Substituted phenothiazine redox shuttles for rechargeable lithium-ion cell

1. A rechargeable lithium-ion cell comprising:

(a) a positive electrode having a recharged potential and comprising LiFePO 4 , Li 2 FeSiO 4 , Li x MnO 2 (where x is about 0.3 to about 0.4), or MnO 2 ;

(b) a negative electrode;

(c) a charge-carrying electrolyte comprising a charge carrying medium comprising a charge carrying medium that includes an organic carbonate and a lithium salt; and

(d) a cyclable redox chemical shuttle comprising 10-methyl-phenothiazine, 10-ethyl-phenothiazine, 3-chloro-10-ethyl-phenothiazine, 10-isopropyl-phenothiazine, 2-perfluoromethyl-phenothiazine, 10-acetyl-phenothiazine 2-cyano-10-perfluoromethylsulfonyl-phenothiazine, 2-methoxy-10-perfluoromethylsulfonyl-phenothiazine, 2-perfluoromethyl-10-perfluoromethylsulfonyl-phenothiazine, 10-perfluoromethyl-phenothiazine, 10-perfluoromethylsulfonyl-phenothiazine, 10-(1,1,1,2,3,3)-hexafluoropropyl-phenothiazine, or mixtures thereof, wherein

the recharged potential is the potential at which the positive electrode becomes delithiated during the first charge cycle to a lithium level corresponding to at least 90% of the available recharged cell capacity.

2. A cell according to claim 1 wherein the chemical redox shuttle is substituted at its nitrogen atom.

3. A cell according to claim 1 wherein the chemical redox shuttle is substituted at one or more ring carbon atoms.

4. A cell according to claim 3 wherein the chemical redox shuttle is 2-perfluoromethyl-phenothiazine.

5. A cell according to claim 1 wherein the chemical redox shuttle is substituted with one or more alkyl groups containing 1 to about 4 carbon atoms.

6. A cell according to claim 1 wherein the chemical redox shuttle comprises 10-methyl-phenothiazine, 10-ethyl-phenothiazine, 3-chloro-10-ethyl-phenothiazine, 10-isopropyl-phenothiazine, 10-acetyl-phenothiazine, or mixtures thereof.

7. A cell according to claim 1 wherein the chemical redox shuttle comprises 2-cyano-10-perfluoromethylsulfonyl-phenothiazine, 2-methoxy-10-perfluoromethylsulfonyl-phenothiazine, 2-perfluoromethyl-10-perfluoromethylsulfonyl-phenothiazine, 10-perfluoromethyl-phenothiazine, 10-perfluoromethylsulfonyl-phenothiazine, 10-(1,1,1,2,3,3)-hexafluoropropyl-phenothiazine, or mixtures thereof.

8. A cell according to claim 1 wherein the cyclable redox chemical shuttle is present in the electrolyte in an amount of from 0.1M to about 0.3M.

9. A cell according to claim 1 wherein the electrolyte comprises a cosolvent.

10. A cell according to claim 1 wherein the chemical redox shuttle has an oxidation potential from about 0.3 V to about 5 V above the recharged potential of the positive electrode.

11. A cell according to claim 1 wherein the chemical redox shuttle has an oxidation potential from about 0.3 to about 0.6 V above the recharged potential of the positive electrode.

12. A cell according to claim 1 wherein the chemical redox shuttle provides overcharge protection after at least 30 charge-discharge cycles at a charging voltage sufficient to oxidize the phenothiazine compound and at an overcharge charge flow equivalent to 100% of the cell capacity during each cycle.

13. A cell according to claim 1 wherein the chemical redox shuttle provides overcharge protection after at least 80 charge-discharge cycles at a charging voltage sufficient to oxidize the phenothiazine compound and at an overcharge charge flow equivalent to 100% of the cell capacity during each cycle.

14. A cell according to claim 1 wherein the negative electrode comprises graphitic carbon, lithium metal, or a lithium alloy.

15. A cell according to claim 1 wherein the charge carrying medium comprises ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, or combinations thereof.

16. A rechargeable lithium-ion cell comprising:

(a) a positive electrode having a recharged potential and comprising LiFePO 4 , Li 2 FeSiO 4 , Li x MnO 2 (where x is about 0.3 to about 0.4) or MnO 2 ;

(b) a negative electrode comprising graphitic carbon, lithium metal or a lithium alloy; and

(c) a charge-carrying electrolyte comprising:

(i) a charge-carrying media comprising ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate or combination thereof;

(ii) a lithium salt comprising LiPF 6 , lithium bis(oxalato)borate, or combination thereof; and

(iii) a cyclable redox chemical shuttle comprising 10-methyl-phenothiazine, 10-ethyl-phenothiazine, 3-chloro-10-ethyl-phenothiazine, 10-acetyl-phenothiazine, or mixtures thereof dissolved in the electrolyte and having an oxidation potential above the recharged potential of the positive electrode.

17. A method for manufacturing a rechargeable lithium-ion sealed cell comprising the steps of assembling in any order and enclosing in a suitable case:

(a) a positive electrode having a recharged potential and comprising LiFePO 4 , Li 2 FeSiO 4 , Li x MnO 2 (where x is about 0.3 to about 0.4), or MnO 2 ;

(b) a negative electrode;

(c) a charge-carrying electrolyte comprising charge carrying medium and lithium salt; and

(d) a cyclable redox chemical shuttle comprising 10-methyl-phenothiazine, 10-ethyl-phenothiazine, 3-chloro-10-ethyl-phenothiazine, 10-isopropyl-phenothiazine, 2-perfluoromethyl-phenothiazine, 10-acetyl-phenothiazine 2-cyano-10-perfluoromethylsulfonyl-phenothiazine, 2-methoxy-10-perfluoromethylsulfonyl-phenothiazine, 2-perfluoromethyl-10-perfluoromethylsulfonyl-phenothiazine, 10-perfluoromethyl-phenothiazine, 10-perfluoromethylsulfonyl-phenothiazine, 10-(1,1,1,2,3,3)-hexafluoropropyl-phenothiazine, or mixtures thereof, wherein

the recharged potential is the potential at which the positive electrode becomes delithiated during the first charge cycle to a lithium level corresponding to at least 90% of the available recharged cell capacity.