Study On Synthesis And Electrochemical Performance Of LiNi_0.8Co_0.2O₂

The performances of batteries are required to enhance quickly to satisfy the development of science and technology and the miniaturization of electronic equipment. Nowadays among the comprehensive performances of many kinds of batteries, lithium ion batteries show a most promising property in the second high-energy battery. Because of high price of Co, the original cathode material for lithium-ion batteries, lithium cobalt oxide, LiCoO2, is now being replaced by a mixed lithium cobalt/nickel oxide, with the approximate composition LiNi0.8Co0.2O2.The main aims of the paper are to synthesize the cathode material LiNi0.8Co0.2O2 by sol-gel method and use doping and coating methods to improve the properties of LiNi0.8Co0.2O2.The cathode material LiNi0.8Co0.2O2 synthesized with the method of sol-gel was researched on the electrochemical properties in order to optimize the methods of preparation through researching the effects of treating temperature, synthesis time. It is found that the proper treating temperature is 800℃, the proper synthesis time 12 hours. The first discharge capacity of material obtained by the above way is 153mAh/g remain 76% after 20 cycles.LiNi0.8-xCo0.2CexO2 (x = 0.01, 0.02,and 0.03) was synthesized by sol–gel method. Experiments of XRD, FTIR, charge-discharge, CV, EIS and DSC were carried out. The results show that Ce-doped materials have better electrochemical performance, the first charge efficiency and capacity retention are improved. The composition with x=0.02 shows the best electrochemical performances, the first discharge capacity is 157mAh/g, the initial charge-discharge efficiency is 88%, the discharge capacity remain 94% after 20 cycles. The slow degradation of the electrochemical property of Ce-doped LiNi0.8-xCo0.2CexO2 during cycling is attributed to the suppression of phase transitions and charge-transfer impedance increasing during cycling. Besides this, Ce doped material shows improved thermal stability.LiNi0.8-xCo0.2YxO2 (x =0.03, 0.04, and 0.05) were synthesized by sol–gel method. Experiments of XRD, charge-discharge and EIS were carried out. The results show that Y-doped materials have lower degree of cation mixing and better layered structure, the first charge efficiency and capacity retention are improved, the composition with x=0.04 shows the best electrochemical performances, the initial charge-discharge efficiency is 88%, the discharge capacity remain 95% after 40 cycles. The increasing of charge-transfer impedance of cathode during cycling is restrained.Al2O3-coated LiNi0.8Co0.2O2 particles are prepared by a precipitation method...