The present invention relates to lithium secondary batteries comprising a negative electrode, a positive electrode, a separator and a lithium-based electrolyte carried in an aprotic solvent, and to the electrolyte compositions. The electrolyte comprises a lithium salt of the formula: Li.sub.2B.sub.12F.sub.xH.sub.12-x-yZ.sub.y where x+y is from 3 to 12, and x and y are independently from 0 to 12, and Z comprises at least one of Cl and Br.