Can ultra-dense cathode agglomerates be treated as solid particles? Direct evidence from single high-nickel NCM particle microelectrode

LiNi_xCo_yMn_1−x−yO₂ (NCM) cathode materials have attracted considerable interest for use in lithium-ion batteries due to their favorable electrochemical properties. NCM cathode materials typically form ultra-dense agglomerates with limited porosity (∼5 %), raising the question of whether these agglomerates can be treated as solid particles in electrochemical evaluations and battery modeling. In this work, we develop and employ a single-particle experimental setup to directly evaluate the kinetics of high-nickel NCM cathode materials at the single-particle scale. We decouple bulk and interfacial transport processes and explore the relationship between electrochemical kinetics and agglomerate structure for LiNi_0.8Co_0.1Mn_0.1O₂ and LiNi_0.9Co_0.08Mn_0.02O₂ cathode materials. In particular, we present a novel investigation into the effect of primary particle size, which has not been directly explored in previous studies. Our extensive dataset of key kinetic parameters—exchange current density (i₀) and diffusion coefficient (D_Li)—demonstrates that electrolyte penetration within ultra-dense agglomerates must be considered in physics-based battery models, challenging the assumption that such agglomerates behave as solid particles. These insights, along with the large kinetic dataset, are essential for refining battery models and optimizing battery design.