Impact of Calendar Degradation on the Performance of LiFePO4-Graphite Li-Ion Cells during Charge-Discharge Cycling at-5°C

In order to elucidate the impact of calendar degradation on charge-discharge cycling under low temperature, we evaluated and compared the performance of fresh and calendar degraded LiFePO4-Graphite Li-ion cells during cycling at -5 degrees C. After exposing fresh and calendar degraded cells to low temperature cycling, the fresh cell exhibited a relatively good performance, while in the case of the calendar degraded cell a poor performance was observed. In addition to this, a high voltage plateau, which usually appears at the beginning of the discharge profiles as a consequence of the occurrence of lithium plating, was not observed in the discharge profiles of the fresh cell. However, in the case of the calendar degraded cell a high voltage plateau appeared at the beginning of the discharge profiles, indicating that lithium plating is more likely to occur in degraded Li-ion cells exposed to low temperature charging. Our investigation results show that calendar degradation can compromise the safety and performance of Li-ion cells during low temperature cycling. (c) 2019 The Electrochemical Society.