Electrolytic Conductivity and Glass Transition, Temperature as Functions of Salt Content, Solvent Composition, or Temperature for LiPF_6 in Propylene Carbonate + Diethyl Carbonate

摘要

The electrolyte system of LiPF_6 in propylene carbonate (PC) + diethyl carbonate (DEC) was measured for its electrolytic conductivity kappa at salt molalities m, solvent compositions w, and temperatures theta in the ranges of (0.2, 2.4) mol kg~(-1), (0, 0.7) mass fraction of DEC, and (-80, 60) deg C, respectively, and for its glass transition temperatures T_g in the same ranges of m and w. The measured kappa-(m,v) data at different theta were further fitted with an extended version of the Casteel-Amis equation in order to observe the change of kappa with simultaneous changes of m and w ad with theta. The kappa surfaces according to these fitted equations all assumed a "dome" shape as a result of kappa peaking in both m and w. Furthermore, as theta lowered, these domes fell in height and shifted in the direction of low m and high w, the direction of lower viscosity eta. The T_g was found to rise with m and fall with the Vogel-Fulcher-Tammann equatio for an evaluation of the vanishing mobility temperature T_O and the apparent activaiton energy E_a for the electrolytes, both shown to form simple surfaces in the mw-coordinates slanting up in the direction of higher eta. Furthermore, when compared to the surface of T_g, that of T_0 was oriented similarity but lower in value by more than 10 K.