Structural changes in the lithium cobalt dioxide electrode: A combined approach with cluster expansion and Bayesian optimization

Lilithium cobalt dioxide (${\mathrm{LiCoO}}_{2}$) is a promising cathode material for rechargeable lithium-ion batteries (LIBs). To improve the electrochemical performance of LIBs, we theoretically investigated the structural changes in a ${\mathrm{LiCoO}}_{2}$ electrode through the thermodynamic convex hull analysis. To construct the convex hull, we combined cluster expansion and Bayesian optimization (BO) with high-throughput density functional theory (DFT) calculations. To improve the BO efficiency, we used hull distance as the target variable of BO, which considerably reduced the number of DFT calculations. At 300 K, the ${\mathrm{O}}_{2}$ gas release by the convex hull was confirmed. The defective stoichiometry of ${\mathrm{CoO}}_{2\ensuremath{-}y}$ deteriorated the layered structure of ${\mathrm{CoO}}_{2}$ and prevented the ${\mathrm{Li}}^{+}$ ion migration. Therefore, we considered that the formation of ${\mathrm{CoO}}_{2\ensuremath{-}y}$ contributed to the cathode degradation. Our findings will provide useful insights into the prevention of LIB degradation.