Electrolytes that include lithium iodide and batteries that include such electrolytes

Abstract

Presented herein are, infer alia, electrolytes for electrochemical cells, such as lithium sulfur secondary batteries. The electrolytes comprise one or more lithium salts. One or more of the lithium salts is lithium iodide. Lithium iodide is a primary electrolytic salt. Secondary batteries that include the disclosed electrolytes are also disclosed.

Description

ELECTROLYTES THAT INCLUDE LITHIUM IODIDE AND BATTERIES THAT INCLUDE SUCH ELECTROLYTESBACKGROUND

[0001] In the pursuit of low cost energy storage, batteries based on sulfur cathodes are very attractive. Sulfur does not suffer from supply chain-related issues that plague lithium ion cathode manufacture, since it is an abundant byproduct of the oil and gas industry that is generated in huge quantities during the refining of petroleum products.

[0002] Sulfur is a high-energy cathode material and has promise as a next generation cathode electroactive material that achieves both high energy density and alleviates supply chain risks. However, in common sulfur batteries, sulfur is dissolved into the electrolyte during the discharge process. This dissolution often necessitates large quantities of liquid electrolyte to avoid unwanted kinetic complications. In turn, large electrolyte quantities require large quantities of electrolyte salts. The soluble sulfur species can also contribute to self-discharge of the sulfur cell, as these soluble sulfur species are electrochemically reduced at the electronically conducting anode surface, causing a cascade of additional reductions through diffusion of the highly reduced species followed by interactions with sulfur material at the cathode.

[0003] Liquid electrolytes for lithium secondary batteries typically consist of polar non-protic organic solvents in which a high concentration of lithium salts are dissolved. The most common lithium salts used for this purpose in lithium sulfur batteries are imides, such as lithium bis(fluorosolfonyl)imide (LiFSI) and lithium bis(trifluorosulfonyl) imide (LiTFSI). However, these compounds are expensive and their use as primary lithium salts in electrolytes adds substantial costs and therefore erodes the low cost benefits of sulfur active materials. Accordingly, electrolyte salts are one of the largest contributors to the total material cost of currently available sulfur cells. Additionally, many of these electrolyte salts, for example LiFSI, are not stable towards water and can generate dangerous byproducts such as hydrogen fluoride (HF). HF is extremely corrosive and poisonous and represents a major safety issue.

[0004] Further, many common solvents for lithium sulfur battery electrolytes comprise or consist of ether blends. Ethers are less oxidatively stable and more flammable than the carbonate and ester solvents typically used in lithium-ion batteries. The use of ethers presents additionalpossible hazards with respect to overcharge of the cell, leading to dangerous conditions or degradation of cell performance.

[0005] Despite these disadvantages, these materials have continued to remain as preferred components in electrolyte formulations for lithium sulfur batteries.SUMMARY

[0006] It is therefore a goal of the present disclosure to provide alternative electrolyte formulations that can be used in lithium sulfur batteries, which are less expensive, safer, less prone to degradation, and / or have inherent protective effects against overcharge and other related problems.

[0007] Lithium iodide (Lil) has previously been evaluated as an additive to sulfur battery electrolytes, but has not been considered suitable as a primary lithium salt for such electrolytes. Lil is simple and low cost as compared to the fluorinated imides currently used for this purpose. Particularly, Lil is inexpensive and does not suffer from the high cost and supply chain risks associated with lithium bis (fluoro sulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The discovery of the utility and benefits of lithium iodide as a primary electrolyte salt is surprising given prior understanding that electrolyte salts must include bulky, non-nucleophilic, and non-oxidizable anions including fluorinated anions, such as FSI, TFSI, triflate, tetrafluoroborate, and hexafluorophosphate and chlorinated lithium salts, such as lithium perchlorate. Despite their drawbacks and expense, LiFSI and LiTFSI have remained by far the most common choices for primary electrolyte salts in secondary lithium sulfur batteries.

[0008] The present disclosure encompasses the recognition that lithium iodide can serve as a primary lithium salt in electrolytes for lithium sulfur batteries, either alone or in a blend of primary lithium salts. The ability of Lil to be used as a primary lithium salt in a lithium sulfur battery is surprising because it is significantly different than conventional primary lithium salts for such purposes. For example, the iodide ion is nucleophilic whereas the anions in traditional lithium electrolyte salts, including FSI and TFSI, are by design non-nucleophilic.

[0009] Additionally, the present disclosure encompasses the recognition that utilizing Lil provides unexpected, advantageous benefits over typically employed electrolytes. For example,Lil has been found to have safety benefits over conventional electrolyte salts, for example imide salts, by providing a measure of overcharge protection. Additionally, the present disclosure demonstrates that Lil provides other unexpected benefits such as improved performance at low temperature and lower self-discharge. Without being confined to any particular theory, it is believed that such benefits may be attributable to oxidation of iodide from Lil to iodine during operation of the lithium sulfur cell, and that the iodine thus produced may shuttle charge to the lithium anode, and / or oxidize soluble sulfur compounds, without deleterious impact on cell performance. Such benefits may be realized in particular in lithium sulfur batteries that use a protected lithium anode, such as a lithium-indium anode, as compared to a conventional lithium metal anode. Use of a blend of primary lithium salts including lithium iodide, such as a blend of Lil and LiFSI, may impart a combination of beneficial properties, for example each attributable one of the constituent salts or through a synergistic effect.

[0010] The present disclosure also provides electrolyte formulations and methods of forming electrolytes based on the strategy of including elemental atoms in an electrolyte formulation during the construction of an electrochemical cell. Without being bound by theory, it is believed the iodine so included is reduced in situ (e.g., after battery assembly or during initial conditioning) to generate lithium iodide as an electrolyte salt.

[0011] Thus, in one aspect, the present disclosure is directed to an electrolyte for a lithium sulfur battery, the electrolyte comprising one or more lithium salts wherein at least 20% of anions in the one or more lithium salts are iodide.

[0012] In certain embodiments, at least 25% (e.g., at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90%) of the anions in the one or more lithium salts are iodide.

[0013] In certain embodiments, at least 20% (e.g., at least 25% at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90%) of all anions in the electrolyte are iodide.

[0014] In certain embodiments, the one or more lithium salts comprises a blend of lithium iodide and at least one other lithium salt (e.g., LiFSI and / or LiTFSI).

[0015] In certain embodiments, the electrolyte comprises anions selected from the group consisting of: nitrate, TFSI, FSI, triflate, perchlorate, TDI, BF4, and PF6.

[0016] In certain embodiments, the one or more lithium salts comprises a blend of lithium iodide and LiFSI.

[0017] In certain embodiments, the electrolyte comprises a solvent selected from the group consisting of dimethoxyethane, dioxolane, tetrahydrofuran, methylcyclopentyl ether, methyl tetrahydrofuran, dimethyl tetrahydrofuran, 1,4-dioxane, glyme, diethoxy ethane, diglyme, triglyme, tetraglyme, n-glymes with n > 5 (e.g., pentaglyme or hexaglyme), and mixtures thereof.

[0018] In certain embodiments, the electrolyte comprises a mixture of dimethoxy ethane and 1,3-dioxolane.

[0019] In certain embodiments, a ratio of dimethoxyethane to 1,3-dioxolane ranges from 3:1 to 1:3.

[0020] In certain embodiments, a total concentration of lithium salts in the electrolyte is less than 2M.

[0021] In certain embodiments, a total concentration of lithium salts in the electrolyte is less than 1.8M (e.g., less than 1.6M, less than 1.5M, less than 1.4M, less than 1.3M, less than 1.2M, or less than IM).

[0022] In certain embodiments, the electrolyte contains no fluorine-containing anions.

[0023] In certain embodiments, the electrolyte contains no lithium salt other than the one or more lithium salts.

[0024] In another aspect, the present disclosure is directed to a lithium sulfur battery comprising a disclosed electrolyte, characterized in that the battery has higher sulfur utilization than a corresponding battery with TFSI and / or FSI in place of the iodide.

[0025] In certain embodiments, a specific capacity of the battery when discharged at C / 10 is at least 1100 mAh per gram sulfur.

[0026] In another aspect, the present disclosure is directed to a lithium sulfur battery comprising a disclosed electrolyte, characterized in that the battery has lower self-discharge than a corresponding battery with TFSI and / or FSI in place of the iodide.

[0027] In certain embodiments, the lithium sulfur battery is characterized in that the electrolyte to sulfur ratio is below 4:1 (e.g., wherein the sulfur is present in a cathode of the battery).

[0028] In another aspect, the present disclosure is directed to a lithium sulfur battery comprising a disclosed electrolyte and a sulfur-based cathode, characterized in that sulfur loading in the cathode is at least 5 mg / cm2.

[0029] In another aspect, the present disclosure is directed to a lithium sulfur battery comprising a disclosed electrolyte and a cathode, wherein (i) the electrolyte contains less than IM of lithium salt, (ii) the battery has an electrolyte to sulfur ratio below 4 pL / mg; and (iii) the cathode has a sulfur loading of at least 4 mg S / cm2.

[0030] In another aspect, the present disclosure is directed to a lithium sulfur battery comprising a disclosed electrolyte, wherein the lithium sulfur battery is operable to cycle at least 20 times (e.g., at least 50 times, at least 100 times, at least 200 times, or at least 500 times).

[0031] In certain embodiments, a lithium sulfur battery comprises a protected lithium anode.

[0032] In certain embodiments, the protected lithium anode is a lithium-indium anode.

[0033] In certain embodiments, a lithium sulfur battery comprises a cathode comprising an electroactive metal sulfide (e.g., a metal-sulfide cathode).

