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

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.