TiO Phase Stabilized into Freestanding Nanofibers as Strong Polysulfide Immobilizer in Li–S Batteries: Evidence for Lewis Acid–Base Interactions

We report the stabilization of titanium monoxide (TiO) nanoparticles in nanofibers through electrospinning and carbothermal processes and their unique bifunctionality—high conductivity and ability to bind polysulfides—in Li–S batteries. The developed three-dimensional TiO/carbon nanofiber (CNF) architecture with the inherent interfiber macropores of nanofiber mats provides a much higher surface area (∼427 m 2 g –1 ) and overcomes the challenges associated with the use of highly dense powdered Ti-based suboxides/monoxide materials, thereby allowing for high active sulfur loading among other benefits. The developed TiO/CNF-S cathodes exhibit high initial discharge capacities of ∼1080, ∼975, and ∼791 mAh g –1 at 0.1, 0.2, and 0.5 C rates, respectively, with long-term cycling. Furthermore, freestanding TiO/CNF-S cathodes developed with rapid sulfur melt infiltration (∼5 s) eradicate the need of inactive elements, viz., binders, additional current collectors (Al-foil), and additives. Using postmortem X-ray photoelectron spectroscopy and Raman analysis, this study is the first to reveal the presence of strong Lewis acid–base interaction between TiO (3d 2 ) and S x 2– through the coordinate covalent Ti–S bond formation. Our results highlight the importance of developing Ti-suboxides/monoxide-based nanofibrous conducting polar host materials for next-generation Li–S batteries.