Electrolyte comprising asymmetric f-ether and co-solvent and electrochemical device comprising same

Abstract

Disclosed herein is an electrolyte comprising an asymmetric F-ether (AFE) and a cosolvent and batteries comprising the same. In some embodiments, the AFE has a formula of R1OR2, wherein R1 includes at least one fluorine atom (F), and R2 is free of F. In some embodiments, the co-solvent is an ether and is not an AFE. An electrochemical device comprising the electrolyte exhibits an improved cycling performance and fast charging performance.

Description

ELECTROLYTE COMPRISING ASYMMETRIC F-ETHER AND CO-SOLVENT ANDELECTROCHEMICAL DEVICE COMPRISING SAMECROSS-REFERENCE|0001] The present application claims the benefit of US Serial No. 63 / 643,737, filed May 7, 2024, the entire content of which is incorporated herein by reference into this application.TECHNICAL FIELD

[0002] The present disclosure relates to an electrolyte comprising an asymmetric F-ether and a cosolvent.BACKGROUND

[0003] Asymmetric F-ether is an ether with two segments connected by an oxygen (O) atom, wherein one segment is fluorinated and the other segment is non-fluorinated. An asymmetric F-ether is a compound with a formula of R'OR2, wherein R1is fluorinated, R2is non-fluorinated. It was studied as a promising solvent for electrolyte because of its decent conductivity, unique solvation structure, and great oxidative stability. However, an electrochemical device with an electrolyte comprising the asymmetric F-ether exhibits certain disadvantages such as relatively low coulombic efficiency (CE) and poor rate capability. Thus, there remains a need for electrolytes with improved cycling performance and fast charging performance.SUMMARY

[0004] Disclosed herein is an electrolyte comprising an asymmetric F-ether (AFE) and a cosolvent and batteries comprising the same. In some embodiments, the AFE has a formula of R’OR2(I), wherein R1includes at least one carbon atom (C) and at least one fluorine atom (F), and R2includes at least one C but does not include any F. In some embodiments, the asymmetric F-ether is a compound with a formula of RlaO(CH2)mOR2a(II), wherein Rlais C1-C10 fluoroalkyl, C3-C10 fluorocycloalkyl, -[(C1-C4 [fluoro]alkylene)-0-]ni-(Ci-Cio fluoroalkyl) or -[(C1-C4 [fluoro]alkylene)-0-]ni-(C3-Cio fluorocycloalkyl), and R2ais Ci-C 10 alkyl, C3-C10 cycloalkyl, -[(Ci- C4 alkylene)-0-]n2-(Ci-Cio alkyl) or -[(C1-C4 alkylene)-0-]n2-(C3-Cio cycloalkyl); m is 1, 2, 3, or 4; and each of nl and n2 is an integer in a range from 1 to 10.

[0005] In some embodiments, the co-solvent is an ether and is not an AFE. In some embodiments, the cosolvent has a formula ofwherein R3ais selected from the group consisting of C1-C10 alkyl, C3-C10 cycloalkyl, C1-C10 fluoroalkyl, C3-C10 fluorocycloalkyl, -[(C1-C4 [fluoro]alkylene)-0-]x-(Ci-Cio alkyl), -[(C1-C4 [fluoro]alkylene)-0-]x-(C3-Cio cycloalkyl), -[(C1-C4 [fluoro]alkylene)-0-]x-(Ci-Cio fluoroalkyl), and -[(C1-C4 [fluoro]alkylene)-0-]x-(C3-Cio fluorocycloalkyl). In some embodiments, R4a, R5aand R6aare independently selected from the group consisting of H, F, C1-C10 alkyl, C3-C10 cycloalkyl, C1-C10 fluoroalkyl, C3-C10 fluorocycloalkyl, -0-(Ci-Cio alkyl), -0-(C3-Cio cycloalkyl), -0-(Ci-Cio fluoroalkyl), -0-(C3-Cio fluorocycloalkyl), -[(C1-C4 [fluoro]alkylene)-0-]y-(Ci-Cio alkyl), -[(C1-C4 [fluoro]alkylene)-0-]y-(C3-Cio cycloalkyl), -[(C1-C4 [fluoro]alkylene)-0-]y-(Ci-Cio fluoroalkyl), - [(C1-C4 [fluoro]alkylene)-0-]y-(C3-Cio fluorocycloalkyl), -O-[(Ci-C4 [fluoro]alkylene)-0-]y-(Ci-Cio alkyl), -O-[(Ci-C4 [fluoro]alkylene)-0-]y-(C3-Cio cycloalkyl), -O-[(Ci-C4 [fluoro]alkylene)-O-]y-(Ci- C10 fluoroalkyl) and -O-[(Ci-C4 [fluoro]alkylene)-0-]y-(C3-Cio fluorocycloalkyl). An electrochemical device comprising the electrolyte exhibits an improved cycling performance and fast charging performance.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Non-limiting embodiments of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure.(0007] Fig. 1 shows the cycling performance of Li / Cu cell comprising Li metal as anode, microporous membrane as separator, Cu foil as cathode, and electrolytes according to some embodiments of the present disclosure.

[0008] Fig. 2 shows the specific capacities at various charge rates (up to 7.5 mA / cm2) of a coin cell comprising Li metal as anode, NMC811 composite electrode as cathode, microporous membrane as separator, and an electrolyte according to one embodiment of the present disclosure.

[0009] Fig.3 shows the cycling performance of a pouch cell comprising example 4-1 as electrolyte in view of specific discharge capacity according to one embodiment of the present disclosure.

[0010] Fig.4 shows the cycling performance of a pouch cell comprising example 4-1 as electrolyte in view of discharge capacity retention according to one embodiment of the present disclosure.10011] Fig. 5 shows the cycling performance of a pouch cell comprising example 4-1 as electrolyte in view of coulombic efficiency (CE) according to one embodiment of the present disclosure.DETAILED DESCRIPTION

[0012] Disclosed herein is an electrolyte comprising a salt, an asymmetric fluorinated ether (F-ether) and a co-solvent, wherein the asymmetric fluorinated ether is a compound with a formula of R'OR2(I), R1includes at least one carbon atom (C) and at least one fluorine atom (F), and R2includes at least one C but is free of F. In some embodiments, the electrolyte is a nonaqueous electrolyte, i.e., substantially free of water.

