Core-shell particles of Ni(OH)(2) (core, 80 mol%) and Ni-1/2 Mn-1/2 (OH)(2) (shell, 20 mol%) were synthesized using a continuously stirred tank reactor (CSTR). This hydroxide core-shell material can be used as a precursor to LiNiO2-LiNi1/2Mn1/2 O-2 core-shell materials, a possible positive electrode material for lithium ion batteries. The reaction was completed with different synthesis conditions to improve the in-situ coating of Ni(OH)(2) particles with a shell of Ni-1/2 Mn-1/2 (OH)(2). Spherical and dense particles of Ni(OH)(2) with a closed coating of Ni-1/2 Mn-1/2 (OH)(2) were synthesized. It was determined that the pH and stirring rate of the reaction must be altered when switching from the core to the shell to produce an optimum shell coating. Without changing reaction conditions some of the shell materials form new particles instead of coating existing particles. The shell and core compositions were verified with powder X-ray diffraction, scanning electron microscopy and ICP-OES elemental analysis.