Electrochemical investigation on high-rate properties of graphene nanoplatelet-carbon nanotube hybrids for Li-ion capacitors

Li-ion capacitors (LICs) are considered a bridging electrochemical energy device between Li-ion batteries and supercapacitors. Graphene nanoplatelet (GNP)-carbon nanotube (CNT) hybrid materials can be a good candidate for negative electrode materials used in LICs. The rate performance of LIC negative electrodes plays a key role in increasing the power density of LICs. In this study, the Li storage kinetics of a GNP-CNT hybrid electrode was investigated. CNTs were directly grown on the GNP surfaces through chemical vapor deposition via transition metal oxide seeding. Natural graphite, GNP, and mixture (GNP and CNT) electrodes were used as the control electrodes. The kinetics was evaluated using electrochemical analysis tools such as galvanostatic charge-discharge cycling at various current densities, cyclic voltammetry, galvanostatic intermittent titration technique, and electrochemical impedance spectroscopy. The results revealed that the direct growth of CNTs on the GNP surfaces led to strong contact between these materials. This contact could play a pivotal role in the improvement of reversible Li storage kinetics characterizing negative electrodes for high-power LICs. (C) 2020 Elsevier B.V. All rights reserved.