HALIDE SOLID ELECTROLYTE, POSITIVE ELECTRODE MATERIAL, AND BATTERY

A halide solid electrolyte contains Li, Al, M, and X. M is at least one element selected from metal elements (excluding Li and Al) and metalloid elements, and X is at least one selected from F, Cl, Br, and I. The solid electrolyte includes a first particle group of first particles made of compound A containing Al and X, and a second particle group of second particles made of compound B not containing Al but containing M and X. In the first particle group, a coefficient of variation CV(CV=(σ/A)×100) obtained using a standard deviation σand an average value Aof a mass ratio Al/X is 10% or less. In the second particle group, a coefficient of variation CV(CV=(σ/A)×100) obtained using a standard deviation σand an average value Aof a mass ratio M/X is 20% or less.