A common route to synthesize lithium-ion battery active materials in the literature is to precipitate transition metals with a desired stoichiometry and then perform a calcination to produce the final active material. While this approach has produced many high performance materials, depending on the details of the solution conditions used during precipitation the stoichiometry of the precipitate can deviate from the stoichiometry of the feed. This stoichiometry deviation is largely ignored; however, a few groups have attempted to address this discrepancy with solution equilibrium models to rationally approach compositional control in the final active material. In this talk, we will present results that show the extent of the deviation of the precipitate stoichiometry from the feed stoichiometry across a number of solution conditions and compare experimental results to equilibrium calculations for one co-precipitation process. In addition, we will show initial results for the rate of precipitation of different transition metals in solution and the potential impact on the resulting final material.