ANODE-LESS LITHIUM ION BATTERY

Abstract

The present invention pertains to an anode-less lithium ion battery comprising a) a cathode comprising a cathode current collector and a cathode electro-active material on the cathode current collector; b) an anode current collector; c) a liquid electrolyte composition between the a) cathode and the b) anode current collector; and d) a separator, wherein the c) liquid electrolyte composition comprises i) at least 70% by volume (vol %) of a solvent mixture with respect to the total volume of the electrolyte composition, comprising at least one fluorinated ether compound and at least one non-fluorinated ether compound, and ii) at least one lithium salt.

Claims

1. An anode-less lithium ion battery comprising: a) a cathode comprising a cathode current collector and a cathode electro-active material on the cathode current collector; b) an anode current collector; c) a liquid electrolyte composition between the a) cathode and the b) anode current collector; and d) a separator, wherein the c) liquid electrolyte composition comprises i) at least 70% by volume (vol %) of a solvent mixture with respect to the total volume of the electrolyte composition, comprising at least one fluorinated ether compound and at least one non-fluorinated ether compound, and ii) at least one lithium salt.

2. The anode-less lithium ion battery according to claim 1, wherein the solvent mixture comprises: from 60 to 90 vol % of at least one fluorinated ether compound; and from 10 to 40 vol % of at least one non-fluorinated ether compound, with respect to the total volume of the solvent mixture.

3. The anode-less lithium ion battery according to claim 1, wherein the solvent mixture comprises: from 80 to 90 vol % of at least one fluorinated ether compound; and from 10 to 20 vol % of at least one non-fluorinated ether compound, with respect to the total volume of the solvent mixture.

4. The anode-less lithium ion battery according to claim 1, wherein the fluorinated ether compound has a chemical formula of C.sub.aF.sub.bH.sub.cO.sub.d, wherein a, b, c and d are all integers, d is an integer from 1 to 3, a is an integer from 3 to 10, and 2*(a+1)=b+c.

5. The anode-less lithium ion battery according to claim 1, wherein the fluorinated ether compound comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and CF.sub.2HCF.sub.2—OCH.sub.2CH.sub.2O—CF.sub.2CF.sub.2H.

6. The anode-less lithium ion battery according to claim 1, wherein the non-fluorinated ether compound comprises dimethoxyethane (DME), 1,3-dioxolane (DOL), dibutyl ether, tetraethylene glycol dimethyl ether (TEGME), diethylene glycol dimethyl ether (DEGME), diethylene glycol diethyl ether (DEGDEE), polyethylene glycol dimethyl ether (PEGDME), 2-methyltetrahydrofuran and tetrahydrofuran (THF).

7. The anode-less lithium ion battery according to claim 1, wherein the cathode electro-active material is selected from the group consisting of LiMQ.sub.2, wherein M is at least one metal selected from Co, Ni, Fe, Mn, Cr and V and Q is o or S; LiNi.sub.xCo.sub.1-xO.sub.2 (0<x<1); spinel-structured LiMn.sub.2O.sub.4; lithium-nickel-manganese-cobalt-based metal oxide of formula LiNi.sub.xMn.sub.yCo.sub.zO.sub.2 (x+y+z=1), lithium-nickel-cobalt-aluminum-based metal oxide of formula LiNi.sub.xCo.sub.yAl.sub.zO.sub.2 (x+y+z=1), and LiFePO.sub.4.

8. The anode-less lithium ion battery according to claim 1, wherein the cathode electro-active material is loaded onto the cathode current collector to have an areal capacity between 1.0 mAh/cm.sup.2 and 10.0 mAh/cm.sup.2.

9. The anode-less lithium ion battery according to claim 1, wherein the lithium salt is selected from the group consisting of: a) LiN(SO.sub.2F).sub.2 (lithium bis(fluorosulfonyl)imide: LiFSI), LiN(CF.sub.3SO.sub.2).sub.2(lithium bis(trifluoromethanesulfonyl)imide: LiTFSI), LiPF.sub.6, LiBF.sub.4, LiClO.sub.4, Li bis(oxalato)borate (LiBOB), LiCF.sub.3SO.sub.3, LiF, LiCl, LiBr, LiI, LiN(C.sub.2F.sub.5SO.sub.2).sub.2, LiN(CF.sub.3SO.sub.2)(R.sub.FSO.sub.2), wherein R.sub.F is C.sub.2F.sub.5, C.sub.4F.sub.9 or CF.sub.3OCF.sub.2CF.sub.2, LiAsF.sub.6, LiC(CF.sub.3SO.sub.2).sub.3, Li.sub.2S; ##STR00007## wherein R′.sub.F is selected from the group consisting of F, CF.sub.3, CHF.sub.2, CH.sub.2F, C.sub.2HF.sub.4, C.sub.2H.sub.2F.sub.3, C.sub.2H.sub.3F.sub.2, C.sub.2F.sub.5, C.sub.3F.sub.7, C.sub.3H.sub.2F.sub.5, C.sub.3H.sub.4F.sub.3, C.sub.4F.sub.9, C.sub.4H.sub.2F.sub.7, C.sub.4H.sub.4F.sub.5, CSF.sub.11, C.sub.3F.sub.5OCF.sub.3, C.sub.2F.sub.4OCF.sub.3, C.sub.2H.sub.2F.sub.2OCF.sub.3 and CF.sub.2OCF.sub.3; and c) combinations thereof.

10. The anode-less lithium ion battery according to claim 1, wherein a concentration of the lithium salt is from 1 M to 8 M.

11. The anode-less lithium ion battery according to claim 1, wherein the d) separator is a porous polymeric material comprising at least one material selected from the group consisting of polyester polyphenylene sulphide, polyacetal, polyamide, polycarbonate, polyimide, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, polyethylene oxide, polyacrylonitrile, polyolefin, or mixtures thereof.

12. The anode-less lithium ion battery according to claim 1, further comprising from 0.05 to 10.0 wt % of at least one film-forming additive, with respect to the total weight of the liquid electrolyte composition.

