Anionic Ordering and Thermal Properties of FeF₃·3H₂O

Abstract

Iron fluoride trihydrate can be used to prepare iron hydroxyfluoride with the hexagonal-tungsten-bronze (HTB) type structure, a potential cathode material for batteries. To understand this phase transformation, a structural description of β-FeF3·3H2O is first performed by means of DFT calculations and Mössbauer spectroscopy. The structure of this compound consists of infinite chains of [FeF6]n and [FeF2(H2O)4]n. The decomposition of FeF3·3H2O induces a collapse and condensation of these chains, which lead to the stabilization, under specific conditions, of a hydroxyfluoride network FeF3-x(OH)x with the HTB structure. The release of H2O and HF was monitored by thermal analysis and physical characterizations during the decomposition of FeF3·3H2O. An average distribution of FeF4(OH)2 distorted octahedra in HTB-FeF3-x(OH)x was obtained subsequent to the thermal hydrolysis/olation of equatorial anionic positions involving F(-) and H2O. This study provides a clear understanding of the structure and thermal properties of FeF3·3H2O, a material that can potentially bridge the recycling of pickling sludge from the steel industry by preparing battery electrodes.

Impact of Anion Vacancies on the Local and Electronic Structures of Iron-Based Oxyfluoride Electrodes

“…x(OH)x hereafter. 15 This sample was heat treated at 250 °C for 12 h, and 350 °C for 1 h to form FeF3-xOx/2x/2 with x∼0.4. X-ray diffraction confirmed the phase purity of the vacancy-containing HTB structure ( Figure S1).…”

Lithium fluoride/iron difluoride composite prepared by a fluorolytic sol–gel method: Its electrochemical behavior and charge–discharge mechanism as a cathode material for lithium secondary batteries

“…Among the available fluoride candidates, the abundant sources and low toxicity level of FeF3 and its related compounds make them particularly attractive as LIB electrode materials. [13][14][15][16][17][18][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] There have been previous reports of the fabrication of composites containing carbonaceous materials [14,24,30] and with controlled crystallinity [26] and nanonization [23,31], all of which enabled significant improvement of the electrode performance of FeF3. A three-electron capacity of 712 mAh g −1 has been obtained for FeF3, with the conversion reaction involving the formation of metallic iron and lithium fluoride.…”

Reversible control of magnetism: on the conversion of hydrated FeF3 with Li to Fe and LiF

“…4). 47 An additional component with magnetic sextet can be attributed to antiferromagnetic FeF 3 , with a magnetic hyperne eld B HF of about 40 T. Table 1 summarizes the tting results. 48 In contrast, the discharged sample features a drastically altered spectrum, as expected based on the results of the changes observed in the magnetic properties during the electrochemical reduction process.…”