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 degrees 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 degrees C), long times (8-10 h), and heavy components in the cell assembly. The cathodes thus obtained deliver a discharge capacity of similar to 550 mAh g(sulfur)(-1) owing to their simple construction, with 100% capacity retention at 0.5C rate over 150 cycles. This translates to similar 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. (C) 2018 Published by Elsevier Ltd.