In Situ Potentiodynamic Analysis of the Electrolyte/Silicon Electrodes Interface Reactions - A Sum Frequency Generation Vibrational Spectroscopy Study

Abstract

The key factor in long-term use of batteries 9 is the formation of an electrically insulating solid layer that 10 allows lithium ion transport but stops further electrolyte 11 redox reactions on the electrode surface, hence solid 12 electrolyte interphase (SEI). We have studied a common 13 electrolyte, 1.0 M LiPF 6 /ethylene carbonate (EC)/diethyl 14 carbonate (DEC), reduction products on crystalline silicon 15 (Si) electrodes in a lithium (Li) half-cell system under 16 reaction conditions. We employed in situ sum frequency 17 generation vibrational spectroscopy (SFG-VS) with inter-18 face sensitivity in order to probe the molecular 19 composition of the SEI surface species under various 20 applied potentials where electrolyte reduction is expected. 21 We found that, with a Si(100)-hydrogen terminated wafer, 22 a Si-ethoxy (Si-OC 2 H 5) surface intermediate forms due to 23 DEC decomposition. Our results suggest that the SEI 24 surface composition varies depending on the termination 25

The electrochemical behavior of poly 1-pyrenemethyl methacrylate binder and its effect on the interfacial chemistry of a silicon electrode

“…The onset potential of the electrolyte reduction was observed at 2.25 V, consistent with the previous study for FEC containing electrolyte [17]. The shoulder at 1.3 V, and the sharp feature at 0.8 V correspond to the decomposition of DEC and EC, respectively [24]. A small feature due to the initial lithiation of crystalline Si(100) at 0.2 V is followed by a steep increase of the cathodic current and lithiation of silicon at 0.11 V. The anodic peaks at 0.32 V and 0.52 V correspond to the delithiation process [25].…”

“…Though the peak distribution pattern of the Si(100) and Si(100)/PPy electrodes below 1300 cm −1 is comparable, the different FTIR peak intensities and ratios indicate variations of thickness and chemical composition of the surface films on the cycled Si(100) and Si(100)/PPy electrodes. In the FTIR spectrum of the cycled Si(100)/PPy, the intense peaks at 2850 and 2930 cm −1 due to the asymmetric C-H stretching, the shoulder at 1020 and the peak at 778 cm −1 due to asymmetric Si-O stretching, and the peak at 1160 cm −1 due to O-C stretching of Si-O-CH 3 group shows the presence of Si containing reduction reaction products [24,28]. Moreover, the FTIR peaks of the cycled Si(100)/PPy in the region from 1300 to 1750 cm −1 is different from the Si(100) electrode suggesting the variation of the film formation process at the electrode/electrolyte interface.…”

Cycling of a Lithium‐Ion Battery with a Silicon Anode Drives Large Mechanical Actuation

“…At a preload of 5.7 kPa, the load increased by 25.8 kPa at full charging, as shown in Figure a. During the first 1000 s of charging, the load increased at a low rate, corresponding to the formation of solid–electrolyte interphases . There is an obvious turning point in the load–time curve at about 3000 s during charging, which will be addressed shortly.…”

Fluorinated End‐Groups in Electrolytes Induce Ordered Electrolyte/Anode Interface Even at Open‐Circuit Potential as Revealed by Sum Frequency Generation Vibrational Spectroscopy

“…We detect Fermi β contributions at 2939 cm −1 and an asymmetric β‐OCH 2 at 2963 cm −1 . Finally, only after lithiation we detect two broad peaks at 2983 and 3024 cm −1 that we attribute to the appearance of an unconjugated fluoroalkene group (ROCHCF 2 ), a reported product of the beta cleavage that intensifies after lithiation . Therefore, we suggest that the a‐Si surface may now be covered with SiOCH 2 CH 2 OCHCF 2 and SiOCH 2 CF 3 .…”