Supervisor:
Daniel Ioan-Stroe

Co-Supervisor:
Kjeld Pedersen, Institut for Materialer og Produktion

Assessment Committee:
Professor Francesco Iannuzzo (Chair)

Professor Dorthe Ravnsbæk, Aarhus University

Ass. Prof. Jonas Mindemark, Uppsala University

Moderator:
Ass. Prof. Tamas Kerekes

Abstract:

In electric vehicle applications, the aging of lithium-ion batteries is an inevitable process that has notable implications on the battery’s lifespan, driving range, and safety aspects. To prolong the battery’s service life, it is crucial to investigate the underlying mechanisms for battery aging under various external factors. In this study, battery state of health monitoring, electrochemical analysis, combined with in-situ testing and post-mortem analysis, were conducted to explore the battery aging mechanisms during both charging and driving process.

We closely monitor the battery’s voltage, current, and temperature during its aging process. Regular performance tests were used to study the detailed degradation. We also introduce innovative methods for analyzing electrodes and materials loss after aging, helping us understand the aging mechanisms better. Our findings emphasize the importance of the solid electrolyte interface (SEI) film formation and the gradual loss of active materials in battery aging. Additionally, we explore the mechanisms of pulse current charging to extend the battery’s lifespan and reveal that pulse current charging helps maintain the structure of electrode materials and reduces changes in the interface film.

To study the battery’s behavior in driving, we simulate real-world conditions to discharge battery with the Worldwide harmonized Light vehicles Test Cycle (WLTC) profile. This helps us closely mimic actual electric vehicle experiences, allowing us to gain insights into the battery’s aging in real life driving. Additionally, we consider temperature and depth of discharge effects during the driving process within this framework.

A comprehensive analysis of the battery aging mechanism was conducted, covering the entire battery system from the cell to the electrode and then to the materials levels. This provides valuable insights for the designing of battery management systems and next-generation batteries.