Chemo-Structural Evolution of LiCoO ₂ (001) under Varied Oxygen Chemical Potentials

Knowledge of LiCoO2 surfaces enables fundamental electrochemical research and emerging applications in energy and electronic devices. In this work, the chemo-structural response of LiCoO2(001) surfaces from the meso-to-atomic scale under varied oxygen chemical potentials (μO) is investigated. Under a traditional ultrahigh-vacuum (UHV) processing regimen (−2.23 eV < μO < −1.48 eV), the LiCoO2(001) surface structure undergoes nanoscale roughening and initial (3×3)R30° reconstruction. Emergent nanofeatures undergo 6-fold size increases under prolonged processing at low μO. The net surface stoichiometry, determined by X-ray photoelectron spectroscopy as Li0.6CoO1.5, consists of coexisting Li0.8CoO1.6(001) and CoO(111) phases. Scanning tunneling microscopy images of exposed flat regions reveal local (7×7)R19.1° reconstruction of the Li-terminated LiCoO2(001) surface and ∼2% oxygen vacancies. Under a higher-pressure processing regimen at high μO (−1.26 eV < μO < −1.19 eV), reached with ambient air and oxygen gas, extended atomically flat LiCoO2(001) terraces of micron widths decorated with Co3O4(111) islands are routinely observed. Such high μO treatments yield a stoichiometric Li1.0CoO2.0(001) surface. The thermodynamic and kinetic impacts of μO on the chemo-structural evolution of LiCoO2(001) surfaces are described, providing new insights on LiCoO2 surface preparation and stability.