Development of bixbyite microdice fabricated cathode for aqueous rechargeable zinc ion batteries†

Abstract

In this study, an ultrasonic-aided reverse micelle formation, followed by the calcination route, was developed for the synthesis of bixbyite microdice aimed at the fabrication of a cathode for ARZIBs. The prepared product was Mn₂O₃ having crystallinity and grain size of 65.12% and 25.61 nm, respectively, with a small percentage of other Mn-based oxides within it. The FESEM image showed dice like microsized Mn₂O₃, revealing the possible formation of a reverse micelle core of approximately 500 nm. XPS narrow spectra revealed the presence of Mn³⁺ in a mixture of Mn with +2 and +4 oxidation states. The crystal planes from the TEM images matched with XRD results and strengthened the formation of bixbyite Mn₂O₃ nanoparticles. The optical band gap of 3.21 eV specified the semiconducting property of the prepared Mn₂O₃, and therefore, the prepared Mn₂O₃ was used as a cathode material in a CR-2032 coin cell of ARZIBs. CV showed a reversible reaction within the cell, indicating the (de)intercalation of Zn²⁺ ions between the anode and cathode. The fresh cell showed high conductivity and low resistance compared with the used cell after BCD testing, confirmed by EIS. The cell delivered high specific discharge capacities of 293.59 ± 4.75 and 252.10 ± 4.66 mA h g⁻¹ at applied current densities of 0.1 and 0.3 A g⁻¹, respectively. Consequently, BCD was performed for 1000 cycles at a current density of 0.3 A g⁻¹. Throughout the cycling, the capacity retention and coulombic efficiency were maintained at 90.35 ± 0.30% and 98.44 ± 0.27%, respectively, suggesting the resilient reversibility of charging and discharging.