Study On Synthesis And Modification Of Ternary Materials LiNi_xCo_yFe_1-x-yO₂ As Lithium Ion Battery

Though LiNi_xCo_yFe_1-x-yO₂ layered ternary materials has advantages in the field of high capacity, low cost and soon, Jahn-Teller effect of Mn in LiNi_xCo_yFe_1-x-yO₂ can lead to structural distortion. Meanwhile, cation mixing of LiNi_xCo_yFe_1-x-yO₂ resultd in bad cycling stability. In this article, manganese of materials was replaced by inexpensive and environmentally friendly Iron. The LiNi_xCo_yFe_1-x-yO₂ layered ternary materials were prepared by rheological phase reaction and solid state method. The effect of anion doping, acid treatment of lithium-rich materials on the structure, morphology and electrochemical performance of materials were studied.In the synthesis of LiNi_xCo_yFe_1-x-yO₂ ternary materials: the LiNi_xCo_yFe_1-x-yO₂ was prepared by rheological phase reaction and solid state method. According to the phase characterization and electrochemical performance test, it is found that the electrochemical performance of the material is the best when the ratio of Ni、Co、Fe is 9:8:1. Then, we have selected LiNi_0.5Co_0.45Fe_0.05O₂ ternary materials which is best ratio, and to futher study the effect of sintering temperature and time on electrochemical performance of this materials. The results showed that the LiNi_0.5Co_0.45Fe_0.05O₂ which was sintering at 700℃ for 12 h had the best electrochemical performance. The initial discharge capacity was 160.4 m Ah·g-1 at 0.2C in the 3.0⁴.5V voltage range, and the discharge capacity was 125.9 m Ah·g-1 after 50 charge-discharge cycles, the capacity retention was 78.5%.In the anion doping of LiNi_xCo_yFe_1-x-yO₂ ternary materials: The LiNi_0.5Co_0.45Fe_0.05O₂-y Fy、LiNi_0.5Co_0.45Fe_0.05O₂-y（SO₄）y、LiNi_0.5Co_0.45Fe_0.05O₂-y（PO₄）y（y=0.02、0.04、0.06、0.08） materials were prepared by rheological phase reaction and solid state method at 700℃ for 12 h, respectively. The test results showed that the cycle stability of materials were greatly improved by anion doping. The cycle stability of materials doped with F- was improved, because Li-F bonds of subject structure protect electrode from eroding, which stemd from the HF of electrolyte. The test results showed the large polyanions（SO₄2-,PO₄3-） can enlarge cell volume and generate an open three-dimensional 3D framework, which enhanced fast mobility of Li+. The large polyanions can also restrict the structural distortion during the cycling process, which improved electrochemical performance of materials.In the lithium-rich and acid treatment modification on LiNi_xCo_yFe_1-x-yO₂ ternary materials: The lithium-rich materials 0.5Li₂MnO₃·0.5LiNi_0.5Co_0.45Fe_0.05O₂ were prepared by rheological phase reaction and solid state method at 700℃ for 12 h, and were treated by acid with HCl、H2SO₄、H3PO₄, respectively. The test results showed that the coulombic efficiency of the first cycle and the electrochemical performance of the lithium-rich materials treated by acid were improved.