Combined high catalytic activity and efficient polar tubular nanostructure in urchin-like metallic NiCo2Se4 for high-performance lithium–sulfur batteries

To realize fast-growing field of electric vehicles, rechargeable lithium-sulfur batteries (LSBs) have recently emerged as one of the most exciting alternatives to lithium-ion batteries (LIBs) owing to their higher theoretical energy density, 6 times higher than LIBs and lower cost. However, a poor utilization of the active material involved by the electrical insulating character of sulfur and lithium sulfides and a rapid degradation during charge/discharge processes still limit their practical application. Therefore, in this work, an urchin-shaped NiCo2Se4 (u-NCSe) nanostructures as efficient sulfur hosts were synthesized to overcome the limitations of lithium-sulfur batteries (LSBs) using selenization of Ni0.33Co0.67(CO3)0.5OH precursor. The u-NCSe showed a hollow structure with different distribution of Ni, Co and Se, which was proved by electron energy loss spectroscopy (EELS). Meanwhile, the high-resolution transmission electron microscopy (HRTEM) images indicated that the NiCo2Se4 nanostructures had a good crystallinity, in agreement with the cubic phase of NiCo2Se4 (space group: C12/m1). Owing to the hollow structure that can relieve volumetric expansion, a superior electrical conductivity to improve electron transfer, a high polarity to promote absorption of lithium polysulfides (LiPS), and outstanding electrocatalytic activity to accelerate LiPS conversion kinetics, S@u-NCSe delivers outstanding initial capacities up to 1403 mAh/g at 0.1 C and retains 626 mAh/g at 5 C with exceptional rate performance. More significantly, a very low capacity decay rate of only 0.016% per cycle is obtained after 2000 cycles at 3 C. Even at high sulfur loading (3.2 mg/cm2), a reversible capacity of 557 mAh/g is delivered after 600 cycles at 1 C. Density functional theory calculations further confirm the strong interaction between NCSe and LiPS, and cytotoxicity measure-ments prove the biocompatibility of NCSe. This work not only demonstrates that transition metal selenides can