Highly defective N-doped carbon/reduced graphene oxide composite cathode material with rapid electrons/ions dual transport channels for high energy density lithium-ion capacitor

Abstract

The energy density of present Li-ion capacitors (LICs) is severely limited by the carbon-based cathode with supercapacitor properties. Herein, to address the low specific capacitance of the cathode, we prepared a structurally stable carbon composite consisting of polypyrrole-derived highly defective carbon nanotubes and highly conductive reduced graphene oxide (rGO) nanosheets, using a facile one-step hydrothermal self-assembly method. The highly defective structures serve as effective electrochemically active sites to enhance ion adsorption for high-performance capacitance characteristics. Meanwhile, the interconnected porous three-dimensional network structures constructed by one-dimensional carbon nanotubes and two-dimensional rGO nanosheets act as rapid electrons/ions dual transport channels, which synergistically promotes fast energy storage/release with abundant defect structures in the material. The carbon composite with optimized structure exhibits significantly improved specific capacitance of 160.6 F g−1 at 0.3 A g−1 and 91.0 F g−1 at a high current density of 60 A g−1 as a cathode material in half-cells pairing with lithium metal. Furthermore, the carbon composite was employed as a cathode paired with a carbon-coated FeOx (FeOx@N-3DG) anode for LIC applications, which demonstrates a superior energy density of 129.1 Wh kg−1 at a power density of 1.7 kW kg−1 and still maintains an outstanding energy density of 32.9 Wh kg−1 at an extremely high power density of 43.9 kW kg−1. The findings of this work provide an effective and rational strategy for designing high energy density LICs cathode materials.