An Organic Flow Cathode for Flexible Lithium-Organic Redox Flow Batteries
As for the organic cathode materials, various quinone-based organic materials have been widely studied for lithium ion batteries due to their abundant active sites and fast electron and ionic transfer kinetics. Due to low electrical conductivities of organic electrode materials, large amount of conductive materials and binders is added for the slurry coating process to assemble the coin-cell type batteries. Moreover, the dissolution of quinone based molecules into electrolyte places additional obstacles. Thus, current research has been focused on suppressing these issues in aprotic electrolytes. Interestingly, the synthesis of organic molecule with high solubility is one of the major research topics in the redox battery system. Thus, such features associated with solubility issues can make our tube-type redox batteries a novel flexible energy storage system. The construction of liquid type electrodes could be a new approach for the development of organic-based redox batteries including a novel flexible energy storage system. Herein, we report the first demonstration of liquid type flexible batteries. In addition the structure dependent electrochemical performances of two polycyclic quinone derivatives, 5,12-naphthacenequinone (NAQ) and 1,2-nenzanthraquinone (BAQ), will be studied. This constitutional isomers as liquid cathode materials can reversibly uptake two lithium ions in liquid phase after dissolving in tetraethylene glycol dimethyl ether (TEGDME) containing 1.3 M lithium bis(trifluoromethane sulfonyl) imide salt (LiTFSI). Importantly, BAQ with an asymmetric structure presented higher redox potential during charging and discharging steps than NAQ, showing two pronounced voltage plateaus with stable cycling performance. Tube-type redox batteries using the organic redox-active materials that dissolved in aprotic electrolyte can be easily scale-up and flexible. And the architecture injected with BAQ showed reliable mechanical flexibility under in-situ bending test of 50 mm min−1, showing energy efficiency of ~80% and coulombic efficiency of ~99.5%.