Unlocking the Full Redox Capability of Organic Charge‐Transfer Complex in High‐Loading Electrodes for Organic Rechargeable Batteries

Abstract

Organic charge‐transfer complex (OCTC) comprising redox‐active donor and acceptor molecules is a promising electrode material group, potentially resolving issues of low power and inferior cycle stability of organic electrodes in rechargeable batteries. Strong intermolecular interactions in OCTC such as π–π interaction and hydrogen bonding enable high electronic conductivity and suppress solubility to solvents. However, full redox activities of OCTC have not been achieved yet despite the inherent redox capabilities of respective donor and acceptor molecules. Here, it is revealed that the limited redox activities of OCTC stem from electrolyte‐incorporated complex formation, which weakens the characteristic intermolecular interactions, thereby hindering the redox reaction, particularly in Li‐based electrolytes. It is further shown that tailoring electrolyte types, specifically using Zn‐aqueous electrolytes, can substantially mitigate the complex formation and unlock the four‐electron redox activity of OCTC (phenazine (PNZ)‐7,7,8,8‐tetracyanoquinodimethane (TCNQ), that is, PNZ–TCNQ), with superior cycle stability retaining 88% of maximum capacity over 100 cycles. Surprisingly, the full redox reaction achieves an unprecedentedly high electrode‐level energy density, delivering ≈10 mAh cm−2 of areal capacity (580 µm‐thick electrodes) in Zn‐aqueous batteries. The findings elucidate the complex interplay between organic electrodes and electrolytes in the charge storage mechanism, highlighting the importance of electrolyte design in developing organic electrode materials.