SULFUR-COATED POROUS CARBON NANOFIBER (S/PCNFs) WEBS AS DIRECT CATHODES FOR LITHIUM-SULFUR BATTERIES

摘要

Sulfur has a high specific capacity of 1675 mAh/g as lithium battery cathodes, but its rapid capacity fading due to polysulfides dissolution presents a significant challenge for practical applications. Here we report a strategy to load sulfur on porous carbon nanofiber for effectively trapping polysulfides and improving the electrochemical cycling performance of sulfur cathode. The sulfurcoated porous carbon nanofiber (S/PCNFs) was fabricated by impregnation of electrospun polyacrylonitrile(PAN)-based PCNFs in S/CS2 solution and subsequent thermal treatment under N2 atmosphere. The morphology phase structure, component of the S/PCNFs were charactered by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and their electrochemistry property was also tested using Land battery test system. The PCNFs were aligned directionally, and sulfur can be loaded into the pores of PCNFs in a highly dispersed state. Sulfur generally exists in a very stable orthorhombic crystalline sulfur in the X-ray diffraction pattern. PCNFs have some crystalline order, which is indicative of graphitic character. The sulfur/PCNFs composite with 57 wt.% sulfur delivered the initial specific capacity up to 875 mAh/g and then stable capacity of 465 mAh/g after 90 cycles at the current density of 50 mA/g. The high specific surface area, developed porous structure, and good electrical conductivity of sulfur/PCNFs play a key role in improving the capacity and cycling stability of Li/S batteries.