Optical fiber sensor based on upconversion nanoparticles for internal temperature monitoring of Li-ion batteries

Abstract

Temperature is a critical parameter for evaluating battery safety during the process of charging and discharging. However, it is a challenge to monitor it accurately because batteries are used in various compact environments such as energy stations. In this study, β-NaYF₄:Er³⁺/Yb³⁺@NaYF₄ nanoparticles were used to fabricate an optical fiber temperature sensor for battery temperature monitoring. The temperature sensing characteristics of the optical fiber sensor were explored in the range of 293–373 K using fluorescence intensity ratio (FIR) technology which can improve the temperature monitoring accuracy. The maximum relative sensitivity of the optical fiber sensor was 1.62% K⁻¹ at 293 K and the temperature detection limit was within ±0.5 °C. By embedding the prepared sensor in a Li-ion battery, the proof of concept was obtained for monitoring the internal temperature of a battery with upconversion nanoparticles (UCNPs). A larger temperature variation was observed under a higher discharge rate. These results indicate that the prepared optical fiber sensor is an active tool for monitoring the thermal behavior and improving the safety of the battery.