[0013] In some embodiments, the asymmetric F-ether (AFE) is a compound with a formula of RlaO(CH2)mOR2a(II), wherein Rlaincludes at least one fluorine (F) and R2ais free of fluorine (F). In some embodiments, Rlais Ci-Cio fluoroalkyl, C3-C10 fluorocycloalkyl, -[(C1-C4 [fluoro]alkylene)- 0-]ni-(Ci-Cio fluoroalkyl) or -[(C1-C4 [fluoro]alkylene)-0-]ni-(C3-Cio fluorocycloalkyl), R2ais a Ci- C10 alkyl, C3-C 10 cycloalkyl, -[(C1-C4 alkylene)-0-]n2-(Ci-Cio alkyl) or -[(C1-C4 alkylene)-O-]n2-(C3- C10 cycloalkyl); m is 1, 2, 3, or 4; and each of nl and n2 is an integer in a range from 1 to 10.[00.1.4] In some embodiments, the co-solvent is an ether with a formula (III):(III), wherein R3ais selected from the group consisting of C1-C10 alkyl, C3-C10 cycloalkyl, C1-C10 fluoroalkyl, C3-C10 fluorocycloalkyl, -[(C1-C4 [fluoro]alkylene)-0-]x-(Ci-Cio alkyl), -[(C1-C4 [fluoro]alkylene)-0-]x-(C3-Cio cycloalkyl), -[(C1-C4 [fluoro]alkylene)-0-]x-(Ci-Cio fluoroalkyl), and -[(C1-C4 [fluoro]alkylene)-0-]x-(C -Cio fluorocycloalkyl). In some embodiments, R4a, Raand R6aare independently selected from the group consisting of H, F, C1-C10 alkyl, C3-C10 cycloalkyl, C1-C10 fluoroalkyl, C3-C10 fluorocycloalkyl, -0-(Ci-Cio alkyl), -0-(C3-Cio cycloalkyl), -0-(Ci-Cio fluoroalkyl), -0-(C3-Cio fluorocycloalkyl), -[(C1-C4 [fluoro]alkylene)-0-]y-(Ci-Cio alkyl), -[(C1-C4 [fluoro]alkylene)-0-]y-(C3-Cio cycloalkyl), -[(C1-C4 [fluoro]alkylene)-0-]y-(Ci-Cio fluoroalkyl), - [(C1-C4 [fluoro]alkylene)-0-]y-(C3-Cio fluorocycloalkyl), -O-[(Ci-C4 [fluoro]alkylene)-0-]y-(Ci-Cio alkyl), -O-[(Ci-C4 [fluoro]alkylene)-0-]y-(C3-Cio cycloalkyl), -O-[(Ci-C4 [fluoro]alkylene)-O-]y-(Ci- C10 fluoroalkyl) and -O-[(Ci-C4 [fluoro]alkylene)-0-]y-(C3-Cio fluorocycloalkyl).

[0015] In some embodiments, one of R4a, R5aand R6ain formula (111) is H. In some embodiments, two of R4a, R5aand R6ain formula (III) are H. In some embodiments, one of R4a, R5aand R6ain formula (III) is F. In some embodiments, two of R4a, R5aand R6ain formula (III) are F.

[0016] In some embodiments, at least one of R4a, R5aand R6ain formula (III) is C1-C10 alkyl, C1-C10 fluoroalkyl, -0-(Ci-Cio alkyl), -0-(Ci-Cio fluoroalkyl), -[(C1-C4 alkylene)-0-]y-(Ci-Cio alkyl), -[(Ci-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl), -O-[(Ci-C4 alkylene)-0-]y-(Ci-Cio alkyl), or -O-[(Ci-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl).(0017] In some embodiments, none of R3a, R4a, R3aand R6aincludes fluorine. 00.18] In some embodiments, R3aincludes at least one fluorine and at least one of R4a, R5aand R6aincludes at least one fluorine.

[0019] In some embodiments, R4ais H, F, C1-C10 alkyl, or C1-C10 fluoroalkyl, R6ais H, F, C1-C10 alkyl, or C1-C10 fluoroalkyl, R5ais -0-(Ci-Cio alkyl), -0-(Ci-Cio fluoroalkyl), -O-[(Ci-C4 alkylene)- 0-]y-(Ci-Cio alkyl), or -O-[(Ci-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl).

[0020] In some embodiments, R4ais H, R6ais H, R5ais -0-(Ci-Cio alkyl) or -0-(Ci-Cio fluoroalkyl).

[0021] In some embodiments, at least two of R4a, R5aand R6ain formula (III) are -0-(Ci-Cio alkyl), -0-(Ci-Cio fluoroalkyl), -[(C1-C4 alkylene)-0-]y-(Ci-Cio alkyl), -[(C1-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl), -O-[(Ci-C4 alkylene)-0-]y-(Ci-Cio alkyl), or -O-[(Ci-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl).1002 1 In some embodiments, at least two of R4a, R3aand R6aare independently selected from the group consisting of -0-(Ci-Cio alkyl), -0-(Ci-Cio fluoroalkyl), -O-(Ci-C4 alkylene)-0-(Ci-Cio alkyl), and -O-(Ci-C4 alkylene)-0-(Ci-Cio fluoroalkyl).

[0023] In some embodiments, R6ain formula (III) can be H, F, alkyl such as methyl (Me) and ethyl, fluoroalkyl such as -CF3, -CHF2, and -CH2F, alkoxy such as -OMe, or fluoroalkoxy such as -OCH2CF3 and -OCH2CHF2.

[0024] In some embodiments, an asymmetric fluorinated ether contains one oxygen atom such as 1- ethoxy-l,l,2,2,2-pentafluoroethane (CF3CF2-O-C2H5). In some embodiments, an AFE contains two or more oxygen atoms such as 3 -(2 -ethoxy ethoxy)- 1,1,1, 2, 2-pentafluoropropane (CF3CF2CH2-O- CH2CH2-O-CH2CH3) and (CF3CH2O)4-Z-C-(OCH2CH3)Z, wherein z is 0, 1, 2, 3 or 4. To avoid any ambiguity, (CF3CH2O)4-z-C-(OCH2CH3)z is an AFE when z is 1 , 2 or 3 while is not AFE when z is 0 or 4.

[0025] “Alkyl” refers to a radical of a straight-chain or branched saturated hydrocarbon group having from 1 to 20 carbon atoms (“Ci -C20 alkyl”). In some embodiments, an alkyl group has 1 to 10 carbon atoms (“Ci-10 alkyl”). In some embodiments, an alkyl group has 1 carbon atom (“Ci alkyl”). Examples of C1-6 alkyl groups include methyl (Ci), ethyl (C2), n-propyl (C3), isopropyl (C3), n-butyl (C4), tertbutyl (C4), sec-butyl (C4), isobutyl (C4), n-pentyl (Cs), 3-pentanyl (Cs), amyl (Cs), neopentyl (Cs), 3- methyl-2-butanyl (Cs), tertiary amyl (C5), and n-hexyl (Ce). Additional examples of alkyl groups include n-heptyl (C7), n-octyl (Cs) and the like. Unless otherwise specified, each instance of an alkylgroup is independently optionally substituted, i.e., unsubstituted (an “unsubstituted alkyl”) or substituted (a “substituted alkyl”) with one or more substituents, e.g., for instance from 1 to 5 substituents, 1 to 3 substituents, or 1 substituent. In certain embodiments, the alkyl group is unsubstituted Ci -Cio alkyl (e.g., -CH3). In certain embodiments, the alkyl group is substituted C1-10 alkyl. Common alkyl abbreviations include Me (-CH3), Et (-CH2CH3), i-Pr (-CH(CH3)2), n-Pr (- CH2CH2CH3), n-Bu (-CH2CH2CH2CH3), or i-Bu (-CH2CH(CH3)2).

[0026] “Cycloalkyl” refers to a radical of a non-aromatic cyclic hydrocarbon group having from 3 to 10 ring carbon atoms (“C3-Cio cycloalkyl”) and zero heteroatoms in the nonaromatic ring system. In some embodiments, “C3-C10 cycloalkyl” is a saturated monocyclic group having from 3 to 10 ring carbon atoms. Examples of C3-C10 cycloalkyl include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl. Unless otherwise specified, each instance of a cycloalkyl group is independently unsubstituted (an “unsubstituted cycloalkyl”) or substituted (a “substituted cycloalkyl”) with one or more substituents. In certain embodiments, the cycloalkyl group is unsubstituted C3-C10 cycloalkyl. In certain embodiments, the cycloalkyl group is substituted C3- Ciocycloalkyl.

[0027] “Fluorocycloalkyl” refers to a radical of a non-aromatic cyclic hydrocarbon group having from 3 to 10 ring carbon atoms (“C3-C10 cycloalkyl”) and at least one fluorine either in the substituent or in the nonaromatic ring.

