New Amorphous Iron-Based Oxyfluorides as Cathode Materials for High-Capacity Lithium-Ion Batteries

Abstract

A novel two-step strategy to prepare amorphous oxyfluorides, containing both divalent and trivalent 3d-metals, as cathode materials for lithium batteries is presented. The first step involves the preparation of hydrated fluorides M 2+ M 3+ 2 F 8 (H 2 O) 2 (M 2+ = Mn, Fe, Co, Ni, Cu; M 3+ = V, Fe) by microwave-assisted solvothermal synthesis. Besides the MnFe 2 F 8 (H 2 O) 2 and CuFe 2 F 8 (H 2 O) 2 phases, three new compounds, Fe 1.3 V 1.7 F 8 (H 2 O) 2 , CoFe 2 F 8 (H 2 O) 2 , and Ni-Fe 2 F 8 (H 2 O) 2 , which are isostructural with Fe 3 F 8 (H 2 O) 2 , have been unraveled. The second step consists in the decomposition of M 2+ M 3+ 2 F 8 (H 2 O) 2 into amorphous oxyfluorides M 2+ M 3+ 2 F 8−2x O x via suitable thermal treatments .. The amorphous materials show a greater electrochemical activity toward Li than their parent phases, among them being CuFe 2 F 6 O, which displays the best performance as a cathode material with a first discharge capacity of 310 mAh•g −1 . We show that such a large capacity results from cumulative insertion and displacement reactions.

Investigation of mixed-metal (oxy)fluorides as a new class of water oxidation electrocatalysts

“…39 Following this strategy, the preparation of new iron-based hydrated uorides M 2+ Fe 2 3+ F 8 (H 2 O) 2 (M ¼ Mn, Co, Ni, Cu) by microwave heating assisted solvothermal synthesis from metal salts, aqueous hydrouoric acid and methanol as solvent was previously reported. 40 These hydrated crystallized phases were further calcinated under ambient air to obtain the corresponding amorphous oxyuorides. Though those resulting amorphous oxyuorides were tested as cathode active material in Li-ion batteries, neither a thoroughly study of the morphology and electronic structure of those new amorphous iron-based mixed-metal oxyuorides nor their viability as OER catalysts have been conducted.…”

“…S1 †) and quantied (8% molar) by Mössbauer spectrometry. 40 This amount has to be taken into account to obtain the 16.2% experimental weight loss.…”

Investigation of Amorphous Mixed-Metal (Oxy)Fluorides as a New Class of Water Oxidation Electrocatalysts

“…It must be noted that CoFeF5 · 7H2O as impurity was detected by XRD ( Figure S1) and quantified (8% molar) by Mossbauer Spectrometry. 34 This amount has to be taken into account to obtain the 16.2% experimental weight loss. Compared to TGA under N2, TGA under ambient air shows identical first weight losses ( Figure S2) but for temperatures above 400°C, slow weight losses related to a hydrolysis occur that leads to spinel oxides (Table S1) according to reaction (3):…”

“…33 Following this strategy, the preparation of new iron-based hydrated fluorides M 2+ Fe 3+ 2F8(H2O)2 (M=Mn, Co, Ni, Cu) by microwave heating assisted solvothermal synthesis from metal salts, aqueous hydrofluoric acid and methanol as solvent was previously reported. 34 These hydrated crystallized phases were further calcinated under ambient air to obtain the corresponding amorphous oxyfluorides. Though those resulting amorphous oxyfluorides were tested as cathode active material in Li-ion batteries, neither a thoroughly study of the morphology and electronic structure of those new amorphous iron-based mixed-metal oxyfluorides nor their viability as OER catalysts have been conducted.…”

Investigation of Amorphous Mixed-Metal (Oxy)Fluorides as a New Class of Water Oxidation Electrocatalysts

“…33 Following this strategy, the preparation of new iron-based hydrated fluorides M 2+ Fe 3+ 2F8(H2O)2 (M=Mn, Co, Ni, Cu) by microwave heating assisted solvothermal synthesis from metal salts, aqueous hydrofluoric acid and methanol as solvent was previously reported. 34 These hydrated crystallized phases were further calcinated under ambient air to obtain the corresponding amorphous oxyfluorides. Though those resulting amorphous oxyfluorides were tested as cathode active material in Li-ion batteries, neither a thoroughly study of the morphology and electronic structure of those new amorphous iron-based mixed-metal oxyfluorides nor their viability as OER catalysts have been conducted.…”