Fluoroethylene carbonate electrolyte and its use in lithium ion batteries with graphite anodes

The electrolyte decomposition during the first. lithiation of graphite is r educed to 85 mA h/g in an electrolyte containing equal volumes of fluoroeth ylene carbonate (Fluoro-EC) and of a co-solvent propylene carbonate (PC). T he volume fraction of Fluoro-EC can be further reduced to 0.05 in a tri-sol vent system with a co-solvent containing equal volumes of ethylene carbonat e (EC) and PC. A Lithium ion cell containing Fluoro-EC PC and EC shows a lo ng cycle life. The capacity decreases by 37% from the initial value in over 200 cycles. Cell current efficiency is 100%, thus solving the poor cell cu rrent efficiency when chloroethylene carbonate (Chloro-EC) is used in place of Fluoro-EC. (C) 1999 Elsevier Science S.A. All rights reserved.