[0028] “Fluoroalkyl” refers to a radical of a straight-chain or branched saturated hydrocarbon group having from 1 to 20 carbon atoms and having at least one fluorine atom (“C1-C20 fluoroalkyl”). In some embodiments, a fluoroalkyl group has 1 to 10 carbon atoms (“C1-C10 alkyl”). In some embodiments, a fluoroalkyl group has 1 carbon atom (“Ci fluoroalkyl”). In some embodiments, Ci fluoroalkyl includes -CH2F, -CHF2, and -CF3. In some embodiments, a fluoroalkyl group has 2 carbon atoms (“C2 fluoroalkyl”). In some embodiments, exemplary C2 fluoroalkyl includes without limitation -CH2CH2F, -CH2CHF2, -CH2CF3, -CHFCF3, -CF2CF3, -CF2CHF2, -CF2CH2F, and -CF2CH3. In some embodiments, a fluoroalkyl group has 3 carbon atoms (“C3 fluoroalkyl”). In some embodiments, C3 fluoroalkyl includes without limitation -CH2CH2CH2F, -CH2CH2CHF2, -CH2CH2CF3, -CH2CHFCF3, -CH2CF2CF3, -CHFCF2CF3, -CF2CF2CF3, -CH(CHF2)2, -CH(CH2F)2, -CH(CF3)2, and -CF(CF3)2

[0029] “Alkylene” refers to an alkyl group wherein two hydrogens are removed to provide a divalent radical, and which may be substituted or unsubstituted. In some embodiments, an alkylene group has 1 to 4 carbon atoms (“C1-C4 alkylene”). Unsubstituted C1-C4 alkylene groups include, but are not limited to, methylene (-CH2-), ethylene (-CH2CH2-), propylene (-CH2CH2CH2-), and butylene (-CH2CH2CH2CH2-). Exemplary substituted C1-C4 alkylene groups, e.g., substituted with one or more alkyl (methyl) groups, include but are not limited to, substituted methylene (-CH(CHs)-, -C(CHs)2-), substituted ethylene (-CH(CH3)CH2-,-CH2CH(CH3)-, -C(CH3)2CH2-, -CH2C(CH3)2-), substituted propylene (-CH(CH3)CH2CH2-, -CH2CH(CH3)CH2-, -CH2CH2CH(CH3)-), and the like. “Fluoroalkylene” refers to a fluoroalkyl group wherein two hydrogens are removed to provide a divalent radical, and which may be substituted or unsubstituted. “[Fluoro]alkylene” refers to an alkyl group with one or more optional fluorine substitutes wherein two hydrogens are removed to provide a divalent radical, and which may be substituted or unsubstituted.

[0030] In some embodiments, the co-solvent has a boiling point of at least 100 °C, at least 110 °C, or at least 120 °C at 1 atm.

[0031] In some embodiments, the co-solvent comprises at least one selected from the group consisting of bis(2,2,2-trifluoroethoxy)methane (BTFM), 1, 1,1, 3,3, 3-hexafluoro-2-(l, 1,1, 3,3,3- hexafluoropropan-2-yloxymethoxy )propane, b i s (3 ,3 , 3 -trifluoropropoxy )m ethane, 1,1,1 -trifluoro-3 - [(2,2,2-trifluoroethoxy)methoxy]propane, bis(2,2,3,3,3-pentafluoropropoxy)methane, 1, 1, 1,2,2- pentafluoro-3-((2,2,2-trifluoroethoxy)methoxy)propane, 2,2,2-trifluoroethyl 1,1,2,2-tetrafluoroethyl ether, l,2-(l,l,2,2-tetrafluoroethoxy)ethane (TFEE), tris(2,2,2-trifluoroethyl)orthoformate (TFEO), tris(2,2-difluoroethyl)orthoformate, 2-[difluoro(2,2,2-trifluoroethoxy)methoxy]-l,l,l- trifluoroethane, 1,1,1 ,2,2-pentafluoro-2- {fluoro[bis(pentafluoroethoxy)]methoxy } ethane, 1,1, 1,2- tetrafluoro-2,2-bi s(trifluoromethoxy)ethane, 2- [ 1 , 1 -bi s(2,2,2-trifluoroethoxy)ethoxy ] - 1,1,1- trifluoroethane, l,l,l-trifluoro-2,2,2-tris(2,2,2-trifluoroethoxy)ethane, l,l,l,3,3,3-hexafluoro-2,2- bi s(2,2, 3 ,3 ,3 -pentafluoropropoxy )propane, 2-[ 1 , 1 -bis(2-fluoroethoxy)ethoxy]- 1,1,1 -trifluoroethane,, lH,lH,5H-octafluoropentyl-l,l,2,2-tetrafluoroethyl ether (OTE), l,l,2,2-tetrafluoroethyl-2,2,3,3- tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether, lH,lH,2’H-perfluorodipropyl ether and mixtures thereof.

[0032] In some embodiments, the co-solvent has a weight concentration in a range from 10 wt% to 80 wt%, 20 wt% to 50 wt%, from 20 wt% to 45 wt%, from 20 wt% to 40 wt%, from 20 wt% to 35 wt%, or from 20 wt% to 30 wt% in the electrolyte composition.

[0033] In some embodiments, the asymmetric F-ether has a weight concentration in a range from 10 wt% to 80 wt%, 20 wt% to 50 wt%, from 20 wt% to 45 wt%, from 20 wt% to 40 wt%, from 20 wt% to 35 wt%, or from 20 wt% to 30 wt% in the electrolyte composition.

[0034] In some embodiments, the co-solvent and the asymmetric F-ether have a total weight concentration in a range from 45 wt% to 90 wt%, from 45 wt% to 85 wt%, from 45 wt% to 80 wt%,from 45 wt% to 75 wt%, from 45 wt% to 70 wt%, from 45 wt% to 65 wt%, from 45 wt% to 60 wt%, or from 45 wt% to 55 wt% in the electrolyte composition.

[0035] In some embodiments, the salt has a weight concentration in a range from 10 wt% to 55 wt%, from 10 wt% to 50 wt%, from 10 wt% to 45 wt%, from 10 wt% to 40 wt%, or from 10 wt% to 35 wt% in the electrolyte composition.

[0036] In some embodiments, the asymmetric fluorinated ether (AFE) comprises at least one selected from the group consisting of:• 1,1,1 ,2,2-pentafluoro-3 -(2-methoxyethoxy)propane,• 3 -(2-ethoxy ethoxy)- 1,1,1, 2, 2-pentafluoropropane (AFE1),• 1,1 ,2,2-tetrafluoro-3-(2-ethoxyethoxy)propane ,• 1,1,1 , 2, 2-pentafluoro-3 -[2-(2-methoxy ethoxy )ethoxy]propane,• l,l,l,2,2,3,3-heptafluoro-4-(2-methoxyethoxy)butane,• 1, 1, l,2,2,3,3-heptafluoro-4-[2-(2-methoxyethoxy)ethoxy]butane,• l,l,l,2,2,3,3,4,4-nonafluoro-6-(2-methoxyethoxy)hexane,• l,l,l,2,2,3,3,4,4,5,5,6,6,7,7,8,8-heptadecafluoro-10-[2-[2- (methoxyethoxy)ethoxy]ethoxy]decane,• 1,1,1 ,3 ,3 ,3 -hexafluoro-2,2-dipropoxypropane,• l-[l-ethoxy-l-(2-fluoroethoxy)ethoxy]-l,l,2,2-tetrafluoroethane, and mixtures thereof.

[0037] In some embodiments, the electrolyte has an ionic conductivity of at least 1.00 mS / cm, at least 1.10 mS / cm, at least 1.20 mS / cm, at least 1.30 mS / cm, at least 1.40 mS / cm, or at least 1.50 mS / cm at 25 °C.

