Advanced asymmetric supercapacitors with a squirrel cage structure FeO@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 FeO@carbon nanocomposite. In this architecture, the carbonized crosslinked bovine serum albumin (C) will play critical roles, serving as a skeleton for the deposition of FeO and a transportation pathway like "high-speed rail" for electrons, maintaining the structural stability as well as accommodating the volume expansion of FeO and facilitating electron transportation and the electrolyte ion diffusion. The iron oxide nanoparticles (FeO) exhibit superior reversible redox characteristics, hence increasing the supercapacitor performance. Benefiting from a stable structure, an aqueous asymmetric supercapacitor using a CNT@Ni(OH) positive electrode (cathode) and FeO@C negative electrode (anode) has also been assembled, which presents a high energy density of 17.3 W h kg at a power density of 700 W kg. The strategy for choice of FeO@C composites will provide new opportunities for future supercapacitors with superior cyclability and high power density.