Abstract
By considering the advantages of lithium-ion batteries (LIBs) with remarkably high energy density and supercapacitors with high power density and long-life cycle, the emerging energy storage device has been introduced recently known as lithium-ion hybrid supercapacitors (LIHSs) or lithium-ion capacitors (LICs) providing the hybrid enhancement of those energy storage devices. However, to obtain the LICs with high power and energy density as well as long-life cycle, the combination of the electrochemical properties between LIBs and supercapacitors still have some difficulties hindering LICs' applications such as instability of life cycles, and the appropriation of coupled materials electrodes which possibly suppress their particular properties of each materials rather than enhancing their features. Herein, the carbon-based composite materials consisting of N-doped reduced graphene oxide (N-rGO) and carbon nanotubes (CNTs) are inspirationally designed as promising candidate negative electrodes to challenge the electrochemical features of the LICs. The N-rGO/CNT composites are functionalized through the acid treatment by adding the functional groups on the network structures to investigate and obtain the remarkably combining benefit properties of high physical and chemical properties of both materials. This creates more defects, larger surface area and higher conductivity that could help to enhance the insertion and diffusion of the lithium ions. On the other hand, the activated carbon (AC) is selected as a positive electrode since it is a well-known electrode for supercapacitors due to its high surface area and appropriate pore sizes. The as-fabricated LIC exhibits the power density of 27748 W kg-1 and the energy density of 183 Wh kg-1 indicating their many potential applications as an ideal energy storage device.