Ultra‐Stable Cycling of High Capacity Room Temperature Sodium‐Sulfur Batteries Based on Sulfurated Poly(acrylonitrile)
Saravanakumar Murugan, Stefan Niesen, Julian Kappler, Kathrin Küster, Ulrich Starke, Michael R. Buchmeiser
Abstract
Abstract We report on a room temperature (RT) sodium‐sulfur (Na−S) battery based on a sodium anode, a sulfurated poly(acrylonitrile) (SPAN) cathode and an electrolyte containing sodium tetrakis(hexafluoroisopropyloxy) borate (Na[B(hfip) 4 ]; hfip=hexafluoroisopropoxide) in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and fluoroethylene carbonate (FEC). The hfip anion as a weakly coordinating anion (WCA) provides high anodic stability, high ionic conductivity, and superior electrochemical performance in carbonate‐based solvents. The Na‐SPAN cell exhibits an initial discharge capacity of 1360 and a remarkable reversible capacity of 1072 after 1000 cycles at 3 C (C=C‐rate, 5.025 ) with an insignificant average capacity decay of less than 0.021 % per cycle. A careful choice of the discharge cut‐off potential (DCP) reveals that a DCP of 0.2 V allows for stable cycling for more than 500 cycles while a DCP of 0.5 V results in a constant capacity decay. The excellent cycle stability at a DCP of 0.2 V is likely to be caused by the high conversion of the SPAN‐bound sulfur into Na 2 S.