[0038] In some embodiments, the electrolyte is electrochemically compatible with lithium metal oxide cathodes such as lithium nickel manganese cobalt oxide (NMC811). In some embodiments, the electrolyte has an oxidation potential of at least 4.00 V, at least 4.10 V or at least 4.25 V over Li / Li+. |0039[ In some embodiments, the salt is a lithium salt comprising at least one selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPFe), lithium borofluoride (LiBF4), lithium hexafluoroarsenide (LiAsFe), lithium trifluoromethanesulfonate (LiCFaSCh), lithium bis(trifluoromethanesulfonyl)imide (LiN(CFsSO2)2, LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium nitrate (LiNOa), lithium fluoroalkylphosphates (Li[PFx(CyF2y+i-zHz)6-x]) (l<x<5, l<y<8, and 0<z<2y-l), lithium bis(perfluoroethanesulfonyl)imide (LiBETI), lithium difluoro(oxalato)borate (LiDFOB), lithium fluorophosphate (Li2POaF), lithium difluoro(bisoxalato)phosphate (LiC4POsF2), lithium tetrafluorooxalato phosphate (I C2PO4F4), lithium difluorophosphate (LiDFP), LiC(CFsSO2)3, LiF, LiCl, LiBr, Lil, lithium acetate, lithium trifluoromethyl acetate, lithium oxalate, and mixtures thereof.

[0040] In some embodiments, the co-solvent comprises a second compound. In some embodiments, the second compound is a non-fluorinated ether. In some embodiments, the second compound is an alkyl ether which may reduce resistance, increase ionic conductivity and / or improve the high-rate performance. In some embodiments, the second compound in the co-solvent is an alkyl ether with a non-fluorine halogen substitute, which may enhance thermal stability and safety. In some embodiments, the second compound in the co-solvent is an alkyl ether with a non-fluorine halogen substitute and a fluorine substitute.[00411 In some embodiments, the non-fluorinated ether as a second compound in the co-solvent is an alkyl ether and is selected from the group consisting of dimethoxy methane, 1,2-dimethoxy ethane, 1,2-di ethoxy ethane, 1,1 -di ethoxy ethane, 1 , 1 -dipropoxy-ethane, 1,2-dipropoxy-ethane, di ethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, tri(ethylene glycol) dimethyl ether, tri(ethylene glycol) diethyl ether, diethylene glycol dibutyl ether, tetra(ethylene glycol) dimethyl ether, tetra(ethylene glycol) diethyl ether, tetra(ethylene glycol) dibutyl ether, or the like.

[0042] In some embodiments, the electrolyte composition further comprises a polymer with a weight percentage in a range from 0.02 wt% to 40 wt% in the electrolyte.

[0043] In some embodiments, the polymer is in situ polymerized after mixing a monomer with a salt, an asymmetric fluorinated ether, and a co-solvent.

[0044] In some embodiments, the monomer is at least one selected from the group consisting of 2,2,3,3-tetrafluorobutane-l,4-diacrylate, 2,2,3,3,4,4,5,5-octafhiorohexane-l,6-diyl diacrylate, 2,2,3,3,4,4,5,5-octafluorohexane-l,6-diyl bis(2-methylacrylate), poly(ethylene glycol) diacrylate (Mn=500 - 5000), tri ethylene glycol di methacryl ate (TEGDMA), diurethane dimethacrylate, tetraallyl silane (TAS), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, triethoxyvinylsilane, allyltriethoxysilane, pentaerythritol tetraacrylate (PETA), pentaerythritol tetramethacrylate (PETMA), tris[2-(acryloyloxy)ethyl] isocyanurate (TAEI), di(trimethylolpropane) tetraacrylate (Di-TMPTA), trimethylolpropane propoxylate triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, and dipentaerythritol hexaacrylate.

[0045] In some embodiments, the present disclosure also provides an electrochemical device comprising the electrolyte composition as disclosed herein.

[0046] In some embodiments, the electrochemical device is a coin cell, a pouch cell, a prismatic cell, or combinations thereof.

[0047] In some embodiments, the electrochemical device comprises a lithium metal oxide such as NMC81 1 as cathode. In some embodiments, the electrochemical device is not a lithium-sulfur battery, which involves chemistry and / or reactions significantly different from lithium metal oxide cathode.

[0048] In some embodiments, the electrochemical device exhibits a capacity of at least 0.5 Ah, at least 1.0 Ah, at least 2.0 Ah, at least 5.0 Ah or at least 10.0 Ah.

[0049] In some embodiments, the electrochemical device exhibits an initial coulombic efficiency (CE) of at least 87.0%, at least 88.0%, at least 89.0%, at least 90.0%, at least 91.0%, at least 92.0%, at least 92.5%, at least 93.0%, at least 93.5%, or at least 94.0% at 25 °C.

[0050] In some embodiments, the electrochemical device exhibits an average CE of at least 98.5%, 98.7%, 98.9%, 99.0%, 99.1%, 99.2%, 99.3% for 120 cycles at 0.33C charge and 0.33C discharge at 25 °C.[0051 [ In some embodiments, the electrochemical device exhibits an initial specific capacity of at least 160 mAh / g, at least 170 mAh / g, at least 180 mAh / g or at least 190 mAh / g at 0.33C charge and 0.33C discharge at 25 °C.

[0052] In some embodiments, the electrochemical device exhibits a specific capacity of at least 136 mAh / g, at least 145 mAh / g, at least 155 mAh / g, at least 160 mAh / g or at least 165mAh / g after 120 cycles, where each cycle is charged and discharged at a rate of 0.33C at 25 °C.

[0053] In some embodiments, the electrochemical device exhibits a capacity retention of at least 85%, at least 87%, at least 90%, at least 91%, at least 92% or at least 93% after 120 cycles, where each cycle is charged and discharged at a rate of 0.33C at 25 °C. Capacity retention is the discharge capacity divided by initial discharge capacity.

[0054] The disclosure will be better understood by reference to the Experimental Details which follow, but those skilled in the art will readily appreciate that the specific experiments detailed are only illustrative, and are not meant to limit the disclosure as described herein, as numerous variations and modifications of these exemplary embodiments are possible without undue experimentation.

[0055] All such variations and modifications are within the scope of the teachings of this disclosure. It will be appreciated that the foregoing description and following examples, no matter how detailed they may appear in text, the disclosure may be practiced in many ways, and the disclosure should be construed in accordance with the appended claims and equivalents thereof.EXAMPLE 1

[9056] Electrolyte examples 1-1, 1-2, 1-3, and 1-4 with compositions in Table 1 were prepared by mixing LiFSI as a salt, 3 -(2 -ethoxy ethoxy)- 1,1,1, 2, 2-pentafluoropropane (AFE1) as AFE solvent, and bis(2,2,2-trifluoroethoxy)methane (BTFM) as a co-solvent. Comparative examples 1 and 2 were prepared by mixing LiFSI as a lithium salt and AFE1 as a solvent without any co-solvent.

[0057] Li stripping / plating coulombic efficiency (CE) is a critical parameter for the evaluation of electrolyte stability on Li metal anode. The Li stripping / plating CE was obtained by stripping / plating cycles in Li / Cu cells comprising Li metal as anode, Cu foil as cathode, microporous membrane as a separator, and electrolytes as prepared. The ionic conductivity of the electrolyte was calculated based on the bulk resistance obtained by electrochemical impedance spectroscopy (EIS) measurements at 25 °C.Table 1 Electrolyte compositionsExamples 1-1 through 1-4 exhibited an ionic conductivity higher than the comparative examples 1 and 2.

