Synthesis, impedance and electrochemical studies of lithium iron fluorophosphate, LiFePO₄F cathode

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• 作者：M. Prabu^a ; ^b ; M.V. Reddy^a ; ^{phymvvr@nus.edu.sg} ; S. Selvasekarapandian^b ; ^{sekarapandian@rediffmail.com} ; G.V. Subba Rao^a ; B.V.R. Chowdari^a ; ^{phychowd@nus.edu.sg}
• 关键词：LiFePO4F ; Tavorite-structure ; Cathode ; Impedance spectroscopy
• 刊名：Electrochimica Acta
• 出版年：2012
• 出版时间：15 December, 2012
• 年：2012
• 卷：85
• 期：Complete
• 页码：572-578
• 全文大小：1396 K

文摘

Tavorite-structured LiFePO₄F is synthesized by solid-state reaction and characterized by Rietveld refined X-ray diffraction, scanning electron microscopy, BET surface area, IR and Raman spectroscopy techniques. The ionic conductivity (¦Ò ionic) of LiFePO₄F estimated using impedance analysis at 27 ¡ãC and at 50 ¡ãC are 0.6(¡À0.1) ¡Á 10^?7 and 5.4(¡À0.1) ¡Á 10^?7 S cm^?1, respectively, with an energy of activation (E_a) = 0.75 eV. Its electrochemical behavior were examined by galvanostatic charge-discharge cycling up to 100 cycles, cyclic voltammetry (CV) and electrochemical impedance spectroscopy using Li-metal as the counter and reference electrode, at 0.1C rate in the voltage range, 1.5-4 V. LiFePO₄F delivers an initial discharge capacity of 115(¡À3) mAh g^?1 which increases to 119(¡À3) mAh g^?1 at the 20th cycle. The capacity degrades slowly thereafter over 100 cycles, with a capacity loss of 19 % . CV data show a clear indication of the Fe^3+/2+ redox couple at 3.3-2.6 V that involves a two-phase reaction. Electrochemical impedance spectra measured at various voltages at selected cycles were fitted to an equivalent circuit and the variation of impedance parameters interpreted.