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FeF3 microspheres anchored on reduced graphene oxide as a high performance cathode material for lithium ion batteries
Abstract
Abstract FeF3 microspheres/reduced graphene oxide (r-GO) composites were synthesized by a simple hydrothermal route with HF vapor. The size of the microspheres was controllable simply by adjusting the amount of graphene oxide in the precursor solution from about 1 to 10 wt%. The FeF3 microspheres/r-GO composites showed improved discharge capacity and cycling stability in the voltage ranges of 1.5-4.5 V and 2.0-4.5 Vat room temperature compared to those of bulk FeF3. For example, the composites delivered an initial discharge capacity of about 196 mAhg-1 at a rate of 0.1C with 0.28% fading per cycle during 50 cycles in the range of 2.0-4.5 V. The composites also showed significantly enhanced rate capabilities in the range of 0.1-20C (e.g., about 170 mAhg-1 at a rate of 1C).
... Promisingly, integrating FeF 3 nanoparticles with carbon-based materials, is an effective way to simultaneously improve electronic and ionic conductivity. For the aim of effective integration, various nanocomposites or strategies have been proposed for FeF 3 cathode preparation, such as encapsulating FeF 3 into carbon materials (core-shell [22][23][24][25], yolk-shell nanostructures [4]), confining FeF 3 into carbon nanofibers [26], porous carbon spheres [27] or matrix [28], and honeycomb-structured carbon frameworks [29,30], as well as immobilizing FeF 3 onto reduced graphene oxide [31,32] and carbon nanofibers [6,33]. Of all tailored architecture mentioned above, carbon-encapsulated core-shell structure should be one of the effective strategies to address the unstable electrode-electrolyte interface and buffer the volume changes during cycling, which has been successfully used in the field of S [34], metal oxide cathodes [35] and Si [36] anode. ...
Iron trifluoride (FeF3) is highlighted as a competitive cathode for next-generation lithium and lithium-ion batteries with higher energy densities and lower cost. However, the FeF3 cathode is typically hindered by rapid capacity fade for their
poor electronic/ionic conductivity and unstable electrode/electrolyte interphase. Herein, a microcubic FeF3@C composite, where the nanosized FeF3 particles (<40 nm) are encapsulated by graphitized carbon and linked through surrounding
amorphous carbon matrix, is firstly synthesized through the Prussian blue microcubes. When using as the cathode of coin�type lithium batteries, it can achieve stable and ultralong lifespan (over 1000 cycles) at FeF3 mass loading of ~2 mg cm− 2, ascribing to the compact and thick wrapping of carbon shell and stable cathode solid electrolyte interphase (CEI) during cycling. Besides, the FeF3–Li pouch cell, FeF3 full batteries with pre-lithiated Li4Ti5O12 (PLLTO) and pre-lithiated meso�carbon microbeads (PLMCMB) anodes are successfully constructed. To interpret the capacity rising of as-prepared FeF3 cathodes within initial cycles, the detailed electrochemical behaviors and electrode kinetics are investigated. The results show that the decay of the high-potential decomposition process cannot catch up with the activation of the low-potential conversion reaction The repeated electrochemical activation within initial cycles causes multiple interface and increased Li+ diffusion coefficient (resulted from the amorphization of FeF3 particle), which induce the capacity rising.
... FeF 3 is a multiphase crystal that mainly includes the following: anhydrous FeF 3 [10], FeF 3 ·0.33H 2 O [11], FeF 3 ·0.5H 2 O [12], and FeF 3 ·3H 2 O [13]. Meanwhile, researchers have found that FeF 3 ·0.33H 2 O has the most stable crystal structure and the best electrochemical performance [14][15][16]. The structure of FeF 3 ·0.33H 2 O belongs to the orthogonal crystal system, the hexagonal tungsten bronze phase, in which iron atoms and fluorine atoms form a hexagonal tunnel, and water molecules are in the middle of the hexagon tunnel. ...
