Epitaxial oriented growth of LDH on Few-Layer graphene/microporous carbon heterostructure sheets for asymmetric supercapacitor application

Abstract

To meet high energy density of asymmetric supercapacitors (ASCs) application, transition metal layered double hydroxide (NiCo-LDH) emerges as a potential cathode material due to high specific capacitance (Cs) from reversible redox and wide voltage window. But sluggish reaction kinetics, poor cycling stability, and poor conductivity limit its application. To improve its electrochemical properties, the few-layer graphene/microporous carbon (FLG/MPC) heterostructure sheet skeleton, which has excellent electrical conductivity, high specific surface area and good hydrophilicity, has been firstly synthesized by one-pot method. The three-dimensional FLG/MPC@LDH-KAc composite sheet network was obtained by epitaxial oriented growth of the NiCo-LDH nanocrystals on the FLG/MPC heterostructure sheets by a hydrothermal process with the assistance of KAc. The epitaxial oriented growth of NiCo-LDH significantly lowers the contact impedance between NiCo-LDH nanocrystals and substrate, and improves structure stability of FLG/MPC@LDH-KAc electrode. The FLG/MPC@LDH-KAc electrode shows high Cs of 1950F/g at 0.5 A/g, and 1384F/g at 20 A/g with a retention of 71.0%. It is noticeable that the ASC consisting of FLG/MPC@LDH-KAc anode and FLG/MPC cathode delivers high energy density of 87.11 Wh kg−1 at the power density of 800 W kg−1 and still maintains 48.89 Wh kg−1 at 16000 W kg−1. These are much higher than those of the reported NiCo-LDH-based ASCs. Furthermore, the ASC maintains 87.6% of the initial Cs after 5000 cycles at 5 A/g, indicating excellent cycling stability. The mechanism behind these phenomena was investigated.