[0034] In another aspect, the present disclosure is directed to a lithium sulfur battery comprising a disclosed electrolyte and a protected lithium anode. In certain embodiments, the protected lithium anode is a lithium-indium anode. In certain embodiments, the lithium sulfur battery comprises a cathode comprising an electroactive metal sulfide (e.g., a metal-sulfide cathode).

[0035] In another aspect, the present disclosure is directed to a method of providing overtemperature protection to a lithium sulfur battery comprising an electrolyte comprising lithium salt (e.g., comprising two or more distinct lithium salts), the method comprising providing the battery, wherein at least 50 mole percent of the lithium salt present in the electrolyte comprises lithium iodide.

[0036] Any two or more of the features described in this specification, including in this summary section, may be combined to form implementations not specifically explicitly described in this specification.BRIEF DESCRIPTION OF THE DRAWING

[0037] Drawings are presented herein for illustration purposes, not for limitation. The foregoing and other objects, aspects, features, and advantages of the disclosure will become more apparent and may be better understood by referring to the following description taken in conjunction with the accompanying drawings, in which:

[0038] FIG. 1 is a cross sectional representation of an electrochemical cell, according to illustrative embodiments of the present disclosure;

[0039] FIG. 2 is a perspective representation of a cylindrical battery, according to illustrative embodiments of the present disclosure;

[0040] FIG. 3 is a perspective representation of a coin cell assembly, according to illustrative embodiments of the present disclosure;

[0041] FIG. 4 shows a charge discharge cycle of an exemplary lithium iodide-containing cell and a control cell without iodide demonstrating that iodide-containing cells slower self-discharge when held at open circuit voltage for 48 hours, according to illustrative embodiments of the present disclosure;

[0042] FIG. 5 shows a charge discharge cycle of an exemplary lithium iodide-containing cell and a control cell without iodide demonstrating that iodide-containing cells have higher specific capacity after holding at open circuit voltage for 48 hours, according to illustrative embodiments of the present disclosure;

[0043] FIG. 6 shows a charge-discharge cycle of an exemplary lithium iodide-containing cell and a control cell without iodide demonstrating that the iodide-containing cell has discharge capacity between 2.2 and 2.3V that is lacking in the control cell, according to illustrative embodiments of the present disclosure; and

[0044] FIG. 7 shows cycling data for an exemplary lithium iodide-containing cell and a control cell without iodide demonstrating that the iodide-containing cell has higher specific capacity than the control cell, according to illustrative embodiments of the present disclosure.

[0045] Schematics are not necessarily drawn to scale.DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

[0046] Described herein are electrochemical cells comprising compositions disclosed herein. For example, in certain embodiments, such electrochemical cells are secondary sulfur batteriesincluding a lithium-containing anode coupled to a cathode by a lithium ion-conducting electrolyte. In some embodiments, such batteries also comprise additional components such as separators between an anode and cathode, anodic and cathodic current collectors, terminals by which a cell can be coupled to an external load, packaging such as a flexible pouch or a rigid metal container, and circuitry to control or limit charge and discharge of the battery. It is further contemplated that the present disclosure regarding secondary sulfur batteries can be adapted for use in sodium-sulfur batteries, and such batteries are also considered within the scope of certain embodiments of the present disclosure.Electrolytes

[0047] In certain embodiments, a provided electrolyte comprises lithium iodide. In some embodiments, lithium iodide is a primary lithium salt in an electrolyte. A primary lithium salt supports lithium ion conductance, for example, between an anode and a cathode coupled by an electrolyte containing the salt.. In some embodiments, an electrolyte also includes an additive salt (e.g., a lithium salt additive) in addition to a primary lithium salt. Additive salts, such as additive lithium salts, can improve some aspect of battery performance other than lithium ion transport. For example, in some embodiments, an additive salt, such as a lithium salt additive, moderates reactivity of anode and / or cathode surfaces, controls solvent decomposition, scavenges adventitious water, acid or other reaction by-products, or some combination thereof. Primary lithium salts typically comprise the bulk of the salt in an electrolyte, while additive salts are generally present at lower concentrations.

[0048] Lithium iodide has not been utilized as a primary lithium salt in lithium sulfur battery electrolytes. There has been a strong preference for primary lithium electrolyte salts that contain bulky, non-nucleophilic anions, having good solubility in organic solvents such as ethers and aliphatic carbonates, which, without wishing to be bound by any particular theory, could be a reason that lithium iodide has not been utilized as a primary lithium salt to date. In some embodiments, lithium iodide is a primary lithium salt in an electrolyte (e.g., any other lithium salt, if present, is present in lesser amounts, or as an additive). In some embodiments, lithium iodide is an electrolytically active salt in an electrolyte. In some embodiments, lithium iodide is the electrolytically active salt in an electrolyte. In some embodiments, lithium iodide is anelectrolytically active lithium salt in an electrolyte. In some embodiments, lithium iodide is the clcctrolytically active lithium salt in an electrolyte. In some embodiments, lithium iodide is included in an electrolyte in combination with another salt, for example another lithium salt. In some embodiments, an electrolyte includes a blend of lithium iodide and one or more other lithium salts, for example as the primary lithium salts in the electrolyte or as the primary lithium salt and an additive in the electrolyte. In some embodiments, an electrolyte includes more than one electrolytically active lithium salt. One or more electrolytically active lithium salts that are included in an electrolyte may include lithium iodide and, optionally, one or more other electrolytically active lithium salts, such as, for example, LiFSI, LiTFSI, and / or LiPFe. In certain other embodiments, an electrolyte contains a primary electrolytically active lithium salt or salt blend that does not include fluorine-containing anions.

[0049] In certain embodiments, a total concentration of salts in an electrolyte is no more than 2M, no more than 1.8M, no more than 1.6M, no more than 1.5M, no more than 1.4M, no more than 1.3M, no more than 1.2M, or no more than IM. In certain embodiments, a total concentration of lithium salts in an electrolyte is no more than 2M, no more than 1.8M, no more than 1.6M, no more than 1.5M, no more than 1.4M, no more than 1.3M, no more than 1.2M, or no more than IM. In certain embodiments, a total concentration of primary lithium salts in an electrolyte is no more than 2M, no more than 1.8M, no more than 1.6M, no more than 1.5M, no more than 1.4M, no more than 1.3M, no more than 1.2M, or no more than IM. In certain embodiments, a total concentration of electrolytically active salts in an electrolyte is no more than 2M, no more than 1.8M, no more than 1.6M, no more than 1.5M, no more than 1.4M, no more than 1.3M, no more than 1.2M, or no more than IM. In certain embodiments, a total concentration of electrolytically active salts in an electrolyte is no more than 2M, no more than 1.8M, no more than 1.6M, no more than 1.5M, no more than 1.4M, no more than 1.3M, no more than 1.2M, or no more than IM. In certain embodiments, a total concentration of electrolytically active lithium salts in an electrolyte is no more than 2M, no more than 1.8M, no more than 1.6M, no more than 1.5M, no more than 1.4M, no more than 1.3M, no more than 1.2M, or no more than IM.

[0050] In certain embodiments, at least 20%, at least 25%, at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99% of anions in an electrolyte are iodide. In certain embodiments, at least 20%, at least 25%, atleast 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99% of all anions in an electrolyte arc iodide. In certain embodiments, at least 20%, at least 25%, at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99% of salt anions in an electrolyte are iodide. In certain embodiments, at least 20%, at least 25%, at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99% of lithium salt anions in an electrolyte are iodide. In certain embodiments, at least 20%, at least 25%, at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99% of primary salt anions in an electrolyte are iodide. In certain embodiments, at least 20%, at least 25%, at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99% of primary lithium salt anions in an electrolyte are iodide. In certain embodiments, at least 20%, at least 25%, at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99% of electrolytically active salt anions in an electrolyte are iodide. In certain embodiments, at least 20%, at least 25%, at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99% of electrolytically active lithium salt anions in an electrolyte are iodide.

[0051] In certain embodiments, an electrolyte comprises one or more organic solvents, such as, for example, dimethoxy ethane, dioxolane, tetrahydrofuran, methylcyclopentyl ether, methyl tetrahydrofuran, dimethyl tetrahydrofuran, 1,4-dioxane, glyme, diethoxy ethane, diglyme, triglyme, tetraglyme, or n-glymes with n > 5 (e.g., pentaglyme or hexaglyme), or a mixture thereof. In certain embodiments, an electrolyte comprises a mixture of organic solvents. For example, a mixture of organic solvents may comprise dimethoxyethane and 1,3-dioxolane. Such mixtures may be mixed at a ratio (e.g., by weight) of dimethoxy ethane to 1,3-dioxolane in a range of 10:1 to 1:10, 5:1 to 1:5, or 3:1 to 1:3. In certain embodiments, a mixture of organic solvents is mixed at a ratio of first organic solvent to second organic solvent in a range of 10:1 to 1:10, 5:1 to 1:5, or 3:1 to 1:3.

[0052] In certain embodiments, electrolytes comprise an electrolytically active salt. Examples of electrolytically active salts include, for example, lithium iodide, LiFSI, LiTFSI, lithium triflate, lithium perchlorate, LiPFe, LiBEt. In certain embodiments, electrolytes compriseadditional non lithium salts such as organic “onium salts” tetraalkylammonium salts (e.g. tctrabutylammonium tctrafluoroboratc, TBABF4), liquid state salts at room temperature (e.g. imidazolium salts, such as l-ethyl-3-methylimidazolium bis-(perfluoroethyl sulfonyl)imide, EMIBeti), and the like.

