Simple fabrication of strongly coupled cobalt ferrite/carbon nanotube composite based on deoxygenation for improving lithium storage

An easy method to synthesize a strongly coupled cobalt ferrite/carbon nanotube (CoFe₂O₄/CNT) composite with oxygen bridges between CoFe₂O₄ and reduced carbon nanotubes (CNTs) by calcining the precursor material was reported. The precursor was prepared by an electrostatic self-assembly of the exfoliated Co(II)Fe(II)Fe(III)-layered double hydroxide (CoFeFe-LDH) nanosheets and acid treated CNTs. The deoxygenation effect of ferrous ion (Fe²⁺) in CoFeFe-LDH nanosheets on the oxygen-containing groups of acid treated CNTs was investigated by X-ray photoelectron spectroscopy (XPS) measurement. After thermal conversion, the obtained CoFe₂O₄ was bonded to the reduced CNTs through Metal–O–C (oxygen bridge), which was characterized by XPS, Fourier transform infrared spectroscopy, and Raman spectroscopy. When applied as an anode for lithium-ion battery, the CoFe₂O₄/CNT composite exhibited a low resistance of charge transfer and Li-ion diffusion, good cycle performance, and high rate capability. At a lower current density of 0.15 A·g⁻¹, a specific discharge capacity of 910 mA·h·g⁻¹ was achieved up to 50 cycles. When current density was increased to 8.8 A·g⁻¹, the CoFe₂O₄/CNT composite still delivered 500 mA·h·g⁻¹.