Two Birds with One Stone: Interfacial Engineering of Multifunctional Janus Separator for Lithium–Sulfur Batteries

Abstract

Li‐dendrite growth and unsatisfactory sulfur cathode performance are two core problems that restrict the practical applications of lithium–sulfur batteries (LSBs). Here, an all‐in‐one design concept for a Janus separator, enabled by the interfacial engineering strategy, is proposed to improve the performance of LSBs. At the interface of the anode/separator, the thin functionalized composite layer contains high‐elastic‐modulus and high‐thermal‐conductivity boron nitride nanosheets and oxygen‐group‐grafted cellulose nanofibers (BNNs@CNFs), by which the formation of “hot spots” can be effectively avoid, the Li‐ion flux homogenized, and dendrite growth suppressed. Meanwhile, at the interface between the separator and the cathode, the homogenously exposed single‐atom Ru on the surface of reduced graphene oxide (rGO@Ru SAs) can “trap” polysulfides and reduce the activation energy to boost their conversion kinetics. Consequently, the LSBs show a high capacity of 460 mAh g–1 at 5C and ultrastable cycling performance with an ultralow capacity decay rate of 0.046% per cycle over 800 cycles. To further demonstrate the practical prospect of the Janus separator, a lithium–sulfur pouch cell using the Janus separator delivers a cell‐level energy density of 310.2 Wh kg–1. This study provides a promising strategy to simultaneously tackle the challenges facing the Li anode and the sulfur cathode in LSBs.