Ionic-Liquid-Assisted Synthesis of Mixed-Phase Manganese Oxide Nanorods for a High-Performance Aqueous Zinc-Ion Battery

Aqueous zinc-ion batteries (ZIBs) provide a safer andcost-effectiveenergy storage solution by utilizing nonflammable water-based electrolytes.Although many research efforts are focused on optimizing zinc anodematerials, developing suitable cathode materials is still challenging.In this study, one-dimensional, mixed-phase MnO2 nanorodsare synthesized using ionic liquid (IL). Here, the IL acts as a structure-directingagent that modifies MnO2 morphology and introduces mixedphases, as confirmed by morphological, structural, and X-ray photoelectronspectroscopy (XPS) studies. The MnO2 nanorods developedby this method are utilized as a cathode material for ZIB applicationin the coin-cell configuration. As expected, Zn//MnO2 nanorodsshow a significant increase in their capacity to 347 Wh kg(-1) at 100 mA g(-1), which is better than bare MnO2 nanowires (207.1 Wh kg(-1)) synthesized bythe chemical precipitation method. The battery is highly rechargeableand maintains good retention of 86% of the initial capacity and 99%Coulombic efficiency after 800 cycles at 1000 mA g(-1). The ex situ XPS, X-ray diffraction, and in-depthelectrochemical analysis confirm that MnO6 octahedra experienceinsertion/extraction of Zn2+ with high reversibility. Thisstudy suggests the potential use of MnO2 nanorods to develophigh-performance and durable battery electrode materials suitablefor large-scale applications.