SULFIDE SOLID ELECTROLYTE FOR ALL-SOLID SECONDARY BATTERY, METHOD OF PREPARING SAME, AND ALL-SOLID SECONDARY BATTERY INCLUDING THE SAME

A sulfide solid electrolyte for all-solid secondary batteries, a method of preparing the same, and an all-solid secondary battery, the sulfide solid electrolyte including lithium, phosphorus, sulfur, and a halogen, wherein: the sulfide solid electrolyte has an argyrodite-type crystal structure, a ratio (I/Iratio) of a peak intensity at a 2θ of 29±0.1° to a peak intensity at a 2θ of 30±0.1° is 0.06 or less, the peak intensities being obtained by X-ray diffraction analysis of the sulfide solid electrolyte, and a ratio (I/Iratio) of a peak intensity at a 2θ of 27.1±0.1° to a peak intensity at a 2θ of 30±0.1° is 0.06 or less, the peak intensities being obtained by X-ray diffraction analysis of the sulfide solid electrolyte.