Improved electrochemical properties of BiF3/C cathode via adding amorphous AlPO4 for lithium-ion batteries

Abstract High voltage BiF 3 electrode based on conversion reaction for lithium ion batteries is not immune to cyclic carbonate-based solid electrolyte interface (SEI) formation by a cathodic reaction even when discharge voltage exceeds 2 V. The SEI formation has considerable negative effect on the electrochemical properties of BiF 3 . To restrict this side-reaction effect, the BiF 3 /C/AlPO 4 composites with different amount of amorphous AlPO 4 have been successfully prepared by solid state milling process. The structure and morphology of BiF 3 /C/AlPO 4 composites are characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The electrochemical performance of BiF 3 /C/AlPO 4 composites has been studied by galvanostatic charge/discharge, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The results show that the addition of amorphous AlPO 4 does not change the bulk structure of BiF 3 , and the BiF 3 /C/AlPO 4 composites still keep face-centered cubic structure of BiF 3 . Besides, the results further confirm that SEI film will be formed on the Bi nanometal surfaces, and the amount of amorphous AlPO 4 is closely relevant with the SEI formation. With the increase of the amount, the SEI formation vanishes gradually. When increasing the amount of amorphous AlPO 4 to 15.0 wt.%, the SEI formation is restricted effectively. Particularly, the BiF 3 /C/AlPO 4 composite with 15.0 wt.% AlPO 4 exhibits the highest initial discharge capacity of 263.6 mAh g −1 , the lowest irreversible capacity of 45.1 mAh g −1 , the best rate capability and cycling stability.