Lithium-selenium battery containing an electrode-protecting layer and method of improving cycle-life

Abstract

Provided is a lithium-selenium battery, comprising a cathode, an anode, and a porous separator/electrolyte assembly, wherein the anode comprises an anode active layer containing lithium or lithium alloy as an anode active material, and the cathode comprises a cathode active layer comprising a selenium-containing material, wherein an anode-protecting layer is disposed between the anode active layer and the separator/electrolyte and/or a cathode-protecting layer is disposed between the cathode active layer and the separator/electrolyte; the protecting layer comprising from 0.01% to 40% by weight of a conductive reinforcement material and from 0.01% to 40% by weight of an electrochemically stable inorganic filler dispersed in a sulfonated elastomeric matrix material and having a thickness from 1 nm to 100 m, a fully recoverable tensile strain from 2% to 500%, a lithium ion conductivity from 10.sup.7 S/cm to 510.sup.2 S/cm, and an electrical conductivity from 10.sup.7 S/cm to 100 S/cm.

Claims

1. A lithium-selenium secondary battery comprising a cathode, an anode, and a porous separator or electrolyte disposed between said cathode and said anode, wherein said cathode and wherein said anode comprises: (a) an anode active material layer, comprising a layer of lithium or lithium alloy, in a form of a foil, coating, or multiple particles aggregated together, as an anode active material, and an optional anode current collector supporting said anode active material layer; (b) a cathode active material layer, comprising a selenium-containing material as a cathode active material, selected from the group consisting of selenium, selenium-carbon hybrid, a selenium-graphite hybrid, selenium-graphene hybrid, conducting polymer-selenium hybrid, metal selenide, Se alloys or mixtures with Sn, Sb, Bi, S, or Te, selenium compounds, and combinations thereof, and an optional cathode current collector supporting said cathode active material layer; (c) an electrolyte and a porous separator layer; and (d) a discrete anode-protecting layer disposed between said anode active material layer and said porous separator and/or a discrete cathode-protecting layer disposed between the porous separator and the cathode active material layer; wherein said anode-protecting layer or cathode-protecting layer comprises a conductive sulfonated elastomer composite having from 0.01% to 40% by weight of a conductive reinforcement material and from 0.01% to 40% by weight of an electrochemically stable inorganic filler dispersed in a sulfonated elastomeric matrix material and said layer of conductive sulfonated elastomer composite has a thickness from 1 nm to 100 m, a fully recoverable tensile strain from 2% to 500%, a lithium ion conductivity from 10.sup.7 S/cm to 510.sup.2 S/cm, and an electrical conductivity from 10.sup.7 S/cm to 100 S/cm when measured at room temperature and wherein said inorganic filler has a lithium intercalation potential from 1.1 V to 4.5 V versus Li/Li.sup.+ and is selected from an oxide, carbide, boride, nitride, sulfide, phosphide, or selenide of a transition metal, a lithiated version thereof, or a combination thereof.

2. The lithium-selenium secondary battery of claim 1, wherein said transition metal is selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Pd, Ag, Cd, La, Ta, W, Pt, Au, Hg, combinations thereof, or combinations thereof with Al, Ga, In, Sn, Pb, Sb, or Bi.

3. The lithium-selenium secondary battery of claim 1, wherein said electrochemically stable inorganic filler is selected from nanodiscs, nanoplatelets, or nanosheets of (a) bismuth selenide or bismuth telluride, (b) transition metal dichalcogenide or trichalcogenide, (c) sulfide, selenide, or telluride of niobium, zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, cobalt, nickel, manganese, or any transition metal; (d) boron nitride, or (e) a combination thereof, wherein said nanodiscs, nanoplatelets, or nanosheets have a thickness from 1 nm to 100 nm.

4. The lithium-selenium secondary battery of claim 1, wherein said conductive reinforcement material is selected from the group consisting of graphene sheets, carbon nanotubes, carbon nanofibers, carbon or graphite fibers, expanded graphite flakes, metal nanowires, conductive polymer fibers, and combinations thereof.

5. The lithium-selenium secondary battery of claim 1, wherein said sulfonated elastomeric matrix material comprises sulfonated versions of the group consisting of natural polyisoprene, synthetic polyisoprene, polybutadiene, chloroprene rubber, polychloroprene, butyl rubber, styrene-butadiene rubber, nitrile rubber, ethylene propylene rubber, ethylene propylene diene rubber, metallocene-based poly(ethylene-co-octene) elastomer, poly(ethylene-co-butene) elastomer, styrene-ethylene-butadiene-styrene elastomer, epichlorohydrin rubber, polyacrylic rubber, silicone rubber, fluorosilicone rubber, perfluoroelastomers, polyether block amides, chlorosulfonated polyethylene, ethylene-vinyl acetate, thermoplastic elastomer, protein resilin, protein elastin, ethylene oxide-epichlorohydrin copolymer, polyurethane, urethane-urea copolymer, and combinations thereof.

6. The lithium-selenium secondary battery of claim 4, wherein said graphene sheets are selected from the group consisting of pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, nitrogenated graphene, hydrogenated graphene, doped graphene, functionalized graphene, and combinations thereof.

7. The lithium-selenium secondary battery of claim 4, wherein said graphene sheets comprise single-layer graphene or few-layer graphene.

8. The lithium-selenium secondary battery of claim 4, wherein said graphene sheets have a length or width between 5 nm to 5 m.

9. The lithium-selenium secondary battery of claim 1, wherein said sulfonated elastomer composite further comprises from 0.1% to 40% by weight of a lithium ion-conducting additive dispersed therein.

10. The lithium-selenium secondary battery of claim 1, wherein said sulfonated elastomer composite further comprises a lithium ion-conducting additive dispersed therein and said lithium ion-conducting additive is selected from Li.sub.2CO.sub.3, Li.sub.2O, Li.sub.2C.sub.2O.sub.4, LiOH, LiX, ROCO.sub.2Li, HCOLi, ROLi, (ROCO.sub.2Li).sub.2, (CH.sub.2OCO.sub.2Li).sub.2, Li.sub.2S, Li.sub.xSO.sub.y, or a combination thereof, wherein X=F, Cl, I, or Br, R=a hydrocarbon group, 0<x1 and 1y4.

11. The lithium-selenium secondary battery of claim 1, wherein said conductive reinforcement material is selected from the group consisting of electron-conducting polymer, a metal particle or wire, a graphene sheet, a carbon fiber, a graphite fiber, a carbon nanofiber, a graphite nanofiber, a carbon nanotube, a graphite particle, an expanded graphite flake, an acetylene black particle, and combinations thereof.

12. The lithium-selenium secondary battery of claim 11, wherein said conductive reinforcement material has a thickness or diameter less than 100 nm.

13. The lithium-selenium secondary battery of claim 1, wherein said sulfonated elastomer composite further comprises a lithium salt dispersed therein and said lithium salt is selected from the group consisting of lithium perchlorate (LiClO.sub.4), lithium hexafluorophosphate (LiPF.sub.6), lithium borofluoride (LiBF.sub.4), lithium hexafluoroarsenide (LiAsF.sub.6), lithium trifluoro-methanesulfonate (LiCF.sub.3SO.sub.3), bis-trifluoromethyl sulfonylimide lithium (LiN(CF.sub.3SO.sub.2).sub.2), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF.sub.2C.sub.2O.sub.4), lithium nitrate (LiNO.sub.3), Li-fluoroalkyl-phosphate (LiPF.sub.3(CF.sub.2CF.sub.3).sub.3), lithium bisperfluoro-ethylsulfonylimide (LiBETI), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-based lithium salt, or a combination thereof.

14. The lithium-selenium secondary battery of claim 1, wherein said sulfonated elastomer composite further comprises a mixture of said sulfonated elastomer and an electron-conducting polymer selected from the group consisting of polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer, a sulfonated derivative thereof, and combinations thereof.

15. The lithium-selenium secondary battery of claim 1, wherein the sulfonated elastomer composite forms a mixture or blend with a lithium ion-conducting polymer selected from the group consisting of poly(ethylene oxide) (PEO), polypropylene oxide (PPO), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride) (PVDF), poly bis-methoxy ethoxyethoxide-phosphazene, polyvinyl chloride, polydimethylsiloxane, poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a sulfonated derivative thereof, and combinations thereof.

16. The lithium-selenium secondary battery of claim 1, wherein said anode-protecting layer or said cathode-protecting layer has a thickness from 1 nm to 10 m.

17. The lithium-selenium battery of claim 1, wherein said electrolyte is selected from a polymer electrolyte, polymer gel electrolyte, composite electrolyte, ionic liquid electrolyte, non-aqueous liquid electrolyte, soft matter phase electrolyte, quasi-solid electrolyte, solid-state electrolyte, or a combination thereof.

