Abstract
Several high-purity methyl perfluorocarboxylates were prepared (>99.5% purity by mole) and investigated
as potential fluorine-rich electrolyte solvents in Li-ion batteries. The most conductive electrolyte,
0.1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in dimethyl perfluoroglutarate (PF5M2) (ionic
conductivity ¼ 1.87 102 mS cm1), is investigated in Si thin-film half-cells. The solid-electrolyteinterphase
(SEI) formed by the PF5M2 electrolyte is composed of similar organic and inorganic moieties
and at comparable concentrations as those formed by ethylene carbonate/dimethyl carbonate
electrolytes containing LiPF6 and LiTFSI salts. However, the SEI formed by the PF5M2 electrolyte undergoes
reversible electrochemical defluorination, contributing to the reversible capacity of the cell and
compensating in part for capacity fade in the Si electrode. While far from ideal these electrolytes provide
an opportunity to further develop predictions of suitable fluorinated molecules for use in battery
solvents.
