A series of spinel-framework structures of Li[Me1/2Mn3/2]O-4 (Me; Ti, Cr, Fe, Co, Ni, Cu, and Zn) was prepared and examined by XRD and electrochemical methods. All samples except Li[Ti1/2Mn3/2]O-4 and Li[Zn1/2Mn3/2]O-4 exhibited approximately 5 V solid-state redox potentials (vs. Li+/Li), probably due mainly to compact crystal fields imposed by the spinel-framework structure of cubic close-packed oxygen linked with tetravalent manganese ions. Of these, Li[Fe1/2Mn3/2]O-4 and Li[Ni1/2Mn3/2]O-4 are very attractive materials in both basic and applied research fields, and the solid-state redox potentials of transition metal ions in such crystal fields are summarized and discussed.