Lithium Permeability Increase in Nanosized Amorphous Silicon Layers

Li permeation through nanosized amorphous Si layers is investigated for temperatures up to 500 °C (773 K) as a function of layer thickness between 12 and 95 nm. For the experiments the Si layers are embedded between 6 Li and 7 Li isotope enriched oxide based Li reservoirs, and the thermally induced isotope exchange (through silicon layers and interfaces) is analyzed by secondary ion mass spectrometry in order to calculate Li permeabilities. The experiments reveal that the interface between silicon and the Li metal oxide does not hinder Li permeation and Li diffusion in silicon controls the overall process. The determined Li permeability increases drastically by orders of magnitude with decreasing silicon layer thickness, accompanied by a decrease in the activation enthalpy of Li permeation. These results can be explained by a gradual transition of trap-limited slow Li diffusion at high silicon thicknesses to interstitial fast Li diffusion at low Si thicknesses.