Selenium preloaded cathode for alkali metal-selenium secondary battery and production process

1. An electrochemical method of producing a pre-selenized active cathode layer for a rechargeable alkali metal-selenium cell, said method comprising:

(a) preparing an integral layer of porous graphitic structure having graphene surfaces with a specific surface area greater than 100 m 2 /g, wherein said porous graphitic structure comprises a graphene material selected from pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, boron-doped graphene, nitrogen-doped graphene, chemically functionalized graphene, or a combination thereof; an exfoliated graphite material selected from exfoliated graphite worms, expanded graphite flakes, or recompressed graphite worms or flakes; or a mixture of graphene material and exfoliated graphite material, and wherein said porous graphitic structure comprises multiple sheets of said graphene material or multiple flakes of said exfoliated graphite material that are intersected or interconnected to form said integral layer and may further comprise an optional binder of 0-10% by weight, an optional conductive filler included in said integral layer, or an optional selenium or selenium-containing compound pre-loaded therein at 0 to 49% by weight;

(b) preparing an electrolyte comprising a non-aqueous solvent and a selenium source dissolved or dispersed in said solvent;

(c) preparing an anode; and

(d) bringing said integral layer of porous graphitic structure and said anode in ionic contact with said electrolyte and imposing an electric current between said anode and said integral layer of porous graphitic structure, serving as a cathode, with a sufficient current density for a sufficient period of time to electrochemically deposit nanoscaled selenium particles or coating directly on said graphene surfaces to form said pre-selenized active cathode layer, wherein said particles or coating have a thickness or diameter smaller than 20 nm.

2. The method of claim 1 , wherein said selenium source is selected from M x Se 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.

3. The method of claim 1 , wherein said anode comprises an anode active material selected from an alkali metal, an alkaline metal, a transition metal, a metal from groups 13 to 17 of the periodic table, or a combination thereof.

4. The method of claim 2 , wherein said metal element M is selected from Li, Na, K, Mg, Zn, Cu, Ti, Ni, Co, Fe, or Al.

5. The method of claim 2 , wherein said M x Se y is selected from Li 2 Se 6 , Li 2 Se 7 , Li 2 Se 8 , Li 2 Se 9 , Li 2 Se 10 , Na 2 Se 6 , Na 2 Se 7 , Na 2 Se 8 , Na 2 Se 9 , Na 2 Se 10 , K 2 Se 6 , K 2 Se 7 , K 2 Se 8 , K 2 Se 9 , K 2 Se 10 , or a combination thereof.

6. The method of claim 1 , further comprising a procedure of depositing an element Z to said porous graphitic structure wherein said element Z is mixed with selenium or formed as discrete Z coating or particles having a dimension less than 100 nm and said Z element is selected from Sn, Sb, Bi, S, Te, or a combination thereof and the weight of element Z is less than the weight of selenium.

7. The method of claim 6 , wherein said procedure of depositing element Z includes electrochemical deposition, chemical deposition, or solution deposition.

8. The method of claim 1 , wherein said nanoscaled selenium particles or coating occupy a weight fraction of at least 70% based on the total weights of said selenium particles or coating and said graphene material combined.

9. The method of claim 1 , wherein said electrolyte further comprises a metal salt selected from 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, sodium perchlorate (NaClO 4 ), potassium perchlorate (KClO 4 ), sodium hexafluorophosphate (NaPF 6 ), potassium hexafluorophosphate (KPF 6 ), sodium borofluoride (NaBF 4 ), potassium borofluoride (KBF 4 ), sodium hexafluoroarsenide, potassium hexafluoroarsenide, sodium trifluoro-metasulfonate (NaCF 3 SO 3 ), potassium trifluoro-metasulfonate (KCF 3 SO 3 ), bis-trifluoromethyl sulfonylimide sodium (NaN(CF 3 SO 2 ) 2 ), sodium trifluoromethanesulfonimide (NaTFSI), bis-trifluoromethyl sulfonylimide potassium (KN(CF 3 SO 2 ) 2 ), or a combination thereof.

10. The method of claim 1 , wherein said solvent is 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 (γ-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.

11. The method of claim 1 , wherein said anode, said electrolyte, and said integral layer of porous graphitic structure are disposed in an external container outside of a lithium-selenium cell and said step of electrochemically depositing nanoscaled selenium particles or coating on said graphene surfaces is conducted outside said lithium-selenium cell and said method further includes a step of incorporating said pre-selenized active cathode layer in said lithium-selenium cell.

12. The method of claim 1 , wherein said anode, said electrolyte, and said integral layer of porous graphitic structure are disposed inside a lithium-selenium cell and said step of electrochemically depositing nanoscaled selenium particles or coating on said graphene surfaces is conducted after said lithium-selenium cell is produced.

13. The method of claim 1 , wherein said anode, said electrolyte, and said integral layer of porous graphitic structure are part of a lithium-selenium cell and said step of electrochemically depositing nanoscaled selenium particles or coating on said graphene surfaces occurs after said lithium-selenium cell is fabricated and is conducted during a first charge cycle of said cell.

