## 3 Results and Discussion  
### Methodology of the New Fast Charge Pattern  
Unlike the rapid charging patterns generated by simulations or by laboratory-scale capacity (mAh) cell studies, rapid charging patterns optimized for commercial-level cells (>Ah) were generated, and DVA was directly performed to analyze the charge/discharge behavior of the cells. The resulting DVA plot showed the capacity increase (dQ) per voltage increase (dV) (or vice versa) on the y-axis, and the voltage (V) or capacity (Q) on the x-axis. Thus, the DVA plot shows in what state (i.e., voltage or capacity) the cell exhibits changes in resistance during charge/discharge due to factors such as phase transition, Li-ion diffusion, electron mobility reduction, and by-product formation. Equation (1) represents the mathematical interpretation above. \[\frac{dV}{dQ}=\frac{d(iR)}{d(it)}=\frac{dR}{dt}(const,i) \tag{1}\]  
Figure 3: Rapid charging patterns: (**a**) A typical step charging pattern; (**b**) the novel constant current step rapid charging pattern; (**c**) a constant current charging pattern; and (**d**) an adaptive rapid charging pattern. In this system, three possible causes of cell resistance can be identified. The first is the Ohmic resistance, which originates from the limitations of electron transport at the interfaces and in the passages of the conductive active materials and the electrical components of the cells such as outer cell-can materials, metal substrates, and metal taps. The second cause is the interfacial resistance that occurs during charge transfer at the interface between the active material and the solid electrolyte interphase (SEI) layer. The third cause is the diffusion resistance due to mechanical and chemical disruption of Li-ion transport across the separator, electrolyte, SEI layer, and the solid active material. Such resistance varies greatly depending on the type of component material used and the manufacturing method employed. Thus, understanding the DVA plot of a commercial cell allows us to understand the complex effects of cell resistance. Figure 4 shows the DVA plot of the 3.3 Ah cell used in the experiments reported herein. Specifying the target CV voltage at the peak location is expected to reduce the internal stress generated in relation to the large increase in the rate of resistance. In contrast to applying the CC steps that are inherently related to the external characteristics, the CV step represents the eigenstate of the cell and can determine the optimum current that varies continuously with the changes in cell resistance based on Ohm's law. To compensate for the rapid charging time required, a number of charge termination steps have been specified. Thus, the signals shown in Figure 4 presumably represent the starting point for the phase transition between LCO and graphite. Typically, the higher the number of phase transitions occurring during graphite charging in non-high voltage applications in the x > 0.5 range for Li\({}_{x}\)CoO\({}_{2}\), the lower the number of phase transitions reported for LCO when compared to I-IV [24; 25; 26; 27], where the LCO stays in the O\({}_{3}\) phase [28; 29; 30; 31; 32; 33]. Therefore, the new CV step-fill pattern designed for a specific 3.3 Ah battery is expected to have a positive impact on reducing anode degradation. Figure 5 shows the variation in charge time and available capacity relative to the cycle number for the 18650 cylindrical battery. As indicated, following repeated charge/discharge cycles, the capacity degrades, and so when the battery is charged at the same charge C-rate as the initial value of the test, the charge time is reduced. Figure 4: The differential voltage analysis plot of the ICR18650-33F 3.3 Ah cell employed herein. Thus, as the number of cycles is increased, charging is performed at a higher C-rate, and degradation is accelerated.