What impact does ammonia have on the microstructure of the precursor and the electrochemical performance of Ni-rich layered oxides?

Abstract

The role of ammonia concentration in determining the particle shape and size of Ni-rich cathode materials during co-precipitation, though recognized as important, remains insufficiently understood in terms of its underlying mechanisms. In this study, we explore the effects of five distinct ammonia concentrations (0.2 mol L⁻¹, 0.3 mol L⁻¹, 0.4 mol L⁻¹, gradually increasing from 0 to 0.4 mol L⁻¹, and decreasing from 0.4 to 0.12 mol L⁻¹) on the microstructure of the Ni_0.95Al_0.05(OH)_2.05 precursor throughout the precipitation process. The results reveal that ammonia concentration significantly influences both nucleation and crystal growth rates, with higher ammonia levels reducing nucleation rates and leading to more uniform agglomerates. Additionally, ammonia concentration affects the thickness-to-length ratio of the precursor's primary particles, which in turn influences the morphology of the LiNi_0.95Al_0.05O₂ cathode materials during lithiation. Importantly, the study demonstrates that the electrochemical properties of LiNi_0.95Al_0.05O₂ are more closely related to the shape of the primary particles than to the secondary particles, highlighting the critical importance of microstructural control in the design of next-generation Li-ion batteries. This study demonstrates the critical impact of ammonia concentration on particle characteristics. The results offer valuable insights for improving battery performance.