Investigation of Fluoride Ion Transport in Some LaF3 and SnF2 Based Solid Electrolytes for All Solid State Fluoride Ion Batteries

Abstract

Fluoride ion conducting materials have been extensively studied for their potential use as solid electrolytes in a range of electrochemical devices, such as sensors, specific ion electrodes, and all-solid-state fluoride ion batteries (FIBs). Recent studies have revealed that FIBs are the promising alternatives to Li-ion batteries, due to their high theoretical energy density, abundant availability of constituent materials, and broad operational temperature range. The current study focuses on the advancement of some LaF3 and SnF2-based fluoride ion conducting solid electrolytes for FIBs covering from their synthesis to the fabrication of cells. The thesis commences by providing the applications and challenges of current Li-ion batteries, beyond Li-ion chemistries, advantages, and challenges of FIBs to the concise overview of various solid fluoride ion conducting solid electrolytes known (Chapter 1). Following the introduction chapter, the subsequent chapter explores the experimental methods, detailing the synthesis approaches and characterization techniques employed in the current study (Chapter 2). The first working chapter describes the structural and transport behaviour of LaF3 solid electrolyte influenced by mechanical milling, doping with bivalent metal fluoride, BaF2 and furthermore, co-doping with BaF2 and CaF2 together (Chapter 3). XRD and impedance studies are mainly conducted to analyze the impact of mechanical milling on the bare LaF3 conductivity in relation to its crystallite size. La0.9Ba0.1F2.9 exhibits higher conductivity compared to LaF3 and the result is explained with respect to the differences in the ionic radii and valence states of the dopant Ba2+ and the host La3+ ions. The transport measurements show that the conductivity of La0.9Ba0.05Ca0.05F2.9 is lower compared to that of La0.9Ba0.1F2.9. Among the prepared LaF3-based electrolytes, La0.9Ba0.1F2.9 exhibits higher ionic conductivity (2.70 × 10-4 S/cm) at 473 K.