Work Function Evolution in Li Anode Processing

Toward improved understanding and control of the interactions of Li metal anodes with their processing environments, a combined X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and density functional theory (DFT) characterization of the effects that O2, CO2, and N2, the main gases in dry-atmosphere battery production lines, induced on a reproducibly clean Li surface at room temperature is presented here. XPS measurements demonstrate that O2 is ten times more effective than CO2 at oxidizing metal Li. Notably, pure N2 is shown to not dissociate on clean metal Li. UPS results indicate that decomposition of O2 (CO2) reduces the work function of the Li surface by almost 1 eV, therefore increasing the reduction energy drive for the treated substrate by comparison to bare metallic Li. DFT simulations semiquantitatively account for these results on the basis of the effects of dissociative gas adsorption on the surface dipole density of the Li surface.