Iron Fluoride Research Articles

Investigation of the sodium storage mechanism of iron fluoride hydrate cathodes using X-ray absorption spectroscopy and mossbauer spectroscopy

Elucidation of a reaction mechanism is the most critical aspect for designing electrodes for high-performance secondary batteries. Herein, we investigate the sodium insertion/extraction into an iron fluoride hydrate (FeF3⋅0.5H2O) electrode for sodium-ion batteries (SIBs). The electrode material is prepared by employing an ionic liquid 1-butyl-3-methylimidazolium-tetrafluoroborate, which serves as a reaction medium and precursor for F− ions. The crystal structure of FeF3⋅0.5H2O is observed as pyrochlore type with large open 3-D tunnels and a unit cell volume of 1129 Å3. The morphology of FeF3⋅0.5H2O is spherical shape with a mesoporous structure. The microstructure analysis reveals primary particle size of around 10 nm. The FeF3⋅0.5H2O cathode exhibits stable discharge capacities of 158, 210, and 284 mA h g−1 in three different potential ranges of 1.5–4.5, 1.2–4.5, and 1.0–4.5 V, respectively at 0.05 C rate. The specific capacities remained stable in over 50 cycles in all three potential ranges, while the rate capability was best in the potential range of 1.5–4.5 V. The electrochemical sodium storage mechanism is studied using X-ray absorption spectroscopy, indicating higher conversion at a more discharged state. Ex-situ Mössbauer spectroscopy strengthens the results for reversible reduction/oxidation of Fe. These results will be favorable to establish high-performance cathode materials with selective voltage window for SIBs.

Iron Fluoride Confined in Carbon Nanofibers for Lithium and Sodium Battery Cathodes

Today, lithium (sodium) battery cathodes based on the intercalation/deintercalation of lithium (sodium) ions are approaching their instinctive limits, which remains a big challenge for the development of next-generation batteries. Iron fluorides (FeF2, FeF3), a potential alternative to current intercalation cathodes, are believed to offer much higher capacity and higher energy due to their reversible conversion reactions during charging/discharging. However, their structural degradation and capacity fading upon cycling could block the road to future applications. To address these issues, we developed a stable iron fluoride cathode based on nanoconfined FeF3 in carbon nanofibers for lithium and sodium batteries. The produced FeF3 /C nanocomposite is free-standing and can be produced using an electrospinning-based strategy with post carbonization and fluorination process. When tested in lithium cells, the nanocomposite can exhibit a high specific capacity up to 550 mAh g– 1 and a cycle stability over 400 cycles [1]. When tested in sodium cells, the nanocomposite can deliver a high specific capacity of 230 mAh g– 1 in sodium-difluoro(oxalato)borate (NaDFOB) electrolyte [2]. The performance especially cycle stability was further improved by atomic layer deposition (ALD) of Al2O3 coating on nanofiber surface [3]. We find the coating can reduce the direct contact between active material and liquid electrolyte, minimize active material dissolution and significantly improve the overall performance.[1] W. Fu, E. Zhao, Z. Sun, X. Ren, A. Magasinski, G. Yushin, Iron Fluoride–Carbon Nanocomposite Nanofibers as Free-Standing Cathodes for High-Energy Lithium Batteries, Advanced Functional Materials 28 (2018) 1801711.[2] Z. Sun, W. Fu, M.Z. Liu, P. Lu, E. Zhao, A. Magasinski, M. Liu, S. Luo, J. McDaniel, G. Yushin, A nanoconfined iron(iii) fluoride cathode in a NaDFOB electrolyte: towards high-performance sodium-ion batteries, Journal of Materials Chemistry A 8 (2020) 4091-4098.[3] Z. Sun, M. Boebinger, M. Liu, P. Lu, W. Fu, B. Wang, A. Magasinski, Y. Zhang, Y. Huang, A.Y. Song, M.T. McDowell, G. Yushin, The roles of atomic layer deposition (ALD) coatings on the stability of FeF3 Na-ion cathodes, Journal of Power Sources 507 (2021) 230281.

