In situ DRIFT-MS insight into the thermal evolution of battery materials

Currently, the Li-ion battery is the reference technology adopted by most of automotive manufacturers (OEMs) to ensure the energy storage required for electrified vehicles. However, these batteries can be the source of incidents with potentially severe consequences, commonly referred to as thermal runaway (TR). Thermal runaway mechanisms are generally studied at the macroscopic scale through the analysis of the gases and heat emitted during this event. However, the chemical reactions occurring at the surface, interface, and interphase of the battery's constituent materials remain poorly documented. Obtaining information on the thermal decomposition processes of battery materials is challenging and rarely accessible. In this work, we propose an analytical approach to characterize the evolution of battery materials during a temperature increase from 20 to 350 °C in controlled atmosphere. The developed experimental setup combines diffuse reflectance infrared FT (DRIFT) analysis at the material level with an online analysis of the outgoing effluents using mass spectrometry. This setup enables real-time observation of surface transformations of the studied materials as well as the gaseous species emitted during their thermal degradation. After disassembling an NMC/C battery at a SOC of 100% in glove box, unrinsed electrode samples are shaped into 6 mm disks and stacked in a DRIFT reactor. The analysis was performed on both negative and positive electrodes (unrinsed). The decomposition mechanisms observed on these two electrodes are compared and discussed. The presented results highlight the relevance and potential of this approach, paving the way for a fast and effective characterization method to enhance the understanding of battery material degradation mechanisms.