Multi-objective optimization of a lithium cell design operating in a cyclic process

Abstract

Multi-objective optimization frameworks of lithium-ion whole-cell design operating in a cyclic process are presented in this paper. The objective functions involved are maximization of capacity, maximization of specific energy in discharge and maximization of cycle energy efficiency. The considered design variables are electrode thicknesses, solid volume fraction and porosity of electrode compartments, and cell mass per unit cross-sectional area. In addition, the constant current value of charge and discharge is optimized. A phenomenological mathematical model developed in GAMS (General Algebraic Modeling System) environment is applied to achieve the stated goals and the multi-objective problems are solved using an epsilon constraint method-based, which is effective for finding solutions in non-convex feasible regions. Solutions for two different cell chemistries are analyzed: LMO and LCO. Pareto curves and surfaces are obtained and sets of solutions with the highest contradictions and with the most balanced agreement between the objectives involved are identified. When comparing optimal LMO designs with optimal LCO designs, the former result on average 48 % less capacity, 19 % less specific energy and 31 % more energy efficiency. Results show that material type-dependent variables such as active solids have a strong influence on the specific energy and cycle energy efficiency. While the electrode thicknesses show a general trend regardless of the type of chemistry, presenting a strong influence on cell capacity values.