[0059] A cell comprising the electrolyte of the examples 1-1, 1-2, 1-3, or 1-4 exhibited a higher coulombic efficiency (CE) than the comparative examples 1 and 2. The cells comprising examples 1-1, 1-2, 1-3, and 1-4 as electrolytes exhibited an initial CE of 93.16%, 95.01%, 92.35%, and 93.54%, respectively, which is higher than the comparative examples. The cells comprising examples 1-1, 1-2, 1-3, and 1-4 as electrolytes exhibited an average CE of 99.09%, 99.10%, 98.94%, and 99.02%, respectively, which is also higher than the comparative examples. The cells comprising examples 1- 1, 1-2, 1-3, and 1-4 as electrolytes exhibited a Li / Cu cycling average CE of 99.38%, 99.41%, 99.35%, and 99.27%, respectively, which is also higher than the comparative examples. Because the CE is already near 100%, a small increase of CE could lead to significant improvement in Li metal stability and cycle life.Table 2 Electrochemical performance of electrolytes and cells comprising the sameof the initial cycle is 0.3 mA / cm2and the capacity of the initial cycle is 3.0 mAh / cm2. b: Average CE is total Li stripping cycle capacity divided by total Li plating cycle capacity using Aurbach CE protocol with a current density of 1.0 mA / cm2, a capacity of 3.0 mAh / cm2and a total of 10 plating / stripping cycles. [Adv. Energy Mater. 2017, 1702097], c: Li / Cu Cycling Average CE is the average of each cycle’s CE for 50 cycles using fully strip cycling protocol with current density of 1.5 mA / cm2and capacity of 3.0 mAh / cm2[Adv. Energy Mater. 2017, 1702097][0060| Fig. 1 shows a comparison between example 1-1 and comparative example 1 in Li / Cu coin cell. The Li / Cu coin cell comprises Li metal as anode, microporous membrane as separator, Cu foil as cathode, and example 1-1 or comparative example 1 as electrolyte. The Li / Cu coin cell was subjected to Li plating / stripping cycles on Cu foil for 50 cycles. The Li plating current density on Cu foil is 1.5 mA / cm2and Li plating capacity is 3.0 mAh / cm2. The Li stripping current density on Cu foil is 1.5 mA / cm2and cut-off voltage for the Li stripping on Cu foil is 1.0 V to ensure fully stripping. The 50-cycle average CE of cell using example 1-1 as electrolyte is significantly higher than that of cell using comparative example 1 as electrolyte, indicating example 1-1 has significantly better electrochemical stability on Li metal.

[0061] Fig. 2 shows the charge rate test of a Li / NMC coin cell comprising Li metal as anode, microporous membrane as separator, NMC811 as cathode, and example 1-1 as electrolyte. The cell was cycled with a set of charge current densities sequentially increasing from 0.15 mA / cm2to 7.5 mA / cm2, equivalent to 0.05C to 2.5C, respectively. The discharge current density was 1.0 mA / cm2(0.33C). The cell with example 1-1 as electrolyte delivered a high capacity retention of greater than 50% at 2.0C and greater than 30% at 2.5C. The cell with comparative example 1 shorted and failed to complete the charge rate test, indicating comparative example 1 has significantly worse rate capability than example 1-1.EXAMPLE 2

[0062] Electrolytes with compositions in Table 3 were prepared by mixing LiFSI as a salt, AFE1 as AFE solvent, and tris(2,2,2-trifluoroethyl)orthoformate (TFEO) as a co-solvent.

[0063] Coin cells were assembled by following the method in example 1 except that the electrolytes of 2-1 and 2-2 were used as electrolyte. The ionic conductivity, initial CE, average CE and Li / Cu cycling average CE were tested according to the method in example 1.Table 3 Electrolyte compositions

[0064] As shown in Table 4, the cells comprising examples 2-1 and 2-2 as electrolytes exhibited an initial CE of 93.45% and 94.32%, respectively, which is higher than the comparative examples. The cells comprising examples 2-1 and 2-2 as electrolytes exhibited an average CE of 98.92% and 99.00%, respectively, which is also higher than the comparative examples. The cells comprising examples 2- 1 and 2-2 as electrolytes exhibited a Li / Cu cycling average CE of 99.35% and 99.29%, respectively, which is also higher than the comparative examples. Each example including comparative ones exhibited an ionic conductivity of at least 1.00 mS / cm.Table 4 Electrochemical performance of electrolytes and cells comprising the sameExample 3

[9065] Electrolytes with compositions in Table 5 were prepared by mixing LiFSI as a salt, AFE1 as AFE solvent, and a co-solvent comprising bis(2,2,2-trifluoroethoxy)methane (BTFM) and 1,2- diethoxy ethane (DEE).

[0066] Coin cells were assembled by following the method in example 1 except that the electrolytes of 3-1, 3-2, and 3-3 were used as electrolyte. The ionic conductivity, initial CE, average CE and Li / Cu cycling average CE were tested according to the method in example 1.Table 5 Electrolyte compositions

[0067] As shown in Table 6, examples 3-1, 3-2, and 3-3 exhibited an ionic conductivity of at least 4.00 mS / cm. The ionic conductivity of the examples 3-1 through 3-3 is much higher than comparative examples. In comparison to examples 1-1 through 1-4 which did not include DEE, the examples 3-1, 3-2, and 3-3 exhibited a higher ionic conductivity. It indicates that the addition of DEE as a second compound in the co-solvent significantly increased the ionic conductivity.Table 6 Electrochemical performance of electrolytes and cells comprising the same0068] Further, a cell comprising the electrolyte of the examples 3-1, 3-2, or 3-3 exhibited a higher coulombic efficiency than the comparative examples 1 and 2. The cells comprising examples 3-1, 3- 2, and 3-3 as electrolytes exhibited an initial CE of 95.26%, 94.11%, and 94.91%, respectively, whichis higher than the comparative examples. The cells comprising examples 3-1, 3-2, and 3-3 as electrolytes exhibited an average CE of 99.20%, 99.23%, and 99.10%, respectively, which is also higher than the comparative examples. The cells comprising examples 3-1, 3-2, and 3-3 as electrolytes exhibited a Li / Cu cycling average CE of 99.24%, 99.25%, and 99.43%, respectively, which is also higher than the comparative examples.

[0069] Examples 1-1 through 1-4 and examples 3-1 through 3-4 exhibited similar CEs.Example 4|0070| An electrolyte comprising a polymer was prepared by mixing LiFSI as a salt, AFE1 as AFE solvent, and bis(2,2,2-trifluoroethoxy)methane (BTFM) as co-solvent, pentaerythritol tetraacrylate (PETA) as monomer, and azobisisobutyronitrile (AIBN) as initiator followed by in situ polymerization at 65 °C for 2 h.

