US 20150288031A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2015/0288031 A1 Zhang et al. (43) Pub. Date: Oct. 8, 2015
(54) FUNCTIONALIZED IONIC LIQUID HOLM. I.2/02 (2006.01) ELECTROLYTES FOR LITHIUM ION HIM I/0525 (2006.01) BATTERIES HIM I/052 (2006.01) (52) U.S. Cl. (71) Applicant: UCHICAGO ARGONNE, LLC, CPC ...... H0IM 10/0567 (2013.01); H0IM 10/0525 CHICAGO, IL (US) (2013.01); H0IM 10/052 (2013.01); H0IM 10/054 (2013.01); H0IM 12/02 (2013.01); (72) Inventors: Zhengcheng Zhang, Naperville, IL HOM IO/0568 (2013.01); HOIM 23OO/OO25 (US), Wei Weng. Woodridge, IL (US); (2013.01); HOIM 2300/0085 (2013.01) Lu Zhang, Woodridge, IL (US); Khalil Amine, Oakbrook, IL (US) (57) ABSTRACT (21) Appl. No.: 14/742,194 An ionic liquid that is a salt has a Formula: (22) Filed: Jun. 17, 2015 R6 Rs Related U.S. Application Data R R s (63) Continuation of application No. 12/895,395, filed on N/ X N xO Sep. 30, 2010, now Pat. No. 9,093,722. R^ YR R1 y NR Publication Classification Ammonium R4 (51) Int. C. Imidazolium HIM I/0567 (2006.01) HIM I/0568 (2006.01) Such ionic liquids may be used in electrolytes and in electro HIM I/O54 (2006.01) chemical cells. Patent Application Publication Oct. 8, 2015 Sheet 1 of 8 US 2015/0288031 A1
FIG. 1A
(Et-E-Me Me & S-O-Si-Me CC : M. M.
8
FIG 1B
& Me Me FrogEt ME
CHC3
1.
5.O O.O. Patent Application Publication Oct. 8, 2015 Sheet 2 of 8 US 2015/0288031 A1
FIG. 2A
FIG. 2B
CHCI Patent Application Publication Oct. 8, 2015 Sheet 3 of 8 US 2015/0288031 A1
FIG. 3A
10.0 9.0 8.0. 7.0 6.0 5.0 4.0 3.0 2.0 ppm (t1) Patent Application Publication Oct. 8, 2015 Sheet 4 of 8 US 2015/0288031 A1
FIG. 4 A FE
-e-Charge 1 O Discharge 1 -- Charge 2 --Discharge 2
Capacity (mAh)
FIG.S
W.A.G. RE
-O-Charge 1 -O-Discharge 1 -O-Charge 2 -O-Discharge 2 Charge 3 Discharge 3 - Charge 4 i i-Discharge 4
O O.5 1. 1.5 2 2.5 3 3.5 4 Capacity (mAh) Patent Application Publication Oct. 8, 2015 Sheet 5 of 8 US 2015/0288031 A1
F.G. 6
dOAdv Plot OO 10 OOO8 PCharge 1. Discharge 1 O. OO6 as Charge 2 OOO4 as Discharge 2
OOO2 N OOOO g O -0.002 -O.OO4 -O. OO6 -OOO8 -O. O10 Woltage, V
FIG. 7
CYCLE RFRANCE
t E >S
-6-1.OM LiTFSITEMMP-FSI charge O -O-1, OMLITFSITEMMP-FSI discharge
O 2O 40 60 80 1OO 12O Cycle Number Patent Application Publication Oct. 8, 2015 Sheet 6 of 8 US 2015/0288031 A1
d S. 1.0 ------|-O-Discharge s U 0.5 0.0 O 10 20 30 40 50 Cycle Number
FG. 9
at Girara site Gre gasfiffa i fitti
3.2 a aarth th 2. 40 30 3.0 H.-- O O.5 1. 1.5 2 2.5
Capacity, mAh/g Patent Application Publication Oct. 8, 2015 Sheet 7 of 8 US 2015/0288031 A1
FIG. 10 i
Capacity (mAh)
FIG. 11
E.
-o- 1.0 MLITFSITEMMP-FSI charge -o- 1.0 MLITFSITEMMP-FSI discharge
Cycle Number Patent Application Publication Oct. 8, 2015 Sheet 8 of 8 US 2015/0288031 A1
F.G. 12
CYCLE PERFORMANCE
-O-Charge -O-Discharge (uvuu).Aq?oedeo
Cycle Number US 2015/0288031 A1 Oct. 8, 2015
FUNCTIONALIZED IONIC LIQUID SUMMARY ELECTROLYTES FOR LITHIUM ION 0006. The present technology provides new ionic liquids BATTERIES for use in electrolytes and electrochemical devices Such as capacitors and lithium ion batteries. The ionic liquids bear CROSS-REFERENCE TO RELATED functional groups so that should allow the ionic liquid itself to APPLICATIONS form passivation films on the Surface of graphite-based anode materials and ensure stable cycling performance. The new 0001. This application is a continuation of U.S. patent ionic liquids also decrease the Viscosity of the electrolytes application Ser. No. 12/895,395, filed on Sep. 30, 2010, compared to conventional ionic liquids, increasing their ionic which is incorporated herein by reference, in its entirety, for conductivity; provide good electrode wettability by introduc any and all purposes. ing Surfactant groups; and tolerate high potential, which reduces problems related to the use of 4.8V transition metal STATEMENT OF GOVERNMENT RIGHTS oxides, especially against overcharge. Finally, the ionic liq uids of the present technology may also exhibit one or more of 0002 The United States Government has rights in this reduced flammability, thereby reducing the risk of burning invention pursuant to Contract No. DE-AC02-06CH11357 and explosion in a misused battery; reduced vapor pressure, between the United States Government and UChicago even at elevated temperatures; and are not environmentally Argonne, LLC, representing Argonne National Laboratory. hazardous.
