Enhancing lithium-sulfur battery performance through the synergistic effects of Congo Red and SnO2 nanoparticles in separator modification layers

The performance of lithium-sulfur batteries (LSBs) is hindered by polysulfide shuttling and sluggish redox kinetics, resulting in rapid capacity fading and poor cycle life. This study presents a new strategy for improving LSB performance by modifying the separator with a Congo Red (CR)-tin dioxide (SnO2) nanocomposite (CR-SnO2), leveraging its synergistic interactions to enhance polysulfide immobilization and lithium-ion transport. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM) confirm the uniform dispersion of SnO2 nanoparticles within the CR matrix, creating a stable and functional separator coating. LSBs employing glass fiber (GF) separators modified with CR-SnO2/SP/PVP, a composite of CR-SnO2, Super P (SP), and polyvinylpyrrolidone (PVP), achieve an initial specific capacity of 1377 mAh g-1 at 0.1C and demonstrate remarkable cycle stability, retaining 91 % of capacity after 300 cycles at 0.5C. Additionally, the modified separator significantly enhances rate performance by reducing charge-transfer resistance and improving redox kinetics. Compared to cells with SnO2/SP/PVP or CR/SP/PVP-modified separators, which show limited performance improvements, the CR-SnO2-modified separator enables superior polysulfide adsorption and enhanced ionic conductivity, effectively mitigating the shuttle effect. This work advances surface and interface science by demonstrating how the functionalization of separator materials with a synergistic organic-inorganic composite can simultaneously regulate polysulfide conversion and facilitate efficient ion transport. The findings provide new insights into interfacial engineering strategies for improving LSB performance and offer a promising approach for developing high-energy, long-cycle LSBs.