The Surface Chemistry of Thin Lithium Metal Electrodes in Lithium-Sulfur Cells

In this work, we explore the surface chemistry of Li metal electrodes used in Li-S batteries when employing a very thin (30 mu m) lithium metal foil. The foil thickness is instrumental for achieving a balanced cell with optimal energy density, but previous work has largely neglected how the change to thinner anodes will influence the critical surface phenomena in the cell. X-ray photoelectron spectroscopy (XPS) was used as the main characterisation tool to follow the evolution of the solid electrolyte interphase (SEI) layer on the Li electrode, complemented by scanning electron microscopy. Based on the XPS analyses, the premature capacity fading observed for the cell with thin Li metal electrode could be ascribed to changes in the composition of the surface layer on the Li electrode, due to that the resulting rougher surface more rapidly consume the LiNO(3)electrolyte additive. This highlights that mitigating the degradation mechanisms at the Li metal surface is of large importance when the Li electrode is scaled down for better cell balancing in Li-S cells.