[0071] A multi-layer pouch cell comprising Li metal as anode, microporous membrane as separator, NMC81 1 as cathode, and polymer electrolyte example 4-1 as electrolyte was cycled between 2.8V to 4.25 V at 25 °C using current density of 1.0 mA / cm2(0.33C) under an external pressure in a range from 0.5 MPa to 5.0 MPa. The specific discharge capacity, discharge capacity retention, and CE are shown in Fig. 3, Fig. 4, and Fig. 5, respectively. The initial specific discharge capacity is 185 mAh / g. The cell retained a specific discharge capacity of 166 mAh / g and a capacity retention of 90% after 127 cycles. As shown in Fig. 5, the coulombic efficiency (CE) is high and consistently greater than 99.00%.Table 6 Electrolyte composition

[0072] Various embodiments of the features of this disclosure are described herein. However, it should be understood that such embodiments are provided merely by way of example, and numerous variations, changes, and substitutions can occur to those skilled in the art without departing from the scope of this disclosure. It should also be understood that various alternatives to the specific embodiments described herein are also within the scope of this disclosure.ASPECTS

[0073] In a first aspect, the present disclosure provides an electrolyte composition comprising:• a salt;• an asymmetric fluorinated ether; and• a co- solvent, wherein the asymmetric fluorinated ether is a compound with a formula of R'OR2(I), R1includes at least one C and at least one F, and R2includes at least one C but does not include any fluorine, and the co-solvent is not an asymmetric fluorinated ether, and wherein the co-solvent is an ether with a formula (III):wherein R3ais selected from the group consisting of C1-C10 alkyl, C3-C10 cycloalkyl, C1-C10 fluoroalkyl, C3-C10 fluorocycloalkyl, -[(C1-C4 alkylene)-0-]x-(Ci-Cio alkyl), -[(C1-C4 alkylene)-O-]x- (C3-C10 cycloalkyl), -[(C1-C4 alkylene)-0-]x-(Ci-Cio fluoroalkyl), and -[(C1-C4 alkylene)-O-]x-(C3- C10 fluorocycloalkyl),R4a, R5aand R6aare independently selected from the group consisting of H, F, C1-C10 alkyl, C3-C10 cycloalkyl, C1-C10 fluoroalkyl, C3-C10 fluorocycloalkyl, -0-(Ci-Cio alkyl), -0-(C3-Cio cycloalkyl), - 0-(Ci-Cio fluoroalkyl), -0-(C3-Cio fluorocycloalkyl), -[(C1-C4 [fluoro]alkylene)-0-]y-(Ci-Cio alkyl), -[(C1-C4 [fluoro]alkylene)-0-]y-(C3-Cio cycloalkyl), -[(C1-C4 [fluoro]alkylene)-0-]y-(Ci-Cio fluoroalkyl), -[(C1-C4 [fluoro]alkylene)-0-]y-(C3-Cio fluorocycloalkyl), -O-[(Ci-C4 [fluoro]alkylene)- 0-]y-(Ci-Cio alkyl), -O-[(Ci-C4[fluoro]alkylene)-0-]y-(C3-Cio cycloalkyl), -O-[(Ci-C4[fluoro]alkylene)-0-]y-(Ci-Cio fluoroalkyl) and -O-[(Ci-C4 [fluoro]alkylene)-0-]y-(C3-Cio fluorocycloalkyl), and x and y are independently an integer in a range from 1 to 10.

[0074] In a second aspect according to the first aspect, the asymmetric fluorinated ether has a formula (II): RlaO(CH2)mOR2a(II), wherein Rlais C1-C10 fluoroalkyl, C3-C10 fluorocycloalkyl, -[(C1-C4 alkylene)-0-]ni-(Ci-Cio fluoroalkyl), -[(C1-C4 fluoroalkylene)-0-]ni-(Ci-Cio fluoroalkyl), or — [(Ci- C4 fluoroalkylene)-0-]ni-(C3-Cio fluorocycloalkyl), and R2ais a C1-C10 alkyl, C3-C10 cycloalkyl, - [(C1-C4 alkylene)-0-]n2-(Ci-Cio alkyl) or -[(C1-C4 alkylene)-0-]n2-(C3-Cio cycloalkyl); m is 1, 2, 3, or 4; and each of nl and n2 is an integer in a range from 1 to 10.

[0075] In a third aspect according to the first or second aspect, the asymmetric F-ether is at least one selected from the group consisting of l,l,l,3,3,3-hexafluoro-2,2-dipropoxypropane, 1 -[1 -ethoxy- 1- (2-fluoroethoxy)ethoxy]-l, 1,2,2-tetrafluoroethane, 1, 1, l,2,2-pentafluoro-3-(2- methoxyethoxy)propane, 3 -(2-ethoxy ethoxy)- 1,1,1 ,2,2-pentafluoropropane, 1 , 1 ,2,2-tetrafluoro-3 -(2- ethoxyethoxy)propane, 1,1,1 , 2, 2-pentafluoro-3 -[2-(2-m ethoxy ethoxy)ethoxy]propane, 1 , 1 , 1 ,2,2,3 ,3 -heptafluoro-4-(2-methoxyethoxy)butane, l,l,l,2,2,3,3-heptafluoro-4-[2-(2- methoxyethoxy)ethoxy]butane, 1,1, 1 ,2,2,3,3,4,4-nonafluoro-6-(2-methoxyethoxy)hexane, l,l,l,2,2,3,3,4,4,5,5,6,6,7,7,8,8-heptadecafluoro-10-[2-[2-(methoxyethoxy)ethoxy]ethoxy]decane, and mixtures thereof.[0076| In a fourth aspect according to the first aspect, at least one of R4a, R?aand R6ain formula (III) is Ci-Cio alkyl, Ci-Cio fluoroalkyl, -0-(Ci-Cio alkyl), -0-(Ci-Cio fluoroalkyl), -[(C1-C4 alkylene)- 0-]y-(Ci-Cio alkyl), -[(C1-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl), -O-[(Ci-C4alkylene)-0-]y-(Ci-Cio alkyl), or -O-[(Ci-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl). In some embodiments, at least two of R4a, R5aand R6ain formula (III) are -0-(Ci-Cio alkyl), -0-(Ci-Cio fluoroalkyl), -[(C1-C4 alkylene)-O-]y- (C1-C10 alkyl), -[(C1-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl), -O-[(Ci-C4alkylene)-0-]y-(Ci-Cio alkyl), or -O-[(Ci-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl).(0077] In a fifth aspect according to the first aspect, the co-solvent comprises a fluorine-free ether, i.e., none of R3a, R4a, R5aand R6ainclude fluorine.

[0078] In a sixth aspect according to the first aspect, the co-solvent comprises a fluorinated ether that is not an asymmetric F-ether, i.e., R3aincludes at least one fluorine and at least one of R4a, R3aand R6aincludes at least one fluorine.

[0079] In some embodiments, R4ais H, F, C1-C10 alkyl, or C1-C10 fluoroalkyl, R6ais H, F, C1-C10 alkyl, or C1-C10 fluoroalkyl, R5ais -0-(Ci-Cio alkyl), -0-(Ci-Cio fluoroalkyl), -O-[(Ci-C4 alkylene)- O-]y-(Ci-C 10 alkyl), or -O-[(Ci-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl). In some embodiments, at least two of R4a, R5aand R6aare independently selected from the group consisting of -0-(Ci-Cio alkyl), - 0-(Ci-Cio fluoroalkyl), -O-(Ci-C4alkylene)-0-(Ci-Cio alkyl), and -O-(Ci-C4alkylene)-0-(Ci-Cio fluoroalkyl).[0080 In a seventh aspect according to the first aspect, R4ais H, R6ais H, R5ais -0-(Ci-Cio alkyl) or -0-(Ci-Cio fluoroalkyl).(0081 ] In an eighth aspect according to any preceding aspect, the co-solvent has a boiling point of at least 100 °C at 1 atm.|0082| In a nineth aspect according to the first aspect, the co-solvent comprises at least one selected from the group consisting of:• bis(2,2,2-trifluoroethoxy)methane (BTFM),• 1 , 1 , 1 ,3 ,3 ,3 -hexafluoro-2-( 1,1,1 ,3 ,3,3-hexafluoropropan-2-yloxymethoxy)propane,• bis(3,3,3-trifluoropropoxy)methane,• 1,1,1 -trifluoro-3 -[(2,2,2-trifluoroethoxy)methoxy ]propane,• bis(2, 2, 3, 3, 3 -pentafluoropropoxy )methane,• 1,1,1 ,2,2-pentafluoro-3 -((2,2,2-trifluoroethoxy)methoxy)propane,• 2,2,2-trifluoroethyl 1,1,2,2-tetrafluoroethyl ether,• l,2-(l,l,2,2-tetrafluoroethoxy)ethane (TFEE),• tris(2,2,2-trifluoroethyl)orthoformate (TFEO),• tris(2,2-difluoroethyl)orthoformate,• 2-[difluoro(2,2,2-trifluoroethoxy)methoxy]-l , 1 , 1 -trifluoroethane,• 1, 1, l,2,2-pentafluoro-2-{fluoro[bis(pentafluoroethoxy)]methoxy}ethane,• 1,1,1 ,2-tetrafluoro-2,2-bis(trifluorom ethoxy )ethane,• 2- [ 1 , 1 -bis(2,2,2-trifluoroethoxy )ethoxy]- 1,1,1 -trifluoroethane,• 1,1,1 -trifluoro-2,2,2-tris(2,2,2-trifluoroethoxy)ethane,• l,l,l,3,3,3-hexafluoro-2,2-bis(2,2,3,3,3-pentafluoropropoxy)propane,• 2-[ 1 , 1 -bi s(2-fluoroethoxy)ethoxy]- 1,1,1 -trifluoroethane, and mixtures thereof.

