Despite promising characteristics of high energy density and low material cost, lithium-sulfur (Li-S) batteries show practical limitations in poor cycling life and low Coulombic efficiency due to the fatal "shuttle effect" of soluble polysulfides. Here, a dual polysulfide confinement strategy is designed by fabricating an in-situ N/P co-doped carbon, which is originating from versatile silk cocoons through a combined technology of phosphoric acid activation and carbonization and acts as both sulfur host and self-standing interlayer in Li-S batteries. The N/P co-doped porous carbon host (NPPC) provides both the physical restriction and chemical adsorption of polysulfides, while the polar interlayer is used as not only an efficient barrier for blocking polysulfides but also a second current collector, which can reuse the sulfur species, enhance the cycling stability and rate capacity. With this rational design, the NPPC/S cathode with the free-standing interlayer exhibits an initial specific capacity of 1412.6 MAh g(-1) at 0.1 C, outstanding cycling stability with the ultra-low capacity decay of 0.032% per cycle over 500 cycles at 1.0 C and splendid rate performance with 758.1 mAh g(-1) at 2.0 C. Our work provides an ecofriendly and dual employed strategy for boosting the commercialization of Li-S batteries.