A new polymer with rich carbonyl delocalized π-conjugated structure for high-performance aqueous zinc ion batteries.

The development of sustainable and clean energy has become a top priority, driven by global carbon peaking and carbon neutrality targets. Organics are widely used in aqueous zinc ion batteries (AZIBs) due to their environmental friendliness, high structural designability, and safety. However, organic materials often face some challenges, including high solubility, low specific capacity, and unclear mechanism, which hinder its further applications. In this paper, two new conjugated organic polymers were synthesized as cathodes for AZIBs by molecular structure design. Notably, the introduction of new actives (C = O) in (poly-(tetraamino-p-benzoquinone-alt-2,5-dihydroxy-1,4-benzoquinone, DHTA) along with the extension of the π-π conjugated structure to form polymers is conducive to the improvement of the specific capacity and reversibility of AZIBs compared to (poly-(1,2,4,5-tetraaminobenzene-alt-2,5-dihydroxy-1,4-benzoquinone, DHPH). The DHTA cathode delivers high initial specific capacity of 282.5 mAh/g at a current of 0.05 A/g and excellent rate performance (56.8 mAh/g at 5 A/g). The excellent rate performance and long cycle life of the as synthesized DHTA can be attributed to the low solubility, extended π-conjugated structure and enhanced electronic conductivity, which result from the polymerization with the introduction of carbonyl groups into organic skeleton. Moreover, the mechanism of Zn storage in DHTA is also explored by various ex-situ characterization techniques and density-functional theory (DFT) calculations. In each repeating unit, DHTA can store two Zn while transferring four electrons to form a stable O⋯Zn⋯N coordination. This work provides a molecular engineering strategy for organic materials, revealing their potential application in zinc ion batteries.