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

Aqueous zinc-ion batteries (ZIBs) provide a safer and cost-effective energy storage solution by utilizing nonflammable water-based electrolytes. Although many research efforts are focused on optimizing zinc anode materials, developing suitable cathode materials is still challenging. In this study, one-dimensional, mixed-phase MnO₂ nanorods are synthesized using ionic liquid (IL). Here, the IL acts as a structure-directing agent that modifies MnO₂ morphology and introduces mixed phases, as confirmed by morphological, structural, and X-ray photoelectron spectroscopy (XPS) studies. The MnO₂ nanorods developed by this method are utilized as a cathode material for ZIB application in the coin-cell configuration. As expected, Zn//MnO₂ nanorods show 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 by the chemical precipitation method. The battery is highly rechargeable and 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-depth electrochemical analysis confirm that MnO₆ octahedra experience insertion/extraction of Zn²⁺ with high reversibility. This study suggests the potential use of MnO₂ nanorods to develop high-performance and durable battery electrode materials suitable for large-scale applications.