Advanced asymmetric supercapacitors with a squirrel cage structure Fe₃O₄@carbon nanocomposite as a negative electrode

Carbon materials have been used as negative electrodes for supercapacitor applications; nevertheless, owing to the low capacitance, they have limited ability to enhance the supercapacitor electrochemical properties. Here, we employ a facile chemical precipitation method for preparing a squirrel cage structure Fe₃O₄@carbon nanocomposite. In this architecture, the carbonized crosslinked bovine serum albumin (C) will play critical roles, serving as a skeleton for the deposition of Fe₃O₄ and a transportation pathway like "high-speed rail" for electrons, maintaining the structural stability as well as accommodating the volume expansion of Fe₃O₄ and facilitating electron transportation and the electrolyte ion diffusion. The iron oxide nanoparticles (Fe₃O₄) exhibit superior reversible redox characteristics, hence increasing the supercapacitor performance. Benefiting from a stable structure, an aqueous asymmetric supercapacitor using a CNT@Ni(OH)₂ positive electrode (cathode) and Fe₃O₄@C negative electrode (anode) has also been assembled, which presents a high energy density of 17.3 W h kg^-1 at a power density of 700 W kg^-1. The strategy for choice of Fe₃O₄@C composites will provide new opportunities for future supercapacitors with superior cyclability and high power density.