Sulfurized solid electrolyte interphases with a rapid Li⁺ diffusion on dendrite-free Li metal anodes

The notorious growth of Li dendrites significantly shortens the longevity and raises safety concerns of high-energy-density Li metal batteries. We proposed a sulfurized solid electrolyte interphase (SEI) to protect Li metal anode in a working Li metal battery. By incorporating Li₂S into the interphase, a polycrystalline and mosaic SEI film with poor crystallinity was achieved. Li₂S, Li₂O, Li₃N, LiNO₃, and LiF nanoparticles were embedded in the sulfurized SEI. A high ionic conductivity of 3.1×10⁻⁷ S cm⁻¹ was achieved for the sulfurized SEI, around one magnitude higher than that of the routine SEI (4.2×10⁻⁸ S cm⁻¹). Therefore, uniform plating/stripping of the Li metal was achieved without Li dendrite formation. The sulfurized SEI enabled stable cycling of Li | Li cells for 500 h at 1.0 mA cm⁻² and for 150 h at 5.0 mA cm⁻². With the protection of a sulfurized SEI film, Li metal anode exhibited a high Coulombic efficiency of 98% during 200 cycles at 1.0 mA cm⁻², while the Coulombic efficiency drastically dropped to 70% at the 200^th cycle on Li metal anode with routine SEI. The pouch cells exhibited a plating resistance of −331 and −108 mV, a stripping resistance of 67 and 54 mV on Li metal anode with routine and sulfurized SEI films, respectively. The sharply decreased resistance, endowed by the sulfurized SEI, futher suggested the rapid Li ion diffusion in working Li-metal batteries. This affords new insights into the SEI structure and its critical role in Li metal protection, and sheds a fresh light on the rational design of electrolyte additives and SEI film in a working Li metal battery.