Iron fluoride packaged into 3d order mesoporous carbons as high-performance sodium-ion battery cathode material

The FeF3 · 0.33H2O nanoparticles packaged into three-dimensional order mesoporous carbons (3D-OMCs) as cathode material of sodium-ion batteries (SIBs) was deliberately designed and fabricated by a facile nanocasting technique and mesoporous silica KIT-6 template. The structure, morphology, elemental distribution and electrochemical performance of FeF3 · 0.33H2O@3D-OMCs nanocomposite are investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM), energy-dispersive X-ray spectroscope (EDS), Raman spectroscopy and electrochemical measurement. The results show that the as-synthesized FeF3 · 0.33H2O nanoparticles are perfectly packaged in 3D-OMCs matrix, and the size and morphology of FeF3 · 0.33H2O nanoparticles can be effectively controlled. Furthermore, it has been found that the FeF3 · 0.33H2O@3D-OMCs nanocomposite can deliver a high first discharge capacity of 386 mAh g−1 and excellent capacity reservation after 100 cycles at a rate of 20 mA g−1 in the voltage range of 1.0–4.0 V. Especially, even up to 100 mA g−1, the discharge capacity is still as high as 201 mAh g−1, indicating a remarkable rate capability. The excellent electrochemical properties of FeF3 · 0.33H2O@3D-OMCs nanocomposite can be because the 3D mesoporous structure of 3D-OMCs can provide an expressway of electron transfer for Na+ insertion/extraction, and alleviate the drastic volume variation of FeF3 · 0.33H2O in the charge-discharge process.