A high-conduction Ge substituted Li₃AsS₄ solid electrolyte with exceptional low activation energy

Lithium-ion conducting solid electrolytes show potential to enable high-energy-density secondary batteries and offer distinctive safety features as an advantage over traditional liquid electrolytes. Achieving the combination of high ionic conductivity, low activation energy, and outstanding electrochemical stability in crystalline solid electrolytes is a challenge for the synthesis of novel solid electrolytes. Herein we report an exceptionally low activation energy (E_a) and high room temperature superionic conductivity via facile aliovalent substitution of Li₃AsS₄ by Ge, which increased the conductivity by two orders of magnitude as compared with the parent compound. The composition Li_3.334Ge_0.334As _0.666S₄ has a high ionic conductivity of 1.12 mS cm ^-1 at 27 °C. Local Li⁺ hopping in this material is accompanied by a distinctive low activation energy E_a of 0.17 eV, being the lowest of Li⁺ solid conductors. Furthermore, this study demonstrates the efficacy of surface passivation of solid electrolyte to achieve compatibility with metallic lithium electrodes.