On the electrochemical properties of lithium-sulfur batteries

We report in this work the electrochemical analysis of lithium-sulfur batteries (LSB) composed of sulfur and activated carbon (AC) as the positive electrode and lithium metallic as the negative electrode. Cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS) techniques were employed for the in-situ characterization of the coin cell battery device. Electrochemical studies were performed at different state-of-charge (SoC) in 5 %-steps, covering the 0 to 100 % range. Our major findings include a high specific capacity of 1044 mAh gsulfur- 1 , which decreased to 200 mAh g-1 after 150 cycles. At the same time, the coulombic efficiency increased during the discharge from 78 % to 99 % due to a progressive activation of the narrow pores present in AC structures. Galvanostatic EIS findings as a function of SoC helped us in predicting the SoC and state-of-health (SoH). A 1500-h self-discharge result was presented and analyzed, indicating the presence of a small leakage current of ca. 600 nA. All electrochemical findings were corroborated by a comprehensive exsitu materials characterization using Raman, scanning electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectrometry techniques. The electrochemical (in-situ) and ex-situ characterization of electrodes and coin cell devices allowed us to provide a critical discussion regarding the overall characteristic exhibited by LSBs.