Understanding the effect of electrolyte on the cycle and structure stability of high areal capacity Si-Al film electrode

High areal capacity silicon-based films are attracting much attention in high energy density lithium-ion batteries (LIBs). However, the enormous volume change of Si, causing film crack and instability of solid electrolyte interphase (SEI) layer, leads to a rapid capacity decay. In this work, the structure evolution and electrochemical performance of Si-Al film (~ 2.5 mAh cm -2 ) are systematically investigated by galvanostatic discharge/charge test, field-emission scanning electron microscopy (FESEM), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). Particularly, the inner structure is carefully analyzed by the cross-sectional images. In the EC-based and FEC-added electrolytes, the columnar structure is remained. Interestingly, the rigid SEI layer formed in FEC-based electrolyte restrains the surface tensile stress, and the Si-Al film is cracked from the inner part and further rearranged towards compact piling up during cycling. The new formed film displays a weak volume expansion and an improved capacity retention of 85.0% after 100 cycles.