Lithium-ion batteries with the FeF3·0.33H2O cathode material enable a high energy density and safety. However, a major challenge of FeF3·0.33H2O is its low conductivity. In this work, Fe1-2x/3MnxF3·0.33H2O (x = 0, 0.01, 0.03, 0.05, and 0.07) are prepared via the solvent thermal method. Systematic investigations have studied the effect of Mn-doping on the physical and electrochemical properties. The results indicate that Mn-doping not only does not destroy the lattice structure of FeF3·0.33H2O, but also reduces the resistance and improves the diffusion coefficient of lithium ion, which provide it with better electrochemical properties. Fe0.98Mn0.03F3·0.33H2O delivers much excellent cycling performance and rate capacity than other materials. It has a 284.2 mAh g−1 initial discharge capacity that remains at 258.9 mAh g−1 after 50 cycles at 0.1 C, giving the high capacity retention rate of 91.1%. Additionally, the initial discharge capacity of Fe0.98Mn0.03F3·0.33H2O is 245, 231, 217, and 203 mAh g−1 at 1, 2, 5, and 10 C in the voltage range of 1.5–4.5 V vs. Li+/Li, respectively.
... It is suggested that FeF 2 is gradually transformed to FeF 3 as the cycle progresses. The ex situ TEM images seen in Fig. 5(e) and (f) validate the gradual change of FeF 2 to FeF 3 during the cycling [20,53,54]. In addition, FeF 3 particles remained embedded in the graphitized carbon layers after 300 cycles (Fig. 5(f)). ...
Sodium-ion batteries (SIBs) are attractive alternatives to lithium-ion batteries due to the high abundance of sodium and cost-effectiveness. Iron difluoride (FeF2) is a conversion-based type of cathode material where the energy storage is least likely to be affected by the large size of the Na⁺ ion. It is also known for its high theoretical capacity of 571 mAh g⁻¹ and is composed of low-cost chemical elements. However, the poor electrical conductivity of FeF2 causes its decreased reversible capacity and cycling stability in SIBs. In this study, FeF2 nanoparticles embedded into graphitic carbon (FeF2@GC) were synthesized from Fe-MIL-88B. By studying the structural changes of bare FeF2 during the cycling, it was revealed that in situ phase transformation of FeF2 into FeF3 is required to attain excellent cycling performance. FeF2@GC showed an improved cycling stability during a prolonged cycling with a reversible capacity of 120.5 mAh g⁻¹ after 300 cycles when tested at a current density of 50 mA g⁻¹.
... [5,8] Among them, iron fluoride (FeF 3 ) has been widely studied because the high theoretical capacity of 712 mAh g À 1 (delivering three electrons) and working potential (about 3.0 V for the redox reaction). [9] Its rich resources, good thermal stability and non-toxic properties provide favorable conditions for large-scale use. [10][11][12] However, the strong ionic character of FeÀ F bonds lead to poor electronic conductivity and inferior kinetics, which greatly limits the capacity for storing lithium. ...
FeF3 is favored by researchers due to its high theoretical specific capacity and high voltage. It is expected to be utilized as cathode material for lithium ion batteries in the future. But the poor electronic conductivity, inferior reaction kinetics and severe volume expansion seriously detained its practical application. Herein, a FeF3@N‐doped carbon nanocomposite was successfully produced by in‐situ fluorinating and dehydrating. And the nanocomposite showed the reversible capacity of 84.9 mAh g‐1 for 200th cycling at high current of 2C, which ~300% higher than that of bare FeF3. Benefited from the N‐doped carbon matrix, the composite electrodes exhibited minor transfer resistance (117.4 Ω, only 44.0% of that of bare FeF3) and tiny polarization voltage (~ 0.19 V). Meanwhile, it provided buffer for volume expansion during the insertion of Li+ and maintained the cyclic stability. This work can supply a simple pathway for designing the ultrahigh‐rate and long life FeF3 cathode materials.
... Especially, iron fluoride has attracted great interests as a prospective new class of cathode materials, which exhibit high theoretical capacity (712 mAh g -1 for 3 etransfer), low cost, abundant sources, low toxicity, and high safety. Among numerous polymorphs of iron fluorides, such as FeF 3 , FeF 3 • 0.33H 2 O, FeF 2.5 • 0.5H 2 O, FeF 3 • 0.5H 2 O and FeF 3 • 3H 2 O, FeF 3 • 0.33H 2 O is of the most attention due to its unique tunnel structure which is greatly beneficial to the Na + storage performance [26][27][28][29] . Unfortunately, the high electro-negativity of fluorine induces a large band gap, and thus leading to a poor electronic conductivity, a very low actual capacity and fast capacity fading [30] . ...
