Annealing-Free Thioantimonate Argyrodites with High Li-Ion Conductivity and Low Elastic Modulus

Abstract

Although Li-ion superconducting sulfides have been developed as solid electrolytes (SEs) in all-solid-state batteries, their high deformability, which is inherently beneficial for room-temperature compaction, is overlooked and sacrificed. To solve this dilemmatic task, herein, highly deformable Li-ion superconductors are reported using an annealing-free process. The target thioantimonate, Li5.2Si0.2Sb0.8Br0.25I7.5, comprising bimetallic tetrahedra and bi-halogen anions is synthesized by two-step milling tuned for in situ crystallization, and exhibits excellent Li-ion conductivity (sigma(ion)) of 13.23 mS cm (averaged) and a low elastic modulus (E) of 12.51 GPa (averaged). It has a cubic argyrodite phase of approximate to 57.39% crystallinity with a halogen occupancy of approximate to 90.67% at the 4c Wyckoff site. These increased halogen occupancy drives the Li-ion redistribution and the formation of more Li vacancies, thus facilitating Li-ion transport through inter-cage pathway. Also, the facile annealing-free process provides a unique glass-ceramic structure advantageous for high deformability. These results represent a record-breaking milestone from the combined viewpoint of sigma(ion) and E among promising SEs. Electrochemical characterization, including galvanostatic cycling tests for 400 h, reveals that this material displays reasonable electrochemical stability and cell performance (150.82 mAh g(-1) at 0.1C). These achievements shed light on the synthesis of practical SEs suffice both sigma(ion) and E requirements.