Highly active Fe7S8 encapsulated in N-doped hollow carbon nanofibers for high-rate sodium-ion batteries

Nanostructured iron sulfides are regarded as a potential anode material for sodium-ion batteries in virtue of the rich natural abundance and remarkable theoretical capacity. However, poor rate performance and inferior cycling stability caused by sluggish kinetics and volume swelling represent two main obstacles at present. The previous research mainly focuses on nanostructure design and/or hybridizing with conductive materials. Further boosting the property by adjusting Fe/S atomic ratio in iron sulfides is rarely reported. In this work, Fe7S8 and FeS2 encapsulated in N-doped hollow carbon fibers (NHCFs/Fe7S8 and NHCFs/FeS2) are constructed by a combined chemical bath deposition and subsequent sulfidation treatment. The well-designed NHCFs/Fe7S8 electrode displays a remarkable capacity of 517 mAh g(-1) at 2 A g(-1) after 1000 cycles and a superb rate capability with a capability of 444 mAh g(-1) even at 20 A g(-1) in etherbased electrolyte. Additionally, the rate capability of NHCFs/Fe7S8 is superior to that of the contrast NHCFs/FeS2 electrode and also much better than the values of the most previously reported iron sulfide-based anodes. The in-depth mechanism explanation is explained by further experimental analysis and theoretical calculation, revealing Fe7S8 displays improved intrinsic electronic conductivity and faster Na' diffusion coefficient as well as higher reaction reversibility. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

Nanostructured iron sulfides show potential as anode materials for sodium-ion batteries due to their natural abundance and high theoretical capacity. Improving cycling stability and rate performance through adjusting Fe/S atomic ratio has been rarely explored. Fe7S8 encapsulated in N-doped hollow carbon fibers exhibits superior capacity and rate capability compared to FeS2, showcasing enhanced intrinsic electronic conductivity and faster Na diffusion coefficient.