Modification Of Lithium-rich Manganse-base Solid Solution Li_1.2Mn_0.56Ni_0.16Co_0.08O₂ As Cathode Material For Lithium Batteries

With the rapid development of science and technology,electronic products constantly updated.It hoped that the batteries with higher capacity than before are developed.Among commercial batteries systems,lithium ion batteries exhibit the best electrochemical performance.The layered lithium-rich manganese base solid solution materials get more attentions due to their high specific capacity,environmental friendly and low cost of raw material.In this dissertation,two series of layered lithium-rich manganese base solid solution cathode materials with the theoretical composition of the Li1.2Mn0.56-xMxNi0.16Co0.08O2(M=Ti,Al),and a Li1.2Mn0.56Ni0.16Co0.08O2 pretreated by using the(NH4)2SO4 solution were prepared.The physical and chemical properties of the as-prepared materials investigated by using many advanced techniques,such as the XRD,charging and discharging test,cyclic voltammograms,A.C.impedance,SEM,FTIR and so on.The main research results as following:1.Lithium-rich manganese base solid solution cathode materials with a layer?-NaFeO2 structure were prepared by using a solid phase sintering method.The composite with the theoretical composition of Li1.2Mn0.544Ti0.016Ni0.16Co0.08O2 exhibits the best electrochemical properties in as-prepared titanium doping composites.It shows the discharge capacities of 217,165,143,133 mAh/g in the first cycle,and 210,184,161,184 mAh/g in the 40th cycle at the current of 20,200,400,1000 mA/g,respectively.The high-rate discharge performance of the composite improved by the titanium doping.It found that electrochemical reaction of the material determined by the impedances of charge transfer and Li+ diffusion.The titanium doping composite shows the lower impedance of charge transfer than that of the undoped ones.2.The composite with the theoretical composition of Li1.2Mn0.552Al0.008Ni0.16Co0.08O2 exhibits the best electrochemical properties in as-prepared aluminum doping composites.It exhibits the discharge capacities of 222,174,167,131 mAh/g in the first cycle and 217,195,166,146 mAh/g in the 40th cycle at the current of 20,200,400,1000 mA/g,respectively.The as-prepared aluminum doping composite exhibit better high-rate performance and cycle reversibility than those of undoped one does.3.The composite with the theoretical composition of Li1.2Mn0.56Ni0.16Co0.08O2 treated with 0.050 g/cm3(NH4)2SO4 shows the best electrochemical performance in all as-prepared ones.The coulomb efficiency of the composite treated with 0.050 g/cm3(NH4)2SO4 solution(?96%)is higher than that of the composite without treating(?72%)at the current of 20 mA/g.The composite treated with 0.050 g/cm3(NH4)2SO4 solution exhibits the discharge capacities of 240,197,189,157 mAh/g in the first cycle,and 229,202,187,137 mAh/g in the 40th cycle at the current of 20,200,400,1000 mA/g,respectively.The surface treatment method with(NH4)2SO4 solution obviously decreased the irreversible capacity of the solid solution,and increased the discharge capacity in the first cycle.