Mo2P2O11: A Potential Cathode Material for Rechargeable Sodium-Ion Batteries

Due to the limiting lithium reserve and increasing price of lithium, alternatives to Li-ion batteries are growing rapidly. The world is now focusing on developing electrodes beyond Li-ion-based rechargeable batteries for portable electronics. Iron, nickel, and Co-based NASICON structured materials give stable capacity with reversible intercalation of almost one sodium in the host lattice. In the current work, we suggest a cathode material made of 3D framework-structured molybdenum polyanionic phosphate (Mo2P2O11) for a reversible sodium-ion battery. Mo2P2O11 was synthesized using the heat treatment of the MoO2HPO4·H2O precursor at 560 °C, having the morphology of stacked flakes. Characterization techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive X-ray were utilized for confirming the structure and morphology of the materials. For electrochemical performance, cyclic voltammetry, charge–discharge, and stability tests have been performed. Mo2P2O11 work through the active participation of the Mo6+/4+ redox couple with reversible intercalation of Na+ ions. The electrode exhibits reversible intercalation at 3.0 V versus Na and a steady capacity of ∼90 mA h/g, that is, ∼1.4 Na per formula unit, achieving a Coulombic efficiency of nearly 100%. The current finding opens up a new route for using transition-metal phosphates as efficient and stable charge storage cathode materials for sodium-ion batteries.