First-Cycle Evolution of Local Structure in Electrochemically Activated Li2MnO3

Abstract

X-ray absorption spectroscopy is utilized to determine changes in the local structure of Li2MnO3 resulting from electrochemical extraction and insertion of lithium. Specially prepared electrodes allow for a first-cycle charge close to 100% of theoretical, even in crystalline Li2MnO3 prepared at 850 °C. After full delithiation to ∼5 V, the local Mn environments are similar to those of the freshly prepared Li2MnO3 electrodes but with increased disorder. On discharge, significant reduction of Mn is observed accompanied by rearrangement of Mn resulting in Jahn–Teller distorted, Mn3+ local environments. It is also shown, as expected, that the electrochemical and structural behavior of pure Li2MnO3 is markedly different than that observed for the structurally similar Li2MnO3 component of lithium- and manganese-rich composite cathodes.