No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
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.
FeF3/C nanocomposites, where FeF3 nanocrystals had been dispersed into a porous carbon matrix, were successfully fabricated by a novel vapour-solid method in a tailored autoclave. Phase evolution of the reaction between the precursor and HF solution vapour under air and argon gas atmospheres were investigated. The results showed that the air in the autoclave played an important role in driving the reaction to form FeF3. The as-prepared FeF3/C delivered 134.3, 103.2 and 71.0 mA h g-1 of charge capacity at a current density of 104, 520, and 1040 mA g-1 in turn, exhibiting superior rate capability to the bare FeF3. Moreover, it displayed stable cycling performance, with a charge capacity of 196.3 mA h g-1 at 20.8 mA g-1. EIS and BET investigations indicated that the good electrochemical performance can be attributed to the good electrical conductivity and high specific surface area that result from the porous carbon matrix.
A novel α-Fe2O3/graphene composite is prepared by a simple in situ wet chemistry approach. The α-Fe2O3 particles with diameter around 130 nm are homogeneously anchored on graphene nanosheets to form a 3D quasi-laminated architecture. Such a well-organized flexible structure can offer sufficient void space to facilitate the electrolyte penetration, alleviate the effect of the volume change of α-Fe2O3 particles and avoid particle–particle aggregation during lithium insertion/desertion. In addition, graphene not only improves the electric conductivity of the composite electrode but also maintains the structural integrity of the composite electrode during long-term cycling. As anode material for Li-ion batteries, the α-Fe2O3/graphene composite electrode exhibits a stable capacity of 742 mAh g−1 up to 50 cycles. The synthesis technique is suitable for practical large-scale production of graphene-based metal oxide composites as advanced electrode materials for rechargeable Li-ion batteries.
Graphene-wrapped FeF3 nanocrystals (FeF3/G) have been successfully fabricated for the first time by a vapour-solid method, which can be generalized to synthesize other metal fluorides. The as-synthesized FeF3/G delivers a charge capacity of 155, 113, and 73 mA h g(-1) at 104, 502, and 1040 mA g(-1) in turn, displaying superior rate capability to bare FeF3. Moreover, it exhibits stable cyclability over 100 cycles with a charge capacity of 185.6 and 119.8 mA h g(-1) at 20.8 and 208 mA g(-1), respectively, which could be ascribed to the buffering effect and lowered resistance from the graphene. This versatile vapour-solid method and the improved cyclability provide a promising avenue for the application of metal fluorides as cathode materials.
Reversible extraction of lithium from
(triphylite) and insertion of lithium into
at 3.5 V vs. lithium at 0.05 mA/cm2 shows this material to be an excellent candidate for the cathode of a low‐power, rechargeable lithium battery that is inexpensive,
nontoxic, and environmentally benign. Electrochemical extraction was limited to ∼0.6 Li/formula unit; but even with this restriction
the specific capacity is 100 to 110 mAh/g. Complete extraction of lithium was performed chemically; it gave a new phase,
, isostructural with heterosite,
. The
framework of the ordered olivine
is retained with minor displacive adjustments. Nevertheless the insertion/extraction reaction proceeds via a two‐phase process,
and a reversible loss in capacity with increasing current density appears to be associated with a diffusion‐limited transfer
of lithium across the two‐phase interface. Electrochemical extraction of lithium from isostructural
(M = Mn, Co, or Ni) with an
electrolyte was not possible; but successful extraction of lithium from
was accomplished with maximum oxidation of the
occurring at x = 0.5. The
couple was oxidized first at 3.5 V followed by oxidation of the
couple at 4.1 V vs. lithium. The
interactions appear to destabilize the
level and stabilize the
level so as to make the
energy accessible.
The structure and electrochemistry of
-based carbon metal fluoride nanocomposites (CMFNCs) was investigated in detail from 4.5 to 1.5 V, revealing a reversible
metal fluoride conversion process. These are the first reported examples of a high-capacity reversible conversion process
for positive electrodes. A reversible specific capacity of approximately 600 mAh/g of CMFNCs was realized at 70°C. Approximately
one-third of the capacity evolved in a reaction between 3.5 and 2.8 V related to the cathodic reduction reaction of
to
The remainder of the specific capacity occurred in a two-phase conversion reaction at 2 V resulting in the formation of a
finer Fe:LiF nanocomposite. Upon oxidation, selective area electron diffraction characterization revealed the reformation
of a metal fluoride. Evidence presented suggested that the metal fluoride is related to
in structure. A pseudocapacitive reaction is proposed as a possible mechanism for the subsequent
oxidation reaction. Preliminary results of
and
CMFNCs were used in the discussion of the electrochemical properties of the reconverted metal fluoride. © 2003 The Electrochemical
Society. All rights reserved.
