Design and synthesis of n-conjugated aromatic heterocyclic materials with dual active sites and ultra-high rate performance for aqueous zinc-organic batteries

Acid anhydride cathode materials garner considerable interest for aqueous zinc ion batteries (AZIBs) due to ideal specific capacity and structural diversity, however, serious solubility leads to capacity degradation. Herein, 1,4,5,8-naphthalene tetracarboxylic acid dianhydride - 2,3-diamino phenothiazine (NTDP) featuring multiple active sites (6 with C--N and 2 with C--O) and large pi-conjugated backbone, was designed and synthesized utilizing solid-phase method. The smallest energy gap (AE) and the lowest LUMO levels (against monomers) induced by multiple active sites and n-conjugated backbone with high aromaticity, NTDP exhibited excellent specific capacity (307.5 mA h g-1 under 0.05 A/g), ultrahigh rate performance (194.9 mA h g-1 under 20 A/g) and impressive cycling stability (190.0 mA h g-1 over 9000 cycles with a capacity retention of 91.2 % at 15 A/g). The reversible Zn2+ insertion/removal mechanism on multiple active centers (C--O and C--N) was proposed through XPS, FT-IR, and Raman. The specific capacity of the NTDP//zinc flexible cell was 112.6 mA h g-1 at 3 A/ g under various folding angles (45 degrees, 90 degrees, 135 degrees, and 180 degrees bends), suggesting its practical potential for flexible devices. This work will offer opportunities for the rational design of battery structures.