On the electrochemical properties of lithium‑sulfur batteries

Abstract

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 ex-situ 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.