High-Entropy Argyrodite Glass-Ceramic Electrolytes for All-Solid-State Batteries

Only Lithium argyrodite superionic conductors with the general formula Li₆PS₅X (X = Cl, Br, I) have been intensively investigated in recent years and further successfully adopted in the field of solid-state batteries (SSBs). The transport properties of argyrodite solid electrolytes usually strongly depend on the degree of occupational disorder. Increasing disorder through complex doping or substitution has been shown to directly affect ionic conductivity. Herein, we explore a high-entropy lithium argyrodite of nominal composition Li_6.6P_0.2Si_0.2Sn_0.2Ge_0.2Sb_0.2S₅I. This material can be readily prepared by mechanochemistry. Using complementary diffraction techniques, nuclear magnetic resonance spectroscopy, and charge-transport measurements, we show that upon tailoring crystallinity and defect concentration by post-annealing at temperatures up to 220 °C, a high room-temperature ionic conductivity of about 0.9 mS/cm (~4.4 mS/cm bulk conductivity) can be achieved. Both as-prepared and annealed (at 220 °C) samples were also tested in pellet-stack SSB cells. The mechanochemically prepared glass-ceramic solid electrolyte was found to exhibit superior performance, even outperforming commercially available Li₆PS₅Cl. Collectively, the results highlight the importance of considering structural aspects on different length scales when optimizing the properties of lithium argyrodites for SSB applications.