18. The lithium-selenium battery of claim 1, wherein said electrolyte comprises an alkali salt selected from the group consisting of lithium perchlorate (LiClO.sub.4), lithium hexafluorophosphate (LiPF.sub.6), lithium borofluoride (LiBF.sub.4), lithium hexafluoroarsenide (LiAsF.sub.6), lithium trifluoro-methanesulfonate (LiCF.sub.3SO.sub.3), bis-trifluoromethyl sulfonylimide lithium (LiN(CF.sub.3SO.sub.2).sub.2, lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF.sub.2C.sub.2O.sub.4), lithium nitrate (LiNO.sub.3), Li-fluoroalkyl-phosphates (LiPF.sub.3(CF.sub.2CF.sub.3).sub.3), lithium bisperfluoroethylsulfonylimide (LiBETI), an ionic liquid salt, sodium perchlorate (NaClO.sub.4), potassium perchlorate (KClO.sub.4), sodium hexafluorophosphate (NaPF.sub.6), potassium hexafluorophosphate (KPF.sub.6), sodium borofluoride (NaBF.sub.4), potassium borofluoride (KBF.sub.4), sodium hexafluoroarsenide, potassium hexafluoroarsenide, sodium trifluoro-methanesulfonate (NaCF.sub.3SO.sub.3), potassium trifluoro-methanesulfonate (KCF.sub.3SO.sub.3), bis-trifluoromethyl sulfonylimide sodium (NaN(CF.sub.3SO.sub.2).sub.2), sodium trifluoromethanesulfonimide (NaTFSI), bis-trifluoromethyl sulfonylimide potassium (KN(CF.sub.3SO.sub.2).sub.2), and combinations thereof.

19. The lithium-selenium battery of claim 1, wherein said electrolyte contains a solvent selected from the group consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), methylethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, propylene carbonate (PC), gamma-butyrolactone (-BL), acetonitrile (AN), ethyl acetate (EA), propyl formate (PF), methyl formate (MF), toluene, xylene or methyl acetate (MA), fluoroethylene carbonate (FEC), vinylene carbonate (VC), allyl ethyl carbonate (AEC), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), tetraethylene glycol dimethylether (TEGDME), poly(ethylene glycol) dimethyl ether (PEGDME), diethylene glycol dibutyl ether (DEGDBE), 2-ethoxyethyl ether (EEE), sulfone, sulfolane, room temperature ionic liquid, and combinations thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 Schematic of a prior art lithium metal battery cell, containing an anode layer (a thin Li foil or Li coating deposited on a surface of a current collector, Cu foil), a porous separator, and a cathode active material layer, which is composed of particles of a cathode active material, a conductive additive (not shown) and a resin binder (not shown). A cathode current collector supporting the cathode active layer is also shown.

(2) FIG. 2 Schematic of a presently invented lithium metal battery cell containing an anode layer (a thin Li foil or Li coating deposited on a surface of a current collector, Cu foil), a sulfonated elastomer composite-based anode-protecting layer, a porous separator/electrolyte layer (or a layer of solid-state electrolyte), and a cathode active material layer, which is composed of particles of a cathode active material, a conductive additive (not shown) and a resin binder (not shown). A cathode current collector supporting the cathode active layer is also shown.

(3) FIG. 3 The cathode specific intercalation capacity curves of four LiSe cells: one including an anode-protecting layer (sulfonated SIBS elastomer composite prepared as in Example 1), one including a cathode-protecting layer (sulfonated PB composite as prepared in Example 2), one including both an anode-protecting layer and a cathode-protecting layer, and one including no electrode-protecting layer (the baseline cell).

(4) FIG. 4 The specific capacity values of two lithium-selenium cells (initially the cell being lithium-free): one featuring a sulfonated elastomer composite-based anode-protecting layer and the other no anode-protecting layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) This invention is directed at a lithium-selenium secondary battery, which is preferably based on an organic electrolyte, a polymer gel electrolyte, an ionic liquid electrolyte, a quasi-solid electrolyte, or a solid-state electrolyte. The shape of a lithium metal secondary battery can be cylindrical, square, button-like, etc. The present invention is not limited to any battery shape or configuration or any type of electrolyte.

(6) The invention provides a lithium metal secondary battery, comprising a cathode, an anode, and electrolyte (e.g. solid-state electrolyte) or separator-electrolyte assembly (porous separator and liquid electrolyte, gel electrolyte, quasi-solid electrolyte, etc.) disposed between the cathode and the anode. The anode comprises an anode active material layer containing a lithium metal (e.g. particles, foil or coating of lithium or lithium alloy) as an anode active material. The foil or coating of lithium or lithium alloy may be supported by a current collector (e.g. a Cu foil, a Ni foam, a porous layer of nanofilaments, such as graphene sheets, carbon nanofibers, carbon nanotubes, etc. forming a 3D interconnected network of electron-conducting pathways).

(7) In some embodiments, the cathode contains a cathode active material layer comprising a selenium-containing material, as a cathode active material, selected from selenium, a selenium-carbon hybrid, a selenium-graphite hybrid, a selenium-graphene hybrid, a conducting polymer-selenium hybrid, a metal selenide, a Se alloy or mixture with Sn, Sb, Bi, S, or Te, a selenium compound, or a combination thereof. These elements, including Se, may be supported by surfaces of a carbon material (e.g. carbon nanotube or carbon nanofiber), a graphite material (e.g. expanded graphite flakes), graphene sheets, or lodged in the pores of a porous carbon, graphite, or graphene structure (e.g. activated carbon particles, graphite foam, or graphene foam).

(8) There is an anode-protecting layer disposed between the anode active material layer and the separator (or solid-state electrolyte) and/or there is a cathode-protecting layer between the cathode active material layer and the separator (or solid-state electrolyte). The anode-protecting layer or cathode-protecting layer contains a thin layer of a conductive sulfonated elastomer composite (anode-protecting layer) having from 0.01% to 40% by weight of a conductive reinforcement material and from 0.01% to 40% by weight of an electrochemically stable inorganic filler dispersed in a sulfonated elastomeric matrix material and this layer of conductive sulfonated elastomer composite has a thickness from 1 nm to 100 m, a fully recoverable tensile strain from 2% to 500%, a lithium ion conductivity from 10.sup.7 S/cm to 510.sup.2 S/cm, and an electrical conductivity from 10.sup.7 S/cm to 100 S/cm when measured at room temperature. The electrochemically stable inorganic filler has a lithium intercalation potential no less than 1.1 V versus Li/Li.sup.+ (preferably from 1.1 V to 4.5 V, more preferably from 1.1 to 3.5 V, and most preferably from 1.1 to 2.5 V).

(9) The sulfonated elastomer composite-based anode-protecting layer is disposed (interposed) between the lithium metal and the porous separator (or solid-state electrolyte). The sulfonated elastomer composite-based cathode-protecting layer is disposed (interposed) between the porous separator (or solid-state electrolyte) and the cathode active layer.

(10) Preferably, the sulfonated elastomer composite layer has a lithium ion conductivity no less than 10.sup.6 S/cm (typically from 10.sup.5 S/cm to 510.sup.2 S/cm, measured at room temperature), and a thickness from 10 nm to 20 m.

(11) In some embodiments, the sulfonated elastomer composite has from 0.01% to 40% by weight (based on the total weight of the sulfonated elastomer composite) of a conductive reinforcement material dispersed in a sulfonated elastomeric matrix material, wherein the conductive reinforcement material is selected from graphene sheets, carbon nanotubes, carbon nanofibers, metal nanowires, conductive polymer fibers, or a combination thereof.

(12) The conducting reinforcement material is preferably in a filamentary or sheet-like form, such as a nanotube, nanofiber, nanowire, nanoplatelet, or nanodisc. In some embodiments, the conductive reinforcement material is selected from graphene sheets, carbon nanotubes, carbon nanofibers, carbon or graphite fibers, expanded graphite flakes, metal nanowires, conductive polymer fibers, or a combination thereof. These are electron-conducting materials and the sulfonated elastomer matrix is a lithium ion- and sodium ion-conducting material. By combining such a sulfonated elastomer and a conducting reinforcement (0-50% by weight, preferably 0.1%-30%, and more preferably 0.1-15%), one obtains a composite that is both electron conducting and ion-conducting and capable of allowing electrons and lithium ions to migrate in and out of the particulate without much resistance.

(13) The graphene sheets to be dispersed in a sulfonated elastomer matrix are preferably selected from pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, nitrogenated graphene, hydrogenated graphene, doped graphene, functionalized graphene, or a combination thereof. The graphene sheets preferably comprise single-layer graphene or few-layer graphene, wherein the few-layer graphene is defined as a graphene platelet formed of less than 10 graphene planes. The carbon nanotubes (CNTs) can be a single-walled CNT or multi-walled CNT. The carbon nanofibers may be vapor-grown carbon nanofibers or electrospinning based carbon nanofibers (e.g. electrospun polymer nanofibers that are subsequently carbonized).

(14) Preferably, the sulfonated elastomeric matrix material contains a sulfonated version of an elastomer selected from natural polyisoprene, synthetic polyisoprene, polybutadiene, chloroprene rubber, polychloroprene, butyl rubber, styrene-butadiene rubber, nitrile rubber, ethylene propylene rubber, ethylene propylene diene rubber, metallocene-based poly(ethylene-co-octene) (POE) elastomer, poly(ethyl ene-co-butene) (PBE) elastomer, styrene-ethylene-butadiene-styrene (SEBS) elastomer, epichlorohydrin rubber, polyacrylic rubber, silicone rubber, fluorosilicone rubber, perfluoroelastomers, polyether block amides, chlorosulfonated polyethylene, ethylene-vinyl acetate, thermoplastic elastomer, protein resilin, protein elastin, ethylene oxide-epichlorohydrin copolymer, polyurethane, urethane-urea copolymer, or a combination thereof.

(15) The electrochemically stable inorganic filler has a lithium intercalation potential no less than 1.1 V versus Li/Li.sup.+ (preferably from 1.1 V to 4.5 V, more preferably from 1.1 to 3.5 V, and most preferably from 1.1 to 2.5 V). The presence of this inorganic filler makes the anode-protecting layer significantly more electrochemically stable. The inorganic filler is preferably selected from an oxide, carbide, boride, nitride, sulfide, phosphide, or selenide of a transition metal, a lithiated version thereof, or a combination thereof. Preferably, the transition metal is selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Pd, Ag, Cd, La, Ta, W, Pt, Au, Hg, a combination thereof, or a combination thereof with Al, Ga, In, Sn, Pb, Sb, or Bi.

