Three-dimensional mesoporous <i>γ</i> -Fe ₂ O ₃ @carbon nanofiber network as high performance anode material for lithium- and sodium-ion batteries

Abstract

Abstract Electrode materials that can function well in both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) are desirable for electrochemical energy storage applications, especially under high rate. In this work, a three-dimensional (3D) mesoporous γ -Fe 2 O 3 @carbon nanofiber ( γ -Fe 2 O 3 @CNF) mat has been successfully synthesized by sol–gel based electrospinning and carbonization. It delivers a specific capacity of 820 mAh g −1 at 0.5 C after 250 cycles, 430 mAh g −1 at 6 C after 1000 cycles, and 222 mAh g −1 at ultrahigh rate of 60 C for LIBs, while for SIBs it delivers a specific capacity of 360 mAh g −1 at 1 C after 1000 cycles and 130 mAh g −1 at 60 C. Besides, the result of ex situ microstructure examination shows the polycrystalline nature of γ- Fe 2 O 3 nanoparticle still exists in LIB even after 1000 cycles, while it vanishes in SIB, suggesting that the relatively larger volume expansion occurred during Na + insertion/deinsertion, resulting in pulverization of the particles. The CNFs maintained their pristine 3D network structure after the charge/discharge, which demonstrated the critical role of a robust conductive electrode in promoting fast Li + /Na + transportation. More importantly, they act as an electrical bridge between Li + /Na + and γ -Fe 2 O 3 nanoparticles, therefore suppressing the cell impedance growth and γ -Fe 2 O 3 volume expansion, resulting in the enhancement in both cyclic and rate capability.