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 11 Sn 2 PS 12 superionic conductor has high room temperature Na + -ion conductivity; excellent phase stability has been demonstrated in a solid-state electrolyte. The PS 4 anion rotation exists in Na 11 M 2 PS 12 -type superionic conductors, but this rotation is affected by the isovalent cation substitutions of the M site. In combination with ab initio 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 4 anions that comprise the framework. The fundamental reason for the charge fluctuation is the material structure forming a micro-parallel capacitor with MS 4 anions, which governs the differential capacitance. Our study provides a fundamental and comprehensive understanding of the structure-controlled charge transfer of Na 11 M 2 PS 12 -type material and can guide solid-state battery optimization and design.