Facile hybridization of Ni@Fe₂O₃ superparticles with functionalized reduced graphene oxide and its application as anode material in lithium-ion batteries

In our present work we developed a novel graphene wrapping approach of Ni@Fe₂O₃ superparticles, which can be extended as a concept approach for other nanomaterials as well. It uses sulfonated reduced graphene oxide, but avoids thermal treatments and use of toxic agents like hydrazine for its reduction. The modification of graphene oxide is achieved by the introduction of sulfate groups accompanied with reduction and elimination reactions, due to the treatment with oleum. The successful wrapping of nanoparticles is proven by energy dispersive X-ray spectroscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The developed composite material shows strongly improved performance as anode material in lithium-ion batteries (compared to unwrapped Ni@Fe₂O₃) as it offers a reversible capacity of 1051 mA h g^-1 after 40 cycles at C/20, compared with 460 mA h g^-1 for unwrapped Ni@Fe₂O₃. The C rate capability is also improved by the wrapping approach, as specific capacities for wrapped particles are about twice of those offered by unwrapped particles. Additionally, the benefit for the use of the advanced superparticle morphology is demonstrated by comparing wrapped Ni@Fe₂O₃ particles with wrapped Fe₂O₃ nanorice.