Green Plasma Enhanced Synthesis of Multi-Phase NiMnO₃ Cathode for Aqueous Zn-Ion Batteries

Rechargeable Zn-ion batteries have the potential to address the need for cheap and widely accessible energy storage. Metal-doped manganese oxide cathodes are a common and effective choice for Zn-ion batteries. Zn-ion battery development can be advanced by overcoming the poor cycle life that many metal-doped Mn-oxide cathodes suffer from. Plasma-treated water (PAW) is created using low input power of 0.145 kWh per liter of PAW and is used to accelerate the reduction and precipitation of MnO 4 − and nickel acetate (Ni(Ac)) to form a multiphase NiMnO 3 electrode with Ni 2+ and Ni 3+ doped into the MnO 6 octahedra, which exhibits capacitance dominated charge storage mechanisms. The electrode shows initial specific capacitance of 60.1 F g −1 and a capacitance retention of 100.8% after 10,000 cycles and 92.2% after 12,000 cycles. The beneficial layer of nanoflake morphology is formed during cycling, which causes a rapid increase in specific capacitance due to the larger electrochemically active surface area and the associated surface adsorption-based (pseudo-capacitive) type charge storage. We also demonstrate the capability of our multiphase NiMnO 3 electrode to be coupled with a Zn metal anode in a battery cell which exhibits 330 mAh g −1 peak specific capacity and capacity retention of 63.8% after 380 cycles.