Iodine-driven artificial SEI layer for high performance lithium metal batteries in an SO2-based electrolyte

Abstract

Lithium metal anodes offer high theoretical capacity with a low redox potential; however, an unstable solid electrolyte interphase (SEI), lithium dendrite formation, and limited cycling performance limit their practical applications. While SO2-based inorganic electrolytes provide high ionic conductivity and inherent nonflammability, their high reactivity with lithium forms thick and unstable SEI layers that are primarily composed of LiCl and lithium–sulfur–oxy compounds. In this study, we demonstrate an SEI engineering strategy using a molecular iodine (I2)-containing LiAlCl4–3SO2 electrolyte to control the composition of the SEI formed at the interface of the lithium metal electrode. The I2 acts as a redox mediator that promotes the formation of Li2S and Li2O-enriched artificial SEI layers in lithium metal, replacing the typical LiCl-dominant interfacial film. This Li2S/Li2O-rich artificial SEI exhibited enhanced Li+ transport properties and mechanical stability compared to the native SEI, thereby suppressing lithium dendrite formation and mitigating parasitic reactions during cycling. The electrochemical evaluation demonstrated improved cycling stability in both Li//Li symmetric cells and Li//LiFePO4 full cells across various current densities.