Orientation dependence of microstructure and electrochemical properties of LiCoO₂ cathode films deposited on single-crystalline La _2/3-xLi_3xTiO₃

Two different types of single-crystalline lithium lanthanum titanate (LLT) I LiCoO₂ assemblies were prepared by depositing HT-LiCoO₂ on the LLT surfaces of(1 10)_p and (112)_p to investigate the effects of the orientation dependence of microstructures on the electrochemical properties of the assemblies. Cyclic voltammetry shows that the (110)_p assembly exhibits very small peak separation between anodic and cathodic reactions, while the peak separation is considerably large in the case of the (112)_p assembly. In the HT-LiCoO₂ thin film cathode formed epitaxially on LLT, four differently-oriented domains can be formed under the orientation relationships of (11 1)_p//(000l) LiCoO₂, and (110)_p//(1l2O)LiCoO₂ between LLT (macroscopically cubic) and HT-LiCoO₂ (rhombohedral). The HT-LiCoO₂ domains with their layered structure aligned perpendicular to the interface are dominantly formed for the (110)_p assembly, whereas those with the layered structure inclined about 20° against the interface are dominantly grown for the (1l2) assembly. Such a selective growth behavior of the HT-LiCoO₂ on the LLT surface is considered to play an important role for the observed orientation dependence of the electrochemical properties of the LLT/LiCoO₂ assemblies.