Cyclic Nonequilibrium Processing of Halide Solid Electrolytes for Low‐Pressure Operation of all‐Solid‐State Batteries

ABSTRACT Sluggish ionic transport and high rigidity of inorganic solid electrolytes (SSEs) necessitate ultra‐high external pressures in all‐solid‐state batteries (ASSBs), posing a major barrier to their deployment. Herein, we propose a cyclic nonequilibrium thermal process for Li 3 InCl 6 (LIC) solid electrolyte, which is implemented through repeated quenching to concurrently optimize ionic transport and deformability. The initial quench refines particle size, whereas subsequent quenching induces local amorphization, thereby suppressing grain boundary resistance and enhancing compressibility. Meanwhile, additional Li vacancies are introduced, accelerating bulk phase ionic transport. These coupled mesoscopic and microscopic structural evolutions increase the room‐temperature ionic conductivity (IC) of LIC from 1.3 to 6.8 mS/cm, while reducing the Young's modulus from 42.3 to 17.6 GPa. The optimized LIC enables a stable cycling of ASSBs at a low operation pressure of 2 MPa with a high areal capacity of 7.7 mAh/cm 2 , highlighting cyclic nonequilibrium processing as a promising route for practical ASSBs.