Functional separator with a nitrogen/oxygen-rich interlayer for enhancing performance of Li–S batteries

Abstract

Lithium–sulfur (Li–S) batteries have attracted considerable attention due to their high theoretical energy density. However, their practical application is hindered by critical issues, including uneven lithium deposition and polysulfide shuttling. To address these critical issues, surface functionalization with nitrogen- (N-) and oxygen- (O-) containing polar groups has proven effective in stabilizing battery interfaces by suppressing polysulfide migration and promoting uniform lithium deposition. Here, we propose a facile strategy to construct an N- and O-rich interlayer via a simple one-step hydrolysis process. The resulting hydrolyzed polyacrylonitrile–poly(vinylidene fluoride-co-hexafluoropropylene) interlayer introduces abundant N- and O-containing polar groups onto a commercial separator (CS) to form the modified separator N–O@CS, which exhibits enhanced electrolyte wettability, mechanical strength, and electronic polarizability, thereby effectively regulating polysulfide migration and lithium deposition. Specifically, at 0.2 A g⁻¹, the cells achieve a high capacity of 675.5 mAh g⁻¹ with a retention of 95.3% after 200 cycles, outperforming those with CS (468 mAh g⁻¹, 72%) and N@CS (603 mAh g⁻¹, 90.1%). Furthermore, at a higher current density of 0.5 A g⁻¹, the cell with N–O@CS retains 62.3% of its initial capacity after 600 cycles. This study offers a simple and effective strategy to fabricate high-performance Li–S batteries.