Lithium ion batteries have been utilized in a wide range of applications. On-going research and development efforts are expanding the application of these materials for use in electric vehicles and household energy storage solutions. Much of these efforts have focused on improving the performance of lithium ion battery materials through achieving alterations to the composition of the cathode material, which has been seen as the limiting factor in terms of capacity and overall battery lifetime. For example, LiNi1/3Mn1/3Co1/3O2 (often referred to as NMC 111) is becoming a material of focus for commercial-scale production. A significant challenge in synthesizing this material is the propensity for Ni/Li based cation mixing in the octahedral sites of the product. While several studies have correlated the synthetic and processing methods with observations for cation mixing and electrochemical performance of the final material, these studies have not performed an in-depth analysis of the cation mixing phenomenon in situ on a mechanistic level. A detailed investigation is presented on the correlations between the processing conditions (e.g., thermal and compositional) for NMC 111 using a pre-lithiated precursor material. The relationship between cation mixing, sintering temperature and sintering time, as well as potential methods for the reversal of cation mixing were investigated through the use of in situ, variable temperature XRD methods. The importance of this knowledge and determining the ideal processing conditions for NMC 111 (and by extension, cathode materials in general) is further demonstrated through a final analysis of the quality of Li⁺ distribution in these materials as assessed by microscopy techniques and electrochemical coin cell tests.