Synergistic Effect in Carbon Coated LiFePO4 for High Yield Spontaneous Grafting of Diazonium Salt. Structural Examination at the Grain Agglomerate Scale

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• 作者：L茅na茂c Madec ; Donatien Robert ; Philippe Moreau ; Pascale Bayle-Guillemaud ; Dominique Guyomard ; Jo毛l Gaubicher
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：August 7, 2013
• 年：2013
• 卷：135
• 期：31
• 页码：11614-11622
• 全文大小：459K
• 年卷期：v.135,no.31(August 7, 2013)
• ISSN：1520-5126

文摘

Molecular grafting of p-nitrobenzene diazonium salt at the surface of (Li)FePO₄-based materials was thoroughly investigated. The grafting yields obtained by FTIR, XPS, and elemental analysis for core shell LiFePO₄鈥揅 are found to be much higher than the sum of those associated with either the LiFePO₄ core or the carbon shell alone, thereby revealing a synergistic effect. Electrochemical, XRD, and EELS experiments demonstrate that this effect stems from the strong participation of the LiFePO₄ core that delivers large amounts of electrons to the carbon substrate at a constant energy, above the Fermi level of the diazonium salt. Correspondingly large multilayer anisotropic structures that are associated with outstanding grafting yields could be observed from TEM experiments. Results therefore constitute strong evidence of a grafting mechanism where homolytic cleavage of the N₂⁺ species occurs together with the formation and grafting of radical nitro-aryl intermediates. Although the oxidation and concomitant Li deintercalation of LiFePO₄ grains constitute the main driving force of the functionalization reaction, EFTEM EELS mapping shows a striking lack of spatial correlation between grafted grains and oxidized ones.