Electrochemical and Structural Effects of In Situ Li₂O Extraction from Li₂MnO₃ for Li-Ion Batteries

Li2MnO3 is an attractive cathode material due to its low cost, nontoxicity and potentially high capacity. However, its electrochemical inactivity, its poor electronic conductivity, and uncertainty about its underlying mechanism have limited its development. In this work, an in situ technique for extraction of Li and O during deposition of the thin film cathode is developed to investigate structural and electrochemical effects in a controlled fashion. MnO2 has been observed in samples with severe O and Li deficiency (capacity of 115 mAh g(-1)), while Li2MnO3 cathodes with slight excess of O and Li (capacity of 225 mAh g(-1)) can be synthesized by tuning growth conditions appropriately. Formation of a MnO2 phase, especially in Li and O deficient structures, could be a possible reason for irreversible capacity loss in Li2MnO3 related materials. Further investigation into stoichiometric and microstructure variations enabled by this technique allows rapid investigation of Li2MnO3 as well as other Li-rich composites.