Continuous-flow organic electrosynthesis of a conjugated bipolar polymer cathode for high-performance low-temperature aqueous aluminum-ion batteries

Abstract

Aqueous aluminum-ion batteries represent a promising energy storage technology, leveraging their exceptional capacity, low cost, and inherent safety. However, their practical implementation has been hampered by severe performance degradation at subzero temperatures and a scarcity of cathode materials with high capacity. Here, we present a conjugated bipolar polymer poly(2,3-diaminonaphthalene-1,4-dione) (PDND) synthesized via continuous-flow organic electrosynthesis. This molecular design incorporates a quinone-amine redox system that unifies n-type (quinone) and p-type (amine) moieties, thereby enhancing charge storage capacity. The extended quinone–amine backbone enhances p–π conjugation, enabling efficient π–electron delocalization and continuous charge transport pathways along the polymer chain, resulting in high electronic conductivity. Furthermore, the planar π-conjugated quinone units and arylamine linkages construct synergistic dual-interaction networks between the polymer chains, including dense hydrogen-bonding and strong π–π interaction, ensuring structural stability. Consequently, the Al//PDND battery delivers a high capacity of 302 mAh g⁻¹, outstanding cycling stability (≥1000 cycles), and remarkable rate capability (up to 2 A g⁻¹). Notably, it operates effectively at –25 °C using a standard aqueous electrolyte without antifreeze additives, underscoring the superior low-temperature performance endowed by PDND. Through in situ/ex situ spectroscopic studies, we elucidate a multi-ion co-storage mechanism involving the reversible insertion of Al³⁺, H⁺, and ClO₄⁻ ions.