(16) In certain embodiments, the inorganic filler for reinforcing the elastomer matrix may be selected from an oxide, carbide, boride, nitride, sulfide, phosphide, or selenide of a transition metal, a lithiated version thereof, or a combination thereof. Preferably, the transition metal is selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Pd, Ag, Cd, La, Ta, W, Pt, Au, Hg, a combination thereof, or a combination thereof with Al, Ga, In, Sn, Pb, Sb, or Bi.

(17) These inorganic fillers for reinforcing the elastomer shell are preferably selected to have an intercalation potential (the electrochemical potential at which lithium intercalates into these materials) higher than the intercalation potential of the active material encapsulated in the particulate. For instance, lithium intercalates into Si at approximately 0.4-0.5 V (vs. Li/Li.sup.+) and the intercalation potential of lithium titanate (Li.sub.4Ti.sub.5O.sub.12) is 1.1-1.5 V. The lithium titanate may be considered as a lithiated version of titanium oxide (TiO.sub.2), which has a lithium intercalation potential >2.5 V. The inorganic filler must have a lithium intercalation potential higher than 1.1 V versus Li/Li.sup.+, preferably higher than 1.2 V, more preferably higher than 1.4 V, and most preferably higher than 1.5 V. These electrochemical potential conditions are found to be surprisingly capable of avoiding the formation of SEI on/in the encapsulating shell and preventing repeated formation and breakage of SEI on active material particles, which otherwise would result in continued and rapid decay of battery capacity.

(18) Other examples of metal oxide are NbO.sub.2 and its lithiated version and titanium-niobium composite oxide (e.g. represented by a general formula TiNb.sub.2O.sub.7) and its lithiated versions. They typically have a lithium intercalation potential higher than 1.1 V versus Li/Li.sup.+.

(19) The niobium-containing composite metal oxide for use as an inorganic filler in the encapsulating elastomer shell may be selected from the group consisting of TiNb.sub.2O.sub.7, Li.sub.xTiNb.sub.2O.sub.7 (0x5), Li.sub.xM.sub.(1y)Nb.sub.yNb.sub.2O.sub.(7+) (wherein 0x6, 0y1, 11, and M=Ti or Zr), Ti.sub.xNb.sub.yO.sub.7 (0.5y/x<2.0), TiNb.sub.xO.sub.(2+5x/2) (1.9x<2.0), M.sub.xTi.sub.(12x)Nb.sub.(2+x)O.sub.(7+) (wherein 0x0.2, 0.30.3, and M=a trivalent metal selected from Fe, Ga, Mo, Ta, V, Al, B, and a mixture thereof), M.sub.xTi.sub.(22x)Nb.sub.(10+x)O.sub.(29+) (wherein 0x0.4, 0.30.3, and M=a trivalent metal selected from Fe, Ga, Mo, Al, B, and a mixture thereof), M.sub.xTiNb.sub.2O.sub.7 (x<0.5, and M=B, Na, Mg, Al, Si, S, P, K, Ca, Mo, W, Cr, Mn, Co, Ni, and Fe), TiNb.sub.2xTa.sub.xO.sub.y (0x<2, 7y10), Ti.sub.2Nb.sub.10vTa.sub.vO.sub.w (0v<2, 27y29), Li.sub.xTi.sub.(1y)M1.sub.yNb.sub.(2z)M2.sub.zO.sub.(7+) (wherein 0x5, 0y1, 0z2, 0.30.3, M1=Zr, Si, and Sn, and M2=V, Ta, and Bi), P-doped versions thereof, B-doped versions thereof, carbon-coated versions thereof, and combinations thereof. In such a niobium-containing composite metal oxide, niobium oxide typically forms the main framework or backbone of the crystal structure, along with at least a transition metal oxide.

(20) Transition metal oxide is but one of the many suitable inorganic filler materials for reinforcing the elastomer matrix. The inorganic filler may be selected from an oxide, carbide, boride, nitride, sulfide, phosphide, or selenide of a transition metal, a lithiated version thereof, or a combination thereof. Preferably, these and other inorganic fillers are in a form of nanoparticle, nanowire, nanofiber, nanotube, nanosheet, nanobelt, nanoribbon, nanodisc, nanoplatelet, or nanohorn having a dimension (diameter, thickness, or width, etc.) less than 100 nm, preferably less than 10 nm. These inorganic filler materials typically have a lithium intercalation potential from 1.1 V to 4.5 V versus Li/Li.sup.+, and more typically and preferably from 1.1 V to 3.5 V, and most preferably from 1.1 V to 1.5 V. The lithium intercalation potential of a filler dispersed in the elastomeric matrix material may be higher than the lithium intercalation potential of the active material encapsulated by the filled elastomer.

(21) The inorganic filler material for reinforcing an elastomer matrix material may also be selected from nanodiscs, nanoplatelets, or nanosheets (having a thickness from 1 nm to 100 nm) of: (a) bismuth selenide or bismuth telluride, (b) transition metal dichalcogenide or trichalcogenide, (c) sulfide, selenide, or telluride of niobium, zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, cobalt, nickel, manganese, or any transition metal; (d) boron nitride, or (e) a combination thereof. These nanodiscs, nanoplatelets, or nanosheets preferably have a thickness less than 20 nm, more preferably from 1 nm to 10 nm.

(22) Preferably, this anode-protecting layer or cathode-protecting layer is different in composition than the electrolyte per se as used in the lithium-selenium battery and maintains as a discrete layer (not to be dissolved in the electrolyte). Preferably, there is a close contact between the anode active material layer and the anode-protecting layer. The anode-protecting layer may contain a liquid electrolyte that permeates or impregnates into the sulfonated elastomer composite.

(23) We have discovered that the anode-protecting layer provides several unexpected benefits: (a) the formation of dendrite has been essentially eliminated; (b) uniform deposition of lithium back to the anode side is readily achieved (no dendrite and no or little dead Li particles separated from the anode active layer; (c) the layer ensures smooth and uninterrupted transport of lithium ions from/to the lithium foil/coating and through the interface between the lithium foil/coating and the protective layer with minimal interfacial resistance; and (d) cycle stability can be significantly improved and cycle life increased. The cathode-protecting layer also acts to stop the permeation of selenium and lithium polyselenide there this protective layer (hence, preventing the shuttle effect), yet allowing diffusion of lithium ions.

(24) In a conventional lithium-selenium cell, as illustrated in FIG. 1, the anode active material (lithium) is deposited in a thin film form or a thin foil form directly onto an anode current collector (e.g. a Cu foil). As previously discussed in the Background section, these lithium secondary batteries have the dendrite-induced internal shorting and dead lithium issues at the anode.

(25) We have solved these challenging issues that have troubled battery designers and electrochemists alike for more than 30 years by developing and implementing a new anode-protecting layer disposed between the lithium foil/coating and the separator layer. This protective layer comprises a sulfonated elastomer composite having a recoverable (elastic) tensile strain no less than 2% (preferably no less than 5%) under uniaxial tension and a lithium ion conductivity no less than 10.sup.6 S/cm at room temperature (preferably and more typically from 110.sup.5 S/cm to 510.sup.2 S/cm). The sulfonated elastomer composite contains a sulfonated elastomer composite network having a rotaxane structure or a sulfonated elastomer composite structure at a crosslink point of said sulfonated elastomer composite network.

(26) As schematically shown in FIG. 2, one embodiment of the present invention is a lithium-selenium battery cell containing an anode layer (a thin Li foil or Li coating deposited on a surface of a current collector, Cu foil), a sulfonated elastomer composite-based anode-protecting layer, a porous separator, a cathode-protecting layer, and a cathode active material layer, which is composed of particles of a cathode active material (e.g. Se-containing material), a conductive additive (not shown) and a resin binder (not shown). A cathode current collector (e.g. Al foil) supporting the cathode active layer is also shown in FIG. 2. The lithium metal or alloy in the anode may be in a form of particles (e.g. surface-protected or surface-stabilized particles of Li or

(27) Li alloy).

(28) Sulfonated elastomer composite exhibits an elastic deformation of at least 2% when measured under uniaxial tension. In the field of materials science and engineering, the elastic deformation is defined as a deformation of a material (when being mechanically stressed) that is essentially fully recoverable upon release of the load and the recovery is essentially instantaneous. The elastic deformation is preferably greater than 5%, more preferably greater than 10%, further more preferably greater than 30%, and still more preferably greater than 100% but less than 500%.

(29) It may be noted that although FIG. 2 shows a lithium coating pre-existing at the anode when the lithium battery is made, this is but one embodiment of the instant invention. An alternative embodiment is a lithium-selenium battery that does not contain a lithium foil or lithium coating at the anode (only an anode current collector, such as a Cu foil or a graphene/CNT mat) when the battery is made. The needed lithium to be bounced back and forth between the anode and the cathode is initially stored in the cathode active material (e.g. lithium polyselenide; not S alone). During the first charging procedure of the lithium-selenium battery (e.g. as part of the electrochemical formation process), lithium comes out of the cathode active material, migrates to the anode side, and deposits on the anode current collector. The presence of the presently invented sulfonated elastomer composite layer enables uniform deposition of lithium ions on the anode current collector surface. Such an alternative battery configuration avoids the need to have a layer of lithium foil or coating being present during battery fabrication. Bare lithium metal is highly sensitive to air moisture and oxygen and, thus, is more challenging to handle in a real battery manufacturing environment. This strategy of pre-storing lithium in the lithiated (lithium-containing) cathode active materials, such as and Li.sub.2Se.sub.x, makes all the materials safe to handle in a real manufacturing environment. Cathode active materials, such as Li.sub.2Se.sub.x, are typically less air-sensitive.

