Hydrothermal phase formation of orthorhombic LiMnO2 and its derivatives as lithium intercalation compounds

Different from a conventional solid state reaction, a hydrothermal reaction mechanism is very difficult to illuminate and sometimes it remains undisclosed. Making an attempt to understand the hydrothermal phase formation process of o-LiMnO2 obtained between the reaction of spinel type Mn3O4 precursor and LiOH aqueous solution, the possible reaction route was postulated and experimentally testified. Firstly, the selective dissolution of Mn2+ from the tetrahedral site of [MnII]tet4a[MnIII2]oct8dO4, which is considered as to be an ionic exchange reaction with Li+, and an additional Li+ intercalation into the host structure of precursor would give rise to the formation of meta-stable Li2Mn2O4 ([LiI]tet4a[LiI]oct8c[MnIII2]oct8dO4). Secondly, the phase would be simultaneously transformed to thermodynamically stable o-LiMnO2 phase under hydrothermal state during hydrothermal reaction. Through the above reaction process, the solid solution range of o-LiCoxMn1−xO2 was as large as x ≤ 0.14, and that of o-LiFexMn1−xO2 was x ≤ 0.05. Co doped o-LiMnO2 has higher capacity and good cyclability upon cycling, being substantially more stable to cycle than the unsubstituted and Fe doped materials.