Controllable synthesis of sulfurized polyacrylonitrile nanofibers for high performance lithium–sulfur batteries

Sulfurized polyacrylonitrile (SPAN) is regarded to be one of the most promising cathode materials for lithium–sulfur (Li–S) batteries because of its unique chemical structure and high cyclic ability. However, the physicochemical properties of SPAN correlate with the synthesis and process conditions. In this work, flexible and freestanding SPAN nanofiber cathodes are prepared via the electrospinning technique followed by a sulfurization process. And the effect of synthesis temperatures on microstructure and electrochemical performance of SPAN are systematically investigated. According to the spectroscopic analysis, short –Sx– (2 ≤ x ≤ 3) chains are covalently bonded to the cyclized and dehydrogenated PAN backbones through C–S bonds during the synthesis temperature between 300 and 600 °C. Among which, the SPAN nanofiber prepared at 500 °C shows not only a low charge transfer resistance but also the best cell performance. Upon 200 cycles, it displays a high reversible capacity of 1280 mAh g–1 with a fading rate as low as 0.02% per cycle at 400 mA g–1. Highly stable long-term cycling at higher current densities and good rate capability are also achieved. The work provides significant guidance for the development of advanced SPAN cathode materials.