What differentiates the transport properties of lithium electrolyte in ethylene carbonate mixed with diethylcarbonate from those mixed with dimethylcarbonate?

This paper reveals the grounds that differentiate the transport properties of the lithium electrolyte in ethylene carbonate (EC) mixed with diethyl carbonate (DEC) from those mixed with dimethyl carbonate (DMC). The EC/DMC solvent is known to be significantly more conductive than the EC/DEC counterpart, for which the reason is not yet fully quantitatively unraveled. We measure the density, specific conductivity, viscosity, diffusion coefficient of each component, of a 1 mol kg−1 LiPF6 solution in the binary solvent as a function of the EC-fraction (xEC). The 2.4 times higher molar conductivity in DMC than in DEC is explained by the 1.4 times higher diffusivity multiplied by the 1.7 times higher ionic dissociation (2.4=1.4×1.7). The addition of EC renders these contributions comparable. In the binary solvent, DMC is more influenced by the dynamics of the ions than DEC is. Raman and 13C NMR spectroscopy suggests that EC is equally preferred over DEC and DMC in solvating Li+, since the EC-fraction in the solvation shell always exceeds that in the net solvent composition. The static and dynamic sizes of the transporting entities are discussed.