Résumé
Lithium/sulfur batteries have been under intense study for the last two decades, due to the high specific capacity promised by elemental sulfur as an active material. Sulfur is also cheap, abundant and non-toxic compared to conventional transition metal oxides. The Li/S electrochemical cell is traditionally composed of a sulfur-based electrode, an organic liquid electrolyte and a lithium metal electrode. Lithium metal technologies have received a renewed interest, due to the light weight and low operating voltage of the lithium electrode, which makes it the ultimate choice to be combined with high-energy positive electrode materials. In this paper, operando X-ray absorption and phase contrast tomography were employed to characterize the lithium metal electrode morphology and heterogeneity in a liquid Li/S cell. It was observed that oxidation of the lithium foil occurs in a heterogeneous fashion with pit formation from the beginning of discharge, with the pits growing in diameter, depth and quantity during the discharge. Using Faraday’s law, the local current density distribution was calculated to confirm the strongly heterogeneous behavior of the lithium metal electrode. We demonstrate that decreasing the current density leads to lithium stripping/plating occurring more homogenously, with the formation of a smaller number of pits.