Impacts of Current Rates on the Degradation Behaviors of Lithium-Ion Batteries under Over-Discharge Conditions

With the popularity of lithium-ion batteries, especially the widespread use of battery packs, the phenomenon of over-discharge may be common. To gain a better insight into over-discharge behavior, an experimental study is carried out in the present work to investigate the impact of current rate, i.e. cycle rate, charge rate and discharge rate on the degradation behavior of a lithium-ion battery under over-discharge condition. It is found that battery capacity experiences obvious degradation during over-discharge cycling, while the current rate is shown to have little impact on the degraded capacity within a unit cycle. Therefore, nearly all the over-discharged batteries present a linear degradation rate as the over-discharge cycling proceeds, 0.05%/cycle. The impact of current rate on the degradation is revealed by influencing the cycle time, whereby a high current rate usually brings about a shorter cycle time and further accelerates the degradation. Among, the cycle rate is exhibited to have the largest impact on the degradation of the over-discharged battery, followed by the discharge rate and charge rate. Moreover, the degradation behaviors of these batteries are demonstrated through the evolution of battery surface temperature, charge/discharge voltage and internal resistance.