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The reductive decomposition mechanism of electrolyte solutions for lithium secondary batteries has been investigated by electron spin resonance (ESR) with the aid of molecular orbital (MO) calculations. Discussion is focused on the initial reactions with the ultimate goal of suppressing decomposition. Solvent-related radical species were observed by ESR measurements in all of the electrolyte solutions after reductive electrolysis. The MO calculations suggest that the electron transfer from the electrode to the solvent molecule coordinated with the lithium cation upon cathodic polarization of the electrode is thermodynamically favorable. It is concluded that this electron transfer is the initial process in the decomposition of electrolyte solutions by electrochemical reduction. The radical species observed by ESR is attributed to the radical anion of the solvent coordinated with the lithium cation. Furthermore, ESR analysis indicated that the solvent radical anion and the neighboring solvent molecules coordinated with the same lithium cation are in electron-transfer equilibrium. The subsequent decomposition is initiated from this equilibrium.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.120.194.195 Downloaded on 2015-02-07 to IP

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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 Ϫ3 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.