Enabling Conversion‐Type Iron Fluoride Cathode by Halide‐Based Solid Electrolyte

AbstractThe practical application of low‐cost and energy‐dense iron fluoride cathodes is hindered by the first cycle electrochemical irreversibility, cycling instability, and large voltage hysteresis. Here, it is reported that these challenges may be overcome by the utilization of halide‐based solid electrolytes (SEs). The excellent electrochemical stability of halide‐based SEs enables a complete conversion and deconversion of FeF2 that cannot be achieved with sulfide‐based SEs. Due to restricted and reversible decomposition of SE, prevention of Fe dissolution, mechanical confinement of active material, as well as improved electrode kinetics, solid‐state FeF2 cathode with halide‐based SE demonstrates superior electrochemical performance compared with FeF2 electrodes in liquid electrolytes, with a high 1st cycle coulombic efficiency (≈100%), high specific capacity (≈600 mAh g−1), long cycle life (>100 cycles), and high‐rate performance (up to 2 C). The results suggest solidifying the batteries is a viable approach to addressing the long‐standing key challenges of iron fluoride cathodes.

Iron (II) fluoride cathode material derived from MIL-88A

We report an eco-friendly, simple, and scalable method of FeF 2 cathode production. MIL-88A was synthesized in a water medium without any additives. It was used as a source of iron (3 +) ions during pyrolysis. The porous structure of such a sacrificial agent allowed us to incorporate poly-vinylidene fluoride molecules as a guest component into a host MIL-88A framework. Pyrolysis in Ar-flow results in two simultaneous processes: reducing Fe 3+ into Fe 2+ and forming porous carbon shells for FeF 2 nanoparticles. Applying complex analysis of high-resolution TEM images, porosity measurements, and XANES spectroscopy, we have revealed that obtained iron fluoride is composed of nanoparticles with elongated and hexagonal shapes. Both iron fluorides were attributed to tetragonal FeF 2 structure type, contained only Fe 2+ ions, and were covered with porous carbon shells. The obtained material was used as a cathode for a lithium-ion battery and showed good stability and a high capacity of 425–330 mA h/g. The proposed water-based synthesis of MIL-88A as a precursor in combination with mild pyrolysis conditions and good electrochemical performance make this material promising for cathode application. • We report the green and reproducible synthesis of MIL-88a. • For the first time, MIL-88a was applied as an iron and carbon source to produce FeF 2 . • MIL-88a was used as a host for polyvinylidene fluoride. • We obtained stable FeF 2 nanoparticles in a porous conductive carbon matrix. • This material was tested in a lithium-ion battery as a conversion cathode.

Elucidation of discharge–charge reaction mechanism of FeF2 cathode aimed at efficient use of conversion reaction for lithium-ion batteries

• Fe 3+ ion was generated by repeating the discharge–charge reaction of FeF 2 with EC:DMC electrolyte. • Lithium carbonate was generated as a discharge product in EC:PC electrolyte. • The elution amount of iron with EC:DMC electrolyte was larger than that with EC:PC. Iron-based conversion-type materials, which are inexpensive and have low environmental impact, are promising as cathodes for large-scale Li-ion batteries. Among these materials, iron fluoride (FeF 2 ) is notable for its relatively high operating voltage and large reversible capacity. Here, the effect of the electrolyte type on the FeF 2 conversion reaction was examined, revealing that the cyclabilities of FeF 2 were improved by changing the electrolyte solvent from chain carbonate to cyclic coronate. During the discharge process, lithium carbonate was generated on the surface of the electrode with EC:PC electrolyte. On the other hand, lithium phosphate was produced on the surface electrodes regardless of which electrolyte was used. In addition, the amount of iron elution in EC:DMC was larger than that in EC:PC. The primary factor in the deterioration of the cycle was the elution of iron into electrolyte rather than the side reactants generated during the discharge–charge reaction. In addition, Fe 3+ formed on the electrode surface by repeating the discharge–charge reaction, and this is the cause of the plateau appearing at 3.0 V during the discharge process of FeF 2 after a few cycles.

FeF3·0.33H2O@C nanocomposites derived from pomegranate structure as high-performance cathodes for sodium- and lithium-ion batteries

Iron fluoride is an excellent cathode material for alkali metal-ion batteries due to its high operating voltage and extremely high specific discharge capacity. To overcome its voltage hysteresis and compensate for capacity fading due to volume change and electrode dissolution, a FeF3·0.33H2O@carbon nanocomposite with a pomegranate-like structure (FeF3·0.33H2O@C) is designed and successfully synthesized via hydrothermal synthesis followed by a solid-phase process. The FeF3·0.33H2O@C nanocomposite derived from pomegranate structure effectively can reduce electrode polarization via its unique hierarchical carbon-coated architecture. Additionally, combining other structural advantages (e.g., coordination of volume expansion, reduction of Fe dissolution, and inhibition of nanoparticle coarsening) can result in high reversibility and rate performance. For Lithium-ion battery, the nanocomposite cathode demonstrates a discharging capacity of 225 mA h g−1 at 0.1C, as well as an excellent long-cycle performance with a capacity retention rate of 93% after 200 cycles. When the cathode materials are used in sodium-ion batteries, the nanocomposite cathode achieves an exceptionally high energy density of 1015 Wh kg−1, which is more than twice that of the commercial LiCoO2 cathode (504 Wh kg−1).

