Electricity storage device, and charging method and manufacturing method therefor

[Problem] Electricity storage devices in which carbon active material is used in both positive and negative electrodes are known to have the problem that the discharge capacity decreases as the charge and discharge cycle is repeated, i.e., the problem of poor cycle characteristics. One cause of the problem is that an excessive progress of intercalation in the process of intercalation of anions into the positive electrode active material (excessive progress of the stage structure) may lead to the inability to perform reversible intercalation, or to the decomposition of electrolyte, for example. [Solution] An electricity storage device in which the voltage profile during constant current charging has five or more change points at which the slope changes from small to large, large to small, small to large, and so on with respect to an increase in charge capacity, and in which the maximum voltage during use of the electricity storage device is near a voltage indicated by the change point furthest toward the high potential side, from among the change points at which the slope changes from small to large. The electricity storage device prevents charging or discharging into a stage in which irreversible intercalation occurs, and therefore improves cycle characteristics.