Research Progress on Fiber‐Optic Operando Monitoring in Lithium‐Ion Batteries

As lithium‐ion batteries advance toward higher energy densities and harsher operating conditions, their internal processes become increasingly heterogeneous and strongly coupled across thermal, mechanical, and chemical fields. Yet conventional battery management systems still rely on external macroscopic signals—voltage, current, and surface temperature—creating a “black‐box” paradigm that only indirectly infers internal dynamics. Embedded fiber‐optic sensing, with its microscale footprint, electromagnetic immunity, and chemical robustness, enables direct intracell monitoring of thermomechanical states and molecular fingerprinting via vibrational spectroscopy—offering a powerful pathway to decode internal battery mechanisms. This review first introduces the fundamental principles of fiber‐optic sensing technology for internal temperature and pressure monitoring in lithium‐ion batteries, as well as the working principles of fiber‐optic spectroscopic techniques, followed by a comparative summary of the advantages and information acquisition capabilities of typical fiber‐optic sensing technologies. Subsequently, specific research studies are discussed to elaborate on the applications of fiber‐optic technology in sensing temperature, pressure, and other parameters during irreversible processes inside lithium batteries. Representative applications of fiber‐optic infrared and Raman spectroscopic techniques for chemical information detection within batteries are also addressed. Finally, a brief summary of fiber‐optic sensing/spectroscopic technologies is provided, along with a prospect for their future development.