Lithium Permeability Increase in Nanosized Amorphous Silicon Layers

Abstract

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 6Li and 7Li 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.

Neutron reflectometry to measure in situ the rate determining step of lithium ion transport through thin silicon layers and interfaces

“…Otherwise, the time constants would be expected to be independent of Si layer thickness. The in situ NR experiments confirm the results obtained by ex situ SIMS experiments 41 that Li transport through thin Si layers is strongly dependent on the Si layer thickness and is consequently controlled by the Li permeation/ diffusion process in the Si layers and not by the transport of Li through the LiNbO 3 /Si interface. This shows that the LiNbO 3 /Si interface is not an obstacle for the Li transport process.…”

“…Amorphous LiNbO 3 was used as a Li reservoir due to its high Li diffusivity, stability against air corrosion and heating procedures. 26,29,40,41,43 The high diffusivity of Li in amorphous LiNbO 3 as compared to crystalline and even nanocrystalline LiNbO 3 had earlier been shown. [44][45][46][47] Similar results were found for other Li metal oxides like LiTaO 3 , LiAlO 2 or LiGaO 2 studied partly also by NR, secondary ion mass spectrometry (SIMS), nuclear magnetic resonance spectroscopy or impedance spectroscopy (see ref.…”

“…[30][31][32][33][34][35][36][37][38] This work describes the use of neutron reflectometry to measure the transport of Li across Si layers in a multilayer. It is the latest in a series of related articles 26,29,35,[39][40][41] of increasing sophistication and quality of information. More information on this issue is given in the first section of the ESI † accompanying this work.…”

“…The MLs were produced by ion-beam sputter deposition. 42 There, 26,29,35,[39][40][41] Li and 7 Li isotopes, respectively. Each of these two isotope enriched Li reservoir layers are adjacent to a Si layer.…”

“…26 and 29. Up to now, with the exception presented below, only ex situ investigations for the determination of Li permeabilities in Si layers are published which were done by NR or SIMS (see the ESI † accompanying this work). 26,29,[39][40][41] Ex situ means that the isothermal annealing procedure necessary to initiate the Li permeation process was interrupted and the sample was cooled to room temperature before analysis is carried out. Ref.…”