Unraveling Lithium-Ion Migration Mechanisms in Novel Quasi-Layered Argyrodite Solid Electrolyte for All-Solid-State Battery.

All-solid-state electrolytes are regarded as key materials for replacing liquid electrolytes in the future, whereas Argyrodite solid electrolytes with outstanding ionic conductivity have not been thoroughly studied as candidates for lithium batteries. In this work, an in-depth theoretical investigation of the lithium-ion migration mechanisms of the novel Argyrodite electrolytes by introducing 50% disorder in 4a/4c sites of P2mm space group crystal structures is conducted. By forming a quasi-layered crystal structure, the influences of the anion framework on lithium-ion migration by doping different elements at various sites regarding ion dynamics, electronic structures, bond valence, transition state search, and weak interactions are elucidated. The high-ionic conductivity of Argyrodite electrolytes primarily originates from the weaker chemical bonding interactions of halide ions at the 4c sites, as well as the higher activity of sulfur ions at the 4a sites, which facilitates lithium-ion migration within layers. Weak dispersion interactions further reduce resistance to lithium-ion migration. Through the analysis of the interlayer ionic conductivity differences, the correlation with the uniformity of Mayer bond orders is presented. More importantly, the potential for directly calculating the ion migration activation energy in solid electrolytes via transition state search methods is proposed, offering advanced ideas for future works.