SOLID ELECTROLYTE COMPRISING HALIDE, PREPARATION METHOD THEREOF AND SECONDARY BATTERY COMPRISING THE SAME

Disclosed is a novel halide-based solid electrolyte composition exhibiting enhanced ionic conductivity, wherein the solid electrolyte composition comprises a lithium yttrium halide with a hexagonal close-packed structure, and when the occupancy of metal ions is defined as the number of metal ions relative to the number of metal ion sites within two consecutive layers constituting a unit cell with a hexagonal close-packed structure in the halide, the sum of the occupancies of metal ions within the two layers is 0.888 or less.