The Resurging of Hydrocarbon Gas as Early Sign of Battery Rollover Degradation

Gas analysis offers real-time critical insights into the various processes occurring within batteries. However, monitoring battery degradation through gas formation remains relatively underexplored. Traditional coin cell setups pose challenges for long-cycle experiments and do not accurately reflect real-life battery usage. In this study, online electrochemical mass spectrometry (OEMS) was used to monitor gas evolution in a 4500 mAh NMC/graphite 21700 cylindrical battery throughout its cycling life. By tracking gas species and quantities, we identified distinct phases of gas evolution corresponding to different stages of degradation. Notably, the resurgence of hydrocarbon gases such as C₂H₄ emerged as an early indicator of rollover degradation. Furthermore, the continuous dissolution and reformation of the solid-electrolyte interphase (SEI) layer was identified as the primary driver of battery degradation. This study demonstrates the potential for integrating miniature gas sensors into battery systems for real-time health monitoring and early degradation detection.