Applications of fiber optic sensors to battery monitoring have been increasing due to the growing need of enhanced battery management systems with accurate state estimations. The goal of this review is to discuss the advancements enabling the practical implementation of battery internal parameter measurements including local temperature, strain, pressure, and refractive index for general operation, as well as the external measurements such as temperature gradients and vent gas sensing for thermal runaway imminent detection. A reasonable matching is discussed between fiber optic sensors of different range capabilities with battery systems of three levels of scales, namely electric vehicle and heavy-duty electric truck battery packs, and grid-scale battery systems. The advantages of fiber optic sensors over electrical sensors are discussed, while electrochemical stability issues of fiber-implanted batteries are critically assessed. This review also includes the estimated sensing system costs for typical fiber optic sensors and identifies the high interrogation cost as one of the limitations in their practical deployment into batteries. Finally, future perspectives are considered in the implementation of fiber optics into high-value battery applications such as grid-scale energy storage fault detection and prediction systems.

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Reflection fiber temperature sensors functionalized with plasmonic nanocomposite material using intensity-based modulation are demonstrated for the first time. Characteristic temperature optical response of the reflective fiber sensor is experimentally tested using Au-incorporated nanocomposite thin films deposited on the fiber tip, and theoretically validated using a thin-film-optic-based optical waveguide model. By optimizing the Au concentration in a dielectric matrix, Au nanoparticles (NP) exhibit a localized surface plasmon resonance (LSPR) absorption band in a visible wavelength that shows a temperature sensitivity ~0.025%/°C as a result of electron–electron and electron–phonon scattering of Au NP and the surrounding matrix. Detailed optical material properties of the on-fiber sensor film are characterized using scanning electron microscopy (SEM) and focused-ion beam (FIB)-assisted transmission electron microscopy (TEM). Airy’s expression of transmission and reflection using complex optical constants of layered media is used to model the reflective optical waveguide. A low-cost wireless interrogator based on a photodiode transimpedance-amplifier (TIA) circuit with a low-pass filter is designed to integrate with the sensor. The converted analog voltage is wirelessly transmitted via 2.4 GHz Serial Peripheral Interface (SPI) protocols. Feasibility is demonstrated for portable, remotely interrogated next-generation fiber optic temperature sensors with future capability for monitoring additional parameters of interest.

In this work, we demonstrate a reflection-based nanocomposite-functionalized fiber H2 sensor for ease of installation and H2 sensing in energy storage, fuel cells, electrolyzers, and other similar devices. High-temperature H2 fiber probes decorated with Au-Pt bimetallic alloy nanoparticles (NPs) in rutile titania matrix are characterized with scanning electron microscopy (SEM) and grazing incidence X-ray diffraction (GIXRD), and tested experimentally with varying H2 concentration and cycling gas conditions. In response to reducing H2, fully reversible reflectance intensity changes at the alloy NPs' localized surface plasmon resonance (LSPR) absorption peak are demodulated in real-time. The reflection fiber probe coated with bimetallic Au-Pt NPs in titania show 15x higher sensitivity than corresponding monometallic Au NPs in titania. The demonstration of reflection hydrogen fiber probe provides an installation advantage in various reactor environment applications, and the investigation of the Au-Pt binary alloy system unfolds new sensitivity-enhancing pathways for NP-based LSPR modulation in reducing H2 environment at high temperatures.