Lithium sulfur batteries, with a high theoretical specific energy of ~2680 Wh/kg, have attracted great attention in the recent years owing to the direct use of sulfur as a cathode, which is cost-effective, environmentally friendly and naturally abundant. However, shuttling of intermediate polysulfides between cathode and anode is one of the major practical limitations for the realization of Li-S batteries. Others include large volume expansion during lithium insertion, low sulfur utilization, and insulating nature of sulfur and lithium disulfide. Over the years, various carbon and inorganic materials (metal oxides, metal-organic frameworks) have been employed as hosts or polysulfide reservoirs to minimize the shuttling effect and improve the conductivity of cathodes in Li-S batteries. Recently, titanium suboxides (Ti_nO_2n-1; n>1), with two Ti³⁺ and (n-2)Ti⁴⁺ (3d⁰) ions, have been utilized as bifunctional sulphur hosts that not only provide good electrical conductivity, but also chemically bind with the intermediate lithium polysulfide preventing their escape. However, formation of titanium suboxides generally requires high temperature processing, which results in highly dense low surface area material reducing the potential polysulfide-host interaction surface.

Here, we report the use of free-standing, binder-free titanium suboxide nanofibers as host material in sulfur cathodes. Titanium suboxide nanofibers are produced by electrospinning titanium isopropoxide solution in presence of polyvinylpyrrolidone and subsequently, heating at 850˚C to create oxygen vacancies through carbothermal reaction. Sulfur impregnation was carried out by rapid melt-diffusion technique to form final sulfur/titanium suboxide cathodes. Lithium-sulfur coin cell batteries were assembled using as-prepared free-standing cathodes (without any current collector and binder) with ~50 wt% sulfur loading (~1.5 mg cm^-2) and cycled at C/5 rate (1C = 1675 mAh g^-1) after conditioning at C/10 rate. The initial discharge capacity was ~976 mAh g^-1 at C/5 rate, which stabilized to an average capacity of ~738 mAh g^-1 after three cycles with coulombic efficiency >97%. The conducting titanium suboxide nanofibers allow the effective utilization of sulfur/Li₂S during discharging/charging of cells and help to maintain high discharge capacity (~700 mAh g^-1) over 100 cycles. The chemical interaction between these inorganic hosts and lithium polysulfide is under investigation and will be discussed in detail. The electrochemical results presented here show the potential of titanium suboxide family (different n values) as foreseeable solution to the shuttling effect for developing high performance Li-S batteries.