Tailored chemically bonded metal phosphide@carbon nanowire arrays on foam metal as an all-in-one anode for ultrahigh-area-capacity sodium-ion batteries

Abstract

Metal phosphides are superior anode materials for secondary batteries but suffer from variable volume and low electronic conductivity. In this work, chemically bonded metal phosphide@carbon nanowire arrays with adjustable structure mounted on foam metal were synthesized via a general facile chemical vapor deposition (CVD)-like approach using an environmentally friendly, solid ionic resin as a phosphorus source. The diameter of the nanowires and thicknesses of the carbon shell could be tailored via control of the synthesis conditions. Using a Fe2P@C array on iron foam as an example, it was demonstrated that the new materials could be used directly as an electrode in sodium-ion batteries (SIBs) without any additives or post-processing. The Fe2P@C electrode delivered a significantly high area capacity of 0.40 mAh cm−2 after 1400 cycles at a current density of 3 mA cm−2, a capacity retention rate of 80.25 %, which is, to the best of our knowledge, one of the most stable, high surface capacity performances achieved in SIBs at this large current density. Tests showed that the Fe2P@C nanowire array on a 3D foam structure provided a larger exposure area for electrolyte penetration, a shorter passage for Na+ diffusion, and faster electronic transfer. In situ TEM revealed that the carbon shell effectively alleviated volume expansion of the Fe2P and in-situ Raman and XRD verified the mechanism and high reversibility of Fe2P@C.