Investigation on physiochemical properties of Mn substituted spinel cobalt oxide for supercapacitor applications

• For supercapacitor application, electrochemical characterization of manganese doped cobalt spinel oxide is reported for the first time.
• Mn ion hinders the crystallite growth and reduces agglomeration of crystallites in the electrode materials.
• Pseudocapacitive performance of cobalt oxide is enhanced by Mn doping.
• Manganese ion dissolution in electrolyte shortens the diffusion path for electrolyte ions during redox process.
• Specific current, specific capacitance and compound stability over long cycling increases with Mn addition.

Investigation on physiochemical properties and electrochemical performance of doped cobalt spinel oxide was carried by doping manganese ions into the cobalt oxide spinel system at various concentrations (5% - 20%) using co-precipitation method. The influence of Mn incorporation on the structure and physical properties of the cobalt oxide were investigated using XRD, FTIR and HRSEM. It was found that, with Mn addition unit cell volume increases and the crystallite growth of the electrode materials was hindered. Jahn teller distortion associated with Mn3+ ions has made the spinel lattice more compressible, aiding facile insertion/exertion of electrolyte ions. From SEM observations, compact agglomerates found in pure cobalt oxide changes to loosely packed agglomerates on Mn addition. From the XPS studies, manganese concentration in the doped samples were identified to be close to the initial doping percentage (MnxCo3-xO4; x = 4.61, 8.25, 14.13 & 18.10%). It also reveals the preferential octahedral occupancy of Mn3+ ions in cobalt oxide spinel lattice. Electrochemical characterization of as synthesized electrode materials was performed with cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). Specific current density of the electrodes increased with increasing Mn content for fixed scan rates. Specific capacitance (SC) values were calculated for the electrode materials from CV and CP. Electrode material doped with 20% Mn exhibits the highest SC of 440 Fg−1. Low equivalent series resistance (ESR) and reduced ion diffusion resistance was observed for Mn doped electrode materials. According to the results, 10% and 20% manganese doped cobalt oxide electrode materials demonstrates superior capacitive behavior than other prepared materials. Mn addition has improved the compound integrity on cycling and also increased the overall electrochemical performance of the electrode materials.