Instrumentation of novel optical sensor technology to detect the real-time electrolyte colour change in Li-on pouch cells

Abstract

The need for new and improved diagnostic tools becomes paramount for Li-ion batteries in order to ensure their optimum performance along with their longevity and safety and there remain aspirational targets for Li-ion batteries regarding fast-charging, energy density, safety and lifetime that must be met to achieve further growth. The study of degradation mechanisms (such as electrolyte degradation, thermal runaway, gassing and cycling aging) at the cell level contributes significantly to the understanding of the aging phenomena and will enable improvements for future generations of LIBs. Among various indicators, the colour change of the electrolyte within Li-ion cells presents a largely unexplored avenue for assessing state of health and predicting early signs of degradation. This research proposes a new methodology for the development of an innovative optical sensor technology and its incorporation into a pouch cell. The sensor comprises of a photodiode and RGB LED, mounted on a single flexible PCB, capable of the real-time detection of electrolyte colour changes inside Li-ion pouch cells. Previous studies have identified electrolyte colour change as a potential marker for battery condition through various invasive testing methods; however, the proposed optical technique represents a step change in in-situ real-time diagnostics. This study elaborates on the process of developing and incorporating the sensors precisely into pouch cells and seeks to demonstrate the capability of these sensors to accurately detect alterations in the colour of the electrolyte as the cell ages, without having adverse effects on the cell's performance and offers the potential for direct correlation of electrolyte change with battery state of health.