Research On Synthesis Of LiFePO₄Cathode Materials And Electrochemical Characterization By Quenching Treatment

Olivine-structured LiFePO₄has been widely researched as a potential candidate cathodematerial because of its advantages of abundant resources, low cost, environmental friendliness,high electrochemical capability and its stability. However, LiFePO₄suffers from a poorelectronic conductivity which hinders its commercialization. Quenching treatment is firstadopted in this paper, and it improves the properties of the material.First of all, we got pure LiFePO₄by high temperature solid phase method and liquidnitrogen quenching method. After that, we charactered their morphology and tested theirelectrochemical properties. The results showed that the two kinds of pure LiFePO₄were bothsingle olivine-structured phase, while the sample prepared by liquid nitrogen quenchingmethod had no obvious agglomeration and the particle size was fine and uniform. The samplealso showed higher discharge capacity and a more sustained platform.And then, chitosan was added as the carbon source to prepare LiFePO₄/C by liquidnitrogen quenching method. The experimental results show that single olivine-structuredphase sample free of impurities was synthetized. Chitosan did not influence the structure,instead, it decreased the size of the sample and homogenized the particles. Compared to pureLiFePO₄, electronic conductivity of LiFePO₄/C was enhanced. Meanwhile, the material hadminor polarization effect, higher discharge capacity and excellent stability of cycles. Powdersynthetized by liquid nitrogen quenching method had discharge specific capacity of143.5mAh·g^-1at0.2C rate，and its initial charge-discharge efficiency was92.3%. After20times ofcharge-discharge cycles, the capacity loss was only3.5%.At last, calcining temperature and calcining time, the two important processingparameters of liquid nitrogen quenching method were optimized. The results showed thatwhen calcining temperature was650℃and calcining time was6h, morphology of thepowder was best and the diameter was about150nm. When the discharge current was low, itsdischarge specific capacity was147.5mAh·g^-1, which had shown significant differencesamong materials prepared in other cases. While the current was5C rate, its capacity was101.5mAh·g^-1. After20times of charge-discharge cycles, the material had discharge specificcapacity of145.7mAh·g^-1, and its capacity retention rate was98.8%without obvious decay.