RECOVERY PROCESSING METHOD OF LITHIUM ION BATTERY, CHARGE/DISCHARGE DEVICE, AND STORAGE MEDIUM

A recovery processing method of a lithium ion battery having a positive electrode and a negative electrode and in which performance has decreased due to a residue of lithium ions in the negative electrode, the method comprises: repeating a cycle a plurality of times, the cycle including: a first process of setting an SOC of the lithium ion battery to a first value, that is equal to or smaller than a value of the SOC in which a gradient of an SOC-voltage curve is a minimum value and that is equal to or greater than the value of the SOC in which the gradient of the SOC-voltage curve is two times the minimum value, by charging; and a second process of setting the SOC of the lithium ion battery to a second value, that is smaller than the first value, by discharging.