Study Of Key Technology To Improve Overcharge/Overdischarge Performance Of LiFePO₄Lithium Ion Battery

With the coming of worldwide energy crisis, lithium-ion battery has attracted wide attention as an ideal energy storage. LiFePO4lithium-ion battery is considered as the most potential battery for its excellent electrichemical performance. However, the charge and discharge platform of LiFePO4lithium-ion battery is so steady that its voltage changed sharply only at the end. It is extremely easy for LiFePO4lithium-ion battery to overcharge and over-discharge. This is harmful to LiFePO4lithium-ion battery and restricts its large-scale application. The mechanism of overcharge and over-discharge has been explored. Considering the way of using LiFePO4lithium ion battery and itself, the key technologies has been studied to improve the overcharge and over-discharge performance of LiFePO4lithium-ion battery. The main contents can be devided into the following three parts.1. The discharge curves of LiFePO4lithium-ion battery at different temperature and different rates were tested. The data indicated that the dV/dSOC could reflect the charging and discharging feature of LiFePO4lithium ion battery better than the voltage. The temperature and rate had little influence on the value of dV/dSOC. Thus, According to the value of dV/dSOC, the overcharge and over-discharge of LiFePO4lithium-ion battery could be prevented effectively.2. The Ti film was coated on the copper current collector by magnetron sputtering. Graphite was used as the active material to prepared the button cell. After several times overcharging, compared to the cells with pure copper current collector, the electrichemical performance of the cells with Ti-coated copper current collector was improved. The CV curves suggested that coating a layer of Ti film on the surface could improve the resistance of the copper foil to the electrochemical corrosion effectively, thereby the resistance to over-discharge performance of full battery were improved.3. The Nb-doped TiO2were synthesized by a sol-gel method. For TiO2has a high Li+insertion potential (1.75V vs Li/Li+), in the process of overcharging, the precipitation of lithium on the negative electrode could be prevented. Nb-doped TiO2with different structures were sintered at various temperature. With the temperature increasing. The Nb-doped TiO2changed from anatase to mixed anatase/rutile, finally completely converted to rutile. The electrochemical tests indicated that the anatase Nb-doped TiO2had excellent conductivity, but the conductivity of rutile Nb-doped TiO2was terrible. The anatase samples sintered at550℃perform the best electrochemical properties. After50cycles, it still deliver a capacity of190mAh·g-1...