Figure 5 . (a) Voltage profile at first cycle, (b) Voltage profile at 80th cycle, (c) Cycling performance, and (d) Coulombic efficiency of baseline, EM1C, EM2C, EM3C, and EM4C samples with NMC622 full-cells.
Figure 5 shows a significant improvement in electrochemical performance by the EM method. Specifically, the three samples presented significantly higher capacity than the baseline sample, and the capacity decreased following the order: EM4C < EM2C < EM3C, respectively. Obviously, the sample EM4C delivers the highest initial capacity of 137.06 mAh.g-1 (Figure 5 a) and maintains 97.87 mAh.g-1 in the 80thcycle (Figure 5 b). Moreover, the EM4C continually illustrates stable coulombic efficiency, around 99% for 80 cycles. . Meanwhile, regarding the sample EM2C and EM3C, there is no significant difference in the capacity behavior, showing a low initial value of 48.43 mAh.g-1, and the capacity declines to 32.50 mAh.g-1 after 80 cycles (Figure 5 d). By activating anodes with the EM method, an artificial SEI layer is formed on anode’s surface and becomes a stable SEI layer. Indeed, the full-cells using these anode pre-lithiated by EM method do not lose the capacity to stabilize the SEI layer. Furthermore, the EM method can enhance the mobility of Li+ ions to optimize the lithiation mechanism, which makes the charge transfer process more accessible since the Li+ ions are not trapped. [29-32] Therefore, the initial Coulombic efficiency and battery performance increase when increasing the cycles for pre-lithiation.
Table 2. Battery performance of 100GR, baseline, CM30, and EM4C sample.