A Theoretical and Experimental Study of the Mass Transport in Gel Electrolytes II. Experimental Characterization of LiPF6-EC-PC-P(VdF-HFP)

The mass transport in a gel consisting of LiPF 6 dissolved in ethylene carbonate (EC), propylene carbonate (PC) and poly(vinylidenefluoride-hexafluoropropylene) (P(VdF-HFP)) was characterized at 25°C. Four diffusion coefficients, two transport numbers, one conductivity and two parameters describing the relationship between a concentration and a potential gradient were obtained in the characterization. The transport properties were obtained by optimizing a Maxwell-Stefan based transport model to data from four types of experiments. The transport model and the characterization method were analyzed in Part I. In order to give the results a comprehensible interpretation and to present a way of benchmarking electrolytes, we introduce the concept of a normalized potential gradient for gel electrolytes. The optimum composition range of the gel in terms of mass transport was found to lie between 5 and 7 wt % LiPF 6 and as little polymer as possible without compromising the mechanical stability. It is suggested that measuring the normalized potential gradient can be used as a screening method when benchmarking electrolytes.