Investigation of the Particle Formation Mechanism during Coprecipitation of Ni-Rich Hydroxide Precursor for Li-Ion Cathode Active Material

Industrial production of cathode active material (CAM) for lithium-ion batteries is conducted by coprecipitation of a hydroxide (Ni x Co y Mn z (OH) 2 ) precursor (referred to as pCAM) in a stirred tank reactor and subsequent high-temperature calcination of the pCAM with a lithium compound. The physical properties of the resulting CAM are significantly affected by the associated pCAM utilized for synthesis. For an economical manufacturing of pCAM and CAM, the pCAM particle size and sphericity during the coprecipitation reaction must be precisely controlled, requiring an in-depth understanding of the Ni x Co y Mn z (OH) 2 particle formation mechanism. Therefore, the development of the secondary particle size and morphology throughout the semi-batch coprecipitation of Ni 0.8 Co 0.1 Mn 0.1 (OH) 2 at various stirring speeds was monitored by light scattering and SEM imaging, respectively. A two-stage particle formation mechanism was identified: In the initial seeding phase, irregular-shaped secondary particles agglomerates are formed, which in the subsequent growth phase linearly increase in size with the third root of time, governed by the growth of individual primary particles. Thereby, the degree of turbulence governs the initial agglomerate size and number formed during seeding, which dictates the growth rate and the secondary particle sphericity. Finally, the proposed particle formation mechanism is compared to mechanisms prevailing in the literature.