Temperature and Concentration Dependence of the Ionic Transport Properties of Lithium-Ion Battery Electrolytes

Lithium-ion battery performance at low temperatures or fast charge/discharge rates is determined by the intrinsic electrolyte transport and the thermodynamic properties of the commonly used binary electrolytes. For the development of future electrolyte solutions, a quantification of the ionic conductivity, the binary diffusion coefficient, the transference number, and the thermodynamic factor over a large concentration and temperature range is mandatory. In this study, we apply previously discussed and established methods for the determination of ionic conductivities and binary diffusion coefficients to two commonly used electrolyte systems (EC:DMC (1:1 w:w) and EC:EMC (3:7 w:w)) as well as to one EC-free electrolyte (EMC:FEC (19:1 w:w)). To quantify transference numbers and thermodynamic factors, we introduce a novel analysis scheme, so that we are ultimately able to report temperature (−10°C–+50°C) and concentration (0.1 M–3.0 M) dependent values as well as approximate relationships for transport and thermodynamic properties required for numerical battery models. Comparison with scarcely available literature data highlights that the hitherto reported concentration and temperature dependencies do not reflect the complexity of ionic transport properties, which will likely lead to imprecise predictions of, e.g., a lithium-ion battery's power limitations or the onset of lithium plating.