Fe-Fe3O4 Composite Electrode for Lithium Secondary Batteries

Pitch addition to the nano-sized Fe3O4 anode and subsequent heat-treatment produced a large fraction of Fe particles (up to 60 wt%) which greatly enhanced the cycle retention and rate capability of the Fe3O4 anode. The 10 wt% pitch added Fe3O4 delivered a discharge capacity of 750 mAh g−1 at 1 C with 96% cycle retention after 50 cycles whereas without the pitch addition the charge capacity immediately dropped after a few cycles. It is believed that the enhancement mainly stemmed from the oxidation of the Fe particles during the lithiation of the nanoparticle Fe3O4 anode. The oxidation of the Fe particles protected the Fe3O4 nanoparticles from the detrimental formation of the Li-Fe3O4 complex prior to the "conversion" reaction by partially consuming the available Li ions, thus stabilizing the structure of the anode. It is possible that the partial reduction of other oxide electrodes such as CoO or NiO nanoparticles may improve the cycle retention and other electrochemical properties.