Influence of Surface Area Calculation Methods on the Interpretation of Lithium-Ion Diffusion Coefficient in Graphite Electrodes

Accurate determination of the lithium-ion diffusion coefficient (D-Li(+)) is essential for understanding mass-transport limitations in graphite anodes and for improving the performance of lithium-ion batteries. However, the calculation of D-Li(+) obtained from pulsed electrochemical techniques critically depends on the assumed active surface area, for which no standardized definition currently exists. In this work, we quantitatively assess how different surface area approximations-geometrical area, scanning electron microscopy-derived area, and Brunauer-Emmett-Teller surface area-affect the diffusion coefficient extracted from galvanostatic intermittent titration technique and intermittent current interruption analyses. Both methods were applied to a commercial graphite electrode using an identical dataset, enabling a direct and unbiased comparison of diffusion trends. We show that the choice of surface area leads to variations in D-Li(+) spanning several orders of magnitude, due to the squared dependence of the area term in the diffusion equation. Overall, our results demonstrate that careful and consistent surface area selection is crucial for reliable diffusion measurements and for ensuring comparability across studies.