Electrochemical behavior of lithium in alkaline aqueous electrolytes - II.Point defect model

A theoretical model for lithium dissolution and passivation in alkaline ele ctrolytes is presented. The production of anodic current via lithium dissol ution is understood in terms of a bilayer model for the passive film that i ncorporates anodic dissolution, bilayer film formation, film dissolution, a nd hydrogen evolution. The total current density, anodic partial current de nsity, and the cathodic (H-2 evolution) partial current density depend stro ngly on the porosity of the LiOH outer layer that forms over a LIH barrier layer. The porosity of the outer layer is postulated to depend on the appli ed voltage and on the electrolyte composition and concentration. The model, which is based on the previously developed point defect model for the form ation and breakdown of passive films, describes the behavior of the system over wide potential and electrolyte (aqueous KOH) composition ranges. Elect rolyte additives, such as sucrose, am included in the analysis. Analytical expressions for the total current density and hydrogen flu?; as functions o f the voltage, are used to describe the experimental data obtained for diff erent electrolyte (KOH) and additive (sucrose) concentrations. The results indicate that the additives decrease the porosity of the outer layer and he nce have similar influences on bath the anodic and cathodic partial current s. The model is also extended to account for the transition from a lithium hydride barrier layer to a Lithium oxide barrier layer as the voltage is in creased from -2.8 to 8 V-SHE. This transition explains the increase in the current at sufficiently positive potentials. (C) 1999 The Electrochemical S ociety. S0013-4651(98)05-082-4. All rights reserved.