Bifunctional separator with sandwich structure for high-performance lithium-sulfur batteries.

Severe "Shuttle effect" and uncontrollable lithium-dendrite growth are ongoing challenges that hinder the practical application of Lithium-sulfur (Li-S) batteries. Herein, a bifunctional separator was modified by Al2O3 and carbon nanotubes (CNTs) via a facile method. Li-S battery assembled with the modified separator shows excellent cycling stability (760.4 mA h g-1 at 0.2 C after 100 cycles) and promising rate performance. The reason is ascribed to synergistic effect of CNTs and Al2O3 double coating layers, the strong physicochemical interaction between Al2O3 and the polysulfides could alleviate the shuttle effect, and the high conductivity of CNTs can facilitate the reaction kinetics of sulfur and its corresponding discharge products, respectively, which can improve the utilization ratio of sulfur. In addition, the double protection layers improve the hardness of the separator, as well as regulate Li+ ion deposition, which can effectively prevent the formation of lithium dendrites, thus the safety of the batteries are significant improved.