[0053] In certain embodiments, an electrolyte comprises ionic liquids, such as l-ethyl-3- methylimidzaolium-TFSI, N-butyl-N-methyl-piperidinium-TFSI, N-methyl-n-butyl pyrrolidinium-TFSI, and N-methyl-N-propylpiperidinium-TFSI, or combinations thereof. In certain embodiments, an electrolyte comprises superionic conductors, such as sulfides, oxides, and phosphates, for example, phosphorous pentasulfide, or combinations thereof.

[0054] In certain embodiments, electrolytes comprise one or more organic solvents, e.g., a weak polar solvent and / or a strong polar solvent and / or a lithium protecting solvent. The term "weak polar solvent", as used herein, is defined as a solvent that is capable of dissolving elemental sulfur and has a dielectric coefficient of less than 15. A non-polar or weak polar solvent is selected from hydrocarbons, fluorinated hydrodcarbons, ethers, carbonates, and thioethers. Examples of non-polar solvents include hydrocarbons such as aromatic or aliphatic solvents including xylene, toluene, mesitylene fluorobenzene, chlorobenzene, perfluorocarbons, and hydrofluorocarbons. Examples of weak polar solvents include ethers, carbonates, and thioethers, dimethoxyethane, 2- methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, dimethyl ether, diethyl ether, diglyme, tetraglyme, dimethyl sulfide, diethyl sulfide and the like. The term "strong polar solvent", as used herein, is defined as a solvent that is capable of dissolving lithium polysulfide and has a dielectric coefficient of more than 15. A strong polar solvent is selected from esters, ketones, sulfoxides, sulfones, nitriles, amides, and the like, sulfate compounds, and sulfite compounds. Examples of strong polar solvents include hexamethyl phosphoric triamide, y- butyrolactone, acetonitrile, N-methylpyrrolidone, 3-methyl-2-oxazolidone, dimethyl formamide, sulfolane, dimethyl acetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, ethylene glycol sulfite, carbon disulfide, and the like. The term "lithium protection solvent", as used herein, is defined as a solvent that forms a good protective layer, i.e. a stable solid-electrolyte interface (SEI) layer, on a lithium surface, and which shows a cyclic efficiency of at least 50%. A lithium protection solvent is selected from saturated ether compounds, unsaturated ether compounds, and heterocyclic compounds including one or moreheteroatoms selected from the group consisting of N, O, and / or S. Examples of lithium protection solvents include tetrahydrofuran, 1,3-dioxolanc, 3,5-dimcthylisoxazolc, 2,5-dimcthyl furan, furan, 2-methyl furan, 1,4-oxane, 4-methyldioxolane, and the like.Electrolyte Formulations

[0055] In certain embodiments, the present disclosure provides electrolyte formulations having lower cost and / or improved performance characteristics. In certain embodiments, the present disclosure provides electrolyte formulations having improved performance characteristics in lithium sulfur batteries. In certain embodiments, such formulations comprise a liquid solvent, lithium iodide as a primary electrolyte salt, and one or more additional salts present as performance additives. In certain embodiments, provided formulations are characterized in that the lithium iodide concentration in the liquid solvent is at least 0.5M, 0.8M, at least IM, at least 1.2M, at least 1.5M, or at least 2M. In certain embodiments, such formulations are characterized in that lithium iodide comprises at least 20%, at least 25%, at least 30%, at least 50%, at least 75%, at least 80%, at least 85%, or at least 90% of the lithium salts present in the electrolyte formulation on a molar concentration basis. In certain embodiments, such formulations are characterized in that lithium iodide comprises at least 20%, at least 25%, at least 30%, at least 50%, at least 75%, at least 80%, at least 85%, or at least 90% of the lithium salts present in the electrolyte formulation on a mass percentage basis.

[0056] In certain embodiments, provided electrolyte formulations are characterized in that they contain a blend of primary lithium salts including lithium iodide and one or more additional lithium salts. In certain embodiments such formulations contain a primary lithium salt composition comprising a blend of lithium iodide and one or more salts selected from the group consisting of: LiFSI, LiTFSI, Lithium triflate (LiOTf), and LiPFe. In certain embodiments such formulations contain a blend of lithium iodide and LiFSI. In certain embodiments such formulations contain a blend of lithium iodide and LiTFSI. In certain embodiments such formulations contain a blend of lithium iodide and LiPFe. In certain embodiments such formulations contain a blend of lithium iodide and LiOTf. In certain embodiments such formulations contain a blend of lithium iodide and LiNO3.

[0057] In certain embodiments, provided electrolyte formulations contain, in addition to the lithium iodidc-bascd primary salt composition, one or more additive salts. In certain embodiments such additive salts are selected from the group consisting of lithium salts, organic onium salts, ionic liquids, and non-lithium metal salts. In certain embodiments such additive salts comprise organic onium salts. In certain embodiments such additive salts comprise sodium, potassium, rubidium, or cesium salts. In certain embodiments, such electrolyte formulations are characterized in that the additive salts comprise less than 30%, less than 25%, less than 20%, less than 15%, less than 10%, or less than 5% of the total salt content in the electrolyte formulation on a molarity basis. In certain embodiments, such electrolyte formulations are characterized in that the additive salts comprise less than 30%, less than 25%, less than 20%, less than 15%, less than 10%, or less than 5% of the total salt content in the electrolyte formulation on a mass percent basis.

[0058] Table 1 presents exemplary compositions of liquid electrolytes according to certain embodiments of the present disclosure.Table 1

[0059] In certain embodiments, the present disclosure provides electrolyte formulations comprising elemental iodine. Without being bound by theory, it is believed that elemental iodine acts as a precursor to lithium iodide when incorporated into a battery having a lithium anode or a lithiated cathode. Such formulations provide electrolytes having lower cost and / or improved performance characteristics. In certain embodiments, an electrolyte comprises elemental iodine. In certain embodiments, an uncycled electrolyte comprises elemental iodine. In certain embodiments, a concentration of elemental iodine in an uncycled electrolyte is higher than a concentration of one or more other ions (e.g., any other ion species) (e.g., lithium cations and / or corresponding counteranions) that may be present in the uncycled electrolyte. In certain embodiments, elemental iodine may be consumed upon cycling (e.g., upon one or more cycles, two or more cycles, three or more cycles, five or more cycles, or ten or more cycles, and, optionally, no more than twenty five cycles, no more than twenty cycles, no more than ten cycles, or no more than five cycles). In certain embodiments, a concentration of elemental iodine may be lower in a cycled electrolyte relative to a concentration of elemental iodine in the electrolyte before it has been cycled. For example, in certain embodiments, elemental iodine in an electrolyte is fully consumed upon cycling (e.g., upon one or more cycles). In certain embodiments, elemental iodine in an electrolyte is partially consumed upon cycling (e.g., upon one or more cycles). In certain embodiments, a cycled electrolyte comprises elemental iodine. In certain embodiments, an (e.g., an uncycled electrochemical cell) electrochemical cell (e.g., battery) comprises an electrolyte (e.g., an uncycled electrolyte) comprising elemental iodine. In certain embodiments, a concentration of elemental iodine in an electrolyte of an uncycled electrochemical cell is higher than a concentration of other ions (e.g., lithium cations and / or iodine anions) that may be present in the electrolyte after cycling of the cell. In certain embodiments, a concentration of elemental iodine may be lower in a cycled electrochemical cell relative to a concentration of elemental iodine in the electrochemical cell before it has been cycled. For example, in certain embodiments, elemental iodine in an electrochemical cell is fully consumed upon cycling (e.g., upon one or more cycles). In certain embodiments, elemental iodine in an electrochemical cell is partially consumed upon cycling (e.g., upon one or more cycles). In certain embodiments, a cycled electrochemical cell comprises elemental iodine.

[0060] In certain embodiments, such formulations comprise a liquid solvent, dissolved iodine, and one or more lithium salts. In certain embodiments, provided formulations arc characterized in that the iodine concentration in the liquid solvent is at least 0.1M, at least 0.2M, at least 0.5M, at least 0.8M, at least IM, at least 1.2M, at least 1.5M, or at least 2M. In certain embodiments, such formulations are characterized in that iodine is present at molar ratio of at least 0.01:1, at least 0.05:1, at least 0.1:1, at least 0.2, at least 0.3, at least 0.5, at least 0.75, at least 1, at least 2, at least 3, at least 5, or at least 10 relative to the molar concentration of lithium salts present in the electrolyte formulation.

[0061] In certain embodiments, a provided lithium iodide-containing electrolyte composition is a solid electrolyte. Such solid electrolytes can be used in the construction of all solid-state batteries, as well as hybrid cells containing both solid and liquid electrolytes. Solid electrolytes comprising Li-I according to the present disclosure provide benefits in terms of reduced cost and / or improved performance. In certain embodiments, a solid electrolyte comprises a polymer. In certain embodiments, a solid electrolyte comprises a glass, a ceramic, an inorganic composite, or combinations thereof. In certain embodiments, a solid electrolyte comprises a polymer composite with a glass, a ceramic, an inorganic composite, or combinations thereof. In certain embodiments, such solid electrolytes comprise one or more liquid components as plasticizers or to form a “gel electrolyte”. In certain embodiments, a provided solid electrolyte composition comprises one or more superionic conductors. In certain embodiments, such superionic conductors are selected from sulfides, oxides, and phosphates, for example, phosphorous pentasulfide, or combinations thereof.

