With the increasing demand for high capacity energy storage systems,a considerable amount of effort has recently been focused on the development of the lithium-sulfur(Li-S)battery due to its high theoretical energy density(2567 W h kg-1)and the abundance,non-toxicity and low cost of sulfur.111 Despite the great promise,successful implementation of the Li-S battery is still hindered by its short cycle life and limited power density.Several problems need be addressed to enable its practical application:i)The low electrical conductivity of sulfur species,which leads to high overpotentials and low utilization of active materials.121 ii)The diffusion of soluble intermediate polysulfide species into the electrolyte,which causes irreversible loss of active material,low coulombic efficiency,short cycle life and increases the device impedance over time.131 iii)The large volume change of sulfur cathodes during the charge and discharge processes(up to 80%),which induces stress in the electrode and undermines its structural integrity,leading to the loss of electrical contact with the conductive additives and the detachment from the current collector.[4]Here we introduce a bi-functional Li-S battery separator obtained by depositing a sulfur-capturing black phosphorus(BP)nanoflakes onto a Celgard,commercial polypropylene separator,151 which is used to overcome the challenges associated to the polysulfide diffusion in lithium-sulfur batteries,and brings the following benefits of the entrapment of various sulfur species via the strong binding energy,and re-activation of the trapped sulfur species due to its high electron conductivity as well as Li ion diffusivity.