| The aggravating energy shortage and environmental degradation have propelled considerable efforts to explore Lithium-ion batteries (LIBs). While three-component layered LiNi0.5Co0.2Mn0.3O2 has attracted much attention in the academia and industry because of its relatively high energy density, some tough problems of this material including the poor rate capability and serious capacity fading under the redox potential up to 4.6 V obstruct its deeper research and application. Synthesis method has much significance of the atomic order and subsequently influences the crystal structure, particle size, micro morphology and electrochemical properties. In this paper, the study of the current research effort on LiNi1-x-yCoxMnyO2 material has been reviewed. Based on these reviews, the synthesis effect of the precursor and the optimal preparing process of the LiNi0.5Co0.2Mn0.3O2 were investigated by adopting co-precipitation method. Additionally,to get over performance degradation of LiNi0.5Co0.2Mn0.3O2,efforts, elemental dopings with Ti and Mg and Li2Ti03 coating modification have also been studied.Spherical LiNi0.5Co0.2Mn0.3O2 was prepared by calcining a stoichiometric mixture of Li2CO3 and Ni0.5Co0.2Mn0.3O2(OH)2 precursor. The precursor was synthesized via a co-precipitation route with sulfate as raw materials, NH3·H2O as complexing agent and NaOH as precipitant. The crystalline structure, morphology were analyzed using X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscope (SEM).And the effects of the pH value and calcination temperature on physical and electrochemical properties of the samples were deeply investigated. The cathode material with the well-ordered structural was obtained at the optimum synthetic conditions of the pH value 11.5 and the calcination temperature of 900 ?. At the same time, the resultant powder of LiNi0.5Co0.2Mn0.3O2 delivered a high discharge capacity of 159 mAh g-1 at 0.1 C,and excellent capacity retention of 92% was retained after 60 cycles.The layered oxide material LiNi0.48Co0.18Mn0.3Mg0.02Ti0.02 has been synthesized via a co-precipitation assisted solid-phase method, and its crystal structure, morphology and electrochemical properties have been systematically investigated. Rietveld refinement of its X-ray diffraction data indicates a higher degree of the well-ordered crystallographic form,which provides LiNi0.48Co0.18N4n0.3Mg0.02Ti0.02O2 with superior cycle performance and rate capability. The initial discharge capacities of the electrode are 151.5 mAh g-1,140.1 mAh g-1, 137.1 mAh g-1 125.2 mAh g-1 and 115.3 mAh g-1 at the current of 0.5C, 1C,2C,3C and 5C,respectively. After 100 cycles at the same rates, 94%,96%,96%,94% and 93% of the initial discharge capacity are retained. The improved electrochemical properties are attributed to the decrease in particle size and suppression of cation mixing due to doping with Mg and Ti. The results of this work indicate that LiNi0.48Co0.18Mn0.3Mg0.02Ti0.02O2 is a promising cathode material for Li-ion batteries.As for LiNi0.5Co0.2Mn0.3O2 materials, poor cycling stability is commonly observed under high-voltage operation (>4.3 V), particularly accompanied by high rate operation.Here, layered LiNi0.5Co0.2Mn0.3O2 was surface-modified by Li2TiO3 coating and investigated during cycling on high rate capability as well as at different cutoff voltage. It was found that Li2TiO3 coating is effective to improve the battery performance, comparing to the bare LiNi0.5Co0.2Mn0.3O2 suffered a seriously capacity fading on cycling. According to the results of charge/discharge experiments, 6 wt.% coated sample delivered a high discharge capacity of 181.5 mAh g-1 at 1C rate (0.6 mA cm-2) under high cutoff voltage4.8 V. After 150 cycles, it still retained 69% capacity. It demonstrates that the coating strategy is an effective route to high energy density and high-voltage stable cathode materials for high performance LIBs. |
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