There is growing interest in thin, lightweight, and flexible energy storage devices to meet the special needs for next-generation, high-performance, flexible electronics. Here we report a thin, lightweight, and flexible lithium ion battery made from graphene foam, a three-dimensional, flexible, and conductive interconnected network, as a current collector, loaded with Li(4)Ti(5)O(12) and LiFePO(4), for use as anode and cathode, respectively. No metal current collectors, conducting additives, or binders are used. The excellent electrical conductivity and pore structure of the hybrid electrodes enable rapid electron and ion transport. For example, the Li(4)Ti(5)O(12)/graphene foam electrode shows a high rate up to 200 C, equivalent to a full discharge in 18 s. Using them, we demonstrate a thin, lightweight, and flexible full lithium ion battery with a high-rate performance and energy density that can be repeatedly bent to a radius of 5 mm without structural failure and performance loss.
We have used density functional theory (DFT) to investigate the ternary phase diagram of the Li-Fe-F system and the reactions of Li with iron fluorides. Several novel compounds, not previously identified in the Li-Fe-F system, are predicted to be stable. Electrochemical voltage profiles, derived from the evolution of the Li chemical potential in the calculated phase diagram, are in reasonable agreement with experimental trends. The effect of particle size on the Fe that precipitates when LixFeF3 reacts with Li is also investigated. We find that when 1 nm Fe particles form, the potential for this reaction is considerably reduced from its bulk value and relate this to the experimental observations. Furthermore, we formulate a model for the significant hysteresis that is observed in the lithiation and delithiation of FeF3. Nonequilibrium paths derived by assuming much faster diffusion of Li than Fe are in reasonable agreement with experimental profiles. Our kinetic model predicts that the iron fluoride reaction follows a different path through the phase diagram during conversion (discharge) and reconversion (charge), which results in the voltage profile hysteresis observed during experiment. The proposed kinetic model also explains why upon extraction of Li from a 3/1 mixture of LiF and Fe a rutile FeF2-like structure can form, even when iron should be oxidized to Fe3+ by extraction of three Li+ per Fe.
We firstly propose a facile, mild and effective thermal-decomposition strategy to prepare high-quality graphene at a low temperature of 300 °C in only 5 min under an ambient atmosphere. Applying the advantage of this strategy that provides an oxidizing atmosphere, pure V(2)O(5)/graphene composite is successfully synthesized and exerts excellent lithium storage properties.
Technological improvements in rechargeable solid-state batteries are being driven by an ever-increasing demand for portable electronic devices. Lithium-ion batteries are the systems of choice, offering high energy density, flexible and lightweight design, and longer lifespan than comparable battery technologies. We present a brief historical review of the development of lithium-based rechargeable batteries, highlight ongoing research strategies, and discuss the challenges that remain regarding the synthesis, characterization, electrochemical performance and safety of these systems.
Researchers must find a sustainable way of providing the power our modern lifestyles demand.
X-ray diffractional and electrochemical studies of the reduction of a spinel-related manganese dioxide, Li0.27(2)Mn2O4:MnO1.93, were carried out in lithium nonaqueous cells. The reduction of this oxide proceeded topotactically. An observed voltage separation of ca. 1V, which begins at a critical composition of Li1.0Mn2O4, was considered from the structural data of LixMn2O4 to be a difference in a solid-state redox reaction of a MnO6-octahedron and an effect of deformation of a MnO69--octahedron from Oh-symmetry to D4h-symmetry Jahn-Teller distortion) upon an electrode potential of LixMn2O4 was discussed.
Nanostructured Li2FeSiO4/C composites have been successfully synthesized by adopting polyethylene glycol (PEG) as the surfactant and L-ascorbic acid as the carbon additive, using a sol-gel method based on the acid-catalyzed hydrolysis/condensation of tetraethoxysilane (TEOS). The Li2FeSiO4/C nanocomposites possess dispersed spherical particles (similar to 50 nm) with narrow particle size distribution, embedded in a continuous carbon matrix. The Li2FeSiO4/C nanocomposites deliver first discharge capacity of 138.2 mAhg(-1) at C/16 and maintain at about 130.4 mAhg(-1) after 40 cycles at various rates at room temperature, which outperform those of Li2FeSiO4/C samples synthesized without PEG. The electrochemical performances of Li2FeSiO4/C were largely enhanced after the introduction of PEG due to the following two aspects. On one hand, the smaller particle size facilitated the shorter diffusion length for lithium ions; On the other hand, the more continuous carbon film coated on the particle surface enhanced the electronic conductivity of the nanocomposites and restrained the side reaction occurring at the electrode-electrolyte interface.
