Influence And Control Of Morphology,Particle Size And Structure Of Lithium Iron Phosphate On Its Properties

When LiFePO₄is used as positive electrode material of battery due to low Li⁺migration rate in LiFePO₄,resulting in electrochemical polarization phenomenon increases and the internal resistance of the battery increases,resulting in poor high rate performance of the material.In addition,some experimental ways used to enhance the electronic conductivity and Li⁺diffusion rate of LiFePO₄cathode materials during the preparation of LiFePO₄cathode materials will cause the LiFePO₄particles themselves to be uncompact and have a low tap density.Based on adjusting the morphology,particle size and particle size distribution of LiFePO₄,this paper solved the problems of poor high performance and low tap density of LiFePO₄.FePO₄precursor was prepared by in-situ polymeration-coprecipitation method,and LiFePO₄/C was prepared by carbothermic reduction method.The effects of preparation conditions of precursor FePO₄on the performance of LiFePO₄/C were investigated systematically,such as the concentration of FeSO₄and NaH₂PO₄,the ratio of raw material n（Fe）:n（P）,initial pH of solution,reaction temperature and reaction time.The results showed that the morphology and particle size of the precursor FePO₄and LiFePO₄/C were consistent,and the morphology and particle size of LiFePO₄/C could be controlled by adjusting the preparation conditions of the precursor FePO₄.The spherical morphology is beneficial to improve the high rate performance and tap density of LiFePO₄/C.The particle size of spherical LiFePO₄/C was 845 nm,the tap density was 1.15 g cm^-3,and the specific discharge capacity was 110.6 m Ah g^-1at 5 C under the suitable conditions of in-situ polymeration-coprecipitation method.Under the premise of ensuring the good electrochemical performance of LiFePO₄,the influence of the compactness and particle size distribution of LiFePO₄particles on the tap density and electrochemical performance of the material and the influence principle were explored.The results showed that there was a contradiction between improving the electrochemical properties of materials by increasing the compactness and increasing the tap density of materials.LiFePO₄/C prepared by in-situ polymeration-coprecipitation method as the first principal particle size,and LiFePO₄/C prepared by in-situ polymeration-hydrothermal method as the second principal particle size,when the particle size and mass ratio conformed to Hudon and Horsfield filling theory,it can make small particles fill the void formed by the accumulation of large particles.The tap density of LiFePO₄can be improved to 1.36 g cm^-3,and the discharge specific capacity was 110.4m Ah g^-1at 5 C.