Impedance studies of biosynthesized Na0. 8Ni0 . 33Co0 . 33Mn0 . 33O2 applied in an aqueous sodium‐ion battery

We studied Na0.8Ni0.33Co0.33Mn0.33O2 nanoparticles synthesized using water-based extract procured from the dried silk of maize (Zea mays lea) plant. The synthesized Na0.8Ni0.33Co0.33Mn0.33O2 was used as the positive electrode in an aqueous sodium ion battery (SIB). X-ray diffraction (XRD) studies of the biosynthesized material reveal that it can be indexed to the trigonal structure of Na0.8Ni 0.33Co0.33Mn0.33O2 with an R 3m space group (160), (ICSD 184736) although impurities of Mn2O3 and NiO were detected. Surface morphological studies from a scanning electron microscope (SEM) disclose that the nanoparticles consist of an interspersion of sheath-like particles with quasi-spherical nanoparticles of uneven dimensions. The sheath-like particles seem to agglomerate to form layers that coalesce into flower-like structures that are spread within the quasi-spherical nanoparticles. The material yielded a rechargeable discharge capacity of about 86 mA h g−1 in a three-electrode system consisting of platinum, the Na0.8Ni0.33Co0.33Mn0.33O2 and Ag/AgCl as the counter, working and reference electrodes respectively at a current density of 10 mA g−1. However, a full cell using P25 Degussa TiO2 and the biosynthesized Na0.8Ni0.33Co0.33Mn0.33O2 as the negative and the positive electrode, respectively, and having a mass ratio of 1:1 yielded a discharge capacity of 49 mA h g−1 at a current density of 5 mA g−1. Impedance studies for a symmetrical cell developed showed that the magnitude of the impedance is highest at 0% and 100 state of charge (SOC).