Improved Mn⁴⁺/Mn²⁺ Contribution in High‐Voltage Zn–MnO₂ Batteries Enabled by an Al³⁺‐Ion Electrolyte

Abstract

Rechargeable aqueous Zn–MnO2 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–MnO2 system with enhanced Mn4+/Mn2+ electrochemical contribution is introduced using an Al3+‐based electrolyte. Compared with conventional Zn2+ electrolytes, the hybrid Al3+/Zn2+ 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 Al3+‐enabled Zn–MnO2 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. Al3+ 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 Mn4+/Mn2+ reaction aided by H+ that dominates the capacitance at higher current rates. Overall, this work demonstrates a practical Zn–MnO2 battery with a high potential for low‐cost stationary energy storage habilitated by multiple ion co‐intercalation.