Associations of lithium alkyl dicarbonates through O•••Li•••O interactions

Associations of several lithium alkyl (vinylene, divinylene, ethylene, and propylene) dicarbonates, resulting from the reductive decomposition of organic carbonates and playing a crucial role on the formation of a solid electrolyte interphase (SEI) in rechargeable Li-ion batteries, have been extensively investigated with density functional theory methods. Lithium alkyl dicarbonates can associate through intermolecular O...Li...O interactions. For their dimers, the cagelike isomer is the most stable structure. Closed pseudoplanar structures turn out to be the global minima for trimers as well as for tetramers. O...Li...O interactions have been characterized with atoms-in-molecules (AIM) and natural bond order (NBO) analysis, and it is found that Li...O behave as ionic interactions. It has also been found that the partial charges of Li ions are decreased in the range of 0.004e to 0.035e when O...Li...O interactions occur or when a Li atom is being shared by more adjacent oxygen atoms, whereas the overall NBO bond orders of Li are considerably increased. Moreover, the BSSE-corrected binding energies of the associates linearly correlate with the total variations of bond orders of all the involved Li ions. The effects of associations on the IR spectra have also been investigated. Both the energetics and IR spectra of lithium alkyl dicarbonates association indicate that lithium alkyl dicarbonates exist on the anode surface, forming 2-dimensional n-mers and even 3-dimensional ones rather than monomers.