LiNi0.5Mn1.5O4 (LNMO) cathode thin films were prepared on Pt-coated stainless steel (SS) substrates by radio frequency magnetron sputtering. The layers were post-annealed at 500, 600 and 700 degrees C to study the impact of thermal treatment on the crystallization of the cathode material. As the annealing temperature increases, interdiffusion occurs between the substrate and the LNMO film, which degrades the electrochemical properties of the cathode film. In order to mitigate this problem, an In-Sn-O (ITO) interlayer was introduced between Pt and the SS substrate. The ITO film is electrochemically stable and acts as an effective diffusion barrier between the substrate and the LNMO layer, which results in improved electrochemical properties of the LNMO film for a lithium ion battery.