Solvation-derived amorphous motifs in lithium-metal SEI

The solid electrolyte interphase (SEI) on lithium metal plays a central role in battery stability, but its structure is still not well understood because much of it is amorphous rather than crystalline. In this work, we show that the amorphous SEI is not featureless disorder. Instead, it contains reproducible structural motifs that reflect how the electrolyte is organized before decomposition. By comparing SEIs formed in a localized high-concentration electrolyte and related ether-based electrolytes, we find that the amorphous SEI retains a structural memory of the liquid-state solvation environment. We further show that this amorphous structure changes systematically with solvent solvating strength, linking SEI formation directly to electrolyte design. These results provide new physical insight into how liquid electrolyte structure shapes the passivation layer on lithium metal. More broadly, this study demonstrates that combining total scattering with pair distribution function analysis is an effective way to probe disordered battery interphases that are difficult to resolve by conventional methods.