Enhanced Battery State Estimation: Part 2 - Reverse Sensitivity Analysis and Electrode Lithium-ion Observer

In lithium-ion batteries, the lithium concentration within the electrolyte is one of the key variables. This paper explores how variations in electrolyte concentration at the terminal boundaries affect different battery parameters through a reverse sensitivity analysis. Analytical derivation is employed as the method, which is universally applicable to various battery types with different parameters. By performing a reverse sensitivity analysis on a LiFePO4 battery cell under an Urban Dynamometer Driving Schedule (UDDS) current profile, the most and least sensitive parameters are identified. These findings are valuable for Part 1 of this study, where observers are introduced to estimate the electrolyte lithium concentration. The designed observers require the lithium-ion concentration at the terminal boundaries, which is difficult to measure directly. Thus, based on the results of this reverse sensitivity analysis, the most suitable measurable parameter can be identified to infer the electrolyte lithium concentration at the boundaries for application in Part 1.