Limitations of the State of Health and Health Indicators for Electric Vehicle Batteries

Estimating the State of Health of Electric Vehicle batteries is a crucial yet challenging task. Various Health Indicators have been proposed to assess degradation, yet several of them may not be obtainable under normal operation. Additionally, battery degradation alone does not provide insights into the battery's functionality for a specific application. To address these limitations, this study analyses experimental data reflecting diverse driving conditions and evaluates the efficacy of various Health Indicators to estimate the State of Health. Results show that the value of the second peak in the Incremental Capacity curve and the use of multiple indicators produce the most accurate results. Furthermore, this study introduces a functional definition of battery degradation through the State of Function, which combines the specific driving requirements with the capacity to estimate how far the battery is from its functional End of Life. This approach provides a more comprehensive understanding of the battery's health and its ability to perform efficiently for a given application.