Patent ID: 8203826

Claim:
A lithium ion capacitor comprising: a positive electrode, a negative electrode, and a non-protonic organic solvent electrolytic solution of a lithium salt as an electrolytic solution, wherein a positive electrode active material is a material capable of reversibly doping a lithium ion and/or an anion; a negative electrode active material is a material capable of reversibly doping a lithium ion; the lithium ion is doped in advance to either one or both of the negative electrode and the positive electrode so that a positive electrode potential after the positive electrode and the negative electrode are short-circuited is 2.0 V (relative to Li/Li + ) or less; when capacitance per unit weight of the positive electrode is C + (F/g), weight of the positive electrode active material is W + (g), capacitance per unit weight of negative electrode is C − (F/g), and weight of the negative electrode active material is W − (g), a value of (C − ×W − )/(C + ×W + ) is 6.8 or more and 22.8 or less; and the weight of the positive electrode active material is larger than the weight of the negative electrode active material.