In order to identify charging characteristics, a series of
charging tests is performed on the batteries at 25 °C. Firstly,
the battery is discharged at 1 C (i.e. 15 A) and 25 °C until the
voltage reach 1.50 V. Then, the battery is kept inside the
chamber for 20 minutes for rest. After the rest, the battery is
charged with a constant current until the voltage reached the
cut-off voltage (i.e. 2.7 V for fast charging and 2.75 V for
standard charging). In this paper, constant current with
magnitudes of 7.5 A, 15 A and 30 A, which corresponding to
0.5 C, 1 C and 2 C, are applied on the battery, where 1 C
represents the charging rate for an empty battery to be fully
charged with 1 hour. The charging profile of the battery is
shown in Fig. 2. The charging profile shows that the charging
time for the battery is inversely proportional to the charging
rate.