Provided is a highly-reliable power storage device cell that can deliver large amounts of power quickly and can also deliver lasting power. Said power storage device cell, which maintains its capacity even after many cycles of rapid charging/discharging, has a capacitor positive electrode (11a), a lithium positive electrode (11b), and a common negative electrode (7) in which electrode layers (5, 6) are formed on a collector foil in which conduction pores (4) are formed. The capacitor positive electrode (11a) and the electrode layer (5) side of the common negative electrode (7) sandwich a first separator (12), forming a capacitor, and the lithium positive electrode (11b) and the electrode layer (6) side of the common negative electrode (7) sandwich a second separator (13), forming a lithium-ion battery. The capacitor positive electrode (11a) and the lithium positive electrode (11b) are directly connected. The electrode layers (5, 6) in the common negative electrode (7) comprise a carbonaceous material in which graphite particles and hard carbon particles are mixed, said hard carbon particles constituting between 5% and 70% of the weight of the carbonaceous material.