Suppressing Li Dendrite Formation in Li2S‐P2S5 Solid Electrolyte by LiI Incorporation

Abstract Solid electrolytes have been considered as a promising approach for Li dendrite prevention because of their high mechanical strength and high Li transference number. However, recent reports indicate that Li dendrites also form in Li 2 S‐P 2 S 5 based sulfide electrolytes at current densities much lower than that in the conventional liquid electrolytes. The methods of suppressing dendrite formation in sulfide electrolytes have rarely been reported because the mechanism for the “unexpected” dendrite formation is unclear, limiting the successful utilization of high‐energy Li anode with these electrolytes. Herein, the authors demonstrate that the Li dendrite formation in Li 2 S‐P 2 S 5 glass can be effectively suppressed by tuning the composition of the solid electrolyte interphase (SEI) at the Li/electrolyte interface through incorporating LiI into the electrolyte. This approach introduces high ionic conductivity but electronic insulation of LiI in the SEI, and more importantly, improves the mobility of Li atoms, promoting the Li depositon at the interface and thus suppresses dendrite growth. It is shown that the critical current density is improved significantly after incorporating LiI into Li 2 S‐P 2 S 5 glass, reaching 3.90 mA cm −2 at 100 °C after adding 30 mol% LiI. Stable cycling of the Li‐Li cells for 200 h is also achieved at 1.50 mA cm −2 at 100 °C.