[0062] In certain embodiments, solid electrolyte compositions comprising elemental iodine are provided. Such solid electrolytes can be used in the construction of all solid-state batteries, as well as hybrid cells containing solid and liquid electrolytes. Solid electrolytes comprising iodine according to the present disclosure provide benefits in terms of reduced cost and / or improved performance. In certain embodiments, an iodine-containing solid electrolyte comprises a polymer. In certain embodiments, an iodine-containing solid electrolyte comprises a glass, a ceramic, an inorganic composite, or combinations thereof. In certain embodiments, an iodine-containing solid electrolyte comprises a polymer composite with a glass, a ceramic, an inorganic composite, or combinations thereof. In certain embodiments, such solid electrolytes comprise one or more liquid components as plasticizers or to form a “gel electrolyte”. In certain embodiments, a providediodine-containing solid electrolyte composition comprises one or more superionic conductors. In certain embodiments, such supcrionic conductors arc selected from sulfides, oxides, and phosphates, for example, phosphorous pentasulfide, or combinations thereof.

[0063] Elements of different implementations described herein may be combined to form other implementations not specifically set forth above. Elements may be left out of the devices described herein without adversely affecting their operation. Various separate elements may be combined into one or more individual elements to perform the functions described herein.Cathodes

[0064] Compositions of the present disclosure have utility in manufacture of electrochemical devices. They may be porous or non-porous. Certain compositions disclosed herein would be adhered to a current collector to form cathodes for secondary sulfur batteries. Provided cathode compositions may comprise one or more additives such as electrically conductive particles, binders, and other functional additives typically found in battery cathode mixtures. Generally, provided compositions include plentiful conductive particles to increase electrical conductivity of a cathode and provide a low resistance pathway for electrons to access such manufactured cathode. In various embodiments, other additives are included in the composition to alter or otherwise enhance a cathode produced according to the principles described herein. Other cathode components include, for example, a current collector, connecting tabs, and the like.

[0065] In certain embodiments, a lithium sulfur battery comprises a cathode comprising one or more electroactive sulfur materials. In some embodiments, an electroactive sulfur material comprises at least one of (i) to (iv) as follows: (i) sulfur in its S8 cyclic octatomic molecular form, (ii) sulfur in the form of lithium sulfide (e.g., Li2S2 and / or Li2S), (iii) sulfur in the form of an electroactive organosulfur compound, and (iv) sulfur in the form of an electroactive sulfur- containing polymer. An electroactive sulfur material may be or comprise a metal sulfide. A metal sulfide may include a transition metal (e.g., Ti, V, Co, Ni, Zr, Nb, Mo, Tc, Rh, Pd, Hf, Ta, W, Re, Ir, or Pt). A cathode composition may comprise an electroactive metal sulfide. In some embodiments, a lithium sulfur battery comprises a metal-sulfide cathode. A metal-sulfide cathode includes one or more electroactive metal sulfides. A metal-sulfide cathode may comprise one or more secondary electroactive species (e.g., other metal chalcogenides) (e.g., non-sulfurchalcogenides) in addition to a metal sulfide electroactive species. In some embodiments, a cathode comprises a blend or mixture of clcctroactivc materials, such as, for example, sulfur (e.g., S8) and a metal sulfide. In some embodiments, a cathode comprises an electroactive sulfur-carbon material (e.g., sulfur confined in a carbon matrix or framework).

[0066] In certain embodiments, cathode compositions (e.g., in cathodes) comprise one or more chalcogenides. In certain embodiments, a chalcogenide has at least one chalcogen anion (oxygen, sulfur, selenium, tellurium, or polonium anion) and at least one electropositive element. In certain embodiments, one or more chalcogenides may be sulfide-, selenide-, or telluride-based. In certain embodiments, one or more chalcogenides comprises a metal sulfide. In certain embodiments, one or more chalcogenides comprises one or more of the following: TiS3, LiTiS2 (LTS), and NbSe3. In certain embodiments, one or more chalcogenides comprises a transition metal oxide and / or a polyanion compound. In certain embodiments, one or more chalcogenides comprises a metal monochalcogenide having the formula MX where M is a transition metal and X is S, Se, or Te. In certain embodiments, one or more chalcogenides comprises at least one transition metal dichalcogenide (TMD) of the formula MX2, where M is a transition metal (e.g., Ti, V, Co, Ni, Zr, Nb, Mo, Tc, Rh, Pd, Hf, Ta, W, Re, Ir, or Pt) and where X is S, Se, or Te. In certain embodiments, one or more chalcogenides comprises a material with a layered crystal structure (e.g., LiTiS2, LiCoO2, LiNiO2, LiMnO2, LiNiO.33MnO.33CoO.3302, LiNi0.8Co0.15A10.0502, or Li2MnO3), a material with a spinel crystal structure (e.g., LiMn2O4 or LiCo2O4), a material with an olivine crystal structure (e.g., LiFePO4, LiMnPO4, or LiCoPO4), and / or a material with a tavorite crystal structure (e.g., LiFeSO4F or LiVPO4F).

[0067] In certain embodiments, cathode compositions contain conductive materials and a binder. In certain embodiments, a conductive material comprises an electrically conductive material that facilitates movement of electrons within a composite. For example, in certain embodiments, a conductive material is selected from the group consisting of carbon-based materials, graphite-based materials, conductive polymers, metals, semiconductors, metal oxides, metal sulfides, and combinations thereof. In certain embodiments, a conductive material comprises a carbon-based material. In certain embodiments, a conductive material comprises a graphite-based material. In certain embodiments, cathode compositions do not contain carbon, orcontains a low amount of carbon (e.g., no greater than 5.0 wt.%, no greater than 3.0 wt. %, no greater than 2.0 wt.%, no greater than 1.0 wt.%, or no greater than 0.5 wt.%).

[0068] In certain embodiments, an electrically conductive material is selected from the group consisting of conductive carbon powders, such as carbon black, Super P®, C-NERGY™ Super C65, Ensaco® black, Ketjenblack®, acetylene black, synthetic graphite such as Timrex® SFG-6, Timrex® SFG-15, Timrex® SFG-44, Timrex® KS-6, Timrex® KS-15, Timrex® KS-44, natural flake graphite, carbon nanotubes, fullerenes, hard carbon, mesocarbon microbeads, and the like. In certain embodiments, a conductive material comprises one or more conductive polymers. For example, in certain embodiments, a conductive polymer is selected from the group consisting of polyaniline, polythiophene, polyacetylene, polypyrrole, and the like. In some embodiments, a conductive polymer is a cationic polymer. In some embodiments, a cationic polymer is a quaternary ammonium polymer. In certain embodiments, a cationic polymer is selected from the group consisting of a polydiallyldimethylammonium salt, a poly[(3-chloro-2- hydroxypropyl)methacryloxyethyldimethyl-ammonium salt, a poly(butyl acrylate- methacryloxyethyltrimethylammonium) salt, poly(l-methyl-4-vinylpyridinium) salt, a poly(l- methyl-2-vinylpyridinium) salt, and a poly(methyacryloxyethyltriethylammonium) salt. In certain embodiments, a cationic polymer is selected from polydiallyldimethylammonium chloride (polyDADMAC), polybrene, epichlorohydrin-dimethylamine (epi-DMA), poly[(3-chloro-2- hydroxypropyl)methacryloxyethyldimethyl-ammonium chloride), poly(acrylamide- methacryloxyethyltrimethylammonium bromide), poly (butyl acrylatemethacryloxy ethyltrimethylammonium bromide), poly(l-methyl-4-vinylpyridinium bromide), poly(l-methyl-2-vinylpyridinium bromide), and poly(methyacryloxyethyltriethylammonium bromide). In certain embodiments, a conductive material comprises one or more metal oxides or sulfides. For example, in certain embodiments, a conductive material comprises one or more oxides or sulfides of a first-row transition metal such as titanium, vanadium, chromium, manganese, iron, cobalt, copper, zinc, or combinations thereof. For example, in certain embodiments, a conductive material comprises one or more oxides or sulfides of a second-row transition metal such as zirconium, indium, tin, antimony, or combinations thereof. In certain embodiments, a conductive material is used alone. In other embodiments, a conductive material is used as a mixture of two or more conductive materials described above.

[0069] In certain embodiments, a binder is included in the provided cathode composition materials. Binders arc generally polymeric materials that help adhere individual particles composing a cathode mixture into a stable composite. Representative binders include polyvinylidene fluoride, poly(vinylidene fluoride-co-hexafluoropropene) (PVDF / HFP), polytetrafluoroethylene (PTFE), Kynar Flex® 2801, Kynar® Powerflex LBG, Kynar® HSV 900, Teflon®, carboxymethylcellulose, styrene-butadiene rubber (SBR), polyethylene oxide, polypropylene oxide, polyethylene, polypropylene, polyacrylates, polyvinyl pyrrolidone, polylmcthyl methacrylate), polyethyl acrylate, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polycaprolactam, polyethylene terephthalate, polybutadiene, polyisoprene or polyacrylic acid, or derivatives, mixtures, or copolymers of any of these. In some embodiments, a binder is water soluble binder, such as sodium alginate, carrageenan, or carboxymethyl cellulose. Generally, binders hold active materials together and in contact with a current collector (e.g., a metal foil such as aluminum, stainless steel, or copper, or a conductive carbon sheet). In certain embodiments, a binder is selected from the group consisting of poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, crosslinked polyethylene oxide, polyvinyl ether, poly(methyl methacrylate), polyvinylidene fluoride, a copolymer of polyhexafluoropropylene and poly vinylidene fluoride, polyethyl acrylate, polytetrafluoroethylene, polyvinyl chloride, polyacrylonitrile, polyvinyl pyridine, polystyrene, and derivatives, mixtures, and copolymers thereof. In some embodiments, a binder is a cationic polymer. In some embodiments, a binder is a quaternary ammonium polymer. In some embodiments, a binder is a cationic polymer as described above.

