An interlayer of metallic Li was formed between two layers of Li-Nb-O. Annealing of the structure results to diffusion of Li into the two layers of Li-Nb-O, improving the ionic conductivity. The thickness of the metallic interlayer is a crucial parameter, as well as the temperature and time of annealing. The substrate strongly influences the electrical and structural properties of the films. Stainless-steel/TiN substrate seems to improve considerably the ionic conductivity of the films, the relaxation time of which is similar to that of the Lipon electrolyte.