Fluoride Ion Batteries Research Articles

Polymer Electrolyte Based All‐Solid‐State Rechargeable Fluoride Ion Batteries

Polymer Electrolyte Based All‐Solid‐State Rechargeable Fluoride Ion Batteries

La1−xSrxF3−x: A Solid-State Electrolyte for Fluoride Ion Battery with High Ionic Conductivity and Wide Electrochemical Potential Window

Fluoride ion conductors are developed for use as solid-state electrolytes in fluoride ion batteries which are one of promising candidates for next-generation storage batteries. Ba-doped LaF3 (La0.9Ba0.1F2.9: LBF) is mainly used as a solid-state electrolyte in fluoride ion batteries. However, room temperature conductivity of LBF is considerably low, on the order of 10−6 S cm−1 and it is still unclear the optimal elements to be doped to LaF3. In this study, we have explored La0.9Sr x Ba0.1−x F2.9 system (x = 0, 0.01, 0.025, 0.05, 0.1), in which Ba in LBF is substituted for Sr and investigated the composition dependence of ionic conductivity. We elucidate that the higher concentration of Sr without Ba can significantly improve the ionic conductivity, and the maximum ionic conductivity of La0.9Sr0.1F2.9 is 1.5 × 10−5 S cm−1 at room temperature, which is one order of magnitude larger than that of LBF. The higher ionic conductivity of LSF is due to the larger grain size and higher sintering density of LSF compared to LBF, which results in lower grain boundary resistance. The LSF total ionic conductivity of 10−4 S cm−1 can be achieved at 350 K, which significantly lowers operating temperature of fluoride ion batteries down to 350 K.

Highly Reversible Conversion-Type CoSn2 Cathode for Fluoride-Ion Batteries.

An all-solid-state fluoride-ion battery (FIB) is one of the promising candidates for the next-generation battery owing to its high energy density and high safety. For the practical application of FIBs, it is an urgent task to operate FIBs at lower temperatures. However, there are still two major difficulties in conventional conversion-type pure metal cathodes: low F- ion conductivities and poor cycle stabilities. Here, the conversion-type Sn-based intermetallic alloy is proposed as a new cathode that can overcome the above issues. The present CoSn2 cathode retains the discharge capacity of 229 mAh g-1 after 250 cycles, even at 60°C. CoSn2 is decomposed into CoF2 and SnF2 nanocrystals in the charging process, and the nanoscale network structure of SnF2 provides the fast F- ion conduction path throughout the cathode, facilitating the battery operation at lower temperatures. Moreover, the formed CoF2 and SnF2 phases are merged into the original CoSn2 phase in the discharging process, leading to a highly reversible redox reaction and the high cycle stability of CoSn2. These findings should pave the way to enhance the performance of all-solid-state FIBs at lower temperatures.

A novel thermal battery based on fluoride ion conduction

Fluoride ion battery was expected to become a new generation of energy storage system because of its high theoretical energy density. However, at room temperature, the ratio property of fluoride ion batteries was poor. Consequently, we conducted an investigation into the potential application of this technology in high-temperature primary discharge. A novel thermal battery based on fluoride ion conduction was reported, which can discharge with a large current at high temperature. Assemblying NiF2|NaF-KF-CsF@MgO|La thermal battery, the ionic conductivity of NaF-KF-CsF electrolyte run up to 2.47 × 10–1 S cm-1 at 550 °C. The battery has much higher ratio property than reported fluoride ion battery systems and the specific capacity can reach 60 mAh g-1(@1.35 V, 200 mA cm-2). Although the results are promising, they are not yet sufficient to meet the practical application scenarios of thermal batteries. Hence, this was a preliminary attempt to apply fluorine ion conduction to the field of thermal battery.

Summary, Future, and Challenges of Fluoride‐Ion Batteries

Due to the limitations of lithium‐ion batteries (LIBs), there is an urgent need to explore alternative energy storage technologies. However, the high‐energy density of fluoride‐ion batteries (FIBs) has attracted widespread attention as a potential successor to LIBs. FIBs are emerging as a low‐cost, safe, and versatile energy storage solution, with a broad operating temperature range. With continuous efforts from researchers, significant progress has been made in the field of FIBs. Nevertheless, compared to traditional batteries, research on FIBs remains limited, and many challenges and unexplored avenues persist. This article elucidates the principles of FIBs, summarizes the materials for both cathodes and anodes, discusses electrolytes, and addresses existing issues. It also outlines future directions and potential applications of FIBs. As it is continued to innovate and explore, FIBs hold promise for revolutionizing energy storage technology, offering enhanced performance, safety, and sustainability.

