Lithium ion solvation by ethylene carbonates in lithium-ion battery electrolytes, revisited by density functional theory with the hybrid solvation model and free energy correction in solution

Abstract

Complex formation between lithium (Li⁺) ions and electrolyte molecules would affect the ionic conductivity through the electrolyte in lithium-ion batteries (LIBs). We hence revisit the solvation number of Li⁺ in the most commonly used ethylene carbonate (EC) electrolyte. The solvation number n of Li⁺(EC)_n in the first solvation shell of Li⁺ is estimated on the basis of the free energy calculated by the density functional theory combined with a hybrid solvation model where the explicit solvation shell of Li⁺ is immersed in a free volume of an implicit bulk solvent. This new hybrid solvation (implicit and explicit) model predicts the most probable solvation number (n = 4) and solvation free energy (−91.3 kcal mol⁻¹) of Li⁺ in a good agreement with those predicted by calculations employing simpler solvation models (either implicit or explicit). The desolvation (n = 2) of Li⁰(EC)_n upon reduction near anodes is also well described with this new hybrid model.