Increasing Battery Safety of Lithium-Ion Batteries by Using Cell-Internal Glass Fiber Sensors for in-Situ Temperature Monitoring

Abstract

Lithium-ion batteries (LIB), featuring high energy density and power density, are used in a wide range of applications. One of the most important requirements for their application is to ensure their safety and continuous performance under different operating conditions. In order to ensure the afore mentioned factors, in-situ monitoring of internal cell parameters, such as temperature, state-of-charge, and state-of-health of LIB is essential. The cell temperature is a critical factor for both the safety and the LIB’s health. Not only the average temperature, but also the temperature distribution within the cell must be considered. However, common battery management systems mostly rely on monitoring the surface temperature of the cells, while neglecting changes of the internal parameters. This is where the integration of optical glass fiber sensors into battery cells, which allow direct monitoring of internal temperature changes during operation, makes a significant contribution.In this work, different approaches for the integration of optical glass fiber sensors into battery cells have been evaluated. The focus was set on the complete integration of the glass fiber at specific positions within the LIB, while ensuring that both, the glass fiber, and the battery components remain intact. Furthermore, the influence of the integrated glass fibers on the performance of the LIB was investigated. Finally, their functionality as temperature sensors was evaluated.In a second step, temperature measurements were performed on LIB during operation, using both internal and external sensors. The results obtained clearly reveal an early detection of temperature changes by internal glass fibers compared to external sensors. This not only confirms the efficiency of the internal sensors, but also leads the path to improved battery safety by early detection of critical temperatures within the cell.