Stabilizing Li–Solid Electrolyte Interface Using MIEC Interlayers—Insights from Operando Electron Microscopy and Modeling

Li–solid electrolyte interface can be stabilized by mixed ion-and-electron conductor (MIEC) interlayers that spatially decouple Li redox and plating. However, the structural evolution of interlayer during lithiation remains poorly understood due to limitations in current operando characterization techniques. Here, we present the first high-resolution observation of MIEC interlayer evolution using operando scanning and transmission electron microscope, with an Ag-C composite as a model system. We show that the formation of Li-Ag percolation network during lithiation is critical to Li transport properties in interlayers. A homogeneous initial Ag distribution enables rapid and complete formation of the network, facilitating subsequent Li deposition at desirable locations. We further established an electro-chemo-mechanical model based on experimental data to elucidate MIEC structural evolution during lithiation and plating. Our optimized MIEC layer enables stable cycling at 2.8 mA cm^–2 and 14 mg_NMC cm^–2 for more than 2600 cycles at 30 °C in all-solid-state lithium metal batteries.

Acknowledgment: Y.Y. acknowledges the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Vehicle Technologies Program under Contact DE-EE0008864.