| The Ni-Co-Mn lithium ion battery cathode materials not only is considered as apromising cathode material for lithium-ion batteries but also have attract a great deal ofattention owing to its outstanding safety performance, low manufacturing cost, highcharge and discharge specific capacity and good recycling performance. This article wasused high-temperature solid-phase method to synthesise xLi[Li1/3Mn2/3]O2(1-x)Li[Ni1/3Mn1/3Co1/3]O2, the microstructure and the morphology of the materialswere investigated by X-ray diffraction (XRD) respectively and scanning electronmicroscopy (SEM), the electric properties of the samples were studied byelectrochemical performance test, AC impedance test and cyclic voltammetry test.The cathode material Ni-Co-Mn was synthesized by high-temperature solid-phasemethod, using LiOH H2O,Ni(OH)2, Co3O4and MnO2and the effect of temperature andtime on the target material structure, morphology and electrochemical performance inthe process of presintering and sintering was studied and the best synthesis conditionswas determined: the precursor was calcined for5h at500℃, then the final product wasobtained after sintering at the high temperature830℃for9h. The SEM and XRDshowed that synthetic materials had uniform particles, neat appearance, complete crystalstructure, high crystallinity, with α-NaFeO2type structure. The constant currentcharge/discharge test and electrochemical impedance analysis were carried out bybutton cell electrochemical test methods. It was concluded that the first dischargespecific capacity is171mahg-1, and the charge and discharge efficiency was up to93%in2.0~4.8V at0.1C. After20cycles the capacity retention reached95%.The Ni-Co-Mn composite cathode material doped with LiF was prepared under theoptimum process conditions. The effect of fluorine doping amount on the physical andchemical properties of xLi[Li1/3Mn2/3]O2(1-x)Li[Ni1/3Mn1/3Co1/3]O(2-z)Fzthe composite cathode material were studied. The XRD showed that the type of crystal structure of theternary composite anode material was not affected by doping F-. When the dopingamount z=0.05,the ternary cathode material had better initial capacity. When z=0.05amounts of doped composite performance was relatively good, and discharge capacityfor the first time reached186.7mAhg–1. After15cycles discharge capacity was only132.8mAhg–1. A small amount of F-doping could make the ternary cathode materialhave better initial capacity, but also had a certain decline in its cycle performance. Withincrease in the amount of mixed F-content, the capacity loss rate of material alsodiffered greatly, energy loss was most obvious when z=0.12. After15cycles,discharge capacity for the first time reduced from155.3mAhg-1reduced to77.9mAhg-1..In order to improve the ternary cathode material performance, it is necessary tofind an effective ion doping.Using the same source of nickel, cobalt, manganese, lithium composite materialand technological conditions, ternary positive composites was doped by Al(NO3)39H2O.The influence of the Al doping amount on the physical and electrochemical propertiesof the anode composite xLi[Li1/3Mn2/3]O2(1-x)Li[Ni1/3Mn1/3Co(1/3-y)Aly]O2was studied.The XRD testing showed that after doping the sample was still α-NaFeO2layeredcrystal structure, and no obvious impurity peak. It means that a small amount of Aldoping would not change the crystal structure of the original ternary material. When Alion doping amount was0.08, xLi[Li1/3Mn2/3]O2(1-x)Li[Ni1/3Mn1/3Co(1/3-y)Aly]O2hadgood electrochemical performance. The charging and discharging test was conducted at0.1C, and the first discharge specific capacity raeched161.1mAh/g. After20cycles,the capacity retention rate was above99%, and the charge and discharge specificcapacity almost no attenuation. There was no room for the charge and dischargeperformance improvement, but the cycle performance and stability of battery materialsgot strengthened obviously. |
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