A phenomenological ageing study of lithium-ion batteries under dynamic loads

Understanding the degradation processes of lithium-ion cells is a current and urging challenge in terms of battery-powered applications. Influenced by operation conditions such as temperature, current, state of charge operating range and cycle depth, the degradation causes the capacity to diminish and the internal resistance to ascent steadily. For a better understanding, these ageing influences are usually examined in laboratory ageing studies. Thus the ageing information can predict cell degradation at given operating conditions and to lower cell degradation by avoiding particularly damaging operations. However, these ageing influences are mostly examined at steady-state conditions, e.g. constant-current profiles. Dynamic influences, which take place in many battery applications, are rarely examined. Hence, this paper aims to study the influence of the operation's dynamics in form of current gradients. The experimental study reveals that discharging dynamics influence the battery degradation. The current gradient is defined in a change of current per time interval. In the experiment, higher current gradients result in a larger degradation rate. Compared to constant-current operation, i.e. without load changes and hence no current gradients, the degradation rate increases about 50% at a current gradient of 1.8 C/s. More moderate current gradients of 0.2 C/s and 0.6 C/s show less effect, but are supporting the trend. Despite the current gradient only varied in four steps, a linear influence of the current gradient on the degradation rate has shown. These results indicate that the discharging dynamic of a load profile has a significant influence on battery degradation.

Automated summary

Understanding the degradation processes of lithium-ion cells is a current and pressing challenge, influenced by various operating conditions. Experimentation has shown that the discharge dynamics of a load profile significantly impact battery degradation, with higher current gradients resulting in larger degradation rates. This linear relationship between current gradient and degradation rate highlights the importance of considering dynamic influences in battery aging studies.