Synthesis Of Porous Fe₃O₄Composites For Lithium-Ion Batteries

Transition metal oxides are considered as the next ideal anode materials for lithium-ion batteries (LIBs). However, based on a unique conversion mechanism, transition metal oxides suffer from poor cycling performance arising from huge volume expansion during the repeated charge-discharge process, resulting in the destruction of the material structure, In addition, transition metal oxides are semiconductors with poor conductivity, which is not conducive to rapid electrochemical reaction, suffering from poor rate capability. In order to overcome above intractable problems, porous/hollow structures of Fe3O4composites are designed to improve the electrochemical performance. The detailed contents are as follows:We report a facile method to fabricate the mesoporous Fe3O4submicrospheres via a one-step hydrothermal reaction. The self-corrosion mechanism is also proposed to explain the formation process of mesoporous Fe3O4submicrospheres. The electrochemical performance is evaluated after coating a thin carbon layer on mesoporous Fe3O4submicrospheres. The capacity of mesoporous Fe3O4/C submicrospheres can maintain926mA h g-1at a current density of100mA g-1after50cycles. Even at a current density of1000mA g-1, the capacity of mesoporous FeO4/C submicrospheres can also keep710mA h g-1. Such a fascinating electrochemical performance can mainly attribute to the uniform carbon coating and the mesoporous structure. The porosity of FeO4/C could not only allow better penetration of electrolyte, but also shorten the diffusion pathways of Li+ions. Meanwhile, the carbon coating greatly enhance the electronic conductivity and maintain the structural integrity against volume expansion during Li+insertion/extraction.The Fe3O4/TiO2composites are successfully synthesized via a facile hydrothermal reaction by using titanium tetrafluoride as precursor. The detailed microstructure of Fe3O4/TiO2is investigated using SEM and TEM. As the anode material for LIBs, the capacity of Fe3O4/TiO2can remain over700mA h g-1at a current density of100mA g-1after50cycles. Ever at the current density of1000mA g-1, the Fe3O4/TiO2can also keep a reversible capacity of530mA h g-1. The excellent electrochemical performance can be attributed to the following reasons:on one hand, the porosity structure of Fe3O4/TiO2could not only allow better penetration of electrolyte, shorten the diffusion pathways of Li+ions, but also buffer the huge volume expansion during the charge-discharge process. On the other hand, the TiO2coating could maintain the structure integrity during the charge-discharge process, improving the cycling performance.The Fe3O4/TiO2composites are prepared by a hydrothermal route by using titanium tetrafluoride and glucose as precursor. Electrochemical tests show that the Fe3O4/C/TiO2composites exhibit the enhanced cycling performance and high rate capability. The Fe3O4/TiO2composites could retain a reversible capacity of711mA h g-1at a current density of100mA g-1after50cycles, even at a current density of1000mA g-1, the capacity of Fe3O4/C/TiO2composites can also maintain600mAh g-1.