A new cathode material for lithium ion battery FeF3 · 0.33H2O/C was synthesized successfully by a simple one-step chemico-mechanical method. It showed a noticeable initial discharge capacity of 233.9 mAh g−1 and corresponding charge capacity of 186.4 mAh g−1. A reversible capacity of ca.157.4 mAh g−1 at 20 mA g−1 can be obtained after 50 charge/discharge cycles. To elucidate the lithium ion transportation in the cathode material, the methods of electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) were applied to obtain the lithium diffusion coefficients of the material. Within the voltage level of 2.05–3.18 V, the method of EIS showed that \( {D}_{{\mathrm{Li}}^{+}} \) varied in the range of 1.2 × 10−13 ~ 3.6 × 10−14 cm2 s−1 with a maximum of 1.2 × 10−13 cm2 s−1 at 2.5 V. The method of GITT gave a result of 8.1 × 10−14 ~ 1.2 × 10−15 cm2 s−1. The way and the range of the variation for lithium ion diffusion coefficients measured by the GITT method show close similarity with those obtained by the EIS method. Besides, they both reached their maximum at a voltage level of 2.5 V.
Fe1−xCoxF3 (x = 0, 0.03, 0.05, 0.07) compounds are synthesized via a liquid-phase method. To further improve their electrochemical properties, a ball milling process with acetylene black (AB) has been used to form Fe1−xCoxF3/C (x = 0, 0.03, 0.05, 0.07) nanocomposites. The structure and performance of the samples have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), charge–discharge tests, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and the galvanostatic intermittent titration technique (GITT). It is found that Co-doping significantly improves the electrochemical performance. Fe0.95Co0.05F3/C exhibits excellent electrochemical performance with discharge capacities of 151.7, 136.4 and 127.6 mA h g−1 at rates of 1C, 2C and 5C in the voltage range of 2.0–4.5 V vs. Li+/Li, and its capacity retentions remain as high as 92.0%, 92.2% and 91.7%, respectively, after 100 cycles. Co-doping could decrease the charge transfer resistance, increase the lithium diffusion coefficient during the lithiation process and improve the electrochemical reversibility. The preparation of Co-doped FeF3/C offers a new method to improve the performance of FeF3: cationic doping, which is a significant step forward for developing high-power lithium batteries.
FeF3 is of great interest as a potential candidate cathode material because of its low cost, abundance, environmental friendliness, and high theoretical capacity of about 237 mAh·g–1 in the voltage range of 2.0–4.5 V. However, FeF3 has drawbacks of poor cycling stability and rate performance because of its low intrinsic electrical conductivity and slow diffusion of lithium ions. These issues should be improved for the practical application of FeF3 in lithium-ion battery systems. In this study, FeF3/ordered mesoporous carbon (OMC) nanocomposites were synthesized by an incipient-wetness impregnation technique in a facile and scalable method. The tubular shaped OMC was utilized as both a conductive agent and a hard template for the formation of nanosized FeF3 particles. The FeF3/OMC nanocomposites showed enhanced capacity, cycling stability, and rate performance compared to bulk FeF3 in the voltage range of 2.0–4.5 V at room temperature.
Iron fluoride cathodes have been attracting considerable interest due to their high electromotive force value of 2.7 V and their high theoretical capacity of 237 mA h g(-1) (1 e(-) transfer). In this study, uniform iron fluoride hollow porous microspheres have been synthesized for the first time by using a facile and scalable solution-phase route. These uniform porous and hollow microspheres show a high specific capacity of 210 mA h g(-1) at 0.1 C, and excellent rate capability (100 mA h g(-1) at 1 C) between 1.7 and 4.5 V versus Li/Li(+) . When in the range of 1.3 to 4.5 V, stable capacity was achieved at 350 mA h g(-1) at a current of 50 mA g(-1) .
