Preparation And Properties Of LiNi 0.8 Co 0.15 Al 0.05 O 2 And LiNi 0.4 Al 0.2 Mn 0.4 O 2 Cathode Materials

The layer-structured Li-Ni-Co-Mn-O ternary materials with a high capacity,good cycle performance and thermostability had been extensively studied.The cost of ternary materials is very high for the scarce resource of Co,and it is poisonous and harmful to the environment.This paper has reviewed the development of cathode materials of Lithium Ion Battery,and the LiNi0.8Co0.15Al0.05O2 was synthesized by solid-state method by using Ni（OH）₂,Al（OH）₃,CoCO₃ and LiNO₃.The effects of different calcination temperature,calcination time and lithium content on the structure and electrochemical properties of the composites were studied by X-ray diffraction,scanning electron microscopy,charge-discharge test and cyclic voltammetry.The results showed that the structure of Li1.15 [Ni0.8Co0.15Al0.05]O2 was integrity under the sintering condition of 800 ℃ and 16 h.The initial discharge capacity was 155.6 mA·h·g-1,and discharge capacity was 149.17 mA·h·g-1 after 20 cycles,the capacity retention was 96.1% under 2.7⁴.2 V voltage range,0.1 C current.When the discharge rate was 5 C,the initial discharge capacity was 106.05 mA·h·g-1 and the capacity retention remains 84.6% after 20 cycles.On the basis of LiNi_0.4Co_0.2Mn_0.4O₂ studies,this paper synthesized the LiNi_0.4Al_0.2Mn_0.4O₂ by solid-phase method and using Al to replace Co.And the effects of different calcination temperature,calcination time and lithium content on the structure,morphology and electrochemical properties of the composites were studied by X-ray diffraction,scanning electron microscopy,charge-discharge test,cyclic voltammetry test and AC impedance test.The results showed that the Li1.1Ni0.4Al0.2Mn0.4O2,which prepared at 900 ℃ for 12 h has the best electrochemical performance.Under the 2.7⁴.2 V voltage range,0.1C current charge-discharge test,the initial discharge capacity was 108.58 mA·h·g-1,the discharge capacity was 102.46 mA·h·g-1 after 20 cycles,and capacity retention was 94.36%.When the discharge rate was 5 C,the initial discharge capacity was 86.51 mA·h·g-1 as well as 89.38% capacity retention after 20 cycles.The charge transfer resistance Rct was 175.4 Ω.In order to further study the kinetic process in the electrode reaction,the diffusion coefficient of Li⁺ in the solid phase was calculated by AC impedance spectroscopy method.The results showed that the diffusion coefficient of Li⁺ in the solid phase was from 4.89×10-15 to 7.42×10-15 cm²·S^-1 of Li_1.15[Ni_0.8Co_0.15Al_0.05]O₂.And the DLi⁺ of Li_1.1[Ni_0.4Al_0.2Mn_0.4]O₂ udner 4.0 v and 4.2 v was 1.48 × 10-14 cm²·S^-1 and 1.58 × 10-14 cm²·S^-1,respectively,which was a litter higher than that of Li_1.15[Ni_0.8Co_0.15Al_0.05]O₂.From the diffusion coefficient and electrochemical properties,the capacity of LiNi_0.4Al_0.2Mn_0.4O₂ has decreased,but the discharge performance at a higher magnification is better than that of LiNi0.8Co0.15Al0.05O2 cathode material.