Fabrication of CoFe2O4 and NiFe2O4 nanoporous spheres as promising anodes for high performance lithium-ion batteries

Abstract

CoFe₂O₄ and NiFe₂O₄ nanoporous spheres are fabricated using a facile solvothermal method followed by post-thermal treatment, and their potential applications in lithium-ion batteries are explored in this work. The obtained nanoporous spheres, assembled from a large amount of secondary small particles, have a uniform size distribution with diameters in the range of 300–500 nm. These nanoporous CoFe₂O₄ and NiFe₂O₄ are composed of numerous nanoparticles and form a channel structure with a width in the range of 10–20 nm. Furthermore, the growth mechanism of nanoporous spheres is proposed based on the contrast experiments. The important applications of the developed CoFe₂O₄ and NiFe₂O₄ nanoporous spheres in lithium ion batteries have been demonstrated by using them as anode materials. At a current density of 1000 mA g⁻¹, lithium-ion batteries based on CoFe₂O₄ and NiFe₂O₄ nanoporous spheres show capacities of 300 mA h g⁻¹ and 180 mA h g⁻¹ after 1000 cycles, respectively. Even at a current density of 3000 mA g⁻¹, their capacities still reach 255 mA h g⁻¹ and 173 mA h g⁻¹ after 1000 cycles. Although CoFe₂O₄ and NiFe₂O₄ exhibited excellent long cycling life stability at high current densities, it was found that the capacity and the ratio of capacity retention of CoFe₂O₄ are more superior to those of NiFe₂O₄. The reasons have been explained from these structural features. It is believed that the aforementioned excellent performance of lithium-ion batteries arises from the unique porous feature of the developed nanoparticles. That is, well-defined porous nanostructures could buffer the volume expansion, shorten the diffusion path during insertion/extraction processes of Li⁺ in the electrode materials, increase the electrolyte/electrode contact area, and provide more insertion/extraction sites of Li⁺.