<p>This study investigated the distribution discipline of impurities in solid or liquid phases, specifically Mg²⁺ and Al³⁺, during the preparation of LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) precursor by integrating theoretical and practical approaches. A thermodynamic model of the Ni²⁺-Co²⁺-Mn²⁺-Mg²⁺-Al³⁺-NH₃-OH⁻-H₂O system was developed based on the principles of mass conservation and complexation-precipitation equilibrium. To illustrate the competitive dynamics between complexation and precipitation reactions during the co-precipitation process, plots depicting the variation of lg[NH₃] versus pH were constructed, which also provided a theoretical basis for the selection of the actual production conditions of the NCM811 precursor. NCM811 precursors containing Mg²⁺ and Al³⁺ impurities were produced using the co-precipitation method at the conditions of 200 mL H₂O, 55&#xa0;°C, 12&#xa0;h, pH = 11.0 ± 0.1, [N] = 4.0&#xa0;M. The experimental results demonstrated that the actual distribution rate of Mg²⁺ in the solid phases exceeded 95%, while the precipitation rates of Ni²⁺, Co²⁺, and Mn²⁺ were 99.75%, 98.67%, and 99.98%, respectively. Furthermore, the actual distribution rate of Al³⁺ in the solid phases significantly increased from approximately 20% to over 99% as the Al³⁺ concentration increased from 0.005&#xa0;mol/L to 0.025&#xa0;mol/L in the co-precipitation reaction. The research can provide a theoretical foundation for the differential purification of nickel-cobalt-manganese minerals.</p>