[0070] In certain embodiments, a cathode further comprises a coating layer. For example, in certain embodiments, a coating layer comprises a polymer, an organic material, an inorganic material, or a mixture thereof that is not an integral part of the porous composite or the current collector. In certain such embodiments, a polymer is selected from the group consisting of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, poly(vinyl acetate), poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate), poly(methylmethacrylate-coethyl acrylate), polyacrylonitrile, polyvinyl chloride-co- vinyl acetate, polyvinyl alcohol, poly(l-vinylpyrrolidone-covinyl acetate), cellulose acetate, polyvinyl pyrrolidone, polyacrylate, polymethacrylate, polyolefin, polyurethane, polyvinyl ether,acrylonitrile-butadiene rubber, styrenebutadiene rubber, acrylonitrile-butadiene styrene, a sulfonated styrcnc / cthylcnc-butylcnc / styrcnc triblock copolymer, polyethylene oxide, and derivatives, mixtures, and copolymers thereof. In some embodiments, a coating layer comprises a cationic polymer. In some embodiments, a coating layer comprises a quaternary ammonium polymer. In some embodiments, a coating layer comprises a cationic polymer as described above. In certain such embodiments, an inorganic material comprises, for example, colloidal silica, amorphous silica, surface-treated silica, colloidal alumina, amorphous alumina, tin oxide, titanium oxide, titanium sulfide (TiS2), vanadium oxide, zirconium oxide (ZrO2), iron oxide, iron sulfide (FeS), iron titanate (FeTiO3), barium titanate (BaTiO3), and combinations thereof. In certain embodiments, an organic material comprises conductive carbon.

[0071] Suitable materials for use in cathode mixtures are disclosed in Cathode Materials for Lithium Sulfur Batteries: Design, Synthesis, and Electrochemical Performance, Lianfeng, et al., Interchopen.com, Published June 1st 2016, and The strategies of advanced cathode composites for lithium-sulfur batteries, Zhou et al., SCIENCE CHINA Technological Sciences, Volume 60, Issue 2: 175-185(2017), the entire disclosures of each of which are hereby incorporated by reference herein.

[0072] In certain embodiments, the cathode comprises one or more of the following features: (a) a “stack” of multi-functional materials (e.g., wherein the stack comprises, for example, particles with gradient structures that balance the transport of ions and electrons for improved power capability, energy density, and life; bi -functional cathode additives that simultaneously store Li and conduct electrons, replacing expensive and space-wasting carbons; a binding molecule that spatially constrains the electrochemical reaction storing the energy and thereby extends life; electrolyte components that improve the basic efficiency of the electrolyte, providing improved energy density; and / or a cathode design that enables greater safety and energy density); (b) a tight electrode layer; (c) a tight tertiary structure; (d) porosity control; (e) a core-shell structure; (f) a cross-linked polymer shell; (g) a self-doped polymer shell; (h) an ion conductive binder; (i) a dual layer hybrid cathode; (j) a polymer that traps poly sulfide; (k) a three-dimensional structure with high surface area (e.g., to hold both carbon and lithium, e.g., to intercalate); and (1) a three- dimensional structure within which carbon is replaced with a metal disulfide (e.g., and / or wherein the battery comprises a polymer electrolyte for sulfur).Anodes

[0073] In certain embodiments, a secondary sulfur battery comprises a lithium anode. Any lithium anode suitable for use in lithium- sulfur cells may be used. In certain embodiments, an anode of a secondary sulfur battery comprises a negative active material selected from materials in which lithium intercalation reversibly occurs, materials that react with lithium ions to form a lithium-containing compound, metallic lithium, lithium alloys, and combinations thereof. In certain embodiments, an anode comprises metallic lithium. In certain embodiments, lithium- containing anodic compositions comprise carbon-based compounds. In certain embodiments, a carbon-based compound is selected from the group consisting of crystalline carbon, amorphous carbon, graphite, and mixtures thereof. In certain embodiments, an anode does not contain carbon, or contains a low amount of carbon (e.g., no greater than 5.0 wt.%, no greater than 3.0 wt. %, no greater than 2.0 wt.%, no greater than 1.0 wt.%, or no greater than 0.5 wt.%). In certain embodiments, a material that reacts with lithium ions to form a lithium-containing compound is selected from the group consisting of tin oxide (SnO2), titanium nitrate, and silicon. In certain embodiments, a lithium alloy comprises an alloy of lithium with another alkali metal (e.g., sodium, potassium, rubidium or cesium). In certain embodiments, a lithium alloy comprises an alloy of lithium with a transition metal. In certain embodiments, lithium alloys include alloys of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, Sn, In, Zn, Sm, La, and combinations thereof. In certain embodiments, a lithium alloy comprises an alloy of lithium with indium. In certain embodiments, a lithium alloy comprises an alloy of lithium with aluminum. In certain embodiments, a lithium alloy comprises an alloy of lithium with zinc. In certain embodiments, an anode comprises a lithium-silicon alloy. Examples of suitable lithium-silicon alloys include: Lil5Si4, Lil2Si7, Li7Si3, Lil3Si4, and Li21Si5 / Li22Si5. In certain embodiments, a lithium metal or lithium alloy is present as a composite with another material. In certain embodiments, such composites include materials such as graphite, graphene, metal sulfides or oxides, or conductive polymers.

[0074] In some embodiments, an anode is protected against redox shuttling reactions and hazardous runaway reactions by any of the methodologies reported in the art, for example, by creating a protective layer on a surface of an anode by chemical passivation or by deposition orpolymerization. For example, in certain embodiments, an anode comprises an inorganic protective layer, an organic protective layer, or a mixture thereof, on a surface of lithium metal. In certain embodiments, an inorganic protective layer comprises Mg, Al, B, Sn, Pb, Cd, Si, In, Ga, lithium silicate, lithium borate, lithium phosphate, lithium phosphoronitride, lithium silicosulfide, lithium borosulfide, lithium aluminosulfide, lithium phosphosulfide, lithium fluoride or combinations thereof. In certain embodiments, an organic protective layer includes a conductive monomer, oligomer, or polymer. In certain embodiments, such polymer is selected from poly(p-phenylene), polyacetylene, poly(p-phenylene vinylene), polyaniline, polypyrrole, polythiophene, poly(2,5- ethylene vinylene), acetylene, poly (perinaphthalene), polyacene, and poly(naphthalene-2,6-di-y 1), or combinations thereof. In some embodiments, a protected anode (e.g., a protect lithium anode) is protected by alloying a first (e.g., primary) anode element or material (e.g., lithium) with a second (e.g., secondary) anode element or material (e.g., a transition metal, such as, for example, indium). An anode may be a protected lithium anode, for example a lithium- indium anode comprising an alloy of lithium and indium.

[0075] Moreover, in certain embodiments, inactive sulfur material, generated from an electroactive sulfur material of a cathode, during charging and discharging of a secondary sulfur battery, attaches to an anode surface. The term "inactive sulfur", as used herein, refers to sulfur that has no activity upon repeated electrochemical and chemical reactions, such that it cannot participate in an electrochemical reaction of a cathode. In certain embodiments, inactive sulfur on an anode surface acts as a protective layer on such electrode. In certain embodiments, inactive sulfur is lithium sulfide.

[0076] It is further contemplated that the present disclosure can be adapted for use in sodiumsulfur batteries. Such sodium- sulfur batteries comprise a sodium-based anode, and are encompassed within the scope of the present disclosure.

[0077] It is further contemplated that the present disclosure can be adapted for use in batteries with an anode-free configuration. In certain embodiments, the battery has an anode-free configuration and comprises one or more of the following: (a) a thin layer of garnet, (b) a structure (e.g., a complex 3D structure) with a coating deposited by atomic layer deposition (ALD) (e.g., wherein the ALD coating comprises one or more members selected from the group consisting of lithium phosphorus oxynitride (LiPON), garnet, an oxide, perovskite, a sulfide, Li3BO3-Li2CO3 (LBCO), a sodium super ionic conductor (NASICON), and alumina); (c) a polymer (e.g., polyethylene oxide (PEG) or a block copolymer); (d) lithium phosphorus oxynitride (LiPON), and (e) a solid-electrolyte interface (SEI) layer (e.g., an artificial SEI layer formed in situ).Preparation of Electrodes

[0078] There are a variety of methods for manufacturing electrodes for use in a secondary sulfur battery. One process, such as a “wet process,” involves adding the solid cathode materials to a liquid to prepare a slurry composition. These slurries are typically in the form of a viscous liquid that is formulated to facilitate a downstream coating operation. A thorough mixing of a slurry can be important for coating and drying operations, which affect performance and quality of an electrode. Suitable mixing devices include ball mills, magnetic stirrers, sonication, planetary mixers, high speed mixers, homogenizers, universal type mixers, and static mixers. A liquid used to make a slurry can be one that homogeneously disperses an active material, a binder, a conducting material, and any additives, and that is easily evaporated. Suitable slurry liquids include, for example, N-methylpyrrolidone, acetonitrile, methanol, ethanol, propanol, butanol, tetrahydrofuran, water, isopropyl alcohol, dimethylpyrrolidone, propylene carbonate, gamma butyrolactone and the like.

