Enhanced ionic conductivity and lack of paddle-wheel effect in pseudohalogen-substituted Li argyrodites

Summary

Superionic conductors are key to the development of safe and high-energy-density, all-solid-state batteries. Using a combined theoretical and experimental approach, we explore the feasibility of increasing the ionic conductivity through pseudohalogen substitution in the Li argyrodite structure. Under the guidance of calculated thermodynamic stability, BH₄-substituted Li argyrodite, Li_5.91PS_4.91(BH₄)_1.09, was successfully synthesized via a mechanochemical method. As-synthesized BH₄-substituted Li argyrodite displays an ionic conductivity of 4.8 mS/cm at 25°C. Ab initio molecular dynamics simulation trajectory analysis was used to investigate how BH₄ facilitates Li-ion diffusion and indicates only a weak correlation with the B–H bond motion. We find that the enhanced conductivity mainly originates from the weak interaction between Li and BH₄ and find no evidence of a paddle-wheel effect from the polyanion. This work provides insight into how cluster ions enhance Li diffusion and systematically describes how to explore superionic conductors with pseudohalogen substitution.