Unlocking the potential of ionic liquid-functionalized aqueous electrolytes for aqueous ammonium-bromine/ion batteries

Aqueous ammonium-ion batteries are promising candidates for grid-scale energy storage owing to their non-flammability, eco-friendliness, and low-cost. Nevertheless, their further development suffers from electrolyte/electrode instability and limited energy density. Herein, we develop an aqueous ammonium-bromine/ion battery composed of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) organic materials as the anode, Br2/Br− redox couple as the cathode, and ionic liquid-functionalized aqueous solution as the electrolyte. The experimental investigation and theoretical calculation results reveal that two organic cations (TPA+ and BMIM+) in the functionalized electrolyte can insert into the PTCDA anode with different intercalation chemistry, which enhances the reversibility of NH4+ storage. Furthermore, organic cations not only construct a hydrophobic interfacial layer to expel water molecules from the anode surface, but also stabilize the active species at the cathode side by forming a solid complexation phase. Consequently, the as-developed aqueous ammonium-bromine/ion batteries present satisfactory electrochemical performance at both room temperature and low temperature, which promotes its potential application in grid-scale energy storage.