Lithiation Mechanism of Methylated Amorphous Silicon Unveiled by Operando ATR-FTIR Spectroscopy

The lithiation mechanism of methylated amorphous silicon, a-Si1-x(CH3)(x):H, with various methyl contents (x = 0 - 0.12) is investigated using operando attenuated total reflection Fourier transform infrared spectroscopy. As in hydrogenated amorphous silicon, a-Si:H, the first lithiation proceeds via a two-phase mechanism. The concentration of the invading Li-rich phase nonmonotonously depends on the methyl content of the active material. This behavior is tentatively explained by two distinct effects: a softening of the material due to a methyl-induced lowering of its reticulation degree and its cohesion, and the presence of nanovoids at high enough methyl content.