Valence-controlled manganese oxide by solvent-assisted permanganate reduction for advanced aqueous zinc-ion batteries

Manganese oxide-based cathodes (MnOx) play a pivotal role in advancing aqueous Zinc-Ion batteries (AZIB) due to their high theoretical capacity, low cost and environmental friendliness. However, given the MnOx's diverse structural, valence and textural properties, it is challenging to pinpoint the ideal manganese oxide material type and optimize simple and tunable synthesis routes to achieve great capacity retention and rate capability properties. In this work, we develop for the first time a synthesis method controlling the crystallization pathways and valence properties of MnOxmaterials through permanganate reduction using different reducing agents (Ethanol and Propanal) followed by heat treatment under 500 °C, thus achieving the synthesis of multivalent E500-MnOx(MnO2) and Trivalent P500-MnOx(Mn2O3). As cathode materials in AZIB, P500-MnOxreached a specific capacity of 315 mAh·g−1without any apparent capacity decay, while E500-MnOxshowed a lower specific capacity of 150 mAh·g−1at 100 mA·g−1with a capacity retention of only 65 %. Through Ex-Situ XRD and SEM imaging, P500-MnOxexhibited a reversible cycling mechanism compared to its E500-MnOxcounterpart which had preoccupied insertion sites.