TECHNICAL FIELD BRIEF DESCRIPTION OF THE DRAWINGS 0003. The present technology relates to ionic liquids, 0007 FIGS. 1A and 1B. H-NMR of triethyl-(methylene including room temperature ionic liquids, that may be used in pentamethyldisiloxane)phosphonium iodide (IL1-I, FIG. electrolytes, electrolytic solutions and electrochemical 1A) and triethyl-(methylenepentamethyldisiloxane)phos devices. More particularly, the present technology relates to phonium bis(trifluoromethylsulfonyl)imide (IL1-TFSI, FIG. functionalized ionic liquids which are usable as electrolytes 1B). for lithium ion batteries having a high ionic conductivity, 0008 FIGS. 2A and 2B. H-NMR of 1-ethyl-3-(methyl good solid electrolyte interphase (SEI) formation, high wet enepentamethyldisiloxane) imidazolium iodide (IL2-I, FIG. tability, and high voltage stability. 2A) and 1-ethyl-3-(methylenepentamethyldisiloxane)-1H imidazol-3-ium bis(trifluoromethanesulfonyl)imide (IL2 BACKGROUND TFSI, 2B). 0009 FIGS. 3A and 3B. H-NMR of 1-ethyl-3-(ethylen 0004 Ionic liquids are substances, which are made up only emethylsulfone)-1H-imidazol-3-ium bromide (IL3-Br, FIG. from ions and have a melting point of <100° C. or are, ideally, 3A) and 1-ethyl-3-(ethylenemethylsulfone)-1H-imidazol-3- liquid at ambient temperature. They have been proposed for ium bis(trifluoro-methanesulfonyl)imide (IL3-TFSI, FIG. use in electrolytes for lithium and lithium-ion batteries, as 3B). they exhibit relatively favorable electrochemical stability and (0010 FIG. 4. Li/MCMB half cell charge discharge pro high ionic conductivity. Despite the potential advantages, files using conventional 0.8M LiTFSI in tetraethylphospho ionic liquids have not been widely used as electrolytes for nium bis(trifluoromethanesulfonyl)imide ionic liquid. lithium and lithium ion batteries due to a number of signifi (0011 FIG. 5. Li/MCMB half cell charge discharge pro cant disadvantages. Although lithium-ion cells using files using 0.8M LiTFSI in triethyl-(methylenepentamethyl LiMnO and Li TiO2 as electrode materials show satisfac disiloxane)phosphonium bis(trifluoromethylsulfonyl)imide tory cycling behavior using ionic liquid as electrolyte solvent, (IL1-TFSI). this cell configuration suffers from the relatively small volt (0012 FIG. 6. dOdV profile of Li/MCMB half cell using age of 2.5V. In addition, the cell has low rate capability due to 0.8M LiTFSI in triethyl-(methylenepentamethyldisiloxane) the high viscosity and poor wettability of the ionic liquid with phosphonium bis(trifluoromethylsulfonyl)imide (IL1-TFSI). electrode materials. 0013 FIG. 7. LiNiCoos AloosO/Li half cell charge 0005 Moreover, early experiments to cycle lithium-ion discharge cycling performance using conventional 0.8M batteries using carbonaceous negative electrode materials and LiTFSI intetraethylphosphonium bis(trifluoromethanesulfo ionic liquid-based electrolytes failed. Any ionic liquid sample nyl)imide ionic liquid. tested was reduced at the low potential at which the interca 0014 FIG. 8. LiNiCoos AloosO/Li half cell charge lation of lithium into the graphite proceeds. It is believed that discharge cycling performance using 0.8M LiTFSI in tri the reduction of the ionic liquids proceeds due to the forma ethyl-(methylenepentamethyldisiloxane)phosphonium bis tion of dimeric species. For commercial applications, lithium (trifluoromethylsulfonyl)imide (IL1-TFSI) at 55° C. metal is, however, not advantageous. Due to the high reactiv (0015 FIG.9. MCMB/Lihalf cell charge discharge cycling ity of its Surface, lithium is potentially hazardous, especially performance using conventional 0.8M LiTFSI in tetraeth at elevated temperatures. Proposals to stabilize lithiated ylphosphonium bis(trifluoromethanesulfonyl)imide ionic graphite electrodes for use in lithium-ion batteries include liquid. admixture of Small amounts of highly active film forming (0016 FIG. 10. MCMB/Li half cell charge discharge additives. Such additives could protect against the continued cycling performance using 0.8M LiTFSI in triethyl-(methyl reduction of the electrolyte itself at the surface of the low enepentamethyldisiloxane)phosphonium bis(trifluorometh potential graphite. However, in most cases, the additives have ylsulfonyl)imide (IL1-TFSI). issues associated with the poor solubility in ionic liquid elec (0017 FIG. 11. MCMB/LiNiso Nils Aloo O, full cell trolytes. charge discharge cycling performance using conventional US 2015/0288031 A1 Oct. 8, 2015
0.8M LiTFSI in tetraethylphosphonium bis(trifluo unsubstituted or optionally substituted with one or more romethanesulfonyl)imide ionic liquid. alkyl, halo groups or one or more halogens. In some embodi 0018 FIG. 12. MCMB/LiNissCoos Alos.O. full cell ments the aryl groups are substituted with 1, 2 or 3 alkyl charge discharge cycling performance using 0.8M LiTFSI in groups and/or 1-5 halogens. triethyl-(methylenepentamethyldisiloxane)phosphonium bis 0026 Aralkyl groups are alkyl groups as defined above in (trifluoromethylsulfonyl)imide (IL1-TFSI). which a hydrogen or carbon bond of an alkyl group is replaced with a bond to an aryl group as defined above. In DETAILED DESCRIPTION Some embodiments, aralkyl groups contain 7 to 16 carbon 0019. The following terms are used throughout as atoms, 7 to 14 carbon atoms, or 7 to 10 carbon atoms. Sub described below, unless context clearly indicates otherwise. stituted aralkyl groups may be substituted at the alkyl, the aryl 0020 Alkyl groups include straight chain and branched or both the alkyl and aryl portions of the group. Representa chain Saturated hydrocarbon groups having from 1 to 14 tive aralkyl groups include but are not limited to benzyl and carbons unless indicated