Site-Occupation-Tuned Superionic LiScCl₃₊Halide Solid Electrolytes for All-Solid-State Batteries

The enabling of high energy density of all-solid-state lithium batteries (ASSLBs) requires the development of highly Li⁺-conductive solid-state electrolytes (SSEs) with good chemical and electrochemical stability. Recently, halide SSEs based on different material design principles have opened new opportunities for ASSLBs. Here, we discovered a series of LiScCl₃₊ SSEs (x = 2.5, 3, 3.5, and 4) based on the cubic close-packed anion sublattice with room-temperature ionic conductivities up to 3 × 10^-3 S cm^-1. Owing to the low eutectic temperature between LiCl and ScCl₃, LiScCl₃₊ SSEs can be synthesized by a simple co-melting strategy. Preferred orientation is observed for all the samples. The influence of the value of x in LiScCl₃₊ on the structure and Li⁺ diffusivity were systematically explored. With increasing x value, higher Li⁺, lower vacancy concentration, and less blocking effects from Sc ions are achieved, enabling the ability to tune the Li⁺ migration. The electrochemical performance shows that Li₃ScCl₆ possesses a wide electrochemical window of 0.9-4.3 V vs Li⁺/Li, stable electrochemical plating/stripping of Li for over 2500 h, as well as good compatibility with LiCoO₂. LiCoO₂/Li₃ScCl₆/In ASSLB exhibits a reversible capacity of 104.5 mAh g^-1 with good cycle life retention for 160 cycles. The observed changes in the ionic conductivity and tuning of the site occupations provide an additional approach toward the design of better SSEs.