WO2025181602A1 - Co-salt systems with sulfonyl-containing solvents, electrolytes made therewith, and electrochemical devices made using such electrolytes - Google Patents

Abstract

An electrolyte for electrochemical devices with an alkali-metal anode having an anode-active material comprising an alkali metal is disclosed in which the electrolyte includes at least one sulfonyl solvent and a co-salt system. The co-salt system includes a lithium cation primary salt at a relatively high concentration and a secondary salt at a relatively low concentration. The secondary salt and its concentration are selected to increase the solubility of the primary salt. The concentration of the secondary salt may be increased to increase the solubility of the primary salt until the presence of the secondary salt begins to diminish the overall performance of the electrolyte. The primary salt may comprise two or more lithium cation salts and the secondary salt may comprise two or more salts.

Description

CO-SALT SYSTEMS WITH SULFONYL-CONTAINING SOLVENTS, ELECTROLYTES MADE THEREWITH, AND ELECTROCHEMICAL DEVICES MADE USING SUCH ELECTROLYTES RELATED APPLICATION DATA _{[0001] This application claims the benefit of priority of U.S. Provisional Patent Application} Serial No.63/558,023, filed February 26, 2024, and titled “Co-Salt Systems with Sulfonyl- Containing Solvents, Electrolytes Made Therewith, and Electrochemical Devices Made Using Such Electrolytes,” which is incorporated by reference herein in its entirety. FIELD OF THE DISCLOSURE _{[0002] The present disclosure generally relates to the field of electrolytes for electrochemical} devices. In particular, the present disclosure is directed to co-salt systems with sulfonyl-containing solvents, electrolytes made therewith, and electrochemical devices made using such electrolytes. BACKGROUND _{[0003] Lithium-ion batteries have been widely used in many applications, such as portable} electronic devices and electric vehicles. Existing lithium-ion batteries with graphite anodes, however, do not always meet the various performance requirements for certain applications. The energy density of lithium-ion batteries has been approaching its theoretical energy-density boundary. The use of graphite anodes having 375 mAh g^-1 specific capacities is the main cause for the relatively low energy density of existing lithium-ion batteries, and so exploration of new anode materials may result in improvements in the performance of these batteries. In recent years, lithium- metal anodes have been attracting much attention because of their relatively high specific capacity (3860 mAh g^-1) and the lowest potential (0 V vs. Li/Li⁺). _{[0004] However, there are a couple of challenges facing lithium-metal-anode technology,} specifically, relatively short cycle life and lithium-dendrite formation. The cycle life of lithium- metal batteries is associated with the coulombic efficiency (CE) of the plating/stripping of the lithium metal on the anode side of the batteries. Despite intensive efforts to improve the performance of lithium-metal batteries, most electrolytes developed to date have relatively low CE values (<99.4%), thus leading to relatively short battery cycle life. 1 Attorney Docket No.17468-138WOU1 SUMMARY OF THE DISCLOSURE _{[0005] An electrolyte for an electrochemical device having an alkali-metal anode having an} anode-active material comprising an alkali metal, in which the electrolyte includes at least one sulfonyl solvent, a primary salt, wherein the primary salt is a Li cation salt and is at a first concentration, and a secondary salt, wherein the secondary salt has a second concentration lower than the first concentration. _{[0006] Additionally or alternatively, the first concentration of the primary salt is greater than 1} molarity. _{[0007] Additionally or alternatively, the second concentration of the secondary salt is between} 0.1 weight percentage and 30 weight percentage. _{[0008] Additionally or alternatively, the primary salt is LiFSI and the secondary salt is LiTFSI. [0009] Additionally or alternatively, the primary salt is LiFSI and the secondary salt is KFSI. [0010] Additionally or alternatively, the primary salt is LiFSI and the secondary salt is LiHFDF. [0011] Additionally or alternatively, the primary salt is LiFSI and an anion of the secondary salt} is TFSI-. _{[0012] Additionally or alternatively, the primary salt is LiFSI and an anion of the secondary salt} is FSI-. _{[0013] Additionally or alternatively, the primary salt is LiFSI and an anion of the secondary salt} is HFDF-. _{[0014] Additionally or alternatively, a cation of the secondary salt is selected from the group} consisting of Li, Na, K, Rb, Cs, Ag, Mg, and In. _{[0015] Additionally or alternatively, an anion of the secondary salt is selected from the group} consisting of tetrafluoroborate (BF4), hexafluorophosphate (PF6), difluorophosphate (DFP), cyclo- difluoromethane-1,1-bis-(sulfonyl)imide (DMSI), 4,4,5,5-tetrafluoro-1,3,2-dithiazolidine-1,1,3,3- tetraoxide (CTFSI), hexamethyldisilazide (HMDS), and difluro(oxalate)borate (DFOB). _{[0016] Additionally or alternatively, the sulfonyl solvent is a sulfonamide solvent.} 2 Attorney Docket No.17468-138WOU1 _{[0017] Additionally or alternatively, the sulfonyl includes at least one sulfonyl (-SO2-) group,} each with a double bond between each oxygen atom. _{[0018] Additionally or alternatively, the electrolyte has a total salt concentration of from about} 1.0 M to about 5.5 M. _{[0019] Additionally or alternatively, the electrolyte has a total salt concentration of from about} 1.0 M to about 4.5 M. _{[0020] Additionally or alternatively, the electrolyte has a salt-solvent mole ratio in a range from} about 1:7 to about 1:1. _{[0021] An electrochemical cell is provided that includes an alkali-metal anode having an anode-} active material comprising an alkali metal, a cathode, a separator located between the alkali-metal anode and the cathode, and any electrolyte as described herein in operative communication with each of the alkali-metal anode and the cathode. _{[0022] Additionally or alternatively, a multicell battery is provided that includes a plurality of} electrochemical cells as described herein with a pair of output terminals and electrical connections electrically connecting the plurality of electrochemical cells to the pair of output terminals. _{[0023] A method of preparing an electrolyte for a lithium metal battery cell is disclosed that} includes selecting a sulfonyl solvent, selecting a primary salt, the primary salt having a lithium cation, dissolving the primary salt in the solvent to form a primary salt solution having a primary salt concentration, selecting a secondary salt, and dissolving the secondary salt in the primary salt solution to form a co-salt solution having a secondary salt concentration. The secondary salt concentration is selected such that the secondary salt concentration increases the primary salt concentration up to a peak secondary salt concentration beyond which an overall performance of the electrolyte for the lithium metal battery cell is reduced. _{[0024] Additionally or alternatively, the overall performance of the electrolyte for the lithium} metal battery cell is determined based on a number of life cycles of the cell without a short circuit and cycle life. _{[0025] In addition, an electrolyte for an electrochemical device having an alkali-metal