Fluoride Ion Storage and Conduction Mechanism in Fluoride Ion Battery Positive Electrode, Ruddlesden-Popper-Type Layered Perovskite La1.2Sr1.8Mn2O7 Crystal.

Structural characteristics on fluoride ion storage and conduction mechanism in La1.2Sr1.8Mn2O7, and its fluoridated materials, La1.2Sr1.8Mn2O7F and La1.2Sr1.8Mn2O7F2, for an all-solid-state fluoride ion battery positive electrode with a high volumetric capacity surpassing those of lithium-ion ones have been revealed using the Rietveld method and maximum entropy method. In La1.2Sr1.8Mn2O7, once the F- ions are taken into the NaCl slabs in its crystal through the charging process, it forms two stable fluoride compounds, La1.2Sr1.8Mn2O7F and La1.2Sr1.8Mn2O7F2, with the help of the Mn oxidation reaction. In these oxyfluorides, thermal vibrations of the F- ions inserted are much larger, especially in the a-b plane, than along the c axis. When surplus energy, such as an electric field for charging, is applied to these crystals at near room temperature or higher, the anions immediately begin to jump to their neighboring lattice sites, resulting in sufficiently rapid and large ionic conduction. The MEM analyses and density functional theory (DFT) calculations have revealed that the F- ions enable to easily travel along the ⟨110⟩ directions in the NaCl slabs of these crystals. These structural features thus make La1.2Sr1.8Mn2O7 and its fluorides possess both of two features incompatible with each other, ion storage and conduction, indispensable for rechargeable batteries.

Alkaline Earth Bismuth Fluorides as Fluoride-Ion Battery Electrolytes.

Fluoride-ion batteries have several potential advantages over lithium-ion batteries. Materials development is still needed, however, to realize electrolytes with sufficiently high anion conductivity and compatibility with anode and cathode layers. Fluoride compounds are difficult to synthesize directly as single crystals but can be realized from oxide film precursors via topotactic chemistry techniques. Here, we create crystalline alkaline earth bismuth fluoride films BaBiF5 and SrBiF5 through oxide molecular beam epitaxy and topotactic fluorination. We characterize their ionic conductivities and demonstrate their potential as electrolytes. Finally, we realize epitaxial synthesis of BaBiF5 on BaF2 substrates, providing a route to thin film fluoride-ion battery devices.

Toward Practical Fluoride-Ion Batteries: A Review and Perspective on Liquid Electrolyte Development

Toward Practical Fluoride-Ion Batteries: A Review and Perspective on Liquid Electrolyte Development

Data-Driven Material Exploration of High Conductive Fluorides By Multi-Element Substitution

Barium fluoride (BaF2) has a fluorite-type structure and is attracting high attention as a solid electrolyte material for fluoride ion batteries that can be used under high voltage. Previous research has reported that the ionic conductivity increases by 4 to 5 orders of magnitude by partially replacing Ba in BaF2 with La. This indicates that elemental substitution is effective in improving the ionic conductivity of BaF2. However, single element substitution only explore much limited experimental space in elements, so that it should be difficult to discover innovative conductive compositions. By replacing various elements at the same time, the experimental space can be largely expanded and the possibility of finding the optimal composition increases. But, the combination numbers of multi-element substituted compositions are much over 10000, and exhaustive exploration of them is unrealistic. Therefore, we aimed to efficiently search for multi-element substitution compositions with high conductivity by creating a material-conductivity correlated exploring system under data-driven approach using large number of fluoride material database. The purpose of this research was to discover solid solution compositions in the multi-element substituted fluorides and understanding of the relationship between substitutional elements and solid solution formation.Approximately 20 types of multi-element substitution composition candidates were initially picked up using the D-optimal design (Dopt). The target compositions were synthesized to collect their XRD data. Next, we extracted the "number of peaks" from the XRD data as a feature values to express the degree of solid solution in the sample. Furthermore, we made a regression model with the element types and addition ratios as explanatory variables and the "number of peaks" as the objective variable. Using the regression model, approximately 20 candidate were predicted to form solid solution, in which we called as data-driven design of experiments (DOE) approach. Finally, the materials were actually prepared according to the proposal in DOE. The identification results were projected using the principal component analysis (PCA) to draw the material space.The obtained material space shows the number of peaks in the samples prepared using DOE decreased compared to those using Dopt. In detail, the Dopt-derived sample had 41.83 peaks, while the DOE-derived sample had 19.65 peaks on average. This result indicates that we were able to efficiently find preferable compositions that are advantageous for solid solution formation by using the data-driven method.In the presentation, we will also report the high-throughput composition exploration, their conductivities, and also development of virtual X-ray diffraction simulation system for over 10,000 kinds of multi-substituted composition of the fluorides. Acknowledgement s This research was partially supported by Knowledge Hub Aichi, the GIMRT Program of the Institute for Materials Research, Tohoku University (Proposal No. 202303-CRKKE-0048).

