The rapid capacity fading and poor cycling life caused by polysulfide shuttle severely limit the development of high-energy-density lithium-sulfur batteries. Herein, a new type of electronegative modified separator with semifused pores is designed to suppress polysulfide shuttle and simultaneously elevate Li+ conduction. This separator is facilely prepared by lithiation of Nafion/poly(acrylic acid) electrospun fiber mat on a commercial separator. Abundant electronegative groups on the separator strongly repel anionic polysulfides, effectively inhibiting the shuttle effect. Moreover, these groups provide numerous sites for Li+ transfer, and meanwhile the semifused pores work as low-barrier transport pathways, jointly facilitating Li+ conduction. Therefore, the battery exhibits outstanding cycling stability (decay rate of 0.023% per cycle during 1000 cycles at 1.0 C) and decent rate capability (discharge capacity of 730 mAh g(-1) even at 3.0 C). Additionally, the sulfonated poly(ether ether ketone) is taken as an example to verify the universality of this design strategy.