13. The anode-less lithium ion battery according to claim 12, wherein the film-forming additive is selected from the group consisting of cyclic sulphite and sulfate compounds comprising 1,3-propanesultone (PS), ethylene sulphite (ES) and prop-1-ene-1,3-sultone (PES); sulfone derivatives comprising dimethyl sulfone, tetramethylene sulfone (also known as sulfolane), ethyl methyl sulfone and isopropyl methyl sulfone; nitrile derivatives comprising succinonitrile, adiponitrile, and glutaronitirle; and lithium nitrate (LiNO.sub.3); boron derivatives salt comprising lithium difluoro oxalato borate (LiDFOB), lithium fluoromalonato (difluoro)borate (LiFMDFB), vinyl acetate, biphenyl benzene, isopropyl benzene, hexafluorobenzene, tris(trimethylsilyl)phosphate, triphenyl phosphine, ethyl diphenylphosphinite, triethyl phosphite, tris(2,2,2-trifluoroethyl) phosphite, maleic anhydride, vinylene carbonate, vinyl ethylene carbonate, mono-fluorinated ethylene carbonate (4-fluoro-1,3-dioxolan-2-one), difluorinated ethylene carbonate, cesium bis(triflulorosulfonyl)imide (CsTFSI), cesium fluoride (CsF), and mixtures thereof.

14. The anode-less lithium ion battery according to claim 12, wherein the film-forming additive is an ionic liquid.

15. The anode-less lithium ion battery according to claim 14, wherein the ionic liquid is selected from the group consisting of N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl) imide (PYR13FSI), N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl) imide (PYR14FSI), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR13TFSI), and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR14TFSI).

Description

BRIEF DESCRIPTION OF DROWNINGS

[0029] FIG. 1 shows cycle retention (%) of NCM523/Cu cells with electrolyte compositions of E1-E2 and CE1-CE4 at 3.6˜4.2V (0.2 C/0.5 C).

[0030] FIG. 2 shows Coulombic efficiency vs. cycle number of NCM523/Cu cells with electrolyte compositions of E1-E2 and CE1-CE4 at 3.6˜4.2V (0.2 C/0.5 C).

DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0031] Throughout this specification, unless the context requires otherwise, the word “comprise” or “include”, or variations such as “comprises”, “comprising”, “includes”, including” will be understood to imply the inclusion of a stated element or method step or group of elements or method steps, but not the exclusion of any other element or method step or group of elements or method steps. According to preferred embodiments, the word “comprise” and “include”, and their variations mean “consist exclusively of”.

[0032] As used in this specification, the singular forms “a”, “an” and “the” include plural aspects unless the context clearly dictates otherwise. The term “and/or” includes the meanings “and”, “or” and also all the other possible combinations of the elements connected to this term.

[0033] The term “between” should be understood as being inclusive of the limits.

[0034] As used herein, “alkyl” groups include saturated hydrocarbons having one or more carbon atoms, including straight-chain alkyl groups, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, cyclic alkyl groups (or “cycloalkyl” or “alicyclic” or “carbocyclic” groups), such as cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl, branched-chain alkyl groups, such as isopropyl, tert-butyl, sec-butyl, and isobutyl, and alkyl-substituted alkyl groups, such as alkyl-substituted cycloalkyl groups and cycloalkyl-substituted alkyl groups.

[0035] The term “aliphatic group” includes organic moieties characterized by straight or branched-chains, typically having between 1 and 18 carbon atoms. In complex structures, the chains may be branched, bridged, or cross-linked. Aliphatic groups include alkyl groups, alkenyl groups, and alkynyl groups.

[0036] As used herein, the terminology “(C.sub.n−C.sub.m)” in reference to an organic group, wherein n and m are integers, respectively, indicates that the group may contain from n carbon atoms to m carbon atoms per group.

[0037] Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a temperature range of about 120° C. to about 150° C. should be interpreted to include not only the explicitly recited limits of about 120° C. to about 150° C., but also to include sub-ranges, such as 125° C. to 145° C., 130° C. to 150° C., and so forth, as well as individual amounts, including fractional amounts, within the specified ranges, such as 122.2° C., 140.6° C., and 141.3° C., for example.

[0038] Unless otherwise specified, in the context of the present invention the amount of a component in a composition is indicated as the ratio between the volume of the component and the total volume of the composition multiplied by 100, i.e., % by volume (vol %) or as the ratio between the weight of the component and the total weight of the composition multiplied by 100, i.e., % by weight (wt %).

[0039] The constituents of the anode-less lithium ion battery comprising a) a cathode comprising a cathode current collector and a cathode electro-active material on the cathode current collector; b) an anode current collector; c) a liquid electrolyte composition; and d) a separator according to the present invention are described hereinafter in details. It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed. Accordingly, various changes and modifications described herein will be apparent to those skilled in the art. Moreover, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

[0040] The present invention relates to an anode-less lithium ion battery comprising:

[0041] a) a cathode comprising a cathode current collector and a cathode electro-active material on the cathode current collector;

[0042] b) an anode current collector;

[0043] c) a liquid electrolyte composition between the a) cathode and the b) anode current collector; and

[0044] d) a separator,

[0045] wherein the c) liquid electrolyte composition comprises i) at least 70% by volume (vol %) of a solvent mixture with respect to the total volume of the electrolyte composition, comprising at least one fluorinated ether compound and at least one non-fluorinated ether compound, and ii) at least one lithium salt.

[0046] In one embodiment, the solvent mixture according to the present invention comprises [0047] from 60 to 90 vol % of at least one fluorinated ether compound; and [0048] from 10 to 40 vol % of at least one non-fluorinated ether compound, with respect to the total volume of the solvent mixture.

[0049] In another embodiment, the solvent mixture according to the present invention comprises [0050] from 80 to 90 vol % of at least one fluorinated ether compound; and [0051] from 10 to 20 vol % of at least one non-fluorinated ether compound, with respect to the total volume of the solvent mixture.

[0052] In one embodiment, the solvent mixture according to the present invention is free from an organic carbonate.