Sonochemical synthesis and characterization of SnF2 as a potential fluoride-ion conducting solid electrolyte

Fluoride ion batteries (FIBs) are emerging as a promising alternative to conventional lithium-ion batteries, primarily because of their high theoretical energy density and environmentally sustainable characteristics. For the development of a high-performance solid-state fluoride ion battery, an engineered electrolyte is crucial. As the synthesis technique impacts the phase, microstructure, and morphology of the materials, a unique and facile sonochemical route is employed for the first time herein for synthesizing Tin (II) fluoride as a solid electrolyte. The XRD investigations have indicated the formation of the α-SnF2 phase with a monoclinic structure, and space group C2/c. The particle size of SnF2 synthesized using 225 W and 325 W power of probe sonicator is found to be 2 μm and 0.8 μm respectively, as revealed by Scanning Electron Micrographs. SnF2 prepared with 325 W ultrasonic power has exhibited the maximum ionic conductivity of value 3.4 × 10−4 S/cm at room temperature, with a significant enhancement regarding the values reported so far. The anionic transport number of the electrolyte estimated at room temperature using the combined AC-DC technique is found to be 0.96, indicating fluoride ion conduction.

Investigation of Cycling Performance in a Solid-State Fluoride-Ion Battery Based on Copper Fluoride Electrodes

Investigation of Cycling Performance in a Solid-State Fluoride-Ion Battery Based on Copper Fluoride Electrodes

Solvation engineering of non-aqueous electrolytes for room-temperature fluoride-ion batteries

Fluoride-ion batteries (FIBs) with high energy density and low cost are a promising new generation battery system for renewable energy storage. However, their room-temperature operation is strongly impeded by the lack of compatible electrolytes. Herein, we demonstrate that a stable room-temperature FIB can be achieved by tailoring the solvation chemistry of a non-aqueous liquid electrolyte. As validated by computational modeling and spectroscopic investigations, the cost-efficient β-hydrogen-free tetramethylammonium fluoride (TMAF) salt can efficiently prevent Hofmann elimination-induced electrolyte decomposition. Meanwhile, the synergistic effect of strong-polarity solvent and anion acceptor additive endows the high salt solubility (up to 0.7 M) and room-temperature ionic conductivity (6.12×10−3 S cm−1 at 25 °C) for the electrolyte. Owing to the virtue of this new electrolyte design, the Zn||CuF2 and Li||CuF2 FIBs were successfully constructed, delivering high reversibility, stable interface, and extended life. This work offers a new pathway for clearing the formidable bottlenecks in developing high-performance Fluoride-ion batteries.

Pressure Tuning and Sn Particle Size Optimization for Enhanced Performance in PbSnF4-Based All-Solid-State Fluoride Ion Batteries.

