ToF-SIMS Li Depth Profiling of Pure and Methylated Amorphous Silicon Electrodes After Their Partial Lithiation.

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Amorphous silicon (a-Si:H) is a key material in energy storage.
• Understanding lithiation mechanisms is crucial for battery performance.
• Methylation of a-Si:H may alter its electrochemical properties.

Purpose of the Study:

• To investigate the lithiation mechanism in pure and methylated amorphous silicon thin films.
• To analyze the impact of nanovoids on lithium diffusion and concentration profiles.
• To model the observed lithium depth profiles using a developed simulation.

Main Methods:

• Time-of-flight secondary ion mass spectrometry (TOF-SIMS) for depth profiling.
• Partial lithiation of amorphous silicon thin films (a-Si:H and a-Si_0.95(CH₃)_0.05:H).
• Development of a specific model to simulate lithium depth profiles.

Main Results:

• Lithiation causes swelling and roughening of the amorphous silicon active layer.
• No significant lithium diffusion was observed after current-induced lithiation in either material.
• Distinct lithium concentration profiles were observed, with a slow transition in methylated a-Si:H attributed to nanovoids.

Conclusions:

• Nanovoids in methylated amorphous silicon act as quasi-percolating paths for lithium during initial lithiation.
• The developed model successfully simulates the observed lithium depth profiles, supporting the nanovoid hypothesis.
• Methylation significantly alters the lithiation behavior of amorphous silicon thin films.