Asymmetric cathode membrane with tunable positive charge networks for highly stable Li–S batteries

Abstract

Freestanding cathodes with a high sulfur loading more than 4 mg cm−2 are essential for practical high-energy density Li–S batteries. However, Li+ transport is sluggish and polysulfide shuttling is serious in thick cathodes, leading to rapid capacity loss and inferior rate performance. Herein, an asymmetric Li–S cathode threaded with positive charges networks was introduced by a facile phase separation strategy coupled with cationic-crosslinking method. This large-area and flexible cathode membrane shows a gradient distribution of pore structure with a skin sieving layer supported on a thick porous submatrix. This dual sulfur host reveals an inbuilt ability to suppress polysulfide shuttling in Li–S cells. Meanwhile, the positive charge networks derived from post-crosslinking endows the cathode frameworks with boosted Sn2− trapping ability and enhanced ionic transport kinetics. Further adjustment of the cationic networks reveals its ionic exchange mechanism in accelerating the redox reactions at the positive charge interface. As a result, composite membrane with high sulfur loading (9.1 mg cm−2) yields a capacity of over 8.1 mA h cm−2 for long-term cycling. This scalable and functional asymmetric cathode design presents an alternative route toward high energy density Li–S batteries.