Study On Preparation And Performance Of Cathode Materials For Lithium Ion Batteries

The latest development of various kinds of cathode materials for lithium ion second batteries has been reviewed in this paper. To this question, two developing orientations for the cathode material were bought forward by this paper. One is the development of nanometer cathode material in order to exert nanometer materials' especial advantages in lithium ion second batteries; the other is the development of new cathode materials with high energy density for the replacement of present materials. For the above two aspects, we have done the following two main experiments: the synthesis of nanometer LiMn2O4 by sol-gel method—citric acid complexation method and the preparation of new cathode material LiFePO4 by high temperature solid-state reaction. For preparation of nanometer LiMn2O4 with good performance, the effects of synthesis conditions of the citric acid complex method on crystal structure, particle size, microcosmic shape and electrochemistry performance of the products were studied. The best synthesis conditions are listed as follows: the acetate is taken as the chemical reagents; the optimal pH value of the hybrid liquid is 6; the pretreatment temperature is about 400℃; the calcination temperature is 750℃. Although the product obtained by the optimal preparation conditions has a lower initial discharging capacity of 90.7mAh/g, it has an excellent cycling performance considering that it has a slight capacity loss rate of 2.7% when the fiftieth cycle ended. On the other hand, the product prepared with nitrates has a higher discharging capacity of 108.9 mAh/g. When the 30th cycle ended, it's discharging capacity is 36.29mAh/g. So the conclusion is that the products prepared by nitrate have bad cycling performance. The elementary preparation technology of the new cathode material LiFePO4 was investigated and then the synthesis method of it was established, i.e. a pretreatment temperature of 300℃ and a calcination temperature of 650℃. The pure LiFePO4 product manufactured by the above technology has a lower discharging capacity of 81.7mAh/g. The above technology was looked as the further experiment foundation. In order to improve the conductivity of LiFePO4 samples, the chemical reagents were intermingled with grape sugar and various kinds of electric carbon and then obtained a variety of samples by high temperature solid-state reaction. Among these samples, two samples with 5wt% and 15wt% carbon obtained from the grape sugar have an excellent electrochemical performance. The first discharging capacity of the sample with carbon content of 5% is 132.5 mAh/g and the other is 145.4mAh/g. Almost all the products prepared with various kinds of carbon materials have better performance than pure products, especially the product mixed with Vulcan XC-72 carbon, which has a higher first discharging capacity of 130.4mAh/g. From the experiment results, it can be seen that various products have a higher conductivity than that of pure LiFePO4 because of the introduction of all kinds of carbons, so discharging capacity and cycling performance of these products are better than that of pure LiFePO4.