Operational Strategies to Improve the Performance and Long-Term Cyclability of Intermediate Temperature Sodium-Sulfur Batteries

Based on the preliminary investigation of the intermediate temperature sodium-sulfur (IT-NaS) battery (150 °C), herein we advance this energy storage system, by retuning 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 significantly, 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.