Improving the oxygen redox stability of NaCl-type cation disordered Li2MnO3 in a composite structure of Li2MnO3 and spinel-type LiMn2O4†
Abstract
Li2MnO3, a layered lithium-rich manganese oxide, is one of the potential high-capacity positive electrode materials among the Li containing transition metal oxide materials but its low electrical conductivity restricts its electrochemical activity. In our previous study, Li–Mn cation disorder in Li2MnO3 resulting in the formation of a NaCl-type structure was found to improve its electrochemical activity, i.e., a high initial discharge capacity of 320 mA h g−1. However, it still suffered from a poor cycling performance probably due to another problem, e.g., its structural instability, i.e., oxygen emission during charging. In this study, we found that the structural stability of NaCl-type Li2MnO3 was significantly improved by forming a composite with spinel-type LiMn2O4 by mechanical milling. The initial discharge capacity of the composite was close to 400 mA h g−1 and its 15th discharge capacity still showed more than 80% of the initial one, while less than 50% for NaCl-type Li2MnO3. The oxide ions in the composite were found to be more stable than those of NaCl-type Li2MnO3 during the electrochemical redox reaction, which was confirmed by O K-edge XAS measurements, resulting in the higher reversible capacity and better cycling performance.