A solid electrolyte material can include a halide-based material having a crystalline structure including a disorder. In an embodiment, the solid electrolyte material can include a crystalline structure include stacking faults. In another embodiment, the solid electrolyte material can include a crystalline phase including a crystalline structure represented by a space group of the hexagonal crystal system or a space group of a rhombohedral lattice system. In another embodiment, the solid electrolyte material can include a crystalline phase including a crystalline structure represented by a monoclinic space group and a unit cell containing a reduced number of halogen atoms.