Pyromellitic diimide based bipolar molecule for total organic symmetric redox flow battery

Abstract

Non-aqueous redox flow batteries based on total organic electrolytes, consisting of earth-abundant elements, i.e., C, H, N, O, are regarded as a promising technology for sustainable and large-scale energy storage. In particular, bipolar redox-active organic materials (BROMs) are distinctly fascinating as electroactive species because they have multiple oxidation states and can undergo multiple redox processes. By virtue of this unique characteristic, BROMs can be utilized as both anolyte and catholyte in symmetric flow batteries, consequently, helping alleviate cross-contamination issues. Herein we report an all-organic symmetric redox flow battery based on diimide molecule as a bipolar electroactive material. The potential interval between the cathodic peak and the inner and outer anodic peaks led to a promising cell voltage of 2.22 V. The symmetric battery can be operated at a current density of 20 mA cm−2, with a coulombic efficiency of 90% for over 100 cycles. This work proposes an alternative approach to designing multi-electron organic redox active materials to facilitate the advancement of high-density symmetric flow batteries.