Four-Electron-Transferred Pyrene-4,5,9,10-tetraone Derivatives Enabled High-Energy-Density Aqueous Organic Flow Batteries.

Multielectron-transferred molecules hold great potential to enhance the energy density and reduce the cost for aqueous organic flow batteries (AOFBs). However, the extended conjugated units required for increasing redox-active sites and stabilizing the multielectron reaction always decrease the molecular polarity, limiting the solubility in the electrolyte. Herein, we presented an asymmetrical pyrene-4,5,9,10-tetraone-1-sulfonate (PTO-PTS) monomer which not only could reversibly store four electrons but also exhibited a high theoretical electron concentration of 4.0 M and the strongly heat-resistant intermediate semiquinone free radical. As a result, PTO-PTS-based AOFBs demonstrated a high energy density of 59.6 Wh L (89 Ah L) with an ultrastable capacity retention of nearly 100% for above 5200 cycles (60 days). Moreover, the heat-stable PTO-PTS structure further enabled both symmetric and full cells to achieve remarkable cycling durability for over a thousand cycles at 60 °C. The outstanding cell performance and high thermal stability suggest its promising application in large-scale energy storage.