FeF3•0.33H2O crystallizes in hexagonal tungsten bronze structure with more opened hexagonal cavities are considered as next generation electrode materials of both lithium ion battery and sodium ion battery. In this paper the mesoporous spherical FeF3•0.33H2O/MWCNTs nanocomposite was successfully synthesized via a one-step solvothermal approach. Galvanostatic measurement showed that the performances of sodium ion batteries (SIBs) using FeF3•0.33H2O/MWCNTs as cathode material were highly dependent on the morphology and size of the as-prepared materials. Benefitting from the special mesoporous structure features, FeF3•0.33H2O/MWCNTs nanocomposite exhibits much better electrochemical performances in terms of initial discharge capacity (350.4 mAh g⁻¹) and cycle performance (123.5 mAh g⁻¹ after 50 cycles at 0.1 C range from 1.0 V to 4.0 V) as well as rate capacity (123.8 mAh g⁻¹ after 25 cycles back to 0.1 C). The excellent electrochemical performance enhancement can be attributed to the synergistic effect of the mesoporous structure and the MWCNTs conductive network, which can effectively increase the contact area between the active materials and the electrolyte, shorten the Na⁺ diffusion pathway, buffer the volume change during cycling/discharge process and improve the structure stability of the FeF3•0.33H2O/MWCNTs nanocomposite.
... FeF 3 microspheres were also anchored on rGO to achieve highly improved electrochemical performances. The resulting composites delivered an initial discharge capacity of about 196 mAh/g at a rate of 0.1C with 0.28% fading per cycle during 50 cycles in the rage of 2.0-4.5 V [229]. Literature data on performances of various graphene-based cathode materials are listed up in Table 4. ...
As the importance of applications depending on electrical energy storage devices (EESDs), including portable electronics, electric vehicles, and devices for renewable energy storage, has gradually increased, research has focused more and more on innovative energy systems for advanced EESDs in order to achieve enhanced performance. Over the past two decades, graphene-based materials have been considered as ideal electrode materials for lithium-ion, sodium-ion, and lithium/sulfur batteries, as well as supercapacitors, due to theirpromising applications for advanced electrodes. In this review, we will demonstratethe issues and challenges of each type of EESD, with an emphasis placed on the use of graphene-based electrodes. Recent trends related to research into graphene-based composite materials as electrodes in Korea will also be shown and a summary of the overall strategies and future perspectives will be given.
... For example, Rao et al. [48] prepared FeF 3$ 0.33H 2 O/rGO composite via a solvothermal route and obtained a discharge capacity of 700 mAh g À1 at 0.1 C with a retention of 165 mAh g À1 after 30 cycles. Jung et al. [49] synthesized FeF 3 /rGO nanocomposite, and it only reveals a discharge capacity of 196 mAhg À1 at 23.7 mA g À1 with a retention of 168.4 mAh g À1 after 50 cycles. Accordingly, nanosized TiO 2 layer not only can reduce the polarization and avoid drastic volume variation of FeF 3 $0.33H 2 O, but can provide continuous conductive paths between FeF 3 $0.33H 2 O spherical particles and reduce the interfacial resistance between particles. ...
... According to the BJH plots (Fig. 4b) recorded from the nitrogen isotherms of the as-synthesized samples, the average pore diameter is 16.5 nm, FeF 3 $0.33H 2 O/C composite has higher surface area (35.15 m 2 g À1 ), pore volume (0.136 cm 3 g À1 ) and bigger pore size (16.5 nm) than the pristine FeF 3 $0.33H 2 O. The mesoporous structure not only allows electrolyte to penetrate easily and makes electrolyte close contact with the inner-outer surface, which results in a shorter transport path for Li/Na ions and prefers to chemical conversion reaction, but also serves as a good cushion for the material volume changes during Li or Na ion insertion/extraction process, and thus enhancing the cycling performance [6]. Meanwhile, high specific surface area is beneficial to a reversion conversion reaction, because the high surface area of the materials can provide a large quantity of active sites for charge-transfer reactions and a high electrode/electrolyte contact area [9]. ...
... Carbonaceous materials could enhance the electrochemical conductivity, which is benefit for the rate ability. Compared with other carbonaceous materials, graphene has attracted more attentions due to its high conductivity, large surface area and excellent structural stability [14,15]. Wei et al. reported that graphene wrapped TiO 2 microsphere presented an improved electrochemical performance in terms of specific capacity, rate capacity and cycle stability [16]. ...
A facile one-pot solvothermal method has been used to synthesize hierarchical Fe3O4 microsphere and reduced graphene oxide (rGO) composite. The Fe3O4 microspheres are assembled with nanoparticles as primary building blocks and covered by the rGO sheets. When used as an anode material for lithium-ion batteries, the composite displays a high specific capacity, good cycle stability, remarkable rate capability. The synergetic effect of the unique nano/micro hierarchical structure and high conductivity rGO modification promise a good soakage of electrolyte, high structure stability and enhanced electronic transition, leading to an excellent electrochemical performance. This work would open a new doorway for designing the electrode materials of lithium-ion batteries with superior performance.
