The 90th Annual Meeting of the Electrochemical Society of Japan/Mg二次電池正極材料0.3MgCo<sub>2-x</sub>Mn<sub>x</sub>O<sub>4</sub>-0.7Mg(Mg<sub>0.33</sub>V<sub>1.67-y</sub>Ni<sub>y</sub>)O<sub>4</sub>の合成と電池特性、結晶・電子構造の解析