Engineering nano-NiS2 embedded in graphitized carbon skeleton in hollow spherical structure as stable anode material for reversible Li+ storage

Abstract

As a potential anode alternative for Li-ion batteries (LIBs), NiS2 has the advantages of high theoretical capacity (873 mAh g−1), low cost, and good reversibility. However, the application of NiS2 is limited by poor conductivity, sluggish kinetics, and large volume variation. Herein, the hollow spherical NiS2/C-M, or nano-NiS2 embedded in graphitized carbon skeleton, is prepared through construction of the MOF template with hollow cavity, carbonization, and sulfurization. Compared to the aggregated NiS2/C-P particles, the NiS2/C-M composites have more BET surface area to provide more active sites and larger interface between electrolyte and the electrode, greater volume variation tolerance, improved ion and electron conductivity, less active material loss during cycling. As a result, NiS2/C-M exhibits high reversible capacity and excellent rate capability, 1064.2 and 508 mAh g−1 at 0.1 and 2 A g−1, respectively. NiS2/C-M can retain the capacity of 558 mAh g−1 even after 600 cycles at 1 A g−1. The redox mechanism is proposed that NiS2 can reversibly transform to Ni and Li2S via the LixNiS2 intermediate. The formation mechanism of hollow cavity in MOF is explicated to follow the Ostwald’s step rule. This feasible method to fabricate NiS2/C-M may provide a novel approach to develop high-capacity anode for LIBs.