Effect of surface amorphization on potassium storage behavior of NiS porous-hollow spheres

Abstract

Surface modification of electrode materials played an important role in tailoring their electrochemical performance. Here, surface amorphization or distortion, which was fairly common in material synthesis, was studied for its impact on potassium storage behavior. To this aim, contrast experiments were conducted on a series of NiS porous-hollow microspheres, whose shells were composed of interwoven NiS nanosheets. HRTEM characterization showed that each nanosheet comprised crystalline inner core and amorphous outer layer. By adjusting the thickness of this amorphous layer, potassium storage mechanism could be transformed from a diffusion-controlled type to a hybrid of capacitive and diffusive type, accompanied by an improvement in potassium storage performance. At the optimal layer thickness, NiS electrode could deliver a capacity of 182.4 mAh g−1 at 5 A g−1 as well as maintain 427.0 mAh g−1 after 300 cycles at 0.2 A g−1.