Method of improving cycle-life of alkali metal-sulfur secondary battery

1. A method of improving a cycle-life of a rechargeable alkali metal-sulfur cell, said method comprising implementing an anode-protecting layer between an anode active material layer and a porous separator/electrolyte, and/or implementing a cathode-protecting layer between a cathode active material and said porous separator/electrolyte, wherein said anode-protecting layer or cathode-protecting layer comprises a conductive sulfonated elastomer composite having from 0.01% to 50% by weight of a conductive reinforcement material dispersed in a sulfonated elastomeric matrix material and said layer of conductive sulfonated elastomer composite has a thickness from 1 nm to 100 μm, a fully recoverable tensile strain from 2% to 500%, a lithium ion conductivity from 10 −7 S/cm to 5×10 −2 S/cm, and an electrical conductivity from 10 −7 S/cm to 100 when measured at room temperature.

2. The method of claim 1 , wherein said cathode active material layer comprises a sulfur-containing material selected from the group consisting of sulfur-carbon hybrid, sulfur-graphite hybrid, sulfur-graphene hybrid, conducting polymer-sulfur hybrid, metal sulfide, sulfur compound, and combinations thereof.

3. The method of claim 2 , wherein said sulfur-carbon hybrid, sulfur-graphite hybrid, sulfur-graphene hybrid, or conducting polymer-sulfur hybrid is a mixture, blend, composite, chemically or physically bonded entity of sulfur or sulfide with a carbon, graphite, graphene, or conducting polymer material.

4. The method of claim 1 , wherein said conductive reinforcement material is selected from the group consisting of graphene sheets, carbon nanotubes, carbon nanofibers, metal nanowires, conductive polymer fibers, and combinations thereof.

5. The method of claim 1 , wherein said sulfonated elastomeric matrix material comprises a material selected from the group consisting of sulfonated versions 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 method of claim 1 , wherein said steps (d) and (e) are conducted by depositing a layer of first sulfonated elastomer composite onto one primary surface of the anode active material layer to form a protected anode and/or depositing a layer of second sulfonated elastomer composite onto one primary surface of the cathode active material layer to form a protected cathode, followed by combining the protected anode, the separator/electrolyte, and the protected cathode together to form said alkali metal-sulfur cell.

7. The method of claim 1 , wherein said steps (d) and (e) are conducted by depositing a layer of first sulfonated elastomer composite onto one primary surface of the separator and/or depositing a layer of second sulfonated elastomer composite onto the opposing primary surface of the separator to form a coated separator, followed by combining the anode, the coated separator, the cathode, and the electrolyte together to form the alkali metal-sulfur cell.

8. The method of claim 1 , wherein said steps (d) and (e) are conducted by forming a layer of first sulfonated elastomer composite and/or a layer of second sulfonated elastomer composite, followed by laminating the anode layer, the layer of first sulfonated elastomer composite, the separator layer, the layer of second sulfonated elastomer composite, the cathode layer, along with the electrolyte to form the alkali metal-sulfur cell.

9. The method of claim 2 , wherein said metal sulfide contains M x S y , wherein x is an integer from 1 to 3 and y is an integer from 1 to 10, and M is a metal element selected from an alkali metal, an alkaline metal selected from Mg or Ca, a transition metal, a metal from groups 13 to 17 of the periodic table, or a combination thereof.

10. The method of claim 9 , wherein said metal element M is selected from Li, Na, K, Mg, Zn, Cu, Ti, Ni, Co, Fe, or Al.

11. The method of claim 9 , wherein said metal sulfide contains Li 2 S 1 , Li 2 S 2 , Li 2 S 3 , Li 2 S 4 , Li 2 S 5 , Li 2 S 6 , Li 2 S 7 , Li 2 S 8 , Li 2 S 9 , Li 2 S 10 , Na 2 S 1 , Na 2 S 2 , Na 2 S 3 , Na 2 S 4 , Na 2 S 5 , Na 2 S 6 , Na 2 S 7 , Na 2 S 8 , Na 2 S 9 , Na 2 S 10 , K 2 S 1 , K 2 S 2 , K 2 S 3 , K 2 S 4 , K 2 S 5 , K 2 S 6 , K 2 S 7 , K 2 S 8 , K 2 S 9 , or K 2 S 10 .

12. The method of claim 2 , wherein said carbon or graphite material in said cathode active material layer is selected from the group consisting of mesophase pitch, mesophase carbon, mesocarbon microbead (MCMB), coke particle, expanded graphite flake, artificial graphite particle, natural graphite particle, highly oriented pyrolytic graphite, soft carbon particle, hard carbon particle, carbon nanotube, carbon nanofiber, carbon fiber, graphite nanofiber, graphite fiber, carbonized polymer fiber, activated carbon, carbon black, and combinations thereof.