otherwise. For example, a C- alkyl phenethyl groups and fused (cycloalkylaryl)alkyl groups group includes alkyl groups with 1, 2, 3, 4, 5, or 6 carbon Such as 4-indanylethyl. Aralkyl groups may be unsubstituted atoms. In some embodiments, an alkyl group has from 1 to 12 or Substituted. Representative Substituted aralkyl groups may carbon atoms, from 1 to 10 carbons, from 1 to 8, 1 to 6, or 1, be substituted one or more times with alkyl groups or halo 2, 3 or 4 carbon atoms. Examples of straight chain alkyl gens as for aryland alkyl groups. groups include groups such as methyl, ethyl, n-propyl. n-bu 0027. Heteroaryl groups are aromatic ring compounds tyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl, n-decyl, n-dode containing 5 or more ring members, of which one or more is cyl and n-tetradecyl groups. Examples of branched chain a heteroatom selected from N, O, S and P. Heteroaryl groups alkyl groups include, but are not limited to, isopropyl, iso include, but are not limited to, groups such as pyrrolyl pyra butyl, Sec-butyl, tert-butyl, neopentyl, isopentyl, and 2.2- Zolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, dimethylpropyl groups. Alkyl groups may be unsubstituted or pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, thiophenyl, are optionally substituted with one or more hydroxyl or halo benzothiophenyl, furanyl, benzofuranyl, indolyl, azaindolyl gen groups. (pyrrolopyridinyl), indazolyl, benzimidazolyl, imidazopy 0021 Cycloalkyl groups include mono-, bi- or tricyclic ridinyl (aZabenzimidazolyl), pyrazolopyridinyl, triazolopy alkyl groups having from 3 to 12 carbon atoms in the ring(s), ridinyl, benzotriazolyl, benzoxazolyl, benzothiazolyl, ben or, in some embodiments, 3 to 10, 3 to 8, or 3, 4, 5, or 6 carbon Zothiadiazolyl, imidazopyridinyl, isoxazolopyridinyl, atoms. Exemplary monocyclic cycloalkyl groups include, but thianaphthyl, purinyl, Xanthinyl, adeninyl, guaninyl, quinoli are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, nyl, isoquinolinyl, tetrahydroquinolinyl, quinoxalinyl, and cyclohexyl, cycloheptyl, and cyclooctyl groups. In some quinazolinyl groups. Heteroaryl groups include fused ring embodiments, the cycloalkyl group has 3 to 8 ring members, compounds in which all rings are aromatic Such as indolyl whereas in other embodiments the number of ring carbon groups and include fused ring compounds in which only one atoms range from 3 to 5, 3 to 6, or 3 to 7. Bi- and tricyclic ring of the rings is aromatic, such as 2.3-dihydro indolyl groups. systems include both bridged cycloalkyl groups and fused Heteroaryl groups may be unsubstituted or optionally Substi rings, such as, but not limited to, adamantyl, decalinyl, and tuted with one or more alky groups or one or more halogens. the like. Cycloalkyl groups may be unsubstituted or substi In some embodiments the aryl groups are substituted with 1, tuted as alkyl groups are. 2 or 3 alkyl groups and/or 1-5 halogens. 0022 Haloalkyl groups include alkyl groups as defined 0028. Heteroarylalkyl groups are alkyl groups as defined above in which 1 or more of the hydrogenatoms are replaced above in which a hydrogen or carbon bond of an alkyl group by a halogen (i.e., F, Cl, Br, or I). In some embodiments the is replaced with a bond to a heteroaryl group as defined above. haloalkyl group bears from 1 to 3 halogens. In others, the Representative heteroarylalkyl groups include, but are not haloalkyl is perhalogenated Such as perfluorinated or perchlo limited to, furan-2-yl-methyl, imidazol-4-yl-methyl, pyridin rinated. Examples of haloalkyl groups include but are not 3-yl-methyl, and indol-2-yl-propyl. In some embodiments, limited to —CHCl, —CHF, —CF, —CH2CHBr, and the alkyl portion of the heteroarylalkyl group has from 1 to 6 —CHCF. carbon atoms (i.e., 1, 2, 3, 4, 5, or 6). Heteroarylalkyl groups 0023 Hydroxyalkyl groups are alkyl groups which bear at may be unsubstituted or substituted as heteroaryl and alkyl least one hydroxyl group, i.e., OH. In some embodiments the groups are. hydroxyalkyl group bears 1 or 2 hydroxyl groups. 0029 ACs cyclic carbonate has from 3 to 5 carbonatoms 0024 Alkylene groups are alkyl groups, as defined herein, in the ring, providing a 5 to 7 membered carbonate ring. Thus, which are divalent; i.e., they have two points of attachment to for example, a C-s cyclic carbonate includes any of the fol a compound of the present technology. lowing structures: 0025 Aryl groups are cyclic aromatic hydrocarbons con taining 6-14 carbon atoms and do not contain heteroatoms. Aryl groups herein include monocyclic, bicyclic and tricyclic ring systems, including fused rings. Thus, aryl groups include, but are not limited to, phenyl, azulenyl, heptalenyl, biphenyl, fluorenyl, phenanthrenyl, anthracenyl, indenyl, indanyl, pentalenyl, and naphthyl groups. In some embodi ments, aryl groups contain from 6-12 or even 6-10 carbon atoms in the ring portions of the groups. In some embodi ments, the aryl groups are phenyl or naphthyl. Aryl groups may also include fused aromatic-aliphatic ring systems, e.g., 0030 Aluminate is an aluminum oxide anion such as, but indanyl, tetrahydronaphthyl, and the like. Aryl groups may be not limited to Al, O.I. US 2015/0288031 A1 Oct. 8, 2015
0031. A halogen refers to any of fluorine, chlorine, bro during operation of the device. These new ionic liquids mine or iodine atoms. A halide is a halogen anion Such as F. include a salt having a Formula selected from the group Cl, Br or I. consisting of: 0032. An isocyanate group has the chemical formula
N–C–O. 0033. A maleic anhydride group (cis-butenedioic anhy dride) has the structure shown below and may be attached to a compound at carbons 4 or 5.
