Improvement of structural and electrochemical properties of NMC cathode materials by combined doping and coating.

The current available research on Li-ion batteries (LIBs) indicates the demand for new methods of development of cathode materials capable of reducing overall costs and environmental impacts, as well as providing higher energy density, lighter weight and better 1 electrochemical properties . Current efforts in the area have focused on the improvement of cathode materials, resulting in the formulation of the ternary oxides LiNiaCobMncO2 (where 2 a + b + c =1), also called NMCs . The LiNi0.33Co0.33Mn0.33O2 stoichiometry, which represents the "model" material from which several types of NMC with different composition have been derived, exhibits capability of inserting significant amount of lithium in the transition metal sites, admissible specific capacity, and structural stability. Consequently, 3 there is an increased use of this substance in the battery market . In this study, we have developed a facile approach for the synthesis of cathode materials with enhanced properties to improve electrochemical performances of LIBs. Prospective cathode materials NMC and modified NMC for LIBs were successfully synthesized through a novel synthetic method including a citric acid-assisted sol-gel processing followed by drying and calcination at different temperatures. The nature, morphology and size of the materials were characterized by scanning electron microscopy (SEM) and transition electron microscopy (TEM). The phase and structure of the nanostructures were revealed by X-ray diffraction spectroscopy (XRD). To assure a reliable evaluation, rietveld refinement analyses of the data were done to gain the lattice parameters. The electrochemical properties of all electrodes were studied by cyclic voltammetry (CV) and charge/discharge studies. The combined results from structural investigations revealed that Mg/Zr modified NMC (where the modification has been obtained by doping and/or coating) shows a better- organized layered structure compared to the bare NMC, together with a uniform coating layer. As determined by galvanostatic potential limitation, both pristine NMC and Mg/Zr modified NMC gave an efficient charge/discharge behavior in the voltage range between 3.2V and 4.2V, but the optimized materials show a higher capacity, of the order of 200 mAh/g, at 1C and a significant good cycling stability after 100 cycles without fade of capacity (high capacity retention of 100%). These promising results obtained with this synthesis open possibilities for performance improvements by structure doping and surface enhancement.