## 1 Introduction  
Charging electric vehicle batteries at rates comparable to the refueling of gasoline-powered cars remains an unresolved problem. To address this issue and promote further growth in the electric vehicle market, technology capable of rapidly charging lithium-ion batteries while maintaining excellent cycle lives is essential. As such, the development of materials and manufacturing technologies appropriate for high-speed charging has received attention from both battery manufacturers and academia [1; 2; 3; 4; 5]. However, due to a lack of interest in the development of rapid charging patterns, battery companies are providing vehicle original equipment manufacturers (OEMs) with previously analyzed data from typical charging patterns. In this context, the majority of typical rapid charging patterns consist of conventional single or multiple constant-current constant-voltage (CCCV) step charge processes as shown in Figure 1a [6; 7; 8; 9]. To reduce charging times, conventional methods tend to involve charging the battery with a high constant current in a low state of charge (SOC) region prior to charging the battery through a series of decreasing charge current steps as the SOC increases with the aim of minimizing cell degradation. However, these conventional step charging methods do not reflect the environmental variables of the cell and the state caused by internal degradation, which ultimately results in rapid cell degradation, as shown in Figure 1b [6]. Other recently reported rapid charging methods include pulse charging and boost charging [10; 11; 12; 13], which insert intermittent pauses to prevent lithium plating. Such plating is caused by high lithium ion concentrations around the anode due to the high charge current employed in these processes. However, as the design of a rapid charging pattern is related to the balance between the charging time and the cell cycle life, the use of higher charge currents to compensate for pause times can lead to rapid capacity losses. As the environments where batteries are being used and their target applications become more diverse, a thorough understanding and accurate prediction of the behaviors of commercialized cells are becoming increasingly important in the context of developing novel cell charging patterns. To meet the requirements of automobile OEMs, batteries with higher energy densities and higher performances have been developed based on the design of batteries with higher packing densities and complex form factors. However, in the context of automobiles, the lithium-ion battery is difficult to understand through the prediction of cell operations by the analysis of laboratory-scale coin cells, or by predicting or analyzing actual cell operations through simulations. Furthermore, the prediction of battery characteristics becomes more challenging as the cycle life increases. To address this issue, differential voltage analysis (DVA) can aid in understanding commercial cell behaviors in actual applications as changes in voltage with varying capacitance can be plotted as either dQ/dV or dV/dQ (dQ = the capacity increase, dV = the voltage increase) [14; 15]. The observed changes in the peak values of the corresponding plots thereby provide information regarding phase changes, active material losses, and chemical changes within the battery [16; 17; 18; 19; 20; 21; 22]. Thus, we herein report our study into cell resistance characteristics based on DVA, and further propose two adaptive rapid charging patterns that reflect the intrinsic characteristics of the cells in a specific SOC, in addition to considering variations in degradation characteristics as the battery cycle life progresses. Initially, we examined the development of the CV step charging pattern, which is a rapid charging method that allows self-charge control to reflect cell degradation and reduces cycle life degradation. Second, we report on the development of a charging pattern that controls the C-rate of the charging  
Figure 1: Current pattern examples.