Maximising lithium battery performance by capacity balancing: Determining the Pareto fronts for electrode thickness and porosity

Effective battery design is complex, requiring the resolution of multiple conflicting demands. Even where optimal electrode thickness, porosity, and architecture have been determined for isolated electrodes, designing optimal electrode parameters in full-cell configurations remains challenging. The performances of the positive and negative electrodes are linked due to the need to balance their capacities and complicated by differing rate-limiting mechanisms and ion transport asymmetries, under charge and discharge. This work develops a rational strategy for full-cell electrode design. First, validated, physics-based continuum models are used to determine Pareto fronts identifying best target negative and positive electrode thickness and porosity, under charge and discharge. The calculated ion concentrations provide a mechanistic understanding of the charge/discharge asymmetry. These Pareto fronts are then plotted in the areal capacity-volumetric energy density plane to identify the most effective electrode combinations. The approach is illustrated for a lithium-ion cell configuration using a graphite negative electrode and a LiNi_0.6Mn_0.2Co_0.2O₂positive electrode (Gr/NMC622) but can be generalised to other electrode pairs and battery chemistries.