Intrinsic blocking effect of FeSi alloy in LiPF6 electrolyte solutions

Abstract

FeSi anode materials have attracted extensive attention because of their slow volume expansion. However, the side reactions between electrolytes and FeSi anodes have been neglected and rarely studied. In this work, the side reactions and corrosion kinetics of a FeSi alloy and LiPF6 electrolyte were elucidated using corrosion behavior analysis, electrochemical properties, and surface morphology, while the reaction mechanism was analyzed via X-ray photoelectron spectroscopy (XPS). The results show that the reaction rate of the FeSi alloy in the electrolyte decreases with an increase in silicon content and exposure time. The electrolyte transforms Fe (0) on the FeSi alloy interface into Fe (2+), which is further oxidized to Fe (3+). Finally, a fluoride film is deposited and accumulated on the alloy surface, which can prevent the LiPF6 electrolyte corroding the FeSi alloy matrix and prevent the occurrence of side reactions. Electrochemical tests show that the presence of a FeSi2 phase in the FeSi alloy can promote electron transmission, reduce impedance, and achieve a large reversible capacity (927.6 mAh·g−1) after 100 cycles. For lithium ion batteries, the FeSi alloy exhibits better cycle stability and a wider application market than those of the Si anode materials.