van der Waals Interactions in Layered Lithium Cobalt Oxides

The role of van der Waals (vdW) interactions in density functional theory (DFT) + U calculations of the layered lithium-ion battery cathode LixCoO2 (x = 0-1) is investigated using (i) dispersion corrections in the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation functional, (ii) vdW density functionals, and (iii) the Bayesian error estimation functional with vdW correlation. We find that combining vdW corrections or functionals with DFT+U can yield lithiation voltages, relative stabilities, and structural properties that are in much better agreement with experiments for the phases O1-CoO2, O3-CoO2, layered-Li0.5CoO2, spinel-Li0.5CoO2, and LiCoO2 than using DFT+U or vdW-inclusive methods alone or using the hybrid Heyd-Scuseria-Ernzerhof functional. Contributions of vdW interactions to the lithiation voltages are estimated to have a similar magnitude with that of applying a typical U in the range 2-4 eV for cobalt, each accounting for 5-10% of calculated voltages relative to PBE. Relative stabilities of O1 and O3-CoO2 as well as layered- and spinel-Li0.5CoO2 are correctly predicted with vdW-inclusive methods combined with the +U correction.