Thorn-like nanostructured NiCo2S4 arrays anchoring graphite paper as self-supported electrodes for ultrahigh rate flexible supercapacitors

Abstract

Vertically stacked thorn-like nanostructured NiCo2S4 arrays are designed to in-situ grow on the electrochemical oxidized graphite paper by a two-step hydrothermal method where graphite papers act as heterogeneous nuclear sites to rationally construct the unique features of NiCo2S4. Bimetal synergistic effect and the presence of sulfur atoms can improve the ionic and electron conductivity of NiCo2S4. The unique structure of NiCo2S4 fabricated in such way can allow more active sites exposed to reversible redox reactions, as well as provide relatively short ions/electrons transport pathways within the broken crystal structure and rich porous structure. As such, graphite paper supported NiCo2S4 as a self-supported electrode (NiCo2S4@EGP) shows an extraordinarily high rate capability with the specific capacitance of 1276 F g−1 at 1 A g−1, and even 1218 F g−1 at 20 A g−1, as well as the excellent cycle stability with capacitance retention of 86 % after 5000 cycles. When assembling into a flexible asymmetric all-solid-state supercapacitor device, this device reaches a high-power density of 55.3 Wh kg−1 at a power density of 747.6 W kg−1, together with a superior high cycle stability (retained 95 % in 5000 cycles). These results obviously open interesting perspectives of using NiCo2S4@EGP as self-supported electrodes to become an advanced flexible power device.