"-NH-" Homologation Driven Self-Exfoliated Bipolar Covalent Organic Nanosheet as Dual-Ion Binding Anode for High-Performance Aqueous Zinc-Based Dual-Ion Battery.

Rechargeable aqueous zinc-ion batteries (AZIBs) offer safe, low-cost, and sustainable alternatives to lithium-ion systems. However, dendritic Zn growth downgrades Coulombic efficiency and cycling stability, limiting their practical deployment. Replacing Zn-metal anodes with reversible organic anodes capable of efficient Zn2+ storage with average discharge voltage below 0.6 V (vs Zn/Zn2+) is superior yet challenging. Herein, we report a self-exfoliated bipolar few-layer polyimide-based covalent organic nanosheet (tht-NDA-PI-CON) as anode, synthesized via solvent-free organic flux route using "-NH-" homologation strategy, which promotes self-exfoliation by introducing structural flexibility while simultaneously generating electron-rich sp3-NH centres, acting as electronic buffer in between carbonyl and triazine units constructing a bipolar framework, enabling low-energy barrier dual-ion binding kinetics. The porous nanosheet, enriched with redox centres delivers 185 mAh g-1 at 0.2 A g-1 (84.6% contributes from single discharge plateau), high-rate capability (78.6% retention/5 A g-1), and 81% capacity retention over 5000 cycles. Ex situ analyses and first-principles calculations reveal Zn2+ coordination with carbonyl and triazine sites during discharge, while SO4 2- is stabilized by homologated -NH- unit upon charging. When paired with MnO2, full cell delivers record energy density of 82.73 Wh kg-1 with 84.8% capacity retention over 3000 cycles, demonstrating its potential for next-generation Zn-based dual-ion battery technologies.