Insertion of fluorine into a LiFePO electrode material by gas-solid fluorination

• Published in: Dalton transactions : an international journal of inorganic chemistry 2024-04, Vol.53 (17), p.7546-7554
• Main Authors: Kevin, Lemoine, Roméo, Kenmogne-Debah, Léa, Doubtsof, Lawrence, Frezet, Elodie, Petit, Katia, Guerin, Bertrand, Devouard, Moulay-Tahar, Sougrati, Diane, Delbègue, Pierre, Bonnet
• Format: Article
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d4dt00603h

In this study, the insertion of fluorine into LiFePO 4 was carried out under molecular fluorine F 2 at different temperatures. The reactivity strongly depends on the applied fluorination temperature, leading to very different products: core delithiation of the material is observed at low temperatures with the formation of a LiF shell around particles, while the material decomposes to gradually form a mixture of α-FeF 3 and α-Li 3 FeF 6 iron fluorides at higher temperatures. A second thermal treatment under N 2 leads to the formation of LiFePO 4 F in a new way that has not been reported before. Supported by X-ray diffraction, Raman, infrared, Mössbauer spectroscopies, 7 Li nuclear magnetic resonance and electrochemical characterization of the different materials, this report demonstrates various fluorination mechanisms for LiFePO 4 , from chemical delithiation to the stable pure fluorinated form LiFePO 4 F and illustrates an innovative method that can be extended to obtain the triphylite form of NaFePO 4 . This article brings forth a complete study on the insertion of fluorine atoms into a phosphate matrix. Lithium iron phosphate LiFePO 4 (or LFP) is used as a model compound in the reaction with fluorine gas at different temperatures.