anode} having an anode-active material comprising an alkali metal is provided in which the electrolyte 3 Attorney Docket No.17468-138WOU1 includes at least one sulfonyl solvent, a primary salt, wherein the primary salt includes a lithium cation and has a primary salt concentration, and a secondary salt, wherein the secondary salt has a second salt concentration that is lower than the primary salt concentration. _{[0026] Additionally or alternatively, the sulfonyl solvent is one or more solvents selected from} the group of: CH2=CHSO2F, CH2=CHSO2CF3, (CH3)2NSO2F, FSO2N(CH3)SO2F, (CH3)(CH2=CHCH2)NSO2N(CH3)2, CH3CH=CHSO2N(CH3)(CH2CH3), C6H4FSO2CH2CF3, FCH₂SO₂CH=CHCH₂F, CH₂FCH=CHCF₂SO₂N(SO₂F)₂, FSO₂N(CH₃)(CH₂CH₃), FSO2N(CH2CH3)2, and CF3SO2F. _{[0027] Additionally or alternatively, the sulfonyl solvent is one or more solvents selected from} the group of: CH₂SO₂N(CH₃)(SO₂CH₂-), CF₂SO₂N (CH₂CH=CH₂)(CF₂), (FCH₂=CH)CHSO₂N(CH3)CH(CH=CH₂), CH₂SO₂N(CH₃)CH₂CH₂, CH2CH2SO2N(CH2CH3)CH2CH2, and CF2SO2N(CH3)SO2CF2. _{[0028] Additionally or alternatively, the sulfonyl solvent is one or more solvents selected from} the group of: FSO₂N[(CH₂)₂OCH₃]₂, FSO₂N[(CH₂)₂OCH₃][CH₃], CF₃SO₂N[(CH₂)₂OCH₃]₂, and CF3SO2N[(CH2)2OCH3][CH3]. _{[0029] Additionally or alternatively, the sulfonyl solvent is one or more solvents selected from} the group of: FSO₂N(CH₂)₄, CF₃SO₂N(CH₂)₄, and FSO₂N(CH₂CH₂)₂O. _{[0030] Additionally or alternatively, an anion of the secondary salt is selected from the group of} borate-containing anions, sulfonamide-containing anions, sulfonimide-containing anions, phosphate- containing anions, amide-containing anions, and antimonate-containing anions. _{[0031] Additionally or alternatively, the primary salt is selected from the group of LiFSI,} LiTFSI, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)-amide, lithium bis(pentafluoroethanesulfonyl)imide, lithium-cyclo-difluoromethane-1,1-bis-(sulfonyl)imide, lithium 4,4,5,5-tetrafluoro-1,3,2-dithiazolidine-1,1,3,3-tetraoxide, lithium 1,1,2,2,3,3-hexafluoropropane- 1,3-disulfonimide , lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroantimonate, lithium trifluoromethanesulfonate, lithium 2-trifluoromethyl-4,5- dicyanoimidazolide, lithium tetracyanoborate, lithium bis(oxalato)borate, lithium difluoro(oxalate)borate, lithium difluoro(bisoxalato) phosphate, lithium polysulfide, lithium difluorophosphate, LiFSI-polymer, and LiTFSI-polymer. 4 Attorney Docket No.17468-138WOU1 _{[0032] Additionally or alternatively, the secondary salt is selected from the group of LiFSI,} LiTFSI, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)-amide, lithium bis(pentafluoroethanesulfonyl)imide, lithium-cyclo-difluoromethane-1,1-bis-(sulfonyl)imide, lithium 4,4,5,5-tetrafluoro-1,3,2-dithiazolidine-1,1,3,3-tetraoxide, lithium 1,1,2,2,3,3-hexafluoropropane- 1,3-disulfonimide , lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroantimonate, lithium trifluoromethanesulfonate, lithium 2-trifluoromethyl-4,5- dicyanoimidazolide, lithium tetracyanoborate, lithium bis(oxalato)borate, lithium difluoro(oxalate)borate, lithium difluoro(bisoxalato) phosphate, lithium polysulfide, lithium difluorophosphate, LiFSI-polymer, and LiTFSI-polymer. BRIEF DESCRIPTION OF THE DRAWINGS _{[0033] For the purpose of illustrating the disclosure, the drawings show aspects of one or more} embodiments of the disclosure. However, it should be understood that the present disclosure is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: FIG.1 is a graph of capacity retention versus cycle number determined for pouch cells under fast charging conditions in which one set of cells contains a single salt electrolyte and another set of cells contains a two-salt electrolyte according to the present disclosure; FIG.2 is a graph of capacity retention versus cycle number for lithium nickel manganese cobalt pouch cells containing a single salt electrolyte and lithium nickel manganese cobalt pouch cells containing an electrolyte with two salts; FIG.3 is a bar chart showing percent cathode CE for 3/4 layer copper-nickel manganese cobalt (NMC) anode-free cells containing 1) a single salt electrolyte and 2) a co-salt electrolyte; FIG.4A is a graph of discharge capacity versus cycle number for Li + NMC pouch cells containing a single salt electrolyte and pouch cells containing a co-salt electrolyte; FIG.4B is a graph of cell coulombic efficiency versus cycle number for the Li + NMC cells described with respect to FIG.4A; FIG.5A is a sectional view of a schematic of an electrochemical energy-storage cell made in accordance with the present disclosure; FIG.5B is a schematic diagram of an energy-storage battery system made in accordance with the present disclosure; 5 Attorney Docket No.17468-138WOU1 FIG.6 is a graph of discharge capacity versus cycle number for cells with a dual-salt electrolyte and for cells containing a single salt electrolyte; FIG.7A is a graph of discharge capacity percentage versus cycle number for Li + NMC pouch cells under fast charging tests containing a single salt electrolyte, for pouch cells containing a first dual- salt electrolyte, and for pouch cells containing a second dual-salt electrolyte; and FIG.7B is a graph of reverse coulombic efficiency (RCE) percent versus cycle number for the different pouch cells of FIG.7A. DETAILED DESCRIPTION _{[0034] In the context of lithium-metal batteries, limited cycle life is attributable in part to low} CE of the lithium anode, which worsens for cells with most conventional electrolytes during cycling. In addition, some conventional electrolytes are stable with respect to lithium-metal anodes but are oxidatively unstable towards 4V cathode materials, especially at temperatures higher than room temperature (e.g., > ~20°C). Some conventional electrolytes can remain in the liquid phase and maintain moderate conductivity at room and higher temperatures (e.g., > 45℃), but they do not perform well at low temperatures (e.g., < 0℃) due to salt precipitation, phase separation, and electrolyte freezing. _{[0035] Electrolytes with co-salt systems in sulfonyl-containing solvents disclosed herein may} result in fewer side reactions with lithium, leading to a reduction of lithium-deposition surface area, a significant increase of CE for lithium plating/stripping, suppression of lithium dendrite growth, and minimization of oxidative decomposition of the solvent(s) at high voltage (> 4.5V) and/or high temperatures (> 45℃). These electrolytes may be used over a wide temperature range, singly and in various combinations with one another, so as to provide significant improvement in cycle life and high and low temperature stability. Cycling stability of these sulfonyl-containing co-salt electrolytes has been shown in different testing protocols. Lithium-metal cells and batteries with these sulfonyl- containing co-salt electrolytes may have improved cycle life, energy density, and safety. _{[0036] An electrolyte for an electrochemical device comprising an alkali-metal anode having an} anode-active material comprising an alkali metal is disclosed in which the electrolyte includes at least one sulfonyl solvent and a co-salt system. The co-salt system includes a Li cation primary salt at a relatively high concentration and a secondary salt at a relatively low concentration. The secondary salt and its concentration are selected to increase the solubility of the primary salt. The concentration of the