Acid-etched serpentine separator with hierarchical porosity and dual-functional polysulfide regulation for high-performance lithium–sulfur batteries

In this study, we propose the use of the natural clay mineral of serpentine as a functionalized separator coating material to address the polysulfide shuttle effect and interfacial kinetic hysteresis in lithium–sulfur batteries. Through selective magnesium removal by acid etching, the silica-oxygen skeleton of serpentine was reconfigured to form a hierarchical porous structure, and rich Si–O⁻/Si–OH⁻ active sites were exposed on its surface. Under optimum acid etching conditions using 6 M hydrochloric acid, the resulting serpentine 6 M-Srp as a separator coating material can achieve significantly improved polysulfide anchoring under the synergistic effect of chemisorption and catalysis, with an Li₂S deposition capacity of up to 123 mAh g⁻¹ and a decrease in the redox peak polarization voltage by 17.8% compared with that of the PP separator. It is also confirmed that the hierarchical pores of 6 M-Srp shortened the ionic diffusion paths and synergistically optimized interfacial charge transfer, thus improving the lithium ion diffusion coefficient. Cycling tests reveal that the lithium–sulfur battery equipped with a separator coated with 6 M hydrochloric acid-treated serpentine boasts an impressive initial specific capacity of 1141 mAh g⁻¹ at a discharge rate of 0.2C and maintains a robust specific capacity of 729 mAh g⁻¹ even after 100 cycles. Furthermore, rate tests demonstrate the ability of the battery to sustain a specific capacity of 577 mAh g⁻¹ under a higher current density of 1C. Notably, when the current density is reduced back to 0.2C, the specific capacity effectively recovers to 668 mAh g⁻¹, showcasing its stability and resilience. This work provides a low-cost and high-stability separator modification strategy for the practical application of lithium–sulfur batteries.