SOLID ELECTROLYTE, AND ELECTRODE MIXTURE, SOLID ELECTROLYTE LAYER AND SOLID-STATE BATTERY, EACH USING SAME

A solid electrolyte includes: (compound A) a compound that has a crystal phase having an argyrodite-type crystal structure and that is represented by LiPSX, where X is at least one elemental halogen, a represents a number of 3.0 or more and 6.0 or less, b represents a number of 3.5 or more and 4.8 or less, and c represents a number of 0.1 or more and 3.0 or less; and (compound B) a compound that is represented by LiX, where X is as defined above. The compound B has a crystallite size of 60 nm or less. The solid electrolyte according to the present invention preferably exhibits a lithium ion conductivity at 25° C. of 4.0 mS/cm or more.