Advanced asymmetric supercapacitors based on CNT@Ni(OH)2 core–shell composites and 3D graphene networks

Abstract

Asymmetric supercapacitors (ASCs) with carbon nanotube@nickel hydroxide nanosheet (CNT@Ni(OH)₂) core–shell composites as positive electrodes and three-dimensional (3D) graphene networks (3DGNs) as negative electrodes were reported in aqueous KOH electrolyte. The CNT@Ni(OH)₂ core–shell composites were prepared through a facile chemical bath deposition method, while 3DGNs were obtained by freeze-drying of graphene hydrogels. By virtue of their unique microstructures, superb electrochemical properties were achieved in a three-electrode system, e.g., 1136 F g⁻¹ at 2 A g⁻¹ for the CNT@Ni(OH)₂ electrode within 0–0.5 V and 203 F g⁻¹ at 1 A g⁻¹ for the 3DGN electrode within −1–0 V. Benefiting from these merits, the as-fabricated CNT@Ni(OH)₂//3DGN ASC showed a maximum energy density of 44.0 W h kg⁻¹ at a power density of 800 W kg⁻¹ and even retained 19.6 W h kg⁻¹ at 16 000 W kg⁻¹ in the voltage region of 0–1.6 V.