A method of increasing the discharge capacity retention of a non-aqueous lithium ion secondary battery having a positive electrode active material, a combination of a lithium element and a complex metal oxide, a negative electrode, and a non-aqueous electrolytic solution comprising an electrolyte dissolved in a non-aqueous solvent which is a combination of a cyclic carbonate and a linear carbonate by incorporating a disulfide derivative having the formula: R.sup.1--S--S--R.sup.2 wherein each of R.sup.1 and R.sup.2 independently represents a phenyl group, a benzyl group, a tolyl group, a pyridyl group, a pyrimidyl group, an alkyl group having 1 to 12 carbon atom, or a cycloalkyl group having 3 to 6 carbon atoms, in which each group has no substituent groups or has one or more alkyl groups into the non-aqueous electrolytic solution.