An Aqueous Rechargeable Al‐Ion Battery Based on Cobalt Hexacyanoferrate and Al Metal

Abstract Like other aqueous batteries, aqueous rechargeable Al‐ion batteries (ARAIBs) have attracted much attention due to their high safety and low cost. However, the low energy density of ARAIBs limits its popularization and application. In order to solve this problem, in addition to choosing Al metal as the negative electrode, it is also necessary to choose a suitable positive electrode material. Here, a cubic phase cobalt hexacyanoferrate (CoHCF) with excellent rate and cycling performance is used as the positive electrode material. Due to the reversible catalysis of the Cl − /Cl 0 reaction at high potential in saturated AlCl 3 solution, it has the characteristics of high capacity up to 103.5 mAh g −1 . Combined with the Al metal as negative electrode, an ARAIB with an average discharge voltage of 1.56 V and an energy density of 155 Wh kg −1 is constructed, which shows outstanding cycling and rate performances.