Mxene quantum dots decorated reduced graphene oxide networks as multifunctional electrocatalyst for advanced lithium–sulfur batteries

The rGO@Ti3C2 QDs composite microsphere based on Ti3C2 MXene quantum dots has been successfully used as high-efficiency electrocatalysts and LiPSs adsorbents for Li-S batteries. The ingenious functional design and simple, fast synthesis route have effectively enhanced the redox and catalytic activity of LiPSs, providing a new direction for accelerating the practical application of Li-S batteries. [Display omitted] •RGO@Ti3C2 QDs are synthesized via spray drying method and annealing etching method.•Ultrafine Ti3C2 MXene quantum dots serve as adsorbents and catalysts for LiPSs.•Activated graphene host takes advantage of nano-pores and large surface areas, while ensuring high conductivity.•Electrochemical investigation and DFT calculation revealed the catalytic mechanism.•The rGO@Ti3C2 QDs sulfur cathode shows enhanced electrochemical performance for Li-S battery. Lithium sulfur (Li-S) battery has shown great potential as an attractive rechargeable energy storage devices, but the shuttle behavior and slow conversion kinetics of the intermediate lithium polysulfides (LiPSs) are the main obstacles to the practical application of Li-S battery. Herein, a simple and scalable spray drying strategy was used to construct conductive polar Ti3C2 MXene quantum dots (QDs)-decorated reduced graphene oxide (rGO) microsphere (rGO@Ti3C2 QDs) as efficient electrocatalyst and absorbent for Li-S battery. Firstly, the DFT results show that Ti3C2 QDs can effectively adsorb and catalyze LiPSs conversion. This ability can be attributed to the Ti3C2 QDs can provide a large number of LiPSs catalytic active sites. In addition, the rGO provides physical LiPSs constraint and a flexible substrate to prevent QDs from aggregating. Moreover, both parts are conductive, effectively improving the electron/charge transfer. Therefore, this unique structure and composition show high LiPSs adsorption and catalysis, while allowing rapid Li+/electron transfer. As a result, the S/rGO@Ti3C2 QDs electrode provides high initial capacity (1185 mAh/g at 0.2C), good rate capability (758 mAh/g at 3C), and excellent long-term cyclability (500 cycles at 1C with low attenuation of 0.07% per cycle), as well as an excellent electrochemical performance even at high sulfur loading. Meanwhile, the Li-S pouch cell based on S/rGO@Ti3C2 QDs also achieved a high initial energy density of 230.9 Wh kg−1. This work may provide a promising strategy to obtain better electrochemical performance by introducing quantum dots in