SULFIDE SOLID ELECTROLYTE POWDER, SOLID ELECTROLYTE LAYER, AND LITHIUM ION SECONDARY BATTERY

A sulfide solid electrolyte powder includes, in content in a mass basis: less than 50 ppm of Al; and less than 50 ppm of Zr. A particle diameter D50 is less than 1 μm. A BET diameter calculated based on a BET specific surface area may be 0.10 μm to 0.30 μm.