On February 15, 2023, Tokyo University of Science, a research group at the university’s Faculty of Science and Engineering discovered magnesium oxide (Mg 1.33 V 1.67 – x Mn x O 4 , x = 0.1 to 0.4) and clarified the crystal structure and electronic state. It is expected that this will lead to the development of next-generation power storage devices to replace lithium-ion secondary batteries.
Magnesium secondary batteries, which are rich in raw material resources and are expected to achieve high energy density, are attracting attention as next-generation storage batteries to replace lithium-ion secondary batteries. rice field. The research group focused on composite oxides containing three types of metal elements: magnesium (Mg), vanadium (V), and manganese (Mn). We clarified the correlation between the crystal structure and the physical properties when the metal composition ratio was systematically changed.
The research group adjusted the mixing ratio of the raw materials MgO, V 2 O 3 and MnO 2 and produced four types of magnesium oxides with different compositions (Mg 1.33 V 1.67-x Mn x O 4 , x = 0.1 to 0.4). As a result of various analyses, it was found that all oxides are cubic and have a spinel-type crystal structure with space group Fd3m. On the other hand, only the oxide with x = 0.4 showed a diffraction peak corresponding to the perovskite structure of the second phase.
Next, a conductive agent and an adhesive are added to the synthesized magnesium oxide to form a positive electrode, which is then combined with metallic magnesium and an electrolyte to produce a magnesium secondary battery. We evaluated the battery characteristics of the fabricated magnesium secondary batteries by measuring the charge-discharge cycles, and found that all the oxides can be repeated in charge-discharge cycles. Improved cycle characteristics.
Under these conditions, the oxide with x = 0.1 showed a large discharge capacity of 256 mAh/g at the 13th cycle after repeated charge-discharge cycles. The oxide with x = 0.2 shows a large discharge capacity of 215 mAh/g at 10th cycle. In particular, it was found that the use of tetraglyme (G4) electrolyte suppresses dissolution of the negative electrode metal due to its extremely low coordinating ability, contributing to the improvement of battery performance.
Repeated desorption and insertion of Mg2 + leads to increased strain of the VO6 octahedron in the crystal structure, but it is partially relaxed by the Mn ions occupying the 16d sites, so that oxides with x = 0.1 It is considered that the crystal strain is minimized and the host structure is stabilized, resulting in a high discharge capacity.
Future research is expected to lead to the realization of superior magnesium secondary batteries that surpass the battery characteristics of existing lithium-ion secondary batteries.