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

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, Li_5.2Si_0.2Sb_0.8S₄Br_0.25I_1.75, comprising bimetallic tetrahedra and bi-halogen anions is synthesized by two-step milling tuned for in situ crystallization, and exhibits excellent Li-ion conductivity (σ_ion) of 13.23 mS cm⁻¹ (averaged) and a low elastic modulus (E) of 12.51 GPa (averaged). It has a cubic argyrodite phase of ≈57.39% crystallinity with a halogen occupancy of ≈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 σ_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 σ_ion and E requirements.