Room temperature sodium–sulfur (RT Na–S) batteries are gaining attention as an alternative to lithium batteries due to natural abundance and relatively low cost of sodium. Although the cell chemistry of RT Na-S batteries is similar to that of Li-S batteries, Na-based batteries are more challenging due to the larger Na⁺ ions that results in greater volume expansion and slower kinetics during the charge-discharge processes. This, in turn, leads to shorter cycle life, lower power density and lower sulfur utilization compared to Li-based batteries. Notable progress has been made in the last few years to overcome the aforesaid issues by utilizing various carbon hosts for sulfur such as the multiwall carbon nanotubes, hollow carbon, carbon nanofibers and microporous carbon. However, the powder-based carbon/sulfur (insulating) materials are blended together with binders and conducting additives into a slurry with little control on morphology, which ultimately results in discontinuity in the electron transporting network and low sulfur loading in the final cathodes.

Here, we report a novel approach to develop carbon nanofibers (CNFs)/sulfur cathodes using a rapid sulfur melt-diffusion process (~5 seconds). Rapid impregnation of sulfur into free-standing carbon mats eliminates the use of additional components (binders, current collectors and conducting additives) and other time consuming infiltration processes. It is important to mention that rapid melt infiltration approach used here allows precise control of any sulfur loading regardless of the host matrix and can be used for developing high performance sulfur cathodes. Carbon nanofibers (CNFs) used in the present work are produced by electrospinning polyacrylonitrile/dimethylformamide gel and subsequently carbonizing at 1000°C. CR2032 coin cells were assembled using Na metal as anode, 30µL electrolyte (1.5M NaClO₄ and 0.3M NaNO₃ in tetraethylene glycol dimethyl ether) and as-prepared free-standing CNFs/sulfur cathodes with ~50 wt% (~0.85 mg/cm²) sulfur loading. These cells were cycled at C/5 rate (1C = 1675 mAh g^-1) after conditioning 1^st cycle at C/10 rate. The initial discharge capacity was ~231 mAh g^-1 at C/5 rate, which reduced to ~137 mAh g^-1after 20 cycles. The obtained results are comparable to those reported earlier for room temperature Na-S batteries. Electrochemical performance evaluation of CNFs/sulfur cathodes with higher sulfur loading is under investigation.