Ab Initio Atomistic Thermodynamics Study of the (001) Surface of LiCoO₂ in a Water Environment and Implications for Reactivity under Ambient Conditions
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Huang, Xu, Joseph W. Bennett, Mimi N. Hang, Elizabeth D. Laudadio, Robert J. Hamers, and Sara E. Mason. “Ab Initio Atomistic Thermodynamics Study of the (001) Surface of LiCoO2 in a Water Environment and Implications for Reactivity under Ambient Conditions.” The Journal of Physical Chemistry C 121, no. 9 (2017): 5069–80. https://doi.org/10.1021/acs.jpcc.6b12163.
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This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.jpcc.6b12163.
Abstract
We use GGA + U methodology to model the bulk and surface structure of varying stoichiometries of the (001) surface of LiCoO₂. The DFT energies obtained for these surface-slab models are used for two thermodynamic analyses to assess the relative stabilities of different surface configurations, including hydroxylation. In the first approach, surface free energies are calculated within a thermodynamic framework, and the second approach is a surface-solvent ion exchange model. We find that, for both models, the -CoO–H₁/₂ surface is the most stable structure near the O-rich limit, which corresponds to ambient conditions. We find that surfaces terminated with Li are higher in energy, and we go on to show that H and Li behave differently on the (001) LiCoO₂ surface. The optimized geometries show that terminal Li and H occupy nonequivalent surface sites. In terms of electronic structure, Li and H terminations exhibit distinct bandgap characters, and there is also a distinctive distribution of charge at the surface. We go on to probe how the variable Li and H terminations affect reactivity, as probed through phosphate adsorption studies.