[0083] In a tenth aspect according to any preceding aspect, the co-solvent has a weight concentration in a range from 10 wt% to 80 wt% in the electrolyte composition.

[0084] In an eleventh aspect according to any preceding aspect, the asymmetric F-ether has a weight concentration in a range from 10 wt% to 80 wt% in the electrolyte composition. In some embodiments, the co-solvent and the asymmetric F-ether have a total weight concentration in a range from 45 wt% to 90 wt% in the electrolyte composition.

[0085] In some embodiments, the salt has a weight concentration in a range from 10 wt% to 55 wt% in the electrolyte composition. In some embodiments, the salt comprises at least one selected from the group consisting of lithium bis(fluorosulfonyl) imide (LiFSI), lithium perchlorate (LiCIC ), lithium hexafluorophosphate (LiPFe), lithium borofluoride (LiBF4), lithium hexafluoroarsenide (LiAsFe), lithium trifluoromethanesulfonate (LiCFsSCh), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2, LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium nitrate (LiNOi), lithium fluoroalkylphosphates (Li[PFx(CyF2y+i-zHz)e-x]) (l<x<5, l<y<8, and 0<z<2y-l), lithium bis(perfluoroethanesulfonyl)imide (LiBETI), lithium difluoro(oxalato)borate (LiDFOB), lithium fluorophosphate (Li2PO.3F), lithium difluoro(bisoxalato)phosphate (LiC4POsF2), lithium tetrafluoro oxalato phosphate (LiC2PO4F4), lithium difluorophosphate (LiDFP), LiC(CF3SO2)3, LiF, LiCl, LiBr, Lil, Li2SC>4, LisPCh, Li2CC>3, LiOH, lithium acetate, lithium trifluoromethyl acetate, lithium oxalate, and mixtures thereof. In some embodiments, the electrolyte composition is substantially free of LiPFe.[00861 In a twelfth aspect according to any preceding aspect, the co-solvent further comprises a second compound, wherein the second compound is not an fluorinated ether and is selected from the group consisting of dimethoxy methane, dimethoxy ethane, 1,2-di ethoxy ethane, 1,1 -diethoxy ethane, 1,1 -dipropoxy -ethane, 1,2-dipropoxy-ethane, 2-(2-ethoxyethoxy)ethanol, di ethylene glycol dimethyl ether, di ethylene glycol diethyl ether, di ethylene glycol dibutyl ether, triethylene lycol dimethyl ether, triethylene glycol diethyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol dibutyl ether, and mixtures thereof.

[0087] In a thirteenth aspect according to any preceding aspect, the electrolyte composition further comprises a polymer with a weight percentage in a range from 0.02 wt% to 40 wt% in the electrolyte composition, and the polymer is in situ polymerized after mixing a monomer and an initiator with the salt, the AFE, and the co-solvent. In some embodiments, the monomer is at least one selected from the group consisting of 2,2,3,3-tetrafluorobutane-l,4-diacrylate, 2,2,3,3,4,4,5,5-octafluorohexane- 1,6-diyl diacrylate, 2,2,3,3,4,4,5,5-octafluorohexane-l,6-diyl bis(2-methylacrylate), polyethylene glycol) diacrylate with a number average molecular weight in a range from 500 to 5000, triethylene glycol dimethacrylate (TEGDMA), diurethane dimethacrylate, tetraallyl silane (TAS), 2,4,6, 8- tetramethyl-2, 4, 6, 8-tetravinyl cyclotetrasiloxane, triethoxyvinylsilane, allyltri ethoxysilane, pentaerythritol tetraacrylate (PETA), pentaerythritol tetramethacrylate (PETMA), tris[2- (acryloyloxy)ethyl] isocyanurate (TAEI), di(trimethylolpropane) tetraacrylate (Di-TMPTA), trimethylolpropane propoxylate triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, and dipentaerythritol hexaacrylate.

[0088] In some embodiments, the electrolyte possesses an ionic conductivity of at least 1.00 mS / cm at 25 °C. In some embodiments, the electrolyte comprising a polymer (polymer electrolyte) has an ionic conductivity of at least 1.00 mS / cm at 25 °C. In some embodiments, the electrolyte possesses an oxidation potential of at least 4.00 V over Li / Li+.(0089) In a fourteenth aspect, the present disclosure provides an electrochemical device comprising the electrolyte composition according to any preceding aspect.

[0090] In a fifteenth aspect, the electrochemical device further comprises a cathode comprising a lithium metal oxide and an anode comprising lithium metal or lithium alloy. In some embodiments, the lithium metal oxide comprises at least one selected from the group consisting of lithium cobalt oxide (LCO), lithium manganese oxide (LMO), and lithium nickel manganese cobalt oxide (NMC). In some embodiments, the electrochemical device exhibits a capacity of at least 0.5 Ah,[00911 In some embodiments, the electrochemical device exhibits at least one characteristic selected from the group consisting of:• an initial coulombic efficiency (CE) of at least 87.00% at 0.33 C at temperature of 25 °C,• an average CE of at least 98.5% for 120 cycles at 0.33 C at temperature of 25 °C,• an initial specific capacity of at least 160 mAh / g at 0.33 C at a temperature of 25 °C,• a specific capacity of at least 155mAh / g afterl20 cycles where each cycle is charged and discharged at a rate of 0.33C at a temperature of 25 °C, and• a capacity retention of at least 85% afterl20 cycles where each cycle is charged and discharged at a rate of 0.33C at a temperature of 25 °C.

