Probing intraparticle heterogeneity in Ni-rich layered cathodes with different carbon black contents using scanning probe microscopy

Much effort has been made to improve the electrochemical performance of Ni-rich layered cathodes toward high-energy density of Li-ion batteries. Nonetheless, capacity fading and chemo-mechanical behaviors during charge/discharge processes have not been fully understood yet. Herein, we report microstructural changes and capacity degradation of a polycrystalline LiNi_0.88Co_0.09Al_0.03O₂ (NCA) cathode during repeated cycles using electron microscopy and scanning probe microscopy. By varying the content of carbon black (CB; 1–4 wt%) in the NCA cathode, we evaluated cycle performance, capacity-fading, and structural degradation by scanning electron microscopy, scanning spreading resistance microscopy, and Kelvin probe force microscopy based on atomic force microscopy. CB content at 1 wt% in the NCA cathode resulted in a significant increase of electrode resistance and hence a severe capacity decay of full cells. Microscopic analyses for cycled cathode particles surrounded by different CB contents confirmed that the lack of CB around particles developed secondary particle microcracking, local heterogeneity of capacity fading, and formation of NiO-like phase, which could be responsible for degradation of the cathode during repeated cycles. Our results offer a new way to diagnose chemo-mechanical changes of Ni-rich cathodes with different electrochemical properties and highlight the significance of electrode engineering for ensuring effective charge-transport pathways.