0034. An oxalic borate group is a boronanion to which one or two oxalate groups are bound. Oxalic borates thus include but are not limited to B(CO) and FB(CO). As part of a compound of formula I, the Oxalic borate has a single oxalate group and may have a formula Such as —B(F) (CO). 0035. A succinic anhydride group has the structure shown below and may be attached to a compound at carbons 4 or 5. Oxazolium Thiazolium
0041 wherein R is selected from the group consisting of —CHSiCR").OSi(R").OSi(R"), —(R')–(OCHCH.) —(OR"), a C-5 cyclic carbonate, an oxalic borate group, a maleic anhydride group, a Succinic anhydride group, a Sul folane, and a C- alkyl group Substituted with a Substituent selected from an isocyanate, sulfone, sulfolane. —OCOR", Cs cyclic carbonate, or oxalic borate group; 0036) A sulfate group has the chemical formula SO,. 0042 R is a C alkylene group; Hence, alkyl sulfates and aryl sulfates employed in the 0043 R" is an alkyl group: present technology are sulfate monoesters of alkyl and aryl R. R. and R are independently at each occurrence an alkyl, groups as defined herein. Thus alkyl and aryl Sulfates include haloalkyl, alkyl substituted with carboxylate, aminoalkyl, but are not limited to octyl sulfate, dodecyl sulfate and the cycloalkyl, aryl, heteroaryl, aralkyl, or heteroaralkyl group; like. or two of R, R2, and Rjoin together to form a Cas alkylene 0037 Sulfolane is 2,3,4,5-tetrahydrothiophene-1,1-diox group; ide and may be attached to a compound at any of carbons 2, 3, R. R. R. R-7, and Rs are independently at each occurrence H 4, or 5. or an alkyl, haloalkyl, hydroxyalkyl, cycloalkyl, aryl, het 0038 A sulfonate group has the chemical formula eroaryl, aralkyl, or heteroaralkyl group; —SO. Thus, alkyl sulfonates are alkyl groups as defined X is an anion selected from the group consisting of boron hereinbearing a Sulfonate group, e.g., methylsulfonate, ethyl tetrafluoride, aluminate, (oxalate)borate, difluoro(oxalate) sulfonate, dodecyl sulfonate and the like. Fluoroalkyl sul borate, phosphorus hexafluoride, alkylsulfonate, fluoroalkyl fonates are alkyl groups which bear 1 or more fluorine atoms Sulfonate, arylsulfonate, bis(alkylsulfonyl)amide, perchlor and a Sulfonate group. Fluoroalkyl Sulfonates include trifluo ate, bis(fluoroalkylsulfonyl)amide, bis(arylsulfonyl)amide, romethane sulfonate, perfluoroethyl sulfonate and the like. alkyl fluorophosphate, (fluoroalkylsulfonyl)(fluoroalkylcar Likewise, an aryl Sulfonate is an aryl group as defined herein bonyl)amide, halide, nitrate, nitrite, Sulfate, hydrogen Sulfate, which bears a Sulfonate group and optionally, one or more alkyl Sulfate, aryl Sulfate, carbonate, bicarbonate, carboxy alkyl groups. Aryl Sulfonates thus include for example, ben late, phosphate, hydrogen phosphate, dihydrogen phosphate, Zene Sulfonate, naphthalene Sulfonate, dodecylbenzene Sul hypochlorite, an anionic site of a cation-exchange resin, and fonate and cumene Sulfonate. a mixture of any two or more thereof; 0039. A sulfone group has the chemical formula —S(O) 0044 n is an integer from 1 to 4; and R" wherein R is a C- alkyl group. In some embodiments, 0045 m is an integer from 0 to 10. R" is a C- alkyl group 0046. It will be understood that each dashed circle and 0040. In one aspect, the present technology provides ionic plus sign in the chemical formulas represent a cationic aro liquids that bear passivating functional groups. The func matic system. tional groups allow the ionic liquid to passivate the Surface of 0047. In some embodiments of the ionic liquid, the salt has e.g., carbon-based electrodes in an electrochemical device the Formula selected from the group consisting of:
US 2015/0288031 A1 Oct. 8, 2015
0155 triethyl-3-(2-oxo-1,3-dioxolan-4-yl)ethyl)phos oligomers, dimethoxyethane, triglyme, dimethylvinylene phonium bis(trifluoromethylsulfonyl)imide, carbonate, tetraethyleneglycol, dimethyl ether, polyethylene 0156 triethyl-3-(2-oxo-1,3-dioxolan-4-yl)propyl)phos glycols, Sulfones, and gamma-butyrolactone. phonium bis(trifluoromethylsulfonyl)imide, 0170 In some embodiments, the inventive electrolytes 0157 triethyl-3-(2-oxo-1,3-dioxolan-4-yl)methyl)phos further include an electrode stabilizing additive to protect the phonium bis(fluoromethylsulfonyl)imide, electrodes from degradation. Thus, electrolytes of the present 0158 triethyl-3-(2-oxo-1,3-dioxolan-4-yl)ethyl)phos technology can include an electrode stabilizing additive that phonium bis(fluoromethylsulfonyl)imide, can be reduced or polymerized on the Surface of a negative 0159 triethyl-3-(2-oxo-1,3-dioxolan-4-yl)propyl)phos electrode to form a passivation film on the surface of the phonium bis(fluoromethylsulfonyl)imide, negative electrode. Likewise, inventive electrolytes can 0160 triethyl-3-(2-oxo-1,3-dioxolan-4-yl)methyl)phos include an electrode stabilizing additive that can be oxidized phonium bis(oxalato)borate, or polymerized on the surface of the positive electrode to form 0161 triethyl-3-(2-oxo-1,3-dioxolan-4-yl)ethyl)phos a passivation film on the surface of the positive electrode. In phonium bis(oxalato)borate, Some embodiments, electrolytes of the present technology 0162 triethyl-3-(2-oxo-1,3-dioxolan-4-yl)propyl)phos further include mixtures of the two types of electrode stabi phonium bis(oxalato)borate, lizing additives. The additives are typically present at a con 0163 triethyl-3-(2-oxo-1,3-dioxolan-4-yl)methyl)phos centration of about 0.001 to 8 wt %. phonium hexafluorophosphate, 0171 In some embodiments, an electrode stabilizing addi 0164 triethyl-3-(2-oxo-1,3-dioxolan-4-yl)ethyl)phos tive is a substituted or unsubstituted linear, branched or cyclic phonium hexafluorophosphate, and hydrocarbon comprising at least one oxygenatom and at least 0.165 