Boosting the Energy Density of Flexible Asymmetric Supercapacitor with Three Dimensional Fe₂O₃ Composite Brush Anode

Flexible asymmetric supercapacitor is fabricated with three dimensional(3D) Fe₂O₃/Ni(OH)₂ composite brush anode and Ni(OH)₂/MoO₂ honeycomb cathode. Particularly for 3D composite brush anode, a layer of thin Fe₂O₃ film is firmly adhered on a 3D Ni brush current collector with the assist of Ni(OH)₂, functioning as both adherence layer and pseudocapacitive active material. The unique 3D Ni brush current collector possesses large surface area and stretching architecture, which facilitate to achieve the composite anode with high gravimetric capacitance of 2158 F/g. In terms of cathode, Ni(OH)₂ and MoO₂ have a synergistic effect to improve the specific capacitance, and the resulting Ni(OH)₂/MoO₂ honeycomb cathode shows a very high gravimetric capacitance up to 3264 F/g. The asymmetric supercapacitor(ASC) has balanced cathode and anode, and exhibits an ultrahigh gravimetric capacitance of 1427 F/g and an energy density of 476 Wh/kg. The energy density of ASC is 3–4 times higher than those of other reported aqueous electrolyte-based supercapacitors and even comparable to that of commercial lithium ion batteries. The device also shows marginal capacitance degradation after 1000 cycles’ bending test, demonstrating its potency in the application of flexible energy storage devices.