(30) Preferably and typically, the sulfonated elastomer composite has a lithium ion conductivity no less than 10.sup.5 S/cm, more preferably no less than 10.sup.4 S/cm, further preferably no less than 10.sup.3 S/cm, and most preferably no less than 10.sup.2 S/cm. In some embodiments, the sulfonated elastomer composite comprises from 0.1% to 40% (preferably 1% to 35%) by weight of a lithium ion-conducting additive dispersed in a sulfonated elastomer composite matrix material. The sulfonated elastomer composite must have a high elasticity (elastic deformation strain value >2%). An elastic deformation is a deformation that is fully recoverable and the recovery process is essentially instantaneous (no significant time delay). The sulfonated elastomer composite can exhibit an elastic deformation from 2% up to 800% (8 times of its original length), more typically from 5% to 500%, and further more typically from 10% to 300%, and most typically and desirably from 30% to 300%. It may be noted that although a metal typically has a high ductility (i.e. can be extended to a large extent without breakage), the majority of the deformation is plastic deformation (non-recoverable) and only a small amount of elastic deformation (typically <1% and more typically <0.2%).

(31) Further, we have unexpectedly discovered that the presence of an amount of a lithium salt (1-35% by weight) and a liquid solvent (0-50%) can significantly increase the lithium-ion conductivity.

(32) Typically, a sulfonated elastomer composite is originally in a monomer or oligomer state that can be cured to form a cross-linked polymer that is highly elastic. Prior to curing, these polymers or oligomers are soluble in an organic solvent to form a polymer solution. An ion-conducting or electron-conducting additive may be added to this solution to form a suspension. This solution or suspension can then be formed into a thin layer of polymer precursor on a surface of an anode active material layer or an anode current collector. The polymer precursor (monomer or oligomer and initiator) is then polymerized and cured to form a lightly cross-linked polymer. This thin layer of polymer may be tentatively deposited on a solid substrate (e.g. surface of a polymer or glass), dried, and separated from the substrate to become a free-standing polymer layer. This free-standing layer is then laid on a lithium foil/coating or implemented between a lithium film/coating and electrolyte or separator. Polymer layer formation can be accomplished by using one of several procedures well-known in the art; e.g. spraying, spray-painting, printing, coating, extrusion-based film-forming, casting, etc. The cathode-protecting layer may be prepared in a similar manner.

(33) One may dispense and deposit a layer of a sulfonated elastomer composite onto a primary surface of the anode active material layer and/or that of a cathode active material layer. Alternatively, one may dispense and deposit a layer of a sulfonated elastomer composite onto a primary surface or both primary surfaces of a porous separator layer. Further alternatively, one may prepare separate free-standing discrete layers of the sulfonated elastomer composite first. These sulfonated elastomer composite layers are then laminated together with the anode active material layer, separator/electrolyte, and the cathode layer to form a battery cell.

(34) Sulfonation of an elastomer or rubber may be accomplished by exposing the elastomer/rubber to a sulfonation agent in a solution state or melt state, in a batch manner or in a continuous process. The sulfonating agent may be selected from sulfuric acid, sulfonic acid, sulfur trioxide, chlorosulfonic acid, a bisulfate, a sulfate (e.g. zinc sulfate, acetyl sulfate, etc.), a mixture thereof, or a mixture thereof with another chemical species (e.g. acetic anhydride, thiolacetic acid, or other types of acids, etc.). In addition to zinc sulfate, there are a wide variety of metal sulfates that may be used as a sulfonating agent; e.g. those sulfates containing Mg, Ca, Co, Li, Ba, Na, Pb, Ni, Fe, Mn, K, Hg, Cr, and other transition metals, etc.

(35) For instance, a triblock copolymer, poly(styrene-isobutylene-styrene) or SIBS, may be sulfonated to several different levels ranging from 0.36 to 2.04 mequiv./g (13 to 82 mol % of styrene; styrene being 19 mol % of the unsulfonated block copolymer). Sulfonation of SIBS may be performed in solution with acetyl sulfate as the sulfonating agent. First, acetic anhydride reacts with sulfuric acid to form acetyl sulfate (a sulfonating agent) and acetic acid (a by-product). Then, excess water is removed since anhydrous conditions are required for sulfonation of SIBS. The SIBS is then mixed with the mixture of acetyl sulfate and acetic acid. Such a sulfonation reaction produces sulfonic acid substituted to the para-position of the aromatic ring in the styrene block of the polymer. Elastomers having an aromatic ring may be sulfonated in a similar manner.

(36) A sulfonated elastomer also may be synthesized by copolymerization of a low level of functionalized (i.e. sulfonated) monomer with an unsaturated monomer (e.g. olefinic monomer, isoprene monomer or oligomer, butadiene monomer or oligomer, etc.).

(37) A broad array of elastomers can be sulfonated to become sulfonated elastomers. The elastomeric material may be selected from natural polyisoprene (e.g. cis-1,4-polyisoprene natural rubber (NR) and trans-1,4-polyisoprene gutta-percha), synthetic polyisoprene (IR for isoprene rubber), polybutadiene (BR for butadiene rubber), chloroprene rubber (CR), polychloroprene (e.g. Neoprene, Baypren etc.), butyl rubber (copolymer of isobutylene and isoprene, IIR), including halogenated butyl rubbers (chloro butyl rubber (CIIR) and bromo butyl rubber (BIIR), styrene-butadiene rubber (copolymer of styrene and butadiene, SBR), nitrile rubber (copolymer of butadiene and acrylonitrile, NBR), EPM (ethylene propylene rubber, a copolymer of ethylene and propylene), EPDM rubber (ethylene propylene diene rubber, a terpolymer of ethylene, propylene and a diene-component), epichlorohydrin rubber (ECO), polyacrylic rubber (ACM, ABR), silicone rubber (SI, Q, VMQ), fluorosilicone rubber (FVMQ), fluoroelastomers (FKM, and FEPM; such as Viton, Tecnoflon, Fluorel, Aflas and Dai-El), perfluoroelastomers (FFKM: Tecnoflon PFR, Kalrez, Chemraz, Perlast), polyether block amides (PEBA), chlorosulfonated polyethylene (CSM; e.g. Hypalon), and ethylene-vinyl acetate (EVA), thermoplastic elastomers (TPE), protein resilin, protein elastin, ethylene oxide-epichlorohydrin copolymer, polyurethane, urethane-urea copolymer, and combinations thereof.

(38) In some embodiments, a sulfonated elastomer composite can form a polymer matrix composite containing a lithium ion-conducting additive dispersed in the sulfonated elastomer composite matrix material, wherein the lithium ion-conducting additive is selected from Li.sub.2CO.sub.3, Li.sub.2O, Li.sub.2C.sub.2O.sub.4, LiOH, LiX, ROCO.sub.2Li, HCOLi, ROLi, (ROCO.sub.2Li).sub.2, (CH.sub.2OCO.sub.2Li).sub.2, Li.sub.2S, Li.sub.xSO.sub.y, or a combination thereof, wherein X=F, Cl, I, or Br, R=a hydrocarbon group, 0<x1 and 1y4.

(39) In some embodiments, the sulfonated elastomer composite can be mixed with a lithium ion-conducting additive, which contains a lithium salt selected from lithium perchlorate (LiClO.sub.4), lithium hexafluorophosphate (LiPF.sub.6), lithium borofluoride (LiBF.sub.4), lithium hexafluoroarsenide (LiAsF.sub.6), lithium trifluoro-methanesulfonate (LiCF.sub.3SO.sub.3), bis-trifluoromethyl sulfonylimide lithium (LiN(CF.sub.3SO.sub.2).sub.2), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF.sub.2C.sub.2O.sub.4), lithium nitrate (LiNO.sub.3), Li-fluoroalkyl-phosphate (LiPF.sub.3(CF.sub.2CF.sub.3).sub.3), lithium bisperfluoro-ethylsulfonylimide (LiBETI), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-based lithium salt, or a combination thereof.

(40) The sulfonated elastomer composite may form a mixture, blend, or interpenetrating network with an electron-conducting polymer selected from polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer, derivatives thereof (e.g. sulfonated versions), or a combination thereof. In some embodiments, the sulfonated elastomer composite may form a mixture, co-polymer, or semi-interpenetrating network with a lithium ion-conducting polymer selected from poly(ethylene oxide) (PEO), polypropylene oxide (PPO), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride) (PVdF), poly bis-methoxy ethoxyethoxide-phosphazene, polyvinyl chloride, polydimethylsiloxane, poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a derivative thereof (e.g. sulfonated versions), or a combination thereof.

(41) The electrolyte for a lithium-selenium cell may be an organic liquid electrolyte, ionic liquid electrolyte, gel polymer electrolyte, solid-state electrolyte (e.g. polymer solid electrolyte or inorganic solid electrolyte), quasi-solid electrolyte or a combination thereof. The electrolyte typically contains an alkali metal salt (lithium salt, sodium salt, and/or potassium salt) dissolved in a solvent.

