Rapid Atomic Li Surface Diffusion and Intercalation on Graphite: A Surface Science Study

The diffusion of dilute metallic lithium across the surface and into the bulk of atomically clean highly oriented pyrolytic graphite in ultrahigh vacuum is reported. Auger electron spectroscopy and a surface-dependent chemical reaction were utilized to monitor the coverage, oxidation state, and diffusion of Li. A very small diffusion activation energy (0.16 ± 0.02 eV; 15.4 ± 1.8 kJ/mol) is found for Li surface diffusion across the graphite basal plane. A model involving diffusion-rate-limited Li atom transport across the basal plane of graphite through step edge sites into the interior is proposed. These measurements indicate that the diffusion coefficient, D, for Li is very large ( D (300 K) ≈ 5 × 10 –6 cm 2 s –1 ).