Synthesis of Li[(Ni0.5Mn0.5)(1-x)Li-x]O-2 by emulsion drying method and impact of excess Li on structural and electrochemical properties

Abstract

Layered Li[Ni0.5Mn0.5]O-2 (R (3) over barm space group) was synthesized with controlling the Li/(Ni + Mn) ratio by employing an emulsion drying method, and the effect of Li on the transition-metal layer was investigated. Structural analyses of the final products were done by X-ray diffraction, neutron diffraction, and X-ray absorption near-edge spectroscopy. From the structural studies, we found that an excess amount of Li is located at the transition-metal layer and the presence of Li in the transition metal significantly improved structural ordering in the crystal structure. High capacity with good cyclability, faster Li+ chemical diffusivity, less changes in the host structure by Li+ de-/intercalation, and higher thermal stability were achieved for the Li-excess Li[(Ni0.5Mn0.5)(0.94)Li-0.06]O-2 compound relative to Li[Ni0.5Mn0.5]O-2. It is believed that such enhanced electrochemical properties are related to the improved physical and structural proper-ties of Li-excess Li[(Ni0.5Mn0.5)(0.94)Li-0.06]O-2.