Unraveling SEI formation and cycling behavior of commercial Ni-rich NMC Li-ion pouch cells through operando optical characterization

Lithium-ion batteries, relying on Ni-rich NMC (LiNi_xMn_yCo_1−x−yO₂) phases, are widely used in various applications due to their high energy density and extended cycle life. However, further improvements are possible with a deeper understanding of their internal chemistry in real-world conditions. Here, using optical fiber Bragg grating sensors placed inside commercial pouch cells, we demonstrate the feasibility of monitoring the heat release during the formation cycles and real-driving cycling. By collecting temperature data for Li-ion cells using different types of NMCs, we were able to extract the contribution of the anode and the impact of additives on overall heat generation. We also present a comparison of the heat generation of NMC-based batteries under varying power and voltage levels, which provides insights into battery safety in dynamic, real-world environments. Our study reveals the importance of continuously monitoring batteries heat release throughout its lifespan to enhance our understanding of the interconnected materials surfaces and electrolyte reactions.