the capacity to produce 62 grams of bromine, the limiting 50 grams of bromine absorbed by the carbon would result in a cell with an approximate capacity of 30 watt/hours at 1.8 volts or 16.7 amp/hours. In this example, polybromides may form, increasing the net bromine absorbed by the carbon. When polybromides form, the bromine of carbon may increase to 62 grams allowing for an increase in capacity of the cell reaching an absorption rate of 1 : 1 for bromine to carbon. Each electrolyte formula may be adjusted to give the optimal bromine to carbon ration based on the specific performance and concentrations of other additives allowing electrolytes to be customized for the desired system.

OTHER EMBODIMENTS

[0143] It should be apparent that the foregoing relates only to the preferred embodiments of the present invention and that numerous changes and modifications may be made herein without departing from the spirit and scope of the invention as defined by the following claims and equivalents thereof.