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In this paper, solid-phase carbon thermal reduction the prepared LiFePO 4 / C, the LiFePO 4-x F x / C, programmable constant current charging and discharging test system, combined with XRD, SEM, TEM, Raman and FTIR other means, comparative study the LiFePO 4 / C, the LiFePO 4-x F x / C material structure, morphology and electrochemical properties. Focus on the amount of lithium salts, organic carbon and F elements doped LiFePO 4 physical and electrochemical properties. The study found that the excess of 8% of the lithium salt LiFePO 4 / C particle distribution is uniform, showed the best electrochemical performance. 0.2C and 1C discharge capacity for the first time were 156.6 and 143.5mAh / g 2C continuous charge and discharge 100 times the capacity retention rate of 99.6%. Respectively, glucose, polyvinyl alcohol (PVA) and polyethylene glycol (PEG) as the carbon source was synthesized LiFePO 4 / C composites. The results showed that the sample a degree of graphitization of the carbon coating has little effect on the conductivity and the highest glucose sample conductivity as 5.70 × 10-2S/cm, PEG minimum sample of 5.59 × 10-2S/cm; PEG samples electrochemical The best performance, 0.2C magnification initial discharge capacity 155.9mAh / g, 3C magnification of 50 cycles, the capacity of the sample holder was 103%. PEG as a carbon source, 8% of the excess of the lithium salt and orthogonal experiment L9 (33) to examine factors calcination temperature, calcination time and the amount of carbon-doped material LiFePO 4 / C 0.2C when the first discharge capacity as index to determine the optimal synthesis conditions: calcination temperature of 750 ° C the calcining time 12h, the amount of carbon-doped for the FePO 4 : of Li2CO3 in: C = 2:1.08: 2. The the optimal process synthesized LiFePO 4 / C samples having a complete crystal structure of the primary particles is small, uniform particle size distribution, of approximately 500nm, coated with carbon on the surface of the particles, the primary particles by coating carbon connected the formation of aggregates. The smooth, 0.2C, 1C and 2C discharge platform and the polarization smaller (ΔV ≤ 0.2V), respectively 157.6,142.5,134.3 mAh / g discharge capacity; 5C discharge, the discharge capacity for 107.5mAh / g. The the calcination temperature single factor experimental results show that, within the range of 650 ~ 750 ℃, the temperature rises, the conductivity of the sample increases, the discharge capacity increases. But the temperature rose to 800 ℃, the sample but declined specific discharge capacity, from the 750 ℃ 157.6mAh / g dropped 154.39mAh / g (0.2C), taking into consideration to energy conservation, and ultimately to determine the optimum calcination temperature of 750 ℃. Comparative study sample the LiFePO 4-x F x / C electrochemical performance, F doping can effectively improve the high-rate discharge performance and cycle performance. 5C under a LiFePO3.96F0.04 the initial discharge specific capacity up to 109mAh / g, than not doped F the LiFePO 4 / C improve 10mAh / g, 3C magnification 50 cycles, the capacity retention rate 100.3%.
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