Construction of three-dimensional hierarchical nest-like NiS₂ with efficient stress dissipation for superior sodium...

Transitional metal sulfides (TMSs) with high theoretical capacities are promising anode materials for sodium-ion batteries (SIBs). However, the low conductivity and large volume change during charge/discharge processes lead to poor rate capability and inferior cycling stability. In this work, we constructed three-dimensional hierarchical NiS₂ microspheres by hydrothermal method followed by sulfurization. With polyvinylpyrrolidone (PVP) as a directing agent, NiS₂ nanosheets orderly stack concentrically with an opening in the center, giving rise to a nest-like structure. By using PVP with different molecular weight, different morphologies of flower-like or solid NiS₂ microspheres can be obtained. Finite element analysis (FEA) suggests that the unique nest-like structure can effectively dissipate the stress and suppress the volume variation during sodium insertion, thus giving rise to greatly enhanced reversible capacity and cycling stability for sodium storage, as compared to the other two samples with different organized structure.