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.
Highlights
The fastest-growing lithium-ion battery used in energy storage systems is widely used in portable electronic devices, from wireless communications to mobile computing and electric vehicles.1–3 LiFePO4, discovered by the Goodenough group, has been used as a cathode material for secondary lithium batteries, and many research groups have made great efforts to improve its performance.4LiFePO4 is mainly used for high capacity and high-power applications, such as in hybrid vehicles
This cathode material has the disadvantage that its energy density is lower than that of LiCoO2 layer and LiMn2O4 spinel cathode materials, which have a discharge voltage of 3.8–4.0 V, because its discharge voltage is in the 3.5 V region
The crystalline structure of Fe1-xMgxPO4 has an orthorhombic structure with space groups of Pnma
Summary
LiFePO4 is mainly used for high capacity and high-power applications, such as in hybrid vehicles. This cathode material has the disadvantage that its energy density is lower than that of LiCoO2 layer and LiMn2O4 spinel cathode materials, which have a discharge voltage of 3.8–4.0 V, because its discharge voltage is in the 3.5 V region.. This cathode material has the disadvantage that its energy density is lower than that of LiCoO2 layer and LiMn2O4 spinel cathode materials, which have a discharge voltage of 3.8–4.0 V, because its discharge voltage is in the 3.5 V region.5–7 To overcome this problem, a high voltage olivine material is being actively developed in which Fe is replaced with a transition metal.. Previous studies have reported that olivine-type FePO4 irreversibly transforms into an electrochemically inactive quartz-like structure at about 600 ○C, suggesting that the olivine form might be metastable. since the Mg ion is not electrochemically activated, a high capacity can only be obtained when the content is small. Besides the existing studies on the structural and magnetic properties of LiFe1-xMgxPO4 materials with small amounts of Mg ions, basic studies on the structural and magnetic properties of charged Fe1-xMgxPO4 materials are insufficient
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