Investigating the Intercalation Chemistry of Alkali Ions in Fluoride Perovskites

Abstract

Reversible intercalation reactions provide the basis for modern battery electrodes. Despite decades of exploration of electrode materials, the potential for materials in the nonoxide chemical space with regards to intercalation chemistry is vast and rather untested. Transition metal fluorides stand out as an obvious target. To this end, we report herein a new family of iron fluoride-based perovskite cathode materials A x K 1−x FeF 3 (A = Li, Na). By starting with KFeF 3 , approximately 75% of K + ions were subsequently replaced by Li + and Na + through electrochemical means. X-ray diffraction and Fe X-ray absorption spectroscopy confirmed the existence of intercalation of alkali metal ions in the perovskite structure, which is associated with the Fe 2+/3+ redox couple. A computational study by density functional theory showed agreement with the structural and electrochemical data obtained experimentally, which suggested the possibility of fluoride-based materials as potential intercalation electrodes. This study increases our understanding of the intercalation chemistry of ternary fluorides, which could inform efforts toward the exploration of new electrode materials.

New tolerance factor to predict the stability of perovskite oxides and halides

“…1B). Single and double perovskite materials have exceptional properties for a variety of applications such as electrocatalysis ( 10 ), proton conduction ( 11 ), ferroelectrics ( 12 ) (using oxides, X = O 2− ), battery materials ( 13 ) (using fluorides, X = F − ), as well as photovoltaics ( 14 ) and optoelectronics ( 15 ) (using the heavier halides, X = Cl − , Br − , I − ).…”

Bimetallic Co‐Mn Perovskite Fluorides as Highly‐Stable Electrode Materials for Supercapacitors

“…; B=Fe, Mn, Ni, Co, Cu, etc.) have been demonstrated as potential electrode materials for Li/Na‐ion rechargeable batteries . The perovskite phase exhibits the merits of intrinsic 3D diffusion channels and a robust architecture with intersectional tetragonal cavity chains .…”

“…The highly ionic nature of the transition metal‐fluoride bonds elevates the redox potential and the high energy density of the material, and it is also of interest that the highly oxidized transition metals upon high rate cycling might be stabilized by the highly electronegative species. This would lead to better safety by means of the reduced likelihood of material degradation …”

“…have been demonstrated as potential electrode materials for Li/Na-ion rechargeable batteries. [17][18][19][20] The perovskite phasee xhibits the merits of intrinsic3 Dd iffusion channels and ar obusta rchitecture with intersectional tetragonal cavityc hains. [19] The highly ionic nature of the transition metal-fluoride bonds elevates the redox potential and the high energy density of the material, and it is also of interest that the highly oxidized transition metals upon highr ate cycling might be stabilized by the highly electronegative species.…”

“…This would lead to better safetybymeans of the reduced likelihood of materialdegradation. [20] For transition metal-basedF aradaic or pseudocapacitive electrode materials, it is well-known that the redoxs pecies of the transition metal componentsp lay ak ey role in boosting the electrochemical performance of supercapacitors,a nd that bimetallic candidates commonly exhibit superior behavior (including potential window,c onductivity,a ctive sites, stability) to their corresponding monometallic ones,l argely owing to the synergistic effect of bimetallic redox species. [16,21] As typical examples,t he bimetallic CoÀMn oxides/sulfides/layered double hydroxides (Co-Mn-O/Co-Mn-S/Co-Mn-LDH) have shown obviously superiorp erformance in comparison with their corresponding pure Co or Mn based materials.…”