Electrochemical performance of Na2Ti3O7/C negative electrode in ionic liquid electrolyte for sodium secondary batteries

In this study, carbon-coated Na2Ti3O7 (Na2Ti3O7/C) is synthesized by a solid-state reaction method, and its charge-discharge characteristics as a negative electrode material in an ionic liquid electrolyte, Na[FSA]-[C3C1pyrr][FSA] (FSA = bis(fluorosulfonyl)amide; C3C1pyrr = N-methyl-N-propylpyrrolidinium), are investigated at 363 K. The Na2Ti3O7/C negative electrode shows an initial discharge capacity of 215 mAh (g-Na2Ti3O7/C)−1 at a current rate of 20 mA (g-Na2Ti3O7/C)−1 in the voltage range 0.01-2.5 V. The high discharge capacity of the Na2Ti3O7/C negative electrode is attributed to the high operation temperature in the Na[FSA]-[C3C1pyrr][FSA] ionic liquid electrolyte. Although high discharge capacity is achieved, the Na2Ti3O7/C negative electrode shows relatively poor cycle performance because of the irreversible insertion of some Na ions and the formation of cracks.