Effects of Fiber Diameter on Sulfur Loading and Lithium–Sulfur Battery Performance of Semicarbonized and Sulfurized Polyacrylonitrile Cathode Materials

With the rapid development of portable electronic devices and electric vehicles, higher demands are placed on energy storage systems, and sulfurized polyacrylonitrile (SPAN) cathode materials have become the focus of research due to their excellent theoretical specific capacity and other advantages. The magnitude of sulfur content of the active substance in SPAN cathode material is the key issue to determine the electrochemical performance of lithium–sulfur batteries. In this paper, we investigate the effects of fiber diameters of SPAN fibers as cathode materials on the sulfur content in SPAN and the performance of batteries. At the same low molecular weight, the finer the fiber diameter, the larger the specific surface area, the higher the sulfur content in SPAN. When the fiber diameter is 0.5 μm, the sulfur content is about 47 wt %. The first reversible discharge specific capacity at 0.2 C can reach 1284 mAh g –1 sulfur, and the capacity retention is about 92% after 200 cycles. The reduced fiber diameter is beneficial to the formation of a stable structure for electron conduction, which shortens the lithium-ion transfer distance, reduces the charge transfer resistance, and improves the kinetics of the redox reaction. It also effectively alleviates cell polarization during charging and discharging and provides controlled and optimized conditions for obtaining high-capacity and high-property Li/SPAN materials.