Capacity fade characteristics of nickel-based lithium-ion secondary battery after calendar deterioration at 80 °C

In this study, we evaluated the calendar deterioration behavior of nickel-based lithium-ion secondary batteries by storing them at 80 °C for different durations. The results indicate that the battery capacity decreased with the increasing number of storage days in a high-temperature environment. From the differential capacity curves, we found that the change in the overvoltage , which was caused by the electrode reaction, that appeared at approximately 4.2 V was most significant. To analyze this phenomenon, electrochemical impedance spectroscopy of the deteriorated battery was measured at 4.2 V, and it was confirmed that the cathode-based resistance of the battery increased significantly at this potential. Furthermore, post-mortem analysis revealed that the cathode active material of the tested batteries clearly deteriorated; however, no significant change in the active material in the anode was observed. Therefore, it is considered that the cathode materials of nickel-based lithium-ion secondary batteries deteriorate by storing at 80 °C, thereby resulting in reduced battery capacity and increased cathode component resistance after storing at high temperatures.