DFT and thermodynamics calculations of surface cation release in LiCoO₂

Abstract

While complex metal oxides (CMOs) such as LiCoO₂ (LCO) are currently used in multiple electronic devices, their environmental impacts are not well understood. In this work, we apply density functional theory (DFT) and thermodynamics modeling to study LCO surface transformations. We performed Raman studies on bulk LCO, and compared experimental and computational results. Full vibrational analysis of the model LCO surfaces show localized surface modes that are distinct from bulk, varying in Li and OH surface terminations. Central to this study are calculations to assess the dependence of the DFT + thermodynamics methodology on computational parameters, such as the choice of the exchange-correlation functional, and model geometry, specifically varying slab thickness and supercell dimensions. We discuss how the results can be used to establish upper- and lower-bounds for favorable surface cation vacancy formation under varying pH conditions. The model predicts that at a pH of 7, up to 16% of surface Co will undergo dissolution. We go on to discuss how these model results relate to experimental dissolution studies. We also extrapolate how our results can provide useful insights to guide the (re)design of CMOs with tailored ion release behavior.