Strengthen Water O−H Bond in Electrolytes for Enhanced Reversibility and Safety in Aqueous Aluminum Ion Batteries

Aqueous aluminum-ion batteries present a promising prospect for large-scale energy storage applications, owing to the abundance, inherent safety, and the high theoretical capacity of aluminum. However, their voltage output and energy density are significantly hindered by challenges such as complex hydrogen evolution and uncontrollable solvation reactions. In this work, we demonstrate that water decomposition is restrain by increasing the electron density of water protons and increasing the dissociation energy of H₂O through robust dipole interactions with highly polar dimethylformamide (DMF) molecules. Moreover, the incorporation of dimethyl methylphosphonate (DMMP) flame retardant effectively addresses the flammability risk arising from a substantial presence of organic additives The in-depth study with experimental and theoretical simulations reveals that the water-poor solvation structure with reduced water activity is achieved, which can (i) effectively mitigate undesired solvated H₂O-mediated side reactions on the Al anode; (ii) boost the de-solvation kinetics of Al³⁺ while preventing cathode structural distortion; (iii) reduce the flammability of hybrid electrolytes. As a proof of concept, the Al//Al_xMnO₂ full cell employing a hybrid electrolyte demonstrate enhanced stability (deliver 335 mAh g^-1 while retaining 71 % capacity for 400 cycles) compared to those with pure electrolyte.