Lithium manganese rich (LMR-NMC) material is a great candidate for next generation high energy density cathodes. It has high specific capacity, low cost, and decreased usage of Cobalt. However, these materials display poor rate capabilities attributed in part due to low lithium diffusion in cathode particle. The LMR-NMC cathode particles (size ~ 5 to 15 microns) are agglomeration of nanoscale primary particles. In this work, we focus on the link between morphology and performance. There are two characteristic diffusion lengths associated with the morphology of LMR-NMC. The diffusion length associated with primary particle radius and the diffusion length associated with the agglomeration of primary particles. The agglomerate diffusion length varies significantly with how the primary particles agglomerate. Presence of intra-agglomerate closed pores results in higher agglomerate diffusion length compared to open and well dispersed arrangement of primary particles. The electrochemical performance is better with smaller primary and agglomerate diffusion lengths. Tailoring the synthesis of cathode particles to obtain the desired diffusion characteristics is promising avenue to optimize the performance of LMR-NMC cathode materials.