Electrochemical Properties Of LiFePO₄/C Composites Synthesized By Carbothermal Reduction Method

Due to high theoretical specific capacity,long cycle life,and the advantages of environmental friendly,LiFePO₄ has been regarded as one of the most potential cathode material.However,two intrinsic drawbacks,poor electronic conductivity and low lithium ion diffusion efficient,damaged its performance.In this paper,the LiFePO₄/C cathode material was prepared by carbothermal reduction method using the FePO₄ as precursors to improve the conductivity.The influences of heating temperature on the phase composition of FePO₄ and the influences of FePO₄ phases on the properties of the LiFePO₄/C composites were studied.The main results are as follows:1.The study of the effect of different calcining temperature on FePO₄ structure.The results show that different phases of FePO₄ formed by calcining homemade FePO₄·2H₂O powders at different temperatures.Monoclinic FePO₄ phase was obtained below 400℃,while the trigonal FePO₄ phase was obtained at 600℃.Interestingly,a monoclinic/hexagonal mixed-phase of FePO₄ was observed at 500℃.2.The LiFePO₄/C composites were synthesized by carbothermal reduction method using the FePO₄ as precursors by pre-heating at 400℃.The influences of the calcination temperature,calcination time,mole ratio of Fe/Li and carbon source on the properties of LiFePO₄/C composite were investigated.The results showed that the LiFePO₄/C composite syntheaized at the optimal conditions（Li/Fe=1.1,glucose content of 10 wt%-12 wt%,stearic acid content of 6 wt%,650℃,12 h）exhibited excellent capacity performance and cycle performance.3.The LiFePO₄/C composite cathode materials were synthesized by carbon thermal reduction method,using different FePO₄ powders as precursors.The result indicates that all of synthesized LiFePO₄/C powders are pure phases with olivine structure,and the electrochemical properties of synthesized LiFePO₄/C powders are different.The LiFePO₄/C powders synthesized by monoclinic/hexagonal mixed-phase FePO₄ powders as precursors exhibited the excellent electrochemical properties.The discharge capacity was 169 mAh g^-11 at 0.1 C.The 100th discharge specific capacity was 128,116 and 104 mAh/g,retention rate of 100%,113%and 113%,respectively,at 1C,2C and 5C.Moreover,different carbon sources showed same rule.It might be the better reactivity of the monoclinic/hexagonal mixed-phase FePO₄result in an excellent electrochemical properties for LiFePO₄/C powders in the carbon thermal reduction.