Electrochemical Properties and Changes of Crystal and Electronic Structures of Spinel-Type Mg1.33– y V1.67– x + y Mn x O4 ( x = 0.15, 0.06 ≤ y ≤ 0.13) for Magnesium Secondary Batteries

Mg1.33–yV1.67–x+yMnxO4 was synthesized by a solid-state method. Powder X-ray diffraction analysis indicated that the product crystallized in the spinel structure with space group Fd3̅m; inductively coupled plasma atomic emission spectroscopic analysis showed that the Mg content was slightly lower than the nominal composition for all samples. Charge–discharge cycle tests showed that the discharge capacity exceeded 180 mAh/g and that the cycle characteristics were reversible up to 20 cycles at 90 °C for the composition with x = 0.15, y = 0.1. The electronic structure was analyzed by the maximum-entropy method on the basis of Rietveld analysis results. The sample with x = 0.15, y = 0.08 had a lower electron density and Mg insertion was easier than in the samples with x = 0.15, y = 0.1, and y = 0.13. The sample with x = 0.15, y = 0.08 had less distortion at the 16d site than the samples with x = 0.15, y = 0.1, and y = 0.13, and the distortion decreased with increasing V content.