Hollow prismatic/cylindric iron fluoride with a wall thickness of 0.1–0.5 μm and a length of 1–3 μm has been synthesized by a simple and mild solvothermal method. This compound with a mixed crystal structure of FeF3·3H2O and FeF3·0.33H2O, has an initial discharge capacities of 106.7 mAh g−1 and a capacity retention of 60% after 100 cycles at the rate of 0.5C (1 C is 237 mA g−1) in the voltage of 2.0–4.5 V. To overcome the poor electronic conductivity of fluorides, the as-prepared iron fluoride has been ball-milled with 15 wt.% acetylene black (AB) and heat-treated to obtain FeF3·0.33H2O/C nanocomposites. The nanocomposites deliver discharge capacity of 160.2 mAh g−1 at the rate of 0.5C. Even at the high rate of 5 C, the initial discharge capacity is still as high as 137.5 mAh g−1. The capacity retentions reach up to 85.0% and 75.7% after 100 cycles at 0.5 C and 5 C, respectively.
A series of well-defined three-arm star poly(ε-caprolactone)-b-poly(acrylic acid) copolymers having different block lengths were synthesized via the combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). First, three-arm star poly(ε-caprolactone) (PCL) (Mn = 2490–7830 g mol−1; Mw/Mn = 1.19–1.24) were synthesized via ROP of ε-caprolactone (ε-CL) using tris(2-hydroxyethyl)cynuric acid as three-arm initiator and stannous octoate (Sn(Oct)2) as a catalyst. Subsequently, the three-arm macroinitiator transformed from such PCL in high conversion initiated ATRPs of tert-butyl acrylate (tBuA) to construct three-arm star PCL-b-PtBuA copolymers (Mn = 10,900–19,570 g mol−1; Mw/Mn = 1.14–1.23). Finally, the three-arm star PCL-b-PAA copolymer was obtained via the hydrolysis of the PtBuA segment in three-arm star PCL-b-PtBuA copolymers. The chain structures of all the polymers were characterized by gel permeation chromatography, proton nuclear magnetic resonance (1H NMR), and Fourier transform infrared spectroscopy. The aggregates of three-arm star PCL-b-PAA copolymer were studied by the determination of critical micelles concentration and transmission electron microscope. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
To improve the rate capability and cyclability of FeF3 cathode for Li-ion batteries, FeF3 has been modified by forming FeF3/activated carbon microbead (ACMB) composite. The FeF3/ACMB composite is successfully achieved via a simple chemical route. The morphology and structural properties of the samples are investigated by X-ray diffraction and scanning electron microscopy (SEM). SEM observations demonstrate that FeF3/ACMB composite has a distinct spherical morphology. Electrochemical tests show that the FeF3/ACMB composite cathode has higher capacity, better cycleability, and better rate capability than pristine FeF3. Electrochemical impedance spectra indicate that the FeF3/ACMB composite electrode has low electrochemical resistance compared with pristine FeF3, indicating the enhanced conductivity of the FeF3/ACMB composite.
In this communication, for the first time, we demonstrate the fast and facile preparation of porous FeF3 nanospheres using solvent exchange from FeF3 aqueous solution to ethanol. We further demonstrate the use of such FeF3 nanospheres as cathode materials for rechargeable lithium-ion batteries with good rate capability and cycling performance.
The hydrothermal reaction of a mixture of a colloidal dispersion of graphite oxide and ammonium vanadate yielded a hybrid made of graphene and a nanotubular metastable monoclinic polymorph of VO2, known as VO2(B). The formation of VO2(B) nanotubes is accompanied by the reduction of graphite oxide. Initially the partially scrolled graphite oxide layers act as templates for the crystallization of VO2(B) in the tubular morphology. This is followed by the reduction of graphite oxide to graphene resulting in a hybrid in which VO2(B) nanotubes are dispersed in graphene. Electron microscopic studies of the hybrid reveal that the VO2(B) nanotubes are wrapped by and trapped between graphene sheets. The hybrid shows potential to be a high capacity cathode material for lithium ion batteries. It exhibits a high capacity (∼450 mAh/g) and cycling stability. The high capacity of the hybrid is attributed to the interaction between the graphene sheets and the VO2(B) tubes which improves the charge-transfer. The graphene matrix prevents the aggregation of the VO2(B) nanotubes leading to high cycling stability.
Here, a novel architecture of a core–shell structured FeF3@Fe2O3 composite with particle size of 100–150 nm and tunable Fe2O3 content is synthesized by a simple heat treatment process utilizing FeF3 with fine network structure as precursor. The structure, morphology and electrochemical performance of the pristine FeF3 and the FeF3@Fe2O3 composites are studied by XRD, SEM, TEM and discharge–charge measurements. XRD results show that the Bragg peaks of the FeF3@Fe2O3 composites are well indexed to FeF3 and Fe2O3. SEM and TEM images reveal the core–shell structure of the composites. The comparison of the electrochemical performance between the pristine FeF3 and the FeF3@Fe2O3 composites reveals that the in situ Fe2O3 coating (even with small amount, 0.6–5.2 wt%) has great influence on the improvement of electrochemical performance.
