Precipitation of Solids in Electrochemical Cells

Abstract

A mathematical model is developed for an electrochemical cell in which a sparingly soluble product of an electrochemical reaction is precipitated. This model considers the time dependence and the position dependence of the system behavior and includes the interactions between multicomponent transport of electrolyte species in porous media and simultaneous chemical and electrochemical reaction kinetics. The model predicts that cell performance is sensitive to the magnitude of the effective rate constant for precipitation as a result of kinetic, thermodynamic, and morphological effects. In addition, the analysis indicates that local mass transport of the soluble reaction product between the electrode surface and the bulk electrolyte within a pore can influence cell behavior significantly but that redistribution of the dissolved species across a cell is usually unimportant. The calculations also suggest that a local voltage minimum can be obtained during discharge of a cell, depending on the relative rates of nucleation and growth of the solid product. Quantitative information on the precipitation of normalLiCl in a normalLi/SOCl2 static cell with acidic electrolyte is presented. As part of the analysis for this system, a consistent set of transport equations is developed for a concentrated mixture of two binary electrolytes in two neutral solvents.

Modeling self-discharge of Li/SOCl2 cells

“…Several authors have all presented very similar electrochemical models for the discharge of a thionyl chloride cell [2][3][4]. These models consist of equations describing mass balances on reactants, charge-transfer kinetics, porosity change in the cathode, electrolyte flow, temperature changes, and ohmic drops in the liquid and solid phases (see Table 1).…”

“…This kinetic model was incorporated into the electrochemical model described in detail by Jain et al [4]. The equations constituting the electrochemical model have been presented many times [2][3][4][5] and are summarized for reference here in Table 1. There is a slight difference between the electrochemical model here and that used by Jain et al [4] in that Jain used a complex empirical expression to represent the temperature dependence of the salt diffusion coefficient while in this work a simple Arrhenius equation was used.…”

“…2. Comparison of experimental [4] and simulated discharge curves for a 50 load at −55, −18, and 25 • C. charge [2,3,11]. Unfortunately, no data on the degree of swelling seems to be available to validate use of the fitted value.…”

“…This requirement complicates the design because the cathode can expand during discharge. Although several groups have reported models to simulate discharge of Li/SOCl 2 cells [2][3][4][5], the problem of cathode expansion has not been addressed. Others have considered the thermal [6][7][8] behavior of Li/SOCl 2 batteries.…”

Determination of Transport Properties for Solid Electrolytes from the Impedance of Thin Layer Cells

“…[52] represent the coupling of transport rates for individual species in the bulk electrolyte, and their characteristics differ from those of charge coupling that may occur as a result of using Poisson's equation together with local generation and recombination processes (34,35). [52] represent the coupling of transport rates for individual species in the bulk electrolyte, and their characteristics differ from those of charge coupling that may occur as a result of using Poisson's equation together with local generation and recombination processes (34,35).…”