The Role of Al ³⁺ ?Based Aqueous Electrolytes in the Charge Storage Mechanism of MnO <i> _x </i> Cathodes

Rechargeable aqueous aluminium batteries are the subject of growing interest, however, charge storage mechanisms at manganese oxide-based cathodes remain poorly understood. In essense, every study proposes a different mechanism. Here, an in situ spectroelectrochemical methodology is used to unambiguously demonstrate that reversible proton-coupled MnO2-to-Mn2+ conversion main mechanism occurring MnO2 for range slightly acidic Al3+-based electrolytes, with Al3+ hexaaquo complex playing key role proton donor. Zn/MnO2 assemblies, this associated high gravimetric capacities and discharge potentials, up 560 mAh g-1 1.65 V respectively, attractive efficiencies (CE > 99.5% EE 82%) excellent cyclability (almost 100% capacity retention over 1 400 cycles 2 A g-1). Finally, critical analysis data previously published on MnOx electrolytes conducted conclude universal mechanism, i.e., electrodissolution/electrodeposition MnO2.