Magnetic properties of mixed sodium-lithium iron fluorophosphate NaLiFePO4F cathode material

Abstract

Mixed sodium-lithium iron fluorophosphates NaLiFePO4F was synthesized by solid-state route. The crystal and magnetic properties were investigated by X-ray diffraction (XRD) measurement, vibrating sample magnetometer (VSM), and Mössbauer spectroscopy. The crystal structure of NaLiFePO4F was determined to be orthorhombic with space group of Pnma. The cell parameters of NaLiFePO4F are as follows: a0 = 10.9661 Å, b0 = 6.3693 Å, c0 = 11.4342 Å, and V = 798.6377 Å3. The temperature-dependence of the zero-field-cooled (ZFC) and field-cooled (FC) curves was examined by VSM at 100 Oe from 4.2 to 295 K. We determined the Néel temperature (TN = 22 K) and spin reorientation temperature (TS = 13 K). The Mössbauer spectra of NaLiFePO4F were taken at various temperatures ranging from 4.2 to 295 K. At below TS, the electric quadrupole splitting (ΔEQ) decreased and magnetic hyperfine field (Hhf) increased with decrease temperature due to spin-orbit coupling.

Preparation and Electrochemical Performance of Na2−xLixFePO4F/C Composite Cathode Materials with Different Lithium/Sodium Ratios

“…The first is that as the Li + content increases, the unit cell of the cathode material changes from Pbcn to Pnma [ 14 ]. The results of the experiments also show that all samples are electrochemically active, indicating that Na + /Li + ion exchange occurs gradually and that the unit cell volume changes accordingly [ 15 ]. This explains the gradual increase in the electrochemical capacity after the Li + is first added.…”