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

Superionic conductors are key to the development of safe and high-energy-density all-solidstate 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, BH4substituted Li argyrodite, Li5.91PS4.91(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 o 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 paddlewheel effect from the polyanion.This work provides insight on how cluster ions enhance Li diffusion and systematically describes how to explore superionic conductors with pseudohalogen substitution.