Co-activated Conversion Reaction of MoO₂:CoMoO₃ as a Negative Electrode Material for Lithium-Ion Batteries

Extensive studies to develop high-capacity electrodes have been conducted worldwide to meet the urgent demand for next-generation lithium-ion batteries. In this work, we demonstrated a novel strategy to alter the lithiation mechanism of the transition metal oxide to increase the reversible capacity of the electrode material. A representative insertion-type negative electrode material, MoO₂, was modified by introducing a heterogeneous element (Co) to synthesize the solid solution of CoO and MoO₂ (CoMoO₃). CoMoO₃ exhibited a notably improved reversible capacity of 860 mA h g^-1, attributed to the conversion reaction, in contrast to MoO₂ that delivers 310 mA h g^-1, as it is limited by the insertion reaction. X-ray absorption spectroscopy and X-ray diffraction demonstrated that CoO is converted to Co and Li₂O, amorphizing the host structure, whereas the conversion of MoO₂ takes place subsequently. Furthermore, the superior initial Coulombic efficiency of CoMoO₃ (84.4%) to that of typical conversion materials is attributed to the highly conductive Co and MoO₂, which reinforce the electronic conductivity of the active particles. The results obtained from this study provide significant insights to explore high capacity metal oxides for the advanced lithium-ion batteries.