Self-Compensation of Cross Influences using Spectral Transmission Ratios for Optical Fiber Sensors in Lithium-Ion Batteries

In this paper, we discuss some major obstacles and solutions towards an industrialization of optical fiber sensors for cell state monitoring of lithium-ion batteries. We present measurement results based on transmitted light intensities through the optical fiber as indicator for the state of charge. Cells are built with commercial electrodes in a pouch cell setup. To compensate for cross influences and stabilize the measuring signal against manufacturing tolerances, a referencing method is introduced. Thus, ratios of transmitted light intensities at different wavelengths are evaluated to avoid the use of absolute values. The obtained transmission ratios are in good agreement with the state of charge for various C-rates. Finally, possibilities towards an industrial implementation with inexpensive LEDs and phototransistors are discussed.