Reversible and Fast (De)fluorination of High‐Capacity Cu<sub>2</sub>O Cathode: One Step Toward Practically Applicable All‐Solid‐State Fluoride‐Ion Battery

Wang

ACS Appl. Mater. Interfaces

et al. 2022

A fluoride-ion battery (FIB) is a novel type of energy storage system that has a higher volumetric energy density and low cost. However, the high working temperature (>150 °C) and unsatisfactory cycling performance of cathode materials are not favorable for their practical application. Herein, fluoride ion-intercalated CoFe layered double hydroxide (LDH) (CoFe-F LDH) was prepared by a facile co-precipitation approach combined with ion-exchange. The CoFe-F LDH shows a reversible capacity of ∼50 mAh g–1 after 100 cycles at room temperature. Although there is still a big gap between FIBs and lithium-ion batteries, the CoFe-F LDH is superior to most cathode materials for FIBs. Another important advantage of CoFe-F LDH FIBs is that they can work at room temperature, which has been rarely achieved in previous reports. The superior performance stems from the unique topochemical transformation property and small volume change (∼0.82%) of LDH in electrochemical cycles. Such a tiny volume change makes LDH a zero-strain cathode material for FIBs. The 2D diffusion pathways and weak interaction between fluoride ions and host layers facilitate the de/intercalation of fluoride ions, accompanied by the chemical state changes of Co2+/Co3+ and Fe2+/Fe3+ couples. First-principles calculations also reveal a low F– diffusion barrier during the cyclic process. These findings expand the application field of LDH materials and propose a novel avenue for the designs of cathode materials toward room-temperature FIBs.

Section: Resultssupporting

confidence: 80%

A Zero-Strain Insertion Cathode Material for Room-Temperature Fluoride-Ion Batteries

Wang

ACS Appl. Mater. Interfaces

et al. 2022

“…In all-solid FSBs, fluoride ions are apparently transferred between the positive and negative electrodes through a fluoride-ion-conductive solid electrolyte, and then, some metal fluoride and the corresponding metal are reversibly produced at each electrode. − Significantly advanced all-solid FSB was fabricated by Anji Reddy and Fichtner a decade ago, and the all-solid FSB operated at elevated temperatures . Most investigations into all-solid FSBs were performed at temperatures greater than 423 K, while a few have demonstrated their performance at room temperature in recent years. − …”

Section: Introductionmentioning

confidence: 99%

Examination of Morphological Changes of Active Materials for Solution-Based Rechargeable Fluoride Shuttle Batteries Using In Situ Electrochemical Atomic Force Microscopy Measurements

et al. 2022

Batteries using fluoride anions as the carrier might possess high capacity and energy density. Especially, the fluoride shuttle battery (FSB), which uses a fluoride-ion-conductive liquid electrolyte and operates at room temperature, has been reported previously and is deemed a solution to the global energy and environmental crises. Although several electrolyte solutions have been synthesized, and the fluorination/defluorination reactions of various active materials have been evaluated, no subsequent FSBs using those electrolyte solutions have been reported. In this study, two metal species, Bi and Pb, which have different fluorination/defluorination mechanisms in the electrolyte solution composed of alkylammonium fluoride and an ionic liquid, were used as the positive and negative active materials for the FSB. The fluorination/defluorination mechanisms at each electrode during the reactions were explained by in situ electrochemical atomic force microscopy (EC-AFM) measurements. Differences in the morphological changes by two existing mechanisms, direct fluorination and dissolution−deposition, were clarified with evidence. Furthermore, the charge/discharge process of the FSB, with the electrolyte solution combining the active materials, was demonstrated, and the cycling performance and capacity fading mechanism were discussed based on the characteristic morphological change of the active materials at their interface with the electrolyte solution obtained by in situ EC-AFM measurements.

Adv Energy and Sustain Res

“…[ 1–22 ] Therefore, in addition to batteries that use a liquid electrolyte, [ 23–30 ] some all‐solid‐state fluoride‐shuttle systems have been demonstrated. [ 12,31–43 ] As detailed in these previous reports, multivalent electrochemical reactions occur in such devices, and the devices can potentially deliver high energy densities via conversion‐type reactions. Table S1, Supporting Information summarizes the theoretical energy density of some electrode materials.…”

Section: Introductionmentioning

confidence: 97%

FeF₃ as Reversible Cathode for All‐Solid‐State Fluoride Batteries

Inoishi

Setoguchi

Hori

et al. 2022

Fluoride batteries are attracting intensive attention because they can provide a higher energy density than conventional lithium‐ion batteries. Among various metal fluorides, FeF3 is a promising candidate for the cathode material of fluoride batteries because of its high theoretical capacity. In this report, the reversibility of an FeF3 cathode is investigated in conjunction with fluorite‐type Ba0.6La0.4F2.4 as the electrolyte and Pb as the counter‐electrode material. For the first time, the discharge–charge performance of a fluoride battery using FeF3 cathode is investigated. The initial discharge capacity is 579 mAh g−1, and a capacity of 461 mAh g−1 is retained at the 10th cycle. The reversible conversion reaction mechanism for FeF3 is clarified by X‐ray diffraction and X‐ray adsorption spectroscopy. The results revealed that FeF3 is reduced to FeF2 at the first‐stage plateau and then to Fe metal at the second‐stage plateau; they also reveal that the reverse process proceeded during charging. Ex situ scanning electron microscopy observations show that the morphology of the cathode changed reversibly and that, when the battery is in the discharged state, voids are present because of shrinkage of the electrode.