(42) The solvent may be selected from 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), tetraethylene glycol dimethylether (TEGDME), poly(ethylene glycol) dimethyl ether (PEGDME), diethylene glycol dibutyl ether (DEGDBE), 2-ethoxyethyl ether (EEE), sulfone, sulfolane, ethylene carbonate (EC), dimethyl carbonate (DMC), methylethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, propylene carbonate (PC), gamma-butyrolactone (-BL), acetonitrile (AN), ethyl acetate (EA), propyl formate (PF), methyl formate (MF), toluene, xylene, methyl acetate (MA), fluoroethylene carbonate (FEC), vinylene carbonate (VC), allyl ethyl carbonate (AEC), a hydrofluoroether, a room temperature ionic liquid solvent, or a combination thereof.

(43) The electrolytic salts to be incorporated into a non-aqueous electrolyte may be selected from a lithium salt such as lithium perchlorate (LiClO.sub.4), lithium hexafluorophosphate (LiPF.sub.6), lithium borofluoride (LiBF.sub.4), lithium hexafluoroarsenide (LiAsF.sub.6), lithium trifluoro-methanesulfonate (LiCF.sub.3SO.sub.3), bis-trifluoromethyl sulfonylimide lithium [LiN(CF.sub.3SO.sub.2).sub.2], lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF.sub.2C.sub.2O.sub.4), lithium nitrate (LiNO.sub.3), Li-Fluoroalkyl-Phosphates (LiPF.sub.3(CF.sub.2CF.sub.3).sub.3), lithium bisperfluoroethylsulfonylimide (LiBETI), an ionic liquid salt, sodium perchlorate (NaClO.sub.4), potassium perchlorate (KClO.sub.4), sodium hexafluorophosphate (NaPF.sub.6), potassium hexafluorophosphate (KPF.sub.6), sodium borofluoride (NaBF.sub.4), potassium borofluoride (KBF.sub.4), sodium hexafluoroarsenide, potassium hexafluoroarsenide, sodium trifluoro-methanesulfonate (NaCF.sub.3SO.sub.3), potassium trifluoro-methanesulfonate (KCF.sub.3SO.sub.3), bis-trifluoromethyl sulfonylimide sodium (NaN(CF.sub.3SO.sub.2).sub.2), sodium trifluoromethanesulfonimide (NaTFSI), and bis-trifluoromethyl sulfonylimide potassium (KN(CF.sub.3SO.sub.2).sub.2). Among them, LiPF.sub.6, LiBF.sub.4 and LiN(CF.sub.3SO.sub.2).sub.2 are preferred for LiS cells, NaPF.sub.6 and LiBF.sub.4 for NaS cells, and KBF.sub.4 for KS cells. The content of aforementioned electrolytic salts in the non-aqueous solvent is preferably 0.5 to 3.0 M (mol/L) at the cathode side and 3.0 to >10 M at the anode side.

(44) The ionic liquid is composed of ions only. Ionic liquids are low melting temperature salts that are in a molten or liquid state when above a desired temperature. For instance, a salt is considered as an ionic liquid if its melting point is below 100 C. If the melting temperature is equal to or lower than room temperature (25 C.), the salt is referred to as a room temperature ionic liquid (RTIL). The IL salts are characterized by weak interactions, due to the combination of a large cation and a charge-delocalized anion. This results in a low tendency to crystallize due to flexibility (anion) and asymmetry (cation).

(45) A typical and well-known ionic liquid is formed by the combination of a 1-ethyl-3-methylimidazolium (EMI) cation and an N,N-bis(trifluoromethane)sulfonamide (TFSI) anion. This combination gives a fluid with an ionic conductivity comparable to many organic electrolyte solutions and a low decomposition propensity and low vapor pressure up to 300-400 C. This implies a generally low volatility and non-flammability and, hence, a much safer electrolyte for batteries.

(46) Ionic liquids are basically composed of organic ions that come in an essentially unlimited number of structural variations owing to the preparation ease of a large variety of their components. Thus, various kinds of salts can be used to design the ionic liquid that has the desired properties for a given application. These include, among others, imidazolium, pyrrolidinium and quaternary ammonium salts as cations and bis(trifluoromethanesulfonyl) imide, bis(fluorosulfonyl)imide, and hexafluorophosphate as anions. Based on their compositions, ionic liquids come in different classes that basically include aprotic, protic and zwitterionic types, each one suitable for a specific application.

(47) Common cations of room temperature ionic liquids (RTILs) include, but not limited to, tetraalkylammonium, di-, tri-, and tetra-alkylimidazolium, alkylpyridinium, dialkyl-pyrrolidinium, dialkylpiperidinium, tetraalkylphosphonium, and trialkylsulfonium. Common anions of RTILs include, but not limited to, BF.sub.4.sup., B(CN).sub.4.sup., CH.sub.3BF.sub.3.sup., CH.sub.2CHBF.sub.3.sup., CF.sub.3BF.sub.3.sup., C.sub.2F.sub.5BF.sub.3.sup., n-C.sub.3F.sub.7BF.sub.3.sup., n-C.sub.4F.sub.9BF.sub.3.sup., PF.sub.6.sup., CF.sub.3CO.sub.2.sup., CF.sub.3SO.sub.3.sup., N(SO.sub.2CF.sub.3).sub.2.sup., N(COCF.sub.3)(SO.sub.2CF.sub.3).sup., N(SO.sub.2F).sub.2.sup., N(CN).sub.2.sup., C(CN).sub.3.sup., SCN.sup., SeCN.sup., CuCl.sub.2.sup., AlCl.sub.4.sup., F(HF).sub.2.3.sup., etc. Relatively speaking, the combination of imidazolium- or sulfonium-based cations and complex halide anions such as AlCl.sub.4.sup., BF.sub.4.sup., CF.sub.3CO.sub.2.sup., CF.sub.3SO.sub.3.sup., NTf.sub.2.sup., N(SO.sub.2F).sub.2.sup., or F(HF).sub.2.3.sup. results in RTILs with good working conductivities.

(48) RTILs can possess archetypical properties such as high intrinsic ionic conductivity, high thermal stability, low volatility, low (practically zero) vapor pressure, non-flammability, the ability to remain liquid at a wide range of temperatures above and below room temperature, high polarity, high viscosity, and wide electrochemical windows. These properties, except for the high viscosity, are desirable attributes when it comes to using an RTIL as an electrolyte ingredient (a salt and/or a solvent) in a lithium metal cell.

Example 1: Sol-Gel Process for Producing Li.SUB.x.TiNb.SUB.2.O.SUB.7 .(TNO) as an Inorganic Filler for the Elastomer-Based Electrode-Protecting Layer

(49) The synthesis method involves precipitating the precursor to niobium-based composite metal oxide nanoparticles from a solution reactant mixture of Nb(OH).sub.5 (dissolved in citric acid) and water-ethanol solution containing Ti(OC.sub.3H.sub.7).sub.4. Specifically, Nb.sub.2O.sub.5 was dissolved in hydrofluoric acid to form a transparent solution. In order to remove the F ions from the solution, ammonia was added to obtain a white Nb(OH).sub.5 precipitate. After the precipitate was washed and dried, the Nb(OH).sub.5 was dissolved in citric acid to form a Nb(V)-citrate solution. A water-ethanol solution containing Ti(OC.sub.3H.sub.7).sub.4 was added to this solution while the pH value of the solution was adjusted using ammonia. This final mixture containing Nb(V) and Ti(IV) ions was then stirred at 90 C. to form a citric gel. This gel was then heated to 140 C. to obtain a precursor, which was annealed at 900 C. and at 1350 C. to obtain the Li.sub.xTiNb.sub.2O.sub.7 (TNO) powder.

(50) The powder was ball-milled in a high-intensity ball mill to obtain nanoparticles of TNO, which were then dispersed in monomers/oligomers of several different elastomers (e.g. polyurethane, polybutadine, etc.) to form reacting suspensions. The monomers/oligomers were then polymerized to a controlled extent without allowing for any significant cross-linking of chains. This procedure often enables chemical bonding between the elastomer and the metal oxide particles or other inorganic filler species (particles of transition metal carbide, sulfide, selenide, phosphide, nitride, boride, etc.). These non-cured or non-crosslinked polymers were then each separately dissolved in an organic solvent to form a suspension (polymer-solvent solution plus bonded metal oxide particles and a selected conductive additive; e.g. graphene sheets). The slurry was then spray-deposited onto a lithium anode layer (or a pre-fabricated cathode electrode) or made into a thin film via coating/casting. As an anode-protecting layer, the thin film was then laminated with a lithium metal layer, along with an electrolyte/separator, and a cathode layer to form a lithium metal battery cell. As a cathode-protecting layer, the thin film was then laminated with a cathode layer, a lithium metal-based anode active layer, and an electrolyte/separator to form a lithium metal battery cell.

Example 2: Preparation of TiNb.SUB.2.O.SUB.7., TiMoNbO.SUB.7., and TiFe.SUB.0.3.Nb.SUB.1.7.O.SUB.7 .as an Inorganic Filler for the Elastomer-Based Electrode-Protecting Layer

(51) A niobium-titanium composite oxide represented by the general formula TiNb.sub.2O.sub.7 was synthesized, by following the following procedure: Commercially available niobium oxide (Nb.sub.2O.sub.5) and a titanate proton compound were used as starting materials. The titanate proton compound was prepared by immersing potassium titanate in hydrochloric acid at 25 C. for 72 hours. In the process, 1M hydrochloric acid was replaced with a 1M of fresh acid every 24 hours. As a result, potassium ions were exchanged for protons to obtain the titanate proton compound.