RGO–Encapsulated Co/Ni dual–doped FeF3·0.33H2O nanoparticles enabling a high-rate and long-life iron (III) fluoride–lithium battery

Conversion-type iron fluoride promises a high energy density and redox potential, which is considered an extremely promising candidate for next-generation high-specific-energy and low-cost Li-ion battery. Unfortunately, its commercialization is plagued by the poor rate capability and fast capacity degradation resulting from its inferior electronic conductivity and large volumetric expansion. Herein, a three-dimensional sandwich architecture of rGO-encapsulated Ni/Co dual‐doped FeF3·0.33H2O nanoparticles (NC-FF) is fabricated by co-precipitation and subsequent calcination. The results show that the flower-like Ni/Co dual‐doped FeF3·0.33H2O nanoparticles are firmly encapsulated within highly conductive rGO sheets through MOC bonding interaction, which constructs a robust electronic/ionic network and a buffer layer against the severe volume variation. The Ni-doping can facilitate to the capacity improvement by expanding the cell volume, and the Co-doping can promote the rate capability and cycling stability enhancement by accelerating Li+ migration. Benefiting from the synergies of Ni/Co dual-doping and encapsulation of rGO, the NC-FF exhibits a high-rate capability of 200.1 mAh g−1 at 5.0 C and good cycle stability of 177.8 mAh g−1 after 400cycles. Moreover, the NC-FF|Graphite symmetric-cell still shows a high reversible capacity of 396.2 mAh g−1 at 1.0C and good cycle stability of 247.5 mAh g−1 after 100cycles.

Novel iron fluoride based hybrid materials: structural characterization, electric, dielectric and magnetic properties

Novel iron fluoride based hybrid materials: structural characterization, electric, dielectric and magnetic properties

A Bicontinuous Nanostructure Induced in Lithiated Iron Fluoride Electrodes of Lithium-ion Batteries Investigated by Small-Angle X-ray Scattering

A Bicontinuous Nanostructure Induced in Lithiated Iron Fluoride Electrodes of Lithium-ion Batteries Investigated by Small-Angle X-ray Scattering

Use of zinc oxide nanoparticles for detection of fluoride in toothpaste gel

This study aimed to investigate the metal-binding effect of fluoride, contained in different commercial toothpaste gels; the study aimed to determine if the toothpastes contained excessive concentrations of fluoride, which result in white spot lesions. A spectrophotometric method that used spectrophotometric reagents, including zinc oxide nanoparticles and iron chloride, was used to determine fluoride distribution; the analysis was based on the selective attack of fluoride ions on metals. Fluoride concentrations between 0 and 1450 ppm were analyzed. Although the iron–fluoride complex was a more sensitive reagent, the zinc–fluoride complex could serve as a suitable alternative to it for fluoride analysis, partly because the method was less time consuming and more stable. The detection and quantification limits obtained from the linear calibration curves of the zinc–fluoride complexes, in deionized water, were 0.191:1 and 0.579:1 w/w ZnO, respectively. A model calibration curve was suggested to detect the unknown products of fluoride degradation. Dentists could use a fluoride treatment similar to the protocol used in this study, to prevent potential enamel demineralization, and exclude physical cavity preparation and restoration.

Exploiting the Iron Difluoride Electrochemistry by Constructing Hierarchical Electron Pathways and Cathode Electrolyte Interface.

Conversion-type cathodes such as metal fluorides, especially FeF2 and FeF3 , are potential candidates to replace intercalation cathodes for the next generation of lithium ion batteries. However, the application of iron fluorides is impeded by their poor electronic conductivity, iron/fluorine dissolution, and unstable cathode electrolyte interfaces (CEIs). A facile route to fabricate a mechanical strong electrode with hierarchical electron pathways for FeF2 nanoparticles is reported here. The FeF2 /Li cell demonstrates remarkable cycle performances with a capacity of 300 mAh g-1 after a record long 4500 cycles at 1C. Meanwhile, a record stable high area capacity of over 6 mAh cm-2 is achieved. Furthermore, ultra-high rate capabilities at 20C and 6C for electrodes with low and high mass loading, respectively, are attained. Advanced electron microscopy reveals the formation of stable CEIs. The results demonstrate that the construction of viable electronic connections and favorable CEIs are the key to boost the electrochemical performances of FeF2 cathode.

