Structural and Electrochemical Properties of LiNi0.5Mn0.5O2 Thin-Film Electrodes Prepared by Pulsed Laser Deposition

LiNi0.5Mn0.5O2 thin-film electrodes have been prepared by pulsed laser deposition followed by postannealing at different temperatures. The microstructural and morphological characterizations using X-ray diffraction, field-emission-scanning electron microscopy, and Raman spectroscopy measurements show that the structure and phase purity of the thin films are highly dependent on the postannealing temperatures. The films that are postannealed at low temperatures exhibit a relatively lower degree of crystallinity, but a high phase purity. The electronic structure and cation disorder of the LiNi0.5Mn0.5O2 thin-film samples are further investigated by X-ray photoelectron spectroscopy and magnetic property measurement. The charge/discharge behaviors of the thin films that are postannealed at different temperatures indicate that phase-pure LiNi0.5Mn0.5O2 thin films can only be prepared at low annealing temperatures. Electrochemical impedance spectroscopy studies on thin-film electrodes indicate a strong dependence of charge-transfer resistance on the electrode potential. The rate capability and cycling stability in different voltage windows of LiNi0.5Mn0.5O2 thin-film electrodes are further investigated. The relationship between the microstructure and electrochemical properties of LiNi0.5Mn0.5O2 thin-film electrodes has been discussed.