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

Charge-discharge properties of sodium-ion batteries using the Na[FSA]-[C(3)C(1)pyrr][FSA] (FSA: bis(fluorosulfonyl)amide, C(3)C(1)pyrr: 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.