[0053] Non-limiting examples of the organic carbonate include, notably, ethylene carbonate (1,3-dioxolan-2-one), propylene carbonate, 4-methylene-1,3-dioxolan-2-one, 4,5-dimethylene-1,3-dioxolan-2-one, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, propyl butyl carbonate, dibutyl carbonate, di-tert-butyl carbonate, butylene carbonate, mono- and difluorinated propylene carbonate, mono- and difluorinated butylene carbonate, 3,3,3-trifluoropropylene carbonate, fluorinated dimethyl carbonate, fluorinated diethyl carbonate, fluorinated ethyl methyl carbonate, fluorinated dipropyl carbonate, fluorinated dibutyl carbonate, fluorinated methyl propyl carbonate, and fluorinated ethyl propyl carbonate.

[0054] In the present invention, the term “fluorinated ether compound” is intended to denote an ether compound, wherein at least one hydrogen atom is replaced by fluorine. One, two, three or a higher number of hydrogen atoms may be replaced by fluorine.

[0055] In the present invention, the fluorinated ether compound comprises fluorinated mono-ether compounds, fluorinated di-ether compounds and fluorinated tri-ether compounds.

[0056] In one embodiment, the fluorinated ether compound according to the present invention is an aliphatic compound.

[0057] In one embodiment, the fluorinated ether compound has a chemical formula of C.sub.aF.sub.bH.sub.cO.sub.d, wherein a, b, c and d are all integers, d is an integer from 1 to 3, a is an integer from 3 to 10, preferably from 4 to 7, and 2*(a+1)=b+c.

[0058] In a preferred embodiment, the fluorinated ether compound is selected from the group consisting of:

[0059] i) 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,1,3,3-tetrafluoro-1-(1,1,2,2-tetrafluoroethoxy) propane, 1,1,1,3,3-pentafluoro-3-(2,2,2-trifluoroethoxy) propane, 1,1,1,3,3-pentafluoro-3-(1,1,3,3,3-pentafluoropropoxy)propane, 1,1′-oxybis(1,1,2,2-tetrafluoroethane), 1,1,1,3,3-pentafluoro-3-methoxy-2-(trifluoromethyl) propane, 1,1,1,3,3-pentafluoro-3-(fluoromethoxy)-2-(trifluoromethyl)propane, 2,2-difluoro-2-methoxy-1,1-bis(trifluoromethyl)ethane, 2-(ethoxy difluoromethyl)-1,1,1,3,3,3-hexafluoropropane, 2-(difluoropropoxy methyl)-1,1,1,3,3,3-hexafluoropropane, 1,1-bis(difluoromethoxy)-1,2,2,2-tetrafluoroethane, 1,1,2,2-tetrafluoro-3-(1,1,2,2-tetrafluoroethoxy) propane, 1-(2,2-difluoroethoxy)-1,1,2,3,3,3-hexafluoropropane, 1,1,2,2,3-pentafluoro-3-(1,1,2,2-tetrafluoroethoxy)propane, 1-(3,3-difluoropropoxy)-1,1,2,3,3,3-hexafluoropropane, 1-[difluoro(1,1,2,2-tetrafluoroethoxy)methoxy]-1,1,2,2,2-pentafluoroethane, 1,1′-[(difluoromethylene)bis(oxy)]bis(1,1,2,2,2-pentafluoroethane), 1,1,1,3,3,3-hexafluoro-2-fluoromethoxymethoxy propane, pentafluoro[1,2,2,2-tetrafluoro (trifluoromethoxy)ethoxy]ethane, 1,1,2,3,3-pentafluoro-1,3-dimethoxypropane, 1,1,2,2,3,3-hexafluoro-1-methoxy-3-trifluoromethoxypropane, 1,1′-[(difluoromethylene)bis(oxy)]-bis(2,2,2-trifluoroethane), 1,2-bis(difluoromethoxy)-1,1,2,2-tetrafluoroethane, [2-(difluoromethoxy)-1,1,2,2-tetrafluoroethoxy] difluoromethane, 1-[difluoro(trifluoromethoxy)methoxy]-1,1,2,2-tetrafluoro-2-methoxyethane, 1-(difluoromethoxymethoxy)-1,1,2,2-tetrafluoro-2-(trifluoromethoxy)ethane, 1-[(difluoromethoxy)difluoromethoxy]-1,1,2,2-tetrafluoro-2-methoxyethane, and 1-(difluoromethoxy)-2-[(difluoromethoxy)difluoromethoxy]-1,1,2,2-tetrafluoroethane;

[0060] ii) chemical compounds represented by the general formula (A),

##STR00001##

[0061] wherein X is H or F; and

[0062] iii) mixtures thereof.

[0063] In a more preferred embodiment, the fluorinated ether compound comprises 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and CF.sub.2HCF.sub.2—OCH.sub.2CH.sub.2O—CF.sub.2CF.sub.2H.

[0064] In the present invention, the term “non-fluorinated ether compound” is intended to denote an ether compound, wherein no fluorine atom is present.

[0065] Non-limitative examples of suitable non-fluorinated ether compounds according to the present invention include, notably, the followings: [0066] aliphatic, cycloaliphatic or aromatic ether, more particularly, dibutyl ether, dipentyl ether, diisopentyl ether, dimethoxyethane (DME), 1,3-dioxolane (DOL), tetrahydrofuran (THF), 2-methyltetrahydrofuran, and diphenyl ether; [0067] glycol ethers, such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether (DEGME), ethylene glycol diethyl ether, diethylene glycol diethyl ether (DEGDEE), tetraethylene glycol dimethyl ether (TEGME), polyethylene glycol dimethyl ether (PEGDME); [0068] glycol ether esters, such as ethylene glycol methyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate;

[0069] In a preferred embodiment, the non-fluorinated ether compound according to the present invention comprises dimethoxyethane (DME), 1,3-dioxolane (DOL), dibutyl ether, tetraethylene glycol dimethyl ether (TEGME), diethylene glycol dimethyl ether (DEGME), diethylene glycol diethyl ether (DEGDEE), polyethylene glycol dimethyl ether (PEGDME), 2-methyltetrahydrofuran and tetrahydrofuran (THF).

[0070] In a more preferred embodiment, the non-fluorinated ether compound is a mixture of DME and DOL.

[0071] In a more preferred embodiment, the non-fluorinated ether compound is DME.