All-solid-state fluoride ion batteries (ASSFIBs) show remarkable potential as energy storage devices due to their low cost, superior safety, and high energy density. However, the poor ionic conductivity of F- conductor, large volume expansion, and the lack of a suitable anode inhibit their development. In this work, PbSnF4 solid electrolytes in different phases (β- and γ-PbSnF4) are successfully synthesized and characterized. The ASSFIBs composed of β-PbSnF4 electrolytes, a BiF3 cathode, and micrometer/nanometer size (µ-/n-) Sn anodes, exhibit substantial capacities. Compared to the μ-Sn anode, the n-Sn anode with nanostructure exhibits superior battery performance in the BiF3/β-PbSnF4/Sn battery. The optimized battery delivers a high initial discharge capacity of 181.3 mAh g-1 at 8mA g-1 and can be reversibly cycled at 40mA g-1 with a high discharge capacity of over 100.0 mAh g-1 after 120 cycles at room temperature. Additionally, it displays high discharge capacities over 90.0 mAh g-1 with excellent cyclability over 100 cycles under -20°C. Detailed characterization has confirmed that reducing Sn particle size and boosting external pressure are crucial for achieving good defluorination/fluorination behaviors in the Sn anode. These findings pave the way to designing ASSFIBs with high capacities and superior cyclability under different operating temperatures.

A Water-in-Salt Electrolyte for Room-Temperature Fluoride-Ion Batteries Based on a Hydrophobic-Hydrophilic Salt.

Realizing room-temperature, efficient, and reversible fluoride-ion redox is critical to commercializing the fluoride-ion battery, a promising post-lithium-ion battery technology. However, this is challenging due to the absence of usable electrolytes, which usually suffer from insufficient ionic conductivity and poor (electro)chemical stability. Herein we report a water-in-salt (WIS) electrolyte based on the tetramethylammonium fluoride salt, an organic salt consisting of hydrophobic cations and hydrophilic anions. The new WIS electrolyte exhibits an electrochemical stability window of 2.47 V (2.08-4.55 V vs Li+/Li) with a room-temperature ionic conductivity of 30.6 mS/cm and a fluoride-ion transference number of 0.479, enabling reversible (de)fluoridation redox of lead and copper fluoride electrodes. The relationship between the salt property, the solvation structure, and the ionic transport behavior is jointly revealed by computational simulations and spectroscopic analysis.

Rocking-Chair Aqueous Fluoride-Ion Batteries Enabled by Hydrogen Bonding Competition.

Aqueous fluoride ion batteries (FIBs) have garnered attention for their high theoretical energy density, yet they are challenged by sluggish fluorination kinetics, active material dissolution, and electrolyte instability. Here, we present a room temperature rocking-chair aqueous FIBs featuring KOAc-KF binary salt electrolytes, enabling concurrent fluorination and defluorination reactions at both cathode and anode electrodes. Experimental and theoretical results reveal that acetate ions in the electrolyte compete with fluoride ions in hydrogen bonding formation, weakening the excessively strong solvation between H2O and F- ions. This results in the suppression of detrimental HF formation and a reduced desolvation energy of F- ions, enhancing the electrochemical reaction kinetics. The bismuth-based cathode exhibits direct conversion in the optimized electrolyte, effectively suppressing the detrimental disproportionation reactions from Bi2+ intermediates. Additionally, zinc anode undergoes a typical fluorination process, forming solid KZnF3 as the electrode product, minimizing the risks of hydrogen evolution. The proposed aqueous FIBs with the optimized electrolyte demonstrate high discharge capacity, long-term cycling stability and excellent rate capabilities.

Rocking‐Chair Aqueous Fluoride‐Ion Batteries Enabled by Hydrogen Bonding Competition

AbstractAqueous fluoride ion batteries (FIBs) have garnered attention for their high theoretical energy density, yet they are challenged by sluggish fluorination kinetics, active material dissolution, and electrolyte instability. Here, we present a room temperature rocking‐chair aqueous FIBs featuring KOAc‐KF binary salt electrolytes, enabling concurrent fluorination and defluorination reactions at both cathode and anode electrodes. Experimental and theoretical results reveal that acetate ions in the electrolyte compete with fluoride ions in hydrogen bonding formation, weakening the excessively strong solvation between H2O and F− ions. This results in the suppression of detrimental HF formation and a reduced desolvation energy of F− ions, enhancing the electrochemical reaction kinetics. The bismuth‐based cathode exhibits direct conversion in the optimized electrolyte, effectively suppressing the detrimental disproportionation reactions from Bi2+ intermediates. Additionally, zinc anode undergoes a typical fluorination process, forming solid KZnF3 as the electrode product, minimizing the risks of hydrogen evolution. The proposed aqueous FIBs with the optimized electrolyte demonstrate high discharge capacity, long‐term cycling stability and excellent rate capabilities.