(52) The niobium oxide (Nb.sub.2O.sub.5) and the titanate proton compound were weighed such that the molar ratio of niobium to titanium in the synthesized compound was 3. The mixture was dispersed in 100 ml of pure water, followed by vigorous mixing. The obtained mixture was placed in a heat resistant container and was subjected to hydrothermal synthesis under conditions of 180 C. for a total of 24 hours. The obtained sample was washed in pure water three times, and then dried. The sample was then subjected to a heat treatment at 1,100 C. for 24 hours to obtain TiNb.sub.2O.sub.7.

(53) Additionally, a niobium-molybdenum-titanium composite oxide was synthesized in the same manner as above except that niobium oxide (Nb.sub.2O.sub.5), molybdenum oxide (Mo.sub.2O.sub.5), and a titanate proton compound were weighed such that the molar ratio of niobium to titanium and that of molybdenum to titanium in the synthesized compound was 1.5 and 1.5, respectively. As a result, a niobium-molybdenum-titanium composite oxide (TiMoNbO.sub.7) was obtained.

(54) In addition, a niobium-Iron-titanium composite oxide was synthesized in the same manner as above except that niobium oxide (Nb.sub.2O.sub.5), a titanate proton compound, and iron oxide (Fe.sub.2O.sub.3) were weighed such that the molar ratio of niobium to titanium and of iron to titanium in the synthesized compound was 3 and 0.3, respectively. As a result, a niobium-titanium composite oxide (TiFe.sub.0.3Nb.sub.1.7O.sub.7) was obtained.

(55) The above niobium-containing composite metal oxide powders (TiNb.sub.2O.sub.7, TiMoNbO.sub.7, and TiFe.sub.0.3Nb.sub.1.7O.sub.7) were separately added into a monomer of synthetic polyisoprene and a mixture of monomers for urethane-urea copolymer, respectively. Polymerization of the respective reacting mass was initiated and proceeded to obtain linear chains without crosslinking.

(56) This step was found to create some bonding between the composite metal oxide particles. Subsequently, these substantially linear chains were dissolved in a solvent (e.g. benzene and DMAc) to form a solution and a desired amount of graphene sheets or CNTs was added to form a slurry. The slurry was then cast into thin films for use as an anode- or cathode-protecting layer.

Example 3: Preparation of Ga.SUB.0.1.Ti.SUB.0.8.Nb.SUB.2.1.O.SUB.7 .as an Inorganic Filler for the Elastomer Layer

(57) In an experiment, 0.125 g of GaCl.sub.3 and 4.025 g of NbCl.sub.5 were dissolved in 10 mL of anhydrous ethanol under an inert atmosphere (argon) and magnetic stirring. The solution was transferred under air. Then, added to this solution was 6.052 g solution of titanium oxysulfate (TiOSO.sub.4) at 15% by mass in sulfuric acid, followed by 10 mL of ethanol to dissolve the precursors under a magnetic stirring. The pH of the solution was adjusted to 10 by slow addition of ammonia NH.sub.3 at 28% by mass into water.

(58) The paste was transferred into a Teflon container having a 90-mL capacity, which was then placed in an autoclave. The paste was then heated up to 220 C. for 5 hours with a heating and cooling ramp of 2 and 5 degrees C./min, respectively. The paste was then washed with distilled water by centrifugation until a pH between 6 and 7 was obtained. The resulting compound was heated at 60 C. for 12 hours and then ball-milled for 30 min at 500 rpm (revolutions per minute) in hexane. After evaporation of the solvent, the powder was calcinated at 950 C. for 1 hour with a heating/cooling ramp of 3 degrees C./min to produce crystals of Ga.sub.0.1Ti.sub.0.8Nb.sub.2.1O.sub.7. These particles were used as an inorganic filler to reinforce an elastomer matrix.

Example 4: Preparation of Fe.SUB.0.1.Ti.SUB.0.8.Nb.SUB.2.1.O.SUB.7.Powder as a Filler for Elastomer

(59) In a representative procedure, 0.116 g of FeCl.sub.3 and 4.025 g of NbCl.sub.5 were dissolved in 10 mL of anhydrous ethanol under an inert atmosphere (argon) and magnetic stirring. The resulting solution was transferred under air. Then, added to this solution was 6.052 g of titanium oxysulfate (TiOSO.sub.4) at 15% by mass in sulfuric acid and 10 mL of ethanol to dissolve the precursors under a magnetic stirring. The pH of the solution was adjusted to 10 by slow addition of ammonia NH.sub.3 at 28% by mass into water.

(60) The paste was transferred into a Teflon container having a 90-mL capacity, which was then placed in an autoclave. The paste was then heated up to 220 C. for 5 hours with a heating and cooling ramp of 2 and 5 degrees C./min, respectively. The paste was then washed with distilled water by centrifugation until a pH between 6 and 7 was obtained. The compound was heated at 60 C. for 12 hours and then ball-milled for 30 min at 500 rpm in hexane. After evaporation of hexane, the powder was calcinated at 950 C. for 1 hour with a heating/cooling ramp of 3 degrees C./min to obtain Fe.sub.0.1Ti.sub.o8Nb.sub.2.1O.sub.7 crystals for use as an inorganic filler in an elastomer matrix

Example 5: Production of Molybdenum Diselenide Nanoplatelets (as an Inorganic Filler) Using Direct Ultrasonication

(61) A sequence of steps can be utilized to form nanoplatelets from many different types of layered compounds: (a) dispersion of a layered compound in a low surface tension solvent or a mixture of water and surfactant, (b) ultrasonication, and (c) an optional mechanical shear treatment. For instance, dichalcogenides (MoSe.sub.2) consisting of SeMoSe layers held together by weak van der Waals forces can be exfoliated via the direct ultrasonication process invented by our research group. Intercalation can be achieved by dispersing MoSe.sub.2 powder in a silicon oil beaker, with the resulting suspension subjected to ultrasonication at 120 W for two hours. The resulting MoSe.sub.2 platelets were found to have a thickness in the range from approximately 1.4 nm to 13.5 nm with most of the platelets being mono-layers or double layers.

(62) Other single-layer platelets of the form MX.sub.2 (transition metal dichalcogenide), including MoS.sub.2, TaS.sub.2, ZrS.sub.2, and WS.sub.2, were similarly exfoliated and separated. Again, most of the platelets were mono-layers or double layers when a high sonic wave intensity was utilized for a sufficiently long ultrasonication time.

Example 6: Production of ZrS.SUB.2 .Nanodiscs as an Inorganic Filler for the Elastomer Layer

(63) In a representative procedure, zirconium chloride (ZrCl.sub.4) precursor (1.5 mmol) and oleylamine (5.0 g, 18.7 mmol) were added to a 25-mL three-neck round-bottom flask under a protective argon atmosphere. The reaction mixture was first heated to 300 C. at a heating rate of 5 C./min under argon flow and subsequently CS.sub.2 (0.3 mL, 5.0 mmol) was injected. After 1 h, the reaction was stopped and cooled down to room temperature. After addition of excess butanol and hexane mixtures (1:1 by volume), 18 nm ZrS.sub.2 nanodiscs (100 mg) were obtained by centrifugation. Larger sized nanodiscs ZrS.sub.2 of 32 nm and 55 nm were obtained by changing reaction time to 3 h and 6 h, respectively otherwise under identical conditions.

Example 7: Preparation of Boron Nitride Nanosheets as a Filler for the Elastomer Layer

(64) Five grams of boron nitride (BN) powder, ground to approximately 20 m or less in sizes, were dispersed in a strong polar solvent (dimethyl formamide) to obtain a suspension. An ultrasonic energy level of 85 W (Branson S450 Ultrasonicator) was used for exfoliation, separation, and size reduction for a period of 1-3 hours. This is followed by centrifugation to isolate the BN nanosheets. The BN nanosheets obtained were from 1 nm thick (3 atomic layers) up to 7 nm thick.

Example 8: Sulfonation of Triblock Copolymer Poly(Styrene-Isobutylene-Styrene) or SIBS

(65) An example of the sulfonation procedure used in this study is summarized as follows: a 10% (w/v) solution of SIBS (50 g) and a desired amount of graphene oxide sheets (0.15% to 40.5% by wt.) in methylene chloride (500 ml) was prepared. The solution was stirred and refluxed at approximately 40 8 C, while a specified amount of acetyl sulfate in methylene chloride was slowly added to begin the sulfonation reaction. Acetyl sulfate in methylene chloride was prepared prior to this reaction by cooling 150 ml of methylene chloride in an ice bath for approximately 10 min. A specified amount of acetic anhydride and sulfuric acid was then added to the chilled methylene chloride under stirring conditions. Sulfuric acid was added approximately 10 min after the addition of acetic anhydride with acetic anhydride in excess of a 1:1 mole ratio. This solution was then allowed to return to room temperature before being added to the reaction vessel.

(66) After approximately 5 h, the reaction was terminated by slowly adding 100 ml of methanol. The reacted polymer solution was then precipitated with deionized water. The precipitate was washed several times with water and methanol, separately, and then dried in a vacuum oven at 50 C. for 24 h. This washing and drying procedure was repeated until the pH of the wash water was neutral. After this process, the final polymer yield was approximately 98% on average. This sulfonation procedure was repeated with different amounts of acetyl sulfate to produce several sulfonated polymers with various levels of sulfonation or ion-exchange capacities (LECs). The mol % sulfonation is defined as: mol %=(moles of sulfonic acid/moles of styrene)100%, and the IEC is defined as the mille-equivalents of sulfonic acid per gram of polymer (mequiv./g).

