Anode‐Free Aqueous Aluminum Ion Batteries

Abstract Aqueous aluminum ion batteries (AAIBs) possess the advantages of high safety, cost‐effectiveness, eco‐friendliness and high theoretical capacity. However, the Al 2 O 3 film on the Al anode surface, a natural physical barrier to the plating of hydrated aluminum ions, is a key factor in the decomposition of the aqueous electrolyte and the severe hydrogen precipitation reaction. To circumvent the obnoxious Al anode, a proof‐of‐concept of an anode‐free AAIB is first proposed, in which Al 2 TiO 5 , as a cathode pre‐aluminum additive (Al source), can replenish Al loss by over cycling. The Al‐Cu alloy layer, formed by plating Al on the Cu foil surface during the charge process, possesses a reversible electrochemical property and is paired with a polyaniline (cathode) to stimulate the battery to exhibit high initial discharge capacity (175 mAh g −1 ), high power density (≈410 Wh L −1 ) and ultra‐long cycle life (4000 cycles) with the capacity retention of ≈60% after 1000 cycles. This work will act as a primer to ignite the enormous prospective researches on the anode‐free aqueous Al ion batteries.