Diffusion mechanisms in Li0.5CoO2—A computational study

An atomistic study of the order-effect occurring in LixCoO2 at x = 0.5 is presented, and an explanation for the experimentally observed dip in the Li diffusivity is proposed. Configurations where a single half-filled Li-layer arranged in either a linear or a zig-zag pattern are simulated. It is found that the lowest energy phase is the zig-zag pattern rather than the linear arrangement that is currently assumed to be of lowest energy. Atomic interactions are modeled at the density-functional theory level of accuracy, and energy barriers for Li-ion diffusion are determined from searches for first order saddle points on the resulting potential energy surface. The determined saddle points reveal that the barriers for diffusion parallel and perpendicular to the zig-zag phase differ significantly and explain the observed dip in diffusivity.