Visualizing Ion Transport Pathways to Unveil the Origins of Fast Ion Conduction in Copper‐Ion Solid Electrolyte for All‐Solid‐State Batteries

ABSTRACT Despite the inherent safety and energy density advantages, all‐solid‐state batteries (ASSBs) have not yet achieved large‐scale commercialization, primarily due to challenges associated with developing solid‐state electrolytes (SEs), hindered by lacking in‐depth understanding of their ion migration on the view of lattice dynamics. This study utilizes the maximum entropy method (MEM) in conjunction with X‐ray diffraction (XRD) to directly visualize Cu + ion transport pathways in solid state Cu + electrolyte, Rb 4 Cu 16 I 7 Cl 13 . The atomic displacement parameters (ADP) of Cu + ions, ranging from 0.06–0.12 Å 2 at 303 K, are found to be significantly larger than that of other composition ions. The large ADPs align well with MEM‐derived electron density maps, which reveal overlapping electron clouds between Cu1 and Cu2 sites, and confirm the presence of fast and continuous 3D ionic conduction channels. These structural features contribute to an ionic conductivity as high as 0.19–0.27 S/cm within the temperature range of 30°C–120°C, thus enabling all‐solid‐state Cu‐ion batteries with a specific capacity over 110 mAh/g.