Multifunctional G@UC3N4 modified separator for high-performance Li-S batteries

Lithium-sulfur batteries (LSBs) are known for their outstanding theoretical energy density and low cost. However, low sulfur utilization and shuttle effect of the lithium polysulfides (LiPSs) dissolved in the electrolyte seriously limit its commercialization. Herein, graphene@carbon nitride (G@UC3N4) composite modified separator is designed as a multifunctional barrier to enhance the performance of LSBs. UC3N4 with high specific surface area and high pyridinic nitrogen (N) content is prepared by simple secondary heat treatment method, achieving a double physical-chemical limitation for the shuttle of LiPSs. Meanwhile, graphene as a carrier for UC3N4 not only enhances the conductivity of the entire electrode but also accelerates the diffusion of Li+ and the penetration process of the electrolyte. LSBs assembled with G@UC3N4 polypropylene separator exhibit high initial specific capacity (1216.46 mAh g-1 at 1 C) and stable long cycling capability (average decay rate of only 0.047% after 1000 cycles at 2 C, with a coulombic efficiency consistently above 99%).