Observation of the surface layer of lithium metal using in situ spectroscopy

We have investigated the surface of lithium metal using x-ray photoemission spectroscopy and optical spectroscopic ellipsometry. Even if we prepare the surface of lithium metal rigorously by chemical cleaning and mechanical polishing inside a glovebox, both spectroscopic investigations show the existence of a few tens of nanometer-thick surface layers, consisting of lithium oxides and lithium carbonates. When lithium metal is exposed to room air (~50% moisture), in situ real-time monitoring of optical spectra indicates that the surface layer grows at a rate of approximately 24 nm/min, presumably driven by an interface-controlled process. Our results hint that surface-layer-free lithium metals are formidable to achieve by a simple cleaning/polishing method, suggesting that the initial interface between lithium metal electrodes and solid-state electrolytes in fabricated lithium metal batteries can differ from an ideal lithium/electrolyte contact. Published under an exclusive license by AIP Publishing.

Automated summary

The surface of lithium metal contains surface layers composed of lithium oxides and lithium carbonates, even after rigorous cleaning and polishing. When exposed to room air, the surface layer grows at a rate of approximately 24 nm/min. This suggests that achieving a surface-layer-free lithium metal is challenging and can impact the interface in lithium metal batteries.