LiFePO₄@C Composite Cathode Materials For Lithium-ion Batteries Were Prepared By Liquid Phase Method

Owing to its excellent performance,lithium iron phosphate?LiFePO₄?is considered to be one of the most promising lithium ion battery cathode materials,but its low electronic conductivity and ion diffusion coefficient also restrict its rapid development.In view of these two problems,the research on the preparation method and modification of lithium iron phosphate cathode material has important theoretical value and practical significance.Based on a review of issues related to lithium-ion batteries and LiFePO₄@C composite cathode materials,FePO₄·2H₂O precursor was first prepared by the rapid precipitation method and then LiFePO₄@C composite materials were prepared by the liquid phase method.The synthesis process of LiFePO₄@C composites was optimized in type,content of carbon source and sintering temperature of the material.The specific research content is as follows:1.Phosphoric acid?H₃PO₄?and iron powder were used as raw materials.Meanwhile,H₂O₂ was used as oxidant and an appropriate amount of surfactant was added.Nano-sheet FePO₄·2H₂O was synthesized by rapid precipitation method and characterized by XRD,SEM,TG-DSC,FTIR and so on.The effects of the type and content of surfactant,ultrasonic time and aging time on the particle size and morphology of Fe PO₄·2H₂O were investigated.The best type of surfactant was determined as CTAB,its amount was 1.5%of the mass of raw iron powder,the aging time was 4 h and the ultrasonic time was 60 min.Fe PO₄·2H₂O with a nano-sheet monoclinic structure was prepared under the optimal process conditions.The thickness of nano-sheet was about 80 nm with uniform particle size distribution and good dispersibility.2.LiFePO₄@C composites were synthesized by liquid phase method using self-made FePO₄·2H₂O as precursor,organic carbon source was added and the type,content of carbon source and sintering temperature were discussed.The results showed that the particles of LiFePO₄@C composites synthesized with glucose as carbon source were small,the products were in closer contact,the polarization was small in the electrochemical reaction,the discharge specific capacity was high and the rate performance was good.Through the study of the effect of glucose content on the properties of LiFePO₄@C composite materials,it was found that when the glucose content was 10%,the LiFePO₄@C product had good dispersibility,a thin and uniform carbon layer formed and a discharge specific capacity was as high as 160.70 m Ah/g at0.2 C.After 100 cycles,the capacity is basically not reduced at 2 C rate.Comparing the effects of different sintering temperatures on the properties of LiFePO₄@C materials,it was found that when the temperature was 600?,the synthesized product particles were uniform,no impurities were generated,the discharge specific capacity was high and the cycle performance was stable.