Flexible yolk-shelled NiCo2S4 hollow spheres/RGO film electrodes for efficient supercapacitive energy storage

Flexible yolk-shelled NiCo2S4 hollow spheres/reduced graphene oxide (RGO) hybrid lamellar films were successfully fabricated by developing a facile strategy of vacuum filtration. After constructing the sandwich-like structures, the NiCo2S4 hollow spheres were inserted in-between the RGO nanosheets, which effectively prevented the self-restacking of RGO nanosheets and increased the interlayer spacing, leading to fast ion penetration and diffusion. The as-prepared NiCo2S4/2RGO hybrid lamellar films with excellent conductivity delivered an appreciable capacitance of 1000.5 F g(-1) at 1 A g(-1). Moreover, an asymmetric supercapacitor (ASC) was successfully synthesized utilizing activated carbon (AC) and NiCo2S4/2RGO hybrid lamellar films as the negative electrode and positive electrode, which manifested a high energy density (15.4 W h kg(-1)) and power density (2227.3 W kg(-1)) coupled with remarkable cycling stability (80.5% retention over 5000 cycles). After charging, two ASC devices connected in series were capable of lighting two red LEDs connected in parallel for at least 2.0 minutes.