secondary salt may be increased to increase the solubility of the primary salt 6 Attorney Docket No.17468-138WOU1 until the presence of the secondary salt begins to diminish the overall performance of the electrolyte. The primary salt may comprise two or more Li cation salts selected from the primary salts disclosed below and the secondary salt may comprise two or more salts selected from the secondary salts disclosed below. _{[0037] In some embodiments, the molar concentration of the primary salt is greater than 1} molarity. _{[0038] In some embodiments, the concentration of the secondary salt is between 0.1 weight} percentage and 30 weight percentage. _{[0039] In some embodiments, the primary salt is lithium bis(fluorosulfonyl)imide (LiFSI) and} the secondary salt is lithium bis(trifluoromethane)sulfonimide (LiTFSI). _{[0040] In some embodiments, the primary salt is LiFSI and the secondary salt is potassium} bis(fluorosulfonyl)imide (KFSI). _{[0041] In some embodiments, the primary salt is LiFSI and the secondary salt is lithium} 1,1,2,2,3,3-Hexafluoropropane-1,3-disulfonimide (LiHFDF). _{[0042] In some embodiments, the cation of the secondary salt is selected from the group} consisting of Li, Na, K, Rb, Cs, Ag, Mg, and In. _{[0043] In some embodiments, the anion of the secondary salt is selected from the group} consisting of bis(fluorosulfonyl)imide (FSI), bis(trifluoromethanesulfonyl)imide (TFSI), tetrafluoroborate (BF4), hexafluorophosphate (PF6), difluorophosphate (DFP), hexafluoropropane- 1,3-disulfonimide (HFDF), cyclo-difluoromethane-1,1-bis-(sulfonyl)imide (DMSI), 4,4,5,5- tetrafluoro-1,3,2-dithiazolidine-1,1,3,3-tetraoxide (CTFSI), hexamethyldisilazide (HMDS), and difluro(oxalate)borate (DFOB). _{[0044] In some embodiments, the solvent is a sulfonamide solvent. [0045] In some aspects, the present disclosure is directed to sulfonyl-containing co-salt} electrolytes for use in electrochemical devices, such as primary and secondary batteries and supercapacitors, among others. The sulfonyl-containing co-salt electrolytes of the present disclosure are especially effective when used in secondary alkali metal batteries (AMBs), such as lithium-metal batteries (LMBs), in which the anodes are of a non-intercalating type (e.g., plating/stripping type) 7 Attorney Docket No.17468-138WOU1 and include an alkali metal (e.g., lithium (Li), sodium (Na), potassium (K)), or an alloy thereof, as the anode-active material. _{[0046] The sulfonyl-containing co-salt electrolyte may contain A) at least one sulfonyl solvent} containing molecules that each include at least one sulfonyl (-SO₂-) group, each with a double bond between each oxygen atom and the sulfur atom (i.e., O=S=O), along with two substituents, Rn (n = 2), and optionally a nitrogen atom bonded to at least one of the SO2 groups, B) a primary (or dominant) Li cation salt at relatively high concentration, preferably over 1 molarity, most commonly LiFSI, and C) at least one additional secondary salt at lower concentrations than the primary salt, preferably ranging from as low as 0.1 weight percentage to as high as 30 weight percentage. The secondary salts may contain a wide variety of metal cations, including Li, Na, K, Rb, Cs, Ag, Mg, or In, and a wide variety of different anions including FSI, TFSI, tetrafluoroborate (BF4), hexafluorophosphate (PF6), difluorophosphate (DFP), hexafluoropropane-1,3-disulfonimide (HFDF), cyclo-difluoromethane-1,1-bis-(sulfonyl)imide (DMSI), 4,4,5,5-tetrafluoro-1,3,2- dithiazolidine-1,1,3,3-tetraoxide (CTFSI), hexamethyldisilazide (HMDS), and difluro(oxalate)borate (DFOB), amongst others. Detailed examples of chemical structures of certain constituents of the sulfonyl-containing co-salt systems of the present disclosure are presented below. _{[0047] A sulfonyl-containing co-salt electrolyte of the present disclosure may include a} sulfonyl-containing solvent, at least two co-salts suitable for an intended electrochemical device, and, optionally, one or more other components, such as one or more additives and/or diluents added to improve one or more properties or characteristics of the sulfonyl-containing co-salt electrolyte but that do not change the fundamental nature and character of the sulfonyl-containing co-salt electrolyte without such additive(s). In the context of AMBs, at least one salt will typically include the relevant alkali metal(s) as the cation(s). Additional non-exhaustive examples of co-salt combinations for use in the sulfonyl-containing co-salt electrolytes of the present disclosure appear below. _{[0048] Benefits for AMBs, including LMBs, that arise from using a sulfonyl-containing co-salt} electrolyte of the present disclosure include the following, individually and/or in various combinations with one another, depending on the circumstances at issue. A sulfonyl-containing co- salt electrolyte of the present disclosure can have an extremely high stability (e.g., an alkali-metal (e.g., Li) plating/stripping coulombic efficiency (CE) of greater than about 99.0% or greater than about 99.5%) towards the alkali-metal anode (e.g., Li-metal anode) and a high antioxidation capability (e.g., oxidation voltage greater than about 4.3V or greater than about 4.8V), which can 8 Attorney Docket No.17468-138WOU1 lead to improved cycling performance relative to AMBs, including LMBs, utilizing sulfonyl-only solvent, solvent systems or conventional non-sulfonyl solvent systems. The sulfonyl-containing co- salt electrolytes can deliver very high chemical and electrochemical stability at the cathode and anode in an AMB, such as an LMB, enhanced wide-temperature performance, nonflammability performance, low cost, high safety, and/or good compatibility with cell manufacturing and processing. While sulfonyl-containing co-salt electrolytes of the present disclosure are particularly useful for AMBs, their uses are not limited thereto. _{[0049] Without being bound to any particular theories, it is currently believed the embodiments} of sulfonyl-containing co-salt electrolytes of the present disclosure work in any one or more of a variety of ways, depending on the specific co-salt(s) added to the sulfonyl solvent(s). For example, one of the TFSI salts may work by increasing the solubility of the primary salt without the need for additional solvent or cosolvent. As another example, one of the HFDF salts may work by altering the coordination structure of the Li cation, leading to preferential reduction of the primary salt’s anion, which may result in an improved interfacial layer on the surface of the Li metal anode. As a further example, one of the FSI salts may work by increasing the stability of the cathode. Others of the various co-salts discussed below may have the same or other mechanisms for improving electrolyte performance when two or more salts are dissolved into a sulfonyl solvent to create an electrolyte as described herein. _{[0050] As used herein, the primary salt is the salt with the highest concentration and is selected} based on the effectiveness of that salt for a given application, e.g., as part of an electrolyte in an AMB. This effectiveness can be increased by increasing the solubility of the primary salt, which as disclosed herein may be accomplished by including a relatively lower concentration of a secondary salt. The secondary salt, which will be less effective than the primary salt for the given application (i.e., particular cell), and