Fluorinated Alkyl Carbonates as Cosolvents in Li-Ion Cells

Partially fluorinated alkyl carbonate liquid compounds have been found to be excellent electrolyte cosolvents for rechargeable lithium-ion electrochemical cells. The benefits afforded by these and other ingredients of electrolyte solutions in rechargeable Li-ion cells have been investigated in continuing research directed toward extending the range of practical operating temperatures of the cells (from +40 °C down to –40 °C, and possibly even as low as –60 °C). Fluorinated solvents were perceived to be especially attractive in that they will result in inherently safer cells, due to their low flammability. This research at earlier stages was reported in a number of previous NASA Tech Briefs articles; namely, “Update on Electrolytes for Low-Temperature Lithium Cells” (NPO-20407), Vol. 24, No. 1, (January 2000), page 56; “Lithium Alkoxide Electrolyte Additives for Lithium-Ion Cells” (NPO- 20607), Vol. 25, No. 6 (June, 2001), page 52; “Aliphatic Ester Electrolyte Additives for Lithium-Ion Cells” (NPO-20601), Vol. 25, No. 6 (June, 2001), page 53; “Ethyl Methyl Carbonate as a Cosolvent for Lithium-Ion Cells” (NPO-20605), Vol. 25, No. 6 (June, 2001), page 53; and “Alkyl Pyrocarbonate Electrolyte Additives for Li-Ion Cells” (NPO-20775), which precedes this article.