Polymeric Schiff Base with Thiophene Rings for Sodium-Ion Batteries

Polymeric Schiff bases with a low and tunable redox voltage are regarded as promising anode materials for sodium-ion batteries (SIBs). Herein, polymeric Schiff bases with benzene (PSB-1) and thiophene rings (PSB-2) were designed and prepared as electrode materials for SIBs. Compared with PSB-1, the introduction of thiophene rings to the polymeric Schiff base PSB-2 enhances electron delocalization, structural stability, and intrinsic conductivity, contributing to excellent electrochemical performance. After discharging/charging for 200 cycles at 50 mA g-1, a high specific charge capacity of 174.7 mAh g-1 is maintained for the PSB-2 electrode, much higher than that of PSB-1 (77.1 mAh g-1). After incorporation with multi-walled carbon nanotubes, a high reversible capacity of 290 mAh g-1 is achieved even after 450 cycles at 50 mA g-1. Experimental results and theoretical calculations reveal that each repeat unit of PSB-2 can store four sodium ions via the imine bond C=N and sulfurs, of which the imine bond C=N functions as redox centers and the sulfur atoms mainly serve as electron reservoirs. This work demonstrates that the introduction of functional thiophene rings is efficient in improving the sodium-ion storage performance of polymeric Schiff bases.