NixCo1-xS2@N-doped carbon composites for supercapacitor electrodes

In this paper, a series of NixCo1-xS2@N-doped carbon composites were prepared by sulfidation treatment of NiCo-ethylenediaminetetraacetic acid (EDTA) complex, which could be easily obtained by the reaction of EDTA, nickel salt and cobalt salt. The amount of metal salts influenced the crystal structure and morphology of the complex, which further influenced the morphology of the resulting composite. The optimal composite has a structure of NixCo1-xS2 solid solution nanospheres assembled from numerous nanoparticles deposited on carbon nanorods. This structure offers the following advantages: (1) the close contact between NixCo1-xS2 and carbon material not only greatly accelerates electron transport but also favors stability by reducing volume expansion and contraction; (2) the nanoscale primary particles and nanospheres of different sizes can effectively shorten ion diffusion paths. Combined the merits of its composition (Ni/Co ratio of 2.23:1), the optimal sample exhibited a specific capacitance of 1416.5 F g−1 at 1 A g−1. Furthermore, a NixCo1-xS2@N-doped carbon//AC asymmetric supercapacitor was fabricated, which showed a high energy density of 30.16 Wh kg−1 and excellent cycling stability (84.7 % capacitance retention after 5000 cycles). This work not only presents an efficient electrode material, but also opens up a new avenue for the development of other solid solution/carbon composites derived from bimetallic-EDTA complexes for promising supercapacitor application.