Exploring magnetron sputtering preparation of high-quality LiNi0.5Mn1.5O4 films by controlling the oxygen atmosphere at moderate temperature

Abstract

Spinel structured lithium nickel-manganate (LiNi0.5Mn1.5O4, LNMO) is one of the most promising cathode alternatives for lithium-ion batteries for a wide range of mobile electronic devices. In this study, annealing‐free LNMO thin films are deposited onto fluorine-doped tin oxide (FTO) substrates via radio frequency magnetron sputtering at a moderate temperature (400 °C) under different oxygen atmospheres (0%, 2%, 5%, and 8%). The structural and electrochemical performances of these materials are systemically investigated via X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charging/discharging tests. The XRD and Raman results show that too low or too high of an oxygen content reduces the crystallinity of the cubic spinel structure of LNMO, while disordered spinel/short-range ordered (Fd3¯m) is produced at a moderate oxygen concentration. Electrochemical measurements and impedance spectra show that LNMO optimized for 5% O2 on an FTO substrate has a superior cycling stability, a higher specific capacity, a better rate performance, and a lower charge transfer resistance than others. This study investigates the effect of an oxygen atmosphere on films during synthesis at moderate temperatures, which is suitable for the fabrication of flexible batteries, whereas previous studies have generally focused on heating and post-annealing processes. Furthermore, LNMO films prepared on FTO are of great importance for bifacial or thin-film batteries.