Coprecipitation is a popular method to synthesize precursors for lithium-ion battery active materials because it is easy to implement in the lab, fast, scalable, and adaptable to a variety of transition metal compositions. In addition, coprecipitation provides routes to control and modify precursor and resulting final active material particle morphology, resulting in battery materials with tunable size, shape, and polydispersity. In many cases, especially under conditions where morphology control or tunability is desirable, the coprecipitation is run under conditions of either low transition metal concentration in solution and/or conditions where significant fractions of the transition metals stay soluble in the solution. Within these solution environments the composition of the resulting battery precursor particles can deviate from the solution feed conditions, a consequence not often designed for or reported in the battery material synthesis literature but which can significantly influence the resulting composition and thus electrochemical properties of the final active material. In this talk, efforts will be described in our lab to understand the solution environment during coprecipitation of battery particles with the final goal of explicit control over the composition of the resulting precursor particles both with regards to composition and structure. Insights from probing the rate at which transition metals are deposited onto the precipitate particles will also be presented.