Image Number 7 for United States Patent #6884546.
Provided is a secondary battery in which high energy density can be obtained and charging/discharging cycle characteristic can be improved. A positive electrode (13) and a negative electrode (15) are stacked with a separator (16) interposed therebetween, and are enclosed inside an exterior can (11) to which an electrolyte is injected. The negative electrode (15) contains a negative electrode material capable of occluding/releasing lithium in an ionic state. Thereby, lithium metal precipitates in the negative electrode (15) in a state where the open circuit voltage is lower than the overcharge voltage. In other words, lithium is occluded in an ionic state in a negative electrode material capable of occluding/releasing lithium in the beginning of charging, and then lithium metal precipitates on the surface of the negative electrode material thereafter during charging. The amount of precipitation of lithium metal is preferable to be from 0.05 to 3.0 times, both inclusive, the ability of charging capacity of the negative electrode material capable of occluding/releasing lithium. Thereby, a high energy density and an excellent cycle characteristic can be obtained.