An Anti-Aromatic Covalent Organic Framework Cathode with Dual-Redox Centers for Rechargeable Aqueous Zinc Batteries.

Abstract

Covalent organic frameworks (COFs) are promising cathode candidates with high structural stability. However, they contain redox inactive linkages and experience low redox potential. Herein, a full anti-aromatic microporous COF cathode material of TAQ-BQ is designed for aqueous zinc batteries. The anti-aromatic conjugation effectively lowers the energy level of the lowest unoccupied molecular orbital as revealed by theoretical calculations, which corresponds to an elevated redox potential. Besides, the structure contains imino active sites at the linkages, in addition to carbonyl at the active parts. As a result, the TAQ-BQ cathode exhibits a voltage of 1.53 V/1.54 V and between 1.35 and 0.45 V in zinc cells. It delivers 208 mAh g-1 capacity at 0.1 A g-1 and maintains 136 mAh g-1 at 2 A g-1. Stable cycling is realized for 1000 cycles with 87% capacity retention. The co-de/insertion of Zn2+ and protons is identified for energy storage. Our work reveals the promises of COF cathode materials for aqueous zinc batteries.