[0072] In the present invention, the term “anode-less lithium ion battery” is intended to denote, in particular, the lithium ion battery which does not include an anode electro-active material on the anode current collector when the battery is assembled and before the first charge. After the first charge, the anode-less lithium ion battery comprises either a lithium metal thin layer or a lithium alloy thin layer on the anode current collector. That is, while the anode-less lithium ion battery has a negative electrode, the term “anode-less” is used because when manufactured a distinct anode electro-active material is not present in the lithium ion battery.

[0073] In the present invention, the term “anode” is intended to denote, in particular, the electrode of an electrochemical cell, where oxidation occurs during discharging.

[0074] In the present invention, the term “cathode” is intended to denote, in particular, the electrode of an electrochemical cell, where reduction occurs during discharging.

[0075] In the present invention, the nature of the “current collector” depends on whether the electrode thereby provided is either a cathode or anode. Should the electrode of the invention be a cathode, the current collector typically comprises, preferably consists of at least one metal selected from the group consisting of Aluminium (Al), Nickel (Ni), Titanium (Ti), and alloys thereof, preferably Al.

[0076] Should the electrode of the invention be an anode, the current collector typically comprises, preferably consists of at least one metal selected from the group consisting of Lithium (Li), Sodium (Na), Zinc (Zn), Magnesium (Mg), Copper (Cu) and alloys thereof, preferably Cu.

[0077] In the present invention, the term “electro-active material” is intended to denote an electro-active material that is able to incorporate or insert into its structure and substantially release therefrom lithium ions during the charging phase and the discharging phase of a battery.

[0078] In the case of forming a cathode for an anode-less lithium ion battery, the cathode electro-active material is not particularly limited. It may comprise a composite metal chalcogenide of formula LiMQ.sub.2, wherein M is at least one metal selected from transition metals such as Co, Ni, Fe, Mn, Cr, and V and Q is a chalcogen such as 0 or S. Among these, it is preferred to use a lithium-based composite metal oxide of formula LiMO.sub.2, wherein M is the same as defined above. Preferred examples thereof may include LiCoO.sub.2, LiNiO.sub.2, LiNi.sub.xCo.sub.1-xO.sub.2 (0<x<1), and spinel-structured LiMn.sub.2O.sub.4. Another preferred examples thereof may include lithium-nickel-manganese-cobalt-based metal oxide of formula LiNi.sub.xMn.sub.yCo.sub.zO.sub.2 (x+y+z=1, referred to as NMC), for instance LiNi.sub.1/3Mn.sub.1/3Co.sub.1/3O.sub.2, LiNi.sub.0,6Mn.sub.0,2Co.sub.0,2O.sub.2, and lithium-nickel-cobalt-aluminum-based metal oxide of formula LiNi.sub.xCo.sub.yAl.sub.zO.sub.2 (x+y+z=1, referred to as NCA), for instance LiNi.sub.0,8Co.sub.0,15Al.sub.0,05O.sub.2.

[0079] As an alternative, still in the case of forming a cathode for an anode-less lithium ion battery, the cathode electro-active compound may comprise a lithiated or partially lithiated transition metal oxyanion-based electro-active material of formula M.sub.1M.sub.2(JO.sub.4).sub.fE.sub.1-f, wherein M.sub.1 is lithium, which may be partially substituted by another alkali metal representing less that 20% of the M.sub.1 metals, M.sub.2 is a transition metal at the oxidation level of +2 selected from Fe, Mn, Ni or mixtures thereof, which may be partially substituted by one or more additional metals at oxidation levels between +1 and +5 and representing less than 35% of the M.sub.2 metals, including 0, JO.sub.4 is any oxyanion wherein J is either P, S, V, Si, Nb, Mo or a combination thereof, E is a fluoride, hydroxide or chloride anion, f is the molar fraction of the JO.sub.4 oxyanion, generally comprised between 0.75 and 1.

[0080] The M.sub.1M.sub.2(JO.sub.4).sub.fE.sub.1-f electro-active material as defined above is preferably phosphate-based and may have an ordered or modified olivine structure.

[0081] More preferably, the cathode electro-active material has formula Li.sub.3-xM′.sub.yM″.sub.2-y(JO.sub.4).sub.3 wherein 0≤x≤3, 0≤y≤2, M′ and M″ are the same or different metals, at least one of which being a transition metal, JO.sub.4 is preferably PO.sub.4 which may be partially substituted with another oxyanion, wherein J is either S, V, Si, Nb, Mo or a combination thereof. Still more preferably, the electro-active material is a phosphate-based electro-active material of formula Li(Fe.sub.xMn.sub.1-x)PO.sub.4 wherein 0≤x≤1, wherein x is preferably 1 (that is to say, lithium iron phosphate of formula LiFePO.sub.4).

[0082] In a preferred embodiment, the cathode electro-active material is selected from the group consisting of LiMQ.sub.2, wherein M is at least one metal selected from Co, Ni, Fe, Mn, Cr and V and Q is O or S; LiNi.sub.xCo.sub.1-xO.sub.2 (0<x<1); spinel-structured LiMn.sub.2O.sub.4; lithium-nickel-manganese-cobalt-based metal oxide of formula LiNi.sub.xMn.sub.yCo.sub.zO.sub.2 (x+y+z=1), lithium-nickel-cobalt-aluminum-based metal oxide of formula LiNi.sub.xCo.sub.yAl.sub.zO.sub.2 (x+y+z=1), and LiFePO.sub.4.

[0083] In one embodiment, at least one electro-active compound according to the present invention is loaded onto the cathode current collector to have an areal capacity between 1.0 mAh/cm.sup.2 and 10.0 mAh/cm.sup.2, preferably between 3.0 mAh/cm.sup.2 and 8.0 mAh/cm.sup.2 and more preferably between 4.0 mAh/cm.sup.2 and 7.0 mAh/cm.sup.2.

[0084] In the present invention, the expression “thickness of the cathode” is intended to denote a total combined thickness of the cathode current collector and the cathode electro-active material layer.

[0085] In one embodiment, the thickness of the cathode according to the present invention is between 40 μm and 150 μm, preferably between 50 μm and 120 μm, and more preferably between 60 μm and 100 μm.

