Solution-derived glass-ceramic NaI·Na₃SbS₄ superionic conductors for all-solid-state Na-ion batteries

Bulk-type all-solid-state Na-ion batteries (ASNBs) employing inorganic Na-ion conductors and operating at room temperature are considered as promising candidates for large-scale energy storage systems. However, their realization has been impeded by low ionic conductivity, instability in air of the solid electrolytes, and poor ionic contacts among the constituents of the electrodes. Here, we report novel glass-ceramic xNaI·(1 - x)Na₃SbS₄ superionic conductors (maximum Na⁺ conductivity of 0.74 mS cm^-1 at 30 °C, for x = 0.10) obtained from scalable methanol solutions. Comprehensive spectroscopic evidence, density functional theory calculations, and electrochemical analysis suggest the decisive role of I^- incorporated in the disordered domains at the nanoscale in the overall Na⁺ transport. Furthermore, the solution-derived NaI·Na₃SbS₄ forms uniform coating layers on the surface of the active material FeS₂, providing unobstructed ionic transport pathways in the electrodes. The good electrochemical performance of FeS₂/Na-Sn ASNBs at 30 °C is demonstrated.