Long-lifespan sodium ion capacitors enabled by in-situ electrochemically induced graphitization and rearrangement of carbon layers in Fe2O3@C modified vertical-aligned carbon nanotubes

Abstract

Developing high-capacity anodes with fast kinetics and stable structure is critical for the effective implementation of sodium ion capacitors (SICs). In this study, Fe2O3@C nanoparticles modified vertically aligned carbon nanotubes (VACNTs) composites are designed and employed as SIC anodes through a two-step chemical vapor deposition (CVD) process with the aid of a refined Fe3O4/AlOx dispersion catalyst. With nano-sized Fe2O3 coated with defected carbon layers sufficiently loading onto the VACNTs substrates, the resulting composites demonstrate remarkable sodium storage properties, with a high areal specific capacity (1.26 mAh cm−2 at 0.2 mA cm−2) and rate performance (0.19 mAh cm−2 at 5.0 mA cm−2). Moreover, continuous capacity promotion is observed over 1000 cycles, leading to superior cycling performance (0.444 mAh cm−2 at 1 mA cm−2), with 178% retention after 1000 cycles. This improved cycling performance is attributed to the defective structure and high specific surface area of the VACNTs, which accommodates the volume change of the Fe2O3 particles. In addition, the induced locally graphitization and rearrangement of the carbon layers are demonstrated, which results in better kinetics for Na+ transfer, further enhancing capacity retention over long cycles.