Abstract
The performance of energy-dense lithium metal batteries is critically influenced by the properties of the solid electrolyte interphase (SEI). Yet, progress in understanding this layer has been limited by the lack of accurate operando characterization because the SEI evolves dynamically during cycling. Here, we apply dynamic electrochemical impedance spectroscopy (dEIS) to resolve the real-time evolution of the SEI on lithium metal in ether-based electrolytes with varying degrees of fluorination. We find that faster stabilization of the compact SEI resistance correlates with improved passivation and higher Coulombic efficiency. Unexpectedly, compact SEI resistance correlates directly with Li+solvation energy, revealing that weaker Li+solvation increases not only bulk but also interphase resistance. These findings challenge the conventional view of the SEI as a purely solid-phase conductor and instead support a solvent-assisted Li+transport mechanism within the compact SEI. This framework emphasizes the need to balance SEI ionic conductivity with the Li+solvation environment to maximize lithium metal battery performance.
| Original language | English |
|---|---|
| Pages (from-to) | 42701-42710 |
| Number of pages | 10 |
| Journal | Journal of the American Chemical Society |
| Volume | 147 |
| Issue number | 46 |
| DOIs | |
| State | Published - Nov 19 2025 |
Funding
This work is supported by the U.S. Department of Energy, under the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technologies Office, the Battery Materials Research Program, and Battery500 Consortium. SEM imaging was performed at the Stanford Nano Shared Facilities (SNSF), supported by the National Science Foundation under award ECCS-2026822. J.F. acknowledges support from the NSF Graduate Research Fellowship for graduate studies at Stanford. S.L. was supported by the U.S. Department of Energy, Vehicle Technologies Office under the Silicon Consortium Project, directed by Nicolas Eidson, Carine Steinway, Thomas Do, and Brian Cunningham, and managed by Anthony Burrell. The dEIS instruments and data analyses (R.L.S.) and electrolyte studies (Z.B.) were supported by the U.S. Department of Energy’s Vehicle Technologies Office under the U.S.-Germany Energy Storage Consortium, directed by Tien Duong.