Surface defect-enhanced conductivity of calcium fluoride for electrochemical applications

Abstract

Calcium fluoride is widely investigate known to be a promising solid material for optics, electronics, and electrochemistry. In this work, we report the successful preparation of calcium fluoride with enhanced defect structure obtained by the application of vapor pressure followed by high-energy ball milling, creating CaF2 nano-powder, achieving increased ionic conductivities in the order of 1.9 · 10−5 S·cm−1 at room temperature relying on fluoride surface interstitial defect with an activation energy of 0.35 eV. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR). It is revealed that the calcium fluoride electrolyte keeps in its basic cubic structure, becomes nano-powdered material with crystallite/particle size of 12/30 nm. Surface defect structures are enhanced, which is visible with XPS, NMR, and EPR spectroscopy. The synthesized material provided considerable ionic conductivity enhancement introducing attraction for electrochemical testing for fluoride-ion batteries (FIB).