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 angstrom 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 degrees 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.

Automated summary

The revival of ternary halides as solid-state electrolytes shows promise in realizing practical solid-state batteries. A new class of zeolite-like halide frameworks is reported, which can achieve fast Li+ diffusion and high ionic conductivity through the enclosed channels. The grafted halide species further enhance the ionic conductivity. This work reveals a potential class of halide structures for superionic conductors and promotes the innovation of superionic conductor design and broader selection of halide solid-state electrolytes.