DFT and Thermodynamics Calculations of Surface Cation Release in LiCoO2

When exposed to environmental conditions, LCO can release Co cations, a known toxicant. In this study, we build on previous work (Bennett et al., Environ. Sci. Technol., 52, 5792-5802, 2018, Bennett et al., Inorg. Chem., 57, 13300-13311, 2018) using theory and modeling to understand the thermodynamic driving forces of ion release in water. We assess how the calculated predictions for ion release depend on aspects of the structural surface model. For example, we vary the number of atomic layers used to form the slab, we explore different surface terminations and hydroxyl group coverages, and we vary the periodic in-plane supercell to assess how ion release depends on the density of formed vacancies. We also benchmark the DFT + Thermodynamics modeling across a range of computational factors such as the choice of exchange correlation functional and pseudopotential type. Such assessment is critical, as there is no direct experimental information for comparison. We devise a generalizable scheme for predicting a threshold pH at which Co release from LCO becomes favorable. We put forward that this scheme could provide information about how much Co is released from LCO under variable pH conditions, and could therefore be used to inform macroscopic contaminant fate models.