Probing Lithium Storage Mechanism of MoO₂ Nanoflowers with Rich Oxygen-Vacancy Grown on Graphene Sheets

The search for new electrode materials is of paramount importance for the practical apply of lithium-ion batteries (LIBs). Herein, flower-like MoO₂ microislands consist of MoO₂ nanorods grown on both sides of graphene sheets were synthesized via a solvo-thermal method, followed by a simple thermal treatment in argon. Our EXAFS and ESR data suggest there oxygen-vacancies in MoO₂ of the FMMGS hybrids. Besides, by tunning the ratio of glucose and CTAB, samples with different oxygen-vacancies content were synthesized. When used as anode materials for lithium-ion batteries, the oxygen-vacancy-rich FMMGS hybrids exhibited obviously higher capacity, rate capability than any nonvacancy samples. Importantly, synchrotron-radiation-based X-ray absorption near-edge structure (XANES), extended X-ray absorption fine-structure (EXAFS) and ex situ X-ray diffraction (ex situ XRD) were employed to elucidate the Li-ion insertion and extraction processes in the MoO₂ electrode. Our data clearly revealed that Li₂MoO₄ was generated during the Li uptake/removal process, which can be attributed to the existence of abundant oxygen vacancies in MoO₂ microislands. This provides us a useful insight for better understanding of dynamic cycling behavior in various Mo-based electrodes