Impact of Sulfate Adsorption on Particle Morphology during the Precipitation of Ni-Rich Hydroxide Precursors for Li-Ion Battery Cathode Active Materials

Abstract

Nickel-cobalt-manganese-hydroxides (NixCoyMnz(OH)2, with x+y+z = 1) are utilized as precursor for lithium-ion battery cathode active material (CAM). The physical properties and electrochemical performance of CAM are affected by the morphology, crystallinity and impurity content of the associated NixCoyMnz(OH)2 (with x+y+z = 1) employed for the CAM synthesis. To promote the mechanistic understanding of the NixCoyMnz(OH)2 (with x+y+z = 1) formation, the coprecipitation pH23 °C-value was systematically varied from 8.6–12.7 during the synthesis of Ni0.8Co0.1Mn0.1(OH)2, and the obtained powders were characterized by elemental analysis. A dependency of residual sulfur content and crystallinity of the obtained Ni0.8Co0.1Mn0.1(OH)2 on the pH-value in relation to the point-of-zero-charge (pzc) is revealed. This result is rationalized by a pH-dependent sulfate adsorption equilibrium. Furthermore, a suppression of the growth along the (001) plane of the crystallites due to sulfate adsorption is identified. This in turn governs the vertical primary particle size and thus the porosity of the secondary particles, which was verified by substituting the sulfate ion of the metal feed by nitrate or acetate. Adsorption/desorption experiments demonstrate the possibility to decouple secondary particle morphology and residual impurity content. The demonstrated relationships allow formulating design strategies to tailor the NixCoyMnz(OH)2 (with x+y+z = 1) morphology and its impurity content for CAM synthesis.