(Invited) Elucidation of Electrochemical Reactions in Li2MnO3 Using Thin-Film Solid-State Battery

Abstract

All-solid-state is an ideal form of batteries. The all-solid-state batteries are also suitable system for elucidating battery reaction using spectroscopic methods. The present study focuses on the reaction mechanism study of lithium excess cathode materials using all-solid-state batteries. The lithium manganese oxide, Li2MnO3, is a model system of the lithium excess layered rock-salt structure. In the present study, the epitaxial and polycrystalline films with 30 nm-thick with various compositions and morphologies were fabricated using pulsed laser deposition and sputtering methods. These electrodes showed charge-discharge capacity ranging from 150 to 300 mAh g-1 with different degradation characteristics depending on the compositions and morphologies. The reaction mechanisms were studied by in-situ and operando methods using surface X-ray diffraction and operando HAXPES analyses. The Li2MnO3 shows a transformation to a high-capacity phase after activation process by the first charge and the degradation during subsequent cycling depends on the sample stoichiometry and morphology. The transition to the high capacity phase is related the phase change from O3 to O1 type, together with interlayer cation disordering on the Li/Mn layer. The activation process is related to the oxidation of oxygen and a formation new oxygen species. The activation process and the reversible reactions of the lithium-rich layered rock-salt materials are elucidated.