High-performance lithium sulfur batteries enabled by a synergy between sulfur and carbon nanotubes

The urgent demand on high performance energy storage devices makes lithium sulfur batteries with a high energy density up to 2600 Wh kg−1 extremely attractive. However, the low capacity reversibility and poor rate capability still pose a significant hurdle on their real-world applications. Here, a freestanding thin-film composite containing sulfurized polyacrylonitrile with conductive backbone of carbon nanotubes has been fabricated by an electrospinning method followed by vulcanization, and employed as the binder-free cathode for lithium sulfur batteries without any aid of current collectors. A synergic effect from sulfur and carbon nanotubes, when co-spun together, has been discovered on promoting the electrochemical performance of the cathodes by simultaneously creating material porosity and conductive pathway. The optimized composite fibers made from a ternary precursor solution containing 20% carbon nanotubes present the best performance, delivering a high initial discharge capacity of 1610 mAh g−1 at 0.2C and outstanding cycle stability of 1106 mAh g−1 at 1C over 500 cycles. It is anticipated that the porous composite nanofibers and the multi-variant fabrication methodology reported here can be extended to more energy storage applications, particularly for flexible lithium sulfur batteries.