NONAQUEOUS ELECTROLYTE POWER STORAGE ELEMENT

A non-aqueous electrolyte energy storage device according to one aspect of the present invention includes: a positive electrode having a positive electrode active material layer; a negative electrode having a metal negative electrode substrate and a negative electrode active material layer containing graphite; and a separator disposed between the positive electrode active material layer and the negative electrode active material layer, in which the separator has an air resistance of not less than 125 seconds/100 mL, and X represented by the following formula (1) is not more than 890. X=PcTcTa/Pa (In formula (1), Pc is a porosity (%) of the positive electrode active material layer, Tc is a thickness (µm) of the positive electrode active material layer, Pa is a porosity (%) of the negative electrode active material layer, and Ta is a thickness (µm) of the negative electrode active material layer.)