| abstract |
An electrolyte composition for a lithium ion battery comprises 5-25wt% of lithium salt, 2-10wt% of additive and 65-93wt% of solvent; wherein (a) the lithium salt comprises 20-100mol% lithium tetrafluoroborate, and 0-95mol% lithium bis(trifluoromethanesulfonyl)imide; (b) the additive comprises vinylene carbonate, and optionally 30-90mol% fluoroethylene carbonate; and (c) the solvent comprises 70-90mol% ethylene carbonate and 10-30mol% propylene carbonate. The lithium concentration in the composition is preferably between 0.7M and 2.0M. The claimed composition is stable and has low volatility at temperatures above about 55°C, such that it can be used in preparation techniques involving elevated temperatures, most notably extrusion processes. The claimed compositions are also advantageous because they may passivate graphite (which can therefore be used as anode material), have a flash point above 100°C and a low vapour pressure, are stable to common cathode materials and have sufficient ionic conductivity and rate performance. |