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

Abstract

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.

Dual‐IR Window/Electrode Operando Attenuated Total Reflection‐IR Absorption Spectroscopy for Battery Research

“…More specifically, the pair of positive bands at 1736 and 1316 cm À1 bands can be assigned to the DEDOHC (diethyl 2,5dioxahexane dicarboxylate) formed inside the SEI layer, similar to what observed on Sn. [16] The other pair of positive bands at 1820 and 1780 cm À1 , on the other hand, can be assigned to EC and Li-ion associated EC inside the SEI layer. [9] These SEI IR bands observed herein match those reported in the literature but with slight peak shifts and different shapes and relative peak intensities.…”

“…Interestingly, these single beam spectra already showed that the solvent molecules (EC vs. DEC) interacted differently with the anode and cathode at this initial stage. By comparing with the peak positions and relative amplitudes of the reference spectra [16] shown in Figure S2, we assigned the peaks identified by red vertical dashed lines to EC and those by blue lines to DEC. On the LiCoO 2 cathode, only DEC was observed. But on the graphite anode, both EC and DEC were observed, which indicates that EC interacted preferentially with anode.…”

“…[21,25,[28][29][30][31][32] As electrode/electrolyte interfacial compounds are highly air and humidity sensitive, it is highly desirable to study the SEI-related chemistries in operando. [16] The other pair of positive bands at 1820 and 1780 cm À1 , on the other hand, can be assigned to EC and Li-ion associated EC inside the SEI layer. As can be seen in Figure 3b, the formation of SEI initiated at 2.50 V and kept growing until 4.1 V that is characterized by the distinct 3-band SEI structure.…”

“…In spite of the recent achievements on producing power using renewable sources such as solar and wind energies, the intermittent nature of those green sources makes energy storage systems necessary for their sustainable use. [7][8][9][10][11][12][13][14] Although most recent in-situ EChem IR studies [8][9][10][11][12][13][14][15] employed attenuated total reflection (ATR) mode to overcome the problem of hindered ionic diffusion caused by the earlier thinlayer mode, [6,7] they also adopted a half-cell configuration against a Li metal electrode and most likely with an inbetween-electrode physical dimension that was not commensurate with that of real-world batteries, which leaves room for further improvements. [1][2][3][4][5] In LIBs (or rechargeable batteries in general), conversion between chemical and electrical energy occurs through controlled reversible chemical reactions between a set of active chemicals.…”

“…This dictates that, in order to truly understand the underlying chemistries, many key battery processes have to be studied by in-situ/operando techniques; [6] yet many of the latter are still at an early stage of development, which includes in-situ/operando electrochemical (EChem) infrared (IR) spectroscopy. [7][8][9][10][11][12][13][14] Although most recent in-situ EChem IR studies [8][9][10][11][12][13][14][15] employed attenuated total reflection (ATR) mode to overcome the problem of hindered ionic diffusion caused by the earlier thinlayer mode, [6,7] they also adopted a half-cell configuration against a Li metal electrode and most likely with an inbetween-electrode physical dimension that was not commensurate with that of real-world batteries, which leaves room for further improvements. With these observations in mind, we report herein a novel dual-ATR window/electrode configuration that offers a unique advantage of accessing both anode and cathode processes quasi-simultaneously in the same operando real-battery-like cell.…”