Al3+/H+ co-intercalation into hollow hexagonal cone manganese oxide for high-capacity and high-voltage aqueous aluminum-ion batteries

Aqueous aluminum–ion batteries (AAIBs) have attracted considerable attention owing to their high theoretical capacity, high safety, and low cost. However, as a strong Lewis acid, Al 3+ readily coordinates with the lone–pair electrons of water molecules, which significantly polarizes the O H bonds and promotes water dissociation and proton generation. The generated protons can cause severe corrosion of electrode materials, thereby limiting cycling stability and hindering practical applications. In this work, a novel manganese oxide cathode with a hollow hexagonal pyramidal layered nanostructure is successfully synthesized and coupled with 1 M Al₂(SO₄)₃ electrolyte containing 0.06 M K₂SO₄. In situ and ex situ characterizations reveal that the cathode delivers high capacity through a synergistic Al 3+ /H + co–intercalation and deintercalation mechanism. Importantly, the introduction of potassium sulfate induces the formation of a potassium aluminum sulfate passivation layer, which effectively suppresses acid−induced electrode corrosion and enhances cycling stability. As a result, the assembled battery achieves a high specific capacity of 354 mAh g −1 at 0.2 A g −1 and a high discharge voltage plateau of 1.7  V . At 0.5 A g −1 , it maintains 90% of its capacity (based on a maximum activated capacity of 188 mAh g −1 ) over 420 cycles. This work provides a facile and effective strategy for developing high–performance aqueous aluminum–ion batteries.