Volume Deformation of Large-Format Lithium Ion Batteries under Different Degradation Paths

Abstract

Lithium ion batteries experience volume deformation in service, leading to a large internal stress in modules and potential safety issues. Therefore, understanding the mechanism of volume deformation of a lithium ion battery is critical to ensuring the long-term safety of electric vehicles. In this work, the irreversible and reversible deformation of a large-format lithium ion battery under four degradation paths, including cycling at −5°C/1 C, 55°C/1 C and 25°C/4 C, and storage at 55°C/100% state of charge, are investigated using laser scanning. The reversible deformation decreases while the irreversible deformation increases as batteries age, following a linear trend with the state of health. The mechanism behind irreversible deformation is investigated using incremental capacity analysis and scanning electron microscopy. The irreversible deformation of the battery cycled at 25°C/4 C and stored at 55°C becomes extremely large below 80% state of health, mainly because of the additional deposit layers on the anode and increased gas production, respectively. Mechanical calculations show the huge stress in the aged modules. Proper spacers between batteries are suggested to reduce such damage. This study is valuable for understanding the mechanical safety of battery modules.