Lithium-ion Battery Cathode Material Of Lini <sub> 0.8 </ Sub> The Co <sub> 0.2 </ Sub> O <sub> 2 </ Sub> Research

The lithium ion battery has been widely used because of its good performance. But the high price of cobalt makes the cost of LiCoO₂ cathode material relatively high, which prevents the further development of lithium ion battery. In order to reduce the cost of cathode material and not to decay its electrochemical performance, we prepare the material LiNi_0.8Co_0.2O₂ and make research of synthesis conditions and performances of the material.Cathode material LiNi_0.8Co_0.2O₂ was prepared using Ni_0.8Co_0.2(OH)₂ obtained by the coordination-buffer solution method. Physical characters of the synthesized material were tested by the method of XRD, SEM, TG etc. And the electrochemical methods were used to test the capacity, rate performance, cycling capability and kinetics parameter of the material.Ni_0.8Co_0.2(OH)₂ precursor prepared in the condition of pH=11 and NH₃:(Ni+Co)=1:1 has a narrow particle distribution with pure phase. More over, the particles are ball-like with big apparent density and tap density. LiNi_0.8Co_0.2O₂ were synthesized in the range of 600⁸00℃ with different sintering time. LiNi_0.8Co_0.2O₂ synthesized at 720℃ for 10h is ball-like single phase. It has a first discharge capacity of 185mAh · g^-1. The capacity remains 180mAh · g^-1 after 20 cycles and discharge capacity is 130 mAh · g^-1 at 1C rate.LiNi_0.8Co_0.2O₂ synthesized at 600℃ has impurities, and the capacity decreases rapidly with the low voltage plateau. When the temperature increases to 800℃, the capacity of the material also has a bad cycling performance with integrated crystal and relatively high capacity. It indicates that excessively high or low temperature turns against the good performance of the material.The electrochemical reaction resistance increases with the going-on of discharge according to AC impedance test of LiNi_0.8Co_0.2O₂, which indicates that electrochemical reaction happened at the interface is improved with the high voltage of the materials. The impedance of the material synthesized at 720℃ is the lowest while at 600℃ is the greatest according to the impedance test of the materials synthesized at different temperatures. It shows that properly increased temperature is beneficial to the electrochemical reaction, which can also be seen from the charge-discharge results.Diffusion coefficient in the charged state and the discharged state of LiNi0.8Coo.202 prepared at 720 °C for lOh are 4.014 X 10"9cmV and 2.861 X 10"10cm2-s"1 respectively by Chronoamperometry, which shows that diffusion coefficient decreases with the going-on of discharge.