Characterization and Quantification of Depletion and Accumulation Layers in Solid‐State Li+‐Conducting Electrolytes Using In Situ Spectroscopic Ellipsometry

• Published in: Advanced materials (Weinheim) Vol. 33; no. 24; pp. e2100585 - n/a
• Main Authors: Katzenmeier, Leon, Carstensen, Leif, Schaper, Simon J., Müller‐Buschbaum, Peter, Bandarenka, Aliaksandr S.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.06.2021; John Wiley and Sons Inc
• Subjects: Accumulation; accumulation layers; Conduction; Conductors; Depletion; Electrochemistry; Electrode materials; Electrolytes; Glass ceramics; Interface stability; Ion currents; Lithium; Molten salt electrolytes; Optical measurement; Physical properties; Solid electrolytes; solid Li‐ion conductors; solid‐state electrolytes; Space charge; space charge layer; Spectroellipsometry; spectroscopic ellipsometry; Spectroscopy; accumulation layers; solid-state electrolytes; space charge layer; spectroscopic ellipsometry; solid Li-ion conductors
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.202100585

The future of mobility depends on the development of next‐generation battery technologies, such as all‐solid‐state batteries. As the ionic conductivity of solid Li+‐conductors can, in some cases, approach that of liquid electrolytes, a significant remaining barrier faced by solid‐state electrolytes (SSEs) is the interface formed at the anode and cathode materials, with chemical instability and physical resistances arising. The physical properties of space charge layers (SCLs), a widely discussed phenomenon in SSEs, are still unclear. In this work, spectroscopic ellipsometry is used to characterize the accumulation and depletion layers. An optical model is developed to quantify their thicknesses and corresponding concentration changes. It is shown that the Li+‐depleted layer (≈190 nm at 1 V) is thinner than the accumulation layer (≈320 nm at 1 V) in a glassy lithium‐ion‐conducting glass ceramic electrolyte (a trademark of Ohara Corporation). The in situ approach combining electrochemistry and optics resolves the ambiguities around SCL formation. It opens up a wide field of optical measurements on SSEs, allowing various experimental studies in the future. Solid‐state electrolytes are one of the few battery technologies for next‐generation batteries. However, the high interface resistance in contact with electrode materials is still largely unexplained. Spectroscopic ellipsometry combined with in situ electrochemistry reveals highly asymmetric space charge layer occurrence. It opens a new study field to investigate and quantify the charge layer formation in solid‐state electrolytes by optical means.