... Kim et al. reported FeF 3 microspheres/r-GO composites as an electrode material for LIBs, which shows improved discharge capacity and cycling stability. For example, the composites delivered an initial discharge capacity of 196 mAh g À1 at a rate of 0.1 C in the range of 2.0e4.5 V with 0.28% fading per cycle during 50 cycles [24]. And our group recently obtained a graphene loading heterogeneous hydrated forms iron-based fluoride nanocomposite via a modified solegel method for LIBs and SIBs [25]. ...
A reduced graphene oxide loading iron-based fluoride (abbreviated as Fe2F5·H2O/rGO) as a cathode material for sodium ion batteries (SIBs) has been successfully prepared by an ionic-liquid-assisted route. The morphology, structure, physicochemical properties and electrochemical performance are characterized by X-ray powder diffraction (XRD), Rietveld refinement of XRD pattern, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical tests. The XRD result shows that the crystal structure of the as-prepared sample can be indexed to the cubic Fd-3m space group and the lattice parameter is as follow: a = 1.04029 nm and V = 1.12581 nm3. Moreover, the SEM and TEM images reveal that the as-prepared rGO has a rough wavy structure and flexural paper-like morphology, and numerous Fe2F5·H2O particles are firmly adhered on the surface of the rGO to form an uniform Fe2F5·H2O/rGO composite. Electrochemical tests show that the initial discharge capacity of Fe2F5·H2O/rGO sample is 248.7mAh g−1 and the corresponding charging capacity up to 229.7 mAh g−1 at a rate of 20 mA g−1. Especially, the Fe2F5·H2O/rGO possesses good cycling stability, and it can deliver a discharge capacity of 164.2 mAh g−1 at the 100th cycle. Besides, the rate capability tests show that a stable high capacity of 186.0 mAh g−1 can be resumed when the current rate returns to 20 mA g−1 after 20 cycles.
Abstract Rechargeable lithium‐ion and sodium‐ion batteries (SIB) have dominated the energy storage fields such as electric vehicles and portable electronics due to their high energy density, long cycle life, and environmental friendliness. However, the critical bottleneck hindering the further improvement of their electrochemical performance is the unsatisfactory cathode materials, typically exhibiting inherent drawbacks such as low reversible capacity, initial capacity loss, fast capacity decay, and poor rate performance. These issues are mainly attributed to changes in the internal structure of cathode materials, such as irreversible transformation of particle morphology, evolution of crystal structure, and undesired physicochemical interfacial reactions during the electrochemical process. To address above obstacles, abundant research efforts have been devoted to stabilizing the structural evolution of cathode materials and enhancing their electrochemical performance. Herein, we reviewed the research progress on the cathode materials for lithium‐ion and SIBs. The typical cathodes and their structural characteristics, electrochemical behaviors, reaction mechanisms, and strategies for electrochemical performance optimization were summarized. This review aims to promote the understanding of the structure‐performance relationship in the cathode materials and provide some guidance for the design of advanced cathode materials for lithium‐ion and SIBs from the perspective of crystal structure.
FeF3 has been extensively studied as an alternative positive material owing to its superior specific capacity and low cost, but the low conductivity, large volume variation, and slow kinetics seriously hinder its commercialization. Here, we propose the in situ growth of ultrafine FeF3·0.33H2O NPs on a three-dimensional reduced graphene oxide (3D RGO) aerogel with abundant pores by a facile freeze drying process followed by thermal annealing and fluorination. Within the FeF3·0.33H2O/RGO composites, the three-dimensional (3D) RGO aerogel and hierarchical porous structure ensure rapid diffusion of electrons/ions within the cathode, enabling good reversibility of FeF3. Benefiting from these advantages, a superior cycle behavior of 232 mAh g-1 under 0.1C over 100 cycles as well as outstanding rate performance is achieved. These results provide a promising approach for advanced cathode materials for Li-ion batteries.
