Bio-synthesized P2-Na0.57CoO2 nanoparticles as cathode for aqueous sodium ion battery

Abstract

We used aqueous extract obtained from the dry silk of Zea mays lea plant to synthesize Na 0.57 CoO 2 nanoparticles and studied same for use as cathode in aqueous Na ion battery (SIB). Structural characterizations by X-ray diffraction (XRD) show that the Na 0.57 CoO 2 can be indexed to the hexagonal structure of the P 63/mmc (no 194) space group with P2 packing phase. The scanning electron microscope (SEM) micrograph of the Na 0.57 CoO 2 nanoparticles (NPs) revealed an agglomerated sheet-like NPs of various sizes mixed with smaller sized spherical and quasi spherical NPs with uneven dimensions. Charge and discharge capacities of about 68 and 57 mA h g −1 were respectively obtained when cycled at a C-rate of 0.7C using the bio synthesized Na 0.57 CoO 2 and activated carbon as the positive and negative electrode and respectively. The cell retained about 79% of its inceptive capacity at the end of 1000 charge-discharge cycles and maintained about 98% Coulombic efficiency from the 200th to the 1000th cycle when cycled at C-rate of 7C. Hence, the bio-synthesized Na 0.57 CoO 2 NPs is a prospective positive electrode material for SIB. • P2-Na 0.57 CoO 2 nanoparticles were bio-synthesized using aqueous extract from by Zea mays L, dry silk. • Morphological studies reveal that the bio synthesized P2-type Na0.57CoO2 NPs have a nano-sheet-like structure with some distribution of smaller sized spherical and quasi-spherical shaped NPs. • A full cell using developed using the Na 0.57 CoO 2 NPs and activated carbon as positive and negative electrode gave a charge and discharge capacity of about 68 and 57 mA h g -1 respectively.