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Reduction Fe3+ of Impurities in LiFePO4 from Pyrolysis of Organic Precursor Used for Carbon Deposition

Abstract : The structural properties of microcrystalline LiFePO4 prepared with and without carbon coating are analyzed with X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and magnetic measurements for comparison. While nanosized ferromagnetic particles (-Fe2O3 clusters) are evidenced from magnetic measurements in samples without carbon coating, such ferromagnetic clusters just do not exist in the carbon-coated sample. Ferromagnetic resonance experiments are a probe of the -Fe2O3 nanoparticles, and magnetization measurements as well, allowing for a quantitative estimate of the amount of Fe3+. While the fraction of iron in the Fe3+ configuration rises to 0.18% (in the form of -Fe2O3 nanoparticles) in the carbon-free sample, this fraction falls to a residual impurity concentration in the carbon-coated sample. Structural properties show that the carbon does not penetrate inside the LiFePO4 particles but has been very efficient in the reduction of Fe3+, preventing the -Fe2O3 clustering thus pointing out a gas phase reduction process. The carbon deposit characterized by Raman spectroscopy is an amorphous graphite deposit hydrogenated with a very small H/C ratio, with the same Raman characteristics as a-C carbon films obtained by pyrolysis technique at pyrolysis temperature 830±30°C. The impact of the carbon coating on the electrochemical properties is also reported.
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https://hal.archives-ouvertes.fr/hal-00017233
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Submitted on : Wednesday, January 18, 2006 - 10:40:40 AM
Last modification on : Saturday, January 15, 2022 - 3:44:24 AM

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A. Ait Salah, A. Mauger, K. Zaghib, J.B. Goodenough, N. Ravet, et al.. Reduction Fe3+ of Impurities in LiFePO4 from Pyrolysis of Organic Precursor Used for Carbon Deposition. Journal of The Electrochemical Society, Electrochemical Society, 2006, 153 (9), pp.A1692. ⟨10.1149/1.2213527⟩. ⟨hal-00017233⟩

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