Study On LiFePO₄ Cathode Material Preparation Technology By Sol-Gel Combined With Microwave Method And Its Performance

Material performances improving and industrialization is closely related to preparation technologies. The preparation technologies for LiFePO₄ includes high-temperature solid phase, co-precipitation, sol-gel, hydrothermal, carbon thermal reduction, microwave and so on. Each method has its own disadvantages. In order to avoid each method's disadvantages, many researchers tried to combine many methods. The paper studied the processing technology by sol-gel method combined with microwave.Sol-gel is one kind of soft chemical method. The method is commonly used to synthesis high specific capacity material of LiFePO₄ at lower temperature, because it has many advantages such as good chemical uniformity in the precursor solution, easily realizing uniform donation, gel need lower treating temperature, help to improve product's purity and crystallinity degree, easily controlling reaction process. In the paper, a detailed technology was developed based on raw materials selected. In the sol-gel technology, many important parameters were analyzed and investigated, such as solution concentration, pH, water bath temperature and dispersing agent. But it has many disadvantages including larger drying shrinkage, long synthesized period and large difficulty of industrialization. To avoid its disadvantages, microwave drying or it combined with vacuum drying was used. That not only avoided the disadvantages of larger drying shrinkage, long synthesized period, but also saved energy and environment friendship. It was discovered by SEM tests that the particles agglomeration of gel dried by microwave was slighter than by only vacuum drying. By TG-DSC test, two endothermic peaks and one exothermic peak were detected, which showed that drying temperature should be over 199.5℃and that precursor reactivation temperature of LiFePO₄ was at 463.8℃.Microwave is an energy saving, high efficiency, and less pollution heating method and has the characters of heating uniformly and selectively and fast temperature rising rate. In the experiments, influences of samples mass, starting power and its time, keeping temperature power and its time, were investigated. By XRD tests, it was showed that different samples mass needed almost the same synthesis parameters. That just verified the microwave character of bulk heating. But microwave heating time should be controlled at second level.It is most important that the technology needn't special protection atmosphere which is necessary in other technologies. Tests result of the material synthesized by the technology showed that it had high purity, smaller particle size and good charge-discharge performance.