Solvothermal Self-Assembly of Hollow Square-Tubular Polyimides for Aqueous Batteries

In this study, a straightforward and environmentally benign solvothermal method for synthesizing hollow square-tubular polyimides (HST-PIs) is introduced. The process utilizes 1,4,5,8-naphthalenetetracarboxylic anhydride and urea as reactants, replacing traditional toxic organic solvents with water and ethanol. This investigation explores the effects of various reaction conditions, such as the water-to-ethanol volume ratio, reaction time, and temperature, on product morphology, resulting in distinct structures like sheets, columns, and layers. Notably, hollow square-tubular polyimides (HST-PIs) are synthesized under specific conditions: a 2:1 water-to-ethanol volume ratio, 24 h reaction time, and 200 °C temperature. This study attributes self-assembly to three primary non-covalent interactions: hydrogen bonding, π-π stacking, and hydrophobic interactions. The gel permeation chromatography (GPC) analysis indicates that the PIs molecular weight predominantly ranges from 10 000 to 15 000. As an electrode material, hollow square tubular polyimides (HST-PIs) exhibit an initial discharge capacity of 297.9 mAh·g^-1 at a current rate of 0.1 C, with a coulombic efficiency of 79%. After ten cycles, the coulombic efficiency improves to 97% and maintains above 98% in the subsequent cycles. This study presents an innovative and environmentally friendly method for the molecular self-assembly of hollow tubular organic polymers.