Synthesis of metal-fluoride nanoparticles supported on thermally reduced graphite oxide

Abstract

Metal-fluoride nanoparticles, (MF _x -NPs) with M = Fe, Co, Pr, Eu, supported on different types of thermally reduced graphite oxide (TRGO) were obtained by microwave-assisted thermal decomposition of transition-metal amidinates, (M{MeC[N(iPr)]₂} _n ) or [M(AMD) _n ] with M = Fe(II), Co(II), Pr(III), and tris(2,2,6,6-tetramethyl-3,5-heptanedionato)europium, Eu(dpm)₃, in the presence of TRGO in the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF₄]). The crystalline phases of the metal fluorides synthesized in [BMIm][BF₄] were identified by powder X-ray diffraction (PXRD) to be MF₂ for M = Fe, Co and MF₃ for M = Eu, Pr. The diameters and size distributions of MF _x @TRGO were from (6 ± 2) to (102 ± 41) nm. Energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) were used for further characterization of the MF _x -NPs. Electrochemical investigations of the FeF₂-NPs@TRGO as cathode material for lithium-ion batteries were evaluated by galvanostatic charge/discharge profiles. The results indicate that the FeF₂-NPs@TRGO as cathode material can present a specific capacity of 500 mAh/g at a current density of 50 mA/g, including a significant interfacial charge storage contribution. The obtained nanomaterials show a good rate capacity as well (220 mAh/g and 130 mAh/g) at a current density of 200 and 500 mA/g, respectively.

Keywords: ionic liquids; material synthesis; metal-fluoride nanoparticles; microwave irradiation; thermally reduced graphite oxide.

Scheme 1

Synthesis scheme of MF_x@TRGO from [M(AMD)_n] and [Eu(dpm)₃] by microwave (MW)-assisted thermal decomposition on thermally reduced graphite oxide (TRGO) in the ionic liquid [BMIm][BF₄].

Figure 1

Example PXRD of 0.5 wt % PrF₃@TRGO-SH in [BMIm][BF₄] synthesized from [Pr(AMD)₃]. PrF₃ reference reflections in red from COD 1010984. For the diffractogram with indexed reflections see Figure S18 in Supporting Information File 1. The PXRDs for the other samples are given in Figures S4–S19 in Supporting Information File 1.

Figure 2

TEM images of PrF₃@TRGO-400 dispersions from [Pr(AMD)₃] in [BMIm][BF₄].

Figure 3

XPS of PrF₃@TRGO-400 dispersions from [Pr(AMD)₃] in [BMIm][BF₄].

Figure 4

The electrochemical performance of FeF₂@TRGO-400 as cathode material for lithium-ion batteries. (a) The galvanostatic charge/discharge profiles at a current of 50 mA/g. The inset is the profile of the first cycle. (b) The rate performance after an activation over three cycles.