Crystal Structures and Electrochemical Properties of P2/O2-type Mn-based Layered Oxides

Abstract

A new and promising P2-type layered oxide, Na_5/6[Li_1/4Mn_3/4]O₂ is prepared using a solid-state method. Detailed crystal structures of the sample are analyzed by synchrotron X-ray diffraction combined with high-resolution neutron diffraction. P2-type Na_5/6[Li_1/4Mn_3/4]O₂ consists of two [Li_1/4Mn_3/4]O₂ sheets with partial in-plane √3a × √3a -type Li/Mn ordering. Na/Li ion-exchange in a molten salt results in a phase transition accompanied with glide of [Li_1/4Mn_3/4]O₂ layers without the destruction of in-plane cation ordering. P2-type Na_5/6[Li_1/4Mn_3/4]O₂ translates into an O2-type layered structure with staking faults as the result of ion-exchange. Electrode performance of P2-type Na_5/6[Li_1/4Mn_3/4]O₂ and O2-type Li_x[Li_1/4Mn_3/4]O₂ is examined and compared in Na and Li cells, respectively. Both samples show large reversible capacity, ca. 200 mA h g^–1, after charge to high voltage regardless of the difference in charge carriers.