Sliceable, Moldable, and Highly Conductive Electrolytes for All-Solid-State Batteries

All-solid-state batteries (ASSBs) require solid electrolytes with high ionic conductivity, stability, and deformability for optimal energy and power density. We developed lithium-deficient lithium yttrium bromide (LYB) solid electrolytes, Li_3-xYBr_6-x (0 ≤ x ≤ 0.50), using a comelting method with controlled lithium deficiency. These electrolytes exhibit favorable mechanical properties such as high moldability and sliceability. The Li_2.65YBr_5.65 composition has an ionic conductivity of 4.49 mS cm^-1 at 25 °C and an activation energy of 0.28 eV. Compared to Li₃YBr₆, Li_2.65YBr_5.65 demonstrates improved rate performance and cycling stability in ASSBs. High-resolution X-ray diffraction confirms the formation of the LYB phase with a C2/m space group. Structural analysis reveals increased cation disorder and larger polyhedral volumes for x > 0 in Li_3-xYBr_6-x , contributing to reduced Li⁺ migration energy barriers. Bond valence site energy calculations and molecular dynamics simulations reveal enhanced 3D lithium-ion transport. NMR spectroscopy further highlights increased Li⁺ dynamics and impurity elimination.