Lithium Diffusion in Graphitic Carbon

Graphitic carbon is currently considered the state-of-the-art material for\nthe negative electrode in lithium-ion cells, mainly due to its high\nreversibility and low operating potential. However, carbon anodes exhibit\nmediocre charge/discharge rate performance, which contributes to severe\ntransport-induced surface-structural damage upon prolonged cycling, and limits\nthe lifetime of the cell. Lithium bulk diffusion in graphitic carbon is not yet\ncompletely understood, partly due to the complexity of measuring bulk transport\nproperties in finite-sized, non-isotropic particles. To solve this problem for\ngraphite, we use the Devanathan-Stachurski electrochemical methodology combined\nwith ab-initio computations to deconvolute, and quantify the mechanism of\nlithium-ion diffusion in highly oriented pyrolytic graphite (HOPG). The results\nreveal inherent high lithium-ion diffusivity in the direction parallel to the\ngraphene plane (ca. 10^-7 - 10^-6 cm2 s-1), as compared to sluggish lithium-ion\ntransport along grain boundaries (ca. 10^-11 cm^2 s^-1), indicating the\npossibility of rational design of carbonaceous materials and composite\nelectrodes with very high rate capability.\n