Performance validation of sodium-ion batteries using an ionic liquid electrolyte

Charge–discharge properties of sodium-ion batteries using the Na[FSA]–[C3C1pyrr][FSA] (FSA: bis(fluorosulfonyl)amide, C3C1pyrr: N–methyl–N–propylpyrrolidinium) ionic liquid were investigated over a temperature range of 273–363 K. NaCrO2 and hard carbon (HC) were used as positive electrode and negative electrode active materials, respectively, and their fundamental charge–discharge characteristics were examined with coin-type half-cells. A 1.5 mAh coin-type full cell composed of HC/NaCrO2 showed excellent cycle properties, maintaining 90 % of its initial capacity after 1000 cycles at 333 and 363 K. The 1.5 mAh full cell also exhibited a high charge–discharge energy efficiency of 97.5 % at 363 K and C/5 rate. A large-sized prismatic HC/NaCrO2 full cell with a capacity of 27 Ah was fabricated by a mass production process, and its performance was confirmed to be comparable with that of the 1.5 mAh coin-type cell