so at some threshold concentration the secondary salt may result in a decrease in the overall effectiveness of the co-salt electrolyte. In a most preferred embodiment, the concentration of the secondary salt is selected such that a peak effectiveness of the electrolyte results (i.e., the maximum benefit is attained from the increased solubility of the primary salt before further increases in the concentration of the secondary salt begin to reduce that effectiveness). EXAMPLE SULFONYL SOLVENTS FOR CO-SALT ELECTROLYTE SYSTEMS _{[0051] A sulfonyl-containing co-salt system of the present disclosure contains at least one} sulfonyl solvent having any of the following general chemical structures: 9 Attorney Docket No.17468-138WOU1 _{[0052] Structure 1 (R1-SO2-R2):} wherein: each of R1 and R2 may be: -F; -CF₃; -N(SO2F)2; -N(CH3)SO2F, -N[(CH2)xCH3)][(CH2)yCH3)] (x = 0 to 3, y = 0 to 3); -N[(CH₂)_xCH₃][(CH₂)_yCH=CH(CH₂)_z-H] (x = 0 to 2; y=1 to 3, z = 0 to 3); -(CH₂)_xCH=CH(CH₂)_y-H (x = 0 to 3; y = 0 to 3); -C6H5-xFx (x = 0 to 5); -(CH2)x(CH2-yFy)zCH3-wFw (x = 0 to 2, y = 1 to 2, z = 0 to 2, w = 0 to 3); -(CH₂)_x(CH_2-yF_y)_zF (x = 0 to 2, y = 0 to 2, z = 0 to 2); or -(CH2)xCH=CH(CH2-yFy)zF (x = 0 to 3, y = 0 to 2, z = 0 to 2); and R₁ ≠ R₂ or R₁ = R₂. _{[0053] The following are example sulfonyl solvents having general Structure 1: 1) R1 is -} CH=CH2, R2 is -F, and the solvent is CH2=CHSO2F; 2) R1 is -CH=CH2, R2 is -CF₃, and the solvent is CH₂=CHSO₂CF₃; 3) R₁ is -N(CH₃)₂, R₂ is -F, and the solvent is (CH₃)₂NSO₂F; 4) R₁ is-NCH₃SO₂F, R₂ is F, and the solvent is FSO₂N(CH₃)SO₂F; 5) R₁ is -N(CH3)(CH2CH=CH2), R2 is-N(CH3)2, and the solvent is (CH3)(CH2=CHCH2)NSO2N(CH3)2; 6) R1 is -CH=CHCH3, R2 is-N(CH3)(CH2CH3), and the solvent is CH3CH=CHSO2N(CH3)(CH2CH3); 7) R₁ is -C₆H₄F, R₂ is -CH₂CF₃, and the solvent is C₆H₄FSO₂CH₂CF₃; 8) R₁ is -CH₂F, R₂ is -CH=CHCH2F, and the solvent is FCH2SO2CH=CHCH2F; 9) R1 is -CF2CHCH=CHCH2F, R2 is -N(SO2F)2, and the solvent is CH2FCH=CHCF2SO2N(SO2F)2; 10) R1 is -C6H5, R2 is F, and the solvent is C₆H₅SO₂F; 11) R₁ is F, R₂ is N(CH₃)(CH₂CH₃), and the solvent is FSO₂N(CH₃)(CH₂CH₃); 12) R1 is F, R2 is N(CH2CH3)2, and the solvent is FSO2N(CH2CH3)2; and 13) R1 is CF3, R2 is F, and the solvent is CF3SO2F. 10 Attorney Docket No.17468-138WOU1 _{[0054] Compounds of the foregoing examples of Structure 1 include:} Example 1-1: Example 1-2: _[0055] m_{ay Structure 3 (-} R3-SO2N-(R5)R4-): [Structure 2] [Structure 3] wherein: R₃ is annularly connected with R₄ by a covalent bond as shown above in Structure 2 and Structure 3, respectively; each of R₃ and R₄ can be any one of: -CF₂-; -CH2-: -CH((CH2)xH1-yFy)- (x = 0 to 3, y = 0 to 1); -CF((CH₂)_xH_1-yF_y)- (x = 0 to 3, y = 0 to 1); or -CH((CH2-xFx)yCH=CH1-zFz(CH2-x'Fx')vH1-wFw)- (x =0 to 2, x' = 0 to 2, y = 0 to 2, z = 0 to 1, v = 0 to 2, w = 0 to 1); in which R₃ ≠ R₄ or R₃ = R₄; and 11 Attorney Docket No.17468-138WOU1 R₅ can be any one of: -(CH2)xCH3 (x =0 to 3); or -(CH2)xCH=CH2 (x =1 to 3). _{[0056] The following are example sulfonyl solvents having general Structure 2 or general} Structure 3: 1) R3 is -CH2-, R4 is -CH2-, R5 is -CH3, and the solvent is CH2SO2N(CH3)(SO2CH2-); 2) R3 is -CF2-, R4 is -CF2-, R5 is -CH2CH=CH2, and the solvent is - CF₂SO₂N (CH₂CH=CH₂)(CF₂)-; 3) R is -CH(CH=CH₂F)-, R₄ is -CH(CH=CH₂)-, R₅ is -CH₃, and the solvent is -(FCH2=CH)CHSO2N(CH3)CH(CH=CH2)-; 4) R3 is -CH2-, R4 is -CH2CH2-, R5 is -CH3, and the solvent is -CH2SO2N(CH3)CH2CH2-; 5) R3 is -CH2CH2-, R4/R7 is -CH2CH2-, R5 is -CH2CH3, and the solvent is -CH₂CH₂SO₂N(CH₂CH₃)CH₂CH₂-; and 6) R₃ is -CF₂-, R₄ is CF₂, R₅ is CH₃, and the solvent is -CF₂SO₂N(CH₃)SO₂CF₂-. _{[0057] Example compounds of Structure 2 include:} Example 2-1: Example 2-2: _[0058] Example 3-1: Example 3-2: 12 Attorney Docket No.17468-138WOU1 _{[0059] Additional solvents may include Structure 4 (R6-SO2N-(R7)(R8)):} wherein: R6 can be -(CH2)x(CH2-yFy)zF (x = 0 to 2, y = 0 to 2, z = 0 to 2); R7 can be -(CH2)xO(CH2)yCH3 (x=2 to 4, y=0 to 2); and R₈ can be: -(CH2)xCH3 (x=0 to 3); or -(CH2)xO(CH2)yCH3 (x=2 to 4, y=0 to 2). _{[0060] The following are example sulfonyl solvents having general Structure 4: 1) R6 is -F, R7} is -(CH₂)₂OCH₃, R₈ is -(CH₂)₂OCH₃, and the solvent is FSO₂N[(CH₂)₂OCH₃]₂; 2) R₆ is -F, R₇ is - (CH2)2OCH3, R8 is -CH3, and the solvent is FSO2N[(CH2)2OCH3][CH3]; 3) R6 is -CF3, R7 is - (CH2)2OCH3, R8 is -(CH2)2OCH3, and the solvent is CF3SO2N[(CH2)2OCH3]2; and 4) R6 is -CF3, R7 is -(CH₂)₂OCH₃, R₈ is -CH₃, and solvent is CF₃SO₂N[(CH₂)₂OCH₃][CH₃]. _{[0061] Example compounds of Structure 4 include:} Example 4-1: Example 4-2: _{[0062] Additional solvents may include Structure 5 ((R9)R10-SO2):} wherein: R₉ can be -(CH₂)_x(CH_2-yF_y)_zF (x = 0 to 2, y = 0 to 2, z = 0 to 2); and 13 Attorney Docket No.17468-138WOU1 within R₁₀ is a N-containing cyclic moiety, an O-containing cyclic moiety, an only-hydrocarbon-containing moiety, or an N + O-mixture-containing cyclic moiety and R10 can be: -N(CH₂)₄ (1-pyrrolidino five-membered ring); -N(CH2)5 (1-piperidinyl six-membered ring); -N(CH2CH2)2O (4-morpholinyl six-membered ring); -C₅H₉ (cyclopentane); -C6H11 (cyclohexane); -C4H7O (2 or 3-tetrahydrofuran); or a fluorinated analog thereof. _{[0063] The following are example sulfonyl solvents having general Structure 5: 1) R9 is -F, R10} is -N(CH2)4, and the solvent is FSO2N(CH2)4 (five-membered ring); 2) R9 is -CF3, R10 is -N(CH2)4 (five-membered ring), and the solvent is CF3SO2N(CH2)4 (five- membered ring); 3) R₉ is -F, R₁₀ is -N(CH₂CH₂)₂O (six-membered ring), and the solvent is FSO2N(CH2CH2)2O (six-membered ring). _{[0064] Example compounds of Structure 5:} Example 5-1: Example 5-2: _{[0065] A sulfonyl-containing co-salt system of the present disclosure may contain one of these} sulfonyl solvents or a mixture of two or more of the sulfonyl solvents disclosed herein, including both linear sulfonyl solvents and cyclic sulfonyl solvents, with each solvent ranging, for example, from about 0.05% to about 99.95% by volume ratio, by weight ratio, or by mole ratio, of the total amount of the sulfonyl solvent(s) or in a range of about 5% to about 50% by volume ratio, by weight ratio, or by mole ratio of the total amount of the sulfonyl solvent(s). EXAMPLE SALTS FOR CO-SALT ELECTROLYTE SYSTEMS _{[0066] As noted above, a sulfonyl-containing co-salt system and a sulfonyl-containing co-salt} electrolyte of the present disclosure contain one or more non-primary (or secondary) salts mixed with the primary salt in a solvent to form the co-salt system or co-salt electrolyte. As noted, 14 Attorney Docket No.17468-138WOU1 examples of cations that can be used in these sulfonyl-containing co-salt systems and sulfonyl- containing co-salt electrolytes include, but are not limited to, alkali metal cations, alkali earth metal cations, transition metal cations, and post-transition metal cations. Examples of anions that can be used in the sulfonyl-containing co-salt systems and sulfonyl-containing co-salt electrolytes include, but are not limited to, borate-containing anions and derivatives, sulfonamide-containing anions and derivatives, sulfonimide-containing anions and derivatives, phosphate-containing anions and derivatives, amide-containing anions and derivatives, and antimonate-containing anions and derivatives. The amount of the co-salt in the sulfonyl-containing co-salt systems may range, for example, from about 0.05% to about 99.95% by volume ratio, by weight ratio, or by mole ratio of the total amount of the salt(s). General chemical structures of particular example co-salts that may be used as co-salts are presented below. Example Borate-Containing Anions _{[0067] Borate-containing co-salts may, for example, have the following Structure 6 (B-} R₁(R₂)(R₃)(R₄)): wherein, within Structure 6, each of R1, R2, R3 can be -H, -F, -OCxHyCHzFa (x = 1-8; y = 2x, z =0-3, a = 3-z), -OCOCOO (cyclic oxalate structure), or any combination of structures listed. Example Sulfonamide-Containing Anions _{[0068] Sulfonamide-containing co-salts may, for example, have the following Structure 7 (R5-} SO₂N-R₆): wherein, within Structure 7, each of R5 and R6 can independently be -H, -F, -CHxFy (x = 0-3, y = 3- x), -CxHyFzCHaFb (x = 1-8, y = 2x, z = 2x – y, a = 0-3, b = 3-a), -CxHy[OCzHa]n (x = 1-8, y = 2x, z = 1-4, a = 2z, n = 1-8) or any combination of structures listed. 