Lattice orientation control of lithium cobalt oxide cathode film for all-solid-state thin film batteries

For the application to all-solid-state thin film batteries, LiCoO2 thin films are deposited by RF-sputtering with controlling the lattice orientations to maximize lithium-ion diffusivity in film textures. The nano-sized crystalline grains grow up with the (003) preferred orientation parallel to the substrates at room temperature due to the lowest surface energy of this atomic plane. However, because the surface energy difference of atomic planes of LiCoO2 reduces with increasing substrate temperature, the influence of surface energy becomes weaker at high temperature. The LiCoO2 thin films with the (110) preferred orientation are obtained at higher temperatures by dominant influence from the lowest the volume strain energy of this orientation. To take advance of this orientation effect in full cell, the influences of the metallic current collector layer on the structural properties of sputtered cathode are investigated. It turns out that the Li2O buffer layers between the cathode films and the metallic current collector layers can suppress the formation of lithium-deficient phase, Co3O4, and the growth of (003) plane by reducing the lattice match between of LiCoO2 plane and Al(111) plane. The LiCoO2 films with the controlled orientation show enhanced rate performance owing to improved interfacial resistance and lithium-ion conductivity.