Stress Regulation on Atomic Bonding and Ionic Diffusivity: Mechanochemical Effects in Sulfide Solid Electrolytes

Abstract

External pressure is widely applied to the fabrication and assembling of solid-state batteries, which can reduce grain sizes, enhance solid–solid contacts, and further increase the ionic conductivity of solid electrolytes. However, the effect of stress on the intrinsic ionic conductivity of solid electrolytes is not yet fully understood. Herein, a comprehensive first-principles investigation was performed to elucidate the effect of tensile and compressive stresses on the ionic diffusivity of a sulfide solid electrolyte prototype Li10GeP2S12 (LGPS). A reduced and increased ionic diffusivity is observed in LGPS under compressive and tensile stress, respectively. Several descriptors, including the lattice volume, the neck size, the Li vacancy formation energy, and the Li Bader charge, are proposed to reveal the evolution of the ionic diffusivity in LGPS under stress. The ionic diffusivity in LGPS exhibits a better correlation with the activation energy than the pre-exponential factor, which suggests a synergy of stress and temperature on the ionic diffusivity. A more obvious change of ionic diffusivity as the stress is expected under lower temperatures. These results afford a fundamental and deep understanding of the mechanochemical effect in solid electrolytes.