(307e) Revealing the Dynamics of Solid-Electrolyte Interphase (SEI) at Li Metal Anode

Li metal anode (LMA) has dramatic potential to elevate the energy density of state-of-art Li-ion battery. However, commercial implementation of LMA is largely plagued by Li dendrite formation as well as uncontrolled reactivity at electrode/electrolyte interface to form solid-electrolyte interphase (SEI). Developing new liquid electrolyte is a promising route to improve current LMA performance. Despite recent progress of high-performing liquid electrolytes, a fundamental look at the SEI chemistry is necessary to identify key interfacial characteristics attributed to the better LMA performances. A collection of several new ether-based electrolytes, both fluorinated and non-fluorinated, offers a platform for developing systematic understanding. Specifically, we leveraged the power of electrochemistry together with rigorous analyses of X-ray photoelectron spectroscopy (XPS), to probe the SEI passivation behavior at Cu surface in contact with various ether electrolytes in a Li/Cu half-cell. Meanwhile, we have identified several notable pitfalls in the widely adopted protocol of XPS measurements and analyses in the battery field. By understanding and improving experiment design, we managed to correlate the electrochemical data with the quantitative XPS results to gain insights into the detailed formation pathway and kinetics of anion-derived SEI chemistry. We also identified several key reaction intermediates formed upon anion breakdown, dictating the SEI reaction and dissolution in electrolyte. Collectively, these data reveals the dynamic nature of actively forming SEI under varied galvanostatic and potentiostatic conditions. This advanced fundamental understanding has important implications for future rational design and engineering of next-generation electrolytes enabling practical Li metal battery.