Patent ID: 8421418

Claim:
A charging/discharging control unit for a lithium secondary battery, comprising: a lithium secondary battery having a positive electrode and a negative electrode, which are capable of charging/discharging electric charges and an electrolytic solution containing lithium ions; a voltage detecting means for detecting a voltage of said lithium secondary battery; and a current detecting means for detecting charging/discharging currents of said lithium secondary battery; wherein: said charging/discharging control unit of the lithium secondary battery is further comprised of: a controller for controlling a discharge voltage of said lithium secondary battery; and a discharging means for performing a constant voltage discharging operation of said lithium secondary battery; and wherein, when a voltage change value, V 1 -V 0 , of the lithium secondary battery is larger than or equal to a predetermined value, ΔV, where V 0 is a voltage of said lithium secondary battery at an end time of the discharging operation that is less than a reference voltage, Vcut, and V 1 is a voltage of said lithium secondary battery at a time, t 1 , after the end time of the discharging operation, said controller causes said discharging means to perform the constant voltage discharging operation at a voltage, Vd, during a rest time until a next charging operation of the lithium secondary battery is commenced, wherein: a positive active material of said lithium secondary battery contains a composite oxide composed of a transition metal and lithium which undertakes intercalation/deintercalation when a potential measured with a metal lithium electrode (V vs. Li/Li + ) is higher than or equal to 3 V, and is lower than or equal to 5 V; a negative active material of said lithium secondary battery contains graphite having a spacing, d002, between (002) planes in a range of 0.335 to 0.349 nm as determined from an X-ray diffracting method; and within a discharge capacity when charging/discharging operations are performed between 0.01 and 1 V vs. Li/Li + by employing said negative active material in said negative electrode and said lithium metal in a counter electrode, a ratio of portions of said discharge capacity, Cm 2 /Cm 1 , of said negative electrode is in a range of Cm 2 /Cm 1 <0.4, where a portion of said discharge capacity between 0.01 to 0.2 V vs. Li/Li + is set to Cm 1 , and another portion of said discharge capacity between 0.2 to 1 V vs. Li/Li+ is set to Cm 2 .