A new hybrid nanostructure composed of three-dimensionally ordered macroporous (3DOM) FeF3 and an homogenous coating of poly(3, 4-ethylenedioxythiophene) (PEDOT) is successfully synthesized using polystyrene (PS) colloidal crystals as hard template, and the coating of PEDOT is achieved through a novel in situ polymerization method. The special nanostructure provides a three-dimensional, continuous, and fast electronic and ionic path in the electrode. Surprisingly, the advantageous combination of 3DOM structure and homogenous coating of PEDOT endows the as-prepared hybrid nanostructures with a stable and high reversible discharge capacity up to 210 mA h g−1 above 2.0 V at room temperature (RT), and a good rate capability of 120 mA h g−1 at a high current density of 1 A g−1, which opens up new opportunities in the development of high performance next-generation lithium-ion batteries (LIBs).
An FeF3 nanocomposite with carbon materials is prepared by a ball milling process. The effect of the strain induced by ball milling on the electrochemical performance is examined using a combination of synchrotron X-ray diffraction (SXRD) and X-ray absorption spectroscopy (XAS). The strain of the FeF3 particles in the nanocomposite is analyzed by applying the Williamson–Hall method to the SXRD patterns. Heat-treatmenting the FeF3 nanocomposite drastically relieves the strain induced by the ball milling. The electrochemical performance of the FeF3 nanocomposite is also significantly improved by the heat-treatment process at 350 °C. The FeF3 nanocomposite heat-treated at 350 °C delivers 200 mA h g−1 of reversible capacity with good capacity retention in a voltage range of 2.0–4.5 V. The heat-treatment process suppresses the increase in the poralization during the continuous cycling test. The power density of the heat-treated sample is superior to that of the ball milled sample without the heat treatment.
Hierarchical V2O5 microspheres composed of stacked platelets are fabricated through a facile, low-cost, and energy-saving approach. The preparation procedure involves a room-temperature precipitation of precursor microspheres in aqueous solution and subsequent calcination. Owning to this unique structure, V2O5 microspheres manifest a high capacity (266 mAh g-1), excellent rate capability (223 mAh g-1 at a current density 2400 mA g-1), and good cycling stability (200 mA h g-1 after 100 cycles) as cathode materials for lithium ion batteries.
Orthorhombic structure FeF3 was synthesized by a liquid-phase method. The FeF3/MoS2 for the application of cathode material of lithium-ion battery was prepared through mechanical milling with molybdenum bisulfide. The structure and morphology of the FeF3/MoS2 were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical behavior of FeF3/MoS2 was studied by charge/discharge, cyclic voltammetry and electrochemical impedance spectra measurements. The results show that the prepared FeF3/MoS2 was typical orthorhombic structure, uniform surface morphology, better particle-size distribution and excellent electrochemical performances. The initial discharge capacity of FeF3/MoS2 was 169.6 mAh·g−1 in the voltage range of 2.0–4.5 V, at room temperature and 0.1 C charge–discharge rate. After 30 cycles, the capacity retention is still 83.1%.
Li3V2(PO4)3/Cu composite cathode material was prepared via sol–gel method by adding of 1.8 wt% Cu powder into the precursor solution. The structural and physical properties, as well as the electrochemical performance of the material were compared with those of Cu-free Li3V2(PO4)3. X-ray diffraction showed that Cu did not enter the crystal structure of Li3V2(PO4)3. The Li3V2(PO4)3/Cu composite material had a higher electronic conductivity comparing with that of Cu-free Li3V2(PO4)3. Electrochemical impedance spectroscopy showed that the adding of Cu decreased the charge transfer resistance of the electrode. In addition, the lithium diffusion coefficient was prominently enhanced from 1.3 × 10−9 to 2.8 × 10−8 cm2 s−1. Based on the these advantages, the Li3V2(PO4)3/Cu composite material exhibited much better cycling performance than the Cu-free Li3V2(PO4)3.