Solid-state synthesis and ion transport characteristics of the β-KSbF4 for all-solid-state fluoride-ion batteries

All-solid-state fluoride ion batteries (FIBs) have been recently considered as a post-lithium-ion battery system due to their high safety and high energy density. Just like all solid-state lithium batteries, the key to the development of FIBs lies in room-temperature electrolytes with high ionic conductivity. β-KSbF4 is a kind of promising solid-state electrolyte for FIBs owing to its rational ionic conductivity and relatively wide electrochemical stability window at room temperature. However, the previous synthesis routes of β-KSbF4 required the use of highly toxic hydrofluoric acid and the ionic conductivity of as-prepared product needs to be further improved. Herein, the β-KSbF4 sample with an ionic conductivity of 1.04 × 10−4 S cm−1 (30 °C) is synthesized through the simple solid-state route. In order to account for the high ionic conductivity of the as-synthesized β-KSbF4, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) are used to characterize the physicochemical properties. The results show that the as-synthesized β-KSbF4 exhibits higher carrier concentration of 1.0 × 10−6 S cm−1 Hz−1 K and hopping frequency of 1.31 × 106 Hz at 30 °C due to the formation of the fluorine vacancies. Meanwhile, the hopping frequency shows the same trend as the changes of ionic conductivity with the changes of temperature, while the carrier concentration is found to be almost constant. The two different trends indicate the hopping frequency is mainly responsible for the ionic conduction behavior within β-KSbF4. Furthermore, the all-solid-state FIBs, in which Ag and Pb + PbF2 are adopted as cathode and anode, and β-KSbF4 as fluoride ion conductor, are capable of reversible charge and discharge. The assembled FIBs show a discharge capacity of 108.4 mA h g−1 at 1st cycle and 74.2 mA h g−1 at 50th cycle. Based on an examination of the capacity decay mechanism, it has been found that deterioration of the electrolyte/electrode interface is an important reason for hindering the commercial application of FIBs. Hence, the in-depth comprehension of the ion transport characteristics in β-KSbF4 and the interpretation of the capacity fading mechanism will be conducive to promoting development of high-performance FIBs.

Fluorine Chemistry in Rechargeable Batteries: Challenges, Progress, and Perspectives.

The renewable energy industry demands rechargeable batteries that can be manufactured at low cost using abundant resources while offering high energy density, good safety, wide operating temperature windows, and long lifespans. Utilizing fluorine chemistry to redesign battery configurations/components is considered a critical strategy to fulfill these requirements due to the natural abundance, robust bond strength, and extraordinary electronegativity of fluorine and the high free energy of fluoride formation, which enables the fluorinated components with cost effectiveness, nonflammability, and intrinsic stability. In particular, fluorinated materials and electrode|electrolyte interphases have been demonstrated to significantly affect reaction reversibility/kinetics, safety, and temperature tolerance of rechargeable batteries. However, the underlining principles governing material design and the mechanistic insights of interphases at the atomic level have been largely overlooked. This review covers a wide range of topics from the exploration of fluorine-containing electrodes, fluorinated electrolyte constituents, and other fluorinated battery components for metal-ion shuttle batteries to constructing fluoride-ion batteries, dual-ion batteries, and other new chemistries. In doing so, this review aims to provide a comprehensive understanding of the structure-property interactions, the features of fluorinated interphases, and cutting-edge techniques for elucidating the role of fluorine chemistry in rechargeable batteries. Further, we present current challenges and promising strategies for employing fluorine chemistry, aiming to advance the electrochemical performance, wide temperature operation, and safety attributes of rechargeable batteries.

Revealing the Unusual Mechanism of Mixed Cationic and Anionic Redox in Oxyfluorosulfide Cathode for All-Solid-State Fluoride-Ion Batteries

Revealing the Unusual Mechanism of Mixed Cationic and Anionic Redox in Oxyfluorosulfide Cathode for All-Solid-State Fluoride-Ion Batteries

Fluorination/Defluorination Behavior of Y2C in Fluoride-Ion Battery Anodes

Fluorination/Defluorination Behavior of Y₂C in Fluoride-Ion Battery Anodes