Heat Flow Measurement and Analysis during Lithium-Ion Battery Formation Process

An important step often overlooked or rarely investigated in lithium-ion battery manufacturing is the formation process. The formation process is the first full charging cycle of a lithium ion battery, which activates the cells before the lithium-ion cells can be used. The study focuses on using novel thermal measurement tool to monitor heat flow during the first charging/discharging cycle and its subsequent cycles of newly manufactured 18650 cylindrical cells. Thermal models and formulations were developed to identify the complexity of heat influence when three cells were tested simultaneously. A heat flow profile versus formation voltage window was discovered to provide important information to the study. Figure 1 shows a clear voltage window from 2.0 V to 3.7 V was identified to use as a reference range for designing alternative formation current rates. The formation process can then be altered to allow the preferential formation current rates to obtain the highest formation efficiency and improved cell performance. The impact of the lithium-ion battery formation process on battery performance such as capacity and cycle life were also examined in this study.

Figure 1: Heater Power Change as a Function of Cell Voltage during C/10 Formation Current Rate