Electrochemical and Diffusional Investigation of Na2FeIIPO4F Fluorophosphate Sodium Insertion Material Obtained from FeIII Precursor
journal contributionposted on 18.09.2017, 00:00 by Lalit Sharma, Prasant Kumar Nayak, Ezequiel de la Llave, Haomin Chen, Stefan Adams, Doron Aurbach, Prabeer Barpanda
Sodium iron fluorophosphate (Na2FeIIPO4F) was synthesized by economic solvothermal combustion technique using FeIII precursors, developing one-step carbon-coated homogeneous product. Synchrotron diffraction and Mössbauer spectroscopy revealed the formation of single-phase product assuming an orthorhombic structure (s.g. Pbcn) with FeII species. This FeIII precursor derived Na2FeIIPO4F exhibited reversible Na+ (de)intercalation with discharge capacity of 100 mAh/g at a rate of C/10 involving flat FeIII/FeII redox plateaus located at 2.92 and 3.05 V (vs Na/Na+). It delivered good cycling stability and rate kinetics at room temperature. The stability of Na2FePO4F cathode was further verified by electrochemical impedance spectroscopy at different stages of galvanostatic analysis. Bond valence site energy (BVSE) calculations revealed the existence of 2-dimensional Na+ percolation pathways in the a–c plane with a moderate migration barrier of 0.6 eV. Combustion synthesized Na2FeIIPO4F forms an economically viable sodium battery material. Although the capacity of this cathode is relatively low, this study continues systematic work, which attempts to broaden the scope of reversible sodium insertion materials.
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Na 2 Fe II PO 4 FFe III precursorssolvothermal combustion technique3.05 Vsingle-phase productsodium battery materialSynchrotron diffractionelectrochemical impedance spectroscopybond valence site energyDiffusional InvestigationNa 2 Fe II PO 4 F formsFe II speciessodium insertion materialsmigration barrierrate kineticsFe III precursorcycling stabilitydischarge capacityNa 2 FePO 4 F cathodeFe III Precursor Sodium iron fluorophosphate0.6 eVgalvanostatic analysisNa 2 Fe II PO 4 F Fluorophosphate Sodium Insertion Material Obtainedpercolation pathwaysBVSEroom temperature