Lithium alkyl dicarbonates

Lithium alkyl dicarbonates generally strongly associate through intermolecular 0 Li 0 interactions, resulting in various conformations, such as chain-hke. 

Table 4 Calculated results for lithium alkyl dicarbonates at the B3PW91/6-31G(d) level including total binding energies (TBE, kcal/mol), BSSE (kcal/mol), BSSE-corrected binding energies [TBE(BSSE), kcal/mol), ZPE-corrected binding energies [TBE(ZPE), kcal/mol), variations of the total overlap-weighted NAO bond orders for the involved Li ions (Aa) and variations of the total partial charges from NPA for Li ions (-Aq/e).

Lithium alkyl dicarbonates, resulting from alkyl carbonate reductive decomposition, strongly associate through 0 Li 0 interactions, and would grow adopting the closed structure conformation, i.e., they would associate to the cage-like dimer first, then to the closed pseudo-planar trimer, then to the closed tetramer, and so on. Additionally we found that features on the IR spectra caused by associations of lithium alkyl dicarbonates are closer to the... 

Adsorption and Two-Dimensional Association of Lithium Alkyl Dicarbonates on Graphite Surfaces Through (Arene)... 

Adsorption of Lithium Alkyl Dicarbonates on the Basal Plane of the Neutral Graphite Surface... 

Adsorption of lithium alkyl dicarbonates on the basal plane... 

The direct evidence of this reaction mechanism is the observation of carbonyl stretching signature at -1,650 cm" in FTIR spectrum. The decomposition products from lithium salt were also found through the XPS surface analysis, such as alkoxides or oxides, a competition reaction between solvents and salts. However, the formation of alkyl carbonate seems to be predominant when EC is the component of electrolyte because of the more reactive nature of EC toward cathodic reductions [28]. The formation of lithium alkyl carbonate was also confirmed in an independent work, where the reduction products of EC in a supporting electrolyte were hydrolyzed by DjO and then subject to NMR analysis, which identified ethylene glycol as the major products formed, as indicated by the singlet at H spectrum [29]. Therefore, Aurbach and co-workers concluded the reduction products of EC and PC, lithium ethylene dicarbonate (LEDC) and lithium propylene dicarbonate (LPDC), respectively ... 

The selected NMR spectra of these synthesized lithium alkyl ethylene dicarbonate and lithium alkyl propylene dicarbonate are shown in Fig. 5.7. 

The lithium alkyl monocarbonate, EMC and EEC, exhibits much higher thermal stability than the two dicarbonates, EEDC and EPDC. Either the mono- or dicarbonate has multiple thermal processes with different onset temperature. On the base of identification of chemical components of TGA remnants via XPS and NMR after the samples were heated to different temperatnres, they proposed the following competitive decomposition mechanisms (Scheme 5.10). 

Xu K et al (2006) Syntheses and Characterization of lithium alkyl mono- and dicarbonates as components of surface films in Li-ion batteries. J Phys Chem B 110 7708... 

Table 6 The distance (A) from lithium, carbonyl carbon (Cl and C4), and alkyl carbon (C2 and C3) of lithium aUtyl dicarbonates to the nearest graphite carbon.

Only the conformation of perpendicular adsorption (7.5, in Figure 20c) was found for LPD at the two higher levels. In the conformation 7.5 the distances from the carbonyl carbons to the nearest graphite carbon are longer, by 0.04 and 0.11 A, than those in the conformation 7.3 R 4.214, 4.000 A vs 4.172, 3.885 A at 6-3IG ), the distances R for alkyl carbons are also further increased by approximately 0.10 and 0.32 A (5.507,4.974 A vs 5.426,4.657). The results imply that the adsorption of LPD becomes looser than that of lithium ethylene dicarbonate. It is noted that the small basis set 3-2IG considerably underestimates (overestimates) R (adsorption energies before BSSE), however it qualitatively provides similar trends to 4-3IG and 6-3IG about adsorptions of the three lithium dicarbonates. In the following section the 3-21G basis set is used for the C96H24 surface. 

At the onset potential for reduction of about 1.5 V (Li/Li+), alkyl carbonate-based solvents, such as PC, EC, and DMC, are reduced in the presence of Li ions on nonactive electrodes to R0C02Li compounds. The most probable compounds formed in the case of PC and EC are propylene and ethylene lithium dicarbonates, respectively. The mecha-... 

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