15 Attorney Docket No.17468-138WOU1 Example Sulfonimide-Containing Anions _{[0069] Sulfonimide-containing co-salts may, for example, have the following Structure 8 (R7-} SO2N-SO2-R8): wherein, within Structure 8, each of R7 and R8 be -H, -F, -CHxFy (x = 0-3, y = 3- x), -C_xH_yF_zCH_aF_b (x = 1-8, y = 2x, z = 2x – y, a = 0-3, b = 3-a), -C_xH_y[OC_zH_a]_n (x = 1-8, y = 2x, z = 1-4, a = 2z, n = 1-8) or any combination of structures listed. Example Phosphate-Containing Anions _{[0070] Example phosphate-containing co-salts may, for example, have the following Structure 9} (R₉-PO₂-R₁₀) or Structure 10 (P-R₁₁(R₁₂)(R₁₃)(R₁₄)(R₁₅)(R₁₆)): [Structure 9] [Structure 10] wherein, within each of Structures 9 and 10, each of R₉, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, R₁₅, and R₁₆ can independently be any one of the following,-F, -CH_xF_y (x = 0-3, y = 3-x), -OCOCOO (cyclic oxalate structure), -OCxHyFzCHaFb (x = 1-8, y = 0-16, F = 16-x, a = 0-3, b = 3-a), -SiC3H9, or any combination of structures listed. Example Amide Anions _{[0071] Amide co-salt may have the following Structure 11 (R17-N-R18):} wherein, within structure 11 each of R₁₇ and R₁₈ can independently be any one of the following: -H, -SiC₃H₉, -C_xH_yF_zCH_aF_b (x = 1-8, y = 0-16, z = 16-y, a = 0-3, b = 3-a) or any combination listed here. 16 Attorney Docket No.17468-138WOU1 Example Antimonate Co-Salts _{[0072] An antimonate co-salt may, for example, have the following Structure 12 (Sb-} R19(R20)(R21)(R22)(R23)(R24)): wherein, within Structure 12, R19, R20, R21, be any one of the following: -F, - CH_xF_y (x = 0-3, y = 3-x), -C_xH_yF_zCH_aF_b (x = 1-8, y = 0-16, z = 16-y, a = 0-3, b = 3-a) or any combination listed here. EXAMPLE SULFONYL-CONTAINING CO-SALT ELECTROLYTES _{[0073] In some embodiments, one or more of the following salts can be combined with any of} the above described sulfonyl-containing solvents to form a co-salt electrolyte: lithium sulfonyl imide [e.g., linear structure: lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethane- sulfonyl)imide (LiTFSI), lithium (fluorosulfonyl)(trifluoromethylsulfonyl)-amide (LiFTA), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), and cyclic structure: lithium-cyclo-difluoromethane- 1,1-bis-(sulfonyl)imide (LiDMSI), lithium 4,4,5,5-tetrafluoro-1,3,2-dithiazolidine-1,1,3,3-tetraoxide (LiCTFSI), lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide (LiHFDF)], lithium perchlorate (LiClO₄), lithium tetrafluoroborate (LiBF₄), lithium hexafluorophosphate (LiPF₆), lithium hexafluoroantimonate (LiSbF₆), lithium trifluoromethanesulfonate (LiTF), lithium 2-trifluoromethyl- 4,5-dicyanoimidazolide (LiTDI), lithium tetracyanoborate (LiB(CN)4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalate)borate (LiDFOB), lithium difluoro(bisoxalato) phosphate (LiDFOP), Li polysulfide, lithium difluorophosphate (LiDFP), other Li-organic salts (e.g., organolithium lithium, alkoxide lithium, amide lithium, imide, thiolate lithium, phosphonate lithium), and Li-polymer salts (e.g., LiFSI-polymer and LiTFSI-polymer). In addition, any of the above-mentioned salts may have their lithium cation replaced with a different metal cation, such as Na, K, Rb, Cs, Mg, Zn, Al, Ag, and In. _{[0074] In some embodiments, two or more of the above-listed salts may be part of a sulfonyl-} containing co-salt electrolyte in a concentration ranging from about 0.1 M up to about 5.5 M. In some embodiments, a concentration of the salts are in a range of about 0.5 M to about 4.5 M. It is also noted that sulfonyl-containing solvent co-salt systems of the present disclosure may be suitable 17 Attorney Docket No.17468-138WOU1 for Li-ion cells and batteries. In some examples for Li-ion cells and batteries, the salt-solvent mole ratio may be in a range of about 1:7 to about 1:1. EXAMPLE ELECTROCHEMICAL DEVICES _{[0075] Embodiments of this disclosure include sulfonyl-containing co-salt electrolytes each} made using any one or more of the sulfonyl-containing solvent systems described above, including any example mixture and two or more salts, including the lithium-based salts enumerated above and/or mixtures thereof, and any salt or mixture thereof based on an alkali metal other than lithium, such as sodium or potassium. _{[0076] Embodiments of this disclosure further include electrochemical devices, such as batteries} and super capacitors, that each contain co-salt electrolytes with sulfonyl-containing solvents made in accordance with aspects of this disclosure. Example batteries include LMBs, lithium-ion batteries, and batteries based on an alkali metal other than lithium (i.e., AMBs), such as sodium-metal batteries or potassium-metal batteries, among others. Those skilled in the art understand many differing constructions of electrochemical devices that can utilize co-salt electrolytes with sulfonyl- containing solvents made in accordance with the present disclosure, and all suitable ones of such conventional electrochemical-device constructions are incorporated herein as a basis for electrochemical devices made in accordance with the present disclosure, including such conventionally constructed electrochemical devices containing co-salt electrolytes with sulfonyl- containing solvent made in accordance with the present disclosure. _{[0077] As an example, FIG. 5A illustrates an example energy-storage cell 100 made in} accordance with aspects of the present disclosure. Those skilled in the art will readily appreciate that the energy-storage cell 100 can be, for example, a battery cell (e.g., lithium-metal battery cell or cell based on another alkali metal chemistry, among others) or a supercapacitor cell. In addition, those skilled in the art will readily understand that FIG.5A illustrates only some basic functional components of the cell 100 and that a real-world instantiation of the cell, such as a secondary battery or a supercapacitor, will typically be embodied in either a stacked construction containing multiple instantiations of the layered components or a wound construction. Further, those skilled in the art will understand that the energy-storage cell 100 will include other components, such as one or more seals, thermal shutdown layers, and/or vents, among other things, that, for ease of illustration, are not shown in FIG.5A. 18 Attorney Docket No.17468-138WOU1 _{[0078] In this example, the cell 100 includes an anode 104 and a cathode 108 that are spaced} apart from one another and include corresponding active materials 104a and 108a and a pair of respective current