High-capacity π-conjugated organic anode with multielectron redox for zinc-metal-free zinc-ion batteries

Aqueous zinc-ion batteries (ZIBs) features prominently in virtue of their high theoretical capacity, reliable security, eco-friendliness and excellent rate capability. However, conventional zinc anodes suffer from the poor reversibility and unsatisfactory cycle durability due to the serious dendrite growth and parasitic side reactions, becoming a huge technological challenge to their commercial applications. Herein, a redox-active π-conjugated molecule, 2,2′,2’’-(benzene-1,3,5-triyl)tris (1H-naphtho [2,3- d ]imidazole-4,9-dione) (BTHI), is designed as substitute for Zn-metal anode. The BTHI electrode shows a high reversible capacity of 342 mAh g −1 at 0.1 A g −1 (approaching its theoretical capacity of 362 mAh g −1 , 9 electrons transfer), along with rapid kinetics for charge storage. Both ex-situ spectroscopy characterizations and electrochemical experiments demonstrate reversible H + /Zn 2+ co-insertion/extraction behaviors in the BTHI electrode. The density-functional theory (DFT) simulation results further indicate that H + insertion is thermodynamically favored over Zn 2+ uptake and reveal that protons are first inserted into six carbonyl groups , followed by the C N bonds of three imidazole subunits. By pairing the BTHI anode with copper hexacyanoferrate (CuHCF) cathode, a Zn-metal-free BTHI//CuHCF full cell is assembled, which delivers a record high capacity (315 mAh g −1 at 1 A g −1 ), outstanding rate performance (207 mAh g −1 at 10 A g −1 ), and remarkable cycling durability (71.9 % capacity retention rate after 1000 cycles at 10 A g −1 ).