Silica coated ZnFe2O4 nanoparticles as cathode catalysts for rechargeable lithium- air batteries

Abstract

In this work, the preparation and structural characterization of a novel material consisting of silica- coated zinc ferrite ( ZnFe2O4) nanoparticles as cathode catalysts for nonaqueous lithium- air batteries ( LABs) are presented for the first time. ZnFe2O4 nanoparticles ( NPs) were prepared by the normal micelles method, using oleic acid as the capping agent and then coating them with silica, via a reverse microemulsion method, with various thicknesses. The colloidal ZnFe2O4 NPs and silica- coated ZnFe2O4 NPs were characterized by TEM and powder XRD. The particle size of bare ZnFe2O4 NPs was calculated to be 5.8 nm by both TEM image and XRD pattern. They were then coated by silica with layer thicknesses of 9, 11, and 13 nm. The perform- ances of bare and silica- coated ZnFe2O4 NPs were evaluated as cathode catalysts for LABs using 1 M lithium trifluoromethanesulfonate ( TFMS) in tetraethylene glycol dimethyl ether ( TEGDME) as the electrolyte. The primary discharge/ charge capacities of bare ZnFe2O4 NPs and ZnFe2O4 NPs with silica- shell thicknesses of 9, 11, and 13 at 0.1 mAcm 2 were found to be 3300, 4300, 6200 and 5000 mAhg 1, respectively. The overpotential is almost 0.5 V, decreased by silica coating with a thickness of 11 nm, whereas there was no difference at other thicknesses. Cyclability with a discharge capacity of 1000 mAhg 1 was observed for at least 45 cycles for silicacoated ZnFe2O4 NPs with a shell thickness of 11 nm.