Interfacial Reactivity Benchmarking of the Sodium Ion Conductors Na₃PS₄ and Sodium β-Alumina for Protected Sodium Metal Anodes and Sodium All-Solid-State Batteries

Abstract

The interfacial stability of solid electrolytes at the electrodes is crucial for an application of all-solid-state batteries and protected electrodes. For instance, undesired reactions between sodium metal electrodes and the solid electrolyte form charge transfer hindering interphases. Due to the resulting large interfacial resistance, the charge transfer kinetics are altered and the overvoltage increases, making the interfacial stability of electrolytes the limiting factor in these systems. Driven by the promising ionic conductivities of Na₃PS₄, here we explore the stability and viability of Na₃PS₄ as a solid electrolyte against metallic Na and compare it to that of Na-β″-Al₂O₃ (sodium β-alumina). As expected, Na-β″-Al₂O₃ is stable against sodium, whereas Na₃PS₄ decomposes with an increasing overall resistance, making Na-β″-Al₂O₃ the electrolyte of choice for protected sodium anodes and all-solid-state batteries.