Free-Standing Sulfur/Carbon Nanocomposite Cathodes for Lithium-Sulfur Rechargeable Batteries

The traditional, commonly used method for preparing sulfur/carbon (S/C) composites for lithium-sulfur (Li-S) battery cathodes generally involves a complex process that includes three steps conducted at relatively high temperatures. Here, we demonstrate a one-step approach for fabricating S/C nanocomposite using an electrochemical depositing method at room temperature. Carbon felt was selected as the sulfur carrier to fabricate the sulfur/carbon felt (S/CF) nanocomposite. Two types of S/CF nanocomposites with different compositions were prepared under conditions of high current for a short duration and low current for a long duration. For example, after 8 h of depositing at a current density of 5 mA cm-2, we prepared an S/CF nanocomposite with a sulfur content of 42.6%. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption-desorption analysis were employed to examine the morphology and structure of the samples. The resulting S/CF can be directly used as a cathode electrode for Li-S battery applications without the need for a binder and current collector. Galvanostatic test, cyclic voltammetry, and electrochemical impedance spectroscopy were used to assess the electrochemical performance of the S/CF nanocomposites. As a result, the obtained S/CF nanocomposite demonstrated a reversible capacity of 737 mAh g-1 after 100 cycles at a current density of 0.2 C (1 C = 1675 mA g-1). Increasing the current densities to 0.5 and 1 C, the nanocomposite still maintained capacities of 653 and 530 mAh g-1, respectively, after 100 cycles. This indicates that the free-standing S/CF nanocomposite reported in this paper is a promising cathode material for Li-S batteries.