A Battery Ageing Model Applied to Typical Drive Cycles
2022-01-0852
03/29/2022
- Event
- Content
- Battery ageing tests are usually conducted using defined cycles on individual cells under controlled conditions. The applicability of these tests to real world conditions in electric vehicles (EVs) is limited. One problem is that vehicles do not operate under constant conditions, and another issue is that not every cell in a battery pack is cooled equally. This leads to cells operating at different temperatures, which causes different electrical behavior and different ageing. This paper presents two fundamental contributions to help understand the analysis of thermal behavior in a battery pack. The first contribution is the reformulation of an empirical cell ageing law into a dynamic model suitable for varying cell conditions. This model can be combined with a typical electrical and thermal model of a battery to provide a simple yet comprehensive simulation model. The second fundamental contribution is that this paper provides a simple model to look at the impact of differences between cells on their thermal and ageing behavior. This model demonstrates that electrical behavior, thermal behavior, and ageing cause a positive feedback loop that makes hot cells age faster, and the higher temperature accelerates further ageing. The system is inherently unstable towards difference in cell behavior, and this is widely independent of the model parameters. With the instability model and demonstrated, further research will be able to show how this instability can be prevented or limited in impact. Effective measures will have to address either of the three effects to break the positive feedback.
- Citation
- Steffen, T., Fly, A., and Mickelson, S., "A Battery Ageing Model Applied to Typical Drive Cycles," SAE Technical Paper 2022-01-0852, 2022, .