triethyl-3-(2-oxo-1,3-dioxolan-4-yl)propyl)phos one aryl, alkenyl or alkynyl group. The passivating film phonium hexafluorophosphate. formed from such electrode stabilizing additives may also be 0166 In accordance with another aspect, there is provided formed from a substituted aryl compound or a substituted or an electrolyte for use in an energy storage device, the elec unsubstituted heteroaryl compound where the additive com trolyte comprising a room temperature ionic liquid as prises at least one oxygenatom. Alternatively, a combination described herein. of two additives may be used. In some such embodiments, one 0167. In some embodiments, the electrolyte includes a additive is selective for forming a passivating film on the lithium salt in addition to the ionic liquid. A variety of lithium cathode to prevent leaching of metal ions and the other addi salts may be used including for example, LiCFCO: tive can be selective for passivating the anode surface to LiCFCO: LiClO: Li BFI; LiAsF1; LiPF: LiPF prevent or lessen the reduction of metal ions at the anode. (CO): Li PFCO: LiCFSO: LiN(CFSO); LiC 0172 Representative electrode stabilizing additives (CFSO); LiN(SOCFs); lithium alkyl fluorophos include 1,2-divinyl furoate, 1,3-butadiene carbonate, 1-viny phates: LiB(C2O4),l: LiBF2C2O4); LiB12Zr2H); Li laZetidin-2-one, 1-vinylaziridin-2-one, 1-vinylpiperidin-2- BioXoH); or a mixture of any two or more thereof, one, 1 vinylpyrrolidin-2-one, 2,4-divinyl-1,3-dioxane, 2 wherein Z is independently at each occurrence a halogen, is amino-3 vinylcyclohexanone, 2-amino-3-vinylcyclopro an integer from 0 to 12 and j' is an integer from 1 to 10. panone, 2 amino-4-vinylcyclobutanone, 2-amino-5-vinylcy 0168. In some embodiments, the concentration of the clopentanone, 2-aryloxy-cyclopropanone, 2-vinyl-1,2OX lithium salt present in the ionic liquid ranges from about 0.01 aZetidine, 2 vinylaminocyclohexanol, M to about 1.5M, from about 0.05 M to about 1.2 M, or from 2-vinylaminocyclopropanone, 2 vinyloxetane, 2-vinyloxy about 0.4 Mto about 1.0 M. If the concentration of the ionic cyclopropanone, 3-(N-vinylamino)cyclohexanone, 3.5-divi electrolyte salt is less than about 0.01 M, the ionic conduc nyl furoate, 3-vinylazetidin-2-one, 3 vinylaziridin 2 one, 3 tivity of the resulting non-aqueous electrolyte tends to vinylcyclobutanone, 3 vinylcyclopentanone, 3 vinyloxaziri decrease due to an inadequate number of carrier ions in the dine, 3 vinyloxetane, 3-vinylpyrrolidin-2-one, 4.4 divinyl-3 electrolyte. dioxolan 2-one, 4 vinyltetrahydropyran, 5-vinylpiperidin-3- 0169. In some applications of the present electrolyte, such one, allylglycidyl ether, butadiene monoxide, butyl vinyl as a formulation for a lithium ion battery, aprotic solvents are ether, dihydropyran-3-one, divinyl butyl carbonate, divinyl combined with the present ionic liquids to decrease the vis carbonate, divinyl crotonate, divinyl ether, divinyl ethylene cosity and increase the conductivity. Aprotic solvents lack carbonate, divinyl ethylene silicate, divinyl ethylene sulfate, exchangeable protons and include cyclic carbonic acid esters, divinyl ethylene sulfite, divinyl methoxypyrazine, divinyl linear carbonic acid esters, phosphoric acid esters, oligoether methylphosphate, divinyl propylene carbonate, ethyl phos Substituted siloxanes/silanes, cyclic ethers, chain ethers, lac phate, methoxy-o-terphenyl, methyl phosphate, oxetan-2-yl tone compounds, chain esters, nitrile compounds, amide vinylamine, oxiranylvinylamine, vinyl carbonate, vinyl cro compounds, Sulfone compounds and the like. These solvents tonate, vinyl cyclopentanone, vinyl ethyl-2-furoate, vinyl may be used singly, or at least two of them in admixture. ethylene carbonate, vinyl ethylene silicate, vinyl ethylene Examples of aprotic solvents or carriers for forming the elec sulfate, vinyl ethylene sulfite, vinyl methacrylate, vinyl phos trolyte systems include but are not limited to dimethyl car phate, vinyl-2-furoate, vinylcylopropanone, vinylethylene bonate, ethyl methyl carbonate, diethyl carbonate, methyl oxide, B-vinyl-y-butyrolactone, or a mixture of any two or propylcarbonate, ethylpropyl carbonate, dipropylcarbonate, more thereof. In some embodiments the electrode stabilizing bis(trifluoroethyl)carbonate, bis(pentafluoropropyl)carbon additive may be a cyclotriphosphazene that is substituted with ate, trifluoroethyl methyl carbonate, pentafluoroethyl methyl F, alkyloxy, alkenyloxy, aryloxy, methoxy, allyloxy groups, carbonate, heptafluoropropyl methyl carbonate, perfluorobu or combinations thereof. For example, the additive may be a tyl methyl carbonate, trifluoroethyl ethyl carbonate, pen (divinyl)-(methoxy)(trifluoro)cyclotriphosphazene, (trivi tafluoroethyl ethyl carbonate, heptafluoropropyl ethyl car nyl)(difluoro)(methoxy)cyclotriphosphaZene, (vinyl)(meth bonate, perfluorobutyl ethyl carbonate, etc., fluorinated oxy) (tetrafluoro)cyclotriphosphaZene, (aryloxy)(tetrafluoro) US 2015/0288031 A1 Oct. 8, 2015
