Potential positive electrodes for high-voltage magnesium-ion batteries

Abstract

Magnesium-ion batteries (MIBs) with a Mg-metal negative electrode are expected to combine high energy density and high electromotive force, owing to the divalent ion careers and its low redox potential. However, it has been reported to date that the cell voltage of MIBs is not high enough (∼1.5 V), being far below that of lithium-ion batteries (LIBs) (4–5 V). In this work, we have investigated the potentiality of Mg–Co–O and Mg–Ni–O complex oxides as the positive electrode for MIBs, which are composed of these positive electrodes and a Mg negative electrode in acetonitrile with Mg(ClO₄)₂ salt as an electrolyte. These MIBs can exhibit a relatively high open circuit voltage, OCV, and can light a blue diode after charge. However, as the combination of the acetonitrile electrolyte and metal Mg can yield the passivation on the surface of the Mg electrode, we have also checked these materials for a well-established Li ion battery system, and confirmed that the charged battery can show high OCV. In order to attain such a high cell voltage, it would be significant to exploit the unstabilized ion after charge in the host complex oxide.