Microstructural Evolution Dynamics in Rapid Joule Heating Densification of High‐Nickel Cathodes

High-energy density materials are essential for the advancement of next-generation lithium-ion batteries, which power a wide range of applications from portable electronics to electric vehicles. Among them, high-Nickel (Ni) layered oxide cathodes have emerged as promising candidates due to their high capacity and cost-effectiveness. However, pores and excessive grain growth in high-Ni layered oxides compromise energy density and mechanical integrity, while oversized grains hinder lithium-ion diffusion kinetics, necessitating a sintering strategy that promotes densification without inducing abnormal grain growth. Here, a rapid Joule heating technique combined with two-step sintering is introduced that significantly improves the microstructural integrity of high-Ni cathodes. This approach enables fast densification while suppressing grain growth, resulting in cathodes with higher density, reduced porosity, and enhanced mechanical strength. Through in situ X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and 3D ptychography analysis, it is found that the rapid Joule-heated cathodes exhibit mitigated phase separation, suppressed pore evolution, and improved resistance to crack propagation. They deliver superior cycling stability, coulombic efficiency, and rate performance. These results provide insights into the relationship between sintering dynamics and microstructural evolution, offering guidelines for synthesizing fully densified, high-energy density materials.