Electrical Conductivity of Delithiated Lithium Cobalt Oxides: Conductive Atomic Force Microscopy and Density Functional Theory Study

LiCoO2, one of the most popular cathode materials for lithium ion batteries, is well known for undergoing insulator–metal transitions depending on the amount of lithium ions. In this study, we successfully visualize the change in the electrical conductivity of LiCoO2 without synthesizing large single crystals using conductive atomic force microscopy and high-resolution scanning electron microscopy. As expected, the anisotropic conductivity is observed only in the (003) plane. The electronic structures of LiCoO2, CoO2, and Li0.5CoO2 are studied from density functional theory calculation. This systematic calculation is in good agreement with the previously reported experimental finding that electron holes of hybrid orbitals of Co4+ (a1g) and oxygen (2p), which are produced by the lithium vacancy, contribute to the electrical conductivity of delithiated lithium cobalt oxides.