One-step construction of three-dimensional nickel sulfide-embedded carbon matrix for sodium-ion batteries and hybrid capacitors

A three-dimensional design composing of porous carbon matrix (PCM) decorated with nickel sulfide nanoparticles (denoted as NiSx@PCM) was fabricated through a one-step hydrothermal process, and successfully utilized as an electrode material in high performance sodium-ion batteries (SIBs) and sodium-ion hybrid capacitors (SIHCs). The as-prepared NiSx@PCM delivered a high reversible capacity of 650 mAh g−1 over 200 cycles at 0.5 A g−1, outstanding rate capability (167 mAh g−1 at as high as 20 A g−1), and excellent cycle performance (300 mAh g−1 at 1 A g−1 after 800 cycles) in the SIBs. In addition, SIHCs based on NiSx@PCM composite anodes and commercial activated-carbon cathodes behaved carried remarkably high energy densities of 99.3 and 52.2 Wh kg−1 at power densities of 140 and 4480 W kg−1, respectively. The significantly high-performance enhancement should be attributed to the excellent electron/ion transports within the three-dimensional active material-carbon network during charging/discharging with the in-situ growth of the more conductive nickel sulfide nanoparticles throughout the porous carbon matrix. This work presents a facile method to synthesize three-dimensional carbon matrix incorporating metal sulfide nanoparticles, as well as suggests new insights into further advancing next-generation high energy-density/power-density energy storage units by combining the merits of both batteries and supercapacitors.