The electrochemical impact of lithium-ion diffusivity on the discharge rate capabilities of cation ordered (P4332) and disordered (Fd3m) LiMn1.5+δ Ni0.5−δ O4 spinels were studied. Potentiostatic Intermittent Titration (PITT) measurements revealed up to 2 orders-of-magnitude lower lithium diffusion coefficient for the ordered spinel polymorph. The optimum structure of the high voltage spinel is resolved with respect to these ionic studies and our previous electronic transport studies. Modification of the morphology and pore dimensions was accomplished through the tuning of the ethylene glycol used for the synthesis of nanostructured spinel in the modified Pechini process. Glycol will be shown to play a major role on the energy and power density of LiMn1.5+δ Ni0.5−δ O4 electrodes.