(67) After sulfonation and washing of each polymer, the S-SIBS samples were dissolved in a mixed solvent of toluene/hexanol (85/15, w/w) with concentrations ranging from 0.5 to 2.5% (w/v). Desired amounts of graphene sheets and inorganic filler (if not added at an earlier stage) were then added into the solution to form slurry samples. The slurry samples were slot-die coated into layers of sulfonated elastomer composite.

Example 9: Synthesis of Sulfonated Polybutadiene (PB) by Free Radical Addition of Thiolacetic Acid (TAA) Followed by In Situ Oxidation with Performic Acid

(68) A representative procedure is given as follows. PB (8.0 g) was dissolved in toluene (800 mL) under vigorous stirring for 72 h at room temperature in a 1 L round-bottom flask. Benzophenone (BZP) (0.225 g; 1.23 mmol; BZP/olefin molar ratio=1:120) and TAA (11.9 mL; 0.163 mol, TAA/olefin molar ratio=1.1) and a desired amount of graphene sheets (0.1%-40% by wt.) were introduced into the reactor, and the polymer solution was irradiated for 1 h at room temperature with UV light of 365 nm and power of 100 W.

(69) The resulting thioacetylated polybutadiene (PB-TA)/graphene composite was isolated by pouring 200 mL of the toluene solution in a plenty of methanol and the polymer recovered by filtration, washed with fresh methanol, and dried in vacuum at room temperature (Yield=3.54 g). Formic acid (117 mL; 3.06 mol; HCOOH/olefin molar ratio=25), along with a desired amount of anode active material particles, from 10 to 100 grams) were added to the toluene solution of PB-TA at 50 C. followed by slow addition of 52.6 mL of hydrogen peroxide (35 wt %; 0.61 mol; H.sub.2O.sub.2/olefin molar ratio=5) in 20 min. We would like to caution that the reaction is autocatalytic and strongly exothermic. The resulting slurry was spray-dried to obtain sulfonated polybutadiene (PB-SA)/graphene composite layers.

(70) It may be noted that graphene sheets may be added at different stages of the procedure: before, during or after BZP is added or before/during/after the inorganic filler is added.

Example 10: Synthesis of Sulfonated SBS

(71) Sulfonated styrene-butadiene-styrene triblock copolymer (SBS) based elastomer was directly synthesized. First, SBS (optionally along with graphene sheets) is first epoxidized by performic acid formed in situ, followed by ring-opening reaction with an aqueous solution of NaHSO.sub.3. In a typical procedure, epoxidation of SBS was carried out via reaction of SBS in cyclohexane solution (SBS concentration=11 g/100 mL) with performic acid formed in situ from HCOOH and 30% aqueous H.sub.2O.sub.2 solution at 70 C. for 4 h, using 1 wt % poly(ethylene glycol)/SBS as a phase transfer catalyst. The molar ratio of H.sub.2O.sub.2/HCOOH was 1. The product (ESBS) was precipitated and washed several times with ethanol, followed by drying in a vacuum dryer at 60 C.

(72) Subsequently, ESBS was first dissolved in toluene to form a solution with a concentration of 10 g/100 mL, into which was added 5 wt % TEAB/ESBS as a phase transfer catalyst and 5 wt % DMA/ESBS as a ring-opening catalyst. Herein, TEAB=tetraethyl ammonium bromide and DMA=N,N-dimethyl aniline. An aqueous solution of NaHSO.sub.3 and Na.sub.2SO.sub.3 (optionally along with graphene sheets or CNTs, if not added earlier) was then added with vigorous stirring at 60 C. for 7 h at a molar ratio of NaHSO.sub.3/epoxy group at 1.8 and a weight ratio of Na.sub.2SO.sub.3/NaHSO.sub.3 at 36%. This reaction allows for opening of the epoxide ring and attaching of the sulfonate group according to the following reaction:

(73) ##STR00001##
The reaction was terminated by adding a small amount of acetone solution containing antioxidant. The mixture was washed with distilled water and then precipitated by ethanol while being cast into thin films, followed by drying in a vacuum dryer at 50 C. It may be noted that graphene sheets (or CNTs, etc.) and inorganic filler may be added during various stages of the aforementioned procedure (e.g. right from the beginning, or prior to the ring opening reaction).

Example 11: Synthesis of Sulfonated SBS by Free Radical Addition of Thiolacetic Acid (TAA) Followed by In Situ Oxidation with Per-Formic Acid

(74) A representative procedure is given as follows. SBS (8.000 g) in toluene (800 mL) was left under vigorous stirring for 72 hours at room temperature and heated later on for 1 h at 65 C. in a 1 L round-bottom flask until the complete dissolution of the polymer. Thus, benzophenone (BZP, 0.173 g; 0.950 mmol; BZP/olefin molar ratio=1:132) and TAA (8.02 mL; 0.114 mol, TAA/olefin molar ratio=1.1) were added, and the polymer solution was irradiated for 4 h at room temperature with UV light of 365 nm and power of 100 W. To isolate a fraction of the thioacetylated sample (S(B-TA)S), 20 mL of the polymer solution was treated with plenty of methanol, and the polymer was recovered by filtration, washed with fresh methanol, and dried in vacuum at room temperature. The toluene solution containing the thioacetylated polymer was equilibrated at 50 C., and 107.4 mL of formic acid (2.84 mol; HCOOH/olefin molar ratio=27.5) and 48.9 mL of hydrogen peroxide (35 wt %; 0.57 mol; H.sub.2O.sub.2/olefin molar ratio=5.5) were added in about 15 min. It may be cautioned that the reaction is autocatalytic and strongly exothermic! The conductive reinforcement material and/or an inorganic filler was added before or after this reaction. The resulting slurry was stirred for 1 h, and then most of the solvent was distilled off in vacuum at 35 C. Finally, the slurry containing the sulfonated elastomer was added with acetonitrile, cast into films, washed with fresh acetonitrile, and dried in vacuum at 35 C. to obtain layers of sulfonated elastomers.

(75) Other elastomers (e.g. polyisoprene, EPDM, EPR, polyurethane, etc.) were sulfonated in a similar manner. Alternatively, all the rubbers or elastomers can be directly immersed in a solution of sulfuric acid, a mixture of sulfuric acid and acetyl sulfate, or other sulfonating agent discussed above to produce sulfonated elastomers/rubbers. Again, graphene sheets (or other conductive reinforcement material) and inorganic filler may be added at various stages of the procedure.

Example 12: Expanded Multi-Walled Carbon Nanotubes (MWCNTs) as a Supporting and Protective Porous Backbone for Selenium

(76) Fifty grams of MWCNTs were chemically treated (intercalated and/or oxidized) with a mixture of sulfuric acid, nitric acid, and potassium permanganate at a weight ratio of 4:1:0.05 (graphite-to-intercalate ratio of 1:3) for 48 hours. Upon completion of the intercalation reaction, the mixture was poured into deionized water and filtered. The sample was then washed with 5% HCl solution to remove most of the sulfate ions and residual salt and then repeatedly rinsed with deionized water until the pH of the filtrate was approximately 5. The dried sample was then exposed to a heat shock treatment at 950 C. for 45 seconds. Expanded MWCNTs, alone or in combination with another particulate carbon/graphite material, can be packed into a mesoporous structure for supporting the selenium material.

Example 13: Electrochemical Deposition of Se on Various Webs or Paper Structures (External Electrochemical Deposition) for LiSe Batteries

(77) The electrochemical deposition may be conducted before the cathode active layer is incorporated into a lithium-selenium battery cell. In this approach, the anode, the electrolyte, and the integral layer of mesoporous structure (serving as a cathode layer) are positioned in an external container outside of a lithium-selenium cell. The needed apparatus is similar to an electro-plating system, which is well-known in the art.

(78) In a typical procedure, a metal polyselenide (M.sub.xSe.sub.y) is dissolved in a solvent (e.g. mixture of DOL/DME in a volume ratio from 1:3 to 3:1) to form an electrolyte solution. An amount of a lithium salt may be optionally added, but this is not required for external electrochemical deposition. A wide variety of solvents can be utilized for this purpose and there is no theoretical limit to what type of solvents can be used; any solvent can be used provided that there is some solubility of the metal polyselenide in this desired solvent. A greater solubility would mean a larger amount of selenium can be derived from the electrolyte solution.

(79) The electrolyte solution is then poured into a chamber or reactor under a dry and controlled atmosphere condition (e.g. He or Nitrogen gas). A Li metal foil can be used as the anode and a layer of the mesoporous structure as the cathode; both being immersed in the electrolyte solution. This configuration constitutes an electrochemical deposition system. The step of electrochemically depositing nanoscaled selenium particles or coating in the mesopores is conducted at a current density preferably in the range from 1 mA/g to 10 A/g, based on the layer weight of the mesoporous structure.

(80) The chemical reactions that occur in this reactor may be represented by the following equation: M.sub.xSe.sub.y.fwdarw.M.sub.xSe.sub.yz+zSe (typically z=1-4). Quite surprisingly, the precipitated Se is preferentially nucleated and grown on massive internal surfaces of mesopores to form nanoscaled coating or nanoparticles. The coating thickness or particle diameter and the amount of Se coating/particles may be controlled by the specific surface area, electro-chemical reaction current density, temperature and time. In general, a lower current density and lower reaction temperature lead to a more uniform distribution of Se and the reactions are easier to control. A longer reaction time leads to a larger amount of Se deposited on graphene surfaces and the reaction is ceased when the selenium source is consumed or when a desired amount of Se is deposited.

