Analysis of geometric influences on the half cell potential measurement accuracy of lithium iron phosphate (LFP)-based laser-perforated reference electrodes

In lithium-ion battery research, reference electrodes (RE) enable independent measurement points for separate monitoring of half-cell potentials, crucial for investigating degradation mechanisms and optimizing performance. This work investigates how LFP-based laser-perforated reference electrode (PRE) geometry affects potential measurement accuracy and blocking behavior, providing the first systematic study to identify and quantify these effects and their underlying causes for such designs. PRE integration enables representative half-cell measurements but can hinder ion transfer, thus diminishing capacity retention. Furthermore, local ion flux gradients perturb ion concentration around the RE, leading to misrepresented half-cell potentials. Using a two-dimensional COMSOL Multiphysics simulation based on the Doyle-Fuller-Newman (DFN) model, we systematically examined how PRE geometry, particularly pore width, affects local reaction rates, overpotentials, and ion concentration. Results reveal that smaller perforations favor local ion depletion, slow lithiation underneath the RE, and increase potential measurement error. By altering the PRE design and increasing pore width, we demonstrated that ion transfer is less hindered, lithiation is more uniform, and the measured potential error is reduced. We validated the design by performing a provoked plating study, measuring plating onset using a swelling sensor with cross-validation via voltage relaxation method. The optimized design led to a 16.7% reduction in potential measurement error compared to the original PRE design and a 3.9% improvement in cell capacity retention.