A sodium bis(perfluoropinacol) borate-based electrolyte for stable, high-performance room temperature sodium-sulfur batteries based on sulfurized poly(acrylonitrile)

A new type of electrolyte salt based on a weakly coordinating anion (Na-PPB) for RT Na-SPAN batteries has been developed. Na-PPB was synthesized in bulk via a one-pot reaction. NMR spectroscopy reveals high purity of the salt and stability even under ambient atmospheric conditions. Single-crystal X-ray analysis confirmed the molecular structure of Na-PPB with Na+ coordinated by one DME molecule. The electrolyte containing Na-PPB with PC + 10 wt% FEC showed high oxidative stability on Al current collector exceeding 5.5 V. In a Na-SPAN cell, the Na-PPB electrolyte allows for an initial and final discharge capacity (500 cycles) of 1140 mAh/gsulfur and 965 mAh/gsulfur respectively, obtained at 2C (3.35 A/gsulfur). The excellent electrochemical performance and good chemical stability of Na-PPB offers access to the design of novel electrolyte salts for RT Na-SPAN batteries.