Pulverization Control by Confining Fe3O4 Nanoparticles Individually into Macropores of Hollow Carbon Spheres for High-Performance Li-Ion Batteries

In this article, double carbon shell hollow spheres which provide macropores (mC) for ultrasmall Fe 3 O 4 nanoparticle (10–20 nm) encapsulation individually were first prepared (Fe 3 O 4 @mC). The well-constructed Fe 3 O 4 @mC electrode materials offer the feasibility to study the volume change, aggregation, and pulverization process of the active Fe 3 O 4 nanoparticles for Li-ion storage in a confined space. Fe 3 O 4 @mC exhibits excellent electrochemical performances and delivers a high capacity of 645 mA h g –1 at 2 A g –1 after 1000 cycles. Even at 10 A g –1 or after 1000 cycles at 2 A g –1, the porous carbon structure was well maintained and no obvious aggregation and pulverization of the Fe 3 O 4 nanoparticles was observed, although the volume of the active Fe 3 O 4 particles was expanded to 40–60 nm compared to that of the original particles (10–20 nm). This can be due to the in situ embedment of one Fe 3 O 4 nanoparticle into one macropore individually. The uniform dispersion and confinement of the Fe 3 O 4 nanoparticles in the macropores of the carbon shell could effectively accommodate severe volume variations upon cycling and prevent self-aggregation and spreading out from the carbon shell during the expansion process of the nanoscale Fe 3 O 4 particles, leading to improved capacity retention. Our work confirms the effectiveness for pulverization control by confining Fe 3 O 4 nanoparticles individually into macropores to improve its Li-ion storage properties, providing a novel strategy for the design of new-structured anode materials for Li-ion batteries.