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 m2 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 (3d2) and S x2- 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.