The rotating ring-disk electrode system and ab initio molecular orbital calculations were used to investigate the initial reaction in the reductive decomposition of electrolyte solutions for lithium batteries. It was confirmed that electron transfer is induced by the cathodic polarization of the electrode, forming soluble reduced species which can be reoxidized. This electron transfer is an exothermic reaction with a reaction energy of -3 eV, from the electrode to the solvent molecules coordinated with lithium ions. This is the initial reaction in the reductive decomposition of electrolyte solutions for lithium batteries, which must be controlled to improve the performance of lithium-ion and lithium secondary batteries.