In this paper we report the combined, positive effect of triphenyloborane (BPh3) additive on conductivity and lithium cation transference numbers in poly(ethylene oxide) dimethyl ether (PEODME)–lithium trifluoromethanesulfonate (LiCF3SO3, LiTf) electrolytes. The transport mechanism is discussed on the basis of impedance measurements, restricted diffusion t + measurements, ionic association semi-empirical quantitative estimation and spectroscopic studies. A substantial increase in the lithium transference number values in triphenylborane enriched composite electrolytes was observed in comparison with the pure PEODME–LiCF3SO3 electrolyte. This effect is assisted by ionic conductivity enhancement.