Mathematical modeling and optimization of a secondary lithium battery utilizing a fibrillar polypyrrole cathode.

摘要

A mathematical model for a secondary lithium battery with a fibrillar polypyrrole cathode is developed to investigate the dynamic performance of the cell charge and discharge processes. Dilute solution theory and porous electrode theory are used to characterize the transport phenomena of the electrolyte species in the porous polypyrrole electrode and separator. The model is designed to predict the time dependent distributions of the electrolyte concentration, inserted species solid concentration, active material utilization, solid and liquid potentials and current density for a given electrode and separator porosity and thickness. The model evaluates the influence of physical, design, and operation parameters, such as active surface area, diffusion coefficients, exchange current density, electrode and separator porosity and thickness, active material loading or saturation level of the polypyrrole electrode, discharge or charge rate, and operating temperature, on the dynamic behavior of a lithium battery with a fibrillar polypyrrole cathode.; A sensitivity analysis of the cell performance with respect to the model parameters is performed. Results reveal that the most influential physical parameter on the cell performance is the maximal faradaic charge and the most critical cell design parameter is the ratio of the electrode to separator thickness or the ratio of electroactive and counterion material. Battery optimization should revolve around electrode and separator thickness and porosity, while fibril diameter and electrode porosity are not critical. Sensitivity analysis shows that the model electrokinetic parameters have less influence on the cell performance than those parameters describing the double layer charging and that the effects of the intercalation phenomena during discharge are significant.; Model predictions indicate that thin electrodes at low current densities yield the optimal discharge performance and because of the higher active material utilization, batteries with a fibrillar morphology deliver charge at higher rates, cell voltage, power and energy density than equivalent batteries with conventional flat film electrodes.