The electrochemical behavior of nitrogen-doped carbon nanofibers derived from a polyacrylonitrile precursor in lithium sulfur batteries

A 3D assembly of nitrogen-doped carbon nanofibers (NCFs) derived from polyacrylonitrile was synthesized by a combined electrospinning/carbonization technique and was used as the positive current collector in lithium sulfur (Li-S) batteries containing a Li₂S₆ catholyte solution. The physical and electrochemical behavior of the NCFs were investigated and it was found that their electrochemical performances depended on the pyrolysis temperature. Of the samples carbonized at 800, 900 and 1 000 °C, those carbonized at 900 °C performed best, and delivered a reversible capacity of 875 mAh•g⁻¹ at a high sulfur loading of 4.19 mg•cm² and retained at 707 mAh•g⁻¹ after 250 cycles at 0.2 C. The coulombic efficiency of the NCF-900@Li₂S₆ electrode was almost 98.55% over the entire cycle life. In addition, the capacity retention of the electrode reached 81.53% even at a high current density of 1 C for over 150 cycles. It was found that the NCFs carbonized at 900 °C had the highest electrical conductivity, which might be the dominant factor that determined its performance for use as a positive current collector.