Ultra‐Stable Cycling of High Capacity Room Temperature Sodium‐Sulfur Batteries Based on Sulfurated Poly(acrylonitrile)

We report on a room temperature (RT) sodium-sulfur (Na−S) battery based sodium anode, sulfurated poly(acrylonitrile) (SPAN) cathode and an electrolyte containing tetrakis(hexafluoroisopropyloxy) borate (Na[B(hfip)4]; hfip=hexafluoroisopropoxide) in mixture of ethylene carbonate (EC), dimethyl (DMC) fluoroethylene (FEC). The hfip anion as weakly coordinating (WCA) provides high anodic stability, ionic conductivity, superior electrochemical performance carbonate-based solvents. Na-SPAN cell exhibits initial discharge capacity 1360 remarkable reversible 1072 after 1000 cycles at 3 C (C=C-rate, 5.025 ) with insignificant average decay less than 0.021 % per cycle. A careful choice the cut-off potential (DCP) reveals that DCP 0.2 V allows for stable cycling more 500 while 0.5 results constant decay. excellent cycle stability is likely to be caused by conversion SPAN-bound sulfur into Na2S.