Silicon/Hollow γ‑Fe₂O₃ Nanoparticles as Efficient Anodes for Li-Ion Batteries

Nanomaterials have triggered a lot of attention as potential triggers for a technological breakthrough in Energy Storage Devices and specifically Li-ion batteries. Herein, we report the original synthesis of well-defined silicon/iron oxide nanoparticles and its application as anode materials for Li-ion batteries. This model compound is based on earth abundant elements and allows for a full investigation of the electrochemical reactions through its iron oxide magnetic phase. The elaboration of silicon with iron oxide grown on its surface has been achieved by reacting an organometallic precursor Fe­(CO)₅ with Si nanopowder and subsequent slow oxidation step in air yields hollow γ-Fe₂O₃ on the Si surface. This specific morphology results in an enhancement of the specific capacity from 2000 mAh/g_Si up to 2600 mAh/g_Si. Such a high specific capacity is achieved only for hollow γ-Fe₂O₃ and demonstrates a novel approach toward the modification of electrode materials with an earth abundant transition metal like iron. This result further emphasizes the need for precisely designed nanoparticles in achieving significant progress in energy storage

Synthesis of Carbon Nanotubes Networks Grown on Silicon Nanoparticles as Li-Ion Anodes

Using chemical vapor deposition, we grew carbon nanotubes (CNTs) on the surface of Si nanoparticles (NPs) that were coated with a thin iron shell. We studied the CNT growth mechanisms and analyzed the influence of (1) varying annealing times and (2) varying growth times. We show that an initial annealing is necessary to reduce the iron oxide shell and to start the formation of Fe NPs and their consequent coarsening. We characterize the evolution of the catalyst morphology and its influence of the morphology and structure of the CNTs grown. We studied this nanocomposite of Si NPs interconnected by CNTs grown on them as anode material for Li-ion batteries. Compared to the pristine Si NPs, the Si-CNT nanocomposite brings an increase of 40% in specific capacity after 100 cycles at 1800 mA/g_Si with a high stability and a very low capacity loss per cycle of 0.06%. The electrochemical performance demonstrates how efficient the CNT shell on the Si NP is to mitigate the usual failure mechanism of Si NPs. Thus, the in situ growth of CNTs on Si anode materials can be an efficient route toward the synthesis of more stable Si anode composites for a Li-ion battery