Effects of Fast Charging at Low Temperature on a High Energy Li-Ion Battery

Understanding the impact of repeated fast charging of Li-ion batteries, in particular at low temperatures, is critical in view of the worldwide deployment of EV superchargers. In this study, the effects of fast charging using the conventional CCCV protocol on the performances of a high energy cell were investigated. The fast charging capability was confirmed to be negatively affected by low temperatures. The cell was capable of sustaining repeated fast charging at 23 degrees C without notable performance degradation, but quickly degraded when the charging temperature was decreased. Post-mortem analysis revealed several failure modes, including lithium plating, graphite exfoliation, jelly-roll deformation, active materials crumbling, aluminum corrosion and an abnormal SEI growth on the anode side. A loss of lithium inventory, mainly due to lithium plating and subsequent SEI growth was identified to be the major cause of performance degradation related to repeated fast charging at low temperatures. These results clearly put in evidence that repeated fast charging can cause significant degradations in Li-ion cells, with detrimental consequences in safety, performance and service life. Gaining insights into the failure modes related to repeated fast charging shall guide battery developers towards the optimization of Li-ion cells for EV application.