Operando Optical Failure Identification and Early Warning of Thermal Runaway for Batteries

ABSTRACT Operando monitoring of internal multi‐physical processes is critical for analyzing battery failures and issuing risk warnings. However, existing approaches fall short in enabling operando internal measurement, particularly during the drastic failure stage of batteries. To address this challenge, we implant a Fiber Bragg Grating sensor into the battery, enabling concurrent monitoring of internal strain and temperature without compromising the cell performance. For the first time, we unveil the critical role of internal strain in elucidating the failure modes during the thermal runaway (TR) incubation, encompassing abnormal electrode expansion, gas generation, lithium plating, and “anode‐electrolyte‐cathode” chain reactions. Furthermore, we identify the internal strain derivative as a novel clue for early warning of TR, offering an extended warning window of up to 18.8 min compared with commonly‐used voltage clues. This study provides an innovative and scalable approach for operando failure stage identification and early TR warning of lithium‐ion batteries.