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

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.