Near-Theoretical Redox-Site Utilization and Fast Zn²⁺ Storage in a Polyimide-CNT Cathode

Achieving high utilization efficiency together with fast electrochemical transport remains a central challenge for organic cathodes in aqueous zinc-ion batteries. Herein, a π-conjugated imide-linked polyimide based on pyrene-4,5,9,10-tetraone and pyromellitic dianhydride (PMDA-PTO) is reported, where a carbonyl-rich conjugated polyimide framework is integrated with a conductive carbon nanotube (CNT) network to promote electronic percolation and facilitate efficient utilization of redox-active sites together with fast and durable Zn-ion storage. The PMDA-PTO-CNT composite delivers a discharge capacity of 328 mAh g^-1 at 0.05 A g^-1, corresponding to ∼98% utilization of its theoretical capacity, and maintains 316 mAh g^-1 at 20 A g^-1, while sustaining stable electrochemical operation over 10 000 cycles at 5 A g^-1. Electrochemical analyses reveal reduced polarization, enhanced pseudocapacitive behavior, and improved electrochemical transport within the CNT-containing electrode architecture. Ex situ Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and Grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements support a reversible carbonyl-centered cation-storage mechanism within a structurally disordered polymer framework that retains only short-range organization during cycling, while density functional theory (DFT) calculations corroborate the multistep delocalized redox behavior of the conjugated backbone. Collectively, these findings provide insight into structure-transport relationships in quinone-based polymer cathodes and highlight how electronic percolation and redox-site accessibility enable high utilization, fast kinetics, and long-term stability in aqueous Zn-ion batteries.