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

Abstract

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.

Room-temperature reversible F-ion batteries based on sulfone electrolytes with a mild anion acceptor additive

“…46 Recently, a dissolution process of Pb 2+ was proposed and validated by Okazaki et al ., and it is expected to take place before the fluorination of Pb to PbF 2 during discharging. 47 The released Pb 2+ and and Cs + in the electrolyte would combine with F − , and are responsible for the appearance of Pb–F and CsF peaks at 683.6 eV and 682.3 eV, respectively. 48,49 By comparing the relative peak intensities of different compositions in the F 1s spectra (Fig.…”

Advancing Fluoride-Ion Batteries with a Pb-PbF2 Counter Electrode and a Diluted Liquid Electrolyte

“…Similar to the Pb-PbF 2 symmetric cell, the Coulombic efficiency is over 100% and appears to plateau at 101% on the ninth cycle, suggesting some minor degradation processes are taking place (Figure b). The asymmetry between the charge and discharge profiles has already been observed by Yaokawa et al and Okazaki et al, and a detailed mechanistic study would be required to elucidate its origin. , The coin cell setup presented in this work could offer an ideal configuration for conducting such an investigation through in-situ XRD.…”

“…However, their cell exhibited low discharge capacity (110 mAh g –1 on first discharge) and poor cycling (∼0 mAh g –1 on fifth cycle), partly because of the poor performance of the Pb counter electrode . Other studies with two-electrode cells have also resulted in poor performance. − …”

Tracking the Dissolution Surface Kinetics of a Single Fluorescent Cyclodextrin Metal–Organic Framework by Confocal Laser Scanning Microscopy

“…Recently, studying the dissolution of solids at the single-particle level is attracting increasing interest using high-resolution analytical techniques, such as scanning electron microscopy (SEM), atomic force microscopy (AFM), optical microscopy, , fluorescence, and an electrochemical method. , However, SEM and AFM are limited with sophisticated setups and specialized sensors. , Individual crystal faces are analyzed by the electrochemical method at one time . The development of an in situ method for tracking the dissolution process of an entire microcrystal (faces and edges) at the single-particle level is needed with high sensitivity and good resolution, which is the motivation for the studies herein.…”

“…12 However, the bulk of particles average over a large number of particles; thus, the intrinsic role of each particle was curtained, and the phenomena at the single-particle level were not fully considered. 13 Recently, studying the dissolution of solids at the singleparticle level is attracting increasing interest using highresolution analytical techniques, such as scanning electron microscopy (SEM), 14 atomic force microscopy (AFM), 15 optical microscopy, 16,17 fluorescence, 18 and an electrochemical method. 19,20 However, SEM and AFM are limited with sophisticated setups and specialized sensors.…”