Sliceable,\nMoldable, and Highly Conductive Electrolytes\nfor All-Solid-State Batteries

All-solid-state batteries (ASSBs) require solid electrolytes\nwith\nhigh ionic conductivity, stability, and deformability for optimal\nenergy and power density. We developed lithium-deficient lithium yttrium\nbromide (LYB) solid electrolytes, Li<sub>3–<i>x</i></sub>YBr<sub>6–<i>x</i></sub> (0 ≤ <i>x</i> ≤ 0.50), using a comelting method with controlled\nlithium deficiency. These electrolytes exhibit favorable mechanical\nproperties such as high moldability and sliceability. The Li<sub>2.65</sub>YBr<sub>5.65</sub> composition has an ionic conductivity of 4.49\nmS cm<sup>–1</sup> at 25 °C and an activation energy of\n0.28 eV. Compared to Li<sub>3</sub>YBr<sub>6</sub>, Li<sub>2.65</sub>YBr<sub>5.65</sub> demonstrates improved rate performance and cycling\nstability in ASSBs. High-resolution X-ray diffraction confirms the\nformation of the LYB phase with a <i>C</i>2/<i>m</i> space group. Structural analysis reveals increased cation disorder\nand larger polyhedral volumes for <i>x</i> > 0 in Li<sub>3–<i>x</i></sub>YBr<sub>6–<i>x</i></sub> , contributing to reduced Li<sup>+</sup> migration energy\nbarriers. Bond valence site energy calculations and molecular dynamics\nsimulations reveal enhanced 3D lithium-ion transport. NMR spectroscopy\nfurther highlights increased Li<sup>+</sup> dynamics and impurity\nelimination.