Study On Modification Used Glucose And Polypyrrole Of LiFePO₄Prepared By Liquid Co-precipitation Method

Olivine Lithium iron phosphate was considered as one of the most promising cathode materials for power battery because of its good cycling performance、excellent safety performance、stable discharge voltage and high specific capacity. However, its low conductivity maked a poor large current charge and discharge ability and limited its commercial application. Aiming to improve the electrochemical performance of lithium iron phosphate, we studied systematically the influence of liquid co-precipitation process conditions、carbon coating process and polypyrrole on the lithium iron phosphate in this paper.(1)FeCl2、Na2CO3、H3PO4and LiOH were used as raw materials to synthesize LiFePO4by liquid co-precipitation method. At the same time the influence of the liquid phase reaction temperature、reaction time、 solution pH、sintering temperature and sintering time on the LiFePO4cathode material was researched. The results showed that reacting for3h at80℃under the condition of pH=8and then sintering for5h at700℃was the the optimization of LiFePO4synthetic process. The LiFePO4we prepared under above mentioned synthetic conditions showed the following performance:Particle size was2-3microns; Discharge specific capacity and voltage was135mAh/g and3.32V respectively after30cycles at0.5C rate.(2) Glucose and citric acid were used as carbon sources to coating the pure phase LiFePO4respectively. The results showed that the electrochemical performance of LiFePO4/C composite material used glucose as carbon source was better than that citric acid, and its discharge specific capacity and voltage was147.5mAh/g and3.34V respectively at0.5C rate and after30cycles of charge/discharge with the0.5-1microns particle size.The effect of different carbon contents and ways of adding carbon used glucose as carbon source on the LiFePO4cathode material physical properties and electrochemical performance was also studied. Results indicated that the LiFePO4/C composite material used glucose as carbon source and removed crystallization water from precursor before adding carbon was more uniform and less than1microns; in the meantime discharge specific capacity and voltage were158mAh/g and approximately3.32V respectively at0.5C rate after30cycles of charge/discharge, indicating excellent electrochemical performance.(3) LiFePO4/C-PPy composite material was prepared through chemical oxidative polymerization method. Electrochemical test indicated that the discharge specific capacity of LiFePO4/C-PPy composite were167mAh/g、155mAh/g and139mAh/g respectively at0.5C、1C and2C rate after30cycles of charge/discharge; In addition, its discharge voltage is alwayls between3.3V and3.4V, indicating smaller polarization and better high-rate charge/discharge performance. There were46figures,6tables and89references in this paper.