Delithiated Fe1-xMgxPO4 cathode materials: Structural, magnetic, and Mössbauer studies

Abstract

Fe1-xMgxPO4 (x = 0.01, 0.05, and 0.1) cathode materials are synthesized by a two-step method, which combines the solid-state reaction method and the chemical lithium deintercalation method. A study was conducted to investigate the structural and the magnetic properties of Fe1-xMgxPO4. The crystalline structure of the samples was analyzed by X-ray diffractometer (XRD) using the Rietveld refinement. The magnetic properties of the samples were determined from vibrating sample magnetometer (VSM) and Mösssbauer spectroscopy, including their magnetic interactions, Fe ion states, and structural ordering. The Néel temperature (TN) of Fe1-xMgxPO4 decreases with the increase of the Mg content due to the weakening of the antiferromagnetic exchange. Furthermore, for Fe1-xMgxPO4, the effective moment value decreases as expected with increasing Mg content. Mössbauer spectroscopy measurements at different temperatures were made. The spectrum at 295 K was fitted with a doublet, which has an isomer shift of δ = 0.32 – 0.43 mm/s (Fe3+). The large value of the electric quadrupole splitting (∆EQ = 0.95 – 1.87 mm/s) is explained by the asymmetric local environment of the Fe ions. Below the TN, the spectra of Fe1-xMgxPO4 in the eight resonance absorption lines (including two relatively small intensities) were analyzed. We can obtain a spin value for Fe ions (S = 5/2) of Fe0.9Mg0.1PO4 from the Brillouin functional analysis.

Study of Delithiation Process Features in LixFe0.8M0.2PO4 (M = Mg, Mn, Co, Ni) by Mössbauer Spectroscopy

“…Mössbauer spectroscopy is often used to study iron-containing materials including cathodes of lithium-ion batteries. It is used to carry out phase analysis − for determination of charge degree and investigation of exchange interactions . Also, dependences of hyperfine spectral parameters on the charge degree can be used to study the mechanism of the delithiation process. , Previously, we carried out Mössbauer studies of doped lithium iron phosphates ,− in order to detect local states of iron cations with different nearest-cation environments and determine the dopant distribution.…”

“…It is used to carry out phase analysis 26−28 for determination of charge degree 29 and investigation of exchange interactions. 30 Also, dependences of hyperfine spectral parameters on the charge degree can be used to study the mechanism of the delithiation process. 31,32 Previously, we carried out Mossbauer studies of doped lithium iron phosphates 17,33−36 electrochemical cycling using Mossbauer spectroscopy.…”