Current collectors based on multiwalled carbon-nanotubes and few-layer graphene for enhancing the conversion process in scalable lithium-sulfur battery

Abstract

We investigated herein the morphological, structural, and electrochemical features of electrodes using a sulfur (S)-super P carbon (SPC) composite (i.e., S@SPC-73), and including few-layer graphene (FLG), multiwalled carbon nanotubes (MWCNTs), or a mixture of them within the current collector design. Furthermore, we studied the effect of two different electron-conducting agents, that is, SPC and FLG, used in the slurry for the electrode preparation. The supports have high structural crystallinity, while their morphologies are dependent on the type of material used. Cyclic voltammetry (CV) shows a reversible and stable conversion reaction between Li and S with an activation process upon the first cycle leading to the decrease of cell polarization. This activation process is verified by electrochemical impedance spectroscopy (EIS) with a decrease of the resistance after the first CV scan. Furthermore, CV at increasing scan rates indicates a Li+ diffusion coefficient (D) ranging between 10−9 and 10−7 cm2·s−1 in the various states of charge of the cell, and the highest D value for the electrodes using FLG as electron-conducting agent. Galvanostatic tests performed at constant current of C/5 (1 C = 1675 mA·gS−1) show high initial specific capacity values, which decrease during the initial cycles due to a partial loss of the active material, and subsequently increase due to the activation process. All the electrodes show a Coulombic efficiency higher than 97% upon the initial cycles, and a retention strongly dependent on the electrode formulation. Therefore, this study suggests a careful control of the electrode in terms of current collector design and slurry composition to achieve good electrode morphology, mechanical stability, and promising electrochemical performance in practical Li-S cells.[Figure not available: see fulltext.].