Ethylene glycol-mediated rapid synthesis of carbon-coated ZnFe₂O₄nanoflakes with long-term and high-rate performance for lithium-ion batteries

Abstract

Carbonaceous hybrid nanocomposites with a porous flaky structure hold great promise as high-performance electrodes for lithium-ion batteries (LIBs); yet large-scale synthesis is still a challenge. In this work, we successfully develop a novel carbon hybrid structure of carbon-coated ZnFe₂O₄ nanoflakes (ZnFe₂O₄@C NFs) through a fast ethylene glycol (EG)-mediated metal alkoxide method, refluxing at 200 °C in EG and a post-calcination at 500 °C in a N₂ atmosphere. The organic components in the pre-synthesized ZnFe-alkoxide precursor (ZnFe₂(OCH₂CH₂O)₄) can be transferred into an amorphous carbon layer easily surrounding the crystalline ZnFe₂O₄ subunits during the annealing process. The flaky morphologies of the as-prepared ZnFe₂O₄@C hybrids are highly dependent on the refluxing temperature. Upon increasing the refluxing temperature from 140 °C to 200 °C, the sphere-like morphology of the ZnFe₂O₄@C composites gradually evolves into microflowers and separate nanoflakes. When used as an anode for LIBs, the hybrid ZnFe₂O₄@C NFs present excellent electrochemical performance with high discharge capacity, long-term cyclic stability and superior high-rate capability. Even after 1000 cycles at 0.5 A g^-1, the hybrid ZnFe₂O₄@C NFs still deliver a stable reversible discharge capacity of 778.6 mA h g^-1.