Interfacial reactions and phase transformations play a significant role in the capacity and reversibility of lithium batteries. Understanding interfacial structural changes is especially important in alloying or conversion reactions found in higher-capacity intermetallic or metal oxyfluoride systems. Using in-situ X-ray reflectivity, we observe the lithiation of a stratified chromium silicide film with sub-nanometer resolution as a model system for characterizing such lithiation mechanisms. In-situ X-ray reflectivity of the thin film reveals that the sample lithiates to form the 1 nm thick low-electron-density regions at the buried interfaces separating each phase at sufficiently low electrochemical potentials. The reflectivity also indicates a significant accumulation of lithium at the surface at potentials approaching 0 V vs Li/Li +. The lithiation on the surface is fully reversible, whereas that in the film is partially irreversible. The observed mechanism for interfacial lithiation is likely a general feature of intermetallic electrodes and could be optimized for higher surface area nanostructures.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films