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, Li3–xYBr6–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 Li2.65YBr5.65 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, Li2.65YBr5.65 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 Li3–xYBr6–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.