Analysis of a Lithium/Thionyl Chloride Battery under Moderate‐Rate Discharge

Abstract

A one-dimensional mathematical model of a spirally wound lithium/thionyl chloride primary battery is developed and used for parameter estimation and design studies. The model formulation is based on the fundamental conservation laws using porous electrode theory and concentrated solution theory. The model is used to estimate the transference number, the diffusion coefficient, and the kinetic parameters for the reactions at the anode and the cathode as a function of temperature. These parameters are obtained by fitting the simulated capacity and average cell voltage to experimental data over a wide range of temperatures (Ϫ55 to 49ЊC) and discharge loads (10-250 ⍀). The experiments were performed on D-sized, cathode-limited, spirally wound lithium/thionyl chloride cells. The model is also used to study the effect of cathode thickness on the cell capacity as a function of temperature, and it was found that the optimum thickness for the cathode-limited design is temperature and load dependent.

Computational Fluid Dynamics Modeling of a Lithium/Thionyl Chloride Battery with Electrolyte Flow

“…3) and flows toward the reaction sites at the separator-cathode interface, where volume reduction continues to occur due to the cathode reaction. The filling of cathode with electrolyte from the head space toward the end of discharge is consistent with the model developed by Jain et al 5,6 In reality then, the electrolyte flow pattern is a combination of the two idealized, one-dimensional models. The net result is that for the discharge curves shown here, the velocity field does not significantly impact the cell voltage.…”

“…It is also interesting to note that the modified one-dimensional model of Jain et al, 5,6 which assumes that the electrolyte flows down from the head space into the cathode, produced nearly identical discharge curves. This fact prompts us to show that the present twodimensional model is reduced identically to the model of Jain et al 5,6 under one-dimensional assumptions. Appendix B describes this derivation in detail and concludes that the two key equations in Jain and Weidner's one-dimensional model 5 are indeed recovered.…”

“…Other modeling efforts employed concentrated solution theory and porous electrode theory in the various regions of the cell (e.g., separator, porous cathode) to develop one-dimensional models of the battery. [3][4][5][6] These models examined utilization issues at low to moderate currents, but they differ in how the excess electrolyte was treated.In the lithium/thionyl chloride cell, the solvent is also the reactant, and the volume it occupies is more than that of the reaction products. Therefore, more electrolyte is placed in the cell than can occupy the initial void volume of the separator and porous cathode.…”

“…1). Assumptions.-The following assumptions are invoked in this work; they have been justified by Jain et al 6 for cells discharged at low to intermediate rates.1. LiCl precipitation occurs completely and instantaneously at the cathode.…”

Modeling Volume Change in Dual Insertion Electrodes

“…18,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] In many of these models, the dimensions of the porous electrode are often assumed constant and any volume changes in the active material result in only porosity changes. 21,22 Gomadam and Weidner 18 developed a model to allow both porosity and dimensional changes to occur. However, they assume an a priori split between these two.…”