Superionic Conducting Halide Frameworks Enabled by Interface-Bonded Halides

The revival of ternary halides Li-M-X (M = Y, In, Zr, etc.; X = F, Cl, Br) as solid-state electrolytes (SSEs) shows promise in realizing practical solid-state batteries due to their direct compatibility toward high-voltage cathodes and favorable room-temperature ionic conductivities. Most of the reported superionic halide SSEs have a structural pattern of [MCl₆]^x- octahedra and generate a tetrahedron-assisted Li⁺ ion diffusion pathway. Here, we report a new class of zeolite-like halide frameworks, SmCl₃, for example, in which 1-dimensional channels are enclosed by [SmCl₉]^6- tricapped trigonal prisms to provide a short jumping distance of 2.08 Å between two octahedra for Li⁺ ion hopping. The fast Li⁺ diffusion along the channels is verified through ab initio molecular dynamics simulations. Similar to zeolites, the SmCl₃ framework can be grafted with halide species to obtain mobile ions without altering the base structure, achieving an ionic conductivity over 10^-4 S cm^-1 at 30 °C with LiCl as the adsorbent. Moreover, the universality of the interface-bonding behavior and ionic diffusion in a class of framework materials is demonstrated. It is suggested that the ionic conductivity of the MCl₃/halide composite (M = La-Gd) is likely in correlation with the ionic conductivity of the grafted halide species, interfacial bonding, and framework composition/dimensions. This work reveals a potential class of halide structures for superionic conductors and opens up a new frontier for constructing zeolite-like frameworks in halide-based materials, which will promote the innovation of superionic conductor design and contribute to a broader selection of halide SSEs.