Electricity storage device

An energy storage device comprising:

• a positive electrode comprising a nitroxyl compound having a nitroxyl cation partial structure represented by the following formula (1) in an oxidized state and having a nitroxyl radical partial structure represented by the following formula (II) in a reduced state;
• a negative electrode comprising a carbon material, wherein lithium ions can be reversibly intercalated into and deintercalated from said carbon material;
• and
• an electrolytic solution comprising a lithium salt and an aprotic organic solvent,
• the energy storage device being fabricated using for the positive electrode a positive electrode comprising a nitroxyl compound having the nitroxyl radical partial structure represented by the following formula (II), and
• a negative electrode comprising the carbon material into which lithium ions are previously intercalated
• wherein a ratio of the capacity A of lithium capable of being intercalated into and deintercalated from the negative electrode in charge and discharge to a capacity C of lithium capable of being intercalated into and deintercalated from the positive electrode in charge and discharge, A/C, is in the range of 1.1≦A/C≦10.