Photometrical Determination of the State-of-Charge in Vanadium Redox Flow Batteries Part II: In Combination with Open-Circuit-Voltage

Abstract By means of in-situ UV/Vis/NIR spectrometry, separately both in the anolyte as well as in the catholyte of a vanadium redox flow battery (single cell) partial state-of-charge values are determined online. The UV/Vis/NIR spectroscopic experimental set-up is calibrated using the state-of-charge value determined from measurements of the open-circuit-voltage (OCV) in the pristine state of the battery which is related to Nernst’s equation taking into account also H + formation/consumption during the V 4+ /V 5+ redox process. The comparison of both partial state-of-charge values indicates a possible imbalance of the battery, which can occur after long-term operation.