Stability Improvement of LiMn2O4 Thin-Film Cathodes under High Rate and Over-Discharge Cycling

Abstract

Thin films of spinel lithium manganese oxides were prepared by sol-gel method. The annealing time and temperatures were optimized to obtain crystalline thin films. The as-synthesized films were coated with a thin layer of alumina or lithium phosphorus oxynitride by radio frequency sputtering. The coatings were amorphous as characterized by X-ray diffraction. The electrochemical properties of the coated and uncoated thin-film cathodes were characterized and compared. The cells made of the lithium manganese oxide cathodes were discharged at different rates. At higher discharge rates, both the alumina and the -coated samples exhibited higher discharge potential plateaus than the uncoated spinel. As the cells were cycled in a wide voltage window of , the coated cathodes exhibited less capacity fading. For samples immersed in acid solution before cycling, the surface-coated samples showed greater stability.