Guorong V. Zhuang

A Study of Electrochemical Reduction of Ethylene and PropyleneCarbonate Electrolytes on Graphite Using ATR-FTIR Spectroscopy

We present results testing the hypothesis that there is a different reaction pathway for the electrochemical reduction of PC versus EC-based electrolytes at graphite electrodes with LiPF6 as the salt in common. We examined the reduction products formed using ex-situ Fourier Transform Infrared (FTIR) spectroscopy in attenuated total reflection (ATR) geometry. The results show the pathway for reduction of PC leads nearly entirely to lithium carbonate as the solid product (and presumably ethylene gas as the co-product) while EC follows a path producing a mixture of organic and inorganic compounds. Possible explanations for the difference in reaction pathway are discussed.

Solid electrolyte interphase on graphite Li-ion battery anodes studied by soft X-ray spectroscopy

We have measured X-ray absorption and emission near the C 1s edge of graphite electrodes cycled in lithium-ion battery cells. Resonantly excited emission spectra of graphite electrodes exhibit features characteristic of both highly oriented pyrolytic graphite as well as polycrystalline graphite. Spectra of three electrodes cycled in two different electrolytes are presented and compared with spectra of the pristine electrode. A solid electrolyte interphase (SEI) was detected on the electrochemically cycled electrodes. By the use of selective excitation, resonant X-ray emission spectra of the SEI-species were obtained and compared to spectra of reference compounds. The SEI on the cycled graphite anode was shown to comprise lithium oxalate (Li2C2O4), lithium succinate (LiO2CCH2CH2CO2Li) and lithium methoxide (LiOCH3).

Anodic Polymerization of Vinyl Ethylene Carbonate in Li-Ion Battery Electrolyte

A study of the anodic oxidation of vinyl ethylene carbonate (VEC) was conducted with post-mortem analysis of reaction products by ATR-FTIR and gel permeation chromatography (GPC). The half-wave potential (E1/2) for oxidation of VEC is ca. 3.6 V producing a resistive film on the electrode surface. GPC analysis of the film on a gold electrode produced by anodization of a commercial Li-ion battery electrolyte containing 2 percent VEC at 4.1 V showed the presence of a high molecular weight polymer. IR analysis indicated polycarbonate with alkyl carbonate rings linked by aliphatic methylene and methyl branches.

The study of surface Li―Sb alloy formation and electronic structure using photoelectron spectroscopy

The formation of surface Li-Sb alloy and its electronic structures are investigated with x-ray photoelectron spectroscopy (XPS). From the information on core-level shift of Sb 3d and Li 1s XPS spectra, the presence of charge transfer from Li to Sb is confirmed, while the chemical composition of formed alloy is estimated as Li(3)Sb. The density of states from valence band XPS shows a significant nonrigid part of band structures, suggesting strong covalent bonding between Li and Sb.

Resonant photoemission from the 4d → εf shape resonance in Sb(0001)

The observation of resonant photoemission at shape resonance energy in Sb(0001) is reported. When the photon energy was tuned to the transition region of the Sb shape resonance (), a Fano-like profile was observed in the photoelectron cross-section from the half-filled 5p valence orbitals. Two new, significant features appeared at photon energies above the 4d threshold: one in the gap between the filled 5s2 and half-filled 5p bands, and the other at the Fermi level. The former is attributed to final state mixing in the autoionization decay of the ef transition state, and the latter to a two-photon photoionization process directly from the ef transition state.