Hausmannite Mn 3 O 4 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.