A Carboxyl-Functionalized Hexaazatrinaphthylene Small-Molecule Organic Electrode with Ultralong Life for Sodium-Ion Batteries

Organic electrode materials (OEMs) have been emerging as highly promising candidates for sodium-ion batteries (SIBs) due to their unique features such as structural diversity, tunable molecular design, cost efficiency, and high energy density. However, the widespread application of many small-molecule organic electrodes is limited by their severe dissolution behavior when they are used in conventional liquid electrolytes. In this research, a carboxyl-functionalized hexaazatrinaphthylene small molecule (HATN-COOH) with a symmetric planar aromatic structure and abundant electrochemically active groups (six C═N bonds and six C═O bonds) was designed and prepared as an anode material for SIBs. Benefiting from strong π–π stacking interactions and intermolecular hydrogen bonds, the lowly dissoluble HATN-COOH demonstrated a high reversible capacity of 283 mAh g–1 at 0.1 A g–1 and ultralong life after 8000 cycles at 1 A g–1 based on a multistep reversible redox reaction mechanism. Density functional theory (DFT) calculation, combined with ex situ X-ray photoelectron spectroscopy (XPS) and ex situ Fourier transform infrared spectroscopy (FT-IR) confirmed that a highly reversible 12-electron redox mechanism was realized by inserting two-stage sodium ions into the nitrogen site and sodium ions into the oxygen site. This work presents a promising organic electrode material by the rational design of redox-active small-molecule organic electrodes with both strong π–π stacking and hydrogen bond interactions.