Fabrication of N, S co-doped carbon nanofiber matrix with cobalt sulfide nanoparticles enhancing lithium/sodium storage performance

Abstract

In this work, N and S co-doped carbon nanofibers coated with cobalt sulfide nanoparticles (CoSx/N-SCFs) were synthesized by a simple method as anode materials for Li+/Na+ storage. The cobalt sulfide nanoparticles are uniformly embedded in carbon nanofibers in this composite, which effectively shortens the Li+/Na+ diffusion distance and buffers the volume expansion caused by discharge/charge. Besides, the doped N and S improve the conductivity of the carbon nanofibers and expand the carbon interplanar spacing, which facilitates the diffusion of Li+/Na+. The obtained CoSx/N-SCFs electrode shows an excellent reversible capacity of 761.3 mAh g−1 after 1000 cycles at 2 A g−1 for lithium storage and a reversible capacity of 505.1 mAh g−1 after 100 cycles at 100 mA g−1 for sodium storage. Density functional theory calculations further demonstrate that the N, S co-doping increases the electronic conductivity of carbon matrix and reduces Li+/Na+ diffusion barrier, thus effectively enhancing the adsorption of Li+/Na+. This work provides an effective method for synthesizing metal sulfide/carbon nanocomposites as high-performance anode materials.