2019 年 87 巻 5 号 p. 281-288
Mg(Mg0.5V1.4Ni0.1)O4 was synthesized by a solid-phase method under high vacuum. The product was assigned to a spinel structure with space group Fd3m based on the powder X-ray diffraction spectrum. Synthesized materials of uniform composition were confirmed from elemental mapping by STEM-EDS. Charge and discharge cycle tests showed a discharge capacity exceeding 60 mAh/g at 90°C. Cyclability was maintained for 19 cycles of charging and discharging. The electronic structure was analyzed by MEM using the result of Rietveld analysis, which showed that Mg could be easily inserted into the Mg(Mg0.5V1.4Ni0.1)O4 and that the host structure was stable due to the high covalency of M(16d)-O. MO6 octahedral strain was alleviated by increasing the amount of substitution of Ni. The valence of the transition metals was examined by XAFS; the spectra at the V K-edge for all samples showed that V existed in the trivalent and tetravalent states. It was suggested that V could be converted to a higher oxidation state after the 1st charge.