Covalent sulfur for advanced room temperature sodium-sulfur batteries

The room temperature sodium-sulfur (RT Na-S) batteries have attracted extensive attention due to its low cost and high specific energy. Yet, RT Na-S batteries usually suffer from low reversible capacity, short lifespan and inferior Coulombic efficiency. Herein, covalent sulfur based carbonaceous materials was investigated for RT Na-S battery to address these drawbacks. Generally, the covalent S could prevent the formation of sodium polysulfide (Na2Sn, 4 <= n <= 8) effectively, further avoid the dissolution of sodium polysulfide into electrolyte; besides, the covalent S in these carbonaceous materials is reversible during charge/discharge process, which is good for cycling stability. Benefiting from these merits, the covalent sulfur based materials delivers high reversible capacity over 1000 mA h g(-1), long cycling stability for 900 cycles with capacity decay of 0.053% per cycle and superior Coulombic efficiency approximately 100%. This study may provide a new method for designing high performance RT Na-S batteries. (C) 2016 Elsevier Ltd. All rights reserved.