Extended conjugation-induced π electron redistribution for stabilizing organic anodes in aqueous ammonium ion batteries

Abstract

Organic molecules have attracted significant attention as potential anode materials for aqueous ammonium-ion batteries (AAIBs) due to their tunable structure, rich active sites, and abundant resources. However, their practical applications are hindered by structural instability and high solubility. Herein, we design an extended conjugated molecule, benzo[a]benzo[7,8]quinoxalino[2,3-i]phenazine-8,17-dione (TABQ-NQ), by incorporating phenyl groups into the 5,7,12,14-tetraaza-6,13-pentacenequinone (TAPQ) structure. The strengthened intermolecular interactions arising from the extended conjugation contribute to the improved structural integrity of TABQ-NQ. Furthermore, the intramolecular charge redistribution facilitated by the extended conjugation enhances the binding affinity between TABQ-NQ and NH₄⁺ while reducing interactions of TABQ-NQ with H₂O, thereby stabilizing discharge intermediates and preventing further dissolution. As a result, TABQ-NQ exhibits reduced solubility, improved stability, and superior electrochemical performance. The TABQ-NQ anode demonstrates a high initial specific capacity of 190 mAh g⁻¹, with a capacity of 146 mAh g⁻¹ at 0.2 A g⁻¹ after over 650 cycles, corresponding to the capacity retention of 76.8 %, and maintains an initial capacity of 127.5 mAh g⁻¹ at 2 A g⁻¹. Ex-situ characterizations further reveal the low solubility and high redox reversibility of TABQ-NQ. This work provides new insights into the extension of conjugated structures in organic molecules and offers valuable guidance for the development of AAIBs research.