Temperature effect on the lithium electrode kinetics

The effect of temperature on the kinetics of processes occurring on metalli c lithium covered by an ion-conducting passive film, in contact with a LiCl O4 solution in propylene carbonate, is studied by the pulsed voltammetry me thod. Symmetrical anodic and cathodic polarization curves for a lithium ele ctrode in the temperature range -35 to 80 degreesC include a portion of ohm ic current j(ohm) caused by intrinsic ionic conductivity of the passive lay er. Following an increase in overvoltage E, the j(ohm) portion is replaced by a portion of injection current h(inj) with a characteristic exponential dependence j(inj) similar to E-n, where n greater than or equal to 2 and va ries with temperature. The reason for this is presumed to be some structura l imperfectness (structural disordering) of the passive-layer material, whi ch leads to the emergence of dispersions in the hop distances and heights o f energy barriers for charge carriers. When calculating a current-voltage c urve, stochastic charge carrier transport in a disordered solid, which is c haracterized by a wide dispersion of times of interpoint hops, leads to the exponential function j(inj) similar to E-n with n depending on temperature as follows: T: n = 1 + (a - b/T)(-2). Experimental data nicely fit this mo del. Comparing experimental j vs. E curves with theoretical equations permi ts the determination of a set of microscopic transport parameters, which in clude the average hop distance and effective localization radius of the cha rge, the frequency of attempts at hopping, and the average energy-barrier h eight.