Optical fiber sensors for operando monitoring of next-generation batteries: a review

The need for secure, sustainable, long-lasting, and high-performing electrochemical energy systems has grown rapidly due to advances in distributed storage, renewable energy integration, and electric mobility. To meet these objectives, sophisticated operando monitoring instruments have been rapidly developed in recent years. These instruments identify localized mechanical, chemical, and thermal processes that govern battery performance, longevity, and health. Conventional electrical and electrochemical sensors degrade quickly and struggle to operate in harsh environments, and embedding them in small, compact next-generation batteries is challenging. Optical fiber sensors (OFSs) have recently emerged as a transformative platform for real-time, non-invasive battery diagnostics. By harnessing light–matter interactions, OFSs transduce local variations in temperature, strain, refractive index, or chemical composition into optical signals with exceptional sensitivity and resolution. Recent advances in fiber Bragg gratings (FBGs), interferometric architectures, and distributed spectroscopic techniques, such as optical frequency/time-domain reflectometry (OFDR/OTDR) and φ-OTDR-based sensors, have demonstrated multi-parameter sensing in battery monitoring systems. These approaches enable spatially resolved measurements of temperature, pressure, strain, local refractive index, and electrochemical parameters, which are critical for early detection of degradation and thermal runaway. With intrinsic advantages such as electromagnetic immunity, chemical robustness, miniaturization, and multiplexing capability, OFSs represent a compelling and increasingly validated platform for battery diagnostics. This review consolidates recent advances in operando optical sensing, emphasizing transduction mechanisms, structural designs, and integration strategies. It further discusses key challenges in sensor durability, calibration, sensor intrusiveness and scalability, and outlines future directions toward photonic battery management systems with predictive diagnostic capability, integrating optical diagnostics with predictive control for next-generation energy storage technologies.