Orthorhombic structure FeF3 was synthesized by a liquid-phase method using FeCl3, NaOH and HF solution as starting materials, and the FeF3/V2O5 composites were prepared by milling the mixture of as-prepared FeF3 and the conductive V2O5 powder. The properties of FeF3/V2O5 composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge/discharge and cyclic voltammetry measurements. Results showed that the FeF3/V2O5 composites can be used as cathode material for lithium-ion battery. Electrochemical measurements in a voltage range of 2.0–4.5V reveal that the addition of conductive V2O5 improves significantly the electrochemical performance of FeF3, and the FeF3/V2O5 composite prepared by milling for 3h exhibits high discharge capacity and good cycle performance, and its discharge capacity maintains about 209mAhg−1 at 0.1C (23.7mAg−1) after 30 cycles.
Layered LiCo1/3Ni1/3Mn1/3O2 was prepared by a solid state reaction at 1000 °C in air and examined in nonaqueous lithium cells. LiCo1/3Ni1/3Mn1/3O2 showed a rechargeable capacity of 150 mAh g−1 in 3.5–4.2 V or 200 mAh g−1 in 3.5–5.0 V. Operating voltage of Li / LiCo1/3Ni1/3Mn1/3O2 was by 0.2–0.25 V lower than that of a cell with LiCoO2 or LiMn2O4 and by 0.15–0.3 V higher than that with LiNiO2 or LiCo1/2Ni1/2O2 due to a complex solid solution mechanism.
Exploring high performance cathode materials is essential to realize the adoption of Li-ion batteries for application in electric vehicles and hybrid electric vehicles. FeF3, as a typical iron-based fluoride, has been attracting considerable interest due to both the high electromotive force value of 2.7 V and the high theoretical capacity of 237 mA h g-1 (1e- transfer). In this study, we report a facile low-temperature solution phase approach for synthesis of uniform iron fluoride nanocrystals on reduced graphene sheets stably suspended in ethanol solution. The resulting hybrid of iron fluoride nanocrystals and graphene sheets showed high specific capacity and high rate performance for iron fluoride type cathode materials. High stable specific capacity of about 210 mA h g-1 at a current density of 0.2 C was achieved, which is much higher than that of LiFePO4 cathode material. Notably, these iron fluoride/nanocomposite cathode materials demonstrated superior rate capability, with discharge capacities of 176, 145 and 113 mA h g-1 at 1, 2 and 5 C, respectively.
We report the synthesis of a novel hollow porous Fe3O4 bead–rGO composite structure for lithium ion battery anode application via a facile solvothermal route. The formation of hollow porous Fe3O4 beads and reduction of graphene oxide (GO) into rGO were accomplished in one step by using ethylene glycol (EG) as a reducing agent. In this composite structure, the hollow porous Fe3O4 beads were either chemically attached or tightly wrapped with rGO sheets, leading to a strong synergistic effect between them. As a result, the obtained Fe3O4–rGO composite electrodes could deliver a reversible capacity of 1039 mA h g−1 after 170 cycles between 3 V and 50 mV at a current density of 100 mA g−1, with an increment of 30% compared to their initial reversible capacity, demonstrating their superior cycling stability.
The increasing demands from large-scale energy applications call for the development of lithium-ion battery (LIB) electrode materials with high energy density. Earth-abundant conversion cathode material iron trifluoride (FeF(3)) has a high theoretical capacity (712 mAh g(-1)) and the potential to double the energy density of the current cathode material based on lithium cobalt oxide. Such promise has not been fulfilled due to the non-optimal material properties and poor kinetics of the electrochemical conversion reactions. Here, we report for the first time a high-capacity LIB cathode that is based on networks of FeF(3) nanowires (NWs) made via an inexpensive and scalable synthesis. The FeF(3) NW cathode yielded a discharge capacity as high as 543 mAh g(-1) at the first cycle and retained a capacity of 223 mAh g(-1) after 50 cycles at room temperature under the current of 50 mA g(-1). Moreover, high-resolution transmission electron microscopy revealed the existence of continuous networks of Fe in the lithiated FeF3 NWs after discharging, which is likely an important factor for the observed improved electrochemical performance. The loss of active material (FeF(3)) caused by the increasingly ineffective reconversion process during charging was found to be a major factor responsible for the capacity loss upon cycling. With the advantages of low cost, large quantity, and ease of processing, these FeF(3) NWs are not only promising battery cathode materials, but also provide a convenient platform for fundamental studies and further improving conversion cathodes in general.
