A charge storage device such as a battery, wherein a positive electrode comprises a nitroxyl compound having a structure of a nitroxyl cation moiety represented by formula (I) in an oxidized state while having a structure of a nitroxyl radical moiety represented by formula (II) in a reduced state and a reaction represented by reaction formula (A) in which an electron is transferred between these states is used as a positive electrode reaction. The charge storage device can have a higher energy density and can be used at a large current. ##STR00001##