Thianthrene-Based Bipolar Redox-Active Molecules Toward Symmetric All-Organic Batteries

Bipolar redox activity is generally obtained using a single moiety that can be both oxidized and reduced or by tethering two distinct redox active molecules, together with a covalent linker. Herein, we demonstrate an alternative approach using the S_NAr and S_NAr-type reactions of benzene-1,2-dithiols and electron-deficient aromatic halides or halogenated quinones to prepare a family of compact, thianthrene-based bifunctional molecules. The potential of these molecules as electrolytes for redox flow batteries was assessed in static cells as a proof of concept. Cycling in a static cell demonstrated that the thianthrene-quinone, PQtBuTH (8), is highly stable, compared to other symmetric organic active materials, with 44% capacity retention over 450 cycles (16.7 days), and an initial energy density of 1.3Wh/L at a concentration of 0.1 M. Redox flow batteries represent a promising grid-scale energy storage technology, and the development of new symmetric electrolyte systems in organic solvents can potentially mitigate issues associated with membrane crossover and provide high cell voltages.