Influence of RF power on microstructural and electrochemical properties of rf-sputtered LiMn[sub 2]O[sub 4] thin films

Abstract

Thin films of Lithium transition metal oxides (LTMOs) have wide applications as a cathode material in the fabrication of all solid state thin film microbatteries. Among various LTMOs, LiMn2O4 with spinel structure is one of the most promising cathode material as it offers high energy density, high cell voltage, low cost and low toxicity. Hence in the present investigation thin films of LiMn2O4 were prepared by RF magnetron sputtering on gold coated silicon substrates maintained at a constant substrate temperature of 573 K with different RF powers ranging from 40 to 150 watts. The influence of RF power on micro structural and electrochemical properties of LiMn2O4 films was studied. The lattice parameter, Mn-Mn-O interatomic distance and grain size was found to be increased with the increase of RF power as evidenced from XRD and SEM studies. The films deposited at a moderate substrate temperature of 573 K with RF power 100 W exhibited predominant (111) orientation with cubic spinel structure. The calculated lattice parameter, Mn-Mn, Mn-O inter atomic distances for the films deposited at RF power 100 W was 8.215Å, 2.905 and 1.922 Å. From the electrochemical (EC) studies an initial discharge capacity of 38.5 μAhcm−2μm−1 was observed for the films deposited at RF power 100 W in the potential window of 0.0 – 1.2 V.