Improvement in stability of LiMn2O4 thin-film electrodes by oxygen-plasma irradiation to precursor gel

LiMn2O4 thin-film electrodes were prepared by the sol-gel method combined with oxygen-plasma irradiation. Oxygen plasma with a power of 10 or 90 W was irradiated to the precursor thin film prepared from lithium acetate, manganese acetate tetrahydrate and polyvinylpyrrolidone on a Pt plate, and then it was fired at 723 or 973 K. X-ray diffraction and Raman measurements indicated that oxygen-plasma irradiation was effective to increase the crystallinity of the resulting LiMn2O4. Atomic force microscope observation showed that the particle size of LiMn2O4 in the resulting thin-film electrode was decreased and homogeneous distribution of LiMn2O4 particles was achieved. Oxidation of the electrolyte at higher potentials was suppressed and capacity retention at 328 K was dramatically improved for the LiMn2O4 thin-film electrode obtained at 973 K. The improved electrochemical stability is ascribed to the elimination of organic materials from precursor by oxygen-plasma irradiation.