Speaker
Description
Silicon is a promising lithium-ion anode material, storing about ten times more lithium than graphite, but its large volume change and unstable solid-electrolyte interphase (SEI) limit the lifetime and quality of the cell. Whether the crystal lattice or the native-oxide/SEI surface layer governs how deep lithium penetrates remains unsolved, as the two contributions are difficult to separate in polycrystalline or nanostructured electrodes.
This study uses single-crystal Si(100), Si(110) and Si(111) wafers as a model system with one defined surface and one defined oxide, cycled against lithium in liquid-electrolyte coin cells. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) serves as the central method, complemented by X-ray photoelectron spectroscopy (XPS), X-ray reflectometry (XRR), white-light interferometry and focused ion beam (FIB) cross-sections.
On the pristine wafers, XPS resolves an orientation-dependent oxide, with Si(110) being the most oxidic. On cycled Si cells of different orientations, depth-calibrated ToF-SIMS profiles distinguish lithium penetration depths and FIB cross-sections provide an independent thickness of the modified layer. Raman spectroscopy and transmission electron microscopy/electron energy-loss spectroscopy (TEM/EELS) are planned to add the crystalline-to-amorphous transition and the local LixSi phase that ToF-SIMS cannot resolve. This work establishes the depth-resolved analytical chain required to disentangle lattice- and surface-controlled lithiation.
