(1-x) LiNi 1/2 Mn _1/2 O Study On Electrochemical Properties Of Cathode Materials For

Much attention from researches and industries have been attracted to lithium manganese rich cathode materials xLi [Li1/3Mn2/3]O2·(1-x) LiMO2(0≤x≤1), because of their high capacity, high voltage and a new charge-discharge mechanism. This thesis is mainly engaged in the electrochemical performance of lithium-rich manganese material, and in the modification of its capacity retention ability.Lithium-rich materials xLi2MnO3·(1-x)LiNi1/2Mn1/2O2(x=0.1、0.2、0.3、0.4、0.5) were prepared by co-precipitation method. Electrochemical properties were characterized by galvanostatic cycling at45℃. These experiments let to better understanding of Li2MnO3to the electrochemical properties of lithium manganese rich cathode material.Specimens of different aluminum dopping amount were prepared according to formula Li[Ni0.20-y/2Li0.20Mn0.60-y/2]A1yO2(y0,0.03,0.06,0.09). Effects of Aluminum doping on the structure were studied by X-Ray diffraction (XRD) and TEM. Electrochemical properties were characterized by galvanostatic cycling and electrochemical impedance spectroscopy (EIS).Another group of specimens were prepared according to formula xLi2MnO3(1-x)LiNi(1-z)/2Mn(1-z)/2AlzO2,(x=0.1,0.3,0.5),z=0.09. Efforts were put to get best electrochemical properties of the material when combined the effects of aluminum and the Li2MnO3content.The electrochemical studies suggest that, the discharge capacity increases with the amount of Li2MnO3in the sample, as a result of electrochemical activation of Li2MnO3at potential of4.5V. Sample X04(0.4Li2MnO3·0.6LiNi1/2Mn1/2O2)delivers a higher discharge capacity (340.8mAh.g-1); but discharge capacity of material cannot benefit from Li2MnO3more than50%content.As samples were electrochemically cycled at25℃, discharge capacity of Li-rich material decreased dramatically with doping aluminum, but high capacity were obtained when cells were cycling at45℃. The Sample X05-AL09(Li1.20Ni0.i6Mn0.56Al0.08O) shows excellent capacity retention ability and high initial columbic efficiency(85%). It divers a discharge capacity of250.8mAh.g-1as cycling at0.2C/45℃.The electrochemical studies suggest that the capacity retention ability and the initial columbic efficiency were significantly improved by introducing1%to2.5wt%of aluminum into Li-rich material. Aluminum doping improves electrochemical performance of Li-rich materials used in vehicle and energy storage.The electrochemical characters in lithium intercalation/disintercalation were analyzed by electrochemical impedance spectroscopy (EIS) and dQ/dV-V method. Formation of spinel in material during cycling was discussed. Effects of aluminum on the structure and electrochemical performance of lithium rich cathode materials were investigated.