Fabrication and performance evaluation of button cell supercapacitors based on MnO2nanowire/carbon nanobead electrodes

Abstract

The present study provides in detail experimental results on the synthesis and characterization of carbonized MnO₂ nanowires for fabricating large surface area, high power and energy density rechargeable electrodes for supercapacitor/battery applications. High aspect ratio MnO₂ nanowires carbonized with camphoric carbon composed of nanobeads were utilized for this purpose. The graphitic nature of these nanobeads was confirmed through Raman spectroscopy and X-ray photoelectron spectroscopy, where a predominance of sp² hybridization was observed. The relative contributions of the carbon nanobeads’ influence on the capacitive and diffusion controlled processes underlying these thin film electrodes have been mathematically modelled. The electrodes were fabricated into thin films (thickness ∼30 μm) by co-electrophoresis onto titanium foils exhibiting a surface area of ∼50 m² g⁻¹. CHN analyses revealed an electrophoretic co-deposition of carbon nanobeads along with MnO₂ nanowires onto the titanium foils. From the electrochemical studies, an intrinsic correlation between overall specific capacitance, electrode internal resistance and its conductivity has been defined and explained in different electrolyte systems. These electrodes exhibited specific mass capacitance values as high as 1200 ± 18 F g⁻¹. High cyclic stability was observed at the end of 10 000 cycles, which was attributed to the low oxide dissolution of ∼0.02 ppm in the electrolyte as measured by inductively coupled plasma atomic emission spectroscopy studies. Further, a working model of a button cell was also studied based on these thin film electrodes, which exhibited a capacitance of ∼1.2 F. These thin film electrodes exhibited an energy density of 96 Wh kg⁻¹ and a peak power density of 32 kW kg⁻¹.