Elucidating the diffusion pathway of lithium ions in superionic halide solid electrolytes Li_(2+x)Hf_(1-x)In_(x)Cl_(6) for all-solid-state lithium-metal based batteries

All-solid-state batteries(ASSBs) with inorganic solid-state-electrolytes(SSEs) have been regarded as the promising candidate for next-generation energy storage due to their high energy density and outstanding safety performance.However,the representative oxide and sulfide electrolytes suffer from low ionic conductivity and poor(electro)chemical stability,respectively.Herein,we report a series of new halide superionic conductors Li_(2+x)Hf_(1-x)In_(x)Cl_(6) with high ionic conductivity up to 1.05 mS cm^(-1) at 30 ℃ that are simultaneously stable to high voltage.By means of the characterization techniques and bond-valence site energy(BVSE) calculation,insights into the effect of the phase transformation and underlying ionic transport mechanism by In substitution for Hf in Li_(2)HfCl_(6) are provided.Importantly,with the increased amount of aliovalent substitution in Li_(2+x)Hf_(1-x)In_(x)Cl_(6) microcrystal framework,a gradual structure evolution from trigonal to monoclinic phase has been observed,which is accompanied by the redistribution of Li-ions to generate two dimensionally(2D) preferable diffusion pathways through octahedral-tetrahe dral-octahedral sites in In^(3+)-substituted Li_(2)HfCl_(6).Additionally,due to the oxidative stability of Insubstituted Li_(2)HfCl_(6),the bulk-type ASSBs with bare LiCoO_(2) deliver distinguished electrochemical performance.