An asymmetric supercapacitor using sandwich-like NiS/NiTe/Ni positive electrode exhibits a super-long cycle life exceeding 200 000 cycles

Supercapacitor with high energy density and super-long cyclic durability is attractive for the rechargeable energy storage devices. The combination of multiple pseudo-capacitive materials is favorable for improving the energy density of supercapacitor, but the rationally designed electrode structures are highly desirable for achieving the super-long cyclic durability. Here we realize a novel hierarchical NiS/NiTe/Ni positive electrode for supercapacitor, and the assembled asymmetric supercapacitor using the positive electrode demonstrates a super-long cycle life exceeding 200 000 cycles. In the positive electrode, a porous NiTe inner layer acts as the volumetric stain buffer layer between a rigid Ni substrate and a spongy NiS outer layer. In particular, the initiation of volumetric expansion from NiTe inner layer to NiS outer layer, along with the proceeding of volumetric shrinkage from the outer to the inner layer occurring in sequence on the positive electrode play crucial roles in the super-long cycle life, for which sheds a new light on the design/synthesis of multiple pseudo-capacitive materials to achieve the outstanding cyclic stability of supercapacitors.