Synthesis and characterization of LiFePO4/(Ag+C) composite cathodes with nano-carbon webs

LiFePO4/(Ag+C) composite cathodes with a new type of nano-sized carbon webs were synthesized by two methods of an aqueous co-precipitation and a sol-gel process, respectively. Simultaneous thermogravimetric-differential thermal analysis indicates that the crystallization temperature of LiFePO4 is about 455-466 degrees C, which is close to the pyrolysis temperature of polypropylene, 460 degrees C. The silver and carbon comodifying does not affect the olivine structure of LiFePO4 but improves its kinetics in terms of discharge capacity and rate capability. Discharge capacities were improved from 153.4 mA h g(-1) of LiFePO4/C to 160.5 mA h g(-1) and 162.1 mA h g(-1) for LiFePO4/(Ag + C) cathodes synthesized by the co-precipitation and sol-gel methods, respectively. The possible reasons for the small difference in discharge capacity of two LiFePO4/(Ag+C) cathodes were discussed. AC impedance measurements show that the Ag+C co-modification decreases the charge transfer resistance of LiFePO4/(Ag+C) cathodes. (c) 2007 Elsevier B.V. All rights reserved.