Investigation of Non-Aqueous Solvent Decomposition Mechanism on Mg Metal Anode Employing XPS Characterization

Magnesium batteries (Mg-battery) can offer higher volumetric energy density than lithium ion batteries. However, the challenge is to establish the stable electrochemical interface (i.e. electrode-electrolyte interface) that can facilitate Mg²⁺ ion diffusion while impeding electronic transport that can trigger electrolyte decomposition process. Such a designer interface can help us enhance the charge rate, lifetime, operating voltage, and safety of the Mg-battery. However, the main knowledge gap is a predictive understanding of electrochemical interphase formation, especially at Mg-metal anode. Currently, very few non-aqueous solvents were identified as compatible for Mg-battery application due to their ability to withstand both the Mg plating and stripping process. For example, 1-Methoxy-2-(2-methoxyethoxy)ethane (diglyme) being an ethereal solvent, is considered less volatile and reasonably stable against Mg reduction. In order to understand and interpret the reactions and subsequent interphase layer evolution from possible diglyme interaction with Mg-metal anode, in situ X-ray photo electron spectroscopy (XPS) measurements were performed at Pacific Northwest National Laboratory. In the current study, the vapor of diglyme solvent is exposed Mg-metal single crystal substrate and subsequently analyzed using high resolution X-ray photo electron spectroscopy. Detail reaction mechanisms and pathways based on core-level spectra will be discussed in this presentation.