Three types of FeF3 nanocrystals were synthesized by different chemical routes and investigated as a cathode-active material for rechargeable lithium batteries. XRD and TEM analyses revealed that the as-synthesized FeF3 samples have a pure ReO3-type structure with a uniformly distributed crystallite size of 10 to 20 nm. Charge−discharge experiments in combination with cyclic voltammetric and XRD evidence demonstrated that the FeF3 in the nanocomposite electrode can realize a reversible electrochemical conversion reaction from Fe3+ to Fe0 and vice versa, enabling a complete utilization of its three-electron redox capacity (712 mAh·g−1). Particularly, the FeF3/C nanocomposites can be well cycled at very high rates of 1000−2000 mA·g−1, giving a considerably high capacity of 500 mAh·g−1. These results seem to indicate that the electrochemical conversion reaction can not only give a high capacity but also proceed reversibly and rapidly at room temperature as long as the electroactive FeF3 particles are sufficiently downsized, electrically wired, and well-protected from aggregation. The high-rate capability of the FeF3/C nanocomposite also suggests its potential applications for high-capacity rechargeable lithium batteries.
A facile route that combines co-assembly and photothermal reduction was developed to synthesize free-standing, flexible FeF(3)-graphene papers. The papers contain well-dispersed FeF(3) nanoparticles and open diffusion channels in a porous, electrically conducting network of graphene sheets, and demonstrate promising applications as cathodes in high-energy density Li-ion batteries.
A fluoride-based cathode (FeF3·0.33H2O) for lithium batteries, the synthesis of which has been reported recently (C. L. Li et al. Adv. Mater.2010, 22, 3650), is described in terms of structure, morphology, and performance. A self-assembled mesoporous morphology connected with a high specific surface area is obtained through the soft template role of the ionic liquid. The fluoride exhibits a one-dimensional tunnel structure produced by continuous hexagonal cavities, in which hydration water molecules are located. The high Li-intercalation activity of carbon-free FeF3·0.33H2O is expected to be associated with various factors, including electrolyte-infiltratable mesoporosity, wide Li+-insertable channels, and medium conductivities. A single solid-solution reaction mechanism is indicated by potentiostatic intermittent titration technique and ex situ X-ray diffraction at different reactive potentials.
The challenges for further development of Li rechargeable batteries for electric vehicles are reviewed. Most important is safety, which requires development of a nonflammable electrolyte with either a larger window between its lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) or a constituent (or additive) that can develop rapidly a solid/electrolyte-interface (SEI) layer to prevent plating of Li on a carbon anode during a fast charge of the battery. A high Li(+)-ion conductivity (sigma(Li) > 10(-4) S/cm) in the electrolyte and across the electrode/ electrolyte interface is needed for a power battery. Important also is ail increase in the density of the stored energy, which is the product of the voltage and capacity of reversible Li insertion/extraction into/from the electrodes. It will be difficult to design a better anode than carbon, but carbon requires formation of an SEI layer, which involves an irreversible capacity loss. The design of a cathode composed of environmentally benign, low-cost materials that has its electrochemical potential pc well-matched to the HOMO of the electrolyte and allows access to two Li atoms per transition-metal cation would increase the energy density, but it is a daunting challenge. Two redox couples can be accessed where the cation redox couples are "pinned" at the top of the 0 2p bands, but to take advantage of this possibility, it must be realized in a framework structure that can accept more than one Li atom per transition-metal cation, Moreover, such a situation represents an intrinsic voltage limit of the cathode, and matching this limit to the HOMO of the electrolyte requires the ability to tune the intrinsic voltage limit. Finally, the chemical compatibility in the battery must allow a long service life.
Reduction of a colloidal suspension of exfoliated graphene oxide sheets in water with hydrazine hydrate results in their aggregation and subsequent formation of a high-surface-area carbon material which consists of thin graphene-based sheets. The reduced material was characterized by elemental analysis, thermo-gravimetric analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, NMR spectroscopy, Raman spectroscopy, and by electrical conductivity measurements. (c) 2007 Elsevier Ltd. All rights reserved.
To meet the energy and power demands of lithium-based batteries, numerous nanostructured and -decorated material prototypes have been proposed. In particular for insulating electrodes, a decrease of grain size coupled with wiring by a conductive phase is quite effective in improving the electroactivity. In this work, we report a novel electron-wiring method using single-wall carbon nanotubes in an imidazolium-based ionic liquid precursor, which enables them to be well disentangled and dispersed, even unzipped. As a case study, in situ formed iron fluoride nanoparticles (∼10 nm) are collected into micrometer-sized aggregates after wiring of merely 5 wt % carbon nanotubes in weight. These composite materials act as cathodes and exhibit a remarkable improvement of capacity and rate performances (e.g., 220 mAh/g at 0.1C and 80 mAh/g at 10C) due to the construction of mixed conductive networks. Therein, the ionic liquid remainder also serves as an in situ binder to generate a nanographene-coated fluoride, which can even run well without the addition of extra conductive carbon and binder. This nanotechnological procedure based on an ionic liquid succeeds without applying high temperature and pressure and is a significant step forward in developing high-power lithium batteries.
