A robust hierarchical microcapsule for efficient supercapacitors exhibiting an ultrahigh current density of 300 A g−1

Abstract

A unique three dimensional (3D) hierarchical microcapsule structure (NiS_x@NCV) has been put forward, which is realized by the ensemble of N-doped carbon vesicles encapsulating dual-NiS_x (α-NiS/NiS₂) nanoparticles via an in situ nanospace-confined pyrolysis strategy. The NiS_x@NCV shows a high pseudocapacitance of 1600 F g⁻¹ at 1 A g⁻¹ and impressive rate performance (a capacitance retention ratio of 84.5%, from 1 to 25 A g⁻¹). Benefiting from this intriguing configuration, a kind of high performance asymmetric supercapacitor (ASCs) has been fabricated, using 3D NiS_x@NCV microcapsules and nanoporous carbon (NPC) as positive and negative electrodes, respectively. Remarkably, the fabricated ASCs achieve a capability of 135.06 F g⁻¹ at 1 A g⁻¹ and exhibit an outstanding rate capability at 32 A g⁻¹. More importantly, a high capacitance retention ratio of 87% is still achieved even at current densities from 32 to 300 A g⁻¹, which exhibits well the ultrahigh rate performance of the NiS_x@NCV//NPC ASCs. In addition, the NiS_x@NCV//NPC ASCs deliver an attractive energy density of 48.02 W h kg⁻¹ at a power density of 800 W kg⁻¹, and still maintain 30 W h kg⁻¹ even at an ultrahigh power density of 240 kW kg⁻¹. This is attributed to the rich redox reaction and interface effect of dual-NiS_x nanoparticles, abundant active sites and high electrical conductivity from N-doped carbon vesicles.