Pomegranate-like α-MoO_3-x/C nanospheres as a stable and high-performance Li-ion intercalation host

Orthorhombic MoO₃ (α-MoO₃) is extensively investigated as a cathode material in Li-ion batteries with high capacity. However, suffering from the irreversible structural transformation and rapid capacity decline during discharge-charge process are still annoyed issues for α-MoO₃ based electrodes. Herein, novel pomegranate-like oxygen-deficient α-MoO₃/C (α-MoO_3-x/C) nanospheres are prepared. The α-MoO_3-x/C nanosphere is comprised of ultrafine α-MoO_3-x subunits and porous graphitic carbon framework. Interlayer expansions caused by different contents of oxygen vacancies are realized in α-MoO_3-x via a controllable oxidation process. When evaluated as the Li-ion intercalation host, the α-MoO_3-x/C containing appropriate oxygen vacancies is found to be optimal with remarkable rate capability (230.0 mAh g⁻¹ at 1 C, 54.5 mAh g⁻¹ at 50 C) and long lifetime (69.6% retention after 3000 cycles at 10 C). Electrochemical test shows that the behavior of Li-ion intercalation in the intralayers of α-MoO_3-x/C is suppressed effectively and becomes reversible. The structure evolutions during Li-ion intercalation/deintercalation process are investigated by ex situ X-ray diffraction, which reveals that α-MoO_3-x/C undergoes lattice breathing rather than structural collapse compared with pure α-MoO₃. Moreover, α-MoO_3-x/C exhibits enhanced pseudocapacitance and improved Li-ion transport kinetics than pure α-MoO₃. These unique features render α-MoO_3-x/C an advanced intercalation host for Li-ions.