Degradation behavior of 21700 cylindrical lithium-ion battery cells during overdischarge cycling at low temperatures

Lithium-ion battery (LIB) cells are prone to overdischarge or overcharge when connected in series or parallel as a module or pack for large-format applications, such as electric vehicles (EVs) because of variations in battery capacities and difficulty in maintaining similar state-of-charge (SOC) of every single battery. However, the thermo-electrochemical behavior of LIBs during overdischarge has not been investigated at low temperatures. This study unveils the thermo-electrochemical behavior of overdischarged 21700 cylindrical LIB cells at −20 °C and 25 °C. Also, a thermo-electrochemical model was built to explain the heat generation within the cells and correlate them with the observed electrochemical characteristics. It was found that contrary to the severe cell degradation observed in the overdischarged cell compared to the standard cell at 25 °C, both cells show similar degradation behavior under low temperature cycling conditions. Thus, at low temperatures, overdischarge does not adversely affect cell degradation as observed at room temperature. This was attributed to the significant increase in the internal temperature, which results in improved electrochemical characteristics of the cell.