Fast Aqueous Aluminum Ion Storage Enabled by a Triazine-Containing Polyimide Anode

Triazine-based polyimide anode (PI NA ) synthesized from melamine and NTCDA. • Reversible capacity maintained over 0.1-3.2 A·g -1 in Al 2 (SO 4 ) 3 electrolyte. • Fast surface-controlled charge storage contributes up to 78% of total capacity. • Ion diffusion coefficients reach 10 -9 -10 -10  cm 2 ·s -1 , supporting rapid kinetics. • 4-hydroxy-TEMPO//PI NA full cell shows stable cycling and practical fast-charging operation. Aqueous batteries are attractive for safe and cost-effective energy storage owing to their intrinsic nonflammability and high ionic conductivity. However, their high-rate performance is often restricted by sluggish electrode kinetics and interfacial polarization. Herein, a triazine-containing polyimide negative electrode, denoted as PI NA , was synthesized from melamine and 1,4,5,8-naphthalenetetracarboxylic dianhydride, and its electrochemical behavior was evaluated in a series of aqueous electrolytes. Among the electrolytes examined, 1 mol·L -1 Al 2 (SO 4 ) 3 provided the most balanced electrochemical response, combining reversible capacity, Coulombic efficiency, and cycling stability. At a current density of 3.2 A·g -1 , PI NA exhibited a capacity retention of 75.7%. Kinetic analyses revealed a substantial surface-controlled capacitive contribution and apparent chemical diffusion coefficients on the order of 10 -10 -10 -9 cm 2 ·s -1 , consistent with its rapid charge-storage response under the tested conditions. A 4-hydroxy-TEMPO//PI NA aqueous full cell was further assembled as a proof of concept. The cell operated between 0 and 1.0 V and exhibited a median discharge voltage of approximately 0.44 V at 500 mA·g -1 , together with reversible rate behavior and cycling performance. A smartwatch demonstration further showed that the charged cell could provide short-term electrical output. These results highlight the importance of matching polyimide redox chemistry with the ionic and solvation environment of aqueous Al-containing electrolytes. Schematic diagram of the preparation process and electrochemical performance evaluation of the PI NA negative electrode. Download: Download high-res image (254KB) Download: Download full-size image