Mathematical modeling of a zinc/bromine flow cell and a lithium/thionyl chloride primary cell

Three mathematical models are presented, one for the secondary zinc/bromine flow cell and two for the lithium/thionyl chloride primary cell. The objectives in this modeling work are to aid in understanding the physical phenomena affecting cell performance, determine methods of improving cell performance and safety, and reduce the experimental efforts needed to develop these electrochemical systems.; The zinc/bromine cell model is the first such model to include a porous layer on the bromine electrode and to predict discharge behavior. The model is used to solve simultaneously the component material balances and the electroneutrality condition for the unknowns, species concentrations and the solution potential. The independent parameters of the porous layer are defined from the model development and their effect on cell performance during charge and discharge is investigated. A round-trip energy efficiency is defined and its dependence on the thickness of the porous layer and mode of discharge is presented. The predictions of the model show that a maximum round-trip energy efficiency of 70% should be possible under the design conditions considered.; Two models are presented for the lithium/thionyl chloride cell. The first model is a detailed one-dimensional model which is used to solve simultaneously the component material balances, Ohm's law relations, and current balance. The independent design criteria are identified from the model development. Model predictions are used to show that kinetic control predominates for the conditions investigated and that the independent design criteria which directly affect the reaction rate in the porous carbon cathode are those which most influence cell performance. Methods of improving cell lifetime are shown. The model is used in conjunction with a parameter estimation technique to show the experimental data needed to determine the electro-kinetic parameters describing the electrochemical reactions of the cell. The second model presented here is a two-dimensional thermal model for the spirally wound configuration of the lithium/thionyl chloride cell. This is the first model to address the effects of the spiral geometry on heat transfer in the cell. Due to the inherent thermal runaway problem with these systems, heat management is a crucial aspect of the battery design. This model uses a computer package to solve the two-dimensional energy balance for this geometry using the finite element method. Model predictions show that this design offers small improvement in thermal management under normal operating conditions, however, it does improve heat conduction out of the cell under thermal runaway conditions.