Intrinsic Properties of Silicon-Electrolyte Interphase (SiEI) Studied through Individual Inorganic Components

Abstract

The stabilization of a silicon-electrolyte interphase (SiEI) is a great challenge which limits the ability to approach theoretical capacity limits (about 3,600 mAh g-1, almost 10 times higher than that of graphite) in silicon (Si) anodes for next-generation lithium-ion batteries (LiBs). The SiEI is a less studied topic relative to the research devoted to battery components, in part, because of its complexity, reactivity and continuous evolution.1 However, the SiEI plays a key role in prevention of further electrolyte reduction and desolvation of Li+ions, which is directly related to electrochemical performance, lifetime and safety of batteries. For example, the unstable SiEI leads to irreversible capacity losses, poor cycling stability and a limited cycle life.2-4 In this study selected known SiEI components (i.e., SiO2, Li2Si2O5, Li2SiO3, Li3SiOx, Li2O and LiF) were prepared as amorphous thin films. The chemical composition, homogeneity, morphology and local electronic structure across the surface and the bulk were characterized using X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), atomic force microscope (AFM), and scanning-spreading resistance microscopy (SSRM). In addition, the physical, electrochemical and mechanical properties of individual constituents were characterized using electrochemical impedance spectroscopy (EIS), operandoXPS with an electron gun, and AFM (force distance curve) and scanning probe microscopy (SPM)-based nanoindentation. This study delineates the components which are critical for stabilizing the SiEI. These findings enable rational design of new electrolyte additives and functional binders for the development of next generation LiBs.