Hierarchical porous metal ferrite ball-in-ball hollow spheres: General synthesis, formation mechanism, and high performance as anode materials for Li-ion batteries

High yields of CoFe₂O₄, NiFe₂O₄ and CdFe₂O₄ hierarchical porous ball-in-ball hollow spheres have been achieved using hydrothermal synthesis followed by calcination. The mechanism of formation is shown to involve an in situ carbonaceous-template process. Hierarchical porous CoFe₂O₄ hollow spheres with different numbers of shells can be obtained by altering the synthesis conditions. The electrochemical properties of the resulting CoFe₂O₄ electrodes have been compared, using different binders. The as-obtained CoFe₂O₄ and NiFe₂O₄ have relatively high reversible discharge capacity and good rate retention performance which make them promising materials for use as anode materials in lithium ion batteries.