Operando Characterization of Plating and Stripping Dynamics of Li-Mg Alloy Anode and Sulfide Solid Electrolyte Interface

Abstract

All-solid-state lithium metal batteries are projected to offer one of the highest specific energy among rechargeable batteries, positioning them as a front-runner for electric vehicle applications. Lithium metal anodes outperform conventional graphite anodes in terms of cell-level energy density. However, maintaining a conformal metal–electrolyte contact is a great challenge. The volumetric change of the lithium metal anode during stripping produces voids, which deteriorates the Li–electrolyte contact. To address this challenge, β-phase Li solid solution (i.e., Li-Mg alloy) has been shown to exhibit improved contact with the solid electrolyte during stripping. Moreover, Li solid solution has a similar electrochemical potential as Li, making it a potential replacement for Li metal anodes without sacrificing cell-level energy density. In this study, we show that the chemical properties of the alloy play an essential role in the morphological stability of metal–solid electrolyte interface. We compare the stripping behavior of pure Li and Li-Mg alloy anodes in argyrodite electrolyte and characterize the morphological evolution of the interface using operando scanning electron microscopy (SEM). We also analyze the electro-chemo-mechanical properties of Li and Li alloy anodes during stripping with galvanostatic electrochemical impedance spectroscopy (GEIS) to compare the influence of composition change and interfacial void on the electrode overpotential and interface resistance. Our research visualizes the morphological and compositional evolution of alloy metal anode during stripping and rationalizes their improved interfacial stability against solid electrolytes.Acknowledgment: This work was supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Vehicle Technologies Program under Contract DE-EE0008864. Figure 1