Quantifying the Partitioning of Vehicular and Structural Lithium Transport in Binary Carbonate Electrolytes

Lithium-ion batteries use mixed-solvent electrolytes, but the effect of solvent composition on the mechanism of lithium-ion transport is not well understood. Here, we quantify the partitioning between vehicular and structural Li+ transport mechanisms for binary mixtures of dimethyl carbonate (DMC) and propylene carbonate (PC) using a combination of 2D infrared spectroscopy and pulsed-field gradient NMR. The primary transport mechanism varies monotonically, with 65% vehicular transport in pure DMC and only 35% vehicular transport in pure PC. Li+ structural step lengths of 1.2–1.5 Å were determined from the experimental data. The outcomes of this study are compared to previously described molecular dynamics simulations. The results presented here indicate that typical carbonate electrolytes cannot tailor structural transport and that new solvent chemistries may be required to enhance this diffusion pathway.