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, 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, planar π-conjugated quinone units and arylamine linkages construct synergistic dualinteraction networks between 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 o 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.