Ultrathin MgB₂ nanosheet-modified polypropylene separator for high-efficiency lithium-sulfur batteries

The separator is an important component in lithium-sulfur (Li-S) batteries. However, the conventional polypropylene (PP) separators have the problem of easy shuttling of lithium polysulfide (LiPSs). Herein, ultrathin magnesium boride (MgB₂) nanosheets were prepared by ultrasonic-assisted exfoliation technology, and were suction-filtered onto a separator to serve as a separator modification layer. The introduction of a microporous structure into MgB₂ nanosheets after ultrasonic peeling increases the specific surface area and pore volume, with more adsorption sites, which can fully utilize the surface adsorption/catalytic performance of MgB₂ for LiPSs and accommodate the volume expansion of lithium sulfide (Li₂S). Therefore, MgB₂@PP as a separator significantly improves the sulfur utilization and cycle stability in Li-S batteries. When the MgB₂@PP separator is used, the reversible specific capacity of the assembled Li-S battery at 0.1 C (current rate) is 1184 mAh/g, and the specific capacity at 2 C is 732 mAh/g. After 500 cycles at 2 C, it remains at 497 mAh/g.