The aging of lithium-ion cells presents a significant challenge in extending their cycle life, ensuring safety, and maintaining high performance, primarily due to the degradation of key components such as electrodes and electrolytes. As electric vehicles, portable electronics and renewable energy storage systems increasingly rely on these cells, understanding and mitigating degradation processes becomes even more critical. One of the major concerns is the diminished capacity and efficiency that accompanies cell aging, which not only affects performance but also raises safety issues due to potential overheating and, in extreme cases, thermal runaway.
To address these challenges, this study introduces a new approach by developing a novel combined measurement cell that integrates operando dilatometry with operando mass spectrometry. Such integration is key to gaining a comprehensive understanding of both physical and chemical alterations that occur in real-time during electrochemical cycling. Operando dilatometry provides detailed measurements of thickness variations in the working electrode, offering insights into the mechanical stress and structural changes that transpire. Meanwhile, operando mass spectrometry focuses on analyzing gas emission, a crucial indicator of chemical activity and degradation within the cell, thereby delivering a thorough view of the underlying processes.
The results of this study reveal significant correlations among electrochemical behavior, electrode thickness changes, and gas evolution. These correlations uncover both reversible and irreversible growth of constituents on individual particles and the electrode surface. A critical aspect of this is the formation and development of the solid electrolyte interphase (SEI), which results from the degradation of electrolyte components such as solvents or conductive salts. The SEI is essential in stabilizing the electrode surface but also contributes to irreversible capacity loss over time due to its continual growth and thickening.
Operando gas analysis further highlights the presence of decomposition intermediates and products, all intricately linked to the degradation of the electrolyte. These gaseous by-products can indicate the breakdown pathways and provide early warning signals of adverse processes occurring within the cell. Additionally, post-mortem gas chromatography coupled with mass spectrometry is employed to identify several compounds that confirm multiple decomposition pathways. This methodology enhances our understanding of the complex reactions at play and helps in pinpointing specific conditions that accelerate aging.
By employing this integrated and holistic approach, the study significantly deepens the comprehension of aging mechanisms at the electrode level. It not only paves the way for developing better diagnostic tools but also contributes to the design of more resilient lithium-ion cells with extended lifetimes and improved safety profiles. These advancements are imperative for the sustainable development of technologies where lithium-ion batteries are a backbone, ultimately driving progress in various fields reliant on energy storage solutions.
The presented work underlying this poster has recently been published in Batteries: https://doi.org/10.3390/batteries10120445