Two-Dimensional π-d Conjugated Conductive Metal-Organic Framework with Triple Active Centers as High-Performance Cathodes for Flexible Zinc Batteries.

Conductive metal-organic frameworks (C-MOFs) have received extensive interest in high-performance zinc-ion batteries (ZIBs) owing to multi-redox sites and high electrical conductivity. Here, we present a π-d C-MOF by coordinating 2,3,5,6-tetraaminobenzoquinone (TABQ) ligands with Cu ions (2D Cu-TABQ) acting as cathodes for ZIBs. Benefiting from a triple active center (Cu, C=O, and C=N), 2D Cu-TABQ shows an ultra-high reversible capacity of 297.7 mAh g at 0.2 A g. Meanwhile, 2D Cu-TABQ also has superior cycle stability with a capacity of up to 98.2 mAh g after 1000 times at 2.0 A g. Considering the instability of the ligand bonds of C-MOFs in aqueous electrolytes, this work uses gel electrolytes to reduce the dissolution of organic ligands into the electrolyte, thus suppressing the shuttle effect, significantly improving the cycling stability of 2D Cu-TABQ. The flexible battery assembled by 2D Cu-TABQ shows excellent capacity retention (64.4 %) after 50 times at 0.2 A g, which is significantly better than 36.4 % in the common electrolyte, as well as outstanding bending resistance and electrochemical properties at different folding angles. This investigation will highlight the electrochemical application of C-MOFs in flexible zinc ion batteries and offer novel ideas for the structural design of cathodes with multiple active centers.