To address the inability of existing battery management systems in acquiring internal temperature gradients, structural strain, and gas generation signals in lithium-ion cells, which result in inadequate safety monitoring and early-warning capability against thermal runaway, a systematic review of fiber optic sensors for lithium-ion battery safety monitoring and the challenges they face was provided. First, key safety-related monitoring parameters, including temperature, strain, gas evolution, and electrolyte state, were identified. Second, the principles and characteristics of representative sensing technologies, such as Fiber Bragg Gratings(FBG), Tilted Fiber Bragg Gratings(TFBG), Fiber Optic Evanescent Wave Sensing(FOEW), and Distributed Optic Fiber Sensing(DOFS), were reviewed. Third, the research progress in in-situ temperature and strain monitoring, electrolyte state evaluation, gas detection, and thermal runaway risk identification for each technology was summarized. Finally, major challenges in practical application, including integration compatibility, multi-parameter cross-sensitivity, long-term stability, and cost, were discussed. The survey reveals that fiber-optic sensing enables multi-point, millisecond-scale temperature monitoring with ±0.1 ℃ accuracy, strain mapping at ±0.1 με resolution, in-situ gas detection at 0.12% precision, and electrolyte refractive-index tracking down to 10-3. Feeding these multi-parameter, in-situ, real-time data into advanced algorithms can significantly enhance early-warning capability for lithium-ion battery thermal runaway.
