Improved Mn 4+ /Mn 2+ Contribution in High‐Voltage Zn–MnO 2 Batteries Enabled by an Al 3+ ‐Ion Electrolyte

Abstract Rechargeable aqueous Zn–MnO 2 batteries are attracting attention as a cost‐effective and safe energy storage solution, but their commercialization faces challenges due to limited stability, output voltage, and energy density. Herein, a hybrid‐ion Zn–MnO 2 system with enhanced Mn 4+ /Mn 2+ electrochemical contribution is introduced using an Al 3+ ‐based electrolyte. Compared with conventional Zn 2+ electrolytes, the hybrid Al 3+ /Zn 2+ cell offers higher output voltage of 1.75 V, capacities up to 469 mAh g −1 , and outstanding energy densities up to ≈730 Wh kg −1 at 0.3 A g −1 . Besides, the Al 3+ ‐enabled Zn–MnO 2 battery shows 100% capacity and energy density retention after 10,000 cycles at 2 A g −1 . Even at a high mass–loading of 6.2 mg cm −2 , a capacity of ≈200 mAh g −1 is maintained for over 100 cycles. This outstanding performance is related to the contribution of different intercalation and reaction mechanisms, as proved by the combination of electrochemical analysis and ex‐situ x ‐ray diffraction characterization of the cells at different discharge stages. Al 3+ ions, as Lewis strong acid, contribute to capacity in two significant ways: through a highly reversible intercalation/de‐intercalation that substantially boosts capacitance at low current rates, and promoting the Mn 4+ /Mn 2+ reaction aided by H + that dominates the capacitance at higher current rates. Overall, this work demonstrates a practical Zn–MnO 2 battery with a high potential for low‐cost stationary energy storage habilitated by multiple ion co‐intercalation.