Temperature Effect on the Lithium Electrode Kinetics

The effect of temperature on the kinetics of processes occurring on metallic lithium covered by an ion-conducting passive film, in contact with a LiClO₄ solution in propylene carbonate, is studied by the pulsed voltammetry method. Symmetrical anodic and cathodic polarization curves for a lithium electrode in the temperature range –35 to 80°C include a portion of ohmic current j_ohm caused by intrinsic ionic conductivity of the passive layer. Following an increase in overvoltage E, the j_ohm portion is replaced by a portion of injection current j_inj with a characteristic exponential dependence j_inj Eⁿ, where n 2 and varies with temperature. The reason for this is presumed to be some structural imperfectness (structural disordering) of the passive-layer material, which leads to the emergence of dispersions in the hop distances and heights of energy barriers for charge carriers. When calculating a current–voltage curve, stochastic charge carrier transport in a disordered solid, which is characterized by a wide dispersion of times of interpoint hops, leads to the exponential function j_inj Eⁿ with n depending on temperature as follows: T: n = 1 + (a – b/T)^–2. Experimental data nicely fit this model. Comparing experimental j vs.E curves with theoretical equations permits the determination of a set of microscopic transport parameters, which include the average hop distance and effective localization radius of the charge, the frequency of attempts at hopping, and the average energy-barrier height.