Design and synthesis of micron-sized spherical aggregates composed of hollow Fe₂O₃ nanospheres for use in lithium-ion batteries

A novel structure denoted a "hollow nanosphere aggregate" is synthesized by introducing nanoscale Kirkendall diffusion to the spray pyrolysis process. The hollow Fe₂O₃ nanosphere aggregates with spherical shape and micron size are synthesized as the first target material. A solid iron oxide-carbon composite powder that is prepared by a one-pot spray pyrolysis process is transformed into the hollow Fe₂O₃ nanosphere aggregates by sequential post-pyrolysis treatments under reducing and oxidizing atmospheres. The nanoscale Kirkendall diffusion plays a key role in the formation of the hollow Fe₂O₃ nanosphere aggregates with spherical shape and micron size. The unique structure of the hollow Fe₂O₃ nanosphere aggregates results in their superior electrochemical properties as an anode material for lithium ion batteries by improving the structural stability during cycling. The hollow metal oxide nanosphere aggregates with various compositions for wide applications including energy storage can be prepared by the simple fabrication method introduced in this study.