Ionic Conductive and Electrochemical Stable Oxyhalide Solid Electrolyte with Amorphous–Crystalline Heterophase Structure

The development of high-performance solid-state electrolytes is essential for the advancement of all-solid-state batteries (ASSBs). While transition metal halide solid electrolytes have garnered significant attention, the potential employment of the vanadium (V) element has been overlooked. In this study, we present an oxyhalide solid electrolyte, Li4VOCl5, with exceptional electrochemical stability. The tuned amorphous–crystalline heterophase structure, in which the amorphous phase encapsulates crystalline domains and fills grain boundaries, endows Li4VOCl5 with a high ionic conductivity of 0.15 mS cm–1 at room temperature, much higher than those reported for vanadium-based halides. Moreover, enhanced interfacial stability of Li4VOCl5 with LiNi0.8Co0.1Mn0.1O2 (NCM811) is achieved as revealed by in situ Raman spectroscopy. The as-fabricated ASSB coupled with NCM811 delivers a discharge capacity of 180.9 mAh g–1 with a high initial Coulombic efficiency of 90.8%. This contribution demonstrates the feasibility of utilizing oxyhalide Li4VOCl5 as a solid electrolyte for ASSBs, while opening up possibilities for manufacturing V-based ASSBs with improved interface compatibility.