First-Principles Prediction of Layered Oxysulfides as Superionic Sodium Conductors

Developing solid-state electrolytes (SSEs) with high ionic conductivity and wide electrochemical stability is critical for the advancement of all-solid-state sodium-ion batteries. Herein, combining global structure searches with first-principles calculations, we identify a novel class of layered oxysulfide superionic conductors, NaMChO (M = Al, Ga; Ch = S, Se). The predicted thermodynamically stable Cmc 2 1 phase exhibits a wide bandgap of ∼5 eV, ensuring a broad electrochemical window. Remarkably, we reveal an exceptionally low migration barrier of 0.08 eV for NaAlSO, driven by a unique “Kick-off’’ cotransport mechanism. Furthermore, we systematically investigate the structure–property relationships, demonstrating that the ionic conductivity can be effectively modulated via aliovalent doping and isovalent substitution. Specifically, we elucidate the competing roles of lattice softening and the inductive effect in governing ion migration dynamics. These findings not only establish NaMChO as a promising candidate for high-performance SSEs but also provide a robust theoretical framework for the rational design of mixed-anion superionic conductors.