An Azo Polymer with Abundant Active Sites and Extended Conjugation as a Stable Cathode for High-Performance Zinc-Organic Batteries

Abstract

Developing stable cathodes with high capacity and rapid redox kinetics is pivotal for aqueous zinc-organic batteries (ZOBs). A huge challenge lies in balancing the density of active sites and electronic conductivity of organic cathodes. Herein, an azo polymer from 4,5,9,10-pyrene-tetraone (PTAP) possessing high active components and extended conjugated structure was achieved. The extended conjugated system linked by the azo groups facilitates extensive electron delocalization and a low band gap, which endows the PTAP with enhanced electronic conductivity reaching 4.26×10⁻³ S m⁻¹. The azo groups themselves serve as active centers for two-electron transfer, leading to a significant increase in the density of redox-active sites and charge storage efficiency. Moreover, strong intramolecular interactions and unique solvation structure bolster the anti-solubility of PTAP. Consequently, PTAP-based ZOBs exhibited high reversible capacities and rate performance, delivering 442.45 mAh g⁻¹ at 0.2 A g⁻¹ and maintaining 248.61 mAh g⁻¹ even at 10 A g⁻¹. Additionally, a ZOB showed remarkable long-term stability after cycling over 900 hours at 5 A g⁻¹. Mechanistic studies further revealed that multi-step coupling of carbonyl and azo groups accompanied by the Zn²⁺/H⁺ dual-ion insertion is responsible for rapid 12-electron transfer in PTAP. This work provides new insight into the rational design of advanced organic cathodes for high capacity and long life ZOBs.