Electrolytic Conductivity and Glass Transition Temperature as Functions of Salt Content, Solvent Composition, or Temperature for LiPF₆ in Propylene Carbonate + Diethyl Carbonate

The electrolyte system of LiPF 6 in propylene carbonate (PC) + diethyl carbonate (DEC) was measured for its electrolytic conductivity κ at salt molalities m, solvent compositions w, and temperatures θ in the ranges of (0.2, 2.4) mol kg -1, (0, 0.7) mass fraction of DEC, and (−80, 60) °C, respectively, and for its glass transition temperatures T g in the same ranges of m and w . The measured κ−( m, w ) data at different θ were further fitted with an extended version of the Casteel−Amis equation in order to observe the change of κ with simultaneous changes of m and w and with θ. The κ surfaces according to these fitted equations all assumed a “dome” shape as a result of κ peaking in both m and w . Furthermore, as θ lowered, these domes fell in height and shifted in the direction of low m and high w, the direction of lower viscosity η. The T g was found to rise with m and fall with w, indicating a concurrent change in the η of the solution. The measured κ− T data were fitted with the Vogel−Fulcher−Tammann equation for an evaluation of the vanishing mobility temperature T 0 and the apparent activation energy E a for the electrolytes, both shown to form simple surfaces in the mw -coordinates slanting up in the direction of higher η. Furthermore, when compared to the surface of T g, that of T 0 was oriented similarly but lower in value by more than 10 K.