Abnormal Ionic Conductivities in Halide NaBi₃ O₄ Cl₂ Induced by Absorbing Water and a Derived Oxhydryl Group

In hunting for safe and cost-effective materials for post-Li-ion energy storage, the design and synthesis of high-performance solid electrolytes (SEs) for all-solid-state batteries are bottlenecks. Many issues associated with chemical stability during processing and storage and use of the SEs in ambient conditions need to be addressed. Now, the effect of water as well as oxyhdryl group (^. OH) on NaBi₃ O₄ Cl₂ are investigated by evaluating ionic conductivity. The presence of water and ^. OH results in an increase in ionic conductivity of NaBi₃ O₄ Cl₂ owing to diffusion of H₂ O into NaBi₃ O₄ Cl₂ , partially forming binding ^. OH through oxygen vacancy repairing. Ab initio calculations reveal that the electrons significantly accumulate around ^. OH and induce a more negative charge center, which can promote Na⁺ hopping. This finding is fundamental for understanding the essential role of H₂ O in halide-based SEs and provides possible roles in designing water-insensitive SEs through control of defects.