Role of Lithium Iodide Addition to Lithium Thiophosphate: Implications beyond Conductivity

Because of their high conductivity and potential to utilize lithium metal, lithium thiophosphate electrolytes have attracted significant attention to realize solid-state batteries for vehicle applications. However, lithium metal still presents many challenges in potentially maximizing the battery energy density. One important requirement is to limit the amount of lithium metal during cell construction or to operate the cell under limited lithium conditions. Here, the interface between lithium thiophosphate and lithium iodide-doped lithium thiophosphate with lithium metal is investigated. Lithium iodide plays a protective role at the interface and enables improved lithium cycling. Operando transmission electron microscopy analysis reveals delamination and dead lithium at the interface as major challenges for solid-state batteries.