Study of Particle Size Distribution Effects in Battery Electrodes Using Monodisperse NMC Cathode Particles

Studies have shown that using polydisperse active material particles can cause (i) heterogeneous electrochemical reactions within a battery electrode due to reactivity differences among different particle sizes, and (ii) heterogeneous electrode microstructures, leading to varied transport and charge transfer overpotentials throughout the electrode, exacerbating the reaction heterogeneity. The uneven utilisation of the battery electrode subjects certain electrode regions to greater electrochemical stress, with the risk of accelerated degradation. In this work, we focus on the impact of particle size distribution on battery electrode cyclability. First, we synthesised monodisperse polycrystalline LiNi1/3Mn1/3Co1/3O2 (NMC111) particles of two different sizes. Then, three electrodes with different particle size distributions (‘Small’, ‘Big’, ‘Mix’) were fabricated and examined as model systems. Contrary to our hypothesis that the ‘Mix’ electrode would exhibit the worst cyclability, the ‘Small’ electrode showed the best long-term cycling performance, followed by the ‘Mix’ electrode and then the ‘Big’ electrode. The discrepancy is attributed to the greater degree of particle cracking experienced by the big particles, disrupting solid-state charge transport within secondary particles, especially in the ‘Big’ electrode. Overall, this study provides new insights into synthesising monodisperse layered oxide cathodes and how both the average particle diameter and particle size distribution affect battery performance.