Hausmannite Mn3O4 as a positive active electrode material for rechargeable aqueous Mn‐oxide/Zn batteries

Batteries with manganese (di)oxide/zinc chemistry and aqueous‐based electrolytes have the potential to address energy storage demands of stationary applications primarily because of the abundant availability of Zn and Mn‐oxides, their intrinsic low cost, and the high specific/volumetric charge capacities. Herein, we report the use of Mn₃O₄ (hausmannite phase of manganese oxide) as the positive electrode material in a rechargeable near‐neutral Mn‐oxide/Zn battery configuration. Electrochemical investigations reveal that the hausmannite phase can activate for charge/discharge processes during the first 40 to 50 cycles and then a maximum capacity is obtained. This material shows excellent reversibility (~800 cycles) in keeping more than 65% of its maximum capacity. For the first time, the hausmannite activation mechanism was better understood under near‐neutral conditions. By using different characterization techniques (X‐ray powder diffraction [XRD], inductively coupled plasma‐optical emission spectrometry [ICP‐OES], X‐ray photoelectron spectroscopy [XPS], and energy dispersive X‐ray spectroscopy [EDS]) formation of Zn‐based compounds at the electrode surface was confirmed. One of the compounds formed is the layered double hydroxide (Zn₄SO₄[OH]₆ · 5H₂O) that forms as a side product. No direct evidence for intercalation of zinc ions was observed. Electrochemical experiments in different aqueous/organic electrolytes has shown that proton intercalation plays a significant role in the charge‐storage mechanism, while the activation process itself proceeds, most likely, through the formation of Zn‐species at the electrode surface.