Structural change during charge–discharge for iron substituted lithium manganese oxide

• Fe-substituted Li2MnO3 was prepared by coprecipitation–calcination method.
• On initial charging, Fe ion moved to the tetrahedral 8j site.
• Stability of layered rock-salt structure sensitive to the mode of initial charging.

For this study, Fe-substituted Li2MnO3 (Li1+x(Fe0.25Mn0.75)1-xO2, 0 < x < 1/3) was prepared using coprecipitation–calcination. The change in the cation distribution was examined after charge–discharge using a monoclinic Li2MnO3 unit cell (C2/m). At the initial Li-extraction, Fe ion moved to the tetrahedral 8j site. At the end of charging, transition metals moved from 4g and 2b sites in (Mn, Fe)Li layer to 2c and 4h sites in the Li-layer via 4i and 8j sites. The cation random distribution was maintained after the end of discharging. The stability of layered rock-salt phase after cycle testing depended on the mode of charging; although the positive electrode decomposed to a mixture of layered rock-salt and spinel phases by typical galvanostatic charging, the positive electrode remained a single phase with a layered rock-salt structure by application of stepwise charging. Careful control of the charging mode at the initial cycle is important for Fe-substituted Li2MnO3 positive electrode material.