| 초록 |
LiNi1/2Mn3/2O4 with the spinel structure is the one of the promising candidates as a high power electrode material due to its facile Li-ion diffusion and high operating voltage by the virtue of high redox potential (~4.7 V vs. Li+/Li0). This compound can crystallize into two polymorphs depending on the ordered state of Ni and Mn in the octahedral sites, disordered (Fd3m) and ordered (P4332). Such ordering has been controlled by temperature of synthesis at ~700°C. Although many previous studies reported that ordering significantly affects the electrochemical properties, their different behaviors in electrochemical performances are still under the debate. By a systematically controlled synthetic route, samples with different ordered states, amount of Mn3+, and compositions were obtained while their particle sizes were kept virtually constant. From our series of samples, it was attempted to ascertain their separate role on electrochemical properties. The microstructural analyses of the samples were carried out by SEM, BET, and XRD. 6Li MAS NMR was taken to specify the degree of crystallographic ordering in the framework. The resulting samples were tested in Li half cells to study the effect of Ni/Mn ordering and Mn3+ content. In-situ and ex-situ high resolution XRD were measured to study the origin of the different behaviors as metal ordering. The results of these studies will be discussed. |
