An electrolyte in a lithium secondary battery includes an alkyl ammonium salt having a cation of the following Formula 1, a lithium salt, and an organic solvent: ##STR00001## wherein R.sup.1 to R.sup.4 are independently a C.sub.1 to C.sub.6 alkyl, a C.sub.2 to C.sub.6 alkenyl, or substituents thereof. The lithium secondary battery has improved cycle life, high rate characteristics, and a high energy density due to an increase of the average discharge voltage at a high rate.