Open-Framework Iron Fluoride Phosphates Based on Chain, Trinuclear, and Tetranuclear Chain FeIII Building Units: Crystal Structures and Magnetic Properties.

We report the synthesis and characterization of a series of new open-framework iron fluoride-fluorophosphates based on linear, trinuclear, and tetranuclear chain FeIII building units. KFe2(PO3F)2F3 (I) consists of {Fe2(O3F)2F2}10- zigzag chains interconnected by P(O/F)4 tetrahedra forming a three-dimensional (3D) open framework. K2Fe(PO2.5F1.5)2F2 (II) is built up by {Fe(PO2.5F1.5)2F2}2- chains separated by K+ cation layers. The framework for K3Fe3(PO4)(PO3F)2F5 (III) contains two-dimensional {Fe3O4F4(PO3F)2}2- sheets, which are built from trimeric Fe-octahedra insulated by PO3F tetrahedra. The macroanionic framework of K3Fe4(PO4)2F9 (IV) comprises linear {Fe4O8F9}10- chains consisting of tetranuclear magnetic clusters of [Fe4O8F9]10- formed via corner-sharing fluorine atoms decorated with PO4 groups. The magnetic characterization of three iron fluorophosphates reveals diversified magnetism: S = 5/2 spin chains for I, antiferromagnetically coupled triangular Fe units for III, and coupled tetrahedral S = 5/2 spin chains for IV. IV shows strong geometric frustration thanks to its spin motifs of corner-shared tetrahedral clusters.

High-Pressure Synthesis of Trigonal LiFe2F6: New Iron Fluoride with Li+ Tunnels as a Potential Cathode for Lithium-Ion Batteries

High-Pressure Synthesis of Trigonal LiFe₂F₆: New Iron Fluoride with Li⁺ Tunnels as a Potential Cathode for Lithium-Ion Batteries

Mechanistic understanding of the charge storage processes in FeF2 aggregates assembled with cylindrical nanoparticles as a cathode material for lithium‐ion batteries by in situ magnetometry

AbstractTransition metal fluorides (TMFs) cathode materials have shown extraordinary promises for electrochemical energy storage, but the understanding of their electrochemical reaction mechanisms is still a matter of debate due to the complicated and continuous changing in the battery internal environment. Here, we design a novel iron fluoride (FeF2) aggregate assembled with cylindrical nanoparticles as cathode material to build FeF2 lithium‐ion batteries (LIBs) and employ advanced in situ magnetometry to detect their intrinsic electronic structure during cycling in real time. The results show that FeF2 cannot be involved in complete conversion reactions when the FeF2 LIBs operate between the conventional voltage range of 1.0–4.0 V, and that the corresponding conversion ratio of FeF2 can be further estimated. Importantly, we first demonstrate that the spin‐polarized surface capacitance exists in the FeF2 cathode by monitoring the magnetic responses over various voltage ranges. The research presents an original and insightful method to examine the conversion mechanism of TMFs and significantly provides an important reference for the future artificial design of energy systems based on spin‐polarized surface capacitance.

Rgo–Encapsulated Co/Ni Dual–Doped Fef3·0.33h2o Nanoparticles Enabling a High-Rate and Long-Life Iron (Iii) Fluoride–Lithium Battery

Rgo–Encapsulated Co/Ni Dual–Doped Fef3·0.33h2o Nanoparticles Enabling a High-Rate and Long-Life Iron (Iii) Fluoride–Lithium Battery

High-Capacity Sulfide All-Solid-State Lithium Battery with Conversion-Type Iron Fluoride Cathode

High-Capacity Sulfide All-Solid-State Lithium Battery with Conversion-Type Iron Fluoride Cathode

Design of hierarchical and mesoporous FeF3/rGO hybrids as cathodes for superior lithium-ion batteries

