Reversible control of the magnetization of spinel ferrites based electrodes by lithium-ion migration

Abstract

Lithium-ion (Li-ion) batteries based on spinel transition-metal oxide electrodes have exhibited excellent electrochemical performance. The reversible intercalation/deintercalation of Li-ions in spinel materials enables not only energy storage but also nondestructive control of the electrodes' physical properties. This feature will benefit the fabrication of novel Li-ion controlled electronic devices. In this work, reversible control of ferromagnetism was realized by the guided motion of Li-ions in MnFe₂O₄ and γ-Fe₂O₃ utilizing miniature lithium-battery devices. The in-situ characterization of magnetization during the Li-ion intercalation/deintercalation process was conducted, and a reversible variation of saturation magnetization over 10% was observed in both these materials. The experimental conditions and material parameters for the control of the ferromagnetism are investigated, and the mechanism related to the magnetic ions' migration and the exchange coupling evolution during this process was proposed. The different valence states of tetrahedral metal ions were suggested to be responsible for the different performance of these two spinel materials.

Figure 1

Ex-situ characterization of MnFe₂O₄ discharged to different voltage stage. (a) XRD patterns, (b) Raman spectra profiles.

Figure 2

Ex-situ magnetic and electrochemical characterizations. (a) Magnetic hysteresis measurement results of MnFe₂O₄ at different voltage stage. (b) The CV curves of MnFe₂O₄ electrode between 0.01 and 3.0 V at a scan rate of 0.1 mV/s. The inset gives the outcome of γ-Fe₂O₃. Three regions are divided according to the structure variation in the discharge process. (I) remaining spinel structure, (II) changing into rock-salt structure, (III) reduced into metals.

Figure 3

In-situ magnetic results performed simultaneously with the electrochemical discharge/charge processes. (a) Illustrations of the lithium-battery for in-situ magnetic measurement and the schematic of magnetism variation during the discharge/charge process. (b) The magnetism variation of MnFe₂O₄ in the range from 3.0 to 1.0 V. The modulation value of saturation magnetization decay obviously. The inflection point of variation trend is marked by green circle. The inset gives the charge/discharge curves. (c), (d) The magnetism variation of MnFe₂O₄ and γ-Fe₂O₃ in the range from 3 to 1.5 V.

Figure 4

(a), (c) The CV curves of MnFe₂O₄ and γ-Fe₂O₃ in the range from 3 to 1.5 V. (b), (d) The enlarged image of the second charge/discharge cycle for MnFe₂O₄ and γ-Fe₂O₃. The processes are divided by different magnetic variation trend, and marked in different color.

Figure 5

Calculation results based on a statistical model. The magnetic moment of MnFe₂O₄ per formula has been given as a function of Li ions intercalation. X and y stands for the average amount of intercalated Li ions per chemical formula respectively in the tetrahedral and octahedral sites.

Figure 6

The schematic of the spinel magnetic coupling variation in the Li insertion/extraction process between 3.0 V and 1.5 V. (a) State of the high magnetization material. Magnetic ions in oxygen tetrahedrons (A) and octahedrons (B) are coupled antiferromagnetically between each other, and arranged ferromagnetically in their own sites. (b) State of the low magnetization material. The ions in A sites have been transferred to B sites, and the magnetic ions are coupled antiferromagnetically. (c) The magnetism variation mechanism of reversible process in the discharge/charge cycle.