Revealing the activation effects of high valence cobalt in CoMoO4 towards highly reversible conversion

Molybdenum (Mo)-based transition metal oxides normally delivery superior energy density in lithium ion batteries through electrochemical conversion reactions. The main challenge for this kind of electrode material is to promote reversible transformation of Li2O and alleviate the volume expansion during lithiation/delithiation processes. Here, electrochemical reaction mechanism of CoMoO4 investigated by in-situ X-ray diffraction and ex-situ Transmission electron microscopy reveals the irreversible transformation from CoMoO4 to CoO and MoO3 in the first cycle. During subsequent charge/discharge process, high valence state cobalt ions originated from Co2+ provide additional capacity and promote the electrochemical reversible reaction between MoO3 and Li2O, thus facilitating the release of irreversible capacity. Benefited by the contributor of high valence state cobalt ion, when CoMoO4 was utilized as Li-storage anode, high reversible capacity (1585.5 mAh g(-1) at 200 mA h(-1) after 150 cycles) and excellent cyclic stability (similar to 100% retention after 400 cycles at 1000 mA g(-1)) are delivered. Such an optimized anode material expands the potential to develop lithium-ion batteries with significantly higher energy density.