Structure, Morphology, and Electrochemical Investigation of LiMn2O4 Thin Film Cathodes Deposited by Radio Frequency Sputtering for Lithium Microbatteries

Abstract

Spinel lithium manganese oxide (LiMn2O4) cathode thin films were successfully deposited on different substrates such as Si, Pt/Al, and indium tin oxide (ITO)/Pt/Al by radio frequency (RF) sputtering. These thin films were investigated as positive electrodes for lithium microbatteries. The thickness of the deposited films was estimated by surface-profilometer at different deposition time intervals from 30 min to 15 h, and the thickness was found to be 20−600 nm. The structure and surface morphology deposited thin films of LiMn2O4 were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The phase transformation from amorphous to crystalline phase was found at around 700 °C for the electrode films deposited on Si substrate. The LiMn2O4 deposited with ITO interlayer on Pt/Al substrate was found to be well crystallized relatively at lower temperature (≤300 °C). No significant changes were observed on the surface morphology between the as-deposited and the annealed film. Electrochemical performance was measured for LiMn2O4 films deposited with or without ITO interlayer on Pt/Al substrate. The discharge capacity around 60.9 and 67.5 mAh g−1 are obtained, respectively, for the 500 °C-annealed LiMn2O4/Pt/Al film and as-deposited LiMn2O4/ITO/Pt/Al film. Because the crystallization temperature of LiMn2O4/ITO/Pt/Al film was found to be relatively lower (≤300 °C), this work could possibly be extended to design and fabricate flexible lithium microbatteries using polymer substrates.