Advanced Asymmetric Supercapacitor Based on Graphene/Single-Walled Carbon Nanotube and Mesoporous Hollow NiCo2S4 Sub-microsphere Electrodes with High Energy Density

Supercapacitors (SCs) are drawing considerable attention because of their remarkable power density, long cycling stability, quick charging/discharging, and environmentally friendly characteristics. They are currently applied in electronic devices and wearable energy storage systems. Recently, the use of asymmetric supercapacitors (ASCs) has been acknowledged as a valid strategy to improve energy density of SCs due to the combination of electric double-layered anodes and redox-schemed cathodes. Here, mesoporous hollow NiCo2S4 sub-microspheres and porous graphene/single-walled carbon nanotubes are synthesized by a simple and elegant method without any use of templates. The as-synthesized products exhibit improved capacitive performance and extraordinary stability. An assembled asymmetric supercapacitor with graphene/single-walled carbon nanotubes and NiCo2S4 as its negative and positive electrodes, respectively, delivers a maximum energy density of 45.3 W h kg−1 (at 800 W kg−1) and an outstanding cycling life (87.5% over 20,000 cycles). This suggests that the obtained products possess huge potential to become the next generation of electrode materials for future energy storage devices.