Electrochemical Behavior of Lithium in Alkaline Aqueous Electrolytes. II. Point Defect Model

Abstract

A theoretical model for lithium dissolution and passivation in alkaline electrolytes is presented. The production of anodic current via lithium dissolution is understood in terms of a bilayer model for the passive film that incorporates anodic dissolution, bilayer film formation, film dissolution, and hydrogen evolution. The total current density, anodic partial current density, and the cathodic partial current density depend strongly 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 applied voltage and on the electrolyte composition and concentration. The model, which is based on the previously developed point defect model for the formation and breakdown of passive films, describes the behavior of the system over wide potential and electrolyte (aqueous KOH) composition ranges. Electrolyte additives, such as sucrose, are included in the analysis. Analytical expressions for the total current density and hydrogen flux, as functions of the voltage, are used to describe the experimental data obtained for different electrolyte (KOH) and additive (sucrose) concentrations. The results indicate that the additives decrease the porosity of the outer layer and hence have similar influences on both the anodic and cathodic partial currents. 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 increased from −2.8 to . This transition explains the increase in the current at sufficiently positive potentials. © 1999 The Electrochemical Society. All rights reserved.