Monomer-Engineered Quinone-Based Conjugated Polymers for High-Rate Aqueous Zinc-Ion Batteries

Abstract

Conjugated polymers (CPs) with their extended pi-conjugated structures have recently attracted tremendous attention as organic cathodes in aqueous zinc-ion batteries (AZIBs). In this study, two quinone-pyrrole conjugated polymers, QpCP-1 (benzoquinone monomer) and QpCP-2 (anthracenetetrone monomer), were synthesized to investigate the impact of monomer engineering on electrochemical performance, aiming to enhance specific capacity without sacrificing rate performance and cycle life. At 0.1 A g-1, QpCP-1 delivered a higher specific capacity (178 mA h g-1) than QpCP-2 (134 mA h g-1). However, while QpCP-1's capacity declined with increased current density, QpCP-2 demonstrated superior rate capability, retaining 78% of its initial capacity when the current density increased 20-fold (from 0.1 to 2.0 A g-1). This enhanced rate performance is attributed to QpCP-2's extended conjugated structure and increased accessible quinone-rich redox-active sites. Furthermore, QpCP-2 underwent gradual activation, resulting in a 30% increase in specific capacity, and demonstrated remarkable cycling stability over 10,000 cycles at 2.0 A g-1. The charge storage mechanism involving the coinsertion of H+ and Zn2+ was investigated through a series of ex situ characterization techniques. This work provides insights into the potential of CPs in AZIBs by elucidating the impact of monomer engineering and structural influences on electrochemical performance.