A new Bi0.7Fe1.3O1.5F1.7 phase: Crystal structure, magnetic properties, and cathode performance in fluoride-ion batteries

Tsuyoshi Takami,Takashi Kamiyama,Toshiharu Fukunaga,Takeshi Abe,Takashi Saito,Katsumi Kawahara

doi:10.1063/5.0005817

Tsuyoshi Takami, Takashi Kamiyama + Show 4 more

Open Access

https://doi.org/10.1063/5.0005817

Copy DOI

Abstract

We synthesize a Bi0.7Fe1.3O1.5F1.7 (BFOF) phase via a non-topochemical reaction with a fluorination agent. The crystal structure is refined by Rietveld refinement on the neutron diffraction patterns as a hexagonal lattice in the R3¯ space group, along with the defect structure. The sudden decrease in magnetic susceptibility below 250 K and the linear relationship between the magnetization and the magnetic field indicate that BFOF is an antiferromagnetic material. When BFOF is used as a cathode in fluoride-ion batteries (FIBs), a discharge (charge) capacity of 360 (225) mAh/g is achieved at 140 °C. Magnetization and x-ray diffraction measurements confirm that the F ions are transferred from the cathode to the Pb counter electrode during discharge and in the opposite direction during charge, in a manner analogous to the transfer of lithium (Li) ions in Li-ion batteries. These findings contribute to the development of quaternary oxyfluorides serving as FIB cathodes.

Highlights

Oxyfluorides and fluorides have attracted growing interest owing to their superconductivity, ionic conductivity, and use in fluoride-ion batteries (FIBs).1–3 For example, FIBs containing transferrable fluorine that is 50 times more abundant than lithium are leading candidates to replace conventional lithium-ion batteries (LIBs)
Our group put great effort into investigating the battery performance of Fe cathode compounds, such as FeF39,10 and Li8FeS5.11 we deliberately developed a quaternary oxyfluoride containing Bi and Fe
The endothermic peak may correspond to defluorination of BFOF, the exothermic peak comes from decomposition of BFOF

Summary

Introduction

Oxyfluorides and fluorides have attracted growing interest owing to their superconductivity, ionic conductivity, and use in fluoride-ion batteries (FIBs).1–3 For example, FIBs containing transferrable fluorine that is 50 times more abundant than lithium are leading candidates to replace conventional lithium-ion batteries (LIBs). Our group put great effort into investigating the battery performance of Fe cathode compounds, such as FeF39,10 and Li8FeS5.11 we deliberately developed a quaternary oxyfluoride containing Bi and Fe. We refined the crystal structure of BFOF by x-ray diffraction (XRD) and neutron powder diffraction (NPD), and investigated the magnetic, electric, and electrochemical properties.

Results

Conclusion