Experimental and Theoretical Insights into Factors Improving the Performance of Li-ion Batteries with a Si-based Anode by 1,1,2,2-Tetrafluoroethyl-2,2,3,3-tetrafluoropropyl Ether as an Additive (Supporting Information)

Anodes containing Si and SiOx are promising candidates for the fabrication of high energy density Li-ion batteries (LIBs). However, despite their specific capacity advantages, maintaining a sustainable cycling performance remains challenging due to their significant volume expansion and contraction. To enhance the interfacial stability of SiOx, this study uses an electrolyte containing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (D2) as an electrolyte additive and focuses on the solid electrolyte interphase (SEI) formed on the electrode surface. The reduction of D2 forms a robust LiF-based SEI along with a D2-specific fluoroalkyl component, which sufficiently stabilizes the SiOx interface. Therefore, the electrolyte containing D2 contributes not only to improving the charge-discharge cycle life and reducing resistance but also to suppressing gas generation within the battery system. To elucidate the mechanism of performance enhancement by D2, this study employs a wide range of analytical techniques, such as AC impedance spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and time of flight secondary ion mass spectrometry (TOF-SIMS), along with density functional theory (DFT) calculations to predict the reaction pathways of D2. These experimental and theoretical analyses demonstrate that D2 is an excellent additive for anode materials containing SiOx.