Charge fluctuation drives anion rotation to enhance the conductivity of Na 11 M 2 PS 12 (M = Si, Ge, Sn) superionic conductors

Solid superionic conductors exhibit good battery safety and stability, promising to replace organic liquid electrolytes. However, a comprehensive understanding of the factors determining high ion mobility remains elusive. Experiments have confirmed that the Na Sn PS superionic conductor has high room temperature Na -ion conductivity; excellent phase stability has been demonstrated in a solid-state electrolyte. The PS anion rotation exists in Na M PS -type superionic conductors, but this rotation is affected by the isovalent cation substitutions of the M site. In combination with molecular dynamic simulations and joint time correlation analysis of the AIMD data, we show that the transport of Na ions is directly enhanced by the charge fluctuation in their tetrahedral MS anions that comprise the framework. The fundamental reason for the charge fluctuation is the material structure forming a micro-parallel capacitor with MS anions, which governs the differential capacitance. Our study provides a fundamental and comprehensive understanding of the structure-controlled charge transfer of Na M PS -type material and can guide solid-state battery optimization and design.