ENERGY STORAGE DEVICE

One aspect of the present invention is an energy storage device including a positive electrode containing: first positive active material particles containing a metal element capable of forming a conductive metal oxide; and second positive active material particles not containing the metal element, in which the first positive active material particles include a nickel-cobalt-manganese-containing lithium-transition metal composite oxide containing lithium, nickel, cobalt, and manganese as constituent elements, and the first positive active material particles are larger in median diameter than the second positive active material particles.