The Multiobjective Optimal Design Problems and their Pareto Optimal Fronts for Li-Ion Battery Cells

This paper begins with a baseline multi-objective optimization problem for the lithium-ion battery cell. Maximizing the energy per unit separator area and minimizing the mass per unit separator area are considered as the objectives when the thickness and the porosity of the positive electrode are chosen as design variables in the baseline problem. By employing a reaction zone model of a Graphite/Iron Phosphate Lithium-ion Cell and the Genetic Algorithm, it is shown the shape of the Pareto optimal front for the formulated optimization takes a convex form. The identified shape of the Pareto optimal front is expected to guide Design of Experiments (DOE) and product design. Compared with the conventional studies whose optimizations are based on a single objective of maximizing the specific energy, the proposed multi-objective optimization approach offers more flexibility to the product designers when trade-off between conflicting objectives is required. The solutions of the multi-objective optimization include multiple alternatives which may lead to more energy per unit separator area but result in larger weight or vice versa. These alternatives enable the product designers to choose the most appropriate design that best fits the characteristics of the application. Three design cases are employed to illustrate the wide applicability of the developed Pareto optimal front to common design problems in industry. Different objectives are adopted in the three cases to represent different appropriate applications for the cell to be designed, but all the three cases can be solved with the solutions for the baseline multi-objective problem.