Facile hydrothermal synthesis of carbon-coated cobalt ferrite spherical nanoparticles as a potential negative electrode for flexible supercapattery

Battery type electrodes would replace the currently available pseudocapacitive electrodes by the cause of high energy density and long discharge time. In this regard, battery type carbon coated CoFe₂O₄ spherical nanoparticles is prepared by the facile hydrothermal method and tested as the possible negative electrode for supercapattery applications. The phase purity, electronic states of elements, and the presence of carbon is inferred through various sophisticated techniques. The calculated surface area of CoFe₂O₄ and carbon coated CoFe₂O₄ are found to be 9 and 26 m² g^-1, respectively. The morphological analysis confirms the formation of uniform CoFe₂O₄ nanospheres (∼25 nm) with a thin layer of carbon coating (∼2 nm). The amorphous carbon coating over CoFe₂O₄ nanosphere is identified via high-resolution transmission electron microscope. The observed peak and plateau regions in the cyclic voltammogram and galvanostatic charge/discharge curves reveals the battery-type charge storage behaviour of the material. The carbon coated CoFe₂O₄ delivers the maximum length capacitance of 9.9 F m^-1 at 1 mV s^-1 with a useful lifespan over 5000 cycles. The electrochemical impedance spectroscopy reveals that the carbon-coated CoFe₂O₄ delivers the low charge transfer resistance than CoFe₂O₄. Further, the fabricated supercapattery provides the energy density of 160 × 10^-8 Wh cm^-1 at a power density of 67.2 μW cm^-1. As well as, the device shows 93% of coulombic efficiency and 75% of the specific capacitance retention over 11,000 cycles. Overall, it is believed that the carbon-coated CoFe₂O₄ can serve as a good candidate for flexible supercapatteries.