| The samples of cathode material of5V lithium ion battery were synthesized by polymer network in this paper. The samples were researched in modification of Mg ion doping, Cr ion doping and ZnO coating respectively. The structure, physical phase and morphology of synthetic samples were characterized by X-ray diffractometer(XRD) and field emission scanning electron microscope (SEM). The samples’electrochemical performance was studied by electrochemical workstation and battery test system(BTS). The specific research and contents are as follows:(1) The5V battery anode materials of LiNi0.5Mn1.5O4of lithium ion battery were prepared by polymer network. The impact of different calcination temperature on the structure, morphology and electrochemical properties of the samples were studied. The results of the research show that, the particles of5V battery anode materials synthesized by polymer network are small, the distribution of particle size is uniform, the crystallinity of samples is high, the samples’phases are pure and have no impurity ones. The particle size of the samples become biger, the ion migration and electrical conduction get more difficult as the calcination temperature rise, and thus the greater impedance of the samples. The first time discharge specific capacity at0.2C ratio of the samples synthesized at800°C,850°C,900°C reach124mAh/g,129.7mAh/g and124.9mAh/g, respectively. At high discharge rate, the attenuation of the capacity of the samples synthesized at850°C is lowest, which showed the best electrochemical performance.(2) Mg was doped to replace part of Ni. The effect on structure and morphology of the samples doped by a small amount of Mg is not big. But Mg ion doping can improve the stability of the crystalline structure of the samples, the samples doped with5%Mg can reduce the samples’polarization and improve high rate discharge platform. The5C discharge platform of samples blended with5%Mg is4.5V,0.1V higher than pure(4.4V), the discharge platform doesn’t decline form1C(4.6V) to5C, the discharge specific capacity decline lowest, only12mAh/g, the specific capacity retention remains98.2%after30cycle numbers at3C, which has the best cycle performance.(3) The samples of pure phase were studied by Cr ions doping. The samples of LiNi0.45Cr0.1Mn1.45O4and LiNi0.4Cr0.1Mn1.5O4were made respectively. The studies showed that Cr ion doping has no effect on the structure and morphology of the samples basically. Cr ions doping can inhibit the Jahn-Teller effect, impove the cycle life of the electrodes, inhibit capacity attenuation and improve the samples’ charge and discharge cycle performance wonderfully. The retention rates of specific capicaty of the samples whose Mn and Ni was replaced and Ni replaced by Cr remain98%and98.2%, when the two kinds of mixed samples was cycled20times at3C ratio.(4) The cycle performance under high temperature of55℃of5V cathode material in lithium ion battery can be improved significantly by ZnO coating. The samples coated with2%ZnO show the good cycle performance under the condition of high temperature55℃. The first discharge specific capacities of the samples of no coating, the coating amount of2%ZnO and5%ZnO are104.8mAh/g,125.9mAh/g and128.7mAh/g at high temperature of55℃and1/3C ratio. The capacity retention rates are63%,92.3%and89%respectively after20cycle numbers. |
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