Operando Study of Thermal and Chemical Events in Lithium Metal Batteries using Optical Fiber Bragg Grating Sensor

In the era of rapid energy transition, energy storage technologies offer a unique opportunity to facilitate a sustainable, low-carbon transition, thereby paving the way towards a cleaner and more resilient future. Lithium metal batteries have attracted significant research attention due to their groundbreaking high theoretical capacities, exceeding conventional graphite anodes in lithium-ion batteries by a factor of ten (3,860 milliampere hours per gram). However, the commercialization of lithium metal batteries is hindered by substantial challenges, including the growth of dendrites at the negative electrode as a result of uneven lithium plating and stripping. Additionally, the reactivity between lithium metal and the electrolyte leads to the formation of unstable solid-electrolyte interphase (SEI) layers, further compromising battery performance and cycle life.<br/>To address these issues, researchers have extensively developed destructive characterization techniques to observe the lithium metal anode and quantify irreversible lithium metal formation. However, these studies lack real-time operando information, crucial for understanding the dynamic behavior of these systems. Recently, the emergence of optical fiber-based techniques has enabled the tracking of battery properties under realistic conditions, providing chemical, thermal, and mechanical data for lithium-ion and sodium-ion cells.<br/>In this study, we demonstrate the utilization of optical fiber Bragg grating (FBG) sensors to monitor thermal and chemical events in anode-free commercial cells during real cycling conditions. By confirming the operando results with destructive characterization methods such as titration gas chromatography (TGC) and focused ion beam (FIB) imaging, we highlight the capability of this method to monitor the parasitic reactions (as solid electrolyte interface formation) happening in lithium metal cells under diverse conditions, including varying pressure, electrolyte formulation, and rate performances. Overall, the utilization of FBG sensors offers valuable insights into the reactivity, stability, and safety aspects of lithium metal batteries, thereby contributing to the ongoing development and optimization of these energy storage systems.