Operational strategies to improve the performance and long-term cyclability of intermediate temperature sodium-sulfur (IT-NaS) battery

Based on the preliminary investigation of the intermediate temperature sodium-sulfur (IT-NaS) battery (150 °C), herein we advance this energy storage system, by re-tuning the catholyte formulation; namely i) concentration, ii) layer thickness and iii) cut-off limits during galvanostatic charge-discharge cycling, lowering the operating temperature and improving cell design. The systematic implementation of these strategies boosted the cell performance markedly, delivering 112 mAh/g-sulfur, 90% of its theoretical specific capacity (125 mAh/g-sulfur), and 50 deep reversible charge-discharge cycles with coulombic and round-trip energy efficiencies of 97 ± 3% and 73 ± 4%, respectively. Along with the stability and improvement of cycle life, this study demonstrates, for the first time, the practicality of the tubular IT-NaS technology at a temperature as low as 125 °C.