Influence of aluminum source and Ni/Al ratio in a batch stirred tank reactor on the structure, morphology, and electrochemical performance of Ni-rich NMA cathodes

The structural, morphological, and electrochemical performance of Ni-rich LiNi_0.9Mn_0.05Al_0.05O₂ (955NMA) and LiNi_0.85Mn_0.05Al_0.1O₂ (85,510) cathodes strongly depends on the properties of their hydroxide precursors. Ni-Mn-Al hydroxide precursors were synthesized through controlled co-precipitation in a batch stirred tank reactor, where pH, reaction time, metal-ion feed rate, aluminum source, and aluminum concentration were systematically varied to tailor particle morphology, phase composition, and dopant distribution. Two aluminum sources, aluminum nitrate and sodium aluminate produced two distinct hydroxide precursors NMA(OH)₂-1 and NMA(OH)₂-2, which were lithiated to form LiNMA1 (Li_0.992[Ni_0.905Mn_0.049Al_0.046]O₂) and LiNMA2 (Li_0.990[Ni_0.850Mn_0.047Al_0.103]O₂). Structural and compositional analyses revealed that aluminum incorporation and phase formation in Ni–Mn–Al hydroxides are governed by local supersaturation and interfacial growth kinetics. Rapid dilute aluminum addition produced aluminum-free β-phase hydroxides, intermediate conditions generated mixed α/β phases, whereas slow concentrated dosing enabled uniform aluminum incorporation and stabilization of the β-phase structure. LiNMA1 delivers a high initial discharge capacity of 223 mAhg−1 but significant capacity fading with 67% retention after 100 cycles, associated with structural instability. In contrast, LiNMA2 delivers a lower initial capacity 172 mAhg−1 yet excellent cycling stability 91% retention, attributed to improved TM–O framework stability and reduced cation disorder.