Growing NiS2 nanosheets on porous carbon microtubes for hybrid sodium-ion capacitors

Abstract NiS2 is a promising anode material for sodium-ion batteries (SIBs) and capacitors (SICs). However, the sluggish Na+ diffusion and large volume change of bulk NiS2 during sodiation/de-sodiation lead to poor rate capability and fast capacity decay, limiting its practical application. Herein, we design and prepare well-oriented NiS2 nanosheets on porous carbon microtubes (denoted as NiS2/pCMT) as a novel anode material for SIBs/SHCs. The unique porous hollow carbon tubes and NiS2 nanosheets can well relieve the repeated stress/strain and maintain the structural integrity of the composite anode during long-term charging/discharging. As a confirmation, a modelled SHC is constructed by using the NiS2/pCMT composite as anode and coupling with an activated carbon cathode, delivering a high energy density of 136 Wh kg−1 and good cycling stability. The first-principles density functional theory (DFT) calculations confirm that the NiS2 nanosheets surface has a high chemical affinity towards Na+ ions, promising the concentration of Na+ ion on/nearby the surface for fast redox reactions during sodiation/de-sodiation of NiS2. This work provides some new insights for the design and fabrication novel composite electrode materials for applications in beyond lithium-ion batteries/capacitors.