Sulfonyl-based polyimide cathode for lithium and sodium secondary batteries: Enhancing the cycling performance by the electrolyte

A sulfonyl-based polyimide has been synthesized and investigated as cathode for lithium and sodium secondary batteries. The lithium cell delivers a flat discharge plateau at 2.5 V with an average discharge voltage of 2.45 V. Increasing the lithium salt concentration can largely enhance the cycling performance. A stable discharge capacities of 120 mAh g −1 is obtained for long-term cycling (450 cycles) with concentrated electrolyte. The sodium cell provides two plateaus with an average discharge voltage of 2.0 V. The capacity retention rate of the sodium cell is 70% at 100th cycle (86 mAh g −1 ).