One-Dimensional π-d Conjugated Conductive Metal-Organic Framework with Dual Redox-Active Sites for High-Capacity and Durable Cathodes for Aqueous Zinc Batteries.

Aqueous Zn-based batteries (ZIBs) possess huge advantages in terms of high safety, low cost, and environmental friendliness. However, the lack of suitable cathodes with high-capacity, long-cycling, and high-rate capability limits their practical application. Herein, we present a highly crystalline one-dimensional π-d conjugated conductive metal-organic framework by coordinating ultrasmall 1,2,4,5-benzenetetramine (BTA) linkers with copper ions (Cu-BTA-H), as a cathode for ZIBs. The large ratio of active sites and dual redox mechanism of Cu-BTA-H, including the one-electron-redox reaction over copper ions (via Cu 2+ /Cu + ) and the two-electron-redox reaction over organic ligands (via C═N/C-N), effectively enhance its reversible capacity. Meanwhile, the abundant porosity, small band gap, high crystallinity, and stable coordination structure of Cu-BTA-H endow it with fast ion/electron transport and effectively hinder the dissolution of organic ligands during cycling, respectively. Consequently, Cu-BTA-H possesses a high reversible capacity of 330 mAh g -1 at 200 mA g -1 and excellent rate performance and long-cycle stability, with a high capacity of 106.1 mAh g -1 at 2.0 A g -1 after 500 cycles and a high Coulombic efficiency of ∼100%. The proposed conductive MOFs with dual redox-active sites provide an efficient approach for constructing fast, stable, and high-capacity energy storage devices.