| Due to with high reversible specific capacity and low cost,nickel-based cathode material LiNi0.9Mn0.1O2 has attracted much attention for the application in the lithium-ion batteries.However,it suffers from safety problems and rapid capacity fading during cycling.In this project,we aimed to improve its performance.The LiNi0.9Mn0.1O2 cathode compound was synthesized from a mixture of LiOH·H2O and co-precipitated Ni0.9Mn0.1(OH)2 precursor with high temperature solid state method.Different synthesis conditions,doping modification were applied in order to improve the electrochemical performance.We used powder X-ray diffraction(XRD)technique and scanning electron microscopy(SEM),energy spectrum analysis,ICP-OES and electrochemical performance test to characterize the structure,morphology and properties of the obtained materials.LiNi0.9Mn0.1O2 materials were synthesized via co-precipitation and high temperature solid state method,the results showed that cathode material exhibited well crystallized structure.Optimum electrochemical performance was obtained for the sample synthesized at Li/(Ni + Mn)= 1.11 and sintering temperature 780 ℃ for 12 h and in pure oxygen atmosphere.The as-synthesized LiNi0.9Mn0.1O2 materials has the initial discharge specific capacity of 180.8 mAh/g at 0.2C rate and a capacity retention ratio for the battery about 77.18% after 50 cycles at 25℃ and in the voltage range of 2.75~4.2VThe LiNi0.9-xCoxMn0.1O2(x = 0,0.04,0.07,0.1)cathode material was prepared through Co doping.The XRD showed that the doped Co did not change the layer structure but reduced the cation mixed degree as well as improved the electrochemical performance.At 25℃ and in the voltage range of 2.75~4.35 V,the initial discharge specific capacity of LiNi0.83Co0.07Mn0.1O2 reached 205.4mAh/g and its capacity retention ratio for the battery was 77.07% after 100 cycles.The rate capability for this material was also very well as the capacity was 139mAh/g at 5C rate.The low temperature performance of the material had also been improved.When under-20 ℃,the discharge specific capacity was 159.48mAh/g and the low efficiency was 75.33% which was 8% higher than the pristine material.The electrochemical properties were significantly enhanced after modificated by doping ZrO2 and LiF compared to the undoped one.At 25℃ and in the voltage range of 2.75~4.35 V,the initial discharge specific capacity of material doped with 1.5% ZrO2 was 199.8mAh/g and its capacity retention ratio was 89.79% after 50 cycles,in addition,the low efficiency was 75.33% under-20 ℃.At the same condition,the initial discharge specific capacity of material doped with 0.5% LiF was 196.45mAh/g and the capacity fading by 12.23% after 50 cycles as well as the low efficiency was 75.33% under-20 ℃.It is important to determine the change rules of the values for the electrochemical impedance and study the transformation of the resistance for material after discharged through analysing the material resistance changes with the depth of discharge. |