Due to its high theoretical specific capacity and low cost, iron trifluoride (FeF3) is a potential cathode material for the next generation of lithium-ion batteries. However, the problems, such as poor electronic conductivity and volume change during cycling of metal fluoride, seriously hinder its practical application. To solve these problems, the FeF3·0.33H2O nanocrystalline @ Spongy Porous Carbon @ Carbon Fiber ([email protected]@CF) composite is prepared based on the "gravel and glue" strategy. In the composite, the octahedral FeF3·0.33H2O nanocrystals (∼100 nm) coated with oligo-graphene are first uniformly embedded in the porous spongy carbon to form a mixed "mortar", which is then firmly bonded to the kapok carbon fiber. The prepared [email protected]@CF composite offers the initial discharge capacity of 407 mAh·g⁻¹ and remains at 108 mAh·g⁻¹ after 400 cycles when it was used as the cathode with the voltage in the range of 1.5–4.5 V at 0.2 C (1C=237 mAh·g⁻¹). The capacities are much better than 256 mAh·g⁻¹ (first discharge capacity) and 8 mAh·g⁻¹ (400 cycles later) of pure FeF3·0.33H2O electrode. Therefore, the "gravel and glue" design strategy for the carbon-supported composite material in this study offers an effective way to improve the electrochemical performance of FeF3·0.33H2O cathode material.
Developing high-performance cathode materials for lithium-ion batteries is necessary to maximise both energy and power density. One promising cathode material is iron trifluoride (FeF3) having a high theoretical capacity of 712 mAh/g, although achieving this value experimentally is challenging. Our previous works has shown that achievable capacity can be maximised when active materials are in a two-dimensional (2D) form. Liquid-phase exfoliation (LPE) method seems intuitively inappropriate to produce 2D-platelets from non-layered non-Van der Waals (non-VdW) bulk materials. However, in this manuscript, we show that bulk non-layered non-VdW material, FeF3 can be converted from its 3D form to quasi-2D platelets. The XRD, TEM and elemental analysis showed the structure and stoichiometry of these platelets to be similar to that of bulk material. Interestingly, although AFM showed majority of platelets to be quasi-2D, it revealed the platelet aspect-ratio to be thickness dependent, falling from ∼12 for the thinnest platelets to ∼1 for the thickest ones. Lithium storage experiments showed that, once coated in carbon and mixed with single walled nanotubes, FeF3 platelets display good Li storage capability coupled with reasonable stability. At very low currents, this material displays an active-mass normalised capacity of ∼700 mAh/g, very close to the theoretical value. However, the capacity fell off at higher currents with detailed analysis implying FeF3 cathodes in general to display poor rate performance due to low ionic diffusivity.
High-capacity cathode materials of metal fluorides generally undergo low conductivities and sluggish kinetics derived from a multielectron-transfer conversion reaction mechanism, which severely hinder the cycling stability and rate performance towards their commercialization. Herein, a flexible free-standing FeF3/chitosan pyrolytic carbon/reduced graphene oxide (FeF3/C/RGO) film as additive-free cathode was designed and prepared by a facile hydrothermal strategy followed by sequential freeze-drying, thermal reduction and fluorination post-treatments. The ultrafine FeF3 nanoparticles (NPs, ~30 nm) are confined within highly ordered RGO film, effectively reducing the Li⁺ diffusion pathway while the RGO sheets act as a matrix to restrict the complicated interlamination reaction (Fe³⁺⇄Fe²⁺⇄Fe) between adjacent interlayers with the spacing of ~30 nm. Benefiting from the free-standing structure, the FeF3/C/RGO film can achieve an admirable capacity up to 220 mAh g–1 over 200 cycles at 100 mA g–1, showing great potential for wearable and flexible electronic devices.
Lithium ion batteries (LIBs) have dominated the energy industry due to their unmatchable properties, which include high energy density, compact design, and an ability to meet a number of required performance characteristics in comparison to other rechargeable systems. Both government agencies and industries are performing intensive research on Li-ion batteries for building an energy-sustainable economy. LIBs are single entities that consist of both organic and inorganic materials with features covering multiple length scales. Critical insights should be made for understanding the structure to property relationships and the behavior of components under the working condition of LIBs. Cathodes tend to react with the electrolytes and, hence, to undergo surface modifications accompanied by degradation. These side-reactions result in an erosion of battery performance, thereby causing a reduced battery life and power capacity. Recently, techniques for preparing surface coatings on cathode materials have been widely implemented as a measure to improve their stability, to enhance their electrochemical performance. This review will cover different types of surface coatings for cathode materials, as well as a comparison of the changes in electrochemical performance between those materials with and without an applied coating.
