Binder-free, self-standing films of iron oxide nanoparticles deposited on ionic liquid functionalized carbon nanotubes for lithium-ion battery anodes

We report in-situ synthesis and direct deposition of Fe₂O₃ nanoparticles (NPs) on the ionic liquid (IL)-functionalized carbon nanotubes (fCNT). As shown in transmission electron microscope (TEM) and scanning TEM (STEM) images, Fe₂O₃ NPs with the diameter of 3–5 nm are randomly distributed on the sidewall of fCNT, revealing the nanocrystalline structure. The chemical identity and interaction of the fCNT/Fe₂O₃ composite are investigated by FT-IR, Raman and XPS analyses. In particular, the fCNT/Fe₂O₃ composite is solution-processable in a form of binder free and self-standing film. Such a free-standing electrode film based on the fCNT/Fe₂O₃ composite achieve the discharge capacity of 413 mAh g⁻¹ which is much greater than 34 mAh g⁻¹ of the CNT and 191 mAh g⁻¹ of the fCNT due to the redox reaction of Fe₂O₃ NPs. Moreover, the fCNT/Fe₂O₃ composite show the coulombic efficiency of 98% and the capacity fading from 272 mAh g⁻¹ to 182 mAh g⁻¹ after 50 cycles of charge/discharge. - Highlights: • Fe₂O₃ nanoparticles were uniformly deposited onto fCNT via a hydrothermal method. • LIBs were prepared using a binder-free freestanding electrode. • ILs improved processability and solubility of CNTs. • Interactions with ILs preserved the inherently electronic structures of CNTs. • The capacity of the fCNT/Fe₂O₃ composite was higher than those of CNT and fCNT