Mn-Ni Content-Dependent Structures and Electrochemical Behaviors of Serial Li_(1.2)Ni_(0.13+x)Co_(0.13)Mn_(0.54-x)O2 as Lithium-Ion Battery Cathodes

摘要

In this paper, a citric acid-assisted sol—gel route has been successfully used for the nanofabrication of serial solid solutions in a chemical formula of Li_(1.2)Ni_(0.13+x)Co_(0.13)Mn_(0.54-x)O2 at the x value of —0.06, —0.03, 0, 0.03, or 0.06. Powdered X-ray diffraction (XRD) results indicate that all the solid solutions possess the well-established structural characteristics for a homogeneous solid solution of Li2MnO3 and LiNi_(1/3+x)Co_(1/3)Mn_(1/3-x)O2 components with an increasing Li2MnO3 content along with the decrease of x value. Scanning electron microscope (SEM) observation and elemental analyses show that these samples are composed of polyhedral nanoparticles with a chemical composition similar to that of the corresponding raw materials. Applied as lithium-ion battery cathodes, the initial Coulombic efficiency, cycling stability, and rate capability of solid solutions are determined by their chemical compositions, giving an optimal x value within the range of —0.03 and 0.03. That is, the variation of x value in the formula Li_(1.2)Ni_(0.13+x)Co_(0.13)Mn_(0.54-x)O2 should exert a great influence on the electrochemical performances of these cathodes. Anyways, these suggest an effective strategy to understand the relationship between the Mn—Ni content-dependent crystal structures and electrochemical behaviors of solid solutions.