| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS+AS+EN-TuM |
| Session: | Mechanistic Insight of Surface Reactions: Catalysis, ALD, etc. - I |
| Presenter: | Ryan Thorpe, Rutgers, the State University of New Jersey |
| Authors: | R. Thorpe, Rutgers, the State University of New Jersey S. Rangan, Rutgers, the State University of New Jersey A. Howansky, Stony Brook University R.A. Bartynski, Rutgers, the State University of New Jersey |
| Correspondent: | Click to Email |
Cobalt (II) oxide is a promising electrode material for Li-ion conversion batteries, undergoing the following reversible redox reaction upon exposure to lithium:
2Li + CoO ↔ Li2O + Co0.
In order to characterize the phase progression and morphology of the Li-CoO reaction, epitaxial CoO(100) and (111) films were exposed to lithium in an ultra-high vacuum chamber. The early stages of the reaction were then characterized with scanning tunneling microscopy (STM), while the diffusion of Li into the films and resultant reduction of CoO was quantified using angle-resolved x-ray photoemission spectroscopy (ARXPS). From these measurements, a model of the Li-CoO reaction was constructed for each orientation.
For CoO(111) films, the conversion reaction initiated at step edges and defect sites before proceeding across the surface of the film. STM images of CoO(111) after 0.2 ML of Li exposure suggest that the conversion reaction products initially assumed a periodic structure which was in registry with the CoO(111) surface. For larger Li exposures, ARXPS measurements indicated that the reaction proceeded in a layer-by-layer fashion into the bulk, maintaining a planar interface between reacted and unreacted CoO.
The reaction of the CoO(100) surface with 0.1 ML of Li resulted in the formation of 2-3 nm Co metal nanoparticles which decorated the CoO step edges. Upon further lithiation, the conversion reaction proceeded into the film preferentially at step edges. ARXPS measurements suggested that the reaction penetrated deep into the CoO film from these nucleation points before spreading across the rest of the surface. These combined results show the importance of crystallographic orientation in determining the reaction kinetics in a Li-ion battery.