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Nouveaux matériaux fluorés d'électrodes positives à cations 3d mixtes pour batteries à ions lithium : Elaboration, caractérisation structurale et propriétés électrochimiques

Abstract : This work presents an innovative synthetic strategy to develop new fluorinated iron-based materials as positive electrodes for Li-ion batteries. This two-step elaboration method consists in the preparation of fluorinated precursors followed by an appropriate thermal treatment. The study initially focuses on tridimensional mixed valence iron fluorides, Fe2F5(H2O)2 with the inverse weberitestructural type and Fe3F8(H2O)2. The calcination under air leads to the formation of two new hydroxyfluorides, FeF2.5(OH)0.5 and FeF2.66(OH)0.34 with pyrochlore and HTB structural types respectively which present excellent electrochemical capacities ≈ 170 mAh.g-1 (2-4 V). In a second part, the 3d-cation effect on oxyfluorides performances is evaluated from equivalent mixed metal cation hydrates, M2+Fe3+F5(H2O)2 (M = Mn, Ni) and M2+M3+2F8(H2O)2 (M2+ = Mn, Fe, Co, Ni, Cu, M3+ = V, Fe), synthesized solvothermally. Their thermal degradation under air reveals amorphous oxyfluorinated intermediates and among them, CuFe2F6O, obtained from CuFe2F8(H2O)2, with an remarkable capacity of 310 mAh.g-1 (2-4 V). In the last part, mixed ammonium fluorides (NH4)M2+Fe3+F6 (M = Mn, Co, Ni, Cu) are synthesized using mechanochemical and solvothermal routes. Their thermal topotactic oxidation under molecular fluorine F2 leads to the first trivalent mixed-cation fluorides M0.5Fe0.5F3 (M = Mn, Co, Ni, Cu) with pyrochlore typestructure.
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Kévin Lemoine. Nouveaux matériaux fluorés d'électrodes positives à cations 3d mixtes pour batteries à ions lithium : Elaboration, caractérisation structurale et propriétés électrochimiques. Chimie inorganique. Université du Maine, 2019. Français. ⟨NNT : 2019LEMA1030⟩. ⟨tel-02936513⟩

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