Enhanced kinetics and efficient activation of sulfur by ultrathin MXene coating S-CNTs porous sphere for highly stable and fast charging lithium-sulfur batteries

Abstract

3D S-CNT@MXene caged micro-sphere has been synthesized using a simple and green method, which is a promising cathode applied in fast-charging Li-S batteries owing to its superior adsorption towards LiPSs and enhanced electrochemical reaction kinetics. • The ultrafine sulfur nanoparticles dispersed in 3D CNT@MXene cages. • MXene avoid restacking, providing unblocked diffusion channels for ions diffusion. • MXene with terminal groups demonstrated adsorption and catalytic effect to LiPSs. • There is almost no capacity fading after 150cycles at such a high density of 4.0C. The main challenges associated with Li-S batteries are relatively unsatisfactory cycling performance, sluggish reaction kinetics and poor utilization of sulfur cathodes especially under high current densities. Here, 3D S-CNT@MXene cages are synthesized by a simple approach that solve these problems. The 3D cages with interconnected conductive networks can improve sulfur utilization, decrease inherent resistance and enhance reaction kinetics. The ultrathin MXene shell with high surface area and plenty of terminal functional groups can prevent the aggregation of MXene, increase chemical interactions and catalytic effect with sulfur species to promote the adsorption of lithium polysulfides and the nucleation of Li 2 S. Moreover, the porous S-CNT sphere with sulfur nanoparticles on the surface of CNTs can facilitate electron transport, electrolyte infiltration and accommodation sulfur swelling. As a result, the 3D S-CNT@MXene cage cathode delivers a high discharge capacity of 1375.1 mAh g −1 at 0.1C, high rate capacity (910.3 and 557.3 mAh g −1 at 1.0 and 8.0 C), and excellent cycling stability. Remarkably, the composite cathode shows almost no capacity decay (656.3 mAh g −1 ) at a high current density of 4.0C after 150cycles, which shows the best cycling stability reported to date among all other cathodes of Li-S batteries.