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 Fe3O4 nanoparticle (10-20 nm) encapsulation individually were first prepared (Fe3O4@mC). The well-constructed Fe3O4@mC electrode materials offer the feasibility to study the volume change, aggregation, and pulverization process of the active Fe3O4 nanoparticles for Li-ion storage in a confined space. Fe3O4@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 Fe3O4 nanoparticles was observed, although the volume of the active Fe3O4 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 Fe3O4 nanoparticle into one macropore individually. The uniform dispersion and confinement of the Fe3O4 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 Fe3O4 particles, leading to improved capacity retention. Our work confirms the effectiveness for pulverization control by confining Fe3O4 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.