Preparation And Characterization Of LiFePO₄/C Cathode Material For Lithium Ion Batteries

The increasing concerns on energy, environmental and the rapid development of modern science and technology have more demands on batteries. Lithium ion batteries are attractive for use in the field of mobile power source with the favorable properties of high voltage, long cycling life, high energy density, non-memory effect and pollution-free. Olivine-structured LiFePO4is an attractive positive electrode material for lithium-ion batteries because of its low cost, non-toxicity, abundant raw materials, large theoretical capacity (170mAh/g), high thermal stability and high safety.But there are two disadvantages of LiFePO4cathode material by now, one is low conductivity and low ion diffusion rate, the other is low tap density, especially composited with carbon material, the tap density of LiFePO4is further reduced, which influences the volume energy density of corresponding battery. In recent years, research work has been focused on improving the conductivity of lithium iron phosphate material, in which carbon coats on the lithium iron phosphate material to improve its electrochemical properties is the most simple and effective way.LiFePO4/C powders were obtained through high temperature mechanochemistry technology with LiH2PO4, Fe2O3and C6H12O6, LiFePO4was coat on the carbon in order to enhance the material properties of conductivity and rate performance. TG-DTA, XRD, SEM, TEM. FT-IR and PSD methods were utilized to analyze the influence factors on this processing, such as ball milling temperature, time, carbon content, molar ratio of Li to Fe and balls/material weight ratio. Results showed that LiFePO4/C powders acquired at700℃for12h with carbon content was8wt.%, molar ratio Li:Fe was1:0.98, balls/material weight ratio was10:1, showed high distribution without significant aggregation, and the particle size was between500～700nn. The first discharge specific capacity at0.1C was126mAh·g-1. The discharge specific capacity was122mAh·g-1over20cycles at0.1C., the discharge specific capacity was116mAh·g-1over20cycles at0.3C, the discharge specific capacity was111mAh·g-1over20cycles at1.0C. LiFePO4/C powders exhibited good electrochemical performance. High temperature mechanochemistry avoided the aggregation.