Example 14: Electrochemical Deposition of Se on Various Mesoporous Webs or Paper-Based Cathode Structures in LiSe Batteries (Internal Electrochemical Deposition)

(81) As an alternative to the external electrochemical deposition, an internal electrochemical conversion and deposition of Se from an electrolyte-borne selenium source onto massive internal surfaces of mesoporous structures was also conducted using a broad array of mesoporous structures. As a typical procedure, the anode, the electrolyte, and the integral layer of mesoporous structure are packaged inside a housing to form a lithium-selenium cell. In such a configuration, the battery cell itself is an electrochemical deposition system for pre-selennization of the cathode and the step of electrochemically depositing nanoscaled selenium particles or coating on the internal surfaces occurs after the lithium-selenium cell is fabricated and conducted during the first charge cycle of the LiSe cell.

(82) As a series of examples, lithium polyselenide (Li.sub.xSe.sub.y) and sodium polyselenide (Na.sub.xSe.sub.y)-containing electrolytes with desired x and y values (e.g. x=2, and y=6-10) dissolved in solvent were prepared by chemically reacting stoichiometric amounts of selenium and Li.sub.2Se or Na.sub.2Se in polyselenide free electrolyte of 0.5 M LiTFSI+0.2 M LiNO.sub.3 (or 0.5 M NaTFSI+0.2 M NaNO.sub.3) in DOL/DME (1:1, v:v). The electrolyte was stirred at 75 C. for 3-7 hours and then at room temperature for 48 hours. The resulting electrolytes contain different Li.sub.xSe.sub.y or Na.sub.xSe.sub.y species (e.g. x=2, and y=6-10, depending upon reaction times and temperatures), which are intended for use as a selenium source in a battery cell.

(83) In a LiSe cell, one of these electrolytes was selected to combine with an anode current collector (Cu foil), an anode layer (e.g. Li metal foil), a porous separator, a layer of porous graphene structure, and a cathode current collector (Al foil) to form a LiSe cell. The cell was then subjected to a first charge procedure using a current density ranging from 5 mA/g to 50 A/g. The best current density range was found to be from 50 mA/g to 5 A/g.

Example 15: Effects of the Anode-Protecting Layer and/or the Cathode-Protecting Layer

(84) The sulfonated elastomer composite films for anode protection were SIBS as prepared in Example 8. Several tensile testing specimens were cut from the film and tested with a universal testing machine. The results indicate that this series of sulfonated elastomer films have an elastic deformation from approximately 150% to 465%. The addition of up to 30% by weight of a conductive reinforcement material (CNTs, graphene, CNFs, etc.) typically reduces this elasticity down to a reversible tensile strain from 7% to 130%.

(85) For electrochemical testing, the working electrodes (cathode layers) were prepared by impregnating Se into a sheet of expanded CNT mat. Electrochemical measurements were carried out using CR2032 (3V) coin-type cells with lithium metal as the counter electrode (actually an anode of a LiSe cell), Celgard 2400 membrane as separator, and 1 M LiPF.sub.6 electrolyte solution dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC-DEC, 1:1 v/v). Four LiSe cells were prepared: one including an anode-protecting layer (sulfonated SIBS elastomer composite prepared as in Example 1), one including a cathode-protecting layer (sulfonated PB composite as prepared in Example 2), one including both an anode-protecting layer and a cathode-protecting layer, and one including no electrode-protecting layer (the baseline cell). The cell assembly was performed in an argon-filled glove-box. The CV measurements were carried out using a CH-6 electrochemical workstation at a scanning rate of 1 mV/s. The electrochemical performance of the cell featuring sulfonated elastomer composite binder and that containing PVDF binder were evaluated by galvanostatic charge/discharge cycling at a current density of 50 mA/g using an Arbin electrochemical workstation.

(86) Summarized in FIG. 3 are the cathode specific intercalation capacity curves of these four lithium-selenium cells. As the number of cycles increases, the specific capacity of the unprotected cell drops at the fastest rate. In contrast, the presently invented filled sulfonated elastomer composite protection layer provides the battery cell with a significantly more stable and high specific capacity for a large number of cycles. These data have clearly demonstrated the surprising and superior performance of the presently invented sulfonated elastomer composite protection approach. The configuration containing both the anode-protecting layer and the cathode-protecting layer provides the best cycle stability (longest cycle-life), followed by the one containing a cathode-protecting layer, and then the one containing an anode-protecting layer.

(87) The sulfonated elastomer composite-based anode-protecting layer appears to be capable of reversibly deforming to a great extent without breakage when the lithium foil decreases in thickness during battery discharge. The anode-protecting layer also prevents the continued reaction between liquid electrolyte and lithium metal at the anode, reducing the problem of continuing loss in lithium and electrolyte. This also enables a significantly more uniform deposition of lithium ions upon returning from the cathode during a battery re-charge step; hence, no lithium dendrite. These were observed by using SEM to examine the surfaces of the electrodes recovered from the battery cells after some numbers of charge-discharge cycles.

(88) The cathode-protecting layer acts to block or capture the Se and lithium polyselenide species dissolved in the electrolyte, preventing these species from migrating to the anode side. This elastic layer also helps to maintain a good contact with both the separator layer and the cathode active material layer, thereby maintaining good lithium ion pathways without interruption.

Example 16: Sulfonated Elastomer Composite Implemented in the Anode of a LiSe Cell

(89) The LiSe cell initially contained an anode active material layer having an ultra-thin lithium layer (approximately 1.1 m thick) and a cathode active material layer containing lithium selenide-coated graphene paper mat prepared in Example 13 when the cell was made. During the first charging step (the formation procedure), massive lithium ions migrated out of the cathode and deposited onto the initially thin lithium layer. The anode-protecting sulfonated elastomer composite as a lithium-protecting layer was based on the sulfonated polybutadiene (PB) prepared according to a procedure used in Example 9. Tensile testing was also conducted on the sulfonated elastomer films (without the conductive reinforcement material). This series of sulfonated elastomers can be elastically stretched up to approximately 135% (having some lithium salt or conductive reinforcement material dispersed therein) or up to 770% (with no additive).

(90) FIG. 4 shows that the cell having an anode-protecting polymer layer offers a significantly more stable cycling behavior. The sulfonated elastomer composite also acts to isolate the electrolyte from the lithium coating yet still allowing for easy diffusion of lithium ions.

Example 17: Effect of Lithium Ion-Conducting Additive in a Sulfonated Elastomer Composite

(91) A wide variety of lithium ion-conducting additives were added to several different elastomer matrix materials to prepare anode or cathode protection layers. The lithium ion conductivity values of the resulting complex materials are summarized in Table 1 below. We have discovered that these composite materials are suitable electrode-protecting layer materials provided that their lithium ion conductivity at room temperature is no less than 10.sup.6 S/cm. With these materials, lithium ions appear to be capable of readily diffusing through the protective layer having a thickness no greater than 1 m. For thicker polymer films (e.g. 10 m), a lithium ion conductivity at room temperature of these sulfonated elastomer composites no less than 10.sup.4 S/cm would be required.

(92) TABLE-US-00001 TABLE 1 Lithium ion conductivity of various sulfonated elastomer composite compositions as a lithium metal-protecting layer. Sample Lithium-conducting % sulfonated elastomer No. additive (1-2 m thick) Li-ion conductivity (S/cm) E-1p Li.sub.2CO.sub.3 + (CH.sub.2OCO.sub.2Li).sub.2 70-99% 1.3 10.sup.4 to 3.3 10.sup.3 S/cm B1p LiF + LiOH + Li.sub.2C.sub.2O.sub.4 60-90% 4.2 10.sup.5 to 2.6 10.sup.3 S/cm B2p LiF + HCOLi 80-99% 1.2 10.sup.4 to 1.4 10.sup.3 S/cm B3p LiOH 70-99% 8.5 10.sup.4 to 1.1 10.sup.2 S/cm B4p Li.sub.2CO.sub.3 70-99% 4.3 10.sup.3 to 9.5 10.sup.3 S/cm B5p Li.sub.2C.sub.2O.sub.4 70-99% 8.2 10.sup.4 to 1.3 10.sup.2 S/cm B6p Li.sub.2CO.sub.3 + LiOH 70-99% 1.5 10.sup.3 to 1.7 10.sup.2 S/cm C1p LiClO.sub.4 70-99% 4.0 10.sup.4 to 2.2 10.sup.3 S/cm C2p LiPF.sub.6 70-99% 2.1 10.sup.4 to 6.2 10.sup.3 S/cm C3p LiBF.sub.4 70-99% 1.2 10.sup.4 to 1.7 10.sup.3 S/cm C4p LiBOB + LiNO.sub.3 70-99% 1.4 10.sup.4 to 3.2 10.sup.3 S/cm S1p Sulfonated polyaniline 85-99% 3.2 10.sup.5 to 9.5 10.sup.4 S/cm S2p Sulfonated PEEK 85-99% 1.4 10.sup.4 to 1.3 10.sup.3 S/cm S3p Sulfonated PVDF 80-99% 1.7 10.sup.4 to 1.5 10.sup.4 S/cm S4p Polyethylene oxide 80-99% 4.2 10.sup.4 to 3.4 103.sup.4 S/cm.sup.

(93) In lithium battery industry, it is a common practice to define the cycle life of a battery as the number of charge-discharge cycles that the battery suffers a 20% decay in capacity based on the initial capacity measured after the required electrochemical formation. After an extensive investigation, we have come to observe that the cycle-life of a lithium-selenium cell is typically in the range from 500-2,500 cycles when at least an electrode-protecting layer is implemented. In contrast, the typical cycle life of an unprotected LiSe cell is typically in the range from 150-35 cycles.