Although lithium-sulfur (Li-S) batteries with high specific energy exhibit great potential for next-generation energy-storage systems, their practical applications are limited by the growth of Li dendrites and lithium polysulfides (LiPSs) shuttling. Herein, a highly porous red phosphorus sponge (HPPS) with well distributed pore structure was efficiently prepared via a facile and large-scale hydrothermal process for polysulfides adsorption and dendrite suppression. As experimental demonstrated, the porous red phosphorus modified separator with increased active site greatly promotes the chemisorption of LiPSs to efficiently immobilize the active sulfur within the cathode section, while Li metal anode activated by Li₃P interlayer with abundant ionically conductive channels significantly eliminates the barrier for uniform Li⁺ permeation across the interlayer, contributing to the enhanced stability for both S cathode and Li anode. Mediated by the HPPS, long-term stability of 1,200 h with minor voltage hysteresis is achieved in symmetric cells with Li₃P@Li electrode while Li-S half-cell based on HPPS modified separator delivers an outperformed reversibility of 783.0 mAh·g⁻¹ after 300 cycles as well as high-rate performance of 694.5 mAh·g⁻¹ at 3 C, which further boosts the HPPS tuned full cells in practical S loading (3 mg·cm⁻²) and thin Li₃P@Li electrode (100 μm) with a capacity retention of 71.8% after 200 cycles at 0.5 C. This work provides a cost-effective and metal free mediator for simultaneously alleviating the fundamental issues of both S cathode and Li anode towards high energy density and long cycle life Li-S full batteries.