PROBLEM TO BE SOLVED: To provide a surface treatment material which is arranged by processing the surface of a nonaqueous power storage device material so as to increase the wettability between a positive electrode active material, a negative electrode active material, a separator, a conductive material and a collector and a nonaqueous electrolyte, and enables the achievement of a lower resistance.SOLUTION: A surface treatment material comprises modified metal oxide nanoparticles which are modified with a silicon-based functional group as a surface treatment agent for performing a surface treatment on nonaqueous power storage device materials of a positive electrode material, a negative electrode material, a separator, a collector and the like. It is preferable that the metal oxide nanoparticles form an organo silica sol.
