Elsevier, Thin Solid Films, (528), p. 217-223
DOI: 10.1016/j.tsf.2012.08.058
Full text: Download
Today most commercially available lithium ion batteries are still based on the toxic and expensive LiCoO2 as a standard cathode material. However, lithium manganese based cathode materials are cheaper and environmentally friendlier. In this work cubic-LiMn2O4 spinel, monoclinic-Li2MnO3 and orthorhombic-LiMnO2 thin films have been synthesized by non-reactive r.f. magnetron sputtering from two ceramic targets (LiMn2O4, LiMnO2) in a pure argon discharge. The deposition parameters, namely target power and working gas pressure, were optimized in a combination with a post deposition heat treatment with respect to microstructure and electrochemical behavior. The chemical composition was determined using inductively coupled plasma optical emission spectroscopy and carrier gas hot extraction. The films' crystal structure, phase evolution and morphology were investigated by X-ray diffraction, micro Raman spectroscopy and scanning electron microscopy. Due to the fact that these thin films consist of the pure active material without any impurities, such as binders or conductive additives like carbon black, they are particularly well suited for measurements of the intrinsic physical properties, which is essential for fundamental understanding. The electrochemical behavior of the cubic and the orthorhombic films was investigated by galvanostatic cycling in half cells against metallic lithium. The cubic spinel films exhibit a maximum specific capacity of similar to 82 mAh/g, while a specific capacity of nearly 150 mAh/g can be reached for the orthorhombic counterparts. These films are promising candidates for future all solid state battery applications. (c) 2012 Elsevier B.V. All rights reserved.