13. The method of claim 2 , wherein said conducting polymer-sulfur hybrid comprises an intrinsically conductive polymer selected from the group consisting of polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer, a sulfonated derivative thereof, and combinations thereof.

14. The method of claim 1 , wherein said sulfonated elastomer matrix further comprises from 0.1% to 50% by weight of a lithium ion-conducting additive or sodium ion-conducting additive dispersed therein.

15. The method of claim 14 , wherein said lithium ion-conducting additive is selected from the group consisting of Li 2 CO 3 , Li 2 O, Li 2 C 2 O 4 , LiOH, LiX, ROCO 2 Li, HCOLi, ROLi, (ROCO 2 Li) 2 , (CH 2 OCO 2 Li) 2 , Li 2 S, Li x SO y , and combinations thereof, wherein X=F, Cl, I, or Br, R=a hydrocarbon group, 0<x≤1 and 1≤y≤4.

16. The method of claim 14 , wherein said lithium ion-conducting additive is dispersed in said ultrahigh molecular weight polymer and is selected from the group consisting of lithium perchlorate (LiClO 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium borofluoride (LiBF 4 ), lithium hexafluoroarsenide (LiAsF 6 ), lithium trifluoro-metasulfonate (LiCF 3 SO 3 ), bis-trifluoromethyl sulfonylimide lithium (LiN(CF 3 SO 2 ) 2 ), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF 2 C 2 O 4 ), lithium oxalyldifluoroborate (LiBF 2 C 2 O 4 ), lithium nitrate (LiNO 3 ), Li-fluoroalkyl-phosphates (LiPF 3 (CF 2 CF 3 ) 3 ), lithium bisperfluoro-ethysulfonylimide (LiBETI), lithium bis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide, lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-based lithium salt, and combinations thereof.

17. The method of claim 14 , wherein said lithium ion-conducting polymer is selected from a lower molecular version 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, or a combination thereof, wherein said lower molecular version is defined as having a molecular weight less than 500,000 g/mole.

18. The method of claim 1 , wherein said electrolyte is selected from the group consisting of polymer electrolyte, polymer gel electrolyte, composite electrolyte, ionic liquid electrolyte, organic liquid electrolyte, solid-state electrolyte, and combinations thereof.

19. The method of claim 1 , wherein said anode active material layer contains an anode active material selected from the group consisting of lithium metal, sodium metal, potassium metal, a lithium metal alloy, sodium metal alloy, potassium metal alloy, a lithium intercalation compound, a sodium intercalation compound, a potassium intercalation compound, a lithiated compound, a sodiated compound, a potassium-doped compound, lithiated titanium dioxide, lithium titanate, lithium manganate, a lithium transition metal oxide, Li 4 Ti 5 O 12 , and combinations thereof.

20. The method of claim 1 , wherein said cell is a lithium ion-sulfur cell and said anode active material layer contains an anode active material selected from the group consisting of:

(a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc (Zn), aluminum (Al), nickel (Ni), cobalt (Co), manganese (Mn), titanium (Ti), iron (Fe), and cadmium (Cd), and lithiated versions thereof;

(b) alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, or Cd with other elements, and lithiated versions thereof, wherein said alloys or compounds are stoichiometric or non-stoichiometric;

(c) oxides, carbides, nitrides, sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Fe, Ni, Co, Ti, Mn, or Cd, and their mixtures or composites, and lithiated versions thereof;

(d) salts and hydroxides of Sn and lithiated versions thereof;

(e) carbon or graphite materials and prelithiated versions thereof; and combinations thereof.

21. The method of claim 1 , wherein said cell is a sodium ion-sulfur cell or potassium ion-sulfur cell and said anode active material layer contains an anode active material selected from the group consisting of:

(a) sodium- or potassium-doped silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), cobalt (Co), nickel (Ni), manganese (Mn), cadmium (Cd), and mixtures thereof;

(b) sodium- or potassium-containing alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Co, Ni, Mn, Cd, and their mixtures;

(c) sodium- or potassium-containing oxides, carbides, nitrides, sulfides, phosphides, selenides, tellurides, or antimonides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Fe, Ti, Co, Ni, Mn, Cd, and mixtures or composites thereof,

(d) sodium or potassium salts;

(e) particles of graphite, hard carbon, soft carbon or carbon particles and pre-sodiated versions thereof; and combinations thereof.