With the revival of lithium metal anodes, there is an urgent need for matching cathodes to form the next generation batteries with high-capacity and low-cost. A porous hierarchical structure containing FeF3 nanocrystals (3-9 nm) capsulated in conductive carbon nanocages (40~110 nm) was fabricated. The morphology and size of the FeF3 nanocrystals were influenced by the existence of carbon nanocage. During the preparation process, the carbon nanocage inhibited the growth of FeF3 crystal. During the dis/charge process, the carbon nanocages not only restricted the complex conversion reaction (Fe³⁺⇄Fe²⁺⇄Fe) within the confined space, but also functioned as a bridge for the transmission of electrons, thus enhancing the electrochemical performance of the electrode. As a result, the FeF3/C electrode delivered an excellent reversible capacity of 410 mAh·g⁻¹ over 120 cycles at 100 mA·g⁻¹.
Iron fluoride cathode material for rechargeable Li-ion batteries has attracted extensive attention in recent years due to its high theoretical energy density (712 mAh g⁻¹, 1951 Wh kg⁻¹) and plentiful sources. However, its poor electronic conductivity, sluggish kinetics and volume effect during cycling cause the fast capacity fading. In this work, a hierarchical nanoparticle iron fluoride has been successfully prepared by reverse micelle soft-template method to improve the sluggish kinetics of ions diffusion and electrons transport in iron fluoride. Hierarchical nanostructure not only promotes the sufficient infiltration and soak of electrolyte, but also provides a path for the rapid diffusion of lithium ions. As cathode material for batteries, the as-prepared hierarchical nanoparticle material delivers a high initial discharge capacity of 526.9 mAh g⁻¹ and a long-term cycle performance with a low capacity fading rate of 0.55% per cycle for 100 cycles at 23.7 mA g⁻¹, which outperforms most FeF3/C materials. Even up to 600 mA g⁻¹, it displays a superior rate performance with discharge capacity of 207.6 mAh g⁻¹. Furthermore, the simple adjustment of the alcohols-water ratio realizes the fabrication of iron fluoride samples with different morphology, microscopic dimension and crystal structure. The results show that the reverse micelle soft template method is a cost-efficient, tunable and potential feasible strategy for the preparation of high-performance iron fluoride material and it can also be extended to the synthesis of other nanoscale metal fluorides.
FeF2-reduced graphene oxide nanocomposite is in-situ synthesized and assembled into electrode with poly (acrylic acid) binder as a novel sodium ion cathode, which exhibits greatly improved electrochemical performance. The mechanism for the improved performance of the electrode is studied by ex-situ morphology and phase analysis, before and after cycling. The results show that poly (acrylic acid) binder with high adhesion ability can stabilize the electrode structure, thus increase the utilization of active materials. The in-situ hybridization of FeF2 nanoparticles with reduced graphene oxide can confine the sizes of particles, and restrain the particles agglomeration. As a result, the electrode can attain high capacity and stability. The electrode exhibits superior electrochemical performance: high capacity of 175 mAh g⁻¹ at 0.2 A g⁻¹, high rate capability of 78 mAh g⁻¹ at 10 A g⁻¹, and good cycling stability. The results demonstrate the electrochemical performance of metal fluoride electrode can be enhanced by using highly adhesive materials as binders and the nanostructure construction.
The improvement of advanced battery performance has always been a key issue in energy research. Therefore, it is necessary to explore the application of excellent materials in advanced batteries. Transition-metal (Fe, Co, Ni) fluoride-based materials exhibit excellent chemical tailor ability due to their different functional groups, and they have attracted wide research interest for use in next-generation electrochemical energy storage. This review introduces methods to synthesize transition metal (Fe, Co, Ni) fluoride materials and their applications in batteries and supercapacitors. We also present the current challenges and future opportunities of iron fluoride in electrochemistry, including processing techniques, composite properties, and prospective applications. It is believed that in the future, the research and influence of iron fluoride and its composites will be more far-reaching and lasting.
A simple template-free solvothermal route has been successfully developed to prepare iron-based fluoride nanostructures with controlled morphology and composition. Fe and F sources, reactant concentration, solvent composition and solvothermal reaction time play important roles in the control of the nanostructures and composition of the products. FeF3·0.33H2O hollow nanospheres exhibit high reversible capacities and good cycling performance when used as cathode materials for lithium ion batteries, and the hollow structure has an important impact on the electrochemical performance. In addition, the mesoporous structures within the materials provide an easily accessible system for lithium ion and electrolyte transportation diffusion. The small mesopores in the nanoparticles can also make the electrolyte and lithium ion further diffuse into the interior of the electrode materials and increase the electrolyte/electrode contact area.
