Synthesis and electrochemical studies of NaCoPO₄ as an efficient cathode material using natural deep eutectic solvents for aqueous rechargeable sodium-ion batteries.

Abstract

In this work, sodium cobalt phosphate (NaCoPO₄) was successfully prepared by a cost-effective ionothermal method using a deep eutectic solvent (DES) for the first time. The synthesized NaCoPO₄ was used to fabricate a cathode material for aqueous rechargeable sodium-ion batteries. The surface morphology of the prepared materials and its compositional analysis were done by using field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray (EDX) analysis, respectively. The X-ray diffraction (XRD), SEM, and EDX studies revealed that the material has orthorhombic-shaped particle morphology with uniform distribution and is in nanoscale (approximately 50 nm). The nature of the cation inserted (Na⁺ ion insertion) was confirmed by recording CV profiles at different concentrations of the Na₂SO₄ electrolyte. The reversibility of the electrode redox reaction was studied by varying the scan rate in CV studies, and it was found that the electrode exhibits a reversible behavior with a resistive behavior. In GCPL studies, the cell TiO₂/2MNa₂SO₄/NaCoPO₄ showed significant reversibility with a prominent discharge capacity of 85 mAh g^-1 at 0.1°C and 88% of capacity retention after 100 cycles. Thus, the prepared materials could be used as an effective futuristic alternative battery material for rechargeable batteries.