Al-Intercalated MnO2 cathode with reversible phase transition for aqueous Zn-Ion batteries

Although manganese dioxide (MnO2) is of great promise as the cathode material for aqueous Zn-ion batteries (ZIBs), its capacity decreases sharply during cycles due to the irreversible phase transition and Mn dissolution, consequently hindering the large-scale practical application. Herein, for the first time, a novel Al-intercalation engineering of MnO2 cathode has been proposed for aqueous ZIBs, in which the structural regulation and Zn2+ storage performance of Al-intercalated MnO2 (denoted as AMO) cathode are deeply investigated. Electrochemical testing results indicate significant improvement in specific capacity (401.7 mAh g−1) and cycling retention (~94.5% over 2000 cycles) of the AMO cathode, which is owing to the effective Al-intercalation that result in the formation of strong Al-O bonds in tunnel-type MnO2 framework. This reasonable configuration not only optimizes charge/ion state and electronic bandgap, but also ensures reversible phase transition and alleviates the Mn dissolution of AMO cathode, which are further demonstrated by the density functional theory (DFT) calculations and in-situ Raman investigation upon charging-discharging. As a proof of concept, coin-type and flexible aqueous ZIBs based on such AMO cathode are effectively fabricated, and they both achieve excellent electrochemical behaviors, revealing the great potential applications in energy technologies and portable/wearable electronics.