Ultrafine FeSe nanoparticles embedded into 3D carbon nanofiber aerogels with FeSe/Carbon interface for efficient and long-life sodium storage

The key challenge for high-performance sodium-ion batteries is the exploitation of appropriate electrode materials with a long cycling stability and high rate capability. This study reports the synthesis of a composite of ultrafine FeSe nanoparticles (NPs) and carbon nanofiber aerogel (CNFA) as anode material for SIBs. The composite features ultra-small (similar to 5 nm) NPs of FeSe uniformly embedded in interconnect three dimensional (3D) carbon nanofiber with large surface area, highly conductive network, and robust structural stability. As expected, the FeSe-CNFA-700 sample delivers a capacity as high as similar to 313 mA h g(-1) at 2000 mA g(-1) after 1000 cycles and ultrahigh rate capability up to 20000 mA g(-1). The significantly improved electrochemical performance could be attributed to the unique structure that combines a variety of advantages: easy access of electrolyte to the 3D network structure, pseudocapacitve charge storage and fast Na ion diffusion processes. The results confirm the intercalation of Na thorn into the 3D ultrafine FeSe nanoparticles/carbon nanofiber aerogel is enhanced through the strong interaction between FeSe nanocrystals and the carbon layer. The density functional theory calculations demonstrate that the unique FeSe/carbon layer interface in 3D network structure can enhance Na storage due to the small energy barrier and negative adsorption energy. (C) 2018 Elsevier Ltd. All rights reserved.