Binder-free, freestanding cathodes fabricated with an ultra-rapid diffusion of sulfur into carbon nanofiber mat for lithium–sulfur batteries

A rapid (5-s) sulfur deposition technique is demonstrated on electrospun carbon nanofibers to fabricate binder-free, freestanding cathodes for lithium-sulfur batteries. The 5-second procedure melts sulfur into carbon nanofiber mats, which play a significant role as a built-in conductive matrix to provide uninterrupted electron transport pathways throughout the electrode such that the heavy current collector is eliminated. Meanwhile, the large inter-fiber spacing facilitates electrolyte diffusion and provides sufficient space for sulfur integration during cathode fabrication and the volume expansion during lithium-sulfur redox reaction. This technique eliminates the need for slurry processing with insulating binders and toxic solvents while eliminating heavy current collectors. This ultra-rapid technique involving only 140 °C, 5 s, and slight pressure (<250 psi) offers a practical approach to light-weight sulfur cathodes compared to the conventional sulfur melt deposition techniques requiring high temperatures (155–300 °C), long times (8–10 h), and heavy components in the cell assembly. The cathodes thus obtained deliver a discharge capacity of ∼550 mAh g _sulfur ⁻¹ owing to their simple construction, with 100% capacity retention at 0.5C rate over 150 cycles. This translates to ∼250 mA h g _electrode ⁻¹ (based on total mass at the cathode) which is comparable to highly sophisticated electrodes when the weight of the entire electrode and current collector is considered.