14. The method of claim 1 , wherein said nanoscaled selenium particles or coating occupy a weight fraction of at least 80%.

15. The method of claim 1 , wherein said nanoscaled selenium particles or coating occupy a weight fraction of at least 90%.

16. The method of claim 1 , wherein said nanoscaled selenium particles or coating have a thickness or diameter smaller than 10 nm.

17. The method of claim 1 , wherein said nanoscaled selenium particles or coating have a thickness or diameter smaller than 5 nm.

18. The method of claim 1 , wherein said nanoscaled selenium particles or coating have a thickness or diameter smaller than 3 nm.

19. A pre-selenized active cathode layer produced by the method of claim 1 for a rechargeable alkali metal-selenium cell selected from lithium-selenium cell, sodium-selenium cell, or potassium-selenium cell, wherein said graphene sheets are chemically bonded together with an adhesive resin.

20. A rechargeable alkali metal-selenium cell comprising an anode active material layer, an optional anode current collector, a porous separator and/or an electrolyte, the pre-selenized active cathode layer of claim 19 , and an optional cathode current collector, wherein said alkali metal-selenium cell is selected from lithium-selenium cell, sodium-selenium cell, or potassium-selenium cell.

21. The rechargeable alkali metal-selenium cell of claim 20 wherein said electrolyte is selected from polymer electrolyte, polymer gel electrolyte, composite electrolyte, ionic liquid electrolyte, non-aqueous liquid electrolyte, soft matter phase electrolyte, solid-state electrolyte, or a combination thereof.

22. The rechargeable alkali metal-selenium cell of claim 20 wherein said electrolyte contains an alkali salt selected from 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 bisperfluoroethysulfonylimide (LiBETI), an ionic liquid salt, sodium perchlorate (NaClO 4 ), potassium perchlorate (KClO 4 ), sodium hexafluorophosphate (NaPF 6 ), potassium hexafluorophosphate (KPF 6 ), sodium borofluoride (NaBF 4 ), potassium borofluoride (KBF 4 ), sodium hexafluoroarsenide, potassium hexafluoroarsenide, sodium trifluoro-metasulfonate (NaCF 3 SO 3 ), potassium trifluoro-metasulfonate (KCF 3 SO 3 ), bis-trifluoromethyl sulfonylimide sodium (NaN(CF 3 SO 2 ) 2 ), sodium trifluoromethanesulfonimide (NaTFSI), bis-trifluoromethyl sulfonylimide potassium (KN(CF 3 SO 2 ) 2 ), or a combination thereof.

23. The rechargeable alkali metal-selenium cell of claim 20 wherein said solvent is selected from ethylene carbonate (EC), dimethyl carbonate (DMC), methylethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, propylene carbonate (PC), gamma-butyrolactone (γ-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, or a combination thereof.

24. The rechargeable alkali metal-selenium cell of claim 20 , further comprising a layer of protective material disposed between said anode and said porous separator, wherein said protective material is a lithium ion conductor.

25. The rechargeable alkali metal-selenium cell of claim 24 , wherein said protective material consists of a solid electrolyte.

26. The rechargeable alkali metal-selenium cell of claim 20 wherein said anode active material layer contains an anode active material selected from 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 , or a combination thereof.

27. The rechargeable alkali metal-selenium cell of claim 20 wherein said cell is a lithium ion-selenium 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.

28. The rechargeable alkali metal-selenium cell of claim 20 , wherein said cell is a sodium ion-selenium cell or potassium ion-selenium 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.

29. The rechargeable alkali metal-selenium cell of claim 20 wherein said graphene material comprises nanographene sheets or platelets with a thickness less than 10 nm.

30. The rechargeable alkali metal-selenium cell of claim 20 wherein said graphene material comprises nanographene sheets or platelets selected from single-layer or few-layer pristine graphene, wherein few-layer is defined as 10 planes of hexagonal carbon atoms or less.

31. The rechargeable alkali metal-selenium cell of claim 20 wherein said binder material is selected from a resin, a conductive polymer, coal tar pitch, petroleum pitch, mesophase pitch, coke, or a derivative thereof.

32. The rechargeable alkali metal-selenium cell of claim 20 wherein said porous graphitic structure has a specific surface area greater than 500 m 2 /g.

33. The rechargeable alkali metal-selenium cell of claim 20 wherein said porous graphitic structure has a specific surface area greater than 750 m 2 /g.

34. The rechargeable alkali metal-selenium cell of claim 20 wherein said cathode has an active material utilization rate no less than 80%.

35. The rechargeable alkali metal-selenium cell of claim 20 wherein said cathode has an active material utilization rate no less than 90%.

36. The rechargeable alkali metal-selenium cell of claim 20 , wherein said cathode contains at least 95% by weight of selenium based on the total weight of said porous graphitic structure and selenium combined.