Hybrid 3D Vertical Graphene Nanoflake and Aligned Carbon Nanotube Architectures for High-Energy-Density Lithium-Ion Batteries

Abstract

Here, we synthesized a type of three-dimensional (3D) carbon nanostructure through the plasma-enhanced chemical vapor deposition method, which was composed of carbon nanotubes (CNTs) and graphene nanoflakes (GNFs) embedded on the surface of CNTs. The CNTs have a typical hollow structure with an inner diameter of 15 nm, and the CNT@GNF were grown on vermiculite supported with an Fe–Mo catalyst. The diameter of CNTs and the amount of GNFs on the CNT surface can be controlled by adjusting the reaction time, radio frequency (RF) power, and growth temperature. The continuous bombardment of plasma results in a large number of defects on the surface of the CNTs. It was further confirmed that the radio frequency (RF) power played a key role on the generation of GNFs by providing sufficient carbon sources and creating defects as the active sites on surface of the CNTs. Moreover, small amounts (1.2%) of synthesized CNT@GNF material after purification were employed as an efficient conductive agent for the cathode with high contents of LiFePO₄ (LFP) up to 95.8%. As a result, the CNT@GNF-based LFP electrode showed a superior electrochemical performance. After 450 cycles at a current density of 0.5 C, the battery exhibited a specific capacity of 100 mAh g^–1, corresponding to a capacity retention rate of 87%. Additionally, a discharge capacity of 61 mAh g^–1 can still be achieved at 10 C. The largely improved electrochemical performance should be ascribed to the well-established conductive networks by the CNT@GNF material in the electrode. Overall, we synthesized nanocarbons with a unique structure in a facile way, which is promising for the application in lithium-ion batteries.