In-plane Reaction Inhomogeneity in Lithium-ion Battery Full Cells Analyzed by X-ray Absorption Spectroscopy and Ion Chromatography

In power-type lithium-ion batteries (LIBs), the reaction distribution formed during high-rate operation significantly influences their performance.The reaction distribution in the electrode cross-sectional direction has been studied; however, in-plane reaction distribution, that can be an issue for large cells, remains poorly understood.In this study, we applied an electrode-freezing technique that can preserve reaction inhomogeneity at high rates to investigate the relationship between the in-plane reaction distribution and electrode design.The reaction distributions of LiNi1/3Co1/3Mn1/3O2 positive and hard carbon negative electrodes were analyzed using synchrotron-based Ni Kedge X-ray absorption fine structure and ion chromatography, respectively.The results showed that reducing electrode thickness significantly increased the in-plane inhomogeneity, with preferential reaction progress near the current-collector tabs.On the other hand, such pronounced in-plane reaction distributions did not necessarily degrade the power performance of the cell, suggesting the importance of cross-sectional inhomogeneity.This study shows that the dominant direction of reaction distribution in power-type LIBs varies depending on electrode thickness and C-rate, providing useful insights for electrode design optimized for high-rate operation.