Nitrogen-vacancy-regulated Mo₂N quantum dots electrocatalyst enables fast polysulfides redox for high-energy-density lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have great promise in the next generation higher-energy-density storage devices, however, the shuttle effect and sluggish conversion kinetics severely hindered their development. Herein, facile spray drying strategy is selected to construct nitrogen-vacancy-regulated Mo₂N quantum dots embedded in mesoporous carbon matrix (QMo₂N-V) as functional electrocatalyst. The double effect of quantum dots and vacancy engineering in Li-S chemistry is carefully studied. The Mo₂N quantum dots provide abundant active sites for the chemisorption and conversion of polysulfides. Moreover, the nitrogen vacancies reinforce the affinity towards polysulfides and further accelerate their redox conversion due to the regulated local electron structure. Additionally, QMo₂N-V presents hollow spherical structure with excellent conductivity, which works like microreactor to effectively capture the diffused polysulfides and facilitate the in situ fast reaction. Therefore, Li-S batteries with QMo₂N-V separator has a reversible capacity of 510 mAh g⁻¹ after 400 cycles even at 4.0 C, indicating that possess excellent cycling stability. An areal capacity up to 6.6 mAh cm⁻² was achieved with a high sulfur loading of 8.1 mg cm⁻² under lean electrolyte condition (E/S = 5.0 μL mg⁻¹). Overall, this work proposes a combination strategy of quantum dots and vacancy engineering towards fast polysulfides conversion and durable cycling stability, showing great potential in the practical Li-S batteries.