The electrolyte is a crucial component of a Lithium-ion battery. On one side, it affects the rate of the energy release, by controlling the mass transport properties within the cell. It contributes to the formation of extremely complex electrified interfaces with the electrodes on the other, finally dictating the performances of the device. It can therefore come as a real surprise that even an apparently simple question like: "How anions and solvent molecules organize around the Lithium ion in carbonate solutions with different concentrations?" still has no definitive answer. 

Computational scientists of the Inac and Liten have contributed a solid piece of work in this direction. By putting together simulation data ^{[1, 2]} with femtosecond vibrational spectroscopy measurements performed by a chino-american team based in Houston at Rice University, they have provided important insight about the anion influence on the overall structure of the first solvation shell of the Li⁺ ion ^[1]. Shedding light on the formation of such a cation/solvent/anion complex also provides a rational explanation for the ionic conductivity drop of lithium/carbonate electrolyte solutions at high concentrations, an issue of paramount importance for applications.

Figure top: Optimized geometries of the most stable clusters: (a) Li⁺(EC)₂ ClO₄^–, (b) Li⁺(EC)₂ BF₄^–, and (c) Li⁺(EC)₂ PF₆^–.
Figure bottom: Calculated vibrational IR spectra of isolated EC and of (Li⁺(EC)₂(Anion^–)) optimized clusters.