放射光を用いたLiイオン二次電池用正極材料LiNi_0.5Mn_0.5O₂の構造変化の研究

抄録

The cell performance of Li_1-xNi_0.5Mn_0.5O₂ Using Li exhibited a specific capacity of c.a. 150 mAh/g in the voltage range of 2.5 to 4.3 V. XRD and XAFS measurements using synchrotron radiation were carried out to observe the average and the local structural changes during a charging process. As the cell charged, Ni K-edge of XANES spectra showed the chemical shift towards higher energy in the voltage range of 2.5-4.1 V and then no remarkable shift up to 4.3 V. It was found that nickel of x=0 in Li_1-xNi_0.5Mn_0.5O₂ was located in divalent and manganese in tetravalent at the octahedral site. Lithium was removed by the oxidation of Ni, resulting in the ordering of cations in the layer, that is, appearance of the monoclinic phase at x=0.5.