SECONDARY BATTERY

A secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution. The positive electrode includes a lithium-cobalt composite oxide having a layered rock-salt crystal structure. The negative electrode includes graphite. An open circuit potential of the negative electrode measured in a full charge state is from 19 mV to 86 mV. A potential variation of the negative electrode is greater than or equal to 1 mV when the secondary battery is discharged from the full charge state by a capacity corresponding to 1% of a maximum discharge capacity. The maximum discharge capacity is obtained when the secondary battery is discharged with a constant current from the full charge state until the closed circuit voltage reaches 3.00 V, following which the secondary battery is discharged with a constant voltage of the closed circuit voltage of 3.00 V for 24 hours.