A structurally flexible halide solid electrolyte with high ionic conductivity and air processability

In this work, a structurally revivable, chloride-ion conducting solid electrolyte (SE), CsSn${}_{0.9}$In${}_{0.067}$Cl${}_3$, with a high ionic conductivity of 3.45 × 10${}^{-4}$ S cm${}^{-1}$ at 25 °C is investigated. The impedance spectroscopy, density functional theory, solid-state ${}^{35}$Cl NMR, and electron paramagnetic resonance studies collectively reveal that the high Cl${}^{-}$ ionic mobility originates in the flexibility of the structural building blocks, Sn/InCl${}_6$ octahedra. The vacancy-dominated Cl${}^{-}$ ion diffusion encompasses co-ordinated Sn/In(Cl) site displacements that depend on the exact stoichiometry, and are accompanied by changes in the local magnetic moments. Owing to these promising properties, the suitability of the CsSn${}_{0.9}$In${}_{0.067}$Cl${}_3$, as an electrolyte is demonstrated by designing all-solid-state batteries, with different anodes and cathodes. The comparative investigation of interphases with Li, Li-In, Mg, and Ca anodes reveals different levels of reactivity and interphase formation. The CsSn${}_{0.9}$In${}_{0.067}$Cl${}_3$ demonstrates an excellent humidity tolerance (up to 50% relative humidity) in ambient air, maintaining high structural integrity without compromises in ionic conductivity, which stands in contrast to commercial halide-based lithium conductors. The discovery of a halide perovskite conductor, with air processability and structure revival ability paves the way for the development of advanced air processable SEs, for next-generation batteries. (© 2023 The Authors. Advanced Energy Materials published by Wiley-VCH GmbH)