Claims

We claim;1. An electrolyte composition comprising:• a salt;• an asymmetric fluorinated ether; and• a co-solvent, wherein the asymmetric fluorinated ether is a compound with a formula of R'OR2(I), R1includes at least one carbon atom (C) and at least one fluorine atom (F), R2includes at least one C but does not include F, and the co-solvent is not an asymmetric fluorinated ether, wherein the co-solvent is an ether with a formula (III):(iii), wherein R3ais selected from the group consisting of Ci-Cio alkyl, C3-C10 cycloalkyl, C1-C10 fluoroalkyl, C3-C10 fluorocycloalkyl, -[(C1-C4 alkylene)-0-]x-(Ci-Cio alkyl), -[(C1-C4 alkylene)-0-]x-(C3-Cio cycloalkyl), -[(C1-C4 alkylene)-0-]x-(Ci-Cio fluoroalkyl), and — [(Ci- C4 alkylene)-0-]x-(C3-Cio fluorocycloalkyl),R4a, R5aand R6aare independently selected from the group consisting of H, F, C1-C10 alkyl, C3-C10 cycloalkyl, C1-C10 fluoroalkyl, C3-C10 fluorocycloalkyl, -0-(Ci-Cio alkyl), -0-(C3-Cio cycloalkyl), -0-(Ci-Cio fluoroalkyl), -0-(C3-Cio fluorocycloalkyl), -[(C1-C4 alkylene)-O-]y- (C1-C10 alkyl), -[(C1-C4 alkylene)-0-]y-(C3-Cio cycloalkyl), -[(C1-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl), -[(C1-C4 alkylene)-0-]y-(C3-Cio fluorocycloalkyl), -O-[(Ci-C4 alkylene)-O-]y- (C1-C10 alkyl), -O-[(Ci-C4alkylene)-0-]y-(C3-Cio cycloalkyl), -O-[(Ci-C4alkylene)-O-]y-(Ci- C10 fluoroalkyl) and -O-[(Ci-C4 alkylene)-0-]y-(C3-Cio fluorocycloalkyl), and x and y are independently an integer in a range from 1 to 10.

2. The electrolyte composition of claim 1, wherein the asymmetric fluorinated ether has a formula (II):RlaO(CH2)mOR2a(II), wherein Rlais C1-C10 fluoroalkyl, C3-C10 fluorocycloalkyl, -[(C1-C4 alkylene)-0-]ni-(Ci-Cio fluoroalkyl),-[(Ci-C4 fluoroalkylene)-O-]ni-(Ci-C 10 fluoroalkyl), or-[(Ci-C4 fluoroalkylene)- 0-]ni-(C3-Cio fluorocycloalkyl), andR2ais C1-C10 alkyl, C3-C10 cycloalkyl, -[(C1-C4 alkylene)-0-]n2-(Ci-Cio alkyl) or -[(C1-C4 alkylene)-0-]n2-(C3-Cio cycloalkyl); m is 1 , 2, 3 or 4; and each of nl and n2 is an integer in a range from 1 to 10.

3. The electrolyte composition of claim 1 , wherein the asymmetric F-ether is at least one selected from the group consisting of l,l,l,3,3,3-hexafluoro-2,2-dipropoxypropane, 1 -[1 -ethoxy- 1 -(2- fluoroethoxy)ethoxy]- 1 , 1 ,2,2-tetrafluoroethane, 1,1,1 ,2,2-pentafluoro-3 -(2- methoxyethoxy)propane, 3 -(2-ethoxy ethoxy)- 1,1,1 ,2,2-pentafluoropropane, 1 , 1 ,2,2- tetrafluoro-3-(2-ethoxyethoxy)propane, l,l,l,2,2-pentafluoro-3-[2-(2- methoxyethoxy)ethoxy]propane, l,l,l,2,2,3,3-heptafluoro-4-(2-methoxyethoxy)butane, 1,1,1 ,2,2,3 ,3 -heptafluoro-4-[2-(2-methoxyethoxy)ethoxy]butane, 1,1,1 ,2,2,3 ,3 ,4,4- nonafluoro-6-(2-methoxyethoxy)hexane, l,l,l,2,2,3,3,4,4,5,5,6,6,7,7,8,8-heptadecafluoro-10- [2-[2-(methoxyethoxy)ethoxy]ethoxy]decane, and mixtures thereof.

4. The electrolyte composition of claim 1, wherein at least one of R4a, R5aand R6ain formula (III) is C1-C10 alkyl, C1-C10 fluoroalkyl, -0-(Ci-Cio alkyl), -0-(Ci-Cio fluoroalkyl), -[(C1-C4 alkylene)-0-]y-(Ci-Cio alkyl), -[(C1-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl), -O-[(Ci-C4 alkylene)-0-]y-(Ci-Cio alkyl), or -O-[(Ci-C4 alkylene)-0-]y-(Ci-Cio fluoroalkyl).

5. The electrolyte composition of claim 1, wherein none of R3a, R4a, R5aand R6aincludes fluorine.

6. The electrolyte composition of claim 1, wherein R3aincludes at least one fluorine and at least one of R4a, R5aand R6aincludes at least one fluorine.

7. The electrolyte composition of claim 1, wherein R4ais H, R6ais H, R5ais -0-(Ci-Cio alkyl) or -0-(Ci-Cio fluoroalkyl).

8. The electrolyte composition of claim 1, wherein the co-solvent has a boiling point of at least 100 °C at 1 atm.

9. The electrolyte composition of claim 1, wherein the co-solvent comprises at least one selected from the group consisting of• bis(2,2,2-trifluoroethoxy)methane (BTFM),• 1,1, 1,3, 3 , 3 -hexafluoro-2-( 1 , 1 , 1 , 3 ,3 , 3 -hexafluoropropan-2-yloxy methoxy )propane,• bi s(3 ,3 ,3 -trifluoropropoxy)rn ethane,• 1,1,1 -trifluoro-3 -[(2,2,2-trifluoroethoxy)methoxy]propane,• bis(2,2,3,3,3-pentafluoropropoxy)methane,• 1,1,1 ,2,2-pentafluoro-3 -((2,2,2-trifluoroethoxy)methoxy )propane,• 2,2,2-trifluoroethyl 1,1,2,2-tetrafluoroethyl ether,• l,2-(l,l,2,2-tetrafluoroethoxy)ethane (TFEE),• tris(2,2,2-trifluoroethyl)orthoformate (TFEO),• tris(2,2-difluoroethyl)orthoformate,• 2-[difluoro(2, 2, 2-trifluoroethoxy)m ethoxy]-!, 1, 1 -trifluoroethane,• l,l,l,2,2-pentafluoro-2-{fluoro[bis(pentafluoroethoxy)]methoxy}ethane,• 1,1,1 ,2-tetrafluoro-2,2-bis(trifluoromethoxy)ethane,• 2- [ 1 , 1 -bis(2,2,2-trifluoroethoxy)ethoxy]- 1,1,1 -trifluoroethane,• 1,1,1 -trifluoro-2,2,2-tris(2,2,2-trifluoroethoxy)ethane,• 1,1,1 ,3 ,3 ,3 -hexafluoro-2,2-bi s(2,2, 3 , 3 ,3 -pentafluoropropoxy)propane,• 2-[l,l-bis(2-fluoroethoxy)ethoxy]-l,l,l-trifluoroethane, and mixtures thereof.

10. The electrolyte composition of claim 1, wherein the co-solvent has a weight concentration in a range from 10 wt% to 80 wt% in the electrolyte composition.

11. The electrolyte composition of claim 1, wherein the asymmetric F-ether has a weight concentration in a range from 10 wt% to 80 wt% in the electrolyte composition.

12. The electrolyte composition of any preceding claim, wherein the co-solvent further comprises a second compound, wherein the second compound is not an fluorinated ether and is selected from the group consisting of dimethoxy methane, dimethoxy ethane, 1,2-di ethoxy ethane, 1,1- di ethoxy ethane, 1,1 -dipropoxy-ethane, 1,2-dipropoxy-ethane, 2-(2-ethoxyethoxy)ethanol, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, diethylene glycoldibutyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol dibutyl ether, and mixtures thereof.

13. The electrolyte composition of claim 1, further comprising a polymer with a weight percentage in a range from 0.02 wt% to 40 wt% in the electrolyte and the polymer is in situ polymerized after mixing a monomer and initiator with the salt, AFE, and the co-solvent.

14. An electrochemical device comprising the electrolyte composition of any preceding claim.

15. The electrochemical device of claim 14, further comprising a cathode comprising a lithium metal oxide and an anode comprising lithium metal or lithium alloy.

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