collectors 104c and 108c. The current collectors 104c and 108c are electrically connected to corresponding electrical terminals 112b and 112a, such as tabs in a pouch-type construction. At least one porous dielectric separator 116 is located between the anode 104 and cathode 108 to electrically separate the anode and cathode but to allow ions of a co-salt electrolyte 120 with sulfonyl-containing solvent to flow therethrough. As will be appreciated, the electrolyte 120 may be any co-salt electrolyte with sulfonyl-containing solvent described herein or able to be made by a skilled artisan without undue experimentation using only the present disclosure, including the appended claims, as a guide. _{[0079] As those skilled in the art will understand, depending upon the type and design of the} cell 100, each of the anode 104 and cathode 108 comprises one or more suitable materials that gain or lose ions via the co-salt electrolyte with sulfonyl-containing solvent 120 depending on whether the cell is being charged or discharged. Each of the active materials 104a and 108a may be any suitable material for the anode 104 and the cathode 108, respectively. Examples of anode active materials 104a may include alkali-metal-based materials, such as pure lithium, pure sodium, pure potassium, and alloys thereof, among others. Examples of cathode-active materials 108a include crystalline oxides comprising various amounts of cobalt, nickel, and manganese, among many others. Each of the current collectors 104c and 108c may be made of any suitable electrically conducting material, such as copper or aluminum, or any combination thereof. The porous separator 116 may be made of any suitable dielectric material, such as a polymer (e.g., PP, PE, a PP/PE hybrid, etc.), among others, and may be coated or uncoated as needed to meet a certain design. Various battery and supercapacitor constructions that can be used for constructing the cell 100 of FIG.5A, are known in the art. If any of such known constructions is used, a novelty of the cell 100 lies in the co-salt electrolyte with sulfonyl-containing solvent 120 made in accordance with the present disclosure. _{[0080] FIG. 5B illustrates an example multicell battery 150 made in accordance with the present} disclosure. In this example, the battery 150 includes a plurality of electrochemical energy-storage cells 154 (e.g., 154a, 154b through 154n) electrically connected with one another via suitable electrical connections 158. The number of the cells 154a through 154n provided may be any number, for example, 2 to 100 or more, needed to suit a particular application. The electrical connections 158 may be any connections needed to connect the cells 154a through 154n with one 19 Attorney Docket No.17468-138WOU1 another such that the battery 150 meets the design requirements for the application at issue. For example, the electrical connections 158 may be either serial connections or parallel connections, or a combination of serial and parallel connections. In addition, the cells 154a through 154n may be grouped in one or more groups, and each such group may be part of a corresponding battery module. In such a case, the electrical connections 158 may include electrical connections among the modules. Those skilled in the art will readily understand the types and manners of effecting the physical connections needed for the electrical connections 158, which may include, but are not limited to, tab- to-tab connections, busbar connections, wiring connections, and wiring-harness connections, among others. Fundamentally, there are no limitations on the type(s) of electrical connections that can be part of the electrical connections 158. In this example, the electrical connections 158 are electrically connected to a pair of battery output terminals 162a and 162b that will be connected to an electrical load and/or electrical source (neither shown) during deployment of the battery. Not illustrated are the many other components of a battery that could be included aboard the example battery 150, such as, but not limited to, a battery management system, a sensor system, an emergency disconnect unit, and module controllers, among others. EXPERIMENTAL RESULTS _{[0081] This section contains example formulations of sulfonyl-containing co-salt electrolytes} made in accordance with the present disclosure, along with results from cycle-life testing of cells containing these electrolytes in comparison with cells containing single-salt electrolytes. These example formulations are merely illustrative, and those skilled in the art will readily be able to make other formulations without undue experimentation when using this disclosure as a guide. _{[0082] A combination of N,N-dimethyl sulfonyl fluoride (DMSF), lithium} bisfluorosulfonylimide (LiFSI), and lithium bistrifluoromethylsulfonylimide (LiTFSI) has been developed to form an exemplary sulfonyl-containing co-salt system according to the present disclosure. Importantly, it has been demonstrated that pouch-type electrochemical cells containing a LiFSI + LiTFSI in DMSF co-salt electrolyte can suppress short circuiting over more than 175 fast- charging cycles. This compares to testing of like cells containing a sulfonyl solvent with a single salt electrolyte that experienced a short circuit after only 110 cycles. The testing results that revealed this ~50% improvement are presented in FIG.1, which is a graph of capacity retention versus cycle number for pouch cells under fast charging conditions (1.3C-0.5C for charging and 0.4C for discharging). The first cells (for which results are shown with dark lines on the graph labeled 10) are for Li + nickel-metal-cobalt (NMC) pouch cells containing an electrolyte containing 20 Attorney Docket No.17468-138WOU1 a single salt, LiFSI in a single solvent, N,N – dimethyl sulfonyl fluoride (DMSF). The second cells (for which results are shown as lighter lines on the graph labeled 20) are for Li + NMC pouch cells containing an electrolyte with two salts, LiFSI + bistrifluoromethylsulfonylimide lithium salt (LiTFSI), which are also dissolved in DMSF as the single solvent. As can be seen in the graph, the pouch cells having the two-salt electrolyte show greater cycling stability and greater resistance to cell shorting than the pouch cells with the single-salt electrolyte. The cells that contain LiFSI + LiTFSI co-salt electrolyte show improved cycling life compared to a single salt electrolyte. The salts in co-salt electrolyte were 3.3M LiFSI (primary) and 0.06M LiTFSI (secondary) in DMSF solvent. The salt in the single salt electrolyte had a concentration of 2.9M LiFSI in DMSF solvent. _{[0083] A combination of LiFSI and LiTFSI co-salts in DTMS solvent has been developed to} form a co-salt system according to the present disclosure. Importantly, it has been demonstrated that pouch-type electrochemical cells containing a LiFSI + LiFSI co-salt electrolyte can extend the cycle life to over more than 175 C/3 charge C/3 discharge cycles. This compares to testing of like cells containing LiFSI as the only salt that experienced a drop to 80% capacity after only 140 cycles. The test results that revealed this ~28% improvement appear in FIG.2, which is a graph of capacity retention (percent) versus cycle number for Li + NMC pouch cells containing an electrolyte having a single salt (LiFSI) in N,N-dimethyl trifluoromethane sulfonamide (DTMS) (results shown with lighter