High performance bimetal sulfides for lithium-sulfur batteries

To acquire remarkable cathode materials for lithium-sulfur batteries with ultrahigh utilization of active materials and superior cycling stability, we firstly employ carboxylated carbon nanotubes to prepare the NiCo2S4@CNTs/S for lithium-sulfur batteries via a simple hydrothermal method, following by a low temperature annealing. The NiCo2S4@CNTs presents a unique structure, which possesses thin branches filled with densely packed small leaves where a large number of micropores distribute. In the novel superstructure, carboxylated carbon nanotubes can effectively improve the electronic transportation capacity and conductivity of the cathode material. In lithium-sulfur batteries, bimetal sulfides have a strong adsorption of the polysulfides, effectively suppressing the diffusion of lithium polysulfides. The NiCo2S4@CNTs/S electrode shows a capacity of 788 mA h g−1 at the current density of 0.5 C and 758 mA h g−1 at 2 C. Even after 1000 cycles at the current density of 0.6 C the capacity only decays by 0.0489% each cycle. It should be notes that most of Coulombic efficiency of the NiCo2S4@CNTs/S electrode is about 99%, regardless of the current density. More importantly, the NiCo2S4@CNTs can exhibit an outstanding capability of absorbing lithium polysulfides, which provides a promising strategy for preparing advanced lithium-sulfur batteries.