Advancing Measurement Capabilities in Lithium-Ion Batteries: Exploring the Potential of Fiber Optic Sensors for Thermal Monitoring of Battery Cells

TL;DR

The paper addresses the need for internal, spatially resolved temperature sensing in lithium-ion batteries to improve safety and longevity. It demonstrates a Rayleigh-backscatter OFDR approach using inert glass fibers to achieve distributed temperature measurements along the fiber length, enabling internal thermal mapping within cells. The results show quasi-linear temperature responses from 0 to 80 °C with a typical KT around 8–11 μɛ/°C and a practical 2.6 mm spatial resolution at 1 Hz, while fiber bending and pouch-cell integration are feasible with localized artifacts confined to attachment points. The study establishes the feasibility of in-cell thermal monitoring with minimal electromagnetic interference and small form-factor fibers, laying groundwork for integrated battery monitoring and predictive diagnostics, with future work focusing on long-term reliability and non-thermal influences on sensor performance.

Abstract

This work demonstrates the potential of fiber optic sensors for measuring thermal effects in lithium-ion batteries, using a fiber optic measurement method of Optical Frequency Domain Reflectometry (OFDR). The innovative application of fiber sensors allows for spatially resolved temperature measurement, particularly emphasizing the importance of monitoring not just the exterior but also the internal conditions within battery cells. Utilizing inert glass fibers as sensors, which exhibit minimal sensitivity to electric fields, opens up new pathways for their implementation in a wide range of applications, such as battery monitoring. The sensors used in this work provide real-time information along the entire length of the fiber, unlike commonly used Fiber Bragg Grating (FBG) sensors. It is shown that using the herein presented novel sensors in a temperature range of 0 to 80 degree celsius reveals a linear thermal dependency with high sensitivity and a local resolution of a few centimeters. Furthermore, this study presents preliminary findings on the potential application of fiber optic sensors in lithium-ion battery (LIB) cells, demonstrating that the steps required for battery integration do not impose any restrictive effects on thermal measurements.

Figures (11)

• Figure 1: Schematic representation of optical fibers and light propagation or refraction properties: (a) Structure of an optical fiber, showing the core, cladding and coating. (b) Reflection principle of an injected light signal into a fiber with an imprinted FBG. (c) Rayleigh backscatter effect from microscopic particles. (d) Division of the fiber into material-characteristic quasi-segments and corresponding refractive index variations without (${\lambda}_{\mathrm{0}}$) and with (${\lambda}_{\mathrm{1}}$) external influence on the fiber.
• Figure 2: Exemplary test setups with a Weiss climate chamber, a water basin for temperature measurement and an ODiSI 6104 interrogator for various experiments to determine the thermal dependency of different fibers.
• Figure 3: (a) Aluminum model with milled radii ($15, 20, 40$ and $60\mm$) for measuring thermal dependence of fibers in bends. (b) Exemplary test setup with a Weiss climate chamber, an aluminum plate with four milled bending radii and an ODiSI 6104 interrogator to determine the thermal dependence of bent fibers.
• Figure 4: Amplitude of the measurement at different times under homogeneous environmental influences with $1Hz$ at different spatial resolutions: $0.65mm$ (a), $1.3mm$ (b) and $2.6mm$ (c). (d) Change in standard deviation under constant test conditions over time at $1Hz$ with continuous averaged values at different spatial resolutions is shown.
• Figure 5: (a) Exemplary measurement of three spatially resolved, time-independent cooling events at $25\degreeCelsius$ ambient temperature. (b) Relaxation measurement of Fiber C at a constant temperature of $45\degreeCelsius$ with no pressure applied to the fiber.