A 5 V Region Electrochemical Behavior of Nonstoichiometric Li[sub 1+x]Mn[sub 2−x]O[sub 4±z] Spinels

Two series of nonstoichiometric manganese spinels were synthesized in air, chemically analyzed, and characterized by cyclic voltammetry. Some spinels show an extra redox pair of 5 V peak with poor reversibility. The appearance and intensity of this peak are related to chemical compositions of the spinels. The coexistence of both oxygen and lithium excess is a necessary condition for the 5 V peak. The intensity of this peak increases with increasing Li content. Further quantitative analysis indicated that Mn ions in a higher oxidation state (5+, 6+) did not exist at the end of the 5 V charge process. Chemical analysis of the Li content indicates that a fraction of the 5 V capacity likely originates from the extraction of Li ions located at 16d sites. The possible oxidation reaction mechanism during this Li extraction is proposed.