An Aqueous Al-Ion Battery Boosted by Triple-Ion Intercalation Chemistry with a High-Energy MnAl <sub>2</sub>O <sub>4</sub> Nanosphere Cathode

Abstract

AlCl3 water-in-salt electrolyte has successfully expanded the electrochemical window of aqueous Al-ion battery to 4 volts, however, the limited Al intercalation capacity of graphite (165 mAh g-1 ) preclude higher energy density. A high-energy MnAl2O4 cathode was synthesized by a simple two-step hydrothermal method, which can utilize triple-ion intercalation chemistry to achieve a high specific capacity of 330 mAh g-1 with an average discharge voltage of 1.68V versus Al/Al3+ (a record energy density of 555 Wh kg-1 ). Besides, a higher discharge capacity of 830 Wh kg-1 was achieved with higher-concentration electrolyte, showing a potential capacity for cation intercalation. Unique triple-ion intercalation chemistry was firstly investigated thoroughly. Experimental characterization attributes this high voltage to the intercalation of anions, e.g., AlCl4- and Cl- , and Cl- was also revealed an interaction function with intercalated Al3+ cations, which can benefit the design of Aluminium-ion batteries (AIBs) in the future.