Nanoarchitectures composed of FeF3 nanoflowers on carbon nanotube (CNT) branches (FNCB, see figure) are fabricated by functionalization of CNT surfaces with FeF3. FNCB's improved Li-ion and electron transport makes it a candidate for applications in cathode material for lithium rechargeable batteries.
We show a general two-step method for growing hydroxide and oxide nanocrystals of the iron family elements (Ni, Co, Fe) on graphene with two degrees of oxidation. Drastically different nanocrystal growth behaviors were observed on low-oxidation graphene sheets (GS) and highly oxidized graphite oxide (GO) in hydrothermal reactions. Small particles precoated on GS with few oxygen-containing surface groups diffused and recrystallized into single-crystalline Ni(OH)(2) hexagonal nanoplates or Fe(2)O(3) nanorods with well-defined morphologies. In contrast, particles precoated on GO were pinned by the high-concentration oxygen groups and defects on GO without recrystallization into well-defined shapes. Adjusting the reaction temperature can be included to further control materials grown on graphene. For materials with weak interactions with graphene, increasing the reaction temperature can lead to diffusion and recrystallization of surface species into larger crystals, even on highly oxidized and defective GO. Our results suggest an interesting new approach for controlling the morphology of nanomaterials grown on graphene by tuning the surface chemistry of graphene substrates used for crystal nucleation and growth.
The structural transformations that occur when FeF(3) is cycled at room temperature in a Li cell were investigated using a combination of X-ray diffraction (XRD), pair distribution function (PDF) analysis, and magic-angle-spinning NMR spectroscopy. Two regions are seen on discharge. The first occurs between Li = 0 and 1.0 and involves an insertion reaction. This first region actually comprises two steps: First, a two-phase reaction between Li = 0 and 0.5 occurs, and the Li(0.5)FeF(3) phase that is formed gives rise to a Li NMR resonance due to Li(+) ions near both Fe(3+) and Fe(2+) ions. On the basis of the PDF data, the local structure of this phase is closer to the rutile structure than the original ReO(3) structure. Second, a single-phase intercalation reaction occurs between Li = 0.5 and 1.0, for which the Li NMR data indicate a progressive increase in the concentration of Fe(2+) ions. In the second region, the conversion reaction, superparamagnetic, nanosized ( approximately 3 nm) Fe metal is formed, as indicated by the XRD and NMR data, along with some LiF and a third phase that is rich in Li and F. The charge process involves the formation of a series of intercalation phases with increasing Fe oxidation state, which, on the basis of the Li NMR and PDF data, have local structures that are similar to the intercalation phases seen during the first stage of the discharge process. The solid-state NMR and XRD results for the rutile phase FeF(2) are presented for comparison, and the data indicate that an insertion reaction also occurs, which is accompanied by the formation of LiF. This is followed by the formation of Fe nanoparticles and LiF via a conversion reaction.
Graphene has attracted much attention due to its interesting properties and potential applications. Chemical exfoliation methods have been developed to make graphene recently, aimed at large-scale assembly and applications such as composites and Li ion batteries. Although efficient, the chemical exfoliation methods involve oxidation of graphene and introduce defects in the as-made sheets. Hydrazine reduction at 100 has shown to partially restore the structure and conductance of graphite oxide. However, the reduced GO still shows strong defect peaks in Raman spectra with higher resistivity than pristine graphene by 2 to 3 orders of magnitude. It is important to produce much less defective graphene sheets than GO, and develop more effective graphene reduction. Recently, we reported a mild exfoliation-reintercalation-expansion method to form high-quality GS with higher conductivity and lower oxidation degree than GO.5 Here, we present a 180 solvothermal reduction method for our GS and GO. The solvothermal reduction is more effective than the earlier reduction methods in lowering the oxygen and defect levels in GS, increasing the graphene domains, and bringing the conductivity of GS close to pristine graphene. The reduced GS possess the highest degree of pristinity among chemically derived graphene.
For Abstract see ChemInform Abstract in Full Text.