Mitigating shuttle effect of the Li||S battery with Se-deficient commercial MoSe₂ flakes

In lithium-sulfur batteries (LSBs), the dissolution of lithium polysulfides (LiPSs) triggers the shuttle effect to lose active materials irreversibly, leading to the fast deterioration of electrochemical performance. Rational designs on the separator membrane could mitigate the shuttle effect. However, the development of efficient separators economically remains a challenging task, aggressively limiting the commercial use of LSBs. This work reports the engineering of commercial molybdenum diselenides (MoSe₂) flakes to mitigate the shuttle effect of LSBs, by forming rich Se vacancies via a potassium (K) intercalation and de-intercalation reaction. The Se vacancy in MoSe_x flakes significantly enhances the adsorption capacity of LiPSs and accelerates the Li⁺ diffusion kinetics, thereby alleviating the shuttle effect and enhancing the energy storage performance. This directly improves the energy storage performance of the LSBs by incorporating the MoSe_x flakes into the separator membrane, giving a high capacity retention rate of 94.6% at 2 C after 500 cycles, with a reversible specific capacity as high as 452 mAh g⁻¹. This work offers a new strategy for the design and synthesis of vacancy rich transition metal chalcogenides for high-performance LSBs and beyond.