Synthesis And Electrochemical Performance Of Structure LiFePO₄/C

Olivine lithium iron phosphate is one of the most potential cathode materials for the lithium ion batteries. It has a specific of170mAh/g, and a flat discharge potential of3.4V versus Li/Li+. Lithium iron phosphate has been considered as a potential material for kinetics lithium iron batteries for its rich rough material、non-poisonous、environmental compatibility、high reversible capacity and its safety. However, the rate performance of lithium iron phosphate is limited by the low electronic conductivity(about10-9S/cm) and slow lithium ion diffusion(about10-11～10-10S/cm), it blocked the application in commerce application.This paper reviewed the research progress of olivine lithium iron batteries, LiFePO4/C was prepared by hydrothermal synthesis using copoplymer P123as template, and their physical properties and electrochemical performances were investigated.Using LiNO3、NH4H2PO4、FeNO3·9H2O as raw material, P123、 glucose and monohydrate citric acid as carbon source, LiFePO4/C was prepared by hydrothermal synthesis in the water and ethylalcohol mixted solution at the condition of150℃. The results show that the LiFePO4/C synthesized by P123had the best cycling stability and rate performance.By changed the concentration of P123and raw material, the morphology of precursor materials was changed, and we acquired different morphologies of LiFePO4/C. The distinction of different morphologies of LiFePO4/C was studied. The results show the ball-in-ball structure LiFePO4/C with the ratio m(P123):m(LiFePO4)=1.5:1.2has the best electrochemical performances. LiFePO4/C synthesized at the ratio m(P123):m(LiFePO4)=1.5:1.2and m(P123)=2.0g was sonicated to acquire broken ball morphology LiFePO4/C. Owing to the closer contact between the presonicated LiFePO4/C granules, the conductive network forms better than that of the material after being sonicated. The electrochemical performances results show the presonicated LiFePO4/C had a better performance.Using the ratio m(P123):m(LiFePO4)=1.5:1.2, LiFePO4/C was synthesized in the different temperature, ball-in-ball structure LiFePO4/C was synthesized in150℃, combination butterfly structure LiFePO4/C was synthesized in180℃, and under the condition of210℃, we gained LiFePO4/C composed by different morphologies. The hydrophily of EO section of P123will decrease and the hydrophobicity of EO will increase, it will lead to the change of the structure of the P123template. The results indicate that the ball-in-ball structure LiFePO4/C synthesized in150℃had the best electrochemical performances in the high rate, and the LiFePO4/C synthesized in210℃had the best electrochemical performances in the low rate.