Surface-modified Carbon felt to Improve the Electrochemical Performance of Sodium-Sulfur Battery

Abstract

Sodium-sulfur (NaS) batteries have been considered as one of the most promising energy storage systems for smart grid. Although the NaS battery technologies have been widely investigated for a few decades, there still remain some problems to be solved for the better performance. The slow transport rate of sodium ions in a cathode during discharge and charge is one of the problems, which causes a concentration polarization and increases cell resistance. Furthermore, the formation of a sulfur-insulating layer on the β″-alumina solid electrolyte (BASE) during charge seriously decreases charge acceptance of the battery. This thesis would like to introduce an innovative electronically conducting cathode matrix which can markedly improve the battery performance by accelerating the transport rate of sodium ions in the cathode and suppressing the formation of the sulfur-insulating layer. The matrix was prepared by surface modification of a carbon felt with inorganic nanoparticles. A carbon felt was dipped in an inorganic-organic hybrid sol, dried and then heat-treated at 600°C for 2 hours under a flowing argon. The carbon surface of the felt has been examined by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and energy dispersive X-ray spectroscopy (EDX). The cell prepared with the coated carbon felt shows 92% of charge acceptance and 99.9% of coulombic efficiency at 100 mA cm-2 of current density.