Z‐Type Interstice Leap Migration Driving High Ionic Conductivity in Monoclinic LiBiBr₄ Solid State Electrolyte

Abstract Halide solid electrolytes receive much attention due to their electrochemical properties, such as high ionic conductivity, oxidative stability, and ease of preparation. In this work, a bromide solid electrolyte LiBiBr₄, exhibiting ease of processing and high ionic conductivity, is designed for the first time and investigated through a comparative investigation with monoclinic LiAlCl₄ and LiAlBr₄ for the migration path. The processing pressure for LiBiBr₄ with annealing at 120 °C is less than one‐tenth that of other chloride electrolytes (≈5 MPa). Computational analyses unveil crucial mechanistic insights into the three migration mechanisms and the factors that influence them within the monoclinic structure. The distribution and distance of non‐Li polyhedrons to the migration pathways are pivotal for the migration. The strategic positioning of the Bi polyhedron in LiBiBr₄ is far from the Li⁺ pathway. The unique leap migration within the LiBiBr₄ has a lower energy barrier and facilitates an interconnected migration that forms a 3D interstice network. This interconnected leap migration network within LiBiBr₄ constitutes a Z‐type interstice leap migration along the ab‐axis. Thus, the LiBiBr₄ obtains a high ionic conductivity of 0.19 mS cm⁻¹ with the 0.349 eV low activation energy. This discovery and research methods provide significant impetus and support for the development of halogen‐based electrolytes.