Formation, Structural Variety, and Impact of Antiphase Boundaries on Li Diffusion in LiCoO₂ Thin-Film Cathodes

Antiphase boundaries (APBs) are observed in as-synthesized and processed LiCoO₂, which is used widely as a cathode material. Using a combination of scanning transmission electron microscopy and ab initio simulations, we investigate APB formation, structure, stability, and impact on Li ion diffusion. It is found that APB low-coordinated sites give rise to cation defects which, in turn, provide a variety of APB structures. Li diffusion along an APB can enter a correlated mode, leading to a ∼40% decrease in activation energy with respect to that for the uncorrelated hopping of Li ions. We propose that APBs function as additional mass-transfer channels that couple in-plane Li ion diffusion pathways, thus facilitating Li transfer from one two-dimensional basin to another, potentially enabling new energy storage architectures.