[0079] In some embodiments, a prepared composition is coated on a current collector and dried to form an electrode. Specifically, a slurry is used to coat an electrical conductor to form an electrode by evenly spreading a slurry on to a conductor, which is then, in certain embodiments, optionally roll-pressed (e.g., calendared) and heated as is known in the art. Generally, a matrix of an active material and conductive material are held together and on a conductor by a binder. In certain embodiments, a matrix comprises a polymer binder, such as poly vinylidene fluoride (PVDF), poly (vinylidene fluoride-co-hexafluoropropene) (PVDF / HFP), polytetrafluoroethylene (PTFE), Kynar Flex® 2801, Kynar® Powerflex LBG, Kynar® HSV 900, Teflon®, styrene butadiene rubber (SBR), polyethylene oxide (PEG), or polytetrafluoroethylene (PTFE). In certain embodiments, additional carbon particles, carbon nanofibers, carbon nanotubes, are dispersed in a matrix to improve electrical conductivity. Alternatively or additionally, in certain embodiments, lithium salts are dispersed in a matrix to improve lithium conductivity.

[0080] In certain embodiments, a current collector is selected from the group consisting of: aluminum foil, copper foil, nickel foil, stainless steel foil, titanium foil, zirconium foil, molybdenum foil, nickel foam, copper foam, carbon paper or carbon fiber sheets, polymer substrates coated with conductive metal, and / or combinations thereof.

[0081] PCT Publication Nos. WO2015 / 003184, WO2014 / 074150, and WO2013 / 040067, the entire disclosures of which are hereby incorporated by reference herein, describe various methods of fabricating electrodes and electrochemical cells.Separators

[0082] In certain embodiments, a secondary sulfur battery comprises a separator, which divides an anode and cathode and prevents direct electron conduction between them. In certain embodiments, the separator has a high lithium-ion permeability. In certain embodiments, a separator is relatively less permeable to polysulfide ions dissolved in electrolyte. In certain such embodiments, a separator as a whole inhibits or restricts passage of electrolyte-soluble sulfides between anodic and cathodic portions of a battery. In certain embodiments, a separator of impermeable material is configured to allow lithium-ion transport between anode and cathode of a battery during charging and discharging of a cell. In some such embodiments, a separator is porous. One or more electrolyte-permeable channels bypassing, or penetrating through apertures in, an impermeable face of a separator can be provided to allow sufficient lithium-ion flux between anodic and cathodic portions of a battery.

[0083] It will be appreciated by a person skilled in the art that optimal dimensions of a separator must balance competing imperatives: maximum impedance to polysulfide migration while allowing sufficient lithium-ion flux. Aside from this consideration, shape and orientation of a separator is not particularly limited, and depends in part on battery configuration. For example, in some embodiments, a separator is substantially circular in a coin-type cell, and substantially rectangular in a pouch-type cell. In some embodiments, a separator is substantially flat. However, it is not excluded that curved or other non-planar configurations may be used.

[0084] A separator may be of any suitable thickness. In order to maximize energy density of a battery, it is generally preferred that a separator is as thin and light as possible. However, a separator should be thick enough to provide sufficient mechanical robustness and to ensure suitableelectrical separation of the electrodes. In certain embodiments, a separator has a thickness of from about 1 pm to about 200 pm, preferably from about 5 pm to about 100 pm, more preferably from about 10 pm to about 30 pm.Electrochemical Cells

[0085] FIG. 1 illustrates a cross section of an electrochemical cell 800 in accordance with exemplary embodiments of the disclosure. Electrochemical cell 800 includes a negative electrode 802, a positive electrode 804, a separator 806 interposed between negative electrode 802 and positive electrode 804, a container 810, and an electrolyte 812 in contact with negative and positive electrodes 802, 804. Such cells optionally include additional layers of electrode and separators 802a, 802b, 804a, 804b, 806a, and 806b.

[0086] Negative electrode 802 (also sometimes referred to herein as an anode) comprises a negative electrode active material that can accept cations. Non-limiting examples of negative electrode active materials for lithium-based electrochemical cells include Li metal, Li alloys such as those of Si, Sn, Bi, In, and / or Al alloys, Li4Ti5O12, hard carbon, graphitic carbon, metal chalcogenides, and / or amorphous carbon. In accordance with some embodiments of the disclosure, most (e.g., greater than 90 wt %) of an anode active material can be initially included in a discharged positive electrode 804 (also sometimes referred to herein as a cathode) when electrochemical cell 800 is initially made, so that an electrode active material forms part of first electrode 802 during a first charge of electrochemical cell 800.

[0087] A technique for depositing electroactive material on a portion of negative electrode 802 is described in U.S. Patent Publication Nos. 2016 / 0172660 and 2016 / 0172661, in the name of Fischer et al., the contents of each of which are hereby incorporated herein by reference, to the extent such contents do not conflict with the present disclosure.

[0088] Positive electrode 804 (also referred to herein as cathode) comprises a cathode composition. In certain embodiments, the cathode composition comprises about 30 to about 70 wt% electroactive sulfur. In certain embodiments, a cathode comprises at least about 70% of total sulfur present in an electrochemical cell. In certain embodiments, a cathode comprises at least about 80% of total sulfur present in an electrochemical cell. In certain embodiments, a cathode comprises at least about 90% of total sulfur present in an electrochemical cell. In certainembodiments, a cathode comprises at least about 95% of total sulfur present in an electrochemical cell. In certain embodiments, a cathode comprises at least about 99% of total sulfur present in an electrochemical cell. In certain embodiments, a cathode comprises essentially all of the total sulfur present in an electrochemical cell.

[0089] Negative electrode 802 and positive electrode 804 can further include one or more electrically conductive additives as described herein. In accordance with some embodiments of the disclosure, negative electrode 802 and / or positive electrode 804 further include one or more polymer binders as described herein.

[0090] FIG. 2 illustrates an example of a battery according to various embodiments described herein. A cylindrical battery is shown here for illustration purposes, but other types of arrangements, including prismatic or pouch (laminate-type) batteries, may also be used as desired. Example Li battery 901 includes a negative anode 902, a positive cathode 904, a separator 906 interposed between the anode 902 and the cathode 904, an electrolyte (not shown) impregnating the separator 906, a battery case 905, and a sealing member 908 sealing the battery case 905. It will be appreciated that example battery 901 may simultaneously embody multiple aspects of the present disclosure in various designs.

[0091] A secondary sulfur battery of the present disclosure comprises a lithium anode, a porous sulfur-based cathode, and an electrolyte permitting lithium-ion transport between anode and cathode. In certain embodiments, described herein, an anodic portion of a battery comprises an anode and a portion of electrolyte with which it is in contact. Similarly, in certain embodiments, described herein, a cathodic portion of a battery comprises a cathode and a portion of electrolyte with which it is in contact. In certain embodiments, a battery comprises a lithium ion-permeable separator, which defines a boundary between an anodic portion and a cathodic portion. In certain embodiments, a battery comprises a case, which encloses both anodic and cathodic portions. In certain embodiments, a battery case comprises an electrically conductive anodic-end cover in electrical communication with an anode, and an electrically conductive cathodic-end cover in electrical communication with a cathode to facilitate charging and discharging via an external circuit.

[0092] In certain embodiments, a secondary sulfur battery of the present disclosure is defined in terms of its ratio of electrolyte to electroactive sulfur. Electrolyte volume and the ratio (vol / wt)of electrolyte to sulfur in a cathode correlate to energy density of a sulfur battery. Electrolyte may be distributed among different volumes within a cell, for example electrolyte may be contained in porosity of the cathode, in the separator, and in contact with an anode or within an anodic solid electrolyte interphase. Electrolyte may also be contained in other spaces within a battery where it is not in direct contact with the anodic or cathodic active materials— for example electrolyte may be stranded in an annular volume at the edges of a coin cell. In certain embodiments, the present disclosure provides batteries where all or most of the electrolyte is contained within the cathode. Preferably, substantially all of the electrolyte is contained within the cathode and only a minimal amount of electrolyte that is necessary to maintain electrical, physicochemical, and / or electrochemical communication with the separator and an anode surface or SEI is outside of the cathode. Electrolyte contained within the cathode is referred to as “contained electrolyte” and its volume VCE can be estimated as theoretical pore volume, or porosity multiplied by the geometric volume of a cathode film:

[0093] In certain embodiments, a provided secondary sulfur battery is characterized in that at least 50% of the total electrolyte inventory (Vtot) is contained in the cathode (e.g., VCE / Vtot >0.5). In certain embodiments, a provided secondary sulfur battery is characterized in that at least 50% of the total electrolyte inventory (Vtot) is contained in the cathode (e.g., VCE / Vtot >0.8). In certain embodiments, a secondary sulfur battery has at least 60%, at least 65%, or at least 70% of the electrolyte contained in the cathode porosity. In certain embodiments, a secondary sulfur battery has at least 80%, at least 85%, or at least 90% of the electrolyte contained in the cathode porosity. In certain embodiments, a secondary sulfur battery has at least 92%, at least 94%, at least 95%, at least 96%, or at least 97% of the electrolyte contained in the cathode.

