화학공학소재연구정보센터
Journal of Materials Science, Vol.52, No.14, 8630-8649, 2017
Change of local structures for 0.5Li(2)MnO(3)-0.5LiMn(1/3)Ni(1/3)Co(1/3)O(2) in first charge process of different rates
An investigation was carried out into the charging rate dependence of local structural changes in a layered 0.5Li(2)MnO(3)-0.5LiMn(1/3)Ni(1/3)Co(1/3)O(2) solid solution during the initial charging cycle. To clarify the mechanism involved in local atomic rearrangement, a pair distribution function (PDF) analysis was performed using the results of powder neutron diffraction and synchrotron X-ray total scattering measurements. First-principles calculations (VASP code) were used to determine the initial structure when performing the PDF analysis. The bond-length strain (lambda) and the bond-angle strain (sigma (2)) for the optimized model were calculated following the PDF analysis in order to clarify the effect of the charging rate on the crystal structure distortion. Before charging, the distortion was small for MnO6 octahedra compared to that for NiO6 and CoO6 octahedra. During charging at a rate of 1C, the MnO6 octahedra experienced increasing distortion, whereas at 3C the CoO6 octahedra became more distorted. In addition, when charging at 3C, the values of lambda and sigma (2) increased for NiO6 octahedra that had entered the Li layer as a result of cation mixing. This appeared to be related to whether the localized atom was Mn or Co within the average structure during charge process. It is thought that distortion occurs in MO6 octahedra containing whichever element becomes localized, and this depends on the charging rate. This leads to the possibility that decreasing the fractional composition of the element that becomes localized may lead to reduced distortion and improved the cyclability.