Electrochemical insertion of magnesium in a mixed manganese–cobalt oxide

The electrochemical insertion of Mg 2+ into the cation-deficient mixed oxide Mn 2.15 Co 0.37 O 4 is studied in regard to its possible use as a positive electrode in magnesium ion-transfer batteries. The cation vacancies of the mixed oxide offer a pathway for Mg 2+ insertion with a maximum uptake of 0.23 Mg per mole of oxide. Voltammetric and chronopotentiometric measurements indicate a single insertion step located near 2.9 V vs Li/Li + . The strong polarizing effect of Mg 2+ ions induces a more pronounced disordering process than for Li accommodation. This results in a limited stable specific capacity of 30 A h kg -1 when discharge–charge cycles are performed at a C/6 rate within the cycling limits 4.05–1.85 V vs. Li/Li + .