(methoxy)-cyclotriphosphaZene, (diaryloxy)(trifluoro) derivatives of the foregoing, copolymers of the foregoing, (methoxy)cyclotriphosphaZene compounds, or a mixture of cross-linked and network structures of the foregoing. two or more Such compounds. In some embodiments, the 0.175. The inventive functional ionic liquids and the elec electrode stabilizing additive is vinyl ethylene carbonate, trolytic Solution containing the salt are high in electrical con vinyl carbonate, or 1,2-diphenyl ether, or a mixture of any two ductivity and solubility in organic solvents, and are Suitable or more Such compounds. for use as an electrolytic solution for electrochemical devices. Examples of electrochemical devices are electric double 0173 Other representative electrode stabilizing additives layer capacitor, secondary batteries, Solarcells of the pigment may include compounds with phenyl, naphthyl, anthracenyl, sensitizer type, electrochromic devices, condenser, etc., pyrrolyl, oxazolyl, furanyl, indolyl, carbazolyl, imidazolyl, which are nevertheless not limitative. Especially suitable as orthiophenyl groups. For example, electrodestabilizing addi electrochemical devices are electric double-layer capacitor tives may be aryloxpyrrole, aryloxyethylene Sulfate, aryloxy and secondary batteries such as lithium ion battery. pyrazine, aryloxy-carbazole trivinylphosphate, aryloxy 0176). In yet another aspect, an electrochemical device is ethyl-2-furoate, aryloxy-o-terphenyl, aryloxy-pyridazine, provided that includes a cathode; an anode; and an electrolyte butyl-aryloxy-ether, divinyl diphenyl ether, (tetrahydrofuran including an ionic liquid as described herein. In one embodi 2-yl)-vinylamine, divinyl methoxybipyridine, methoxy-4-vi ment, the electrochemical device is a lithium secondary bat nylbiphenyl, vinyl methoxy carbazole, vinyl methoxypiperi tery. In some embodiments, the secondary battery is a lithium dine, vinyl methoxypyrazine, vinyl methyl carbonate battery, a lithium-ion battery, a lithium-sulfur battery, a allylanisole, vinyl pyridazine, 1-divinylimidazole, lithium-air battery, a sodium ion battery, or a magnesium 3-vinyltetrahydrofuran, divinyl furan, divinyl methoxy furan, battery. In some embodiments, the electrochemical device is divinylpyrazine, vinyl methoxy imidazole, vinylmethoxy an electrochemical cell Such as a capacitor. In some embodi pyrrole, vinyl-tetrahydrofuran, 2,4-divinyl isooxazole, 3.4 ments, the capacitor is an asymmetric capacitor or Superca divinyl-1-methyl pyrrole, aryloxyoxetane, aryloxy-phenyl pacitor. In some embodiments, the electrochemical cell is a carbonate, aryloxy-piperidine, aryloxy-tetrahydrofuran, primary cell. In some embodiments, the primary cell that is a 2-aryl-cyclopropanone, 2-diaryloxy-furoate, 4-allylanisole, lithium/MnO, battery or Li/poly(carbon monofluoride) bat aryloxy-carbazole, aryloxy-2-furoate, aryloxy-crotonate, tery. In some embodiments, the electrochemical cell is a Solar aryloxy-cyclobutane, aryloxy-cyclopentanone, aryloxy-cy cell. clopropanone, aryloxy-cycolophosphaZene, aryloxy-ethyl 0177 Suitable cathodes include those such as, but not ene silicate, aryloxy-ethylene sulfate, aryloxy-ethylene limited to, a lithium metal oxide, spinel, olivine, carbon Sulfite, aryloxy-imidazole, aryloxy-methacrylate, aryloxy coated olivine, LiFePO, LiCoO, LiNiO, LiNi phosphate, aryloxy-pyrrole, aryloxyquinoline, diaryloxycy aCoMet Oa. LiMnosNioso, LiMno CoosNio O. clotriphosphaZene, diaryloxy ethylene carbonate, diaryloxy LiMn2O4, LiFeO2, Li Ni,MneCoMet's O. F., A.B., furan, diaryloxy methyl phosphate, diaryloxy-butyl carbon (XO), (NASICON), vanadium oxide, lithium peroxide, sul ate, diaryloxy-crotonate, diaryloxy-diphenyl ether, diary fur, polysulfide, a lithium carbon monofluoride (also known loxy-ethyl silicate, diaryloxy-ethylene silicate, diaryloxy as LiCFX), or mixtures of any two or more thereof, where Met ethylene sulfate, diaryloxyethylene sulfite, diaryloxy-phenyl is Al, Mg, Ti, B. Ga, Si, Mn, or Co; Met' is Mg., Zn, Al. Ga, B. carbonate, diaryloxy-propylene carbonate, diphenyl carbon Zr, or Ti; A is Li, Ag, Cu, Na, Mn, Fe, Co, Ni, Cu, or Zn; B is ate, diphenyl diaryloxy silicate, diphenyl divinyl silicate, Ti,V, Cr, Fe, or Zr; X is P, S, Si, W, or Mo; 0
tion temperature of the separator and can accordingly -continued enhance the high temperature performance of the separator. Additionally, or alternatively, the separator can be a shut Me down separator. The shut-down separator can have a trigger (B-YSi-O-Si-Me TFSI temperature above 130°C. to permit the electrochemical cells Me Me to operate attemperatures up to 130° C. o i-ye y 0180. One skilled in the art will readily realize that all N N + Si-O-Si-Me -> ranges discussed can and do necessarily also describe all Me1 Na Subranges therein for all purposes and that all Such Subranges Me Me also form part and parcel of this present technology. Any listed range can be easily recognized as Sufficiently describ LTFSI ing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a Me Me non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and Me1 NNéN1. N Si-O-Si-Me upper third, etc. Me Me O 0181 All publications, patent applications, issued patents, TFSI and other documents referred to in this specification are herein incorporated by reference as if each individual publi ?—\ * \ cation, patent application, issued patent, or other document N N + - Me -> was specifically and individually indicated to be incorporated M1 Na I by reference in its entirety. Definitions that are contained in y-\ O N N O text incorporated by reference are excluded to the extent that LTFSI they contradict definitions in this disclosure. Me1 n-is-- Br -e- 0182. The present technology, thus generally described, O will be understood more readily by reference to the following y \ O N. N. | examples, which are provided by way of illustration and are Me1 NaN-1N -Me not intended to be limiting of the present technology. e || TFSI O O O EXAMPLES C) II e II TFSI = FC-S-N-S-CF | | 0183 Ionic liquids of the present technology may be syn O O thesized by various methods known in the art. For example, to prepare cationic phosphonium, imidazolium, pyridinium, or quaternary ammonium-based ionic liquids, the correspond ing phosphite, 1-substituted imidazole, pyridine, or tertiary Example 1 amine may be reacted with a suitable electrophile under alky lating conditions and then reacted with a suitable lithium salt Synthesis of IL1-I (i.e., LiX where X is defined as herein). Suitable electrophiles include R groups (as defined herein) bearing, e.g., a halide, 0.184 A mixture consisting of equimolar quantities of tri mesylate, triflate or similar leaving group. By way of non ethylphosphine (20 g, 0.17 mmol) and ICHSiMeOSiMe. limiting example, Scheme 1 shows the synthesis of represen (48 g., 0.17 mmol) was stirred at room temperature for 24 h. tative ionic liquids of the present technology. Preparation of The resulting solid was washed three times with hexane then oxazolium and thizolium-based ionic liquids is similar, but diethyl ether and placed under vacuum to afford IL1-I. Yield: requires deprotonation of the corresponding oxazole or thia 49 g (72%). "H NMR (CDC1) is shown in FIG. 1. Zole with an appropriate base, e.g., an alkali metal hydride prior to reaction with the electrophile. Example 2 Synthesis of IL1-TFSI Scheme1. Representative synthesis of functionalized ionic liquids IL1-I, 0185. A solution of IL1-I (48.8 g., 0.16 mol) in water (300 IL1-TFSI, IL2-I, IL2-TFSI, IL3-Brand IL3-TFSI. mL) was treated with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) (44.6 g., 0.17 mol). The solution was allowed |- M Me to stir at room temperature for a period of 12 hat which time (Et)3P + -o-, -u -- the room temperature ionic liquid IL1-TFSI formed a second layer at the bottom of the flask. IL1-TFSI was dissolved in Me Me CHCl, and washed with deionized water until no residual I (Et)3PGE) Me Me in the rinse can be detected by 0.1 M AgNO, solution. The 9 LiTFSI CHC1 was stirred with carbon black and Al-O for 2 hand Si-O-Si-Me I - filtered. The crude product was dried under high vacuum Me Me (0.02 torr) at 100° C. for 16 h. Yield: 50 g (75%). "H NMR (CDC1) is shown in FIG. 1 US 2015/0288031 A1 Oct. 8, 2015
Example 3 Example 7 Synthesis of IL2-I Comparative Example, Li/MCMB Half Cell Charge Discharge Profiles 0186 Freshly distilled ICHSiMeOSiMe (48.7 g, 0.16 (0190. Li/MCMB half cell charge discharge profiles were mol) was added in one portion to a 500 mL thick walled glass measured using 0.8M LiTFSI in conventional tetraethylphos reactor containing 1-methyl imidazole (13.9 g, 0.16 mol) phonium bis(trifluoromethanesulfonyl)imide ionic liquid. equipped with a magnetic stirrer and a water cooled con See FIG. 4. The charging curve showed that no regular inter denser. The solution was stirred for 16 h at 100° C. The calation of Li was observed. Instead, it showed a plateau at Solution was cooled down to room temperature and stirred higher potential at 0.5V vs Li'/Li indicating ionic liquid co with hexane. The precipitate was filtered and washed several intercalation/reduction reaction on the MCMB electrode. times with hexane and diethyl ether, dried overnight under vacuum. Yield for IL2-I: 60.5 g (95%). "H NMR (CDC1) is Example 8 shown in FIG. 2. Li/MCMB Half Cell Charge Discharge Profiles, FIG. Example 4 5 0191 Li/MCMB half cell charge discharge profiles using Synthesis of IL2-TFSI 0.8M LiTFSI in triethyl-(methylenepentamethyldisiloxane) phosphonium bis(trifluoromethylsulfonyl)imide (IL1-TFSI). 0187. A solution of lithium bis(trifluoromethanesulfonyl) The 1 cycle charging curve showed that a solid electrolyte imide (46.4g, 0.16 mol) in 100 mL of HO was added drop interphase formation (SEI) starting at 0.8V. The 2" cycle and wise to a solution of IL2-I (59.8 g., 0.16 mol) in 150 mL of Subsequent cycles are showed regular lithium interaction and HO. The solution was stirred at ambient temperature for 12 de-intercalation on the MCMB electrode. This is a good h. Dichloromethane (250 mL) was added, and the mixture example that introduction of Some functional ionic liquid was transferred to a separatory funnel. The lower phase (ionic (Si-O Si unit in this case) has SEI formation capability liquid--CHCl) was collected. The ionic liquid was purified and the new IL is completely compatible with graphite based through a short alumina column, and the CH2Cl removed on material. a rotary evaporator. The resultant hydrophobic liquid was washed three times with 150 mL of HO and dried for 12 hat Example 9 100° C. under vacuum to afford IL2-TFSI (69 g, 80% yield) as a pale yellow liquid. "H NMR (CDC1) is shown in FIG. 2 dOdV Profile of Li/MCMB Half Cell, FIG. 6 Example 5 (0192 dOdV profile of Li/MCMB half cell using 0.8M LiTFSI in triethyl-(methylenepentamethyldisiloxane)phos phonium bis(trifluoromethylsulfonyl)imide (IL1-TFSI). Synthesis of IL3-Br dOdV curves clearly shows the reduction of the functional ionic liquid passiviating the Surface of the graphite electrode. 0188 BrCHCHSOMe (14.3g, 0.076 mol) was added in This self SEI formation capability can provide a easy solution one portion to a 250 mL round bottom flask containing 1-me to address the issue of IL compatibility with graphite elec thyl imidazole (6.3 g, 0.076 mol) equipped with a magnetic trode. stirrer and a water cooled condenser. The solution was stirred for 16 hat 100° C. The oil residue was treated with CHCN to Example 10 precipitate the product. The precipitate was filtered and washed several times with pre-cooled CHCN, dried over Comparative Example, LiNios Coos AloosO/Li night under vacuum. Yield for IL2-I: 12.4 g (60%). "H NMR Half Cell Charge Discharge Profile, FIG. 7 (DMSO d) is shown in FIG. 3. 