Coprecipitation is a popular approach to synthesize precursors for transition metal oxide cathode materials used in lithium-ion batteries. Many papers in the literature have reported tuning the particle morphology using careful control of reaction conditions, and the morphology of the precursor particles can also be retained after calcination to obtain final active materials of tunable size and shape. Oxalate coprecipitation provides a route to substitute the more common hydroxide and carbonate coprecipitation; and oxalate provides an advantage where most transition metal ions form stable oxalate precipitates in aqueous solutions exposed to air. Different oxalate polymorphs may occur; however, depending on the detailed reaction conditions. In this talk, we will present studies of pure and blend oxalate coprecipitations using manganese and nickel, and will discuss the impact of feed conditions on the precipitate composition and structure. We will also demonstrate a method to determine the rate of loss of individual transition metals from solution to the solid phase.