Hierarchical hollow, sea-urchin-like and porous Ni0.5Co0.5Se2 as advanced battery material for hybrid supercapacitors

Abstract

Hierarchical Ni_0.5Co_0.5Se₂ containing a hollow inner structure, with a 3D sea-urchin-like overall morphology and very porous nanowires, was first synthesized by a low-temperature selenization method. Benefiting from such a hierarchical structure, the Ni_0.5Co_0.5Se₂ demonstrates a much improved specific area to provide more electroactive sites and a self-supporting 3D structure to make good contact with the electrolyte. More significantly, it is found that the bimetal Ni_0.5Co_0.5Se₂ combines electrochemical advantages from both Ni and Co, showing high electroactivity and low charge transfer resistance. As a result, the hierarchical Ni_0.5Co_0.5Se₂ exhibits a higher specific capacity of 524 C g⁻¹ at 1 A g⁻¹, a superior rate performance of 56% capacity retention when the specific current increases by 50 times and excellent cycling stability of 91% capacity retention after 3500 cycles. In addition, an Ni_0.5Co_0.5Se₂//reduced graphene oxide (RGO) HSC achieves a high specific energy of 37.5 W h kg⁻¹, an ultrahigh specific power of 22.2 kW kg⁻¹ and an outstanding cycling stability up to 10 000 cycles, further confirming the superior performance of hierarchical Ni_0.5Co_0.5Se₂.