Justin Leifeld, A. Parsons, Alexandra Morscher, Xabier Martinez de Irujo-Labalde, Marvin A. Kraft, Oskar G. Soulas, Bibek Samanta, Wiebke Zielasko, Neelam Yadav, Kyra Strotmann, Niina Jalarvo, Bruno V. M. Rodrigues, Adam Slabon, Philipp Adelhelm, Michael Ryan Hansen, David O. Scanlon, Wolfgang G. Zeier, Alexander G. Squires
ABSTRACT Solid electrolytes are central to enabling safe, high‐energy solid‐state sodium batteries. While oxyhalide‐type conductors have rapidly advanced lithium‐based systems, their sodium analogues remain less understood and underdeveloped. This gap arises from their intrinsically amorphous nature, which obscures structure–transport relationships and limits rational design. Here, we elucidate the atomic‐scale origins of sodium‐ion conduction in the mixed‐anion series NaTaO x Cl 6–2 x using a combination of experimental and computational approaches. We reveal that composition‐dependent, disordered yet extended chain motifs emerge as key structural units governing ion mobility. By tuning chain connectivity, we achieve a high ionic conductivity of ∼4 mS cm −1 and a corresponding self‐diffusion coefficient of 6.6–8.2 × 10 −11 m 2 s −1 , ranking among to the fastest reported for sodium oxyhalides. These findings establish clear structure–property correlations in amorphous superionic conductors and provide a blueprint for the targeted design of next‐generation solid electrolytes for sodium solid‐state batteries.