Tracking electrochemical reactions inside organic electrodes by operando IR spectroscopy

IR spectroscopy can be a non-destructive and straightforward probing tool in the battery research. However, its application has been limited due to the difficulties related to the handling and interpretation of ex situ samples along with the lack of widely applicable in situ and operando cells. Herein, we show a simple, operando ATR-IR two electrode pouch cell with an IR-transmissive silicon window and discuss its advantages and limitations. This setup is applied to the study of the polyanthraquinone (PAQ) reaction mechanism in Li- and Mg-organic batteries. During the reduction/oxidation process of the PAQ, not only the conversion of both C O groups into C–O– species is observed, but also the formation of an intermediate semiquinone radical anion as an intermediate product. Furthermore, continuous measurement of IR spectra allows visualization of the gradual solid-electrolyte interphase (SEI) buildup on the cathode during cycling.