Identifying a Li-rich superionic conductor from charge-discharge structural evolution study: Li₂MnO₃

Li₂MnO₃ is a critical member of the Li-rich Mn-based layered material. To understand the process of electrochemical reaction in the monoclinic Li₂MnO₃, the structural evolution is investigated through the first-principles calculations based on density functional theory. During the delithiation process, a phase transformation together with a new trigonal phase at x = 0.5 (Li_xMnO₃) has been reported, which belongs to the space group P3[combining macron]1m. Lithium ions are embedded in Li_0.5MnO₃ until the trigonal Li₂MnO₃ phase is formed with the P3[combining macron]1m symmetry preserved. Phonon and molecular dynamics simulations verify that this trigonal Li₂MnO₃ is dynamically and thermodynamicaly stable. Furthermore, our calculated results reveal that it has high conductivity of 0.36 S cm^-1 in the ab plane, which proves that this trigonal Li₂MnO₃ is a promising lithium superionic conductor.