[0086] In the present invention, the lithium salt is selected from the group consisting of

[0087] a) LiN(SO.sub.2F).sub.2 (lithium bis(fluorosulfonyl)imide: LiFSI), LiN(CF.sub.3SO.sub.2).sub.2 (lithium bis(trifluoromethanesulfonyl)imide: LiTFSI), LiPF.sub.6, LiBF.sub.4, LiClO.sub.4, Li bis(oxalato)borate (LiBOB), LiCF.sub.3SO.sub.3, LiF, LiCl, LiBr, LiI, LiN(C.sub.2F.sub.5SO.sub.2).sub.2, LiN(CF.sub.3SO.sub.2)(R.sub.FSO.sub.2), wherein R.sub.F is C.sub.2F.sub.5, C.sub.4F.sub.9 or CF.sub.3OCF.sub.2CF.sub.2, LiAsF.sub.6, LiC(CF.sub.3SO.sub.2).sub.3, Li.sub.2S;

##STR00002##

[0088] wherein R′.sub.F is selected from the group consisting of F, CF.sub.3, CHF.sub.2, CH.sub.2F, C.sub.2HF.sub.4, C.sub.2H.sub.2F.sub.3, C.sub.2H.sub.3F.sub.2, C.sub.2F.sub.5, C.sub.3F.sub.7, C.sub.3H.sub.2F.sub.5, C.sub.3H.sub.4F.sub.3, C.sub.4F.sub.9, C.sub.4H.sub.2F.sub.7, C.sub.4H.sub.4F.sub.5, C.sub.5F.sub.11, C.sub.3F.sub.50CF.sub.3, C.sub.2F.sub.40CF.sub.3, C.sub.2H.sub.2F.sub.2OCF.sub.3 and CF.sub.2OCF.sub.3; and

[0089] c) combinations thereof.

[0090] In a preferred embodiment, the lithium salt is LiFSI.

[0091] In one embodiment, a molar concentration (M) of the lithium salt in the liquid electrolyte composition according to the present invention is from 1 M to 8 M, preferably from 1 M to 3 M, and more preferably from 1 M to 2 M.

[0092] By the term “separator”, it is hereby intended to denote a monolayer or multilayer polymeric, nonwoven cellulose or ceramic material/film, which electrically and physically separates the electrodes of opposite polarities in an electrochemical device and is permeable to ions flowing between them.

[0093] In the present invention, the separator can be any porous substrate commonly used for a separator in an electrochemical device.

[0094] In one embodiment, the separator is a porous polymeric material comprising at least one material selected from the group consisting of polyester such as polyethylene terephthalate and polybutylene terephthalate, polyphenylene sulphide, polyacetal, polyamide, polycarbonate, polyimide, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, polyethylene oxide, polyacrylonitrile, polyolefin such as polyethylene and polypropylene, or mixtures thereof.

[0095] In a particular embodiment, the separator is a porous polymeric material coated with inorganic nanoparticles, for instance, SiO.sub.2, TiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, etc.

[0096] In another particular embodiment, the separator is a porous polymeric material coated with polyvinylidene difluoride (PVDF).

[0097] According to one embodiment, the c) liquid electrolyte composition further comprises at least one additive, in particular a film-forming additive, which promotes the formation of the solid electrolyte interface (SEI) layer at the anode surface and/or cathode surface by reacting in advance of the solvents on the electrode surfaces. The main components of SEI hence comprise the decomposed products of electrolyte solvents and salts, which include Li.sub.2CO.sub.3, lithium alkyl carbonate, lithium alkyl oxide and other salt moieties such as LiF for LiPF.sub.6-based electrolytes. Usually, the reduction potential of the film-forming additive is higher than that of the solvent when reaction occurs at the anode surface, and the oxidation potential of the film-forming additive is lower than that of the solvent when the reaction occurs at the cathode side.

[0098] In one embodiment, the film-forming additive according to the present invention is an ionic liquid.

[0099] The term “ionic liquid” as used herein refers to a compound comprising a positively charged cation and a negatively charged anion, which is in the liquid state at the temperature of 100° C. or less under atmospheric pressure. While ordinary liquids such as water are predominantly made of electrically neutral molecules, ionic liquids are largely made of ions and short-lived ion pairs. As used herein, the term “ionic liquid” indicates a compound free from solvent.

[0100] The term “onium cation” as used herein refers to a positively charged ion having at least part of its charge localized on at least one non-metal atom such as O, N, S, or P.

[0101] In the present invention, the ionic liquid has a general formula of A.sup.n−Q.sup.l+.sub.(n/l), wherein [0102] A.sup.n− represents an anion; [0103] Q.sup.1+.sub.(n/l) represents a cation; [0104] n and l, independently selected between 1 and 5, represent respectively the charges of the anion A.sup.n− and of the cation Q.sup.l+.sub.(n/l).

[0105] The cation(s) may be selected, independently of one another, from metal cations and organic cations. The cation(s) may be mono-charged cations or polycharged cations.

[0106] As metal cation, mention may preferably be made of alkali metal cations, alkaline-earth metal cations and cations of d-block elements.

[0107] In the present invention, Q.sup.l+.sub.(n/l) may represent an onium cation. Onium cations are cations formed by the elements of Groups VB and VIB (as defined by the old European IUPAC system according to the Periodic Table of the Elements) with three or four hydrocarbon chains. The Group VB comprises the N, P, As, Sb and Bi atoms. The Group VIB comprises the O, S, Se, Te and Po atoms. The onium cation can in particular be a cation formed by an atom selected from the group consisting of N, P, O and S, more preferably N and P, with three or four hydrocarbon chains.

[0108] The onium cation Q.sup.l+.sub.(n/l) can be selected from: [0109] heterocyclic onium cations; in particular those selected from the group consisting of:

##STR00003## [0110] unsaturated cyclic onium cations; in particular those selected from the group consisting of:

##STR00004## [0111] saturated cyclic onium cations; in particular those selected from the group consisting of:

##STR00005##

and [0112] non-cyclic onium cations; in particular those of general formula .sup.+L-R′.sub.s, in which L represents an atom selected from the group consisting of N, P, O and S, more preferably N and P, s represents the number of R′ groups selected from 2, 3 or 4 according to the valence of the element L, each R′ independently represents a hydrogen atom or a C.sub.1 to C.sub.8 alkyl group, and the bond between L.sup.+ and R′ can be a single bond or a double bond.

