Fluorolytic Sol-Gel Preparation of a Composite of Lithium Fluoride and Iron Difluoride As a Positive Electrode Material for Lithium Secondary Batteries

Abstract

A composite of lithium fluoride (LiF) and iron difluoride (FeF2) has been prepared by the reaction of the corresponding metal acetates and anhydrous hydrogen fluoride in ethanol in view of its application as a positive electrode material for lithium secondary batteries. The obtained LiF/FeF2 composite shows weak XRD peaks assigned to LiF and FeF2, and crystallite size is estimated to be 12 nm by the Scherrer’s equation. The composite powder exhibits a high N­2-adsorption capacity with adsorption-desorption loop due to the existence of meso-pores, and BET surface area is calculated to be 119 m2 g−1. In the charge–discharge test, this composite shows an initial charge capacity of 235 mAh (g-LiF/FeF2)−1 and discharge capacity of 225 mAh (g-LiF/FeF2)−1 at 10 mA (g-LiF/FeF2)− 1. Although the discharge reaction from the initial cycle occurs with small overpotential, the charge reaction exhibits large overpotential over 300 mV even at a slow rate below 10 mA (g-LiF/FeF2)− 1.