Structure and ion diffusion of hexagonal Li₅(PS₄)Cl₂ superionic conductor from molecular dynamics simulations

Abstract

All-solid-state battery technology is considered a promising candidate for next-generation batteries. Sulfide-based materials, particularly lithium thiophosphates, show great potential due to their Li-superionic conductivity at room temperature. We have performed a study of the structure and Li-ion diffusion in Li₅(PS₄)Cl₂ using molecular dynamic simulations at various temperatures. Our research proposed a new hexagonal structure with space group P6₃mc for this material. We find that the Li sublattice is disordered over four crystallographic positions in this structure, which provides favorable conditions for fast Li-ion diffusion, ∼10⁻⁷ cm²/s, leading to a superionic conductivity of ∼2 × 10⁻² S/cm with an activation energy of ∼0.3 eV at room temperature. Our simulations indicate that the Li-ion conductivity of Li₅PS₄Cl₂ is almost isotropic. This predicted conductivity is among the highest reported for known solid electrolytes. Based on our computational findings, we proposed a mechanism for the Li-ion diffusion in the hexagonal Li₅PS₄Cl₂ and discussed it in detail. This research shows the potential of computational tools to guide the rational design of next-generation solid-state electrolytes and how predictive modeling can accelerate innovation in materials development.

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