Evaluation of the Diffusion Coefficient of Li in Ag Using a Li~+ Sensor Electrode Mounted in a Bipolar Cell

摘要

For the purpose of obtaining the most trustworthy value of the diffusion coefficient D of Li in Ag foil by avoiding the influence of Li-Ag alloy formation, we attempted to use a Li~+ sensor electrode mounted in a bipolar cell, in which an Ag foil was sandwiched by two facing cylindrical cell compartments. A tungsten oxide electrode doped with Li was prepared for the purpose of sensing the ion concentration of Li~+ in the electrolyte. The sensor electrode was mounted in the Li extraction compartment, and the potential of the Li~+ sensor electrode (the Li~+ con-centration)-time curve in the extraction compartment was measured by stepping the potential of the bipolar electrode in the Li insertion compartment. The Li~+ concentration in the extraction compartment was found to increase within one second after the potential step, and the break through time was found to be independent of the polarization potential in the insertion compartment. The apparent diffusion coefficient, D_(app), was calculated from the break through time. The obtained value was approximately constant at 10~(-6) cm~2 s~(-1) throughout the range of polarization potential examined for foils of 10- and 20- mu m in thickness.