lines on the graph labeled 11) and pouch cells containing an electrolyte with two salts, LiFSI + LiTFSI in DTMS (results shown with dark lines on the graph labeled 21). FIG.2 shows that cells with the LiFSI + LiTFSI co-salt electrolyte showed improved cycling life over cells that contain the single-salt electrolyte. The salts in the co-salt electrolyte had respective concentrations of 2.1M LiFSI and 1M LiTFSI in DTMS solvent. The single salt electrolyte had a concentration of 2.1M LiFSI in DTMS solvent. _{[0084] The cathode coulombic efficiency (CE) of an electrochemical cell is directly related to} its cycle life. FIG.3 is a bar chart showing average percent cathode CE for 3/4 layer copper (Cu)- NMC anode-free cells containing a single-salt electrolyte, LiFSI in DMSF (bars labeled 13), and a co-salt electrolyte, LiFSI + KFSI in DMSF (bars labeled 23), both under C/3 charging and C/3 discharging, illustrating the improved cathode coulombic efficiency (CE) for the cells having the LiFSI + KFSI co-salt electrolyte. The concentration of the salts used in the co-salt based electrolyte were 4.0M LiFSI and 0.5M KFSI in DMSF. The concentration of the salts used in the single salt electrolyte was 2.9M LiFSI in DMSF. 21 Attorney Docket No.17468-138WOU1 _{[0085] The same type of Li-NMC cells used in the test that produced the data summarized in} FIGS.1 and 2 were used to test a LiFSI + LiTFSI co-salt electrolyte versus a LiFSI-single salt electrolyte. FIG.4A is a graph of discharge capacity versus cycle number for Li + NMC pouch cells containing a single-salt electrolyte with LiFSI in DMSF (results shown as dark line labeled 14) and pouch cells containing a co-salt electrolyte, LiFSI + LiTFSI in DMSF, (results shown as lighter line labeled 24), the cycling stability of the cells containing the LiFSI + LiTFSI co-salt electrolyte was better than the cycling stability of the cells containing the LiFSI-single salt electrolyte. FIG.4B is a graph of cell coulombic efficiency versus cycle number for the Li + NMC cells described with respect to FIG.4A, in which the results for the pouch cells containing the single-salt (LiFSI) electrolyte are shown as the line labeled 15 and the results for the cells containing the co-salt electrolyte (LiFSI + LiTFSI) are shown as the line labeled 25. FIG.4B shows that the cells containing the LiFSI + LiTFSI co-salt electrolyte had slower decreases in coulombic efficiency compared with the cells containing the LiFSI-single salt electrolyte, which is consistent with the cycling stability shown in FIG.4A. The solvent used for the co-salt electrolyte in this testing was DMSF, and the salts had concentrations of 3.3M LiFSI and 0.06M LiTFSI. The same solvent was used in the single salt electrolyte and the salt had a concentration of 2.9M LIFSI. _{[0086] FIG. 6 is a graph of discharge capacity versus cycle number for Li + NMC pouch cells} containing an electrolyte having a LiFSI + lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide (LiHFDF) dual-salt system in a N-ethyl-N-methyl sulfonyl fluoride (EMSF) + DMSF solvent (results shown as lighter lines labeled 26) under 1C charging and C/3 discharging at 25ºC and for cells containing a LiFSI single-salt electrolyte containing the same solvent system (results shown as dark lines labeled 16). As can be seen in FIG.6, all of the cells containing the co-salt electrolyte, i.e., the LiFSI (3.0M) + LiHFDF (0.8M) in a DMSF co-salt electrolyte, exhibited better cycling stability and did not experience a short circuit under fast charging conditions. In contrast, the cells containing the single-salt electrolyte, i.e., the LiFSI (2.9M)-DMSF electrolyte, showed poorer cycling stability and experienced a short circuit issue after only 120 cycles. _{[0087] FIG. 7A is a graph of discharge capacity percentage versus cycle number for Li + NMC} pouch cells containing: 1) a 3.1M LiFSI single-salt electrolyte in a DMSF + N-ethyl-N-methyl sulfonyl fluoride (EMSF) co-solvent (volume ratio DMSF:EMSF = 3:1) under fast charging tests (1.3C-0.5C for charge and 0.4C for discharge) (solid lines labeled 30a-30c), 2) a dual-salt electrolyte containing 3.3M LiFSI + 0.06M LiTFSI in DMSF (dashed lines labeled 31a-31c), and 3) a dual-salt electrolyte containing 3.4M LiFSI + 0.75M KFSI in DMSF (dot-dashed lines labeled 32a-32c). As 22 Attorney Docket No.17468-138WOU1 can be seen in FIG.7A, further improvement of the dual-salt electrolyte under fast charging conditions can be achieved by tuning the dual-salt identity and concentrations. In this example, by changing the secondary salt from LiTFSI to KFSI in DMSF, the short circuit under fast charge conditions is eliminated and the cycle life is significantly improved to nearly 250 cycles. _{[0088] FIG. 7B is a graph of percent reverse coulombic efficiency (RCE) versus cycle number} for pouch cells with different electrolytes. The results for Li + NMC pouch cells containing a 3.1M LiFSI single-salt electrolyte in a DMSF + N-ethyl-N-methyl sulfonyl fluoride (EMSF) co-solvent (volume ratio DMSF:EMSF = 3:1) under fast charging tests (1.3C-0.5C for charge and 0.4C for discharge) (results shown as solid line labeled 33) are compared to pouch cells with dual-salt electrolytes. A first pouch cell contains a dual-salt electrolyte having 3.3M LiFSI + 0.06M LiTFSI in DMSF (shown as dashed line labeled 34) and a second pouch cell contains a dual-salt electrolyte having 3.4M LiFSI + 0.75M KFSI in DMSF (shown as dot-dashed line labeled 35). Both of the pouch cells with dual-salt electrolytes show generally reduced RCE growth and delayed or no short- circuit compared to the pouch cell with single salt electrolyte. _{[0089] It is noted that throughout the present disclosure, the term “about”, when used with a} corresponding numeric value, refers to ±20% of the numeric value, typically ±10% of the numeric value, often ±5% of the numeric value, and more often ±2% of the numeric value. In some embodiments, the term “about” can mean the numeric value itself. _{[0090] Various modifications and additions can be made without departing from the spirit and} scope of this invention. Features of each of the various embodiments described above may be combined with features of other described embodiments as appropriate in order to provide a multiplicity of feature combinations in associated new embodiments. Furthermore, while the foregoing describes a number of separate embodiments, what has been described herein is merely illustrative of the application of the principles of the present invention. Additionally, although particular methods herein may be illustrated and/or described as being performed in a specific order, the ordering is highly variable within ordinary skill to achieve aspects of the present disclosure. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention. _{[0091] Exemplary embodiments have been disclosed above and illustrated in the accompanying} drawings. It will be understood by those skilled in the art that various changes, omissions and 23 Attorney Docket No.17468-138WOU1 additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention. 24 Attorney Docket No.17468-138WOU1

Claims

