Towards ultra-stable aqueous zinc-ion batteries via electrochemical polymerization of phthalimido-anchored benzoquinone

Abstract

Designing organic cathode materials with high specific capacity and stability for aqueous zinc-ion batteries (ZIBs) is essential. Small organic molecules suffer from limited conductivity and high solubility, which hamper the charge storage performance of ZIBs. Here, tetra-(phthalimido)-benzoquinone (TPB), which has multiple carbonyl groups, is selected as a monomer for electropolymerization to fabricate polyTPB (PTPB)/carbon cloth (CC). Aqueous ZIBs with PTPB/CC demonstrate ultralong cycling stability, sustaining 30 000 galvanostatic charge–discharge cycles at 10 A g⁻¹. The specific discharge capacity of the ZIB with PTPB/CC reaches 261 mA h g⁻¹ at a charge–discharge current density of 0.1 A g⁻¹. Kinetic analysis demonstrates that charge storage is predominantly governed by surface capacitive-controlled processes. The charge storage mechanism is further probed through ex situ characterization studies. The carbonyl/hydroxyl and amino/imino groups are identified as the active groups for charge storage, and the redox process involves the insertion and extraction of both Zn²⁺ and H⁺. Density functional theory calculations demonstrate that carbonyl oxygen atoms, acting as nucleophilic sites, preferentially bind Zn²⁺ over H⁺ due to a lower Gibbs free energy change (ΔG) and a higher Zn²⁺ concentration in the electrolyte. The five-step Zn²⁺/2e⁻ insertion pathway during discharging is validated to be thermodynamically viable.