Transport Properties of LiPF[sub 6]-Based Li-Ion Battery Electrolytes

TLDR

The electrolyte is critical for high‑current Li‑ion battery performance, yet electrolytes are typically optimized only for conductivity, while high currents also alter temperature and create concentration gradients. The study aims to measure Li salt diffusion coefficient, transference number, and activity—beyond conductivity—to better understand the electrolyte’s role. Transport properties were measured in a propylene carbonate/ethylene carbonate/dimethyl carbonate mixture across temperature and concentration ranges. The transference number remains nearly constant with concentration, whereas activity and diffusion coefficient vary strongly with temperature and concentration, underscoring the importance of temperature dependence for predicting high‑current cell performance.

Abstract

The electrolyte plays an important role in governing the high-current performance of Li-ion batteries. Normally, battery electrolytes are optimized for maximum conductivity. In order to gain a more profound understanding of the role of the electrolyte, properties such as the Li salt diffusion coefficient, the transference number, and the Li salt activity all need to be measured in addition to the conductivity. The situation is further complicated by the fact that high currents change the cell temperature and also create strong concentration gradients in the electrolyte. A full set of transport properties for in a propylene carbonate/ethylene carbonate/dimethyl/carbonate mixture were measured as a function of temperature and concentration. The transference number was found to be fairly constant with concentration. The activity and diffusion coefficient were both found to vary strongly with temperature and concentration. The temperature dependence of the transport properties is shown to be crucial for making predictions of cell performance at high currents.