## 3 Results and Discussion
As shown in Figure 4b, the voltage increment due to the progress of the charge and discharge cycle was relatively smaller than the one for 3C constant charging procedure, and a major amount of charging capacity was obtained before reaching the charging voltage limit of 4.2 V. This might be explained by the pulse current charging effectively mitigating the concentration polarization caused by the application of high current during the resting time of pulse charging [12]. The relaxation of concentration polarization during the resting period of pulse charging might have provided enough time for the diffusion and insertion reaction of lithium ions to proceed, and thus naturally suppressed the electrode over-potential and lithium plating, thereby reducing side reactions and consumption of active materials. One more thing to clarify in Figure 4 is the discharging voltage levels of the battery at different cycles. For the case of an old battery, namely the battery after 150 cycles, due to the increase of internal resistance, the charging voltage increased relatively higher (near 4.2 V). After the 5 min of rest time, the discharging was initiated. With this limited rest time, the voltage did not reach down to an open circuit voltage. In other words, the discharging was initiated at the high voltage level of around 3.7 V before it really reached down to the fully converged open circuit voltage. By comparison, for the case of a fresh battery, i.e., the battery after 10 cycles, due to the low internal resistance, the charging voltage increased only up to 3.9 V. With the limited rest time of 5 min, the voltage dropped to near 3.62 V and then the discharging was initiated. Normally, a battery with higher internal resistance shows lower discharging voltage level. However, in the current study, the discharging processes were started only after a limited rest period, and therefore the voltage of the old battery was higher than the relatively fresh battery since the discharging started from the higher voltage level. Figure 5 provides the charging start voltage (left \(y\)-axis) and the charging capacity (right \(y\)-axis) obtained from the 3C constant current charging method and the 6C pulse charging method. In terms of the voltage, the charging start voltage of the 6C-PC charging method (blue star marked line) in the initial 150 cycles shows a higher value than that of the 3C-CC charging method due to applying the higher input current charging procedure. In the case of 3C-CC charging method (red disk marked line), the charging start voltage increases about 0.185 V for the first 150 cycles, which is 62% higher than the corresponding value in the case of the 6C-PC charging method (0.071 V). With this observation, it is believed that the increase of internal resistance during the 3C constant current charging was greater than that of the 6C pulse current charging. Since the impedance increase in the LIB was mostly due to battery degradation, it is naturally believed that the 3C constant current charging process caused more battery performance deterioration than the 6C pulse current charging one. In Figure 5, the total charging capacity (Q\({}_{\text{total}}\)) is indicated by a hatched bar, and the capacity charged before reaching the upper limit voltage (Q\({}_{\text{v}}\)) is indicated by a filled bar. The charging capacity by the 3C constant current charging appeared somewhat higher up to 60 cycles than that by the 6C pulse current charging. However, as the cycles repeated, for the case of 3C constant current charging, the charging capacity at the 150 th cycle was down to 715.62 mAh, which showed about 90% compared  
to the charging capacity at the 10 th cycle, and the corresponding Q\({}_{V}\) was found to be only 44.52 mAh.