The FeF3 · 0.33H2O nanoparticles packaged into three-dimensional order mesoporous carbons (3D-OMCs) as cathode material of sodium-ion batteries (SIBs) was deliberately designed and fabricated by a facile nanocasting technique and mesoporous silica KIT-6 template. The structure, morphology, elemental distribution and electrochemical performance of FeF3 · 0.33H2[email protected] nanocomposite are investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM), energy-dispersive X-ray spectroscope (EDS), Raman spectroscopy and electrochemical measurement. The results show that the as-synthesized FeF3 · 0.33H2O nanoparticles are perfectly packaged in 3D-OMCs matrix, and the size and morphology of FeF3 · 0.33H2O nanoparticles can be effectively controlled. Furthermore, it has been found that the FeF3 · 0.33H2[email protected] nanocomposite can deliver a high first discharge capacity of 386 mAh g⁻¹ and excellent capacity reservation after 100 cycles at a rate of 20 mA g⁻¹ in the voltage range of 1.0–4.0 V. Especially, even up to 100 mA g⁻¹, the discharge capacity is still as high as 201 mAh g⁻¹, indicating a remarkable rate capability. The excellent electrochemical properties of FeF3 · 0.33H2[email protected] nanocomposite can be because the 3D mesoporous structure of 3D-OMCs can provide an expressway of electron transfer for Na⁺ insertion/extraction, and alleviate the drastic volume variation of FeF3 · 0.33H2O in the charge-discharge process.
The exploration of cathode materials with high electrochemical performances is critical to improve the energy and power densities of lithium ion batteries (LIBs). Iron fluoride (FeF3) has been proposed as an ideal candidate of LIBs cathode material because of the high discharge plateau and theoretical capacity. In this study, a precursor-mediated method was proposed to synthesize FeF3 nanocrystals (NCs) with different microstructures. These FeF3 NCs were obtained through the thermal decomposition of the precipitated ammonium hexafluoroferrate [(NH4)3FeF6] precursor, and the morphology and crystallinity could be adjusted by varying the ethanol/water volume ratio in the procursor precipitation process. Electrochemical studies demonstrated that FeF3 NC, derived from (NH4)3FeF6 precipitated from the solution with the ethanol/water volume ratio of 20, delivered the initial specific capacity of 217.6 mAh g⁻¹ at 0.2C, associated with excellent rate capability up to 20C (93.8 mAh g⁻¹), and showed the capacity retention of 80.6% after 500 cycles at 20C. These results indicate a tunable and convenient strategy towards nanostructured metals fluorides for high power LIBs.
Amorphous FeF3/C nanocomposites, where FeF3 nanoparticles are intimately anchored into a highly-graphitized porous branch-like carbon framework, have been successfully designed and fabricated from the carbonized Fe–MOFs by a novel vapor-solid fluoridation reaction and dehydration reaction. Compared to the FeF3/C nanocomposites obtained from the precursors at various carbonization conditions, the one carried out at 700 °C for 3 h exhibits the most outstanding comprehensive sodium ion storage performance. It can deliver 302, 146, 73 mA h g⁻¹ discharge capacities at current densities of 15, 150, 1500 mA g⁻¹, respectively, exhibiting an excellent sodium ion capacity and rate performance. Moreover, it displays a good cycling performance with a discharge capacity of 126.7 mA h g⁻¹ at 75 mA g⁻¹ after 100 cycles. The outstanding electrochemical features of the FeF3/C nanocomposites could be attributed to its amorphous structure and highly-graphited porous carbon framework, which is beneficial to the ionic and electronic transport and the reaction kinetics of electrode materials.
A simple synthetic method was developed to produce holey graphene with in-plane nanopores by a fast thermal expansion of graphene oxide (GO) in air and further thermal reduction in N2 flow at 900 °C. The as-synthesized holey graphene nanosheets (HGN) shows meso-macroporous structure and higher surface area than chemically reduced graphene oxide (CRGO) by using hydrazine hydrate. The catalysts of HGN-900 supported Pt nanoparticles (Pt/HGN-900) were further prepared through in-situ chemical co-reduction and applied in the electro-oxidation of methanol. The electrocatalytic performance of catalysts was investigated by cyclic voltammetry (CV) and chronoamperometry (CA) analysis. The results indicate that the catalytic activity of Pt/HGN-10min-900 (377.5 mA mg⁻¹pt) is bout 1.83 and 2.77 times higher than that of Pt/CRGO-900 (206.1 mA mg⁻¹pt) and Pt/XC-72 (136.2 mA mg⁻¹pt) catalysts in 0.5 mol L⁻¹ H2SO4 and 1.0 mol L⁻¹ CH3OH, and Pt/HGN-900 catalysts show higher stable current density compared to that of Pt/XC-72 and Pt/CRGO-900 catalysts.
