Ultra-high rate capability of nanoporous carbon network@V2O5 sub-micron brick composite as a novel cathode material for asymmetric supercapacitors

Abstract

A green biomass-derived nanoporous carbon network (NCN) has been prepared and integrated with V₂O₅ sub-micron bricks (SMBs). The large surface area and high pore volume of the NCN can not only provide abundant sites for electrochemical reactions but also stabilize the structure of the V₂O₅ SMBs. The NCN@V₂O₅ SMB composite, acting as a novel cathode material, delivers a high areal capacitance of 786 mF cm⁻² at 0.2 mA cm⁻² and superior cycling stability with 89.5% capacitance retention after 5000 cycles. Besides, the electrode achieves an ultra-high rate capability (82% capacitance retention as the current density increases from 0.2 to 5 mA cm⁻²) since the contribution from the non-diffusion-controlled process is estimated to be as high as 95.5%–98.5% according to the kinetic analysis. Furthermore, the micropores are more favorable than the mesopores at lower current densities (0.2–2 mA cm⁻²), while the contribution of the external surface area becomes more significant for current densities higher than 2 mA cm⁻². Moreover, an asymmetric supercapacitor assembled using this cathode and the NCN anode shows superior electrochemical properties, such as wide operating voltage, long cycle life and large energy density (72.2 μW h cm⁻²). Their excellent electrochemical features and good eco-friendliness confirm the potential of the NCN@V₂O₅ SMBs for use as supercapacitors.