A Highly Fluorinated Lithium Iron Phosphate with Interpenetrating Lattices: Electrochemistry and Ionic Conductivity


Li5Fe2PO4F8, a new member of the family of alkali transition metal fluorophosphates, has been synthesized and characterized using single-crystal X-ray diffraction, 57Fe Mössbauer spectroscopy and magnetic susceptibility measurements. The existence of an infinite {-[PO4(Fe4)2]-} tetrahedral network in an inter-penetrated diamond lattice, along with the presence of seven unique Li sites, presents interesting structural features of this structure-type for energy storage applications. The initial results of (de)lithiation reveal that a relatively low fraction of theoretical capacity may be utilized reversibly (0.2 Li+ ion per formula unit), possibly due to the lack of available free volume for Li+ insertion. The high Li content and the existence of large channels in all 3-dimensions of space also offer opportunities to study this material as a candidate for solid-state electrolytes. The results from electro-impedance measurements reveal the reasonable activation energy of Li diffusion (0.70 eV), which is also supported by theoretical calculations.




The authors acknowledge the funding from Energy Research and Development Center (ERDC) of Missouri S&T.

Keywords and Phrases

Activation Energy; Lithium Compounds; Magnetic Susceptibility; Single Crystals; Solid Electrolytes; Transition Metals; X Ray Diffraction, Energy Storage Applications; Impedance Measurement; Lithium Iron Phosphates; Magnetic Susceptibility Measurements; Single Crystal X-Ray Diffraction; Solid-State Electrolyte; Ssbauer Spectroscopies; Theoretical Calculations, Lithium

International Standard Serial Number (ISSN)

1477-9226; 1477-9234

Document Type

Article - Journal

Document Version


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© 2017 Royal Society of Chemistry, All rights reserved.

Publication Date

01 Aug 2017