What is claimed is: _{1. An electrolyte for an electrochemical device having an alkali-metal anode having an anode-} active material comprising an alkali metal, the electrolyte comprising: at least one sulfonyl solvent; a primary salt, wherein the primary salt is a lithium (Li) cation salt and is at a first concentration; and a secondary salt, wherein the secondary salt has a second concentration lower than the first concentration. _{2. The electrolyte of claim 1, wherein the first concentration of the primary salt is greater than 1} molarity. _{3. The electrolyte of claim 2, wherein the second concentration of the secondary salt is between} 0.1 weight percentage and 30 weight percentage. _{4. The electrolyte of claim 3, wherein the primary salt is lithium bis(fluorosulfonyl)imide (LiFSI)} and the secondary salt is lithium bis(trifluoromethane)sulfonimide (LiTFSI). _{5. The electrolyte of claim 3, wherein the primary salt is LiFSI and the secondary salt is} potassium bis(fluorosulfonyl)imide (KFSI). _{6. The electrolyte of claim 3, wherein the primary salt is LiFSI and the secondary salt is lithium} 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide (LiHFDF). _{7. The electrolyte of claim 3, wherein the primary salt is LiFSI and an anion of the secondary salt} is bis(trifluoromethanesulfonyl)imide (TFSI-). _{8. The electrolyte of claim 3, wherein the primary salt is LiFSI and an anion of the secondary salt} is bis(fluorosulfonyl)imide (FSI-). _{9. The electrolyte of claim 3, wherein the primary salt is LiFSI and an anion of the secondary salt} is hexafluoropropane-1,3-disulfonimide (HFDF-). _{10. The electrolyte of any of claims 7-9, wherein a cation of the secondary salt is selected from the} group consisting of Li, Na, K, Rb, Cs, Ag, Mg, and In. _{11. The electrolyte of claim 3, wherein an anion of the secondary salt is selected from the group} consisting of tetrafluoroborate (BF4), hexafluorophosphate (PF6), difluorophosphate (DFP), cyclo-difluoromethane-1,1-bis-(sulfonyl)imide (DMSI), 4,4,5,5-tetrafluoro-1,3,2- dithiazolidine-1,1,3,3-tetraoxide (CTFSI), hexamethyldisilazide (HMDS), and difluro(oxalate)borate (DFOB). _{12. The electrolyte of any of claims 1-11, wherein the at least one sulfonyl solvent is a sulfonamide} solvent. 25 Attorney Docket No.17468-138WOU1

_{13. The electrolyte of any of claims 1-11, wherein the at least one sulfonyl includes at least one} sulfonyl (-SO2-) group, each with a double bond between each oxygen atom. _{14. The electrolyte of any of claims 1-13, wherein the electrolyte has a total salt concentration of} from about 1.0 M to about 5.5 M. _{15. The electrolyte of any of claims 1-13, wherein the electrolyte has a total salt concentration of} from about 1.0 M to about 4.5 M. _{16. The electrolyte of any of claims 1-13, wherein the electrolyte has a salt-solvent mole ratio in a} range from about 1:7 to about 1:1. _{17. An electrochemical cell, comprising:} an alkali-metal anode having an anode-active material comprising an alkali metal; a cathode; a separator located between the alkali-metal anode and the cathode; and an electrolyte of any one of claims 1 through 16 in operative communication with each of the alkali-metal anode and the cathode. _{18. A multicell battery, comprising:} a plurality of electrochemical cells of claim 17; a pair of output terminals, and electrical connections electrically connecting the plurality of electrochemical cells to the pair of output terminals. _{19. A method of preparing an electrolyte for a lithium metal battery cell comprising:} selecting a sulfonyl solvent; selecting a primary salt, the primary salt having a lithium cation; dissolving the primary salt in the solvent to form a primary salt solution having a primary salt concentration; selecting a secondary salt; and dissolving the secondary salt in the primary salt solution to form a co-salt solution having a secondary salt concentration, wherein the secondary salt concentration is selected such that the secondary salt concentration increases the primary salt concentration up to a peak secondary salt concentration beyond which an overall performance of the electrolyte for the lithium metal battery cell is reduced. _{20. The method of claim 19, wherein the overall performance of the electrolyte for the lithium} metal battery cell is determined based on life cycles without a short circuit and cycle life. 26 Attorney Docket No.17468-138WOU1

_{21. An electrolyte for an electrochemical device having an alkali-metal anode having an anode-} active material comprising an alkali metal, the electrolyte comprising: at least one sulfonyl solvent; a primary salt, wherein the primary salt includes a Li cation and has a primary salt concentration; and a secondary salt, wherein the secondary salt has a second salt concentration that is lower than the primary salt concentration. _{22. The electrolyte of claim 21, wherein the sulfonyl solvent is one or more solvents selected from} the group of: CH2=CHSO2F, CH2=CHSO2CF3, (CH3)2NSO2F, FSO2N(CH3)SO2F, (CH₃)(CH₂=CHCH₂)NSO₂N(CH₃)₂, CH₃CH=CHSO₂N(CH₃)(CH₂CH₃), C₆H₄FSO₂CH₂CF₃, FCH₂SO₂CH=CHCH₂F, CH₂FCH=CHCF₂SO₂N(SO₂F)₂, FSO₂N(CH₃)(CH₂CH₃), FSO2N(CH2CH3)2, and CF3SO2F. _{23. The electrolyte of claim 21, wherein the sulfonyl solvent is one or more solvents selected from} the group of: CH₂SO₂N(CH₃)(SO₂CH₂-), CF₂SO₂N (CH₂CH=CH₂)(CF₂), (FCH2=CH)CHSO2N(CH3)CH(CH=CH2), CH2SO2N(CH3)CH2CH2, CH2CH2SO2N(CH2CH3)CH2CH2, and CF2SO2N(CH3)SO2CF2. _{24. The electrolyte of claim 21, wherein the sulfonyl solvent is one or more solvents selected from} the group of: FSO2N[(CH2)2OCH3]2; 2), FSO2N[(CH2)2OCH3][CH3], CF3SO2N[(CH2)2OCH3]2, and CF3SO2N[(CH2)2OCH3][CH3]. _{25. The electrolyte of claim 21, wherein the sulfonyl solvent is one or more solvents selected from} the group of: FSO₂N(CH₂)₄, CF₃SO₂N(CH₂)₄, and FSO₂N(CH₂CH₂)₂O. _{26. The electrolyte of claim 21, wherein an anion of the secondary salt is selected from the group} of borate-containing anions, sulfonamide-containing anions, sulfonimide-containing anions, phosphate-containing anions, amide-containing anions, and antimonate-containing anions. _{27. The electrolyte of claim 21, wherein the primary salt is selected from the group of LiFSI,} LiTFSI, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)-amide, lithium bis(pentafluoroethanesulfonyl)imide, lithium-cyclo-difluoromethane-1,1-bis-(sulfonyl)imide, lithium 4,4,5,5-tetrafluoro-1,3,2-dithiazolidine-1,1,3,3-tetraoxide, lithium 1,1,2,2,3,3- hexafluoropropane-1,3-disulfonimide , lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroantimonate, lithium trifluoromethanesulfonate, lithium 2-trifluoromethyl-4,5-dicyanoimidazolide, lithium tetracyanoborate, lithium bis(oxalato)borate, lithium difluoro(oxalate)borate, lithium difluoro(bisoxalato) phosphate, lithium polysulfide, lithium difluorophosphate, LiFSI-polymer, and LiTFSI-polymer. 27 Attorney Docket No.17468-138WOU1

_{8. The electrolyte of claim 21, wherein the secondary salt is selected from the group of LiFSI,} LiTFSI, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)-amide, lithium bis(pentafluoroethanesulfonyl)imide, lithium-cyclo-difluoromethane-1,1-bis-(sulfonyl)imide, lithium 4,4,5,5-tetrafluoro-1,3,2-dithiazolidine-1,1,3,3-tetraoxide, lithium 1,1,2,2,3,3- hexafluoropropane-1,3-disulfonimide , lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroantimonate, lithium trifluoromethanesulfonate, lithium 2-trifluoromethyl-4,5-dicyanoimidazolide, lithium tetracyanoborate, lithium bis(oxalato)borate, lithium difluoro(oxalate)borate, lithium difluoro(bisoxalato) phosphate, lithium polysulfide, lithium difluorophosphate, LiFSI-polymer, and LiTFSI-polymer. 28 Attorney Docket No.17468-138WOU1