Probing lithium mobility at a solid electrolyte surface

Solid-state electrolytes overcome many challenges of present-day lithium ion batteries, such as safety hazards and dendrite formation(1,2). However, detailed understanding of the involved lithium dynamics is missing due to a lack of in operando measurements with chemical and interfacial specificity. Here we investigate a prototypical solid-state electrolyte using linear and nonlinear extreme-ultraviolet spectroscopies. Leveraging the surface sensitivity of extreme-ultraviolet-second-harmonic-generation spectroscopy, we obtained a direct spectral signature of surface lithium ions, showing a distinct blueshift relative to bulk absorption spectra. First-principles simulations attributed the shift to transitions from the lithium 1 s state to hybridized Li-s/Ti-d orbitals at the surface. Our calculations further suggest a reduction in lithium interfacial mobility due to suppressed low-frequency rattling modes, which is the fundamental origin of the large interfacial resistance in this material. Our findings pave the way for new optimization strategies to develop these electrochemical devices via interfacial engineering of lithium ions.

Automated summary

Solid-state electrolytes have the potential to address safety and dendrite formation issues in lithium-ion batteries. However, the understanding of lithium dynamics in these materials is currently limited by a lack of in operando measurements. In this study, extreme-ultraviolet spectroscopy was used to investigate a solid-state electrolyte, revealing the distinctive behavior of surface lithium ions and the underlying factors contributing to interfacial resistance. These findings provide insights for the development of improved electrochemical devices through lithium-ion interfacial engineering.