[0094] The ratio of total electrolyte-to-sulfur (E / S) is another parameter that influences the energy density of a battery. The E / S ratio is calculated based on the total volume of electrolyte Vtot and the mass of electroactive sulfur (msulfur):

[0095] In certain embodiments, a secondary sulfur battery has an electrolyte-to-sulfur ratio ilfur. Incertain embodiments, a secondary sulfur battery has an electrolyte-to-sulfur ratio equal to or less than about 5 microliters of electrolyte per milligram of clcctroactivc sulfur. In certain embodiments, a secondary sulfur battery has an electrolyte-to-sulfur ratio equal to or less than about 4.5 microliters of electrolyte per milligram of electroactive sulfur. In certain embodiments, a secondary sulfur battery has an electrolyte-to-sulfur ratio equal to or less than about 3.5 microliters of electrolyte per milligram of electroactive sulfur or less than about 3.0 microliters of electrolyte per milligram of electroactive sulfur. In certain embodiments, a secondary sulfur battery has an electrolyte-to-sulfur ratio equal to or less than about 3.5 microliters of electrolyte per milligram of electroactive sulfur. In certain embodiments, a secondary sulfur battery has an electrolyte-to-sulfur ratio equal to or less than about 3 microliters of electrolyte per milligram of electroactive sulfur. In certain embodiments, a secondary sulfur battery has an electrolyte-to-sulfur ratio between about 1.8 and about 3.5 qL / mg S. In certain embodiments, a secondary sulfur battery has an electrolyte-to-sulfur ratio between about 1.8 and about 2.5 qL / mg S.

[0096] In certain embodiments, a provided electrochemical cell comprises: a cathode comprising a combination of an electroactive sulfur composition and one or more metal sulfide compositions having electrochemical capacity via lithium ion intercalation; an anode comprising lithium metal; and an electrolyte coupling the cathode and anode containing at least a 0.2 molar concentration of dissolved lithium iodide.

[0097] In certain embodiments, a provided electrochemical cell comprising lithium iodide is characterized in that it has lower self-discharge relative to a control cell where the lithium iodide in the electrolyte is replaced by an equimolar amount of a lithium salt selected from the group consisting of: LiTFSI, LiFSI, LIPFe, LiOTf, and combinations of any two or more of these. In certain such embodiments, the improved self-discharge is measured by charging the cells using a constant voltage of 2.4V until the current reaches a threshold of C / 20, then holding the cells in an open circuit condition for 48h prior to discharge. As shown in Figure 4, the decline in the open circuit voltage of the cell containing a lithium iodide electrolyte is slower than a cell with a conventional electrolyte and the final open circuit voltage of the cell containing a lithium iodide electrolyte is slightly higher than the OCV of the conventional electrolyte cell. As shown in Figure 5 the retained capacity of the iodide-containing cell (-1180 mAh / g S) is substantially higher than the non-iodide cell (-890 mAh / g S).

[0098] In certain embodiments, a provided electrochemical cell comprising lithium iodide is characterized in that it has higher discharge capacity in the voltage range from 2.3V to 1 ,8V relative to a control cell where the lithium iodide is replaced by an equimolar amount of a lithium salt selected from the group consisting of: LiTFSI, LiFSI, LIPFe, LiOTf, and combinations of any two or more of these. In certain such embodiments, the higher discharge capacity is at least 20 mAh / g S. Figure 6 shows one charge-discharge cycle for a Lithium iodide cell and for a control cell without iodide. The additional capacity of the iodide-containing cell is clearly visible between 2.3 and 2.2V.

[0099] In certain embodiments, a provided iodide-containing electrochemical cell is characterized in that it has improved specific capacity relative to a comparative cell where the lithium iodide in the electrolyte is replaced by an equimolar amount of a lithium salt selected from the group consisting of: LiTFSI, LiFSI, LIPFe, LiOTf, and combinations of any two or more of these. In certain embodiments, the increased capacity comprises an increase of at least 50 mAh / g S. at a discharge rate of 330. In certain embodiments, the increased capacity comprises an increase of at least 50 mAh / g S at a discharge rate of 330 mA / g S. In certain embodiments, the increased capacity comprises an increase of at least 50 mAh / g S at a discharge rate of 200 mA / g S. In certain embodiments, the increased capacity comprises an increase of at least 50 mAh / g S at a discharge rate of 100 mA / g S. Figure 7 shows the increased specific capacity of a lithium iodide-containing cell relative to an equivalent control cell lacking iodide.

[0100] In certain embodiments, a provided electrochemical cell is characterized in that it has improved low temperature performance relative to a comparative cell where the lithium iodide in the electrolyte is replaced by an equimolar amount of a lithium salt selected from the group consisting of: LiTFSI, LiFSI, LIPFe, LiOTf, and combinations of any two or more of these. In certain embodiments, the improved low temperature performance comprises at least 5% higher rate capability at C / 3 discharge. In certain embodiments, the improved low temperature performance comprises at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 40%, or at least 50%, higher rate capability at C / 3 discharge.EXAMPLES

[0101] In order that the application may be more fully understood, the following examples arc set forth. It should be understood that these examples arc for illustrative purposes only and arc not to be construed as limiting in any manner.Examples la to 1c: Lithium Sulfur Battery That Includes Lil ElectrolyteExample la: Construction of lithium iodide coin cells and comparative cells lacking lithium iodide

[0102] To evaluate the operability and performance advantages of lithium iodide-based electrolytes in Li-S batteries, coin cells were constructed using single layer cathodes comprising sulfur along with additives, conductive carbon and a polymer binder. A homogenized slurry of the cathode components in ethanol was cast on a carbon-coated aluminum current collector and dried to provide a cathode with a loading of 5-6 mg S / cm2 and a thickness of 215 pM. Punches of the dried cathode film were assembled into coin cells using Celgard™ separators and lithium metal anodes. Each cell was loaded with enough electrolyte to provide an E / S ratio of 4 pL / mg-S. Each cell was provided either with a conventional Li-FSI based electrolyte (0.8 M LiFSI, 0.3 M LiNOi in DOL / DME), or with a Li-I electrolyte according to the present disclosure (0.8M Lil, 0.3M LiNCh). Five cells containing each electrolyte composition were cycled using a Maccor battery test system according to the protocols described in Examples lb to 1c.Example lb: Evaluation of self-discharge characteristics of lithium iodide cells

[0103] The self-discharge of the Lil and control cells was measured by charging the cells using a constant voltage of 2.4V to a current threshold of C / 20, the cells were then held in an open circuit condition for 48h prior to discharge. As shown in Figure 4, the decline in the open circuit voltage of the cell containing a lithium iodide electrolyte is significantly slower than the cell with the conventional LiFSI electrolyte. The final open circuit voltage (OCV) of the cell containing a lithium iodide electrolyte is slightly higher than the OCV of the conventional electrolyte cell. As shown in Figure 5 the retained capacity of the iodide-containing cell (-1180 mAh / g S) was substantially higher than the non-iodide cell (-890 mAh / g S).Example 1c: Discharge characteristics of lithium iodide coin cells and comparative cells lacking lithium iodide

[0104] Figure 7 shows the discharge curves of a representative lithium iodide cell (black) and a typical LiFSI cell (red). The Lil cell has additional discharge capacity between 2.3 and 1.8V that is lacking in the LiFSI cell. Figure 8 shows the Cycling stability of Lil cell (black) and control cell (red). The cells were cycled at 330mA / g S (cycles 12-14), 200mA / g S (cycles 15-17), lOOmA / g S (cycles 18-23). At each discharge, the Lil cell has higher specific capacity. Additionally, within each rate group, the Lil cell shows less decline in capacity from one cycle to the next.

[0105] Without limitation to the foregoing description, the following is an enumerated list of non-limiting exemplary embodiments included in the present disclosure. Those of ordinary skill in the art will appreciate that one or more features discussed above may be included with or incorporated into any of the following numbered embodiments to form additional embodiments.1. An electrolyte for a lithium sulfur battery, the electrolyte comprising one or more lithium salts wherein at least 20% of anions in the one or more lithium salts are iodide.2. The electrolyte of embodiment 1, wherein at least 25% (e.g., at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90%) of the anions in the one or more lithium salts are iodide.3. The electrolyte of embodiment 1 or embodiment 2, wherein at least 20% (e.g., at least 25% at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90%) of all anions in the electrolyte are iodide.4. The electrolyte of any one of the preceding embodiments, wherein the one or more lithium salts comprises a blend of lithium iodide and at least one other lithium salt (e.g., LiFSI and / or LiTFSI).5. The electrolyte of any one of the preceding embodiments, further comprising anions selected from the group consisting of: nitrate, TFSI, FSI, triflatc, perchlorate, TDI, BF4, and PFe.6. The electrolyte of any one of the preceding embodiments, wherein the one or more lithium salts comprises a blend of lithium iodide and LiFSI.7. The electrolyte of any one of the preceding embodiments, comprising a solvent selected from the group consisting of dimethoxyethane, dioxolane, tetrahydrofuran, methylcyclopentyl ether, methyl tetrahydrofuran, dimethyl tetrahydrofuran, 1,4-dioxane, glyme, diethoxy ethane, diglyme, triglyme, tetraglyme, n-glymes with n > 5 (e.g., pentaglyme or hexaglyme), and mixtures thereof.8. The electrolyte of any one of the preceding embodiments, comprising a mixture of dimethoxyethane and 1,3-dioxolane.9. The electrolyte of embodiment 8, wherein a ratio of dimethoxyethane to 1,3-dioxolane ranges from 3:1 to 1:3.10. The electrolyte of any of embodiments 1-9, wherein total concentration of lithium salts in the electrolyte is less than 2M.11. The electrolyte of any of embodiments 1-10, wherein total concentration of lithium salts in the electrolyte is less than 1.8M (e.g., less than 1.6M, less than 1.5M, less than 1.4M, less than 1.3M, less than 1.2M, or less than IM).12. The electrolyte of any one of the preceding embodiments, wherein the electrolyte contains no fluorine-containing anions.13. The electrolyte of any one of the preceding embodiments, wherein the electrolyte contains no lithium salt other than the one or more lithium salts.14. A lithium sulfur battery comprising the electrolyte of any one of embodiments 1-13, characterized in that the battery has higher sulfur utilization than a corresponding battery with TFSI and / or FSI in place of the iodide.15. The lithium sulfur battery of embodiment 14, wherein specific capacity of the battery when discharged at C / 10 is at least 1100 mAh per gram sulfur.16. A lithium sulfur battery comprising the electrolyte of any one of embodiments 1-13, characterized in that the battery has lower self-discharge than a corresponding battery with TFSI and / or FSI in place of the iodide.17. A lithium sulfur battery comprising the electrolyte of any one of embodiments 1-13, characterized in that the electrolyte to sulfur ratio is below 4: 1 (e.g., wherein the sulfur is present in a cathode of the battery).18. A lithium sulfur battery comprising the electrolyte of any one of embodiments 1-13 and a sulfur-based cathode, characterized in that sulfur loading in the cathode is at least 5 mg / cm2.19. A lithium sulfur battery comprising the electrolyte of any one of embodiments 1-13 and a cathode, wherein (i) the electrolyte contains less than IM of lithium salt, (ii) the battery has an electrolyte to sulfur ratio below 4 pL / mg; and (iii) the cathode has a sulfur loading of at least 4 mg S / cm2.20. A lithium sulfur battery comprising the electrolyte of any one of embodiments 1-13, wherein the lithium sulfur battery is operable to cycle at least 20 times (e.g., at least 50 times, at least 100 times, at least 200 times, or at least 500 times).21. The lithium sulfur battery of any one of embodiments 14-20, comprising a protected lithium anode.22. The lithium sulfur battery of embodiment 21, wherein the protected lithium anode is a lithium-indium anode.23. The lithium sulfur battery of any one of embodiments 14-22, comprising a cathode comprising an electroactive metal sulfide (e.g., a metal-sulfide cathode).24. A lithium sulfur battery comprising the electrolyte of any one of embodiments 1-13 and a protected lithium anode.25. The lithium sulfur battery of embodiment 24, wherein the protected lithium anode is a lithium-indium anode.26. The lithium sulfur battery of embodiment 24 or embodiment 25, comprising a cathode comprising an electroactive metal sulfide (e.g., a metal-sulfide cathode).27. A method of providing over-temperature protection to a lithium sulfur battery (e.g., a battery according to any one of embodiments 14-26) comprising an electrolyte comprising lithium salt (e.g., comprising two or more distinct lithium salts), the method comprising providing the battery, wherein at least 50 mole percent of the lithium salt present in the electrolyte comprises lithium iodide.

