Research Of LiNi_0.8Co_0.2O₂ Surface Modification And Li_1.5Al_0.5Ge_1.5（PO₄）₃ Powderinto A Plate

With the development of modern electronic technology, requirements of the market on the moving power are higher and higher. Lithium ion battery has been widely applied because of its small volume, light weight, high capacity, no memory effect, high good voltage, etc. For LiNiO₂, there is a disadvantage of poor thermal stability. Appropriate cobalt doping not only can improve the thermal stability, but also can improve the cycle performance. Lithium ion battery cathode material of solid melt LiNi_0.8Co_0.2O₂ with advantages of high reversible capacity and low cost is expected to be the substitute of LiCoO₂, but the electrochemical cycle performance should be further improved. This paper takes surface modified cathode material of LiNi_0.8Co_0.2O₂ with γ-Al₂O₃ and explores the best technology to improve the cycle performance of the cathode material. Study of the different amount of coating and different calcining time shows that γ-Al₂O₃ coating layer does not change the crystal structure of the material. When the charge and discharge voltage is in the range of 3.0 4.3 V, the properties of coated materials are better, and with the concentration of the material higher, the performance of coated material is better; however,the coating ratio over a certain amount will decrease the initial capacity of cathode material. With the increase of the calcining temperature, the improvement on cycle performance is obvious. When the temperature is higher than 550 ℃, the improving effort is not obvious. Research shows that the amount of coating 0.5 wt% and calcining temperature of 600 ℃ are optimal to improve charge and discharge cycle performance of cathode material under the condition of this experiment.The traditional lithium ion battery is commonly used in liquid electrolyte. However, for this kind of batteries, overcharge or internal short circuit may cause combustion and explosion danger, which do not exist for inorganic solid-state batteries. According to the crystal structure, inorganic solid electrolyte is divided into crystalline solid electrolyte, glassy solid electrolyte and glass ceramics solid electrolyte. Conductive glass ceramics Li_1.5Al_0.5Ge_1.5（PO₄）₃ could be obtained by the crystallization treatment on the basis of glass or sintered glass powder. It consists of the conductive main crystal phase and residual glass phase. LAGP conductive glass ceramics, widely concerned, has the properties of high conductivity, high mechanical strength and excellent chemical stability. The prepared LAGP powder can not be directly used in solid-state batteries, and needs to be transformed to the LAGP plate through the later processing. In this paper, using LAGP powder as raw material, research of the different temperature and different calcining time on the plates of 20 mm diameter with the 2g LAGP powder pressed under the pressure of 6 MPa shows that when the calcining temperature is 850 ℃ and the calcining time is 9h, LAGP plate with the thickness of 1.15 mm and the diameter of 19 mm has maximum lithium ionic conductivity, 3.13×10-4 S/cm.