0193 LiNiCoos Aloo O/Li half cell charge discharge Example 6 cycling performance using conventional 0.8M LiTFSI in tet raethylphosphonium bis(trifluoromethanesulfonyl)imide ionic liquid. The conventional IL can not provide high effi Synthesis of IL3-TFSI ciency in the cycling test of the positive half cell. 0189 A solution of lithium bis(trifluoromethanesulfonyl) Example 11 imide (13.2g, 0.046 mol) in 60 mL of HO was added drop wise to a solution of IL2-I (12.4g, 0.046 mol) in 100 mL of LiNiosCoos AloosO/Li Half Cell Charge Dis HO. The solution was stirred at ambient temperature for 12 charge Profile, FIG. 8 h. Methylene dichloride (500 mL) was added, and all was transferred to a separatory funnel. The lower phase (ionic 0194 LiNiCoos Aloo O/Li half cell charge discharge liquid--CH2Cl2) was collected. Ionic liquid was purified cycling performance using 0.8M LiTFSI in triethyl-(methyl through a short alumina column, and the CHCl removed on enepentamethyldisiloxane)phosphonium bis(trifluorometh a rotary evaporator. The resultant hydrophobic liquid was ylsulfonyl)imide (IL1-TFSI) at 55° C. The inventive func washed three times with 150 mL of H2O and dried for 12 hat tional ionic liquid can provide excellent compatibility with 100° C. under vacuum to afford IL3-TFSI (10.2g, 53% yield) lithium oxide cathode material, which is impossible for the as a colorless liquid. "H NMR (CDCN) is shown in FIG. 3. conventional IL as indicated in FIG. 7. US 2015/0288031 A1 Oct. 8, 2015
Example 12 R" is a C alkylene group; R" is an alkyl group; FIG.9 R, R2, and R are independently at each occurrence 0.195 MCMB/Li half cell charge discharge cycling per alkyl, cycloalkyl, aryl, heteroaryl, aralkyl, or het formance using conventional 0.8M LiTFSI in tetraethylphos eroaralkyl, or any two of R, R2, and Rs join together phonium bis(trifluoromethanesulfonyl)imide ionic liquid. to form a C-C cycloalkylene group: Using conventional ionic liquid, the capacity of the MCMB R. Rs, and R are independently at each occurrence H. half cell dramatically decreases with cycle number. alkyl, cycloalkyl, aryl, heteroaryl, aralkyl, or het Example 13 eroaralkyl; each X independently comprises boron tetrafluoride, Li/MCMB Half Cell Charge Discharge Profiles, FIG. aluminate, bis(oxalato)borate, difluoro(oxalate)bo 10 rate, phosphorus hexafluoride, alkyl Sulfonate, fluo roalkyl sulfonate, aryl sulfonate, bis(alkylsulfonyl) 0196. MCMB/Li half cell charge discharge cycling per amide, perchlorate, bis(fluoroalkylsulfonyl)amide, formance using 0.8M LiTFSI in triethyl-(methylenepentam bis(arylsulfonyl)amide, alkyl fluorophosphate, (fluo ethyldisiloxane)phosphonium bis(trifluoromethylsulfonyl)- roalkylsulfonyl)(fluoroalkylcarbonyl)amide, halide, imide (IL1-TFSI). The functionalized ionic liquid showed nitrate, nitrite, Sulfate, hydrogen Sulfate, alkylsulfate, reversible charge/discharge performance. aryl sulfate, carbonate, bicarbonate, perfluoroalkyl group Substituted with carboxylate, phosphate, Example 14 hydrogen phosphate, dihydrogen phosphate, MCMB/LiNisNios Alo-O, Full Cell Charge Dis hypochlorite, an anionic site of a cation-exchange charge Profiles, FIG. 11 resin, or a mixture of any two or more thereof; n is an integer from 1 to 4; and (0197) MCMB/LiNios NicsAl-O, full cell charge dis charge cycling performance using conventional 0.8M LiTFSI m is an integer from 0 to 10. in tetraethylphosphonium bis(trifluoromethanesulfonyl) 2. The electrochemical device of claim 1 that is a lithium imide ionic liquid. Poor capacity retention was observed for secondary battery. the conventional ionic liquid in a full lithium ion cell. 3. The electrochemical device of claim 2 wherein the sec ondary battery is a lithium battery, a lithium-ion battery, a Example 15 lithium-sulfur battery, a lithium-air battery, a sodium ion battery, or a magnesium battery. MCMB/LiNissNicsAllosQ, Full Cell Charge 4. The electrochemical device of claim 1, wherein each Ris Discharge Profiles, FIG. 12 independently (R') (OCH2CH)—(OR"), —CHSiCR") 0198 MCMB/LiNissCoos AloosO full cell charge dis OSi(R")OSi(R"), or a C- alkyl group substituted with a charge cycling performance using 0.8M LiTFSI in triethyl Sulfone group. (methylenepentamethyldisiloxane)phosphonium bis(trifluo 5. The electrochemical device of claim 1, wherein R. R. romethylsulfonyl)imide (IL1-TFSI). Much improved cycling and R are independently at each occurrence C-C alkyl, performance was achieved by using the functionalized ionic hydroxyalkyl, or haloalkyl group. liquid IL1-TFSI. 6. The electrochemical device of claim 1, wherein R is a What is claimed is: C-C alkyl. 1. An electrochemical device comprising: a cathode: 7. The electrochemical device of claim 1, wherein R, Rs. an anode; and and Rare each H. an electrolyte comprising an ionic liquid represented as: 8. The electrochemical device of claim 1, wherein X is ICF CO; CFCO; CIOI: BFI; AsFI; PF; |PF (CO); PFCO; CFSO; N(CFSO); R R R6 Rs C(CFSO); N(SOCFs); an alkyl fluorophosphate: B(CO); BFCO: |B12Y-H.I. BoYo Hell: X X or }( X; or a mixture of any two or more thereof, wherein Y is inde R R N. N pendently at each occurrence a halogen, k is an integer from R1 y R 0 to 12, and k" is an integer from 1 to 10. 9. The electrochemical device of claim 1, wherein the ionic R4 liquid has the Formula: wherein: R is selected from the group consisting of CHSiCR") OSi(R").O. Si(R") —(R')—(OCHCH)— (OR"), a C-C cyclic carbonate, a Sulfolane, an oxalic borate group, a maleic anhydride group, a suc cinic anhydride group, and a C-C alkyl group Sub stituted with a substituent selected from an isocyan 10. The electrochemical device of claim 9, wherein R is ate, sulfone, sulfolane. —OCOR", C-C cyclic —(CH)—(OCH2CH)—(OCH), —CHSiCCH)OSi carbonate, or oxalic borate group; (CH)OSi(CH), or —(CH2)SOCH.
US 2015/0288031 A1 Oct. 8, 2015 12
17. The electrochemical device of claim 1, wherein a con centration of the lithium salt in the ionic liquid is from about 0.01 M to about 1.5 M. 18. The electrochemical device of claim 1, wherein the electrolyte further comprises an aprotic solvent. 19. The electrochemical device of claim 1, wherein the electrolyte further comprises an aprotic gel polymer carrier/ solvent. 20. The electrochemical device of claim 1, wherein the electrolyte further comprises an electrode stabilizing addi tive.