[0113] In the above formulas, each “R” symbol represents, independently of one another, a hydrogen atom or an organic group. Preferably, each “R” symbol can represent, in the above formulas, independently of one another, a hydrogen atom or a saturated or unsaturated and linear, branched or cyclic C.sub.1 to C.sub.18 hydrocarbon group optionally substituted one or more times by a halogen atom, an amino group, an imino group, an amide group, an ether group, an ester group, a hydroxyl group, a carboxyl group, a carbamoyl group, a cyano group, a sulfone group or a sulfite group.

[0114] The cation Q.sup.l+.sub.(n/l) can more particularly be selected from ammonium, phosphonium, pyridinium, pyrrolidinium, pyrazolinium, imidazolium, arsenium, quaternary phosphonium and quaternary ammonium cations.

[0115] The quaternary phosphonium or quaternary ammonium cations can more preferably be selected from tetraalkylammonium or tetraalkylphosphonium cations, trialkylbenzylammonium or trialkylbenzylphosphonium cations or tetraarylammonium or tetraarylphosphonium cations, the alkyl groups of which, either identical or different, represents a linear or branched alkyl chain having from 4 to 12 carbon atoms, preferably from 4 to 6 carbon atoms, and the aryl groups of which, either identical or different, represents a phenyl or naphthyl group.

[0116] In a specific embodiment, Q.sup.l+.sub.(n/l) represents a quaternary phosphonium or quaternary ammonium cation.

[0117] In one preferred embodiment, Q.sup.l+.sub.(n/l) represents a quaternary phosphonium cation. Non-limiting examples of the quaternary phosphonium cation comprise trihexyl(tetradecyl)phosphonium, and a tetraalkylphosphonium cation, particularly the tetrabutylphosphonium (PBu.sub.4) cation.

[0118] In another embodiment, Q.sup.l+.sub.(n/l) represents an imidazolium cation. Non-limiting examples of the imidazolium cation comprise 1,3-dimethylimidazolium, 1-(4-sulfobutyl)-3-methyl imidazolium, 1-allyl-3H-imidazolium, 1-butyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-octyl-3-methylimidazolium In another embodiment, Q.sup.l+.sub.(n/l) represents a quaternary ammonium cation which is selected in particular from the group consisting of tetraethylammonium, tetrapropylammonium, tetrabutylammonium, trimethylbenzylammonium, methyltributylammonium, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium, N,N-dimethyl-N-ethyl-N-(3-methoxypropyl) ammonium, N,N-dimethyl-N-ethyl-N-benzyl ammonium, N, N-dimethyl-N-ethyl-N-phenylethyl ammonium, N-tributyl-N-methyl ammonium, N-trimethyl-N-butyl ammonium, N-trimethyl-N-hexyl ammonium, N-trimethyl-N-propyl ammonium, and Aliquat 336 (mixture of methyltri(C.sub.8 to C.sub.10 alkyl)ammonium compounds).

[0119] In one embodiment, Q.sup.l+.sub.(n/l) represents a piperidinium cation, in particular N-butyl-N-methyl piperidinium, N-propyl-N-methyl piperidinium.

[0120] In another embodiment, Q.sup.l+.sub.(n/l) represents a pyridinium cation, in particular N-methylpyridinium.

[0121] In a more preferred embodiment, Q.sup.l+(n/l) represents a pyrrolidinium cation. Among specific pyrrolidinium cations, mention may be made of the following: C.sub.1-12alkyl-C.sub.1-12alkyl-pyrrolidinium, and more preferably C.sub.1-4alkyl-C.sub.1-4alkyl-pyrrolidinium. Examples of pyrrolidinium cations comprise, but not limited to, N,N-dimethylpyrrolidinium, N-ethyl-N-methylpyrrolidinium, N-isopropyl-N-methylpyrrolidinium, N-methyl-N-propylpyrrolidinium, N-butyl-N-methylpyrrolidinium, N-octyl-N-methylpyrrolidinium, N-benzyl-N-methylpyrrolidinium, N-cyclohexylmethyl-N-methylpyrrolidinium, N-[(2-hydroxy)ethyl]-N-methylpyrrolidinium. More preferred are N-methyl-N-propylpyrrolidinium (PYR13) and N-butyl-N-methylpyrrolidinium (PYR14).

[0122] Non-limiting examples of an anion of the ionic liquid comprise iodide, bromide, chloride, hydrogen sulfate, dicyanamide, acetate, diethyl phosphate, methyl phosphonate, fluorinated anion, e.g., hexafluorophosphate (PF.sub.6.sup.−) and tetrafluoroborate (BF.sub.4.sup.−), and oxalatooborate of the following formula:

##STR00006##

[0123] In one embodiment, A.sup.n− is a fluorinated anion. Among the fluorinated anions that can be used in the present invention, fluorinated sulfonimide anions may be particularly advantageous. The organic anion may, in particular, be selected from the anions having the following general formula:

(E.sub.a-SO.sub.2)N.sup.−R

[0124] in which: [0125] E.sub.a represents a fluorine atom or a group having preferably from 1 to 10 carbon atoms, selected from fluoroalkyls, perfluoroalkyls and fluoroalkenyls, and [0126] R represents a substituent.

[0127] Preferably, E.sub.a may represent F or CF.sub.3.

[0128] According to a first embodiment, R represents a hydrogen atom.

[0129] According to a second embodiment, R represents a linear or branched, cyclic or non-cyclic hydrocarbon-based group, preferably having from 1 to 10 carbon atoms, which can optionally bear one or more unsaturations, and which is optionally substituted one or more times with a halogen atom, a nitrile function, or an alkyl group optionally substituted one of several times by a halogen atom.

[0130] Moreover, R may represent a nitrile group —CN.

[0131] According to a third embodiment, R represents a sulfinate group. In particular, R may represent the group —SO.sub.2-E.sub.a, E.sub.a being as defined above. In this case, the fluorinated anion may be symmetrical, i.e. such that the two E.sub.a groups of the anion are identical, or non-symmetrical, i.e. such that the two E.sub.a groups of the anion are different.