[0106] In this application, unless otherwise clear from context or otherwise explicitly stated, (i) the term “a” may be understood to mean “at least one”; (ii) the term “or” may be understood to mean “and / or”; (iii) the terms “comprising” and “including” may be understood to encompass itemized components or steps whether presented by themselves or together with one or more additional components or steps; (iv) the terms “about” and “approximately” may be understood to permit standard variation as would be understood by those of ordinary skill in the relevant art; and (v) where ranges are provided, endpoints are included. In some embodiments, the term “approximately” or “about” refers to a range of values that fall within 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in eitherdirection (greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context (except where such number would exceed 100% of a possible value).

[0107] It is contemplated that systems, devices, methods, and processes of the disclosure encompass variations and adaptations developed using information from the embodiments described herein. Adaptation and / or modification of the systems, devices, methods, and processes described herein may be performed by those of ordinary skill in the relevant art.

[0108] Throughout the description, where articles, devices, and systems are described as having, including, or comprising specific components, or where processes and methods are described as having, including, or comprising specific steps, it is contemplated that, additionally, there are articles, devices, and systems according to certain embodiments of the present disclosure that consist essentially of, or consist of, the recited components, and that there are processes and methods according to certain embodiments of the present disclosure that consist essentially of, or consist of, the recited processing steps.

[0109] It should be understood that the order of steps or order for performing certain action is immaterial so long as operability is not lost. Moreover, two or more steps or actions may be conducted simultaneously. As is understood by those skilled in the art, the terms “over”, “under”, “above”, “below”, “beneath”, and “on” are relative terms and can be interchanged in reference to different orientations of the layers, elements, and substrates included in the present disclosure. For example, a first layer on a second layer, in some embodiments means a first layer directly on and in contact with a second layer. In other embodiments, a first layer on a second layer can include another layer there between.

[0110] Headers have been provided for the convenience of the reader and are not intended to be limiting with respect to the claimed subject matter. Statements made in the background section are not to be construed as admissions that they are prior art.

[0111] Certain embodiments of the present disclosure were described above. It is, however, expressly noted that the present disclosure is not limited to those embodiments, but rather the intention is that additions and modifications to what was expressly described in the present disclosure are also included within the scope of the disclosure. Moreover, it is to be understood that the features of the various embodiments described in the present disclosure were not mutuallyexclusive and can exist in various combinations and permutations, even if such combinations or permutations were not made express, without departing from the spirit and scope of the disclosure. The disclosure has been described in detail with particular reference to certain embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the claimed invention.

Claims

CLAIMS1. An electrolyte for a lithium sulfur battery, the electrolyte comprising one or more lithium salts wherein at least 20% of anions in the one or more lithium salts are iodide.

2. The electrolyte of claim 1, wherein at least 25% (e.g., at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90%) of the anions in the one or more lithium salts are iodide.

3. The electrolyte of claim 1, wherein at least 20% (e.g., at least 25% at least 30%, at least 40%, at least 45%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90%) of all anions in the electrolyte are iodide.

4. The electrolyte of claim 1, wherein the one or more lithium salts comprises a blend of lithium iodide and at least one other lithium salt (e.g., LiFSI and / or LiTFSI).

5. The electrolyte of claim 1, further comprising anions selected from the group consisting of: nitrate, TFSI, FSI, triflate, perchlorate, TDI, BF4, and PF6.

6. The electrolyte of claim 1, wherein the one or more lithium salts comprises a blend of lithium iodide and LiFSI.

7. The electrolyte of claim 1, comprising a solvent selected from the group consisting of dimethoxyethane, dioxolane, tetrahydrofuran, methylcyclopentyl ether, methyl tetrahydrofuran, dimethyl tetrahydrofuran, 1,4-dioxane, glyme, diethoxy ethane, diglyme, triglyme, tetraglyme, n- glymes with n > 5 (e.g., pentaglyme or hexaglyme), and mixtures thereof.

8. The electrolyte of claim 1, comprising a mixture of dimethoxyethane and 1,3-dioxolane.

9. The electrolyte of claim 8, wherein a ratio of dimethoxyethane to 1,3-dioxolane ranges from 3:1 to 1:3.

10. The electrolyte of claim 1, wherein total concentration of lithium salts in the electrolyte is less than 2M.

11. The electrolyte of claim 1, wherein total concentration of lithium salts in the electrolyte is less than 1.8M (e.g., less than 1.6M, less than 1.5M, less than 1.4M, less than 1.3M, less than 1.2M, or less than IM).

12. The electrolyte of claim 1, wherein the electrolyte contains no fluorine-containing anions.

13. The electrolyte of claim 1, wherein the electrolyte contains no lithium salt other than the one or more lithium salts.

14. A lithium sulfur battery comprising the electrolyte of any one of claims 1-13, characterized in that the battery has higher sulfur utilization than a corresponding battery with TFSI and / or FSI in place of the iodide.

15. The lithium sulfur battery of claim 14, wherein specific capacity of the battery when discharged at C / 10 is at least 1100 mAh per gram sulfur.

16. A lithium sulfur battery comprising the electrolyte of any one of claims 1-13, characterized in that the battery has lower self-discharge than a corresponding battery with TFSI and / or FSI in place of the iodide.

17. A lithium sulfur battery comprising the electrolyte of any one of claims 1-13, characterized in that the electrolyte to sulfur ratio is below 4: 1 (e.g., wherein the sulfur is present in a cathode of the battery).

18. A lithium sulfur battery comprising the electrolyte of any one of claims 1-13 and a sulfurbased cathode, characterized in that sulfur loading in the cathode is at least 5 mg / enr.

19. A lithium sulfur battery comprising the electrolyte of any one of claims 1-13 and a cathode, wherein (i) the electrolyte contains less than IM of lithium salt, (ii) the battery has an electrolyte to sulfur ratio below 4 pL / mg; and (iii) the cathode has a sulfur loading of at least 4 mg S / cm2.

20. A lithium sulfur battery comprising the electrolyte of any one of claims 1-13, wherein the lithium sulfur battery is operable to cycle at least 20 times (e.g., at least 50 times, at least 100 times, at least 200 times, or at least 500 times).

21. The lithium sulfur battery of claim 14, comprising a protected lithium anode.

22. The lithium sulfur battery of claim 21, wherein the protected lithium anode is a lithiumindium anode.

23. The lithium sulfur battery of claim 14, comprising a cathode comprising an electroactive metal sulfide (e.g., a metal-sulfide cathode).

24. A lithium sulfur battery comprising the electrolyte of any one of claims 1-13 and a protected lithium anode.

25. The lithium sulfur battery of claim 24, wherein the protected lithium anode is a lithiumindium anode.

26. The lithium sulfur battery of claim 24, comprising a cathode comprising an electroactive metal sulfide (e.g., a metal-sulfide cathode).

27. A method of providing over-temperature protection to a lithium sulfur battery comprising an electrolyte comprising lithium salt (e.g., comprising two or more distinct lithium salts), the method comprising providing the battery, wherein at least 50 mole percent of the lithium salt present in the electrolyte comprises lithium iodide.

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