Abstract: Non-aqueous rechargeable lithium batteries can be protected against overcharge abuse by incorporating small amounts of suitable additives into the electrolyte. Additives selected from the group consisting of phenyl-R-phenyl compounds wherein R is an aliphatic hydrocarbon, fluorine substituted biphenyl compounds, and 3-thiopheneacetonitrile can provide superior cycling performance along with satisfactory overcharge protection in high voltage lithium ion batteries. 2,2-diphenylpropane can be a preferred gassing agent additive in batteries equipped with electrical disconnect devices.

Abstract: The loss in delivered capacity (fade rate) after cycling non-aqueous rechargeable lithium batteries can be reduced by incorporating a small amount of an improved additive in the battery. Improved additives include boron trifluoride (BF.sub.3), fluoboric acid (HBF.sub.4), or complexes thereof. The invention is particularly suited to lithium ion batteries. Complexes comprising BF.sub.3 and dietyl carbonate or ethyl methyl carbonate can be prepared which are particularly effective additives. Preferably, the additive is dissolved in the electrolyte.