Sulfide-based solid electrolyte particles

A sulfide-based solid electrolyte particle, comprising a solid electrolyte particle having a crystal phase of a cubic argyrodite-type crystal structure and comprising lithium (Li), phosphorus (P), sulfur (S) and a halogen (Ha),

• wherein the solid electrolyte particle has been subjected to a surface modification treatment in which the solid electrolyte particle is directly exposed to an atmosphere having a dew point of −35° C. to 10° C., the atmosphere reacts with the solid electrolyte particle, and no subsequent drying of the solid electrolyte particle is performed;
• a ratio (ZHa2/ZHa1) of an element ratio ZHa2 of the halogen (Ha) at a position, in terms of an SiO2 sputter rate, of 5 nm in depth from the particle surface to an element ratio ZHa1 of the halogen (Ha) at a position, in terms of the SiO2 sputter rate, of 100 nm in depth from the particle surface is higher than 0 and 0.5 or lower, as measured by X-ray photoelectron spectroscopy (XPS);
• and
• a ratio (ZO2/ZA2) of an element ratio ZO2 of oxygen to a total ZA2 of element ratios of phosphorus (P), sulfur (S), oxygen (O) and the halogen (Ha) at the position, in terms of the SiO2 sputter rate, of 5 nm in depth from the particle surface is 0.5 or higher and 1.0 or lower, as measured by XPS.