State of Charge and State of Health Assessment of Viologens in Aqueous-Organic Redox-Flow Electrolytes Using In Situ IR Spectroscopy and Multivariate Curve Resolution

The article by Oliver Nolte, Robert Geitner, Ivan A. Volodin, Philip Rohland, Martin D. Hager, Ulrich S. Schubert​
Image: Foto von Bilakis von Pexels


The article presents the results of research in an area of analytical techniques for flow batteries.

  • Importance - for accurate and informative of RFB electrolyte state (especially assessment of SOC and SOH);
  • Research object - two electrolytes, based on methyl viologen and on bis(3-trimethylammonium)propyl viologen;
  • Research subject - SOC and SOH assessment techniques;
  • Novelty - new IR data treatment approach and its applicability to various electrolyte compositions;
  • Practical result - significant increase of precision of SOC and SOH assessment by the common spectroscopic technique.

The redox flow battery (RFB) field is new compared to other battery technologies and here it is not obvious, how to estimate how much the battery is charged at the moment (e.g. state of charge or shortly SOC) or how significant is its ageing at any point in time (e.g. state of health or shortly SOH) of any RFB. The article offers a new technique that can estimate these SOC and SOH parameters. This technique is based on treatment of RFB electrolyte with infrared radiation (IR). Similar techniques have been already proposed, however, they struggle from standard "IR-caused" artifacts. Any battery electrolyte system is complicated with variety of components. Such multicomponent systems demonstrate non-linear behaviors and, thus, cause artifacts, which decrease accuracy of the IR technique to the nonacceptable values. The novelty of the article is the proposal of the new data treatment approach, which helps to assess the SOC and the SOH accurately even in the multicomponent systems and to avoid measurement artifacts while using the common IR spectroscopic approach.

Furthermore, the proposed method can in addition partially provide information on structure and interactions between active substances in the battery electrolyte.  This may be beneficial for the RFB management system. 

The new IR method is proposed and successfully established on the example of studies of SOC and SOH of two electrolytes based on two different viologen structures, thus, proving that it can be applied for various RFB electrolyte compositions.

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