In situ Raman investigation of resting thermal effects on gas emission in charged commercial 18650 lithium ion batteries

Abstract

The inherent risk of side reactions in lithium ion batteries (LIBs) is a crucial issue for large battery packs. To mitigate this problem, there have been previous studies that have attempted to reveal the possible chemical reactions from decomposition of electrolytes and electrode materials’ reactions during cycling. In particular, the gases expelled during decomposition have garnered research attention as they are explosive, flammable, toxic, and raise the inner pressure of a cell drastically. In addition, it is important to understand thermal effects on gas evolution or degradation of the electrode layer because batteries are normally exposed to a warm operation condition. Herein, the gases expelled within commercial 18650 cylindrical type LIB cells were investigated in moderate thermal conditions in a charged state. The investigation was conducted using a lab-made in situ Raman spectroscopic analysis system and performing comprehensive transient electrochemical analyses. Our Raman spectroscopy system could explore the battery reactions non-disruptively, which is critical for the interior of a cell. Through this in situ technique, the gas expelling trends upon the thermal conditions were elucidated; furthermore, detrimental effects of gas generation reactions to a cell integrity were proposed through comparison with the electrochemical results.