Study On Synthesis And Electrochemical Behaviours Of Li_1+x[Ni_0.5Co_0.2Mn_0.3]_1-xO₂（0﹤x﹤1） Cathode Material As Lithium Ion Batteries

The recent development and introduction of layered lithium-rich Li_1+xM_1-xO₂（M=Ni，Co，Mn，…，0<x <1） as a new class of cathode matericals, which have ananomalously high capacity （200-300mAh/g）, favorable thermal stability and safety,have broad prospects on the application of electric vehicles （EV） and hybrid electricvehicles （HEV）. However, it must overcome these problems, such as the initialirreversible capacity and lower rate performance, to apply in EV and HEV.In this paper, to improve the electrochemical properties of layered lithium-richLi_1+x[Ni_0.5Co_0.2Mn_0.3]_1-xO₂（0<x <1）, the cathode matrials were prepared by usingco-precipitation method. Li_1+x[Ni_0.5Co_0.2Mn_0.3]_1-xO₂（0<x <1） were characterized byphysical characterization and electrochemical techniques, and the influences ofcalcining temperature, calcining time and lithium content on structure, morphologyand electrochemical properties were studied in detail. The results demonstrate thatLi_1+x[Ni_0.5Co_0.2Mn_0.3]_1-xO₂（0<x <1） have batter electrochemical properties when itis calcined at8500C for14h and x is equal to0.115. The initial discharge capacity ofLi_1+x[Ni_0.5Co_0.2Mn_0.3]_1-xO₂（0<x <1） is224.6mAh/g, and the capacity retention ofthe material after50cycles at0.2C in the voltage range of2.0-4.6V is84.1%.Electrochemical impedance technique （EIS） and galvanostatic intermittenttitration technique （GITT） were performed to study the kinetics of the electrodereactions for Li_1+x[Ni_0.5Co_0.2Mn_0.3]_1-xO₂（0<x <1）, and lithium ion diffusioncoefficient （DLi⁺） was calculated. The kinetics of the electrode reactions forLi_1+x[Ni_0.5Co_0.2Mn_0.3]_1-xO₂（0<x <1） are controlled by Li⁺diffusion in the voltagerange of3.7-4.5V and by charge transfer in the voltage range of4.5-4.8V.The electrochemical properties of3wt%AlPO₄-coated Li_1+x[Ni_0.5Co_0.2Mn_0.3]_1-xO₂（0<x <1） have been effectively improved. The initial discharge capacity of3wt%AlPO₄-coated Li_1+x[Ni_0.5Co_0.2Mn_0.3]_1-xO₂（0<x <1） is238.14mAh/g, and theirreversible capacity has reduced by11.86mAh/g. The capacity retention of3wt%AlPO₄-coated Li_1+x[Ni_0.5Co_0.2Mn_0.3]_1-xO₂（0<x <1） after50cycles at0.2C in thevoltage range of2.0-4.6V is86.3%. Meanwhile, the discharge capacity of3wt% AlPO₄-coated Li_1+x[Ni_0.5Co_0.2Mn_0.3]_1-xO₂（0<x <1） at0.1C,0.2C0.5C,1C and2Care229.6,220.2,200.9,171.3, and123.9mAh/g, respectively.