Preparation of a spinel LiMn2O4 single crystal film from a MnO wafer

Abstract

Spinel LiMn2O4 is a very promising material for positive electrodes in a wide range of Li-ion battery applications due to its lower cost and more environmental friendliness than any other electrode materials. Although the bulk properties of LiMn2O4 have been studied intensively, there have been few reports about the structure and properties of LiMn2O4 surfaces in spite of the importance of solid/electrolyte interfaces. This is caused by the difficulty in preparing LiMn2O4 samples with accessible flat surfaces suitable for atomistic observations. To address this, we have successfully prepared a single crystalline LiMn2O4 film with an atomically flat surface by solid-state reaction from a MnO wafer with LiOH.H2O powder. X-ray diffraction (XRD) reveals the single crystalline growth of LiMn2O4 films depending on the orientation of a MnO wafer. Atomic force microscopy observations revealed that a LiMn2O4 (111) film has an atomically flat surface with steps of a {111} interlayer height. Electron energy-loss spectroscopy (EELS) study of the (111) film revealed that the sample consists of Li, Mn3+ and Mn4+ with a composition similar to LiMn2O4. The (111) film sample is also investigated by cyclic voltammetry and galvanostatic experiments, revealing that a crushed powder sample from the film has electrochemical activity as usual positive electrode material.