In Situ Insights into Cathode Calcination for Predictive Synthesis: Kinetic Crystallization of LiNiO 2 from Hydroxides.

Calcination is a solid-state synthesis process widely deployed in battery cathode manufacturing. However, its inherent complexity associated with elusive intermediates hinders predictive synthesis of high-performance cathode materials. Here, we use correlative in situ X-ray absorption/scattering spectroscopy to investigate the calcination of nickel-based cathodes, focusing specifically on LiNiO 2 synthesized from hydroxides. By combining in situ observation with data-driven analysis, we reveal concurrent lithiation and dehydration of Ni(OH) 2 and, consequently, the low-temperature crystallization of layered LiNiO 2 alongside lithiated rocksalts despite its thermodynamic unfavorability. Following early nucleation, layered LiNiO 2 undergoes sluggish crystallization and structural ordering while depleting rocksalts until full lithiation. Subsequent high-temperature sintering induces rapid crystal growth, accompanied by undesired delithiation and structural degradation. These observations are further corroborated by mesoscale modeling, emphasizing that, even though calcination is thermally driven and favors transformation towards thermodynamically equilibrium phases, the actual phase propagation and crystallization can be kinetically tuned via lithiation to achieve structural and morphological control during the calcination process. This article is protected by copyright. All rights reserved.