Effects of chelators on the structure and electrochemical properties of Li-rich Li${}_{1.2}$Ni${}_{0.13}$Co${}_{0.13}$Mn${}_{0.54}$O${}_2$ cathode materials

In this study, carboxylic acids, namely concentrated citric acid and ethylene diamine tetra-acetic acid (EDTA) solution, are used as chelators to synthesize Li-rich layered Li${}_{1.2}$Ni${}_{0.13}$Mn${}_{0.54}$Co${}_{0.13}$O${}_2$ (LLNMC) by sol-gel method. We investigate the influence of these chelators on the morphology crystal properties and electrochemical performance of LNMC. Based on XRD data, the synthesized materials can be characterized as a combination of two phases, a rhombohedral R-3m phase (LiNi${}_{1/3}$Mn${}_{1/3}$Co${}_{1/3}$O${}_2$) and a monoclinic C2/m phase (Li${}_2$MnO${}_3$), which, according to the stoichiometry, are xLi${}_2$MnO${}_3$•(1-x)LiNi${}_{1/3}$Mn${}_{1/3}$Co${}_{1/3}$O${}_2$ with x = 0.5. The morphology and local structure were studied using electron microscopy (SEM, TEM and HRTEM) and Raman spectroscopy, respectively. A clear evidence for the effect of chelating agent was observed from electrochemical tests carried out by galvanostatic charge-discharge cycling and electrochemical impedance spectroscopy. The sample prepared via EDTA as organic complexing agent exhibits the best electrochemical properties, with higher capacity and rate capability.