Vibrational Assignments of Lithium Alkyl Carbonate and Lithium Alkoxide in the Infrared Spectra An Ab Initio MO Study

Abstract

Lithium electrode stability in various nonaqueous solvents is kinetic in origin and is caused by a film formed on the lithium surface by reaction of the active metal 1 or the active Li-C intercalation anode 2 with solvents. This film is called solid electrolyte interphase (SEI). 3-5 An SEI is formed at the negative electrode/electrolyte interface because of irreversible reactions. These reactions will ideally form a stable, protective film on negative electrode, allowing the electrode to continue to operate without further reaction. So the SEI passivation layer plays a major role in determining electrode and battery behavior and properties include cycle life, shelf life, safety, and irreversible capacity loss. Main components of an SEI are Li 2 CO 3 , ROCO 2 Li, ROLi, LiF, Li 2 O, and LiCl which are measured by techniques such as X-ray photoelectron spectroscopy, 6-10 infrared spectroscopy, 11-21 and X-ray diffractometry. 22,23 In addition, reaction gas products such as alkane, alkene, H 2 , CO 2 , and CO are measured by gas chromatography. 13,[24][25][26][27] Using an infrared spectroscopy, mainly observed components of an SEI are Li 2 CO 3 , ROCO 2 Li, and ROLi. Therefore standard data of these compounds are important of the investigation of the SEI with IR. For ROCO 2 Li-type compounds infrared spectra of the CH 3 OCO 2 Li, C 2 H 5 OCO 2 Li, C 3 H 7 OCO 2 Li, and C 4 H 7 OCO 2 Li have been measured by Behredt et al. 28 and infrared spectra of CH 3 CH(OCO 2 Li)CH 2 OCO 2 Li is obtained by Aurbach et al. 11 For ROLi-type compounds infrared spectra of the CH 3 OLi, C 2 H 5 OLi, C 4 H 9 OLi, LiOC 2 H 4 OLi, and LiOCH 2 CH(OLi)CH 3 have been measured by Aurbach et al. 11,12 There is not enough information for band assignments of the vibration modes of ROCO 2 Li-and ROLi-type compounds, so we calculated the structural information for these compounds. In this work, we calculated the geometry, energy, dipole moment, and norWe conducted ab initio molecular orbital calculations on stable monomer and dimer structures of lithium alkyl carbonates (methyl, ethyl, and propyl carbonate lithium) and lithium alkoxides (lithium methoxide, lithium ethoxide, lithium propoxide, and lithium butoxide). We confirmed that both lithium alkyl carbonates and lithium alkoxides adopted the dimer structure. The dimerization energies were approximately constant and independent of the alkyl group chain length. The dimerization energy was 214 kJ/mol for lithium alkyl carbonates and 266 kJ/mol for lithium alkoxides. Assignments of the vibration modes for each calculated frequency of lithium alkyl carbonates and lithium alkoxides were carried out. Vibrational frequency analysis recognized a dramatic vibrational frequency shift in the parts of the structure which changed significantly between the monomer and dimer structures (the lithium carbonate structure for lithium alkyl carbonates and the COLi structure for lithium alkoxides). Good agreement was achieved between calculated and experimental vibrational frequencies by shifting the frequency of ...

Near-Shore Aggregation Mechanism of Electrolyte Decomposition Products to Explain Solid Electrolyte Interphase Formation

“…We also point out that the Li 2 EDC can easily have bent form, contributing to the CN increase as well. These structural features are consistent with the previous studies by ab initio CBC calculation, 30,31 classical MD calculation 28 and DFT-MD calculation. 36 On the other hand, rather straight SFCs with π conjugation in the Li 2 DOB provide smaller CNs.…”

Control of Surface Chemistry and Electrochemical Performance of Carbon-coated Silicon Anode Using Silane-based Self-Assembly for Rechargeable Lithium Batteries

“…5a-a', the C-Si surface shows strong IR features below 900 cm , related to the reduction of organic carbonate solvents. 16,17,[22][23][24]31,32,[40][41][42] With 1-(trimethylsilyloxy)-1,3-butadiene, Fig. 5b-b', the CSi surface also shows strong IR features below 900 cm .…”

Solution based synthesis of mixed-phase materials in the Li2TiO3–Li4SiO4 system

“…Show FTIR scans from supernatant liquid and bulk. Figure 3 shows FTIR spectra from sol and bulk dried precipitates of a 1:1 sol of L2S:LT. Lines indicate reported IR shifts of ethylithium [56][57][58]. The large stretching vibration mode observed around 3400 cm -1 is indicative of O-H bonds, present in solvent and precursor compounds.…”