Unraveling Bridging‐Oxygen‐Driven Ultrafast Amorphization in Superionic Oxyhalide Conductors via in Situ Synchrotron X‐Ray Scattering

ABSTRACT The energy‐ and time‐consuming mechanochemical synthesis of high‐performance solid electrolytes (SEs) remains a critical bottleneck for the scaling of all‐solid‐state batteries. Despite the recognition that oxygen incorporation in structure serves as a viable strategy to develop high‐performance halide SEs, systematic investigations into how oxygen in structure modulates synthesis kinetics, local structure, and ion transport are scarce. Herein, we report the synthesis of amorphous oxyhalide NaTaOCl 4 as a model system, achieved via minute‐scale ball milling, a dramatic improvement over the multi‐day synthesis of conventional NaTaCl 6 . Complementary structural characterizations and ab initio molecular dynamics (AIMD) simulations demonstrate that, low‐coordinated bridging‐oxygen‐dominated Ta−O−Cl environments induce substantial lattice distortions, enabling ultrafast amorphization. Time‐resolved in situ synchrotron x‐ray scattering experiments reveal distinct reaction pathways: NaTaOCl 4 undergoes rapid fragmentation of precursors into metastable intermediates followed by bridging‐oxygen‐driven amorphous formation, whereas NaTaCl 6 experiences a moderate crystallization process prior to prolonged amorphization. By extending this design to a series of mixed‑anion oxyhalides, we establish a universal rapid synthesis strategy. For instance, NaTaO 0.5 Cl 5 exhibits high ionic conductivities of 3.39 mS cm −1 after only 30 min of ball‐milling. This work establishes a strategy that employs oxygen as a structural bridging‐agent to develop high‐conductivity SEs and provides atomic‐scale insights into ultrafast mechanochemical reaction.