Iron fluoride (FeF3) is considered as a promising cathode material for Li-ion batteries (LIBs) due to its high theoretical capacity (712 mAh/g) with a 3e− transfer. Herein, we have designed a strategy of hierarchical and mesoporous FeF3/rGO hybrids for LIBs, where the hollow FeF3 nanospheres are the main contributor to the specific capacity and the 2D rGO nanosheets are the matrix elevating the electronic conductivity and buffering the volume expansion. The unique FeF3/rGO hybrid can be rationally synthesized by a non-aqueous in-situ precipitation method, offering the merits of large specific surface area with rich active sites, fast transport channels for lithium ions, effective alleviation of volume expansion during cycles, and accelerating the electrochemical reaction kinetics. The FeF3/rGO hybrid electrode possesses a high initial discharge capacity of 553.9 mAh/g at a rate of 0.5 C with 378 mAh/g after 100 cycles, acceptable rate capability with 168 mAh/g at 2 C, and feasible high-temperature operation (320 mAh/g at 70 °C). The superior electrochemical behaviors presented here demonstrates that the FeF3/rGO hybrid is a potential electrode for LIBs, which may open up a new vision to design high-efficiency energy-storage devices such as LIBs based on transition metal fluorides.

Halogen Transfer to Carbon Radicals by High-Valent Iron Chloride and Iron Fluoride Corroles.

High-valent iron halide corroles were examined to determine their reactivity with carbon radicals and their ability to undergo radical rebound-like processes. Beginning with Fe(Cl)(ttppc) (1) (ttppc = 5,10,15-tris(2,4,6-triphenylphenyl)corrolato3-), the new iron corroles Fe(OTf)(ttppc) (2), Fe(OTf)(ttppc)(AgOTf) (3), and Fe(F)(ttppc) (4) were synthesized. Complexes 3 and 4 are the first iron triflate and iron fluoride corroles to be structurally characterized by single crystal X-ray diffraction. The structure of 3 reveals an AgI-pyrrole (η2-π) interaction. The Fe(Cl)(ttppc) and Fe(F)(ttppc) complexes undergo halogen transfer to triarylmethyl radicals, and kinetic analysis of the reaction between (p-OMe-C6H4)3C• and 1 gave k = 1.34(3) × 103 M-1 s-1 at 23 °C and 2.2(2) M-1 s-1 at -60 °C, ΔH⧧ = +9.8(3) kcal mol-1, and ΔS⧧ = -14(1) cal mol-1 K-1 through an Eyring analysis. Complex 4 is significantly more reactive, giving k = 1.16(6) × 105 M-1 s-1 at 23 °C. The data point to a concerted mechanism and show the trend X = F- > Cl- > OH- for Fe(X)(ttppc). This study provides mechanistic insights into halogen rebound for an iron porphyrinoid complex.

Control of Shape and Size in Iron Fluoride Porous Sub-Microspheres: Consequences for Steric Hindrance Interaction

Iron-based fluorides are promising alternates for advanced sodium-free battery cathodes due to their large theoretical capacity. However, the rational structural control on the iron-based fluorides toward high-performance batteries is still challenging. To this end, a controllable porous structure on FeF3·0.33H2O sub-microspheres is achieved by a polyethylene glycol (PEG)-assisted hydrothermal method via adjusting the volume of PEG-400. Experimental and molecular dynamic results verify that the formation of small amethyst-like sub-microspheres is mainly ascribed to the steric hindrance reaction of PEG-400, which makes it difficult for F− to combine with Fe3+ to form coordination bonds, and partially hinders the nucleation and growth of FeF3·0.33H2O nanospheres. As a sodium-free battery cathode, the FeF3·0.33H2O sub-microspheres with porous structure and smaller particle size exhibit excellent electrochemical performance with regard to cycle capacity and rate capability (a remaining capacity of 328 mAh g−1 and up to 95.3% retention rate when backs to 0.1 C after 60 cycles).

Dissolved valence state of iron fluorides and their effect on Ni-based alloy in FLiNaK salt

In this study, the stable dissolved valence state of iron fluorides in molten LiF - NaF - KF (FLiNaK) salt and their effect on GH3535 alloy were systematically investigated. Results of in situ ultraviolet–visible (UV–Vis) absorption spectroscopy and electrochemical analysis indicated that Fe (II) in molten FLiNaK salt is unstable and gets converted to more stable Fe (III) through the disproportionation reaction: 3 Fe (II) = 2 Fe (III) + Fe. Thus, the corrosion of GH3535 alloy is aggravated by the addition of iron fluorides due to the redox reaction: Fe (III) + Cr = Fe + Cr (III), resulting in the formation of the Cr-depletion layer and Fe-rich layer.