Mn–Ni Content-Dependent Structures and Electrochemical Behaviors of Serial Li_1.2Ni_0.13+xCo_0.13Mn_0.54–xO₂ as Lithium-Ion Battery Cathodes

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 Li1.2Ni0.13+xCo0.13Mn0.54-xO2 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 LiNi1/3+xCo1/3Mn1/3-xO2 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 Li1.2Ni0.13+xCo0.13Mn0.54-xO2 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.