A Dual-Active-Site Mechanism Enabled by a Fused Quinone Imine for Dissolution-Resistant and High-Capacity NH₄⁺ Storage

Aqueous ammonium-ion batteries (AAIBs) are promising for next-generation energy storage due to their safety, abundance, and fast kinetics, yet challenges such as electrode dissolution and poor conductivity hinder their development. Herein, hexaazatribenzanthraquinone (HAQ) is synthesized via activation of −NH₂ groups in 1,2-diaminoanthraquinone, converting them into redox-active C═N groups. This transformation enhances active site utilization and extends the conjugated structure, suppressing dissolution and improving electronic conductivity. HAQ exhibits a narrowed HOMO-LUMO gap (0.743 eV), indicating enhanced electron delocalization and charge transfer. It operates via a dual-active-site mechanism involving C═O and C═N groups, enabling a high six-electron transfer with ultra-low energy barriers. Consequently, HAQ delivers a high capacity of 202 mAh g⁻¹ at 0.2 A g⁻¹ and exceptional cyclability (90% capacity retention after 6000 cycles at 8 A g⁻¹). Moreover, the HAQ//α-MnO₂ full cell delivers a high specific capacity of 168 mAh g⁻¹ at 0.2 A g⁻¹ and retains 98% of its initial capacity after 5000 cycles at 2 A g⁻¹. A combined ex/in situ and DFT study reveals a two-step, six-electron NH₄⁺ storage mechanism regulated by reversible hydrogen bonding. This work provides an effective molecular design strategy to simultaneously enhance dissolution resistance and electronic conductivity in organic electrodes for advanced AAIBs.