Revisiting the Initial Stage of Coprecipitation: Key Role of Bottom-Liquid Ammonia Concentration in the Nucleation of Me(OH) ₂ Precursors

The Me(OH) 2 precursor is a fundamental determinant of the electrochemical performance of LiNi x Co y Mn 1– x– y O 2 (NCM) cathode materials. Although coprecipitation is widely recognized as the industry standard for producing high-tap-density precursors, research has mainly focused on steady-state growth parameters, leaving the initial nucleation stage in the bottom liquid largely underexplored. This study addresses this gap by systematically investigating the impact of ammonia concentration in the bottom liquid on the early stage morphogenesis of Me(OH) 2 . The results show that an optimal ammonia concentration of 5–6 g·L –1 significantly accelerates the formation of primary particles, serving as a kinetic catalyst for initial grain refinement. Interestingly, while the final product shows a uniform, smooth morphology across different ammonia levels, suggesting that long-term particle development is strongly influenced by pH, the initial ammonia environment governs the rapid formation of the particle core. This research offers crucial insights into the “incubation period” of coprecipitation, opening new avenues for precise control of morphology and batch-to-batch consistency in the large-scale production of lithium-ion battery (LIB) materials.