[0132] Moreover, R may represent the group —SO.sub.2—R′, R′ representing a linear or branched, cyclic or non-cyclic hydrocarbon-based group, preferably having from 1 to 10 carbon atoms, which can optionally bear one or more unsaturations, and which is optionally substituted one or more times with a halogen atom, a nitrile function, or an alkyl group optionally substituted one of several times by a halogen atom. In particular, R′ may comprise a vinyl or allyl group. Furthermore, R may represent the group —SO.sub.2—N—R′, R′ being as defined above or else R′ represents a sulfonate function —SO.sub.3.

[0133] Cyclic hydrocarbon-based groups may preferably refer to a cycloalkyl group or to an aryl group. “Cycloalkyl” refers to a monocyclic hydrocarbon chain, having 3 to 8 carbon atoms. Preferred examples of cycloalkyl groups are cyclopentyl and cyclohexyl. “Aryl” refers to a monocyclic or polycyclic aromatic hydrocarbon group, having 6 to 20 carbon atoms. Preferred examples of aryl groups are phenyl and naphthyl. When a group is a polycyclic group, the rings may be condensed or attached by σ (sigma) bonds.

[0134] According to a fourth embodiment, R represents a carbonyl group. R may, in particular, be represented by the formula —CO—R′, R′ being as defined above.

[0135] The organic anion that can be used in the present invention may advantageously be selected from the group consisting of CF.sub.3SO.sub.2N.sup.−SO.sub.2CF.sub.3 (bis(trifluoromethane sulfonyl)imide anion, commonly denoted as TFSI), FSO.sub.2N.sup.−SO.sub.2F (bis(fluorosulfonyl)imide anion, commonly denoted as FSI), CF.sub.3SO.sub.2N.sup.−SO.sub.2F, and CF.sub.3SO.sub.2N.sup.−SO.sub.2N.sup.−SO.sub.2CF.sub.3.

[0136] In a preferred embodiment, the ionic liquid contains: [0137] a positively charged cation selected from the group consisting of imidazolinium, pyridinium, pyrrolidinium and piperidinium ions optionally containing one or more C.sub.1-C.sub.30 alkyl groups, and [0138] a negatively charged anion selected from the group consisting of halides, fluorinated anions, and borates.

[0139] Non-limiting examples of C.sub.1-C.sub.30 alkyl groups include, notably, methyl, ethyl, propyl, iso-propyl, n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, isopentyl, 2,2-dimethyl-propyl, hexyl, 2,3-dimethyl-2-butyl, heptyl, 2,2-dimethyl-3-pentyl, 2-methyl-2-hexyl, octyl, 4-methyl-3-heptyl, nonyl, decyl, undecyl and dodecyl groups.

[0140] In one preferred embodiment, the film-forming additive according to the present invention is selected from the group consisting of N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl) imide (PYR13FSI), N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl) imide (PYR14FSI), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR13TFSI), and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR14TFSI).

[0141] In another embodiment, the film-forming additive according to the present invention is selected from the group consisting of cyclic sulfite and sulfate compounds comprising 1,3-propanesultone (PS), ethylene sulfite (ES) and prop-1-ene-1,3-sultone (PES); sulfone derivatives comprising dimethyl sulfone, tetramethylene sulfone (also known as sulfolane), ethyl methyl sulfone and isopropyl methyl sulfone; nitrile derivatives comprising succinonitrile, adiponitrile, and glutaronitrile; lithium nitrate (LiNO.sub.3); boron derivatives salt comprising lithium difluoro oxalato borate (LiDFOB), lithium fluoromalonato (difluoro)borate (LiFMDFB), vinyl acetate, biphenyl benzene, isopropyl benzene, hexafluorobenzene, tris(trimethylsilyl)phosphate, triphenyl phosphine, ethyl diphenylphosphinite, triethyl phosphite, tris(2,2,2-trifluoroethyl) phosphite, maleic anhydride, vinylene carbonate, vinyl ethylene carbonate, mono-fluorinated ethylene carbonate (4-fluoro-1,3-dioxolan-2-one), difluorinated ethylene carbonate, cesium bis(trifluorosulfonyl)imide (CsTFSI) and cesium fluoride (CsF), and mixtures thereof.

[0142] In one preferred embodiment, the film-forming additive according to the present invention is vinylene carbonate.

[0143] In the present invention, the total amount of the film-forming additive(s) may be from 0 to 30 wt %, preferably from 0 to 20 wt %, more preferably from 0 to 15 wt %, and even more preferably from 0 to 5 wt % with respect to the total weight of b) the liquid electrolyte solution.

[0144] The total amount of the film-forming additive(s), if contained in the liquid electrolyte solution of the present invention, may be from 0.05 to 10.0 wt %, preferably from 0.05 to 5.0 wt %, and more preferably from 0.05 to 2.0 wt % with respect to the total weight of b) the liquid electrolyte solution.

[0145] In a preferred embodiment, the total amount of film-forming additive(s) accounts for at least 1.0 wt % of b) the liquid electrolyte solution.

[0146] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0147] The invention will be now explained in more detail with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.

EXAMPLES

[0148] Raw Materials

[0149] Dry cell: NCM523/Cu (current collector; 15 μm)/CCS (ceramic coated separator), commercially available from Lifun Technology (Model No.: 402035)

[0150] Fluorinated ether compounds: [0151] 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), commercially available from SynQuest [0152] CF.sub.2HCF.sub.2—OCH.sub.2CH.sub.2O—CF.sub.2CF.sub.2H (C.sub.6F.sub.8H.sub.6O.sub.2), synthesized within Solvay [0153] difluoroethyl acetate (DFEA) available from Solvay [0154] Methyl 2,2,2-trifluoroethyl carbonate (F.sub.3EMC) available from Solvay

[0155] Non-fluorinated ether compound: [0156] 1,2-dimethoxyethane (DME), commercially available from Enchem Other solvents [0157] fluoroethylene carbonate (FEC), commercially available from Enchem [0158] ethylene carbonate (EC), commercially available from Enchem [0159] ethyl methyl carbonate (EMC), commercially available from Enchem [0160] Li salt: lithium bis(fluorosulfonyl)imide (LiFSI), commercially available from Nippon Shokubai

A/Formulation of the Electrolyte Compositions:

[0161] The electrolyte compositions were prepared for the Inventive Examples of E1-E2 and Comparative Examples of CE1-CE4. Their constituents are summarized in Table 1 below:

TABLE-US-00001 TABLE 1 Examples Solvent mixture Li Salt E1 DME/TTE 1M LiFSI (20/80)*(91.94)** (8.06)** E2 DME/C.sub.6F.sub.8H.sub.6O.sub.2 1M LiFSI (20/80)*(91.94)** (8.06)** CE1 DME 1M LiFSI (100)*(91.94)** (8.06)** CE2 DME/DFEA 1M LiFSI (20/80)*(91.94)** (8.06)** CE3 FEC/F3EMC 1M LiFSI (20/80)*(91.94)** (8.06)** CE4 FEC/EMC 1M LiFSI (20/80)*(91.94)** (8.06)** *vol % with respect to the total volume of the solvent mixture **vol % with respect to the total volume of the liquid electrolyte composition

[0162] When preparing the electrolyte composition of E1, 1M LiFSI was first dissolved in 20 vol % of DME with respect to the total volume of the solvent mixture and was mixed using a magnetic stirrer within a glove box. After the solution became transparent, 80 vol % of TTE was added to the solution with respect to the total volume of the solvent mixture.

[0163] The electrolyte compositions of E2 were prepared in the same manner as E1, except C.sub.6F.sub.8H.sub.6O.sub.2 was used as a fluorinated ether compound instead of TTE. The solvent mixture for E1-E2 comprised 20 vol % of DME and 80 vol % of a fluorinated ether compound, respectively, with respect to the total volume of the solvent mixture.

[0164] When preparing the electrolyte composition of CE1, 1M LiFSI was dissolved in DME using a magnetic stirrer within a glove box.

[0165] When preparing the electrolyte composition of CE2, 1M LiFSI was first dissolved in 20 vol % of DME with respect to the total volume of the solvent mixture and was mixed using a magnetic stirrer within a glove box. After the solution became transparent, 80 vol % of DFEA was added to the solution with respect to the total volume of the solvent mixture.

[0166] When preparing the electrolyte composition of CE3, all the required compounds were added to one bottle and they were mixed until a transparent solution was obtained. 1M LiFSI was dissolved in a solvent mixture of 20 vol % of FEC and 80 vol % of F3EMC for CE3.

[0167] The electrolyte composition of CE4 was prepared by dissolving 20 vol % of FEC within 80 vol % of EMC first with respect to the total volume of the solvent mixture, and then 1M LiFSI was dissolved in said solvent mixture.

B/Preparation of the Anode-Less Cells:

[0168] 1-Drying and Electrolyte Injection

[0169] The NCM523/Cu dry cell without electrolyte from Lifun Technology was dried under vacuum at 55° C. for 2 days. The electrolyte composition as prepared was injected to the dry cell by pipetting (4.0 g/Ah). After injection, the dry cell was left under vacuum and the cell pressure released right after the vacuum. There were 3 times of vacuum-releasing process to wet the cathode materials After releasing the vacuum, the cell was left for additional 1 hour for sufficient wetting.

[0170] 2-Sealing and 1.sup.st Aging

[0171] After wetting, the cell was sealed by using a vacuum sealing machine under the pressure (up to 350 kPa), wherein the cell was sandwiched with two plates having screwing tools. Subsequently, the cell was left at room temperature for 1 day (1.sup.st aging).

C/ Activation of Cells and Measurement of Initial Cell Performance

[0172] 1-2.sup.nd Aging (=Activation/Formation of the anode-free cell) [0173] The cell was charged to a 30% level of State Of Charge (SOC) for 3 hours and then was left at 45° C. for another 1 day (2.sup.nd aging). [0174] 2-Degassing [0175] The gas generated during the activation of the anode-free cell was removed by opening the cell and re-sealing the same.

D/ Performance Measurement of the Anode-Less Cells

[0176] The anode-free cells were tested at various conditions as detailed below:

[0177] 1-Capacity check for 3 cycles [0178] Charging: 0.1 C/4.2V/0.05 C at constant current and constant voltage (CC-CV) [0179] Discharging: 0.1 C/3.6V (CC)

[0180] 2-Continuous cycling test (up to 200 cycles) [0181] Charging: 0.2 C/4.2V/0.05 C (CC-CV) [0182] Discharging: 0.5 C/3.6V (CC)

E/ Cycle Tests—Capacity Retention:

[0183] The cycling ability of each cell was evaluated. Then, each cell was subjected to a repetition of cycles of charge and discharge. One cycle consisted of a charging phase at a charging current of C followed by a discharge phase at a discharge current of C. The following results were obtained as shown in Table 2 below:

TABLE-US-00002 TABLE 2 Number of cycles at 80% Examples of capacity retention E1 150 E2 196 CE1 Short-circuit CE2 Short-circuit CE3  23 CE4  19

[0184] FIGS. 1-2 show the variation of the capacity retention and the Coulombic efficiency of E1-E2 and CE1-CE4 as a function of the cycle number.

[0185] Notably, it was observed that the discharged capacity of E1-E2, all according to the present invention, decreased slowly as the number of cycles increased (FIG. 1). In particular, FIG. 2 clearly shows that the number of cycles at 80% of capacity retention for Inventive Examples, i.e., E1-E2, each comprising the electrolyte composition according to the invention, were much higher than those for Comparative Examples, i.e., CE1-CE4.

[0186] Among Inventive Examples of E1-E2, the number of cycles at 80% of capacity retention of E1 was the lowest, i.e., 150 cycles. However, such lowest number of E1 was already much higher than the number of cycles of Comparative Examples of CE1-CE4. The highest number of cycles at 80% of capacity retention among CE1-CE4 was 23 cycles from CE3, while CE1 and CE2 resulted in almost immediate short-circuits. It was hence clearly demonstrated that the cycling ability was improved according to the present invention.

[0187] Further, one can note that the Coulombic efficiency of Inventive Examples E1-E2 shown in FIG. 2 remained essentially constant up to at least 150 cycles and decreased as the cycles further increased, but very slowly, whereas the Coulombic efficiency of Comparative Examples CE1-CE4 decreased rapidly around 10˜20 cycles.