Ab initiostudies on the stability and electronic structure ofLiCoO2(003) surfaces

Abstract

The electronic structures of $2\ifmmode\times\else\texttimes\fi{}2$ polar (003) surfaces of ${\mathrm{LiCoO}}_{2}$ have been studied using the first-principles projector augmented-wave (PAW) method within the generalized gradient approximation (GGA), based on the density functional theory (DFT). Several geometry structure models were considered with different terminations in order to obtain the most stable structure. From cleavage energies of separation it reveals that, for ${\mathrm{LiCoO}}_{2}$ (003), the configuration with O termination on one side and Li termination on the other side was the most stable one. Because the exposed Li-O groups easily react with the electrolytes so that the structure is destroyed, this conclusion can indirectly explain the phenomenon that ${\mathrm{LiCoO}}_{2}$ coated by MgO possesses the more stable structure [J. Electrochem. Soc. 149, A466 (2002)]. It is also found that structure relaxation is considerably large, and the electronic density of states (DOS) shows large difference between (003) surfaces and bulk, with, for example, a decrease of the band gap between the valance band and the empty band in (003) surfaces region compared to the bulk. It is possible to reconstruct for the polar (003) surfaces of ${\mathrm{LiCoO}}_{2}$ crystallite.