Synthesis And Electrochemical Properties Of LiMn₂O₄ And LiFePO₄ As Cathode Of Lithium Ion Batteries

Up to now, people realized that the Li-ion battery is a new generation of high specific capacity battery with merits of high voltage and long life and a little self discharging etc. Recently, this battery is still under improving constantly. The investigation of negative and electrolytes have progress more quicker, while the studies on positive material is slower. The major positive material for studying containing LiCoO2, LiNiO2, LiMn2O4 and LiFePO4 etc. However, the spinel LiMn2O4 and olivine LiFePO4 are very hopeful material with low price and few toxic and higher specific capacity, etc. Based on decreasing the production cost and enhancing the stability of the material, this work will studying the preparation method of these material for enhancing their stability through using doping and choosing optimal technology.First of all, to counter the weak points of longer synthesis time, poor electrochemical behavior, long process of reaction and higher cost, etc., the auther created a modified sol-gel method with citric acid for shorten the preparing step, exploring optimal synthesizing temperature and technology, used the doping and covered some film on the product and so on.To improve the behavior of spinel LiMn2O4, We used the doping with the donor Li+, Al3+,and Cl-. The examination results of galvanostatic charge-discharge experiments shown that the stability of charge-discharge of Li+, Al3+,and Cl- doped spinel LiMn2O4 have enhanced. The LiMn2O4 coated with LiCoO2 and Al2O3 film were enhanced the stability.The experiments shown that the modified sol-gel method can prepare the spinel LiMn2O4 with original capacity higher than 130mAh/g and shorten the synthesizing step, decreasing the citric acid and so on.To counter the synthesis of olivine LiFePO4 with Fe(C2O4)2 and Fe(CH3COO)2 mostly , we are the first to used the sol-gel method with Fe3+ through high temperature to make LiFePO4. We prepared the olivine LiFePO4 with good electrochemical behavior and its discharge specific capacity as high as 140mAh/g.This work have explored the influence of Ag, Cu, Mg-doped LiFePO4 to the behavior of LiFePO4 through high temperature reaction for reducing Fe3+ and used Fe2O3 instead of Fe(NO3)3·9H2O. We also used the carbon from different source as a reducing reagent, prepared the olivine LiFePO4 through high temperature reduction, the prepared sample has the discharge specific capacity reached 130mAh/g. Based on this exploration to carry out experiment, the prepared sample get high discharge specific capacity to 150mAh/g and excellent behavior, we have discussed the mechanism briefly.The article have reported the examination of prepared sample through electrochemical method for their charge-discharge behavior, the XRD method for their crystalline structure, explored the influence of different experimental factor to the behavior of all sample.