Multifunctional tri-layer aramid nanofiber composite separators for high-energy-density lithium-sulfur batteries

Lithium-sulfur (Li-S) battery has attracted much attention due to their high theoretical energy density. However, severe shuttling effect, sluggish reaction kinetics and uncontrolled dendrite formation of Li anode greatly deter their practical applications. Different to conventional separator engineering strategies that are always focused on surface coating of functional interlayer on commercial polyolefin separators, herein, we proposed a structural engineering tactic by rationally tuning the porous structure and composition of the p-aramid nanofiber (ANF) composite separator to address simultaneously the above problems. A two-step film-casting process combined with a phase inversion approach was developed to fabricate a multifunctional tri-layer ANF composite separator. This innovative separator was especially engineered to comprise a conductive and catalytic NiFe2O4 modified multi-walled carbon nanotubes/ANF layer for rapid and efficient conversion of lithium polysulfides, a microporous ANF layer for fast ion transport, and a dense nanoporous ANF layer for lithium dendrite inhibition. This tri-layer ANF-based separator possessed high porosity, excellent thermal stability, and superb electrolyte wettability. Batteries with the tri-layer ANF- based separator exhibited outstanding cyclic stability with high capacity of >3 mAh cm−2 at high sulfur loading (4 mg cm−2) and high current density (4 mA cm−2). This work opens up new opportunities for design of functional separators based on high performance polymers using the structural engineering strategy.