The crystalline and magnetic microstructures and the morphological features of β-FeF3 3H2O, HTB-FeF30.33H2O, and r-FeF3 iron fluorides hydrothermally synthesized and annealed in the argon atmosphere have been studied. The dehydration process of plate-like β-FeF33H2O particles is studied in detail, and the model for corresponding structural modifications is proposed. The developed model is used to synthesize ultradispersed HTB-FeF30.33H2O and r-FeF3 materials. The r-FeF3 phase is found to be partially in the superparamagnetic state, with the particle size being comparable with the average size of coherent scattering regions. © V.V. MOKLYAK, V.O. KOTSYUBYNSKY, I.P. YAREMIY, P.I. KOLKOVSKYY, A.B. HRUBYAK, L.Z. ZBIHLEY, 2016.
Graphitized carbon-coated FeF3 nanoparticles were synthesized by facile polymerization using FeCl3 as an iron precursor, citric acid (C6H8O7) as a carbon source and chelating agent, and ethylene glycol (EG) as a cross-linker. During the synthesis, Fe(0) was formed in situ to catalyze the formation of graphitic carbon and was subsequently transformed into FeF3. The prepared FeF3/graphitic carbon composite (FC853) exhibited an initial discharge capacity of about 188 mA h g⁻¹, with an excellent capacity fading rate of 0.24% per cycle for 50 cycles at 0.1C in the voltage range of 2.0-4.5 V, which is superior to the corresponding parameters of bare FeF3. This composite also exhibited an increased discharge capacity of about 374 mA h g⁻¹ in the 1st cycle, reaching 421 mA h g⁻¹ after slow activation processes in a wide voltage range of 1.5-4.5 V. In addition, the rate performance of FC853 was significantly improved compared to that of bare FeF3. The enhanced electrochemical Li ion storage properties of this FeF3 composite were mainly attributed to the controlled FeF3 nanoparticle size and the conductive graphitic carbon layers wrapping FeF3 surfaces during prolonged cycles.
Iron fluorides (FeFx) for Li-ion batteries cathode are still in the stage of intensive research due to their low delivered capacity and limited lifetime. One formidable reason for cathode degradation is the severe aggregation of FeFx nanocrystals upon long-term cycling. To maximize their capacity and cyclability, we herein propose a novel and applicable way, by using thin-layered nickel ammine nitrate (NAN) matrix as a feasible encapsulation material to well disperse FeF3 nanoparticles. Such core-shell hybrids with smart configurations are constructed via a green, scalable and in-situ encapsulation approach. The outer thin-film NAN matrix with prominent electrochemical stability can keep encapsulated on FeF3 nanoactives all through the cyclic testing, protecting them away from adverse aggregation into bulk crystals and thus leading to drastic improvements on electrode behaviors (e.g., high electrode capacity up to ~423 mA h g-1, obviously prolonged cyclic period and promoted rate capabilities). This present work may set up a new and general platform to develop intriguing core-shell hybrid cathodes for Li-ion batteries, not merely in the case of FeFx but also applicable for wide spectrum of other cathode materials.
The FeF3-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode materials were synthesized via a wet chemical process followed by a solid state reaction. The physical properties of the as-prepared samples were conducted using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicated that the surface of cathode particles was covered by FeF3 film (about 5–15 nm thick). Compared with the bare cathode, the FeF3-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 one delivered the higher coulombic efficiency, better rate capability, longer cycle life, and better structure stability. A high capacity retention of 95% (190 mAh g− 1) after 100 cycles at 0.5 C rate was obtained for the FeF3-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode. Besides, the results from cyclic voltammetry and electrochemical impedance spectra revealed that the noteworthy enhanced electrochemical properties of the surface-modified sample were due to the presence of FeF3 coating layer, which suppressed the side reaction between the Li[Li0.2Mn0.54Ni0.13Co0.13]O2 particles with electrolyte and further stabilized the Li[Li0.2Mn0.54Ni0.13Co0.13]O2 structure with cycling.