Operandoobservations Of Reversible Alpha-Bif(3)Conversion In Liquid Electrolyte By Synchrotron Radiation Diffraction And(7)Li Nuclear Magnetic Resonance

The electrochemically-driven conversion reaction of BiF(3)with Li(+)ions is of interest for potential application as a positive electrode system in conversion type rechargeable batteries. Here, we use synchrotron radiation diffraction and(7)Li nuclear magnetic resonance (NMR) for complementaryoperandoobservations of reversible or quasi-reversible conversion reactions of alpha-BiF(3)nanocomposite electrode at room temperature. The nanocomposite electrode was fabricated by ball milling and subsequent heat treatments. A pronounced XRD peak broadening indicated a disordered fine crystalline state in the electrode. Theoperandosynchrotron radiation diffraction measurements revealed a quasi-reversible smooth crystallographic transformation between alpha-BiF(3)and metallic Bi. Theoperando(7)Li NMR measurement quantitatively showed reversible conversion reactions. The series ofin-situ(7)Li NMR spectra contained sharp signals from Li(+)ions in the electrolyte and a broad signal associated with a solid phase of LiF. These signals followed a stoichiometric relationship that conformed to a three-electron BiF(3)conversion pathway.